Cable Granulator

Overview

A cable granulator is a specialized size-reduction machine designed to process scrap electrical cable and wire into separated granules of copper and plastic insulation. Unlike crushers or impact mills that create a wide particle-size distribution, granulators use shearing action between rotating and fixed blades to produce uniform 2–6 mm fragments. A downstream density separator then partitions copper (heavy, ~8.9 g/cc) from plastic insulation and PVC (light, ~1.2–1.4 g/cc), yielding two high-purity streams suitable for smelters and plastic recyclers.

Cable granulation is a critical step in the electrical wire recycling chain. One ton of mixed scrap cable typically yields 50–65% copper by weight and 30–45% plastic/insulation, with 2–5% loss to fines and dust. Market demand for separated copper granules is strong, refined scrap copper trades at 90–98% purity commands premium pricing compared to unsorted cable.

How it works

Material enters via the feed unit. Stripped or unstripped cable (with insulation intact) is loaded into a conical hopper where an electromagnetic vibrator prevents bridging and a rotary screw meters material at controlled rates into the granulator inlet.

Inside the granulator chamber, a high-speed rotor fitted with 24 hardened or tungsten-carbide cutting blades rotates at 1000–2500 rpm. As cable passes through, the rotating blades shear against fixed counter-knives, cutting the cable into 2–6 mm granules. The rotor speed is controlled via a VFD or stepped pulley system allowing optimization for different cable diameters and insulation materials.

Granules pass through the screen cartridge, a rotating perforated drum (2–6 mm aperture) that classifies material by size. Granules smaller than the screen opening pass through; oversized material re-enters the rotor chamber for further reduction.

The classified granules then enter the air classifier table. A vibrating inclined mesh deck is positioned at a shallow angle (15–25°). As material flows down the deck, an upward air stream (50–100 cfm) lifts light plastic fragments preferentially, while heavier copper granules settle and roll down faster. A vibration motor oscillates at 50–60 Hz to maintain particle mobility and sharpen separation.

Two separate discharge chutes collect the streams: heavy copper to one bin, light plastic fines to another. Copper granules typically achieve 98%+ purity with <2% plastic contamination.

Throughout the process, fine dust (copper powder, vaporized plastic) is captured. An induced-draft fan draws air through the rotor and screen housing into a primary cyclone where coarse dust settles into a hopper. Air continues to a baghouse with 2–4 cartridge filters, removing particles down to 0.1 micron before safe atmosphere discharge.

The entire assembly is mounted on a welded structural steel frame. Power is delivered by a 10–20 hp electric motor connected via V-belt and pulleys to the rotor and screen drum, with the motor providing continuous torque to overcome blade resistance.

Material Selection and Wear

Tungsten-carbide coated blades cost 2–3x more than hardened steel but extend service life from 200–500 hours to 1000–2000 hours. Operators choose based on cable feed rate and hardness (aluminum cable vs. copper vs. mixed exotic alloys). The fixed counter-knives are typically high-carbon steel (HRC 62–64) and require replacement every 300–600 hours.

Screen cartridges can be swapped in under 5 minutes; a facility typically keeps 3–4 spare drums with different apertures to quickly adapt to varying feed materials or particle-size specifications.

Air Classifier Tuning

The separation table air velocity is operator-adjustable. Higher air flow improves light-material removal but increases dust loading on the baghouse. Lower air flow produces heavier plastic contamination in the copper stream. Optimal tuning typically requires 50–80 cfm for mixed cable at 200 kg/hr throughput; pure copper wire may only need 30–40 cfm.

Safety and Environmental

The rotor and fixed knives rotate at high speed and pose severe laceration or amputations hazards. All access covers feature interlocked guards that cut power if opened. Tungsten-carbide dust generated during blade sharpening is classified as a respiratory hazard and requires wet-shop practices. Plastic fines from the light material stream must be tested before landfill or combustion to ensure low vinyl chloride (PVC) content, as thermal decomposition of vinyl chloride generates dioxins.