Plastic-bonded, injection-molded magnets

Plastic-bonded HF magnets consist of hard ferrite powder embedded in a plastic matrix. depending on the operating temperatures and ambient conditions, the matrix materials PA6, PA12 or PPS are used.

Plastic-bonded HF magnets are characterized by very high media resistance and an excellent price/performance ratio. Remanences up to typ 305mT or max. energy product BHmax of up to 18kJ/m³ are achieved.

Material:
Composite material

Matrix material: 
Polyamide 6 (PA 6), polyamide 12 (PA 12) and polyphenylene sulphide (PPS) are used as the plastic matrix in injection-molded magnets. The maximum application temperatures depend on the magnet and matrix material.They are 160°C for grades bonded with PA 6, 140°C for grades bonded with PA 12 and 220°C for grades bonded with PPS. The maximum operating temperature depends on the duration, the magnet dimensions and the specific application.

Production process:
The first stage of the production process of plastic-bonded, injection-molded magnets is the production of the magnetic compound. This is done by mixing the plastic granulate and the magnetic powder in a twin screw extruder before they are extruded and granulated. The next step is processing the compound with modified injection molding machines. When injection molding anisotropic magnets, a magnetic field in an axial, radial, diametric or multi-polar direction is also created during the injection process. It generates the preferred direction of the magnetic material parallel to the given orientation. In the case of plastic-bonded, injection-molded magnets, a mechanical machining of the finished injection-molded part is generally not required.

Defining features:
Plastic-bonded, injection-molded HF-magnets are more elastic compared to sintered magnets. However, they do not achieve the mechanical properties of technical plastics due to the high filling levels. Press-fitting onto shafts, for example, is possible under certain circumstances. Furthermore, gearing can even be molded directly from plastic-bonded magnet material. However, such pressed connections or gearing can only be used for low loads.

Magnetic characteristics:
The magnetic characteristics of plastic-bonded, injection-molded magnets vary depending on the filling degrees and the magnetic powder being used. The possible maximum operation temperatures vary, depending on the magnetic and matrix material, between +120°C and +220°C. In case of unfavourable shapes, in particular those with thin wall thicknesses or narrow pole pitches, there can be deviations in the material data due to solidification processes that are too quick or orienting field strengths that are too low.

Corrosion resistance:
The chemical resistance of plastic-bonded, injection-molded HF-magnets, as is generally the case with composite materials, is determined by the plastic matrix as well as the magnetic filling material. Magnets with polyphenylene sulphide (PPS) as carrier material have a significantly better chemical resistance than PA-bonded magnets (oils, greases, fuels, etc.). However, the chemical resistance has to be tested in individual cases.

Plastic-bonded SmFeN magnets consist of SmFeN powder embedded in a plastic matrix. Depending on the operating temperatures and ambient conditions, the matrix materials PP, PA12 ore PPS are used.

In contrast to the plastic-bonded isotropic NdFeB magnets, anisotropic SmFeN powder is predominantly used. As a result, significantly higher remanences of up to typically 760mT or max. energy product BHmax of up to 110kJ/m³ are achieved.

Compared to NdFeB magnets, SmFeN magnets are only exposed to minor fluctuations in raw material prices, so that price stability over a defined project duration is conceivable.

Material:
Composite material

Matrix material:
Polypropylene (PP), polyamide 12 (PA 12), and polyphenylene sulfide (PPS) are used as plastic matrices in injection-molded magnets. The maximum operating temperatures depend on the magnet and matrix material. They range up to 160°C. The maximum operating temperature depends on the duration, the magnet dimensions and the specific application.

Production process:
The first stage of the production process of plastic-bonded, injection-molded magnets is the production of the magnetic compound. This is done by mixing the plastic granulate and the magnetic powder in a twin screw extruder before they are extruded and granulated. The next step is processing the compound with modified injection molding machines. When injection molding anisotropic magnets, a magnetic field in an axial, radial, diametric or multi-polar direction is also created during the injection process. It generates the preferred direction of the magnetic material parallel to the given orientation. In the case of plastic-bonded, injection-molded magnets, a mechanical machining of the finished injection-moulded part is generally not required.

Defining features:
Plastic-bonded, injection-molded SmFeN magnets have greater elasticity compared to injection-bonded, pressed magnets. However, due to the high filling degrees, they do not achieve the mechanical properties of technical plastics. That means it is possible, for example, to inject gearings straight from plastic-bonded magnetic material. However, these gearings can only be subjected to low stresses since the sliding properties are less favourable than those of unfilled plastics.

Magnetic characteristics:
The magnetic characteristics of plastic-bonded, injection-molded magnets vary depending on the filling degrees and the magnetic powder being used. The possible maximum operation temperatures vary, depending on the magnetic and matrix material, between +120°C and +140°C. In case of unfavourable shapes, in particular those with thin wall thicknesses or narrow pole pitches, there can be deviations in the material data due to solidification processes that are too quick or orienting field strengths that are too low.

Corrosion resistance:
As with composite materials in general, the chemical resistance of plastic-bonded, injection-molded SmFeN magnets is determined by both the plastic matrix and the magnetic filler. Magnets with polypropylene (PP) as a carrier material have significantly better water resistance than PA-bonded magnets.However, use in water must be tested on a case-by-case basis.