Coextruded fuel vapour return lines under SAE J2260 permeation limits

In fuel vapour return-line coextrusion, EMS-Grivory Grilamid L 22A W 40 X PA12-I is fed as dried virgin pellet to the outer and inner layers of a five-layer automotive fuel tube on a three-extruder line with a 45 mm main extruder and two 30 mm satellite extruders, each having a 30:1 L/D ratio and barrier screws. The resin is pre-dried in a closed-loop desiccant dryer at 80 °C for 4–6 h to residual moisture of <0.10 wt%; barrel temperatures are set in the 220–250 °C range, with the die head held at 250 °C. In this configuration, melt pressure before the spiral mandrel die is maintained at 12–18 MPa, and the vacuum calibration tank is operated at -0.08 MPa with water at 35–45 °C to prevent inner-diameter ovality. The layer distribution for an 8 mm OD tube with 1.0 mm wall thickness uses the unreinforced PA12 outer layer at 40–50 wt% of total wall mass, the PA12 inner layer at 10–20 wt%, a maleic anhydride-grafted tie layer at 10–15 wt%, and an EVOH barrier layer at 8–12 wt%. Where the outer layer is separately compounded, the base resin is used at 96–98 wt% with 2–4 wt% UV and heat-stabiliser masterbatch; where an electrostatic dissipative inner layer is specified, a carbon-black-filled conductive PA12 compound is used and this grade is not substituted in that conductive layer. The line operator must not introduce PA6 or PA66 regrind, because the higher melting point of those polymers creates unmelted particulate defects at the mandrel touchdown point. Industry compliance is assessed against SAE J2260, ISO 13775-1, and DIN 73378-1; dimensional stability after fuel immersion is verified according to ISO 62, tensile retention according to ISO 527-2, and elevated-temperature burst pressure according to the tubing specification’s heat-ageing programme. Downstream processing includes continuous vacuum calibration, corona treatment of the outer surface, laser diameter gauging at 0.01 mm resolution, spark testing at 15 kV, and post-extrusion annealing in a hot-air tunnel at 120 °C for 15 min to relieve orientation. Finished product types are straight fuel feed lines, vapour return lines, tank vent lines, and preformed hose assemblies with injection-moulded quick connectors.

Because compressed-air brake circuits on Class 6–8 commercial vehicles require extruded monolayer tubing that passes the SAE J844-2014 low-temperature impact, collapse-resistance, and boil-out oil-ageing requirements while retaining burst strength after 500 h at 125 °C, the resin is processed as the primary wall at 100% virgin pellet. A carbon black masterbatch is added at 2.0–2.5 wt% only for UV-stabilised coiled trailer line, and internal clean regrind from start-up and diameter-change scrap may be reintroduced up to 20 wt% after the same drying step. Drying is conducted at 80 °C for 6 h to maintain residual moisture below 0.10 wt%; moisture above 0.15 wt% produces microvoiding at the vacuum calibration zone and lowers burst retention at −40 °C. Extrusion is run on a 30–45 mm single-screw machine with a 30:1 L/D ratio, a grooved feed section, and a spiral mandrel die; a gear pump between screw and die holds melt pressure at 10–15 MPa to avoid surging. Vacuum calibration at -0.06 MPa to -0.09 MPa and a 40–50 °C water bath are followed by a post-shrink oven at 110 °C for 10 min. Compliance is demonstrated on finished tube to ISO 7628-1 and DIN 74324-1 where referenced by the OEM specification; ISO 1133-1:2022 melt mass-flow rate and ISO 527-2 tensile data are used for incoming lot-to-lot control. The terminal products are straight and coiled air brake tubes in 6 mm, 8 mm, 10 mm, and 12 mm OD, supplied in black, blue, and red identification colours.

Why does PA12 remain the pressure-sheath polymer in buried fuel gas distribution lines governed by ISO 17484-1?

Natural gas service lines in buried distribution networks operate with continuous hoop stress and must resist slow crack growth after decades of soil contact; polyamide 12 grades with controlled melt viscosity are extruded into solid-wall pipe because the polymer’s low water absorption reduces the plasticisation-induced creep divergence observed in PA6 at 50% relative humidity. In this application, EMS-Grivory Grilamid L 22A W 40 X PA12-I is used as the base resin in a gas-pipe compound at 92–95 wt%, with 5–7 wt% carbon black masterbatch for weathering resistance and 0.3–0.5 wt% of a heat-stabiliser package that does not contain plasticising monomers; yellow identification pigment is added at 1–2 wt% if required by the national grid specification. The pipe is extruded on a 60–75 mm single-screw pipe line with 30:1 L/D, a spiral mandrel die, and vacuum calibration at -0.03 MPa to -0.06 MPa; melt temperature is controlled at 220–245 °C, and barrel zones are not permitted to exceed 260 °C because above this limit thermo-oxidative degradation increases oxygenated chain ends and reduces slow crack growth resistance. Pipe samples are tested to ISO 17484-1 for dimensions, hydrostatic strength, and impact; creep rupture curves are verified to ISO 9080, and oxidative induction time to ISO 11357-6. The terminal product types are SDR 11 and SDR 13.6 gas service pipe coils and straight lengths from 20 mm to 63 mm OD, used for buried distribution laterals, meter risers, and repair couplings. Published data for this specific grade in larger-diameter transmission mains is limited.

