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Example operation of maintenance skills for bearing replacement of motorized spindle motor

Example operation of maintenance skills for bearing replacement of motorized spindle motor

Nov 27, 2020

It is also very important to design and manufacture disassembly tools according to the needs. During the disassembly, according to the drawings, the disassembly method, sequence and the matching conditions of the bearing shall be investigated to ensure the safety of the disassembly operation.

Remove the outer ring of interference fit, set several screws for the outer ring extrusion screw on the circumference of the outer ring in advance, tighten the screw evenly on one side and disassemble at the same time. These screw holes are usually covered with blind plugs, tapered roller bearings and other separate bearings. Several cuts are set on the shielding shoulder of the shell. The blocks are used to remove them with a press or gently tapped.

The disassembly of the inner ring can be pulled out by a press. At this time, pay attention to let the inner ring bear its pulling force. Moreover, the drawing fixture shown is mostly used. No matter what kind of fixture, it must be firmly stuck on the side of inner ring. Therefore, it is necessary to consider the size of the shaft shoulder, or to study the processing of groove at the shoulder, so as to use the drawing fixture.

The inner ring of large bearing is disassembled by oil pressure method. Oil pressure is applied through the oil hole of the bearing to make it easy to draw. The bearing with large width is disassembled by oil pressure method and drawing fixture.

Induction heating method can be used to dismantle the inner ring of Nu and NJ cylindrical roller bearings. The method of drawing the inner ring by heating the inner ring in a short time. The induction heating method is also used when a large number of inner rings of this kind of bearing need to be installed.

It is hoped that the bearing package will be opened just before installation. General grease lubrication, do not clean, directly fill with grease. It is not necessary to clean the bearings with lubricating oil. However, the bearings used for instruments or high-speed use should be cleaned with clean oil to remove the antirust agent coated on the bearings. The bearing without antirust agent is easy to rust, so it can not be placed. Moreover, the bearing sealed with grease can be used directly without cleaning.

The bearing installation method varies with the bearing structure, fit and condition. Generally, due to the shaft rotation, the inner ring needs interference fit. Cylindrical bore bearing is usually pressed in by press or hot charging. In the case of taper hole, it is directly installed on the taper shaft or installed with sleeve.

When it is installed to the shell, there are many clearance fits and the outer ring has interference. It is usually pressed in with a press or has a cold shrink fit method after cooling. When dry ice is used as coolant, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate anti rust measures are needed.

The spindle structure of engraving machine is generally supported by angular contact ball bearing. The configuration of the bearing depends on the size and direction of the load, the speed of the spindle and the working requirements of the spindle.

The angular contact ball bearing can work normally under the condition of axial preload. Preloading can not only eliminate the axial clearance of the bearing, but also improve the stiffness of the bearing and the rotation accuracy of the spindle, restrain the vibration and the sliding phenomenon of the ball when it rotates. Generally speaking, the greater the preload, the better the effect of improving the stiffness and rotation accuracy; but on the other hand, the greater the preload, the higher the temperature rise, which may cause burns, thus reducing the service life and even not working normally. Therefore, the best preload value of bearing should be selected according to the motorized spindle with different speed and load.

When the ball bearing rotates at high speed, the centrifugal force and gyroscopic moment will be produced by the ball. At this time, the centrifugal force is far greater than the force on the ball when cutting. Therefore, the main parameter of bearing design is not the working load, but the rotation speed. In order to solve the problem of centrifugal force in high-speed rotation, the following measures can be taken for rolling bearing itself:

(1) The diameter of the ball should be reduced as far as possible, that is to say, the radial size of the ball should be reduced;

(2) In order to reduce the quality of ball, Si3N4 ceramic material with low density was used to make ball. Si3N4 ceramic material has the advantages of low density, large elastic modulus, small thermal expansion coefficient, high temperature resistance, non-conductive, non-magnetic and thermal conductivity. At present, hot pressed Si3N4 ceramics are used to make balls, and bearing steel is still used for raceway. This kind of bearing is called ceramic hybrid bearing.

Non contact bearing

Non contact bearing refers to aerostatic bearing, hydrostatic bearing and magnetic bearing.

Aerostatic bearing is used in high precision, high speed and light load. The spindle unit with air bearing can rotate at more than 150000r / min, but the output torque and power is very small. It is mainly used for small hole grinding, drilling and finishing of parts.

At present, hydrodynamic and hydrostatic bearings are mainly used in heavy load and high power applications. This kind of bearing adopts the method of combining the dynamic and static force of the liquid to make the spindle support and rotate in the oil film. It has the advantages of small radial and axial runout, high stiffness, good damping characteristics and long life, so it is suitable for both rough and finish machining.

Magnetic bearing (AMB) is a new intelligent bearing which uses magnetic force to suspend the spindle without contact. It has good high-speed performance, no contact, no friction, no wear, high precision, no lubrication and sealing, and can realize real-time diagnosis and online monitoring. Therefore, it has been studied by many countries such as the United States, France, Switzerland, Germany and China. It is a suitable and ideal spindle bearing for ultra-high speed spindle, but its price is expensive, and some technical problems have not been solved completely, so its popularization and application are limited.