A shuttering magnet (magnetic box) is a switchable NdFeB permanent-magnet fixture that clamps side forms to the steel casting table during the pour, replacing mechanical bolting — press the stainless-steel button to engage the magnetic circuit, and pry it up with the dedicated release tool to let go. Standard holding force runs 450–2600 kg; match it to mould height and place a box every 400–600 mm along the form. The most common cause of lost pull force is an air gap from concrete slurry on the contact face of the magnetic array, and the operating environment must stay below 80 °C to avoid permanently demagnetising the NdFeB.
As the precast concrete industry shifts toward higher automation and stricter structural tolerances, choosing the right magnetic clamping system is no longer just about suction power — it is about long-term reliability on the formwork table. This guide covers the technical architecture, selection and maintenance of shuttering magnets (magnetic boxes) so you can eliminate mould displacement during high-frequency pouring.
1. What a precast concrete shuttering magnet is
A precast concrete fixed shuttering magnet — commonly called a magnetic box — is a high-efficiency switchable magnetic component engineered to secure side forms to the casting table during concrete pouring.
Unlike traditional mechanical bolting, these magnetic boxes use adjustable fastening screws to press down and firmly lock the steel or wooden side moulds. This dynamic mechanism strengthens the connection between the magnetic block and the angle steel, effectively preventing mould displacement under the intense vibration of concrete consolidation. Today the technology is widely adopted across precast facilities in Europe, America, the Middle East and Southeast Asia. Depending on the production layout, these magnetic systems are further classified into shuttering magnets, insert magnets and magnetic chamfers.
2. The internal engineering structure
To withstand the harsh environment of a precast plant, a premium shuttering magnet relies on robust mechanical integration. The internal anatomy comprises four core assemblies:
- High-performance magnetic array — assembled from top-tier NdFeB (neodymium) permanent magnets configured to maximise vertical pull force.
- Spring screw accessories — provide the flexible mechanical connection needed for smooth activation and release.
- Stainless-steel buttons (grade 201 or 304) — ensure the activation handle resists corrosion and concrete-slurry intrusion.
- Reinforced external shell — a heavy-duty casing that shields the internal magnetic array from direct impact and abrasive wear.
3. Technical specifications and how to size them
Standard suction models range from 450 kg to 2600 kg pull force. Optimal suction matching is customised to your actual mould height and structural requirements. The mainstream specifications used globally include 800 kg, 1000 kg and heavy-duty 2600 kg stainless-steel magnetic boxes.
| Holding force class | Typical side-form height | Form material | Suggested spacing along form | Typical use |
|---|---|---|---|---|
| 450–800 kg | ≤ 150 mm | Plywood / light steel | 500–600 mm | Wall panels, light partitions |
| 1000 kg | 150–250 mm | Steel / aluminium | 450–550 mm | Structural walls, beams |
| 1500 kg | 250–350 mm | Steel | 400–500 mm | Deep beams, columns |
| 2000–2600 kg | > 350 mm or high vibration | Heavy steel | 400 mm | Tall moulds, high-frequency lines |
4. Magnetic box vs mechanical bolting
The core value of a magnetic system is speed of change-over and a casting bed that stays undamaged. The trade-off is a higher unit cost that pays back through labour and downtime savings on high-mix lines.
| Criterion | Shuttering magnet | Mechanical bolting |
|---|---|---|
| Mould change-over speed | ✓ Seconds — press & release | ✕ Slow — drill / bolt / unbolt |
| Damage to casting table | ✓ None — no holes | ✕ Bolt holes wear the table |
| Repositioning flexibility | ✓ Free — any layout | ✕ Fixed hole pattern |
| Resistance to pour vibration | ✓ High with adjustable clamp | ✓ High |
| Unit cost | Higher up-front | ✓ Lower up-front |
| Best fit | High-frequency, high-mix precast | Low-mix, repetitive single mould |
5. Industrial applications
These template magnets are universally compatible with steel moulds, aluminium moulds and plywood/wooden side forms. Positioned directly on the steel formwork table, they are critical for fabricating a wide range of prefabricated concrete components, including:
- Prefabricated architectural stairs
- Exterior and interior structural wall panels
- Precast balconies, beams and customised precast modules
6. Standard operating procedure (SOP)
Installation: position the shuttering magnet at the designated mould intersection. Firmly press the stainless-steel clamping handle downward. Once engaged, the magnetic core securely adheres to the steel table while the bayonet clamps the side mould. Tighten the auxiliary side screws to lock the assembly.
Deactivation: upon completion of the concrete curing cycle, use a professional magnetic box release tool (crowbar) to pry up the button. This safely disengages the magnetic circuit, allowing easy removal without scratching the formwork table.
Watch the factory process video
7. Preventative maintenance guidelines
Holding force is only as good as the contact interface and the internal mechanism. Follow these five checks to keep every box at its rated capacity:
| Check | What to do | Why it matters |
|---|---|---|
| Surface cleanliness | Keep the contact face of the internal magnetic array clean and smooth. | Slurry buildup creates an air gap that dramatically reduces actual pull force. |
| Debris prevention | Stop iron filings and concrete from penetrating the internal springs. | Clogged springs restrict the flexibility of the clamping handle. |
| Anti-rust protection | Regularly clean and apply anti-rust lubricant to the shell and moving parts. | Corrosion seizes the mechanism and shortens service life. |
| Temperature threshold | Keep the operating environment below 80 °C. | Prevents permanent thermal demagnetisation of the NdFeB magnets. |
| Release discipline | Only ever release with the dedicated tool on the button. | Protects the shell, the array seating and the casting table. |
8. Our enterprise quality-control architecture
A failure in a magnetic box can jeopardise the dimensional tolerances of an entire precast structure. Every shuttering magnet leaving our facility therefore passes through a rigid, multi-stage QC closed-loop protocol:
- Raw material inspection (IQC) — metallurgical and grade validation of incoming steel sheets and raw NdFeB permanent magnets.
