Magnet Encoder Rings in Wheel-Bearing Speed Sensors

Insert overmoulding of magnetically encoded rings onto steel wheel-bearing hubs for anti-lock braking systems forces the ready-to-mould PA12 compound to fill a thin ring channel over a heated steel insert without exceeding the 270 °C thermal exposure limit of the magnetically active filler system. Barlog Plastics KEBABLEND M 45/72 PA12 is metered at 100 wt% as supplied; production reclaim from sprues and rejected parts is limited to 10 wt%, and the reclaim stream must be dried to 0.10 % residual moisture per ISO 62:2008 before blending. Compliance for the finished encoder ring is governed by IATF 16949:2016 clause 8.3.4.1, PPAP Level 3, ISO 26262-5:2018 for an ASIL B wheel-speed signal chain, RoHS Directive 2011/65/EU Annex II, and REACH Regulation (EC) No 1907/2006 Article 33. The injection moulding process uses a four-cavity cold-runner tool mounted on a 1200 kN hydraulic clamp, with cylinder temperatures 220/240/250/255 °C, melt temperature 252 ± 3 °C, mould wall temperature 85 °C, injection speed 45 cm³/s, and hold pressure 70 MPa for 4.0 s; after demoulding the ring is magnetised in a capacitor-discharge fixture at 900 V with a 48-pole pattern. The terminal article is an active wheel-speed encoder ring integrated into the inboard side of a passenger-car wheel bearing, typically overmoulded as a black multipole ring with a face width of 2.5 mm and an outer diameter of 72 mm.

The 10-pole claw-pole stepper motor magnet in office automation equipment is driven by dimensional tolerance rather than maximum energy product, because out-of-roundness on the rotor outside diameter above 0.03 mm generates torque ripple and acoustic noise in the 400–1200 min⁻¹ operating range. Formulation addition is 96 wt% KEBABLEND M 45/72 PA12 with 4 wt% color masterbatch in PA12 carrier; no external lubricant is introduced because mould deposit formation on the 90 °C cavity surface increases ejection force and contributes to angular position error. The material is injection moulded in an 8-cavity cold-runner tool on an 800 kN all-electric machine using a 20:1 L/D screw and a hardened non-return valve. Standards applicable to the component are IEC 62368-1:2023 for audio/video, information and communication technology equipment, RoHS Directive 2011/65/EU Annex II, and REACH Article 33; magnetic property measurement follows IEC 60404-8-1:2015. Holding pressure is kept at 60 MPa for 2.8 s because longer holding at the 90 °C mould temperature causes overpacking at the gate and increases out-of-roundness after moisture conditioning to 0.3 % water content per ISO 62:2008. After demoulding, shot weight is monitored to ±0.3 % and parts are magnetised in a 10-pole fixture at 1100 V. The downstream terminal product is a bonded rotor magnet sleeve assembled into a printer or copier stepper motor with press-fit tolerances governed by dimensional stability limits on the customer drawing.

What Limits Flow Length in Seat-Mounted HVAC Actuator Feedback Magnets?

In HVAC actuator feedback magnets, the limiting parameter is the ratio of flow length to wall thickness because the ready-to-mould magnet compound must fill narrow rotor cavities around a brass shaft where design wall thickness can drop to 0.9 mm. For this part geometry, KEBABLEND M 45/72 PA12 is introduced at 100 wt% without regrind when the cavity includes walls below 1.0 mm; on thicker sections, up to 8 wt% regrind is reintroduced only after the lot has passed melt-flow verification within 12 % of virgin material per ISO 1133-1:2022. Compliance is managed under IATF 16949:2016 clause 8.4.2.3, ISO 26262-5:2018 for ASIL A climate-control actuation, RoHS Directive 2011/65/EU Annex II, and REACH Article 33; weld-line tensile validation follows ISO 527-2:2012. Injection moulding runs on an 800 kN electric machine with melt temperature capped at 245 °C because the magnetically active filler in this grade begins to exhibit irreversible thermal loss during prolonged exposure above 250 °C; mould temperature is held at 80 °C, injection speed is set to 80 cm³/s, and gate land length is maintained at 0.8 mm to limit shear heating. The terminal product is a two-pole or four-pole rotor with integrated feedback magnet for an automotive seat-mounted HVAC damper actuator.

