Overmoulded encoder rings for wheel speed sensors are produced as multi-pole ring magnets that are inserted into a steel or stainless steel carrier. The active magnet track is injection moulded from Barlog Plastics KEBABLEND M FE 161101, a ferrite-filled PA12 compound. Brake corner demands include calcium chloride brine, wet road spray, and thermal cycling from -40 °C to 150 °C. The granulate is dried to a residual moisture below 0.1 % before plastication; higher residual moisture drives hydrolysis of the PA12 backbone and creates splay defects on the pole faces. The melt is processed in a screw machine with a shut-off nozzle, with melt temperature held between 240 °C and 260 °C. The tool temperature is set to 60–90 °C to improve ferrite particle wetting and reduce the formation of a non-magnetic skin layer. The filler loading is fixed by the compound supplier; the moulder adjusts only regrind content. For ABS encoder rings, regrind from sprues and runners is limited to 10 wt% of the shot mass to limit viscosity drift and pole-face contamination. A direct edge gate or film gate is positioned at the inner diameter; radial melt flow aligns the ferrite platelets in the polar direction and raises remanent flux after magnetization. The finished ring is pulse-magnetized after ejection with a multi-pole fixture that matches the pole count of the sensor target. Dimensional acceptance is referenced to ISO 294-4 shrinkage testing; ferrite-filled PA12 compounds in this density class generally show a mould shrinkage of 0.6–1.0 %, but the production tool must be used to validate anisotropic shrinkage because gate location and wall thickness change the value. Automotive compliance is anchored to IATF 16949:2016 process control, REACH Regulation (EC) No 1907/2006 Article 33 SVHC communication, and RoHS Directive 2011/65/EU Annex II, with a 0.1 wt% homogeneous material limit for lead, mercury, hexavalent chromium, PBB, and PBDE; cadmium is limited to 0.01 wt%.

What Limits Torque Density in Magnetic Coupling Halves Moulded from Ferrite-Filled PA12?

Torque transmission in synchronous magnetic couplings depends on the maximum energy product of the magnet ring, the pole count, and the air gap between the two coupling halves. Ferrite-filled grades such as KEBABLEND M FE 161101 are selected when the magnet must withstand hot demineralised water, glycol brines, or mild chemical process fluids in sealless pump executions. The coupling half is injection moulded as a ring with either moulded pole projections or a smooth bore that is magnetized after assembly. The material is dried at 80 °C for 4–8 h in a desiccant dryer with a supply air dew point of -30 °C or lower. Melt temperature is limited to 240–260 °C, and the residence time at melt temperature must not exceed 8 min because prolonged heating reduces molecular weight and lowers mechanical retention of the ferrite particles. The compound is processed as supplied; the ferrite fraction is fixed, and melt blending with additional ferrite powder is not permitted. Regrind from the same grade is limited to 10 wt%. A melt cushion of 2–4 mm and a hold pressure of 450–700 bar are maintained; a cavity pressure drop below 350 bar before gate seal indicates inadequate packing and can leave voids behind the pole faces. The magnetizing fixture applies a field of 800–1000 kA/m to saturate the ferrite; incomplete saturation produces torque ripple and acoustic noise in the pump. The finished magnet is tested for flux density with a Helmholtz coil and for geometrical runout on a coordinate measuring machine. Compliance for the coupling assembly is referenced to ISO 2858 for dimensional interchangeability of end-suction pumps and IEC 60404-8-1 for hard magnetic material specification. REACH Article 33 and RoHS Annex II declarations are required from the compound supplier when the part is placed on the EU market. Published data for this specific product configuration is limited; the supplier datasheet must be consulted for the demagnetization curve and temperature coefficient of remanence.

