The beverage manufacturer's management asked the NSK experts to visit the site to get an idea of the bearing installation situation and make recommendations that would extend the service life of the bearings. This is because the automated labeling system, which places a flexible plastic sleeve around the bottles, is of great importance within the production process. The deep groove ball bearings therefore had to be replaced weekly to avoid unplanned downtime.

The operator of the sleeve system suspected that the powder layer on the inside of the sleeves was initially the cause of contamination and subsequently of the bearing failures. However, NSK's analysis revealed that it was not a case of contamination. Rather, the cause was of a completely different nature.

After examining six failed bearings as part of the AIP program ("Added Value Program"), the NSK specialists discovered that residual magnetism in the bearing was the reason for the regular failure. This magnetism acted like an eddy current brake. It was caused by the handling of the sleeve: the foil tube is opened and pulled over a device. The bearings are located on a guide unit that is held in position by magnets. This enables the rollers to guide the plastic film correctly.

The identification of residual magnetism as the cause was the result of a process that began with the disassembly and analysis of the failed bearings. All bearings were found to have a very shiny surface on the outer ring of the bearing, indicating faulty rotation and slippage of the bearing in its seat.

Residual magnetism and rough raceway surface
Another characteristic of the failed bearings was a slightly rough raceway surface, with scoring in some areas. Although this appearance is typical for bearings with a metal cage, it was more pronounced than one would expect. Apart from these defects, however, the bearings were in good general condition. There were few signs of contamination ingress or other major sources of damage on the surfaces of the rolling elements and running surfaces.

The NSK experts identified magnetism as the cause of the failure by analyzing the ambient conditions. The magnets are located in close proximity to the bearings on the guide unit. They caused a polarization between the balls and the cage on one side and the races on the other. This explains the unsteady bearing rotation that the operator had noticed, as well as the damage that had occurred. According to the results of the analysis, there was also a lack of lubricant, which then led to metallic contact between the rolling partners and thus to additional wear.

The plant operator then initially checked whether it was possible to arrange the magnets at a greater distance from the bearings. However, this proved to be unfeasible and he asked NSK for a proposal to improve the situation.

This proposal was to use a contactless sealed and lifetime-lubricated deep groove ball bearing with a plastic cage, which reduces the build-up of magnetism and polarities. These properties are offered by an NSK miniature deep groove ball bearing in size 627 with a plastic cage made of polyamide resin (T1X), increased internal clearance (C5) and a double-sided cover washer (ZZ) or contactless sealing washer (VV).

The solution was put into practice - and led to a considerable increase in bearing service life from one week to one year. This means an annual saving of €10,874 in costs for replacement bearings and assembly work. as