You can ask a plant manager what a color change costs and probably hear a number for resin. Even if you can ask the operator who has spent forty minutes waiting for the last streak of red to disappear, you’ll hear something else entirely.
The answer is somewhere between the two, and it’s almost always bigger than anyone wants to admit. On paper, a changeover looks like a routine line item. On the floor, it seems a small crisis that repeats every time the schedule calls for a new color.
The Costs Nobody Puts on the Spreadsheet
Resin is an easy part to count. The remaining hides in plain sight. Scrap parts keep coming out speckled or streaky long after the switch. Every rejected shot is material, energy, and machine time you’ll never get back.
The press remains idle while good production time slips away. A technician who should be prepping the next job often ends up babysitting the barrel. Carbon bakes onto the barrel wall quietly and shows up later as black specks, and leftover pigment hangs up in the tool; while contaminating a run you thought was clean.
None of them looks dramatic on its own. Together it’s a steady drain. If your floor runs several colors a week, that drain never really stops.
Why “Just Run It Out” Never Works
Most shops handle changeovers by running the next resin until the old color finally gives up. This feels practical and requires no extra product on the shelf. But it’s slow, it burns through material, and leaves stubborn residue clinging to the screw and barrel.
That’s where a purging compound for injection molding comes in handy. It’s a ready-to-use, pre-mixed material that scrubs as it travels through the barrel, carrying out burned streaks, foreign contaminants, un-melted resin, and tarnished leftovers.
What You Get When the Purge Is Done Right
Molders who purge properly often notice the difference quickly. There are fewer scrap parts, less carbon building up in the barrel, and no ghost of the last color lurking in the tool. Color-change time and overall changeover time come down, and downtime shrinks with them. The savings really stack up on floors that switch colors often. It’s because you’re not saving once; you’re saving on every changeover, every week.
A Routine Your Whole Team Can Repeat
The best purge is one every changeover performs the same way. So it helps to write the routine down and keep it near the machine. You can start by setting all zones to the temperature range recommended for the grade of compound you’re using. Pull the injection unit back, empty the screw and barrel, and clean the hopper and feed throat. After that, feed one to two barrel capacities of compound into the feed throat.
With the screw fully forward, increase the backpressure to its highest level. Once the compound starts coming through the nozzle, raise the screw speed to the highest safe level, and ease the backpressure off when the material coming out looks nearly clean.
Finish by pulling the screw back and running a few short, preferably high-speed, shots. If you are still seeing contaminants, you should repeat the feeding, backpressure, and shot steps until the barrel runs clean. Whatever compound stays in the machine gets pushed out by the next resin, so there’s no additional cleanup to worry about.
Bottom Line –
Pull the numbers from your last ten changeovers, including time to first good part, scrap count, material used, and labor hours. Multiply the lost time by your machine hourly rate and add the cost of the scrap. Most teams are surprised by the total. A small improvement per changeover turns into a big number over a month of multi-color production. Once it’s on paper, the case for a standardized process practically writes itself.
Choosing the right purging compound for injection molding is only half the process. A good quality product used inconsistently wastes time, while a solid routine combined with the right compound makes changeovers predictable and inexpensive.
Do you want to cut scrap and downtime? Book a free consultation with the UNICLEANPLUS purging experts and find the right grade for your resins and machines.