212
MODERN GASWORKS PRACTICE
a high-quality article is obtained by the method. In the experiments 1 conducted the casting slip was prepared from Stourbridge fireclay and grog, the latter being used in various sizes. Sodium carbonate or silicate is added. to the slip in sufficient quantity to produce a smoothly flowing mixture without reducing the consistency to such an extent as to allow the grog to settie. The amount required is determined in each particular case by trial; it varies with the nature of the clay, the size of the grog, and the proportion in which the clay and grog are mixed. With some clays the best results are obtained by using a mixture of equal parts of silicate and soda-
Fig. 111.—A Steam-dmvbn Rbtobt-mouldixg Machine showing Lower Portion of Steam Cylindek and Uppbr Pakt of Clay Cylinder, the latter with Piston up so that it may be chakged with Clay.
Fig. 112.—Rbtobt passing THROUGH MOULDING DiB.
ash ; others give better results with a larger proportion, of silicate. This mixture is usually referred to as the “ alkali mixture,” and on an average the quantity used amounts to 0-3 per cent, of the weightof the dry clay used. A sketch of the plant employed is given in Fig. 113. The mixture of clay and grog passes from the con-veyor to the elevator, thence to the primary mixer, or “ biunger.” The blunged mixture then passes to the agitator, from which it runs direct to the mould. The time occupied in casting a retort is about fifteen minutes ; the core is removed in about twenty-four hours ; and the retort is removed from the mould in. another twenty-four hours. A typical mould is shown in Fig. 114.
1 Report of Refractory Materials Committee, Inst. Gas- Eng., 1920.