Ball screws have become indispensable in many industrial environments. They are also called rolling screw drives with balls or rolling elements. Amongst other things, they convert rotational movements into precise linear movements or vice versa and are therefore often used as drive elements for linear movements wherein the screw is usually driven while the nut is connected to the part to be moved.
HOW DO BALL SCREWS WORK?
In a ball screw, the balls inside the nut ensure particularly low-friction movement by transmitting the force evenly between the screw and the nut. These balls move between the screw and the ball nut. In the standard version, the ball screw is not preloaded, thus combining precision with a long service life. The precision can be further increased by preloading the nut on the screw, maximizing precision and travel accuracy. Once the balls reach the end of the nut, they are returned to the other end via a recirculation system. The recirculation ensures smooth movement of the nut even at high load capacities, because the load is distributed over a large number of balls.
These properties make ball screws the perfect candidates for precise linear drive movements. With high repeat accuracy, they ensure precise and fast positioning. Ball screws can also be used in systems with multiple screw drives, where the power transmission and motion conversion of two parallel systems are realised together.
Ball screws are also increasingly used to act as a substitute for hydraulic systems, such as servo-assisted steering, presses, or injection moulding machines.
The biggest difference between these two screw drives is probably their type of friction: In ball screws, rolling friction prevails, whereas classic trapezoidal screw drives operate mainly with dynamic friction. This results in several advantages when using ball screws:
Ball screws have significantly lower friction than trapezoidal screws, therefore they are more efficient and require less energy.
While conventional trapezoidal screws must overcome a breakaway torque during start-up, this is not the case for ball screws: The stick-slip phenomenon does not come into play here, resulting in a reduction in drive torque by about 65 percent. Ball screws do not have self-retainment, thus without external force, there is no movement of the ball nut possible.
Ball screws have a significantly greater potential speed of movement and are therefore ideally suited for dynamic operations with high precision.
Another difference is the adjustability of the thrust movement: Ball screws are significantly more precise than trapezoidal screw drives and can be adjusted without backlash or with preload to further increase the repeat accuracy. This makes ball screws particularly suitable for drive technology, CNC technology as well as for modern robotics projects, where they make possible high feed rates with maximum precision under a wide range of loads.
Our standard product range includes rolled ball screws. On top of that, we deliver ground or whirled ball screws. During the rolling process, the thread grooves are rolled in with a cold working method. This leads to high material strength and surface quality. The gothic pointed profi le with a contact angle of 45° and an optimised osculation guarantees for ideal operating characteristics and high load capacities. This also allows for high effi ciency. From raw material tailored to our specifi cations, to thread rolling and inductive hardening, to the fi nal fi nishing, NEFF’s manufacturing process ensures a consistent high quality of our ball screws. The ball screws in stock range from Ø12 to Ø80 with pitches up to 60 mm. Thread profi les with up to six threads guarantee high load ratings. guaranteed. The standard pitch variation corresponds to tolerance grade T7 (52 µm/300 mm). Thanks to the seamless process chain in the spindle production, we are able to deliver spindles with an accuracy of tolerance grade T3 (12 µm/300 mm).
The wide range of flanged ball nuts allows for a variaty of different connectivity options for diverse applications. The flanged ball nuts are available from stock either with a flattened flange for limited mounting space according to DIN 69051 or as type KGF-N in accordance with the widespread NEFF standard.
A flanged ball nut unit preloaded without clearance consists of a flanged nut and a cylindrical nut. It is available either in accordance with the NEFF standard or the DIN standard. The preload is at the maximum 5% of the dynamic load rating Cdyn. If the preloaded is more than 2% we recommend the pitch accuracy T5. This type is characterised by a very high stiffness.
NEFF cylindrical ball nuts are highly suited for the use in housing bores because of the compact construction and the integrated feather key groove. The design of the series KGM-N in accordance with the NEFF standard is particularly robust.
Cylindrical ball nut units preloaded without clearance consist of two cylindrical ball nuts. These units are either available in accordance with the NEFF standard or with the DIN standard. The preload is at the maximum 5% of the dynamic load rating Cdyn. If the preloading is more than 2% we recommend the pitch accuracy T5. This type is characerised by a very high stiffness.
Thanks to the screw-in thread, the ball nut can be axially fixed. On top of that, the KGM-E series can be used for applications with a piston tube connection, for example as a drive element for electric cylinders.
