For applications requiring a non-lead weighting compound with the chemical resistance of a long-chain polyamide, Avient Gravi-Tech™ GRV-NP-069-BMX Nylon 12 is supplied as a high-density injection-molding compound in which a polyamide 12 continuous phase carries a proprietary high-specific-gravity filler. The designation 6.9 g/cm³ represents the nominal density class of the grade and is measured on molded plaques by ISO 1183-1:2019, method A, or ASTM D792-20. The GRV prefix identifies the Gravi-Tech product family, NP identifies the polyamide base, and BMX is a supplier-configuration suffix that should remain part of the purchase specification because it controls filler, colour, and packaging configuration. The material is a thermoplastic feedstock, not a metal injection molding feedstock, and therefore requires no debinding or sintering.

• Base resin: polyamide 12
• Nominal specific gravity: 6.9
• Process category: injection molding thermoplastic
• Density test method: ISO 1183-1:2019, method A / ASTM D792-20
• Regulatory status: supplier RoHS and REACH declarations should be retained with the lot record

In comparison with unfilled polyamide 12, which exhibits a nominal density of approximately 1.01 g/cm³ under the same standard, the filled compound reduces the volume of polymer per unit mass and shifts melt rheology toward shorter flow lengths, higher apparent viscosity, and elevated screw wear. The high filler content also changes the failure mode: unfilled polyamide 12 typically yields ductile deformation, whereas the high-density compound exhibits low elongation and brittle or quasi-brittle fracture. Design stress should therefore be based on tensile and flexural data from the supplier lot certificate, not from generic polyamide 12 databases.

Does the 6.9 g/cm³ value represent filler loading or a nominal density?

In Avient’s Gravi-Tech coding, the numerical field is best interpreted as a nominal specific gravity rather than a direct statement of filler weight percentage. Two compounds with the same 6.9 g/cm³ target can use different filler systems with different base resin viscosity, particle size distribution, and coupling packages. The relationship between filler loading and compound density follows a volumetric additive model only when filler density and packing efficiency are known. Lot-specific density is determined after molding by water displacement per ISO 1183-1:2019, method A, because compression-molded plaque or injection-molded specimen geometry can influence internal void content. Published data for this specific configuration is limited where the filler type is proprietary; the supplier’s certificate of analysis is the controlling document for density, moisture, and rheological acceptance windows.

Before processing, moisture must be reduced to a target of less than 0.10% by weight because polyamide 12 undergoes hydrolysis in the melt at elevated temperature. The recommended starting condition for desiccant-bed drying is 80 °C for 4–6 h with a closed hopper and delivered air dew point of −40 °C or lower. Drying beyond 8 h at this temperature is generally unnecessary and may increase oxidation of surface additives, leading to darkening or surface deposit formation. Loss-in-weight or hopper-mounted moisture analyzers are not sufficiently precise for this compound; moisture should be verified by Karl Fischer titration according to ISO 15512:2019 or equivalent. If ambient relative humidity exceeds 60%, pellets from an open bag should be dried before use, and partially used containers should be resealed with desiccant.

Screw and barrel wear in metal-filled polyamide 12 compounding

Processing the material on a standard reciprocating screw with a general-purpose steel barrel is possible for short validation runs, but production campaigns require wear-resistant barrel and screw materials. The high-specific-gravity filler is abrasive; processing on a 25–35 mm screw with a 20:1–24:1 L/D ratio and a compression ratio of 1.5:1–2.5:1 is a practical starting point for medium-size parts. A bimetallic barrel with tungsten-carbide-lined feed throat and a hardened AISI H13 or equivalent screw with check-ring clearance of 0.05–0.10 mm are typical for sustained operation. Screw rotation should be kept in the range of 60–120 rpm; excessive screw speed raises melt temperature and increases abrasion. Shot sizes should occupy 30–70% of the barrel capacity to limit residence time and filler separation in the wear-prone transition zone. Production sites reporting rapid wear on standard nitrided surfaces should plan for spare screw and barrel refurbishment; exact wear rate depends on filler type, regrind fraction, and melt temperature.

When gate freeze time limits packing and density repeatability

Because the compound has higher thermal conductivity than unfilled polyamide 12 and a narrow melt-processing window, gate dimensions control how long the packing phase can compensate for volumetric shrinkage. In amorphous or lightly filled polyamide 12, gate seal time may be influenced mainly by part thickness and cooling rate. In this high-density formulation, the altered thermal diffusivity can shorten the effective packing window. The mold design should use a round or trapezoidal gate thickness of 50–75% of the adjacent wall thickness and a land length of 0.5–1.0 mm to delay freeze-off. If the gate freezes before the part reaches stable density equilibrium, pack-out is incomplete, leading to internal voids, sink at thick-section bosses, and shot-to-shot mass variation. Cold runner diameters should be full-round and not less than 5 mm for small parts and 7–10 mm for larger parts. Hot-runner systems with valve gates are preferred over tip-gated systems because the high-density filler increases wear at gate tips and may produce stringing. Venting of 0.01–0.02 mm depth at the last-to-fill regions is required to prevent burning caused by adiabatic compression of trapped air in a filled system with reduced gas permeability.

