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Glenn H Phelps, technical director at Metallized Carbon, has revealed how the company’s Metcar mechanical carbon materials are being put to use in the food processing industry.

The secret to continuously baking or processing cakes, pizza, chicken, beer and other foods and beverages is the mechanical carbon materials used in the food processing equipment, which produces these foods safely and cost effectively.

Metallized Carbon’s oil/grease-free, self-lubricating mechanical carbon materials are used in conveyors on processing lines, packaging lines, and food-handling canning machines.

Their use solves problems associated with typical oil/grease lubricants, which may contaminate food or cause equipment failure.

The Metcar materials are used for bearings on conveyors for continuous food baking ovens and on continuous roasting ovens.

Metcar sleeve, thrust, pillow block and flange bearings are used in horizontal revolving ovens, vertical rotating rack ovens, and tunnel ovens for baking cookies, cakes, pies, doughnuts, bagels, bread, pizzas, taco shells and pretzels.

Metcar bearings are also used in continuous roasters for roasting chicken, turkey, ham and coffee, as well as equipment where parts run submerged in liquids.

The Metcar materials come in various grades depending upon the use, and several have been accepted by the Food and Drug Administration (FDA) as ‘Generally Recognised as Safe’ (GRAS) for food-contact applications.

These grades contain no FDA-prohibited substances and are impervious to liquids.

Imperviousness is achieved by filling the base carbon-graphite material’s available porosity by vacuum/pressure impregnating the material with thermal setting resins, molten copper, molten bronze, or molten nickel chrome.

The impervious part surfaces can be easily washed or steam cleaned and there is no porosity within the material where bacteria could grow.

For contact with liquids with a pH above six, Metcar grades impregnated with copper and bronze are recommended.

For acidic foods with pH below six – for example, vinegar, fruit juice or wine – Metcar grades impregnated with thermal setting resins or nickel chrome are recommended.

The materials are available as either finished parts machined to customer specifications, or as oversized blanks that customers can machine themselves.

Sizes up to 18in in diameter are available.

At high temperatures (greater than 148C/300F), traditional oil/grease lubricants may volatilise or carbonise and lose their lubricating qualities.

This can cause high friction, high wear, galling and possibly seizing of metallic rubbing parts, resulting in costly maintenance and downtime.

Polymeric seals in oil/grease-lubricated bearings can fail by melting or carbonising and allow the oil/grease lubricant to flow out and contaminate the food.

Bearings manufactured from Metcar materials are self-lubricating, non-galling, dimensionally stable, uniform throughput, and have high compressive strength.

They are good candidates for bearings and other mechanical components because they provide long wear life when operating at elevated temperatures.

The most commonly used Metcar grades for high-temperature applications are Metcar grade 1515 (copper impregnated, carbon graphite), and Metcar grade 1126 (bronze impregnated, carbon graphite), all of which are appropriate to temperatures as high as 371C/700F.

Oil/grease-lubricated metal bearings normally should not be used when the food processing equipment parts must run submerged in low-viscosity beverages or liquefied foods, for example, potable water, milk, beer, soda, fruit juices, and pharmaceuticals.

This is because oil/grease lubricants can dissolve, wash away or contaminate the product being handled.

Metcar materials are chemically resistant to all liquids except for extremely strong oxidising acids and alkalis and can provide long wear life in submerged applications.

Metcar grade M-400 and M-106 (resin impregnated, carbon graphite) are most appropriate for this application.

Several Metcar grades primarily used in the food processing industry have met additional stringent testing allowing them to be used for pharmaceutical uses, as well as in public water supplies.

For example, Metcar grades M-101, M-400 and M-312 have passed the stringent tests required for US Pharmacopoeia Class VI Approval, compulsory for materials used in dental implants, implant tubing, prosthetic devices such as artificial heart valves, and drug containers.

Metcar grade M-400, M-106 and M-133 have also been tested and approved for equipment parts used in contact with the UK’s public water supply.

To meet this standard, the materials passed the tests associated with the UK’s Water Regulations Advisory Scheme.

Metcar grade M-702 is available for dry running in dry nitrogen or in vacuum.

This grade is used in mechanical seals where dry nitrogen is used as the barrier gas between two mechanical seals, and is approved for use in critical pharmaceutical mixers.

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