Calculating Direct Machine Downtime Penalties from Moisture Induced Part Defects
Calculate downtime penalties by summing unabsorbed press hourly burden, loaded labor, scrapped resin mass, purge cycles, and hot runner clearing expenses.
Purging Compound
Meaning
Specialized thermoplastic resin cleans the internal surfaces of extrusion and injection molding equipment by displacing residual color or degraded polymer. Using a purging compound reduces the amount of time and material wasted during a color change or a material swap. The cleaning agent is designed to have a high affinity for the metal surfaces of the screw and barrel.
Mechanical Action
High-viscosity grades create a scrubbing effect that pulls stubborn deposits from the flight of the screw. Because the purging compound flows through the system as a solid plug, it pushes out the previous resin without mixing with it. This action prevents the formation of streaks and black specks in the subsequent production run.
Transition Efficiency
Effective cleaning allows a molder to move from a dark color to a light color in a few minutes. Without the use of a purging compound, the machine might require a full teardown and manual cleaning to remove all traces of the previous pigment. The cost of the cleaning resin is usually much lower than the value of the downtime it saves.
Reducing the time between production runs increases the total capacity of the plant and allows for smaller batch sizes to be scheduled profitably.
Scrap Reduction
Minimizing the number of intermediate parts produced during a changeover lowers the total waste generated by the plant. Consistent use of a purging compound protects the polished surfaces of the tooling from the abrasive effects of degraded material. Operators follow specific temperature profiles to maximize the effectiveness of the chemical or mechanical agents within the blend.