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Home > Repairing a damaged part |
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Solarkote® capped sheet should be handled carefully to avoid scratching its surface. It is easier to avoid scratches than to remove them. Scratched surfaces can be restored to a good finish by a process of polishing and/or sanding. Sawed edges and machined surfaces can also be polished to a high gloss. Where power-operated polishing equipment is not available, it is possible to hand-polish minor scratches from the surface of the sheet. Rubbing with soft flannel and a good grade of automotive paste wax can polish minor scratches. Before sanding, buffing or polishing, clean the Solarkote® surface carefully. The buffing wheels and compounds should also be free from dirt and grit. Separate buffs should be dedicated to acrylic surfaces. Running the buffing wheel against a hard metal edge to remove hardened tallow, grease or other binders should clean the buffs. The friction of buffing, sanding or polishing too long or too vigorously in any one spot can generate enough heat to soften or “burn” the Solarkote® surface, resulting in visual distortion and possibly discoloration.This is especially true in the situation of a clear Solarkote® cap. To avoid this, keep the Solarkote® surface constantly in motion relative to the wheel, use light pressure and change the direction of buffing often. Air-cooling buffing wheels are often used to help reduce heat from friction. Polishing techniques vary with the equipment available and the size or shape of the acrylic parts polished. Sanding and buffing can cause thickness variation in the scratched area of the Solarkote® surface. If skillfully done, these operations cause only minor optical distortions that should not be objectionable for most applications. On occasion, critical sections, even though scratched, should not be sanded or buffed. They should simply be washed and waxed. A clear Solarkote® topcoat offers the thermoformer/fabricator/end user the opportunity to restore a slightly abraded surface to an "as-good-as-new condition" if the proper protocol is used. The following protocol has been defined using materials from 3M12. If executed properly, this process will restore a slightly scuffed Solarkote® surface to a lustrous, very high gloss.
If there is a deeper scratch in a Solarkote® surface, it should not be sanded unless the surface imperfections are too deep to be removed by light buffing. This process will result in some optical distortion, and should only be attempted if the final part can tolerate a "less than 'class A' surface." The way to tell if sanding is necessary is to rub a fingernail over the scratch. If it can be felt, then sanding is required. For situations that must be sanded, sand by hand, NOT BY POWER TOOL. Progressively finer grit 17 sandpaper/polishing compound should be used up to grits of 12,000. These grits are available as cushioned abrasive cloth. Use the finest sandpaper that will remove the imperfections. Coarse paper can cause scratches deeper than the original imperfection, and additional finishing operations will be needed. First try using 600-grit sandpaper wrapped around a rubberpadded sanding block. Sand over the scratch using increasingly larger areas of sanding. If this does not readily remove the scratch, step down to 400-grit sandpaper. The sanding should be done in directions mutually 30° apart to produce a diamond pattern. After sanding and stepping back up to 600-grit sandpaper, polish the sheet as described below. Do not use disc or belt sanders when dry. The greater danger of heat generation with mechanical sanders makes the use of water or oil coolants doubly desirable. Wet sanders are preferred, but dry orbital sanders can be used with care. Open-coat sandpaper should be used, since it does not become clogged as fast as closed-coat sandpaper. The Solarkote® surface should be clean and dry at the start of each buffing operation. Some polishing compounds leave the surface clean after buffing. If these polishing compounds are not used, washing the surface should follow the last step in polishing. If the part has previously been sanded or is deeply scratched, an abrasive-coated wheel is used first. The abrasive is a standard polishing compound composed of very fine alumina or similar abrasive and tallow. When most of the scratches have been reduced on the first wheel, the Solarkote® surface is buffed on the second wheel charged only with tallow. These first two wheels should be air-ventilated, cotton muslin rag wheels and should operate at 3,000 to 4,500 surface feet per minute (SFPM). To calculate: SFPM equals 1/4 the diameter of buffing wheel in inches multiplied by the spindle speed in rpm. The Solarkote® surface is next brought to a high polish by a soft, loose buff in which no abrasive or tallow is used. These cleaning buffs should be very loose and made of imitation chamois or cotton flannel. The wheels should be 10 to 12 inches in diameter and run at 3,000 to 4,500 SFPM. A hand-applied coat of wax may be used in place of buffing on the finish wheel, if desired. Polished Edges of Solarkote® Capped Sheet Solarkote® capped sheet edges should be free of chips and major irregularities to avoid a notching effect. Notches can become sites for cracks to start, and notched areas are more susceptible to chemical attack than notch-free areas. Sometimes good machine-finished edges are used as a decorative element in the design of a part made of sheet. Well-polished edges, however, may be required for decorative applications. Saw marks can be removed from the edges of Solarkote® capped sheet by scraping with a hard steel or Carboloy scraper, square-ground to a straight, smooth edge. After scraping, the edges should be sanded on a wet belt sander with 320-grit then 400-grit sandpaper. A fast method to polish sheet edges is to make buffs of layers of medium density 100 percent wool felt about 3/16 to 1/4 inch thick. The felt should have a specific gravity of about 0.27. The wheels should be 10 to 12 inches in diameter and should be held between hard faceplates about three inches smaller in diameter than the buff. The wheels should be run at a speed of 3,000 to 4,500 SFPM. The edges are buffed on a felt wheel that is charged with abrasive and tallow. The final polish is given to the edges with a soft cotton buff. Felt wheels should not be used on large flat areas, since there is a tendency to burn and distort the sheet. Whenever possible, a number of sheet or formed parts should be locked together in a jig leaving only the edges exposed, so that the edges may be planed, sanded and polished simultaneously. This technique is faster and gives better results without rounding the edges. Lapidary wheels surfaced with high-density felt also may be used for polishing flat surfaces. To prevent heat buildup, the sheet may be buffed with a paste or liquid wax with an abrasive. |
