Views: 1 Author: PEAK Publish Time: 2024-02-02 Origin: Original
When the wear of tractor parts reaches the specified limit, they must be repaired or replaced, otherwise the wear of the parts will increase sharply and even cause accidental damage. The commonly used methods for repairing tractor parts can be divided into the following five categories.
1. Adjustment, flipping, and transposition method
(1) Adjustment method. Many machine parts and components are designed with adjustment considerations in mind. By adjusting the thread to change the valve clearance, and by adding or removing shims to change the axial position of the large and small bevel gears.
(2) Flip method. Move non working or less stressed parts to the working part by flipping the part. If a gear pair is in transmission, the direction of transmission is generally fixed, so one side of the gear teeth is subjected to greater force and more wear, while the other side is subjected to less force and less wear. So, if necessary, the gear can be flipped 180 °.
(3) Transposition method. Used for components with symmetrical positions or combinations where the relative position of the working surface can be changed, such as driving wheels, final drive gears, etc., which can be left and right adjusted, and chain rail pins can rotate 90 ° relative to the pin hole after wear.
In addition, some parts have reserves, such as the chain track pitch of a tractor, which is twice as large as the tooth pitch of the drive wheel. Only half of the teeth participate in work, so after the drive wheel wears out, it can rotate one tooth relative to the chain track. The steering worm gear of Z-25 is circular, and the transmission part in contact with the worm gear during operation is a fan-shaped surface. Therefore, increasing the distance between the worm gear and the worm gear can cause the worm gear to rotate at an angle relative to the worm gear.
2. Repair dimension method
Due to the limitations of the stiffness, strength, and thickness of the quenched or carburized layer, some parts only have one repair size, while others have several repair sizes. In order to simplify the repair process, ensure quality, and reduce costs, the national regulatory department standardizes the repair dimensions of the main assembly components based on factors such as the maximum wear size, wear characteristics, and machining allowance of the parts. Some parts with standardized repair dimensions are organized and supplied by the supply department.
Among the repair size parts supplied domestically, the hole type parts are the reduced repair size (such as main bearings and connecting rod bearings), and the shaft type parts are the enlarged repair size (such as pistons). Usually, only one part of the assembly is supplied.
The repair dimension method is also applicable for repairing thread and key fits. The advantages of this method are simplicity, reliability, and the ability to extend the service life of parts, but it restricts the exchange of parts and poses difficulties for the supply of parts and the organization of repair production.
3 Additional parts method
The additional parts method is to use a specially designed part to be embedded in the worn area of the part, in order to compensate for the wear of the part and restore its fitting relationship. This method is suitable for repairing parts with significant wear, such as valve seats, cylinders, bearing holes on gearbox housings, shaft parts, and damaged screw holes.
When the shaft is severely worn and allowed in terms of structure L and strength, the shaft neck can be machined to a certain size, and then the shaft sleeve can be repaired by pressing someone on the top of the shaft, and the shaft can be machined to the nominal size or repair size as needed.
When the threaded hole is damaged, if the structure permits, it can be drilled with a large tap and another plug with internal and external threads can be made. The external thread of the plug is the same as the thread tapped after the hole is enlarged, while the internal thread of the plug is the same as the thread of the original screw hole.
When using the additional parts method to repair parts, the following points should be noted:
(1) Materials. Generally the same as the material of the parts. For cast iron parts, cast iron sleeves can be used, and sometimes steel sleeves made of grade 20 carbon steel can also be used.
(2) Size. The thickness of the sleeve depends on the material. The thickness of the steel sleeve shall not be less than 2-2.5 mm, and the thickness of the cast iron sleeve shall not be less than 4-5 mm.
(3) Processing requirements. At the mating parts of the repaired parts, the surface smoothness should reach △ 6 to △ 10 to ensure a tight fit on the mating surface. In addition, for ease of installation, the lower edge of the sleeve and the upper edge of the hole should be machined into a 30 ° to 45 ° chamfer. When inserting a sleeve on the shaft, the chamfer at the end of the shaft neck is 10 ° to 26 °.
According to the hardness requirements, the sleeve can undergo heat treatment after processing.
4. Coordination with parts
To prevent loosening of additional parts, the following methods can be used:
(1) Utilize interference fit. The size of its interference is related to the material, size, surface smoothness, and insertion method of the parts. For example, when inserting the valve seat ring of Dongfanghong-54/75 tractor, the interference used for hot pressing is 0.2-0.0 25 mm, with a cold press interference of 0.1-0.0 15 mm,
(2) Spot weld the matching end face between the sleeve and the parts.
(3) Use stop screws. The number of stop screws depends on the diameter of the parts. Parts with a diameter of less than 20 mm can use one stop screw, while parts with a diameter of 30-50 mm can use two symmetrical stop screws. For parts with a diameter greater than 120 mm, three stop screws spaced 120 ° apart can be used.
The additional parts method can repair worn journals or apertures with high repair quality and will not damage the heat treatment of the parts. But compared to the repair size method, its process is complex, the cost is high, and it will reduce the strength of the parts. In addition, the additional parts method is also limited by the structure of the parts and has certain limitations.
Partial replacement method for 5 parts
The partial replacement method of parts is to remove the worn parts of the parts and replace them with new ones, in order to restore the working ability of the parts.
On tractors, some parts have several working faces, and the degree of wear on these working faces varies during use. Often, one part of the parts has been worn or damaged, while the other part is intact or only has minimal wear. Such parts can be repaired using the local replacement method.
For example, in the gear set of a gearbox, the teeth of the gear with the highest load often wear severely or break, while the other gears wear less. In this case, the damaged part of the gear can be annealed, then the damaged part can be cut off on the lathe and pressed into the gear ring. Finally, the new gear ring can be welded onto the gear along the end face using electric welding.
The partial replacement method of parts has high repair quality and can save high-quality metal, but its process is complex and requires a relatively high level of technical proficiency in operation.
