Means and methods of control. The condition of parts and connections can be determined by inspection, touch testing, using measuring tools and other methods.
During the inspection, the destruction of the part is revealed (cracks, chipping of surfaces, breaks, etc.), the presence of deposits (scale, carbon deposits, etc.), leakage of water, oil, fuel: By checking by touch, wear and collapse of threads are determined on parts as a result of pre-tightening, elasticity of seals, presence of burrs, scratches, etc. Deviations of joints from a given gap or tension of parts from a given size, from flatness, shape, profile, etc. are determined using measuring instruments.
The choice of control means should be based on ensuring the specified indicators of the control process and analysis of the costs of implementing control for a given product quality. When choosing control means, you should use control means that are effective for specific conditions, regulated by government, industry and enterprise standards.
The selection of controls includes the following steps:
analysis of the characteristics of the control object and indicators of the control process;
determination of the preliminary composition of controls;
determination of the final composition of control means, their economic justification, preparation of technological documentation.
Depending on the production program and the stability of the measured parameters, universal, mechanized or automatic control means can be used. During repairs, universal measuring instruments and tools are most widely used. Based on their operating principle, they can be divided into the following types.
1. Mechanical instruments - rulers, calipers, spring instruments, micrometers, etc. As a rule, mechanical instruments and instruments are characterized by simplicity, high reliability of measurements, but have relatively low accuracy and control performance. When making measurements, it is necessary to observe the Abbe principle (comparator principle), according to which it is necessary that the axis of the instrument scale and the controlled size of the part being tested are located on the same straight line, i.e. the measurement line must be a continuation of the scale line. If this principle is not followed, then the skew and non-parallelism of the guides of the measuring device cause significant measurement errors.
2. Optical instruments - eyepiece micrometers, measuring microscopes, collimation and spring-optical instruments, projectors, interference devices, etc. Using optical instruments, the highest measurement accuracy is achieved. However, devices of this type are complex, their setup and measurement are time-consuming, they are expensive and often do not have high reliability and durability.
3. Pneumatic instruments - lengths. This type of instrument is used mainly for measuring external and internal dimensions, deviations in the shape of surfaces (including internal ones), cones, etc. Pneumatic instruments have high accuracy and speed. A number of measuring tasks, for example, accurate measurements in small-diameter holes, can only be solved with pneumatic-type devices. However, devices of this type most often require individual calibration of the scale using standards.
4. Electrical appliances. They are becoming increasingly common in automatic control and measuring equipment. The prospects of the devices are determined by their speed, the ability to document measurement results, and ease of management.
The main element of electrical measuring instruments is a measuring transducer (sensor), which perceives the measured value and produces a signal of measuring information in a form convenient for transmission, conversion and interpretation. Converters are classified into electric contact (Fig. 2.1), electric contact scale heads, pneumoelectric contact, photoelectric, inductive, capacitive, radioisotope, mechanotronic.
Types and methods of non-destructive testing. Visual inspection allows you to identify visible violations of the integrity of the part. Visual-optical inspection has a number of obvious advantages over visual inspection. Flexible fiber optics with a manipulator allows you to inspect significantly larger areas that are inaccessible to open viewing. However, many dangerous defects that appear during operation are mostly not detected by visual optical methods. Such defects include, first of all, small-sized fatigue cracks, corrosion lesions, structural transformations of the material associated with natural and artificial aging processes, etc.
In these cases, physical methods of non-destructive testing (NDT) are used. Currently, the following main types of non-destructive testing are known: acoustic, magnetic, radiation, capillary and eddy current. Their brief characteristics are given in table. 2.3.
Each type of non-destructive testing has several varieties. Thus, among the acoustic methods one can distinguish a group of ultrasonic methods, impedance, free vibrations, velosymmetric, etc. The capillary method is divided into color and luminescent, the radiation method into X-ray and gamma methods.
