Bearing assembly error is a small problem that affects big things

- Jun 04, 2019-

The mounting method of the bearing varies depending on the bearing structure and the fit. In general, since the shaft is mostly rotated, the inner ring needs an interference fit. Cylindrical bore bearings, press with multiple presses, or use hot charging methods. For taper holes, mount directly on the taper shaft or with a sleeve.


When installed in the outer casing, the general clearance fits a lot, and the outer ring has an interference amount, which is usually pressed by a press or a cold shrink fit method after cooling. When dry ice is used as the coolant and the shrinkage is installed, the moisture in the air will condense on the surface of the bearing. Therefore, appropriate rust prevention measures are required. Bearing installation generally requires the use of specialized tools such as bearing heaters.

1. Installation of cylindrical bore bearing


(1) Method of pressing with a press


Small bearings are widely used in press presses. The pad is placed in the inner ring and pressed quietly to the inner ring with a press to closely contact the shaft shoulder. Installing the inner ring on the outer ring pad is the cause of the indentation and crushing on the raceway, so it is absolutely prohibited.


When operating, it is best to apply oil to the mating surface beforehand. If you have to use a hammer to knock on the installation, you should put a block on the inner ring. This practice has often become the cause of bearing operation, so it is limited to the case of low interference, not for large interference, or medium and large bearings.


For non-separable bearings such as deep groove ball bearings, where the inner ring and the outer ring need to be installed with interference, use the pad pad and use the screw or oil pressure to press the inner ring and the outer ring at the same time. The outer ring of the self-aligning ball bearing is easy to tilt, and even if it is not an interference fit, it is better to install the pad.


For separate bearings such as cylindrical roller bearings and tapered roller bearings, the inner and outer rings can be mounted on the shaft and the outer casing respectively. When the inner and outer rings are respectively assembled, the key is to stabilize. Stabilize the two together so that the center of the two does not deviate, and the press-in will cause the raceway surface to be stuck.


(2) Method of hot loading


Large bearings require a lot of force when pressed in, so it is difficult to press in. Therefore, the method of heating the bearing in the oil to expand it and then attaching it to the shaft is widely used. With this method, it is possible to complete the work in a short time without adding undue force to the bearing.


The heating temperature of the bearing is based on the bearing size and the required interference. The precautions for hot loading operations are as follows:


(a) Do not heat the bearing to above 120 ° C;


(b) In order to prevent the bearing from directly contacting the bottom of the oil groove, it is best to consider placing the bearing on the metal mesh table or lifting the bearing;


(c) Heating the bearing to a temperature 20 ° C to 30 ° C higher than the required temperature so that the inner ring does not become cold during operation and is difficult to install;


(d) After installation, the bearing is cooled down and the width direction is also contracted, so use a shaft nut or other suitable method to tighten it to prevent a gap between the inner ring and the bearing shoulder.

2, the installation of tapered bore bearing


The tapered bore bearing directly fixes the inner ring to the tapered shaft or is mounted to the cylindrical shaft with an adapter sleeve and a disassembly sleeve. Large-scale self-aligning bearings are often installed with oil pressure.


3, operation check


After the completion of the bearing installation, in order to check whether the installation is correct, the operation check is performed, and the small machine can be rotated by hand to confirm whether the rotation is smooth. The inspection items have poor running due to foreign matter, scars, and indentations, uneven rotation due to poor installation, poor machining of the mounting seat, excessive torque due to too small clearance, and installation error sealing friction. . If there is no abnormality, the power running can be started.


Since the large machine cannot be rotated manually, the power is turned off immediately after the load is not started, and the inertia operation is performed to check whether there is vibration, sound, whether the rotating parts are in contact, etc., and it is confirmed that there is no abnormality and then enters the power running.


The power running starts from the no-load low speed and slowly increases to the rated condition rated operation. The items to be checked during the test run are whether there is abnormal noise, transfer of bearing temperature, leakage of lubricant, and discoloration. If an abnormality is found during the test run, stop the operation immediately, check the machine, and remove the bearing check if necessary.


Bearing temperature inspection is generally estimated from the appearance of the casing. However, the oil hole is used to directly measure the temperature of the outer ring of the bearing, which is more accurate. The bearing temperature starts to increase gradually. If there is no abnormality, it is usually stable after 1~2 hours. If the bearing or the mounting is defective, the bearing temperature will rise sharply and an abnormally high temperature will occur. The reasons are such as excessive lubricant, too small bearing clearance, poor installation, excessive friction of the sealing device, and the like. In the case of high-speed rotation, the selection of the lubrication method of the bearing is also the cause.


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