How plastic plain bearings replace conventional linear guides ...
... and economize the filling of PET bottles.Like many beverages manufacturers, Krones AG relies on modern block systems in the filling of PET bottles. These consist of few function modules and require less storing space compared to traditional system concepts. To prevent the individual system components from influencing each other and deteriorate the overall efficiency, the company from Neutraubling has made few design refinements, in which plastic plain bearings undertake a "supporting" role. They guarantee the required mechanical properties, fulfill all hygiene guidelines and additionally save a lot of money.
iglidur® J bearings show vibration dampening features and appeal among other things by their good chemical resistance and the low moisture absorption.
In the case of Krones' pull-back star, three iglidur® J products are used in the staple carrier. The two upper glide bushings thereby form the fixed bearing, the lower glide bushings, the torque arm, functions as floating bearing. Per rotation of the decoupling system, the bearing must travel a stretch of around 100 mm, which
– based on the service life – corresponds to an overall mileage of 2900 km. In the process accelerations up to 1.35 g and speeds of 170 mm/s are achieved. Krones' developers rely on iglidur® J flange bushings also for cam rollers. They guarantee the clean and uniform rolling of the plastic cam rollers on the cam track. The radial forces of the cam rollers are reliable and smoothly transferred to the staple carrier. The turning bolt in turn is mounted in an iglidur® X plastic bushing. With its rolling-off movement at the control cam, it provides for a precise and position-based opening and closing of the bracket. The carriage is also equipped with soft stainless steel round guides like the staple carrier housing. If required, for instance, in emergency stop situations the carriage should complete the switching movement within 180 m. This requires a reliable and stick-slip-free gliding movement, as the entire system accelerates at 2.45 g and achieves a speed of 0.44 m/s on the short stretch of 40 mm. The compression springs, which holds the staple carrier on the pitch circle, are guided on one side with an iglidur® J plastic bushing. They center the compression springs on the staple carrier and prevent mechanical damages of the highly polished round guide surface.
As the pull-back star works within the germ-free filler, high hygienic and aseptic conditions are called for. Only particularly devised function elements can furthermore cope with the constant moisture and chemically aggressive ambient conditions.
Air humidity between 90 and 100 percent.
Temperatures up to 95°C,
aggressive cleaners - a combination of diluted acids and alkalis, for instance caustic soda with nitric acid, phosphoric acid and peracetic acid, as well as
superheated steam and hot water.
The pull-back star from Krones consists of several components: Upper part of star (1), slidable staple carrier (2), decoupling unit (3), transfer (4) and base (5)