Alnico Magnets – A Comprehensive Guide

If you are looking for a detailed resource with all information about alnico magnets – then read this guide.

You will find everything – from magnet composition, manufacturing process, uses, classification criteria, magnetic strength, quality testing, and much more.

Keep reading.

What is Alnico Magnet?

Alnico magnets are made from a special iron alloy – alnico. Besides, they are the first permanent magnets.

Alnico is distinctly known for 3 main elements in its composition:

• Aluminum
• Nickel
• Cobalt

Alnico Magnets History

Alnico are the oldest permanent magnets ever invented. The history dates back to the 1930s when an alloy with aluminum, nickel, and cobalt was made.

Back then, they were the best permanent magnets. Today, we have rare-earth magnets. Since the 1970s, they have replaced alnico in some applications.

Again, the invention of ferrite magnets also reduced the demand for magnets made from AL-NI-CO alloy.

Also, it is important to note that the use of magnets dates back over 2500 years. Initially, magnetic lodestones were a perfect choice for most applications.

More resources:

• History of Magnetism – Source: University College London
• Alnico – Source: Wikipedia

Benefits of Alnico Magnets

• High magnetic strength (although rare earth magnets offer the perfect alternative)
• They are easy to magnetize
• Offer superior corrosion resistance
• These magnets can withstand extremely high temperatures as high as 555 °C
• During the manufacturing process, the tooling cost is low

On the other hand, even if you choose alnico permanent magnets, it is worth noting that they are:

• Susceptible to demagnetization due to low coercivity
• Brittle in nature hence, cold working is not recommended during the manufacturing process
• Less powerful than rare earth metals
• Fluctuating prices of cobalt and nickel, the prices tend to fluctuate

Alnico Magnets Manufacturing Process

There are two options:

• Casting technique
• Sintering technique

Even as you contemplate which method to use during alnico magnet production, it is important to note the following:

Choosing Raw Materials

The main alnico alloy composition is:

• Aluminum
• Nickel
• Cobalt

The three form the main elements in these magnets. However, in some circumstances, you may add other elements such as:

• Iron
• Titanium
• Copper

Ideally, these elements will help improve the magnetic force in alnico permanent magnets.

Casting vs Sintering- What is the Best Option

When it comes to casting magnets, you can:

• Achieve a range of magnetic properties
• Make larger magnets
• Have magnets with complex shapes, designs, and configurations

When you are considering high-scale production – sintering is a perfect alternative. Additionally, sintering works well with small magnets.

Casting Alnico Magnets

If you want to make these magnets through the casting technique, you will follow this simple process:

Prepare Material for Making Magnets

Magnet material composition may vary depending on the specific performance objectives you wish to achieve. It determines the alnico magnet grade.

A normal alnico grade may consist of:

Take for example, if you want to make Alnico 6 magnet, the material composition will be as follows (the percentages are by weight):

• Aluminum – 8%
• Nickel – 16%
• Cobalt – 24%
• Copper – 3%
• Titanium – 1%
• The remaining amount will be iron

Once you have all material ready, you will mix and heat the material in an induction furnace. The heating temperature is about 1750°C.

At this stage, you should analyze the material composition to ensure they are perfect ratios. Machines such as x-ray spectrometry help to determine the material composition in alnico grade magnets.

Casting Magnet

First, prepare a shell mold.

Usually, green sand works best for making mold. In most circumstances, the design for the mold should be slightly larger than the size required size of the magnet.

Remember, when casting magnets, the sand characteristics will determine the final surface finish.

The mold design pattern allows for:

• Possible shrinkages and machining to allow for precise size and design. Remember, there are applications requiring tight tolerances.
• Runners and cavities allow material to flow easily into the mold

You will pour molten magnet material into the mold.

As you pour content into the mold, it will cause the shell of the mold to melt or disintegrate. Finally, you will allow the content of the mold to cool before ejection.

Remember, you can use a single mold to cast more than one alnico permanent magnet. In such situations, the mold design should have a gate. These gates will allow molten material to flow to individual molds for each magnet.

Finally, you will have material resembling the mold structure.

Fettling Process

Here, you will remove excess material from the cast part. That is, you will remove any runner gates alongside other excess material on the surface.

Usually, grinders work well in this process. However, it is worth noting that the process is delicate. Remember, these magnets are brittle.

Heat Treatment Process

Heat treatment is a critical process in magnet casting. It introduces desired magnetic characteristics.

Additionally, the process helps alnico acquire excellent temperature performance characteristics.

Among the key fundamental aspects to note during the heat treatment process include:

• Heat treatment temperature is about 1250°C
• The process takes place in magnetizers
• Cool the magnet in a strong magnetic field
• To stabilize the magnetic field, the alnico magnets will remain in a tempering oven for several days

Finishing Operations

Use a grinder to shape the magnet to a suitable size and shape. You can achieve very tight tolerances depending on the unique specific requirements.

Note: Remember, the finishing operations may not be necessary at times. This is because certain customers can handle this stage themselves.

Of course, after this, you need to test quality, apply coating (where possible), and magnetize. Will discuss that later in this guide.

First, let’s see how the sintering process works.

Sintering Alnico Magnets

The process involves the following stages:

Preparing Materials

Start by grinding the material into very fine powder. With the powder ready, mix all materials to the right proportion.

