Worked in the Industry for 10 years with a years training with abrasives in Germany
A No.4 finish is categorically a sanitary or pharmaceutical level finish which is practical yet decorative. To achieve such a finish the grits and type of abrasive vary greatly:
POLY PTX Fleece Wheels – Grit 60 – Grit 400
POLY PTX Mix Wheels – Grit 60 – Grit 280
POLY PTX Flap Wheels – Grit 60 – Grit 240
POLY PTX SC Fleece Sleeve – Medium & Fine
The higher in this grit range you go the brighter the finish will be and the fainter the linear scratch marks become.
Matching a 2B finish using Linear finishing wheels is simply not possible. A 2B finish is created during the manufacturing process where the metal is cold rolled from the mill and has a slight lustre but no reflectivity. Since the fleece wheels (or any linear wheel) will be putting a scratch pattern into the surface which the 2B finish does not have.
Optically the closest you can get is approximately grit 280-400 using the POLY PTX Fleece Wheels. The differences are that a scratch pattern will be present and the reflectivity will be higher compared to the 2B finish.
Alternatively, using an abrasive blasting technique may get the finish closer to 2B due to there being no scratch pattern present, however it is still not 100%.
It is necessary to prepare the surface before using polishing compounds and this constitutes a no.7 Light Polish.
This is where it depends on the condition of the metal in the first place. If there is scale on the surface, you might have to start with a coarse grit such as a grit 40. This is the worst-case scenario as most pieces will be a 2B finish as the starting point which has a surface roughness equivalent to about grit 150.
Trizact or silicon carbide is a great abrasive to use to prepare for mirror polishing. Trizact also has more cutting power for the equivalent grit, so it is much faster to prepare. We would generally recommend going to grit 400, then to grit 600 and then 1200 if required. It is very dependant on the type of polishing compound being used in the next step. The Trizact abrasives leaves a matte appearance and is fantastic at removing scratches and creates the ideal base to start mirror polishing.
The products used for this process are the POLY PTX Trizact Sleeve and POLY PTX Superpolish Sleeve, we highly recommend using the inflatable POLY PTX Expansion roller as it virtually elimates chatter marks and ensures a great finish.
Our POLY PTX Wheels are balanced like the tyres on a car, weights are inserted if required to ensure they run centred.
