RU2588980C1 - Method of repair of heat-loaded elements of machines and equipment - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to repair of motor transport equipment and can be used for recovery of serviceability of heat-loaded elements, their gas ducts and exhaust systems. Method involves cleaning and degreasing of surface of defective area, forming circular band on it by winding heat-resistant material and its fixing at faulty section, wherein heat-resistant material band used is carbon fibre on basis of polyacrylonitrile providing resistance of band to temperatures of up to 1,400 °C. On cleaned and degreased surface of defective area polymer binder is applied, and circular shroud is formed by winding of said carbon fibre in several layers with thickness of each layer 0.5-2.0 mm, impregnating each layer with said polymer binder, winding of each next layer of band is performed after hardening of previous layer.

EFFECT: invention provides reliable closing defects in form of cracks, burnouts, holes, including large size on elements operated at excess pressures, at high temperatures and temperature drops, as well as in aggressive environments.

3 cl, 2 ex, 2 tbl

Description

The invention relates to the field of repair of motor vehicles, road-building machines, power equipment and can be used to restore the health of heat-loaded elements of their gas paths and exhaust systems that have defects in the form of cracks, burnouts and holes.

The formation of defects in heat-loaded elements of machines and equipment is caused by many factors, among which are the effects of temperature extremes, thermal shock (when moisture gets on a heated element), abrasive and aggressive environments (sand, salt from roads - for vehicles), corrosion, and so on. As is known, the mechanism of corrosion destruction of metal elements is accompanied by moisture adsorption on the metal surface, as a result of which a chemical reaction occurs between the base metal acting as the anode and its impurities, which are the cathode. As a result of a chemical reaction, many galvanic cells are formed, which is accompanied by the destruction of iron and the formation of rust. Electrochemical corrosion is promoted by elevated temperatures, aggressive environments, uneven distribution of residual deformations in the metal after heat and mechanical treatment.

The destruction of metals also leads to cyclically changing temperatures, which contribute to the thermal fatigue of materials (the number of cycles that a material can withstand without breaking, while the number of cycles is proportionally dependent on the amplitude of the stresses in the cycle).

The above factors lead to a significant reduction in the life of the heat-loaded elements, the need for periodic repairs, which increases the downtime of the equipment. The operation of faulty heat-loaded elements leads to a deterioration in the working conditions of personnel, a decrease in the power of the equipment, the ingress of toxic gases into the atmosphere, etc.

Known traditional methods of repair by welding cracks, holes, burnouts (see RF patent No. 2306214, IPC V23P 6/00, publ. 2007).

Common disadvantages of such methods are limited capabilities, as they can be used to repair small defects. Welding can be used very limitedly in the repair of products that are in the assembly, for example, as part of a propulsion system, since damage to nearby components is possible. Not all materials have good weldability, and the thermal stresses that almost always accompany the welding process additionally load the assembly, which includes the element being repaired.

There is a known method of repairing thin-walled structures, according to which the boundaries of the zone of structural damage are determined, the damaged zone is cut out, a compensating patch is made from several layers of prepreg and a mixture of liquid glue with filler, the size of each subsequent patch layer, in addition to the first, is selected larger than the previous one by the amount of overlap, from the first the prepreg layer forms the bottom of the damaged area and is partially pressed inward, fill the defect cavity with a mixture of liquid epoxy glue with a filler, and lay other layers on top of the mixture of glue with filler, thereby forming a compensating patch (see RF patent No. 2181083, IPC B29C 73/04, B29K 101/00, B29L 31/00, publ. 2002).

As a result of the analysis of the known method, it should be noted that it does not provide a sufficient quality of repair, since significant stresses are formed at the overlap edges, leading to peeling of the first layer of the prepreg and, as a result, of the entire compensating patch. As a result, the strength and service life of the reduced compound are very small. Another disadvantage is the decrease in the sealing ability of the joint due to cracking of the cured epoxy adhesive under the influence of repeated temperature fluctuations and vibration loads.

A known method of sealing a defect in an article, comprising filling a defect with a sealing composition containing an epoxy resin and an iron-containing powder, followed by curing, the defect being first filled with a sealing composition comprising 100 parts by weight anaerobic sealant based on oligoester acrylates, an epoxy resin in an amount of 50-300 parts by weight, an amine type hardener in an amount of 10-100 parts by weight and iron-containing metal powder in an amount that ensures the thixotropic state of the composition, after curing, clean the outer surface of the cured composition until a metallic luster appears, then wet it with the same anaerobic sealant and apply the specified sealing composition again with the surface of the applied layer overlapping (see RF patent No. 2084323 IPC В23Р 6/00, publ. 1997).

