- How Do I Choose The Appropriate Permanent Magnets?
- Do I Choose North Pole Or South Pole For My Applications?
- What Is The Pulling Force Of A Magnet? How The Force Is Measured By Industrial Standard?
- What Decides The Pulling Force Of A Magnet? How To Increase The Pulling Force Of A Magnet?
- Why Does The Pulling Force Vary Between Different Vendors?
1. How Do I Choose the Appropriate Permanent Magnet?
There are 6 distinct types of permanent magnets available on the market. Each type is made from a specific material and exhibits different features and magnetic characteristics. Below is a simple guide on how to choose the appropriate type of magnet for your needs.
- Neodymium magnets provide highest pulling force but the cost is also high. Most of them can only be used in the room temperature but custom made can reach 392 degree Fahrenheit
- Ceramic Magnet cost is low but the pulling force is also low. However it can be used in high temperature environment
- SmCo Magnets provide strong pulling force and also high working temperature. But SmCo magnet cost is the highest
- AlNiCo Magnets have the best machinability so can be made very precisely. It also has very stable magnetic characteristics nut not very strong pulling force. The cost is high
- Rubber Magnets are low cost, low magnet strength, and low maximum operating temperature. These are most commonly used for advertisements such as car signs, fridge magnets, business cards, etc.
- Bonded Magnets are also low cost, low magnet strength, and low maximum operating temperature. These are utilized when specific shapes or complex conformations are needed.
2. Do I Choose North Pole or South Pole for My Applications?
If the magnet needs to be attracted to a steel surface, either N pole or S pole will provide the same holding force. However, if the magnets are being used in pairs or “with each other”, then selecting the right Pole is crucial. Keep in mind that with magnetic forces, “opposites attract, likes repel”. The questions come up often with countersunk magnets or magnets with pre-applied adhesive.
Please select your magnets from the following guideline:
- If you are planning to use the magnets on a steel or magnetic surface, either North or South pole would work. Choosing a preference for polarity is NOT necessary.
- If you are planning to use these magnets in pairs, select North Pole for half of your order, and South Pole for the remaining half of your order. This is to ensure that they all pair up.
- If you are planning to use the magnets with a magnet you already have, you will need to know your magnet’s polarity and then select a magnet with the opposite polarity.
3. What Is The Pulling Force of A Magnet? How The Force Is Measured By Industrial Standard
Pulling force is the maximum force required to separate the magnet from a low carbon steel plate under the following conditions:
- The force is perpendicular to the touching surface
- The magnet and the steel plate are fully in contact
- The steel plate is 20 mm ( 0.787" ) thick
- The steel plate surface is smooth and clean
Based on these factors, the pulling force will be smaller for any of the following situations,
- The magnetic surface is less magnetic than low carbon steel
- The pulling force is not perpendicular to the surface. For example when hanging an item on the fridge
- The magnetic surface is thinner than 20 mm ( 0.787")
- The steel / magnetic surface is rough
- The magnet and the steel / magnetic surface are not directly touching. For example, if the surface is painted or covered with debris
In the real world, the actual pulling force is smaller than the industrial measured pulling force.
4. What Decides The Pulling Force Of A Magnet? How to Increase The Pulling Force Of A Magnet?
The following factors determine the actual pulling force of a magnet:
- Geometric shape and dimensions of the magnet
- Magnetic remanence (Br)
- The magnetism of the material the magnet will attract to
- The thickness of the material the magnet will attract to
- The surface conditions of the contact
To Generalize, the Pulling Force of a magnet is decided by its Gauss ratings and the geometric parameters of the magnet.
Choose a round magnet over a rectangle magnet if a round magnet can be used
Increasing the thickness of a magnet is more preferable than increasing the width or length only
Generally speaking, the pulling force is proportional to the thickness of the magnet and the square rood of the area of the surface in contact. Ideally, increasing the thickness is more effective than increasing the length or width only when the thickness is less than the width and length.
The higher the Gauss rating, the greater the pulling force. The Gauss rating is determined by the magnet material and grade. For example, grade N52 neodymium magnet has a larger pulling force than the grade N42 neodymium magnet, if both magnets have the same dimensions.
Increase the thickness of the steel or magnetic material.
Improve the surface conditions will increase the pulling force. Cleaning the surfaces of both the magnet and magnetic surface by removing paint or debris will increase the pulling force.
5. Why Does The Pulling Force Vary Between Different Vendors?
The pulling force of a magnet is decided by its grade and dimensions. The same size magnets have the same pulling force as long as they are the same grades.
Magnet industry is standardized and has defined a way to determine magnetic pulling force. This helps consumers choose the appropriate magnets for their applications. Unfortunately, there are some internet sellers that have their magnets mislabeled, which causes confusion among buyers. However, if the magnets are correctly labeled, the pulling force should be the same throughout all vendors for the magnets of the same grade and same size.