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Slides carry on withstanding kaolin slurry

A Hepcomotion product story
Edited by the Engineeringtalk editorial team May 4, 2001

Reliability is critical for machinery destined for remote regions, and that's the reason cited by Carpco for its continued choice of Hepco linear motion systems

Kaolin is now by far the largest single constituent of paper.

Generally this white china clay accounts for 60% of the raw materials involved in its manufacture, with wood pulp amounting to just 30%.

Typically paper mills seek kaolin that is a minimum of 85% free from contaminants such as iron oxides, titanium minerals and carbon.

The reasons are both economical and environmental.

Quite simply the purer the kaolin, the naturally whiter the resultant paper.

This means less processing is involved and importantly, less bleach needed to achieve the desired brightness.

Berkshire-based Carpco - part of Outokumpu Technology - has masterminded a superior method of releasing these colour-influencing impurities using superconducting magnetic separation.

Their helium-cooled, Cryofilter systems require substantially less power than competitor systems and are designed to be exceptionally reliable in less than ideal environmental conditions.

As a result they are widely used in areas of the world that are rich in kaolin deposits but relatively remote and undeveloped; the Brazilian Amazon jungle is a typical location.

Reliability is therefore critical and that is also the reason cited by Carpco for its continued choice of Hepco linear motion systems.

"We recently discovered an American customer had been operating his Cryofilter machine for six years with its original Hepco bearings!" confirmed Chief Design Engineer, Bob Peters.

"And this is in an environment that is harsh, to say the least.

Not only do the linear systems have to withstand the kaolin slurry but also frequent wash-down procedures." The Hepco Heavy Duty system most commonly used by Carpco comprises, an aluminium construction beam, matching slide and carriage assembly with four, 95mm vee-wheels.

It is supplied to Carpco ready-mounted in a steel cradle manufactured by a fabricator local to Hepco in Tiverton.

Low maintenance cap wipers that ensure a trouble-free working life irrespective of the prevailing conditions, enhance the performance of the linear system.

Central to the Cryofilter system is the patented reciprocating canister train containing two active matrix-containing canister sections, sandwiched between three magnetically balanced dummy chambers.

This is fed into and out of the superconducting magnet (5 Tesla) by two Hepco linear systems.

"Essentially we have a double filter system so whilst one active chamber is being processed, the other is outside the magnet, being washed," Bob Peters explained.

Every two minutes the slides reciprocate, travelling a distance of about 3m.

This results in an almost continuous operation and a processing capacity of 40 tonnes of kaolin per hour.

Bob Peters continues, "Apart from one or two services, our machines are generally required to work 24 hours per day, 365 days per year." Thrust load is limited to 2 tonnes to protect the precious magnets and typically the slide systems between them carry a weight of 1.5 tonnes; this is well below their rated capacity of 4 tonnes.

Recirculating systems were not even considered by Bob Peters when designing the linear motion assembly for the Cryofilter machines.

"Once the slurry gets into the balls they simply wouldn't last," he explains.

"The kaolin is OK when it's wet but when it dries, it hardens and that will ultimately cause a failure - something that is unacceptable given the nature of our work.

Our machines carry a two year warranty and we therefore only include components that can meet that specification." Although most of the Carpco machines in the field use a pneumatic ram to deliver the kaolin slurry to the magnet, recent Hepco developments have allowed the inclusion of a rack a pinion drive in later designs.

This option marries the guidance system with a 3.0 MOD rack and 20-tooth pinion, providing even more linear driving force for arduous heavier duty applications.

Higher load and drive requirements can be met by the belt driven Heavy Duty Driven Linear System (HDLS).

Carpco is also using Hepco Pacific SimplicityT bearings on its small laboratory systems.

These are ideally suited for this application as they continue to operate effectively in the most arduous of conditions and will not catastrophically fail.

"We have grown technically with Hepco," Bob Peters concludes "It's a good relationship.".

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