They have the same basic characteristics as conventional screws; the main difference between recirculating ball screws and conventional screws lies in the way movement is transformed. With conventional screws, this transformation is determined by two surfaces (the screw and nut thread surfaces) sliding against each other. In recirculating ball screws, on the other hand, transformation of movement is determined by the rolling of balls between the two surfaces. This creates a rolling friction that is much, much lower than sliding friction.
This is why recirculating ball screws have numerous advantages compared to conventional screws:
- Firstly, they have extremely high efficiency (generally higher than 90%), making them approximately three times more efficient than conventional screws. Consequently, much less power is dissipated as heat, with evident advantages as far as applied motor and energy savings are concerned.
- A long working life due to excellent resistance to wear.
- High-speed performance capabilities.
- High positioning precision as a result of being able to eliminate play.
Since they are easily installed and require no maintenance, recirculating ball screws have been successfully applied in a wide range of industries.
The recirculating ball screw, both in its ground and rolled versions, is a component for which demand is constantly increasing, with clients requiring fast delivery times and competitive prices.
In order to satisfy these needs, Officina Meccanica B.B. has set up a production strategy that aims to meet every customer’s needs. As far as screws are concerned, our warehouse is always well stocked with both finished and semi-finished products of different diameter and length in order to guarantee fast delivery times, while, in terms of nuts, B.B. is mainly involved in the production of the DIN 69051/5 type to ensure interchangeability and virtually immediate availability.
Right-hand helixes are standard; left-hand helixes can be machined on request.
Whenever customers’ requirements depart from standardisation parameters, Officina Meccanica B.B. is obviously ready to provide full support in designing and appropriately sizing new, tailor-made products.
“GOTHIC ARCH” PROFILE
Recirculating ball screws manifest complex interactions between the balls and the nut rolling track and between the balls and the screw rolling track.
Following in-depth experimentation, B.B. has identified a particular rolling track profile, the so-called “gothic arch”, which guarantees major advantages both in terms of the Hertzian pressure occurring between ball and screw tracks as well as axial load capacity.
This profile is made up of two symmetrical arches which have a bend radius that is larger than that of the balls themselves. These arches meet on the axis of symmetry, forming a point; the two arches are related to the ball radius in such a way as to produce an optimum contact angle.
This solution definitively prevents ball slippage or wedging.
With the internal recirculation system the whole rolling track of the nut is divided into several circuits in which the balls run in a closed cycle; at the end of each revolution the balls are brought back to their original position by a deviating return piece.
In order to obtain larger load capacities the number of circuits must be increased according to the information in the technical characteristics table.
For long-pitch nuts there is a system where all the balls run along the entire length of the rolling track, exiting one end and re-entering the other via special deflectors.