Polishing and Linear Brushing

by Multipunch

POLISHING AND LINEAR BRUSHING

Polishing and buffing are finishing processes for smoothing a workpiece’s surface using an abrasive and a work wheel. Technically polishing refers to processes that use an abrasive that is glued to the work wheel, while buffing uses a loose abrasive applied to the work wheel. Polishing is a more aggressive process while buffing is less harsh, which leads to a smoother, brighter finish. A common misconception is that a polished surface has a mirror bright finish, however most mirror bright finishes are actually buffed.

Polishing is often used to enhance the looks of an item, prevent contamination of instruments, remove oxidation, create a reflective surface, or prevent corrosion in pipes. In metallography and metallurgy, polishing is used to create a flat, defect-free surface for examination of a metal’s microstructure under a microscope. Silicon-based polishing pads or a diamond solution can be used in the polishing process.

The removal of oxidization (tarnish) from metal objects is accomplished using a metal polish or tarnish remover; this is also called polishing. To prevent further unwanted oxidization, polished metal surfaces may be coated with wax, oil, or lacquer. This is of particular concern for copper alloy products such as brass and bronze.

The term chem-mechanical was coined to describe the action of corrosive slurry on silicon in a polishing process. Multiple rotating heads, each studded with silicon wafers, get forced against a large rotating buffing pad, which is bathed in a corrosive slurry. Material removal at elevated temperature progresses first through oxidation, then through oxide removal by abrasion. This cycle repeats with each rotation of a head. Potassium Hydroxide and Silox (white paint-base) can be combined with deionized water to form such a slurry. 

Brushed finishes typically have a detrimental effect on corrosion resistance. In particular, the brushed texture limits the ability of the fluid to bead on the material surface. In the case of stainless steel the grooves of the finish can accumulate chloride ions which break down the chromium oxide passivation layer, enabling rusting to occur.

The intensity of the brushed finish is specified as a surface roughness and is typically between 0.5-1.5 micrometres Ra