In other words, knowing where your workpiece sits on that ladder is the difference between a magnet that runs for ten years and one that quietly loses its grip in month three. This guide explains, in plain language, why heat kills holding force, where the limits of each technology actually come from, and how to specify a high temperature lifting magnet that survives your hot line — not just one that survives the demo.
Why heat is the enemy of magnetic lifting
Heat reaches a magnetic lifter through three doors at once — and the same three paths apply whether the unit hangs on a crane magnet, sits on a telescopic beam, or rides on a forklift:
- Conduction — the hot workpiece sits directly on the magnet’s pole face.
- Radiation — nearby hot steel and furnace glow warm the whole unit.
- Self-heating — the magnet’s own coil warms up whenever it is energized.
As internal temperature climbs, two things happen. First, the steel being lifted becomes less receptive to the magnetic field. Then the magnet itself weakens. Neither is dramatic at first — that’s the trap. A magnet does not fail loudly; it just holds a little less every week until someone recalculates the safety factor the hard way.
So every serious high temperature lifting magnet design fights on two fronts: keep the workpiece heat out, and keep the components below their own temperature limits. Which components those are depends entirely on the technology inside. (For a side-by-side of the two technologies beyond temperature, see our electro-permanent magnet vs electromagnet comparison.)
The hard ceiling: 768°C, when steel stops being magnetic
Before comparing products, fix one physical fact in place. Iron loses its ferromagnetism at its Curie point, about 770°C; in practice steel is considered non-magnetic above roughly 768°C (Goudsmit Magnetics; Truninger AG). Below that line, however, magnetism fades gradually — which is why lifting force drops well before the ceiling arrives.
Practical rule: no lifting magnet — electromagnetic or permanent — can grip steel much above 700°C. If a supplier quotes “works at 800°C”, they are quoting the ambient temperature their housing survives, not the steel you can lift.
Therefore, always measure the workpiece surface temperature at the actual lift point instead of judging by colour. A billet that looks evenly hot can easily be 150°C cooler on the end that touches the magnet.
How heat attacks electromagnets and electro-permanent magnets differently
Both technologies move the same steel, but heat hits them in different places. Understanding this one section will let you read any supplier’s high-temperature datasheet correctly.
Electromagnets: the coil is both the engine and the victim
A lifting electromagnet generates its entire field from a continuously energized coil. Heat therefore attacks the insulation system: enamel on the magnet wire, the potting compound, and the winding’s temperature class. Wire grades are classed B, F, H and beyond — corresponding to long-term limits of roughly 130°C, 155°C and 180°C (per IEC insulation classes) — and ultra-high-temperature units move up to class C materials with multi-layer heat shielding.
Because the coil is powered the whole time it holds the load, an electromagnet heats itself. That is why duty cycle matters: standard units are rated TD-60% (energized 60% of the cycle), high-frequency versions TD-75% (industry convention, e.g. Kino Cranes, Voitto Crane). For example, run a TD-60% magnet on a 25-cycles-per-hour line and it overheats — and an overheated coil delivers less force exactly when the steel is hottest.
The upside: with no permanent magnets inside, there is nothing to irreversibly demagnetize. Consequently, with enough insulation, shielding and water cooling, electromagnets remain the mainstream answer for the hottest duty, up to the ~700°C practical ceiling.
Electro-permanent magnets: the magnets hold, so the magnets are at risk
Un imán electropermanente (EPM) does the opposite trick. Permanent magnets provide the holding force; the coil fires only for a 0.1–1 second pulse to switch the magnet on or off. In normal operation, meanwhile, the coil carries zero current, so the unit generates almost no heat of its own — the usual figure quoted is around 95% menos energía than a comparable electromagnet, and it cannot drop the load in a power cut.
The trade-off, however, is that permanent magnets sit right at the pole face, close to the heat. Every permanent-magnet material has a maximum operating temperature. Stay below it and the magnet recovers fully on cooling. Exceed it and the magnet loses strength permanently — not a resettable derating but a permanent cut in holding force. Cross the Curie temperature of the magnet material and the loss becomes total.
