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Barrel Residence Time
There is a time and temperature dependence
for the rate at which thermoplastic materials will degrade. Plastics may degrade when exposed
to "high" temperature for a short period of time, or degrade when exposed to "low" temperature
for a long period of time ("high" and "low" temperatures will be different for different materials).
During processing, temperature settings and the amount of time material is in the injection cylinder
are important. The actual residence time may be determined experimentally, or roughly estimated
by formula calculation. Experimentally, one can measure the amount of time taken to change one
material to the next (use of different colored materials to decipher). Estimation by use of the
following formula:
rated capacity of injection cylinder (g) x cycle time (s)
shot weight (g) x 30
Note: Be aware that some material may be in
the injection cylinder, or barrel, for longer than the calculated value as some material may hang-up
in the system.
* Resources: "The Dynisco Injection Molders
Handbook, 1st Edition 1996" written by Tony Whelan and John Goff
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