To assess the ability of a material to perceive a certain deformation under conditions as close as possible to production, technological tests are used. Such assessments are of a qualitative nature. They are necessary to determine the suitability of a material for the manufacture of products using a technology that involves significant and complex plastic deformation.
To determine the ability of sheet material up to 2 mm thick to withstand cold stamping (drawing), the method of testing for drawing a spherical hole using special punches having a spherical surface (GOST 10510) is used. The test scheme is shown in fig. 9.3.
Rice. 9.3. Scheme of the test for drawing a spherical hole according to Eriksen
During the test, the pulling force is fixed. The design of the device provides for automatic termination of the drawing process at the moment when the force begins to decrease (the first cracks appear in the material). A measure of the ability of a material to draw is the depth of the elongated hole.
A sheet or tape less than 4 mm thick is tested for kink (GOST 13813). The test is carried out using the fixture shown in Fig. 9.4.
Rice. 9.4. Bend Test Diagram
1 - lever; 2 - replaceable leash; 3 - sample; 4 - rollers; 5 - sponges; 6 - vise
The sample is first bent to the left or right by 90 0, and then each time by 180 0 in the opposite direction. The criterion for the end of the test is the destruction of the sample or the achievement of a given number of kinks without destruction.
Wire made of non-ferrous and ferrous metals is tested for twisting (GOST 1545) with the determination of the number of full turns until the destruction of samples, the length of which is usually (- wire diameter). The kink test (GOST 1579) is also used according to a scheme similar to the sheet material test. Carry out a winding test (GOST 10447). The wire is wound in tight-fitting turns on a cylindrical rod of a certain diameter (Fig. 9.5).
Fig.9.5. Wire winding test
The number of turns should be within 5 ... 10. An indication that the sample has passed the test is the absence of delamination, peeling, cracks or tears in both the base material of the sample and its coating after winding.
For pipes with an outer diameter of not more than 114 mm, a bend test (GOST 3728) is used. The test consists in a smooth bending of a pipe section in any way at an angle of 90 0 (Fig. 9.6. a) so that its outer diameter in no place becomes less than 85% of the initial one. GOST sets the value of the bend radius R depending on pipe diameter D and wall thickness S. The sample is considered to have passed the test if no metal discontinuities are found on it after bending. Samples of welded pipes shall pass the test in any position of the weld.
The beading test (GOST 8693) is used to determine the ability of the pipe material to form a flange of a given diameter (Fig. 9.6.b). A sign that the sample passed the test is the absence of cracks or tears after flanging. Flanging with preliminary distribution on the mandrel is allowed.
The expansion test (GOST 8694) reveals the ability of the pipe material to withstand deformation during expansion into a cone up to a certain diameter with a given taper angle (Fig. 9.6.c). If, after distribution, the sample does not have cracks or tears, then it is considered to have passed the test.
For pipes, a flattening test to a certain size is provided (Fig. 9.6.d), and for welded pipes, GOST 8685 provides for the position of the seam (Fig. 9.6.d), hydraulic pressure test.
To test wire or rods of round and square section intended for the manufacture of bolts, nuts and other fasteners by the upsetting method, a draft test (GOST 8817) is used. The standard recommends a certain degree of deformation. The criterion of validity is the absence of cracks, tears, delaminations on the side surface of the sample.
Rice. 9.6. Pipe test schemes:
a - on the bend; b - on board; c - for distribution; d, e - for flattening
For bar materials, a bending test is widely used: bending to a certain angle (Fig. 9.7.a), bending until the sides are parallel (Fig. 9.7.b), bending until the sides touch (Fig. 9.7.c).
Rice. 9.7. Bend test patterns:
a - bend to a certain angle; b - bend until the sides are parallel; c - until the sides touch
5. Technological tests of metals and alloys
The ability of metals and alloys to undergo various types of technological processing (processing by pressure, cutting, welding) depends on their technological properties. To determine the technological properties, tests are carried out on technological samples that are most often used in working conditions. Technological samples include tests for bending, upsetting, flattening, beading, pipe bending and many others. Many technological samples and test methods are standardized.
According to the results of technological tests, the possibility of manufacturing a high-quality product from a given material is determined under conditions corresponding to the technological process adopted in this production.
The bending test (GOST 14019 - 80) is used to determine the ability of materials to withstand specified bending deformations without destruction. Sample / (Fig. 6, a) with the help of a mandrel 2 is bent under the action of the force of the press between rollers 3 to a given angle a. The ability of a material to withstand bending deformation is characterized by a given bending angle a. When the sample is bent through 180°, the material is able to withstand the ultimate bending strain. Samples that have passed the test must not have cracks, tears, delaminations.
The bending test is subjected to sheets up to 30 mm thick, long products - bars, channels, corners.
Rice. 6. Technological tests:
a - for bending, b - for draft, c - for flattening pipes, d - for beading pipes, e - for bending pipes; 1 - sample, 2 - mandrel, 3 - rollers,
4 - sample before upsetting, 5 - sample after upsetting, 6 - pipe
The upset test (GOST 8817-82) is used to determine the ability of a metal to withstand a given plastic deformation. Sample 4 is deposited in a hot or cold state using a press or hammer to a certain height h (Fig. 6.6). The slump test is carried out on round or square samples with a diameter or side of a square in a cold state from 3 to 30 mm, in a hot state - from 5 to 150 mm. The height of steel samples should be equal to two diameters, and samples of non-ferrous alloys - at least 1.5 diameters. The sample is considered to have passed the test if no cracks, tears or breaks appear on it.
Pipe flattening test (GOST 8695 - 75) is used to determine the ability of pipes to flatten to a certain height H (Fig. 6, c) without cracks and tears. The end of the pipe 6 or its segment 20...50 mm long is flattened between two parallel planes. If the pipe is welded, then the seam on the pipe should be located along the horizontal axis, as shown in the figure. Flattening of pipes is carried out smoothly at a speed of no more than 25 mm/min. The sample is considered to have passed the test if no cracks or tears appear on it.
The pipe beading test (GOST 8693-80) is used to determine the ability of pipes to be beaded at an angle of 90 °. The end of the pipe 6 (Fig. 6, d) is beaded with the help of a mandrel 2 with a force P of the press until a flange of a given diameter D is obtained. The working surface of the mandrel must be cleanly machined and have high hardness (HRC not less than 50). The radius of curvature of the mandrel, which forms the bead, must be equal to twice the thickness of the pipe wall (R=2s). Beading is considered to be of high quality if no tears or cracks are found on the flange.
Pipe bend test (GOST 3728-78) is used to determine the ability of pipes to bend without cracks and tears at an angle of 90 °. Before testing, pipe 6 (Fig. 6, (3)) is filled with clean, dry river sand or other filler. The test consists in smooth bending of the sample in any way that allows bending the sample so that its outer diameter D in no place becomes less than 85% from the initial For testing pipes with an outer diameter of up to 60 mm, their segments are used, with a diameter of 60 mm or more - longitudinal tapes 10 mm wide cut from pipes.
A weldability test is performed to determine the strength of a welded butt joint. The welded sample is subjected to bending (see Fig. 6, a) at a given angle a or tested in tension. The strengths of the welded and unwelded specimens of the test metal are then compared.
6. Structure of metals, alloys and liquid melts
Metals are simple substances that have free electrons not associated with certain atoms, which are able to move throughout the volume of the body. This feature of the state of a metallic substance determines the properties of metals.
Metal atoms easily donate outer (valence) electrons, thus turning into positively charged ions. The electrons released from the atoms are continuously chaotically mixed throughout the entire volume of the metal, like molecules in gases. Therefore, such free electrons are often called an electron gas. Free electrons, colliding with positively charged ions during their movement, can reconnect with them for some time. In such cases, positively charged ions turn into neutral atoms. Thus, metals consist of an ordering of positively charged ions located in space, electrons moving among them, and a small number of neutral atoms. The metals are aluminium, iron, copper, nickel, chromium, etc.
Alloys are systems consisting of two or more metals or metals and non-metals. Alloys have all the characteristic properties of metals. For example, carbon steel and cast iron - alloys of iron with carbon, silicon, manganese, phosphorus and sulfur; bronze - an alloy of copper with tin or other elements; brass - an alloy of copper with zinc and other elements. In industry, alloys are widely used, obtained by fusion of components, followed by crystallization from a liquid state. Much less often - alloys obtained by sintering powders of metals and non-metals.
