This retractable star wheel from the Krones company is used in the filling of PET bottles. Here, different bearing products are used in several places, which - due to the environmental conditions in the plant - have to meet special requirements.
For each revolution of the decoupling star, for example, the bearings have to cover a distance of around 100mm, which - in terms of service life - corresponds to a total mileage of a full 2,900km. High accelerations and speeds of 170mm/s occur. As the retractable star wheel operates within the aseptic filler, high aseptic and hygienic requirements apply here to all bearings. In addition, only specially designed functional elements can cope with the constantly humid and chemically aggressive ambient conditions: humidity between 90 and 100%, temperatures up to 95°C, aggressive cleaning agents - a combination of low-concentration acids and alkalis, such as caustic soda with nitric acid, phosphoric acid and peracetic acid, as well as hot steam and water.
In the case of the Krones retractable star wheel, three iglidur J plain bearings are now found in the clamp carrier. The two upper gliding bearings form the fixed bearing; the lower gliding bearing, the torque arm, acts as a floating bearing. The Krones developers also rely on iglidur J flange bearings for the cam roller. They ensure that the plastic cam roller rolls cleanly and evenly on the cam track. The radial forces of the cam roller are transmitted reliably and with low friction to the clamp carrier. The rotary latch in turn is mounted in an iglidur X plastic bearing. With its rolling motion on the control cam, it ensures precise and positionally correct opening and closing of the clamp. Like the clamp carrier housing, the carriage is also equipped with soft stainless steel round guides.
If required, for example in emergency stop situations, the carriage must complete the switching movement within 180ms. This requires a reliable and stick-slip-free sliding movement, as the entire system is accelerated to 2.45g and reaches a speed of 0.44m/s over the short travel distance of 40mm.
The compression springs, which hold the clamp carriers on the pitch circle, are guided on one side by a iglidur J plastic sliding bush. They centre the compression springs to the clamp carrier and prevent mechanical damage to the highly polished round guide surface.