EXCLUSIVE SHAFTS FOR BALL BUSHES
For a complete ball bush system the shaft should be considered as important as the inner race of a ball bush, so for high performance and precision guidance the same level of technical characteristics are necessary. Therefore the shaft must be made of the correct material, the heat treatment has to be done in the proper method. The grinding is the most important factor to achieve the smooth and quiet running for the ball bushes. ASK has many years experience in the supply of shaft for ball bush and supplies the high quality shaft so that the ball bushes can achieve the maximum performance.
Characteristic of Exclusive Shafts for Ball Bushes
As a background of technological strong for many years, exclusive shafts for ball bushings have gained high reliability according to consistent management system from material, heat treatment, straightening, grinding, lathe processing to testing and shipment.
High carbon chromium bearing steel or martensite stainless steels are used in the manufacture of ASK ball bush shaft. As a guide for ball bushes, the surface of the shaft contacting with the rolling steel balls is required to have a hardness of HRC 58-64. For durability against rolling fatigue, the hardness must penetrate to a minimum depth of 1.5mm and the surface finish should be precision ground to a minimum surface roughness of 0.8S~1.6S.
In our many years experience in the induction hardening of ball bush shaft we have built up a significant amount of “know how”that others find it difficult to match. ASK shafts have uniformity of hardness in both axial and circumferential planes. For stability and straightness this is vital- uneven stresses result in bowed shaft. See diagrams below for typical cross section of shaft with figure showing a typical micro hardness check across the same section.
■Diameters of Shafts
According to the application or required clearance (or preload), the tolerance of the shaft must be selected. For the special precise running, the shafts are manufactured with the tolerance h5 shown in right table. By using the shaft with h5 tolerance, the zero clearance or slight preload can be achieved.
At this time the user have to notice whether if there is no excessive preload between shaft and ball bush by checking the smooth running of ball bush on the shaft. If the bush cannot be moved on the shaft with the slight push by hand then the preload is excessive. Excessive preload will lead to reduced life expectancy.
When large deflections occur along a shaft, the preload will take place repeatedly and become a reason for short service life.
ASK has established deflection standard, shown at right table, to prevent such preload, and the shafts will be finished by High grade if no special precision is required.
DOCUMENT FOR DESIGN
Calculation of Deflection
When the shaft is under load, the deflection occurs normally. In this case, the calculation formulas of reaction force, sharing force, bending moment, deflection and inclination are shown follows.
Shafts under Axial Load
Example of Calculation for Deflection
Example of Installation
Installation is really important in selecting diameters of shafts. As a method of installation, typical instances are shown as follows. When installing 2 shafts parallel, install one shaft correctly at first, and then use it as a basis to adjust the parallelism of another. The distance between 2 shafts can be measured by micrometer or dial gauge. Please pay a lot of attention so that an error of shaft installation will greatly influence the service life of shafts.