Nine all-round knowledge of bearings necessary for the air compressor industry

1. Bearing installation

Whether the bearing is installed correctly affects the accuracy, life and performance. Therefore, the design and assembly departments should fully study the installation of bearings. It is expected that the installation will be carried out according to the working standard. Items of working standards are usually as follows:

(1) Clean the bearing and bearing-related parts

(2) Check the size and finishing of related parts

(3) Installation

(4) Inspection after installing the bearing

(5) Lubricant supply

It is desirable to unpack the bearing just before installation. General grease lubrication, no cleaning, directly filled with grease. Lubrication with lubricating oil generally does not need to be cleaned, but bearings for instruments or high speeds should be cleaned with clean oil to remove the rust inhibitor applied to the bearings. Bearings from which the anti-rust agent has been removed are prone to rust, so they cannot be left alone.

Furthermore, bearings that have been sealed with grease can be used directly without cleaning. The installation method of the bearing varies with the bearing structure, fit, and conditions. Generally, since the shaft is mostly rotated, the inner ring needs an interference fit. Cylindrical bore bearings are mostly pressed in with a press, or hot-packed. In the case of a tapered hole, install it directly on the tapered shaft, or install it with a sleeve.

When installing to the shell, generally there is a lot of clearance fit, and the outer ring has an interference, which is usually pressed in with a press, or there is also a shrink fit method for installation after cooling. When dry ice is used as the coolant and the shrink fit is installed, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate anti-rust measures are required.

2. Bearing material

The rings and rolling elements of rolling bearings are repeatedly subjected to high contact pressure while making rolling contact with sliding. The cage is in sliding contact with both sides of the ring and rolling elements or one of them, and bears tension and compression on the other side. Therefore, the main requirements for the materials and performance of bearing rings, rolling elements and cages are as follows:

(1) The properties required by the materials of ferrules and rolling elements: high rolling fatigue strength, high hardness, and high wear resistance;

(2) The performance required by the cage material: good dimensional stability and high mechanical strength.

(3) Good processability is required. Depending on the application, it is also required to have good impact resistance, heat resistance, and corrosion resistance.

3. Storage of bearings

When storing bearings, the size and weight of the bearings to be stored must first be fully considered, and the second is to consider the necessary handling space and equipment to ensure that the bearings will not be collided during storage and retrieval. Bearings should not be placed directly on the ground.

Therefore, appropriate shelves should be configured, and the bottom layer of the shelf should be 30cm above the ground. Under normal packaging conditions, the anti-rust effect is 13 years depending on the storage environment. If it is necessary to store for nearly 10 years under special circumstances, the storage method of immersing in turbine oil (used as bearing lubricant) and other oils can be adopted.

(1) The work of installing the bearing

There are many ways to install bearings, and the same job will be handled after installation. After the bearing is installed, be sure to apply the bearing lubricant to the outer ring obliquely.

A. Application of lubricant: When grease lubrication, apply lubricant to cover all roller surfaces, and restore the position of the outer ring after application. When lubricating with oil, apply the oil to all roller surfaces, and restore the position of the outer ring after the application.

B. After coating, cover with plastic film to prevent dust.

(2) Precautions for dismounting bearings

The disassembly of the bearing is carried out during regular maintenance or when the bearing needs to be replaced due to abnormal operation. When regular maintenance needs to replace the bearings, when disassembling the bearings, it is necessary to understand the cause of the abnormality, so as to prevent the abnormality from occurring again, and at least keep the following items.

A. Collect and retain used lubricant.

B. Keep the damaged bearing.

C. Keep records of abnormal events in operation.

D. Keep records of the bearing condition when the operation is abnormal.

4. Bearing maintenance

In order to make the bearing fully play and maintain its due performance for a long time, it is necessary to do a good job in regular maintenance. It is very important to improve productivity and economy to find faults early and prevent accidents before they happen through appropriate periodic inspections.

(1) cleaning

When the bearing is removed for inspection, first use photography and other methods to make a record of its appearance. Also confirm the amount of remaining lubricant and sample the lubricant before cleaning the bearing.