Compressing Powder

First, you will start by making a die. The mold’s shape will resemble the magnet’s shape or design.

Second, with both the powder and die ready, pour the material then compress under intense pressure. As a result, you will get a packed material resembling the final magnets you wish to produce.

Usually, the pressing can either be perpendicular or parallel.

Sintering Process

The sintering process help to align the magnetic axis.

After pressing the powder material in the die, place it in a furnace. The specific furnace condition for this process should be:

• Temperature should be about 1200°C in a heat shield furnace
• Atmosphere within the environment should have hydrogen

The process does not necessarily melt the material. It helps fuse powder particles forming a solid material.

Cooling Alnico

The cooling step is an important process in determining the type of alnico magnets. Normally, the cooling process takes place in the presence or absence of a magnetic field.

• Presence of a magnetic field produces anisotropic magnets
• Absence of a magnetic field you get isotropic magnets

Like the casting process, at this point, you will have solid material ready for the next stages. Whether you opt for casting or sintering, the other processes share many similarities in each stage.

Testing Alnico Magnets

Testing is an important process when making alnico magnets. It helps determine quality before subsequent processes.

Some of the most common magnet testing techniques are:

Painting or Coating Magnet

At times, you may wish to paint or coat the magnets. In most cases, you will magnets with different paintings to identify the poles.

For alnico, coating or painting may not be necessary. They offer better corrosion resistance.

However, the certain condition may require special treatments. It may include environments with:

• Inorganic acids
• Alkali solution
• Salty water

How to Magnetize Alnico Magnets

Magnetization activates magnetic characteristics. In fact, before magnetization, they are slugs.

For magnetization, you can choose:

• Static method – a suitable technique for small magnetic field
• Pulse method – a perfect choice for alnico magnets with powerful fields

You will use a magnetizer.

More resources:

Alnico Material – Source: Science Direct

Alnico Permanent Magnets Facts – Source: IQS Directory

Magnet Manufacturing Process – Source: BE Magnet

How Magnet is Made – Source: Made How

Alnico Magnets vs Neodymium Magnet

Neodymium is a popular permanent magnet made from rare-earth material. Since their invention, they have replaced alnico permanent magnets in many applications.

But, when should you decide whether to choose alnico or neodymium magnets?

More resources:

Neodymium Magnet – Source: Bemagnet

Neodymium – Source: Wikipedia

Alnico Magnets vs Ceramic Magnet

At times, it becomes difficult to decide whether you should choose alnico or ceramic magnets. Let’s look at some critical facts:

More Resources:

Neodymium Vs Ferrite Magnets – Source: Bemagnet

Ceramic Magnets – Source: IQS Directory

Types of Alnico Magnets

For this section, we will focus on the major classification criteria:

Isotropic vs. Anisotropic Alnico Magnets

Classify Alnico Permanent Magnets Based on Shape

Insert images combines all the magnets:

Classification by Grades

Varying chemical composition produces different alnico magnet grades. Still, other variables that play an integral role in this classification criteria include;

• Residual induction
• Coercive force
• Operating temperature
• Maximum energy

Some common grades include:

Magnet Safety – Handling Magnets made from Alnico Material

Whenever you are handling permanent magnets made from alnico, you should be aware of the hazards or possible negative implications. Remember, the safe use of magnets is a common practice everywhere.

Here are some safety concerns you should consider:

• Be aware of the magnets chipping – the strong magnetic field may cause magnets to “fly” causing injuries. Therefore, it is advisable to have protective gear while handling alnico magnets.
• Swallowing magnets may cause choking and blockage in the digestive system. This is dangerous, especially for kids.
• Always keep magnetically sensitive items away from alnico magnets. They may affect the normal operations of some items
• Consider necessary safety gear when cutting magnets. It will help prevent unnecessary damage or breaking of magnets.

In short, you must pay attention to all safety regulations and instructions from your alnico magnets manufacturer.

How Temperature Affects Alnico Permanent Magnets

Their performance at extreme temperatures is better than ceramic magnets or rare-earth magnets.

Take for example:

• At extreme temperatures of about 550 °C, they can remain stable and in good working condition.
• Even at low temperatures -70 °C to -100 °C, these magnets do not lose their magnetism.

Although the increasing temperature may lead to loss of magnetism, for alnico, it is not that significant. Losing magnetism will depend on the magnet’s size and shape.

But even with the excellent resistance to high temperature, the external magnetic field may cause demagnetization.

As a general rule, here is the maximum working temperature for magnets made from alnico.

Note: The temperatures may vary slightly depending on the magnet grade.

Alnico Magnets Uses

Even with the invention of rare earth these magnets still play a fundamental role in manufacturing:

• Sensors
• Loudspeakers
• Guitar pick-ups
• Relays
• Lifting magnets
• Household objects
• Electro permanent magnets
• Loudspeakers
• Traveling wave tubes
• Microphones
• Motors

Among the main industries that have benefited from magnets made from alnico include aerospace, electronics, military, and other engineering applications.

Conclusion

As you can see, Alnico permanent magnets have the best temperature properties. Additionally, they have a wide range of properties and manufacturing processes that determine the alnico magnet prices.

For all your Alnico magnets, contact us now.