A purging compound can look like it is doing its job because the machine eventually gets clean.
But “eventually” is not a very useful measure.
A good purge program should produce repeatable results while reducing the time, scrap, labor, and material required to get from one production run to the next. If a processor only looks at the cost per pound of the purging compound — or whether the machine looks clean at the end — it can miss most of the value.
So how do you know whether your purge program is actually working?
The best way is to measure it.
Here are seven metrics plastics processors can use to evaluate purge performance and identify where there is room to improve.
Start with one of the easiest measurements: time.
Track the time from the end of the previous production run until the machine is ready to produce acceptable parts or material again.
This can include:
The important part is consistency.
If one operator completes the same changeover in 30 minutes and another needs 75 minutes, the issue may not be the purging compound itself. The procedure may need to be standardized.
A short changeover can still be expensive if it generates a large amount of scrap.
Track the pounds of material that cannot be sold or reused during the transition.
That may include:
This becomes particularly important when processing expensive engineering resins or making frequent color and material changes.
Reducing ten minutes of downtime is valuable. Reducing ten minutes of downtime and 50 pounds of scrap is much more valuable.
Using more purging compound does not automatically mean better cleaning.
In fact, one of the easiest ways for a purge program to become unnecessarily expensive is allowing operators to feed material until the machine “looks clean” without establishing a repeatable amount.
The proper purge quantity depends on the process, machine, resin, contamination level, temperature, and cleaning objective — not simply machine size. Asaclean has previously discussed defining purge volume based on the actual need rather than relying only on tonnage or screw diameter.
Once a successful procedure is established, document the amount required.
That gives operators a baseline and makes unusual material consumption easier to identify.
This is one of the most useful measures in the entire purge process.
The machine may appear clean, but production has not truly restarted until acceptable product is coming off the line.
Track:
Time from the beginning of the changeover to the first good part or acceptable production material.
This captures more than purge time alone.
It includes the real production impact of:
For many processors, first-good-part time is a better business metric than simply recording how long the purge itself took.
A purge that looks successful initially may not have solved the underlying problem.
If black specks, streaking, gels, or residual color return shortly after production restarts, track how often that happens.
Recurring contamination may indicate:
Asaclean recently covered how machine leakage and wear can contribute to persistent black specks even after a purge appears complete.
That is why “Did the contamination disappear?” and “Did it stay gone?” are two different questions.
Material cost is easy to see on a purchase order.
Labor cost is easier to overlook.
Track whether the purge requires:
A process that uses slightly more purging compound but eliminates hours of maintenance work may be the less expensive option overall.
The goal is not necessarily to minimize the pounds of purge used.
The goal is to minimize the total cost and disruption of the changeover.
Finally, ask whether the process works the same way every time.
An effective purge program should not depend entirely on having your most experienced technician standing at the machine.
Compare results across:
Large differences may point to a training or procedure issue.
Once the process is optimized, document the critical steps so operators have a consistent procedure to follow.
There is no single number that defines success for every plastics processor.
A plant running frequent color changes will have different priorities from a processor struggling with carbon contamination or running expensive high-temperature resins.
But a good purge program should generally move the important numbers in the right direction:
That is the difference between simply using a purging compound and operating a purging program.
For many processors, time to first good part is one of the most useful measures because it captures the total production impact of the changeover rather than purge time alone.
No. Material consumption is important, but it should be evaluated alongside downtime, scrap, labor, startup losses, and production quality.
Differences in temperature, procedure, purge quantity, machine settings, timing, and operator technique can all influence the outcome. A documented procedure helps improve repeatability.
Review performance whenever processing conditions, materials, equipment, or recurring problems change. Even an established program can benefit from periodic evaluation.
If your plant is evaluating its purge program, start by establishing a baseline.
Record what the current process costs in time, material, scrap, and labor. Then compare any change against those same measurements.
Asaclean’s purging experts can help processors evaluate existing procedures, identify opportunities for improvement, and determine which purging approach fits the application.
Learn more about how to reduce production downtime and protect your profits with a purging compound.