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The application of thermal spraying skills in the production of sliding bearings
Source: China Bearing Network Time: 2013-07-23
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The thermal spray technique is a method in which a heat source is used to heat the sprayed material to a molten or semi-molten state, and is sprayed at a certain speed to the surface of the pretreated base and formed by coating the fine particles, and then imparts special functions and skills to the external surface of the substrate. It is an important part of the external engineering skills. Different coating materials and different process methods can be used to prepare the wear-resistant, wear-resistant, corrosion-resistant, high-temperature oxidation, thermal barrier, electromagnetic shielding, insulation, etc. Functional coating.
The commonly used thermal spraying methods are flame spraying, arc spraying, plasma spraying, coating materials including metals, metal alloys, ceramics, cermets, plastics and other composite materials. Thermal spraying methods and skills are now widely used in aerospace, Metallurgy, power, military equipment, petrochemical, machinery production, transportation, bioengineering and other fields of the national economy.
At present, most of the functional coatings produced by thermal spraying techniques are mostly used for the protection, strengthening and correction of parts. There are few reports on the parts directly produced by thermal spraying. This paper analyzes a kind of sliding bearing made by thermal spraying. Methods and processes, because of the special process, can also be used as a thermal spray skill and data accumulation process to make special parts exploration.
1. Conventional sliding bearing manufacturing method Sliding bearing is a commonly used mechanical component. It consists of a rotating journal and a fixed bearing housing. The bearing housing inside and outside the journal is called the bearing bush or bearing bushing. Because the shaft is often used in operation. Accepting certain loads and transmitting motion and power, so commonly used materials are various steels and cast irons, which are relatively wear-resistant; common materials for bearing bushes or bearing bushings are bearing alloys, bronzes, aluminum-based alloys, zinc-based alloys, etc. (mainly alloys of tin, lead, antimony or other metals) because of its good wear resistance, high plasticity, good running-in function, good thermal conductivity, good anti-adhesiveness and good adsorption with oil, in heavy load, high speed In the case of more use, but the strength of the bearing alloy is smaller, the price is more expensive, usually used centrifugal casting method to cast steel, iron and other bearing housing work appearance, constitute the operation of the sliding bearing.
2, the use of thermal spraying skills to produce sliding bearing lining process The current analysis of thermal spray skills to correct the sliding bearing information and literature, the German mass automobile company also has plasma sprayed internal combustion engine connecting rod inner hole wear-resistant aluminum bronze coating Invention patent. However, due to the constraints of existing thermal spraying equipment and operation methods, various functional coatings prepared by thermal spraying skills are mostly limited to the outer and outer parts of the parts and the outer surface of the inner hole, once the hole diameter is less than φ35 or hole depth. Larger construction is difficult. If the cavity of the part is special, it cannot be constructed.
In this paper, the following method of sliding bearing parts is used to analyze the process of making sliding bearing inner lining by using thermal spraying technology. The parts are shown in Fig. 1 a, the inner diameter of the hole is φ20, the length is 30, and the inner hole is the appearance of the work. There is a 3mm thick bearing alloy. This part is usually made by centrifugal casting method. Because the aperture is too small, there is currently no thermal spray inner hole spray gun to complete such a mission.
In order to solve the problem of thermal spray coating on the outer surface of the above-mentioned parts, the author proposed a new thermal spraying construction method. A new tooling was made. The main layout consisted of a mandrel, a nut and a baffle with a melting point of 183 °C. Low-melting alloy, uniformly deposited on the outer surface of the mandrel 1, and finally coated with a refractory coating on the outer surface of the low-melting alloy. The refractory coating is made of special binder and refractory material with high temperature resistance.
When spraying, the tooling can be clamped on the rotating working table for thermal spraying, preheating the tooling to about 100 °C, and then spraying the required bearing alloy coating with the arc spraying equipment, and the coating appearance should be applied after the thickness of the coating is drawn. Finishing, remove the surface floating ash, continue to spray steel, stainless steel and other supporting materials on the coating surface to reach the required diameter scale. Finally remove the two nuts and baffles, heat to the ablation temperature of the low melting point alloy, withdraw the heart The shaft can obtain the required plain bearing blank of the bearing alloy. For the connection between the bearing alloy coating and the supporting material, the roughening of the brushing, sandblasting, etc. can be selected after the alloy coating is sprayed. The process is roughened and then the support material is sprayed.
The sliding bearing lining made by the thermal spraying technique is an amorphous bearing alloy, which has higher hardness than the base material and has a certain porosity, can accommodate a part of the grease, and is superior in performance to the sliding bearing lining obtained by the casting method. In addition, because the thermal spray skill of the casting method is used to make the bearing alloy lining, the thickness of the bearing alloy can be appropriately reduced during the part drawing to save valuable metal.
3. Relevant problems that require attention When using the thermal spraying skills to make the above-mentioned sliding bearings and similar parts, in addition to the safety rules of thermal spraying operations, the following related problems should be considered.
(1) Appropriate coating data and spraying process should be selected according to the working conditions of the work. For example, the arc spraying method is used to spray the bearing alloy on the inside and outside of the bearing parts. In order to avoid excessive oxidation of the alloy data during spraying, nitrogen can be used as the Spray medium gas.
(2) If the appearance of the coating has precision and roughness requirements, and the requirements for mechanical processing to obtain the required skill requirements, it is necessary to reasonably describe the thickness of the coating and the dimensions of the tooling, reserve the processing amount and ensure the working thickness of the coating. For the sliding bearing analyzed in this paper, the inner hole of the blank should be used as the rough reference when machining the machining. The outer cylinder surface is processed first; then the outer cylinder is used as the fine reference to machine the inner hole to ensure the thickness of the remaining coating is uniform.
(3) The contact force and residual stress between the two coatings. Because the coating is sprayed on the surface after spraying the coating, the supporting coating is thicker, such as the lack of contact between the two coatings. Well, it can cause the working coating to fall off during the processing or during the application. For this reason, the thermal expansion coefficient and the contact force of the two materials should be fully considered. If necessary, a transition coating can be sprayed on both centers to depict the composite coating. Layer, gradient coating to add contact strength. During the coating depiction, it is necessary to think about the problem of whether the two coatings can be fully connected. In practice, it is necessary to do ample process test. In addition, before the control is sprayed The temperature in the spraying reduces the residual stress, and if necessary, the heat treatment process to eliminate the internal stress in the later stage.
(4) The workpiece and tooling are easy to disassemble and assemble, and the tooling can be reused. Because the coating data is in a molten and semi-molten state during spraying, it is cone-shaped to the workpiece under the motion of high-speed airflow, and some coating materials are inevitably required. Paste on the exterior of the tooling, think about the ease of assembly and disassembly of the tooling and the workpiece, and repeat the application. Before spraying, apply the release agent to the exterior of the tooling.
In this paper, the production of sliding bearing lining is taken as an example to analyze the process of thermal spraying technology and data accumulation process. According to this idea, other messy parts and other functional coatings can be made, such as inner hole wear-resistant, Corrosion-resistant coatings for hydraulic valve bodies, spiral cooling channels, etc. It is necessary to confess. This method is currently not suitable for large-scale, large-scale production of products, and can only be used for single-piece small batches with special functional requirements and special layout parts. produce.
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