A common feature of non-destructive testing methods is that directly measured by these methods are physical parameters such as electrical conductivity, absorption of x-rays, the nature of reflection and absorption of x-rays, the nature of reflection and absorption of ultrasonic vibrations in the products under study, etc. By changing the values of these In some cases, parameters can indicate changes in the properties of the material, which are very important for the operational reliability of products. Thus, a sharp change in the magnetic flux on the surface of a magnetized steel part indicates the presence of a crack in that location; the appearance of additional reflection of ultrasonic vibrations when the part is sounded signals a violation of the homogeneity of the material (for example, delaminations, cracks, etc.); by changing the electrical conductivity of a material, one can often judge a change in its strength properties, etc. Not in all cases it is possible to give an accurate quantitative assessment of the detected defect, since the relationship between physical parameters and parameters to be determined during the inspection process (for example, crack size, the degree of decrease in strength properties, etc.), as a rule, is not unambiguous, but is statistical in nature with varying degrees of correlation. Therefore, physical methods of non-destructive testing in most cases are more qualitative and less often quantitative.
Typical defects in parts. The structural parameters of the car and its components depend on the state of the interfaces and parts, which is characterized by fit. Any violation of the fit is caused by: a change in the size and geometric shape of the working surfaces; violation of the relative position of working surfaces; mechanical damage, chemical and thermal damage; changes in the physical and chemical properties of the part material.
Changes in the size and geometric shape of the working surfaces of parts occur as a result of their wear. Uneven wear causes the appearance of such defects in the shape of working surfaces as ovality, taper, barrel-shaped, corsetedness. The intensity of wear depends on the loads on the mating parts, the speed of movement of the rubbing surfaces, the temperature conditions of the parts, the lubrication regime, and the degree of environmental aggressiveness.
Violation of the relative position of the working surfaces manifests itself in the form of changes in the distance between the axes of cylindrical surfaces, deviations from parallelism or perpendicularity of axes and planes, deviations from the coaxiality of cylindrical surfaces. The causes of these violations are uneven wear of working surfaces, internal stresses that arise in parts during their manufacture and repair, residual deformations of parts due to exposure to loads.
The relative position of the working surfaces is most often violated in case parts. This causes distortions in other parts of the unit, accelerating the wear process.
Mechanical damage to parts - cracks, breaks, chipping, risks and deformations (bending, twisting, dents) occur as a result of overloads, impacts and fatigue of the material.
Cracks are typical for parts operating under cyclic alternating loads. Most often they appear on the surface of parts in places where stress is concentrated (for example, near holes, in fillets).
Breaks, characteristic of cast parts, and spalling on the surfaces of cemented steel parts occur as a result of exposure to dynamic shock loads and due to metal fatigue.
Risks on the working surfaces of parts appear under the influence of abrasive particles that contaminate the lubricant.
Parts made of rolled profiles and sheet metal, shafts and rods operating under dynamic loads are subject to deformation.
Chemical-thermal damage - warping, corrosion, carbon deposits and scale appear when the car is used in difficult conditions.
Warping of the surfaces of parts of significant length usually occurs when exposed to high temperatures.
Corrosion is the result of chemical and electrochemical exposure to the surrounding oxidizing and chemically active environment. Corrosion manifests itself on the surfaces of parts in the form of continuous oxide films or local damage (stains, cavities).
Carbon deposits are the result of water being used in the engine cooling system.
Scale is the result of water being used in the engine cooling system.
A change in the physical and mechanical properties of materials is expressed in a decrease in the hardness and elasticity of parts. The hardness of parts may decrease due to the application of the material structure when heated to high temperatures during operation. The elastic properties of springs and leaf springs are reduced due to material fatigue.
Limit and permissible dimensions and wear of parts. There are dimensions of the working drawing, permissible and maximum dimensions and wear of parts.
The dimensions of the working drawing are the dimensions of the part indicated by the manufacturer in the working drawings.
Acceptable are the dimensions and wear of a part at which it can be reused without repair and will work flawlessly until the next smooth repair of the vehicle (unit).
Limits are the dimensions and wear of a part at which its further use is technically unacceptable or economically infeasible.
Wear of a part during different periods of its operation does not occur evenly, but along certain curves.
The first section of duration t 1 characterizes the wear of the part during the running-in period. During this period, the surface roughness of the part obtained during its processing decreases, and the wear rate decreases.
The second section of duration t 2 corresponds to the period of normal operation of the interface, when wear occurs relatively slowly and evenly.
