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Linear Bearing, Guide and Shaft Materials for Washdown Applications
Choosing Linear Bearings, Guides and Shafts for Washdown Applications

Choosing Linear Bearings, Guides and Shafts for Washdown Applications

The design and build of automation equipment in washdown environments presents challenges for design engineers. A “washdown environment” is one that utilizes cleaning with pressurized or superheated water, chemicals, or a combination of both by means of either automation or hand washing. Generally, the overall goal of a washdown application is to kill and eliminate bacteria or other microorganisms that can cause and spread disease.

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There are set standards and regulations that a company must comply with in washdown applications. These regulations are inspected by multiple local, state, and federal organizations to ensure materials and machines are compliant and have met the standards for cleanliness and performance. Some of these organizations include, but are not limited to the FDA, HACCP, GRAS, USDA, 3-A Sanitary Standard, Inc., NSF International, and ASTM.

There are multiple choices for linear motion designs that are best suited for washdown applications. These products and materials aid in achieving the standards that are required to operate in certain industries. PBC Linear offers a variety of products and materials that meet these standards.

Washdown Linear Bearings

Products best suited for washdown applications

Simplicity® linear plain bearings exhibit substantial benefits when compared to other styles of linear bearings. These self-lubricating bearings are available in three grades of Frelon liners including FrelonGOLD®, Frelon® J, and Frelon® W(FDA compliant), and help to decrease the amount of material deposits and potential for bacteria build-up. The Frelon liner is not only self-lubricating, but also offers wiping action on the shaft, enabling smooth linear motion. These capabilities lengthen the life of the linear motion system and avoid catastrophic failure. The range of outer shell materials and bearing raceway materials are designed to perform extremely well in a wide variety of conditions where washdowns, intermittent spray, or even submersion in a variety of chemicals may occur. Customers interested in more details on this topic can download the full Simplicity Chemical Reaction Chart.

Washdown Linear Guides

Redi-Rail® Linear Guides are highly resistant to corrosion in washdown applications. Their rails are aluminum and contain an antimicrobial powder coating and are embedded with 440 stainless steel shafts. Sliders are composed of 440 stainless steel bearings, with the option of 3, 4, or 5 wheels.

Commercial Rail Linear Guides are corrosion resistant and cost effective. They contain a 3-wheel slider composed of 440 stainless steel sealed bearings that ride on roll-formed 304 stainless steel rails.

V-Guide Systems are v-wheel bearings constructed of 420 stainless steel and 304 stainless steel shields or nitrile rubber seals, and 400 series stainless steel rails.

Materials best suited for washdown environments

The corrosion resistance and durability of stainless steel is typically preferred for general use in direct food contact areas. There are variations in stainless steel grades, mostly in the levels of chromium and nickel, that include a 300 and 400 series stainless steel.

Washdown Capable Linear Shafts

300 Series Stainless Steel, used in linear shafts, rails and bearing shells, features relatively soft and non-magnetic properties, and cannot be hardened. It is widely accepted for food and medical applications and may be varied slightly for different strengths and weaknesses (303, 304, and 316).

  • 303, also referred to as "A1" under ISO standards, is a free machining version of 304 due to added sulfur and phosphorous. While its corrosion resistance is good in mild environments, it is subject to pitting and crevice corrosion in chloride containing environments over 60°C.
  • 304 is known as "A2" or "18/8" due to its 18-percent chromium and 8-percent nickel make-up. It is the most common grade of stainless steel with excellent forming and welding characteristics. 304 is typically used in food processing equipment (beer brewing, milk processing, and wine making) due to its corrosion resistance and excellent ambient and low temperature toughness properties.
  • 316, also known as "A4" or "18/10", is the most commonly used alloy for food and pharmaceutical grade applications. The addition of up to a maximum of 3 percent molybdenum helps prevent corrosion from industrial chemicals and solvents, making it more resistant than 304.

400 Series Stainless Steel contains several types, but the most widely available and most used is the 440 stainless. It can be heat treated and hardened for use in cutlery, linear shafting, and in applications requiring higher wear resistance. Due to its carbon makeup, it will oxidize under washdown conditions.

If weight is a concern in some washdown environments, engineers can use coated aluminum for protection against pitting and cracking. Anodizing, ceramic coating, or other types of coatings with PTFE or other fillers may be used, but they don’t provide the resistance or life that stainless steel offers. Stainless steel is preferred in more caustic chemical washdown environments.

Finding the right materials for linear bearings and guides is crucial for many reasons, including durability in washdown environments. Electroless nickel coatings have gained popularity due to their excellent corrosion and wear resistance, along with a smooth polished appearance. Some formulations include a PTFE infusion, enhancing non-stick properties, and most are FDA compliant.

Non-metal materials, such as plastics, polymers, and fillers, are increasingly used in mechanical drive components, guides, bearings, fasteners, and more. These materials are favored for their cost-effectiveness, lightweight nature, and ease of manufacture. However, certain solid plastics, like injection-molded bearing inserts, can present challenges in washdown applications. Many absorb liquid, leading to swelling that increases the risk of binding and catastrophic failure.

Selecting the right materials is essential to ensure the reliability and efficiency of linear bearings and guides, particularly in demanding washdown environments.

To learn more about linear bearing and guide design and optimization for washdown, download our Linear Motion Design for Washdown Applications white paper.

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