Injection Molding Scrap Grinder — Inline Sprue & Runner Recycling

On cold-runner molds, sprues and runners alone commonly run 15–30% of shot weight, depending on part size and cavity layout — small multi-cavity parts sit at the high end. Add start-up purge, colour-change scrap, short shots and QC rejects, and many shops find 20% or more of purchased resin coming off the press as non-product. Weigh one shift’s scrap per press — that number, in kg/hr, is exactly how you size a grinder.

It is the closest thing to virgin you can get from recycling: same grade, same colour, and only one previous heat history. Each pass through the barrel does shave polymer properties slightly, which is why molders blend regrind with virgin at a controlled ratio — commonly 10–25% on non-appearance and non-structural parts — rather than running 100% regrind. The practical rules: grind it clean and fresh, keep polymers and colours strictly separate, store regrind dry, and dose at a consistent percentage so your process stays stable.

Beside-the-press wins when scrap is continuous and segregation matters: the RE8’s 950 × 650 mm footprint fits next to the machine, runners go straight in, and there is no risk of mixing polymers. Central grinding wins when you run many presses on common materials, have bulky rejects that need a bigger throat, or want one operator handling all reprocessing — an RE20 or RE30 ground batch-wise covers an entire shop. Many plants do both: small grinders on long-running presses, one central machine for everything else. Our machine selection guide covers the trade-offs in detail.

Work from scrap weight, not press count. A press producing 30 kg/hr of moldings with 20% runner weight generates about 6 kg/hr of scrap — an RE8 at 35–45 kg/hr covers several such presses with ease. The throat matters as much as capacity: the part of the scrap that decides your model is the largest reject you want to feed whole. RE8 and RE12 take sprues, runners and small parts; bigger rejected moldings need the 16″–30″ throats of the larger models. Send us your part weights and scrap estimate for a free sizing recommendation.

Yes — RE-series grinders process engineering polymers including ABS, nylon and polycarbonate. Glass-filled grades are abrasive, so expect blades to need resharpening more often than on unfilled PP or PE; the 5-blade set is removable and resharpenable, and spare blade sets are available from Mumbai. Keep one rule absolute: never let metal inserts, screws or tramp metal enter the chamber — metal breaks blades. See our nylon waste shredding page for filled-material specifics.

Every machine is quoted to the job. What moves the number is capacity, throat size, motor rating, MS or SS construction and the automation you add — a blower, a conveyor, a control panel. Our guide to what drives machine cost walks through each of those; send us your material and daily volume and we will size the machine and quote it, usually the same day.

Power and blades, essentially. A 3 HP RE8 running beside a press draws very little — a few units per shift — and the 5 HP RE12 not much more; every model ships with an overload-protection starter so a jam trips the motor instead of damaging it. Blade resharpening is the main consumable cost, driven by your running hours and how abrasive your materials are. There are no other consumables, and the all-metal construction is built for continuous shop-floor duty with simple cleaning and lubrication.

Yes — bring a sample lot of your actual scrap (runners, rejects, purge pieces) to our works at Andheri East, Mumbai, and we will run it through the machine so you can check regrind size, throughput and how your material behaves. For outstation molders we arrange video trials on your material. Contact us to book a slot — Mon–Sat, 9 AM to 7 PM.