Positively charged ions and neutral atoms in the process of crystallization of a metal or alloy from a molten (liquid) state are grouped in a strictly defined sequence, forming crystal lattices - a correct, ordered arrangement of atoms in a unit cell. Crystal lattices are characterized by type and size.
The crystal lattices of metals and alloys can be of various types. Body-centered cubic lattices (BCC) (Fig. 7, a) form iron Fe a , chromium Cr, molybdenum Mo, etc. Face-centered cubic lattices (FCC) (Fig. 7.6) form iron Fe v . copper Cu, aluminum Al, lead Pb, etc. Hexagonal close-packed (hcp) (Fig. 7, c) is formed by zinc Zn, magnesium Mg, cobalt Co, etc.
Rice. 7. Schemes of crystal lattices:
a-body-centered cubic (BCC). b - face-centered cubic (fcc). c - hexagonal close-packed (hcp)
The dimensions or periods of the lattice - the distances awe between the centers of atoms or ions located at the nodes of the lattice - are measured in angstroms (1A = 10~10 m).
With a change in temperature or pressure, the type and period of the lattice can change, which leads to a change in the physicochemical properties of metals and alloys.
All metals and alloys have a crystalline structure. In the process of crystallization, positively charged ions, arranged sequentially in the form of elementary crystal lattices, form crystals in the form of grains (Fig. 8, a) or dendrites 1 (Fig. 8, b). The resulting crystals grow, crystallize from the liquid melt at first freely, do not interfere with each other, then they collide and the growth of crystals continues only in those directions where there is free access to the liquid metal. As a result, the original geometrically correct shape of the crystals is violated. In crystallized metals and alloys, grains and dendrites have an irregular, geometrically distorted shape.
When heated, the heat absorbed by metals is spent on the vibrational movements of atoms and, as a result, on the thermal expansion of the metal. During melting, the volume of metals increases by 3...4%. As the temperature rises, the vibrational motions of atoms or ions increase, the crystal grains disintegrate, and the alloy, passing through the solid-liquid state, turns into a melt.
During the transition to the melt, the crystal structure of the metal is not completely destroyed. In the melt, there are always the smallest areas in which the original, hereditary structure of the metal, close to crystalline, is preserved. In addition, there are always refractory particles (furnace lining residues mixed with other elements) that can form additional centers crystallization and cause the onset of crystallization. The artificial creation of crystallization centers in the melt with a simultaneous change in its cooling rate is used to control the crystallization of the alloy in order to obtain the desired structure and properties of the alloy in the solid state.
Rice. Fig. 8. Scheme of crystallization of the alloy in the form of grains (a) and dendrites (b)
Bibliography
1) Gevorkyan V.G. Fundamentals of welding business - M .: Vyssh. school, 1985. - 168 p., ill.
2) Material science and technology of metals. - M.: graduate School, 2001. - 637 p.
3) Kurdyumov G.V. The phenomenon of quenching and tempering steel. - M.: Metallurgizdat, 1960. - 64 p.
4) Lakhtin Yu.M. Materials Science. - M.: Mashinostroenie, 1993. - 448 p.
5) Gulyaev A.P. Metal science. - M.: Metallurgy, 1986. - 544 p.
6) Zarembo E.G. Transformations in the structure and properties of steel. - M.: VIIIT, 1990
7) Steklov O. I. Fundamentals of welding production - M .: Vyssh. school, 1986. - 224 p., ill.
8) Khrenov K.K. Welding, cutting and soldering of metals - M.: Mashinostroenie, 1973. - 408 p.
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ORGANIZATION AND TECHNOLOGY OF TESTS
Tests are one of the stages of creation finished products, on which the quality, reliability, durability and, ultimately, the competitiveness of products depend to a large extent.
Definition of the test process.
The concept of “testing” covers a large range of works, including: experimental determination of the main parameters and characteristics of products, experimental testing of the design of assembly units, assemblies and products in general.
In the process of testing, the operating modes, starting and switching on of the product are worked out. ultimate goal experimental development is the creation of a product that best meets the technical requirements for product design. In a number of cases, according to the test results, it turns out to be necessary not only to change the design of individual assembly units and assemblies, but also to significantly change the general scheme of the machine.
The main objectives of the tests products are:
Assessment of the correctness of the design and working scheme of the units and the product as a whole, adjusting them in the process of working out;
Checking and testing the functioning of units, assembly units and the product itself in operational conditions, testing their interaction in the overall design scheme;
Determination of the main parameters and characteristics of units and products in the full operational range of conditions for their use;
Investigation and elimination of the causes found during the testing of faults that can lead the product to an inoperable state when the product is operating at the stand or in real conditions;
Tests are assigned in accordance with the requirements design documentation and in close connection with the main values of the design parameters of the product, the principles of developing its design and are part of the overall process of creating products.
Object (product, products, etc.);
Means of testing (testing equipment, verification and recording tools);
test executor;
NTD for testing (program, methodology).
Controlled
exploitation,
operational
periodical,
inspection
TESTS
Technical operation, consisting in the establishment of one or more characteristics of a given product, process or service in accordance with an established procedure.
The test system includes the following main elements:
1. Object (product, product)
3. Means for carrying out tests and measurements (test equipment and verification or recording means)
4. Performer of the test
5. NTD for testing (program, methodology).
Classification of the main types of tests
Research phase
Research - if necessary, carried out at any stage life cycle products.
So, purchased materials can be checked before the start of manufacturing the product, parts of the product manufactured - during the operating room.
Research tests are carried out to study the behavior of an object under one or another external influencing factor, or in the event that the necessary amount of information is not available.
In the workshops of pilot production, models, mock-ups, prototypes are made according to sketches, which are then tested.
In the process of research testing, the performance, the correctness of the design solution, possible characteristics, patterns and trends in parameter changes, etc. are evaluated.
Research tests are mainly carried out on a type representative.
At the research stage
Research tests are carried out how defining or how estimated.
Determinative- the goal is to find the values of one or more quantities with a given accuracy and reliability.
Estimated - tests designed to establish the fact of the suitability of the test object.
At the development stage
Finishing tests - at the R&D stage to assess the impact of technical documentation changes to ensure the required product quality indicators. The need for finishing tests is determined by the developer. Tests are subjected to experimental and prototype products and their constituent parts. If necessary, the developer involves the manufacturer in the tests.
Preliminary tests - determination of the possibility of presenting samples for acceptance tests.
Tests are carried out in accordance with the standard or other documents.
In the absence of these documents, the decision to carry out is made by the developer.
The program of preliminary tests is as close as possible to the operating conditions of the product. The organization of the tests is the same as in the finishing tests.
Preliminary tests are carried out by certified test departments using certified test equipment.
Based on the test results, an act, a report are drawn up and the possibility of presenting the product for acceptance testing is determined.
Acceptance test (PI) are carried out to determine the feasibility and possibility of putting products into production. (Acceptance tests in a single production are carried out to resolve the issue of the expediency of their transfer to operation).
A typical representative of products for testing is selected based on the condition of the possibility of distributing the results of its tests to the entire set of products.
Acceptance tests are carried out by certification departments on certified test equipment.
with PI, all the values \u200b\u200bof indicators and requirements established in the technical building are controlled.
PI of the upgraded products is carried out by comparative testing of the proposed and manufactured products.
At the production stage
Qualification tests (QI) apply when; assessing the readiness of an enterprise to release specific serial products, as well as when putting into production products under licenses and products mastered at another enterprise.
The need for a clinical trial is established by the acceptance committee.
Acceptance testing (PSI) carried out to decide on the suitability of products for delivery or use.
Tests are carried out by the service technical control enterprises, if necessary, involving the customer. All products are subjected to tests or a sample is made in a batch (if there are methods that allow evaluating the entire batch from a sample).
During testing, the values of the main parameters and the performance of the product are monitored.
The test procedure is established by GOST or TU, and for a single production in those. assignment.
Periodic testing (PI) carried out for the purpose of:
Periodic quality control of products;
Stability control tech. process between successive tests;
Confirmation of the possibility of extending the manufacture of products according to the current documentation;
Confirmation of the quality level of products released during the controlled period;
Confirmation of the effectiveness of the methods used in the acceptance control.