Polymeric materials are resistant to temperature extremes and aggressive environments, which is the key to their use in the repair of heat-loaded elements. It is also very significant that the constant reduction in the cost of polymeric materials and fillers and the high adaptability of repairs during their use make it possible to restore the efficiency of heat-loaded elements at lower cost.

The disadvantages of this method are the impossibility of its use in eliminating defects such as a hole, the high fragility of the cured sealing composition, low strength when exposed to repeated temperature fluctuations and the application of mechanical loads.

A known method of repairing an exhaust silencer of an automobile system, adopted as a prototype, using fiberglass tape, the essence of which is sealing defects (in the form of holes, corrosion damage and burnouts) of an exhaust silencer of an automobile by forming an annular bandage made of fiberglass and a polymer binder. The bandage is formed by winding several layers of fiberglass (at least 2) at the site of damage. The size of the bandage is determined by the size of the damage. The first layer should slightly exceed the boundaries of the damage, and each subsequent layer should be several mm higher than the previous one. As the fabric used fabric based on fiberglass. As a binder for fiber glass impregnation, a polymeric material based on epoxy or polyester resin is used. Fiberglass impregnation with a polymeric binder can be carried out both before applying the fabric to the place of damage - at first the fabric is impregnated, and then an annular band is formed from it by winding, and after the band is formed - at first the annular band is completely formed, and then it is impregnated with a polymeric binder (see U.S. Patent No. 3531345, IPC B32B 7/00, publ. 1970).

The undoubted advantage of this method in comparison with the above is the refusal to use the patch applied to the place of the defect, and the formation of the ring defect in place of the defect. The use of an annular bandage eliminates the edge peeling of the patch from the reconstructed structure (due to circular winding) and provides a significantly higher strength of the reconstructed structure (due to the tightness) than when using patches.

However, the disadvantage of this method is that the fiberglass tape used as a bandage has a very limited temperature range at which it retains its properties, as well as a fairly high elongation under the influence of loads, which significantly reduces the strength of the bandage and, therefore, makes it impossible the use for overhaul of elements of systems whose functioning is characterized by high temperatures, temperature and pressure drops.

A significant disadvantage of this method is the rather large thickness of the formed band (since the band is not formed layer-by-layer from fiber, as in the proposed method, but from the finished fiberglass) and, as a result, low values of adhesive strength and the likelihood of leakage of the reconstructed structure.

Another disadvantage of this method is the lack of layer-by-layer curing of each wound layer of the bandage. In this method, the layers are wound in a row and their complete curing occurs after the end of the process of forming the bandage. When winding pre-impregnated with a polymeric binder fiberglass during curing of the bandage, significant residual stresses arise, which significantly reduce the strength of the resulting bandage. When the fabric is impregnated after winding, uneven impregnation of the glass fabric with a polymer binder is possible, which leads to the occurrence of stress concentration sites and the destruction of the bandage under vibration loads (during operation of the equipment).

An object of the present invention is to provide high strength and tightness for sealing defects in the form of cracks, burnouts, holes, including significant sizes, on elements operating at excessive pressures, at high temperatures and temperature extremes, in aggressive environments.

The solution to the technical problem is achieved due to the fact that in the method of repairing heat-loaded elements of machines and equipment, according to which an annular bandage is formed by winding from a defective area of the element from a heat-resistant material and fixed on a defective area of the element being repaired, according to the invention, carbon fiber is used as a heat-resistant bandage material which, when wound, is impregnated with a polymer binder. Moreover, the annular bandage is formed by winding carbon fiber in several layers, and the winding of each subsequent layer of the bandage is carried out after curing the previous one.

The technical problem is also aimed at the fact that carbon fiber or fabric is used as a carbon fiber to create an annular bandage, and epoxy adhesive is also used as a polymer binder.

In addition, the solution to the technical problem is achieved due to the fact that soot is additionally introduced into the epoxy adhesive as a heat-conducting dispersed filler in an amount of 10 wt.% Or shungite in an amount of 20 wt.%.

