The harms caused by unbalanced rotor are various. When the rotor rotates, unbalanced centrifugal force will occur due to unbalanced rotor, which will cause deflection deformation and internal stress of the rotor. Such deformation and internal stress will cause fatigue of the rotor and even lead to rotor breakage. This force will also be transmitted to the machine base through bearings, causing vibration and noise of the machine equipment, accelerating wear of bearings and seals, reducing the working accuracy and efficiency of the machine, shortening the service life of the machine, and sometimes even leading to loose mating and component breakage, resulting in major accidents and causing huge economic losses. Practice shows that over 30% of the faults in motors with excessive vibration are caused by unbalanced mass of the rotor itself. Rotating parts and components corrected by dynamic balance can eliminate and slow down mechanical vibration, extend service life of the components and reduce noise.
Imbalance is an absolute value, while speed only converts imbalance into dynamic load. Balancer equipment transforms dynamic load into electrical signal through sensors and finally restores imbalance through amplifier filter. The speed selection depends on many factors such as balancer equipment, natural frequency of rotor, etc. According to the dynamic balance theory, the rotor imbalance has no relationship with the speed.
Factors of unbalance in rotor of universal joint dynamic balancer:
1. Rotor structure of cardan dynamic balancer is asymmetric. The most typical example is crankshaft. The asymmetry in crankshaft structure is determined by its working characteristics. Therefore, the crankshaft must be weighed in design. Every crankshaft must be balanced before leaving the factory. The remaining unbalance can only be put into service if it meets the requirements.
2. Impairment of rotor caused by defects of raw material or blank is a common phenomenon in mechanical engineering, such as uneven density of raw material, pore, sand hole and loose structure of blank, and uneven weld seam will cause rotor imbalance.
3. Errors in machining or assembling the rotor of the universal joint dynamic balancing machine.
If there are errors in the process of machining or assembling the rotor, the mass distribution of the rotor will also be changed, which will destroy the balance state of the rotor. For example, different shafts of rotor and journal axis, different tightening degree of connecting screw or winding deformation caused by welding will cause rotor imbalance. A certain degree of rotor imbalance is caused by the above reasons. The sum of all the imbalance vectors distributed on the rotor can be considered to be a vector concentrated on the "focus". Dynamic balance is a technique for determining the position and size of the imbalance rotor's focus and then removing or adding a weight of the same size at its corresponding position.
Factors affecting the corrected cardan joint balance:
1. The imbalance caused by manufacturing tolerances specified in the design specification for main parts of universal coupling.
2. The unbalance caused by eccentricity of the counterpart between the cardan joint and the shaft.
3. Gap between mating parts in universal joint.
4. Unbalance caused by uneven or asymmetrical distribution of accessories in universal joint.
5. Imbalance caused by uneven material or wear of parts of universal joint.