Type tests (TI) control of products of the same standard size, according to a single methodology, which is carried out to assess the effectiveness and feasibility of changes made to the design or technical process.
The tests are carried out by the manufacturer with the participation of representatives of the state acceptance or by a testing organization.
Inspection tests (AI) carried out selectively in order to control the stability of the quality of samples of finished products in operation.
Carried out by special authorized organizations (Gosnadzor, departmental control, etc.).
Certification tests (SI) are carried out to determine the compliance of products with safety and security requirements environment, and in some cases the most important indicators of product quality, economy, etc.
SI is an element of a system of measures aimed at confirming the compliance of the actual characteristics of products with the requirements of scientific and technical documentation.
SI is carried out by independent testing centers.
Based on the results of the SI, a certificate of conformity of products to the requirements of scientific and technical documentation is issued.
Certification implies mutual recognition of test results by the supplier and the consumer of products, which is especially important in foreign trade operations.
OPERATION STAGE
Controlled Operation (CA)
PE is carried out to confirm the compliance of products with the requirements of scientific and technical documentation in the conditions of its use, to obtain additional information about reliability, recommendations for eliminating shortcomings, and increasing the efficiency of use.
For PE, samples are isolated, creating conditions close to operational ones.
Samples that have passed qualification or periodic tests are put on the PE.
The results of PE (information about failures, maintenance, repair, consumption of spare parts, etc.) are entered by the consumer into notices that are sent to the manufacturer (developer), or a log at the place of operation.
Operational Periodic Tests (EPT) are carried out to determine the possibility or expediency of further operation of the product in the event that a change in its quality indicator can pose a threat to health safety, the environment, or lead to a decrease in the effectiveness of its use.
Each unit of operated products is subjected to tests at established intervals of operating time or calendar time.
Tests are carried out by the state supervision bodies.
Combination of the following types of tests is allowed:
Preliminary with finishing;
Acceptance with acceptance (for single production);
Acceptance with qualification (for series production);
Periodic with standard ones with the consent of the consumer, except for products subject to State acceptance;
Certification with acceptance and periodic.
TEST LEVEL
State - for acceptance qualification, inspection, certification and periodic.
Interdepartmental -
Departmental - for acceptance, qualification and inspection tests.
State tests - tests of the most important types of products carried out in the parent organizations for testing these types of products.
Interdepartmental tests - are carried out, as a rule, during acceptance tests with the participation of representatives of interested departments (ministries).
According to the conditions and place of testing, there are:
Laboratory - carried out in laboratory conditions.
Bench - conducted on test equipment in testing or research departments (serial and special equipment).
Polygons - performed on a test site (for example, a car).
Natural - tests performed under conditions appropriate to the use of the product for its intended purpose. The product is being tested.
Using models - carried out on a physical model (simplifying, reducing).
Sometimes tests of physical models are combined with physical-mathematical and mathematical models.
Time (period) of the event.
Normal - methods and conditions of testing provide obtaining the necessary amount of information about the properties of the object in the same time interval as during operation.
Accelerated - the necessary information is obtained in a shorter time than with normal tests. This can be achieved by more stringent test conditions.
Abbreviated - conducted on a reduced program.
By defined characteristic objects
Functional - are carried out in order to determine the indicators of the purpose of the object.
stability - determine the ability of the product to implement its functions and maintain parameter values within the limits. established NTD during exposure to certain factors (agr. environment, shock waves, etc.)
transportability - is determined to determine the possibility of transportation without destruction and with the ability to perform its functions.
Boundary - to determine the dependencies between prev. admissible values of parameters of objects and modes of operation.
Technological - are carried out during the manufacture of products in order to ensure its manufacturability.
According to the impact
Indestructible - after testing, the object can function.
Destructible - cannot be used for operation.
Product testing– experimental determination of the quantitative and qualitative characteristics of the properties of an object (product) taking into account the modes of operation and external influencing factors.
The sequence of preparation and testing can be represented as the following main stages:
1. Drawing up annual and quarterly plans for testing;
2. Development of a test program, preparation of existing, and, if necessary, design and manufacture of test tools (equipment and measuring instruments); certification of test equipment, including verification of measuring instruments;
3. Development of test methods (methods) and their certification;
4. Selection of samples for testing;
5. Carrying out tests in accordance with the program and test procedure, with the registration of the values of the characteristics of the test conditions and the characteristics of the properties of the tested samples, as well as the determination of their errors;
6. Study, if necessary, of the tested samples after the end of the tests with the registration of the values of the characteristics and the determination of their errors;
7. Processing of test data, including assessment of completeness, accuracy and reliability;
8. Making decisions on the results of tests and on the use of samples, registration of test results in the form of a protocol, as well as other materials.
Planning - the first stage of test preparation,
The main document that establishes the timing of testing for fixed types of products is the test schedule, which indicates:
Type of tests;
Product name and address of the manufacturer;
Deadline for submitting samples for testing;
The body involved in the selection of samples (samples) for testing;
Deadlines for conducting tests and issuing a conclusion with a recommendation to make appropriate decisions.
The schedule for testing products is formed on the basis of: tasks for creating samples of new (modernized) products, a plan for new equipment.
Test program - the main working document for testing specific products. The test program is an organizational and methodological document that is mandatory for implementation, which establishes:
3. Tasks of product testing
4. Types and sequence of parameters and indicators to be checked
5. Timing
6. Test methods.
The test program is developed, as a rule, for each category of tests separately, taking into account the conditions and technical support for their implementation.
Test program in general case contains the following sections:
Scope and purpose of the test sequence;
Nomenclature of determined characteristics (indicators), technical requirements to products;
General terms tests.
Test Methods are developed separately for various types of tests (for reliability, safety, etc.) and provide for the determination of one or more indicators (characteristics) established in the test program, as well as all the characteristics of the object and test conditions necessary for this.
The test procedure usually includes the following information:
1. The purpose of the test, the categories of tests for which this type of test is required.
3. Selection of test samples depending on the test category.
4. An indication of the equipment used for testing with reference to the test conditions and to the standards according to which the equipment is certified.
5. Description of the procedure and sequence of tests.
7. Evaluation of test results.
8. Instruction on the execution of test results.
9. Requirements for safety and environmental protection.
When developing test methods, it is necessary to use international (foreign) standards for product test methods.
The test methodology should be focused on automating test processes, as well as processing and recording test and measurement results using microprocessor technology, high-precision electronic sensors and converters, modern recording equipment using digital and magnetic media, etc. the test methodology should correspond to the world level and reflect the accumulated experience in testing.
In all materials related to the preparation of testing, designing and creating test tools, certification of test equipment, development and certification of test methods, as well as all materials of observations, measurements and processing of test results, including negative ones, recorded on various media ( observation and test logs, oscillograms, magnetic tapes, computer memory disks, etc.) should be systematized in chronological order as tests are carried out, without any exceptions, and be kept for a period established by the parties participating in the test.
Test results - this is an assessment of the characteristics of the properties of the object, establishing the compliance of the object with the regulated requirements according to the test data, the results of the analysis of the quality of the object's functioning during the test. The test results are the result of processing the test data.
The test results are recorded in a protocol containing conclusions on the compliance of products with the requirements of scientific and technical documentation and on stability. technological process(based on a comparison of the results obtained with the results of previous periodic or acceptance or qualification tests). The protocol is approved by the enterprise (organization) that conducted the tests.
The protocol drawn up based on the test results contains:
1. Name of the testing organization, category and level of testing.
2. Information about the tested products, with the name and symbol products. Date of manufacture of products, batch number, serial numbers of test samples according to the numbering system of the manufacturer. List of measured parameters and their characteristics, as well as product requirements, conditions of its operation, storage and transportation.
3. Description of the tests (type of tests, name of the test procedure, conditions and place of the tests, their time and duration).
4. Information about test equipment: lists of test equipment and measuring instruments; accuracy characteristics of test equipment and measuring instruments, information about their certification; information about the means of processing test data.
5. Test results together with test data or the name and designation of the data protocol, with suggestions from the test department and recommendations for improving or refining products.
