Design Advice for Washdown Environments
Engineers tasked with designing linear motion systems within the food packaging, bottling, pharmaceuticals or similar industries are continually challenged to minimize unwanted bacteria in linear motion components. Typically, these challenges are found within washdown environments, and can include common applications that rely on processing, packaging, handling, and automation equipment. This article offers four main points that explain how to design linear systems that minimize bacteria buildup and keep your operation running clean.
Linear Bearing and Linear Guide Design
There are two main issues to be aware of when choosing a bearing for washdown environments. The first concern lies with the two-piece, open-ended bearings that contain grooves or inserts. They should be avoided in washdown environments because microscopic bacteria have a tendency to hide in the crevices, grooves, and plastic bearing inserts, therefore increasing the chances of contamination and disease. The second concern can be seen in recirculating ball bearing type products that require grease lubrication for metal-to-metal contact. In this scenario, the lubrication picks up material from food items being processed, eventually becoming trapped inside multiple crevices and also cavities around the balls and raceways of the bearing. The result is a potential breeding ground for unwanted bacteria.
The solution, or recommendation for these types of washdown applications is to implement one-piece, bonded bearings for the simple fact that there are no grooves, crevices, or spaces between the liner and bearing shell. In essence, residues will not gain a foothold on our linear plain bearings and will therefore inhibit any bacteria growth. In addition, our plain bearings are also PTFE based with bonded linear material, making them self-lubricating and requiring no external lubrication that would potentially collect contaminated materials or bacteria.
When it comes to multiple component sub-assemblies, there is a danger of bacteria build-up around the connectors and joints. Design engineers can eliminate potential areas of contamination collection by using newer technology that incorporates dual rail load capacities and functionality into one single rail design.
Rail Design and Rail Selection
Our general recommendation is to minimize component assembly as much as possible in washdown environments. Many traditional methods for linear assemblies include various connection points that create crevices, joints, or cracks where liquid can penetrate, or bacteria can begin to accumulate.
Unique two-piece slide systems are ideal for washdown environments because they reduce the amount of connection points that come with multiple component assemblies, and they are designed with smooth, curved edges that do not have recesses where buildup can occur.
When mounting linear rails, it is a good practice in washdown applications, especially where contamination and bacteria buildup are a concern, to use standoffs as a way to maximize cleanability around the linear motion system. As a side note, be sure to calculate shaft or rail deflection when using standoffs to ensure proper operation.
To the right is an exaggerated example of good practice when mounting with standoffs.
The location of fasteners and linear components is important to consider for washdown environments. Fasteners can protrude, creating a gap that is potentially another area for contamination to accumulate, especially when mounted on the washdown side.
To help eliminate these hazardous areas we recommend bringing the fastener up through the bottom of the rail when mounting. In addition, for fasteners that enter the washdown area, use a dome nut (or similar) for easier cleaning.
For components that are not FDA compliant or that don't meet other regulations for food contact, it is recommended to cover those components with stainless steel shields or covers that have been radius on all corners.
For more information on LEE Linear solutions for washdown environments read: Linear Motion Design for Washdown Environments.