Bearing cleaning is divided into rough cleaning and fine cleaning, and a metal grid frame can be placed at the bottom of the container used. Use a brush, etc. in oil to remove grease or stickies during rough cleaning. At this time, if the bearing is rotated in oil, be careful that the rolling surface will be damaged by foreign objects. When fine cleaning, turn the bearing slowly in the oil and do it carefully. The cleaning agent usually used is neutral anhydrous diesel oil or kerosene, and sometimes warm lye is used as needed. But no matter what kind of cleaning agent is used, it must be filtered frequently to keep it clean. After cleaning, apply anti-rust oil or anti-rust grease to the bearing immediately.

(2) Inspection and judgment

In order to judge whether the disassembled bearing can be used again, it is necessary to focus on checking its dimensional accuracy, rotation accuracy, internal clearance, mating surface, raceway surface, cage and sealing ring, etc. Regarding the inspection results, it can be judged by those who use inertial bearings or those who are proficient in bearings. Judgment criteria vary depending on mechanical performance, importance, and inspection cycle. In case of the following damages, the bearings must not be reused and must be replaced.

5. Adjustment of bearing axial clearance

The axial clearance inside the bearing can be achieved by moving the axial position of the outer ring.

(1) Adjusting shim method

Fill a set of soft material (soft steel sheet or elastic paper) gaskets between the bearing end cover and the end face of the bearing seat; when adjusting, first install the bearing end cover without the gaskets, and tighten the screws on the bearing end cover evenly. screw, turn the shaft by hand until the rolling body of the bearing is in contact with the outer ring and there is no gap inside the shaft; at this time, measure the gap between the end cover of the bearing and the end face of the bearing housing, plus the shaft required for the normal operation of the bearing This is the total thickness of the gasket required to be filled, and then fill the prepared gasket between the bearing end cover and the end face of the bearing seat, and finally tighten the screws.

(2) Adjusting bolt method

Press the pressure ring on the outer ring of the bearing, and pressurize it with the adjusting bolt; before pressurizing and adjusting, first measure the pitch of the adjusting bolt, and then slowly tighten the adjusting bolt until there is no gap inside the bearing, and then calculate the adjustment The corresponding rotation angle of the bolt. For example, if the pitch is 1.5mm, and the clearance required for the normal operation of the bearing, then the rotation angle required by the adjusting bolt is 3600×0.153l.5=360; at this time, reverse the adjusting bolt 360, and the bearing will obtain an axial clearance of 0.5mm , and then fix it with a stop washer.

6. Bearing damage and countermeasures

(1) Damage to the bearing

Generally, if the bearing is used correctly, it can be used until the fatigue life is reached. However, there may be accidental premature damage and cannot withstand use. Such early damage, as opposed to fatigue life, is the limit of quality use called failure or accident. Most of them are caused by inattentiveness in installation, use, and lubrication, foreign matter intruding from the outside, and insufficient research on the thermal influence of the shaft and housing.

(2) Regarding the damage state of the bearing

The jamming of the ring and rib of the roller bearing can be considered as the cause. Insufficient lubricant, unsuitable, defective oil supply and discharge structure, intrusion of foreign matter, bearing installation error, excessive deflection of the shaft, etc. These reasons overlap. Therefore, it is difficult to know the real cause of the damage only by investigating the bearing damage. However, if you know the machinery used for the bearing, the conditions of use, the structure around the bearing, the situation before and after the accident, and the damage state of the bearing and several reasons, you can prevent similar accidents from happening again.

7. Matters needing attention when measuring radial clearance of bearings

(1) Use special instrument measurement method as much as possible.

(2) The measurement by hand push method requires the measurer to have higher measurement skills. The measurement error of this method is relatively large, especially when the clearance is in an edge state, it is easy to cause errors, and the instrument measurement should prevail at this time.

(3) When measuring the feeler gauge, it should be operated according to the standard, and the method of rolling the roller from the feeler gauge should not be used for measurement.

(4) During the measurement process, it should be ensured that the ball falls into the bottom of the ditch. The closed bearing should be measured before it is closed. When using a loaded instrument, the measured value should also subtract the increase in clearance caused by the load.

(5) For multi-row bearings, the clearance of each row is required to be qualified, and the arithmetic mean value of the clearances of each row is taken as the radial clearance of the bearing.

Sollant Focus on Energy Saving