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Injection Molding Purge Cycle Odor

It is well known throughout the plastic injection molding industry that there’s one job nobody wants. Which one? The purge.

Why is that? The odor that emanates during the purge cycle is terrible. It can fill the room or the plant and will overcome even the most tested noses. I know owners that have waited until the plant is vacated before starting the process. If you have a lot of molding machines, that may not be practical.

What causes that? It’s the chemicals use during the process.

While many owners have tried various methods to reduce or eliminate the odor, I have seen one solution that has worked time and again for going a long way to reducing the problem. Source capture air purification equipment.

It’s not the particle filter that does the work, although that will reduce the smoke that’s also a part of the process. It’s the odor adsorbent material incorporated into the after filter. Most of this adsorbent material is either straight coconut shell carbon or a blend of different materials. You particular purge chemical may have different levels of a particular VOC that would require a work-up to determine the best blend. There are test methods to determine the most efficacious blends, which usually involve running the collector for a few weeks and sampling the adsorbent to see what element is doing the work. Based on that lab test, the exact blend can then be incorporated and then rechecked if necessary.

What kind of collector package should you try? It depends on your particular situation. If you only have one machine, you have a variety of collectors to choose from. Maybe an overhead model would work best. It doesn’t take up any floor space and the collection arm cam be positioned directly over the cavity. If you have a number of machines, a portable collector that can be easily moved from one machine to another might be best.

Here are some examples of machines you may consider.

Portable With New Arm

Portable Air Cleaner with Collection Arm

Wall Mount unit with source capture arm

Wall Mount Unit with Collection Arm

In either case, they will need to be maintained, so keep that in mind. The maintenance will involve replacing the adsorbent material periodically. How often depends on how many purge cycles and how much adsorbent is in use.

Don’t go cheap on the adsorbent. It may pay off to have more up-front and have fewer replacement cycles. The replacement process can be a bit of a mess and you’ll want to prepare for it, or better, increase the time between replacement cycles.
Adsorbent is generally considered to be either recyclable if you have enough, which most people don’t, or put into the waste stream, if your municipality allows it. You may want to check beforehand.

The particulate filter may also need to be replaced every so often, and that will depend on how clean the plant is. Make sure to use the same efficiency filter when you replace so as not to effect the life of the adsorbent. You may wind up plugging the adsorbent faster if you go a less efficient pre-filter.

Some owners may decide to just exhaust the odor outside. That can be a costly solution based on the number of purge cycles and how much exhaust air. If the plant is air conditioned or heated, you’re throwing away energy dollars with each purge. And your neighbors may have an issue with the odor.

Here are calculators you can use to estimate the cost of throwing heat or air conditioning away.

In addition to all of these reasons to collect the off gas from the process, there may be health reasons as well. Some employees may be more effected than others.

Here’s an article that talks about what some of those issues may be for women.

If you are a responsible owner, you may want to consider source capturing the off gas from your plastic injection molding processes.

Air Quality Engineering

Air Quality Engineering