Color Changes Without Downtime: How Purging Compound Cuts Scrap
On paper, a color change is trivial: run out the old color, feed the new one. In practice it is one of molding's biggest hidden costs — the machine stands idle, the operator flushes the barrel with production resin, and streaked transition parts go straight to scrap. Multiplied by the number of changes per week, the downtime and wasted material often cost more than every other loss on the line combined.
Why Flushing with Production Resin Does Not Work
Molten plastic does not move uniformly through a barrel: flow near the walls and in dead zones is slow, so old pigment and degraded material survive there long after the core of the barrel runs clean. That is why flushing with the new color takes forever — fresh material passes through the middle while old pigment keeps bleeding off the walls, shot after shot.
Purging compound is formulated precisely for those zones: mechanical grades scrub the walls with fillers of controlled abrasiveness, while low-residue formulas displace the previous material without leaving traces of their own.
The Numbers
A typical dark-to-light change flushed with production resin: 45–90 minutes of downtime and 20–50 kg of wasted material. With the right purging compound: 15–20 minutes and 1–2 barrel volumes of compound. For plants with several changes a day, the difference adds up to hours of production per week.
The second effect is less visible but more valuable: preventive purging stops the carbonized deposits that build up in barrels and hot runners over time and then shed into the product for months as black specks — the complaint that is hardest to diagnose.
The Right Grade for the Job
The Asaclean (Asahi Kasei) range covers the full process spectrum: U Grade as the universal choice for technical polymers and hot runners, UP and CP for polypropylene and polyethylene, PT for polycarbonate and clear parts, SX for super-engineering resins up to 370°C, and food-certified UB.
Perotec Systems is the Asaclean partner for the region — browse the full purging compound range or contact us with your material and machine list and we will recommend a grade and procedure.
Frequently Asked Questions
How long does a color change take with and without purging compound?
Flushing with production resin on darker colors can take an hour or more, wasting tens of kilograms of material. With the right purging compound a changeover typically drops to 15–20 minutes with a fraction of the material.
Where do black specks on parts come from?
Most often from carbonized deposits of material that sat too long in dead zones of the barrel, nozzle or hot runners. Regular preventive purging stops deposits from forming and breaking off into the product.
Which Asaclean grade should I choose?
It depends on material and temperature: U Grade is the universal choice for technical polymers (170–300°C), UP and CP for PP/PE, PT for polycarbonate and clear parts, SX for super-engineering resins up to 370°C, and UB for food-contact production. We will help you match a grade to your process.