Introduction
Many metals are inherently dull in their natural form and many of them lose their gloss after being machined or after other processes they may be subjected to. In most cases when they are used in a product, they need to be brought to a mirror finish before the product reaches the market.
Some of the more difficult metals or alloys include: Stainless steel, Brass, Copper Aluminum and Zinc. Many of the better known processes are described here and can include Sanding, Sand Blasting, Magnetic polishing, Filing, Lapping, Ultrasonic Polishing, Electro Polishing and Rumbling and Tumbling.
Stainless Steel, Copper, Brass, Aluminum and Zinc
The components made from these metals are difficult to polish. Consequently, there are no hard and fast rules. But basically you will need the following:
- Sand paper of varying grits ranging from 400 to 2000 grit.
- A suitable polishing compound.
- Buffing wheels or polishing wheels.
- Soft polishing cloth or paper for end mirror polishing.
The Process of Sanding
This involves the cleaning of the surface using a coarse grit abrasive either attached to a paper or a cloth. The surface is vigorously rubbed until most of the unwanted material is removed. This is gradually followed by using finer and finer grits along with a suitable polishing compound and finally a stage of buffing with designated wheels and a high quality buffing bar to get a mirror finish.
Buffing compounds are chosen to accord to the metal being polished. The harder the metal, the chosen compound will be coarser.
Important Guidelines
Sanding is by far the most preferred polishing method used in almost all industries.
It is therefore critical that these factors are given due importance especially when there is mass production.
1. Cutting Down – Polishing Process
As far as possible the polishing process time must be reduced. Reducing the time taken to remove the initial rust or dirt can be done faster as this does not require any special technique. Only the initial grit of the paper or wheel must be much coarser. Filing the waste material is another method employed. This stage is where the actual time can be cut down.
2. Intermediate Polishing Process
Mostly, there must be an intermediate stage of polishing before the component is sent to the next stage. Here, the grit can be finer in nature along with a rubbing compound as this stage is the key to a good finished component.
3. The Finishing Polishing Process
The final process of finishing can be divided in two parts. Generally, buffing wheels with a tried and tested polishing bar is used to remove all the scratches that may be left behind.
4. Achieving a Super Finish – Polishing Process
A super mirror finish polish is required in some components. Here, a very fine soft cloth is used and rubbed very gently till all the remnants of the previous stages are removed completely. Buffing compounds are chosen to accord to the metal being polished. The harder the metal, the chosen compound will be coarser
Sanding can be used on most metal surfaces even if they are bent or curved. However, it is not very easy or practical to mirror polish narrow corners or pockets. There are some other processes that may be considered for these specific purposes.