Plants for manufacture of roofing tile are generally located at the
source of the raw material to be used. However, this is not, in all cases,
the most efficient location because of the requirements of manpower, fuel
supply and transportation. These considerations sometimes require that the
plant be located some distance from the clay deposit and, in this instance,
the raw shale is shipped by freight car to the factory.
The first step is the mining of the clay or shale. The most successful
method of securing a shale of generally consistent content is by the use of
a planer as shown in our photo No. 1. This large planer moves back and
forth across the face of the bank. While so doing, an endless chain of
claws moving vertically scratch the surface of the bank causing shale to
fall on a conveyor belt. This belt dumps the shale on small cars for
transportation to the grinding room. Other methods of "winning" the clay is by power shovel and by hand, using trucks to carry the material to freight cars or direct to the
factory.
Our next photo No. 2 shows a dry pan and screens. It is in this
machine that the shale is ground to almost powder-like form. To produce a
clay product of finest quality, it is necessary to grind the raw shale to
the correct particle size.
The dry pan shown in the photograph revolves
and the huge heavy rollers rotate on top of the pans crushing the shale that
passes between them.
Only shale particles of the desired size photo no. 3 can pass through the screen to be
carried by conveyor to storage bins. The finely ground material is then moved into a pug mill in which it is thoroughly mixed with water and chemicals of the correct proportions. This phase of the operation requires constant attention in order to produce a product of consistant quality. This wet mass is then extruded through an
auger machine in the shape desired. The basic principle of the auger
machine is similar to that used in the ordinary meat grinder. It consists
of a large revolving auger, or spiral bit, inside of the metal case.
This auger forces the clay through the mouth of the machine as shown in
photo No. 4. Various shapes are used in order to produce different
patterns of tile. The tile shown in this picture is Straight Barrel Mission tile.
Several patterns of roofing tile and many of the fittings used must be
made by the use of presses. Various type presses are used, the basic
principle of all being that a clot of prepared clay is put through the
upper and lower dies of the press, the dies are forced together, and the excess
clay is squeezed out, forming the piece of tile. The piece is then removed
from the press, excess clay trimmed off, and the wet tile moved on for
surface and color treatment, if necessary. Photo No. 5.
The next procedure is the drying of the ware, photo No. 6. This can be
done by different methods, such as forced drying with fans, using generated
heat or waste heat from the kilns. Time of drying varies considerably,
being determined by the size of the tile being dried but generally takes
from two to four days
In the manufacture of all clay products the problem of drying the
molded ware is a serious one. Incorrect drying results in high manufacturing
losses, so constant checking is mandatory for economical operation.
Varying weather conditions and sudden changes in outside temperatures affect
conditions of humidity and temperature inside the dryers, and this in turn
directly affects the ware being dried. Only ware that has been found
properly dried is moved into the kilns for burning.
The natural color of burned or vitreous shale is red with some
variation in shade. Designers, owners, or architectural precedents often demand the use of other than the natural red color. For such requirements the surface
of the tile can be treated in various ways to produce tiles of many
surfaces and colors. The gamut of colors includes red, white, blue, green, yellow, brown plus many others. Some of these colors are produced in both a high
glaze and matte finish. Some are finished by hand
photo No. 7.
and then colored to closely simulate the ancient hand made tiles of distant lands. Modern tiles are made to answer the need for modernistic design. Colonial tiles are made which duplicate in size, surface, color and texture, the heavy hand-split wooden shakes.
Great care must be used to setting roofing tile in order to prevent the
material from falling in the kiln while burning. The dried ware is set
with what is termed "kiln furniture." This furniture is composed of large slabs
of fire clay, which are used to enclose several tiles. It is accomplished
by setting these slabs (inside the kilns) in the same manner that children
use to make a "house of cards". The tile is set in the openings between
the slabs of kiln furniture. If this furniture is not very carefully placed,
the kiln may fall, and if this happens, usually very high losses result.
It is the duty of the head kiln setter to check each row or "hack," as the
kiln setters proceed with their work in order to be sure that the furniture is
spaced correctly.
Photo No. 8 shows Spanish tile being set in kilns after drying and
before burning. When completely set the kiln is closed and burned with
natural gas approximately 1800 degrees to 1900 degrees Fahrenheit.
The time of burning varies according to the ware being fired, but in all
cases the firing requires several days. In burning, the burner brings the
heat up slowly and at the end reduces heat gradually in order to prevent
losses in the kilns.
This article would not be complete unless it included a word of praise
for the men who actually made Ludowici tile. Many of the artisans who
produce the world famous Ludowici roofing tile have been plying their art
for a very long time. Their traditional pride in the finished product is
the principal factor in causing it to be considered without a peer in its
line.
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