The third section characterizes a period of sharp increase in the intensity of surface wear, when maintenance measures can no longer prevent this. During the time T that has passed since the start of operation, the interface reaches a limiting state and requires repair. The gap in the interface, corresponding to the beginning of the third section of the wear curve, determines the values of the maximum wear of parts.
Sequence of inspection of parts during defects. First of all, visual inspection of parts is carried out in order to detect damage visible to the naked eye: large cracks, breaks, scratches, chipping, corrosion, soot and scale. Then the parts are checked on devices to detect violations of the relative position of the working surfaces and the physical and mechanical properties of the material, as well as for the absence of hidden defects (invisible cracks). Finally, the dimensions and geometric shape of the working surfaces of the parts are controlled.
Control of the relative position of working surfaces. Deviation from alignment (displacement of the axes) of the holes is checked using optical, pneumatic and indicator devices. Indicator devices are most widely used in car repairs. When checking deviations from alignment, rotate the mandrel, and the indicator indicates the value of the radial runout. Deviation from alignment is equal to half of the radial runout.
The misalignment of the shaft journals is controlled by measuring their radial runout using indicators installed in the centers. The radial runout of the journals is defined as the difference between the largest and smallest indicator readings per shaft revolution.
The deviation from parallelism of the hole axes is determined by the difference |a 1 - a 2 | distances a 1 and a 2 between the internal generatrices of the control mandrels at length L using a punch or an indicator bore gauge.
The deviation from the perpendicularity of the axes of the holes is checked using a mandrel with an indicator or gauge, measuring the gaps D 1 and D 2 over a length L. In the first case, the deviation of the axes from perpendicularity is determined as the difference in the indicator readings in two opposite positions, in the second - as the difference in the gaps |D 1 - D 2 |.
The deviation from parallelism of the hole axis relative to the plane is checked on the slab by changing the deviation indicator of the dimensions h 1 and h 2 along the length L. The difference in these deviations corresponds to the deviation from parallelism of the hole axis and the plane.
The deviation from the perpendicularity of the hole axis to the plane is determined at diameter D as the difference in indicator readings when rotating on a mandrel relative to the hole axis or by measuring the gaps at two diametrically opposite points along the periphery of the gauge. The deviation from perpendicularity in this case is equal to the difference in the measurement results |D 1 -D 2 | on diameter D.
Monitoring hidden defects is especially necessary for critical parts on which vehicle safety depends. For control, crimping, paint, magnetic, luminescent and ultrasonic methods are used.
The crimping method is used to identify cracks in body parts (hydraulic test) and to check the tightness of pipelines, fuel tanks, and tires (pneumatic test). I install the body part for testing on a stand, seal the external holes with covers and plugs, after which water is pumped into the internal cavities of the part to a pressure of 0.3... 0.4 MPa. Water leakage shows the location of the crack. During a pneumatic test, air at a pressure of 0.05...0.1 MPa is supplied inside the part and immersed in a bath of water. Bubbles of escaping air indicate the location of the crack.
The paint method is used to detect cracks with a width of at least 20...30 microns. The surface of the part being tested is degreased and red paint diluted with kerosene is applied to it. After washing off the red paint with a solvent, cover the surface of the part with white paint. After a few minutes, red paint will appear on the white background, penetrating into the crack.
The magnetic method is used to control hidden cracks in parts made of ferromagnetic materials (steel, cast iron). If a part is magnetized and sprinkled with dry ferromagnetic powder or poured with a suspension, then their particles are attracted to the edges of the cracks, as if to the poles of a magnet. The width of the powder layer can be 100 times greater than the width of the crack, which makes it possible to identify it.
Magnetize parts on magnetic flaw detectors. After inspection, the parts are demagnetized by passing them through a solenoid powered by alternating current.
The luminescent method is used to detect cracks wider than 10 microns in parts made of non-magnetic materials. The controlled part is immersed for 10... 15 minutes in a bath with a fluorescent liquid that can glow when exposed to ultraviolet radiation. Then the part is wiped and a thin layer of magnesium carbonate powder, talc or silica gel is applied to the controlled surfaces. The powder draws the fluorescent liquid from the crack onto the surface of the part.
After this, using a fluorescent flaw detector, the part is exposed to ultraviolet radiation. Powder impregnated with fluorescent liquid reveals cracks in the part in the form of luminous lines and spots.