The solution of the technical problem becomes possible due to the use of a carbon fiber bandage material having a higher heat resistance than the glass fiber proposed in the prototype. Due to the fact that the winding of carbon fiber is carried out in layers with the impregnation of each layer with a polymer binder, providing a certain time for its curing, it becomes possible to reduce residual stresses and elongation values under the action of loads, which significantly increases the strength of the bandage. Also, layer-by-layer winding of carbon fiber reduces the likelihood of uneven impregnation of carbon fiber with a polymer binder, which reduces the likelihood of stress concentration points and the destruction of the bandage under vibration loads.

The use of a carbon tape or fabric as the bandage material, and also using epoxy adhesive as a polymer binder, makes it possible to reduce the bandage thickness while repairing significant damage sizes, which allows to increase the adhesive strength values and reduce the likelihood of leakage in the reconstructed structure.

The use of soot in the amount of 10 wt.% Or shungite in the amount of 20 wt.% As a heat-conducting dispersed filler makes it possible to significantly increase the temperature range at which the bandage retains its properties.

The essence of the claimed method is illustrated by tables, where:

- in the table. 1 shows the properties of carbon fibers based on polyacrylonitrile (PAN), recommended and tested in the proposed method;

- in the table. 2 presents similarly the properties of epoxy polymers obtained using ED-20 epoxy and various types of hardeners.

The claimed method is as follows.

The claimed method can be carried out both manually and using standard equipment, both at the equipped workplace, involving the dismantling of the item being repaired, and without dismantling the item directly on the equipment where the item being repaired is installed.

A method of repairing heat-loaded elements of machines and equipment is that in the defective area of the element by winding, an annular bandage is formed from a heat-resistant material, which is fixed on the defective area of the element being repaired.

The defective element that is to be repaired is initially cleaned from rust and dirt to a metallic luster. If the defect is a crack, then to prevent its further propagation, a crack is drilled from both ends. If the defect is burnout or hole, then the drilling operation, as a rule, is not necessary, unless the burnout and hole contours have sharp angles.

Then the surface of the defective element is degreased with a solvent or acetone.

As heat-resistant material, carbon fiber is used. When winding, the latter is impregnated with a polymer binder, which is used as an epoxy adhesive.

The preparation of a binder based on epoxy adhesive (for example, ED-20) is carried out according to the technology widely used by specialists. The prepared binder composition is applied to the cleaned, defatted surface of the defective element, distributing it evenly over the surface.

Next, an annular bandage is formed on the repaired surface. To form the bandage, carbon fiber is used, which provides the bandage resistance to high temperatures (up to 1400 ° C). The properties of the fiber used in the implementation of the claimed method are given in table. one.

When forming the bandage, the element is wound at the location of the carbon fiber defect, which is used as a carbon tape or fabric. The use of the thread is impractical due to the complexity of the process of winding it.

When the fiber is wound, it is preloaded. An interference fit is necessary to prevent sagging of the fiber (due to which peeling of the cured brace may occur) and to ensure a strong bond. Moreover, the annular bandage is formed by winding carbon fiber in several layers, and the winding of each subsequent layer of the bandage is carried out after curing the previous one. In this case, each layer is impregnated with the prepared binder, for example, using a roller. Winding is carried out on standard winding equipment or manually, as noted above. Each layer is wound up to a thickness of 0.5-2.0 mm. It has been experimentally established that with smaller thicknesses it is impossible to provide reliable strength and sealing properties of the bandage. And at large thicknesses, fiber delamination is possible due to the occurrence of significant residual stresses. After the formation of the bandage to prevent unwinding, the open end of the tape material is fixed on the repaired element in a known manner, for example using wire. Next, the obtained annular layer of the bandage is cured at room temperature (for 8 hours) or increased - but not more than 100 ° C, for 4 hours.

After curing the first layer of the annular bandage, as described above, the next layer is wound on it. This layering is carried out until the required thickness of the bandage is reached. The thickness of the bandage depends primarily on the size of the damage, as well as on the operating conditions of the structure (range of operating temperatures, operating aggressive media and current loads). It was experimentally established that when repairing heat-loaded machine elements in case of damage up to 30 mm, the thickness of the band is optimal 4-5 mm, and in case of damage over 30 mm the thickness of the band is recommended to be increased to 8-10 mm. The smaller thickness of the bandage does not provide the required strength and tightness of the structure, and with a band thickness of more than 10 mm, there is a possibility of the band detaching from the part being restored. Each subsequent layer of the band tightens the previous ones, which allows you to increase the tightness of the band on the element with each subsequent layer.

