Coatings surface preparation

Test samples have been prepared from a 3 mm hot-rolled steel sheet which showed an intact mill scale (Degree A of Swedish Standards, SIS-055900), Thereafter they were shot blasted with S-280 to reach the ASa3 standard, prior to the application of the paint coating. Surface preparation B St 2 was obtained by wire brushing a steel sheet of Grade B obtained in turn by oxidation of Grade A sheet in a contaminant free atmosphere. In "Table I.", the characteristics of the paints used in this study are shown. 

The highest mass fragment, obtained from the fresh HAPS-coated glass surface, occurred at m/z = 477 and contains four Si—O bonds in its structure. This is twice the size of the largest HAPS fragment (m/z = 221) obtained from the as-coated surface prepared with the previously used batch of APS. 

Most etching, anodizing, or conversion coating surface preparation will produce joints of superior durability under stress and corrosive, saltwater exposure conditions. Mill-finish, vapor-degreased, or mechanically abraded surface joints performed poorly in comparison, regardless of alloy choice. 

ASTM D2651 describes practices that have proved satisfactory for preparing various metal surfaces for adhesive bonding or coating. Surface preparations for aluminum alloys, titanium alloys, and copper and copper alloys are included in this standard. ASTM D2093 describes recommended surface preparations for plastic adherends. 

Coatings Surface preparation Protection under disbonded coatings... 

NACE Standard Practice for the Application of Internal Plastic Coatings for Oilfield Tubular Goods and Accessories (RP0191) addresses initial inspection of equipment to be coated, surface preparation, coating application, coupling/ connection makeup, and quality control. 

Type Coating Systems for Atmospheric Exposure (primer/midcoat/to coat) Surface Preparation Number of Coats DFT c. C3 5-M... 

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Surface preparation, always important in obtaining optimal coatings performance, is critical for marine coatings (see Metal surface treatments). Surface preparation usually comprises about half of the total coating costs, and if inadequate may be responsible for early coating failure. Proper surface preparation includes cleaning to remove contaminants and roughening the surface to faciUtate adhesion. 

Coatings for tanks have to be chosen so that they can withstand the particular conditions [10]. The high-grade modern systems demand very good surface preparation of Sa IVi, which cannot always be achieved in practice, because of their ribbed construction and confinement. The increased frequency of defects has to be reckoned with. 

In Section 4.3 several recently developed and experimental surface preparation methods for steel such as conversion coatings, plasma spray and sol-gel that attempt to simultaneously improve durability and bond strength over grit blasting will be discussed. 

Surface preparation of the core foil was originally simple acid etching. As the importance of durable surface treatments became known, a more stable chemical conversion coating with an organic primer-like coating became standard. Still, water ingression into honeycomb structure continued to cause the occasional... 

Protective coating Cladding Painting Plating Sensitivity to contaminants Suitability Type surface preparation... 

Application of protective paints consists of surface preparation of steel, priming coat and finishing coats. Wherever possible, steel should be blast-cleaned before painting. Primers thoroughly wet the metal to promote adhesion of finishing paints and carry inhibitive pigments. For example, red lead oxide will minimize the spread of rust on metal surfaces. The total thickness of fmishing coats must be at least 0.125 mm for adequate protection and life. Four coats of paint usually are necessary to achieve this. 

It is difficult to give precise costs of floor treatments as size of total area, areas to be coated at one time, degree of surface preparation required and other factors all influence costs. Table 9.2 is a rough guide to comparative applied costs. 

Bituminous This term is used for products obtained from both petroleum and coal tar sources but the petroleum products are the more widely used. These materials are very resistant to moisture and tolerant to poor surface preparation. They are only available as black, dark brown or aluminum pigmented. The last has reasonable outdoor durability but, without the aluminum, the film will crack and craze under the influence of sunlight. Normally they cannot be over-coated with any other type of paint, because not only will harder materials used for over-coating tend to crack or craze but there is also a possibility that the bitumen will bleed through subsequent coats. The best use is as a cheap waterproofing for items buried or out of direct sunlight. 

Coal tar epoxies These are a combination of epoxy resins and selected coal tars. Properties can vary, depending on the coal tar-to-epoxy ratio. The ideal compromise appears to be approximately 50/50. Coal tar epoxies are only available in black or dark brown. They cost less than straight epoxies and generally have better wetting properties, so they can be used on slightly less than perfect surface preparation. There are similar re-coating problems as for the two-pack epoxies. 

The coating remains relatively soft and flexible, and is not suitable for areas where people may walk or touch the surface. The best use is for steelwork in enclosed areas or with difficult access where surface preparation and application are not easy. 

Zinc silicate This material has good corrosion resistance and can withstand temperatures up to 540°C, particularly when over-coated with silicone-based aluminum. The zinc silicate requires a high standard of surface preparation before application. 

Two-pack epoxy Section 12.3.3. These are widely used to give the maximum protection to concrete surfaces, floors and walls. They can be applied as relatively thin coatings by spray or as thick epoxy surfaces applied by trowel. In all cases, the application must be preceded by adequate surface preparation (see Section 12.6.1). To allow maximum penetration into the concrete the first coat must have a low viscosity. Coal tar epoxies are used where protection is the main requirement. 

Surface preparation of concrete consists mainly of removing laitence, form oils and air pockets. Laitence is the fine cement powder that floats to the surface of concrete when it is placed. Coatings applied over such a powdery, weak layer will lose adhesion. Form oils are used for the easy stripping of forms or shuttering. Their presence will also cause loss of adhesion of subsequent coatings. Forms should be coated with non-migratory hard coatings and the use of oils or waxes prohibited. 

To state the means by which the required life of the coating is to be achieved. This includes surface-preparation standards, paints and systems, application, storage, handling and transport, quality control ... 

If at the end of the exercise the cheapest system is beyond the budget available then either the budget must be increased or changes in the initial protection will be required. Whenever possible, the level of surface preparation should not be lowered, since if at a later date more money is available the protective coating can be built up but the surface cannot be re-prepared. 

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