LATI LATAMID 12 H FE85 is a heat-stabilized polyamide 12 molding compound filled with approximately 85% ferrite by weight. The material is classified as a magnetizable thermoplastic for injection-molded bonded magnets, specifically for parts requiring moderate magnetic flux density, high electrical resistivity, and dimensional stability in humid environments. Typical geometries include multipole rotor rings, encoder disks, speed-sensor target wheels, and position-sensor inserts in automotive or appliance actuators. The polyamide 12 matrix differentiates the product from ferrite-filled PA6 and PA66 compounds because it absorbs less moisture under equilibrium conditions, as characterized by ISO 62, and it can be processed at lower melt temperatures. In production, the high filler loading requires abrasion-resistant barrel and screw materials because ferrite particles accelerate wear in conventional nitrided steel units. The compound is not magnetized in the feed state; it is magnetized after molding in a capacitor-discharge fixture that applies a defined field pattern to the part.

High-ferrite filler content and injection-unit wear

The 85% ferrite loading produces a compound with a density above 3.2 g/cm³ when measured according to ISO 1183-1. This places the material among the high-specific-gravity thermoplastic compounds; the density value depends on the ferrite type, coupling system, and measurement temperature. In injection molding, the compound develops higher melt viscosity than unfilled polyamide 12. Screw recovery times and filling pressures therefore increase, and the abrasive filler makes a bimetallic barrel, hardened screw, and hardened check ring necessary. Published data for this specific configuration is limited regarding detailed rheology; however, production-scale settings on machines from 80 to 250 metric tons clamp force commonly require reduced screw speed, low compression ratio, and low back pressure to avoid excessive shear heating. A general-purpose screw with an L/D ratio of 18:1 to 24:1 is typically employed, with continuous hardened flight lands. The barrel heaters should be profiled so that the melt temperature measured at the nozzle is between 200 °C and 240 °C. Melt residence time should be kept below 10 minutes at the upper end of the range to prevent polyamide 12 matrix degradation; lower barrel profiles are preferred if the shot size is small relative to machine capacity.

At ambient relative humidity above 60%, the dried compound should be transferred to the machine through closed conveying or a hopper dryer, because surface moisture pickup can occur within minutes and affect molded-surface quality. The use of open hoppers in unconditioned molding rooms is not advisable for this filler class.

Mechanical property measurements on the compound should be performed on dry-as-molded specimens because moisture reduces the apparent modulus. Class-level tensile modulus values for ferrite-filled PA12 are generally in the range of 10,000–14,000 MPa under ISO 527-1/-2; the reported value is sensitive to filler particle size, coupling, and specimen thickness. Charpy impact strength is lower than unfilled PA12 due to the high filler content, and the fracture surface typically shows brittle behavior. Notched Charpy tests under ISO 179-1/1eA are suitable for ranking grades, but the actual component should be tested in the magnetized state because the brittle failure mode of a ring under shock is not captured by small coupon data.

Weld-line strength is the principal molding conflict in magnetizable rings. With the high ferrite content, weld lines formed after core pins can show a reduction in tensile strength of more than 30% relative to weld-free specimens when tested under ISO 527-1/-2. The precise retention is governed by gate position, melt temperature, and mold temperature, not solely by the base polymer. In multipole rings, the weld line should be placed away from the magnetic sensing band or in a pole transition zone where the local flux density is inherently low. Increasing mold temperature to 80–100 °C improves weld-line mixing and surface knit-line visibility. Sequential valve gating or a diaphragm gate is preferred for rings above 50 mm diameter to maintain a single advancing melt front and reduce the number of weld lines.

What limits dimensional stability in humid sensor applications?

