Types and technical requirements of frame

The frame supports and fixes the stator core in the motor, and supports the rotor and protects the motor winding through the coordination of the frame and the end cover in the bearing end cover structure. There are many types of frame structure, including integral frame, separate frame, cast iron frame, cast steel frame, steel plate welding frame (including box frame) and aluminum alloy die casting frame. However, from the point of view of manufacturing process, the representative ones are integral cast iron frame with foot and separate steel plate welding frame. The former is the most commonly used stand in small and medium-sized motors, while the latter is used for large hydro generators and DC motors with special requirements. Figure 1-16 shows a typical frame structure.

The matching surface between the base and the end cover is called the stop, and there are two kinds of inner stop and outer stop in the motor structure. If the seat stop surface is inner circle, it is called inner stop; If the base stop surface is cylindrical, it is called outer stop.

The parts that need to be processed on the machine base include the end stop, the inner surface of the iron core, the foot plane, the foot hole, and the bolt hole for fixing the end cover, the junction box and the lifting ring. For the separated frame, it is also necessary to process the split surface (i.e. joint surface), split through hole and pin hole, etc.

The technical requirements of frame processing should be based on the function and working conditions of the frame, as well as the relative position of stator core and end cover. The technical requirements of general machine base processing are as follows:

1. The dimensional accuracy shall meet the requirements of the drawing

Both the base stop and the inner circle of the iron core are the mating surfaces, and their dimensional accuracy is the highest. In small asynchronous motors, the tolerance of these two dimensions is often H8. The center height of motor is an important installation dimension. Due to the requirement of uniformity of gas and acid, the tolerance grade of the center height of the frame (that is, the height from the axis of the frame to the supporting surface of the foot) is often higher than that of the center height of the motor. The accuracy of other installation dimensions is second.

2. The shape accuracy shall meet the requirements of the drawing

The foot plane is the datum plane of motor installation, and it has flatness requirements. The cylindricity of the inner cylinder of the iron core is also strictly regulated.

3. The position accuracy shall meet the requirements of the drawing

There is coaxiality requirement for the axis of one end of the notch and the inner cylinder of the core block facing the other end of the notch. There are strict regulations on the circular runout of the end face of both ends of the end face to the common axis of the end face, the radial circular runout of the inner circle of the iron core to the above-mentioned axis, and the parallelism of the foot plane to the above-mentioned axis. Several end cover fixing screw holes at both ends also have higher requirements for the position of the above axis and end face. Radial circular runout is a comprehensive tolerance, which controls the error of coaxiality and roundness at the same time. Generally, the roundness error of parts is much smaller than the coaxiality error, and the radial run out error is easy to detect. Therefore, the radial run out tolerance is often used to replace the coaxiality tolerance in production, which improves the accuracy of coaxiality relatively.

4. The roughness shall meet the requirements of the drawing

The results show that the surface roughness of the circumferential surface of the notch and the inner circle of the core is the smallest (RA = 3.2um), while the surface roughness of the other machined surfaces is larger (RA = 12.5um) μ m）。

5. other requirements