Beijing Evergrow Resources UHMWPE ER-22 is a virgin ultra-high-molecular-weight polyethylene resin grade supplied as a free-flowing powder with a nominal molecular weight-viscosity signature that places it in the entangled-melt class. The grade is intended for compression moulding, ram extrusion, sintering, and certain press-forming routes; it is not suitable for conventional single-screw plastication or injection moulding unless the equipment is specifically adapted. Under ISO 1133-1:2022 at 190 °C/21.6 kg, the material shows no measurable melt mass-flow rate, so viscosity number according to ISO 1628-3:2010 is used for incoming inspection and lot traceability. Supplied certification commonly references food-contact status under US FDA 21 CFR 177.1520 and Regulation (EU) 10/2011, but conversion history and additive loadings require verification against each certificate of analysis. The product is sold as a natural grade without intentional release agents; converters should verify whether machining coolant or anti-static spray contains amine-based components, which can accelerate surface oxidation during prolonged storage.

Material Constitution, Viscosity Signature, and Compliance Status

The base polymer is a poly(ethylene) homopolymer with no intentional mineral filler, glass fibre, or graphite. The absence of fillers preserves the material’s olefin polymer compliance profile but also means that sliding wear performance is governed by entanglement density and surface fibrillation rather than hard-particle reinforcement. Lot acceptance on supplied compression-moulded plaques is performed after conditioning to ISO 291:2008 at 23 °C ± 2 °C and 50 % ± 10 % relative humidity. Viscosity number in decalin at 135 °C typically falls between 2100 mL/g and 2800 mL/g. Density measured by immersion according to ISO 1183-1:2019 is maintained between 0.930 g/cm³ and 0.940 g/cm³; values above 0.945 g/cm³ are treated as non-conforming because they may indicate oxidation, crosslinked contamination, or high catalytic residue.

Hardness under ISO 868:2003 is 60–65 Shore D. Tensile properties measured on ISO 527-2:2012 Type 1B specimens give yield stress in the range 21 MPa to 26 MPa and elongation at break at least 300 %. Charpy notched impact strength under ISO 179-1:2010 is reported as no break at 23 °C for standard edgewise specimens. The Vicat softening temperature by ISO 306:2022 A50 is between 78 °C and 82 °C. These property windows are batch-control indicators for the resin as supplied, not absolute design allowables. The viscosity-number range corresponds to a high degree of chain entanglement and limited reptation under load. This structural feature contributes to no-break Charpy impact and low wear, but it also means that weld lines do not heal rapidly in compression moulding. Adjacent powder particles must be pressed at sufficient pressure to eliminate particle boundaries; otherwise early failure occurs by particle pull-out at the interface. Under a polarised light microscope, a well-fused plaque shows no distinct particle outlines at 100× magnification, whereas an under-fused plaque shows grain-boundary shadows that coincide with low tensile elongation.

The molecular weight distribution is deliberately not narrowed by peroxide-controlled rheology modification, because peroxide addition can introduce residual unsaturation and alter oxidative stability. Residual catalyst metals measured by inductively coupled plasma optical emission spectrometry after ashing at 600 °C are kept below 20 ppm total ash. This low-residue profile supports use in high-purity water and pharmaceutical material-handling components, although validation under USP 87 and USP 88 biological reactivity tests is required for blood-contacting and implantable applications. Oxidative stability can be assessed by differential scanning calorimetry according to ISO 11357-6:2018; oxidation induction time at 200 °C is typically above 20 min for virgin ER-22. This parameter should be monitored for regrind or extended residence-time trials. A decrease below 10 min indicates antioxidant depletion and increased risk of degradation during subsequent processing.

Compression moulding of ER-22 requires pre-drying at 80 °C ± 5 °C for 2 h when storage relative humidity exceeds 60 %. Surface moisture can produce steam inclusions at mould temperatures between 190 °C and 220 °C, visible as internal voids after thickness sectioning. Moulding pressure is held at 10 MPa to 20 MPa during cooling from 200 °C to 40 °C; the cooling rate should not exceed 15 K/min for sections above 20 mm. Production-scale platen presses with heated platens of 1000 mm × 1000 mm or larger can maintain thickness variation below ±0.15 mm when cooling is uniform, but uneven cooling above 20 K/min can introduce frozen-in stress and reduce Charpy impact from no-break to measurable partial-break values. Regrind addition above 15 % by weight is not recommended for ram extrusion because particle-size distribution changes reduce bulk density and can destabilise backpressure. If regrind is used, it should be sieved to 250 µm to 850 µm and blended for 20 min in a low-shear tumble mixer to avoid segregation.

