Page 10 of catalogue Ball screws of SKF Linearsysteme GmbH

Recommendations for assembly

Recommended assembly procedure
Ball Screws are precision Components and should be handled with care to avoid shocks. When stored out of the shipping crate they must lie on wooden or plastic vee blocks and should not be allowed to sag. Screw assemblies are shipped, wrapped in a heavy gauge plastic tube which protects them from foreign material and possible pollution. They should stay wrapped until they are used. Radial and moment loads Any radial or moment load on the nut will overload some of the contact surfaces, thus signicantly reducing life (g. 1). Alignment SKF linear guidance components should be used to ensure correct alignment and avoid non-axial loading. The parallelism of the screw shaft with the guiding devices must be checked. If external linear guidance proves impractical, we suggest mounting the nut on trunnions or gimbals and the screw shaft in self-aligning bearings. Mounting the screw in tension helps align it properly and eliminates buckling. Lubrication Good lubrication is essential for the proper functioning of the screw and for its long term reliability (1). Before shipping, the screw is coated with a protective uid that dries to a lm. This protective lm is not a lubricant. Depending on the selected lubricant, it may be necessary to remove this lm before applying the lubricant (there may be a risk of non-compatibility). If this operation is performed in a potentially polluted atmosphere it is highly recommended to proceed with a thorough cleaning of the assembly. Designing the screw shaft ends Generally speaking, when the ends of the screw shaft are specied by the customer’s engineering personnel, it is their responsability to check the strength of these ends. However, we offer in pages 36 to 39 of this catalogue, a choice of standard machined ends. As far as possible, we recommend their use. Whatever your choice may be, please keep in mind that no dimension on the shaft ends can exceed do (otherwise traces of the root of thread will appear or the shaft must be made by joining 2 pieces). A minimum shoulder should be sufcient to maintain the internal bearing. Operating temperature Screws made from standard steel (see page 9) and operating under normal loads can sustain temperatures in the range -20 °C to +110 °C. Between +110 °C and +130 °C, SKF must be notied so that it adapts the annealing procedure and checks that the application can be successful with a hardness below the standard minimum value (see page 9). Above +130 °C, steels adapted to the temperature of the application should be selected (100Cr6, special steel, etc…). Consult SKF for advice. Operating at high temperature will lower the hardness of the steel, alter the accuracy of the thread and may increase the oxidability of the materials or change lubricant properties.

g. 1

YES!

NO!

Axial loads

Radial loads

g. 2

(1) SKF can help you to define this value in relation with the actual conditions of service.

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