To read part I (introduction) of this series, click here.
To read part II (regulatory environment and safety) of this series, click here.
To read part III (lubrication) of this series, click here.
All bearings should be manufactured using components produced from high purity material. While bearings are most commonly produced from SAE 52100 chrome steel, for most food processing applications, martensitic stainless steel, similar to AISI 440C, is recommended. 400 series stainless steel offers the best combination of corrosion resistance and fatigue life.
For certain sizes of ball bearings, nitrogen-enhanced martensitic stainless steel is also available. This material is more expensive, but offers up to five times the corrosion resistance when compared to traditional “440C type” materials. This material also exhibits very low noise levels and extended fatigue life due to its fine structure that contains smaller chromium nitrides (as opposed to chromium carbides).
Bearing components such as shields, slingers and cages should be manufactured from AISI 302 or 304 stainless steel. While deep groove ball bearings can be manufactured from AISI 300 series steel, which has outstanding corrosion resistance when compared to martensitic 400 series steels, they typically are not used in food processing applications due to their compromised fatigue strength. Load ratings for ball bearings manufactured from 300 series austenitic steel are approximately 20% of the ratings for 400 series. However, if the applied loads are very light they could be considered.
If bearings are required to operate immersed in water or resist chemical attack, hybrid ball bearings can be used. The rings are produced from martensitic stainless steel, and the balls are ceramic-silicon nitride. The bearing cage can be produced from a fluoro-resin or Teflon, which provides lubrication. These bearings are maintenance free and extend life in these severe conditions.
Mounted bearings are used extensively in food processing equipment and conveyors. This type of bearing usually consists of a radial ball bearing, sometimes a roller bearing, mounted and held within a housing. The bearing inside is known as an insert. Various housing styles allow for different mounting arrangements. One of the more common housing configurations is known as a pillow block.
Insert bearings should be produced from 440C stainless steel. Other options to consider for the insert are AISI 52100 chrome steel bearings that are either zinc chromate plated or black oxide coated. Several options are available for corrosion resistant, food safe housings.
In the meat and poultry sectors, high strength housings are often required. Cast or ductile iron housings with electro less nickel plating offer strength and can withstand most wash downs with the added benefit of being cost effective. However, cast stainless steel, 300 series, is the best choice when facing high concentrations of chlorine or other chemicals in the wash down solutions. Thermoplastic housings are an effective alternative in high moisture environments with caustic wash down solutions. While they are not as strong, they are light weight and do not chip or flake as compared to a housing with plating.
Housing surfaces should also be smooth with flat mounting bases without recessed areas. This assists with effective wash down and eliminates the possibility of food by products or debris getting caught under the mounting surfaces which can lead to bacterial growth.
Due to the wide array of products along with price and availability, both a lubrication specialist and the bearing manufacturer should be consulted before making a final lubricant selection.
There are a wide range of lubrication options to take into account for optimal application performance. Food processing engineers and designers are advised to consult a bearing applications specialist for assistance to best navigate these regulations. If you have a question regarding lubrication in the food industry (or any industry!) click here to pose it to our experts.