Typical uses for GRV-NP-069-BMX Nylon 12 are small-to-medium mass-loading components in consumer equipment, cosmetic packaging, eyewear, and luxury goods where a dense, metallic tactile response is required without secondary machining of a cast metal part. The polyamide 12 matrix provides lower moisture-driven dimensional movement than polyamide 6 or polyamide 66; this is relevant in humid environments. The compound can be overmolded or assembled with metallic inserts, but the difference in coefficient of linear thermal expansion between the high-density polymer and steel, aluminum, or brass must be accommodated with flexible snap geometry or mechanical fastening, not rigid adhesive bonds. When used as a balancing weight in rotating assemblies, the part should be designed with a center of gravity defined in the CAD model, and mold-flow simulation input should include filler-specific density and thermal properties rather than generic nylon 12 values. Shot-mass control is the primary process indicator for density consistency; a 0.1–0.2% shot-mass drift may be significant in a narrow balancing tolerance.

The comparison shows that GRV-NP-069-BMX Nylon 12 occupies a density range between reinforced engineering thermoplastics and sintered stainless steels. It is not a replacement for structural metal in load-bearing threads or high-cycle fatigue locations; however, it can eliminate secondary machining of small metal weights where the geometry includes thin ribs, snap features, or overmolded strain relief that would be costly in cast or sintered metal. The material’s density benefit is greatest when the part requires inertial mass rather than high tensile ductility, because the high filler fraction reduces ultimate elongation and notched impact relative to unfilled or glass-filled polyamide 12.

Mechanical test data must originate from molded specimens, not generic polyamide 12 databases

Design calculations should be based on lot-specific tensile, flexural, and notched impact data measured on ISO 294-1 or ASTM D3641 injection-molded specimens. Tensile properties are evaluated under ISO 527-2:2012, flexural properties under ISO 178:2019, and notched Izod impact under ISO 180:2019, type 1A, or ASTM D256. For a high-density, heavily filled polyamide 12, supplier-published or generic datasheet values are less useful than molded-specimen data because filler orientation, weld-line location, and cooling rate alter measured stiffness and strength. Published data for this specific configuration is limited; the supplier’s certificate of analysis should be obtained for the actual lot. As a general design boundary, elongation at break is expected to be lower than unfilled polyamide 12, with a transition from ductile to brittle behavior visible in notch-sensitivity tests. Sharp internal corners, knit lines, and gate vestige should be located away from primary load paths. The material is more suitable for compressive or inertial loading than for thin-section snap-fit arms requiring high strain.

In humid environments, the polyamide 12 matrix absorbs less moisture than short-chain polyamides, but the metal-filled compound can still undergo surface oxidation if filler particles are exposed by wear or machining. Exposure to strong acids, concentrated salt solutions, or hot water above 80 °C may hydrolyze the polyamide matrix. Solvent resistance to aliphatic hydrocarbons is generally good; oxygenated solvents, brake fluids, and methanol-containing fuel blends should be tested because small-molecule absorption can plasticize the polymer at the filler interface. Ultraviolet exposure can cause surface chalking and a slight change in metallic appearance; UV-stabilized black or painted parts show better retention. For outdoor applications, validation should follow ISO 4892-2 or ASTM G155 with colour and impact retention criteria.

Density verification, lot release, and Cpk control

Incoming material control for high-density compounds is driven by mass-per-molded-part rather than pellet density alone. The supplier’s certificate usually reports density by ISO 1183-1:2019, method A, melt flow by ISO 1133-1:2022, moisture by ISO 15512, and RoHS compliance by X-ray fluorescence screening or digestion analysis. For production, a balance in the 0.001 g resolution range should be used to weigh molded parts from stable cycles. A minimum of 20 consecutive cycles after process stabilization is used to calculate process capability indices for shot mass and critical dimensions. If the Cpk for mass falls below 1.33, the process may be producing density gradients from inconsistent pack, degraded material in the hot runner, or moisture variation. Density verification by water displacement on randomly selected molded parts should be performed at lot changeover and after any change in regrind ratio. Regrind use should be limited to 10–20% by weight unless process trials demonstrate stable density and surface appearance; higher regrind fractions increase the probability of filler-polymer separation in the hopper and higher shot-weight variability.

On a production line with a 60-ton hydraulic injection molding machine and a 22:1 L/D screw, short-shot, jetting, and gate blush have been observed when fill speed is set too high or the melt temperature is at the lower end of the processing window. The high-density filler reduces melt elasticity and can produce a rough flow front at shear rates above the recommended range. A medium-high injection velocity with a profiled speed that slows during final fill reduces jetting and vent erosion. The screw decompression stroke should be kept below 3 mm because excessive decompression draws air into the melt and produces surface splay. If splay appears, the first intervention is reducing decompression and verifying dryer dew point, not increasing melt temperature. In thin-wall counterweights below 1.5 mm, the material can exhibit premature gate freeze and density deficits at the last-to-fill regions; raising mold temperature to 80 °C and using sequential valve gating improves fill, but the exact setting is tool-specific. Published data for this specific configuration is limited; therefore, molding trials with scientific injection molding templates are recommended before locking production parameters.