Easy-off bearings cut maintenance times and intervals

Sapphire Energy Recovery operates high-throughput shredding machines in four major conurbations throughout the UK, processing end-of-life car and van tyres by converting them into chips that are then used as an alternative to coal in cement manufacture.

After shredding, the tyre chips are graded for size by a classifier with 36 sets of bearings. The classifier shafts' set-screw style bearings were being damaged by both the fine metal wires in the tyres and the water used for cooling. As a result they had a life, typically, of less than six months.

Changing the classifier bearings could then take anything up to two hours per bearing, depending on the problems encountered and the skill of the operators. Corrosion sometimes meant that the bearings needed to be loosened by heat, for example, and in some cases the whole shaft had to be replaced.

Sapphire is one of the UK's leading end-of-life car and van tyre processors, and its processing centres often operate for 24 hours a day. Addressing the planned and emergency maintenance requirements of these machines became a priority for Sapphire's Reliability Manager Andy Booth, and he called in the specialist Dodge distributor, Bearing Transmission and Pneumatics, to discuss the problem.

Maintenance-friendly bearings

Bearing Transmission and Pneumatics suggested that Sapphire try a type of ball bearing from Baldor's range called the Dodge Grip Tight. This adapter-style bearing has a mechanical maintenance feature that loosens it by simply turning a nut. The action automatically pulls the bearing off, thereby avoiding any need for forcible removal or expansion heating; this, in turn, eliminates fretting corrosion and prevents shaft damage.

These bearings were a little more expensive than the set screw type that Sapphire had been using, but demonstrations - and examples of field experience in the most hostile conditions - convinced Andy Booth that the easy-off mechanism would make changeovers a predictable operation.

Sapphire purchased some Grip Tight bearings and installed them as and when the previous bearings failed. Although predictable maintenance was Andy Booth's major requirement, it soon became obvious that the bearings offered a superior life too. The Grip Tight's built-in flinger seal is protecting the bearings in the hostile environment to such as en extent that they are lasting typically twice as long as the previous set screw types.

Bearing changes in 15 minutes

Now, following the use of Grip Tight over a period of some 24 months, and a number of maintenance changeovers, Andy Booth knows that the Grip Tight justifies its reputation: changeovers are predictable and take only 15 minutes maximum following production operator training, including the time required to remove and refit machine casings. Moreover, there has been no shaft damage to date.

Andy Booth comments; "The aggressive nature of tyre shredding meant that repairing these machines was taking up far too much of our time, and reducing our productivity. Grip Tight bearings have given us back predictability of maintenance, with the welcome bonus of much longer life, protecting some of our company's most crucial assets. Our operational team now has the time to be more proactive, focusing its major efforts on preventive maintenance rather than breakdown maintenance."

Edward Fielding of Bearing Transmission and Pneumatics states: "Our work means that we tend to see a lot of bearing failures, and we have come to regard the Dodge Grip Tight as a genuine problem solver. Although the major requirement was to simplify changeover, this bearing also manages to survive much longer in very hostile operating conditions."