Structural maneuverability of the motor shaft
Sufficient strength and rigidity are prerequisites for safe and reliable operation of the motor shaft. Especially for large and medium-sized motors, they should be rigorously checked or demonstrated according to actual working conditions. However, in addition to this, the motor shaft structure processability must also be taken seriously when designing the motor shaft, which is often overlooked, which seriously affects the machining accuracy and processing efficiency. Xiaobian today discusses this topic and talks about how to determine the structural parameters of the shaft.
●The amount of cutting for shaft machining should be minimum
The amount of cutting of the shaft is generally measured by the process factor K of the shaft, and K is calculated according to equation (1).
K=QZ/QB........................(1)
In formula (1):
QZ - gross weight;
QB - the weight of the shaft after machining.
Usually K = 1.15 to 1.3. The design should minimize the unnecessary protruding shoulders and reduce the diameter difference between the steps to achieve the purpose of reducing the process factor K.
●The number of steps of the axis should be reduced as much as possible
The fewer the steps, the more convenient the processing. Especially when using automatic machine tool processing, the number of steps is small to make tool adjustment more convenient.
●The length of the joint between the shaft and the bracket should not be too large.
The matching parts of the shaft and the bracket of the medium and large motors are shown in Fig. 1. If all the diameter D is used, the pressing stroke of the pressing shaft will be the full length L1, the contact area is large, the pressure required is also large, and the contact surface is easily scratched.
After the improved structure, the diameter of the middle section is reduced to D-2. As a non-mating part, the diameter of the mating parts at both ends differs by 1 mm, and the pressing stroke is shortened to L2, which overcomes the above disadvantages. The radial positioning of the mating of the L2 portions at both ends facing the bracket is sufficiently reliable.
In this way, at first glance, increasing the number of steps seems to increase processing difficulties. In fact, such large shafts are not machined on automated machine tools, and the number of steps does not have a major impact on tool requirements. After the diameter of the middle section is reduced, the length of the finished car part (L2+L2) is shorter than the original value L1, and the quality of the finished car is also relatively easy to guarantee. The joint between the shaft and the bracket can also be made into two structures with a diameter difference of 1 mm, as shown in Fig. 2.
● The width of the keyway should be as uniform as possible and placed on the same busbar so that all keyways can be milled out in one setup.
According to the national standard, the width of the shaft end keyway is determined according to the diameter of the shaft extension. In the motor design, the width of the other keyways should be as large as the width of the keyway of the shaft end. Sometimes, due to the versatility of some components (such as slip ring devices, etc.), the keyway on the mating portion allows for a different width than the keyway of the shaft extension.
●The center holes at both ends should be the same size
This facilitates machining, and the center hole is preferably a B-type structure with 120 protective cone holes (see Figure 3).
image 3
● If the strength of the shaft is permitted, the grinding machine should be equipped with a grinding wheel over-travel groove. The width of the overrunning groove and the size of the rounded corners should be as uniform as possible.
●Chamfer slope and fillet radius should be as consistent as possible to save time for tool change or tool adjustment.
