Linear Motion Control - 2010-07-13
Ever-increasing precision and ever-increasing speeds are key trends for linear drives. Cooling plays an important role in connection with this. NSK – the world’s largest manufacturer of ball screws – first developed a number of ball screw series with integrated cooling in the 1980s. These used a hollow-shaft through which coolant was routed. Now, the development team has gone step further, enabling NSK to launch high-speed ball screws with nut cooling.
The development work was prompted by clients from the machine tool and plastics machinery industries. They have to fulfil increasing precision requirements so that their machinery can manufacture products such as aviation components with extremely high dimensional accuracy or plastic components such as ultrathin mobile phone casings.
To achieve this kind of precision, the machine or tool must maintain a constant temperature as differences in temperature can cause changes in dimensions, warping or other adverse effects on quality. When the demands placed on them are as high as this, ball screws without cooling quickly reach their limits. However, a system that also keeps the nut cool enables an even more precise temperature to be maintained.
But this involves overcoming design challenges – which NSK has succeeded in doing. These challenges included solving the familiar problem that cooling causes the material to contract, affecting the nut’s preload. Following extensive trials, NSK’s development team identified a preload level that is not affected by cooling.
Comparisons show that the cooling performance of the new ball screws with nut cooling is at least as good as that of cooled hollow-shaft – and in many cases, considerably better. In particular, nut cooling is far more effective for high-speed, short-stroke applications.
This makes the new cooling system particularly suitable for machines that perform relatively small movements at high speed with short cycle times. Many machine tools that process automotive components fit this description, as do injection moulding machines which produce plastic components to high standards of dimensional accuracy.
The new series with nut cooling can be used to directly replace existing products with cooled shafts because the dimensions are identical. In addition to their technical merits, the new ball screws with nut cooling have a major commercial advantage: they are inexpensive to manufacture. This is because it is considerably easier to drill a through-hole in a nut than to produce a hollow-shaft ball screw. Users stand to benefit both from this advantage and from the fact that the new components can be easily integrated into existing cooling systems.
The cooled nut body can be supplied with shaft diameters of 40, 45, 50 and 63 mm. Depending on the screw shaft, models with leads of 16, 20, 25 and 30 mm are available.