The ultrasonic method, characterized by very high sensitivity, is used to detect internal cracks in parts. There are two methods of ultrasonic flaw detection - sound shadow and pulse.
The sound shadow method is characterized by the location of a generator with an ultrasonic vibration emitter on one side of the part, and a receiver on the other. If, when moving the flaw detector along the part, no defect is found, the ultrasonic waves reach the receiver, are converted into electrical impulses and, through an amplifier, reach the indicator, the arrow of which is deflected. If there is a defect in the path of sound waves, they are reflected. An audible shadow is formed behind the defective area of the part, and the indicator needle does not deviate. This method is applicable for testing parts of small thickness with two-way access to them.
The pulse method has no restrictions on the scope of application and is more widespread. It consists in the fact that the pulses sent by the emitter, having reached the opposite side of the part, are reflected from it and return to the receiver, in which a weak electricity. The signals pass through an amplifier and are fed into a cathode ray tube. When the pulse generator is started, the horizontal scan of the cathode ray tube, which represents the time axis, is simultaneously turned on using the scanner.
The moments of operation of the generator are accompanied by initial pulses A. If there is a defect, pulse B will appear on the screen. The nature and magnitude of the bursts on the screen are deciphered using reference pulse patterns. The distance between pulses A and B corresponds to the depth of the defect, and the distance between pulses A and C corresponds to the thickness of the part.
Monitoring the size and shape of the working surfaces of parts makes it possible to assess their wear and decide on the possibility of their further use. When checking the size and shape of a part, both universal tools (calipers, micrometers, indicator bore gauges, micrometric weights, etc.) and special tools and devices (gauges, rolling pins, pneumatic devices, etc.) are used.
Welded joints are checked to determine possible deviations from technical specifications presented for this type of product. A product is considered to be of high quality if deviations do not exceed acceptable standards. Depending on the type of welded joints and further operating conditions, products after welding are subjected to appropriate control.
Inspection of welded joints can be preliminary, when the quality of the starting materials, the preparation of the welded surfaces, and the condition of the tooling and equipment are checked. Preliminary control also includes welding of prototypes, which are subjected to appropriate tests. At the same time, depending on the operating conditions, the prototypes are subjected to metallographic examination and non-destructive or destructive testing methods.
Under current control understand checking compliance with technological conditions, stability of welding conditions. During routine inspection, the quality of layer-by-layer seams and their cleaning are checked. Final control carried out in accordance with technical specifications. Defects discovered as a result of inspection are subject to correction.
Non-destructive methods for testing welded joints
There are ten non-destructive methods for testing welded joints, which are used in accordance with the technical specifications. The type and number of methods depend on the technical equipment of the welding production and the responsibility of the welded joint.
Visual inspection- the most common and accessible type of control that does not require material costs. All types of welded joints are subjected to this control, despite the use of further methods. An external examination reveals almost all types of external defects. With this type of control, lack of penetration, sagging, undercuts and other defects that are visible are determined. External examination is performed with the naked eye or using a magnifying glass with 10x magnification. External inspection involves not only visual observation, but also measurement of welded joints and seams, as well as measurement of prepared edges. In mass production conditions, there are special templates that allow you to measure the parameters of welds with a sufficient degree of accuracy.
In single production conditions, welded joints are measured using universal measuring tools or standard templates, an example of which is shown in Fig. 1.
ShS-2 template set is a set of steel plates of equal thickness located on the axes between two cheeks. Each axle has 11 plates, which are pressed on both sides by flat springs. Two plates are intended for checking edge cutting units, the rest are for checking the width and height of the seam. This universal template can be used to check bevel angles, gaps and seam sizes of butt, T and corner joints.
The impermeability of containers and pressure vessels is checked by hydraulic and pneumatic tests. Hydraulic tests can be carried out with pressure, pouring or pouring water. For the pour test, the welds are dried or wiped dry, and the container is filled with water so that no moisture gets on the seams. After filling the container with water, all seams are inspected; the absence of wet seams will indicate their tightness.
Irrigation tests subject to bulky products that have access to the seams on both sides. One side of the product is watered with water from a hose under pressure and the seams on the other side are checked for tightness.
