II  Processing Factors

 

(a) Pre-milled rubber is fed into the extruder	cold rubber compound can be fed into the
(b) Output will be uniform	Output depends on the nature of the      Compound
� Production equilibrium can be attained within a short time.	It takes longer time to attain production  Production equilibrium

 

III.                  Economic Factors

 

(a) Frequency of replacement  of the screw due to wear is low.	Freuent replacement of the screw is  Needed due to the high rate of wear of the  screw.
(b) Since a mixing mill has to be installed for warming up the feed Stock the capital investment is high.	Capital investment is low since no    warming up mill is required
� The operating cost and the number  of labourers required will be more since  a mill has to be operated side by side.	Operating cost is lower since no mill is to be operated
(d) Output of the machine will be high	Output is lower.

Whichever be the type of machine used products of consistant quality can obtained only if the compound fed into the machine is uniform in viscosity, temperature and volume.  Care should be taken to maintain the temperature of the barrel, screw, and head and die cantant.  The common defects that appear in the extrudate their causes and remedies are given below.

 (1)   Die swell or change in dimension of the extrudate 

As the compound comes out from the die, it shrinks along its length resulting in slight increase in overall dimension of the extrudate.  The factors affecting the die swall are (a) nature of the compound (b) uniformity of the veyor systems.  Usually use of precrasslilnked polymer like SP rubbers, high structure fillers and high loading of fillers in the compound reduce the dieswell of the extrudate.  To get uniform dimension, the compound shall be uniform in rate of feed, viscosity and temperature.  In crease in the speeds of the screw and the take off conveyor system reduce the die swell to a certain extent.  Increase in the temperature of the die head and die can also reduce the dieswell.

TABLE � 1. MACHINERY DETAILS 

ScrewSize (Diameter: inch)	Motor H.P.	Maximum Advisable Speed (R.P.M.)	Average Capacity Lbs./hour	Average Die Area (Sq. inches)	Maximum Die area (sq. inches)
1.5 2.5 3.5 4.5 6.0 8.0   10.0 12.0	3-5 5-8 20-30 30-40 50-70 100-150 125-175 150-200	80 80 90 90 78 78   78 78	50 200 450 850 1450 3600   6700 9500	0.45 0.75 1.50 2.50 5.0 9.6   16.0 24.0	0.75 1.50 3.0 5.5 10.0 20.0   35.0 50.0