High chrome alloy

Both Weir-Warman and KSB-GIW, the largest manufacturers of slurry pumps, have experimented with the use of high chrome alloys with chromes in excess of 30% for slurry pumps handling phosphate rock. 

After cleaning, these bundles should be dried as soon as possible and laid up under nitrogen until they are presulfided. This will allow the sulfide layer to be laid down on an active surface. Sometimes the bundles are divided into hot and cold effluent bundles. The hot effluent bundles will be closest to the reactors, and probably will be made of a high chrome alloy or austinitic stainless steel. These can be cleaned in the same way (also see Reference 3). 

Induction Furnace. The high frequency coreless induction furnace is used in the production of complex, high quaUty alloys such as tool steels. It is used also for remelting scrap from fine steels produced in arc furnaces, for melting chrome—nickel alloys and high manganese scrap, and more recentiy for vacuum steelmaking processes. 

Crystalline films of TiB2 obtained by CVD are used at lower temperatures as protective coatings. The interaction of these films with various substrates is studied" and desirable properties of the substrate in cases when the coating is deposited according to Eq. (a) are formulated. Substances meeting the requirements in this respect are W, Ta, Mo, WC, TiC, graphite, Fe-Ni-Co-Mn alloy (Kovar) and some high-chrome steels. 

The apparatus is shown in Fig. 4.1. The body of the extraction vessel is made from Pyrex. Separation is effected by absorption of a batch containing both phases into a porous 2 cm diameter nickel-chrome alloy disc (A), the upper surface of which is domed. The disc is mounted on the end of a stainless-steel shaft (B) turned by a geared high-torque electric motor. The disc-shaft-motor assembly can he transported along its axis of rotation to any of three stations. The assembly is shown at its bottom station, with the porous disc within the inner vessel (C), around which is a collar (D) forming the first annular pocket (E). The collar itself forms the inner wall of the second annular pocket (F), the outer wall of which extends upwards to support a Perspex Hd (G) on which the rotor (H) is situated. The inner vessel and both annular pockets are fitted with drain valves. A stiff piece of platinum wire is passed through the Hd into the glassware as far as the level of the first annular pocket. 

Corrosion of the glass-making melters must be maintained at an absolute minimum to increase the lifespan of the melter. Laboratory-measured corrosion rates indicate that melter lifetimes of several years can be achieved with high chrome oxide or zircon refractories metallic melters may have lifetimes of several months if alloys such as Inconel 690 are used. These conclusions have been reached on the basis of extrapolation of laboratory tests. Long-term tests, particularly with waste glasses in engineering-scale continuous melters, have not yet been made. 

Blown film dies, like those for cast film, are generally manufactured from steel, and are often plated with chrome or nickel to harden the surface and increase its durability, as well as making it easier to clean. In some cases, the die lips are coated with PTFE-based coatings or special alloys. For processing of highly corrosive plastics such as PVDC, special high-nickel alloys can be used. 

The input to muffles or radiant tubes is limited by the strength, durability, and conductivity of their wall materials. The great temperature difference across a muffle or tube wall not only reduces its useful life but also causes the products of combustion to exit at a very high temperature, raising the fuel bill. For both reasons, muffle and tube walls are made as thin as practical, using a material that has both high thermal conductivity and resistance to heat. Alloy steels and silicon carbide are the most suitable materials for muffles and radiant tubes. Silicon carbide radiant tubes can withstand higher temperatures and are more resistant to oxidation than nickel-chrome alloy steel tubes, but the latter are less brittle and cheaper. 

Because slurry pumps are often cast in brittle alloys such as the high-chrome white iron, it is important to eliminate sharp edges that may act as stress risers. The manufacturers establish the radii R, R, R R R/ and R shown in Figure 8-29 to allow a smooth casting, but also to improve on the hydraulics. The effect of each parameter on the hydraulics as described in sales brochures is not always well proven. 

Corrosion can have very detrimental effects on the wear resistance of certain white irons. If the matrix wears out and exposes the carbides to a corrosive environment, they may quickly deteriorate, causing a further loss of wear resistance. Manufacturers of slurry pumps have gone beyond the specifications of ASTM A532-87 to increase the chromium contents to 30% with 50% chromium carbides in a martensitic matrix. These materials have found applications in phosphate matrix and phosphoric acid pumping. These new alloys are intermediary between white irons and superalloys. Walker (1990) reported that the use of these alloys leads to a substantial increase of the wear life over conventional white iron castings (Ni-hard, 27% high chrome). 

FIGURE 10-3 Mictograph showing grain stmcture of Moballoy, a proprietary high-chrome, abrasion-resisting alloy. (Courtesy of Mobile Pulley and Machine Works, Inc.)... 

Tipper JL, Firkins PJ, Ingham E, Fisher J, Stone MH, Farrar R. Qrrantitative analysis of the wear and wear debris from low and high carbon content cobalt chrome alloys used in metal on metal total hip replacements. J Mater Sci Mater Med 1999 June 10(6) 353-62. 

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