During hydraulic testing with pressure, the vessel is filled with water and an excess pressure is created that is 1.2-2 times higher than the working pressure. The product is kept in this state for 5 - 10 minutes. The tightness is checked by the presence of moisture in the filling and the amount of pressure reduction. All types of hydraulic tests are carried out at positive temperatures.
Pneumatic tests in cases where it is impossible to perform hydraulic tests. Pneumatic tests involve filling the vessel with compressed air at a pressure exceeding atmospheric pressure by 10-20 kPa or 10-20% higher than the working one. The seams are moistened with a soap solution or the product is immersed in water. The absence of bubbles indicates tightness. There is an option for pneumatic testing with a helium leak detector. To do this, a vacuum is created inside the vessel, and outside it is blown with a mixture of air and helium, which has exceptional permeability. The helium that gets inside is sucked out and ends up on a special device - a leak detector that detects the helium. The tightness of the vessel is judged by the amount of helium captured. Vacuum control is carried out when it is impossible to perform other types of tests.
The tightness of the seams can be checked kerosene. To do this, one side of the seam is painted with chalk using a spray gun, and the other is moistened with kerosene. Kerosene has a high penetrating ability, so if the seams are not tight, the reverse side will turn dark or stains will appear.
Chemical method The test is based on the interaction of ammonia with a control substance. To do this, a mixture of ammonia (1%) with air is pumped into the vessel, and the seams are sealed with tape impregnated with a 5% solution of mercury nitrate or a solution of phenylphthalein. In case of leaks, the color of the tape changes where ammonia penetrates.
Magnetic control. With this inspection method, seam defects are detected by scattering magnetic field. To do this, connect the electromagnet core to the product or place it inside the solenoid. Iron filings, scale, etc., which react to the magnetic field, are applied to the surface of the magnetized joint. In places of defects on the surface of the product, accumulations of powder are formed in the form of a directed magnetic spectrum. To ensure that the powder moves easily under the influence of a magnetic field, the product is lightly tapped, giving mobility to the smallest grains. The magnetic scattering field can be recorded with a special device called a magnetographic flaw detector. The quality of the connection is determined by comparison with a reference sample. The simplicity, reliability and low cost of the method, and most importantly its high productivity and sensitivity, allow it to be used on construction sites, in particular during the installation of critical pipelines.
Allows you to detect defects in the seam cavity that are invisible during external inspection. The weld seam is illuminated with X-ray or gamma radiation penetrating the metal (Fig. 2), for this purpose the emitter (X-ray tube or gamma installation) is placed opposite the controlled seam, and on the opposite side - X-ray film installed in a light-proof cassette.
The rays, passing through the metal, irradiate the film, leaving darker spots in areas of defects, since defective areas have less absorption. The X-ray method is safer for workers, but its installation is too cumbersome, so it is used only in stationary conditions. Gamma emitters have significant intensity and allow you to control metal of greater thickness. Due to the portability of the equipment and the low cost of the method, this type of control is widespread in installation organizations. But gamma radiation poses a great danger if handled carelessly, so this method can only be used after appropriate training. The disadvantages of radiographic testing include the fact that transmission does not allow identifying cracks that are not located in the direction of the main beam.
Along with radiation monitoring methods, they use fluoroscopy, that is, receiving a signal about defects on the device screen. This method is more productive, and its accuracy is almost as good as radiation methods.
Ultrasound method(Fig. 3) refers to acoustic testing methods that detect defects with a small opening: cracks, gas pores and slag inclusions, including those that cannot be determined by radiation flaw detection. The principle of its operation is based on the ability of ultrasonic waves to be reflected from the interface between two media. The most widely used method is the piezoelectric method of producing sound waves. This method is based on the excitation of mechanical vibrations by applying an alternating electric field in piezoelectric materials, which use quartz, lithium sulfate, barium titanate, etc.
To do this, using the piezometric probe of an ultrasonic flaw detector placed on the surface of the welded joint, directed sound vibrations are sent into the metal. Ultrasound with an oscillation frequency of more than 20,000 Hz is introduced into the product in separate pulses at an angle to the metal surface. When meeting the interface between two media, ultrasonic vibrations are reflected and captured by another probe. With a single-probe system, this may be the same probe that generated the signals. From the receiving probe, oscillations are fed to an amplifier, and then the amplified signal is reflected on the oscilloscope screen. To control the quality of welds in hard-to-reach places on construction sites, small-sized flaw detectors of lightweight design are used.
