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Home | Shredding and recycling of plastic lumps and purgings

Shredding & Recycling Plastic Purge Lumps from Injection Molding & Extrusion

Start-up Scrap Recycling: Turn Purge Waste into Valuable Regrind
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three piles of plastic material: purge, shredded purge and granulated purge
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One of the most common material applications of plastics shredding is the processing of so-called plastic lumps, which are usually generated as a waste product during the extrusion of plastics. The economic potential of this "purge" is enormous. It is expensive to dispose of the unused purge lumps. Recycling offers the possibility of seamlessly reintegrating production scrap into the manufacturing process instead of using new resources.

Customer applications: Plastic lumps and purgings shredding with WEIMA

Practical examples of successful shredding with WEIMA shredders
Plastic purge shredding
Shredding plastic purge with a WEIMA S5.18 lift-up @ Plastic Recycling Inc. South Carolina
A WEIMA S5.18 lift-up single-shaft shredder shreds plastic purge at Plastic Recycling Inc. in South Carolina.
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A crane that transports the PE blocks into the S7.20
Plastic purge shredding
PE lumps shredding with a WEIMA S7.20 shredder @Remondis Staffanstorp, Sweden
A WEIMA S7.20 single-shaft shredder shreds large and heavy PE lumps at a recycling plant of Remondis in Staffanstorp, Sweden.
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Plastic purge shredding
HDPE lumps | purge shredding with a WEIMA WLK 1500
A WEIMA WLK 1500 single-shaft shredder shreds hard HDPE lumps to a homogenous size for further recycling.
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WEIMA CSO Kay trained in front of a glazed office
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WEIMA portfolio for shredding plastic lumps and purgings

The right machine for any material
WEIMA WLK 1500 yksiakselinen murskain
Single-shaft shredder
WLK series
Machines in the WLK series are ideally equipped for a wide range of plastics tasks. The machine design is characterized in particular by its durability and robustness. Thanks to the conveyor belt cut-out, all machines can be seamlessly integrated into any production line. They also offer a wide range of options in terms of drive and cutting geometry.
To the machine
Single-shaft shredder
W5 series
With rotor lengths of 1,400 to 2,200 mm, the shredders in the W5 series shred large-volume plastic lumps and chunks with ease. The hydraulically upward pivoting screen basket and the inspection flap allow foreign objects to be removed quickly and facilitate maintenance. Large quantities of plastic flakes can be transported via the wide conveyor belt cut-out.
To the machine
Single-shaft shredder
S7 series
With their extremely sturdy design and large rotor diameters of up to 700 mm, shredders of the S7 series offer almost unlimited possibilities for the shredding of plastic waste. They are up to any challenge and can be equipped with a powerful hydraulic drive.
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Applications from industrial plastics production

Big plastic injection lumps in a WLK 800 shredder
Plastic waste in WEIMA single-shaft shredder
Shredded petrochemical lumps
Plastic lump from the production of PP
Injection lump
Shredded and grinded plastic waste from injection moulding
Huge petrochemical lump in WEIMA WLK single-shaft shredder
Plastic lump from PE extrusion
Plastic lump in the WEIMA shredder
Mixed extrusion lumps from production
Extrusion lump from extrudate
Shredded plastic waste from WEIMA shredder shredder
Shredded PE and HDPE lumps
Shredded plastic from automobile production
Plastic lump from laminate production PVC
Waste from plastic extrusion
High-density polyethylene waste for inhouse recycling
Shredded plastic
Shredded polycarbonate lump from extrusion process
Two-stage shredding with a WEIMA shredder and granulator
Mixed PP lumps from the extruder
plastic lump from laminate production PVC
Extrusion lumps from the plastic production
Various petrochemical lumps from injection moulding
Thermoplastic lumps
Shredded petrochemical lumps
Extrudate within an extrusion line
Extrusion pellets and granulate from plastic production
Stacks of plastic lumps
PP lumps are shredded in the WEIMA shredder

Recycling of plastic lumps

Key facts at a glance
Stacks of plastic lumps
Stack start-up lumps before shredding
Plastic lamps for plastics recycling
Purge Lumps – Many Names, One Challenge
In plastics processing, especially during extrusion and injection molding, material waste is generated at the start of production. These solid plastic residues are known by many names: purge lumps, purge cakes, start-up scrap, sprues, butzen, rejects, or simply purge waste. But no matter the name, they all refer to the same issue: bulky, hard-to-recycle plastic waste that takes up space and should be handled efficiently.
plastic lump from laminate production PVC
Various petrochemical lumps from injection moulding
How Are Plastic Purge Lumps Created?
In injection molding processes, plastic waste and production scrap occur regularly, especially when parts are out of spec, edge trims are needed, or sprues and start-up purges form. Such purge waste is also created during machine trials, production breaks, or when restarting equipment. If the scrap is mono-material, it is considered high-quality and can ideally be regranulated and reintroduced into the production cycle.
Plastic lump from PE extrusion
Bulky, Heavy – But Far From Useless
Large, voluminous, and difficult to handle – that’s what purge lumps typically look like in the plastics industry. But anyone who considers them worthless underestimates their potential. Around the world, companies like Rowad Plastic and Napco National rely on WEIMA shredding technology to handle the first step of plastic purge recycling. Whether you're a plastics manufacturer, processor, or chemical company, the challenge is always the same: reduce start-up lumps to a uniform particle size suitable for further processing or reuse. In practice, single-shaft shredders, often combined with downstream granulators, are proven solutions for reliably processing even the largest purge blocks.
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Did you know?
Thermoplastics are plastics that, unlike thermosets and elastomers, can be formed as often as required - as long as they are not overheated, otherwise they may decompose. Well-known thermoplastics include polypropylene (PP), polycarbonate (PC), polyamide (PA), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS).

