Concept comparison Which is more suitable: ball screw or sliding screw?

Related Vendors

August Steinmeyer GmbH & Co. KG

FAULHABER Drive Systems

Taiwan Machine Tool & Accessory Builders' Association (TMBA)

Wuxi InfiMotion Technology Co., Ltd.

Which component is used depends on the application area. Not only precision, dynamics, or efficiency are decisive—space requirements and cost factors also play a role.

Whether a ball screw or a sliding screw is the better choice for an application depends on several factors. A clear case is, for example, the feed axis of a machine tool. Enormous forces are at work here. Accordingly, particularly robust, reliable and durable components should be used for driving and positioning. These must ensure not only high force transmission but also high dynamics and precision over a long service life. "In many cases, a ball screw is advantageous in a machine tool," explains Wolfgang Klöblen, Head of Development at August Steinmeyer.

Advantages of ball screws

Ball screws are central elements in linear drives for machine and apparatus construction. They ensure play-free and dynamic implementation of rotational and linear movements. The components consist of a spindle, nut, deflection, and balls. The balls circulate in a return system between the thread of the nut and that of the spindle. "Force transmission occurs—as the name suggests—via rolling balls, resulting in a particularly high efficiency and high rigidity," Klöblen continues. Furthermore, the so-called rolling friction offers additional advantages such as low wear and energy consumption, minimal heat generation, and high positioning accuracy. Further applications where a ball screw is the preferred choice include automotive steering and actuators in aviation, according to the Head of Development.

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Advantages of sliding screws

A cost-effective alternative or complement to the ball screw is the sliding screw. It covers additional application areas. While ball screws offer significantly more leeway for higher loads, they also reach their structural limits in miniature form at a certain point when it comes to use in ultra-compact spaces. That's when sliding screws come into their own.

Sliding screws consist of only two components: a spindle and a nut. Unlike ball screws, the nut's thread is in direct contact with the spindle through surface contact. This results in sliding friction, which also leads to more heat generation, higher wear, and increased energy consumption. "Typical applications are found in device engineering, for example when small masses need to be moved evenly and with high accuracy," explains Detlef Rode, Head of Development at the Suhl location of the Steinmeyer Group. "Therefore, sliding screws are not necessarily suitable for continuous operation, but rather for occasional movements or single adjustments—for example, when optics in devices at the ophthalmologist need to remain in a certain position—then the inherent self-locking due to their design is advantageous."

More safety through self-locking

In safety-critical applications, the self-locking feature of sliding screws is even indispensable: it can prevent the spindle from continuing to rotate in the event of a power failure. Otherwise, unwanted lowering of the load can lead to damage to the system or machine and pose a hazard to the operator. "If a drive fails, the nut of a sliding screw immediately stops and holds its position, so no additional brake is required," Rode continues. Additionally, intentionally switching off the drive when holding a position can prevent heat from entering the system and avoid distortion. Sliding screws are also very robust and can withstand short-term overloads and shocks. Furthermore, they impress with their quiet operation.

At Feinmess Suhl GmbH (a company of the Steinmeyer Group), sliding screws are produced with variable nut designs, which offer the possibility of functional integration—for example, with a linear guide. This allows for a simple pin to be used as an anti-rotation mechanism for the nut. "Through the innovative spindle-nut system, a mirror on a construction laser, for instance, can be moved without additional linear guidance," explains Rode. The reduced number of components not only allows for a more compact design of the screw drives but also of the entire assembly. "This opens up numerous design possibilities and facilitates the implementation of customer-specific geometries and innovative applications."

Comparison of ball screw and sliding screw

Compared to ball screws, sliding screws are appealing due to their manageable acquisition costs, but they also offer a lower efficiency of typically 20 percent to 40 percent, or up to 80 percent in special cases without self-locking. Through various processes, such as lapping, friction between the nut and spindle can be minimized, thereby reducing wear. Nevertheless, the high efficiency of a ball screw exceeding 90 percent remains unmatched.

Materials and lubricants

In terms of material selection, sliding screws offer the advantage that they are not dependent on hardened steel. For example, bearing metals such as brass or bronze and certain plastics can be used for the nut. "A PEEK nut, for instance, can provide a self-lubricating effect, which is particularly advantageous in vacuum, UHV, or EUV environments," explains Rode. In addition to various materials and lubrication concepts, there are also different coatings to minimize friction and wear or eliminate the need for grease, as well as components made of stainless or non-magnetic steel for particularly sensitive medical devices such as MRIs or CTs.

But ball screws are also offered in special versions with alternative materials such as ceramics or plastic, as well as various types of wipers, lubricants, or preservatives, to meet the requirements even in extreme environments—from clean rooms to space. (dm)