In the claimed method of repair, the material of the bandage, consisting of carbon fiber and a polymeric binder, due to the layer-by-layer wet winding with curing of each layer, provides the creation of a durable bandage that is resistant to high temperatures, pressures and other operational factors.

As the initial fiber in the manufacture of carbon filaments, ribbons, fabrics, most often use viscose or polyacrylonitrile.

The properties of carbon fibers used in the implementation of the claimed method are given in table. one.

Carbonized and graphitized carbon fibers can be used to create the bandage. Any type of fiber can be used to repair small damages (up to 40 mm), and carbon fiber carbon-based fibers (tapes, fabrics) are not recommended for repairing damage above 40 mm to repair elements that experience significant pressure during operation, since they have relatively high values of elongation, which leads to a decrease in the strength of the bandage.

Low values of thermal expansion coefficients of carbon fibers minimize the possibility of thermal stresses in the formed bandage. In addition, such materials have practically no shrinkage. All this makes it possible to obtain bandages based on carbon fibers in which there are no (or minimal) residual stresses that traditionally arise when using other fibers (glass, boron, organic, etc.). If there were such stresses, then in this case, the carbon fibers would change their stress-strain state under the influence of the initial residual stresses that inevitably arise in the process of obtaining plastic (a fiber with a layer of a binder applied to it after curing of the latter turns into carbon fiber). Whereas with practically zero initial values of residual stresses, carbon fibers allow you to create strong and durable bandages.

In Russia, serial production of structural carbon fibers based on polyacrylonitrile on an industrial scale is carried out by Argon LLC. The following types of carbon fiber materials are industrially produced at this enterprise:

- Carbon fibers (threads and plaits) of the UKN-P-5000 grades (TU 1916-169-05763346-96), UKN-M / 6k (TU 1916-146-05763346-96), Grapan, KAZh, GZh-20 and GZh -23;

- Carbon fabrics of the UT-400, UT-900, UOL brands;

- Carbon tapes of brands LUP (GOST 28006-88), LU-24P (TU 6-06-31-560-86), ELUR (GOST 28006-88), Pendant (TU 6-12-31-787-92), ЛЖУ-М and ЛЖУ-П.

There are other brands of domestic carbon fibers, ribbons and fabrics in the literature, but all of them are not industrially produced and are produced in pilot plants in small quantities.

The main purpose of the binder material applied to the fiber (tape, fabric) is to ensure the solidity of the bandage, transmission and distribution of stresses (i.e. the transformation of the material into carbon fiber).

In addition, the binder determines the heat, moisture, fire, and chemical resistance of the resulting bandage.

An ideal binder material for the proposed method of creating a bandage should have high adhesive strength and resistance to prolonged exposure to various climatic factors. This is necessary so that the resulting composition (bandage) does not change its properties during operation of the element.

The main requirement for the selection of a binder material is the correspondence of its relative elongation to a similar parameter of the fibrous material. This is necessary so that when loading the structure does not occur cracking of the composition.

It was experimentally established that the elongation of the polymer binder in the cured state should be higher than that of the fiber, but not more than 10 ... 20% of its elongation (with a fiber elongation of 0.2%, the elongation of the binder should be 0.22 ... 0.24 %). If the relative elongation is lower than or equal to the elongation of the material, then it is possible cracking of the binder during loading of the structure. If the relative elongation of the binder is higher than that of the fiber by more than 20%, then there is a possibility of delamination of the band from the element being repaired.

Most preferably, an ED-20 brand epoxy resin is used as the binder base. Epoxy dianes are the most common and make up 85-90% of the total number of all epoxies produced in Russia and abroad.

Aliphatic and aromatic amines, anhydrides, phenolic resins, etc. are used as hardeners of epoxy resins. The properties of epoxy binders obtained using some hardeners used in the implementation of this method are given in table. 2.

Of all the given in table. The two types of hardeners are most preferred aliphatic amines, which make it possible to obtain carbon plastics without additional heating (cold curing binders) and have relative elongation values close to carbon fibers. In addition, aliphatic polyamines are one of the most common and cheapest hardeners of epoxy resins.

When repairing elements operating at elevated temperatures, carbon black is additionally introduced into the binder - epoxy adhesive as a heat-conducting dispersed filler in an amount of 10 wt.% Or shungite in an amount of 20 wt.%. This amount of filler provides the maximum increase in heat resistance of the epoxy polymeric material without reducing the adhesive strength. Lower concentrations of fillers do not allow to increase the operating temperature range of epoxy glue. And high concentrations of filler lead to a sharp drop in adhesive strength and, as a result, to a decrease in the quality of repairs. The optimal amount of filler was established experimentally - tests using differential scanning calorimetry and pull-out.

