Bearings will inevitably need to be maintained or replaced after a period of operation. In addition, bearing steel is relatively hard and brittle, and it is easier to stretch under gravity, which seriously threatens the safety of operators. Therefore, we need the right skills to disassemble the bearing quickly.
Classification of bearing disassembly
Provided the support dimensions are properly designed, bearings with a clearance fit can be removed with alignment as long as they are not overused, causing them to deform or corrode and get stuck on the mating parts. Reasonable dismounting of bearings in the case of interference fit is the core of bearing dismounting technology. Bearing interference fit is divided into inner ring interference and outer ring interference. The following two situations will be introduced separately.
1 Bearing inner ring interference, the outer ring clearance fit
(1) Cylindrical shaft
Correct bearing removal requires the use of tools. For small size bearings, the conventional tool is a puller. The puller is divided into two claws and three claws, and there are threads and hydraulics.
The thread puller is a relatively traditional tool. Its operation is to align the center screw with the center hole of the shaft, apply a small amount of grease to the center hole of the shaft, hook the hook on the end face of the inner ring of the bearing, and twist the center rod with a wrench. The bearing can be pulled out. The hydraulic puller uses a hydraulic device instead of the thread. When the middle piston is continuously extended, the bearing will be continuously pulled out, which is faster than the traditional thread puller, and the hydraulic device can be quickly retracted.
In some designs, the distance between the end face of the bearing inner ring and other components is small and does not have the operating space of traditional puller claws. At this time, a two-piece splint (as shown in the figure below) can be used, and a splint of the appropriate size can be selected to disperse the disassembly pressure. Parts of the splint can be made thinner to penetrate into narrow spaces.
For the disassembly of the integral bearing of the railway vehicle axle, there is also a special mobile disassembly device.
As the bearing size increases, the force required to remove the bearing also increases. Universal pullers cannot be used, and special tooling needs to be designed for disassembly. The minimum force required for disassembly can be estimated based on the installation force required for the bearing to overcome the interference fit. The calculation formula is as follows:
F=0.5 *π *u*W*δ* E*(1-(d/d0)2)
F = Force (N)
μ = friction coefficient between inner ring and shaft, generally around 0.2
W = inner ring width (m)
δ = interference fit (m)
E = Young’s modulus 2.07×1011 (Pa)
d = bearing bore diameter (mm)
d0=Inner ring outer raceway middle diameter (mm)
π = 3.14
When the disassembly force is too great to be disassembled by ordinary methods, and the disassembly force generated by the conventional method is likely to damage the bearing, an oil hole is generally designed at the end of the shaft. The oil hole extends to the bearing position and penetrates radially to the shaft surface with an annular groove. When disassembling, use the hydraulic pump to pressurize the inner ring from the shaft end to reduce the disassembly force.
When the bearing size is too large and the simple hard drawing type can no longer be disassembled, the heating disassembly method is required. Complete tools are required before operation, such as jacks, height gauges, spreaders, etc. The operation method of heating disassembly is to directly wind the coil on the raceway of the inner ring to heat it to expand it, so that the bearing can be easily disassembled. The same heating method applies to cylindrical bearings with separable rollers. This method can remove the bearing without damage.
(2) Conical shaft
Since the areas of the two end faces of the inner ring of the tapered bearing are significantly different, the disassembly is usually performed by heating the large end face of the inner ring of the bearing. Using a flexible coil intermediate frequency induction heater, the inner ring of the bearing is removed by rapidly heating the inner ring of the bearing to generate a sufficient temperature difference between the bearing inner ring and the shaft. Since tapered bearings are used in pairs, after removing one inner ring, the other inner ring must be exposed to heating. If the configuration of the inner ring of the bearing is in a position where the large end face cannot be heated, the cage needs to be destroyed, the rollers should be removed, the inner ring body should be exposed, and the coil should be directly placed on the raceway for heating.
The heater heating temperature must be set not to exceed 120 degrees Celsius, because bearing disassembly requires a rapid process of generating temperature differences and operation, not temperature. If the ambient temperature is very high or the interference is very large and the temperature difference is insufficient, dry ice (solid carbon dioxide) can be used as an auxiliary means. Placing dry ice on the inner wall of the hollow shaft quickly reduces the temperature of the shaft (typical for such large-sized workpieces), thereby increasing the temperature difference.
For the disassembly of the tapered inner bore bearing, do not completely remove the clamping nut or mechanism at the end of the shaft before disassembly, but only loosen it to avoid the accident of bearing falling.
The removal of large-sized tapered shafts requires the use of removal oil holes. Taking the four-row tapered bearing TQIT with a tapered inner hole of a rolling mill as an example, the inner ring of the bearing is divided into three parts, two single-row inner rings and a double inner ring in the middle. There are three oil holes at the end of the roll, corresponding to the marks 1, 2, and 3, where 1 corresponds to the outermost inner ring, 2 is the double inner ring corresponding to the middle position, and 3 corresponds to the innermost inner ring with the largest diameter. When disassembling, disassemble in the order of serial numbers, and pressurize holes 1, 2, and 3 progressively. When the bearing can be lifted by driving after all is completed, remove the hinge ring at the end of the shaft, and the bearing is disassembled.
2 The bearing outer ring interference fit
In the case of an interference fit on the outer ring of the bearing, the premise of removing the bearing is that the diameter of the shoulder of the outer ring cannot be smaller than the supporting diameter required by the bearing. The outer ring can be removed using the drawing tool diagram shown below.
If some applications require complete coverage of the shoulder diameter of the outer ring, the following two design options should be considered at the design stage:
• Two or three notches can be reserved at the steps of the bearing housing, so that the puller claws have a force point for easy disassembly.
• Design four penetrating threaded holes on the back of the bearing seat to reach the end face of the bearing. Usually, it can be sealed with a screw plug. When disassembling, replace it with a long screw. Tighten the long screw to gradually push out the outer ring.
When the bearing is large or the interference is large, the flexible coil induction heating method can also be used. Disassembly is done by heating the outer diameter of the box. The outer surface of the box should be regular and flat to prevent local overheating. The center line of the box should be perpendicular to the ground, and a jack should be used to assist if necessary.