- First article inspection (FAI) — the first unit of every batch is benchmarked against engineering drawings to prevent systemic errors.
- Scheduled spot checks — QC engineers audit active lines every four hours to hold mechanical tolerances.
- In-process quality control (IPQC) — continuous inspection during welding, assembly and shell coating to catch defects in real time.
- Pre-shipment final inspection (OQC) — microstructural examination and 100% vertical magnetic pull-force testing before packaging.
9. Frequently asked questions
What is a shuttering magnet (magnetic box)?
A shuttering magnet — also called a magnetic box — is a switchable NdFeB permanent-magnet fixture that secures steel, aluminium or plywood side forms to the steel casting table during concrete pouring. Pressing the stainless-steel button engages the magnetic circuit so the core adheres to the table while an adjustable bayonet clamps the side mould, preventing mould displacement under vibration. It replaces mechanical bolting and can be repositioned for every new mould layout.
How much pull force (kg) of shuttering magnet do I need?
Standard models range from 450 kg to 2600 kg holding force. Match the force to your mould height and the vibration energy: light plywood forms up to ~150 mm typically use 800 kg boxes; steel side forms 150–300 mm use 1000 kg; tall or heavily vibrated moulds use 1500–2600 kg. As a rule of thumb, allow one box every 400–600 mm along the form and keep a safety margin of at least 2× the expected lateral concrete pressure.
Magnetic box vs mechanical bolting — which is better for precast?
Magnetic boxes engage and release in seconds with no drilled holes in the table, so mould change-over is far faster and the casting bed stays undamaged. Mechanical bolting has a lower unit cost but is slow, wears out the table with bolt holes, and cannot be repositioned freely. For high-frequency, high-mix precast production the magnetic system pays back quickly through labour and downtime savings.
How do you release a shuttering magnet after the concrete has cured?
Use the dedicated magnetic box release tool (a purpose-made crowbar) to pry up the stainless-steel button. This mechanically breaks the magnetic circuit and lifts the core off the table, allowing removal without scratching the formwork surface. Never hammer or lever the shell directly — always act on the release button.
Why is my shuttering magnet losing pull force?
The most common cause is an air gap created by concrete slurry, rust or iron filings on the contact face of the magnetic array. Even a fraction of a millimetre of buildup dramatically reduces actual holding force. Keep the contact face clean and smooth, prevent debris from clogging the internal springs, and apply anti-rust lubricant to the shell and moving parts.
What temperature can shuttering magnets withstand?
Keep the operating environment below 80 °C. NdFeB (neodymium) permanent magnets begin to lose magnetism as they approach their working temperature limit and can suffer permanent thermal demagnetisation above it. In steam-cured precast lines, verify that the box specification matches the curing chamber temperature and, where needed, specify high-temperature grade magnets.
Are shuttering magnets compatible with steel, aluminium and plywood moulds?
Yes. The box sits on the steel formwork table and clamps the side form regardless of the form material — steel, aluminium or plywood/timber. The magnetic circuit acts between the box and the steel table, while the adjustable bayonet and side screws mechanically press the side mould, so non-ferrous forms are clamped just as securely.
What quality control and certification should the supplier provide?
Ask for a documented QC loop: incoming raw-material inspection (IQC) of steel and NdFeB grade, first-article inspection (FAI) per batch, in-process inspection (IPQC) during welding and coating, and pre-shipment final inspection (OQC) with 100% vertical pull-force testing. Chontan performs metallurgical grade validation, scheduled spot checks every four hours and full pull-force verification on every unit before dispatch.
Who wrote this, and why you can check it
We make these parts, we don't resell them
Qingdao Chontan Industry has been supplying the precast and prestress industries for over 20 years, from our own factory in Chengyang District, Qingdao. Everything in these guides comes from producing, testing and shipping the components they describe — not from a catalogue.
Our own test floor, not an outsourced claim
Anchors are verified in-house before they leave:
- 30 T – 300 T universal tensile testers for pull-out and tensile testing
- Low-temperature impact testing — the test that catches brittle behaviour
- Metallographic structure analysis and hardness testing
- Material sampled for microscopy before the first manufacturing operation
- Dimensional inspection against drawings, with purpose-made gauges during production
Facts are attributed to the standard, not to us
Where these guides quote a limit — a load, a wear limit, an inspection interval, a cover formula — it is attributed to the standard that sets it (EN 1992, EN 10204, EN 13101, DIN 405, VDI/BV-BS 6205, ACI 318, the Machinery Directive). We tell you which document to read, so you never have to take our word for it.
What we will not do
- We do not publish another manufacturer's load tables as our own data.
- We do not quote a rating without its conditions — concrete grade, embedment, edge distance.
- Illustrative numbers are labelled illustrative; design from your supplier's tested data.
- Where we are uncertain, we say so and point you to the primary source.
Need shuttering magnets tested to their rated pull force?
20+ years of export experience. 450 kg to 2600 kg stainless-steel magnetic boxes, customised to your mould height. 100% vertical pull-force tested before shipment, OEM private label available. We'll quote against your production layout in 24 hours.
