In the case of the machine-built tire, the result is the same, but the
stock is handled as follows: After the rubber-coated fabric has been
cut on the bias cutter, the strips are spliced and rolled up in rolls
on a spindle which is placed in the so-called tire-building machine.
The tire core is mounted on a stand attached to the machine, so that it
can be revolved by power, and the fabric is drawn onto the core from
the spindle under a certain definite tension. The tire-machines roll
the fabric down by power, and the beads are put into place before the
tire and core are removed from the machine. Thereafter the process is
the same as in the case of the hand-built tires.
After the cover rubber is in place the tire is ready to have the tread
applied. The tread is made up independently of the tire by laying up
narrow strips of rubber, in different widths, in such a way that the
center of the tread is thicker than the edges. In the case of the
so-called single-cure tires, which are wholly vulcanized at one time,
this tread is applied to the tire directly after the cover, a strip of
fabric called the breaker-strip generally being placed underneath, and
the building of the tire so completed.
In the general method of curing, the tire is allowed to remain on
the core, and is either bolted up in a mold and put into an ordinary
heater, or it is laid in a mold and put into a heater press, where the
hydraulic pressure keeps the two halves of the mold forced together
during the vulcanizing process. After the vulcanizing is completed, the
tire is removed from the mold, the inside is painted with a French
talc mixture, the tire inspected and cleaned, and so made ready for the
market. In some methods of curing, instead of the tire being put in a
mold, it is put into a so-called toe-mold, which is virtually a pair of
side flanges only reaching up as high as the edges of the tread on the
side of the tire. After the flanges are fastened into place, the whole
is cross-wrapped, the cross-wrapping coming in direct contact with
the tread. The tire in this condition is then put into the heater and
vulcanized, giving the so-called wrapped tread tire. Still another form
of curing is to inflate a kind of canvas inner tube inside the tire and
place the whole in a mold. This is known as the air-bag mold process.
[Illustration: PNEUMATIC-TIRE ROOM--SHOWING TIRE-BUILDING MACHINES.]
How Are Inner Tubes Made?
Inner tubes for pneumatic tires may be classed under three headings,
according to the methods used in their manufacture, viz., seamed tubes,
rolled tubes, and tube-machine tubes. By far the greater number of
tubes come under the first two headings. For seamed tubes, the rubber
is taken from the calender in the form of sheets from one-sixteenth to
three-sixteenths of an inch in thickness. These sheets are cut into
strips of proper length and just wide enough to make a tube of proper
cross-section diameter when the two long edges are folded over and
fastened together with rubber cement. These two long edges are cut on a
bevel so that they make a good lap seam. The tube is then pulled over a
mandrel of proper size and a thin piece of wet cloth rolled around it,
and then it is spirally cross-wrapped with a long, narrow piece of wet
duck for its entire length. The whole is then put into a regular heater
and the tube vulcanized. After vulcanizing the wrapping is removed and
the tube stripped from the mandrel, turning the tube inside out, so
that the smooth side which is vulcanized next to the mandrel appears
outside, and the rough side showing the marks of the cross-wrapping is
inside. The valve hole is then punched in the tube, the valve inserted
and the open ends of the tube buffed down to a feather edge. The tube
in this state passes to the splicers, who cement the buffed ends and
splice them together, placing one open end within the other, making a
lapped seam around the tube about 2¹⁄₂ inches long. The cement used
in splicing is generally cured by an acid which chemically vulcanizes
the rubber without the application of heat. The tube is thus finished
and ready for the market. Rolled tubes are made from very thin sheet
rubber by rolling same over a mandrel of proper size, until the
required number of layers of thin rubber have been rolled on to give
the tube the desired thickness. The tube is then wrapped, cured and
spliced, in exactly the same manner as a seamed tube.
What Is Rubber?
Crude rubber is a vegetable product gathered from certain species of
trees, shrubs, vines and roots. Its characteristic peculiarities were
early recognized by the natives of the tropical countries in which it
is found. Records of the earliest travelers in these countries show
that the natives had used various articles, such as receptacles, ties,
clubs, etc., made from rubber, but it was not until about 1735 that
rubber was first introduced into Europe. In civilization rubber was
first used for pencil erasers and in waterproof cloth, and finally in
cements. Vulcanizing, or the curing of rubber, was not discovered until
1844, and thereafter the development of the rubber industry was very
rapid, especially in Great Britain.
[Illustration: WRAPPING ROOM--PNEUMATICS.]
There are many kinds and grades of rubber, and to-day these can be
divided into two chief classes, wild and cultivated.
[Illustration: PNEUMATIC-TIRE ROOM, SHOWING TIRE FINISHING.]
[Illustration: HOW THE CRUDE RUBBER IS SECURED