Purgings and plastic lumps are a fact of life in injection molding and extrusion. Every startup, every material change, and every off-spec run generates material that has to go somewhere. In most facilities, that somewhere is either a dumpster or a growing pile of scrap that eventually gets processed, or does not. Neither outcome is good for cost control or sustainability goals.
With the right equipment and a consistent process, purgings and lumps can be converted into usable regrind rather than written off as waste. The challenge is that this material is genuinely difficult to process: it is dense, irregular in shape, hard to feed, and in some cases large enough that standard granulators cannot handle it without pre-reduction.
Why Purgings and Lumps Are a Distinct Processing Problem
A purge log pulled from an injection molding machine is not like a runner or a sprue. It is solid, often cylindrical or irregular in cross-section, and can weigh several kilograms. Feeding that directly into a standard granulator, even a heavy duty granulator, risks jams, knife damage, and uneven throughput as the machine struggles with material it was not designed to handle at that size.
The same logic applies to plastic lumps: thick-walled rejects, agglomerated material, and oversized scrap that results from process upsets. The common thread is bulk. These materials need to be reduced to a feedable size before granulation can deliver consistent output.
Pre-Reduction: The Step That Makes Everything Downstream Work
The most reliable way to process purgings and lumps is to treat pre-reduction as a dedicated step rather than an afterthought. The ZBS lump and purge shredder is designed specifically for this application: it accepts large, irregular material and reduces it to chunks that a granulator can feed and cut efficiently.
Some operations use a multi-purpose shredder for this step, particularly when the scrap stream is varied and the same machine needs to handle purgings on one run and sheet scrap or rejected parts on another. A multi-purpose shredder with the right rotor configuration and cutting geometry can manage that variability without the jams and inconsistency that come from forcing a general-purpose machine to handle material outside its design range.
The Case for an Integrated Shred-Granulate Approach
Where throughput and floor space allow, the ZCS shredder-granulator combination integrates both pre-reduction and granulation in a single machine, eliminating the handling step between the two processes. Material enters the shredder section, is pre-reduced, and transitions directly to the granulating chamber where it exits as finished regrind. No intermediate bin, no transfer conveyor, no manual intervention.
For facilities processing purgings regularly, such as injection molders doing multiple material changes per shift, the reduction in handling labor alone can justify the integrated approach. Operators are not moving heavy purge logs or managing an intermediate scrap pile; the machine handles the full sequence.
Practical Tips for Consistent Results
Even with the right equipment, a few operational habits make a significant difference in regrind quality from purgings and lumps. Feeding material at a consistent rate rather than dumping large quantities at once lets the shredder work efficiently and prevents the throughput spikes that cause particle size variation on the granulator side. Keeping blade clearances within specification is especially important with dense purge material, which puts more stress on cutting edges than lighter scrap streams.
Checking screen condition regularly also pays dividends. A worn or partially blocked screen does not just affect particle size. It also increases back-pressure in the cutting chamber, which accelerates heat buildup and further wear. Maintaining screens and knives on a consistent schedule is simpler with a machine designed for this application than with a general-purpose granulator pressed into service for material it was not built to handle.
Turning Scrap Into a Material Asset
Purgings and plastic lumps do not have to be a loss category. Facilities that invest in the right pre-reduction and granulation equipment, and that manage the process consistently, routinely recover material that would otherwise go to landfill or waste disposal. The regrind quality achievable from well-processed purge material can be high enough to blend back into production at meaningful ratios.
ZERMA America offers a range of shredder and granulator solutions built for this exact challenge. Contact our team to discuss your material stream, or browse available equipment and spare parts at Virtus Equipment Direct.
Have Questions? We’re Here to Help.
Reach out to the ZERMA America team directly:
- (239) 219-1100
- sales@zerma-america.com
- Watch the ZBS lump and purge shredder on YouTube
- Watch the ZCS shredder-granulator combination on YouTube
Shop Online at Virtus Equipment Direct
Virtus Equipment Direct is our new online store for plastics recycling and size-reduction professionals. Browse machines, spare parts, knives, screens, and maintenance kits, all in one place. Visit virtus-equipment.com/direct to explore our catalog and place an order today.
