Polishing stainless steel to a mirror shine

Polishing stainless steel is officially the last part of a whole series of steps that ultimately aim to achieve a (high) gloss result.

For a shiny result, preprocessing is essential. We begin the process with pre-grinding. In this process, you still take off material, creating new scratches. By sanding with an increasingly fine grit, the scratch pattern also becomes finer and the grinding marks increasingly shallow. Material is still taken off at each step. What is important is that the different grains follow each other well. The steps should not be too large. So we do not go from grit 60 to grit 180, but add a step with grit 120. In fact, grit 120 can sand away the scratch made with grit 60. With a sanding disc K180 this is not going to work. In the end result, the under scratch made with K60 will always remain visible.

You cannot easily polish away this under scratch afterwards either. The only thing you can do is to start again with sanding from that conscious grit 60. Careful sanding and good looking, cleaning and checking is essential!

Make sure you always sand at right angles to the previous step. This makes it easier to see if the scratch from the previous step has been removed.

The entire stainless steel polishing process takes a lot of time. Efficiency is therefore of great importance. Because every step we can skip saves time and therefore money.

The choice of disc type is important in this. One disc with grit 60 can give a completely different grinding pattern than grit 60 of another brand. The hardness of the material being machined is also an important factor.

There are also different methods of polishing. It can be done with a variable-speed angle grinder, with a satinizer or a flexible shaft machine with caramel wheel.

You can read more about the sanding belts we have available here.

We can even polish with a TopGrinder or other tabletop machine:

Therefore, it is impractical to present here a definite step-by-step plan that will suffice in every situation. However, we can provide some rules of thumb. It is important to clean the product after each step to remove any contamination and abrasive material to avoid false scratches.

1. Does it have to be mill scale removed? Mill scale is usually a blue-black oxide layer on steel that is formed during hot rolling of the metal. This hard layer is often difficult to remove. Use an aggressive abrasive for this operation, such as a fibre disc with ceramic grain. The purple Clean &Strip discs from 3M can also be a solution.
2. After removing the mill scale, we can start sanding with 150-mm sanding discs in grit 120, (180), 240, (320), 400 and K600. We like to use Klingspor PS73 discs. We always grind the next step at right angles to the previous step in order to blend the scratch pattern. For the last step, we use grinding grease, to get a finer result faster. The sanding is done with the MT-One, an angle grinder with adjustable speed. We start with 2,500 RPM. The choice of pad depends on the shape of the workpiece. Tight lines and few contours are best polished with a harder pad such as the FL36155. For products with more contours or holes, you prefer to use a softer pad such as the DY57543.
3. After pre-grinding, we can move on to pre-polishing. Use a machine with adjustable speed like our Mt-One. A very convenient quick-change system for the polishing wheels is the PTL system. Read more about the unique Push-Turn-Lock system on our page about stainless steel machining. When using 150 mm polishing wheels, set the polisher back to 2500 Rpm. Hold the polishing paste against the rotating disc and while pre-polishing, keep adding paste until an even surface is created. Pre-polishing starts with a sisal/cotton wheel combined with a green polishing paste. This paste with an ultrafine abrasive grain, in combination with the fairly stiff disc, still provides minimal material removal and thus removes grinding marks from the previous stages. Do not proceed to the next step until all these grinding marks are actually polished away.
4. In this step, we will polish stainless steel to a high-gloss result. This is achieved by working with a cotton rag rug in combination with a pink paste. Each time, work at right angles to the tracks of the previous polishing operation.  
5. If you want an even shinier result, we go to a Mirror finish, which again has several gradations. A Mirror10 super finish is achieved with a flannel rag wheel and a white paste. Reduce the speed to 1,000 RPM to introduce less heat. Heat can actually open up the material, which can cause pitting.
6. Cleaning: And then there is the result! Remove the residue of the polish with Wener lime and a soft cloth. And then look at all the beauty!

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If you need advice, please call 033-4558788 for a no-obligation consultation or demo.

Photo: Metalfinish Joure

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