Need help mirror polishing stainless steel?

What is Mirror polishing?

Mirror polishing is a process primarily used on stainless steel where the surface finish is brought up to a point where there is high reflectivity. However what needs to be done to achieve this?

The surface of metal can be defined as valleys and peaks. In order to achieve a No. 8 finish the Ra (roughness value average) must be below 0.025 Ra, for reference a brushed (hairline finish) is 0.8 Ra. In order to reduce the roughness average you must first go through the grits (from coarse to fine) and then finish with a polishing compound or 3 or even 5. It can be overwhelming to know what product is correct to use for your project.

What happens if I polish without prepping stainless steel?

It is enticing to skip straight to using polishing compound on stainless steel without the need for preparing the metal but much like painting the surface preparation is very important. If this step is skipped, you will be left with deep scratches still visible in the finished product as the polishing compound would only remove light scratches. While also accentuating the surface imperfections.

What abrasives should I use to prep for Mirror Polishing?

It is necessary to prep the surface before using polishing compounds. 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.

What abrasives to use with polishing compound?

There are a few different ways to apply mirror polishing compound and it depends on the object you want to polish. For flat surfaces; discs or sleeves would work great as there is a good contact patch between them and a bit of heat is needed. For pipes and tubes; belts or polishing mops are ideal.

The super polish abrasive range contains sleeves, discs and belts specifically designed for polishing and they do not clog, which affects the lifespan. These are available through 111 Abrasives Australia. (Check out our range of discs, belts, polishing mops and sleeves.)

How should I apply polishing compound?

A common question is should I apply the compound onto the workpiece or the polishing pad. The answer is to load up the pad with the polishing compound. If using a polishing compound bar load it onto the pad while the machine is running at low speed. Also make sure a clean pad is used for each different compound and not to mix them together. Generally, three compounds are used to achieve a mirror finish, a grey cutting compound, a white polishing compound and a green super finish compound. (We will go in depth into different compounds in a future blog post).

How can I simplify this process?

This process can be simplified by using the BRIGHTEX system by Eisenblätter with their 2-step polishing. Step 1 is the BRIGHTEX Berry which is a cutting compound (but already leaves a great finish) and step 2 is the BRIGHTEX Sun which is a final compound which makes mirror finishing a breeze and enhances the finish to a deep shine.