Water absorption is the primary limitation in magnetizable polyamide compounds intended for air-gap-sensitive magnetic sensors. According to ISO 62, unfilled polyamide 6 absorbs approximately 2.8–3.2% moisture at 23 °C and 50% relative humidity, while unfilled polyamide 12 absorbs less than 1% under the same exposure. In the LATAMID 12 H FE85 system, only the 15% polyamide 12 matrix is hygroscopic; the ferrite filler does not contribute to moisture uptake. The equilibrium moisture gain of the compound is therefore proportionally reduced, which reduces hygroscopic expansion and the associated growth of a rotor outside diameter. This behavior is critical in multipole rings where the magnetic air gap between the ring and Hall sensor can be on the order of 1–3 mm; a diameter shift of even 0.1% alters the field magnitude detected by the sensor. Dimensional change is measured according to ISO 294-4 shrinkage procedures or ISO 1110 conditioning followed by length measurement; production trials should establish the specific post-molding dimensional stabilisation step required for the use environment.

When the part is moved from a dry mold to a 50% relative humidity environment, moisture diffuses into the matrix over several days. The diffusion rate is controlled by the polyamide 12 phase, but the high filler loading reduces the proportion of the matrix available for water sorption. In production, parts are often conditioned in a controlled cabinet at 23 °C and 50% relative humidity before magnetic field application because dimensional changes after magnetizing can alter pole geometry. If the application is exposed to condensing humidity or continuous water immersion, the compound should be evaluated for property retention under ISO 175 or ISO 62 water-immersion conditions. Published data for this specific LATI grade under long-term water immersion is limited; qualification testing on the finished magnetized part is required.

Moisture absorption plasticizes the PA12 matrix and reduces stiffness, but the magnetic remanence and coercivity of the ferrite filler are not governed by matrix moisture. The primary moisture-related risk is dimensional growth and possible loss of interference fit on a metal shaft. Tests according to ISO 62 at 23 °C and 50% relative humidity can be coupled with radial deformation measurements to predict sensor air-gap changes. If the ring is press-fitted onto a steel hub, the hygroscopic expansion of the plastic ring may reduce press-fit retention; expansion allowance should be included in the hub design.

Magnetizing the molded component after ejection

The as-molded compound is not in a magnetized state. Magnetization is performed in a capacitor-discharge magnetizing fixture that generates a pulsed magnetic field through a copper coil formed around the part. For ferrite-filled thermoplastics, the peak field required to achieve practical saturation is higher than the intrinsic coercivity of the ferrite filler; production fixtures generally use peak fields above 800 kA/m to compensate for air gaps and coil resistance. The required field is validated by measuring the resulting hysteresis curve on a toroidal or cylindrical test body according to IEC 60404-5. Magnetic remanence and coercivity are not uniform across all pole geometries; they depend on pole count, wall thickness, fill orientation, and peak current. Published data for this specific configuration is limited, so magnetizing fixture design and operating voltage should be determined through DOE trials on molded dummy rotors.

Flow-induced filler orientation creates an additional process conflict. Platelet-shaped ferrite particles align along the flow direction in the fountain-flow region, producing higher remanence in the flow direction than in the transverse direction. For a radially magnetized ring, this anisotropy distorts the magnetic pole symmetry. The mold should fill radially from a central diaphragm gate to orient flow lines in the radial direction. The anisotropy ratio can be measured after molding by comparing hysteresis loops obtained on toroidal coupons magnetized in the radial and axial directions according to IEC 60404-5. If the application requires near-isotropic magnetic behavior, a multi-gate cold-runner layout should not be used unless melt-front convergence is deliberately managed.

Because the binder is a thermoplastic and the ferrite particles are electrically insulating relative to metal magnets, the compound exhibits high electrical resistivity. This reduces eddy-current heating in alternating magnetic fields and makes the material suitable for some speed-sensor applications operating at excitation frequencies above 1 kHz. The electrical resistivity should still be measured according to IEC 62631-3-1 if the part will be located near a coil or if the application demands low losses. The mechanical properties after magnetization do not change appreciably; however, magnetization fixture clamping forces should be controlled to avoid fracturing thin-walled rings during the magnetic pulse.

