---
title: "How Does a Lifting Magnet Crane Handle Steel Scrap?"
url: https://yzcranes.com/how-does-a-lifting-magnet-crane-handle-steel-scrap/
date: 2026-09-07
modified: 2026-09-05
lang: en
author: "liudatou"
description: "A lifting magnet crane handles ferrous scrap with a round or rectangular electromagnet that produces a strong field the moment it energizes. Mainstream round magnets run 1.0–2.1 m in diameter..."
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word_count: 2231
---

# How Does a Lifting Magnet Crane Handle Steel Scrap?

A[ lifting magnet crane](https://yzcranes.com/) handles ferrous scrap with a round or rectangular electromagnet that produces a strong field the moment it energizes. Mainstream round magnets run 1.0–2.1 m in diameter and lift 5–32 tons of scrap per bite. The magnet itself weighs about 20%–30% of the crane's rated capacity, and buyers have to deduct that share from the start. For scrap yards, steel mill stockhouses, and steel trading markets, no attachment loads loose steel faster. One bite, one drop, and nobody hooks a load by hand. But magnets only hold ferrous material, and they draw hard safety lines around power loss and high temperature. Selection, power support, and daily operation all follow clear rules.

## How a Lifting Magnet Works

A lifting magnet is basically one large electromagnet. A field coil winds inside a steel housing, with a wear-resistant pole plate on the bottom face. Feed direct current into the coil, and a strong magnetic field forms. Flux lines pass through the ferrous material sitting against the poles, close the magnetic circuit, and pin the load tight against the magnet face. Cut the current, and the field collapses; the material falls under its own weight.

### Energize to Lift, Cut Power to Drop

Field work runs in a four-beat cycle. First the trolley moves over the pile. The magnet lowers and energizes, then the load hoists and travels to the drop point. Last, power cuts and the material drops. If the crew keeps the travel path clear, a skilled operator finishes one cycle in 40–60 seconds.

But two physical facts come first. Holding force drops fast as the air gap grows. Flat steel plates lie flush against the pole face, so holding force comes close to the nameplate rating. Shredded scrap leaves big gaps between pieces, and the real bite often reaches only 30%–50% of plate capacity. The magnet also grabs ferrous material only. Carbon steel and alloy steel stick without trouble. Austenitic stainless steel (304, 316), aluminum, copper, concrete, and wood do not stick at all. Expecting a magnet to lift copper or aluminum? Physics does not negotiate.

Power supply splits two ways. Fixed workshops run conductor bars with a rectifier cabinet that converts AC into 220 V DC excitation. Mobile gantry cranes and crawler cranes carry a diesel generator and make their own power. One electrical fact belongs here: magnet coils draw at a low power factor. Because of that, the plant's distribution room must size cables, breakers, and transformer capacity around this load; treating it like an ordinary motor leaves the switchgear undersized.

## Electromagnet, Electro-Permanent Magnet, and Hydraulic Grapple

For the same scrap job, three attachment routes exist: the electromagnet, the electro-permanent magnet, and the hydraulic orange-peel grapple. The differences are large.

| Comparison | Lifting Electromagnet | Electro-Permanent Magnet | Hydraulic Orange-Peel Grapple |
| ---------- | --------------------- | ------------------------ | ----------------------------- |
| Working principle | Energized continuously during the lift | Pulse charges the magnet; no power draw during work | Hydraulic cylinders close the tines |
| Typical capacity | Round Φ1.0–2.1 m; lifts 5–32 t scrap | Mostly small-mid sizes; 1–10 t | Bucket 0.5–5 m³; grabs 3–20 t scrap |
| Energy use | Continuous draw, about 5–25 kW | Power only at charge and release | Hydraulic pack 15–60 kW |
| Power-loss behavior | Loses magnetism at once; backup mandatory | Stays magnetized; best safety record | Holding valve keeps the load briefly |
| Best materials | Scrap, sections, billets, heavy plate | Neat plates and cut pieces; machine loading | Irregular scrap, big lumps, non-ferrous |
| Reference price | RMB 80,000–400,000 per set with rectifier | RMB 50,000–250,000 per set | RMB 150,000–600,000 per set |

Electro-permanent magnets save on electricity and win on safety, but they cannot scale up and only suit neat material. The hydraulic grab bucket ignores material type and bites big lumps and non-ferrous metal. Yet it costs more and demands heavy hydraulic maintenance. For scrap yards and steel mill stockhouses, the mainstream answer remains the lifting electromagnet.

