CUPOLA LINING BRICK.
The severe service to which the linings of blast-furnaces are now subjected, makes it essential in a good lining not only to be hard friction, but "highly refractory" as well. Years ago any brick that met the first condition was acceptable ; but with the practice of the present day—close-top furnaces, improved hot blasts, high pressure, etc.—it has become of the greatest importance that the brick used should be highly refractory.
To make a lining possessing these qualities requires not only that the stock used be of the best quality, but that the mechani cal structure of the clay be such as to permit its being worked into a compact body. With these given, however, there may be an entire failure in making a hard-friction brick, so much is there depending upon the proper manipulation of the clays and the burning of the brick.
The nature of the service required of the brick in the differ ent parts of the furnace differs so widely, that no single brand of brick can be made to answer all purposes.
In speaking of this subject The Harbison & Walker Co., of Pittsburgh, Pa., say : "Our practice for many years has been to make three grades of brick, each adapted to a particular part of the furnace. ' Benezet ' is always used in the bottom, hearth, and bosh ; ' Clarion' in the lining above the bosh, and ' No. 2 Star' in the top. All the brick are plainly branded to avoid any inter change of stock.
" We are confident that the best results will be sccured by using the block or tile-lining above the bosh. Such is nearly the uniform practice at the present time. In the hearth and bosh 9 and 13 -inch brick are generally used. For the hearth and lower part of the bosh, these answer every purpose ; but for the upper part of the bosh, we think the blocks will do better.
" To meet emergiencies a large number of these brick are car ried in stock of each of the three grades of stock necessary in a lining : Benezet," Clarion,' and ' No. 2 Star.' Block or tile linings, however, are only made to order, as it is necessary to adapt the form of the blocks to each particular furnace. It is important, therefore, that those using such a lining should an ticipate their wants by ordering two to four months in advance." The manufacture of blocks and tiles requires great care, par ticular caution being exercised to see that the mixtures of the clays and calcine are in correct proportions. To agree with the shrinkage allowed for in the molds as being exact and uni form to size ordered, it is important to have this, as it is sary that the clay should be ground regularly as to stiffness ; great care is also required in dressing the tiles when suf ficiently hard to handle, seeing that not only the tiles are smooth and level on the face and sides, but also that the edges are sharp ; the tile, when finished, being equal in appearance to a wood block the same size and shape.
One defect in making large tiles or blocks—that is, those containing more clay than the moulder can handle and put in the mould at one time—is that in preparing it on the table it is roiled in sand. Two or more separate balls of clay coming to gether in the same mould are liable to make and leave what are termed sand-cracks, the sand preventing the clay .from being properly united together in the mould ; the tile or block in such case coming out of the kiln cracked or broken, and in place of being salable goes back to the mill. A machine for making tiles and blocks is now in use, which not only does away with these sand-cracks, but also makes more solid and better work at less cost. This machine is in all respects the same as the smaller size sewer-pipe press, only that in place of the die a box is bolted to the bottom with a flat plate around the outside of the bottom of the box. Below this is another iron plate or table underneath, and in the center of which it is connected with a screw secured to framing in the floor ; on the screw are four cross-handles for working the same. The mould, after being sanded, is placed on the bottom plate, the screw given a turn, tightening the mould up to the top plate, the lever is pulled as in making sewer-pipe, forcing the clay into the mould, the pressure being sufficient to force the clay past the box and under the bottom of the top plate to the sides and ends of the mould ; the steam being then cut off by the lever, the screw is again given a turn, liberating the mould from the upper plate sufficiently to allow the cut-off wire to be drawn between the top of the mould and the underside of the plate. The mould is then drawn out on to a block at one side to be struck or planed and another mould run between the plates as before mentioned. In this way of making blocks and tiles every one is perfect and comes out of the kiln perfectly sound. This plan of making fire-clay blocks and tiles is recommended to such of our readers as are large makers, and to manufac turers who have not heretofore cared to make locomotive and similar tiles on account of the great loss arising from the reasons before described.