SILICA FIRE-BRICK.
This class of refractory brick, also called " Dinas" fire-brick and British silica fire-brick, consists almost entirely of silica, and was invented by the late Mr. W. Weston Young, a land surveyor, of Newton-Nottage, Glamorganshire, Wales.
The company first established to manufacture this kind of brick was organized by the inventor in the year 1822. The material at the " Dinas " (the well-known rock of that name in the Vale of Neath), from which Mr. Young procured it, is nearly pure silex ; but from its lying on the limestone and occasionally intermixing with it, there is, taking the average of the general working, perhaps about five per cent. of calcareous matter and one per cent. of metallic, either iron or copper. The Dinas rock is believed to be the millstone grit of the Car boniferous System, and the geological equivalent of the bed, termed " ganister " at Sheffield, England, which is used as a lining for the Bessemer-converter, as well as for the manufac ture of fire-brick now conducted in that locality.
The use of the "Dinas" was discovered about 1790, when the fine part of it was taken to one of the copper works and used as a cement, and for mending their furnaces while at work, by placing it with a long iron-handled ladle or spade where the wash of the metal had destroyed the brick ; and, from its re markable property of swelling in high heats, it fixed itself firmly. It gradually gained from one copper work to another till its use became general; in fact, they are not able to find any other sand that will answer the purpose so well. Its fire proof qualities being known, many attempts were made to pro duce a brick from it; but all the common combinations of different clays, etc., failed.
When set in its own cement, for very high and long con tinued heats "Dinas " or silica brick will exceed in duration any other known brick. It does not suit every situation, as, in fact, no fire-brick will. The nature of it at once tells you it must not be placed near alkaline substances ; neither will the effluvia from some lead-ores suit it. Perhaps it does not exceed Stourbridge brick for gates ; but for the bodies of furnaces of most kinds it exceeds, as said before, that and every other known brick in duration. The manner in which the brick is
made gives it a rough coat compared with most others ; indeed it is peculiar in this respect. But, as it is made in machines perfectly square, all the managers of iron and steel works prefer it with a rough coat ; they say it sets better in the work. This brick ought to be kept dry if possible, for being open in its texture, it imbibes moisture freely. The fire-place, roofs, sides, and bridge of the furnace, also the lower part of the stack, should be built of " Dinas ;" the back part and the re mainder of the stack will do best if built of No. i fire-brick, and the slabs for leaving the flues and doors are also best made of this material.
One of the troubles of clay brick, which silica brick escapes, is its so-called " dropping " when placed in the roof. This means either one of two things—first, that a crack has formed across the brick which leaves a piece free enough to fall when any change of temperature loosens it—this is the peculiar property of a pure clay; and second, the formation of a crust of fused clay and ashes on the surface which cracks off and falls when the brick cools.
In the construction of open-hearth steel and glass furnaces in the United States, silica brick have taken the place of the highest grades of fire-brick, and now that high grade silica brick of domestic manufacture are to be had, their use is rapidly extending to other furnaces.
All silica brick expand under the action of high heats. The expansion of the best silica brick of American manufacture varies from one-eighth to three-sixteenths of an inch per foot according to the temperature carried in the furnaces in which they are used.
This expansion should be provided for in some manner in building furnaces, and this is done in various ways. Some users of silica brick merely loosen the tie-bolts of the furnace as it heats up. Others insert a thin board (say one-half inch) every four feet across the roof of the furnace, to allow for the longitudinal expansion, and the board burns out on the furnace heating up, the space being filled up by the expanding brick.