Huge headstock glides with grace and safety

Cumberland Europe has succeeded in making a 2.5 tonne piece of industrial machinery glide like a ballerina across the stage, by using precision guide rails from Hoerbiger-Origa.

Cumberland Europe has succeeded in making a 2.5 tonne piece of industrial machinery glide like a ballerina across the stage, by using precision guide rails from Hoerbiger-Origa.

Cumberland Europe is an OEM based in Gloucestershire specialising in building granulators for reclaiming waste plastic, as well as other related equipment, for plastic processing companies.

It is a subsidiary company of the leading US ancillary equipment producer ACS (AEC-Cumberland-Sterling) Group.

Materials wastage is an unavoidable part of manufacturing plastic items, but fortunately the waste can be instantly recycled by using in-line granulators.

Cumberland has a number of standard designs, but for many of its customers these are adapted to suit specific requirements.

"Most of our machines have only a single infeed," explains Roger Cochrane the design engineer who lead the project, "but for a manufacturer of margarine tubs we needed to develop a triple infeed.

Their throughput is so high and so fast that they have to handle scrap with military efficiency!".

With thermoforming, the process used to make the tubs, there are three kinds of scrap: at start up all throughput is scrapped until a consistent quality product is produced; during production there is 'skeletal' waste, ie the trimmings of the sheet stock from which arrays of tubs are formed; and sub-standard production, which has to be scrapped.

"As the design evolved, it became apparent that forming the three infeeds into a single headpiece was the best way to proceed.

This stands over the actual granulator, so needs to be moveable to allow access for maintenance, granulator blade sharpening etc.

"As the design stage neared completion we realised that the headpiece would weigh about 2.5 tonnes, so we had to think carefully about how we would move it, and sought specialist advice from Hoerbiger-Origa".

After some calculations Hoerbiger-Origa recommended the use of its GDLF-D heavy duty roller guides.

These are fitted with new patented profiled rollers, designed to create a precision level of guidance, superb dynamic characteristics and extend the life expectancy.

The race roller is guided axially on race wires mounted in a groove to keep it from running laterally against the cassette and creating extra friction.

This means less wear, less noise, easier run.

The race rollers are arranged crosswise in the cassette to ensure an even support and equal load carrying capacity in all directions.

The race rollers rest on needle bearings for instant dynamic reaction (cutting out stick-slip) low noise and smooth performance at speeds up to 10m/s.

The raceway design is equally innovative, being formed by pressing of a tough spring steel for low structural weight and high load rating.

Trials at Cumberland's plant demonstrated that the massive load could be moved effortlessly, but this in itself created several new potential problems, as Cochrane recalls: "Having 2.5 tonnes moving freely could be a Health and Safety nightmare, so we had to be certain of our design.

We considered massive end stops and impregnable guarding, but the space consumption was prohibitive.

We looked at an automated servo drive, but this would have required arrays of sensors and interlock, any of which could fail.

Finally we settled on that most adaptable of control systems, the human brain." The actual drive mechanism is a handwheel operated rack and pinion and there is so little friction in the load bearing guide rails that a moment's backpressure by the operator will stop the headpiece instantly.

"By retaining human control we have developed a system that can sense any danger and react instantly.

We are convinced that we have arrived at the best possible design".

Supplying the guide rail was not Hoerbiger-Origa's only involvement with the project.

It also provided compact pneumatic cylinders to control the nip pressure for the feed rollers on the start-up and skeletal infeeds.

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