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GENERAL ENGINEERING INFORMATION FOR BALL BUSHINGS:
PDF Catalogue of Linear Bearings
Ball bushings (also known as linear bearings or bushes) are anti-friction bearings for linear motion. They offer the familiar advantages of ball bearings. e.g Long service life, high precision and efficiency.
NB Ball Bushings are manufactured in Japan by Nippon Bearing Co. which is one of the largest Japanese ball bushing manufacturers. All of the shafts, rails and housings shown in this catalogue are manufactured in Germany. All parts are normally on short lead times (less than 7 days).
Construction and Materials:
The outer ring of the ball bushing is made from hardened rolling bearing steel. The cylindrical ground and precision formed cage is made from one single part and is held in position by solid steel endplates.
This design saves, in many applications, the use of sealed ball bushings. The special features of these extremely robust units are high rigidity, reliability and durability, especially during assembly.
Speed, Lubrication and Friction:
The coefficient of friction µ of NB ball Bushings without seals is very low at approx 0.001 to 0.003. Standard lubrication practices as applied to anti-friction bearings can be used for all ball bushings. Either oil or grease can be used as a lubricant but in most cases grease is preferable. If necessary NB ball bushings can be used without lubrication.
Speeds of up to 2 m/s and accelerations of up to 60 m/s2 are generally safe.
Mounting:
When mounting a standard ball bushing into a housing an H7 fit for the housing bore is generally required. The ball bushing is secured in the housing by retaining rings, fixing screws or adhesive.
To achieve pre-load the recommended tolerance for the housing bore can be, in certain cases, JS6 to M6.
Using our housings guarantees best fit and repeatability.
Life expectancy: (Load capacity and calculation)
The size of the ball bushing is dictated by its load bearing capacity and its life expectancy.
The nominal life span is calculated using this formula:
where:
C = Dynamic load capacity taken from the tables in this catalogue
F = Dynamic equivalent load
L = Travel in metres
For more precise calculations some other factors need to be included:
fH = Shaft hardness (When using our shafts the factor is 1. For other shafts see table below)
fT = factor for Temperature. An allowance must be made when operating at higher temperatures (i.e >80º C) – see table below
fL = factor for Life. See chart below if exceeding 105 m of travel
Therefore:
| Factors | 1 | 0.9 | 0.8 | 0.7 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.1 | |
| fH | Hardness HRC | 60 | 56 | 55 | 54 | 52 | 49 | 46 | 42 | 33 | 20 |
| fT | Temperature | 80 | 100 | 125 | 160 | 200 | on demand | ||||
| fL | Travel life | 1 | 1.3 | 2 | 3 | 5 | 8 | 15 | 35 | 120 | 1000 |