There are many reasons for the deformation of agricultural machinery parts, mainly including the effects of residual stress, external load, and the use and repair, etc., which are described as follows:
(1) Effect of residual stress. Some castings meet the technical requirements during processing, but they have been deformed after a period of use. The reason for this natural deformation is mainly due to the fact that the casting has not been subjected to aging treatment or improper handling. When the casting is cooled from a high temperature, due to the thickness of each part, the cooling rate at the wall thickness is slow, and elastic stretching occurs on the thin portion of the first cooling, which generates a certain residual stress in the interior of the mechanical part. stress. In contrast, gray cast iron precipitates graphite from austenite to ferrite and undergoes volume expansion. When cooling occurs quickly, the phase transition temperature is reached first. First, volume expansion occurs, tensile stress occurs, and wall thickness produces compressive stress. This stress is called phase change stress. The existence of these residual internal stresses in the castings, long-term interaction and gradual internal stress relaxation, resulting in deformation of the parts. In addition, the cutting heat of the machine tool in the machining process and the heat treatment on the surface of the machine will also cause internal stress and cause the deformation of the machine.
(2) Influence of external loads. Such basic components as the cylinder block, rear axle housing, etc., are subjected to unbalanced external loads during use, gradually causing damage to the correct position of the mating surface. Especially when working under overload conditions or under harsh conditions, the external loads will cause more severe deformations caused by the local effects of the basic components. For example, the gearbox and flywheel housing of a wheeled tractor are connected by only a few bolts. The gearbox of the tractor and the rear axle housing of the chain tractor are also fixed together with only a few screws. The front and rear gearboxes of the gearbox are thin and have low strength. Deformation or even cracks occur.
(3) The effect of temperature. Due to improper use, such as poor heat dissipation or dry friction or semi-dry friction, the parts are subjected to high temperatures, and the elastic limit of the metal decreases with increasing temperature, so that the parts cannot be restored to elasticity after deformation. Shape, causing deformation of the machine.
(4) The effect of repairs. Due to mechanical processing such as welding and turning, mechanical stress may cause new stress in the metal. Take necessary measures, such as flooding the welded parts into the water, and only expose the solder joints, and spray the soap to the machined surface to prevent deformation of the parts. In addition, for the parts that can continue to be used after disassembly, shape detection should be performed and corrections made when necessary. Otherwise, the deformed parts may be installed again.
Deformation of the machine will result in changes in the associated parts of the relationship, so that the machine can not function properly, or even cause major failures. Therefore, we must add prevention as soon as possible:
(1) When purchasing agricultural machinery such as tractors and harvesters, or other farm machinery accessories, select products from reputable manufacturers. These manufacturers have strong technical strength, excellent equipment, and attach importance to product quality. The mechanical processing technology of the parts is more stringent. The residual stress is very small or not. It is not easy to deform under normal use.
(2) The maintenance of agricultural machinery should be strengthened during use. The load outside the machine should be balanced. If the engine should be fueled (diesel) or ignited (petrol engine) at a time, avoid knocking. Start steadily and avoid impact loads. Traction hooks should be in a neutral position and should not be biased. Every effort should be made to avoid long-term overload operations.
(3) The engine should work under normal water temperature, and the temperature of each transmission component should not exceed the regulation (the working temperature of the general gearbox and rear axle is 70-95°C). Secondly, lubricants with qualified grades and qualified quality should be used. When they are insufficient, they should be added in a timely manner. When repairing, it should strictly implement the process rules and take measures to prevent new mechanical stress.
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