MOULDING STIFF-CLAY BRICK.
For the moulding of stiff-clay brick many different machines have been made, and England and Germany stand prominent with the United States in the construction of suitable machinery for this purpose. We have selected such machines of this class as seem to have the most prominent features, together with the latest improvements for the purpose of description.
Before entering upon a detail of this machinery itself, it is necessary to give the reader a full explanation of the require ments which brick made by this class of machines should meet ; also reciting the defects which improper constructions of the moulding devices often impart to stiff-mud-made brick. Owing to defects in manufacture, brick often disintegrate in the North ern climates by the action of the weather.
In New York, where the manufacture of brick reaches over one hundred millions per annum, it was noticed that stiff-mud made brick would not last as well as those made of soft clays, and attention was called to the fact in the National Convention of Brick Manufacturers, by experienced and conscientious brick manufacturers. Fortunately some experts of large experience in the manufacture and operating of brick-making machinery were present at the convention, and as these experts were per sons of practical knowledge acquired in Germany, England, Australia, and America, they afterward pointed out by publica tion wherein the cause of the disintegration of the brick could be found, namely, in the improper construction of the moulding devices.
A gentleman stated that he constructed a machine in Ger many, some twenty-five years since, and obtained a contract from a railroad company to furnish the brick for some buildings along the road ; the brick being admired for their beauty and seeming density. After two winters had passed, however, these nice-looking brick commenced to shell off and presented a very shabby appearance. This led him to study the philosophy pertaining to the flow of clay through dies, and how to prevent the lamination of the clay in the brick, which was the only cause of his ill-success in his first attempt in making stiff-mud brick. He found, like all his coadjutors, that the flow of the clay must be equalized as it passes the mouth-piece, and that the pressure back of it must conform to these requirements. The use of lubricating dies of proper construction and change of forcing augers remedied the difficulties, and the brick that he afterwards made of the same clay, with the same machine, are now as good as when they were put into the walls ; this statement being verified by an examination made of the brick only a short time ago.
Manufacturers of this class of machinery in America went through the same experience, but were later in discovering the remedy.
' It can be readily seen, that when brick are made on a die that does not lubricate the corners properly, the clay will hang back and that the centre will flow faster than the corners. This
makes a disruption in the bond of the material, and the brick will be moulded with the clay in layers, or so called lamina tions.
These laminations are generally in an oval form, when made in auger mills, whereas stiff-mud brick made on plunger machines have straight laminations across the narrower cross sections of the brick.
The causes of these defects are often found outside of the construction of the moulding part of the machine, being also produced when the clay is worked too dry, or when it has been improperly tempered.
The defective brick which elicited the acknowledgments of the makers before the Convention were made with a machine of excellent construction, but so designed as to force out only one stream of clay for end-cut brick, and at a rapid rate. The opening for the die being in a straight range with the end of the shaft, hence the clay was gathered in from a large area around one central point, which caused the brick to become shelly lengthwise, when the clay was being worked rather stiff.
To overcome this objection, the constructors of the Giant, Acme, Centennial and Mascot machines have adopted a die for end-cut brick, with two openings, and use an auger of large dimensions. These orifices are placed far enough apart to avoid this central point of the shaft, and are spaced so that the pressure of the wings of the screw propellers acts alike over the whole surface of the opening. A very compact and solid brick is the result, even from non-lubricating dies.
When the die is made lubricating after the Niedergeswss Patent, very little difference is noticed in the centre stream of a three-stream die, if placed far enough away from the propeller.
In the Acme Brick Machine, the die front is made telescopic, so as to allow for such adjustment.
While end-cut brick do very well for paving purposes, they are not liked so well by bricklayers, owing to the smooth ness of the surfaces where the mortar is put on, and also be cause the ends are not so smooth when cut by the wire or knife, whereas side-cut brick have smooth edges all around, and are just rough enough to hold the mortar well.
Until the Niedergesss Patent Lubricating Brick Die was in troduced, the making of side-cut brick was an uncertain pro cess. Occasionally a quality of clay was found that would work pretty well with a dry die, or the imperfect lubricating dies of the past, yet the defects heretofore named were more or less apparent ; while many clays could not even be moulded, owing to the tendency of the clay to stick in the corners, es pecially when the temper of the clay was uneven.
There has heretofore been another serious trouble in having dies retain their proper size so that the brick will be uniform in measurement. In very gritty clay the wear is very rapid, even when the die is made of hard material. This has also been overcome by the die which is illustrated in Fig. 25.