All materials related to the preparation of testing, designing and creating test tools, certification of test equipment, development and certification of test methods, as well as all materials of observations, measurements and processing of test results, including negative ones, recorded on various media (logs observations and tests, oscillograms, magnetic tapes, computer memory disks, etc.), should be systematized in chronological order as tests are carried out, without any exceptions, and be stored for a period established by the parties participating in the test.
Organizations conducting product testing ensure, in the prescribed manner, the storage of all documents related to product testing: test programs and methods, work logs, reports, acts, protocols, conclusions, etc.
ORGANIZATION OF ACTIVITIES
TESTING LABORATORIES
(CENTERS)
Testing laboratories (centers) can be both independent legal entity as well as being a unit within an organization.
Typical structure testing laboratory has the following form
Supervisor laboratory (center) carries out general management and formulates the policy of its activities.
Responsible for the quality assurance system, develops and monitors the implementation of the provisions of the “Quality Manual” of the laboratory (c).
Deputy The test manager is responsible for the implementation of all technical tasks associated with testing.
Secretariat performs office management functions, receives and registers orders for testing, archives working documentation, etc.
Group Specialists for testing, they directly test products and draw up test reports in the designated area.
Technical Competence testing laboratory (center) is determined by the presence in it of:
Qualified personnel;
necessary measuring instruments for testing and control;
premises with appropriate environmental conditions;
documented work processes;
regulatory and methodological documents for methods and test tools;
test quality assurance systems.
Staff testing laboratory should have adequate education and qualifications.
This takes into account the following points:
Basic education;
Special professional education before starting work in the laboratory;
Education and training on special issues after starting work in the laboratory;
Knowledge of methods and means of measurement, testing and control necessary for carrying out specific tests obtained in the course of advanced training;
Experience working in test groups.
The laboratory should have the necessary documentation and information regarding qualifications, practical experience and training. These data are given in the “Quality Manual”. job description establishing the functions, duties, rights and responsibilities, qualification requirements to education, technical knowledge and work experience.
Great attention in the testing laboratory should be given to measures to improve the skills of personnel. They should be conducted for both new and experienced employees.
Distinguish external and internal training.
External - takes place in traditional forms - participation in conferences and seminars; study in courses; in educational institutions (higher level than the student or similar but required for work).
internal - self-training; regular discussion by employees of problems related to qualifications (similar to the famous Japanese “quality circles”).
Such discussions should be held without moral pressure on employees from management. Initiative in solving problems aimed at improving tests should be encouraged.
International organization "EUROLAB", uniting testing laboratories different countries Europe, has established four qualification levels for testing personnel:
1. Elementary level - non-special education and special training.
2. Basic level - the basic professional education required to perform work in the laboratory.
3. Advanced level - higher basic professional education for work in the laboratory and more advanced knowledge.
4. highest level – higher education, ability to solve complex test problems, in-depth knowledge of testing and management (management).
Each of these 4 levels provides for three gradations of qualification: sufficient, good and excellent. By means of these criteria, personnel are assessed in the accreditation of testing laboratories for compliance with EN45001.
The success of the trials depends to a large extent on the availability of test equipment and measuring instruments.
Depending on the field of application, the test equipment is divided into:
general industrial;
Industry;
Special (equipment made in single copies, and equipment intended for testing products manufactured only at this enterprise).
If necessary, the missing equipment is designed and manufactured in advance - industry and special test equipment and stands for a specific type of product.
General provisions and procedure attestations test equipment
Test equipment that reproduces normalized external influencing factors and loads is subject to certification.
Purpose of certification - determination of the normalized accuracy characteristics of the equipment, their compliance with the requirements of the NTD and the establishment of the suitability of the equipment for operation.
To the normalized accuracy characteristics test equipment include specifications, which determine the ability of the equipment to reproduce and maintain test conditions in the specified ranges, with the required accuracy and stability, for a specified period.
Certification is subject to prototypes, mass-produced and modernized equipment, equipment made in single copies, imported equipment.
The test equipment recognized by the results of certification as suitable for use is allowed for operation.
Operation and maintenance documentation must be available. Faulty equipment that gives questionable results when tested should be taken out of service and marked appropriately to indicate its unsuitability.
After repair, its suitability must be confirmed by tests (verification, calibration).
Each item of test or measurement equipment must have registration feature. containing the following information:
Equipment identification;
Name of the manufacturer (company), type (brand), factory inventory number;
Dates of receipt and commissioning;
Current location (if necessary);
Condition at the time of receipt (new, worn, with an extended period of validity, etc.);
Repair and maintenance data;
A description of any damage or failure, alterations or repairs.
Calibration or verification of measuring and testing equipment, if necessary, is carried out before putting it into operation and then in accordance with installed program.
The overall equipment calibration program should ensure traceability of measurements taken by the laboratory against national and international reference instruments, if any.
If such traceability is not possible, then the testing laboratory needs to provide convincing evidence of the correlation or accuracy of the test results (for example, by participating in an appropriate interlaboratory testing program).
exemplary the measuring instruments available in the laboratory should only be used for calibration of the working equipment and not used for other purposes, they should be calibrated by a competent authority that can ensure their traceability to a national or international standard.
The premises of the testing laboratory must provide the conditions necessary to adversely affect the accuracy and reliability of the tests.
The test rooms must be protected from the effects of such WWF as: increase in t 0 , dust, humidity, noise, vibration, electromagnetic disturbances, and also meet the requirements of applicable test methods, sanitary norms and rules, labor safety and environmental protection requirements.
The premises must be large enough to eliminate the risk of damage to equipment and the occurrence of hazardous situations, to provide employees with freedom of movement and accuracy of action.
If necessary, they are provided with devices regulating test conditions and emergency power supplies.
The conditions for the admission of persons who are not related to the personnel of this laboratory should be determined, which is one of the conditions for ensuring the confidentiality of information about the activities of the laboratory for third parties.
Data on the state of production facilities and a plan for their placement constitute a separate section of the Quality Manual.
The testing laboratory should have well-regulated and documented work processes which accompany the entire testing process from order acceptance to the issuance of a test report. Thus, uniqueness is achieved in the performance of technological operations in the laboratory.
In GOST 51000.3-96, special attention is paid to procedures that have a significant impact on test results.
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The procedure for handling product test samples (this process is also called “sample management”) includes:
Proper preparation and conduct of sampling, their labeling;
Compliance with the conditions of transportation and storage.
Samples of products submitted for testing must be identified for compliance normative documentation and be accompanied by appropriate selection protocol.
The registration system should guarantee the confidentiality of the use of the samples or test items, for example with respect to other customers. If necessary, introduce a procedure that ensures the storage of products in the warehouse.
At all stages of storage, transportation and preparation of products for testing, the necessary precautions are taken to prevent damage to products as a result of contamination, corrosion or excessive loads that adversely affect test results.
Receipt, storage, return (or disposal) of samples are carried out according to clearly established rules.
Proper sample management is one of the most important steps in ensuring test quality.
When conducting tests in the laboratory, it is necessary to use the methods established by the standard or specifications for testing processes.
These documents must be at the disposal of the personnel responsible for carrying out the tests.
If there is no established test method, an agreement between the customer and the laboratory on the method to be used should be documented.
The work carried out by the testing laboratory is reflected in a protocol showing accurately, clearly and unambiguously the test results and other information related to them.
Each test report must contain at least the following information:
Name, address of the testing laboratory and place of testing, if it has a different address;
The designation of the protocol (for example, serial number 0 and the numbering of each page, as well as the total number of pages;
Name and address of the customer;
Characteristics and designation of the test sample;
Dates of sample receipt and testing;
Designation of the terms of reference for the test, description and procedures (if necessary);
Description of the sampling procedure (sampling);
Any changes made to technical task to conduct tests or other information related to a particular test;
Data relating to the performance of non-standard test methods or procedures;
Measurements, observations and results obtained, supported by tables, graphs, drawings and photographs, and, if necessary, any registered failures;
Statement of measurement error (if necessary);
Signature official responsible for the preparation of the test report and the date of its compilation;
A statement that the protocol applies only to the specimens that have been tested;
A statement excluding the possibility of partial reprinting of the report without the permission of the testing laboratory.
Of great importance for ensuring the quality of tests are procedures related to operation of measuring instruments, tests and control. It is important to consider here:
Maintaining a register of test, measurement and control means indicating the necessary technical and metrological characteristics;
Labeling and storage of this equipment;
Availability of methods for performing measurements, tests and control at each workplace;
Compliance with external operating conditions;
Availability of maintenance and repair schedules, as well as verification and calibration documentation;
Appointment of responsibility
To establish the complex of mechanical properties of metals, samples from the material under study are subjected to static and dynamic tests.