### Why the Backup Magnet System Saves Lives

A lifting magnet fears two words: power outage. Picture a full bite of scrap hanging six meters up when plant power dies, and without backup measures the whole load falls within seconds. This is not scare talk. The industry has recorded scrap dropping from six or seven meters and punching through a truck cab below. A bare magnet with no backup drops its load the instant power fails — who would run that setup?

The proper fix is a power-fail magnetizing system: a battery bank mounts next to the rectifier cabinet, switches over the instant plant power cuts, and holds the magnet's field for 15–30 minutes. That window gives the operator time to lower the load safely to the ground. Think of it like backup power for an elevator: invisible in normal times, priceless the moment the lights go out. Because of that hard requirement, GB/T 3811 (Crane Design Code) and GB 6067.1 (Safety Rules for Lifting Appliances) set this rule. Magnet cranes must hold magnetism after power loss, and audible and visual alarms must warn the operator.

One detail gets missed often. After switch-off, for example, residual magnetism often keeps small iron pieces stuck to the pole face. Proper control cabinets carry a reverse-demagnetize function. It sends a brief reverse current, wipes the residual field clean, and lets the load drop completely.

## Typical Scrap and Steel Jobs

### Loose Scrap, Sections, Billets, and Coils

**Loose scrap**: Sheared pieces, turnings, borings, and shredder residue work best with a round magnet. The looser and fluffier the pile, the bigger the air gap and the lower the real bite. Estimate output on loose-state weight, not on the plate-lifting nameplate value.

**Sections and pipe**: I-beams, angles, and long pipe need a rectangular magnet or a large-diameter round magnet with multi-point contact. Long loads swing and slip after lift-off, so hoist and trolley speeds stay low and no one stands below.

**Billets and heavy plate**: Flat contact and minimal air gap bring out the magnet's full holding force, so this is the most common job in continuous-casting shops and heavy-plate warehouses.

**Steel coils**: An upright coil offers only a small end-face contact area and poor magnetic efficiency, so magnets waste their bite here and coil yards rely on C-hooks or coil tongs instead.

Overall, four user types cover most of the market:

- Scrap recycling yards running a gantry crane or overhead crane
- Steel mill raw-material and finished-goods shops
- Steel trading markets
- The cutting bays of shipyards and steel structure fabricators

## Key Selection Parameters

### Magnet Diameter, Dead Weight, and Generator Power

Magnet diameter sets lift capacity, and the common size-to-capacity relationships run roughly as follows:

| Magnet Diameter | Reference Dead Weight | Scrap Lifting Capacity | Matching Crane Class |
| --------------- | --------------------- | ---------------------- | -------------------- |
| Φ1.0 m | About 1.2–1.8 t | 5–7 t | 10 t class |
| Φ1.2 m | About 1.8–2.5 t | 7–10 t | 10–16 t |
| Φ1.5 m | About 2.8–3.8 t | 10–16 t | 16–25 t |
| Φ1.8 m | About 4.5–6 t | 16–24 t | 25–32 t |
| Φ2.1 m | About 7–9 t | 24–32 t | 32–50 t |

**The dead-weight share is the calculation buyers get wrong most often.**

The magnet itself usually accounts for 20%–30% of the crane's rated capacity. Take a 25 t crane with a Φ1.65 m magnet. The magnet weighs about 5 t, which leaves roughly 20 t of net scrap per bite. When requesting quotes, buyers must confirm whether rated capacity already deducts magnet weight. Then they match net lift to daily output instead of trusting the nameplate.

**Power supply needs margin, too.**

Fixed shops get by with conductor bars and a rectifier cabinet. Mobile gantry cranes need a diesel generator instead, sized at 1.5–2 times excitation power, commonly 30–150 kW, with startup headroom. Mobile magnet power runs through a cable reeling drum with heavy rubber-sheathed cable. If drum torque drifts out of adjustment, the drum rips the cable apart. That cable failure ranks as the most frequent small fault on mobile magnet gantries. Buyers should therefore confirm torque protection and limit switches on the drum. Magnets usually run a TD 50% duty cycle (on-time ratio), so three-shift scrap yards should pick the TD 60% high-duty version, or the coil overheats and holding force fades.

## Safety Red Lines

### Backup Power, No People Below, and Hot-Material Limits

**First, the backup system ships with the crane and gets tested on schedule.**

Run a power-fail switchover test once a week and confirm battery capacity holds beyond 15 minutes. Battery banks generally need replacement every 2–3 years, so do not wait for an incident to reveal dead cells.

**Second, no one stands under the magnet or inside the working radius.**

Mixed pedestrian and truck traffic is an old scrap-yard habit. Fence off the work zone with floor markings and barriers, and keep no equipment or piping above drop points. Loads must never hang suspended for long, and a loaded magnet never passes over people.

