Linear Ball Bearings Technical Information
Load Rating and Life Expectancy The life (L) of a linear bearing can be obtained from the following equation with the basic dynamic load rating and the load applied to the bearing:
Relation Between Ball Circuits and Load Rating
Linear ball bearings are constructed so that the ball circuits are spaced equally. The load rating varies according to the loaded position. The load ratings of the linear ball bearings from the dimensional tables are per track and increased loading can be achieved by equally sharing the load between the tracks. The table shows the increased value by the number of ball circuits in such cases. Notes: (1) 3 track bearing is equal. (2) Open bearing load is de-rated by 50% if going against the opening.
( )
L: Rated life (km) C: Basic dynamic load rating (N/lbf) P: Working load (N/lbf)
f w : Load coefficient f h : Hardness factor f t :
Number of Rows
Temperature coefficient
4
5
6
f c : Contact coefficient The lifespan (Lh) of a linear ball bearing in hours can be obtained by calculating the traveling distance per unit time. The lifespan can be obtained from the following equation if the stroke length and the number of strokes are constant:
Co
Co
Co
Co
Load Rating Specified on the Tables
Co max
Co max
Co max
L h : Lifespan (hr) L: Rated life (km) s: Stroke length (m) n 1 : Number of strokes per minute (cpm) 50: Constant base line (km)
Co max MAX Load Rating
Load Ratio Co max /Co
1.414
1.463
1.280
Sample Calculations
1. Obtaining the rated life L and lifespan L h of the Simplicity ® linear ball bearing used in the following conditions: • Linear ball bearing: EP20G • Stroke length: 50 mm • Number of strokes per minute: 50 cpm • Load per bush: 490 N The basic dynamic load rating of the linear ball bearing is 860 N from the dimension tables on page 79. From equation (1), therefore, the rated life L is obtained as follows:
2. Select the ball bearing type by satisfying the following conditions: • Number of linear bushing used 4 • Stroke length 1 m • Traveling speed 10 m/min. • Number of strokes per minute 5 cpm • Lifespan 10,000 hr • Total load 980 N From equation (2), the traveling distance within the lifespan is obtained as follows:
860
270 km
From equation (1), the basic dynamic load rating is obtained as follows:
From equation (2), the lifespan Lh is obtained as follows:
270 2 • 0.05 • 50 • 60 10 3
Assume the following with a pair of shafts each with two linear ball bearings: f c = 0.81 f w = f t = f h = 1 As a result, EP20G is selected from the dimension table as the Simplicity ® linear ball bearing type satisfying the value of C.
901 hr
2 • s • n 1 • 60
152 Round Shaft Technology • pbclinear.com
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