Magnets have long been used in manufacturing and other industrial applications. Magnetic chucks are being widely adopted as a work-holding mechanism. In situations where using clamps or screws to hold workpieces is not feasible, magnetic chucks offer a clamp-less workpiece holding alternative.
However, one question that manufacturers have about magnetic chucks is regarding their strength. After all, if you will be holding heavy objects, it is natural to wonder how strong magnetic chucks are before using them. The last thing you need is your workpiece slipping off during the machining process.
Magnetic chucks come with different sizes and magnetic strengths. So, when choosing a magnetic chuck, it is essential to ensure it is designed to handle that specific application. There are separate magnetic chucks for grinding machines, lathes, and other tools. As long as you match the magnetic chuck with its intended usage, you can expect it to offer sufficient strength. Still not sure how strong are magnetic chucks? Read on to learn more about this topic.
1. How is the strength of a magnetic chuck measured?
The easiest way to measure the strength of a magnetic chuck is by looking at its N/cm² or Newton per Square Centimetre rating. The N/cm² rating of a magnetic chuck is used to show the holding strength of a magnetic chuck.
This unit shows how much pulling force a magnet can exert for a specific surface area. So when you see a magnetic chuck with a rating of 50 N/cm², the chuck can exert a force of 50 Newtons for every square centimeter of the magnet surface.
Since a magnetic chuck has a large surface area, estimating how much force it exerts across a square centimeter of its surface is more accessible. Therefore, when you are interested in the holding strength of a magnetic chuck, you have to look at its N/cm² rating.
Since no clamps are involved in magnetic chucks, the holding strength is the only thing that keeps workpieces in place on a magnetic chuck. However, in most applications, you won't need a magnetic chuck that exceeds 100 N/cm². A strong magnetic chuck will not only be more expensive, but it will also draw more power if it is an electromagnetic or electro-permanent one. So, matching the holding force with the usage application is going to give you the best results.
2. What factors affect the strength of a magnetic chuck?
Various factors impact the strength of a magnetic chuck. Nonmagnetic materials can't be held using a magnetic chuck. So, if you plan on working on ferromagnetic materials, the magnetic chuck will have zero holding strength.
However, even if you are using a ferromagnetic material, there are still some things that can affect the strength of the chuck. Here are all the factors that directly impact the holding power of a magnetic chuck that you should know about:
2.1 Mild steel vs. hard alloy steel: Steel is one of the most commonly used metals in the manufacturing industry. However, the alloy content of the steel is going to impact how well it can be held by a magnetic chuck.
Mild steel, such as SAE 1020 steel, is very close to iron in terms of its magnetic properties. On the other hand, hard alloy steel doesn't offer good magnetic properties and, therefore, won't stick to a magnetic chuck well enough.
For example, a 416 steel alloy has some magnetism, but it is only half the magnetic ability of the SAE 1020 steel. This means the 416 steel is a bad magnetic conductor and can't utilize the full strength of a magnetic chuck. So, when you are working with steel and magnetic chucks, make sure that the material is mild steel. In general, most stainless steel alloys are not going to be a good fit for magnetic chucks.
2.2 The surface area of the workpiece: The surface area of the workpiece is another factor that affects a magnetic chuck's strength. Even if your magnetic chuck produces up to 200 N/cm² of holding force, it won't translate into a solid hold if the workpiece is not big enough.
Magnets rely on their magnetic field to pass through a metal to hold it in place. If the surface area of the metal workpiece is too small, not enough magnetic flux will pass through it, and the holding power will be reduced.
Most magnetic chucks come with additional accessories to hold smaller workpieces. These accessories support the workpiece so it can be safely secured to the magnetic chuck.
2.3 Type of magnetic chuck: The type of magnetic chuck you use has a significant impact on how much strength it can produce. There are three major types of magnetic chucks: permanent, electromagnetic, and electro-permanent magnetic chucks.
While each of these types of magnetic chucks has its pros and cons, the electro-permanent variety is widely regarded as the strongest option. Electropermanent magnetic chucks are usually larger than the other two types, which allows them to hold heavier workpieces. Not to mention, they use a combination of permanent and electro-permanent magnets, which gives them a stronghold.
Due to their high holding strength, electro-permanent magnetic chucks are used in most metal machining applications.
3. Fine pole vs standard pole magnetic chucks (which one is stronger?)
By now, it should be clear that you have to consider the holding force rating of a magnetic chuck when buying one. However, the holding strength rating is far from the only metric you need to look at if you want to determine the strength of a chuck.
You also have to look at the type of poles a magnetic chuck has when determining if it is the right option for you or not. In general, you will find two types of pole arrangements in magnetic chucks:
3.1 Standard pole magnetic chucks: A standard pole magnetic chuck usually has a pitch of around 22(18+4). In standard pole magnetic chucks, the poles are located at a standard distance from one another.
A standard pole magnetic chuck is usually better if you want to hold larger workpieces. That is because the poles are located further from one another, so a larger workpiece can benefit from the widespread magnetic field.
In general, a standard pole magnetic chuck can easily produce more than 150 N/c㎡ of holding power with ease. However, the force will not be concentrated in the case of a standard pole arrangement.
3.2 Fine pole magnetic chucks: In a fine pole magnetic chuck, the poles are located much closer to one another compared to the standard arrangement. The pole pitch in a fine pole chuck is around 4(3+1), which means the poles are located fairly close to one another. Despite a more dense pole arrangement, the magnetic field produced by a fine pole magnetic chuck doesn't penetrate the workpiece as deeply as the standard pole.
