EMS-Grivory Grilamid® L 20 A Z is an unplasticized polyamide 12 supplied for injection moulding and thin-wall/profile extrusion. In fuel vapour line extrusion, the dried pellets are fed to a 45 mm single-screw extruder with an L/D ratio of 30:1, a barrier-flight screw, and a compression ratio between 2.8:1 and 3.2:1. Barrel set points are typically 220 °C in the feed zone, 230 °C to 240 °C in the compression zone, and 245 °C in the metering zone; adapter and die temperatures are held at 240 °C to 250 °C. The melting peak of the resin under differential scanning calorimetry, measured according to ISO 11357-3:2018, lies near 178 °C, and the dry density is approximately 1.01 g/cm³ per ISO 1183-1:2019. Drying is mandatory: pellets exposed to relative humidity above 60 % for more than 24 h must be dried in dehumidified-air equipment at 80 °C for 4 h to 6 h, with a dew point of -30 °C or lower, to bring residual moisture below 0.10 wt%. Moisture above 0.12 wt% causes hydrolysis in the melt, reducing relative viscosity and producing microvoids that lower burst strength after long-term hot fuel exposure. Melt temperature must not exceed 250 °C; at 260 °C and above, chain scission becomes measurable as increased melt-flow rate, yellowing, and gel particles retained on a 100 µm screen pack. A 120/80/40 mesh pack is positioned before the breaker plate to capture degraded polymer fractions and contaminants, with normal pressure drop of 8 MPa to 14 MPa; filter blinding is indicated when pressure drop exceeds 18 MPa. Mono-wall tube wall thickness for gasoline and diesel vapour return lines is commonly 1.0 mm to 1.5 mm, with vacuum calibration at 0.06 MPa to 0.08 MPa. The first quench bath is maintained at 20 °C to 30 °C and a second annealing bath at 50 °C to 60 °C, because unannealed PA12 tube retains orientation and may exhibit axial shrinkage above 0.3 % during later thermal exposure. Compliance is evaluated under SAE J2260 or an OEM-specific derivative, and long-term strength regression follows ISO 9080:2022 at 80 °C and 100 °C in the relevant fuel simulant. Service incompatibilities include concentrated sulfuric acid, formic acid, m-cresol, and hot polar solvents; aliphatic hydrocarbons, diesel, lubricating oils, and zinc chloride solutions are generally tolerated, but methanol-rich blends above 15 % by volume at temperatures above 60 °C require lot-by-lot qualification.

What limits the zero-defect ovality window in PA12 air brake tubing?

Air brake tubing for commercial trucks and trailers is extruded from Grilamid® L 20 A Z as mono-wall product in outside diameters of 6 mm, 8 mm, 10 mm, 12 mm, and 16 mm. The governing installation document is SAE J844, with dimensional and marking requirements referenced to ISO 7628-1:2018 and performance criteria to ISO 7628-2. Ovality control is the primary production conflict: at the 8 mm OD size, post-die ovality above 0.10 mm is rejected at final gauge inspection because coiled tube with residual ovality exhibits asymmetric wall stress and reduced cold-impact resistance. The vacuum calibration tank operates at 0.05 MPa to 0.07 MPa, with the first water bath at 18 °C to 25 °C and the second bath at 45 °C to 55 °C to relax orientation. Melt temperature is held at 225 °C to 245 °C, and the die is set at 235 °C to 245 °C. Below 220 °C, melt fracture appears on the inner wall as rough circumferential ridges; above 250 °C, oxidative degradation may reduce burst pressure retention after 1,000 h at 100 °C in ISO 7628-2 hot-oil or hot-air testing. Residual moisture must remain below 0.10 wt%; at 0.12 wt% or higher, steam release creates microvoids that reduce the 20 °C burst pressure by more than 10 % relative to dry resin. The finished tube is conditioned and checked for impact at -40 °C, with no fracture permitted. Post-extrusion coil winding must be performed only after the tube surface temperature has dropped below 40 °C to avoid permanent flat spots at the coil core.

Quick-connect fittings and snap-fit connector bodies from unfilled PA12 require a different processing boundary than continuous tube extrusion. The resin is plasticized in a reciprocating screw with L/D between 18:1 and 22:1, compression ratio between 2.5:1 and 3.0:1, and shot size between 30 % and 70 % of barrel capacity to limit residence time. Barrel temperatures from feed to nozzle are 220 °C, 235 °C, 245 °C, and 250 °C, with the hot runner manifold held at 245 °C and valve-gate tips at 250 °C. Thin snap arms of 0.8 mm wall thickness demand fill times of 0.3 s to 0.8 s; slower filling leads to premature gate freeze at the 0.8 mm valve gate and short shots in the flexible arm. Holding pressure is 60 MPa to 80 MPa for 5 s to 8 s, followed by screw rotation with low back pressure of 1 MPa to 3 MPa. Mould temperature is set between 40 °C and 80 °C; at the lower boundary, as-moulded PA12 may become too brittle for snap-fit engagement after -40 °C conditioning, while at the upper boundary cycle time increases by 10 % to 15 % and ejection may be impeded on polished cores. Shrinkage is measured per ISO 294-4:2018: for a 2 mm plaque, unfilled PA12 typically shows in-flow shrinkage of 0.8 % to 1.1 % and transverse shrinkage of 0.9 % to 1.3 %. Initial tooling for connector housings uses a 1.1 % cavity allowance. After conditioning at 23 °C and 50 % RH per ISO 291:2008, a 60 mm long connector body typically shows linear dimensional change below 0.05 mm after 168 h, whereas a PA66 part of similar geometry may move 0.15 mm to 0.20 mm. This low moisture uptake stabilizes snap-fit retention and electrical clearances, but continuous exposure to engine coolant at 120 °C for 1,000 h must be qualified separately because glycol and organic-acid inhibitors can plasticize the surface layer by 0.1 mm to 0.2 mm.