When the magnet operates inside a wet-runner BLDC coolant pump, the material selection condition shifts from short-term magnetisability to retention of mechanical integrity after continuous immersion in a 50/50 ethylene glycol–water mixture at 110 °C and 0.5–1.5 bar system pressure. KEBABLEND M 45/72 PA12 is fed at 100 wt%; blending with PA6 or PA66 is not permitted because phase separation at the PA12/PA6 interface under glycol exposure reduces tensile strength retention below the 80 % limit measured per ISO 527-2:2012 after 1000 h. The relevant chemical resistance programme is ISO 175:2010 method A, with additional component-level endurance validation by the pump manufacturer under a 3000 h thermal cycle, because published data for this specific configuration is limited. The compound’s PA12 matrix is selected for low equilibrium moisture uptake, and the moulding operation uses a pre-drying step of 80 °C for 4 h to a residual moisture content below 0.08 %, followed by injection moulding around a stainless steel shaft with cylinder temperatures 230/240/245/245 °C, mould temperature 90 °C, hold pressure 55 MPa for 3.0 s, and a four-pole magnetising fixture at 1000 V. Automotive coolant pump programmes add IATF 16949:2016 clause 8.4.2.3 supplier quality obligations, while material restrictions follow RoHS Directive 2011/65/EU Annex II and REACH Article 33. The terminal product is a sealed rotor magnet assembly for EV thermal-management coolant circulation, in which the magnet is fully encapsulated and no exposed magnetically active filler edge is permissible.

If Anisotropic NdFeB Powder Demands Reduced Gate Shear and Orientation Field Control

Anisotropic bonded NdFeB systems for e-bike torque-sensor rings and industrial servo encoders require the ready-to-mould PA12 compound to behave as a low-viscosity carrier during cavity filling, because magnetic alignment of the filler must be preserved before the solidification front arrests particle rotation. KEBABLEND M 45/72 PA12 is fed at 100 wt%; adding 2 wt% external wax to increase cavity fill is not recommended because wax migration to the magnet surface disrupts the 0.7 T Halbach-array orientation field and reduces remanence repeatability by more than 3 %. Standards referenced for the component are IEC 60404-8-1:2015 for magnetic property classification, ASTM D638-14 for tensile property benchmarking, ISO 1183-1:2019 for density verification, and RoHS Directive 2011/65/EU Annex II plus REACH Article 33 for documentation. Processing is performed in an injection moulding machine equipped with a Halbach-array magnetising field assembly of 0.7 T inside the cavity, using a melt temperature window of 230 ± 5 °C, mould temperature 70 °C, injection speed 35–50 cm³/s, and gate land length 0.6 mm; above 235 °C the PA12 carrier viscosity drops and the melt-flow index exceeds 18 g/10 min per ISO 1133-1:2022, causing filler separation at the flow front. Published data for this specific configuration is limited; process validation on individual tool sets remains necessary because the demagnetising field at the cavity wall reduces alignment depth. The terminal product is a high-remanence multipole encoder ring for e-bike mid-drive torque feedback or a closed-loop industrial servo position sensor.

Post-Mould Flattening and Multipole Magnetisation of Linear Encoder Track Elements

Position feedback for automated guided vehicle steering and service robot joints uses injection-moulded linear magnet track elements whose pole-pitch accuracy after magnetisation cannot exceed 0.05 mm over a 1000 mm travel length, because magnetic encoder noise increases directly with pitch deviation. The compound is fed at 100 wt% Barlog Plastics KEBABLEND M 45/72 PA12, with 5 wt% regrind permitted only after moisture content is reduced to 0.08 % per ISO 62:2008; no fillers, binder resins, or processing waxes are introduced downstream. The applicable safety standard is ISO 13849-1:2023 for functional safety of machinery control systems, supplemented by IEC 60404-8-1:2015 for magnetic material classification, RoHS Directive 2011/65/EU Annex II, and REACH Article 33. Processing takes place in a 600 kN all-electric injection moulding machine with barrel temperature profile 215/235/240/245 °C, mould temperature 75 °C, injection speed 40 cm³/s, and holding pressure 50 MPa for 3.5 s; after demoulding the track element is flattened under a heated clamping fixture at 70 °C for 20 min and magnetised by a linear magnetising head with a pole pitch of 2.0 mm at 850 V. The terminal product is a magnetic track scale or ring segment for linear position feedback in automated guided vehicles, robot joints, or packaging machines.