Adolf Heil.

The manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others online

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. 10,000

) )

Magnesia usta .

200 „

Litharge .

. 3,500


Paraffin wax .

250 ,,

8. Pneumatic Inner Tubes and Tyres, Pedal and Brake Rubbers and
Cab Tyres. — In the manufacture of inner tubes, which can be carried
out with comparatively simple plant, attention must be chiefly
directed towards producing mixings which are absolutely clean and
free from grit. Such a mixing for ordinary inner tubes would con-
sist of rubber, which has been very carefully washed, and sulphur ;
for second qualities a cheaper compound can be used, but then it
becomes a question of reducing the porosity of the rubber to a mini-
mum. Mixings containing ingredients which when added on the
mixing rolls are likely to flake, or to become granular, should be
rejected ; on the other hand, the following mixings have been tried
and can be recommended for the purpose : —

(suitable for motor

cycle inner tubes

Sulphur .

1,250 gms
75 „

Sulphur .

. 10,000 gms.
900 „

C. Columbian

. 5,000 „


B. Para


50 „

5,000 „
. 5,000 „

Manaos .
Sulphur .

5,000 ,,

1,000 „

. 4,000 ,,

200 „



Inner tubes, which are cut out of sheet and made up on a
mandrel, should be made from sheet doubled on the calenders ; this
is placed round the mandrel and cut from end to end of the latter

by means of a special cutting machine, the cut edges being at the
same time pressed together so as to form an absolutely tight seam.
The inner tubes are wrapped, just as they are made up, on the
wrapping-machine (fig. 67), and are then vulcanised at 135° C. The



tubes are drawn off the mandrels with the aid of compressed air,
being at the same time turned ; holes are made for the valves, and
the tubes are then cut to the right length, the ends solutioned with
a pure Para solution, moistened with chloride of sulphur solution,
and united. Motor tubes are often moulded, in which case the
necessary amount of gas-producing materials is put inside the tube;
a mixture of bicarbonate of soda and tartaric acid in tabloid form
being the most convenient agent to employ.

The manufacture of pneumatic tyre outer-povers, on the other
hand, necessitates the use of considerable mechanical arrangements ;
in particular, a large number of moulds which are best made of cast
steel. Of these there are two kinds to be considered — drum moulds
and core moulds, which latter are used especially for motor tyres.
The manufacture of drum -cured covers is in principle as follows : —
Cotton fabric, proofed on the calenders, is cut on the bias, and two
layers are then rolled down on to the drum. The first layer of
fabric carries the rubber cover known as the tread, which lies on
the side next the mould. The strip is rolled into the cavity which
forms the beaded edge, this being filled up with a cord of a hard-
rubber mixing, and the second layer of fabric is then put on. The
drum is now wrapped round with a cotton cloth on the machine
depicted in fig. 68, and then with Avire, and is run into the heater
on a large trolley. It should be noted that vulcanisation should
not set in before the layer of rubber has had time to spread itself
evenly over the surface of the mould, otherwise markings similar
to air-markings will result. These are not, however, to be attri-
buted to the shrinking of the rubber, but rather to the fact that
when it was rolled on to the drum the layer of rubber was not
evenly spread out, and that this could not be remedied once
vulcanisation, which proceeds energetically even at 130° C, had
set in. For this reason, in the case of drum-cured covers, care
should be taken to heat up the moulds slowly, after which the
vulcanisation may be carried through more rapidly. Tyre covers
which used to be made of pure Para, to-day consist of mixings
similar to, or even of lower quality than, the following: —

Congo .

. 10,000 gms.

Whiting .

3,000 gms

Pitch or asphalt .

1,000 „

Sulphur .

1,500 ,,

Reclaimed rubber

. 8,000 ,,

Dark substitute

. 10,000 „


750 ,,

The manufacture of motor-tyres was built up on the principle
of the pneumatic core-tyre, and in course of time has developed
into its present degree of perfection.


The principal

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Online LibraryAdolf HeilThe manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others → online text (page 14 of 21)