Beijing Evergrow Resources supplies UHMWPE ER-24 as an ultra-high-molecular-weight polyethylene resin intended for compression molding, ram extrusion, and subsequent machining into wear components. The ER-24 grade belongs to the PE-UHMW classification under ISO 11542-1; its solution viscosity number exceeds 2000 cm³/g when determined by ISO 1628-3 in decalin at 135 °C. Unlike HDPE, the material does not produce a conventional melt flow rate under ISO 1133-1:2022, because the molar mass is sufficiently high to prevent meaningful flow in a standard melt indexer. Supplier documentation for ER-24 should be used for particle size distribution, bulk density, and gel count. Published open-literature data for this specific configuration is limited; the technical envelope below therefore relies on the ISO 11542-1 class definition and standard conversion practices for PE-UHMW rather than a certified lot datasheet.

For unfilled PE-UHMW stock shapes, density is normally 0.930–0.945 g/cm³ when tested to ISO 1183-1, tensile yield stress is 20–25 MPa under ISO 527-2, and elongation at break is above 300%. Notched Charpy impact strength at 23 °C exceeds 100 kJ/m² under ISO 179-1/1eA and typically remains high at subambient temperatures. Shore D hardness is in the 60–72 range per ISO 868. Vicat softening temperature for PE-UHMW is near 80 °C under ASTM D1525, but this is a short-term thermal test; load-bearing service is limited to lower temperatures. These values describe the unfilled PE-UHMW material class and should be verified against the ER-24 certificate of analysis before die design, regulatory submission, or wear-rate testing.

How Does ER-24 Differ From High-Density Polyethylene and PTFE in Sliding Wear?

UHMWPE ER-24 differs from HDPE primarily in molar mass and entanglement density. HDPE grades typically show solution viscosity numbers below 500 cm³/g, whereas PE-UHMW exceeds 2000 cm³/g; this shifts conversion from injection molding and film extrusion toward sintering, ram extrusion, and compression molding. Under dry sliding against ground 316L stainless steel, PE-UHMW exhibits a dynamic coefficient of friction of approximately 0.10–0.22 by ASTM D1894 or pin-on-disk testing per ASTM G99. HDPE is slightly higher at 0.15–0.25, virgin PTFE is lower at 0.04–0.10, and dry PA66 is higher at 0.20–0.30. In block-on-ring wear testing per ASTM G77, unfilled PE-UHMW class materials typically show specific wear rates below 1 × 10⁻⁶ mm³/N·m at moderate pressure-velocity products, while unfilled HDPE can wear at rates an order of magnitude higher. PTFE remains lower in friction but suffers higher creep and can be displaced under concentrated loads; PE-UHMW is therefore selected when abrasive contamination, impact loading, and sliding motion occur together.

For conversion of ER-24 powder into sheet, production-scale compression molding presses with clamp forces from 1000 kN to 3000 kN are used. The powder is consolidated at platen temperatures of 190–210 °C and pressures of 5–15 MPa; hold time is typically 20–60 min depending on sheet thickness. Controlled cooling at 5–15 °C/h through the crystallization range reduces warp and internal voids. Ram extrusion of rod and profile uses barrel temperatures from 190–230 °C and back pressure of 5–20 MPa; die-land length-to-diameter ratios above 6:1 improve particle fusion. On production lines, the dominant defects are internal weld lines from insufficient compaction, oxidative yellowing from excessive residence time, and centerline porosity from trapped air. These failures are controlled by vacuum deaeration, by matching charge weight to cavity volume, and by avoiding temperature increases above the recommended band. Because PE-UHMW does not form a stable melt pool in the conventional thermoplastic sense, process optimization targets particle interfacial diffusion rather than melt-flow filling.

The sintering kinetics of PE-UHMW are controlled by diffusion of chain ends across particle boundaries above the crystalline melting temperature. The melting point of unfilled UHMWPE is typically 130–136 °C by ISO 11357-3 differential scanning calorimetry, with a degree of crystallinity between 40% and 60%. During compression molding, the first stage heats the powder to a homogeneous 200 °C; the second stage applies pressure to remove voids; the third stage crystallizes the sheet under controlled cooling. Because molecular weight is extremely high, the rate of interparticle fusion is slow compared with HDPE. Hold times must therefore be extended, and local temperature overshoot above 230 °C can cause oxidative degradation without improving flow. Gel particles and unmelted powder cores can act as stress raisers in finished parts; class-defined PE-UHMW resins are inspected for gel count and foreign-particle contamination using optical methods specified by the supplier.

Because PE-UHMW ER-24 is converted to final parts by machining, the material’s high coefficient of linear thermal expansion—typically 1.5 × 10⁻⁴ K⁻¹ to 2.0 × 10⁻⁴ K⁻¹ by ASTM D696—must be accommodated in mounting holes and wear clearances. This expansion value is roughly an order of magnitude higher than steel; a part machined at 20 °C and later warmed to 40 °C grows by approximately 3–4 mm per meter. In production settings, this mismatched expansion causes buckling of wear strips that are rigidly bolted without slotted holes. The recommended compensation is to use oversized mounting holes, slotted bolt patterns, and expansion gaps of 2–3 mm per meter of length for indoor temperature swings. Tight machining tolerances above ±0.05 mm are possible, but they require temperature-controlled inspection and stress-relieved stock shapes to prevent post-machining movement.