Loose Tube Buffer Extrusion: Filtration Pressure and Post-Extrusion Shrinkage

Optical fibre loose tube buffering uses Grilamid® L 20 A Z as a thin-wall protective jacket around gel-filled fibres at line speeds from 250 m/min to 600 m/min. The melt passes through a 30 µm to 60 µm screen pack because any gel particle above 60 µm can create local wall-thickness variation that translates into microbending attenuation under temperature cycling, as specified in IEC 60794-1-22. The single-screw extruder is usually 30 mm to 45 mm in diameter with L/D of 24:1 to 30:1; barrel temperatures are set at 210 °C, 225 °C, 235 °C, and 240 °C, with the crosshead die at 240 °C. Vacuum calibration at 0.04 MPa to 0.06 MPa and water at 20 °C to 35 °C locks outside diameter to a tolerance of ±0.025 mm on a 2.0 mm tube. Post-extrusion shrinkage is measured on a 100 mm sample after 2 h at 85 °C; shrinkage above 0.5 % tightens the loose tube around the fibre bundle and degrades excess fibre length, normally maintained at 0.05 % to 0.15 %. Moisture in the pellets above 0.10 wt% cannot be tolerated because steam bubbles in the thin wall produce intermittent diameter spikes and local thinning. Thermal-oxidative stability is evaluated per ISO 188:2011 at 150 °C for 1,000 h, with tensile elongation at break required to remain above 50 % after conditioning. The main process conflict is residence-time compression at high line speed: at 600 m/min and a barrel capacity of 10 kg, residence time can drop below 120 s, leaving unmelted skins if the screw lacks shearing elements. A Maddock mixer with 1.0 mm to 1.5 mm clearance is therefore specified; plain metering screws are not suitable for this thin-wall process.

For subsea hydraulic control line sheathing, Grilamid® L 20 A Z is applied as the outer jacket over seam-welded or seamless stainless steel tube bundles. The jacket is extruded through a crosshead die in pressure-tooling configuration because adhesion to the steel substrate is not required and the jacket must remain removable at termination points. Melt temperature is controlled at 230 °C to 250 °C, and die geometry is selected to achieve a wall thickness of 1.0 mm to 1.5 mm. The line is cooled in a water trough at 10 °C to 20 °C, then spark tested at 10 kV to 15 kV for pinhole detection. Water absorption of PA12 at saturation is approximately 1.5 % per ISO 62:2008, and flexibility is retained at -20 °C, which is relevant for deployment over sheaves. Published data for this specific configuration under API 17E and ISO 13628-5 is limited, so each jacket lot must undergo tensile adhesion, abrasion, and UV ageing tests defined by the umbilical supplier. The principal service boundary is high-temperature creep: above 65 °C, unfilled PA12 jacket softens and can deform under clamp forces above 2 kN, requiring a reinforced grade or increased wall thickness. Pre-drying follows the same 80 °C, 4 h dry-air procedure; lot-to-lot variation in pellet moisture after sea-freight container handling has been observed to raise extrusion pressure by 5 % to 10 % if re-drying is omitted.

When Connector Housings Demand Moisture-Independent Dielectric Stability

Electrical and electronic connector housings use unfilled PA12 when dimensional change from humidity is more critical than short-term heat deflection temperature. The comparative tracking index of unfilled PA12 is typically reported in the 600 V class under IEC 60112:2020, but the exact value depends on the colour package and lubricant additive batch, and the supplier laboratory report is mandatory for each lot. Injection moulding is performed at melt temperatures of 230 °C to 250 °C and mould temperatures of 40 °C to 80 °C, with pellet drying at 80 °C for 4 h; residual moisture must remain below 0.10 wt% to prevent silver streaks near thin latch features. Dielectric strength measured according to IEC 60243-1:2013 on 1.0 mm specimens is typically in the range of 25 kV/mm to 35 kV/mm, but this value degrades after condensation cycling described in IEC 60068-2-30:2005. The application boundary is continuous service above 90 °C: creep under connector mating forces exceeds 0.5 % strain in 1,000 h when loaded above 10 MPa at 90 °C, as indicated by tensile creep curves per ISO 899-1:2015. Such designs require a glass-filled polyamide or PBT grade instead. The resin should not be used in contact with strong mineral acids or with salt spray containing high concentrations of oxidizing chlorides for more than 1,000 h unless additional corrosion-protective measures are applied to the metal contacts.