Stainless steel comes in several common finishes. It is important to know what these common finishes are and why they are important. Recent innovations in abrasive technology can shorten process steps to achieve the desired finish, including the desired surface gloss.
Stainless steel can be tricky to work with, but the finished product has one of the best looks and is worth all the work. It is well known that using a finer grit in a sanding sequence can remove previous scratch patterns and improve the finish, but there are general steps to consider when using multiple grit sequences to achieve the desired finish.
Stainless steel comes in several common finishes. It is important to know what these common finishes are and why they are important. Recent innovations in abrasive technology can shorten process steps to achieve the desired finish, including the desired surface gloss.
The Specialized Steel Industry of North America (SSINA) describes industry standards and cases where different surface finish numbers are used on products.
number one. This finish is obtained by rolling stainless steel which is heated prior to rolling (hot rolling). Very little finishing is required, so it is considered a rough finish. Common products with No. 1 finish are air heaters, annealing chambers, boiler baffles, various furnace components, and gas turbines, among others.
2B completed. This lustrous cold-rolled finish resembles a foggy mirror and requires no finishing. Parts with No. 2B finishes include regular bakeware, chemical plant equipment, cutlery, paper mill equipment, and plumbing fixtures.
Class #2 also has #2D trim. This finish is a uniform dark silver gray for thinner coils that have been reduced in thickness by a minimal cold rolling process, as is typically used with factory finishes. Pickling or descaling must be carried out after heat treatment to remove chromium. Etching may be the final step in the production of this finish. When a painted finish is required, a 2D finish is preferred as a base as it provides superior paint adhesion.
Lacquer No. 3 is characterized by shorter, relatively coarse, parallel polishing lines. It is produced by mechanical polishing using progressively finer abrasives, or by passing coils through special rollers that press patterns into the surface that mimic the appearance of mechanical wear. This is a moderately reflective finish.
For mechanical polishing, grit 50 or 80 is usually used initially, and grit 100 or 120 is usually used for final polishing. Surface roughness typically has an average roughness (Ra) of 40 micro inches or less. If the manufacturer needs to sand welds or make other repairs, the resulting polish line is often longer than the manufacturer or polisher can polish. The third place most often falls on brewing equipment, food processing equipment, kitchen equipment and scientific instruments.
Finish No. 4 is the most common and is used in the household and food industries. Its appearance is characterized by short parallel polished lines running evenly along the length of the reel. It is obtained by mechanical polishing of the surface No. 3 with increasingly fine abrasives. Depending on the requirements of the application, the final finish can be from 120 to 320 grit. Higher grit gives a finer polish line and a more reflective surface.
The surface roughness is typically Ra 25 µin. or less. This finish is widely used on restaurant and kitchen equipment, shop windows, as well as equipment for the food and dairy industries. As with Polish #3, if the operator needs to sand welds or make other touch-ups, the resulting polish lines are often longer than on factory or roller polished products. Other areas where the #4 finish is found include tank trucks, hospital surfaces and equipment, instrumentation or control panels, and drinking fountains.
Lacquer No. 3 is characterized by shorter, relatively coarse, parallel polishing lines. It is produced by mechanical polishing using progressively finer abrasives, or by passing coils through special rollers that press patterns into the surface that mimic the appearance of mechanical wear. This is a moderately reflective finish.
Finish #7 is highly reflective and has a mirror-like appearance. No. 7 finish, polished to 320 grit and polished, can often be found on column caps, trim, and wall panels.
The abrasive materials used to achieve these surface finishes have made significant advances that can help manufacturers produce more parts safely, quickly, and cost-effectively. New minerals, stronger fibers and a dirt-repellent resin system help streamline the finishing process.
These abrasives provide fast cuts, long life, and can reduce the number of steps required to get the job done. For example, louvre discs with micro-cracks in the ceramic grains run slower, extending their lifespan and providing a uniform finish.
In addition, in technologies similar to abrasive aggregates, the grains are bonded to each other, which speeds up the cut and provides a better finish. This job requires fewer steps and less abrasive equipment, and most operators see increased efficiency and reduced costs.
Michael Radaelli is Product Manager for Norton|Saint-Gobain Abrasives, 1 New Bond St., Worcester, MA 01606, 508-795-5000, michael.a.radaelli@saint-gobain.com, www.nortonabrasives.com.
Manufacturers face the challenge of finishing the corners and radii of stainless steel parts. To mix hard-to-reach welds and castings requires a five-step process requiring a grinding wheel, a multi-grain square pad, and a uniform grinding wheel.
First, operators use a grinding wheel to make deep scratches on these stainless steel components. Grinding wheels are often hard and less forgiving, putting the operator at a disadvantage in the first place. The sanding step is time consuming and still leaves scratches that need to be removed with three additional steps of polishing pads of varying grits. Use a uniform grinding wheel after this step to achieve the desired surface finish.
By replacing the grinding wheel with a ceramic-based louvre, the operator can perform finishing operations in the first step. Keeping the same grit sequence as in step 2, the operator replaced the square louvre plate, saving time and improving the quality of the finish.
Removing the 80 grit square pad and replacing it with a concave agglomerated nonwoven center circle followed by a 220 grit concave center circle allows the operator to achieve the desired sheen and overall finish and eliminates the need for the last step of the original. process (using the uniform wheel to close the steps).
With improvements in the paddle wheels and nonwoven production technology, the number of steps has been reduced from five to four, resulting in a 40% reduction in finishing time, labor savings and product cost savings.
The abrasive materials used to achieve these surface finishes have made significant advances that can help manufacturers produce more parts safely, quickly, and cost-effectively.
WELDER, formerly known as Practical Welding Today, represents the real people who make the products we use and work on every day. This magazine has served the North American welding community for over 20 years.
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Post time: May-05-2023