End cover casting and its processing technology

●In order to facilitate mold making, modeling and machining, the geometric shapes of the inner and outer end caps should be simple and have a linear contour as much as possible. There must be a proper slope in the length direction of the end cap to make it easy to draw the mold during casting.

●The wall thickness of gray cast iron parts should generally not be less than 5 mm to avoid the formation of white iron and cracks; however, thick sections should not be used to prevent shrinkage, porosity and cracks. The difference between the thickness of the workpiece should not be too large, so that the entire casting can be uniformly cooled, and excessive internal stress and cracks can be prevented.

●For parts with insufficient strength and rigidity, Π-shaped or T-shaped cross-section structure should be adopted to avoid local increase in thickness. When considering the rigidity of the end cover, it must be noted that the stress load on the end cover due to clamping and cutting during the machining process is much greater than when the motor is running. In order not to cause deformation of the end cap during clamping and processing, the rigidity of the end cap is usually increased by adding ribs. This is particularly important for end caps with larger windows.

●In order to facilitate processing, the bearing chamber is made with a through hole. However, the through-hole bearing chamber is easily deformed when it is directly clamped. Therefore, three or four straps are generally designed on the outside of the end cover for clamping by the jaws. The outer end of the material bearing with stepped holes protrudes longer and has better rigidity, which can clamp the outer end of the bearing for processing.

●There should be a distance of 5~10mm between the lug of the end cover of the small motor and the end surface of the base. In this way, the cutting distance of the processed end face is shortened, and at the same time, the joint between the end cover and the base is more stable.

How to select the accuracy level and type of fit

●The inner diameter of the bearing matched with the rolling bearing adopts level 7 accuracy;

●The matching type depends on the bearing type and structural requirements.

●The end caps of small motors generally adopt level 7 accuracy, the end caps of medium-sized motors generally adopt level 6 accuracy, and the end caps of large end caps adopt level 9 accuracy.

General rules for selection of matching accuracy and roughness: H8/s7 is used for the stop of the small motor base and end cover, and H7/j6 is used for the stop of the medium motor base and end cover. The processing roughness is selected according to the type of fit, accuracy grade and diameter.

End cap design principles

●The size of holes and bolt holes should be reduced as much as possible

If the holes and bolt holes have one more specification, then the drilling and tapping will require one more tool replacement procedure. Therefore, the specifications of the four end holes on the end cover of most large asynchronous motors and the four bearing sleeve fixing holes are the same.

●The structure of the end cover should be easy to assemble and disassemble

In order to facilitate assembly, the position of each end hole on the end cover to the axis of the spigot should meet the requirements of the drawing, or should not be greater than a quarter of the difference between the diameter of the through hole and the bolt diameter, and the spigot of the end cover should be chamfered .

Taking into account the convenience of disassembly, a certain gap must be maintained between the end cap lugs and the base when designing the end cover, so that after the end cap bolts are unscrewed, a tool can be inserted into the gap to pry the end cap off. In order to reduce the vibration and noise of the motor, the end cover is often designed to be completely close to the machine base. Therefore, two opening screw holes must be provided in the opposite direction of the outer edge of the end cover. The diameter of the bottom hole or the small diameter of the thread should not be smaller than the end cover Tighten the bolts so that when disassembling, screw the two bolts into the opening screw holes to separate the end cover from the base.

●The machining allowance of the end cap should be appropriate

The machining allowance of the casting is determined according to the shape, size and machining accuracy of the workpiece. It is necessary to consider the modeling error and the proper machining allowance after casting deformation. The position of the casting during casting must also be considered. Generally, the machining allowance of the top surface of the casting should be slightly larger than that of the side and bottom surfaces.

●End cover casting hole

Due to the high hardness of the cast iron surface layer, it is easy to damage the tool. Therefore, some casting holes that need to be machined will become very small and difficult to cast if the machining allowance is left. The hole should not be cast, and it is more mechanically processed. Convenience.