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4 Materials Best Suited for Washdown Design

March 02, 2017 - Rockford, IL  -  Posted by PBC News

In a “washdown environment,” equipment needs to be cleaned either by hand or by automatic means with water, chemicals, or a mixture of these. Manufacturers that handle food, beverages, or pharmaceuticals are required to follow and maintain regulations, standards, and inspections, allowing them to produce goods and properly maintain equipment.

To ensure the successful performance of machine components in sanitary, washdown, or chemically cleaned environments, engineers must carefully choose materials for bearing, shafting or rail, and seal components.  Here are 4 of them:

Bearing on Shaft
Stainless steel’s corrosion resistance and durability 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. 

300 Series Stainless Steel
Featuring relatively soft and non-magnetic properties, 300 Series Stainless Steel cannot be hardened. It is widely accepted for food and medical applications, and features various types that have slightly different formulations with varying strengths and weaknesses. These types include 303, 304, and 316.

303 is also referred to as “A1” under ISO standards. It is a free machining version of 304 due to added Sulphur 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, or “A4” (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
There are several types of 400 series stainless available, 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.

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

Electroless Nickel Coatings
These coatings have become popular because of their corrosion and wear resistance combined with a smooth polished appearance. Some forms include a PTFE infusion to aid in non-stick properties. Most forms of this coating are FDA compliant as well.

Plastics, Polymers & Fillers
Due to cost, weight, manufacturability, etc., these non-metal materials are increasingly being used, “under the hood,” inside of mechanical drive components, guides, bearings, fasteners, and more. Many solid plastics, such as injection molded bearing inserts, present drawbacks in washdown applications in that most will absorb liquid, causing the component to swell and increasing the potential for binding and catastrophic failure. 



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