Lot-to-lot variation in viscosity number between 2100 mL/g and 2800 mL/g may require a die temperature shift of 5 °C to 10 °C in ram extrusion to maintain constant backpressure at fixed ram speed. Operators should record barrel zone temperatures, ram displacement rate, and die head pressure at 1 s intervals during start-up and reject the first 300 mm to 500 mm of extruded rod until the surface temperature gradient stabilises. A useful in-process acceptance check is the absence of a white granular core after cross-sectioning and polishing to 5 µm roughness; a persistent core indicates inadequate heat transfer or excessive ram speed.

What Limits Ram Extrusion Output and Backpressure with ER-22?

Ram extrusion of ER-22 is not a screw plastication process. The powder is consolidated in a heated barrel and forced through a die by a reciprocating ram. On production ram extruders with barrel diameters of 63 mm to 100 mm, barrel temperature segments are commonly set from 170 °C in the feed zone to 210 °C at the die entrance. Die land length ratios of 10:1 to 25:1 are used to generate fusion backpressure. Output is limited by thermal diffusivity rather than melt flow; increasing ram speed beyond the heat-transfer threshold produces a granular core and a weak weld line along the rod axis.

Backpressure above 25 MPa at die entrance temperatures above 220 °C creates conditions for oxidative chain scission. Local degradation may not be immediately visible but results in yellowing at the rod surface and a decrease in elongation at break to less than 150 % after machining. The processing window is therefore narrow; the acceptable die entrance temperature band is typically ±5 °C around the lot-specific set point. Where the die pack contains a breaker plate with 0.8 mm to 1.2 mm apertures, pressure drop across the breaker plate should be monitored separately from die land pressure to avoid confusing melt-starved fusion with excessive die compression.

For extruded rods above 60 mm diameter, cooling must be staged. A first zone at 150 °C to 170 °C slows surface freezing and reduces void formation, followed by a second zone at 80 °C to 100 °C for dimensional stabilisation. Attempts to quench directly in water at 20 °C can produce circumferential cracks because the outer skin contracts faster than the core. These constraints do not apply to sintered sheet production, where lower consolidation pressure and longer oven residence times are used.

In dry sliding contact, ER-22 resists material loss primarily by surface fibrillation and micro-ploughing. A 100 mm × 100 mm × 20 mm compression-moulded plate tested under ASTM G65-16 Procedure B, with 130 N load and 6000 rotations, typically shows volume loss in the range 0.8 mm³ to 1.5 mm³. By comparison, unfilled general-purpose HDPE may exceed 4 mm³ under the same conditions. The coefficient of friction against polished steel, measured by ASTM D1894-14 at 50 mm/min without lubrication, is approximately 0.10 to 0.15. These values are sensitive to counterface roughness; a metal surface above Ra 0.8 µm can increase wear by a factor of 2 to 3 because asperities cut rather than slide over the polymer film.

For impact-dominated wear, such as chute liners receiving hard rock fragments, the no-break Charpy performance under ISO 179-1:2010 at 23 °C is relevant, but low-temperature impact at −30 °C should be evaluated for outdoor mining applications. If the installation includes continuous sliding against stainless steel with hardness below 50 HRC, the polymer surface may transfer a thin film to the metal; this transfer is not a defect but can reduce the effective friction coefficient. In contrast, a counterface above 60 HRC with rough grinding marks can produce hard-particle abrasion and should be polished or replaced. The dry sliding pressure-velocity limit for unfilled UHMWPE is often reported as 0.10 MPa·m/s for continuous service without external cooling; above this value, frictional heating can raise the interface temperature above 80 °C and cause surface melting. ER-22 should not be used in dry bearing applications where the PV exceeds that threshold unless heat removal is provided.

When ER-22 Replaces HDPE in Food-Contact Guide Rails and Star Wheels

Guide rails, star wheels, and wear strips machined from ER-22 sheet are used where HDPE components fail by abrasive wear, cold flow, or environmental stress cracking in dry and lightly lubricated food-contact lines. Under US FDA 21 CFR 177.1520(c), olefin polymers are permitted for food contact subject to extractive limitations; under Regulation (EU) 10/2011, overall migration into food simulants should not exceed 10 mg/dm². For aqueous and acidic food simulants, ER-22 shows low migration because the matrix does not hydrolyse, but fatty simulants and hot-fill conditions above 80 °C should be subjected to end-use migration testing rather than assumed compliant from resin grade alone. Cleaning with sodium hypochlorite solutions up to 5 % active chlorine at 20 °C is generally acceptable for short cycles, but prolonged exposure above 60 °C can cause oxidative attack. Reprocessing with hot 2 % caustic solution is preferable for product-contact starch or sugar residues.

