Other types of machines have been introduced; the above is a representative form.
The rough sheets must now be perfectly dried, as water impairs the final product. This is done in drying rooms by steam heat, generally, at a temperature of about 90° F. (32° C.) The windows, if there are any, are painted to exclude sunlight, which operates to deteriorate raw gum. When absolutely dry the caoutchouc is removed and stacked away for use.
Masticating Machine.
To prepare pure gum for the manufacture of sheet rubber and as a starting point for many other preparations, the india rubber is “masticated” in special apparatus. The machine consists of a fixed cylinder within which is a corrugated roller set eccentrically and rotated by power. The perfectly dry sheets in the masticator are pressed and rolled and ground and produce a mass of even consistency. Here the welding or cohering action again appears in its fullest development. The perfect dryness of the mass enables it to keep reuniting as fast as divided. The action is assisted by the heat generated, which is not inconsiderable. Sometimes the caoutchouc is warmed before introduction, and sometimes the roller is heated by passing steam through it.
Masticating Machine.
The masticating machine the French picturesquely term the wolf (loup) or devil (diable). It is given from sixty to one hundred turns a minute, and a machine large enough to treat fifty pounds of gum in a charge, requires five horse-power to drive it. In it the sheeted gum is ultimately brought to the state of a perfectly homogeneous dark brown translucent mass.
The masticated rubber is peculiarly amenable to mechanical and chemical treatment. It can be shaped by heat and pressure, and it is the most soluble form and is used for making cement and solution, and is moulded into blocks for the manufacture of sheet and thread rubber. In the process neutral body pigments, such as oxide of zinc, or soluble transparent ones, such as alkanine may be introduced; easily decomposed matter cannot be incorporated on account of the heat.
In all these machines special provision is made to prevent any oil from getting into the gum. There is no greater enemy to india rubber than oil or fats of any description. The flanges in the masticator that roll just inside the bearing are for this purpose.