Assembly of plain bearings

Sliding bearing is a kind of sliding friction bearing, which is characterized by stable operation, reliability and low noise, and can withstand heavy loads and large impact loads.

 

(1) Assembly of integral sliding bearing

Integral sliding bearings, commonly known as bushings, are also the simplest form of sliding bearings. They are mainly assembled by pressing and hammering. Hot-loading is used in special occasions. Most bushings are made of copper or cast iron. Care should be taken when installing, and it can be assembled by hitting with a wooden hammer or a hammer block. 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.

 

Bearings deformed after assembly should be trimmed for inner holes. Smaller ones can be cut with a reamer, while larger ones can be scraped. At the same time, pay attention to control the matching clearance with the shaft within the tolerance range. In order to prevent the shaft sleeve from rotating during operation, the contact surface between the shaft sleeve and the box body is equipped with positioning pins or seam screws. Due to the different hardness of the box body and the shaft sleeve material, when drilling, it is easy to make the drill bit deviate from the soft material. The rigidity of the drill bit when the hole is made.

 

(2) Assembly of split bearings

Split bearing, also known as split bearing, has the characteristics of simple structure, convenient adjustment and disassembly.

 

① Assembly of bearing shell and bearing body

The contact between the upper and lower bearing pads and the bore of the bearing body must be good. If it does not meet the requirements, use the bearing body hole of the thick-walled bearing pad as the benchmark to scrape the back of the bearing pad, and at the same time, make the steps at both ends of the bearing pad close to both ends of the bearing body. Thin-walled bushes only need to make the mid-section of the bearing bush about 0.1mm higher than the mid-section of the bearing body, and it is not necessary to repair and scrape.

 

② The bearing bush is installed in the bearing body

Displacement is not allowed in either radial or axial direction, and the steps at both ends of the bearing bush are usually used for stop positioning or positioning pin positioning.

 

③ The scraping of the bearing bush

The split bearing pads generally use the matching shaft grinding points. Generally, the bearing pads are scraped off first, and then the bearing pads are scraped. In order to improve the efficiency, the bearing pads and covers can not be installed when scraping off the bearing pads. The contact point of the current bearing pad is 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 and ground. When scraping, the tightness of the shaft can be adjusted with the increase of scraping times by changing the thickness of the gasket. When the bearing cover is fastened, the shaft can be easily rotated without obvious clearance, and the contact point can be scraped as required.

 

④ Measurement of bearing clearance

The size of the bearing clearance can be adjusted by the shim at the mid-section surface, or it can be obtained by directly scraping the bearing bush. The bearing clearance is usually measured by pressing the lead method. Take several pieces of lead wire with a diameter larger than the bearing clearance and place them on the journal and the mid-section surface, then tighten the nut to press the mid-section surface tightly, then unscrew the nut and remove the bearing cover. Carefully Take out the flattened lead wire, and measure the thickness with a micrometer for each section taken. 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, and the smaller clearance value is taken when the diameter is larger. If the shaft diameter is 60mm, the bearing clearance should be between 0.09-0.15mm.

 

Assembly of rolling bearings

Rolling bearings have the advantages of low friction, small axial size, convenient replacement, and simple maintenance.

 

 

 

(1) Technical requirements for assembly

 

① The end face marked with the code of the rolling bearing should be installed in the visible direction, so that it can be checked during replacement.

② 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.

③ After the bearing is assembled on the shaft and in the housing hole, there should be no skew.

④ Among the two coaxial bearings, one must move with the thermal expansion of the shaft.

⑤ When assembling rolling bearings, it is necessary to strictly prevent dirt from entering the bearing.

⑥ The assembled bearing must operate flexibly, with low noise, and the working temperature should generally not exceed 65℃.

 

(2) Assembly method

 

When assembling the bearing, the most basic requirement is to make the added axial force act directly on the end face of the ring of the installed bearing (when installed on the shaft, make the added axial force directly act on the inner ring, When on the hole, the applied force should act directly on the outer ring).

 

Try not to affect the rolling elements. Assembly methods include hammering method, press assembly method, hot charging method, freezing assembly method, etc.

 

① Hammering method

Use a hammer to place a red copper rod and some soft materials before hammering. Be careful not to let foreign objects such as copper powder fall into the bearing raceway, and do not directly hit the inner and outer rings of the bearing with a hammer or punch, so as not to affect the bearing. Matching accuracy or bearing damage.

 

② Screw press or hydraulic press assembly method

For bearings with large interference tolerances, screw presses or hydraulic presses can be used for assembly. Before pressing, the shaft and bearing should be leveled and coated with a little lubricating oil. The pressing speed should not be too fast. After the bearing is in place, the pressure should be quickly removed to prevent damage to the bearing or shaft.

 

③ Hot-loading method

The hot-loading method is to heat the bearing in oil to 80℃-100℃, so that the inner hole of the bearing is expanded and then fitted to the shaft, which can prevent the shaft and the bearing from being damaged. The shrink-fit method is not suitable for bearings with dust caps and seals that are already filled with grease.

 

(3) The clearance of the tapered roller bearing is adjusted after assembly. The main methods are gasket adjustment, screw adjustment, and nut adjustment.

 

(4) 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. After the assembly, the tight ring and the shaft remain relatively static during operation, and it always leans against the shaft. Otherwise, the bearing will lose the rolling action and accelerate the wear.