Polishing
Mechanical polishing removes fine scratches and machining marks with progressively finer abrasives to give a smooth, often reflective surface, from satin to mirror (below Ra 0.1 µm). It is used for appearance, cleanability and preparation before plating.
What it is
Polishing works through a sequence of abrasives such as belts, flap wheels and compounds, each finer than the last, until the target finish is reached. It can be done by hand, on polishing lathes, or on automated machines.
Stainless steel for food and pharma equipment is polished to specified finishes to make surfaces easier to clean, while decorative parts are polished before chrome or nickel plating.
Typical applications
- Food, dairy and pharma equipment
- Decorative hardware and fittings before plating
- Moulds and dies
- Shafts and rollers
- Architectural stainless steel
Suitable materials
- Stainless steel
- Brass and copper
- Aluminium
- Carbon steel
- Some plastics
Points to consider
- Specify Ra or a grit/finish number, or supply a reference sample.
- Polishing slightly rounds edges; mask sharp functional edges.
- Welds and deep scratches take extra work; minimise them upstream.
- Food-grade finishes are often specified as Ra ≤ 0.8 µm or finer.
Frequently asked questions
What Ra is a mirror polish?
A mirror polish is typically below about Ra 0.1 µm. General bright polish is around Ra 0.2–0.4 µm.
What does No. 4 and No. 8 finish mean?
They are common stainless steel finish names: No. 4 is a brushed satin finish and No. 8 is a mirror finish.
Should parts be polished before plating?
Yes, for bright decorative plating. Plating reproduces the surface beneath it, so polishing first gives a bright plated finish.