Ms. learned from a friend's chat that he had handled a typical fault: a customer's motor had experienced a broken shaft, with the breakage occurring at the shaft extension root. Based on years of experience, her initial analysis suggested that the customer's operating conditions were quite unusual, and it was very likely that the motor was being driven by a pulley.
The subsequent investigation largely confirmed the analysis and inferences; the motor was an H355 8-pole motor with a power of 160kW, and the customer was using a belt pulley to drive the crusher. Based on the stress on the motor, no motor manufacturer would recommend belt drive, especially for driving crushing equipment.
Problems with belt drives for motors
For motors using pulley connections, if the pulley is too heavy or the belt is installed too tightly when some customers equip the motor output shaft, the motor output bearing will be subjected to continuous alternating bending stress during operation. The maximum bending moment generated by this stress on the shaft is near the bearing support point of the output shaft. Repeated impacts cause fatigue, which gradually causes cracks in the shaft and eventually leads to complete breakage.
Generally, large motors should avoid using belt drives as much as possible. The technical specifications and manufacturer's manuals for motors stipulate that belt drives are not recommended for motors of H280 and above. The reason or theoretical basis is as mentioned earlier: belt drives inherently add bending stress to the motor shaft while it is under normal load. Combined with an excessively tight belt, this results in the motor shaft constantly bearing a large alternating load during operation. Stress concentration is most severe at the shaft extension and bearing areas, easily leading to shaft breakage.
If the motor is not concentric with the driven equipment, the motor shaft will bear additional alternating loads, which may be beyond the design expectations. During motor operation, this can lead to metal fatigue damage to the motor shaft. When the additional load on the motor shaft extension or a relatively weak point of the shaft is too large, it will cause radial bending deformation of the motor shaft. More seriously, this will further worsen the operating conditions of the motor shaft. Combined with the torque of the load it bears, this will eventually lead to the motor shaft breaking. The fracture location is usually near the bearing, mostly on the inside of the end cover.
Crusher Classification and Introduction
● Box-type crusher
Box crushers (also known as square box crushers or hammer crushers) are suitable for crushing various brittle mineral materials. Materials to be crushed include coal, salt, chalk, gypsum, alum, bricks, tiles, limestone, bluestone, shale, and coal gangue. The compressive strength of the material should not exceed 300 MPa, and the moisture content should not exceed 30%.
●Jaw Crusher
Jaw crushers, also known as jaw breakers or tiger's mouth crushers, consist of a crushing chamber formed by two jaw plates: a moving jaw and a stationary jaw. They mimic the jaw movements of an animal to crush materials. Widely used in mining, metallurgy, building materials, highway, railway, water conservancy, and chemical industries for crushing various ores and large materials, such as river pebbles, granite, basalt, quartz, iron ore, diabase, limestone, calcite, dolomite, barite, talc, gypsum, and bentonite in sand and gravel production lines.
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