In column-assist electric power steering, the torque sensor rotor is injection moulded as a thin-walled cylindrical magnet that is press-fitted onto a steel shaft. The PA12 compound is selected because the moisture saturation at 23 °C/50 % RH is approximately 0.7–0.9 wt% under ISO 62:2008, whereas PA6 reaches 2.6–2.9 wt%; lower moisture uptake limits dimensional drift and magnetic signal error. The rotor is moulded with three point gates equally spaced at 120° to create a uniform radial melt front; unbalanced filling or unequal gate vestiges produce sinusoidal encoder signal errors above 0.5° of mechanical angle. The filler loading is fixed by the compound supplier, and the processor only controls regrind ratio, which is limited to 10 wt% for torque ripple targets tighter than 0.3 N·m. The melt temperature is held between 245 °C and 265 °C, the mould wall is 70–95 °C, and screw decompression after plastication is set to 3–5 mm to avoid nozzle drool. The finished rotor is pulse-magnetized with 16 or 32 alternating poles; the pole count is defined by the magnetization head rather than the mould. The assembly is qualified under vehicle-level electromagnetic immunity testing per ISO 11452-2, and the material must be traceable to REACH Article 33 and RoHS 2011/65/EU Annex II restrictions for EU supply. Long-term dimensional stability is evaluated after accelerated conditioning per ISO 1110:2019; dimensional change of the magnet under hot-humid ageing may be below 0.1 %, but published data for this specific ferrite-filled PA12 grade is limited.

Magnetic Encoder Scales and Rotational Position Feedback for Industrial Servo Drives

Multi-track encoder rings for industrial servo motors use a two-track magnetic pattern with a separate reference track. KEBABLEND M FE 161101 is selected when the encoder operates at a read gap of 0.3–0.8 mm between the magnet surface and an MR or Hall sensor array. The ring is injection moulded with a tool temperature of 80–100 °C to slow the surface solidification rate; a lower tool temperature produces a resin-rich skin that shields the ferrite particles and reduces the magnetic field at the sensor face. The gate is located at the outer rim, forcing the melt to flow inward and orienting platelet-shaped ferrite particles tangential to the encoder track. Tangential orientation improves flux density at the sensor face and reduces edge harmonics. The filler content in the compound is fixed; the moulder adjusts only regrind concentration, which is kept between 0 wt% and 10 wt% to limit lot-to-lot viscosity drift. The process recipe is monitored with cavity pressure sensors; the in-cavity pressure at 0.5 s after velocity-pressure switch-over is held between 350 bar and 550 bar. A switch-over position that occurs too late creates flash on the track edges and distorts the pole-to-pole spacing. The encoder ring is pulse-magnetized after moulding with a reference track fixture and verified on a flux mapping stage that reports pole-to-pole pitch error. In industrial servo drives, the position signal may be used in a safety-relevant loop; compliance is evaluated at system level under IEC 61800-5-2:2016. The raw material marking follows DIN EN ISO 1043-1 for the PA12 matrix and the ferrite filler. SVHC communication under REACH Article 33 and restricted substance limits under RoHS 2011/65/EU Annex II apply when the magnet is supplied into the EU. The maximum continuous service temperature of the magnet is limited by the PA12 matrix; the supplier datasheet should be consulted for the specific thermal ageing curve.

Condensing boiler and dishwasher circulation pump rotors are overmoulded onto a graphite or ceramic shaft bearing. The PA12 ferrite compound is selected because the rotor runs in water-glycol or aqueous detergent media with a pH range of 7–9.5. The material absorbs less water than PA6 and demonstrates lower swell, which helps maintain the air gap between the magnet and the stator. The granulate is dried at 80 °C for 4–8 h to a residual moisture below 0.1 %; the dryer outlet air dew point is set to -30 °C or lower. The melt temperature is held between 235 °C and 250 °C, and the holding pressure is set to 350–500 bar. Hold time is extended until the gate seal reaches 95 %; premature release before gate freeze creates sink marks and axial runout above 0.05 mm on the bearing journal. The rotor is gated at the hub centre or through a ring gate to prevent weld lines crossing the active pole faces; weld lines reduce local remanence and produce unbalanced magnetic pull. The filler loading is fixed by the compound supplier; regrind from validated runners is limited to 10 wt%. The rotor is magnetized as a 4-pole or 6-pole permanent magnet and balanced by removing material from a designated balancing ring, not from the magnet poles. The compound is not recommended for continuous exposure to chlorinated water above 3 ppm free chlorine at elevated service temperatures because oxidative attack on the PA12 matrix may occur. Compliance for domestic appliances is anchored to EN 60335-1:2012+A2:2019 and RoHS 2011/65/EU Annex II; XRF screening is used to verify restricted substance concentrations on homogenized sections. Magnetic performance after water immersion at 60 °C for 1000 h should be measured, because matrix swelling can alter the air gap even though the ferrite filler is hydrolytically stable.

