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

Problem

• What was needed: iglidur polymer plain bearings made of the iglidur J material with TPU outer jacket as two-component roller
• Requirements: The systems run continuously; up to 66,000 bottles per hour are fed through in large breweries. A wear-resistant and durable bearing solution was therefore needed.
• Industry: Beverages sector, bottling plants
• Success for the customer: The iglidur J roller with TPU outer jacket has turned out to be the ideal solution, because it rotates smoothly and above all wear-free on the axis and ensures a smooth operation. Krones no longer has any complaints and the service life is significantly extended.

The clamping star wheels of Krones AG, Neutraubling, can easily grab glass and PET bottles up to a size difference of 20 mm. On a carousel, the bottles are transferred to subsequent machines at high speed.

Problem

Krones AG is one of the world's leading suppliers of beverage bottling and packaging technology. The company plans, develops and manufactures machines and complete plants for the fields of process, filling and packaging technology and intralogistics.
Krones AG strives to find the right solution for every requirement. Example: Inspection, filling and labelling of glass and PET bottles. Here, the so-called clamping star wheels prove their efficiency, especially in the field of inspection technology. On a carousel, the bottles are led past cameras at a high speed, which detects the condition and type of the individual bottle, as well as potential contamination. The bottles are then passed via a clamping star wheel to other areas, for example to the labelling.
 
A PEEK rotary axis passes between the individual clamping units of the clamping star wheel, which ensures the opening and closing of the clamps by means of a control bolt. The rollers in particular used to wear out quickly here, so that system downtimes and complaints from customers became more frequent.
 
This is problematic precisely because the clamping star wheel is highly stressed in the day-to-day operations of breweries. A clamping star wheel compensates for a diameter tolerance of 20 mm and therefore grips different bottle sizes without having to be changed. In the upper output range, up to 66,000 bottles are guided through per hour in large breweries, which equates to 66,000 opening and closing cycles per hour. In order to increase the life of the roller, therefore, numerous attempts have been carried out with a variety of materials. Krones initially contacted various plastics suppliers, but the desired results did not materialise.

Solution

The solution to the problems came from the use of two-component rollers in the spring clips. These were jointly developed by Krones and igus for the clamping star wheel, with the aim of significantly extending the service life. For the inside roller, the polymer material iglidur J was selected, which has proven itself for years in all industrial sectors of the packaging and bottling equipment. It is complemented by a TPU outer jacket.
 
Initial trials with rollers made of iglidur J material first found that the coefficient of friction from the inside outwards was not big enough to permanently provide for wear-free movements on the expensive PEEK cam. Only the new double-component model with a good coefficient of friction inside and a poor friction coefficient outside led to success. The iglidur J roller with TPU outer jacket has 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 a smooth operation. Krones  no longer has any complaints and the service life is significantly extended.
 
Before the two-component rollers were installed in Krones' first plants, they were tested for almost a year. While orange colour was selected for the TPE outer jacket initially, this is now delivered in the corporate colour blue. The blue colour matches the machines better and also has RoHS approval, which is why these rollers have been installed since summer 2009. The tribo-optimised plastic rollers are supplied in six different installation sizes. It has something to do with the size of the bottles and thus 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, which is customary in the American market, has to be correspondingly large for effective handling. Due to the size and heaviness of the bottle "only" 20,000 bottles can be channeled per hour via the multifunction star wheel in these bottling plants.

In each clamping unit - here for the inspection equipment - eight lubrication-free and maintenance-free iglidur rollers are installed.

The new double-component roller developed for Krones is an option made of iglidur plastic roller and TPU outer jacket. It ensures smooth and wear-free movements on the expensive PEEK rotation axis.

The roller is made of the tribo-optimised polymer material iglidur J, the outer jacket is made of TPU.