Small and medium-sized asynchronous motors generally use cast iron end covers with bearings. The end cover has a bearing chamber where the bearings are placed and a stop that matches the base. The end cover plays the role of supporting the rotating part, determining the relative position of the rotor and the stator, protecting the inside of the motor and guiding the wind. The rigidity of the end cover structure, the dimensional accuracy and shape tolerance of the stop and the bearing chamber directly affect the uniformity of the air gap between the stator and the rotor and the quality of the motor. Therefore, the key issue in the processing of the end cover is how to control the accuracy of the spigot and the bearing chamber, the coaxiality between the two, and the circular beating of the stepped end of the spigot facing the axis line.

The rotating parts of large motors mostly use seat bearings, and their end covers are only used to protect the inside of the motor and to guide the wind. Therefore, compared with the bearing end cover, its processing requirements are relatively low. In this article, Ms. Participant only discusses the processing technology of commonly used bearing end covers, because most of the motor rotating parts are supported by bearing end covers, and the solution of key technical problems is undoubtedly of great practical significance.

End cap type summary

●According to the different types of bearings, there are two types of end covers with sliding bearings and rolling bearings. For the end cover with sliding bearing, the bearing chamber must have a lubricating oil pool and space for placing an oil ring or oil slinger, so the structure is very complicated. In general, the inspection and maintenance of sliding bearings are frequent, and the radial gap between the bearing and the shaft is large, which has a serious impact on the uniformity of the air gap of the motor. Now it is rarely used in the newly designed small and medium-sized motors.

The rolling bearing adopts semi-solid lubricating grease, which greatly simplifies the structure of the end cover, and is more convenient for casting and processing. At the same time, the tight fit of the rolling bearings makes it easy to ensure the uniformity of the motor air gap, with low friction loss and easy maintenance. Therefore, end caps with rolling bearings are most used in small and medium-sized motors. The noise of rolling bearings is loud, and oil-containing powder metallurgical bearings are often used in low-noise motors.

● According to the different structure of the bearing room, it can be divided into the through hole bearing room and the stepped hole bearing room end cover. When using a through-hole bearing chamber end cover, an outer bearing cover must be used to prevent the grease from flowing out. This kind of end cover has simple structure, easy processing and convenient maintenance. Therefore it is most commonly used.

The stepped hole bearing end cover, whose stepped part can act as an outer bearing cover, can reduce the number of parts and simplify the motor structure. Motors with a center height of less than H160 use this end cover, and everyone is also used to call the end cover End cap without holes.

● According to the different materials used in the end cover, it can be divided into three types: cast iron, steel and aluminum alloy. Cast iron (commonly used grades are HT150-HT250) is cheap, has better manufacturing and processing properties, and has sufficient mechanical strength. Therefore, cast iron end caps are widely used in small and medium-sized motors. Only in special occasions, such as traction motors and explosion-proof motors, when the mechanical strength requirements are high, cast steel end caps or high-strength cast iron end caps are used.

In mass-produced fractional horsepower motors, in order to reduce weight and reduce processing man-hours, aluminum alloy die-cast end caps are used. However, the mechanical strength and wear resistance of aluminum alloy are poor, and the price of the material is more expensive. Therefore, aluminum alloy die casting is not suitable for the end with an outer diameter of more than 300 mm.

● According to the different positions of the end cover, it can be divided into front end (non-drive end) and rear end cover (drive end). Generally, the structures at both ends of the squirrel cage motor are interrelated and can be used universally. The depth of the front cover of the DC motor and the slip ring AC motor is larger than that of the rear cover, and there are special bosses for installing the discharge brush holder and observation holes for inspecting the commutator and slip ring, so the structure of the front cover is more complicated. Manufacturing and processing are also difficult. In order to make the front and rear end caps universal, slip rings are often installed outside the end caps.

● According to the different forms of spigot, it can be divided into inner spigot end cap and outer spigot end cap. The stop surface of the machine base on the inner circle is called the inner stop. The stop surface of the machine base on the outer circle is called the outer stop. The coaxiality between the end cover and the base is ensured by the fitting of the spigot. The end surface of the spigot is the base surface for the assembly between the motor shafts and must be in close contact. For this reason, there must be sufficient clearance at the end face of the stop. Small motors often use inner stop, large and medium-sized motors usually use outer stop.

● According to whether there is a flange on the end cover, it can be divided into flange (flange) end cover and non-protruding end cover. The through hole on the flange of the end cover is used for installing the motor. Generally, the motor is installed with the foot hole of the base. Therefore, the flangeless end cover is most commonly used.

Technical requirements for end cap processing

The bearing end cover is the connecting piece between the stator and the rotor. The accuracy of the air gap of the motor is ensured by the matching accuracy of the stop and the bearing chamber, and the impact of the loading and unloading wear on the accuracy is small. Therefore, the requirements for the roughness of the stop and the bearing chamber are higher. Pay attention to the following aspects when processing end caps:

● The dimensional accuracy, cylindricity and roughness of the bearing chamber;

● The dimensional accuracy, cylindricity and roughness of the stop;

● Coaxiality between the bearing chamber and the spigot;

● The circular beating of the end face of the axis line;

● The depth of the end cap.