Picture this: You are on the floor, ready to switch your machine from a dark blue HDPE to a natural white. You start feeding the new resin, but twenty minutes later, you are still seeing streaks of blue in the parison. Or worse, those little black carbon specks keep popping up in the final bottles.
This is the nightmare of every machine operator. It kills your cycle time and creates a mountain of scrap. The solution? You need to understand the basics of purging.
So, What Actually is Purging?
In simple terms, purging is the process of cleaning the internal components of your blow molding machine—specifically the screw, barrel, and die head—without taking everything apart.
Many beginners make the mistake of thinking they can just “flush” the machine with the next production resin. The problem is that standard resin is designed to flow smoothly, not to clean. It tends to layer over the old color or carbon buildup rather than scrubbing it out. That is why you need a specialized Purging Compound for Blow Molding. These compounds are engineered to scrub the metal surfaces and push out the stubborn contamination that virgin resin leaves behind.
It’s Not One Size Fits All
Before you dump just any cleaner into the hopper, you need to know your machine type. AtUNICLEANPLUS, we see two main setups, and the cleaning steps are different for each:
- Extrusion Blow Molding: This is the continuous process. Here, you usually keep the screen packs in (unless it is super dirty) and rely on screw velocity changes.
- Accumulator Head: This is trickier. You have to manage the “pot” where plastic sits. You can’t just run it through; you have to fill and empty the accumulator in stages (25%, 50%, 75%, then 100%) to get it truly clean.
Key Steps for a Successful Purge
Using a Purging Compoundfor Blow Molding isn’t hard, but you have to follow the rules to get the best results. Here are a few tips from the UNICLEANPLUS technical team:
- Turn up the Heat: Don’t purge at your normal running temp. We recommend increasing the die temperatures by about 55°F – 65°F. This helps soften the stubborn deposits inside the head.
- Clean the Hopper First: It sounds obvious, but a lot of operators forget this. If your feed throat is dirty, you are just feeding contamination back in.
- The “Stop and Go” Method: Don’t just run the screw full blast. Run it, then stop the screw and let the purging compound rest or “soak” for a few minutes. This allows the chemical agents to expand and loosen the carbon. Then, start it up again at a safe high velocity to blast the junk out.
Stop Wasting Resin
If you are currently using hundreds of pounds of virgin resin just to change colors, you are literally throwing money away. A proper commercial purging grade works faster and uses way less material.
Not sure which grade fits your specific thermoplastic resin? UNICLEANPLUS offers specialized grades for mechanical and chemical purging. You can even reach out to our team to get a Free Sample and try it on your next changeover. Trust me, your scrap bin will look a lot emptier.