RU2413213C2 - Procedure for revealing cracks in material of part - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: part is completely immersed into liquid and maintained there for certain time not less, than eight hours equal to production cycle. Further, the part is taken out of liquid, and liquid is removed off whole surface of the part. Vibration is induced into material of the part, for example, by tapping surface of the part with a heavy object or by placing the part on a vibration bench. Presence of a micro-crack is revealed by detecting traces of liquid on surface of the part. Also, material of the heavy object has hardness less, than that of the part; weight of the object, force and impact frequency as well as a place of impacts are chosen depending on material and configuration of the part to receive oscillations of resonance frequency in material of the part intensifying escape of liquid on surface of the part.

EFFECT: increased reliability at revealing micro-cracks on surface of part.

Description

The invention relates to the field of production, repair and fault detection of parts and can be used in the repair of internal combustion engines (ICE).

A known electromagnetic method for detecting cracks [1, p. 46], which consists in the fact that when passing a magnetic flux through a part with cracks, there is a change in the magnitude and direction of the magnetic flux due to unequal cross-section of magnetic permeability. A change in the magnitude and direction of the magnetic flux is recorded by applying to the surface of the test part a magnetic powder after magnetization or in the presence of a magnetizing field. The powder settles along the edges of the crack, copying the shape of the crack, and thereby detects it. The positive side of the method is that it allows you to detect small cracks on the surface of the part. The disadvantage is that for the implementation of the method requires complex and expensive equipment, which small enterprises are not always able to purchase, if they can be purchased, they have very low efficiency due to low load during the year - this is, firstly. Secondly, the magnetic powder after determining the crack must be removed from the surface of the part, and the part must also be demagnetized. Otherwise, the part in the process of operation will attract to itself wear products, metal shavings, and during operation, forced wear of the part, for example, the necks of the crankshaft of an internal combustion engine, can occur.

The closest in technical essence to the proposed invention is the method [2, p. 111] for determining microcracks (latent defects) in the material of the part, which consists in the fact that the surface of the part is pre-cleaned of oily-mud and other contaminants, penetrant is applied (penetrating liquid) , identify the defect, if any, and produce the final cleaning of the surface of the part. With this method, it is important that the fluid that penetrated (is drawn into) the microcracks subsequently quickly leaves the crack on the surface of the part and flows along the crack, thereby indicating the presence of a crack on the surface of the part. Various methods are used to intensify the exit of liquid to the surface, for example, the part is heated. This method is simple to implement, it can be used in small enterprises, the disadvantage is that the part must be heated, which increases the duration and complexity of the operation, it can be fire hazard.

The invention consists in the following. A crack on the surface of the part is a cavity - a capillary, where liquid penetrates when applied to the surface of the part. For a more accurate determination of the presence of a crack, it is desirable that the liquid fill in fact the volume of the capillary. With the available volume of the crack, the filling depends on the type of penetrant, which, for example, is a solution based on kerosene or just kerosene, as well as on the exposure time and surface location in space. It is necessary to determine the presence of a crack over the entire surface of the part, since the determination of the presence of a crack on a limited surface area is not enough. It may happen that it was on an unchecked surface area that a crack appeared that was not noticed (not checked). This crack during operation can lead to the destruction of the part with the ensuing negative consequences. For example, the destruction (breakdown) of the ICE connecting rod during operation can lead to the destruction of the engine as a whole, which can no longer be restored. Therefore, the part that needs to be checked for cracks must be completely immersed in a container with penetrant and withstand a certain time. The longer the exposure time, the fuller and deeper penetrant penetrates into the material of the part. By the term “specific time”, the authors do not mean to immerse a part in a liquid and just wait, it would be irrational and would have low productivity. The dive operation must be coordinated with the working day, that is, the dive must be performed at the end of the next working day and before the start of the next working day. That is, according to this scheme, the length of time a part is in the fluid will be at least fifteen hours, which is quite enough, even with excess, for complete penetration of the fluid into the capillaries of the crack along the entire surface of the part. Or, by immersing the part in liquid, the worker will perform other operations. With this approach, the apparent duration of the process of finding the part in the liquid practically does not waste time, and the filling of cracks (capillaries) with liquid will be guaranteed. Or, the length of the part in the liquid must be coordinated with the production cycle, which is especially effective in mass and mass production. The next step is to clean the surface of the liquid. After stripping, the main task is that it is necessary to force the liquid to leave the capillary (crack) on the surface of the part, which, spreading over the surface, copies the shape of the crack, thereby indicating the presence of a crack on the surface of the part. There are quite a few methods that allow liquid to escape to the surface of the part from the capillary: this is heating the part, applying a special coating to the surface of the part, etc. In the proposed method, to intensify the rise of liquid from the capillary (cracks), it is proposed to create a vibration in the material of the part, for example, by installing the part on a vibration table. There may be many options for inducing vibration in the material of the test part. When testing parts of small sizes, such as ICE connecting rods, vibration can be induced by manually applying gentle blows, but with a high frequency using a hammer. Laboratory and production tests conducted on the KamAZ ICE connecting rods showed the feasibility and effectiveness of the method for detecting microcracks by inducing vibration in the connecting rod material using a conventional copper hammer. Moreover, the tests were carried out in two versions: by applying to the surface of the connecting rod assembly with a kerosene cover, and after 1-2 minutes, kerosene was removed from the surface and wiped the surface dry. Then, with the help of a copper hammer, mild high-frequency shocks (induced vibration) were applied to the connecting rod material on the lower head. Kerosene clearly appeared on the cleaned surface, copying the shape of the crack. The second option was that the same connecting rod after complete drying (so that no kerosene remained in the crack) at room temperature was immersed in a bath of kerosene for 24 hours. Then the connecting rod was taken out of the bath with kerosene, cleaned the surface and induced vibration, as in the first version. At the same time, the trace of the kerosene that appeared was clearly wider and longer than with the first option. Thus, immersion of a part in a bath with liquid (instead of simply applying liquid to the surface of the part) in combination with inducing vibration in the material of the test part allows for smaller cracks to be detected than using known methods. The increase in the length of time the part is in the liquid allows the liquid to penetrate deeper into the capillaries and completely fill their volume, thereby increasing the reliability of determining microcracks on the surface of the part. In addition, the proposed method allows to determine cracks on the entire surface of the part, and not just on a limited surface area, as is the case with the application of known methods.

