Key points for assembling rolling bearings
A bearing is a precision machine. Since it is a machine with high performance, it is necessary to maintain precision. For this reason, delicate handling is required. When assembling bearings, it is also necessary to handle them with care. Let's take a look at the key points of assembling rolling bearings.
Assembling rolling bearings
Rolling bearings are important parts that support the rotating shafts of a machine. Compared to common machines, they have extremely high precision, so they must be handled carefully to prevent rust, dirt, scratches, and intrusion of foreign matter.
There are various points to consider when assembling rolling bearings, including preparation in advance and the type of mounting method.
Preparation before assembly
Before installing a rolling bearing, the following points should be kept in mind during the preparation work.
- Make sure that the bearing to be installed is the product as designed.
- Do not open the bearing packaging until just before assembly.
- Handle bearings in an environment free from dust, dirt, and moisture.
- Use open type bearings and bearings containing grease without washing the rust-preventive oil. (When grease is used, such as in bearings used for high-speed rotation, the rust-preventive oil should be cleaned before use.)
- Check the dimensions of parts used for assembly carefully.
- Remove rust and burrs from parts, if any. If there is dust or dirt on the parts, wipe it off with a rag.
- Apply a thin layer of oil to the parts where the bearings touch.
In addition to the bearing itself, be aware of the following points: keep the work area clean, take care not to shock the bearing, and be careful not to touch the bearing with bare hands or leave it unattended after cleaning to prevent rust from forming.
Checking the dimensions of the bearing fit and condition of the finish
When installing rolling bearings, it is essential to check the dimensions of the fitting part and the condition of the finish. It is also recommended to check the cleanliness of the area by placing a vinyl sheet under the mounting area.
- Check if the fit dimensions of the outer diameter of the shaft and the inner diameter of the housing are as designed.
- Make sure that the rounded part with a step on the shaft is lower than the height of the bearing shoulder. If the shaft shoulder is higher than the inner ring, it will not be possible to hook the pull-out jig, so be sure to check the rounding and at the same time, do not forget to lower the shoulders.
Key points for assembly
There are various points to be considered when assembling rolling bearings. Some of these are checking the selection of the fit, the mounting method, and post-installation. Let us look at how to select a fit and check the bearing after mounting it.
When the inner ring rotates and the outer ring is stationary, the inner ring has a ‘tight fit’ and the outer ring has a ‘clearance fit’. On the other hand, if the inner ring is stationary and the outer ring rotates, the inner ring should have a ‘clearance fit’ and the outer ring should have a ‘tight fit’. The amount of movement when either the inner or outer ring is stationary and the other is moved is indicated and called the ‘internal clearance (clearance)’ of the bearing. The amount of movement in the radial direction is called ‘radial clearance’ and the amount of movement in the axial direction is called ‘axial clearance’. As for the operating clearance, it is common to select a positive value.
Checking after installing a bearing
After installing the bearings, checking is essential. First, make one slow rotation of the shaft by hand. If you feel a certain weight at that time, it can be said that the bearing has been installed normally. The key point to check is to see if there is any part that feels heavier or lighter every half revolution. Also, make sure to mark where you can see the axis with a pen or the like when you turn it by hand. If the axis always stops at the same point, it is possible that the axis is unbalanced or the bearings are not installed straight, so be careful.
In addition, it is also important to check whether abnormal noise is occurring. Gently turn it by hand and check if it makes a constant sound to determine if there is any abnormality. If an abnormality is found after the bearing has been assembled, it is important to disassemble it again, identify the factors causing the abnormality, and take countermeasures.
Points for disassembling rolling bearings
Let's take a look at the key points of disassembling rolling bearings.
- Confirm the type, structure, and installation method of the specified bearing, and determine the disassembly procedure and method.
- Prepare disassembly tools appropriate for the size of the bearing to be used.
- Remove the outer bearing cover and check the amount and color of the grease.
- In the case of a roller bearing, pull the bearing out from the shield while lightly hitting it with a hammer while applying a hammer to the bearing.
- When removing the bearing, check for wear, scratches, rust, pressure marks, etc.
- Clean the bearings and check if the outer diameter of the shaft and the inner diameter of the housing are as specified. If the fit is loose, correct it at the same time.
The check points for looseness are as follows
- If the outer diameter of the shaft is less than +0.005mm → Check the fit standard and consider correction or replacement.
- If the inner diameter of the haunting is +0.02 to 0.03 mm → Correction is required.
- If the inner diameter of the housing is +0.03 mm or more → Please note that it is necessary to correct or replace the housing.
How to disassemble
The key to disassembling a rolling bearing is the condition of the bearing when it is installed. If the fit of the inner ring is tight, it is common to loosen the outer ring, and the bearing should be pulled out after the outer ring is removed from the bearing housing.
Here are the various methods of removal.
Using a press
To pull out the bearing with a press, make sure that the bearing is not deformed by the load applied during pulling, has a high-precision thickness, and is firmly applied to the inner and outer rings, respectively. It is important to increase the pressure of the press while checking the gauge, and not to apply it all at once.
Using a pulling jig
When using a pull-out jig, it is necessary to make sure that the jig's jaws completely cover the sides of the inner ring. When screwing in with a handle, be careful not to apply force to the balls or rollers. Another method is to use a puller. To avoid damaging the balls, inner and outer rings, make sure that the supporting part is properly applied to the inner ring as well.
How to remove a tapered bore bearing
Tapered bore bearings mounted on a shaft using a removal sleeve can be removed by tightening a special nut. It is also possible to remove the bearing by screwing in the bolt holes provided on the removal sleeve nut.
Another method is to use a hammer to pull out the sleeve. Hold the side of the inner ring firmly with a clamp tightened on the shaft, loosen the nut several times, and then use a piece of metal to strike the sleeve with a hammer to remove it.
When using a labyrinth notch, provide two notches on the back side of the labyrinth. It can be easily removed by driving a wedge into the notch.
Using hydraulic pressure (oil injection)
When removing large bearings, the oil injection method using hydraulic pressure is effective. The shaft portion of the inner ring is tapered, which is a characteristic of large rolling bearings. In this method, an oil hole is provided in the shaft, through which pressurized oil is injected to expand the inner ring. As a result, it can be removed with reduced friction.
How to remove a bearing with a loose fit
If the fit is loose, provide several drilled holes in the bearing housing to hammer out the inner ring and use a copper rod to hammer out the inner ring. If the inner ring cannot be hammered out by the above method, make two notches at the symmetrical positions of the part where the side of the inner ring contacts the bearing housing, and hammer out the inner ring using a copper rod.
Removal by heating
It is also possible to heat the bearing and remove it by thermal expansion. If the bearing can be discarded, heat it directly with a torch lamp or similar device. If you want to reuse it, heat it by blowing steam on it and remove it.