Air-cooled extrusion blow moulding of HDPE 97B on accumulator-head machines with 20:1 to 24:1 L/D single-screw extruders is normally conducted with rear barrel zone set points of 165 °C to 175 °C, compression zones at 180 °C to 190 °C, and plastication zones at 185 °C to 195 °C. The melt temperature measured with an infrared pyrometer at the die exit is controlled within ±2 °C to limit parison length variation below 1.2% across a 55 s cycle. For a 120 L tight-head industrial drum with nominal wall thickness of 1.8 mm and a projected area of approximately 0.35 m², clamp force is maintained at 700 kN to 900 kN; closure speeds below 40 mm/s are used because faster flash pinch-off compresses the melt bead to less than 0.4 mm and produces stress cracking at the chime under the 1.2 m drop test of UN packagings. Parison sag resistance is verified by extruding a 450 mm open-hang parison and recording neck-down against the die gap at 12 s and 20 s; HDPE 97B maintains hang times above 12 s at 190 °C, but reprocessed regrind above 8 wt% can reduce sag time by 2 s through viscosity loss, especially when the regrind contains cast-film fractions with lower molecular weight. Blow pressure is set at 0.6 MPa to 0.9 MPa and held for 18 s to 25 s before exhaust, while mould cooling water enters at 8 °C to 12 °C to keep part shrinkage below 0.8% when measured by ASTM D955-21. Moisture on regrind is controlled by a dehumidifying hopper dryer operating at 80 °C for 2 h whenever storage relative humidity exceeds 60%; surface splay from wet regrind is routinely mistaken for resin degradation but disappears after drying.

What Limits Sheet Gauge Uniformity in Heavy-Gauge Thermoforming?

Coextruded or monolayer HDPE 97B sheet produced on a single-screw extruder with a 30:1 L/D barrier screw and a flexible-lip flat die is typically run at melt temperatures of 190 °C to 210 °C and roll-stack temperatures of 75 °C to 90 °C on the matte finish roll to reduce sheet curl. Sheet gauge uniformity for a 4 mm to 8 mm blank is held within ±1.5% across a 1600 mm width by adjusting the die lip gap at 25 locations; processors rely on an online beta or X-ray gauge connected to a 10 Hz closed-loop controller because manually measured cold sheet samples lag the process by 4 min. Oven zone temperatures in the thermoforming stage are set from 260 °C to 320 °C and the sheet surface temperature is checked with a pyrometer at 165 °C to 175 °C immediately before transfer; lower surface temperatures cause plug-assisted thinning at the corners of a 300 mm deep draw, while higher temperatures produce blistering and webbing in the clamp frame. The sag depth of a 900 mm square blank is limited to 60 mm by controlling top and bottom oven bank output independently; plug displacement speed is reduced to 120 mm/s on parts with draw ratios above 1:1 to reduce material tearing at the screen or grid apertures. Differential shrinkage and warpage after forming are evaluated by conditioning the part at 23 °C and 50% RH for 24 h and measuring dimensional change to ASTM D2732-14; values above 0.6% typically indicate excessive residual stress from too-cold sheet regions or forced ejection. For food-contact trays, the formulation must satisfy 21 CFR 177.1520 olefin polymer requirements including n-hexane extractives below the specification limit; processors retain CofA documentation confirming the base resin and any masterbatch comply with the specific use condition from 40 °C to 80 °C.

When HDPE 97B is extruded into solid-wall drainage and cable duct pipe through a grooved-feed single-screw extruder at 28:1 to 32:1 L/D, the barrel temperatures are depressed to 180 °C in the grooved feed section to prevent premature melting in the pressure wedge, while the downstream zones are raised to 200 °C to 215 °C to reduce spiral-mandrel weld lines. A gear pump is inserted between the screw tip and the pipe die to hold melt pressure fluctuation below 0.2 MPa, because wall-thickness variation in the 3 mm to 6 mm wall range is amplified by 3% for every 0.4 MPa pressure surge. Vacuum calibration tank pressure is set at -0.03 MPa to -0.05 MPa, and the tank water temperature is staged from 25 °C to 15 °C over 4 m of cooling length to avoid vacuum plate marking on the hot surface. HDPE 97B requires no pre-drying in pipe extrusion at ambient relative humidity below 50%, but regrind from edge trim above 20 wt% should be dried at 80 °C for 2 h to prevent microvoids in the inner wall. Long-term ring stiffness for buried drainage pipe is measured according to ISO 9969:2016 at 23 °C; a typical 6 mm wall structured pipe may show SN4 classification when the elastic modulus exceeds 800 MPa under short-term loading, but published data for this specific HDPE 97B formulation is limited and must be validated by the pipe producer. Pressure pipe applications require hydrostatic design basis testing per ASTM D2837-15; HDPE 97B should not be substituted for a PE100 or PE4710 material without long-term pressure regression at 80 °C and confirmation of the minimum required strength on the actual pipe line.

For thin-wall blow-moulded bottles below 2 L, conventional shuttle machines with 18 mm to 25 mm flash gaps produce acceptable parts, provided melt temperature at the die is held between 175 °C and 195 °C and the mould cooling water stays at 10 °C to 15 °C.

Blow-Moulded Agricultural Sprayer Tanks and Automotive Fluid Reserve Bottles

For hollow parts with complex three-dimensional parting lines, the pinch-off land geometry is specified at 0.3 mm to 0.5 mm depth and 2 mm to 4 mm width to remove flash without excessive weld flash inside the article. On automotive windshield washer reservoirs, the extrusion-blow process uses HDPE 97B with a carbon-black masterbatch at 2.0 wt% to 2.5 wt%, because the UV stabilizer package in the natural resin is not sufficient for engine compartment exposure above 1000 h under SAE J2527. ESCR performance is checked on the moulded article by notching the pinch-off seam and exposing samples to 10% Igepal CO-630 at 50 °C per ASTM D1693-21; F50 values above 100 h are typical for unpigmented HDPE 97B at 0.35 mm notch depth, but welds are weaker than the base material and may fail before 80 h if the parison was stretched below 1.3:1 drawdown ratio. Screw speed on the extruder is limited to 40 rpm to 60 rpm on a 90 mm barrel to avoid shear heating above 215 °C; a melt screen pack of 20/40/80 mesh is placed behind the die to remove regrind gels and weld the melt stream before the parison head. The extruder head is purged with high-viscosity HDPE after colour changes rather than with acrylic purge compounds, which can leave amine residues that produce odour in potable-water tank liners.

In extrusion of thick welding rod used for tank liners and chemical duct, HDPE 97B is shaped through a heated crosshead die at 180 °C to 200 °C and drawn to a 3 mm or 4 mm round profile with a haul-off ratio of 1.2:1 to 1.5:1; drawing above 1.6:1 introduces die swell memory that causes irregular bead shape when the rod is later fused by hot-gas welding at 280 °C to 340 °C. The melt index of the rod must track the sheet substrate within 0.05 g/10 min to ensure uniform fusion flow; a mismatch larger than 0.1 g/10 min between rod and sheet produces underbead notching at the weld root. Weld integrity is evaluated by a short-term tensile test across the joint per DVS 2203-5 and by a bend test at 180° over a 10 mm former; cracks at the weld interface indicate incomplete plasticization, which is corrected by raising the hot gas temperature in 10 °C increments. Published data for this specific configuration is limited; field results on polyethylene tank fabrications show acceptable weld factors of 0.8 to 0.9 only when the rod is cut from the same HDPE 97B lot as the parent sheet.