Mounted Bearings: A Key Ingredient in Food Processing Equipment - Part 1

Mounted bearings play a crucial role in the food processing industry, where machinery and equipment must meet stringent hygiene and performance standards. In this technical article, AST® Bearings explores three important design elements to consider when selecting mounted bearings for food processing applications. We discuss material options here in Part 1.

The U.S. food processing industry consists of approximately 21,000 companies and $750 billion in annual revenue. This industry makes extensive use of automation, which requires the seamless operation of many moving parts. Sealed ball bearings, including those mounted in housings, are the unassuming - but vital - component at the heart of this automation. These bearings are often exposed to extremely harsh environments and operating conditions. Meat processing equipment, for example, is subject to routine high-pressure wash-downs, often with bleach and other harsh chemicals. Equipment reliability can be greatly improved when designers make the right decisions in specifying bearings.
 
Mounted bearing units are typically used to support shafts, align conveyor tracks, or maintain conveyor belt tension. These components are assemblies made of a housing and a retained bearing. There are multiple housing variations available, with the pillow block and two-bolt flange styles the most common in food processing equipment. These units are good for low torque, lightly loaded applications. Another housing configuration is the take-up unit, ideal for use in conveyor applications. In the meat and poultry sectors, high strength housings called plummer blocks are often required to transfer ample power and support heavy loads.

Material
When selecting a housing, the type of material is an important consideration. Cast iron or ductile steel are the most common materials used. These housings are painted to provide a minimal amount of surface protection. For food processing equipment subject to wash-down environments, stainless steel is more suitable. Other corrosion resistant housing options include nickel-plated cast iron and thermoplastic. While lacking the strength of iron and steel, thermoplastic housings are highly resistant to moisture, including a wide variety of wash-down chemicals. All housings, regardless of material type, should have smooth surfaces with flat mounting bases and be free from recessed areas. This design allows for effective cleaning and eliminates the possibility of food by-products or debris getting caught in the housing, which can lead to bacterial growth and unsanitary conditions.

The bearings mounted in housings are often referred to as insert bearings. Selection of these bearings is based on shaft size, loading conditions, and rotational speed. Insert bearings are typically manufactured from 52100 chrome steel, which is suitable for most applications. In corrosive or wash-down environments, however, 440C stainless steel is highly recommended. The inner ring on an insert bearing is commonly extended on one side. This design allows for the use of set screws or locking collars to secure the rotating shaft of the equipment to the inner ring of the bearing. The most common and economical method for securing the shaft in place incorporates two set screws set 90⁰ apart. Eccentric locking collars can be used instead of screws when a stronger connection is needed to prevent slippage or fretting between the bearing bore and the shaft. Both methods have a disadvantage of shifting the shaft centerline off the centerline of rotation of the bearing. This condition can introduce vibration, which is undesirable and can reduce bearing life. Concentric locking collars should be selected when this is of concern. These collars have the added benefit of improving the strength of the connection between the shaft and the bearing bore, as well as increasing the push-off force required to remove the bearing.

In the next installment of this series, AST looks at sealing solutions and lubrication considerations for mounted bearings. Watch for Part 2 of Mounted Bearings for Food Processing Equipment, coming July 3, 2024.