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acrylic finishing |
Finishing
Machined surfaces of Perspex® from Lucite® are usually matt unless diamond cutting tools are used. Machine marks are best removed by scraping with a sharp blade set at 90° or sanding and then the gloss finish restored by polishing.
Sanding
Bench mounted or portable sanders may be used - as may belt sanders -to remove machine marks or saw cut marks from the edge of Perspex®. Sanding should be carried out dry and only very light pressure applied to prevent softening or melting of the surfaces. After any sanding operation it will be necessary to anneal the work if cementing or surface decoration is intended.
Polishing
Power buffing with rotating calico mops is the traditional polishing technique for Perspex®. Edges must first be scraped or sanded to remove all machine marks then a mild abrasive buffing soap may be applied. Moderate speeds and only very light pressure is needed otherwise overheating will occur.
Diamond polishing can be used for straight edges and gives excellent results without the rounded edges often produced by buffing. Diamond polishing produces very little stress in the surface.
Flame polishing is ideal for polishing thin edges of Perspex®, especially clear extruded sheet for point-of-sale items because it is fast and effective. A good routered or scraped edge is essential for flame polishing. Specialised equipment is available otherwise a small blow-torch type gas-air flame can be used. The technique requires some practice to achieve the desired level of skill. Only the slightest impingement of the hottest part of the flame is required rapidly passing the jet across the work. Great care must be taken not to ignite the surface and it should be noted that flame polishing can produce highly stressed edges. Annealing of the work piece will be necessary if the flame polished edges are to be cemented or decorated.
Flame polishing can be difficult on certain heavily pigmented colours resulting in a matt finish or discolouration. Please read the section on Flammability below.
Hand polishing is suitable for the restoration of the original gloss finish after minor surface scratching. Deep scratches should first be removed using 600 grade waterproof abrasive paper applied wet with a light circular motion. To avoid optical distortions, the abraded area should be much larger than the damaged surface to "feather" the edges. Final polishing of the matt abraded area can be carried out using proprietary acrylic polishes available from your distributor of PERSPEX® sheet. Good quality metal polish intended for use on silver plate can be used provided the product has been tested and found to be compatible with PERSPEX®.
I polished the edge of this acrylic shelf below by hand.
Flammability
All Perspex® grades are combustible and if ignited will continue to burn. Little smoke is evolved when Perspex® burns.
The combustion products when Perspex® burns vary with temperature and the amount of oxygen present. A full study of the combustion gases evolved under widely different conditions has been made (see Reference). The conclusions were that carbon monoxide was always the major toxic gas present with carbon dioxide, water and methyl methacrylate.
Reference
A study of DIN 53436 and NBS (Potts’ PA) as fire models for the assessment of the toxicity of combustion products of plastics. British Plastics Federation Publication 314/1 April 1987.
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