Bearings for sanitary environments. Source: NSKNobody wants to bite into their glazed donut to find out what looks like frosting is actually mixed with bearing grease. Manufacturers go to great lengths to ensure that this cannot happen.

The food and drug processing industries present special challenges for equipment manufacturers. Some processes require machinery to operate in extremely high or low temperatures or subject the machines to washdowns with high-pressure water or chemicals. Washdowns are performed to eliminate bacteria or microorganisms and to prevent contamination between batches of different substances. In addition to the obvious health concerns related to the food, beverage and drug industries, equipment for these applications must conform to strict governmental regulations and are subject to routine inspections.

To withstand these harsh operating environments, machines and components must be manufactured from non-corrosive materials. Stainless steel, plastic and rubber are commonly used materials that are resistant to corrosion. Other materials such as ceramics, glass, copper, gold and more expensive materials such as titanium can be used in specialized applications. Aluminum has poor corrosion resistance and should be avoided if possible. Paint is typically not an option as it would be washed away by the high-pressure water.

Bearings are a widely used commodity in food and drug processing applications and are subject to these same extreme environments. To meet these demands, manufacturers produce corrosion-resistant bearings that have a long life and also comply to safety regulations. In addition to bearing material, seal material and lubrication are also subject to FDA and European Commission (EC) regulations. The U.S. government’s Code of Federal Regulations (CFR) Title 21 defines materials acceptable for contact with food. Regulation (EC) No 1935/2004 provides general principles of safety and inertness for all food-contact materials (FCMs) for European countries.

Bearing manufacturers comply with these public safety concerns and regulations by addressing three different important criteria: materials, lubrication and sealing.

Materials

Comparison of corrosion rate 52100, X65Cr13 and SV30. Source AST BearingsMaterials such as stainless, ceramic or polymer for bearing components and housings reduce or eliminate corrosion and do not require paint or coatings that can chip, which pose a risk of contamination. Proper material selection also increases bearing life, which reduces maintenance costs.

The initial standard material for stainless bearings was AISI 440C (X1 02CrMo17). Although it has higher corrosion resistance than standard 52100 bearing steel, it also features a courser grain structure with larger carbides, which has an adverse impact on bearing noise level. This stainless was superseded by some manufacturers in the 1980s with X65Cr13, sometimes referred to as 440D or ACD 34.

X65Cr13 stainless combined the corrosion resistance of 440C stainless with a fine grain structure that brought noise levels down to that of bearings manufactured out of 52100 steel. Many companies have introduced proprietary stainless steel variations to improve performance and increase bearing life. For example, AST Bearings manufactures a line of miniature and small-size bearings out of SV30 (X30CrMoN15-1) nitrogen-alloy stainless steel. SV30 combines all of the benefits of X65Cr13, while also allowing for passivating or surface coating of the bearing rings.

Nickel and chrome plating are alternative options to produce corrosion resistant bearings. As the image below shows, plating material composition is important to maximize protection against corrosion.

Results of various bearing insert coatings after a 24-hour salt fog test. Source ABB Motors and Mechanical Inc.

Lubrication

The ingredients of food-grade lubricants are regulated and designed for safe interaction with food. Lubricants designated as H1 by the National Sanitation Foundation (NSF) are intended for applications where the potential for incidental or accidental contact with food exists under normal-use conditions. H2 lubricants are used where there is virtually no risk for contamination or contact with food. H3 lubricants are soluble or edible oils used to clean or prevent rust.

Due to the challenges of food-grade lubricants, as many as 60% of companies do not adhere to the food-grade regulations, which causes health concerns if non-compliant lubricants come into contact with food.

Traditional solid and dry-film lubricants are frequently used in plain bearing applications. Solid and dry-film lubricant forms a dry layer or coating that excludes moisture and reduces friction, binding and wear. They often contain additives such as corrosion, oxidation and rust inhibitors. Common examples include molybdenum, graphite and fluoropolymers such as polytetrafluoroethylene (PTFE). Major advantages to these lubricants are that they cannot be washed out and do not interact with anything they contact.

In addition to food-grade greases, some bearings also incorporate a different type of solid lubrication (sometimes referred to as solid grease, solid oil or molded oil). The definition and composition of solid lubrication varies by manufacturer. SKF defines its solid oil lubrication as an oil-impregnated polyolefin that is molded into the bearing. NTN defines its solid grease as an ultra-high-polymer polyethylene resin mixed with a food-grade synthetic oil grease. NSK uses a molded oil described as oil-impregnated polyolefin resin. The grease undergoes a special heat treatment process that solidifies the grease, trapping the lubricant inside.

Solid lubrication has several features advantageous to food and beverage equipment compared to other lubricants. Deep-groove ball bearings, spherical roller bearings, cylindrical roller bearings and needle roller bearings are all available with solid lubrication.

• Solid lubricant offers reduced leakage as the base oils are retained in a solid mixture. This ensures the bearing is always lubricated and eliminates the risk of contamination.
• As the bearing has a constant source of lubrication, bearing life is increased. Additionally, the solid lubricant does not emulsify when exposed to water, which is important to withstand washdowns.
• Solid lubricant does not experience the shearing resistance found in bearings with standard grease lubricants, which translates to lower operating torque characteristics.
• Solid lubricant helps prevent the ingress of contaminants but does not replace the need for external sealing.

