DRY-CLAY PULVERIZERS.
The machinery for pulverizing is a matter largely determined by the nature of the clay to be handled. As a general thing, if the clay is reasonably free from stone, a dry pan crusher is the best, although by no means the cheapest. The pan having a perforated bottom, the clay running through the perforations falls into an elevator boot, and is then conducted as high as the building will permit. When up to its furthest height, it is run over inclined screens lying at an angle of about 45°, the clay fine enough for the press runs through the meshes of the sieve, while the tailings are conveyed back to the dry pan to be re ground. There are other ways to prepare clay, requiring a somewhat less expensive plant, and which do very well, pro vided the clay is not too strong. Smooth rolls geared together, having a differential motion, are the prototype of this class of machinery, usually called disintegrators. These have been greatly improved by the many excellent machines made by different makers. The object to be attained, and which has made a departure from the old-fashioned smooth rolls a neces sity, is to prevent the clay from being laminated or rendered flaky. Clay, instead of being crushed or flattened, should be treated exactly in the opposite way, viz. : It should be torn to pieces, and to attain this object to perfection is the goal to be arrived at by the manufacturers of pulverizing machinery. In using a dry pan this difficulty is to some extent, although not altogether, obviated by the continued stirring up of the clay before the rollers. It is sometimes the practice to run clay through the reels after going through the disintegrator, instead of over the inclined screens, as before mentioned.
When stones are mixed with the clay in the bed, the ordinary method of manipulation must be abandoned. It is not long since
that a bed of clay having many stones interspersed through out its mass was considered practically useless for dry-press front brick, no matter how excellent the clay may have been in itself. As a general thing, when this is the case, it is only nec essary to adopt a method of manipulation by which the stones are taken out of the clay and thrown to one side. Unless there are a very few, it is poor practice to crush them up with the clay. Inventors in the line of clay pulverizing machinery have striven hard to produce a machine that will accomplish easily and surely this much-to-be-desired object.
From the pulverizers the clay is next carried by means of an elevator belt or otherwise to the hopper of the brick machine.
There have been of late so many improvements made in machines for moulding clay by the dry-clay process that there are now in the market a large number of such brick presses which are claimed to be fully adapted to the purpose for which they are designed. In selecting a machine of this character care should be had that it be as simple as possible in its mechan ism, that the material used in its construction is of the best quality. Owing to the enormous strain to which machines of this class are exposed, a large amount of money is annually lost because of the poor quality of the iron or steel used in castings or other parts, thereby causing breakages to occur which would not otherwise take place. It of course becomes apparent that in matters of this character the purchaser has to rely largely upon the reputation of the makers of the machines, and the subject should receive attention at the time when the contract of purchase is made.