The advantages of ultrasonic testing of welded joints include: greater penetrating ability, which makes it possible to control materials of large thickness; high performance of the device and sensitivity, determining the location of a defect with an area of 1 - 2 mm2. The disadvantages of the system include the difficulty of determining the type of defect. Therefore, the ultrasonic testing method is sometimes used in combination with radiation testing.
Destructive testing methods for welded joints
Destructive testing methods include methods of testing control samples in order to obtain the required characteristics of a welded joint. These methods can be used both on control samples and on sections cut from the joint itself. As a result of destructive testing methods, the correctness of the selected materials, selected modes and technologies is checked, and the qualifications of the welder are assessed.
Mechanical testing is one of the main methods of destructive testing. Based on their data, one can judge the compliance of the base material and the welded joint with the technical specifications and other standards provided for in this industry.
TO mechanical tests include:
- testing the welded joint as a whole in its various sections (welded metal, base metal, heat-affected zone) for static (short-term) tension;
- static bending;
- impact bending (on notched samples);
- for resistance against mechanical aging;
- measurement of metal hardness in various areas of the welded joint.
Control samples for mechanical testing are welded from the same metal, using the same method and by the same welder as the main product. In exceptional cases, control samples are cut directly from the controlled product. Variants of samples for determining the mechanical properties of a welded joint are shown in Fig. 4.
Static stretch test the strength of welded joints, yield strength, relative elongation and relative contraction. Static bending is carried out to determine the ductility of the joint by the bending angle before the formation of the first crack in the tensile zone. Static bending tests are carried out on samples with longitudinal and transverse seams with the seam reinforcement removed flush with the base metal.
Impact bend- a test that determines the impact strength of a welded joint. Based on the results of hardness determination, one can judge strength characteristics, structural changes in metal and the stability of welds against brittle fracture. Depending on the technical conditions, the product may be subject to impact rupture. For small diameter pipes with longitudinal and transverse seams, flattening tests are carried out. A measure of plasticity is the size of the gap between the pressed surfaces when the first crack appears.
Metallographic studies welded joints are carried out to establish the structure of the metal, the quality of the welded joint, and identify the presence and nature of defects. Based on the type of fracture, the nature of destruction of the samples is determined, the macro- and microstructure of the weld and the heat-affected zone are studied, and the structure of the metal and its ductility are judged.
Macrostructural analysis determines the location of visible defects and their nature, as well as macrosections and fractures of the metal. It is carried out with the naked eye or under a magnifying glass with 20x magnification.
Microstructural analysis carried out with a magnification of 50-2000 times using special microscopes. With this method, it is possible to detect oxides at grain boundaries, metal burnout, particles of non-metallic inclusions, the size of metal grains and other changes in its structure caused by heat treatment. If necessary, chemical and spectral analysis of welded joints is performed.
Special tests performed for critical structures. They take into account operating conditions and are carried out according to methods developed for this type of product.
Elimination of welding defects
Welding defects identified during the inspection process that do not meet the technical specifications must be eliminated, and if this is not possible, the product is rejected. IN steel structures Removal of defective welds is carried out by plasma-arc cutting or gouging, followed by processing with abrasive wheels.
Defects in seams subject to heat treatment are corrected after tempering the welded joint. When eliminating defects, certain rules must be followed:
- the length of the removed section must be longer than the defective section on each side;
- The width of the opening must be such that the width of the seam after welding does not exceed its double width before welding.
- the sample profile should ensure reliable penetration at any location in the seam;
- the surface of each sample should have smooth outlines without sharp protrusions, sharp depressions and burrs;
- When welding a defective area, overlap of adjacent areas of the base metal must be ensured.
After welding, the area is cleaned until the shells and looseness in the crater are completely removed, and smooth transitions are made to the base metal. Removal of buried external and internal defective areas in connections made of aluminum, titanium and their alloys should be performed only mechanically - by grinding with abrasive tools or cutting. Cutting down followed by polishing is allowed.
