Basic knowledge of bearing assembly determines bearing life
Sliding bearing is a kind of bearing with sliding friction, which is characterized by stable and reliable operation hours, low noise, and which can withstand heavy loads and large impact loads. According to different structural forms, it can be divided into integral type, split type and tile type.
1. Assembly of integral sliding bearing
Integral sliding bearings are commonly known as bushings, and they are also the simplest form of sliding bearings. They are mainly assembled by pressing and hammering. In special occasions, hot-fitting is used. Most bushings are made of copper or cast iron. You should be careful when assembling, and you can assemble it by hitting with a wooden hammer. Whether it is knocked in or pressed in, it must be prevented from tilting. After assembly, the oil groove and oil hole should be in the required position.
Deformed bearings should be trimmed after assembly. Smaller sizes can be cut by reaming, and larger sizes can be scraped. At the same time, we need to control the matching clearance with the shaft within the tolerance range. In order to prevent the shaft sleeve from rotating when it is working, the contact surface of the shaft sleeve and the box body is equipped with positioning pins or seam screws. Because the hardness of the box body and the shaft sleeve are different when drilling, it is easy to deflect the drill bit to the soft material side. The solution: one is to punch the hard material with a sample before drilling, and the other is to use a short drill to increase the drilling.
2. Assembly of split bearings
Split bearings have the characteristics of simple structure and convenient adjustment and disassembly. Two bushes are inserted, and a gasket is used at the joint to adjust a reasonable gap.
2.1 Assembly of bushes and bearing body
The upper and lower bushes must be in good contact with the inner holes of the bearing. If they do not meet the requirements, take the inner holes of the thick-walled bushes as the reference, and scratch the back of the bushes. At the same time, the steps of the two ends of the bushes should be close to the ends of the bearing body. Thin-walled bushes only need to make the middle parting surface of the bearing bush higher than the middle parting surface of the bearing body by about 0.1mm, and no scraping is necessary.
2.2 The bearing shell is installed in the bearing body
No displacement is allowed in the radial or axial direction. Usually, the steps at both ends of the bearing bush are used to stop the positioning or locate the positioning pin.
2.3 Matching scraping of bearing bush
Split bearing shells generally use matching shaft grinding points. Generally, the bearing shells are scraped first, and then the bearing shells are scraped. In order to improve the efficiency, the bearing shells and covers are not installed when the bearing shells are scraped. The contact points of the current bearing shells are basically When the requirements are met, the upper bearing bush and the upper cover are pressed tightly, and the contact point of the lower bearing bush is further corrected when the upper bearing bush is scraped. The tightness of the shaft can be adjusted with the increase of the number of scraping by changing the thickness of the gasket. When the bearing cover is tightened, the shaft can easily rotate without obvious gap, and the scraping is completed when the contact point meets the requirements.
2.4 Measurement of bearing clearance
The size of the bearing gap can be adjusted by the gasket at the center dividing surface, or it can be obtained by directly scraping the bearing bush. The lead pressure method is usually used to measure the bearing clearance. Take a few pieces of lead wire with a diameter larger than the bearing clearance and place them on the journal and the center dividing surface. Then tighten the nut to compress the center dividing surface. Then unscrew the nut and remove the bearing cap. Take out the flattened lead wire and measure the thickness with a micrometer for each section. The bearing clearance can be known according to the average thickness of the lead wire.
Generally, the clearance of the bearing should be 1.5‰-2.5‰ (mm) of the shaft diameter. The smaller the clearance value is when the diameter is larger. If the shaft diameter is 60mm, the bearing clearance should be between 0.09-0.15mm.
3. Rolling bearing assembly
Rolling bearings have the advantages of low friction, small axial size, convenient replacement, and simple maintenance.
3.1 Technical requirements for assembly
The end face marked with the code of the rolling bearing should be installed in the visible direction for checking when replacing it.
The arc radius at the step of the journal or housing hole should be smaller than the arc radius at the corresponding position on the bearing.
After the bearing is assembled on the shaft and the housing hole, there should be no skew.
Of the two coaxial bearings, one of the two bearings must move with the shaft due to thermal expansion.
When assembling the rolling bearing, it is necessary to strictly prevent dirt from entering the bearing.
The assembled bearings must run flexibly, with low noise, and the operating temperature should generally not exceed 65℃.
3.2 Assembly method
When assembling the bearings, the most basic requirement is to make the added axial force directly act on the end face of the bearing ring (when installed on the shaft, the added axial force should directly act on the inner ring. When it is on the hole, the applied force should act directly on the outer ring).
Try not to affect the rolling elements. The assembly methods include hammering method, press assembly method, hot assembly method, freezing assembly method and so on.
Use a hammer to pad the copper rod and put some softer materials before hammering. Be careful not to let foreign matter such as copper powder fall into the bearing raceway. Do not directly hit the inner and outer rings of the bearing with a hammer or punch, so as not to affect the bearing. The matching accuracy may cause bearing damage.
Screw press or hydraulic press assembly method
For bearings with larger interference tolerances, screw presses or hydraulic presses can be used for assembly. Before pressing, the shaft and bearing should be leveled, and a little lubricating oil should be applied. The pressing speed should not be too fast. After the bearing is in place, the pressure should be removed quickly to prevent damage to the bearing or shaft.
Hot loading method
The hot mounting method is to put the bearing in oil and heat it to 80℃-100℃, so that the inner hole of the bearing is expanded and then set on the shaft, which can prevent the shaft and the bearing from being damaged. For bearings with dust caps and seals, which have been filled with grease, the hot mounting method is not applicable.
The clearance of tapered roller bearings is adjusted after assembly. The main methods are adjustment with spacers, adjustment with screws, adjustment with nuts and so on. When assembling the thrust ball bearing, the tight ring and the loose ring should be distinguished first. The inner diameter of the tight ring is slightly smaller. The assembled tight ring and the shaft remain relatively static during operation, and they always lean against the shaft. At the end of the step or hole, otherwise the bearing will lose its rolling effect and accelerate wear.