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36
1919
In the manufacture of rubber and its products there are at
least 6 stages:—
1. Purification.
2. Rolling.
3. Mastication and Mixing.
4. Calendering.
5. Vulcanization.
6. Making up of the finished articles.
I.—Purification consists in the removal of various impurities
and formerly the process used to be carried out in this
country. Some of the lower grades of African rubber contained
a considerable amount of impurities and it was stated that such
unconsidered trifles as Negroes skulls have been found in the
crude rubber. The impurities in some instances amounted to as
high as 10 per cent., but recently the importance of purity in the
rubber has become appreciated to such an extent that no purification
is carried out in many works in this country. In the Agnes
Road Works no purification takes place, and the crude rubber
contains less than 2 per cent. of impurities.
The rubber is imported in two forms—the smoked and unsmoked
varieties.
(2) Rolling.
The material is then passed between grooved rollers over
which hot water passes from a series of fine jets. All particles
of sand and dirt are removed, and the rubber leaves the machine
in the form of rough sheets. These sheets are hung up so as to get
rid of the water incorporated with the rubber in its passing through
the washing machines.
(3) Mastication and Mixing.
After drying, the rubber is removed to the grinding mills,
so that it can be brought into a condition in which it can be mixed
with the materials necessary for giving it consistence and any
required colour and to prepare it for the subsequent process of
vulcanization. Portions of the mixture are placed in buckets
and the contents covered with naphtha. The naphtha combines
with the rubber and the compound then forms a dough or thick
paste.