The selected tractor reducer case is a large-scale casting designed by a company, which is produced in large quantities. It requires high requirements for the machining accuracy of the main plane, the dimensional accuracy of the hole and the surface roughness. HT250 is the most commonly used case of tractor reducer. Gray cast iron has good wear resistance, fluidity, vibration damping and machinability. The main chemical components of HT250 are shown in the table.
The casting of tractor reducer case adopts mechanical modeling. The upper and lower half molds are made by using the independently developed three degree of freedom vibration casting machine, and one casting is placed in each case. The self-developed multi degree of freedom vibration casting machine is shown in the figure. The vibration amplitude in each direction is 10ram, and the vibration amplitude and vibration frequency can be adjusted. The molten iron is melted in electric furnace and poured by 300kg subcontracting. The pouring temperature is higher than 1300 “C. the shot blasting room is cleaned with shot blasting machine. The grinding and shovel cleaning of tractor box castings are carried out on the cleaning line. The tractor box castings must be annealed to eliminate internal stress. Technical requirements for castings:
(1) The tractor box casting meets the mechanical property requirements of HT250, ensuring that the tractor box casting is free of shrinkage cavity and porosity, and the internal and external surfaces are free of defects such as air hole, sand inclusion, slag hole and crack, so as to make the surface smooth and beautiful.
(2) The mounting hole of each bearing or shaft shall be smooth and free of casting defects, and the surface roughness shall not be greater than ra2.5.
(3) In order to eliminate the internal stress of the box casting during solidification, the temperature of the tractor box casting needs to be heated to 500.560. C. Heat preservation for a period of time, and then slowly cool down to 150.200. C after the furnace. At this time, the internal stress of the tractor box casting is basically eliminated.