Magnets: Types, Applications and Principles

Chapter 1: Understanding the Principle of Magnets

This chapter delves into the basics of magnets, covering manufacturing techniques and their operative mechanisms.

Defining a Magnet

Magnets are entities that generate a distinct force on other objects without physical interaction. This magnetic force can either attract or repel. Although many substances exhibit some magnetic force, only a few have a sufficiently strong force to be designated as magnets. The Earth itself is akin to a colossal magnet.

Magnets possess two areas where the magnetic force peaks, known as the poles. These poles are opposite on a rectangular bar magnet, labeled the North Pole (north-seeking) and the South Pole (south-seeking).

Mechanism of Magnetism

Magnetism results from the actions of minuscule particles called electrons. Atoms, which form all matter, consist of electrons, neutrons, and protons. Electrons orbit around the nucleus, generating small-scale magnetic forces. In certain materials, numerous electrons align their spins uniformly, leading to a combined magnetic force that emerges as a significant magnet.

Creating a magnet can be achieved by rubbing metal with an established magnet, ensuring the motion is unidirectional to align electrons. Similarly, electric current can produce magnets. As electricity involves electron flow, electrons moving in a wire create a magnetic field similar to electrons spinning around atomic nuclei. This type of magnet is termed an electromagnet.

Nickel, cobalt, iron, and steel are ideal for creating permanent magnets due to their electron configuration. Once magnetized, these metals maintain their magnetic properties indefinitely, known as hard magnets. Meanwhile, some metals exhibit temporary magnetic behavior when near hard magnets, classifying them as soft magnets.

Most elements, such as wood or water, possess very weak magnetic traits. However, magnets strongly attract objects containing metals like iron, nickel, or cobalt. They can also attract or repel other nearby hard magnets because each has two opposing poles: north and south. Opposite poles attract, while like poles repel each other.

Magnetic Production Process

Commonly, magnets are produced through powder metallurgy. Different magnet types have varied manufacturing methods. For example, electromagnets are crafted via metal casting techniques, while flexible magnets are formed by plastic extrusion. In plastic extrusion, raw materials are heated, blended, and forced through an opening under pressure. Below is a general guide on magnet manufacturing procedures.

Powder Preparation

Iron, boron, and neodymium are melted in a furnace devoid of air to avoid chemical reactions. As the alloy cools, it is fragmented into small metal pieces, later pulverized into a fine powder between 3 to 7 microns in diameter. Because the powder can ignite when exposed to oxygen, it must remain shielded from air.

Compaction Procedure

Isostatic compaction or pressing places powdered metal into a mold, with a magnetic force applied to align particles during compaction. Hydraulic pressure then compresses the material close to its required thickness. Typically, pressures from 10,000 to 15,000 psi are utilized. For diverse designs, the powder is sealed in an evacuated container before shaping with gas pressure.

Material Heating

Post-compaction, the powdered metal is transferred to an oven for sintering, where heat is applied to form solid metal pieces. Sintering includes three key stages. Initially, low heat removes moisture and contaminants. Next, a higher temperature close to the alloy's melting point is sustained, allowing particles to bond. Finally, the material cools gradually to complete sintering.

Annealing Process

After heating, the annealing phase begins. This involves controlled heating and cooling to eliminate internal stresses, enhancing the material’s strength.

Finishing Magnets

Typically, the sintered magnets undergo machining, including grinding for smooth surfaces or cutting into smaller segments. Given the material's hardness and brittleness, diamond wheels are preferred for slicing and grinding. Precision slicing often reduces further grinding needs, though caution is required to minimize cracks.

In some cases, a shaped diamond grinding wheel achieves precise dimensions, closely matching the intended final shape, termed "near net shape." Excess material is removed in a final machining step, creating a smooth surface where necessary before a protective coating is applied.

Magnetization Process

After finishing, magnets undergo magnetization to develop an external magnetic field, achieved using a solenoid, configured for different sizes and shapes. The solenoid can include fixtures for specific patterns. Large assemblies might be magnetized together to reduce handling of charged magnets. Substantial magnetizing field requirements are crucial in this process.

All magnet selection aspects must involve both engineering and production discussions. Up until manufacturing completion, the material is merely compressed metal. Although isostatic pressing aligns the powder, no magnetic effect occurs. Aligning the material with a strong electromagnet while powered creates a permanent magnet.