Static tests are tests in which the load applied to the sample increases slowly and smoothly.
4.2.1. Static tests include tensile, compression, torsion, bending, and hardness testing. As a result of static tensile tests, which are carried out on tensile machines, a tensile diagram (Fig. 4.6 a) and a conditional stress diagram (Fig. 4.6 b) of ductile metal are obtained.
Rice. 4.6. Change in deformation depending on stress: a – tensile diagram of a plastic material; b - diagram of conditional stresses of plastic material
It can be seen from the graph that no matter how small the applied stress, it causes deformation, and the initial deformations are always elastic and their magnitude is directly dependent on the stress. On the curve shown in the diagram (Fig. 4.6), elastic deformation is characterized by the OA line and its continuation.
Above point A, the proportionality between stress and strain is broken. Stress causes not only elastic, but also plastic deformation.
Shown in Fig. 4.6 the relationship between the stress applied from the outside and the relative deformation caused by it characterizes the mechanical properties of metals:
The slope of the straight line OA (Fig. 4.6a) shows metal hardness or a description of how the load applied from the outside changes the interatomic distances, which in the first approximation characterizes the forces of interatomic attraction; the slope of the straight line OA is proportional to modulus of elasticity (E), which is numerically equal to the voltage divided by the relative elastic strain (E = s / e);
Voltage s PTS (Fig. 4.6b), which is called limit of proportionality, corresponds to the onset of plastic deformation. The more accurate the strain measurement method, the lower point A lies;
Voltage s control (Fig. 4.1b), which is called elastic limit, and at which the plastic deformation reaches a predetermined small value established by the conditions. Often use values of permanent deformation of 0.001; 0.005; 0.02 and 0.05%. The corresponding elastic limits are denoted s 0.005, s 0.02, etc. The elastic limit is an important characteristic of spring materials that are used for elastic elements of devices and machines;
Voltage s 0.2, which is called conditional yield strength and which corresponds to a plastic deformation of 0.2%. The physical yield strength s t is determined from the tensile diagram when it has a yield plateau. However, during tensile testing of most alloys, there is no yield plateau on the diagrams. The selected plastic deformation of 0.2% characterizes the transition from elastic to plastic deformations quite accurately, and the stress s 0.2 is easily determined during testing, regardless of whether or not there is a yield plateau on the diagram. stretching. The permissible voltage, which is used in the calculations, is usually chosen less than s 0.2 by 1.5 times;
The maximum voltage s in, which is called temporary resistance, characterizes the maximum bearing capacity of the material, its strength prior to destruction, and is determined by the formula
s in \u003d P max / F o
The allowable voltage, which is used in the calculations, is chosen less than s in 2.4 times.
The plasticity of the material is characterized by relative elongation d and relative narrowing y:
d \u003d [(l k - l o) / l o] * 100,
y \u003d [(F o - F k) / F o] * 100,
where l o and F o are the initial length and cross-sectional area of the sample;
l to - the final length of the sample;
F k - cross-sectional area at the rupture site.
4.2.2. Hardness- the ability of materials to resist plastic or elastic deformation when a more solid body is introduced into it, which is called indenter.
There are different methods for determining hardness.
Brinell hardness is defined as the ratio of the load when a steel ball is pressed into the material under test to the surface area of the resulting spherical indentation (Fig. 4.7a).
HB=2P/pD,
D is the ball diameter, mm;
d – hole diameter, mm
Rice. 4.7. Hardness test schemes: a - according to Brinell; b - according to Rockwell; c - according to Vickers
Rockwell hardness is determined by the depth of penetration into the tested material of a diamond cone with an angle at the top of 120 ° or a hardened ball with a diameter of 1.588 mm (Fig. 4.7.b).
A cone or ball is pressed in with two successive loads:
Preliminary P o \u003d 10 n;
General R \u003d R o + R 1, where R 1 is the main load.
Hardness is indicated in conventional units:
For scales A and C HR = 100 - (h - h o) / 0.002
For scale B HR = 130 - (h - h o) / 0.002
To determine the hardness, a diamond cone at a load of 60 N (HRA), a diamond cone at a load of 150 N (HRC) or a steel ball with a diameter of 1.588 mm (HRB) is used.
Vickers hardness measured for parts of small thickness and thin surface layers obtained by chemical-thermal treatment.
This hardness is defined as the ratio of the load during indentation into the tested material of a diamond tetrahedral pyramid with an angle between the faces of 136 o to the surface area of the resulting pyramidal imprint (Fig. 4.7.c):
HV \u003d 2P * sin a / 2 / d 2 \u003d 1.854 P / d 2,
a \u003d 136 o - the angle between the faces;
d is the arithmetic mean of the lengths of both diagonals, mm.
The value of HV is found from the known d according to the formula or from calculation tables according to GOST 2999-75.
microhardness, taking into account the structural heterogeneity of the metal, it is used to measure small areas of the sample. In this case, the pyramid is pressed in as in determining the Vickers hardness, with a load P = 5-500 N, and the arithmetic mean of the lengths of both diagonals (d) is measured in microns. A metallographic microscope is used to measure microhardness.
4.2.3. The resistance of a material to destruction under dynamic loads characterizes impact strength. It is defined (GOST 9454-78) as the specific work of destruction of a prismatic sample with a concentrator (notch) in the middle with one blow of a pendulum impact tester (Fig. 4.8): KS = K / S o (K is the work of destruction; S o is the cross-sectional area of the sample in concentrator site).
Rice. 4.8. Impact test scheme
Impact strength (MJ / m 2) denote KCU, KCV and KCT. The letters KS mean the symbol of impact strength, the letters U, V, T - the type of concentrator: U-shaped with a notch radius r n = 1 mm, V-shaped with r n = 0.25 mm; T is a fatigue crack created at the base of the notch; KCU is the main criterion for impact strength; KCV and KCT are used in special cases.
The work expended on the destruction of the sample is determined by the formula
And n \u003d P * l 1 (cos b - cos a),
where P is the mass of the pendulum, kg;
l 1 is the distance from the axis of the pendulum to its center of gravity;
b - angle after impact;
a - angle before impact
4.2.4.Cyclic durability characterizes the performance of the material under conditions of repeatedly repeated stress cycles. Stress cycle - the totality of voltage changes between its two limit values s max and s min during the period T (Fig. 4.9).
Rice. 4.9. Sinusoidal voltage cycle
There are symmetrical cycles (R = -1) and asymmetric (R varies widely). Different kinds cycles characterize various modes of operation of machine parts.
The processes of gradual accumulation of damage in the material under the action of cyclic loads, leading to a change in its properties, the formation of cracks, their development and destruction, are called fatigue, and the ability to resist fatigue is called endurance (GOST 23207 - 78).
A number of factors influence the fatigue of machine parts (Fig. 4.10).
Rice. 4.10. Factors Affecting Fatigue Strength
Fatigue failure compared to static load failure has a number of features:
It occurs at stresses less than at static load, lower yield limits or tensile strength;
Destruction begins on the surface (or close to it) locally, in places of stress concentration (deformation). Local stress concentration is created by damage to the surface as a result of cyclic loading or notches in the form of traces of processing, exposure to the environment;
Fracture proceeds in several stages, characterizing the processes of damage accumulation in the material, the formation of fatigue cracks, the gradual development and merging of some of them into one main crack, and the rapid final destruction;
Fracture has a characteristic fracture structure, reflecting the sequence of fatigue processes. The fracture consists of a fracture site (the place where microcracks form) and two zones - fatigue and fracture (Fig. 4.11).
Rice. 4.11. Scheme of a fatigue fracture fracture: 1 – crack initiation site; 2 – fatigue zone; 3 - doloma zone
4.3. Structural strength of metals and alloys
Structural strength metals and alloys is a complex of strength properties that are in the greatest correlation with the service properties of a given product.
Material resistance brittle fracture is the most important characteristic that determines the reliability of the structure.
The transition to brittle fracture is due to a number of factors:
The nature of the alloy (type of lattice, chemical composition, grain size, contamination of the alloy);
Design feature (presence of stress concentrators);
Operating conditions (temperature conditions, the presence of a load on the metal).
