THE MANIPULATION OF MASTICATED SHEET RUBBER.
The manipulation of pure sheet rubber is simple, yet is liable to
lead to disappointment. When two pieces are laid face to face and cut
across with a sharp knife, or scissors, the edges will adhere with
considerable tenacity. This may be increased by applying some thick
solution of india rubber in a volatile solvent, and by manipulating the
sheets so as to bring the entire surfaces of the cuts together. Finally
the material may be charged with sulphur by absorption or by Parkes’
process, and cured in a glycerine or calcium chloride bath, all of
which are described in chapter XI. The same treatment will affect the
cement used in making the joint also, bringing about its vulcanization.
Such in a few words is the main process in the treatment of this class
of goods. Where it is desired to prevent adherence, soapy water or
powdered talc is used.
Adherence may be produced between the surfaces of the sheets if they
are clean, by pressure and a little warmth. The method of making toy
balloons will give an example of how the article is dealt with by the
manufacturer.
A pile of pieces of masticated sheet rubber is made. Every piece
has one side coated with powdered talc, and two talc-coated sides
are placed in contact in each pair. As they are piled up, the outer
surfaces of each pair are moistened with water. A steel punch or die,
pear shaped in outline, is used to cut down through the pile, cutting
all the pieces into that shape.
The pile is then taken apart in pairs. The separation takes place
between the wet surfaces, the edges of each pair adhering slightly
so as to enclose the talc-coated surfaces. The neck is opened if
necessary. A rather weak or thin solution of india rubber in benzole
is now brushed over the freshly cut edges. By pulling out the centre
of each piece the edges are brought into contact, and adherence is
produced.
If the Parkes process of vulcanizing, chapter XI., is employed they are
cured to the slight extent necessary upon a tray coated with talc. The
balloons are then ready for inflation.
They are rather delicate articles to make except for immediate use as
the thin material is liable to become over vulcanized.
In the chemical laboratory sheet rubber can be used for covering the
ends of glass stirring rods. These answer very nicely for cleaning out
from beakers the last particles of a precipitate. The sheet is cut of
proper size and is bent around the end of the rod and cut off close
with a pair of scissors. It adheres where cut. It is then pinched with
the fingers to bring the edges into better contact and the operation is
complete. A slight heat makes it adhere better.
To connect glass tubes in setting up laboratory apparatus the same
material was formerly used. It was wrapped around the joint, tied with
thread and slightly warmed. At present this form of connection is
wholly displaced by ready made rubber tubing.
It is interesting to observe in all articles made from this sheet the
marks of the original cutting knife. These may be observed in inflated
balloons, as parallel lines running all over the surface, and magnified
by the expansion due to the inflation.