The bearing disassembly method is here! Non-destructive disassembly! Any bearing can be removed like this!
After the bearing has been in operation for a period of time, there will inevitably be the need for maintenance or replacement of damage. In the early stages of the development of the machinery industry, the popularity of professional knowledge and the awareness of safe operation procedures are insufficient. Today we will only talk about the disassembly of bearings.
Any operation must be based on safety, and bearing disassembly is no exception. The bearing is very likely to be worn at the end of its use. In this case, if the disassembly method is improper and the external force is unreasonably applied, it is very likely to cause the bearing to break and cause metal fragments to splash and bring danger. It is strongly recommended to add a protective blanket to cover during the bearing disassembly operation to ensure operational safety.
1 Classification of bearing disassembly
In the case of the correct design of the support size, the bearing with clearance fit can be removed as long as it is not overused to cause deformation or rust and jams on the matched part. The core of bearing disassembly technology is to disassemble the bearing reasonably under the interference fit. Bearing interference fit is divided into inner ring interference and outer ring interference. The following two situations will be introduced separately.
1.1.Bearing inner ring interference, outer ring clearance fit
1. 1.1Cylindrical shaft
The correct bearing removal is inseparable from the use of tools. For small-sized bearings, the conventional tool is a puller. The puller is divided into two types: two-jaw and three-jaw, which are divided into thread and hydraulic.
The thread puller is a more traditional tool. The 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 bearing inner ring, 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 piston in the middle is continuously extended, the bearing will be continuously pulled out. It is faster than the traditional thread puller and the hydraulic device can quickly retract.
In some designs, the distance between the end face of the bearing inner ring and other parts is small, and there is no operating space for the traditional puller claws. At this time, a two-piece splint (as shown in the figure below) can be used, and the appropriate size of the splint can be selected and disassembled separately. pressure. The part of the splint can be made thinner, so as to penetrate into the narrow space.
When there is a large batch of small size bearings that need to be disassembled, a quick disassembly hydraulic device can also be used (as shown below)
For the disassembly of the integral bearing of the railway vehicle axle, there is also a special mobile disassembly device.
When the size of the bearing increases, the force required to disassemble the bearing also increases. Universal pullers cannot be used, and special tooling is required 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 = the friction coefficient between the inner ring and the shaft, generally about 0.2
W = inner ring width (m)
δ = amount of interference fit (m)
E = Young's modulus 2.07x1011 (Pa)
d = bearing inner diameter (mm)
d0=Medium diameter of inner ring and outer raceway (mm)
π = 3.14
When the disassembly force is too large to be removed by ordinary methods, and the disassembly force generated by conventional methods is likely to damage the bearing, an oil hole is generally designed at the end of the shaft, and the oil hole extends to the bearing position and then penetrates radially to the shaft surface. And add an annular groove, use hydraulic pump to pressurize from the shaft end to expand the inner ring during disassembly, reducing the disassembly force.
When the bearing size is too large and the simple hard-drawing type can no longer be disassembled, it is necessary to use the heating disassembly method. Before operation, you need to prepare complete tools, 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, 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.
1.1.2 Cone shaft
Since the areas of the two end faces of the inner ring of a tapered bearing are significantly different, the large end face of the inner ring of the bearing is usually heated for disassembly. The flexible coil intermediate frequency induction heater is used to quickly heat the inner ring of the bearing to generate a sufficient temperature difference with the shaft, thereby disassembling the inner ring of the bearing. Since tapered bearings are used in pairs, after removing one inner ring, the other inner ring must be exposed to heating. If the bearing inner ring is in a position where the large end face cannot be heated, the cage must be destroyed, the rollers removed, the inner ring body is exposed, and the coil is directly placed on the raceway for heating.
The heating temperature of the heater must not exceed 120 degrees Celsius, because bearing disassembly requires a rapid temperature difference and operation process, 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 to place dry ice on the inner wall of the hollow shaft to quickly reduce the temperature of the shaft (usually for such large-sized workpieces) , Thereby increasing the temperature difference.
For the disassembly of the tapered bore bearing, do not completely remove the clamping nut or mechanism at the end of the shaft before disassembling, just loosen it to avoid bearing falling accidents.
The disassembly of the large-sized tapered shaft requires the aid of a disassembly oil hole. Take the four-row tapered bearing TQIT with a tapered inner bore 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 marking 1, 2, 3, where 1 corresponds to the outermost inner ring, 2 corresponds to the double inner ring in the middle position, and 3 corresponds to the innermost inner ring with the largest diameter. When disassembling, disassemble in the order of serial number, and pressurize 1, 2, and 3 holes in steps. When all the bearings can be lifted after the driving, remove the hinge ring at the end of the shaft and the bearing is removed.
