I. importance must be attached to improving the pass rate of bearing clearance

Radial clearance is one of the main quality indexes for bearing matching.Radial clearance refers to the total clearance between the inner and outer ring channel and the rolling body in the direction of diameter. 

Therefore, the bearing clearance is not only a major parameter of whether the finished bearing is qualified after the qualified finished parts are matched, but also an important factor of whether the bearing can work normally.Clearance value does not meet the technical standards, will affect the load in the rolling body between the reasonable distribution, bearing rotation precision, vibration value, life will be affected, so it is important to improve and ensure the clearance pass rate of bearings. 

Second, the analysis of radial qualified rate of causality

Product quality in the formation process, once the problem is found to find the reason immediately.Using the form of causal analysis, we analyze the low pass rate of radial clearance deviation. 

There are five factors that affect the quality of bearing clearance.If not considering material and environmental factors, can be used to analyze the main testing instrument, process method and personnel quality on the quality of the bearing clearance, bearing inner and outer ring and ball past matching method is to inside, the diameter of the outer channel deviation separation with instrument is good, and according to the standard clearance to calculate an inner ring channel diameter size value and an outer ring channel diameter size, and then select the corresponding size of copper ball, after the three assembly, with the axial clearance tester to test the axial clearance upper and lower limit value, does not meet the technical requirements, selection again.As for the radial clearance value of the bearing, it is difficult to guarantee the accuracy if the axial clearance value is used.Because the measured axial clearance value is only the upper and lower limit value, and the upper and lower limit value is different due to the channel curvature and the different methods, so the radial pass rate of the bearings selected by this method is unstable.Sometimes high and sometimes low, rework times are relatively frequent, the product clearance quality can not be determined. 

3. Improve the pass rate of radial clearance by using matching instruments

On the premise of ensuring the machining quality of bearing parts and ensuring the accurate indication of test instruments, it is an effective method to improve the qualified rate of radial clearance of bearing to reasonably match the inner and outer rings of bearing with special matching instruments for bearing inner and outer rings:

1. Supporting principle of supporting instrument

In the process of bearing assembly, the clearance of the bearing must comply with the standard provisions. The radial clearance deviation formula of radial radial radial ball bearing is as follows:

U = X - Y - 2 z or z X - Y = U + 2

Where, U= radial clearance of centripetal ball bearing without load, X= diameter deviation of the outer groove, Y= diameter deviation of the inner groove, Z= diameter deviation of the steel ball,

The U value in the formula can be consulted from the national standard, and the Z value has been marked in the steel ball inspection.The task of matching with the matching instrument is to measure the (x-y) value once with the matching instrument after the size sorting of the bearing inner and outer rings, and then select the appropriate size of the steel ball for assembly, and then check the radial clearance value with the radial clearance instrument. 

2. Supporting methods

First of all, use the bearing inside and outside groove diameter size standard parts to check matching instrument.Because the matching instrument is measured by the two-point comparison method, the calibration instrument needs two standard parts, namely the inner ring and the outer ring groove diameter standard parts.The supporting instrument is equipped with three micrometers, the left and right micrometers respectively reflect the diameter deviation of the inner and outer groove, and the middle micrometer once reflects the value of (x-y). 

For example, the actual diameter deviation of the outer ring standard part channel is + 8um, and the actual diameter deviation of the inner ring standard part channel is -5um, so x-y=+8-(-5)=13um. 

During calibration, align the internal and external channel diameter standard parts with their respective measuring points, and the pointer of a micrometer in the middle of the matching instrument should point to the position of + 13um to prove that the instrument has been calibrated well.On the contrary, the dial indicator pointer does not point to the position of +13 um, it needs to readjust the instrument. 

As the size of the inner and outer groove diameter has been sorted before matching, so the micrometer on the left and right sides of the matching instrument can be omitted, as long as the middle of a micrometer reflects the value of (x-y) can be selected with a certain size of the steel ball.The radial clearance value of the bearing thus arranged conforms to high standards. 

What should be reminded is that, in the process of supporting the inner and outer rings, we should insist on frequent use of standard parts to calibrate the instrument, to prevent meter running, otherwise, measured (x-y value is not accurate, the bearing clearance value will be wrong.In terms of application effect, the qualified rate can reach 98-100% by popularizing the use of matching instruments.