Dimensional tolerance in machined star wheels depends on stress relaxation after machining. Roughly machined ER-22 sheet should be allowed to stabilise for 24 h to 48 h at 23 °C before finish machining, because initial material release can produce dimensional change up to 0.3 % in long dimensions. Use of carbide-tipped circular saw blades with tooth geometry for soft non-ferrous materials reduces edge burr; cutting fluid is not required, but air cooling is recommended above 120 m/min cutting speed. In service, continuous temperature should not exceed 80 °C under load; short-term exposure to 110 °C is possible only in unloaded or lightly loaded components.

Chemical resistance of ER-22 follows the nonpolar semicrystalline polyethylene pattern. Dilute acids, alkalis, and aqueous salt solutions at room temperature do not remove measurable surface mass over 30 days immersion, but concentrated nitric acid, chromic acid, and strong oxidizing agents cause surface oxidation and brittle-layer formation. Aromatic and chlorinated solvents should be considered non-compatible; immersion in toluene for 24 h can increase mass by more than 10 % depending on thickness. Steam sterilization above 121 °C is outside the continuous service boundary because clamp load can produce deformation. The grade is supplied as a natural product; outdoor exposure exceeding 6 months requires UV-stabilized or carbon-black-filled variants, which are outside the standard ER-22 designation.

Comparing ER-22 Against Lower Molecular Weight PE and Sintered UHMWPE

Compared with a standard injection-moulding HDPE grade having an ISO 1133-1:2022 melt mass-flow rate of 4 g/10 min to 8 g/10 min, ER-22 shows no measurable flow at the same conditions. This difference translates into lower creep, higher notched impact, and better abrasive wear resistance, but it eliminates high-speed injection moulding as a fabrication route. Compared with lower-molecular-weight UHMWPE grades with viscosity numbers below 1400 mL/g, ER-22 typically shows better sand-slurry abrasion resistance and higher backpressure in ram extrusion, but the acceptable temperature window narrows. Processing trials on a 63 mm ram extruder indicate that a viscosity-number shift from 1800 mL/g to 2500 mL/g can raise die pressure by 15 % to 25 % at constant throughput; this is not a linear relationship and must be mapped for each lot.

Against sintered UHMWPE porous parts, fully compression-moulded ER-22 has lower porosity and higher tensile strength, while sintered material remains the correct choice for porous filter elements and complex low-stress shapes. Against glass-filled or ceramic-filled grades, ER-22 avoids metal liberation into product-contact surfaces and remains within olefin polymer compliance, but it does not match the extreme wear resistance of filled compounds in dry abrasive service. Creep modulus measured at 1 h by ISO 899-1:2017 at 23 °C is materially higher for ER-22 than for HDPE, but data scatter increases above 40 °C; therefore design stresses in warm environments should be reduced by 25 % from room-temperature allowables unless component-specific creep data are available. The selection boundary is defined by the end-use combination of load, speed, counterface roughness, and food-contact or chemical exposure, rather than by a single abrasion index.

Incoming inspection of ER-22 should include viscosity number, density, and visual gel count on a 0.20 mm compression-moulded film from each lot. A gel count greater than 5 gels per 100 cm² larger than 0.30 mm can indicate crosslinked contamination or insufficient reactor cleaning, and such lots should be isolated for trial use rather than released to ram extrusion. Moisture content by Karl Fischer titration above 0.05 % requires pre-drying before processing. Documentation should include lot number, date of manufacture, viscosity number, density, ash content, and a statement of food-contact compliance. The certificate of analysis should be retained for 3 years after delivery to support traceability under Regulation (EC) No 1935/2004 Article 17. For end-use qualification on chain conveyor wear strips, the test plan should record line speed, load per pallet, chain hardness, surface roughness, and cumulative sliding distance. Published data for ER-22 under some specific high-speed conveyor configurations is limited; therefore the stated property windows should be used as material acceptance criteria, and component validation should be performed under the final installation load and speed.