Sealing

Proper sealing is critical in washdown or food and beverage applications. Manufacturers use many sealing configurations, all designed to keep lubricant in the bearing and water and contaminants out. This is especially important in washdown applications to keep the grease from washing out of the bearing. If the bearing may come in contact with food, material selection for bearing seals is critical and must comply with FDA 21 CFR, EC 1935/2004 and NSF/ANSI Standard 51.

Examples of food-grade bearings

Although not a comprehensive list, the items below represent how some bearing manufacturers are combining material, lubrication and sealing solutions to address the needs of the food and beverage industry. Many other manufacturers also provide food-grade bearings and some of the manufacturers below provide additional product lines intended for the food and beverage industry.

ABB

Source: ABBFood-safe mounted bearings

• Bearing types: Ball bearing insert; mounted (pillow block, tapped base, hanger, flange unit, take-up)
• Bearing material: Stainless steel housing; laser identified smooth surface to minimize crevices
• Lubrication: H1 food-grade synthetic grease; no Zerk fitting
• Sealing: Lubricated for life; Hydro Armor seal; IP69 rated for water
• Company profile; website; catalog (.pdf)

Source: ABBEZ Kleen washdown bearings

• Bearing types: Ball bearing insert; mounted (pillow block, tapped base, hanger, flange unit, take-up)
• Bearing materials: Corrosion-resistant nickel composite plated insert; stainless steel or polymer housing with no cavities or fillings
• Lubrication: H1 registered food-grade lubricant; Zerk fitting for relubricating
• Sealing: Hydro Armor triple-lip seal with a rubberized finger; ideal for washdown applications
• Company profile; website; catalog (.pdf)

Source: ABBUltra Kleen washdown bearings

• Bearing types: Ball bearing insert; mounted (pillow block, tapped base, hanger, flange unit, take-up)
• Bearing material: Stainless steel set screw insert; stainless steel housing with no cavities or fillings
• Lubrication: H1 registered food-grade lubricant; Zerk fitting for relubricating
• Sealing: Hydro Armor triple-lip seal with a rubberized finger; ideal for washdown applications
• Company profile; website; catalog (.pdf)

CeramicSpeed

Source: CeramicSpeedCorrotec FDA and Corrotec FDA+

• Bearing type: Ball bearing
• Bearing materials: Stainless steel bearings with ceramic balls
• Lubrication: FDA approved lubricant; lubricant type and fill level customized according to the bearing’s application; Corrotec FDA+ is a program where all bearing components comply with FDA requirements, not just the lubricant
• Sealing: Lubricated for life (option)
• Website; catalog (.pdf)

Graphalloy

Source: GraphalloyBearing solutions for food applications

• Bearing type: Plain bearing
• Bearing material: FDA accepted grade graphite/metal alloy
• Lubrication: Self-lubricating; works without external lubrication
• Sealing: None
• Company profile; website

NSK

Source: NSKSpacea-series ball bearings

• Bearing types: Deep-groove ball; ball bearing insert; pillow block; spherical roller; tapered roller
• Bearing materials: Stainless steel; nickel-alloy coated; hybrid (ceramic balls with fluororesin self-lubricating cages); aqua (fluororesin on outer/inner rings)
• Lubrication: Food-grade H1 or H3 compliant grease; molded-oil solid lubricant (oil-impregnated polyolefin resin)
• Sealing: Rubber seals; double shields
• Company profile; website; catalog (.pdf)

NTN Bearing Corporation

Source: NSKSentinel series

• Bearing types: Radial ball; ball bearing insert; mounted (pillow block, flange unit)
• Bearing materials: Stainless steel; stainless steel or thermoplastic housing
• Lubrication: Food-grade solid lube (polymer impregnated with H1 food-safe oil)
• Sealing: Combined elastomeric seal in tandem with outer flinger design
• Company profile; website; food industry catalog (.pdf); beverage bottling catalog (.pdf)

SKF

Source: SKFFood line ball bearing units

• Bearing types: Ball bearing insert; mounted (pillow block, tapped base, flange unit, take-up)
• Bearing materials: Stainless steel or zinc coated insert bearing; blue polypropylene composite housing with over-molded FDA and EC approved rubber base seal
• Lubrication: Food-grade H1 grease
• Sealing: Lubricated for life
• Company profile; website; catalog (.pdf)

Source: SKFSolid oil bearings with food-grade option

• Bearing types: Deep groove ball; angular contact; cylindrical roller; tapered roller; spherical roller
• Bearing material: Stainless steel
• Lubrication: Food-grade H1 grease option
• Sealing: Blue seals, colored so that damage is easy to visually detect, are manufactured out of synthetic rubber materials that are compliant with FDA and EC requirements.
• Company profile; website; brochure (.pdf)

Timken

Source: TimkenSurvivor housed units for the food industry

• Bearing types: Ball Bearing Insert; mounted (pillow block, tapped base, flange unit)
• Bearing materials: Corrosion-resistant thin dense chrome (TDC) bearings; nickel-plated cast iron or polymer housings
• Lubrication: Zerk fitting with nylon cap for relubricating
• Sealing: Buna-N rubber seals
• Company profile; website; brochure (.pdf)

Source: EDT by TimkenEDT Corporation by Timken

• Bearing type: Insert bearings (plain and ball); mounted (pillow block, flange unit, take-up)
• Bearing material: Polymer or stainless insert bearing; polymer or stainless housing
• Lubrication: H1 grease; H1 solid lube; H1 graphite solid lube; H1 food-grade synthetic
• Sealing: Seal and shield options; plain bearings do not require seals
• Company profile; website; catalog (.pdf)