There are several criteria for assessing the structural strength of metals and alloys:
Criteria determining reliability metals against sudden fractures (critical brittle temperature; fracture toughness; work absorbed during crack propagation; survivability under cyclic loading);
Criteria determining durability material (fatigue strength; contact endurance; wear resistance; corrosion resistance).
To assess the reliability of the material, the following parameters are also used: 1) impact strength KCV and KCT; 2) temperature threshold of cold brittleness t 50 . However, these parameters are only qualitative, unsuitable for strength calculations.
The KCV parameter evaluates the suitability of the material for pressure vessels, pipelines and other structures of increased reliability.
The KCT parameter, determined on samples with a fatigue crack at the base of the notch, is more indicative. It characterizes the work of crack development during impact bending and evaluates the ability of the material to slow down the fracture that has begun. If the material has KCT = 0, then this means that the process of its destruction goes without the cost of work. Such material is fragile, operationally unreliable. And vice versa, the larger the KCT parameter determined at operating temperature, the higher the reliability of the material under operating conditions. KCT is taken into account when choosing a material for structures of especially critical use ( aircraft, turbine rotors, etc.).
The cold brittleness threshold characterizes the effect of a decrease in temperature on the tendency of a material to brittle fracture. It is determined from the results of impact testing of notched specimens at decreasing temperature.
The transition from ductile to brittle fracture is indicated by changes in the fracture structure and a sharp decrease in impact strength (Fig. 4.12), observed in the temperature range (t in - t x) (boundary temperatures of ductile and brittle fracture).
Rice. 4.12. Influence of test temperature on the percentage of ductile component in the fracture (B) and the impact strength of the material KCV, KCT
The structure of the fracture changes from fibrous matte with ductile fracture (t > tc) to crystalline shiny with brittle fracture (t< t х). Порог хладноломкости обозначают интервалом температур (t в – t н) либо одной температурой t 50 , при которой в изломе образца имеется 50 % волокнистой составляющей, и величина КСТ снижается наполовину.
The suitability of the material for operation at a given temperature is judged by the temperature margin of viscosity equal to the difference between the operating temperature and t 50 . At the same time, the lower the brittle transition temperature in relation to the operating temperature, the greater the temperature margin of viscosity and the higher the guarantee against brittle fracture.
4.4. Ways to increase the strength of metals
It is customary to distinguish between technical and theoretical strength. Technical strength is determined by the value of properties: elastic limit (s 0.05); yield strength (s 0.2); tensile strength (s in); modulus of elasticity (E); endurance limit (s R).
Under the theoretical strength understand the resistance to deformation and destruction, which the materials should have according to physical calculations, taking into account the forces of interatomic interaction and the assumption that two rows of atoms are simultaneously displaced relative to each other under the action of shear stress.
Based on the crystal structure and interatomic forces, it is possible to approximately determine the theoretical strength of the metal according to the following formula:
t theor » G / 2p,
where G is the shear modulus.
The theoretical value of strength, calculated according to the specified formula, is 100 - 1000 times greater than the technical strength. This is due to defects in the crystal structure, and primarily to the existence of dislocations. The strength of metals is not a linear function of dislocation density (Fig. 4.13).
Rice. 4.13. Scheme of dependence of resistance to deformation on density and other defects in metals: 1 - theoretical strength; 2-4 - technical strength (2 - whiskers; 3 - pure unhardened metals; 4 - alloys hardened by alloying, hardening, thermal or thermomechanical treatment)
As can be seen from Figure 4.13, the minimum strength is determined by some critical dislocation density a, approximately equal to 10 6 – 10 8 cm -2 . This value refers to annealed metals. The value of s 0.2 for annealed metals is 10 -5 - 10 -4 G . If a a> 10 12 - 10 13 cm -2, then in this case cracks may form.
If the dislocation density (the number of defects) is less than the value a(Fig. 4.13), then the resistance to deformation increases sharply and the strength quickly approaches the theoretical one.
Strength increase is achieved:
The creation of metals and alloys with a defect-free structure, i.e. obtaining whiskers ("whiskers");
Increasing the density of defects, including dislocations, as well as structural obstacles that impede the movement of dislocations;
Creation of composite materials.
4.5. Influence of heating on the structure and properties of deformed metal (recrystallization)
Plastic deformation (Fig. 4.14) leads to the creation of an unstable state of the material due to increased internal energy (internal stresses). The deformation of the metal is accompanied by its hardening or the so-called hardened . Spontaneously, phenomena should occur that return the metal to a more stable structural state.
Rice. 4.14. Influence of heating on the mechanical properties and structure of hard-worked metal
Spontaneous processes that bring the plastically deformed metal to a more stable state include the removal of crystal lattice distortion, other intragranular processes, and the formation of new grains. To relieve the stresses of the crystal lattice, high temperature is not required, since in this case there is a slight movement of atoms. Already a slight heating (for iron 300-400 o C) removes lattice distortions, namely, it reduces the density of dislocations as a result of their mutual annihilation, merging of blocks, reduction of internal stresses, reduction in the number of vacancies, etc.
The correction of a distorted lattice during the heating of a deformed metal is called return or vacation. In this case, the hardness of the metal decreases by 20-30% compared to the original, and the ductility increases.
In parallel with the return at a temperature of 0.25 - 0.3 T pl occurs polygonization (collection of dislocations into the walls) and a cellular structure is formed.
Recrystallization is one of the ways to relieve internal stresses during deformation of materials. Recrystallization , i.e. the formation of new grains, proceeding at higher temperatures than the return, can begin at a noticeable rate after heating above a certain temperature. The higher the purity of the metal, the lower the recrystallization temperature. There is a relationship between recrystallization and melting temperatures:
T rivers \u003d a * T pl,
where a is a coefficient depending on the purity of the metal.
For commercially pure metals a = 0.3 - 0.4, for alloys a = 0.8.
The recrystallization temperature is important practical value. In order to restore the structure and properties of the work-hardened metal (for example, if necessary, continue the pressure treatment by rolling, drawing, drawing, etc.), it must be heated above the recrystallization temperature. This processing is called recrystallization annealing.
The recrystallization process can be divided into two stages:
Primary recrystallization or processing recrystallization, when the grains elongated due to plastic deformation turn into small rounded randomly oriented grains;
Secondary or collective recrystallization, which consists in the growth of grains and proceeds at a higher temperature.
Primary crystallization consists in the formation of new grains. These are usually small grains that appear on the interfaces of large deformed grains. Although intragranular processes of eliminating defects (return, rest) occur during heating, they, as a rule, do not end completely, on the other hand, the newly formed grain is already free from defects.
By the end of the first recrystallization stage, it is possible to obtain a structure consisting only of very fine grains, having a diameter of a few microns. But at this moment, the process of secondary crystallization begins, which consists in grain growth.
Three essentially different grain growth mechanisms are possible:
- embryonic, consisting in the fact that after primary crystallization, the seed centers of new crystals reappear, their growth leads to the formation of new grains, but there are fewer of them than the grains in the initial state, and therefore, after the completion of the recrystallization process, the grains will become larger on average;
- migratory , which consists in moving the grain boundary and increasing its size. Large grains grow by "eating" small ones;
- coalescence of grains , consisting in the gradual "dissolution" of grain boundaries and the combination of many small grains into one large one. In this case, an inequigranular structure with low mechanical properties is formed.
The implementation of one of the main growth mechanisms depends on:
From temperature. At low temperatures, growth occurs due to the coalescence of grains, and at high temperatures, due to the migration of grain boundaries;
From the initial state (from the degree of deformation). At a low degree of deformation (3-8%), primary recrystallization is difficult, and grain growth occurs due to grain coalescence. At the end of the process, giant grains are formed. At a high degree of deformation (more than 10%), the coalescence of grains becomes more difficult, and growth occurs due to the migration of grain boundaries. Smaller grains are formed. Thus, after annealing, an equilibrium structure is obtained, mechanical properties change, hardening of the metal is removed, and plasticity increases.
