Excavator Scrap Magnet

Overview

An excavator scrap magnet turns a standard excavator into a machine for moving ferrous metal in bulk. A large round electromagnet hangs from the stick; when the operator energises it, the magnet grips loose steel, plate, turnings, and shredded scrap, and when the current is reversed and dumped the load drops cleanly. The complication is power. The magnet needs steady DC at high current, which the excavator does not supply, so the attachment carries its own hydraulic generator set that runs off the machine auxiliary flow. This makes the system self-contained: any excavator with an auxiliary hydraulic circuit can run the magnet without an electrical conversion.

The magnet itself is the Lifting Magnet. Power comes from the Hydraulic Generator Set mounted on the boom, switching is done by the Magnet Controller, and the magnet hangs on the Suspension and Swivel. The Power Cabling carries current to the moving magnet and the Generator Cooling keeps the set in range.

The lifting magnet

The Lifting Magnet is a sealed electromagnet built for abuse. Its cast Magnet Shell forms the outer magnetic pole and the structural case. Inside, a wound Excitation Coil creates the field when DC flows, and a central Pole Plate channels that flux down into the scrap below. The coil is locked in and protected by Epoxy Potting, a filled epoxy that also carries coil heat out to the shell. The bottom face takes constant impact as the magnet is dropped onto piles, so a replaceable Wear Ring of manganese steel protects it. The supply lands at a sealed Terminal Box. Lifting capacity depends heavily on the scrap: a magnet that holds several tonnes of clean plate may grab only a fraction of that in light shredded material, because air gaps between pieces weaken the magnetic pull.

Making the power

The Hydraulic Generator Set is what lets the magnet run on a hydraulic carrier. A Hydraulic Motor is driven by the excavator auxiliary flow and spins an Alternator through a flexible Drive Coupling, turning on Ball Bearing supports. The alternator makes three-phase AC, which a Rectifier diode bridge converts to the DC the coil needs. The whole set rides on a Genset Frame bolted to the boom, guarded against flying scrap. Because output tracks engine and pump speed, the operator runs the machine at a set rpm to hold magnet voltage steady, and the genset is sized so the magnet reaches full field even when the coil is hot and its resistance has risen.

Control and release

The Magnet Controller does more than switch the magnet on and off. Holding a load is simple, but releasing it fast is the hard part: a big coil stores energy and will keep the magnet sticky for seconds after the supply is cut. To drop a load on demand, the controller uses Reversing Contactor reversing contactors to briefly flip the coil polarity, and a Discharge Module module to bleed the stored energy through resistors so the field collapses at once. The sequence is run by a Control Board with its Microcontroller and Bare PCB, driving Relay pilots, all inside a sealed Control Enclosure. The operator commands it from a Cab Toggle toggle. Clean, fast release is what makes the magnet productive, since the operator can place each load exactly without waiting for the field to fade.

Suspension and cabling

The magnet must hang freely and turn as scrap is sorted, so the Suspension and Swivel uses three Sling Chain legs gathered at a Master Link on the stick through a Hang Bracket. A Cable Swivel lets the magnet spin without twisting the supply. That supply is the Power Cabling: a heavy rubber Power Cable runs down the boom to the moving magnet, and a spring Cable Reel takes up slack as the magnet rises and falls so the cable is never snagged or stretched. Connections to the genset use a Wire Bundle and rated Connector ends.

Cooling, use, and variants

The genset and the hydraulic return both shed heat, so the Generator Cooling runs a Cooling Fan over the alternator and rectifier and an Oil Cooler on the return line, switched by a Thermostat. In service the scrap magnet works in yards, shredding plants, and steel mills, loading rail cars and furnaces and sorting ferrous from non-ferrous waste. Variants scale the magnet diameter and genset power to the carrier and the duty: deep-field magnets for loose turnings, flat high-force magnets for plate and billet, and higher-voltage coils where long cable runs would otherwise drop too much voltage. Compared with a grapple, the magnet handles loose ferrous material faster and without crushing it, but it grips only steel and iron, so a yard often carries both tools and swaps them on the quick coupler as the work changes.