Where metal ball bearings reach their limits: an opportunity for the polymer version?
Daniel Chen | March 4, 2021
Metal ball bearings have become indispensable in mechanical and plant engineering. However, there are sectors where conventional metal ball bearings reach their limits, such as the food industry and medical technology. There the factor of hygiene plays a major role, whereby lubricants become a no-go. This is where plastic ball bearings come into the limelight, which the Cologne-based motion plastics specialist igus manufactures with the aid of its high-performance polymers. They are absolutely lubrication-free and pose no hygiene risk.
The evolution of the ball bearing
Since 1869, when the Frenchman Jules Suriray invented the ball bearing, the requirements that a rolling bearing should meet have been clearly defined. In the course of time, however, these changed constantly. The bearings were primarily intended to fix axes and shafts, absorb radial or axial loads and to enable low-friction rotation of a mounted component, for example a wheel. In the early days, wheels were based on sliding friction, which means that the wheel ran right on the shaft. This type of friction resulted in high coefficient of friction, strong heat development and even wear. From then on, the principle of rolling friction prevailed, causing the wheel to move by means of the ball bearing, consisting of a fixed metal inner ring, a metal outer ring and rolling elements in the form of lubricated metal balls located in the space between them. The metal balls were evenly separated by a cage.
If you look inside engines or turbines, ball bearings are to be found everywhere in mechanical engineering and have become indispensable. However, the metal ball bearing is not considered the primary solution, as ball bearings today have to meet additional requirements in industrial applications. In many industries the lubrication of ball bearings is considered an enormous hygiene risk, so that operators of packaging plant or users of medical technology have to resort to alternatives that offer a technical advantage. With a “cost-down and tech-up promise”, igus has been ensuring great success within the industry for years.
Would you like to know in which applications xiros ball bearings made of polymer are used? Then just take a look here:
Technical advantages of xiros polymer ball bearings
Besides the fact that xiros polymer ball bearings are corrosion-free and heat-resistant, they can also be used in chemical environments. The maintenance costs of plant and machines can be saved and the dependability can be increased. The polymer ball bearings are characterised by a low-friction dry operation, which means that xiros ball bearings do not require even a drop of lubricant. This allows the rolling resistance to be reduced to a minimum. The reason: the balls do not have to overcome the resistance of the lubricant so that they can start with a low breakaway torque.
“In order to guarantee nearly comparable running characteristics, metal ball bearings require more attention from the user. Without time-consuming lubrication, which also causes material costs, the bearings will rust, deform due to the high frictional forces and, in the worst case, cause plant failure. Engineers avoid these problems when they use polymer ball bearings.”
But polymer ball bearings can also reach their limits. For example, speeds beyond 5,000 revolutions per minute can only be achieved in the short term, as polymers deform more quickly than metals at higher speeds and the resulting heat generation. Bearings made of metal, on the other hand, have the edge when it comes to higher speeds and the absorption of higher loads. Here, the metallic version scores due to a combination of hardness and elasticity.
135 trillion test movements in the in-house test laboratory
Yes, metal ball bearings are ahead in these disciplines, but the evolution of ball bearing technology allows a new shuffling of the cards. What exactly is meant by this? igus has always carried out basic research and operates a test laboratory with around 135 trillion test cycles annually. In addition to investigations of coefficient of friction and wear rates, corrosion behaviour is also on the agenda. In a corrosion test, a metallic 2-hole flange bearing and its polymer version from igus faced each other.
You can find out how the two ball bearings performed in an 80°C hot sea salt water bath here: