Finding the Right Finish: Understanding Polishing

The Perfect Polish

Stainless steel is a strong, corrosion-resistant alloy made of various combinations of chromium and other elements. Manufacturers use it in many industries for countless applications and products, including tanks. These include beverage production, brewing, dairy processing, HVAC, oil and gas production, pharmaceutical manufacturing, and several others.

Polishing a tank or other equipment is a physical process that removes material from a stainless-steel surface. Polishing your equipment produces multiple benefits, including ease of sanitization and increasing the surface’s resistance to corrosion, wear, and other environmental factors. As a result, it lengthens the service life of equipment. Polishing also improves the appearance of stainless steel, enhancing its smoothness, uniformity, and shine.

Some people are surprised that manufacturers can improve stainless steel in this way. While stainless steel has tremendous strength and durability, it isn’t impervious to corrosion and damage. Polishing enhances stainless steel’s natural characteristics, improving its durability.

The Polishing Process

Manufacturers polish stainless steel by applying various grades of abrasive media (sometimes called grit) to the surface. Typically, they do this in steps from coarse to fine abrasion.

This process removes impurities and minimizes or removes tiny cracks or crevices that can harbor bacteria or other harmful contaminants. Polishing can ensure that stainless-steel tanks meet specific customer or governmental requirements, including 3-A and BPE standards.

Common Material Finishes

Paul Mueller Company has extensive experience polishing stainless-steel process tanks and other products. We offer 10 different material finishes to accommodate any type of use. Material finish names are not industry standard, so it is always recommended to reference your needed Roughness Average (Ra) when specifying equipment finish requirements. 

• Hot-Rolled (HR) Finish: A hot-rolled finish results in a rough and dull appearance on the material’s surface.
• 2B Mill Finish: This finish features a smooth, bright, moderately reflective appearance suitable for “as-is” specifications, or we may achieve it as a preliminary finish for further polishing.
• #3 Finish: We create this finish using the equivalent of an 80-grit abrasive. It has a pronounced grit line and a 75 Ra average.
• #4 Finish: This is a bright finish with visible grain for use where sanitary surfaces are required. It has a 35 Ra target, but customers can request a 32 Ra maximum finish to comply with 3-A standards.
• #6 Finish: This finish has a 25 Ra target, which we achieve using the equivalent of a 240-grit abrasive. It results in higher reflectivity, finer grit lines, and improved product release and cleanability.
• #7 Finish: This finish has a 15 Ra target. If a customer’s product has critical product contact surfaces and requires minimal grit lines, they typically need this type of finish. We achieve it using the equivalent of a 320-grit abrasive.
• Bead Blast: This process follows sandblasting to create a satin, gray appearance that resembles a 2B finish.
• Radial Spin Polish: We use this process when performing inside, outside, knuckle, and straight flange surfaces. It follows a circular pattern and produces an aesthetically pleasing sanitary finish.
• Circumferential Spin Polish: This is similar to radial spin polishing. It further reduces the visibility of the circular pattern, creating a premium finish for high-visibility tanks.
• Sheet Polish: In this process, stainless-steel material is polished as sheets before forming. The formed items can be produced at a lower cost but will have a finish showing visible weld lines. In certain cases, follow-up spin polishing may be applied to refine the surface after manufacturing. Throughout this process, the surface maintains its Ra value.
• Electropolish: This electrochemical process removes a thin layer of material to enhance surface smoothness, improve corrosion resistance, and create a bright, reflective finish. It is commonly used to provide the level of product release and cleanability required by the medical, chemical, pharmaceutical and electronic industries. The electropolish process removes impurities and surface materials but may not remove nonmetallic inclusions that may be present in the parent material. The degree of improved performance depends on the weld and material finishes specified prior to the electropolish.

Custom Requirements

The material finishes listed above are standard designations of finish type. However, you can designate a required Ra for your equipment, and we will apply proper methods to meet your requested finish down to a 10 Ra.

Learn More About Stainless Steel Polishing

Few materials can compare to polished stainless steel’s strength, durability, and cleanliness characteristics. It is an excellent material for processing and storage tanks.

If you have questions about how polishing can ensure your stainless-steel products meet applicable functional and visual standards, we’re happy to answer them.