Solving real-life challenges in the machine tool industry is one of NSK’s primary aims for this fast-moving marketplace. At the EMO 2017 exhibition in Hanover, Germany, the company displayed ball screws with nut cooling particularly suited to high-speed linear drive applications as they help dissipate the inevitable heat that is generated. As a result, the ball screws offer improved cooling performance and better economy in comparison with traditional solutions such as hollow shaft spindles.
NSK’s high-speed ball screws with nut cooling create an important pre-condition for machining where high dimensional accuracy is required as minimal temperature-related dimensional changes occur. The design meets ever-increasing accuracy requirements from manufacturing companies, particularly those machining components such as aero-engine parts, or moulds that produce mobile phone cases with extremely thin walls.
Keeping a constant temperature in the machine is one of the prerequisites for this precision, as temperature variations can lead to thermal expansion and result in dimensional changes in the machined product or other forms of quality loss.
In developing the ball screws, a number of challenges had to be overcome. For instance, NSK succeeded in resolving the problem of the material contracting as a result of cooling, which influenced the preload of the nut. After a comprehensive test programme, NSK developed a cooling system that was compatible with preload levels, so they were not affected by cooling. The design is particularly effective in high-speed applications with short strokes, such as machines used to produce automotive components, as well as injection moulding machines, where stringent dimensional accuracy requirements must combine with highly dynamic cycles.
In many cases, the ball screws with nut cooling can be installed as a one-to-one replacement for an existing series with cooled spindles. As well as the technical advantages, there are economic benefits: they cost less to manufacture as it’s significantly easier to drill a hole in a nut than manufacture a spindle with a hollow shaft.
The cooled nuts can be supplied for 40, 45, 50 and 63 mm shaft diameters. Depending on the spindle shaft, variants with 16, 20, 25 and 30 mm pitch are available.