One-sentence summary: an electromagnet risks its insulation; an electro-permanent magnet risks its magnets. Electromagnets degrade gradually and recover when cooled; a cooked EPM stays cooked.
High temperature limits: the magnet material ladder
For an electro-permanent magnet, the working limit is set by the weakest magnetic material inside. EPMs use two magnet sets — a fixed set and a reversible set — so both must survive the duty. Typical material limits:
| Magnet material | Max operating temp (typical grades) | Role in an EPM |
|---|---|---|
| Neodymium (NdFeB) N | 80°C | Standard room-temperature work |
| NdFeB M / H / SH | 100 / 120 / 150°C | Warm plate, warm billet, most mill duty |
| NdFeB UH / EH / TH | 180 / 200 / 220°C | Hot-section work with shielding |
| Samarium-cobalt (SmCo) | ~350°C | Fixed magnet for high-temp builds; costs noticeably more |
| AlNiCo | up to ~540°C | The heat champion; weaker magnetically, so needs a larger pole area |
| Iron-chromium-cobalt (e.g. 2J12) | Curie ~680–700°C; stable at 400°C | Special reversible magnets for high-temp circuits |
Grade figures per published manufacturer data (e.g. Magswitch material tables; AlNiCo datasheets).
Moreover, AlNiCo has a counter-intuitive trait worth knowing: its resistance to demagnetization actually improves as temperature rises — the only common lifting-magnet material that behaves this way. That, plus its Curie point near 850°C, is why every serious EPM design for hot work ends up with AlNiCo in the circuit (Goudsmit; Senz Magnet).
Matching a high temperature lifting magnet to its duty band
Here is the same ladder translated into buying decisions. Find your band, read across.
| Workpiece temp | Electro-permanent magnet | Electromagnet | What changes in the design |
|---|---|---|---|
| 0–150°C | Standard NdFeB + AlNiCo build. Best cost and performance. | Standard build, B/F-class insulation. | Nothing special. EPM also saves ~95% energy vs continuous excitation. |
| 150–350°C | High-temp NdFeB grades to 220°C, then SmCo; high-temp AlNiCo reversible magnets. | F/H-class wire, high-temp potting, watch duty cycle. | 1–5 mm insulation pad at the pole face; radiation shields; forced-air cooling. |
| 350–500°C | AlNiCo-only magnetic circuit; short-time duty. EPM loses force density, so expect a bigger, costlier unit. | C-class insulation, heat shielding; still the more economical long-run choice. | Insulation pads 20 mm+, ceramic stand-offs, active cooling. |
| 500–700°C | Custom full-AlNiCo, short-time only, with factory consultation. Rarely the right tool. | The mainstream answer: full water jacket, multi-layer insulation, long stable runs. | Water-cooling loop, temperature monitoring, hot-state force derating. |
The honest summary: below about 350°C, an electro-permanent magnet is usually the better machine — lower energy, safer on power loss, no thermal run-in. Above about 450–500°C for continuous duty, buy an electromagnet, even from us. An EPM pushed past its magnets’ limit does not get warmer and weaker; it gets permanently weaker.
Cooling and shielding that actually work in plants
Temperature ratings are earned with hardware, not marketing. What real high-temperature builds include:
- Insulation pads at the pole face (1–5 mm for warm duty, 20 mm+ or ceramic stand-offs for extreme duty) — the first and cheapest line of defence against conduction.
- Radiation shields — reflective plates around the magnet body to bounce radiant heat away from the unit.
- Forced-air cooling from roughly the 150–220°C band upward, to strip accumulated heat between lifts.
- Water cooling for serious duty. Water-jacketed electromagnets run continuously at 500°C+ workpiece temperatures. EPMs can be water-cooled too: copper tubes routed around the magnet body (they don’t conduct magnetism, so holding force is unaffected) support ambient conditions around 400°C, and in automated handling lines water-cooled EPMs have been engineered for material temperatures up to about 650°C — always as a case-by-case design with the factory, never an off-the-shelf rating.
Hot steel lifts less: the derating rule everyone forgets
There is a second, quieter reason hot work needs bigger magnets. As steel heats up, its magnetic permeability drops, so the same magnet grips the same section with less force. At around 600°C, suppliers report lifting force reduced substantially versus room temperature — datasheets and field experience often land near half the cold-state figure (Truninger hot-load guidance; supplier hot-state ratings).
