Deep groove ball bearings are the most widely used in practical applications and the most contacted in the maintenance process. In this paper, the performance and reuse judgment criteria of deep groove ball bearings are deeply discussed with examples.

 

1 Performance overview The main purpose of deep groove ball bearings is to bear radial loads, but they are also commonly used to bear combined radial and axial loads. When the speed is very high and it is not suitable to use the thrust bearing, this kind of bearing can be used to bear the axial load. In practical applications, the radial bearings on the non-motor side of pumps and fans are of this type, and the motor side bearings of some pumps and fans are also of this type. This kind of application example widely exists on the pumps and fans on the process line of a factory owner. For example, the bearings on the non-motor side of the following equipment bear radial loads: 1306-2BGC drain pump (N0.6224); FF0601 boiler Circulating pump (NO.6316), etc., and the motor side and non-motor side bearings in the following equipment that bear the combined radial and axial loads: 1411-1A finished acid delivery pump (NO.6312); 0901A fan and 0904C Fan (6314C3), etc. Compared with other types of bearings with the same external dimensions, it has the characteristics of the least friction and the highest allowable speed. It is suitable for rigid double-supported shafts and short shafts whose distance between the supported shafts is less than ten times the inner diameter of the bearing. This is because there is a relative position error between the inner ring (shaft) and the outer ring (housing) of deep groove ball bearings, and the mutual inclination angle of the two axes should generally not exceed 6′～16′ (determined according to the clearance). value, the bearing cannot work normally, which is a practical problem that should be paid great attention to when installing this type of bearing. Generally, single row deep groove ball bearings have better vibration and sound.

 

2 Judgment Standards for Reuse of Deep Groove Ball Bearings During the use of rolling bearings, it is often necessary to check their operating conditions, or check the quality of the bearings during maintenance. There are many ways to judge whether a bearing can be reused, such as based on the type and degree of damage to the bearing raceway working surface, rolling element surface and mating surface, or based on the bearing clearance and the size of the bearing assembly surface. The following is a brief description of the criteria for bearing reuse in terms of bearing clearance and bearing assembly surface size.

 

2.1 Bearing clearance

Some maintenance personnel think that the smaller the clearance of the bearing, the better. In fact, this is a conceptual error. Due to this conceptual ambiguity, blind replacement is often caused, resulting in unnecessary waste. A necessary condition for proper bearing operation is to have the correct clearance. Generally, when the working clearance of the ball bearing is zero or there is a negative clearance state with a slight preload, its operation will not produce adverse consequences. The grade code of bearing radial clearance can be divided into (from small to large) C1, C2, basic radial clearance (unsigned), C3, C4, C5. In the clearance standard of the bearing, the clearance of the standard grade is suitable for the standard fit under the general load. At this time, the working clearance of the bearing in operation can roughly meet the requirements of the maximum service life. Most of the bearings of the above-mentioned pumps and fans have the basic level of clearance, and only the bearings of the 0901A and 0904B fans have the C3 level of clearance.

 

Rolling bearings will increase the internal clearance of the bearing due to wear during operation. The increase of bearing clearance will reduce the load-bearing area inside the bearing and increase the running noise. Therefore, when considering the reuse standard of the bearing clearance, it should first be used according to the working conditions of the main engine to allow the use of bearings with increased clearance. If the main engine has no special requirements, the following recommended values can be referred to:

 

(1) According to the use value of the general-purpose rolling bearing clearance (except C2 grade):

δ limit = maximum value of δ original clearance level + 2 × maximum value of ordinary level of δ clearance

 

(2) The limit use value of the clearance of rolling bearings with clearance grade C2:

δ limit = the maximum value of δ original clearance level + the maximum value of ordinary level of 0.5 × δ clearance

 

(3) When the amount of wear of the bearing is uneven in the circumferential direction, there will be a phenomenon that the clearance varies from place to place around the circle. At this time, the following formula can be used to judge the possibility of continued use:

 

2.1.1 The following takes the 6314C3 bearing of the 0901A fan as an example for specific explanation:

 

