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machine building
ball screws typically operate at a minimum of 90 per cent efficiency, plus they run at cooler temperatures, and they produce a considerably smoother movement. due to recirculating balls supporting the load,
ball screws have a higher load capacity than lead screws of a similar size. ball screws are also more versatile than lead
screws. They are available in higher accuracy grades for greater positional accuracy, and they can be adjusted to increase/decrease preload. but there are some drawbacks. Obviously cost is
one, as outlined above, which is further increased by the need for braking mechanisms to eliminate the risk of back driving. back driving occurs when the motor shuts off and the ball screw free-falls as a result. brakes must be fitted as a safety precaution in this case. This is particularly pertinent if the load is to be carried vertically. With moving balls within the mechanism, it is
likely to be noisier than a lead screw, and will also require regular lubrication to ensure the balls move freely. Furthermore, the overall size of ball screw device is larger than a comparable lead screw due to the need for the balls to be recirculated.
What to Use Where: the rUle of thUMb
So, which should it be – ball screw or lead screw? Whilst a definitive answer isn’t practical – each
application will have other factors and trade-offs that may need to be taken into account – generally speaking, lead screws are more suitable for transfer applications for which speed, accuracy, precision and rigidity are not as critical. That is because most lead screws are not well suited to high throughput, high speed applications or those with continuous or long cycle times. Typically, you will find lead screws in use in fluid handling, data storage applications and life science equipment. ball screws, on the other hand, are mostly better
for high precision applications where accuracy and control are critical. They are also a good option for high load applications and for where thrust force is required to move those loads across a distance in a smooth motion, whilst maintaining speed. examples of applications include 3d printers and automobile and aeroplane manufacturing. a recent real-world example of ball screws in
action can be found at Pernamatic engineering. matara supplied them with an XY linear system featuring compact linear rails and guides, and precision ballscrews, which is now in use in a cnc corner Transfer machine for uPVc double glazed Windows. The SFnhR precision 20mm ballscrews, machined in-house at matara, are highly efficient and have a high load capacity at fast speeds, making them ideal for this application where each uPVc window frame has the weld automatically cleaned from it in just 80 seconds. So, when deciding on whether a ball screw or
lead screw is right for your machine, whilst they both perform the same task of converting rotational motion into linear movement, the way in which they realise this and type of end result you achieve are markedly different.
Matara UK
www.matara.com
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