Pressure-Velocity Limits and Filled UHMWPE Trade-Offs

The permissible pressure-velocity product for unfilled PE-UHMW in continuous dry service is generally below 0.1 MPa·m/s for low wear and below 0.2 MPa·m/s for intermittent duty. Above this threshold, frictional surface heating accelerates wear and can soften the polymer. This ceiling is a critical difference from filled UHMWPE grades containing molybdenum disulfide, glass fiber, or crosslinked polymer networks. Filled grades may increase compressive strength and reduce wear under dry sliding but usually sacrifice notched impact toughness and elongation at break. ER-24 should not be assumed to be internally lubricated or crosslinked; its selection is based on retained ductility, impact resistance, and machinability. If a specification demands surface resistivity below 10⁹ Ω per IEC 62631-3-2, an antistatic grade—not ER-24—must be used unless supplier documentation confirms otherwise. In abrasive slurry tests such as ASTM G75, PE-UHMW class materials often show lower relative abrasion than HDPE but may rank below rigid ceramic-filled polymers; the decision therefore balances particle size, impingement angle, and impact energy rather than coefficient of friction alone.

Crosslinked UHMWPE differs from ER-24 class material in network structure, elongation, and oxidative wear resistance. Radiation crosslinking at 50–100 kGy reduces elongation at break to 200–300% or lower and improves wear resistance in reciprocating bearing studies, but it also reduces toughness and cannot be reprocessed by melting. Non-crosslinked PE-UHMW retains its higher elongation and is preferred for impact-dominant wear strips, conveyor guides, and marine structural surfaces. If ER-24 is supplied as a non-crosslinked compression-molding resin, substitution of a crosslinked grade without redesign can lead to premature cracking at bolt holes and reduced resistance to high-rate impact; if a crosslinked grade is substituted into a sliding wear-only application, wear rate may improve but the impact safety margin decreases. The component specification must therefore state whether network density, gel fraction per ASTM D2765, or elongation at break is the controlling parameter.

In chemical service, UHMWPE ER-24 resists dilute acids, alkalis, and many polar solvents at ambient temperature, but it is not suitable for strong oxidizing acids, halogens, or high-temperature aromatic and chlorinated solvents. Swelling in aliphatic hydrocarbons is low at room temperature but increases with chain relaxation; continuous service above 60 °C under load produces creep rates that can exceed dimensional tolerances in close-clearance wear guides. The upper short-term service temperature is commonly stated near 90 °C, but the load-bearing ceiling is lower. Ultraviolet exposure causes chain scission and surface embrittlement; outdoor components require carbon black or hindered amine stabilizers unless the part is shielded from sunlight. Because UHMWPE is difficult to bond, assembly designs use mechanical fasteners, dovetail slots, or thermal welding; adhesive bonding is not reliable unless a validated surface treatment such as plasma or flame treatment is applied and tested to an appropriate shear-strength standard.

When the Grade Is Evaluated for Food-Contact and Pharmaceutical Sliding Surfaces

For food-contact and pharmaceutical sliding surfaces, UHMWPE ER-24 may be evaluated under FDA 21 CFR 177.1520 for olefin polymers intended for food-contact use; the finished article must meet the end-use limitations and extractive specifications applicable to the polymer and its additives. In the European Union, compliance is typically assessed under Regulation (EU) No 10/2011 and its amendments, with an overall migration limit of 10 mg/dm² for food simulants. REACH registration under Regulation (EC) No 1907/2006 must be confirmed from the supplier safety data sheet; substances of very high concern are restricted to below 0.1 wt% per article. RoHS Directive 2011/65/EU Annex II restrictions on lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE are normally met by unfilled polyethylene resin, but finished-component compliance depends on pigments and processing aids. USP <88> Class VI testing is not an automatic property of every PE-UHMW stock; if pharmaceutical contact or bioprocessing use is intended, a lot-specific certificate is necessary. The grade should not be assumed suitable for implantable medical use unless authorized through an appropriate regulatory pathway.

In dry bulk handling, UHMWPE ER-24 liners are used to reduce wall friction and promote mass flow; the mating steel surface should be finished to 0.4–0.8 µm Ra to avoid abrasive wear of the polymer. In conveyor chain guides, the material is machined into wear strips and slide rails; bolt-hole edges should be countersunk to prevent stress concentrations. For outrigger pads and marine fender facings, the grade’s low water absorption and high impact strength provide dimensional stability under intermittent compression. Field results on production-scale equipment show that edge loading, shaft misalignment above 1°, and obstructed expansion gaps are common causes of early wear; these failure modes are often misattributed to resin quality when they are actually traceable to machining or assembly conditions. ER-24 therefore requires the same lot-specific verification of density, tensile yield, and impact strength as any engineering polymer, particularly when the finished part is subjected to high-cycle sliding or food-contact extraction testing.