Due to the periodic suction, compression, and discharge of the compressor, the force acting on the main bearing also varies periodically with the position of the piston. The structural form of the horizontal compressor determines that the main bearing is subjected to greater force at its horizontal centerline position. Therefore, the bearing shell of the main bearing is composed of four lobes on the upper, lower, left, and right sides. The lower tile is supported on the bearing seat and fixed with 4 bolts. The two side tiles (or station tiles) are wedged between the main bearing and the bearing seat by inclined iron and inclined iron bolts. The upper tile is pressed onto the side tiles by the main bearing bolts through the tile cover. Lubricating oil is injected through the oil hole on the upper tile.
The main bearing tile is cast with cast steel, and the inner layer is cast with bearing alloy. In order to compensate for the weak joint between the bearing shell and the bearing alloy, axial and circumferential dovetail grooves are machined on the bearing shell to increase the joint force between the bearing shell and the bearing alloy.
In order to ensure better lubrication of the spindle during operation, a certain gap is left between the spindle and the bearing, and a light rotation fit is generally used. Based on experience, the gap between the main shaft and the bearing shell is δ=(1/10000~1/1000) D, where D is the diameter of the shaft neck.
① Dismantling and inspection of thick walled main bearing shell
Remove the oil blocking cover and measure the axial clearance between the main shaft shoulder and the bearing shell, as well as the top clearance of the main shaft bearing. Remove the screws of the tile cover, tighten the top screw to loosen the tile cover, hook the lifting ring of the tile cover with a steel wire rope, lift out the tile cover, and measure the gap between the main shaft and the side tile, the back of the side tile and the inclined iron, and the inclined iron and the bearing seat hole with a feeler gauge. Remove the inclined iron screw cap and use a copper rod to knock down the inclined iron. Twist the lifting ring tied with hemp rope on the side tile and hang the hemp rope loosely on the crane hook. Lift the side tile along the tangent direction of the side tile mouth, causing the side tile to rotate around the main spindle neck out of the bearing seat to the upper tile position. When the side tile leaves the bearing seat, insert a wooden stick between the side tile and the bearing seat, lift the side tile, remove the inclined iron, and leave a mark of the position of the inclined iron.
The dismantling of the bottom tiles on both sides cannot be carried out simultaneously. When disassembling, align the crane hook with the centerline of the main shaft, fasten it with a steel wire rope in the main shaft oil groove, lock the hook, and lift the main shaft (or use a jack to lift the main shaft). Before lifting, loosen the bolts on the other side of the main bearing tile and the diagonal iron bolts. In special circumstances, when checking one side of the bottom bearing, the bolts of the other side of the main bearing may not necessarily loosen. However, the lifting amount of the main shaft should be strictly controlled, not exceeding 1mm, because excessive lifting may damage the main bearing and its bolts, and also make the distance between the upper part of the bearing seat hole and the main shaft too small, making it difficult for the bottom bearing to rotate out. When the spindle is 1mm away from the bottom tile, use a square wood or steel frame to firmly pad the spindle, loosen the hook, remove the four positioning bolts of the bottom tile, and leave a mark on the bottom tile position on the machine base. Thread an 8mm lead wire through the bottom tile at both ends and tie it to a knot. Secure one end to the bolt on the bottom tile fixing pad and tie the knot to the small hook of the overhead crane. Lift and move the small sports car, rotate the bottom tile along the main axis to the upper tile position, and then use the lifting ring bolt to lift the bottom tile.
② Welding repair of thick walled tile bearing alloy
When the bearing alloy layer on the bearing shell is insufficient, local bearing alloy fractures, or local defects exist, welding repair can be temporarily used for repair.
When welding, the original bearing alloy layer on the bearing shell should be melted to a certain depth first, and then welded with strip-shaped bearing alloy. If there is unevenness on the surface, it can be ironed flat and then processed according to the general method of bearing shell processing.
When using this method to weld the bearing alloy layer of the bearing shell, the following conditions should be met: the bearing alloy layer on the bearing shell must be free of delamination and fully degreased; The peeling surface of the bearing alloy layer on the bearing shell shall not exceed 1cm2, and there shall be no more than two places on each tile; The welding repair alloy used during welding should be of the same grade as the alloy on the original bearing.
The steps for repairing bearing alloy with acetylene flame welding: Heat the back of the old tile, partially or completely remove the original bearing alloy, then immerse it in 10%~15% hydrochloric acid for 5-10 minutes, take it out and rinse it with hot water (70-100 ℃), rinse it with 10% alkaline solution to neutralize the acid remaining on the tile, and then rinse it clean with hot water.
Cast tin and bearing alloy into long rods with diameters of 15-25mm respectively.
Use acetylene flame to hang weld a base tin of about 0.1mm, and then hang weld the bearing alloy to achieve the required thickness (considering machining quantity).
When welding repair, the welding speed should be fast, the welding marks should be arranged smoothly, and the bearing alloy and tile body should be prevented from detaching due to high temperature. Each time, no more than three weld beads shall be continuously welded along the semi-circular edges at both ends of each side. After welding one side, it should be cooled and turned around to weld the other side until it cools down, then continue welding. The temperature of the tile body during the entire welding repair process is ≤ 200 ℃.
③ The gap between the main journal and the main bearing shell. The radial clearance can be taken according to the following empirical formula:
In the formula, D axis - main journal diameter, mm. Generally, D axis ≤ 180mm. When the D axis is greater than 180mm, the δ diameter can be taken as 0.001D axis.
The side clearance of the bearing shell is generally taken as half of the top clearance.
The bearing shell must have a fixed axial displacement on one side, and its axial clearance can be taken as δ diameter ≥ 0.001D axis when there is no clear regulation. The axial clearance of the other bearing shell is 1-3mm.
In practical use, the clearance between the upper and side tiles of the compressor spindle neck can be found in Table 1.
Table 1 Clearance between main journal upper and side tiles Unit: mm
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