Three consequences for your specification — and they matter twice as much on a crane magnet, where the load sits out of the operator’s reach:
- Size the magnet on the hot-state safe working load, not the cold-state pull-off figure.
- Keep the established safety factor (commonly 3:1 for lifting magnets) applied to the hot number.
- Ask the supplier to state both figures in writing. If they can’t, they haven’t tested it.
Six questions to ask before you order a high-temperature lifting magnet
- What is the measured workpiece surface temperature at the lift point? Not the furnace temperature, not the line’s nominal temperature — the steel where the pole face lands.
- Continuous or short-time duty at that temperature? A 10-second pick from a 480°C line is a different machine from 20 minutes of dwell on a 480°C slab.
- Which magnet material grades are inside, and what is each grade’s max operating temperature? For an EPM this is the single most important number.
- What is the hot-state SWL versus the cold-state SWL? In writing, with the test method.
- What insulation class are the coil, potting and cables? For an electromagnet, also ask the duty cycle rating (TD%) your cycle pattern actually requires.
- What shielding and cooling is included — and what does it cost to maintain? Water systems need checks; insulation pads wear and need replacement.
In short, these six questions do double duty: they get you a magnet that lasts, and they quickly reveal which supplier has actually built for your temperature band.
Frequently asked questions
How hot can a high temperature lifting magnet go?
Can a lifting magnet pick up red-hot steel?
Yes — up to a point. Purpose-built high-temperature electromagnets routinely handle billets and slabs in the 600–700°C range with heavy insulation and water cooling. Above roughly 768°C steel passes its Curie point and is no longer ferromagnetic, so no magnet of any type can grip it. The working ceiling for magnetic lifting is therefore about 700°C.
What temperature permanently damages an electro-permanent lifting magnet?
When the internal permanent magnets exceed their maximum operating temperature. For common neodymium grades that is 80–220°C depending on grade, ~350°C for samarium-cobalt, and up to ~540°C for AlNiCo. Below the limit, any strength loss recovers on cooling; above it, the loss is permanent. This is why the magnet grade — not the housing — defines an EPM’s true temperature rating.
Why does my magnet hold less when the steel is hot?
Two effects stack: the hot steel’s magnetic permeability falls, so it accepts less flux, and the magnet itself weakens with temperature. The combined result at ~600°C is often around half the room-temperature lifting force. If you are selecting a magnetic lifter for hot work, always size on hot-state figures with the safety factor applied to them.
Choosing between technologies and sizing the magnet
Are electro-permanent magnets or electromagnets better for hot work?
Depends on the band. Up to ~350°C, an electro-permanent magnet usually wins: it holds with permanent magnets, uses ~95% less energy, cannot drop the load in a power cut, and barely heats itself. From ~500°C upward on continuous duty, a water-cooled electromagnet is the reliable choice because nothing inside it can be permanently demagnetized. Between 350°C and 500°C, it comes down to duty cycle and total cost — worth an engineering conversation either way.
Can water cooling be added to an electro-permanent lifting magnet?
Yes. Copper cooling tubes routed around the magnet body can hold ambient conditions near 400°C without affecting holding force (copper is non-magnetic), and custom water-cooled EPMs have been engineered for material temperatures up to about 650°C in automated lines. Treat these as engineered-to-order solutions: confirm with the manufacturer against your real duty cycle before specifying.
Tell us your temperature, not just your tonnage
Send us the workpiece type, its measured surface temperature at the lift point, section size and your cycle rate — we’ll come back with the right technology for that band, including an honest recommendation if an electromagnet (not our product) is the better answer.
Request a free selection assessment See billet & slab lifting magnetsKey sources: Goudsmit Magnetics (Curie temperatures of magnetic materials); Truninger AG (hot-load handling guidance, steel ferromagnetism above ~768°C); Magswitch (permanent-magnet grade temperature limits); Kino Cranes / Voitto Crane (lifting electromagnet temperature grades and duty-cycle conventions); HVR MAG engineering data.
