RUBBER PLANTING 227 



Calendering. 



At the present day by far the largest proportion 

 of sheet rubber is prepared in machines known as 

 calenders. Indeed, the calenders are among the most 

 important machines in modern rubber factories. A 

 calender consists of a series of heavy rollers revolving 

 alternately in opposite directions. A common type 

 has three rollers arranged one above the other. The 

 rubber mixture is fed between the upper and middle 

 rollers. The sheet thus formed, varying in thickness 

 according to the distance at which the rollers are set, 

 adheres to the middle roller and passes back between 

 the middle and lower rollers. For packing the sheet 

 thus obtained, the following method is adopted. A 

 sheet of cloth is unwound from a drum on one side 

 of the machine. The cloth passes between the middle 

 and lower rollers, and is rolled up together with the 

 rubber sheet on the opposite side of the machine, If it 

 is desired to make the rubber adhere closely to the 

 cloth, the middle and lower rollers are made to revolve 

 at different rates of speed, and the friction thus caused 

 produces the desired adhesion. The rubber is then said 

 to be " frictioned " on to the cloth. Frictioned sheet 

 is used in the manufacture of a large variety of articles 

 in which alternate layers of cloth and rubber have to be 

 incorporated. 