On multi-cavity hot-runner tools with 16 or 32 cavities mounted in 80–120 tonnes hydraulic injection moulding machines, pneumatic push-in fitting bodies are produced from EMS-Grivory Grilamid L 22A W 40 X PA12-I using 25:1 L/D screws and reverse-taper shut-off nozzles. The material is pre-dried at 80 °C for 5 h; melt temperature is set to 240–260 °C, mould temperature to 65–75 °C, and holding pressure to 60–80 MPa for 1.2 s/mm of wall section. The formulation addition ratio in this sector is 100% virgin resin for pressure-bearing bodies; regrind from cold-runner scrap may be added up to 15 wt% provided it is dried and not derived from parts with visible burn marks or oil contamination. No external release agent is used, because stearate contamination on the collet lip can reduce interference-fit retention by 30% after 85 °C oil-air ageing. Compliance is carried out to ISO 14743 for push-in connectors and to the thread form and pressure-test clauses of ISO 228-1; tensile modulus and notched Charpy impact are measured on conditioned plaques to ISO 527-2 and ISO 179-1 as incoming lot checks. The moulded products are male stud elbows, swivel tees, straight unions, reducing connectors, and thread adaptors for compressed air systems supplied to packaging machinery, railway braking panels, and industrial robot gripper circuits.

When thin-wall halogen-free sheathing is required for engine-bay sensor cable

When engine-bay sensor cable harnesses are routed near exhaust manifolds, the sheathing must resist hot oil drip, short-term dry heat, and mechanical abrasion from metal clips while avoiding halogenated compounds that can corrode connector pins during thermal runaway. The grade is applied as a thin-wall extruded sheath at 100% resin for standard wall thicknesses of 0.25–0.60 mm; if a flame-retardant cable designation is required under OEM internal specifications, a halogen-free phosphorus-nitrogen masterbatch is incorporated at 5–10 wt%, and a colour masterbatch is added at 1–3 wt%. Drying is conducted at 80 °C for 6 h, because residual moisture in cable extrusion produces pinholes at draw-down ratios above 1.4. The sheathing is processed on a 45 mm crosshead extruder with a 24:1 L/D screw, melt temperature 225–245 °C, and cooling trough water at 20–30 °C; line speed is trimmed to maintain a 1.6–1.9 draw-down ratio and final sheath concentricity of ≥80%. Addition of amine-based heat stabilisers is not recommended in this process because amine diffusion can accelerate copper conductor oxidation. Compliance is evaluated to ISO 6722-1:2011 for road vehicle cables, with tensile retention after ageing tested according to ISO 527-2, cold impact at −40 °C, and hot water resistance according to ISO 62; the halogen-free status is confirmed by IEC 60754-1 and IEC 60754-2 if the harness specification calls for low acid-gas emission. The terminal products are engine-bay sensor pigtails, ABS wheel-speed sensor cables, gearbox connector harnesses, and industrial automation cables used in machine-tool environments.

Technical monofilament extrusion for paper-machine clothing and food-contact filtration mesh

Producing technical monofilament from this PA12 grade in diameters of 0.15–2.00 mm requires single-screw extruders of 30–45 mm, gear pumps, and multi-stage godet stands that impose a total hot draw ratio of 1:4.0–1:4.8 before annealing. The pellet feed is 100% resin with 0.1–0.3 wt% of a nucleating masterbatch to refine spherulite size and 0.3–0.5 wt% of a hydrolysis-resistant antioxidant package; no plasticiser is added because plasticiser migration reduces mesh dimensional stability in hot-air drying sections. Pre-drying follows the same 80 °C for 6 h schedule, and the melt temperature is limited to 225–245 °C. After the spinneret, filaments are quenched in a 25–35 °C water bath, drawn in 3 stages at 100–140 °C, and annealed at 150 °C under controlled shrinkage of 5–8%. For food-contact filtration, the monofilament mesh is evaluated to FDA 21 CFR 177.1500 and EU Regulation 10/2011 with migration testing specific to the final mesh structure, not to the pellet alone. The finished goods are paper-machine clothing seams, dryer screen monofilaments, belt filter mesh, sieve cloth for food processing, and screen printing fabrics. High-speed weaving trials indicate the main processing limitation is filament ovality above 0.03 mm if the quench bath temperature is not maintained within ±3 °C.