Salt solutions high-nickel cast irons


It consists of a hollow, cylindrical metal drum lying on its side trunnions that permit its rotation a sturdy, straight, adjustable knife and a shallow feed pan into which it dips. A large gear mounted on one trunnion is driven by a pinion actuated by motor or pulley. A cast-iron or welded steel frame furnishes the supports. The drum is cooled by water or brine introduced and wasted through the trunnions. A coating of liquid forms on the drum as it dips in the feed pan as the drum turns, the film at once begins to cool, so that after traveling about three-fourths of the rotation, it is hard and solid. It meets the knife, which scrapes it off, the coating breaking into flakes, chips, or other fragments characteristic of the material. The flakes drop into an apron from which they may be shoveled into shipping drums, or they may drop directly into a screw conveyor that moves them to a chute and packing boxes or barrels. The drum is usually made of a special grade of cast iron with a very smooth surface, which may be chromium-plated. The drum is also made of stainless steel, nickel, or bronze. The motion is generally a steady rotating one, but for certain products it has been found better to move the drum in a series of short jerks. Successful application of the flaker depends upon a low adhesion of the solidified material to the surface of the drum. Should the adhesion be too high, the knife will be unable to lift off the solid and will ride on the material instead of on the drum. The adhesion of some troublesome materials is lessened by a wetting roll, which leaves a film of moisture on the metal just before the coating is formed.  [c.158]

Dilute alkali solutions do not corrode cast iron at any temperature, but hot solutions exceeding about 30% concentration will attack it, with an accompanying evolution of hydrogen, to form a ferrite. Broadly speaking, if corrosion rates are to be held below 0-2 mm/y the temperature should not exceed 80°C. Corrosion rates may range as high as 1 -25-2-5 mm/y in boiling solutions of more than 50% concentration. Molten caustic soda (650°C) may attack cast iron initially at rates around 20 mm/y, but it is probable that this figure decreases somewhat after a few days. In spite of these high corrosion rates, caustic-concentration and fusion pots are made from cast iron, since the material is relatively cheap, and the thick wall necessary for mechanical strength also gives the pot long life. It is of the utmost importance to ensure that concentration and fusion pots are cast in sound metal, as any unsoundness, particularly at the bottom of the pan, will lead to pitting attack and premature failure. The addition of 1 to 3% nickel to metal for these castings is said to be beneficial.  [c.595]

The corrosion rates of the Ni-Resist irons in salt solutions depend upon the chemistry of the salt. Solutions which are alkaline or neutral in reaction are not generally corrosive to high nickel irons and even brines containing calcium and magnesium chloride can be safely handled by the austenitic irons (Table 3.53). Those salts which hydrolyse to give an acidic solution are more corrosive to high-nickel irons although the corrosion rate is still less than for unalloyed cast iron in the same medium. The corrosion rates of Type 1 Ni-Resist and cast iron given in Table 3.54 demonstrate that the austenitic iron shows better resistance than the nickel-free cast iron in a wide range of salt solutions.  [c.610]

Cadmium. Compositions of cadmium plating baths are shown in Table 4. Whereas cadmium provides better corrosion resistance to steel and other substrates than 2inc when exposed to marine environments, 2inc is better in industrial, sulfur-bearing atmospheres. Resistance of cadmium is improved with chromate conversion coatings bright, yellow iridescent, oHve drab, and black finishes are used. Cadmium is readily solderable, provides lubricity on threaded fasteners, and has been used as a high temperature protective coating in the aircraft industry when diffused into nickel plating. Ohve-drab chromated cadmium plate is used on nickel-plated aluminum electrical connectors to extend salt spray resistance. For diffusion processes, for low hydrogen embrittlement, and for plating directiy on cast iron, cadmium—cyanide plating solutions are used without brighteners in other appHcations, brighteners produce attractive lustrous deposits.  [c.155]

The coefficient of thermal expansion is primarily determined by the frit composition, although mill additions can have a minor influence. As a general rule, superior acid and thermal shock resistance obtain with low expansion enamel, and the skill of the frit manufacturer is to obtain good resistance and also to maintain a sufficiently high expansion to prevent distortion of the component (pressing or casting). Several workers have produced a set of factors for expansion in relation to the enamel oxides that constitute the frit, which provides a guide to the frit producer. However, as these factors are derived from a study of relatively simple glasses smelted to homogeneity it must be emphasised that they are only a guide. The effect of substituting certain oxides for others in a standard titanium superopaque enamel is given in Table 16.2. The use of a nickel dip improves adhesion by minimising iron oxide formation, but it should be noted that some iron oxide formation is necessary to produce enamel/metal adhesion. In the commonest methods of testing for adherence to sheet iron, the coated metal is distorted by bending, twisting or impact under a falling weight. In the worst cases the enamel is removed leaving the metal bright and shiny, but in all others a dark coloured coating remains with slivers of fractured enamel adhering to a greater or lesser degree. With cast iron enamelling it is not possible to distort the metal and in this case an assessment of adhesion is obtained by dropping a weight on to the enamel surface and examining for fractures. Erroneous results can obtain in that often thicker enamel coatings appear to be better bonded and resistant to impact, whereas in fact the converse is true. Providing the bond is adequate this test really gives an indication of the strength of the enamel itself.  [c.738]


See pages that mention the term Salt solutions high-nickel cast irons : [c.208]    [c.332]   
Corrosion, Volume 2 (2000) -- [ c.3 , c.126 ]