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EVEXIXG PUBLIC1 LEDGER-PHILADELPHIA, WEDNESDAY, SEPTEMBER 24, 191ft
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The New Internal Hydraulic Expansion Process of
Curing Has Brought National Speedway Adjust
ments Down to One Out of Every 2000 Tires Sold
fTrHE average tire and that is to say
most nrcs, irom me most expen
sive to the cheapest, are built up
on an inflexible iron core.
Then this uncured assembly is laid
in the lower half of a heavy two-piece
iron mold, and then covered by the upper
half. The mold remains open about half
an inch sometimes a full inch because
the unshaped tire has to carry an excess of tread stock to fill
uut the depressions in the mold's tread design (for non-skids).
This Is Where the Pinch Comes
To close the mold and keep it closed during curing, re
quires a crushing pressure of from 100,000 to 300,000 lbs.
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And this is the mischief maker.
Some slight error in assembly, trilling in itself, can grow
into a serious flaw under this terrific external pressure. 'The
fabric may be sheared off around the circumference of the
tire. Generally this buckling is not visible in the finished tire,
as the breaker strip prevents its showing on the tread. So
when a premature blowout occurs everybody wonders why!
In clincher and Q. D. clincher tires the mold pressure
frequently displaces the bead from its proper position. The
bead is crowded upinto the sidewall and rim cuts arc the
consequence.
In straight side tires the wire braid or cables in the
bead may be pushed out of place by the mold pressure, and1
they fail to function properly as an anchor on the rim. That
is what causes the tire to blow off the rim when attached
and inflated.
In the fabric used in good grade tires one strand is just
as strong as another as it comes from the mill. But under
pressure the fabric is sometimes pulled into a thinner gauge
to make room for other stock finding a level, or pushed into
a thicker gauge to fill out a light spot in the carcass.
That ig another reason why tires, instead of lasting till
the tread is worn right down past the breaker strip, will
sometimes blow out before the tread has shown any particu
lar sign of wear.
The finest materials in the world will
not save a tire that has developed mechani
cal defects during the process of curing
under external pressure or distorted during
removal from a solid iron core.
Mold Pinch
This is a "budding" of the
fabric under pressure it is
pinched up into the cushion
and tread stock. And as this is
the point of greatest strain on
a tire, where the full load is
concentrated, the casing soon
gives ivay and bloivs out.
Fabric Bruise
The fabric sometimes gets
crowded out- of place under
mold pressure, either to malce
room for other stock or to fill
out light spots in the carcass.
This bruises the fabric on the
inside of the carcass a weak
ness that is certain to result
in a premature blowout.
Rim Cuts
Frequently in clincher and Q. D. clincher
tires" the bead is pushed up into the sidewall
when that crushing external pressure is ex
erted on the mold. Then, when the tire is
inflated, the fabric begins to tear strand by
strandand the immediate result is a rim
cut. In straight side tires the result is called
a "rim jumper." The mold pressure pushes
the bead wires out of place, with the result
that the tire fits loosely on the rim and is
bloivn off.
This Is How Internal Hydraulic Curing Banishes
Blowouts, Rim Cuts and Stone Bruises
Caused by Structural Defects
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a collapsible core that is taken apart
and removed before the tire is placed
in the mold. In this way the tire re
tains its proper shape, and no part is
displaced or distorted.
n No Pressure Required
to Close the Mold
The mold used is of the usual 2-piece construction. But
it is made large enough to accommodate the tire without an
overlap. Thus the two halves are brought together closing
completely around the tire without applying an ounce of
pressure. .
Curing by Internal
Hydraulic Expansion
Before the tire is placed in the mold, it is fitted with a"
specially constructed inner tube of the exact shape and size
of the inside of the finished casing.
Then when the tire is in the mold, this tube is filled with
water to a pressure of 200 lbs. to the square inch a wholly
unique process, evolved from a long series of experiments.
This pressure is maintained throughout the entire period
of curing. As the mold is closed before any pressure is
applied, pinching, bruising and distortion are impossible.
THE CONSTRUCTION IS PERFECT.
The materials are in keeping-with the methods used in
building them into a finished tire. They are the finest that
world's markets afford.
There is only one other tire in America with as high a
rubber content in its tread no other with better stock
throughout.
The Prices
It does cost more to cure tires by internal hydraulic ex
pansion. But when built they area&te to liv.e"up. to tjieir
guarantee. ' ' .
There are practically no seconds. Adjustments are
negligible.
And these savings cut. a big slice off the manufacturing
costs.
Though the National Speedway process is more expen
sive than tlie methods employed by other manufacturers,
the resultant elimination of "seconds" and adjustments lias
so considerably reduced costs that we have been able to list
National Speeaway Tires considerably lower than otfier
tires of similar rating. Juqt try ONE National Speedway
Tire and see for yourself how good they are.
Every Tire Guaranteed for 6000 miles
If your regular dealer does not handle, buy direct from
National .Rubber Products Corporation
660-662 North Broad Street
Philadelphia
Hell Phone Poplar 3197
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