During the use of agricultural machinery, some parts ch […]
During the use of agricultural machinery, some parts change the original geometry and size of the parts due to wear, deformation, damage, breakage, corrosion or other damage, thereby destroying the matching characteristics and working ability between the parts, so that the parts and assemblies Even the normal operation of the whole machine is affected. The task of part repair is to restore the size, geometry and mechanical properties of damaged parts with repair value. The purpose of parts repair is to restore the fit and work ability of the parts under the principle of economic rationality and effectiveness.
Repairing failed mechanical parts has the following advantages over replacing new parts: repairing parts generally saves material, saves processing, disassembly, adjustment, transportation, etc., reduces maintenance costs, reduces the consumption of new spare parts, and avoids waiting for accessories. Shorten the downtime, generally do not need high precision, large, critical equipment, easy to organize production, use new technology to repair old parts can also improve some of the performance of the parts.
1 repair method classification
There are three basic methods for repairing agricultural machinery parts: resizing repair techniques, repairing size repair techniques, and special repair techniques. Resilience repair techniques include welding and surfacing, thermal spraying, electroplating, electroless plating, spark coating and molten metal layers; repairing dimensions include machining, fitter, add-on method, partial replacement, transposition Etc. Special repair techniques include correction of deformation, surface strengthening, sealing and sealing, bonding and gluing, and pressure processing.
At present, the repairing techniques commonly used in production should be based on the principle of repairing and supplementing, and vigorously promote and adopt advanced and effective repairing techniques under economic and reasonable conditions. After the mechanical parts are damaged, there are many repair methods. In addition to the basic methods of machining (such as car, boring, planing, grinding, milling, etc.), there are also various process options, such as welding repair, repair, spraying, and plating. Covering, riveting, inserting, matching, modification, correction, expansion, compression, bonding, etc. With the rapid development of science and technology, the improvement of repair technology has been promoted, and new science and technology has been widely applied to the repair process of mechanical parts. However, in the repair of specific parts, the structural characteristics, use requirements, working environment and other factors of the parts should be analyzed. According to the characteristics and application scope of different repair methods, technical and economic analysis is used to determine a more reasonable and economical repair process.
2 commonly used repair techniques
(1) Welding repair. A variety of agricultural machinery parts made from commonly used materials can be repaired by welding. The failure modes of these parts are wear, breakage, cracks, pits, and the like. The advantages of the welding repair method are as follows: the covering layer has a high bonding strength with the original parts, the processing equipment is simple, the processing efficiency is high, the shape and size of the parts are not limited, and the cost is low. The main disadvantages are: high temperature during welding, which may cause changes in metal structure, thermal stress, cracking and deformation. Commonly used welding methods are surfacing, welding and brazing. Surfacing is to cover a layer to several layers of material with performance requirements on the surface of the part, not only to repair worn parts, but also to improve the wear resistance of the parts. Weld repair is often applied to large parts made of cast iron, such as the body, cracks or defects, re-manufacturing waste time and manpower, material and force, welding repair is an effective repair method. Brazing is the heating of the solder material and the weldment to the melting point of the solder, and the solder is used to weld the part.
(2) Repair. Large castings are cracked, and the hole can be drilled at the end of the crack to prevent the crack from extending. The reinforcing plate is used for reinforcement and repair to close it (drilling and tapping around the damaged part and repairing the nail to repair the larger one) Cracks, broken holes). This method is often used for the repair of body cracks.
(3) Spraying. The metal wire is melted by thermal energy, and the molten metal droplet is blown with compressed air of 5-6 kg/cm3 to atomize the molten metal into particles having a diameter of 0.01 to 0.013 mm and sprayed at a speed of 140 to 300 m/s. On the surface of the workpiece prepared in advance, the particles are deformed by the impact, and after cooling, adhere to the surface of the part to form a sprayed layer. The use of electric arc to melt metal is called electric spraying; the acetylene flame is used to melt metal by gas spraying; and the high-frequency induction current is used to melt metal by high-frequency electric spraying. The spraying method has the advantages of simple equipment, convenient use, low production cost and wide application.
(4) Plating. Apply a thin layer of chrome or other metal to the surface to restore the original size. Electroplating can improve the corrosion resistance, wear resistance and decorative appearance of the surface of the parts, and can also appropriately increase the geometrical dimensions of the parts, and has been widely used in agricultural machinery repair. Some important mechanical parts with high processing precision, such as gears, journals, etc., are out of wear and are most suitable for electroplating repair.
(5) Riveting. After the relevant parts are loosened, they are repaired by riveting process to restore their normal working condition.
(6) Inlay. In the wear parts of the parts (such as the journal, the inner hole, etc.), a new metal sleeve is set in a static fit to restore its original size.
(7) Optional. When parts or directions are worn out, if the structure allows, you can take the method of turning, turning, etc. (such as the flywheel ring gear), flipping or turning the part at an angle to replace the damaged part with the intact side. Meet the requirements for continued use.
(8) Modification. After the parts are worn, the dimensions are changed by boring, cutting, sawing, expanding, scraping and other processes to achieve new geometric shapes and matching properties.
(9) Correction. Use the plastic characteristics of the metal material to restore the correct geometry of the part. The direction of the force or moment is consistent with the direction in which the deformation is required, such as pressure correction, tap correction, flame correction, and the like. It can be used to repair deformed parts such as crankshafts, connecting rods, and racks.
(10) swell. Many hollow parts with simple shapes, if the material is plastically good, can be repaired by inflation.
(11) Compression. With the pressure piercending method, the outer diameter of the hollow and solid parts can be increased by reducing the height of the parts. Reduce the inner diameter of the hollow part to repair the outer or inner diameter of the non-ferrous metal sleeve.
(12) Bonding. The bonding repair method utilizes a bonding process of a chemical material, that is, a synthetic polymer compound, to form a chemical bond with a surface of a part to produce a large adhesive repairing part. In the repair of agricultural machinery parts, it is often used for the bonding of rupture parts and the adhesion of worn parts.