Лако-красочные материалы — производство

The most important of the nonmetal materials of construction are the cements and the stoneware products.

Stoneware is the one usable material which has complete resistance to acids. To be sure, lead may be used in its stead in certain cases, but every plant chemist has found that even the most carefully leaded ap­paratus will require, in due course, expensive repairs. If a piece of equipment must give uninterrupted service for an unlimited period, only stoneware can be used, or in a few cases, acid-resistant stone such as Volviclava, Granazit, or Bingersandstein.

Stoneware stopcocks of small sizes are widely used and last indefin­itely if properly handled. Hot liquids are injurious to them because of the danger of cracking, and proper lubrication must be used to prevent freezing. So-called reinforced stoneware stopcocks, which are more resistant to shock and also to heat, have a protective housing made of leaded sheet iron. They have entirely replaced the older hard lead (anti­mony-lead ) type. Stoneware is also used for supply lines, valves, and centrifuges. The basket of a stoneware centrifuge is placed in a steel bas­ket in such a way that it is not thrown out by centrifugal force. Very com­plicated constructions are used, but these cannot be gone into here.

Stoneware reservoirs find wide use. They are prepared either in one piece or by joining several pieces together. Vessels having capacities up to 5000 liters can be prepared, but they are expensive and very sensitive to small temperature variations. Acid-resistant reservoirs can also be prepared in the plant by a good mason. An iron vessel is layered with cement, and acid-resistant bricks or glazed stoneware tile are laid over the hardened cement using ordinary cement mortar. The individual tiles are separated by about 6 mm., and the joints are filled with acid — resistant cement which is supplied in high quality by various companies. First, the joints are half filled with the cement and dried by heating the whole apparatus with steam coils for perhaps 14 days. When this first layer of cement is dry, the joints are completely filled and the drying process is repeated. Lining a 5000-liter vessel in this way takes about 2 months. When the mortar has set, the vessel is filled with 2 per cent sulfuric acid and is allowed to stand for 3 days. This treatment hardens the acid-resistant cement and at the same time tests the joints for leaks. Vessels lined in this way, if carefully made, resist even hot 80 per cent sulfuric acid and can be used under pressure or vacuum. Vessels can also be lined with two layers of acid-proof tile laid in such a way that the second layer of tile covers the joints in the first layer. These instal­lations, however, are very costly and are little more resistant than those properly lined with a single layer.

Alkaline and neutral liquids can be kept in concrete reservoirs which are usually reinforced with iron. The reinforcement must be calculated very carefully, because large stresses are created when such a reservoir is warmed. Concrete vats are also used in dye manufacture, but it is advisable to line them with acid-resistant tile, since even very weak acid corrodes concrete very rapidly. Stirrers can also be made of con­crete and can be used to good advantage in special cases.

The floors in manufacturing areas should be covered with acid-proof slabs and the cracks filled in with sulfur which adheres to the stone and is not washed away by hot water the way asphalt is. Good cement floors are suitable in areas where the floors remain dry.

Glass finds only limited application because of its fragility, but there are many times when it must be used. It is indispensable, for example, in chlorination reactions at elevated temperatures (see dichlorobenzal — dehyde). Chlorine lines are frequently made of glass, and stirrers con­sisting of glass rods attached to iron or wood shafts are widely used.

Fused quartz is used very little, although quartz lamps are used to an increasing extent in chlorinations.

Porcelain is used only in the laboratory and dye house. The highly praised hard glass vessels would be recommended except that they fre­quently shatter.

Enamel is a special form of glass, used particularly for covering cast iron. The preparation of a good, acid-proof enamel is difficult, and a double coating is often used on manufacturing equipment. The enamel used is not as attractive as that used on household articles, but is much more resistant. An enameled apparatus with a defect in only one spot must almost always be removed, and, therefore, extreme care is required in its use. Metal stirrers are never used in enameled vessels — only wood is used. Very complicated enameled equipment is made and is very expensive. Enameled ladles are widely used.