Surface Sanding and Polishing
In rough grinding, the focus is on the amount or rate of material removal. However, in surface sanding and polishing applications, much more attention is paid to surface quality. Main examples include sanding, polishing, and finishing. These operations are sometimes referred to as surface conditioning, which aims to improve the surface without changing the basic shape/dimension of the workpiece. Material removal should be minimal and reasonably uniform, often involving many stages. Read more
Purpose - Part 2
Every surface, when magnified under a powerful microscope, looks like a cross-section of a mountain landscape. To obtain a smoother, more even surface, the contours have to be removed – the "peaks" leveled. This can be done by rubbing an abrasive back and forth over the surface, covering a larger area instead of concentrating on a spot. When a very smooth surface is required, using a liquid is an effective, low-friction way of removing the 'spent' grains and rubbing the surface finer.
Settings: Rotational Speeds - Part 1
The same basic grinding principle applies to surface applications. Coarser abrasives and higher speeds remove more material. Contact at high speed between the abrasive and surface spreads the feed force over a larger area and more grains, which retain their sharpness and stay attached to the backing longer. The speed shouldn't be so fast that the grains don't penetrate the cracks or hollows. If this happens, only the topmost edges will be removed, and the surface will not be totally smooth.
Settings: Rotational Speeds - Part 2
The key challenge is balancing the speed of our tools. At high speeds, the force is spread over a larger area, which can be efficient. However, at lower speeds, the abrasive can penetrate deeper into cracks. Finding the right speed ensures a thorough sanding and polishing job. This is done by setting the correct operating speed based on several factors: coarseness and flexibility of the abrasive, shape of the backing, and whether a liquid coolant or paste is used.
Technique
To get a smooth/even surface, the pad/abrasive should never be kept still at one spot during surface grinding. If it is, the abrasive tends to dig into the material, and the surface will not be fine. The feed force should be continuously adjusted to the rotational speed, which should be kept at 60-80% of the max rotational speed of the tool. When the surface has been made as smooth as possible with a coarse-coated abrasive, a finer quality or a nylon-coated abrasive can be used for finishing.
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