Better bearings last longer in hot spots

Tom Shelley reports on bearings aimed at meeting the requirements of challenging environments, particularly in the food and beverage industries

Bearings have been developed to meet the requirements of environments that involve abrasive materials, corrosive conditions and high temperatures, doubling and in some cases quadrupling useful working lives.

The food and beverage industries often offer particularly difficult challenges, and to meet them, SKF has developed special solutions as well as extending the ranges of standard products that it offers for such applications.

Food and beverage sector expert David Oliver did admit that these, "Tend to be more expensive products" but added that, "You have to look at lifetime costs" during the course of the recent launch of SKF's UK "Solution Factory" at Luton.

A particularly difficult application cited by Oliver was a producer of wafers for confectionary, with 13 ovens, each of which had 72 plates with a wheel on each corner and a top roller for baking tongs. Oven temperature was 230°C and every 16 weeks, all the bearings had to be taken out and relubricated with food grade grease. This took one to three days. The solution was to turn to graphite sacrificial bearing cages which slowly abraded to provide lubricant, extending the period between maintenance operations to a year, while the temperature could be raised by 10°C to 15°C. This led onto the idea of SKF making complete wheels with integral bearings, allowing the graphite cages to be made much larger, extending lifetimes to four years, and allowing temperatures to be raised still further. The solution is now offered generally and is rated at up to 350°C and in large sizes for furnaces.

The company produces a whole range of food industry suited bearings for use at more conventional temperatures, with bearings made of stainless steel or zinc coated with glass reinforced polyester or polyamide housings and elaborate seals, using a design originally developed for agricultural applications. Sizes are currently up to 40mm, to be expanded up to 50mm in February 2011. Housings are to be offered in stainless and zinc plated steel in addition to plastics. All bearings conform to ISO 22000,

Lubrication is always a problem in food industry applications because of the need for chemical wash downs, and one solution in the past has often been to apply excessive greasing to purge water. As an alternative, the company currently offers is what it calls, "Solid oil", with a synthetic oil lubricant retained in a polymer matrix, which completely fills the internal space in a bearing and encapsulates the cage and rolling elements. No seals are required and the material is resistant to chemicals, but not organic solvents. We noticed that at room temperature, the samples we tried showed slightly increased friction, particularly on startup, so its adoption may require use of slightly larger motors. Nonetheless, as well as the food industry, its adoption has found favour in applications in paper making, pneumatically operated couplings, overhead cranes and hoists, and chemical mixers. In low temperature applications, such as on ski lifts, starting torque is lower than for conventional greases. Minimum startup temperature is -40°C and maximum operating temperature is 85°C although it can go to 95°C intermittently and bearings can be heated to 100°C for mounting.

The "Solution Factories" embrace all possible applications for bearings, including the food and beverage industries, and include the offering of design and maintenance consultancy, condition monitoring and training.

Pointers

* Particular bearings have been developed for the food and beverage industries, with new additional products to become available in February 2011.

* Sacrificial graphite cages allow bearings to be routinely used at up to 350°C.

* "Solid oil" bearings are available for food industry and a wide range of other applications

* Support of all kinds is being centralised in "Solution Factories"

Author
Tom Shelley

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