Fasteners for Washdown Environments (part 2)

Continuing our article series about Fasteners for Washdown Environments, here we’ll take a look at various finishes, features, and applications found in Food, Beverage, and other hygienic manufacturing settings. If you missed part one of this series, click here.

To recap our Part 1 article, Washdown Environments are those in which frequent cleaning occurs, using hot water and chemicals to rinse, disinfect, and sanitize the working area. We last covered the general guidelines of washdown-grade hardware, as well as common material choices. Now on to finishes!

Fastener Finishes

The exterior surface finish of materials used in washdown environments is of special concern, especially in the eyes of regulatory bodies in food and pharmaceutical sectors. Materials used in these environments must freely drain and easily release any soil particulates as a function of both how they’re shaped and how they’re finished. Smoother finishes and fewer (or no) cavities promote all the important drainability aspects of washdown-rated fasteners.

Previously we discussed that stainless steel alloys are the preferred fastener material in washdown environments. Both of the most common stainless alloys, Type 304 (also known as 18-8) and Type 316 (18-10), are offered in finishes termed ‘mill finish’ and ‘polished finish’.

• Mill finish describes no secondary processing performed on the fastener – it has moderate surface roughness and a dull appearance.
• Polished finish describes a post-machining process that grinds down surface roughness, resulting in both low texture profiles and a bright appearance.
  

Polished finishes on stainless materials are preferred, as their smoother surface achieves better water sheening and fewer texture irregularities where soils can accumulate. When specifying polished finishes, use the recommended <32 Ra surface roughness value as described in ASME B46.1.
When specifying other material types beyond stainless steel such as UHMW plastic or titanium, surface finish still comes into play. Specify a <32 Ra equivalent or ‘no texture’ finish to ensure materials are smooth and freely draining.

To close out the topic of finishes, there are a few more special offerings that should be mentioned:

• Black oxide finishing is commonly suggested to improve corrosion resistance but is not advisable in washdown environments. The black oxide coating will degrade under chemical wash and would be considered a contaminant by inspectors.
• Plating of any sort is typically avoided (zinc plating, nickel plating, etc), as the plating will flake off over time.

• Passivation is an acid cleaning process performed on machined fasteners that removes foreign materials. This is a great option to apply to stainless steel fasteners in cases where foreign material ingress must be avoided.

• Electropolishing is an advanced option that can outperform both standard polishing and passivation combined. Often this is not necessary except for extreme chemical and salt exposure, or where very bright material aesthetics are desirable.

Have a washdown project but unsure of which level of finish to specify? E&T Fasteners can help advise on and supply multiple finish options, usually pulling orders directly from stock and delivering to the site right away. See more about our fastener offerings here.

Features and Applications

After selecting a style, material, and finish, our fastener selection process for washdown environments has one final step. Now we must consider the overall conditions of the application, looking for any places where we might have further opportunity to improve cleanliness. Here are a few examples of these applications below.

• Using acorn nuts in place of hex cap nuts covers the exposed threads on the end of a bolt or screw, which reduces the chance of harboring soils in the threads and allows for much better water drainage off the rounded acorn nut.
• Switching flat-head and Phillips-head screws to hex cap screws eliminates the cavity used for the driver tool, where soils can accumulate over time. Also, hex cap screws have less chance to strip out, reducing the risk of metallic shavings posing a contamination concern.
• Threaded spacers with round or hex stud bodies can be used to replace exposed threaded studs or rods. These spacers provide a smooth exterior surface that is much easier to clean than bare threads.
• Covering threaded rods with plastic sleeves is a good idea for aesthetics, but a bad idea for washdown environments. The sleeve tube fits loosely around the threaded rod, creating a large volume of space that can fill with wash water and soils. Instead of using sleeves, replace long threaded rods with solid round bar rods, and thread only the ends where needed.
• Solid pin or similar “bolt-through” fasteners should never be installed by drilling through a hollow structural member (square tubing, rectangular tubing, etc). This creates a path for soils to enter the tube, creating an uncleanable void space full of debris. Any pins used in washdown environments should connect between solid plate tabs or angle iron brackets, never through hollow members.
• Spring lock washers make a great replacement for tooth or split lock washers, providing a smooth outside circumference free of any small cavities to harbor product.

Suggesting fastener and hardware alternatives for your unique application is our specialty! Speak with an E&T Fasteners representative for more information on options and design alternates to help improve your washdown-grade project.

About E&T Fasteners

With sales and support teams spanning the Continental US, E&T Fasteners serves your hardware, fastening, and component needs both domestically and internationally. We are a stocking distributor of metallic, plastic, and exotic alloy fasteners, backed by our technical staff directly experienced in your unique applications. We can assist your specifying and selection efforts, providing engineered solutions, record-fast lead times, and stellar customer service from quote through delivery. Please let us know how we can help!