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MAGNETS INFORMATION

  • Background and History
  • Design
  • Magnet Selection
  • Surface Treatment
  • Magnetizing
  • Dimension Range, Size and tolerance
  • Safety principle for manual operation

Background and History

Permanent magnets are a vital part of modern life. They are found in or used to produce almost every modern convenience today. The first permanent magnets were produced from naturally occurring rocks called lodestones. These stones were first studied over 2500 years ago by the Chinese and subsequently by the Greeks, who obtained the stone from the province of Magnetes, from which the material got its name. Since then, the properties of magnetic materials have been profoundly improved and today’s permanent magnet materials are many hundreds of times stronger than the magnets of antiquity. The term permanent magnet comes from the ability of the magnet to hold an induced magnetic charge after it is removed from the magnetizing device. Such devices may be other strongly magnetized permanent magnets, electro-magnets or coils of wire that are briefly charged with electricity. Their ability to hold a magnetic charge makes them useful for holding objects in place, converting electricity to motive power and vice versa (motors and generators), or affecting other objects brought near them.


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Design

Superior magnetic performance is a function of better magnetic engineering. For customers who require design assistance or complex circuit designs, QM's team of experienced application engineers and knowledgeable field sales engineers is at your service. QM engineers work with customers to improve or validate existing designs as well as develop novel designs that produce special magnetic effects. QM has developed patented magnetic designs that deliver extremely strong, uniform or specially shaped magnetic fields that often replace bulky and inefficient electro-magnet and permanent magnet designs. Customers are confident when hey bring a complex concept or new idea that QM will meet that challenge by drawing from 10 years of proven magnetic expertise. QM has the people, products and technology that put magnets to work.


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Magnet Selection

Magnet selection for all applications must consider the entire magnetic circuit and the environment. Where Alnico is appropriate, magnet size can be minimized if it can be magnetizing after assembly into the magnetic circuit. If used independent of other circuit components, as in security applications, the effective length to diameter ratio (related to the permeance coefficient) must be great enough to cause the magnet to work above the knee in its second quadrant demagnetization curve. For critical applications, Alnico magnets may be calibrated to an established reference flux density value.

A by-product of low coercivity is sensitivity to demagnetizing effects due to external magnetic fields, shock, and application temperatures. For critical applications, Alnico magnets can be temperature stabilized to minimize these effects  There are four classes of modern commercialized magnets, each based on their material composition. Within each class is a family of grades with their own magnetic properties. These general classes are:

  • Neodymium Iron Boron
  • Samarium Cobalt
  • Ceramic
  • Alnico

NdFeB and SmCo are collectively known as Rare Earth magnets because they are both composed of materials from the Rare Earth group of elements. Neodymium Iron Boron (general composition Nd2Fe14B, often abbreviated to NdFeB) is the most recent commercial addition to the family of modern magnet materials. At room temperatures, NdFeB magnets exhibit the highest properties of all magnet materials. Samarium Cobalt is manufactured in two compositions: Sm1Co5 and Sm2Co17 - often referred to as the SmCo 1:5 or SmCo 2:17 types. 2:17 types, with higher Hci values, offer greater inherent stability than the 1:5 types. Ceramic, also known as Ferrite, magnets (general composition BaFe2O3 or SrFe2O3) have been commercialized since the 1950s and continue to be extensively used today due to their low cost. A special form of Ceramic magnet is "Flexible" material, made by bonding Ceramic powder in a flexible binder. Alnico magnets (general composition Al-Ni-Co) were commercialized in the 1930s and are still extensively used today.

These materials span a range of properties that accommodate a wide variety of application requirements. The following is intended to give a broad but practical overview of factors that must be considered in selecting the proper material, grade, shape, and size of magnet for a specific application. The chart below shows typical values of the key characteristics for selected grades of various materials for comparison. These values will be discussed in detail in the following sections.

Magnet Material Comparisons

Material
Grade
Br
Hc
Hci
BH max
T max(Deg c)*
NdFeB
39H
12,800
12,300
21,000
40
150
SmCo
26
10,500
9,200
10,000
26
300
NdFeB
B10N
6,800
5,780
10,300
10
150
Alnico
5
12,500
640
640
5.5
540
Ceramic
8
3,900
3,200
3,250
3.5
300
Flexible
1
1,500
1,380
1,380
0.6
100

* T max (maximum practical operating temperature) is for reference only. The maximum practical operating temperature of any magnet is dependent on the circuit the magnet is operating in.