The essence of the claimed method will be more clear from the following examples.

Example 1

The method described above was used to repair the muffler of the exhaust system of the KAMAZ automobile, on which a longitudinal crack was detected. The length of the repaired area was 50 mm.

Work can be carried out both outdoors and indoors. At the same time, the ambient temperature should not be lower than + 10 ° С (ventilation is required for work in the room).

The area with a defect in the form of a crack was cleaned of dirt and dust by wiping with acetone (GOST 2768). You can use white spirit to wipe instead of acetone. In order to avoid further propagation of the crack, it was drilled along the edges.

A polymer binder was applied to the cleaned repaired area and distributed evenly over the surface. An ED-20 epoxy resin with an amine hardener - polyethylene polyamine (PEPA) was chosen as a binder.

As a fibrous material to create a bandage was used carbon fiber brand UKN-2-500. The winding of the fiber on the outer surface of the muffler was carried out by fixing the muffler in the spindle of the winding machine, and the wound fiber was placed perpendicular to the element being repaired. When winding the fiber created its preliminary tension. During winding, the material was abundantly impregnated with a binder using a roller. The winding was carried out to a layer thickness of an annular bandage of 1.0 mm (for ease of control), after which the obtained layer of bandage was cured at room temperature for 8 hours. Then, the next layer with a thickness of 1.0 mm was wound in the manner described above. The free end of the material was fixed at the end of the winding of the layer using wire. A total of 8 layers were wound, each 1 mm thick. The number of layers depends on the size of the damage and the operating conditions of the part being repaired. After the last layer was cured (at room temperature for 8 hours), the muffler was installed at a regular place in the exhaust system of the car.

During the operation of the vehicle, this bandage provided reliable sealing of the reconstructed area (exhaust gas leaks through the repair site were not fixed within 1 year of operation), resistance to aggressive media (water, unburned fuel residues, anti-icing reagents), as well as vibration and shock loads . The service life of this bandage is more than 1 year.

Example 2

By the method described above, the collector of the KAMAZ automobile was repaired. The length of the repaired area is 30 mm.

The difference from the above described example is that the ED-20 epoxy resin with an amine hardener - polyethylene polyamine (PEPA) and dispersed filler, namely carbon black, in the amount of 10 wt.% With respect to the polymer weight was chosen as the binder. The use of dispersed filler allowed to significantly increase the operating temperature range of epoxy glue. UT-900 carbon fiber in the form of a tape was used as a fibrous material to create a bandage.

A binder was applied to a previously prepared surface, as in the previous example. The steps for obtaining a bandage are similar to those described above. A total of 4 layers were wound, each of which was 1 mm thick, also for ease of control. During the operation of the vehicle, this bandage provides reliable sealing of the reconstructed area (no exhaust gas leaks through the repair site during 1 year of operation), resistance to aggressive environments (water, unburned fuel residues, anti-icing reagents), as well as vibration and shock loads . The service life of this bandage is more than 1 year.

The method is simple, technologically advanced, does not require additional funds and special equipment, and allows you to dramatically expand the size boundaries of the repaired defects.

Thus, the use of the inventive method provides a high-strength hermetic bandage that works reliably at operational excessive pressures, high temperatures and temperature extremes, under the action of aggressive media.

Claims (3)

1. A method of restoring heat-loaded machine elements, including cleaning and degreasing the surface of a defective area, forming an annular band on it by winding a heat-resistant material and fixing it on a defective area, characterized in that carbon fiber based on polyacrylonitrile is used as a heat-resistant material of the band, providing resistance bandage to temperatures up to 1400 ° C, while on the cleaned and degreased surface of the defective area, a polymer binder is applied, and The annular bandage is carried out by winding layers of the aforementioned carbon fiber with a thickness of each layer of 0.5-2.0 mm with impregnation of each layer with said polymer binder, and the winding of each subsequent layer of the bandage is carried out after curing of the previous layer. 2. The method according to p. 1, characterized in that the carbon fiber is a carbon tape or fabric, and an epoxy adhesive is used as the polymer binder. 3. The method according to p. 2, characterized in that the soot in the amount of 10 wt.% Is added to the epoxy adhesive in addition to a heat-conducting dispersed filler. % or shungite in an amount of 20 wt. %