Undercuts are eliminated by surfacing a thread seam along the entire length of the defect.
In exceptional cases, it is possible to use fusion of small undercuts with argon-arc torches, which allows smoothing out the defect without additional surfacing.
Sagging and other irregularities in the shape of the seam are corrected by mechanical processing of the seam along its entire length, avoiding underestimation of the overall cross-section.
The seam craters are welded.
The burns are cleaned and welded.
All corrections to welded joints must be carried out using the same technology and the same materials that were used when applying the main seam.
Corrected seams are subjected to re-inspection using methods that meet the requirements for this type of welded joint. The number of corrections to the same section of the weld should not exceed three.
The following methods for detecting hidden defects on parts have been used in ARP: paints, varnishes, fluorescent, magnetization, ultrasonic.
Crimping method used to detect defects in hollow parts. Crimping of parts is carried out with water (hydraulic method) and compressed air (pneumatic method).
a) The hydraulic method is used to detect cracks in body parts (block and cylinder head). Tests are carried out on special stand, which ensures complete sealing of the part, which is filled with hot water under a pressure of 0.3-0.4 MPa. The presence of cracks is judged by water leakage.
b) The pneumatic method is used for radiators, tanks, pipelines and other parts. The cavity of the part is filled with compressed air under pressure and then immersed in water. The location of the cracks is judged by the air bubbles escaping.
Paint method based on the properties of liquid paints for mutual diffusion. Red paint diluted with kerosene is applied to the degreased surface of the part. Then the paint is washed off with a solvent and a layer of white paint is applied. After a few seconds, a crack pattern appears on a white background, increased in width several times. Cracks as wide as 20 microns can be detected.
Luminescent method based on the property of some substances to glow when irradiated with ultraviolet rays. The part is first immersed in a bath of fluorescent liquid (a mixture of 50% kerosene, 25% gasoline, 25% transformer oil with the addition of a fluorescent dye). The part is then washed with water, dried with warm air and powdered with silica gel powder, which draws the fluorescent liquid from the crack onto the surface of the part. When a part is irradiated with ultraviolet rays, the boundaries of the crack will be detected by a glow. Luminescent flaw detectors are used to detect cracks larger than 10 microns in parts made of non-magnetic materials.
Magnetic flaw detection method widely used in detecting hidden defects in automotive parts made of ferromagnetic materials (steel, cast iron). The part is first magnetized, then poured with a suspension consisting of 5% transformer oil and kerosene and fine iron oxide powder. The magnetic powder will clearly outline the boundaries of the crack, because Magnetic stripes form at the edges of the crack. The magnetic flaw detection method has high productivity and allows you to detect cracks up to 1 micron wide.
Ultrasound method is based on the property of ultrasound to pass through metal products and be reflected from the boundary of two media, including from a defect. There are 2 methods of ultrasonic flaw detection: transmission and pulse.
Transillumination method is based on the appearance of a sound shadow behind a defect, with the emitter of ultrasonic vibrations located on one side of the defect, and the receiver on the other.
Pulse method is based on the fact that ultrasonic vibrations, reflected from the opposite side of the part, will return back and there will be 2 bursts on the screen. If there is a defect in the part, then ultrasonic vibrations will be reflected from it and an intermediate burst will appear on the tube screen.
The purpose of the control is to identify defects in castings and determine compliance chemical composition, mechanical properties, structure and geometry of castings to the requirements of technical specifications and drawings. Both finished castings and technological processes for their manufacture can be subject to control. Control methods are divided into destructive and non-destructive.
Destructive testing can be produced both on special samples cast simultaneously with the casting, and on samples cut from various areas of the controlled casting. The latter is used when fine-tuning the technological process or during control and acceptance tests. In this case, further use of the casting for its intended purpose becomes impossible. Destructive testing methods involve determining the chemical composition and mechanical properties of casting metal, studying its macro- and microstructure, porosity, etc.
Unbrakable control does not affect the further performance of the castings, and they remain fully serviceable. Non-destructive testing methods include: measuring the size and roughness of the casting surface, visual inspection of their surface, X-ray, ultrasonic, luminescent and others special methods control.