Source: Ruge, Wohlfahrt (2013) Technologie der Werkstoffe

Heavy duty machine design

WEIMA shredders are engineered to handle highly abrasive materials and can be individually equipped with wear-reducing options. Thanks to the thick-walled machine frame, they operate with exceptional stability and long service life – even when processing tough plastic purgings. This significantly reduces downtime and sustainably lowers maintenance costs.

More about wear protection

Vautid jacket on a rotor

WEIMA rotor with Vautid protection

Vautid weld on for shredder rotor

Vautid weld-on for shredder rotor

Concha Vautid no rotor PowerLine

Proteção contra o desgaste do rotor Vautid

Casco do rotor Vautid

Revestimento de rotor Vautid

ANteção antidesgaste com revestimento de tinta

WEIMA WKS rotor concha vácuo

Proteção contra o desgaste do revestimento do rotor

Revestimento Vautid para pré-triturador

Precise cutting at high throughput with profiled V-rotor

The V-rotor, specially developed by WEIMA, can be used universally and is made from solid material. Its aggressive material feed with up to two rows of blades guarantees a high throughput with low power requirements. It can be fitted with hardened steel cutting blades in edge lengths of 30 mm and 40 mm. These can be reversed several times when worn, which drastically reduces maintenance costs.

Rotor and cutting technology

Profiled V-Rotor from WEIMA

Profiled V-Rotor with counter knives

Free material tests in the WEIMA technical center
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Success stories

Plastic purge recycling with WEIMA
Group photo of employees at Mississippi location of commercial plastics recycling inc.
August 2, 2025

Drawing from the full: How CPR, Inc. efficiently recycles start-up lumps

Commercial Plastics Recycling, Inc. processes over 8,000 tons of PET start-up material annually with shredding technology from WEIMA - reliably, efficiently and sustainably. Two single-shaft shredders ensure uniform regrind, maximum system availability and a tangible contribution to the circular economy.

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November 23, 2023

Plastic Recycling, Inc. Transforms Plastic Purge with WEIMA Shredder

From the southeastern U.S. to the heartland of Indiana, Plastic Recycling, Inc. remains committed to their mission of recycling plastics and transforming them into something new and valuable. With the WEIMA shredder as their trusted partner, they're writing a story of progress, resilience, and a better world for generations to come.

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Frequently Asked Questions about Plastic Lump Shredding

Everything you need to know about safely and efficiently shredding plastic purgins.
Which WEIMA machine is best for shredding large plastic lumps and blocks?

For large and heavy start-up lumps we recommend a robust single-shaft shredder from WEIMA’s W5 or S7 series. These machines are built with reinforced frames, heavy-duty rotors and large intake openings to handle massive volumes of hard plastics like HDPE or PP. With the right geometry they deliver a steady throughput and create a homogeneous output for recycling.

How does the shredding process work for start-up lumps?

First, the lumps are fed into the shredder (e.g., WEIMA W5.22 or S7.20) which breaks them down mechanically into smaller flakes. Then optional separation units (e.g., magnets) remove metal parts or contaminants. The resulting material is uniform, clean and ready for re-granulation or reuse, closing the loop in the production chain.

Can other production waste be processed together with start-up lumps?

Yes. Our shredders can shred not only start-up lumps, but also thick-walled molded parts, production rejects, or plastic sheets. The key is choosing the right machine—WEIMA will help you configure your system to achieve maximum efficiency and material purity.

What are the economic benefits of recycling these lumps instead of disposing them?

By shredding start-up lumps you transform what was once costly scrap into a valuable secondary raw material. Disposal fees drop, shipping and storage costs shrink and you reduce your dependence on expensive virgin resin. Many WEIMA customers report rapid pay-back periods by reintroducing shredded material into their production.

Which materials and processes are suitable for this type of shredding?

Start-up lumps from extrusion and injection moulding of thermoplastics such as PP, PE, ABS, PC, PA and similar are particularly suitable. WEIMA machines handle flexible and rigid plastics alike and can be integrated into lines with automatic feeders, conveyors and downstream granulators. Even blocks with heavy contamination or irregular geometry can be processed with the right machine configuration.

What about wear, maintenance and machine robustness in these high-stress applications?

WEIMA shredders for these applications are equipped with thick steel frames, wear-protected cutting tools (e.g., Vautid steel) and high‐torque drives designed for continuous operation. Maintenance is simplified through features like large inspection doors and quick‐change knives. Properly set up, downtime is minimal and operational reliability high.

How do we select the right machine size and configuration for our production line?

The selection depends on purge size, material type, throughput requirement and available floor space. WEIMA recommends submitting sample lumps for a free test in our technikum, so you can see actual performance and output characteristics. From there, we propose a customised solution including shredder size, feed conveyor, separator and downstream equipment.