Polishing Acrylic – It’s Easy to Get Rid of Even Deep Scratches
Posted by admin in Articles on May 29, 2018
Removing scratches and maintaining optical clarity of acrylic is not difficult to do all. Here’s what the Handbook of Acrylics has to say on the matter.
Scratches, gouges, and marks on acrylic surfaces can be removed by hand or machine sanding.
Wet or dry sandpaper should be used, with a coarse enough grit to remove the blemish and progressively finer grits to finish the process. The sanding surface should be kept wet with water to minimize generated heat and to prevent clogging of the sandpaper.
A uniform and flexible back-up pad, such as neoprene foam, can be used behind the sandpaper to help distribute pressure. A slightly larger area should be covered with each finer grade of paper to prevent localized sanding distortions.
Scratches left by the sanding, or hairline surface scratches developed in service, can be removed by buffing and polishing.
Such finishing can be done for purely aesthetic reasons or, in the case of transparencies, to improve optical quality. Used first is an abrasive wheel, which consists of a buffing pad made of stitched cotton or flannel and an abrasive compound composed of very fine alumina, or similar material, combined with tallow or wax binders.
The wheel should run at about 1800 surface feet per minute. After this operation, a buff of only tallow is used to refine the acrylic surface further. A high luster is finally achieved by carefully buffing with a wheel without abrasive or tallow.
These operations should be done with extreme care to prevent overheating the acrylic surface and the developing of a rippled surface which has the potential for subsequent crazing.
The preferred method of cleaning acrylic is washing with mild detergent and water. A soft, clean cloth or chamois should be used with only a light application of pressure.
Oil or grease spots can be removed with aliphatic naphtha. Do not use alcohol, gasoline, acetone, benzene, chlorinated hydrocarbons, strong caustics, lacquer thinner, or household window cleaning compounds.
When cleaning acrylic you should also be aware of the surface coating and texturing.
Several types of coatings are applied to the surfaces of acrylic to improve resistance to abrasion, provide reflective qualities, and enhance visual transmission and electrical conductivity.
Films, such as paints and inks, are used for either decorative purposes or to provide special optical effects. The basis for successful application is substrate preparation, cleaning, and a compatible coating chemistry. Each coating is usually intended for a limited range of acrylic grades.
Acrylic sheets are made significantly more resistant to abrasion through the application of special coatings. One coating is described by its manufacturer as crosslinked fluoroplastic polymer containing silica.
Other manufacturers are working to develop coatings based on different polymer systems. In general, these coatings improve light transmission, reduce haze, and improve the solvent resistance of coated surfaces.
They are characterized by excellent resistance to weather and environment, and are finding application in the areas of public transportation, buildings, and display windows. Vacuum-deposited and chemically plated thin films of aluminum, silver, chromium, or gold are routinely applied to acrylics.
Film thicknesses range from 1 to 1000 microinches (2.54 to 2540 m x 10'8). In the case of very thin films (approximately 1 microinch [2.54 m x 10-8]), the materials can be transparent and are used in heater elements, radio-frequency shields, passband filters, and antireflective devices.
Thick films (approximately 1000 microinches (2540 m x 10'8) are opaque and are used in decorative products or reflective items.
Acrylic can be easily painted. A special application involves back painting clear acrylic material, a procedure which protects the paint from damage and provides a unique beauty.
Inherent in this application is the need for clean acrylic surfaces. Oils or greases can be removed by using aliphatic naphtha, hexane, kerosene, or white gasoline. For general cleaning, water and a mild detergent, followed by a thorough rinsing, is preferred.
Acrylic-based paints are recommended for outdoor applications with alkyd paints acceptable for indoor items.
Acrylic can also be effectively silk-screened, a process widely used in the sign industry. It is possible by using this process to form shapes from flat silk-screened material, thereby simplifying the color application process.
It is also possible to obtain acrylics with various textured surfaces. These textures are applied either during polymerization of the stock or as a secondary operation by using embossing techniques.
No matter what coating and texture your acrylic has, one of the great things about this material is when the first stage of failure – crazing – appears, the acrylic panel can easily be restored to its original condition by sanding and repolishing the surface.
If the acrylic panel is allowed to progress to the next stage of failure – crazing transforming into small cracks – steps could then be taken to replace the acrylic window. The onset of crazing to the progression of cracks is a long process and there are aquarium windows that have had evidence of crazing for many years without cracks developing.