Cast titanium parts are used, as a rule, in critical components and assemblies of various machines, and for this reason, much attention is paid to the control of castings and the parameters of the technological process of their production. Control operations account for up to 15% of costs in the production of titanium castings. The chemical composition of the alloy, the mechanical properties of the cast metal, external and internal defects of the casting, its geometric dimensions and surface roughness are controlled. A number of stages of the casting manufacturing process are also subject to control.
The chemical composition of the alloy in castings is controlled for the content of alloying components and impurities. As is known, it depends on the chemical composition of the consumable electrodes and foundry waste involved in smelting. Therefore, control of the chemical composition of cast metal is usually carried out from a group of melts in which one batch of consumable electrodes and one batch of waste with a known content of alloying components and impurities were used.
Alloy control for carbon content is carried out from each heat, since metal smelting is carried out in graphite skull crucibles and the carbon content in the metal can vary from heat to heat.
To determine the content of alloying components and impurities, a DFS-41 type quantometer is used, and to control the content of oxygen, hydrogen and nitrogen, devices EAO-201, EAN-202, EAN-14 are used, respectively.
The mechanical properties of cast metal - tensile strength, yield strength, elongation, transverse contraction and impact strength - are controlled after each melt by testing standard samples cut from bars cast together with the castings, or from elements of the gating system.
In the process of mastering casting manufacturing technology, the hardness of the surface layer of the casting and the structure of the metal are also monitored.
After being knocked out of the molds, the castings are subject to careful visual inspection. For titanium casting, it is specific to control the surface of castings in order to identify non-welds. To detect them, magnifying glasses are used, and in difficult cases, luminescent control. Through visual inspection, defects such as non-fills, areas of burnt formation and increased roughness, external sinks, and surface blockages are also detected.
Internal defects in titanium castings - cavities, pores, blockages - are identified using fluoroscopy. For this purpose, X-ray machines of the RUP -150/300-10 type are used.
Control of the geometry of castings and their surface roughness does not differ from similar control of castings from other alloys.
The quality of castings (geometric accuracy, surface quality) is greatly influenced by the initial molding materials - graphite powder and binder. The original graphite powder is controlled for ash content. The ash content should not exceed 0.8%, and the humidity should not exceed 1%. The grain composition of graphite powder is determined on the 029 device. The grain composition must comply with the standards established in the technological instructions for this molding composition.
In organic binders, dry residue, density and viscosity are controlled. To control ready-to-compact graphite mixtures for strength, gas permeability, and crumbling, standard methods and instruments of brands 084M, 042M, 056M are used.
The heat treatment of graphite molds is carefully controlled by measuring temperature parameters.
A particularly large amount of control of various parameters is carried out during vacuum skull melting of titanium alloys. Before melting begins, the tightness of the working chamber of the installation and the residual pressure are checked. Leakage monitoring must be carried out at least once per shift. In addition, leakage is checked after every, even minor, repair of the furnace chamber or vacuum system.
Before the start of melting and during melting, the presence of coolant and its pressure at the inlet and outlet of the cooling systems of all installation components (crucible, electrode holder, chamber, cooling of vacuum pumps, etc.) are monitored. Typically, the means for monitoring the operating parameters of a scull installation are built-in.
During welding of the electrode and its melting, the parameters of the electric arc are controlled - current and voltage. For this purpose, recording control devices are used along with indicating devices. During this period, monitoring the coolant temperature using recording devices is also mandatory.
During the melting process, it is necessary to monitor pressure changes in order to timely detect depressurization of the installation (water entering the chamber, melting of current leads, the occurrence of leaks, etc.). Usually, when draining metal from the crucible, the residual pressure rises sharply, but such an increase is normal and is not of an emergency nature.
Before the metal is drained, the centrifugal machine is turned on. To control the table rotation speed, a voltmeter type M-4200 is usually used.
Signals from many smelting control devices are perceived not only by the smelter, but are also transmitted to actuators. Thus, based on signals of a sudden increase in pressure in the chamber, a drop in coolant pressure, or an unacceptable increase in its temperature, the electric arc is immediately switched off. A whole range of control operations is performed by devices for automatically conducting the smelting process.
When mastering new technological processes and casting nomenclature, as well as new equipment, use various additional types of control and corresponding equipment.