Page 30 - Plastics News April 2022

FEATURE

The following preventive-maintenance RPM or temperature setting after thor- • Do not rotate screw until heats are
purging program is recommended for ough cleaning. at operating temperature and prop-
injection, extrusion or blow molding • Make certain that all auxiliary er heat soak is achieved.
processes and includes these four steps: equipment is disconnected. • Follow any additional startup pro-
1. Purging the screw and barrel with • Clean the hopper and feed throat. cedures necessary for the process.
a mechanical or hybrid purge com- • Once the operating temperature
pound. This first step removes the • Clear the barrel by starving the has been reached, slowly rotate the
contamination and buildup on the screw, leaving the barrel free of res- screw—do not rotate screw at full
screw and in the barrel. Tougher in. speed.
purging applications may require • Introduce the proper CPC at a ratio
additional purging cycles. of 100%. Typically, only one barrel • If the purge coming out of the ma-
chine has any contamination, in-
2. Intermittent purging before, dur- capacity is required for a normal troduce more of the CPC and flush
ing and after production runs. purge process; older equipment the system until thoroughly clean.
This step varies depending upon and more difficult purging appli-
the resin and colors being run. cations may require an additional • Using the resin required for the
However, purging every two to purge cycle. next production run, flush out re-
three days with a chemical or hy- • Load the CPC into the hopper or maining purge.
brid CPC would be a good place to feed throat and charge the entire • Ready the machine and begin pro-
start. Evaluation will determine the barrel. duction.
optimal type of CPC and whether • Purge continuously until the purge By following these procedures, you are
longer periods may be introduced. is clean and free of any contamina- now reassured that the machine is prop-
3. Sealing the barrel with non-glass tion. erly shut down for the weekend or holi-
CPC for extended shutdowns is • During the process the CPC expe- days, and can be confident that when it
great for removing oxygen from riences a thermal mixing reaction starts up again, good parts will be pro-
the barrel (eliminating any oxida- that breaks down any color or de- duced. You will be thrilled to be up and
tion), as well as preventing any graded polymer in the barrel and running so quickly. With the proper rec-
carbon buildup that may be in the on the screw. ommendations and training from your
initial stages. Some people are not CPC supplier, purging will no longer
comfortable doing this, so leaving • Although soaking is not required, it seem complicated. This knowledge and
residual purge is fine. The impor- may be necessary for tough purging training in the proper method of shut-
tant thing is to remove the previous applications. In some cases, reduc- ting down will yield proven results in
material. ing the temperatures slightly and less time and processors will save money
allowing the CPC to stand in the
4. Purging the hot-runner/manifold barrel will result in a more effective by having less scrap and wasted material
system, die and accumulator head. purge. to throw away.
After the screw and barrel have What to Expect from Your CPC Sup-
been systematically purged clean, • Once the barrel is completely clean, plier
the final stage is designed to ensure charge the entire barrel with the Taking into consideration that no two
the mold and its components have CPC and stop screw rotation and CPC’s are alike, here’s what you ought
been purged clean and are free of turn off all heaters on the machine. to expect from your CPC supplier:
contamination. Raising the tem- Caution: Do not rotate screw while the
perature may be necessary to help system is cooling down. • Offers a tested and proven purge
clean certain areas of these compo- Procedures for Startups compound that is better than virgin
nents. resin, regrind or home remedies.
Here are key procedures to follow for
Procedures for Shutdowns startups: • Provides information to ensure the
proper CPC is selected for the ma-
Here are key purging procedures to fol- • Turn machine power on and raise terial and machine application.
low for shutdowns: the operating temperature to 350-
Typically, there is no need to modify the 375 F.

30 PLASTICS NEWS April 2022