The ballscrew selection requires a good understanding of the application criteria that this vital machinery component needs to meet. There are multiple factors you must take into consideration, so here is a guide to selecting the correct ballscrew for your purposes before contacting ballscrews suppliers.
LOSTPED: Sizing and Selecting Ballscrews
The acronym LOSTPED is useful for sizing and selecting ballscrews for industrial applications. It stands for: Load, Orientation, Speed, Travel, Precision, Environment and Duty Cycle.
Load involves identifying the mass being moved as well as the forces required to move it via the machinery function.
Orientation is about the load bearing requirements, in particular the angle of support, be it horizontal, vertical or diagonal.
Speed is pretty self-explanatory and is concerned with the velocity and acceleration of the load being moved.
Travel involves the stroke length during the machinery’s load moving process.
Precision requires a calculation of the positional accuracy as well as the requisites for repeatability of the function and maintenance of accuracy.
Environment consists of any special considerations you must make for the likes of rough or harsh conditions the ballscrew will need to operate in.
Duty Cycle is concerned with the cycle rate of the ballscrew.
Pre-Loading Ballscrew Manufacture
The precision and repeatability can be greatly affected by the ball recirculation inside the ball nut. This is why most ballscrews suppliers provide ball nuts with a variety of ballscrew pre-load options. This enables you to reduce the axial movement as the ballscrews rotate around the screw, in some cases even eliminating it entirely. This part of the ballscrew design process produces superior repeatability.
Pre-loading involves either using a designed offset in the ballscrew’s raceway spiral which can alter the angle of ball engagement and force the balls into a pre-load condition. Another method involves intentionally over-sizing the balls inside the ball nut housing. Both methods help to reduce the backlash and friction occurring between the ballscrew and the ball nut.
Ballscrew Speed and Acceleration Requirements
There are two types of speed requirements to consider during the ballscrew sizing and selection process. These are the characteristic speed and the critical speed. The former will be determined by the bearing system’s limitations as it will only be able to withstand a certain operational velocity while maintaining optimal performance. Critical speed is the rotational speed level when a ‘screw whip’ can be created, which means the ballscrew is moving fast enough to start vibrating and oscillating excessively.
The characteristic speed of ballscrews will be influenced by the likes of the bearing’s operational limits as well as temperature and vibration levels. Critical speed can be controlled by increasing the screw diameter and using screw supports, as well as using appropriate end bearings.
If you require any industrial ballscrews manufactured by the world’s leading ballscrews manufacturers, then contact YB Components who are the UK’s leading ballscrews suppliers.