You can expect around 100 N/c㎡ of holding force from a fine pole magnetic chuck. But a fine pole magnetic chuck is not meant to hold larger workpieces. Instead, it is meant to hold smaller workpieces that a standard pole magnetic chuck can't handle due to large gaps between neighboring poles.
So, if you are working with a small workpiece with low thickness, a fine pole magnetic chuck will offer higher holding strength. However, for larger and heavier workpieces, you have to rely on a standard pole magnetic chuck since it offers a stronger holding force.
4. Do magnetic chucks lose their holding strength?
Ideally, a magnetic chuck should be able to sustain its magnetic holding force throughout its life span. While magnets naturally lose some magnetism with time, it is not a noticeable change. However, there are situations where a magnetic chuck may lose its holding power or not hold workpieces at all. Here are some conditions where a magnetic chuck may lose its holding force:
4.1 Coil failure in electromagnetic chucks: Unlike permanent and electro-permanent chucks, there are no true magnets inside electromagnetic chucks. Instead, an electromagnetic chuck relies on current passing through a set of coils to create a magnetic field.
If one or more of the coils inside an electromagnetic chuck fail, the chuck will lose some or all of its holding power. So, if you have an electromagnetic chuck, you should perform regular maintenance on its coils to make sure all electrical connections are intact.
4.2 Top plate damage: Magnetic chucks transfer magnetism to the workpiece through their top plate. If the top plate of the magnetic chuck is damaged, it will result in air gaps between the workpiece and the surface of the chuck.
So, a damaged or uneven top plate is going to significantly reduce the contact point between the chuck's surface and the workpiece. Some magnetic chucks are more sensitive to air gaps than others. So, depending on how severe the top plate damage is, you may experience varying levels of magnetism loss.
4.3 Wear and tear: Permanent magnetic chucks rely on manually aligning the internal magnets with the top plate to hold a workpiece. Over time, the continuous movement of the magnets will wear out the internal mechanism. As a result, you may find it difficult to get the desired holding power from it.
5. How do you test the suction force of a magnetic chuck?
While the holding power rating of a magnetic chuck tells a lot about its suction force, the only way to test it is with the help of a workpiece. You have to take a metallic workpiece and place it on the magnetic chuck to see how well it holds.
However, if you want to be scientific with your approach to testing a magnetic chuck, you can use a magnetic pull test kit. A magnetic pull test kit has a metallic test piece on one end and a digital scale to measure how much force it takes to break away a workpiece from the magnetic chuck.
You can attach the magnetic pull test kit's ferrous end to the magnetic chuck's surface and pull it away to get a reading for how much force it took before the magnet releases the test piece.
6. Suggestions for some reliable magnetic chucks
Now that you know how strong magnetic chucks are and how their strength is measured, you are probably looking for some reliable magnetic chucks to buy. Here are some high-quality magnetic chucks you can consider:
6.1 High Precision Electro Permanent Magnetic Chuck For Sale
If you are looking for an affordable yet strong electro-permanent magnetic chuck, then this product is a good option. The High Precision Electro Permanent Magnetic Chuck by GME Magnet has a holding power of 26 Kg/c㎡. This equates to 254.973 N/c㎡, making it a strong and reliable magnetic chuck. No matter how heavy your workpieces are, this chuck can easily hold them during heavy operations such as grinding, drilling, and cutting.
Material: Carbon steel
Type: Electro permanent
Features:
Strong holding power
Easy operation
Quick mounting and release
It can be moved from one machine to the other
6.2 Electro Permanent Magnet Chucks For The Milling Machine
Another strong and reliable electromagnetic chuck you can buy for heavy-duty applications is GME Magnet's Electro Permanent Magnet Chucks For The Milling Machine.
Milling machines are known for their high-pressure operation, and they rely on electro-permanent magnetic chucks to hold workpieces in place. With a holding force of 26 Kg/c㎡ or 196.133 N/c㎡ , you can put it in any heavy-duty application.
Material: Carbon Steel
Type: Electro permanent
Features:
Consistent holding power
Safe for use
It can be set easily
Highly accurate operation
7. FAQs about magnetic chuck strength
7.1 What is the magnetic chuck strength you should look for?
There is no single magnetic chuck strength that is fit for every single usage application. However, you should aim for more than 100 N/c㎡ of holding force if you work on moderate-level workpieces. For extremely heavy workpieces, you should aim for a magnetic chuck with a rating of 200 N/c㎡ or more.
7.2 Can permanent magnetic chucks be automated?
Permanent magnetic chucks don't need external power to operate; therefore, they can't be integrated into a CNC machine's control unit. The only way to operate permanent magnetic chucks is by manually operating a liver.
7.3 Can you adjust the holding power of a magnetic chuck?
Yes, a magnetic chuck that comes with its control unit allows you to adjust the holding power. You can reduce the holding power, which reduces the amount of current the chuck can draw.
Conclusion
If you were wondering how strong magnetic chucks are, this article should answer your question. A magnetic chuck can hold a significant amount of weight without failure or the need for additional clamps.
We have also provided some suggestions for high-strength and durability magnetic chucks for heavy-duty applications. Feel free to contact GME Magnets if you want assistance in choosing the right type of magnetic chuck for your manufacturing use.