Paintings, Surface Finishing

Where the molding is to be painted, it is a good precaution to avoid using waxes or silicone release agents in the first place, or use these only as a primary release agent. 

Primers with particularly good adhesion to RP surfaces are offered by several paint manufacturers and, for a durable surface, it is advisable to use them. They can be applied without previous abrading, if the surface is clean and dry. When normal paint primers are used, it is advisable, however, to rub down the surface with a fine abrasive, to obtain good keying. 

Most paint systems can be used on RPs. For stoving finishes, the molding should be post-cured at 80C before the finish is applied airdrying finishes can usually be applied without post-curing. Most cellulose finishes are also suitable, but with these, it is particularly important to ensure that the resin has fully cured, to prevent the solvents attacking any uncured resin. 

Humidity resistance Grease and oil resistance General chemical resistance General corrosion resistance (industrial atmospheres) Exterior durability (pigment) 

While the process was found to offer significant advantages, such as manufacturing versatihty, fast color-change, and use of near-zero volatile organic compounds (VOC), there were also some drawbacks. These are particularly entrapment of air, need for a sophisticated system to adjust parallelism on the mold halves, difficulty of coating vertical surfaces, and increased cycle time and limitation of possible locations for the ejector system. 

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A variety of thermosetting resins are used in SMC. Polyesters represent the most volume and are available in systems that provide low shrinkage and low surface profile by means of special additives. Class A automotive surface requirements have resulted in the development of sophisticated systems that commercially produce auto body panels that can be taken direcdy from the mold and processed through standard automotive painting systems, without additional surface finishing. Vinyl ester and epoxy resins (qv) are also used in SMC for more stmcturaHy demanding appHcations. 

Rotary atomisation produces an excellent surface finish. The spray has low velocity, which allows the electrostatic forces attracting the paint particles to the ground workpiece to dominate, and results in transfer efficiencies of 85—99%. The pattern is very large and partially controlled and dkected by shaping ak jets. The spray when using a metallic cup has relatively poor penetration into recessed areas. Excessive material deposited on the edges of the workpiece can also be a problem. 

Synthetic resins are extensively used, e.g., in surface finishes, in the fabrication and repair of boat and motor vehicle bodies, in the manufacture of laminated boards, for electrical components, in pattern making and in paints and varnishes. Non-rubber adhesives made from fish glues and from cotton derivatives (e.g. cellulose acetate) tend not to be sensitizing but, depending upon composition and the manner of use, many other types may pose significant dermatitic and fume hazards. 

Nowadays, however, zinc-coated steel sheets, either continuously galvanised or electroplated, are often used as a basis material for overcoating with plastic materials or paints. The coatings are usually applied continuously and have a range of uses both externally and internally. Many surface finishes are obtainable, e.g. plain or embossed, and in an extensive range of colours, to suit almost any requirement . 

There are three standards controlling surface finish in common use. They are issued by the Steel Structures Painting Council (USA), the Swedish Standards Organisation and the British Standards Institution. They are roughly equivalent. 

In BS 4232, Surface Finish of Blast Cleaned Steel for Painting, first quality corresponds to SA3,2nd to SA2-5 and 3rd toSA2of the much more extensive Swedish Standards Commission s SIS 055 900-1962, RusI Grades for Steel Surfaces and Preparation Grades Prior to Protective Coaling, Stockholm (1962) see also BS 7079 Part A1 (1989)... 

Various types of surface finishes are available for plastics and RP products, such as smooth, textured, molded-in color, and inmold coating. A textured product surface can be obtained through either a textured mold cavity or a postmold paint process. The former method is the most commonly used. A... 

Paint Spray - Surface Finishing - Surface Coating... 

Phenylenediamine gasoline antioxidants will discolor paint if allowed to remain on the exterior finish of a vehicle. The PDA antioxidants will react with oxygen to impart a color change to the paint. It is always recommended that gasoline which spills or overflows onto a painted surface be washed off as soon as possible. 

Infrared drying sheets of textiles, paper and films, surface finishes of paints and enamels, and surface drying of bulky nonporous articles. 

When a painting is finished, the artist often applies varnish or lacquer to the painting surface. Varnishes, and often paints, are thinned with turpentine. Turpentine can be used to remove surface varnish. Turpentine is moderately toxic if inhaled or ingested. Carbon tetrachloride, toluene, and methyl alcohol are also used to remove varnish (see Figure 10.2). Carbon tetrachloride and toluene are highly toxic if routinely inhaled. 

Paintability is generally not a problem under dry normal conditions. Unusually high relative humidity conditions can affect adhesion of the paint film or cause chemical crystal blooming on the paint surface due to the increased moisture content of the wood. Natural or clear finishes are generally not used for treated wood because the chemicals may cause darkening or irregular staining. 

Douglas fir plywood with acetylated faces, when exposed to the weather on a test fence for two years without a surface finish developed only a slight roughening and checking whereas the controls weathered and checked badly (76). The weathering of exterior paints on panels with acetylatecT faces were considerably better than on the controls. Presurface acetylation also seemed to improve the weathering properties of painted wood (36, 37). 

Equipment for the catering trade, particularly for bars, also offers opportunities for electroplated plastics items such as display heads for beer pumps may be made by combining electroplating with painted surfaces drip trays for glasses are moulded from plastics and finished with nickel-chromium to enhance their resistance to abrasion and for convenience in cleaning. 

The effect of composition, the nature, and the ratios of the constituents on the properties of paints, are factors of utmost importance in paint formulations. An indication of likely service environment, life expectancy of the coatings, method of application, color, surface finish, drying time, and cost are also taken into consideration. All of this information. 

Surface Finishes. Of almost equal importance are surface finishes and surface coatings. For instance, E-coating (or electrophoretic painting) is an effective contaminant-containment for many machined metal surfaces such as aluminum and magnesium surfaces, and for magnets. Other surface treatments applied in past and current IBM disk drives are listed in Table A1. 

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