Achieving a Non-Stick Mirror Finish in Stainless Steel Wire Baskets

January 31, 2017 | Custom Wire Baskets, Steel Wire Products

Mirror Finished Stainless Steel Barrels Inside Beverage Processing Plant.jpg

In sanitary applications for the food and biotechnology/medical industries, the finish of the baskets, trays, and other equipment used in the process can be critically important. Rough surfaces have miniscule peaks and valleys that can allow product to stick to them.

This makes it difficult to remove any leftover debris during the cleaning phase in between production cycles—leading to numerous problems such as:

  • Contamination of product
  • Longer washing cycles
  • Faster degradation of equipment 

To maintain sanitation standards, make cleaning & sanitation easier, and reduce prolonged exposure to harmful chemicals, using a smooth, featureless finish is a must.

But, how can you measure a mirror finish, much less achieve one for stainless steel wire baskets?

What a Mirror Finish Really Means

The term mirror finish sounds pretty self-explanatory; it’s a finish that’s smooth enough to provide a reflective surface. However, just because a piece of steel wire is smooth enough for you to see yourself in it that doesn’t mean it has achieved a true mirror finish.

To really define a mirror finish, you have to analyze the Roughness Average (Ra) of the object in question. Ra value is defined as the average value of the departures from its centerline throughout a defined sample length. In other, less scientifically accurate words, you could consider Ra the height difference in the peaks and valleys there are on a microscopic level in an object’s surface.

For an object’s finish to be considered a “mirror” finish, the Ra value of the objects surface in micro inches (µin) has to be between 4-8µin; or 0.000004-0.000008”.

Achieving a Mirror Finish

Achieving a true mirror finish in stainless steel can be fantastically difficult to do with traditional polishing processes. An abrasive pad would need to be at least 400-500 grit to achieve a mirror finish, and it’s likely that you would need to start with much rougher, lower-grit abrasive pads to sand down larger burrs and sharps first.

Worse yet, the performance of abrasive pads depends heavily on the condition of the pad, the angle at which it’s applied, and the condition of the machine doing the polishing.

Instead of polishing with abrasive pads, the preferred method of achieving a mirror finish is to use the electropolishing process.

By submerging stainless steel wire in an electrolytic bath and applying an electric current, the surface layer of the wire is stripped away. The reason this particular process is so effective at creating a mirror finish is that the electrical current is concentrated on the peaks of the material—resulting in the elimination of peaks for a more uniform surface.

This also removes most burrs/sharps from the surface of the wire, and eliminates discoloration from welds as well—all while requiring less time and labor than mechanically polishing the surface with a series of increasingly fine grit pads.

The end result is a microscopically smooth surface that’s resistant to sticking, free of occlusions, and significantly easier to clean and sterilize.

This is why Marlin Steel’s engineers tend to prefer the electropolishing process for achieving a mirror finish in stainless steel parts.

Using the right tools and having the right know-how can mean the difference between a perfect wire basket for your application, and a time-wasting tool that actually hurts productivity. Learn how Marlin leverages advanced factory automation, degreed mechanical engineers, and process innovation to create the perfect custom steel wire baskets for the food and pharmaceutical industries today!

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