A Sheeting Tank containing Coagulum for Crepe
Preparation.
Behind wall in background are the tanks in which latex is standardized. Note vent, to the left, through which latex flows and wooden “stopper” on edge of tank.
Standard Latex.—Enough has been written (see [Chapter VII.]) to familiarise the reader with the use of this term for the description of latex diluted daily to a level of dry rubber content. Whatever may be the practice elsewhere, it is now fairly general on estates in Malaya to reduce all latices to a uniform “strength” for the preparation of sheet rubber. It is claimed that only in this manner can uniformity of product be achieved.
The selection of a standard has been the outcome of general experience. It has been found that if too high a standard is taken difficulties arise, such as (1) unsatisfactory and uneven coagulation, (2) too thick a coagulum for easy working in general, (3) too extended a period of drying and smoke-curing, and hence too dark a colour in the finished rubber.
A “Battery” of Sheeting Tanks (Pataling Estate).
Dilution Tanks, Raised, on the Left.
On the other hand, too low a standard also brings trouble in its train. The coagulum is too porous, will not stand handling, and the resultant sheet is too thin unless an abnormal thickness of coagulum is prepared. Furthermore, over-dilution means an increase in the number of tanks required for any original volume of latex. This involves an increase in floor area, and perhaps in the size of the building. The soft sheets, when rolled, may spread to such a width as to cause the edges to be squeezed under the cheek-blocks of the machines, etc.
For all practical purposes, whether sheets are prepared in pans or in tanks, it has been found that the optimum results are obtained by the adoption of a standard approximating and not exceeding 11⁄2 lbs. dry rubber per gallon. Primarily this standard has a direct connection and interdependence with the distance between the partitions (or between the slots) in coagulating tanks. The distance found most practicable is 11⁄2 inches. This thickness of coagulum, when prepared from latex not exceeding a standard of 11⁄2 lbs. dry rubber per gallon, is found to yield a very satisfactory sheet in all respects.