Steels, Chrome Special

Alloy steels are more resistive than carbon steels. Chrome-vanadium, chrome-vanadium-aluminum, chrome-nickel-vanadium-aluminum steels stainless steels (18 per cent chromium and 8 per cent nickel, 0 24 per cent chromium and 20 per cent nickel) and BTG metal (12 per cent chromium, 60 per cent nickel, 2.5 per cent tungsten) have been fovmd to be completely resistant. BTG metal is the special alloy developed for the Claude ammonia synthesis, where operating pressures extend to 15,000 psig and temperatures to 560°C. 

Type Heat treated mold steel Standard hot working Highly alloyed chrome Special case hardening Special through hardening... 

Extruder screws are typically built of steel alloy, and the channels may be chrome-plated to minimize scratching and other damage. The tops of the flights are often hardened with special alloys to reduce wear. 

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. 

Condition Example Alloy steel Nitrided steelt Chrome platedi Special alloys ... 

Embedded in the refractory brickwork are lifters made of heat-resisting and wear-resisting cast steel. Purely chrome-alloy steel grades with about 30% chromium content have been found suitable for the purpose, the more so as they are relatively inexpensive. Ceramic internal fittings are not suitable for rotary coolers. Nor have special lifter bricks proved satisfactory, as their heads spall or wear down too rapidly. Scoops (or flights) made of wear-resisting steel and designed to scatter... 

In ball mills, metal balls are used as the grinding media. The balls are made of a variety of materials. Steel balls are forged. High chrome balls are cast with 28% chrome and are available from special foundries. About 1 kg of balls is used per ton of stone. Small balls with a diameter of about 25 mm (1 in) are preferred to larger ones in order to maximize the area of contact between balls and stones. 

Molding of CSM requires some special care in the type of metal due to the acidic nature of CSM even with the presence of an acid acceptor. A hard surface (minimum 45 Rockwell C), abrasion and corrosion resistant and non-porous steel needs to be employed. A hard chrome plate at least 0.1 mm thick is recommended. Stainless steel is a more expensive but more effective alternative. Lower mold temperatures reduce mold fouling and corrosion if economics will allow. Molds need to be cleaned at least weekly with an alkali solution with ultrasonic vibration. 

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