Magnetic Separation Method

Magnetic separation utilizes a magnet to extract magnetic materials from a mixture efficiently. Effective in separating ferromagnetic minerals like cobalt, iron, or nickel, this method isn't applicable for non-magnetic metals like silver or gold. Various mechanical approaches aid in isolating magnetic elements; magnets within separator drums capture magnetic particles, forming a concentrate.

Magnetic separation is essential in electromagnetic cranes for waste management and shipping, efficiently extracting unwanted metals. Commonly utilized in recycling facilities, this method removes metal impurities and purifies ores. Traditionally, magnetic pulleys, overhead magnets, and drums were prevalent in the industry.

It is particularly beneficial in mining iron due to its magnetic attraction. Within food and pharmaceutical sectors, it removes metal contaminants and enhances product purity, contributing to effective recycling techniques.

Chapter 2: What are the different types of magnets?

Different types of magnets are categorized as follows:

Alnico Magnets

Alnico magnets come in cast, sintered, and bonded forms, with cast alnico magnets being the most common. They are an essential category of permanent magnet alloys composed of nickel (Ni), aluminum (Al), iron (Fe), and cobalt (Co), with minor additions of titanium (Ti) and copper (Cu). Alnico magnets exhibit relatively high coercivities due to the shape anisotropy of the iron (Fe) or cobalt (Co) particles, which are precipitated within a weakly ferromagnetic or non-ferromagnetic nickel-aluminum matrix. After cooling, isotropic alnico magnets are tempered at high temperatures for several hours.

Spinodal decomposition is a phase separation process where the final sizes and shapes of particles are determined early in the process. Alnico magnets are known for their excellent temperature coefficients, meaning they experience minimal changes in field output with temperature variations. These magnets can operate at the highest temperatures of any magnet type.

Demagnetization of the alnicos can be reduced if the working point is improved, such as for making use of a longer magnet than before in order to increase the length to diameter ratio which is a good rule of thumb guide for the Alnico magnets. All external demagnetizing factors must be taken into consideration however. A huge length to diameter ratio and a good magnetic circuit may also be required.

Bar Magnets

Bar magnets are rectangular objects made from steel, iron, or other ferromagnetic materials with strong magnetic properties. They have two poles: a north pole and a south pole.

When a bar magnet is suspended freely, it aligns itself such that its north pole points towards the Earth's magnetic north pole.

There are two main types of bar magnets. Cylindrical bar magnets, also known as rod magnets, have a high thickness in diameter, which enhances their magnetic properties. The second type is rectangular bar magnets, which are commonly used in manufacturing and engineering applications due to their greater magnetic strength and field compared to other magnets.

When a bar magnet is broken in half, each piece will still have both a north and a south pole, even if broken into smaller parts multiple times. The magnetic force of a bar magnet is most intense at its poles. When two bar magnets are brought near each other, opposite poles attract, while like poles repel. Bar magnets are effective at attracting ferromagnetic materials like cobalt, nickel, and iron.

Bonded Magnets

Bonded magnets consist of two primary components: a non-magnetic polymer and hard magnetic powder. The powder can be derived from various magnetic materials such as alnico, ferrite, neodymium, cobalt, and iron. Additionally, multiple types of magnetic powders can be combined to create hybrid mixtures. The properties of these powders are meticulously optimized through precise chemical processes and step-by-step manufacturing, ensuring that bonded magnets perform effectively regardless of the materials used.

Bonded magnets have numerous advantages in that the near net shape manufacturing requires no or low finishing operations when compared to other metallurgical processes. Therefore value added assemblies can be made economically in one operation. These magnets are a highly versatile material and they consist of multiple processing options. Some advantages of bonded magnets are that they have excellent mechanical properties and great electrical resistivity when compared with sintered materials. These magnets are also available in different complex sizes and shapes. They have good geometric tolerances with very low secondary operations. They are also available with multipole magnetization.

Ceramic Magnets

Ceramic magnets, also known as ferrite magnets, are a type of permanent magnet and are the most cost-effective compared to other magnet types. Made from iron oxide and strontium carbonate, these magnets offer medium magnetic strength and can operate at high temperatures. Their key advantages include corrosion resistance and ease of magnetization, making them a popular choice for a wide range of applications, including industrial, technical, and commercial uses. Ceramic magnets come in various grades, with Grade 5 being commonly used, and they are available in different shapes such as blocks and rings. They can also be custom-manufactured to meet specific customer requirements.