When PA6 magnetizable grades are replaced in actuator sensor rings

Compared with ferrite-filled PA6 or PA66 systems, the PA12 base gives the LATAMID 12 H FE85 material a lower moisture uptake, a lower processing temperature, and a lower modulus at equal filler loading. The trade-off is a lower heat deflection temperature; the continuous use ceiling of ferrite-filled PA12 is generally below that of ferrite-filled PA66 or PPS. If the replacement involves a sensor ring operating above 120 °C continuous, thermal aging and creep testing under ISO 75-1/-2 or ISO 899-1 should be conducted because PA12 matrix softening can reduce the mechanical stability of the magnetized ring. In under-hood automotive actuator sensors with continuous temperatures below 100 °C and high relative humidity, the PA12 system often provides lower post-molding dimensional drift than PA6 grades. The material also processes at melt temperatures roughly 30–50 °C lower than ferrite-filled PPS, which allows water-heated molds and reduces energy input, but it cannot match PPS in continuous-use temperature or chemical resistance to hot transmission fluids.

Values in the table are representative class ranges drawn from public materials databases and are not guaranteed product values; the current LATI technical datasheet should be consulted for release specifications. The comparison demonstrates the position of ferrite-filled PA12 between higher-temperature PPS ferrite grades and higher-energy NdFeB-bonded systems.

Relative to a ferrite-filled PA6 grade of the same filler content, the LATAMID 12 H FE85 system typically exhibits lower water absorption and slower mold shrinkage ratio, but also a lower heat deflection temperature. Relative to a ferrite-filled PPS compound, it offers lower processing temperature and reduced barrel wear, but cannot match continuous-use temperature or hot fluid resistance. Relative to an NdFeB-bonded PA12 compound, it provides lower magnetic remanence and lower cost but higher electrical resistivity and no rare-earth supply dependency. These differences are not absolute; they are governed by the specific filler surface chemistry and coupling package. A direct substitution therefore requires revalidation of the air gap, press fit, pole pattern, and environmental aging profile rather than a simple material swap.

In automotive transmission and engine-compartment environments, the material must withstand hot oil and humidity cycling. Polyamide 12 has good resistance to hydrocarbon oils and greases, but strong acids, hot glycol-containing coolants, and oxidizing agents can degrade the matrix. Chemical resistance should be evaluated according to ISO 175 using the actual fluid and temperature profile. Under hot oil above 120 °C, the PA12 matrix may soften and allow creep under interference-fit loads; the design should be subjected to thermal aging at the upper use temperature with the magnetized part in place on the shaft. For under-hood sensors where temperature spikes above 120 °C are brief, short-term exposure can be acceptable, but continuous use near the ceiling requires confirmation by ISO 75-1/-2 or tensile creep data.

The LATI LATAMID 12 H FE85 compound is available as a raw material for injection molding; compliance with specific regulations such as REACH, RoHS, and automotive OEM material specifications depends on the final article and the production supply chain. Ferrite-filled polyamide 12 is generally not intended for direct food contact unless the grade is explicitly certified against FDA 21 CFR or EU 10/2011 conditions. The end user must verify migration limits and extraction conditions on the finished part, because the high filler content can influence surface roughness and cleanability.

Tooling for the ferrite-filled PA12 compound should avoid long flow paths from small gates. Because the filler increases viscosity, weld lines can form behind core pins in multipole rings; gate location should be selected so that the weld line is placed away from the sensor-active pole zone. Hot-runner systems must use hardened valve pins and nozzle tips because ferrite accelerates wear in shutoff gaps. Mold venting is required at the end of fill; vent depth below 0.02 mm on the parting line prevents flash while allowing gas escape. Ejection systems should address the high density of the material, which increases part weight and can require larger ejector pin area to avoid surface marking. After ejection, parts should be placed on non-magnetic work holders if they are magnetized in a subsequent operation to avoid distortion of the magnetic pattern.

For applications that demand tight magnetic pole registration, the molded part should be inspected using a Hall-sensor scanning fixture or flux density map after magnetization. This inspection is not described by a single international standard; it is usually defined by the end application according to the pole count and the allowable flux density tolerance.