General method for bearing disassembly | non-destructive disassembly
After a bearing has been running for a period of time, it is inevitable that there will be a need for maintenance or damage and replacement. In the early days of the development of the machinery industry, there needed to be more popularization of professional knowledge and awareness of safe operating procedures. Today, we will only talk about the disassembly of bearings.
It is common for some people to disassemble bearings rapidly without properly inspecting them. While this may appear efficient, it is important to consider that not all damage is visible on the surface of the bearing. There may be damage inside that cannot be seen. Moreover, bearing steel is hard and brittle, meaning that it can crack under its weight, leading to disastrous consequences.
It is crucial to follow scientific procedures and use proper tools when installing or disassembling a bearing to avoid any potential damage. Accurate and quick disassembly of bearings requires skills and knowledge, which are extensively discussed in this article.
Safety first
Safety should always be the top priority of any operation, including bearing disassembly. Bearings are likely to experience wear and tear towards the end of their lifespan. In such cases, if the disassembly process is not carried out correctly and an excessive amount of external force is applied, there is a high possibility of the bearing breaking apart. This can cause metal fragments to fly out, posing a serious safety hazard. Therefore, it is highly recommended to use a protective blanket while disassembling the bearing to ensure safe operation.
Classification of bearing disassembly
When the support dimensions are designed correctly, bearings with clearance fits can be removed by aligning the bearings, as long as they are not deformed or rusted due to excessive use and stuck on the matching parts. Reasonable disassembly of bearings under interference fit conditions is the essence of bearing disassembly technology. Bearing interference fit is divided into two types: inner ring interference and outer ring interference. In the following paragraphs, we will discuss these two types separately.
1. Interference of the inner ring of the bearing and clearance fit of the outer ring
1. Cylindrical shaft
Bearing disassembly requires the use of specific tools. A puller is usually used for small bearings. These pullers come in two types – two-claw and three-claw, both of which can be threaded or hydraulic.
The conventional tool is the thread puller, which works by aligning the center screw with the center hole of the shaft, applying some grease to the center hole of the shaft, and then hooking the hook on the end face of the bearing’s inner ring. Once the hook is in position, a wrench is used to turn the center rod, which then pulls out the bearing.
On the other hand, the hydraulic puller uses a hydraulic device instead of the thread. When pressurized, the piston in the middle extends, and the bearing is pulled out continuously. It is faster than the traditional thread puller, and the hydraulic device can quickly retreat.
In some cases, there is no space for the claws of a traditional puller between the end face of the inner ring of the bearing and other components. In such situations, a two-piece splint can be used. You can select the appropriate size of the splint and disassemble it separately by applying pressure. Parts of the plywood can be made thinner so that they can fit into narrow spaces.
When a larger batch of small-sized bearings needs to be disassembled, a quick-disassembly hydraulic device can also be used (as shown below).
▲Quickly disassemble hydraulic device
For the disassembly of integral bearings on railway vehicle axles, there are also special mobile disassembly devices.
▲Mobile disassembly device
If the size of a bearing is large, then more force will be required to disassemble it. In such cases, general pullers won’t work, and one will need to design special tools for disassembly. To estimate the minimum force required for disassembly, you can refer to the installation force needed 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 the inner ring and the shaft, generally around 0.2
W = inner ring width (m)
δ = interference fit (m)
E = Young’s modulus 2.07×1011 (Pa)
d = bearing inner diameter (mm)
d0=middle diameter of the outer raceway of the inner ring (mm)
π= 3.14
When the force required to disassemble a bearing is too great for conventional methods and risks damaging the bearing, an oil hole is often designed at the end of the shaft. This oil hole extends to the bearing position and then penetrates the shaft surface radially. An annular groove is added, and a hydraulic pump is used to pressurize the shaft end to expand the inner ring during disassembly, reducing the force required for disassembly.
If the bearing is too large to be disassembled by simple hard pulling, then the heating disassembly method needs to be used. For this method, complete tools such as jacks, height gauges, spreaders, etc., need to be prepared for operation. The method involves heating the coil directly onto the raceway of the inner ring to expand it, making it easier to disassemble the bearing. This same heating method can also be used for cylindrical bearings with separable rollers. By using this method, the bearing can be disassembled without causing any damage.
▲Heating disassembly method
2. Tapered shaft
When disassembling a tapered bearing, the large end face of the inner ring needs to be heated since its area is significantly larger than the other end face. A flexible coil medium frequency induction heater is used to heat the inner ring quickly, creating a temperature difference with the shaft and allowing for disassembly. As tapered bearings are used in pairs, after removing one inner ring, the other will inevitably be exposed to heat. If the large end surface cannot be heated, the cage must be destroyed, the rollers removed, and the inner ring body exposed. The coil can then be placed directly on the raceway for heating.
▲Flexible coil medium frequency induction heater
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, the interference is very large, and the temperature difference is insufficient, dry ice (solid carbon dioxide) can be used as an auxiliary means. The dry ice can be placed on the inner wall of the hollow shaft to quickly reduce the temperature of the shaft (usually for such large-sized cnc parts), thereby increasing the temperature difference.
For the disassembly of tapered bore bearings, do not completely remove the clamping nut or mechanism at the end of the shaft before disassembly. Only loosen it to avoid bearing falling accidents.
The disassembly of large-sized tapered shafts requires the use of disassembly oil holes. Taking the rolling mill’s four-row tapered bearing TQIT with a tapered bore 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 marks 1 and 2,3, where one corresponds to the outermost inner ring, two corresponds to the double inner ring in the middle, and three corresponds to the innermost inner ring with the largest diameter. When disassembling, disassemble in a sequence of serial numbers and pressurize holes 1, 2, and 3, respectively. After all is completed, when the bearing can be lifted while driving, remove the hinge ring at the end of the shaft and disassemble the bearing.
