There is probably little doubt that the beet enameled brick can be made from a well-made hand-made blank, but there is just as little doubt that hand-made blanks are often poorly made. The hand-made blank is made from soft clay, so that there is more moisture to be gotten rid of to get the bricks ready for the press than with some of the stiff clay processes. In getting rid of so much moisture it is difficult to do it uniformly and regularly, one day with another, so that while it is, as I have said, undoubtedly capable of making the best finished product, it is the most wearing process on the manage-ment.
A description of methods employed in this country for handmade brick will probably be of interest. The clay is pugged stiffer than for common so-called mud building brick; in fact, its stiffness is as great as possible for it to be, and yet be capable of being driven into a mold. The method of delivering to the brickmaker is a matter of the manager's ingenuity, and the best method to-day becomes old-fashioned to-morrow, in these times of rapid improvements. The molds are better made of brass, and should be one-half inch deeper than the desired depth of brick. On the making table should be firmly fastened a wooden block that fits the mold loosely, but neatly; on top of this block should be fastened a wooden or metal piece, the size of the indent desired in the bottom of the brick. Two holes of about 5-16 of an inch in diameter should be drilled through the wooden block parallel with its top face and with their centers 21-32 of an inch below it These holes should be one to two inches from end of block; 5-16-inch iron rods should then be driven through these two holes, allowing the ends to project about a half inch each side of the block. The tops of these rods will then make four supports for the brick mold, and the mold will telescope on the block one-half inch. The distance from block to top of mold will be the desired thickness of brick.
In molding the brick the clot is formed partially by beating and partially by rolling, and as the clay is so stiff it must be driven into the mold with great force in order that it may completely fill the corners. The mold and block should first be lightly oiled with kerosene of 110 degrees fire test. After the mold is filled, the surplus clay should be cut off to the level of the top of mold with a wire, tightly stretched on a steel bow. The piece cut off the top should be placed on the table with the cut edge down, and the additional clay for the next brick placed on top of it This will insure a more solid brick. The offbearing boys should be furnished with boards covered with canvas that neatly fit the mold. This board should be placed over the brick, and then, while the fingers hold the mold by the cross rod, the thumbs should press upon the board and press the brick out of the mold on to the drying floor. This will be found to be quicker and better than to shake the brick loose from the mold, and will insure a true, straight brick and clean molds. The use of oil on mold should be as slight as possible. After block and molds have been gotten into good working condition oiling will not have to be done oftener than every four or five brick. The floor upon which brick are placed to dry should be true and straight, and not too hot The drying floor may be heated by furnaces or by steam, either live or exhaust. Great care must be taken to remove all the brick from drying floor in exactly the same condition, as far as moisture is concerned. The dried blanks should either be piled and covered or piled in air-tight bins and allowed to stand a day or two before being pressed. This will even up the moisture to some extent The points to be watched are that the molder forms a solid lump of clay out of which to make his brick, and that he drives them uniformly, and without allowing the clot to cut on edge of mold when driving. Also, the drying should receive great attention. A man and two boys will easily make 2,500 brick per day.
The soft-mud machine process has never been practically tried by the writer, but the details would be the same as the hand process, except in the mere making of the blanks.
The objection to all of the stiff-mud processes is the difficulty of getting a blank free from air and laminations. Experience with a few clays cannot enable one to lay down rules for all clays, but the tendencies of certain types of machine can undoubtedly be pointed out with some degree of accuracy, especially when that experience has been combined with close study of the working of machines on clay generally.
The plunger machines all tend to make a blank filled with air holes just below the surface. In the repress, the cavities containing air become reduced in size and the air compressed. Where the bricks are afterward dipped in the slip or enamel the surface becomes softened, and the air in these cavities expands and forms numerous blisters upon the enameled face.
The auger machines tend to laminate the day. If these laminations come within about one-half inch of the surface to be enameled, the dipping into the liquid slip or enamel will develop blisters, often of enormous size. The remedies are to adopt a moisture, or stiffness, in making the blanks, at which the tendency to lamination is reduced to a minimum, and much good may be done by placing a number of knives in the die to cut the surface of the bar of clay to a depth of a little over half an inch. This seems to break up the laminations to a very great degree, but if the clay is one that does not easily knit together again it may lead to cracks across the face of brick. Clays differ very much In their tendency to laminate, and some may be worked in a much stiffer condition than others. There is also undoubtedly considerable difference In the tendency of different machines to laminate the clay. On account of the headers and quoins to be made, it is more convenient to make side-cut than end-cut brick, and the writer's experience has been that the laminations are less injurious in side-cut than in end-cut brick. Large die resistance seems to reduce the laminations or throw them so far below the surface as to be less injurious. Each person will have to study the working of the clay he proposes to use, and from that study, determine the style of machine best adapted to it.
The treatment of stiff-mud, machine-made brick is the same as the hand-made brick, except that they do not require so much drying, and, as the brick can be delivered upon boards from the cutting table, a different system of drying can be used. A very satisfactory plan has been found to be to have steam-heated racks just in front or back of brick machine, upon which the boards, with a convenient number of brick upon them, may be placed to dry. This plan requires considerable attention, as the end bricks dry first, and a man must constantly watch them and get them off the drying pipes when in proper condition.
The writer has examined the working of roller die machines with considerable interest, and, from what he has seen, concludes that there is much less tendency to lamination in this type of machine, even when the clay is stiff enough to go directly to the repress. The bricks from several machines of this type have been examined and not a trace of lamination discovered. There was at that time some difficulty with the wearing qualities of the roller die, which may since have been overcome. It is easily seen that a machine that will make a brick that can be repressed at once will effect a wonderful saving, both in time and money, and will also affect somewhat the uncertainties of the business. The whole attention may be concentrated upon the proper making of the blanks, instead of being divided among several operations.
For the single-fire process, where the dipping is done after the pressed brick is thoroughly dry, and for the double-fire process, laminations and air in brick are not quite so objectionable, but the repressing, even without immediate dipping, will develop some blisters if the laminations or air are present.