A shaft often requires two fulcrums, that is, two sets of rolling bearings for support. The bearing configuration just solves the problem of how the bearing on the fulcrum fixes the shaft system axially, and how to avoid the bearing from jamming after thermal expansion. Based on the understanding of bearing knowledge, Eric Bearing Limited shares the typical knowledge of bearing configuration and hopes to help everyone.
Before we configure, we must understand some points related to bearings: The expansion and contraction of the shaft caused by temperature changes.
Bearings are easy to install and disassemble. The tilt of the inner and outer rings due to shaft deflection and installation errors.
The method of reading and preloading of the entire rotating system including bearings. Bear and transfer loads at the most suitable location.
Avoid bearing jamming, understand three typical bearing configuration forms:
1.The two pivots are fixed in one direction
This configuration is to allow each fulcrum to axially fix the shaft system in one direction. The shortcomings are: because both fulcrums are fixed by the bearing cover, when the shaft is heated and extended, it will inevitably cause the bearing to be subjected to an additional load, affecting the service life. Therefore, this form is only suitable for occasions where the working temperature rise is not high and the shaft is short (span L≤400mm).
2.One point is fixed in two directions, the other point moves
For a fixed fulcrum, deep groove ball bearings can be used when the axial force is not large, and the left and right sides of the outer ring are fixed. When the axial force is small, the outer ring can be fixed by a hole with an elastic retaining ring. In order to withstand the axial force to the right, the inner ring of the fixed fulcrum must also be axially fixed. For the floating fulcrum, deep groove ball bearings are often used, and cylindrical roller bearings can also be used when the radial force is large. When using deep groove ball bearings, there is a large gap between the outer ring of the bearing and the bearing cover, so that the shaft can be freely extended when thermally expanded, but the inner ring needs to be fixed axially to prevent the bearing from loosening. When the cylindrical fulcrum is used as the fulcrum, because the inner and outer rings can move relatively in the axial direction, the inner and outer rings should be fixed axially to avoid excessive displacement of the outer ring. When designing, it should be noted that there is no unnecessary or insufficient axial fixation of the inner and outer rings of the bearing.
3.Swimming support at both ends
When both fulcrums are designed as swimming supports, the position of the shafting components must be positioned by other measures.
KOYO bearing anti-rust phosphating
The phosphating used for protection belongs to thick film phosphating, the film thickness is more than 20um, and the film weight is generally 10 ~ 30g / m2, or even heavier. In order to obtain good protection performance, parts should be dipped in oil, grease or wax after phosphating to further improve corrosion resistance. More commonly used in strong parts, springs, etc.
In principle, this type of film cannot be used as the bottom layer of organic coatings. It is very sensitive to mechanical deformation. When subjected to deformation, the film will crack and loosen, causing parts to separate from the paint film. In addition, the paint consumes a lot, and the gloss and finish are poor.
1.Slow Phosphating
The bath liquid is composed of one or two of zinc dihydrogen phosphate, dihydrogen phosphate, iron dihydrogen phosphate and free phosphoric acid. As there is no oxidant, as the treatment area increases, the Fe2 + ion concentration continues to increase, and the sediment increases accordingly. The processing time takes 40 to 60 minutes.
2.Accelerate high temperature phosphating
Adding N03-, CI03-, etc. to the above phosphating solution can greatly shorten the phosphating time. Their role is to produce hydrogen ions produced by the reaction of steel oxide and acid and ferrous ions produced by the dissolution of iron to maintain the Fe2 + The content is always at a level.
In the phosphating solution containing the accelerator, although the zinc content is initially reduced, at a certain acid ratio, the entire process of the bath solution can be maintained at a constant level. The composition of the phosphating film will not be affected by the treatment area. There have been significant changes. In addition, the sedimentation in the phosphating tank with accelerator is significantly reduced compared to without accelerator. The corrosion resistance of the phosphating film is unchanged, and the life of the bath is significantly extended.
During the production process, the solution should be regularly tested and supplemented to maintain a uniform quality film. There are many ways to put the parts into the slot. For larger work, use special spreaders or net baskets; for large quantities of small pieces, use rollers.
For the purpose of energy saving, the decrease in phosphating temperature does not affect the formation of a sufficiently thick film, which is undoubtedly the direction people are pursuing. The latest research results show that adjusting the composition can reduce the original temperature from 92-98 ℃ to 65-85 ℃, and the phosphating film can be dripped with standard copper sulfate solution for 20-30 minutes without corrosion.
High carbon steel and high carbon low alloy can form black or dark gray black film, medium and low carbon steel can only form silver gray to gray film, if black phosphating film is required, three methods are available: one is dyeing before phosphating, The second is black phosphating (blackening agent is added to phosphating solution), and the third is blacking after phosphating.
