Plastic-bonded, injection-moulded magnets are typical composite materials that are created by embedding hard ferrite or rare earth magnetic powder in thermoplastic plastics (matrix material PA6, PA12, PPS). The proportion of the magnetic powder dictates the magnetic and mechanical properties.
The filling degrees of plastic-bonded, injection-moulded magnets vary between a magnet powder content of between 84% and 94% (percent by weight). The magnetic values are therefore below those of plastic-bonded, injection-moulded magnets. Plastic-bonded, injection-moulded magnets can be produced in complex shapes and in combination with insert parts - all in a single process.
A typical data sheet for a permanent magnetic material contains its key magnetic and mechanical characteristics. The magnetic characteristics are usually measured in accordance with DIN EN 60404-5. In addition to magnetic values, the data sheet also contains mechanical characteristics such as density, hardness and strength properties.
You can find all data at a glance here:
INJECTION-MOULDED HARD FERRITE MAGNETS
Polyamide 6 (PA 6), polyamide 12 (PA 12) and polyphenylene sulphide (PPS) are used as the plastic matrix in injection-moulded magnets. The maximum operation temperatures are dependent on the magnet and matrix materials. They are 160°C for qualities bonded with PA 6, 140°C for qualities bonded with PA 12 and 220°C for qualities bonded with PPS. As a result of the magnetic properties, the maximum operation temperatures may deviate from the values above.
The first stage of the production process of plastic-bonded, injection-moulded magnets is the production of the magnetic compound. This is done by mixing the plastic granulate and the magnetic powder in a hot melt kneading machine or a twin screw extruder before they are extruded and granulated. The next step is processing the compound with modified injection moulding machines. When injection moulding 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-moulded magnets, a mechanical machining of the finished injection-moulded part is generally not required.
Plastic-bonded, injection-moulded 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.
The magnetic characteristics of plastic-bonded, injection-moulded 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 +200°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.
The chemical resistance of plastic-bonded, injection-moulded 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
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