Ferrite magnets can operate at high temperatures, although their magnetic properties decrease as the temperature rises. They require specialized machining skills for precision shaping. An advantage of ceramic magnets is their resistance to surface rust, thanks to a protective film of magnetic powder on their surface. They are typically bonded to products using superglue. However, ceramic magnets are very brittle and can easily break if dropped or subjected to impact, so they require careful handling to avoid damage.

Electromagnets

Electromagnets are magnets whose magnetic field is generated by an electric current. Typically, they consist of a wire wound into a coil. When current flows through the wire, it creates a magnetic field. This field vanishes when the current is turned off. Electromagnets are usually composed of wire turns wound around a magnetic core made from ferromagnetic material. The core concentrates the magnetic flux, resulting in a more powerful magnet.

Electromagnets offer the advantage of quickly adjusting the magnetic field by regulating the electric current in the winding, unlike permanent magnets. However, they require a continuous current supply to maintain their magnetic field. Electromagnets also have some drawbacks: they heat up rapidly, consume significant amounts of energy, and can discharge large amounts of energy if there is an interruption in the current. Despite these challenges, they are commonly used in various electrical devices such as generators, relays, electro-mechanical solenoids, motors, loudspeakers, and magnetic separation equipment. Additionally, they are useful in industry for moving heavy objects and picking up iron and steel scrap. Electromagnets attract ferromagnetic materials like nickel, cobalt, and iron. Like most magnets, similar poles repel each other, while opposite poles attract.

Flexible Magnets

Flexible magnets are designed to bend and flex without breaking or sustaining damage. Unlike rigid magnets, these magnets can be deformed, rolled, or bent without losing their magnetic properties. The flexible magnet shown in Figure 2:6 illustrates this capability. Typically, flexible magnets consist of a synthetic substrate, such as vinyl, coated with a thin layer of ferromagnetic powder. The substrate is made from a very pliable material, and when the ferromagnetic powder is applied, it imparts magnetic properties to the entire surface.

Various production methods are used to manufacture flexible magnets, but most involve applying ferromagnetic powder to a synthetic substrate. The ferromagnetic powder is mixed with an adhesive binding agent to ensure it adheres to the substrate. Flexible magnets come in various forms, including sheets of different designs, shapes, and sizes, as well as strips that are thinner and longer than the sheets. These magnets are commonly used in applications such as motor vehicles, doors, metal cabinets, and buildings.

On the market they are usually sold and packaged in rolls. Flexible magnets are versatile with their bendable properties and they can wrap around machines so easily as well as other surfaces and components. A flexible magnet is supported even with surfaces which are not perfectly smooth or flat. Flexible magnets can be cut and shaped into desired shapes and sizes. Most of them can be cut even with a traditional cutting tool. Flexible magnets are not affected by drilling, they will not crack but they will form holes without damaging the surrounding magnetic material.

Industrial Magnets

An industrial magnet is a powerful magnet used across various sectors in the industrial field. These magnets come in various shapes and sizes and are known for their diverse grades and qualities, which help retain residual magnetism. Industrial permanent magnets can be made from materials like alnico, rare earth, or ceramic. They are crafted from ferromagnetic substances that are magnetized by an external magnetic field and can maintain their magnetized state over an extended period. Industrial magnets hold their magnetic properties without external support and feature two poles where the magnetic intensity is highest.

Samarium-cobalt industrial magnets are known for their ability to withstand high temperatures up to250 °C.. These magnets are highly resistant to corrosion due to their lack of iron content. However, their production is costly because of the high price of cobalt. Despite the expense, samarium-cobalt magnets are valued for their ability to produce very strong magnetic fields and are commonly used in applications involving high operating temperatures, such as in motors, sensors, and generators.

Alnico industrial magnets are made from a combination of aluminum, cobalt, and nickel, with possible additions of copper, iron, and titanium. Compared to samarium-cobalt magnets, alnico magnets can endure even higher temperatures, up to 525 °C, making them highly heat-resistant. They are also more susceptible to demagnetization due to their sensitivity. Industrial electromagnets, on the other hand, are adjustable and can be turned on and off as needed.