**Third, hot material carries a temperature red line.**

Fresh slag and red-hot billets run 600–800°C. Coil insulation ages fast at that heat, and ferrous material near the Curie point (about 770°C) loses magnetic force off a cliff, so above 600°C holding force has already faded sharply. Lifting material above 600°C requires a high-temperature magnet with a thickened insulating bottom plate, heat-resistant coil, and radiation shield, and even then short contact and fast grab-and-release are the rule. Above 700°C, switch to an orange-peel grapple outright.

**Fourth, never yank buried material.**

When the magnet grabs a big piece pinned under the pile, a hard hoist makes the crane work like a crowbar. Wire rope, coil, and structure all take damage. Loosen the pile first, then lift. If operators fail to loosen it, the hoist mechanism absorbs the full shock.

## Why Choose Yuzhong

A magnet crane has three supply interfaces. They are the crane itself, the magnet with its rectifier and backup cabinet, and the power supply. Buying them separate creates the classic finger-pointing mess. The crane builder blames magnet current mismatch, the magnet maker blames unstable crane power, and nobody owns the failure.

Yuzhong (Henan Yuzhong Crane Group) supplies the package as one integrated system. The overhead crane or gantry crane, lifting magnet, rectifier cabinet, and power-fail backup all commission together in the same factory, where test beds calibrate excitation parameters, generator sizing, and backup switchover timing before delivery. The rig then works the moment power lands on site.

Founded in 1978 in Changyuan, Henan, Yuzhong has spent 48 years on lifting equipment alone. Its MG series gantry cranes cover 5–500 t with 10–40 m spans. Buyers can verify scrap-yard deliveries against projects across 120+ export countries. Siemens electrical components and IP66 protection keep outdoor yards running through dust and damp. From magnet diameter to backup duration to foundation wheel loads, Yuzhong issues full custom drawings and bilingual parameter sheets within 24 hours. The buyer then deals with one responsible party from quote to commissioning.

## Frequently Asked Questions

### Will the magnet drop its load during a power outage?

Not on a proper unit with a power-fail backup system. When plant power cuts, the battery bank switches over within fractions of a second and holds magnetic force for 15–30 minutes. That gives the operator time to lower the load to a safe spot, sound the alarm, and clear the area. A bare magnet without backup loses its field the instant power fails and drops the load at once. Standards ban that configuration outright. Purchase contracts should state backup duration and battery capacity, and weekly switchover tests should stay non-negotiable.

### Can a lifting magnet pick up stainless steel?

It depends on the grade. Austenitic stainless steels such as 304 and 316 stay non-magnetic at room temperature and will not stick. Ferritic and martensitic grades such as 430 and 410 are magnetic, but they hold weakly and lift inefficiently. Aluminum, copper, and brass do not stick at all. If the scrap stream carries heavy stainless and non-ferrous content, the right answer is a hydraulic grab bucket, or a dual-attachment setup with a quick coupler that swaps between lifting magnet and grapple.

### Does the magnet's dead weight waste crane capacity?

Yes, and buyers must build that weight into selection as a hard cost. The magnet accounts for 20%–30% of rated capacity. A 25 t crane with a 5 t magnet leaves about 20 t of net scrap lift. The correct formula reads rated capacity = magnet weight + net load. Daily output should match net lift rather than nameplate tonnage. Adding a magnet to an existing crane means checking rated tonnage and structural margin first. Bolting it on by guesswork is how structures get hurt.

### How much does a lifting magnet system cost?

A domestic round electromagnet with rectifier control cabinet runs about RMB 80,000–400,000. Small Φ1.0–1.2 m units run 80,000–150,000, the mainstream Φ1.5–1.8 m sizes run 150,000–300,000, and Φ2.1 m and above run 300,000–400,000. Electro-permanent magnets and imported brands cost more, and hydraulic orange-peel grapples run about RMB 150,000–600,000. Buying magnet and crane as one integrated package usually costs 10%–15% less than buying separate, and it also removes interface debugging and blame-shifting.

### Can a lifting magnet handle hot steel slag?

Above 600°C, a standard magnet is off-limits. The job requires a high-temperature type with an insulating bottom plate, heat-resistant coil, and radiation shield. Even then, short contact and fast grab-and-release are the rule. Above 700°C, ferrous material nears the Curie point and holding force essentially disappears, so an orange-peel grapple takes over. Even high-temperature magnets age faster on frequent hot work. Buyers must therefore tell the supplier the real material temperature. After all, quoting a normal-temperature scrap price and hoping for the best does not work.