As a key component of an electric motor , the rationality of its structure and the manufacturability of its processing have a significant impact on the motor's performance. Many undesirable characteristics of the motor, such as stator rubbing, low-frequency electromagnetic noise, and vibration, are related to the machining of the motor frame. Therefore, the frame structure should be rationally selected based on the motor's performance requirements and processed according to technical specifications to reduce and eliminate non-compliance factors caused by frame machining. Ms. Can has compiled and will share information on motor frame types and some basic technical requirements with you today.
Basic types of motor frames
●Based on whether the frame is magnetic, motors can be divided into magnetic and non-magnetic frames. Magnetic frames are used for DC motors and pivot-type synchronous motors. Non-magnetic frames are used for asynchronous motors, pole-rotating synchronous motors, and other motors with laminated stator cores.
●Based on the different base blanks, they can be divided into welded and cast bases. Welded bases are made of steel. Cast bases can be made of cast steel, cast iron, or aluminum alloy; magnetic bases are almost always made of cast steel or welded steel plate structures.
● Non-magnetic motor bases are generally made of gray cast iron. Cast iron bases are relatively inexpensive, easy to manufacture, and their mechanical strength is sufficient for most small and medium-sized motors. Only in cases where high mechanical strength is required, such as explosion-proof motors and marine motors, are high-strength cast iron or cast steel bases used.
● In recent years, small AC motors and micro motors have increasingly adopted frames made of aluminum-silicon alloy or aluminum-magnesium alloy through die casting. The advantage of this structure is that the aluminum alloy can be directly cast onto the stator core, eliminating the need for machining the inner circle of the frame, saving on some fasteners, and also making the small motor lighter. Its disadvantages are that aluminum alloy is more expensive, has lower mechanical strength, and poorer wear resistance.
● For large motors, due to their small production volume and large weight, welded frames made of shaped steel and steel plates are commonly used. Compared with cast iron frames, welded frames are lighter under the same mechanical strength and structural rigidity conditions. Welding does not require special molds, resulting in lower costs, shorter production cycles, and the ability to meet the requirements for customized motor shapes.
●According to the different base structures, they can be divided into integral bases and separate bases.
Separate base structures have weaker structural rigidity and require more machining time; improper assembly can also lead to the entire machine failing to meet requirements. However, their unique advantages are ease of installation and maintenance; when designed properly, issues such as assembly accuracy and structural rigidity are no longer limiting factors.
One-piece frame designs are relatively common, typically featuring a cylindrical cross-section. The frame has two or four feet at the bottom for motor mounting. Cylindrical frames offer the best manufacturability, but for certain motors, where dimensional limitations exist while maximizing power is required, polygonal frame cross-sections are often designed to fully utilize available space. Polygonal frames are more complex to manufacture, increasing processing costs.
●Other classification methods. Based on the different protection and cooling methods, the frame can be divided into open type, protective type, enclosed type, and explosion-proof type. Enclosed and explosion-proof frames generally have heat sinks on their outer surface, while other frames do not. Based on whether or not they have feet, they can be divided into frames with feet (such as B3 and B35) and frames without feet (such as V1 and B5).
Machine base machining technical requirements
The main parts of the machine base that need to be machined include the end stops, end faces, inner circles, base planes, base holes, fixed end covers, junction boxes, and hoisting bolts. For split-type machine bases, it is also necessary to machine the mating surfaces, mating screw holes, and pin holes. The technical requirements that the machine base should meet during machining can be summarized as follows.
● The dimensional accuracy and surface roughness of each machined part should conform to the specifications in the drawing. The accuracy and surface roughness requirements for the end stops and inner circle are particularly high, and the center height must also be accurate.
● The geometric tolerances of each machined surface shall conform to the specifications in the drawings. The coaxiality of the end stops and inner circles, and the runout of the end faces facing the axis, are critical to the machining of the machine base. It is particularly important to note that if geometric tolerances are not specified, their maximum and minimum values should be within the dimensional tolerance range; the base plane should be parallel to the axis.
● The distance between the foot holes and the center line of the machine base should be symmetrical and meet the specified tolerances.
●After the magnetic base is machined, the thickness of all parts of the yoke should be uniform. The graduations of the magnetic pole holes should be equal, and their positions must conform to the specifications in the drawings.
●The mating surfaces of the split base must be stable and reliably positioned, and the original requirements must still be met when disassembled and reassembled.
