Press Release

NSK Develops Nut Cooling Ball Screw

Designed to Accommodate the Increasing Speed and Precision of Machine Tools

Tokyo, Japan, March 5, 2010 - NSK Ltd. (NSK; Headquarters: Tokyo, Japan; President and CEO: Norio Otsuka) announced today that it has developed a nut cooling ball screw that has a cooling mechanism in the nut, a feature that was designed to accommodate the increasing speed and precision of machine tools. NSK will launch this product in May 2010 and plans to expand the lineup in the future. It expects annual sales to reach 1 billion yen by 2012.

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Development background

NSK started marketing hollow shaft ball screws, which are cooled by a coolant flowing through the screws' hollow shafts, in the 1980s. This sort of ball screw has accommodated the development of higher speed and greater precision in machine tools. In recent years, the feeding speed of objects to process on machine tools has been increased even further in order to boost productivity, especially in the processing of automotive and aircraft parts. Also, the precision of machine tools for die machining and microfabrication has improved. Consequentially, there is demand to reduce temperature variation in the entire machine, not just the screw shaft, in order to prevent adverse effects on precision. At the same time, demand for large products such as windmill equipment and rolling stock has increased greatly, and the speed of large machine tools has increased as a result.

The need has therefore increased for a new cooling system that is inexpensive, simple, compact, and that improves the cooling function in order to facilitate the increasing speed and precision of machine tools.

Product features

Preloaded form in which the preload does not increase even if the nut is cooled (patent pending)
When a nut is cooled, its constriction may increase the preload, which in turn will have a number of consequences such as causing the ball screw's preloaded torque to increase and its service life to decrease. For this new product, NSK analyzed the preload alteration and used a preloaded form in which the preload does not increase even if the nut is cooled.
Inexpensive, simple, compact nut cooling mechanism
NSK designed a new cooling mechanism in which coolant flows though a through-hole in the nut. This new design enables costs to be reduced greatly compared to drilling a hollow screw shaft. The new product can replace existing products, since the outer diameters of the conventional product and the nut are the same. Moreover, coolant can be supplied simply by attaching piping to the lubricant feed and discharge holes in the outer periphery of the nut flange.
Equivalent or greater cooling capacity as conventional hollow shaft ball screws (patent pending)
NSK optimized the cooling mechanism inside the nut by analyzing the cooling capacity and performing trial evaluations. In this way the company has achieved a cooling capacity for the screw shafts — which are directly linked to feeding speed precision in machine tools — equivalent or greater than that of conventional hollow shaft ball screws. If the nut has a short drive range, the new product will provide even greater cooling capacity than hollow shaft ball screws, and so it is ideal for automotive part and other machine tools that frequently run through continuous processing with high-speed short-stroke feeding.
Table insulated from thermal effects
The new product can reduce the effects on the table of heat generated by the ball screw, since the nut that is in contact with the table is cooled directly. This will contribute to even more precise machining.