How to Choose the Right Precast Concrete Magnet for Your Project

Selecting the right precast concrete magnets (formwork magnets) is crucial to ensuring accurate, safe, and efficient formwork operations in precast production. The magnet's strength, size, and compatibility with various formwork systems must be carefully evaluated to meet the specific requirements of your project.

From wall panels and beams to hollow-core slabs, the magnets you choose must meet the structural and operational needs of your application. This article outlines key considerations, such as magnetic force, load conditions, and contact surfaces, to help ensure optimal performance in your precast workflow.

Understanding Precast Concrete Magnets

construction of shuttering magnet

Precast concrete magnets are specially designed magnetic components used to securely hold formwork in place during the concrete pour. They generate a strong magnetic field (typically achieved through neodymium magnets), enabling quick, tool-free attachment to steel surfaces. These magnets significantly reduce installation time and improve dimensional accuracy.

Precast magnets are widely used in a variety of structural components, including precast wall panels, beam formwork, hollow-core slabs, and column formwork. Each use case may require different magnet sizes and holding forces.

Core Components of Precast Concrete Magnets

shuttering magnet structural

1. Steel Housing

The housing is typically made of high-strength, corrosion-resistant steel. It protects the magnets from impact, moisture, and chemical attack-critical for long-term use in demanding construction environments. A well-constructed housing ensures a consistent clamping force and a longer product life.

2. Neodymium Magnet Core

The core of each precast magnet is a rare-earth neodymium magnet, renowned for its exceptional holding power. Unlike ferrite magnets, neodymium magnets are compact and have a high force density, ensuring a secure hold even under vibration or heavy formwork loads.

3. Release Lever or Button

A built-in mechanical release system (typically a lever or button) allows for quick, tool-free installation and removal. This feature improves efficiency, reduces fatigue, and minimizes the risk of formwork misalignment.

Key Factors to Consider When Selecting Precast Concrete Magnets

1. Magnetic Force (e.g., 900kg, 1800kg, 2100kg)

Magnetic force is the most critical factor when selecting precast magnets, as it directly impacts stability during pouring and vibration. The required magnetic force depends on the size, weight, and configuration of the formwork, as well as the intensity of concrete vibration.

For light-load applications such as edge formwork, window coverings, or small wall panels, a 900kg magnet generally provides sufficient clamping force. Medium- to large-sized wall panels, columns, and beams may require a 1800kg magnet. For high-load applications, such as large floor slabs, precast bridge components, or high-rebound vibration systems, magnets with a magnetic force of 2100kg or higher are recommended to ensure a secure hold.

2. Formwork Material Compatibility (Steel or Aluminum)

Magnets are only suitable for steel surfaces. If you are using aluminum formwork, additional steel plates or adapter solutions will be required.

3. Operating Temperature and Environmental Conditions

Extreme heat, cold, humidity, or concrete splashing can degrade magnetic performance. Magnets are likely to demagnetize in places where the temperature is above 80 degrees. For outdoor or high-frequency use, please choose magnets with sealed housings and corrosion-resistant coatings.

Load Requirements and Safety Considerations

1. Calculating the Magnetic Force Based on the Panel Weight and Concrete Vibration

The required magnetic force must account for the panel's weight plus the additional stress from concrete vibration during casting. As a rule of thumb, select a magnet with a holding force at least 3 to 5 times the vertical load to prevent shifting or lifting under vibration.

2. Importance of Safety Margins for Load Resistance

Always include a safety margin in your force calculations. Overloading a magnet can lead to displacement, alignment issues, or in worst cases, formwork failure. Standard practice recommends maintaining at least a 30% buffer above your calculated force.

3. Surface Condition Impact on Holding Power

Rust, oil, concrete residue, or uneven surfaces reduce magnetic adhesion. Always clean the formwork base and magnet surface before use to ensure consistent performance.

4. Ensuring Consistent Contact for Secure Fixation

Proper alignment and full contact between the magnet and the steel surface are essential. Even small air gaps or tilt angles can drastically reduce holding force. Use leveling pads or guide rails if necessary to maintain full, flush contact.

Tips for Choosing a Trustworthy Magnet Supplier

Look for a supplier with a proven track record in precast concrete, not just a generic magnet distributor. Experience with formwork systems, engineering-grade materials, and factory-direct pricing are key indicators of credibility. Certifications such as ISO 9001 or CE also demonstrate reliable quality control.

How to Maintain Precast Concrete Magnets

How to clean the shuttering maget

1. Keep the Contact Surface Clean

Precast concrete magnets rely on a tight fit between the magnet's bottom and the steel formwork platform. Any foreign matter-such as concrete residue, grease, or release film-can create air gaps, significantly weakening the magnetic holding force. Always inspect and clean the bottom before use.

2. Cleaning Recommendations

Use a stainless steel scraper to remove debris from the magnet's surface-avoid iron tools, as they will be attracted to the magnet. For hardened concrete or stubborn residues, use a polishing machine equipped with a wire polishing disc to restore smoothness and full contact.

3. Handle with Care

The internal magnet is made from sintered rare-earth materials, which are hard yet brittle, similar to ceramics. Dropping, striking, or throwing magnets can cause internal cracks or deformation. Avoid using iron hammers or applying force during demolding.

4. Storage Recommendations

After use, magnets should be cleaned and stored on a non-ferrous (stainless steel) cart to prevent magnetic sticking. Avoid storing magnets on iron surfaces, which can make removal difficult and cause accidental damage.

5. Environmental Conditions

Store and use precast magnets in environments below 80°C, and away from corrosive substances such as strong acids and alkalis. Elevated temperatures or chemical exposure can reduce magnetic strength and damage structural integrity.

Choosing the right precast concrete magnet isn't just about picking the strongest one-it's about choosing the smartest one for your specific project. By considering factors like magnetic force, compatibility, surface conditions, and supplier reliability, you can avoid costly delays and ensure safe, efficient production.

Need help picking the right model? Contact our technical team or explore our product range to find your perfect fit today!