Tapered roller bearings are widely used in the industrial field because of their remarkable advantages of bearing composite loads (both radial and axial).Tapered roller bearing axial clearance is correct or not directly determines the operating life of the bearing, and the adjustment of the clearance is a precision, high technology content of the project, often need professional personnel and special equipment to implement, especially in the field of mass production, such as the auto industry, for each bearing system by artificial clearance adjustment will pay a heavy labor costs, and inefficient.However, if clearance detection and adjustment are carried out with special equipment, certain fixed assets investment and corresponding equipment maintenance cost are required.In view of this situation, timken adopts set-right ™ technology and USES product tolerance control method to preset clearance of tapered roller bearings, avoiding the adjustment process during assembly, which not only greatly improves the assembly efficiency, reduces the production cost of customers, but also ensures the accuracy of clearance adjustment.
Traditional clearance adjustment methods for tapered roller bearings mainly use manual or professional equipment to measure clearance or torque. A professional adjustment process can achieve the same accuracy as set-right ™, but there are certain interference factors and restrictions.If clearance measurement and torque measurement are used to adjust clearance, there are higher requirements in measuring equipment precision, personnel skills, equipment structure design and calculation of the impact of rotating torque of non-bearing parts.
Timken set-right ™ technology is defined as enabling 99.73% of cone roller bearings to achieve the desired clearance value after assembly by controlling the values of the tolerance variables for each assembly component and using probability and statistical principles to avoid additional clearance adjustment.This includes the concepts of probability theory, statistical principles, dimensional chain calculation and six sigma lean production.The technology has been adopted by many customers for decades, and is widely used in automobile wheel end, industrial gearbox, construction machinery and other fields.Compared with the above traditional clearance adjustment methods, the advantages are summarized as follows:
1. Reduce the labor cost and technical ability requirements of the production line
2. All assembly components do not need to be selected and can be quickly and accurately assembled, which is most suitable for mass production
3. Avoid the steps of measuring and adjusting the data in the assembly site
4. Special equipment and fixture without clearance adjustment
5. Cancel clearance adjustment of conventional gaskets and other parts
Easy, fast and accurate aftermarket maintenance the following details the principles and application of set-right ™ technology.
I. principle of set-right ™
The bearing, shaft, bearing housing, spacer and other components that constitute the bearing system have their own design tolerances. In the process of production, manufacturing and processing errors will be caused by equipment, materials, personnel and environment and other factors. The manufacturing errors of qualified products will fluctuate within the minimum and maximum range of design tolerances.The final size of some parts will be close to the tolerance allowable boundary, but the processed size of most parts will conform to the normal distribution of statistical probability, as shown in figure 1.The abscissa is the tolerance value, and the ordinate is the frequency of the occurrence of a tolerance value
And the more the number of statistical parts, the more smooth curve and more in line with the middle of the size of more, the size of the two ends of the characteristics of less.
According to the characteristics of normal distribution, about 99.73% of the values will fall within the average ±3 range (see figure 2). Sigma () refers to the standard deviation and reflects the degree of dispersion of the data, that is, the size of the fluctuation range of the actual machining size.If the six sigma lean production management method is implemented in the actual production, the qualification rate and quality stability will be further improved.The dimensional tolerance range of parts required on the drawing reflects the design requirements, which can also be understood as customer requirements.In the actual production process, the fluctuation and mean distribution of the actual machining size of the parts within the specified tolerance range reflect the machining accuracy and the quality management ability of the process.In the six sigma lean production management, due to the strengthening of the quality control of parts manufacturing process, value and mean distribution position (in FIG. 1) can be timely adjusted according to the requirements of the final product, which improves the processing accuracy and reduces the dimensional fluctuation.Combined with the characteristics of normal distribution, when part sizes within the design tolerance range can not meet the requirements of the final product, the use of 6 production management, without increasing the design requirements, can make 99.73% of parts machining size meet the requirements of the final use.Based on this theory, the Set of timken u-right ™ technology also requires all parts of bearing installation system for six sigma production control, make the final assembly parts dimension cumulative tolerance within 99.73% of the bearing system (bearing system installation clearance) within the scope of six sigma, and accord with normal distribution, make the most of the bearing clearance around the system requirements in the middle of the value of volatility.If the (standard deviation) value is smaller, it indicates that the production process is more stable, the product size changes are smaller, and the final clearance range is smaller, which is more conducive to the operation of most bearings in the clearance range with a high fatigue life.See figure 2.
FIG. 2 illustrates the normal distribution curve of standard deviation
Determine the independent variables affecting the bearing clearance
Before calculating and analyzing the dimensional tolerances of each part in the bearing system, it is necessary to determine the independent variables affecting the bearing clearance, which are certain dimensions on the corresponding parts.Generally speaking, in a standard bearing system, the independent variables that will affect the bearing clearance are: the inner diameter of the inner ring, the height of the inner ring, the outer diameter of the outer ring, the height of the outer ring, the outer diameter of the shaft, the inner diameter of the bearing housing, the width of the shaft or the shoulder of the bearing housing, the width of the separation ring, etc.These variables exist independently, but they act together to set the bearing clearance value.It is worth noting that, because clearance of tapered roller bearings refers to axial clearance, some of the radial variables such as outer diameter of the shaft, outer diameter of the outer ring and other radial variables must be converted into axial values before the subsequent calculation.Figure 3 below is the definition of independent variables in a simple bearing system. The yellow dot is an independent variable.For different bearing applications, the number and definition of independent variables should be treated differently.
Iii. Analyze data and calculate by steps
1. Complete the collection of tolerance data of each independent variable
2. Convert all radial variables to values of axial variables
Calculate (standard deviation) for each independent variable
4. Apply formulas to each independent variable
The system (standard deviation) and 6 values after assembly are calculated
5. Will get the system of six sigma and bearing application required by the clearance value comparison, check whether the scope of six sigma value within the scope of the clearance required, if is greater than the required range, it must be by adjusting the tolerances of each independent variable to reduce sigma value, thus narrow the scope of the six sigma value, namely the narrowed parts design and manufacturing tolerance of a size.
6. After the nominal size and tolerance calculation of all parts in the bearing system are completed, the production can be organized after the manufacturer confirms the dimensional tolerance requirements of the parts, so as to realize the no-selection and no-adjustment setting of clearance.
Examples of set-right ™ applications
1. Take the application of automobile non-drive wheel as an example.The structure of the wheel end system is shown in figure 4.
2. Identify independent variables
Because this application is a non-driving wheel, the bearing is rotating on the outer ring and the inner ring is stationary, so the outer ring and the hub are closely matched, while the inner ring and the shaft are loosely matched.Thus, 10 independent variables affecting the axial clearance of the bearing can be determined.
The serial number
The name of the
The tolerance of mm
Mm in the normal distribution
Outer bearing inner ring large end face seat height
Bearing manufacturer control
+ / - 0.040
Inner ring of inner bearing large end face seat height
Bearing manufacturer control
+ / - 0.040
Outer bearing outer ring large end face seat height
Bearing manufacturer control
+ / - 0.020
Inner bearing outer ring large end face seat height