KOYO bearing installation and disassembly method
KOYO bearing installation method
The installation of KOYO bearings should be based on the bearing structure, size and the matching nature of the bearing components. The pressure should be directly applied to the end face of the tightly fitting ring, and the pressure should not be transmitted through the rolling elements. The installation of KOYO bearings generally adopts the following methods:
1.Press fit
When the inner ring of the KOYO bearing is tightly fitted with the shaft, and the outer ring is loosely fitted with the housing hole, you can press the bearing on the shaft with a press, and then install the shaft together with the KOYO bearing into the hole of the bearing housing. At the end face of the inner ring of the KOYO bearing, a soft metal material is used to assemble the assembly sleeve (copper or mild steel). The inner diameter of the assembly sleeve should be slightly larger than the journal diameter, and the outer diameter should be slightly larger than the bearing inner ring rib Small, so as not to press on the cage. When the outer ring of the bearing is tightly fitted with the hole of the bearing seat, when the inner ring is loosely fitted with the shaft, the bearing can be pressed into the hole of the bearing seat first. At this time, the outer diameter of the assembly sleeve should be slightly smaller than the diameter of the seat hole. If the KOYO bearing ring and the shaft and the seat hole are tightly matched, the installation of the inner ring and the outer ring should be pressed into the shaft and the seat hole at the same time. The structure of the assembly sleeve should be able to press the end surfaces of the inner and outer rings of the bearing at the same time.
2.Heating coordination
By heating the bearing or bearing housing, the thermal expansion is used to transform the tight fit into a loose fit installation method. It is a common and labor-saving installation method. This method is suitable for the installation of bearings with a large interference. The front ring of the hot-loaded bearing or the separable bearing is placed in the oil tank and heated evenly at 80-100 ℃, and then removed from the oil and installed on the shaft as soon as possible. After cooling, the end face of the inner ring and the shoulder are not tight, and the bearing can be axially tightened after cooling. When the outer ring of the bearing is tightly fitted with the bearing seat made of light metal, the hot assembly method of heating the KOYO bearing seat can be used to prevent the mating surface from being scratched. When heating the bearing with an oil tank, there should be a grid at a certain distance from the bottom of the tank, or hang the bearing with a hook. The KOYO bearing cannot be placed on the bottom of the tank to prevent sunken impurities from entering the bearing or uneven heating. A thermometer must be in the oil tank , Strictly control the oil temperature not to exceed 100 ℃, to prevent the occurrence of tempering effect, so that the hardness of the ferrule is reduced.
3.Installation of tapered bore bearings
The tapered bore bearing can be directly installed on the tapered journal or the tapered surface of the adapter sleeve and the withdrawal sleeve. The tightness of the fit can be measured by the reduction of the radial clearance of the KOYO bearing. Therefore, before installation The radial clearance of the bearing should be measured. During the installation process, the clearance should be measured frequently to achieve the required amount of clearance reduction.Generally, the lock nut is used for installation, and the method of heating installation can also be used.
4.Thrust bearing installation
The fit of the thrust bearing's circumference and the shaft is generally a transition fit, and the fit of the seat ring and the bearing seat hole is generally a clearance fit, so this KOYO bearing is easier to install. The center shaft spring of the two-way thrust bearing should be fixed on the shaft to prevent Relative to the axis. The installation method of KOYO bearings is generally the case of shaft rotation, so the cooperation between the inner ring and the shaft is an win-win fit, and the cooperation between the outer ring of the bearing and the bearing chamber is a clearance fit.
KOYO bearing disassembly method
The disassembly of the bearing should be carried out as carefully as it was installed. Be careful not to damage the bearing and various parts, especially the disassembly of the interference fit bearing, which is difficult to operate. Therefore, in the design stage, it is necessary to consider the ease of disassembly in advance, and it is also very important to design and make disassembly tools as needed. When disassembling, research the disassembling method and sequence according to the drawings, and investigate the matching conditions of the bearings to obtain foolproof operation.
1.Disassembly of the outer ring
To disassemble the interference fit outer ring, set several screws for the outer ring to squeeze the screw on the circumference of the housing in advance, and tighten the screw on one side while disassembling. These screw holes are usually covered with blind plugs, tapered roller bearings, and other separate bearings. Several cutouts are provided on the housing shoulders, using pads, using a press to remove, or gently tapping to remove.
2.Disassembly of cylindrical bore bearings
The disassembly of the inner ring can be easily pulled out with a pressure machine. At this time, pay attention to the inner ring to withstand its pulling force.
The hydraulic method is used to disassemble the inner ring of large bearings. Oil pressure is applied through the oil hole provided on the shaft to make it easy to pull out. Bearings with large widths are used in combination with the drawing method for disassembly.
Induction heating method can be used to remove the inner ring of NU and NJ cylindrical roller bearings. The method of heating the local area in a short time to make the inner ring expand and pull.
3.Disassembly of tapered bore bearings
Remove the relatively small KOYO bearing with adapter sleeve, support the inner ring with a block fastened on the shaft, turn the nut back several times, and use the block to knock and remove with a hammer. For large bearings, it is easier to disassemble by hydraulic pressure. The oil is pressurized in the oil hole on the tapered hole shaft to expand the inner ring and disassemble the KOYO bearing. During operation, the bearing may suddenly come out, and it is better to use the nut as a stopper.
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