Bearing design in the food processing sectorJody Dascalu | March 11, 2023
The food industry is a major sector in the United States economy, according to the USDA agriculture, food, and related industries contributed around $1.25 trillion to GDP in 2021, which is a 5.4% share of the total GDP. Bearings are used extensively in the food processing industry, from agriculture, to processing, and to packaging.
Machinery components in food processing areas must be food-grade and resilient to harsh conditions, this includes bearings. In the manufacturing industry, uptime and reliability play a major role in success. Production equipment must be certified to be safe for direct or incidental contact with food and must be resilient to wear as machine breakdowns result in costly repairs and lost production hours.
Strict regulatory requirements
Food safety is a crucial aspect of the food processing sector. These regulations help keep consumers safe from food-borne illnesses and deceptive and dangerous acts. All materials used in food processing and packaging need to comply with federal, state, and local codes.
In the United States, the food processing industry is heavily regulated by government agencies such as The Food Safety Inspection Service of the U.S. Department of Agriculture (USDA-FSIS) and the Food and Drug Administration (FDA).
The USDA-FSIS oversees meat, poultry, and egg processing while the FDA is responsible for all other food processing businesses. State agencies and local authorities also play a role in the oversight of food processing facilities.
Consequently, bearings are required to comply with local, state, and federal requirements. Some components of bearings that are impacted by the industry of operation are lubrication, materials, and shielding options.
Some typical food industry applications for bearings are bakeries, bottling, meat processing, dairies, fruit and vegetable processing, and packaging. Housing materials are often mixed and matched in accordance with the bearing insert materials based on the application and preference of manufacturers. Housings are often made from stainless steel, thermoplastic composites, teflon-coated iron, or nickel-plated iron. Bearing inserts may be made from stainless steel or dense chrome, and be zinc or black oxide coated.
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Bearings are often made of AISI/ASTM 52100 steel, which is a high carbon chromium-containing low alloy steel. This type of steel has high wear resistance and good rolling fatigue strength.
In the food processing industry, stainless steel austenitic grades 304 and 316 are often used as they have high chromium content. These types of steel are often referred to as food-grade stainless steel. Steel 316 is slightly more resilient against chlorides due to the content of two to three percent molybdenum, which makes it ideal for processing food high in salt. Overall, 300 series stainless steel has exceptional corrosion resistance making this material suitable for this industry. Some bearings for the food industry may be made from martensitic 400 series stainless steel as well. Martensitic stainless steel is an alloy with more chromium and usually no nickel in it while austenitic stainless steels have from 8 to 10% nickel content.
Lubrication of bearings in the food industry
Lubrication plays an important role in extending the life of bearings and improving their performance. Special lubricants are required to withstand severe conditions in cooking processes and during sanitization. The choice of bearing lubrication is subject to regulatory requirements in the specific operation type or product and depends on the specifications of the application.
Steel bearings will often use solid lubricants in the food industry. These lubricants are composed of supermolecular weight polyethylene and lubricating grease. Solid lubricants have a few advantages for this application such as:
● Longer life -This means that machinery can run for extended life cycles without maintenance and reduce the risk of exposure to food processing areas.
● Better leak resistance -Solid lubricants do not leak when exposed to water.
● Reduced contamination risk -Solid lubricants reduce the risk of empty pockets forming in the bearing and becoming filled with contaminants.
NSF H1 lubricants are formulated from the USDA list of approved ingredients and are acceptable for incidental food contact making them certified for use in food processing areas. The lubricant must be odorless, colorless, and tasteless, and there is a 10 ppm limit for lubricant base oil that may be present in food in cases of incidental contact.
There is a specific list of chemical compounds, and additives allowed in the lubricant according to The Code of Federal Regulations Title 21 (21 CFR). Regulators around the world refer to 21 CFR to define food-grade lubricants. Lubricants must be H1 Registered or ISO 21469 certified to be accepted in global markets of food manufacturing. The NSF white book is referenced frequently when choosing lubricants for bearings.
Hybrid ball bearing
Bearings that are immersed in water or are used in harsh chemicals should be hybrid ball bearings. The bearing cage may be made of a fluororesin such as teflon. Hybrid bearings do not require significant maintenance.
Hybrid ball bearings may also last 4 to 8 times longer than steel bearings. This type of bearing extends the time between replacements and can result in reduced MRO spending. Hybrid ball bearings combine steel outer rings with ceramic balls. The bearings are greased for the life of the components and do not need to be relubricated, which further reduces maintenance costs.
They have four times lower surface roughness than their metal counterparts and run cooler by up to 17°C when compared to all steel bearings. This can extend the lifetime of the lubricant and the machine to reduce maintenance costs. The balls are also twice as hard and have a higher resistance to contamination and particles. The friction coefficient between steel and ceramic is lower for steel to steel so micro-welding does not occur.
Preventing contamination is key in the food processing industry. Relubrication-free bearings do not need to be relubricated even with frequent washdowns. The bearing may be completely sealed to increase performance and limit the risk of contamination.
In food processing facilities bearings may be in contact with potentially corrosive food and beverage ingredients. They are often regularly exposed to cleaning chemicals and high-pressure washdowns. Many food processing facilities have harsh operating conditions, with some bearings being used in high and low-temperature processes. Working conditions often include steam resulting in high moisture and the potential for corrosion. As a result, bearing design is vital to ensure smooth and safe operation in the food sector.