Why Don’t We Wear Shoes Made of Lead?
By Stefan Niermann
Why don’t we wear shoes made of lead? This may seem like a silly question but bear with us while we get to our main point about equipment design. The fact is that it takes energy to move mass. The more mass is involved, the more energy it takes to move that mass. We don’t wear shoes made of lead because it would take an excess of muscle power to move our legs with the additional weight.
A similar principle applies to machine and equipment design, as well as in automation. Just as we would not place extra weight on our feet with lead shoes, engineers also try to avoid designing their applications with excess weight. Every excess gram of weight either slows movement down or increases energy requirements.
In the textile industry, for example, linear bearings must be moved at speeds of over 20m/s and in some cases at a frequency of over 100Hz, with accelerations of more than 6m/s2. These speeds and accelerations can only be done with a minimum of dead weight.
How can you make a design lighter? The easiest way is by strategic material selection. Notably, aluminum is two and a half times lighter than steel, while plastic is five times lighter than steel.
Another advantage of plastic is that if used in plastic sliders in linear systems, it can prevent dents or marks on its aluminum rails. This advantage can be achieved by making plastic sliders with a large plastic surface area. With a larger surface area, the weight of the slider is distributed evenly, preventing an excess of pressure in any one area. This same effect is applied in the build of snowshoes.
For technical reasons, recirculating ball bearing guides cannot be moved continuously on aluminium rails. Under normal loading conditions, the contact point of individual balls would leave dents in the surface of the rail and damage the ball guide.
How important is it to you to keep weight reduced in your application? We would be happy to hear from you and answer any questions you may have. Contact us at www.igus.ca via Livechat or give us a call at 1-800-965-2496.
