Are supplied magnets and assemblies compliant to RoHS?

RoHS is the abbreviation of “The Restriction of the Use of Certain Hazardous Substance in Electrical & Electronic Equipment”. According to European Community directive 2002/95/EC of 27th January 2003, the content of hazardous material of Pb, Cd, Hg, Cr6+, PBDEs and PBBs in all parts should be controlled within specified PPM. This directive was launched from 1st July 2006. All our magnets and magnetic assemblies have been convinced conforming to EU directive 2002/95/EC by SGS or other recognized third party.

How to make a magnet output maximum holding force?

Different magnetization pattern and forming magnet with pole pieces can output various holding force even if magnet with same dimension and at same property. Below figures offer reference on design a component for holding application.

Holding Factor 1 magnetised through thickness	Holding Factor 1.3 magnetised through thickness with iron backing plate
Holding Factor 3 alternate poles on one surface	Holding Factor 3.5 magnetised through thickness ,But with iron backing plate
Holding Factor 5.8 magnetised through thickness but in iron U-shape	Holding Factor 18 magnetised through thickness ,but with two iron pole pieces

The above mentioned holding factors base consideration of anistropic hard ferrite magnet. Besides above examples, there are many other variants for certain applications. The indicated values are approximate one and depend on the strength of the iron backing plates, and on the volume of the magnet as well as on the structure of the magnet system.

What should be considered in designing permanent magnet?

Basic problems of permanent magnet design revolve around estimating the distribution of magnetic flux in a magnetic circuit, which may include permanent magnets air gaps, high permeability condition elements and electrical currents. Exact solutions of magnet design require complex and comprehensive analysis of many factors. From the view of a permanent magnet supplier, below factors on magnet should be considered.

1) Magnet material type (covering magnetic, physical and mechanical
? properties)
2) Magnetization pattern
3) Geometry
4) Dimension and tolerance
5) Coating type
6) Cost
7) Working environment
8) Assembling process
9) Special requirement

It is not always possible to maximize all requirements at the same time. Below table offers brief comparison on different type permanent magnet and is intended to be beneficial to your design.

What degree of homogeneity of property, surface gauss and flux we can keep?

Both highest property and homogeneity are goals we have been struggling for and will stick at. Magnetic property homogeneity means property deviation range between the same lot products or between different production lots. It is a systematic engineering to keep homogeneities of property, surface gauss and flux. Besides material composition, powder particle size and processes of molding, sintering, machining process and coating also determine homogeneities of magnetic property, surface gauss and flux.

In powder making process, we control the powder particle size to keep homogenous magnetic property; in molding process, we stabilize the molding force pressure and change manual material-feeding with automatic material-feeding to get uniform density of semi-product; in sintering process, we stabilize sintering temperature and change coal heating furnace with electric-power furnace in sintering hard ferrite magnet to get homogenous magnetic property; in machining process, we control the deviations of dimension and angle between geometric axial and anisotropic axial to improve homogeneity of magnet dimension, dimension ratio and pole deviation; in coating process, we control coating layer thickness (determining air gap), and time and concentration of acid in washing magnet to enhance homogeneity of dimension and dimension ratio.

These actions are doubtlessly helpful to fulfill our goals. For information on values of homogeneity, please contact us.

What is called angle of orientation/anisotropy direction of the magnet?

In fact it is called the angle of orientation/anisotropic direction and geometric axis of magnet. For particular applications, customer requires conformity of the two axes or orientation/anisotropy direction and a machined slot. Limited by process technology, absolute conformity of axes is impossible. It happens on molding, sintering and machining processes. The job we can do is to utmostly reduce the angle of the axes. Our talent partner has accumulate rich experience on controlling the angle and found a scientific way to measure the angle.

What is called “Quality Coefficient K” on hard ferrite magnet?

Quality Coefficient K is a data to evaluate quality and grade of raw material of ferrite magnet. The calculation of K value follows below equation:

K=Br+0.4iHc??(Br in unit of mT, iHc in unit of kA/m)

In sintering process, increasing temperature by per 10? can promote remanence Br by 5mT and meanwhile decrease intrinsic coercive force by 12kA/m. If the used material is qualified, then the K value is a constant one in spite of temperature change. Magnet with higher K value is with capability of outputting higher remeance Br and intrinsic coercive force.

What items should be negotiated before purchasing a magnet and included in an inquiry?

The below checklist maybe helpful in constructing and communicating specifications for permanent magnet:

1) Material type

2) Typical, Minimum and / or maximum magnetic properties (Br, Hc, iHc, (BH)max)

3) Geometry

4) Dimension and tolerance

5) Orientation direction (and tolerance of orientation direction if critical)

6) Magnetizing status

7) Coating

8) Acceptance test or performance requirements

9) Inspection sampling plan

10) Packing and identification

11) Other requirement.

Why there are some crystal/shinning points on the surface of sintered ferrite magnet?

If the sintering temperature is approaching the upper limit of the designed temperature of the used material, then some crystal/shinning points will appear on the surface of sintered ferrite magnet. Magnet with this phenomenon does not influence its function. Generally, such kind of magnet is with higher remanence Br and lower intrinsic coercive force iHc but within the property range.

Why measuring surface gauss by gauss meter to express flux density is not scientific?

Flux density expresses the concentration of line of force per unit area passing from one pole to the other. Magnet material type, dimension ratio and air gap determines the measured flux density.

In measuring surface gauss, the position change of hall probe sensitively influence the reading result. Placing probe at the magnet edge area can get much higher value than by placing hall probe at the central area of magnet. Due to technology problem, the reading on “N” pole and “S” will be quite different particularly the measured magnet is an anisotropic axially magnetized hard ferrite magnet. Sometimes, the surface gauss difference between 2 poles will be over 100Gs.