Industrial magnets have various applications, such as:

They are used to lift sheet steel, iron castings, and iron plates. These powerful magnets are commonly employed in manufacturing industries to facilitate the handling and transfer of heavy objects. By placing the magnet on top of the object and activating it, the magnet securely holds the item, allowing for efficient relocation to the desired location. One of the key advantages of industrial lifting magnets is the significant reduction in the risk of musculoskeletal issues among workers.

Utilizing industrial magnets helps protect manufacturing workers from injuries by eliminating the need for manual lifting of heavy materials. This enhances productivity in manufacturing settings, as manual handling of heavy objects is both time-consuming and physically demanding, impacting overall efficiency. Industrial magnets streamline these processes, contributing to improved workplace safety and productivity.

Neodymium Magnets

Rare earth magnets, such as neodymium magnets, are permanent magnets known for their exceptionally strong magnetic fields, producing strengths of over 1.4 teslas. These powerful magnets have a wide range of applications. They are commonly used in hard disk drives, where they help magnetize the tracks and segments to store data. Neodymium magnets are also integral to the function of loudspeakers, headphones, microphones, and earphones, enhancing audio quality with their strong magnetic properties.

The current-carrying coils that are found in these devices are used together with permanent magnets to alter electricity into mechanical energy. Another application is that the small sized neodymium magnets are mostly used to place dentures perfectly in place. These magnets are used in residential and commercial buildings on the doors for safety reasons and total security. Another practical use of these magnets is in making therapy jewelry, necklace, and jewelry. Neodymium magnets are greatly used as anti-lock brake sensors, these anti-lock brakes are installed in cars and numerous vehicles.

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Chapter 3: What are some common applications of magnets?

This chapter will explore various applications of magnets across different industries and technologies.

Applications of Magnets

Magnets are employed in a wide range of applications across various contexts and purposes. They come in sizes ranging from tiny components to large structures. In everyday life, magnets are integral to many devices; for instance, hard disks in computers use magnetic elements to store and retrieve data. Additionally, magnets are found in televisions, radios, and speakers, playing a crucial role in their operation.

Magnetic Stripe

Magnetic stripe technology enables data storage on plastic cards by encoding information into tiny magnetic bits along a stripe on the card. This technology underpins credit and debit cards, significantly reducing cash transactions globally. Known as magstripe technology, it has led to the creation of highly durable cards with robust data integrity. Thanks to magnetic stripe cards, financial institutions and banks can efficiently handle a wide range of card-based transactions and processes.

Magnetic stripes are integral to countless transactions daily and are widely used in various identification cards. Card readers can quickly extract details from these magnetic cards, which are then sent to banks for authorization. However, in recent years, a new technology has increasingly rivaled magnetic card transactions: contactless payment systems. This modern method uses signals from a small chip to transfer transaction details, eliminating the need for a magnetic stripe. Apple Inc. has been a pioneer in advancing contactless payment systems.

In speakers, a small coil of wire and a magnet work together to convert electronic signals into sound vibrations. Similarly, generators utilize magnets to transform mechanical energy into electrical energy. Magnets are also crucial in various mechanical and electrical motors, where they convert electrical energy into mechanical motion.

Magnets play a key role in lifting large metal objects that are too heavy for manual handling, such as in crane operations. They are also used in the separation and filtering of metallic ores from crushed rocks, and in the food processing industry to remove small metal contaminants from grains. These are just a few examples of the diverse applications of magnets.

Drawbacks of Magnets

Several significant drawbacks are associated with different types of magnets. Ferrite magnets, for instance, are produced through molding and sintering, making them challenging to machine. As a result, ferrite magnets typically have simple shapes and large dimensional tolerances. Samarium Cobalt magnets are quite brittle, which complicates the processing of small-sized products. Additionally, many magnets suffer from degradation at very high temperatures. Neodymium magnets, on the other hand, are prone to corrosion and thus require protective coatings to maintain their durability.

Conclusion

Magnets come in different forms, from simple bar magnets to very large permanent industrial magnets. Every type of magnet has two poles and even if they are cut in half, they will still have these two poles. Magnets are of great importance to the human community, but however they can be demagnetized at excessive temperatures and pressure.

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