Rating Life Linear Ball Bearings
Rating Life Hardness Factor (fH)
Contact Coefficient (fc) – Table 2 Generally two or more linear bearings are used on one shaft. Thus, the load on each linear system differs depending on each processing accuracy. Because the linear bushings are not loaded equally, the number of linear bushings per shaft changes the permissible load off the system.
The shaft must be sufficiently hardened when a linear bushing is used. If not properly hardened, permissible load is lowered and the life of the linear ball bearings will be shortened.
FIG. 1
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
CONTACT COEFFICIENT Table 2
Number of Linear Systems per Shaft
Contact coefficient - FC
1 2 3 4 5
1.00 0.81 0.72 0.66 0.61
Load Coefficient (fw) – Table 3 When calculating the load on the linear system, it is necessary to accurately obtain object weight, inertial force based on motion speed, moment load, and each transition as time passes. However, it is difficult to calculate those values accurately because reciprocating motion involves the repetition of start and stop as well as vibration and impact. A more practical approach is to obtain the load coefficient by taking the actual operating conditions into account.
50
40
60
30
20
10
Temperature Coefficient (fT) If the temperature of the linear system exceeds 100°C, hardness of the linear system and the shaft lowers to decrease the permissible load compared to that of the linear system used at room temperature. As a result, the abnormal temperature rise shortens the rating life.
FIG. 2
LOAD COEFFICIENT Table 3
1.0 0.9 0.8 0.7 0.6 0.5
Operating Conditions
FW
Operation at low speed (15 m/min. or less) without impulsive shock from outside Operation at intermediate speed (60 m/min. or less)without impulsive shock Operation at high speed (over 60 m/min.) with impulsive shock from outside
1.0 to 1.5
1.5 to 2.0
2.0 to 3.5
100
150
200
250
Temperature of Linear System (°C)
Notes: Maximum temperature of plastic retainer 212°F or 100°C. Maximum temperature 176° per Table 6 on page 134.
154 Round Shaft Technology • pbclinear.com
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