With stainless steel and other metals so predominant in industrial food manufacturing equipment, it seems counterintuitive to suggest a larger role for plastic wear rings and bearings. But for a large category of food production and transportation machines, advanced polymers are a better way to reduce friction and handle load than traditional metal bearings.
In this article, we’ll describe the wear rings and bearings commonly used in the food and beverage industry, discuss material choices for them, delve into their chemical compatibility and show examples of current use.
Wear rings
Wear rings, also called guide rings, are single-element bearings. Typically used in linear, reciprocating applications, they provide a robust method for guiding two elements over a long linear distance. Note that some wear rings are designed to wear out, serving as the sacrificial element in a design in which two surfaces rub against one another.
When created from polytetrafluoroethylene (PTFE) or a high-modulus plastic, wear rings are ideal for many food and beverage applications because:
- The material is biologically inert.
- Wear rings are a single element, which means fewer places for microbes to grow.
- Their design makes them easier to install and replace than bearings containing balls.
- Their low-friction properties make them well suited for applications with high loads but relatively low speeds, such as in industrial mixers.
Wear rings can be designed as sleeve bushings, flange bushings or thrust bearings. When a flange is added to the wear ring design, it can be used as a guide for mounting or as a thrust washer to accommodate loading that is parallel to the machine shaft.
Design variations can be achieved by changing the type of plastic used. Fillers and additives improve performance — for example, increasing heat resistance or reducing friction. Plastic sleeve wear rings can be self-lubricating and are lightweight.
Chemical compatibility
Both cleaning and disinfecting are critical in food and beverage applications. Cleaning is the act of removing residual materials from equipment; disinfecting ensures harmful bacteria cannot grow in or on equipment. It is not realistic to expect cleaning alone to remove all chances of bacterial growth, as microscopic traces of material capable of growing bacteria are often left behind.
The sanitization process helps ensure that the remaining microorganisms are reduced to levels not considered harmful. Carbohydrates, like starches and sugars, are relatively easy to remove from equipment. Proteins, such as milk and meats, present more of a challenge.
Many chemicals are used in cleaning (detergents) and sterilization (disinfectants). Acids, alkalis (bases), chelates and solvents are the base chemicals typically used. Common alkalis used include sodium hydroxide and potassium hydroxide. Common acid chemicals include inorganics like phosphoric, nitric, sulfamic and hydrochloric acid, as well as organics like hydroxyacetic, citric and gluconic acids. Sanitizing chemicals include chlorines and peroxides.
The combinations of chemicals used in cleaning and disinfecting are the reason polymer-based bearing and wear rings perform better in many food and beverage applications. The chart below shows the compatibility of several polymers and bronze with common cleaning and sanitizing chemicals.
