Summary of Various Methods for Disassembling Bearings
After the bearing has been running for a period of time, it is inevitable that there will be a need for maintenance or damage and replacement. Safety-oriented bearing disassembly is no exception. Bearings are very likely to wear at the end of their use. In this case, if the disassembly method is improper and the external force is unreasonably applied, it is very likely that the metal fragments will splash after the bearing is broken and bring danger.
The method 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 caught 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.
Bearing inner ring interference, the outer ring clearance fit
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, which are divided into thread and hydraulic.
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 a 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 can be used, and the appropriate size of the splint can be selected to disperse the disassembly pressure. Parts of the splint can be made thinner to penetrate into narrow spaces.
When there are larger batches of small-sized bearings that need to be removed, quick-release hydraulic devices can also be used. For the disassembly of the integral bearing of the railway vehicle axle, there is also a special mobile disassembly device.
When the bearing size increases, the force required to disassemble the bearing also increases, and the general-purpose puller cannot be applied, 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, and 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. Generally, an oil hole is designed at the end of the shaft, the oil hole extends to the bearing position and then radially penetrates the shaft surface, and an annular groove is added. When disassembling, use a hydraulic pump to pressurize the inner ring from the shaft end to reduce the disassembly pressure.
Heat disassembly method
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 the 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.
Since the areas of the two end faces of the inner ring of the tapered bearing are significantly different, 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 heat. If the inner ring of the bearing is arranged in a position where the large end face cannot be heated, the cage needs to be destroyed, the rollers are 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 be set not to exceed 120 degrees Celsius because the 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, and the dry ice can be placed on the inner wall of the hollow shaft to quickly reduce the temperature of the shaft (such large-sized workpieces are generally), 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 the bearing falling.
The removal of large-sized tapered shafts requires the use of removal oil holes. Take the rolling mill conical bore four-row tapered bearing TQIT as an example. The bearing inner ring 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, of which 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 is lifted after all is completed, the hinge ring at the end of the shaft is removed, and the bearing is disassembled.
If the bearing needs to be used again after disassembly, the force applied during disassembly must not be transmitted through the rolling elements. For separable bearings, the bearing ring 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 removed, and different tools should be used according to its type, size, and matching method.
Removing bearings mounted on cylindrical shaft diameters
Smaller bearings can be removed from the shaft by lightly tapping the side of the bearing ring with a suitable punch, preferably with a mechanical puller. The pull should act on the inner ring or adjacent components. The disassembly process can be simplified if the shaft shoulders and the housing shoulders are provided with grooves to accommodate the puller grips. In addition, some threaded holes are machined in the position of the hole shoulder to facilitate the bolt to push the bearing out.
Large and medium-sized bearings often require more force than a machine tool can provide. Therefore, the use of hydraulic power tools or oil injection, or both, is recommended. This means that oil holes and oil grooves need to be designed on the shaft.
When disassembling the inner ring of needle roller bearings or NU, NJ, and NUP cylindrical roller bearings, the hot disassembly method is suitable. Two commonly used heating tools: are heating rings and adjustable induction heaters.
Heating rings are usually used to install and remove inner rings of small and medium-sized bearings of the same size. The heating ring is made of light alloy. Heating rings are radially slotted and equipped with electrically insulating handles.
If inner rings of different diameters are frequently disassembled, it is recommended to use a debuggable induction heater. These heaters quickly heat the inner ring without heating the shaft. When removing the inner ring of a large cylindrical roller bearing, some special stationary induction heaters can be used.
Removing bearings mounted on tapered shaft diameters
Small bearings can be removed by pulling on the inner ring with a mechanical or hydraulically-assisted puller. Some pullers are equipped with spring-operated arms, and the use of this self-centering design of the puller simplifies the procedure and avoids damage to the journal. If the puller claws cannot be used on the inner ring, the bearing should be disassembled through the outer ring or by using a puller combined with a puller.
When using the oil injection method, the disassembly of medium and large bearings is safer and easier. This method injects hydraulic oil between two conical mating surfaces through oil holes and oil grooves under high pressure. The friction between the two surfaces is greatly reduced and an axial force is created that separates the bearing and shaft diameter.
Removing the bearing on the adapter sleeve
For the small bearing installed on the adapter sleeve with the straight shaft, you can use a hammer to knock the small steel block that acts evenly on the end face of the inner ring of the bearing to remove it. Before doing so, it is necessary to loosen the adapter sleeve lock nut several turns.
Small bearings mounted on the stepped shaft of the adapter sleeve, can be removed by hitting the small end face of the adapter sleeve lock nut with a hammer through a special sleeve. Before doing so, it is necessary to loosen the adapter sleeve lock nut several turns.
For bearings mounted on a stepped shaft with an adapter sleeve, the use of a hydraulic nut makes bearing removal easier. To do this, a suitable stop must be installed close to the hydraulic nut piston. Oil injection is the easier method, but an adapter sleeve with oil holes and oil grooves must be used.
Removing the bearing on the withdrawal sleeve
When removing the bearing on the withdrawal sleeve, the locking device must be removed. (such as lock nuts, end plates, etc.). For small and medium-sized bearings, disassembly can be performed with a lock nut, hook wrench, or impact wrench.
For medium and large bearings mounted on withdrawal sleeves, they can be easily dismantled with hydraulic nuts. It is recommended to install a stop behind the hydraulic nut on the shaft end. 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 mating position.
Bearing outer ring interference fit
The premise of removing the bearing when the bearing outer ring has an interference fit is that the diameter of the outer ring shoulder cannot be smaller than the supporting diameter required by the bearing. The outer ring can be removed by using the drawing tool diagram as 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:
1. 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.
2. Design four penetrating threaded holes on the back of the bearing seat to reach the end face of the bearing. Usually, the seal can be blocked with bolts. When disassembling, replace them 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. 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 it if necessary.
In the end
The above is a general introduction to the disassembly method of bearings for various situations. Due to the wide variety of bearings and their wide range of applications, the disassembly process and precautions are also different. It is believed that by mastering the correct bearing disassembly method, you can effectively maintain and replace the bearing and improve the operation efficiency of the equipment.