Mounted Bearings: A Key Ingredient in Food Processing Equipment - Part 2

In the previous installment of this technical article, we explored material options for mounted bearings used in food processing applications. Here we will examine sealing solutions and lubrication considerations. The following is Part 2 of a two-part post. You can read Part 1 here.

Sealing
Contamination is a leading cause of premature bearing failure. Sealed bearings should always be used in food processing applications to ensure trouble-free equipment operation. The typical bearing seal configuration consists of nitrile rubber, bonded to a steel insert, with a flexible lip that contacts the circumference of the inner ring. A stamped steel shield is often affixed to the outer side of the seal which protects the rubber from damage. While these contact seals increase rotational torque, they are very effective at preventing the ingress of foreign debris and retaining lubricant in the bearing. Specially designed double and triple lip seals are also available. While these styles of seals increase torque significantly, this disadvantage is seen as a design trade-off to improve bearing life in severely contaminated environments.

Lubrication
Lubricant selection is critical to bearing life and performance, yet it is often overlooked by designers and engineers. Bearing life depends on “proper” lubrication, meaning both type and amount. Operating temperature is the primary consideration when selecting a lubricant. Temperature directly affects the viscosity of the lubricant base oil, which in turn impacts the lubricant’s ability to support application loads. Food processing applications are often subjected to temperature extremes and caustic wash-downs, which can degrade the quality of a lubricant significantly. Manufacturers of food processing equipment are often required to use a special class of lubricants, referred to as food-grade lubricants. These lubricants are classified into three categories, based on the probability of contact with food products. While currently under the purview of the NSF, the USDA created the original food-grade designations H1, H2 and H3, which are still used today. These designations are defined as follows:

• H1 lubricants are those used in food processing equipment and on machine parts where there is a possibility of incidental food contact.
• H2 lubricants are those used in food processing equipment and on machine parts where there is no possibility of food contact.
• H3 lubricants, also known as soluble or edible oil, are those used to clean and prevent rust on hooks, trolleys, and similar equipment.

H2 lubricants are the most often selected grease for mounted bearings used in food processing environments, but each application must be examined closely. Bearings subjected to wash-down should use a lubricant that has water wash-out resistance. Calcium, lithium, and aluminum complex greases, as well as polyurea types, are all excellent choices. PFPE greases can operate at high temperatures and have excellent resistance to a variety of chemicals but are more expensive. Synthetic lubricants in general perform better than mineral based lubricants and protect against the growth of microorganisms. Lubricant additive packages, such as anti-wear and anti-corrosion, are also available. Grease lubrication in an insert bearing can break down and degrade over time, particularly when operating at elevated temperatures. Mounted bearing units are commonly supplied with a grease fitting that allows for the re-lubrication of the insert bearing. Proper lubrication is essential to equipment performance. Maintenance technicians should define a procedure and schedule for re-lubrication of mounted bearing units, based on duty cycles and operating conditions.

Summary
The future of the food processing industry will continue to focus on automation design, including the increasing use of robotics and the development of energy-saving, sustainable facilities and equipment. Bearings will continue to play a crucial role in the efficiency, sanitation, and safety of food processing equipment. Proper bearing selection can prevent contamination, reduce required maintenance, and improve overall production quality. Designers and engineers should always consult with a qualified bearing specialist when selecting mounted units to ensure reliable equipment performance and compliance to stringent industry regulations.