Bearing Design Considerations for the Food Processing Industry – Part 3
We have come to the last installment of our feature article on design considerations for bearings used in food processing machinery. We hope the previous posts have provided you with a clear understanding of the various materials and closures to evaluate when specifying a bearing for your food or beverage application. In this final entry, we examine bearing lubrication considerations for food processing equipment.
Lubricant selection is critical to bearing performance and life, yet it is often overlooked by designers and engineers. Bearing life in harsh environments such as those found in food processing 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.
Lubricant selection not only depends on the operating conditions the bearing will encounter; it may also be subject to regulatory requirements. Manufacturers of food processing machinery 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. The USDA created the original food-grade lubricant designations H1, H2 and H3. In 1999, the National Sanitation Federation (NSF) evolved globally and took over the regulatory oversight of food-grade lubrication, while retaining the original H-system designation. The 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. They are generally regarded as safe and FDA-compliant mineral oil. The equipment surfaces that contact edible products must be clean and free of the oil before reuse.
H1 lubricants typically have synthetic, hydrocarbon base oils with urea, polyurea, or aluminum complex thickeners. H2 lubricants typically have mineral or PFPE base oils with calcium soap or PTFE thickeners. Solid lubricants can be used in very demanding applications. These are oil-filled polymers, or grease and polymer mixtures, that solidify once heated and cooled. Solid lubricants can eliminate problems with grease leakage and emulsification, especially when water is present.
Lubricants need to provide good wear and corrosion resistance. Those used in high temperature applications such as meat, poultry, and beverage processing should have high temperature oxidation stability. Machinery used in beef, pork, and poultry processing is typically exposed to washdown procedures, which use high pressure water and anti-bacterial solutions that can displace the grease. To avoid this displacement, greases with high resistance to water washout are used, with fill amounts in the range of 70-100% (as opposed to a typical fill amount of 30%). While the large fill amount limits rotational speed, it significantly improves bearing life.
Thousands of greases and oils are readily available, designed for a wide variety of operating conditions. Features, benefits, and price are all important factors to consider when making a choice. Both a lubrication specialist and the bearing manufacturer should be consulted before making a final lubricant selection.
Bearing life plays a key role in optimizing uptime, efficiency, and reliability of equipment used in the food processing industry. Bearings are exposed to extremely harsh conditions in these applications, and designers must consider protection from corrosion and contamination while maximizing lubricant life. Materials, sealing solutions, and lubrication - along with operational loading - should be carefully evaluated in the bearing selection process to achieve desired bearing life.
Bearings used in meat processing facilities must be able to withstand harsh cleaning procedures. Greases with high resistance to water washout should be used, in fill amounts of 70-100% of available volume.