Lifting Magnets: Permanent vs Electromagnetic — Capacity and Safety Guide

In the rigging world, hooks and shackles are reliable because they are mechanical. You can see the pin, you can feel the latch, and you know exactly how the load is secured.

Lifting magnets requires a different kind of trust.

To the uninitiated, lifting a 5,000 lb steel plate with a magnet looks like magic. To a rigger, it is pure physics and unforgiving physics at that. Unlike a sling that might stretch before it breaks, a magnet is binary. It either holds the load, or it drops it completely. There is rarely a warning sign.

At Holloway Houston , we sell and service these devices daily. We know that when used correctly, they are the fastest, most efficient way to move steel. But we also know that "rated capacity" on a magnet is a theoretical number based on perfect conditions.

This guide will break down the differences between permanent and electromagnetic lifters, and more importantly, how to calculate the real capacity of the magnet based on the rust, scale, and thickness of the steel you are moving.

What Are Lifting Magnets?

A lifting magnet is a Below-the-Hook Lifting Device (as defined by ASME B30.20) that uses a magnetic field to grip ferrous materials. They eliminate the need for drilling holes, welding lugs, or struggling to slide slings under a flat plate sitting on the ground.

• The Mechanism : They align magnetic domains to create a flux path through the steel load. The steel becomes part of the magnetic circuit.
• The Constraint : They only work on ferrous material (steel, iron). They do not lift stainless steel, aluminum, or brass.

Industrial lifting magnets provide a fast, non-marring method for handling steel plate, round bar, and machined parts. Because they grip the top surface, they are ideal for loading cutting tables or pulling parts out of crates where access is limited.

Permanent Lifting Magnets

These are the most common units found in fabrication shops and machine shops. They are self-contained and require no electricity.

How They Work

Permanent lifting magnets use "rare earth" magnetic material (usually Neodymium-Iron-Boron).

• The Switch : Inside the housing, there is a magnetic rotor. When the lever is in the "OFF" position, the magnets are shielded internally. When you pull the lever to "ON," the magnets rotate to align with the steel poles, directing the magnetic flux down into the load.
• Safety Lock : The lever features a mechanical lock that prevents it from springing back to the "OFF" position during a lift.

Pros and Cons

• Advantage : Fail-Safe. Because they don't need electricity, a power outage won't drop the load. They are portable and rugged.
• Limitation : Capacity. They max out earlier than electromagnets (typically around 6,600 lbs). They also require manual actuation—someone has to climb onto the table to pull the lever.

Electromagnetic Lifters

When you need to move heavy slabs, bundles of rebar, or scrap metal, permanent magnets usually aren't enough. You need power.

How They Work

Electromagnetic lifters use an electrical current flowing through a coiled wire to generate a magnetic field.

• Variable Force : Unlike permanent magnets, the strength can often be adjusted. This allows an operator to "dribble" plates (picking up a stack and dropping them one by one).
• Remote Operation : The operator can energize and release the magnet from the crane cab or a pendant, keeping them out of the danger zone.

The Power Risk (and Solution)

The biggest danger with an electromagnet is power failure. If the shop lights go out, the magnet turns off, and the load drops instantly.

• Requirement : ASME B30.20 requires a battery backup system capable of holding the load for at least 20 minutes in the event of primary power loss.

Product Note : Holloway Houston carries electromagnetic lifters with integrated battery backup systems and audible alarms to ensure fail-safe operation in critical environments.

Permanent vs Electromagnetic: Comparison Table

Choosing the right tool depends on your workflow. If you are moving single plates to a burn table, a permanent magnet is faster. If you are unloading a truck of billets, an electromagnet is safer.

Factors That Reduce Lifting Magnet Capacity

This is the most critical section of this guide.

If you buy a 2,000 lb lifting magnet, it is rated to lift 2,000 lbs of clean, flat, low-carbon steel at least 2 inches thick.

In the real world, steel is rusty, painted, thin, or bowed. Every one of these factors creates an "Air Gap" or magnetic resistance that drastically lowers the capacity.

1. Surface Condition (Air Gap)

Magnetic flux struggles to travel through air, paint, rust, or scale.

• Rust/Scale : A heavy layer of mill scale acts like a physical spacer. It pushes the magnet face away from the clean steel.
• Paint : A standard industrial coating can reduce lifting capacity by 10-20%.
• Roughness : Cast iron or rough-forged surfaces have peaks and valleys. The magnet only touches the peaks, reducing the contact area.

2. Material Thickness (Saturation)

A magnet needs a certain thickness of steel to absorb all its magnetic flux.

• Thin Plate : If the plate is too thin (e.g., 1/4 inch), the magnetic field "bleeds through" the back of the plate. The steel becomes saturated before the magnet can develop its full pull.
• The Derate : A 2,000 lb magnet might only be good for 500 lbs on 1/4 inch plate. Always consult the manufacturer’s thickness derating chart.

3. Material Alloy

Magnets love Low Carbon Steel (1018, A36).

• High Carbon / Alloy Steel : As you add carbon or alloy elements, the magnetic permeability drops.
• Tool Steel : Hardened steels retain magnetism (become permanently magnetized) and are harder to lift and release.

4. Load Dimensions (Peeling)

If you lift a long, thin plate with a single central magnet, the ends of the plate will droop.

• The Peel Effect : This drooping causes the plate to peel away from the magnet surface, breaking the seal.
• Solution : Use a spreader beam with two smaller magnets to support the full length of the plate.

Safety Requirements for Magnetic Lifting

Because magnetic lifting is a friction-based, non-positive connection, safety protocols are stricter than for slings.

1. Never Lift Over People : This is the Golden Rule. Magnets can release without warning due to a power spike, a bump against an obstacle, or shift in the load.
2. Verify the Break-Away Force : Before lifting the load to height, lift it 2 inches and verify stability.
3. Keep the Face Clean : Metal chips, filings, and grit on the magnet face create an air gap. Wipe the magnet face clean before every lift.
4. Inspection (ASME B30.20) :
   • Check the lifting bail for deformation (cracks).
   • Check the face for smoothness (scratches or gouges reduce contact).
   • For electromagnetic lifters, test the battery backup and warning horn weekly.

When to Use Magnets vs. Clamps

We discussed Lifting Clamps in our previous guide. Here is the quick decision matrix:

• Use Magnets : For flat handling, finished parts (no scratch marks), or high-volume repetitive lifts.
• Use Clamps : For vertical lifting (flipping plates), lifting stainless steel/aluminum, or dragging plates (side loading). Magnets offer zero resistance to sliding sideways; never use a magnet to drag a load.

Shop Lifting Magnets at Holloway Houston

Whether you are outfitting a CNC machine shop or a steel service center, you need magnets that are reliable and rated for reality.

Holloway Houston stocks a full line of permanent and electromagnetic lifters. We don't just sell them; we can test them on our pull-test beds to verify their holding force before they ever reach your facility.

We stock permanent lifting magnets and electromagnetic lifters for flat plate, round bar, and structural steel handling. All units rated per ASME B30.20.

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• Related : Electromagnetic Lifters | Lifting Clamps