Tractor Gearbox Manufactured in China

The main function of the gearbox is to support the drive shaft, ensuring that the center distance between axes is parallel and guaranteeing the correct installation of tractor gearbox components in connection with other parts.

As gray cast iron exhibits excellent casting and machinability properties, along with good wear resistance, vibration damping, and a low price, the rough cabinet is typically made of cast iron. For the China 75 tractor gearbox, the material selected is HT150. The taper angle on the front and rear planes is very small. The margin on the plane is 5mm. The flat margin around is 3.2 to 3.6mm, and the maximum margin is 4.5mm. For bearings with a diameter of 80mm, except for a margin of 10mm in diameter, the margin for all bearing bore diameters is 9mm. Holes and the 30mm diameter hole for the splash gear fork shaft are not cast out as follows. The fillet radius not specified is 3 - 5mm, and the non-specified taper angle is 1 degree to 1.3 degrees. The allowable subsurface fault movement is 1mm. The casting wall thickness tolerance is 2mm. For casting non-processed surfaces, deep holes are allowed a single tolerance of 2mm, with a maximum size of 5mm, and the total number should not exceed 10. The depth of all ribs on deep holes should not exceed 3mm. The casting process allows for two-thirds of casting defects within the surface depth allowance. Casting defects beyond this scope can be repaired by cast iron welding following the welding repair technological procedure.

From a structural perspective in terms of technological features, it is a thin-walled shell cavity-shaped part with a complex shape, presenting difficulties in casting and having poor stiffness and susceptibility to deformation. Machining requires high precision. The outer surface of the part has many planes that need processing. There are supporting holes distributed on the front and back surfaces. To better meet processing requirements, especially for processing, four auxiliary reference planes are used as orientation planes. In addition to supporting holes, there is also a series of threaded holes on the connected surfaces.

The main technical requirements for tractor gearboxes are as follows: The size and geometric precision accuracy of bearing bores. These are used to install bearings. Errors in size and geometry can lead to errors and poor fit with bearings, causing deformation of the bearing raceway, a decrease in the rotational precision of bearings, and an increase in working temperature. The diameter tolerance level is IT7. No special provisions are made for shape tolerance, and its value should be within the hole tolerance range. Bearing hole pitch tolerance is determined by the standard deviation of gear center distance requirements. This affects gear backlash. Excessive backlash can cause impacts during driving, and if it is too large, it cannot guarantee the normal lubrication of gears and may even lead to transmission jamming. The center distance tolerance of tractor transmission pores is approximately 0.12mm at the IT9 level.