The Perils of using Regrind in Plastic Injection

Plastic injection processing long ago made the transition from art to a science of replication. As globally-minded manufacturers, it is paramount that we recognize the dangers of utilizing regrind. It is most certainly imperative that we keep and reuse these materials, but where many companies fail is in their approach towards handling these materials.

We should first consider the methods of utilization most common to the industry:

Hand Mixing:

Many companies choose to reuse their reground materials by hand mixing. It is important to note that it is very hard to maintain a stable process using this method. Most often, consistency varies which primarily promotes process fluctuations, and depletes our ability to controlled process variances.

Gravimetric Blending:

While Gravimetric blenders are a step up from manual blending it is important to note that drop- down ratios vary due to regrind types..some are flake, others inconsistent granules... As the materials are blended and introduced into the feed throat, failures can occur in consistency. Custom molders may run into problems trying to maintain their processes with any regularity. Operations that "marry" tooling and materials to a particular press may have better luck with this particular approach. Color changes are simplified with these units and "running color changes" are easily performed. However regrind can complicate critical processes demanding tight tolerances.

Re-extruded Material:

One of the best approaches towards regrind utilization is having an extrusion company re-extrude your ground scrap. Base resin can be added back in to improve molecular chain breakdown, and once consistency has been proven, reprocessed materials can be documented as a separate process from a virgin material run.This improves a plant's ability to control scrap and overall efficiencies. It is important to note that this method requires close monitoring to avoid base resin mixing, and in any operation, light colors are susceptible to foreign color contamination. Converting colors to black can improve your bottomline and reduce the potential of failing color checks.

Lastly, some companies choose to eliminate grinding altogether, or grind their scrap for resale. Regardless of the approach your company chooses, utilization of scrap must be uniform, and failure to consistently address reprocessing your scrap can lead to elemental failure. Assess the needs of your facility and choose the method that best fits your operation.

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Garrett MacKenzie: plastic411.com Editor & Technical Writer

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The Perils of using Regrind in Plastic Injection

Hand Mixing:

Gravimetric Blending:

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