If the bearing is to be used again after disassembly, the forces exerted during disassembly must not be transmitted through the rolling elements. For separable bearings, the bearing ring, together with the rolling element cage assembly, can be disassembled separately from the other bearing ring. When disassembling non-separable bearings, you should first remove the bearing rings with a clearance fit. To disassemble bearings with an interference fit, you need to use different tools according to their type, size, and fit method.
Disassembly of bearings mounted on cylindrical shaft diameter
Cold disassembly
Figure 1
When dismantling smaller bearings, the bearing ring can be removed from the shaft by tapping the side of the bearing ring gently with a suitable punch or a mechanical puller (Figure 1). The grip should be applied to the inner ring or adjacent components. If the shaft shoulder and the housing bore shoulder are provided with grooves to accommodate the puller’s grip, the disassembly process can be simplified. Additionally, some threaded holes are machined at the hole shoulders to facilitate the bolts to push out the bearings. (Figure 2).
Figure 2
Large and medium-sized bearings often require more force than machine tools can provide. Therefore, it is recommended to use hydraulic power tools or oil injection methods, or both together. This means that the shaft needs to be designed with oil holes and oil grooves (Figure 3).
image 3
Hot disassembly
When dismantling the inner ring of needle roller bearings or NU, NJ, and NUP cylindrical roller bearings, the thermal disassembly method is suitable. There are two commonly used heating tools: heating rings and adjustable induction heaters.
Heating rings are typically used for the installation and disassembly of the inner rings of small and medium-sized bearings of the same size. The heating ring is made of a light alloy and is radially slotted. It is also equipped with an electrically insulated handle.(Fig. 4).
Figure 4
If inner rings of different diameters are frequently disassembled, it is recommended to use an adjustable induction heater. These heaters (Figure 5) quickly heat the inner ring without heating the shaft. When disassembling the inner rings of large cylindrical roller bearings, some special fixed induction heaters can be used.
Figure 5
Removing bearings mounted on conical shaft diameters
To remove small bearings, you can use a mechanical or hydraulically powered puller to pull the inner ring. Some pullers come with spring-operated arms that have a self-centering design to simplify the procedure and prevent damage to the journal. When the puller claw cannot be used on the inner ring, the bearing should be removed through the outer ring or by using a puller combined with a puller blade. (Figure 6).
Figure 6
When disassembling medium and large bearings, utilizing the oil injection method can increase safety and simplify the process. This method involves injecting hydraulic oil between two conical mating surfaces, using oil holes and grooves, under high pressure. This reduces friction between the two surfaces, creating an axial force that separates the bearing and shaft diameter.
Remove the bearing from the adapter sleeve.
For small bearings installed on straight shafts with adapter sleeves, you can use a hammer to knock the small steel block evenly on the end face of the inner ring of the bearing to remove it (Figure 7). Before this, the adapter sleeve locking nut needs to be loosened several turns.
Figure 7
For small bearings installed on adapter sleeves with stepped shafts, they can be disassembled by using a hammer to tap the small end face of the adapter sleeve lock nut through a special sleeve (Figure 8). Before this, the adapter sleeve locking nut needs to be loosened several turns.
Figure 8
For bearings mounted on adapter sleeves with stepped shafts, the use of hydraulic nuts can make bearing removal easier. For this purpose, a suitable stop device must be installed close to the hydraulic nut piston (Figure 9). The oil filling method is a simpler method, but an adapter sleeve with oil holes and oil grooves must be used.
Figure 9
Disassemble the bearing on the withdrawal sleeve
When removing the bearing on the withdrawal sleeve, the locking device must be removed. (Such as locking nuts, end plates, etc.)
For small and medium-sized bearings, lock nuts, hook wrenches or impact wrenches can be used to disassemble them (Figure 10).
Figure 10
If you want to remove medium and large bearings that are installed on a withdrawal sleeve, you can use hydraulic nuts for easy removal. However, it is highly recommended to install a stop device behind the hydraulic nut at the shaft end (as shown in Figure 11). This stop device will prevent the withdrawal sleeve and hydraulic nut from flying out of the shaft suddenly, if the withdrawal sleeve gets separated from its mating position.
Figure 11 Tingshaft bearing
2. Interference fit of bearing outer ring
If the outer ring of a bearing has an interference fit, it is important to ensure that the outer ring shoulder diameter is not smaller than the support diameter required by the bearing before dismantling. To disassemble the outer ring, you can use the drawing tool diagram shown in the figure below.
If the outer ring shoulder diameter of some applications requires complete coverage, the following two design options should be considered during the design stage:
• Two or three notches can be reserved at the step of the bearing seat so that the puller claws have a strong point for easy disassembly.
• Design four through-threaded holes on the back of the bearing seat to reach the bearing end face. They can be sealed with screw plugs at ordinary times. When disassembling, replace them with long screws. Tighten the long screws to gradually push out the outer ring.
If the bearing is large or the interference is significant, the flexible coil induction heating method can be used for disassembly. This process is carried out through the outer diameter of the heating box. The outer surface of the box must be smooth and regular to prevent local overheating. The center line of the box should be perpendicular to the ground, and if needed, a jack can be used to assist.
The above is a general overview of the disassembly methods for bearings in different situations. Since there are various types of bearings used widely, the disassembly procedures and precautions may vary. If you have any specific requirements, please feel free to consult the Dimond Rolling Mill Bearing Engineering Technical Team. We will utilize our professional knowledge and skills to solve different issues for you. By following the correct bearing disassembly method, you can efficiently maintain and replace bearings and improve equipment operating efficiency.
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