When Differential Shrinkage Demands Gate-to-Pole-Flux Alignment in Overmoulded Sensor Rings

Overmoulding a ferrite-filled PA12 ring onto a steel or stainless steel bush generates residual stress because the linear thermal expansion coefficient of the metal is approximately 11–13 × 10^-6 K⁻¹ while the magnet compound is 50–80 × 10^-6 K⁻¹. The stress concentrates at the axial edges and at gate marks. If the mould temperature is below 60 °C, the PA12 freezes rapidly against the metal and forms a low-elongation skin that cannot accommodate post-ejection shrinkage; a radial crack at the inner diameter often appears after the first thermal cycle from -40 °C to 120 °C. To prevent this failure, the steel insert is preheated to 100–120 °C and the tool is held at 80–100 °C. The melt temperature is kept at the low end of the processing window, 240–250 °C, to limit the enthalpy released into the tool. The gate is moved from the inner diameter to the outer diameter so that the melt front reaches the insert last; this sequence allows the compound to pack against the metal surface and form a compressive interfacial stress rather than a tensile stress. Injection speed is controlled at 80–120 mm/s; higher speed can push shear heating above 260 °C and degrade the PA12 near the gate, while lower speed creates a drooping melt front and air entrapment on the pole faces. Cavity pressure sensors record an in-cavity pressure of 400–500 bar; a pressure decay of more than 20 % before gate freeze indicates an undersized gate or premature switch-over. The moulded part is stress-relieved at 120 °C for 2 h in air and slow-cooled before pulse magnetization. The dimensional acceptance is checked on a coordinate measuring machine with a diametral runout limit of 0.03 mm and a flatness limit of 0.02 mm on the pole face. The filler loading is fixed by the compound supplier; regrind from the same family is limited to 10 wt% and is not used for first-production validation. Standards include ISO 294-3 for plaque shrinkage, ISO 527-2 for tensile properties, and IEC 60404-8-1 for hard magnetic material specification. Published data for this specific overmoulded configuration is limited; the residual stress should be validated by thermal cycling and crack detection on serial parts.

For automatic transmission electrohydraulic control units, the shift position sensor magnet is injection moulded as a small arc or cylindrical sleeve and pressed into a stainless steel bracket. The magnet operates in hot automatic transmission fluid at 90–130 °C; PA12 is selected because the polymer matrix resists hydrocarbon fluids and does not swell excessively in ATF. The material is dried at 80 °C for 4–6 h to a residual moisture below 0.1 %. The melt temperature is held between 240 °C and 255 °C, and the mould temperature is 70–90 °C. The component is moulded in an eight-cavity tool with a hot-runner valve gate; the gate vestige is kept below 0.05 mm because a large vestige on the pole face creates a local magnetic field distortion. Cavity-to-cavity fill weight variation must remain below 1.5 % to maintain consistent magnetic output. The filler fraction is fixed; regrind from clean sprues is limited to 10 wt%. The magnet is magnetized axially or diametrically after insertion onto the shaft, using a fixture field of 700–900 kA/m. The finished sensor magnet is subjected to a hot-fluid immersion screening at 150 °C for 500 h; the assembly is then checked for cracks, adhesion loss, and flux deviation. Compliance is anchored to REACH Article 33 and RoHS 2011/65/EU Annex II for EU market supply, and the part is supplied under PPAP documentation aligned with IATF 16949:2016 when used in automotive production. Published data for this specific product configuration is limited; the fluid compatibility and flux retention must be verified with the production fluid grade.