★ bearing shape restrictions
Bearing shape restrictions
Outline restrictions
For the required nominal load Once the final value, you must consider the bearing dimensions required for installation including installation and fixed bearing considered here. And having the required bearing load ratings of matching the size of the shaft. These factors help determine the bearing structure and size, you can also exclude certain bearing types. In some cases, due to space constraints even before the rated load is determined to rule out a choice.
For example, if the bearing shape is very narrow, the ball bearing is the only type available in this work. Or, if you must use a very small diameter of the bearing housing, you will need to install two or more on the same axis of roller bearings in order to achieve adequate load rating.
When the size and requirements of the shaft relative measure bearing load ratings are very different, there has been another common contradiction. If the shaft is large but light loads, even if the requirements of the rated load is small, but they have made an expensive, large bearing high rated load, in this case, the best contact with the bearing manufacturers in order to make one of the most cost-effective Solution.
Examples
The basic working conditions. Suppose bearings in the gear unit bearings must support one end of a shaft diameter of about 25mm, and a spur gear mounted on the shaft.
Duty cycle and bearing loads. Force analysis and transmission gear duty cycle showed that: Bearing in about 3/4 of the time to bear radial load of 1780N, speed 11000r / min, in the quarter of the running time, bearings to withstand radial the load of 890N, speed of 3500r / min. Good positive engagement almost no axial force, there is no other effective oblique engagement or axial component. It is expected in two directions the maximum axial force is 89N, maximum vibration force of 89N.
Size limit. Due to the internal design of the gear unit by limiting the maximum allowable outside diameter of the bearing of 70mm, the maximum calculated degree of disturbance 6, the position of the maximum misalignment 0,0015. It is not required by aligning bearings.
surroundings. Engagement with the bearing lubrication as lubrication: oil sump from a large fuel injection, the maximum expected temperature of 140 F.
reliability. Bearing had to work must have a good reliability, the use of reliable failure rate of 8%.
Select Step
1. Bearing diameter of about 25mm.
2. The bearing outer diameter of 70mm.
3. The estimated maximum pitch diameter D (mean bearing inner and outer diameters) as follows:
(25 + 70) /2=47.5 (mm)
4. Calculate the maximum DN value:
47.5 × 11000 = 0,52 × 106
5. Select the basic bearing type required to determine the value of the modified DN. First, identify the type of amendments by the lubricating bearing speed limit factor. Richard from Figure 1, the use of small oil sump continuous operation, the coefficient is 0.85. When using a large sump intermittent operation, coefficient of 0,95, low coefficient take continuous operation, the correction DN values ??are:
1. 52 × 10) / 0,85 = 0,61 × 106
1. Results obtained with step 5 DN values ??and Figure 1, we find angular contact ball bearings and industrial-grade, precision cylindrical roller bearings, as well as the speed range of deep groove ball bearings (speed limit) is equal to or greater than the correction of DN value, therefore, these bearing type is initially selected.
2. From equation (D) to calculate the equivalent load:
3. Determine the basic reducer working life. 1 obtained from the expression, typical operating life of ordinary gear units 20000h.
4. Given the reliability failure rate correction working life. Life adjustment factor of 1,8% of the use of the expression given reliability failure rate of 85%; therefore amended the working life L as follows:
20000 / 0.85 = 23529 (h)
10, calculates the required rated by Equation (E) dynamic load C:
11, with the vibration correcting C. In this case, the minimum stable load 890N is greater than the maximum vibration load 89N, than the load stability of the load and the vibration of 0.1, using Table 1-6, using linear interpolation of the two closest load insert a correction coefficient between the rate of the coefficient is calculated as follows:
(1.00 + 1.020) /2=1.010
The rated load correction value:
C = 1.010 × 29746 (N)
