On the disassembly and installation of agricultural machinery

At present, China’s agricultural machinery repair is mainly replacement repair, which can not be separated from disassembly. Disassembly and installation is an important part of agricultural machinery repair, which needs to be completed with high quality and low cost to meet the needs of agricultural machinery repair. There are many kinds of agricultural machinery, such as plough and harrow with relatively simple structure, tractor and combine with complex structure, etc. Some machines are made up of thousands of parts. Some parts are processed precisely (for example, when grinding and repairing the plunger sleeve, the taper should not be greater than 0.002 mm). The assembly relationship between parts is strictly required, and the disassembly and assembly work is heavy. The disassembly and assembly work of a tractor accounts for about 50% of the overhaul work. Disassembly is an important process in the repair process. The purpose of disassembly is to check and repair the damaged parts. Installation process is the key process in repair. If the parts, components and assemblies are not installed correctly, the machine will not work properly.

1 Disassembly

The disassembly of agricultural machinery is carried out according to the structural characteristics and technological sequence. The general principle is to remove the assembly as a whole, the assembly as a component, and then the component as a part; from the accessory to the main part, from the exterior to the interior. Attention shall be paid to the following items during disassembly:

(1) Avoid unnecessary decomposition. When repairing agricultural machinery, not every assembly and accessory can be disassembled as carefully as possible. Unnecessary disassembly will not only cause the waste of labor time, but also cause the damage of consumable parts (generally, the paper pad and oil seal cannot be used again after disassembly). Reducing the number of disassembly and assembly can prolong the service life of parts. If the assembly and disassembly times of the static fitting parts are too many, the fit tightness will disappear. In the long use process, the moving parts have been running in well, which are more closely matched than any processed parts. It is difficult to restore the original matching position after disassembly and reassembly. This will accelerate the wear of parts and shorten their service life. Therefore, it is best to determine the technical status of the components of the assembly by using the non disassembly tester before deciding whether to disassemble them.

(2) Each kind of machinery has its own characteristics. Before disassembling, it is necessary to understand the structural characteristics and working principle of the dismantled machinery. If the installation structure of the small bevel gear of the tractor is different, the small bevel gear of some tractors can be pulled out from the rear as long as the front locking nut is unscrewed. Some tractor gears have both retaining ring and threaded connection. First remove the retaining ring, and then remove the small bevel gear while withdrawing the screw thread. For example, some structures or connectors are in the interior, which is not easy to observe. For the connecting bolts between the gearbox and the rear axle of dongfanghong-c1802e tractor, in addition to those seen from the outside, there are two bolts in the central transmission room of the rear axle. The gearbox and the rear axle body cannot be disassembled without removing the two bolts. The power take-off shaft of the tractor passes through the hydraulic distributor housing which is fixed on the rear axle cover. If the PTO shaft is not removed first, the cover plate cannot be taken out even after all the screws of the cover plate are unscrewed. For example, the fuel pump of dongfanghong-1602 tractor can be directly removed from the body, while the fuel pump of jdt-650 tractor must be removed first from the starter or the end cover of the clutch chamber at the rear end of the starter. Therefore, in order to decompose agricultural machinery smoothly, we must be familiar with the structure of agricultural machinery.

(3) Prepare for installation during disassembly. Disassembly is not for the purpose of repair and better installation and use. Therefore, the convenience and correctness of installation shall be considered during disassembly. During the manufacturing of parts, the requirements of parts in use and repair shall be considered. Generally, the parts that need to be marked shall be marked on the non working surface (steel seal or mark with electric flame pen). During the disassembly, the check mark shall be checked, and the parts with unclear mark shall be marked again. So as to restore the original matching relationship as much as possible during installation. These marks are used to keep the relative position of mating parts (such as crankshaft and flywheel, timing gear, connecting rod and connecting rod pad cover, etc.); marks that are not interchangeable for similar parts (such as bearing bush, counterweight, etc.). In order to improve installation efficiency and facilitate cleaning, parts shall be classified into shelves according to size and material, and small parts (such as flap pins, etc.) which are easy to be lost shall be packed and stored.

(4) Tools should be used correctly when disassembling. During disassembly, avoid striking hard to avoid damaging parts. The most commonly used tool for disassembly is the wrench. There are many kinds and sizes of spanners. Do not lengthen the handle length of spanner at will for labor saving. The extension handle is easy to break the screw. Therefore, it is required to use different spanners to screw different diameter screws. It is often seen that when tightening the main bearing bush nut, use a force bar of more than one meter long, and two people try their best to screw it. As a result, the nut is deformed, the lighter one reduces the connection strength, the heavier one breaks the bolt or causes the part deformation. When screwing the screw, the spanner with proper size of wrench opening should be selected. If the wrench opening is large, it is not suitable to continue to use. If it continues to be used, it is easy to make the nut edge round, resulting in difficulty in disassembly. The special puller or press is generally used for the disassembly of pulley and bearing. When using the press, pay attention to protect the working surface of parts.

2 Assembly

The assembly of agricultural machinery after repair is not to complete the task by assembling the parts together, but to ensure a certain assembly accuracy to ensure the good working performance of the machine, components and components. Attention shall be paid to the following items during assembly:

(1) Ensure that the fit clearance between parts is correct. There are clearance fit and interference fit between parts according to their work requirements. If the fit relationship is not correct, such as the gap fit is not correct, abnormal noise, impact or jamming will occur; if the interference of the fitting parts is too small, the parts are not firmly combined and easy to loosen; if the interference is too large, the parts are easy to crack in the assembly process.

(2) Ensure that the relative position between parts is correct. When assembling parts or assemblies, the perpendicularity, parallelism and coaxiality between parts must be ensured to be correct. If the flywheel and crankshaft must be coaxial, otherwise the engine will run unevenly.

(3) Maintain the original relationship of manufacturing and processing. When the engine is manufactured, some parts are assembled and processed together. In repair and assembly, in order to ensure the correct relationship of the machined surface or the accurate geometry, it is not interchangeable. For example, crankshaft bearing seat and bearing cap, connecting rod and connecting rod bearing cap shall be installed according to the marks.

(4) Assemble the original parts according to the marks. All marked parts shall be installed in sequence according to the marks during disassembly.

(5) Ensure the sealing device is in good condition. During assembly, all sealing gaskets and “O” rings shall be replaced to ensure reliable sealing.