The method is implemented as follows. Surface contaminants are removed from the surface of the part for which it is necessary to check for the presence (or absence) of microcracks on the surface. That is, the surface of the part must be clean before inspection. Then the part is completely immersed in the penetrant bath and kept in the bath for at least eight hours for the penetrant to penetrate completely into the pores (microcracks) on the surface of the part. This operation is performed either at the end or at the beginning of the work shift so that the exposure time is as long as possible. This approach is especially effective in the serial production of repairs, for example, ICE, as well as in single production. After holding the part in the bath, the surface of the part is completely removed (cleaned) from traces of penetrant and wiped dry. They induce vibration in the material of the part, for example, by tapping the surface of the part with a heavy object (for example, a hammer). Moreover, the mass of the object, the strength and frequency of the shocks must be such that vibrations at the resonant frequency occur in the material of the part. The impact location is selected in the area of the surface of the part where the crack is most likely to occur, for example, for a connecting rod it is the surface area near the lower head where the connecting rod is installed. After tapping, the surface is visually checked for the presence of a penetrant trace that exits from the microcrack to the surface of the part under the action of vibration, thereby indicating the presence of microcracks. The absence of traces of penetrant on the surface after tapping indicates the absence of microcracks, and the part can be transferred to the assembly of the product.

The application of the proposed method for determining cracks in the material of a part in comparison with known methods can increase the productivity and probability of detecting microcracks on the surface of a part, thereby increasing the reliability of a particular part in an assembled product.

Information sources

1. Machine repair. M., publishing house "Ear". 1967. 504 p. (Textbooks and study guides for agricultural technical schools) Auth: I.E. Ulman, I.M. Gershtein, B.C. Nasonov et al. UDC 631.3.004.67 (075.8).

2. Reliability and repair of machines / VV Kurchatuin, NF Telnov, KA Achkasov and others; Ed. V.V. Kurchatkina. - M .: Kolos, 2000 .-- 776 p.: Ill. (Textbooks and teaching aids for higher education institutions).

ISBN 5-10-003278-2.

Claims (1)

A method for determining microcracks on the surface of a part, which consists in preliminarily wetting the surface of the part with easily penetrating liquid, after some time they clean the surface of the part dry and, judging by the appearance of a trace of liquid, microcracks are judged, characterized in that the part is completely immersed in liquid and withstand a certain time in the liquid for at least eight hours, equal to the production cycle, then the part is removed from the liquid, liquid is removed from the entire surface of the part, They vibrate in the material of the part, for example, by tapping the surface of the part with a heavy object or placing the part on a vibrating table, microcracks are judged by the appearance of traces of liquid on the surface of the part, and the material of the heavy object has a hardness less than the part, the mass of the object, strength the frequency of impacts, as well as the place of application of impacts, is selected depending on the material and configuration of the part, so that resonance frequency oscillations occur in the material of the part, intensifying the liquid exit to the surface etali.