Introduction. Drawing up a test program for a turbogenerator
1 Working programm tests of turbogenerator TVV-63-2
1.1 Overvoltage test with a frequency of 50 Hz
1.2 Winding insulation test with increased rectified voltage
1.3 Determining the characteristics of the generator. Determination of the operability of an intermediate relay with a coil of copper wire. Selection of the maximum voltage relay and additional thermostable resistor for thermal compensation. Determination of the initial temperature of the stator winding of an electric machine. Calculation of the magnetizing and control windings for testing stator steel
Conclusion
Introduction
One of the main parameters of the operation of any power plant and power system is the continuity of energy generation and supply to consumers. The continuity of power generation is ensured by the high reliability of all power - auxiliary and main, power and low-current equipment. Therefore, absolutely all power plant equipment is subject to periodic repairs and tests: the frequency of these works is strictly regulated by the PTE and Test Standards. None of the equipment at the power plant can be put into operation if the period for its repair and testing has expired.
In this term paper a test program for the turbogenerator is compiled, the operability of the intermediate relay is determined, the maximum voltage relay and the additional thermostable resistor are selected, the initial temperature of the stator winding is determined, and the magnetizing and control windings are calculated for testing the stator steel.
I. Drawing up a test program for a turbogenerator
Tab. 1.1 Main parameters of the generator
Turbogenerator type TVF-63-2 Rated power 78.75 MVA / 63 MW Stator voltage, nominal 10.5 kW Stator current, nominal 4330 A Capacitance of one stator phase relative to ground and two other grounded phases 0.25 μF Excitation system High-frequency, VTD-490-3000U3 Rotor winding resistance, at 15 º С0.103 Ohm Stator cooling system Indirect, with hydrogen Rotor cooling system Direct, with hydrogen 1.1 Work program for testing the turbogenerator TVV-63-2
1.1.1 Overvoltage test with a frequency of 50 Hz 1. Test conditions. the generator stator winding circuit is disassembled, each phase is tested separately, the other two phases are short-circuited and grounded; the generator winding is cleaned of dirt, washed and dried; in the cooling system and through the winding, a distillate with a resistivity of at least 75 kOhm/cm circulates. Distillate consumption is nominal; tests are carried out at night with the general lighting of the engine room turned off and the local lighting turned on. At the last stage, local lighting is also turned off to monitor the corona of the stator winding; the test scheme is shown in Figure 1.2. The test voltage is calculated by the formula: where is the rated voltage of the generator; 3. The circuit is connected to a linear voltage, in which there are fewer higher harmonics than in the phase voltage, and therefore, the possibility of distortion of the test voltage sinusoid is less. 4. Before starting the test, it is necessary to adjust the breakdown voltage of the arrester FV to 110% of the test voltage: The test circuit is disconnected from the test object and the test voltage rises at idle. The set voltage is set to 21.12 kV, and the spark gap balls approach each other until breakdown occurs. The test voltage decreases to 50% and rises again until a breakdown occurs: the breakdown voltage of the arrester should be in the range (1.05-1.1), that is, 20.16-21.12 kV. The control breakdown of the ball gap FV is carried out by raising the voltage c three times. Carrying out tests with increased voltage of frequency 50 Hz. The voltage rises from zero smoothly, at a rate of about 2% / s-0.38 kV / s. Therefore, the entire procedure for raising the voltage will last about 1-2 minutes. In the process of raising the voltage, it is necessary to listen to the generator for crackling or hissing of partial discharges. At the same time, it is necessary to observe the winding - whether smoldering or sparking will appear on the surface of the winding. In the process of raising the voltage, it is necessary to make intermediate readings on voltmeters and the partial discharge indicator. In the event of a discrepancy in the readings of the voltmeter or a sharp increase in the readings of the partial discharge indicator, the voltage rise should be stopped and the cause of the abnormality should be immediately investigated. When the full test voltage is reached, it is maintained for 1 min and gradually decreases to the rated voltage. At rated voltage for 5 minutes, the insulation is checked visually, for which it is desirable to completely turn off the lighting in the machine room, subject to safety measures. At the same time, yellow and red glow concentrated at individual points, smoke, smoldering bandages, etc. should not be observed. Blue and white light is allowed. Upon completion of observations of corona winding, the voltage gradually decreases to zero, the winding is discharged and grounded. Machine room lighting is switched on. All three phases of the stator winding are tested in turn. Necessary equipment. high voltage test facility according to the diagram in figure 1.1; spring stopwatch with a division value of 0.2 s; discharge-grounding rod; the winding temperature is taken as the average value of the readings of the regular stator thermal control. Figure 1.1 Scheme of the installation for testing the generator with an increased voltage of industrial frequency 50 Hz. 1.1.2 Winding insulation test with increased rectified voltage 1 Test conditions: the stator winding circuit is disassembled, the neutral is disassembled; water from the stator winding is drained, the winding is purged with compressed air; the tests are carried out phase by phase, while the other two phases are short-circuited and grounded. The voltage rises in five steps of 1/5 of the full test voltage, kV, At each stage, this voltage is held for 60 s. At each stage, the leakage current through the insulation is measured 15 s and 60 s after a constant voltage is established: i. Based on the measured voltage of a given stage and leakage currents, and for each stage, the insulation resistance values \u200b\u200bare calculated for 15 s and 60 s, Ohm, At each stage, the absorption coefficient is calculated, During the test, a graph of the dependence of the leakage current on the test voltage is built. The leakage current must not exceed the limits given in Table 2. Table 1.2 Leakage current limits from test voltage The multiplicity of the test voltage in relation to the nominal / 0.511.5 and above Leakage current , mA0.250.51 If in the process of raising the voltage, the value of the leakage current begins to increase sharply and goes beyond the permissible limits, then the tests must be stopped until the cause of the sharp increase in the leakage current is clarified. Upon reaching the full design test voltage, it is maintained for one minute and then gradually decreases to zero over two minutes. When the voltage drops to zero, it is necessary to discharge the winding by applying grounding through the current-limiting resistor of the grounding rod. After 10 s, it is necessary to apply a dead ground to the output of the tested phase. The coefficient of nonlinearity is calculated, where is the maximum leakage current at full test voltage; Leakage current at a test voltage of approximately 0.5×Unom of the generator; Full test voltage; Test voltage equal to approximately 0.5 × Unom of the generator. The non-linearity coefficient must be less than three. Measuring apparatus and equipment. apparatus for testing insulation AIM-90 (with a milliammeter up to 5mA). spring stopwatch with a division value of 0.2 s. grounding rod. 1.1.3 Characterization of the generator 1. Removing the characteristics of a three-phase short circuit (SC). 1.1 The test conditions for short circuits, which are set when removing the characteristics of a three-phase short circuit, must be designed for a long-term flow of the rated current of the generator. 1.2 The short circuit characteristic within at least one and a half times the rated stator current has a rectilinear character, therefore it is enough to take 4-5 points of the characteristic up to. 3 If the determination of the short circuit characteristics of the generator is not accompanied by a change in its losses, then maintaining the rated speed is not necessary. 4 The characteristic is taken with a gradual increase in the rotor current and simultaneous recording of steady-state values at each stage of the rotor current and current in all phases of the stator. 5 Deviation of short circuit characteristics taken during testing from the factory one should be within the allowable measurement errors. Special attention is paid to the fact that the characteristic tends to the origin of coordinates. Otherwise, repeated tests are made, and if the result is repeated, then an assumption is made about the presence of turn short circuits in the rotor winding. In this case, turning on the machine is not allowed. 2. Removal of characteristics of idling of the generator (ХХ). 1 Before raising the voltage on the generator to take the characteristic, measure the residual voltage on the generator with the rotor winding open. 2 To remove the characteristics of the idling of the generator, the voltage is gradually raised to a predetermined value at the rated speed of rotation. Typically, the voltage on the generator rises to 115% of the nominal. Test voltage, kV, 2.3 During the start-up tests of the generator, the removal of the idling characteristic is combined with a check of the turn insulation. To do this, the voltage on the generator rises to a voltage corresponding to the rated current of the rotor, but not lower than 130% of the rated voltage. The duration of this test -5 minutes. Test voltage, kV, By reducing the voltage on the generator, the main points of the characteristic are removed. The last point is taken with the excitation current turned off. Total shoot 10 -15 points at approximately equal voltage intervals. The resulting idling characteristic is shifted by Di0
.