① Determine the limit of the clearance of deep groove ball bearing 6314C3 (Japanese standard) in general use. According to Table 1, it can be found that the maximum value of the original clearance of the 6314C3 bearing is 51 μm, the minimum value of the original clearance is 25 μm, and the maximum value of the normal-grade clearance of the bearing is 30 μm, so the clearance limit of the 6314C3 bearing in general use For: δ=51+2×30=111μm

 

② The actual measured internal clearance value of the 6314C3 bearing after operation is: δ maximum clearance = 95 μm δ minimum clearance = 65 μm to judge whether the bearing can continue to be used: δ average clearance = 12 (95 + 65) = 80 μm

 

2.1.2 Conclusion: After the 6314C3 bearing is operated, although the clearance value of the bearing does not exceed the service limit (95<111), the wear is uneven, and the difference in the internal clearance of the bearing is too large, which has exceeded the reuse standard (37.5>30) , so the bearing can no longer be used.

 

2.2 Bearing assembly surface size

In the supporting part of the machine, the bearing should be positioned and fixed according to different requirements in the three directions of radial direction, axial direction and circumferential surface (cut surface). In general, the axial fixation is achieved by axial closure or partial radial fit, and the bearing on the automatic side of the mechanism support is often not fixed in the axial direction to compensate for the axial installation or thermal expansion and contraction of the mechanism system. Dimensional changes in . The radial and tangential fixation of the bearing is generally achieved by the inner diameter of the bearing and the shaft, and the outer diameter and the inner hole of the bearing housing.

 

2.2.1 Bearing fit. The choice of bearing fit must be determined according to the manufacturing accuracy of the bearing itself and the service conditions of the bearing. Whether the fit is correct or not has a great impact on the performance and life of the bearing. The accuracy grades of bearings can generally be divided into five types: ordinary grade (G), advanced grade (E), precision grade (D), ultra-precision grade (C) and most precise grade (B). The precision grade code "G" is generally not marked on the bearing model, but it must not be omitted when indicating the bearing clearance group, such as 3G314 (equivalent to domestic bearing 6314C3), the prefix "3" indicates that the clearance is C3.

 

For bearings with ordinary grade (G) accuracy, under the premise of ensuring normal fit requirements, the limit value of the tolerance of the inner diameter and outer diameter should not exceed twice the original tolerance value. The inner diameter and inner diameter of deep groove ball bearings of various sizes Refer to Table 2 and

 

3. The "*" mark in the table indicates that the shaft diameter should be increased or the inner diameter of the bearing seat should be reduced during use, so as to ensure normal fit interference and clearance.

 

①Determine the reuse standard of the inner diameter and outer diameter tolerance of 6314 bearings. It can be found from Table 4 that the outer diameter of the 6314 bearing is 150, and the inner diameter is 14×5=70. From Table 2 and Table 3, it can be found that the reuse standard of the 6314 bearing is: upper difference of inner diameter +15*μm, lower difference - 15μm; the upper difference of the outer diameter is 0μm, and the lower difference is -36*μm.

 

② In a factory 1306-2B, the GC drainage pump experienced excessive vibration (greater than 70 μm) shortly after the overhaul. During disassembly and maintenance, it was found that the inner ring of the lower bearing (NO6224) was slipping. After measurement, it was found that the shaft diameter of the lower bearing became smaller, from the original ?120+0.025+0.003 to ?120-0.08-0.16. According to the 6224 bearing reuse standard, we can deduce that the journal reuse value should be ?120+0.005+0.003. However, the actual value of the shaft diameter is far from this range, so it is theoretically known that this shaft can no longer be used. But because there was no spare shaft at that time, emergency measures were taken, such as punching holes in the lower shaft diameter, and then adding new bearings, trying to achieve the matching size of the bearing and shaft, but the actual effect was not good, and the problem could not be solved at all.

 

3 Epilogue

In factory practice, it is often judged whether the bearing can continue to be used from the operating conditions of the mechanical equipment and whether it can meet the performance requirements of the equipment. Although the reuse standard mentioned in this article only considers the technical characteristics of the bearing itself, it can still be used as a theoretical basis and reference in daily bearing inspection and maintenance, eliminating subjective assumptions, giving full play to the use potential of bearings, reducing spare parts and maintenance costs, and improving the quality of bearings. Equipment operating rate.