28 декабря, 2015 
Pokraskin Iron is the most important construction material in the dye industry and is used in all possible types and forms.
Cast iron is used for sulfonation and nitration vessels, as well as for evaporating apparatus, stopcocks, stirring mechanisms, autoclaves, and all apparatus for handling neutral or alkaline liquids. Still greater use of this valuable and easily cast metal is restricted by its inadequate tensile strength.
It is well known that the properties of cast iron are highly dependent
upon its chemical composition. Ordinary gray cast iron is used as an acid-resisting metal, i. e., one which is attacked very little by concentrated acids, and its resistance may be improved by added ingredients, the identity of which is kept secret by many foundries. Gray cast iron fulfills all the requirements for use with sulfuric acid of at least 75 per cent and with mixed sulfuric and nitric acids. It becomes passive, and hence quite resistant, in fairly dilute acids also. One should never depend on good luck, however, and should rely only on an actual test to determine whether cast iron is suitable for a particular application. Furthermore, a cast iron vessel should be cleaned out carefully after each operation. After a shut-down, cast iron vessels should be washed out, de-acidified with hot soda solution, and then washed with boiling water, leaving the vessel completely dry. Wooden water baths surrounding vessels should be kept filled to prevent shrinking, and the water should be made strongly alkaline with soda to prevent rotting of the wood.
The supports for stirrers in vats, autoclaves, and other vessels are made from cast iron. Light gears should be milled, and it is desirable to mount all larger gears with ball bearings, thus saving power and lubricants. Cast iron is used for filter press stands and head pieces, but not for the drawbars because if its insufficient tensile strength. Autoclaves for use up to 40 atmospheres working pressure can be made from cast iron. Cast steel must be used for higher pressures, however, since cast iron is blistery in very large pieces and much too thick walls would be required. For example, the cast steel autoclave shown in Figure 43 has a wall thickness of 80 mm. and weighs 10 tons. With a diameter of 1200 mm. and a working pressure of 40 atmospheres, the autoclave would have to have walk 400 mm. thick if it were made of cast iron, and the vessel would weigh over 60 tons. Such a monstrosity would be unusable technically, because of the large strains which would arise on heating. Fusion kettles in naphthol plants are made of cast iron, and an addition of 1 to 3 per cent of nickel increases the alkali resistance enormously. Fused alkalis, especially potassium hydroxide, have a strong corrosive action on iron.
Cast iron having very high resistance to acids is marketed in the form of an alloy containing 12 per cent of silicon and 4 to 6 per cent of aluminum. These ferro-aluminum-silicon alloys are attacked readily only by hydrochloric acid, the most corrosive acid. They were first used in England under the names “Ironac” and “Tantiron.” “Kieselguss,” “Acidur,” and “Clusiron” are imitations which are all easily cast, but which are very hard and brittle so that they have to be worked on an emery wheel. These alloys are exceptionally well suited for nitric acid
distillation equipment and for other special purposes. Because of their brittleness, however, they are not usable for autoclave liners.
Where high strength is important, wrought iron, ingot iron, or steel must be used. These are used for the drawbars of filter presses and hydraulic presses. (The head pieces of the latter must be of cast steel because cast iron is too weak.) Recently, welded electrosteel has also been used. Steel is also used for the spiral manometer tubes where ammonia is involved. Wrought iron is used for the bands on vats and for the reinforcing iron for concrete.
In recent years, a number of especially resistant iron alloys have appeared on the market and have been rapidly adopted. They are, essentially, nickel-chrome-iron alloys, usually containing very little carbon. These alloys are very resistant to acids and alkalis and are used chiefly where high resistance to chemicals is the deciding factor. The different VA-steels, and the English S-80, are examples of these alloys which vary in composition depending on the particular application. These alloys withstand concentrated nitric acid, and other acids, except hydrochloric, scarcely attack them at all. They are especially important in modem high pressure syntheses. Potassium hydroxide scarcely attacks these alloys even in fusion mixtures, and they are quite satisfactory, therefore, for indanthrene fusions. (Nickel is also suitable in this particular case.)
Copper was more widely used earlier, but is still indispensable today. It is used for making scoops (but not for diazotizations), for centrifuge baskets, supply lines, and especially for drying plates where it is used almost exclusively. Copper is attacked by air-ammonia mixtures and is often tinned for protection. Alcohol distillation apparatus are usually made of copper.
Tin is rarely used as such, but is widely used for alloys such as bronze[72] and lead-tin bath metal,! and for tinning iron and copper equipment.
Zinc, likewise, is generally not used as such, but as brass and bearing metals. It is also used as the coating on galvanized plate.
Aluminum, on the other hand, is receiving increasing attention because of its high resistance to dilute and concentrated nitric acid. It is frequently used for nitric acid feed lines and for nitrating vessels, but it is rapidly corroded by factory air.
Nickel is rarely used, except in special alloys.
Lead is by far the most important of all the nonferrous metals and is quite indispensable. It is found in the form of lead tubing in almost all filter presses and in lines carrying acid and alkaline liquids. Head pieces and discharge pipes of filter presses are covered with lead plate. Frequently, when lead-coated metal is heated, the lead loosens and large blisters are formed and the coating finally breaks. This difficulty can be avoided by applying the lead coating, not directly, but on an underlayer with which the lead alloys. Apparatus, in which the lead is intimately bound with the base, is said to be homogeneously leaded, and such equipment plays a very important role in the dye industry. It has been proposed by Kiihnle, Kopp, and Kausch that round pieces, such as autoclave liners, etc., be leaded by rotating the pieces rapidly and then pouring in the lead. All the pores of the metal are thus completely sealed, and pieces up to 6000 liters and 10 tons in size can be treated in this way. The iron or copper must be tinned before being leaded or the coating does not adhere well. The lead coatings are often quite thick, up to 2 mm. or more, and the amount of lead used in a large apparatus may thus weigh thousands of kilograms.
This brief treatment, of course, in no way covers adequately the use of metals in the dye industry, but it may suffice to show the great importance that materials of construction have in this field.
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