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One of the main quality indexes of bearing matching is radial clearance. Radial fag bearing clearance refers to the total clearance between the inner and outer ring channels and the rolling element in the diameter direction.
Therefore, bearing clearance is not only a main parameter to identify whether the finished bearing is qualified after matching the qualified finished parts, but also an important factor to determine whether the bearing can work normally. If the clearance value does not meet the technical standards, it will affect the reasonable distribution of load between rolling elements, and the rotation accuracy, vibration value and service life of the bearing will be affected. Therefore, it is undoubtedly very important to improve and ensure the clearance qualification rate of the bearing.
In the process of product quality formation, once a problem is found, it is necessary to find the cause immediately. Using the form of causal analysis, we analyze the low qualified rate of radial clearance deviation.
There are five factors affecting the quality of bearing clearance. If the material and environmental factors are not considered temporarily, the influence of testing instruments, process methods and personnel quality on the bearing clearance quality can be mainly analyzed. In the past, the matching method of bearing inner and outer rings and steel balls was to sort the diameter deviation of inner and outer ring channels with instruments, and calculate the diameter value of an inner ring channel and an outer ring channel according to the standard clearance, Then select the copper ball of corresponding size. After the three are assembled, use the axial clearance tester to test the upper and lower limit values of axial clearance. If they do not meet the technical requirements, they will be re selected. As for the radial clearance value of bearing, it is known by the axial clearance value of INA Bearing, which is difficult to ensure the accuracy. Because the measured axial clearance value is only the upper and lower limit values, and the upper and lower limit values are different due to the channel curvature and different methods, the radial qualification rate of the bearing selected by this method is unstable. Time is high and time is low, and the rework times are frequent, so the clearance quality of the product can not be determined.
On the premise of ensuring the processing quality of bearing parts and the accuracy of the indication of the test instrument, using the special matching instrument for the inner and outer rings of the bearing to reasonably match the inner and outer rings of the bearing is an effective method to improve the qualification rate of the radial clearance of the bearing:
During the assembly of the bearing, the clearance of the bearing must comply with the provisions of the standard. The radial clearance deviation formula of the centripetal ball bearing is:
U=X-Y-2Z
Or X-Y = u + 2Z
Where u = radial clearance of radial ball bearing without load, um
X = outer ditch diameter deviation, um
Y = inner ditch diameter deviation, um
Z = ball diameter deviation, um
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 matching task of NSK bearing sleeve instrument is to measure the (X-Y) value at one time with the matching instrument after sorting the dimensions of the inner and outer rings of the bearing, and then select the steel ball with appropriate size for assembly, and then check the radial clearance value with the radial clearance instrument.
Firstly, the supporting instrument is calibrated with the standard parts of the inner and outer groove diameter of the bearing. Because the supporting instrument is measured by two-point comparison method, the calibration instrument needs two standard parts, namely, inner ring and outer ring groove diameter standard parts. The supporting instrument is equipped with three dial indicators. The left and right dial indicators reflect the diameter deviation of inner and outer grooves respectively, and the middle dial indicator reflects the value of (X-Y) at one time.
For example, if the actual diameter deviation of the outer ring standard part channel is + 8 um and the actual diameter deviation of the inner ring standard part channel is – 5 um, then X-Y = + 8 – (- 5) = 13 um.
During calibration, align the internal and external channel diameter standard parts with their respective measuring points. The pointer of a dial indicator in the middle of the supporting instrument shall point to the position of + 13 um to prove that the instrument has been calibrated. On the contrary, if the dial indicator pointer does not point to the + 13 um position, the instrument needs to be readjusted.
Since the inner and outer groove diameters have been sorted before matching, the dial indicators on the left and right sides of the supporting instrument can be omitted. Only the value reflected by the middle dial indicator (X-Y) can be used to select a certain size of steel ball. In this way, the radial clearance of the bearing meets the requirements of high standards.
It should be reminded that during the matching process of the inner and outer rings, the standard NTN bearing parts should be used frequently to calibrate the instrument to prevent the meter from running. Otherwise, the measured (X-Y) value will be inaccurate and the allocated bearing clearance value will be wrong. In terms of application effect, promote the use of the supporting instrument, and the qualified rate can reach 98-100%.