Polishing
Mint Design has the capability to achieve various mechanical finishes depending on the desired aesthetics or function of the part. Everything from a #3 finish all the way up to a #8 mirror finish polishing on plastics, chrome/nickel plating, aluminum, brass, copper, mild and stainless steel. We can do everything from small parts that fit in the palm of your hand, to large parts that require portable surface finishing and buffing machines. We also have the ability to polish tubing such as hand rails or any other type of tubing that would require a consistent finish along the entire length of the part. A good example of this is our #4 finish applied to exhaust pipe tubing. As can be seen here.
Here are the industry standard mechanical finishes for surface finish.
Mechanical Finish Designations
#3 Finish – also referred to as Grinding, Roughing or Rough Grinding
This finish is coarse in nature and usually are a preliminary finish applied before manufacturing. An example would be deburring or removing excess weld material. It is coarse in appearance and applied by using 36-100 grit (61 RA, 69 RMS min) abrasive. When the finish is specified as #3, the material is polished (either linear or random) to a uniform 60 – 80 grit. This finish is also well suited to carbon steel and iron parts preparing for most painting operations.
#4 Architectural Finish – also referred to as Brushed, Directional or Satin Finish
A #4 Architectural Finish is characterized by fine polishing grit lines that are uniform and directional in appearance. It is produced by polishing the metal with a 120 – 180 grit belt or wheel finish and then softened with an 80 – 120 grit (52 RA, 58 RMS min) greaseless compound or a medium non woven abrasive belt or pad. An alternative can also be achieved by random polishing grit lines as opposed to being directional.
#5 Dairy or Sanitary Finish
This finish is commonly used for the medical and food industry – almost exclusively used on stainless steel. This finish is much finer than a #4 Architectural Finish. Great care should be taken in removing the surface defects in the metal – like pits – that could allow bacteria to grow. A #4 Dairy or Sanitary Finish is produced by polishing with a 180 – 240 grit belt or wheel finish softened with 120 – 240 grit (15 RA, 17 RMS min) greaseless compound or a fine non woven abrasive belt or pad.
#6 Finish or Fine Satin Finish
Produced by polishing with a 220 – 280 grit (approx. 14 RA, 16 RMS min) belt or wheel softened with a 220 – 230 greaseless compound or very fine non woven abrasive belt or pad. Polishing lines should be soft and less reflective than a #4 Architectural Finish.
#7 Finish
Produced by polishing with a 280 – 320 belt (12 RA, 14 RMS min) or wheel and sisal buffing with a cut and color compound. This is a semi-bright finish that will still have some polishing lines but they should be very dull. Carbon steel and iron are commonly polished to a #7 finish before chrome plating. A #7 finish can be made bright by color buffing with coloring compound and a cotton buff. This is a good way to keep polishing costs down when a part needs to be shiny but not flawless.
#8 Finish or Mirror Finish
This finish is produced by polishing with at least a 320 grit belt or wheel finish. The part is sisal buffed and then color buffed to achieve a mirror finish. The quality of this finish is dependent on the quality of the metal being polished. Some alloys of steel and aluminum cannot be brought to a mirror finish. Castings that have slag or pits will also be difficult – if not impossible – to polish to a #8.
Here are two examples of aluminum parts polished to a #8 finish:
Aluminum is quite difficult to keep scratch free due to the softness of the material. Also over time the surface will oxidize and require frequent re-polishing to keep the same luster.
