The calculation of blank size and assembly quality of metal dust cover is one of the important items to ensure the service performance of the bearing with this sealing structure
Abstract: Metal shield is used as a seal bearing part , the calculation of blank dimension and assemble quality is one of the important items which ensuring the perforormance of seal structure bearing, so its action is very important.
Keywords: metal shield; blank dimension; assemble
1 Preface
The metal dust cover is a common sealing part of the bearing. Its basic structure is in the form of slotted outer crimping and inner bending. See Figure 1 for details, also known as the crimped dust cover. The structural dust cover has good dust-proof performance, rigidity and installation reliability, and is easy to process on the assembly line. It is widely used in various small and medium-sized sealed structural bearings. At the same time, the assembly of the metal dust cover has the following advantages:
Fig. 1 dust cover
(1) The assembly riveting rate can reach more than 99%, which is firm and reliable. The cover will not fall off during use. It has beautiful appearance, compact structure and good rigidity.
(2) It is easy to operate and has high assembly efficiency. For deep groove ball bearings with an inner diameter of 30 ~ 60mm, 3000 ~ 4000 sets can be assembled every day.
(3) The difference between the vibration values of the bearings before and after the installation of the dust cover is very small. According to statistics, for the deep groove ball bearings required by the vibration acceleration Z1 group, the difference between the average vibration values before and after the installation of the dust cover is only 0.5dB. For example, the vibration value of group Z1 of 6207Z bearing is required not to be greater than 39db. A random inspection was conducted on 50 bearings. The average vibration value of this batch of bearings before the dust cover was installed was 38dB, and the average vibration value after the dust cover was installed was 38.5db. The bearing vibration value after the dust cover was installed still met the requirements.
2. Structure and size of metal dust cover
The metal dust cover shall be extruded by the gland die during assembly to force the dust cover to deform in the outer ring groove so that it can be embedded in the outer ring groove to achieve extrusion. See Figure 1 for the structure of the crimped dust cover. It is very important to determine the blank size of dust cover reasonably to ensure the assembly quality of bearing.
The stamping process of the metal dust cover includes three steps: cutting, forming and bending. How to determine the blanking size of the blank of the dust cover is the key to the processing. The following formula is the relationship between the blank outer diameter, groove bottom diameter and the relevant size of the dust cover in the actual process.
D0=[0.414（DZ22 - DZ32 ）+ D1 2 +6πRZD1+4DZ1H] 1/2
D0 - outer diameter of sheet,
DZ2 - diameter of the central layer at the big end of the dust cover slope,
DZ3 - diameter of the center layer at the small end of the dust cover slope,
D1 - center diameter of curling arc,
RZ - center radius of curling arc,
DZ1 - diameter of the center layer of the outer diameter of the dust cover,
H-center distance of two arcs.
Figure 2 blank drawing
Fig. 3 dimension diagram of dust cover
D1=0.5（DF+D2 ）
DF - outer diameter of dust cover,
D2 - inner diameter at the crimping of dust cover.
DZ1= DF- SF
SF- sheet metal thickness.
DZ2= D3- 0.414 SF
D3 - diameter of large end of dust cover slope
DZ3= DZ2- 2B
DZ3 - diameter of the center layer at the small end of the dust cover slope
B - the distance from the non-circular end face of the dust cover to the beam.
RZ=RF+x SF
RF - radius of arc in crimping,
X - coefficient of center layer during rounding, selected according to table 1.
Table 1 coefficient of central floor
Formula (7) lists the calculation formula of groove bottom diameter:
It can be seen from Fig. 2 and Fig. 3 that the groove bottom diameter D is at the 45 ° angle of the crimping. Similarly, according to the law that the area of the dust cover remains unchanged after forming, the calculation formula of the groove bottom diameter D can be determined:
D=[0.414（DZ22 - DZ32 ）+ D1 2 + πD1RZ] 1/2。 （7）
For the notch radius R and included angle in the blank α It can be determined according to the size of the crimping of the dust cover.
3. Assembly of metal dust cover
The metal dust cover is assembled on the press, and its assembly method is shown in Figure 4. Place the bearing on the press platform, and the gland die is rigidly pressed by the force of the press to complete the gland process. In the actual assembly process, the assembled metal dust cover often has quality problems such as life cover and concave center. The specific causes are analyzed as follows.
(1) During the assembly process, the press is adjusted to a fixed position, the closing height is fixed, and the tooth processing depth of the bearing outer ring is not uniform, resulting in inconsistent tightness of the gland.
(2) There are problems such as the size error defect of the dust cover itself, human factors, the accuracy of the press and the looseness of the slider of the press. In view of the above situation, in addition to improving the processing dimensional accuracy of the toothpick and the quality of the dust cover, it is also very important to transform the pressure punch of the press. The research shows that adding a buffer device to the pressure punch of the press will greatly improve the quality of the cover. The specific transformation scheme is as follows.
The design of the pressure head buffer device is shown in Figure 5. Add polyurethane to the pressure head. Cylindrical surface B can guide and float up and down. The elasticity of the polyurethane itself can be used as a buffer to adjust the closing height during the capping process. In addition, the crimping position of the crimping cover can be decomposed into radial force and axial force after being subjected to vertical pressure (i.e. buffer force), ensuring the reliability of the capping. For the capping process, the buffer device of the pressure head has solved the quality problems of the loose cap and the concave cap, and the qualification rate of the capping has reached more than 99%.
4 Conclusion
In the bearing components, although the dust cover does not have a significant impact on the speed and load-bearing and other important working indicators of the bearing as the inner ring, outer ring and rolling element of the bearing, the dust-proof structure plays an important role in ensuring the cleanliness of the bearing and maintaining the effective lubrication of the lubricating oil in the bearing, and in fact indirectly ensures the working performance of the bearing.
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