Moulds for Plastic Magnets

Plastic magnets are molding materials produced by mixing magnetic powders in a plastic resin or an elastomer. Using injection molding, it is possible to manufacture magnetic molded products with a high degree of freedom in the shape.
Compared to sintered magnets, it is possible to produce products that are lightweight and have shapes with thin walls. However, the magnetic force is larger in sintered magnets.

The following types of magnetic powders are used.

(1) Ferrite type
- Barium ferrites
- Strontium ferrites

(2) Rare earths type - Samarium - cobalt
- Samarium - iron - nitrogen
- Neodymium - iron - Boron

Further polyamides (nylon) such as PA6, PA66, PA12, etc. are used as binders.
In some cases, PPS (polyphenylene sulfide) and PVC (polyvinyl chloride) are also used as binders.

In the case of plastic magnets, in some cases the devices for generating magnetic fields are incorporated in molds for giving polarities to the molded product inside the mold.
There are many methods for this such as having a structure in which permanent magnets are embedded inside the cavity, strong magnetic fields are generated using coils, or receiving the supply of magnetic fields from the molding machine, etc.
Therefore, for all components of molds, it is necessary to separate the use of magnetic materials (steel, nickel, etc.) and non-magnetic materials (stainless steel, copper alloys, etc.).
In addition, since the mold gets worn strongly due to magnetic powders, it is necessary to take measures to enhance the resistance to wear.
Since the molded products taken out stick to each other due to magnetic force, care should be taken in the handling of molded products after they are taken out (making suitable trays, etc.).

This article was composed from notes taken from posts in misumi-techcentral.com