Wear-resistant plastic rollers in clamping star wheels double service life

Krones AG is one of the world's leading suppliers of beverage filling and packaging technology. The company plans, develops and manufactures machines and complete lines for the areas of process, filling and packaging technology as well as material handling.
Krones AG endeavours to find the right solution for every requirement. Example: Inspection, filling and labelling technology for glass and PET bottles. Here, so-called clamping stars prove their efficiency especially in the field of inspection technology. On a carousel, the bottles are guided past cameras at high speed, which recognise the condition and type of the individual bottle as well as possible contamination. The bottles are then passed on to other areas, such as labelling, via a clamping star.

A PEEK-rotary axis passes between the individual staple packs of the staple star, which - controlled by a control pin - ensures that the staples are opened and closed. The rollers in particular used to wear out quickly, resulting in frequent system downtimes and complaints from customers.

This is particularly problematic as the clamp star is subjected to high loads in the day-to-day operation of breweries. A clamping star compensates for a diameter tolerance of 20 mm and therefore grips different bottle sizes without having to be changed. In the upper performance range, up to 66,000 bottles per hour are passed through in large breweries, which means that 66,000 opening and closing processes take place every hour. In order to increase the service life of the rollers, numerous tests were therefore carried out with a range of materials. Krones initially contacted various plastic suppliers, but the desired results were not achieved.

The solution to the problem was the use of two-component rollers in the spring clips. These were developed jointly by Krones and igus® for the staple star, with the aim of significantly extending the downtime. The polymer material iglidur® J, which has proven itself for years in all industrial areas of packaging and filling technology, was selected for the inner roller. It is supplemented by a TPU-outer jacket.

Initial tests with rollers made of iglidur® J material initially showed that the friction coefficient difference from the inside to the outside was not large enough to ensure permanent wear-free movements on the expensive PEEK-rotary axis. Only the new two-component variant with a good coefficient of friction on the inside and a poor coefficient of friction on the outside led to the result. The iglidur® J roller with TPU outer jacket turned out to be the ideal solution for the requirements on site, because it rotates smoothly and above all wear-free on the axis and ensures smooth operation. Krones no longer has any complaints and the service life has been significantly extended.

Before the two-component rollers were installed in the first Krones lines, they were tested for almost a year. While the colour orange was initially chosen for the TPU-outer jacket, it is now supplied in the company colour blue. The blue colour matches the machines better and also has RoHS approval, which is why these rollers have now been installed since summer 2009. The tribo-optimised plastic rollers are supplied in six different sizes. This has something to do with the size of the bottles and therefore the opening angle of the clamps. The rollers are available for bottle diameters from 50 mm to 110 mm. The opening angle for a 3 litre Coke bottle, for example, which is common on the American market, must be correspondingly large for effective handling. Due to the size and weight of the bottles, "only" 20,000 bottles per hour can be channelled over the multifunctional star wheel in these bottling lines.