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Surface Treatment

Magnets may need to be coated depending on the application for which they are intended. Coating magnets improves appearance, corrosion resistance, protection from wear and may be appropriate for applications in clean room conditions.
Samarium Cobalt, Alnico materials are corrosion resistant, and do not require to be coated against corrosion. Alnico is easily plated for cosmetic qualities.
NdFeB magnets are particularly susceptible to corrosion and are often protected in this way. There are a variety of coatings suitable for permanent magnets, Not all types of coating will be suitable for every material or magnet geometry, and the final choice will depend on the application and environment. An additional option is to house the magnet in an external casing to prevent corrosion and damage.

Available Coatings

Su rface

Coating

Thickness (Microns)

Color

Resistance

Passivation


1

Silver Grey

Temporary Protection

Nickel

Ni+Ni

10-20

Bright Silver

Excellent against Humidity

Ni+Cu+Ni

Zinc

Zn

8-20

Bright Blue

Good Against Salt Spray

C-Zn

Shinny Color

Excellent Against Salt Spray

Tin

Ni+Cu+Sn

15-20

Silver

Superior  Against Humidity

Gold

Ni+Cu+Au

10-20

Gold

Superior  Against Humidity

Copper

Ni+Cu

10-20

Gold

Temporary Protection

Epoxy

Epoxy

15-25

Black, Red,Grey

Excellent Against Humidity
Salt Spray

Ni+Cu+Epoxy

Zn+Epoxy

Chemical

Ni

10-20

Silver Grey

Excellent Against Humidity

Parylene

Parylene

5-20

Grey

Excellent Against Humidity, Salt Spray. Superior Against Solvents, Gases, Fungi and Bacteria.
 FDA Approved.


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Magnetizing

Permanent magnet supplied under two conditions, Magnetized or no magnetized, is usually not marked its polarity. If the user require, we could mark the polarity by the means agreed on. When pacing the order, the user should inform the supply condition and if the mark of the polarity is necessary.

The magnetization field of permanent magnet is related to the permanent magnetic material type and its intrinsic coercive force. If the magnet need magnetization and demagnetization, please contact with us and ask for technique support.

There are two methods to magnetize the magnet: DC field and pulse magnetic field.

There are three methods to demagnetize the magnet: demagnetization by heat is a special process technique. demagnetization in AC field. Demagnetization in DC field. This asks for very strong magnetic field and high demagnetization skill.

Geometry shape and magnetization direction of permanent magnet: in principle, we produce permanent magnet in various shapes. Usually, it includes block, disc, ring, segment etc. The detailed illustration of the magnetization direction is below:

Directions of Magnetization
(Diagrams Indicating Typical Directions Of Manetization)

oriented through thickness

axially oriented

axially oriented in segments

oriented laterally multipole on one face

multipole oriented in segments on outside diameter*

multipole oriented in segments on one face

radially oriented *

oriented through diameter *

multipole oriented in segments on inside diameter*

all available as isotropic or anisotropic material

*only available in isotropic and certain anisotropic materials only


radially oriented

diametrical oriented


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Dimension Range, Size and tolerance

Except for the dimension in the direction of magnetization, the maximum dimension of the permanent magnet is not exceed 50mm, which is limited by the orientation field and sintering equipment. The dimension in the unmagnetization direction is up to 100mm.

The tolerance is usually +/-0.05 -- +/-0.10mm.

Remark: Other shapes can be manufactured according to customer's sample or blue print

Ring
Outer Diameter
Inner Diameter
Thickness
Maximum
100.00mm
95.00m
50.00mm
Minimum
3.80mm
1.20mm
0.50mm
Disc
Diameter
Thickness
Maximum
100.00mm
50.00mm
Minimum
1.20mm
0.50mm
Block
Length
Width
Thickness
Maximum100.00mm
95.00mm
50.00mm
Minimum3.80mm
1.20mm
0.50mm
Arc-segment
Outer Radius
Inner Radius
Thickness
Maximum75mm
65mm
50mm
Minimum1.9mm
0.6mm
0.5mm



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Safety principle for manual operation

1. The magnetized permanent magnets with strong magnetic field attract the iron and other magnetic matters around them greatly. Under common condition, the manual operator should be very careful to avoid any damage. Due to the strong magnetic force, the big magnet close to them takes the risk of damage. People always process these magnets separately or by clamps. In this case, we should ware the protection gloves in operation.

2. In this circumstance of strong magnetic field, any sensible electronic component and test meter may be altered or damaged. Please see to it that the computer, display and magnetic media , for example the magnetic disc ,magnetic cassette tape and video record tape etc., are far from the magnetized components, say farther than 2m.

3. The collision of the attracting forces between two permanent magnets will bring enormous sparkles. Therefore, the flammable or explosive matters should not be placed around them.

4. When the magnet is exposed to hydrogen, it is prohibited to use permanent magnets without protection coating. The reason is that the sorption of hydrogen will destroy the microstructure of the magnet and lead to the deconstruction of the magnetic properties. The only way to protect the magnet effectively is to enclose the magnet in a case and seal it.


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