If the bearing needs to be used again after disassembly, the force applied during disassembly must not be transmitted through the rolling elements. For separate bearings, the bearing ring that is assembled with the rolling element cage assembly can be disassembled separately from the other bearing ring. When disassembling the non-separable bearing, the bearing ring with clearance fit should be removed first, and the bearing with interference fit should be disassembled. It is necessary to use different tools according to its type, size and matching method.
1.2 Remove the bearing installed on the cylindrical shaft diameter
When disassembling the inner ring of needle roller bearings or NU, NJ, and NUP cylindrical roller bearings, the thermal disassembly method is suitable. Two commonly used heating tools: heating ring and adjustable induction heater.
The heating ring is usually used to install and remove the inner ring of small and medium-sized bearings of the same size. The heating ring is made of light alloy. The heating ring has a radial slot and is equipped with an electrically insulated handle (Figure as below).
If you often disassemble inner rings of different diameters, it is recommended to use a adjustable induction heater. These heaters (Figure) can quickly heat the inner ring without heating the shaft. When disassembling the inner ring of a large cylindrical roller bearing, some special fixed induction heaters can be used.
1.3 Remove the bearing installed on the tapered shaft diameter
A mechanical or hydraulic power puller can be used to pull the inner ring to remove the small bearing. Some pullers are equipped with spring-operated arms. Using this puller with a self-centering design can simplify the procedure and avoid damage to the journal. If the puller claw cannot be used on the inner ring, the bearing should be removed through the outer ring or the puller combined with the puller (Figure).
When using the oil injection method, the disassembly of medium and large bearings will be safer and simpler. This method injects hydraulic oil between two conical mating surfaces through an oil hole and an oil groove under high pressure. The friction between the two surfaces is greatly reduced, and an axial force that separates the bearing and the shaft diameter is generated.
1.4 Remove the bearing on the adapter sleeve
For small bearings installed on an adapter sleeve with a straight shaft, a hammer can be used to knock the small steel blocks uniformly acting on the end face of the bearing inner ring to remove it (Figure). Prior to this, the adapter sleeve lock nut needs to be loosened a few turns.
For small bearings installed on the adapter sleeve with stepped shaft, a hammer can be used to knock the small end face of the adapter sleeve lock nut through a special sleeve to remove (Figure). Prior to this, the adapter sleeve lock nut needs to be loosened a few turns.
For the bearings installed on the adapter sleeve with stepped shaft, the use of hydraulic nuts can make the bearing removal easier. To this end, a suitable stop device must be installed close to the piston of the hydraulic nut (Figure). The oil injection method is a simpler method, but an adapter sleeve with an oil hole and an oil groove must be used.
1.5 Remove the bearing on the withdrawal sleeve
When removing the bearing on the withdrawal sleeve, the locking device must be removed. (Such as lock nut, end plate, etc.)
For small and medium-sized bearings, lock nuts, hook wrenches or impact wrenches can be used for disassembly.
For medium and large bearings installed on the withdrawal sleeve, hydraulic nuts can be used to easily remove them. It is recommended to install a stop device behind the hydraulic nut on the shaft end (Figure). The stop device can prevent the withdrawal sleeve and the hydraulic nut from flying out of the shaft when the withdrawal sleeve is suddenly separated from the matching position.
2 Bearing outer ring interference fit
The premise of removing the bearing when the outer ring of the bearing has an interference fit is that the diameter of the outer ring shoulder should not be smaller than the supporting diameter required by the bearing. You can use the drawing tool as shown in the figure below to remove the outer ring.
If the shoulder diameter of the outer ring of some applications requires complete coverage, the following two design options should be considered in the design stage:
Two or three notches can be reserved on the step of the bearing seat, so that the puller claw has a strong point for easy disassembly.
Four threaded holes are designed on the back of the bearing seat to reach the end face of the bearing. Normally, it can be sealed with plugs. When disassembling, replace with long screws. Tighten the long screws 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. Disassemble 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, with jack assist if necessary.
The above is a general introduction to the disassembly methods of bearings in various situations. Due to the wide variety of bearings and wide applications, the disassembly process and precautions are also different. I believe that by mastering the correct method of bearing disassembly, you can effectively maintain and replace the bearing and improve the efficiency of equipment operation.
More bearing knowledge or inquiries, ask the bearing specialist.