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Magnetic Elastomer


Magnetic elastomer is produced using heavily charged Strontium ferrite powders mixed with synthetic rubber or PVC, and it is manufactured either by extrusion to different shapes, or by calendering into fine sheets. In certain cases, an orientation can be introduced mechanically or by means of an external magnetic field, but the product is always magnetised during a second operation. The first application appeared in the 60s. This was the refrigerator door closing system, and such applications have now multiplied and exist in various forms, from the simple mounting product to more technical products such as motors or detectors using permanent magnets.

FLEXIBLE COMPOSITES
 
Flexams are flexible calendered composites, which are easy to use. They bend to the required shape, they can be easily cut to size. Their performance levels are not as high as 100 % dense ferrites, and they are used when the available surface area is large because of their high coefficient of friction, or in order to avoid scratching paintwork.
 
Presentation

Flexam has the appearance of a brown sheet, which is more or less flexible depending on its thickness and its composition. It is never elastic like rubber. Hardness 60 to 65 Shore D.
 
Composition

Flexams are composites formed from a synthetic elastomer charged with strontium ferrite grains. The choice of powders as basic polymers provides a range of properties:
- magnetic properties,
- mechanical properties,
- resistance to heat and to hydrocarbons,
- compliant with food standards and with standards for use in toys.
 
Magnetic properties
 

There are 3 main varieties:
 
- Flexam, which is the most common. Calendering produces a certain amount of alignment, which improves performance.
 
- Flexor 15, which is anisotropic, must be magnetised in the direction of its thickness. This is the most performant of the standard versions.
 
- Flexor 45, is the family of special varieties (refer to the paragraph on specific mixtures).
Flexor 45 is produced using the most performant powders. A choice of polymers provides different mechanical properties.
 
The magnetic properties also depend on the retained implementation.

VarietyBr : GaussHcB : OerstedBH : MGO
Flexam 18507500.5
Flexor 15220018001.15
Flexor 452300 à 25001500 à 22001.2 à 1.5


Magnetisation

Sheets and rolls are normally magnetised on one face only, with a distance between poles of 3.5 mm.
These values provide a good attraction distance compromise, particularly through standard paints.
For the attachment of metal-sheet sandwiches, specify "magnetisation on both faces". In this case, the polar pitch is 7 mm.
 
Operating conditions

Magnetic elastomers have a practically unlimited operating life under normal operating conditions.
 
Effect of temperature:
 
As with ferrites, the level of induction decreases with temperature (‑0.2 % per °C). As a general rule, the elastomer is not guaranteed above 75°C.
 
Chemicals:
Good resistance to water, alcohol, household detergents and bad weather conditions.
 
They have a fairly low resistance to solvents, oil and hydrocarbons, and this needs to be checked for each individual case.
 
Implementation
 
Flexam and Flexor can be easily cut with scissors, a cutter or shears. However, they are highly abrasive materials and it is recommended to use coated blades for large-scale operations. We can cut these materials to order:
- either into simple rectangular formats, with rounded or angular corners,
- or into more complex shapes, using special tools,
- or into forms such as actuator control rings or thick profiles, by machining thick parts.
 
Adhesive bonding
Depending on the operating temperature, use a neoprene or epoxy adhesive.
 
Special mixes
 
For maximum operating conditions specify:
- either Flexor W45, with a neoprene base, for a temperature resistance up to 130°C,
- or Flexor H40, with a hypalon base, for resistance to oils (limited to a temperature of 100°C).
 
Depending on the applications, we can develop the following for you:
- harder mixtures, for more precise cutting with tools,
- more flexible mixtures, easy to roll,
- varnishes which block chemical migrations, for the protection of paints at high temperatures.
 
Adhesive
To facilitate installation, these sheets can be supplied in an self-adhesive version. Two versions are possible:
- adhesive 6140: 2 kg / cm², with a fairly good resistance to heat.
This has a texture which provides good mechanical strength.
- adhesive 6530: 1 kg/cm². Without a screening medium.
This means that the adhesive is free to creep slightly and therefore enables:
- pre-cutting of detachable parts,
- rolls to be produced.
 
Caution: comply with the storage recommendations given on the packages, and with the use-by dates for the adhesive. Beyond the use-by date, the adhesive tends to turn into a permanent cement.

LAMINATED COMPOSITES

Placam and Placor produce flat components with good magnetic performance and mechanical rigidity, that are also easy to use.
 
Composition
A sheet of Flexam or Flexor is colaminated with an extra-soft iron pole plate.
 
Presentation
 
For the standard version, the non-magnetic plate is pre-enamelled in white, and protected with a peel-off film to be removed at the time of use (this is essential for painting or bonding with adhesive).
Also available as plain zinc electroplated sheet metal.
The magnetic face is coated with a colourless film, which has a temperature resistance of up to 70°C.
For automobile bodywork, liable to be exposed to direct sunlight, and therefore to temperatures in excess of the above maximum, specify the Automobile protection film.
 
Applications
 
Attachment of large surface areas (ski-rack, driving school signs, for example). The metal sheet provides a good level of distribution between the attraction face and the attachment points, thus reducing the peeling effect that causes problems with flexible elastomers.
Mechanical parts: magnets for position sensors, magnetic keyboards, spark plug wrench grips.
 
Magnetic properties
 
This combination provides a set of particularly advantageous properties:
- magnetic: the magnetic circuit created behaves like a magnet of twice the thickness (force up to 800 Gauss at the surface);
- mechanical: it is possible to cut out thin components, with good geometrical tolerances and without the brittleness of ferrites.
The metal sheet provides a good distribution of the mechanical strains in large parts.
 
Magnetisation
 
For the standard version, multipolar magnetisation on one face with a pitch of 10 mm.
In order to privilege remote action, it is possible to produce a longer pitch.
 
Conditions of use
 
Magnetic elastomers have a practically unlimited utilisation life under normal conditions.
Temperature effect: like ferrites, induction decreases with temperature (-0.2 % per °C). As a general rule, the elastomer is not guaranteed above 75°C.
 
Chemicals: good resistance to water, alcohol, household detergents and bad weather conditions.
They have a fairly low resistance to solvents, oil and hydrocarbons, and this needs to be checked for each individual case.
 
Implementation

Placam-Placor enable precise parts to be cut out, suitable for being screwed or riveted onto an assembly. The screw or rivet heads can be sunk into the thickness of the elastomer by creating a countersink.
 
Cutting-out

Combining two materials as dissimilar as these results in some difficulty in the cutting up process, so we can supply rectangular parts to your dimensions (preferably sub-multiples), or disks, rings or other shapes. For rectangular parts, rounded corners can be ordered if necessary. Cutting out with standard shears can produce disappointing results.
Standard cutting-up tolerances: +/- 0.25 mm
Thickness: ‑0 , +0.25 mm
Parts cut out using tools, internal-external cut-outs. The tool defines the dimension of the metal sheet: the elastomer can have a dimensional discrepancy of a few tenths of a millimetre.

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