4 Reading of instrument readings is carried out only when the parameters are established simultaneously on all instruments at the command of the test supervisor or an observer measuring the rotor current. Both counting and recording of instrument readings are made in scale divisions indicating the measurement limit. 5 After the completion of measurements, before analyzing the circuit, it is necessary to build a characteristic and make sure that there are no large number of doubtful points that make it difficult to build a characteristic. 6 To obtain the characteristics of idling in the area of increased voltage, without a significant increase in voltage on the generator, it is removed at a reduced rotation speed, followed by recalculation according to the formula where UNOM- voltage at rated rotation speed; nNOM
- nominal rotation speed; n1
- the rotation speed at which the measurements were made. 7 Simultaneously with the removal of the characteristics of idling during commissioning tests, the symmetry of the voltage is checked. To do this, in a steady state close to nominal, the voltages between the three phases are measured. Measurement is made by one voltmeter that increases measurement accuracy. Voltage unbalance DU is determined by the ratio of the difference between the largest UMAX
and least UMIN measured voltages to its average value of the line voltage USR:
The coefficient of asymmetry should not exceed 5%. 8 According to the characteristic of idling, the rotor current is determined, corresponding to the rated voltage of the generator at idling. It must match the calculated value. If the rotor current is higher than the calculated one, then errors in the calculations or installation should be looked for (increased air gap or incorrect installation of the rotor in height, deviations in the quality of steel). 9 Measuring apparatus and equipment. a voltmeter of class 0.5 or 0.2, connected through a “voltmeter key”, which allows you to quickly switch the voltmeter to other linear voltages during testing; a frequency meter with limits of 45-55 Hz, and to take the characteristics of idling at a reduced frequency, a frequency meter with a low measurement limit of 40 Hz; class 0.2 millivoltmeter connected to a standard or specially installed class 0.2 shunt in the rotor circuit. Fig.1.2 Scheme of three-phase short circuit and no-load characterization II. Determination of the operability of an intermediate relay with a coil of copper wire
Table 2.1 Initial data Rated voltage of the relay, , V110Minimum relay actuation voltage, , V100 Relay coil resistance at 20 º FROM, , Ohm8500Maximum relay temperature, , º C85 Rated voltage of the DC network, , B110 The minimum voltage of the operational DC network at which the circuit must operate, V: Minimum relay operation current, A: Relay winding resistance at maximum temperature 85 ºС, Ohm: 3 Current in the hot winding of the relay with a resistance of 10039 Ohm at a possible minimum voltage in the DC network, A: Conclusion on the performance of the relay. Since the current in the relay winding in the heaviest mode is less than the minimum current of the relay operation, it can be concluded that the relay under study cannot be used under these conditions. III. Selection of the maximum voltage relay and additional thermostable resistor for thermal compensation
Table 3.1 Initial data Required relay actuation voltage, Vmsr, V55 Permissible actuation error, %2 Relay temperature change range, º C10 - 30 Relay winding resistance change, %, In a given temperature range, the resistance of the relay winding, and hence the response voltage, change by 8%. To solve this problem, it is necessary to apply a circuit in which the current flowing through the relay would not depend on the temperature of the relay. According to /2, table 3-5/, we select a low-voltage relay RN51 / 6.4, which has the following characteristics: All other voltage 55-6.4 = 48.6 ATis extinguished on the resistance of a resistor made of a temperature-independent resistive material - constantan or manganin. Additional resistor resistance, Ohm, The total change in the resistance of the relay circuit with an added resistor in a given temperature range,%, Since the total change in the resistance of the relay circuit with the added resistor, and hence the change in the resistance of the relay operation did not exceed 2% - the maximum allowable rate, then we can conclude that the calculated relay and resistor can be used in a given temperature range. IV. Determination of the initial temperature of the stator winding of an electric machine turbogenerator relay resistor stator Table 4.1 Initial data Readout#12345Timet, s10204090160Overheat0C57,955,952,344,937.9 The calculation is made graphically (Figure 4.1) and in digital form. The cooling time constant, T, s is determined: where t- time interval; qH- overheating of the machine at the beginning of the time interval ti ; q- overheating of the machine at the end of the time interval ti. For the calculated value of the cooling time constant, the arithmetic mean value of TCP is taken: Initial overheating of the machine by the analytical method:
tOKR =
200
FROM
qMBP =
qH+tOKR ;
qMBP =
59,67+20 =79,67 0
FROM.
Rice. 4.1 The process of cooling the electric machine after it is turned off in semi-logarithmic coordinates. Initial overheating of the machine by a graphical method:
Initial temperature of the stator winding of an electrical machine at ambient temperature tOKR =
200
FROM
qMBP =
qH+tOKR ;
qMBP =
59.74 + 20 \u003d 79.74 0С. The difference between the analytical and graphical methods is 0.09%. Rice. 4.2 Scheme for measuring the resistance of the stator winding of an electric machine immediately after it is turned off V. Calculation of the magnetizing and control windings for testing stator steel
Table 5.1 Initial data Outer diameter, dH, M3.05Inner diameter, dB, m1.36Total length of the stator back, l, m6.7Ventilation duct width, lk, m0.01Number of ventilation ducts, n60Stator tooth height, he, m0.27Steel fill factor, k0.93Heat capacity become, m , kW × h/(kg × deg)1.429 × 10-4
It is assumed that 1/3 of the power is spent on losses during external environment for convection and radiation. To power the magnetization windings, a voltage of 380 V is selected. The number of turns of the magnetizing and control windings. The current consumed by the magnetizing winding, active and full power. Heating rate of active steel. Back length: Back height: Clear cross-section of the back: Average back diameter: Weight of stator active steel: Required temperature rise rate a = 5 0S/h. Power required for this: The value of induction is determined to create specific losses R0
\u003d 1.072 W / kg / 1, table and Fig. 3 / B = 0.825 T If you turn on the magnetizing winding for the line voltage of the auxiliary network of 380 V, then the following number of turns will be required: It is practically impossible to create a fractional number of turns. Therefore, we choose one turn W=1. In this case, the inductive resistance of the magnetizing winding will inevitably decrease against the calculated value, the magnetizing current and induction will increase. You can use the switching taps of the auxiliary transformer and switch it to the minimum voltage (+10% of the nominal) 418 V. This voltage will allow you to create induction in the stator: To create induction B \u003d 0.577 T according to the schedule / 1, Fig. 3 / we determine the required specific ampere-turns: 0= 71 A-w/m Full ampere turns: With one turn W= 1 magnetizing current is numerically equal to: =AW/W,= 552 /1 = 552A.
The total power of the magnetizing winding: = I×
U,= 552 × 418 = 230.7 kVA.
Active power at induction B = 0.577 T is calculated from the value of specific losses / 1, Fig. 3 / p0 = 0.621 W / kg: P = p0
×
g, P = 0.621 × 197799.525 = 122833.505W = 122.8 kW. Power factor of the magnetizing circuit: The cable for the magnetization winding, based on the current density allowed in this case j = 2.0 A / mm2, must have a cross section of at least: Given that the voltage on the control winding with an equal number of turns with the magnetizing winding will be close to a voltage of 380 AT, choose one turn for the control winding WTo= 1, EMF of the control winding with induction in the stator AT= 1 Tldefined: Additional resistor R (Fig. 5.1) for a 300 V voltmeter, 150 div. and internal resistance RВ = 30 kΩ is chosen so that at 724 V (corresponding to V = 1 T), its readings would be equal to 100 divisions: Rice. 5.1 Scheme of induction heating of the generator stator by magnetization of the stator steel Conclusion
In this course work, a test program for a turbogenerator was compiled. The operability of an intermediate relay under certain conditions was determined, a maximum voltage relay and an additional thermostable resistor for thermal compensation were also selected. A calculation was also made to determine the initial temperature, graphical and analytical methods. Calculated, for certain generators, control and magnetizing windings. Bibliographic list of information sources
1.Volumes and standards for testing electrical equipment / Pod. total ed. B.A. Alekseeva, F.L. Kogan, L.G. Mamikoyants. -6th ed. -M.: NTs ENAS, 1998. 2.Handbook for setting up electrical equipment power stations and substations / Pod. ed. E.S. Musaelyan -Moscow: Energoatomizdat, 1984. .Musaelyan E.S. Adjustment and testing of electrical equipment of power stations and substations. -Moscow: Energoatomizdat, 1986.
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