Grit blasting

A grit blasting often forms the basis for surface preparation. The equipment, which may be used needs to offer a number of features. Of these the first is that the inserts should be presented to the grit stream in a uniform and continuous pattern so that the blasting medium is distributed evenly over the work area. The second requirement is that of dust removal. The process continuously removes material from the inserts and at the same time the grit itself is reduced in size. This dehris must be removed so that the size distribution of the grit remains constant to ensure that a clean, uniform surface is maintained. 

Surface hardened steels show a different reaction to the standard treatment of mild steel. Normal grit blasting with chilled iron will only polish the surface and not remove the scale adequately. Aluminium oxide, or corundum, is the best choice for cleaning these materials. 

Aluminium is used increasingly to reduce the weight of bonded components. This metal should never be cleaned with ferrous grit, which will impact into the surface and can give rise to a significant rust effect. It is also worth noting that spontaneous combustion can occur in the dust exhaust system where aluminium dust is mixed with that of iron oxide. The use of aluminium oxide should be used although a caustic etch can also be effective (See Section 10.4.1). 

Grit blasting processes are unnecessary with plastic inserts (See Section 10.3.3). 

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Steel Shot and Grit. Steel shot and grit are also widely used ia grit blasting and abrasive finishing. In 1989, 220, 196 metric tons of metallic abrasives were produced in the United States with a combined value of 89.55 million (20). 

Hardness. Glass hardness tests usually measure the resistance to abrasion by grinding or grit-blasting, resistance to scratching, or penetration by an indenter. The method to be used depends on expected service conditions. Knoop hardness (Table 4) is commonly used, because other methods usually fracture the glass. 

AppHcation of an adhesion-promoting paint before metal spraying improves the coating. Color-coded paints, which indicate compatibiHty with specific plastics, can be appHed at 20 times the rate of grit blasting, typically at 0.025-mm dry film thickness. The main test and control method is cross-hatch adhesion. Among the most common plastics coated with such paints are polycarbonate, poly(phenylene ether), polystyrene, ABS, poly(vinyl chloride), polyethylene, polyester, and polyetherimide. 

Zinc arc spraying is an inexpensive process in terms of equipment and raw materials. Only 55—110 g/m is required for a standard 0.05—0.10 mm Zn thickness. It is more labor intensive, however. Grit blasting is a slow process, at a rate of 4.5 m /h. AppHcation of an adhesive paint layer is much quicker, 24 m /h, although the painted part must be baked or allowed to air dry. Arc sprayed 2inc is appHed at a rate of 9—36 m /h to maintain the plastic temperature below 65°C. The actual price of the product depends on part complexity, number of parts, and part size. A typical price in 1994 was in the range of 10—32/m. ... 

Other Metals. Metals such as the austenitic series. Types 301—347, and the ferritic series. Types 409—446, of stainless steels may be enameled, as well as a number of other alloys (17). The metal preparation usually consists of degreasiag and grit blasting. Copper, gold, and silver are also enameled. These metals are usually prepared for appHcation by degreasiag. Copper is pickled usiag either a nitric acid [7697-37-2] or a sulfuric acid [7664-93-9] solution, followed by a dilute nitric acid dip. Silver may be pickled in hot dilute sulfuric acid followed by a dip in a nitric acid solution (18). 

Faeilities, sueh as eonvenient air and eleetrieal eonneetions, should be prearranged for operating tools, ete. Suffieient hose lengths and eonneetors are required as well as eleetrieal extension eords. Install air driers or water separators in the air system, sinee dry air is neeessary for sueeessful grit blasting of turbine parts. 

Solid-solid Persons walking Grit blasting Conveying of powders Belts and pulleys Fluidized beds... 

Copper slag Smelting Complete utilization Grit blasting... 

Tin slag Smelting Major utilization Some in tips Grit blasting and road building... 

The seemingly simple question of the relation the characteristics of a mechanically prepared metal surface and adhesion to that surface has sporadically occupied attention for many decades without any very general conclusion being reached [69]. In some recent work, Amada et al. [70,71] grit-blasted a steel substrate, varying the angle between the gun and the specimen surface, and measured the adhesion of a plasma-sprayed alumina coating. They examined profiles of the... 

Primary amine Mild steel Grit blast 35 0... 

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