Answer & Explanation:
Whichever way heat is supplied to the barrel. It is necessary that the temperature inside the barrel must be maintained at optimum levels. If the heat supplied exceed what is needed, the granules will form a useless fluid. However, if heat supplied is less than required, it affects the flow rate of granules, that is, flow rate of granules will be non-uniform and abrupt
The temperature of barrel is therefore maintained by continuous flow of air over it The air either flows over the barrel by natural circulation or forced convection
(1) Increase in temperature or overheating will have affect the characteristic of the granules by reducing their viscosity which will consequently affect the reliability of granules. Thus, overheating limits increasing the process variable to increase process speed
Note
It is possible that when the molten plastic is coming out of the die orifice the granules will be aligned in the direction parallel to the axis of orifice
When no constraint is provided, the molecules will be contracted in the direction of extrusion and this will block the exit for the extrusion process. This phenomenon is known as die swell.
(2) To prevent die swell in the case of the crystalline thermoplastic materials, the extrusion line must ensure that
There is decrease in the rate of extrusion from the die orifice
There is an increase in the length of the die land
reaction catalyst or additives are added to increase the melt temperature of the granules
