Introduction to terms

According to the ISO standard, a rotating body supported by a bearing is called a rotor. Rotors are mostly the main rotating parts in power machinery and working machinery.

The rotating part of a motor or certain rotating machines (such as turbines). The rotor of a motor is generally composed of an iron core with a coil, a slip ring, and a fan blade.

The main components of high-speed rotating power machinery or working machinery such as electric motors, generators, gas turbines, and turbo compressors.

The main rotor rotates at a high speed, and when its speed is close to the critical speed, the shaft deforms due to deflection. Even mechanical damage caused by resonance. The natural frequency of the transverse vibration of the rotor is multi-level, so its corresponding critical speed is also multi-level. When the rotor's working speed is lower than the first-order critical speed, it is called a rigid rotor, and when the rotor's working speed is higher than the first-order critical speed, it is called a flexible rotor.

The working speed of any type of rotor must not be close to the critical speed. The critical speed of the rotor depends on its manufacturing material, structural form, geometric size, supporting characteristics and other factors.

Working principle

For example, in an induction motor, a rotor composed of a shaft iron core and a closed conductor embedded in the iron core generates a high speed driven by the rotating magnetic field generated by the stator winding. Rotational movement. The two ends of the rotor adopt rolling bearings and are installed and fixed in the end cover of the motor shell.

Because no matter what type of rotor, centrifugal inertia force will be generated when it is running, which will affect the strength and mechanical efficiency of the rotor. Therefore, the rotor is properly balanced and the mass of its parts is redistributed in order to reduce the centrifugal inertia force generated during the rotation.

When the unbalanced mass of the rotor is approximately distributed on the same plane perpendicular to the axis of rotation, such as the balance of a single disc cam, the weight and position of the balance can be increased or removed to achieve static Balance, even if the center of gravity of each part of the rotor coincides with the axis of rotation.

When the unbalanced weight of the rotor is in the parallel plane of the vertical rotation axis, the unbalanced weight will only appear after the rotor is rotated. This kind of dynamic unbalance is eliminated by changing the balance weight. The weight and position of the system can eliminate inertial force and inertial couple to achieve dynamic balance. Avoid vibration of the rotor on the elastic support.

Rotor classification

Typical rotors include turbine rotors, motor rotors, various pump rotors, and turbo compressor rotors. When the rotor rotates at a certain speed, it will deform greatly and cause resonance. The speed at which resonance is caused is called the critical speed of the rotor.

In engineering, a rotor whose working speed is lower than the first-order critical speed is called a rigid rotor, and a rotor whose working speed is greater than the first-order critical speed is called a flexible rotor.

Because the rotor rotates at a high speed, it needs to be balanced. Static balance is mainly used to balance the inertial force of the disc rotor. The dynamic balance of the rigid rotor can balance the inertial force and the inertial couple through the universal balancing machine, and eliminate the vibration of the rotor on the elastic support.

The dynamic balance of flexible rotors is more complicated. From the principle of distinction, there are two types of vibration mode balance method and influence coefficient method.

Common faults

The rotor has many faults due to difficulty in commutation, high speed, and various faults. Common faults include commutator damage, bearing damage, fan blade damage, brush wear, and rotor winding burnt.

The commutator is damaged

The common faults of the commutator are the surface burning hole, the commutator segment flying out, the short circuit between the commutator segment and the commutator segment, and the commutator Out of circle, excessive wear of commutator, protruding mica sheet, virtual connection of commutator sheet and coil lead, etc.

If the commutator surface is burned with holes, the commutator segments fly out, the commutator segment and the commutator segments are short-circuited, the commutator wears excessively, the commutator should be replaced, and the rotor should be replaced. The winding also needs to be replaced.

For the failure of commutator out of circle, after processing with a horizontal lathe, it can continue to be used.

If the commutator piece and the coil cause a virtual connection, the fault point of the virtual connection can be flushed, riveted or welded as appropriate. If the fault point cannot be found, only the commutator can be replaced, and the rotor winding also needs to be replaced.

The mica sheet of the commutator is protruding. After the side with the teeth of the hacksaw blade is polished thin, the mica is lowered for a while, and then chamfered and polished.

Bearing damage

The commonly used bearing models for power tools are 608, 629, 101, 102, 200, 201, etc.

The common faults of the bearing are excessive clearance, bearing chipping, running jacket, running inner jacket, locking and so on. For faults such as excessive bearing clearance, bearing cracks, lockup, etc., new bearings need to be replaced. For some running jackets with too large gaps, thin iron sheets can be used (for example, some iron beverage bottles can be used) or the casing can be replaced. For some gaps that are not particularly large, you can apply AB universal glue to solve it. For some running inner sleeves, you can use pitting on the shaft to solve the problem.

Damaged wind blades

When the wind blades are often broken, deformed or loose, the old parts can be removed or replaced with new ones. For the deformation of the iron blades, needle-nose pliers can also be used for correction. For the loose between the fan blade and the shaft, you can also apply AB universal glue to stick it firmly.

Brush wear

Under normal circumstances, when the length of the brush is worn to 1/3 of the original length, it should be replaced. If the brush is too short, it is easy to burn the commutator and cause the rotor to be scrapped. The size of the brush is generally expressed by length×width×height. When replacing it, in addition to the same size, it must be replaced with the same brand. In general, the two brushes should be replaced at the same time.

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