Your Polishing Questions Answered (Issue 2)

Mon 16th July 2018

1. What grit is a bright polish?

We get asked this question a lot. We also have stockholders tell us with complete confidence that a bright polish is ‘a 400 grit’. The first thing that needs to be established is what the substrate is. If it is a 2m x 1m 0.7mm stainless steel sheet the process route will be completely different to a small bracket or a length of flat bar.

If we are talking standard sheets then the process is completely mechanical using mops and polishing compounds. These compounds are bovine free fatty liquids with very small grains of abrasives suspended in them. The liquid id applied to the surface of the sheet and a wide bank of polishing mops rotate and oscillate on the surface of the sheet to give the required reflectivity – abrasive belts such as those used to give a Dull Polished finish are not used to create a bright polished finish on standard sheet.

For smaller items or lengths of bar, for example, quite often abrasives are used. This is usually done through stages by a hand (or semi-hand) polishing operation and the abrasives used will progress through finer and finer grits and mops until the level of reflectivity is achieved. This is a completely different process route and whilst achievable on small pieces it would be very difficult and time consuming to produce a uniform finish on larger items.

2. I ordered some Dull Polished sheet with laser coating but the laser coating still ‘blew off’ – why?

There are lots of different laser quality coatings available to apply to the surface of stainless steel sheets and plates. However all of them do come with a caveat that the adhesive levels of the protective tape that make it suitable for laser cutting require a minimum of seven days to cure from the application date – subject to being stored and applied in median temperatures. All protective tapes have a specification sheet produced by the manufacturer and distributor and you should be able to source these freely from the polishing company that applies the product. You should also ensure that if material is being cut on a Fibre Laser line you don’t order tape that is only suitable for a Co2 Laser Line.

3. I had a plate dull polished both sides but on one side there is a line down each long edge that is not polished. Why?

Most sheet and plate is produced with the A side having the two long edges ‘burr down’ from when it is slit to width prior to being cut to length. This means that if the B side is polished and the burr is ‘high’ there will be a narrow band running parallel to the burr that is un-polished. The higher the burr – the wider this un-polished area will be.