Solid profile production for dry-running conveyor wear rails begins on a non-rotating ram press rather than a single-screw extruder because GUR 4022 exhibits no measurable melt mass-flow rate under ISO 1133-1, condition 190°C/21.6 kg. The powder is compacted and frictionally heated in a heated barrel whose wall zones are typically set at 190°C, 210°C, and 225°C from feed to die. Ram face pressure for a 40 mm solid profile is maintained between 20 MPa and 35 MPa, and the linear output is limited to 0.2–1.0 m/h; exceeding this range causes core porosity because the viscoelastic sintering front cannot advance through the full cross-section. Pre-drying is applied when the resin has been stored at relative humidity above 70%; the powder is spread on trays and dried at 80°C for 2 h. Die land temperature is held 10–20 K below the final barrel zone to generate a smooth skin, but die temperatures below 170°C produce surface tearing and longitudinal cracks. The extruded profile is cooled gradually by ambient air or 40–60°C water spray, then annealed at 100°C for 4 h to reduce machining-induced distortion. The resulting stock is converted into bottle-handling star wheels, guiderails, chain guides, and wear strips; abrasion resistance is measured against the relevant test standard for the end-user specification, most commonly ASTM G65 dry-sand rubber-wheel or DIN 53516 abrasion testing.

Why Does Compression-Molded GUR 4022 Require Cooling Rates Below 5 K/min?

Compression molding of GUR 4022 blocks and sheets involves a two-stage thermal cycle. The powder is cold-compacted in the mold cavity at 5–10 MPa to remove entrapped air and to equalize bulk density before the platens are heated. The mold wall is raised to 200–215°C and platen pressure is increased to 10–20 MPa; holding time for a 25 mm sheet is 15–30 min. During cooling, the pressure is kept on the mold until the core temperature falls below 80°C. The cooling rate between 200°C and 80°C must not exceed 5 K/min. The reason is thermal contraction: UHMWPE has a coefficient of linear thermal expansion measured by ISO 11359-2 near 1.8×10⁻⁴ K⁻¹, so cooling from 200°C to 20°C produces approximately 3.2% linear shrinkage. If the skin solidifies while the core remains above 100°C, the subsequent crystallization of the core creates tensile residual stress and visible bowing, edge lift, or internal cracks. This is a known production failure on platen presses with short cooling-water cycles. Blocks are typically molded with 25–100 mm thickness and allowed to normalize at ambient conditions for 48 h before machining. Silo liners, hopper liners, chain tunnel guides, and truck-bed wear plates are then cut, planed, or routed from the blocks. Installation requires mechanical anchoring because the material cannot be solvent-welded and does not form load-bearing adhesive bonds. At thicknesses above 100 mm, the limitation of platen heat transfer dominates, and published cooling-rate data for GUR 4022 in this configuration is limited; manufacturers frequently extend the dwell time rather than increase platen temperature.

Sintered Porous Structures and Interparticle Void Architecture

Porous fluidizing plates, pneumatic mufflers, and venting elements are produced from GUR 4022 by restrained sintering of compacted powder. The powder is first sieved into narrow particle-size fractions, commonly 80–120 µm, 120–180 µm, and 180–250 µm, because the interparticle void size is controlled primarily by powder particle size and compaction pressure. The fraction is filled into a metal mold and compacted at 0.5–5 MPa; this pressure range is deliberately low to preserve the void network. The mold is then heated to 200–220°C for 30–60 min for a 10 mm wall section. During sintering, polymer chains interdiffuse across particle boundaries and form necks, while the overall porosity remains between 30% and 50% depending on compaction pressure. Pore size distribution is measured by capillary flow porometry under ASTM F316 or bubble-point method under ISO 4003. The sintered parts are used as air diffuser plates, fluidized-bed distributor plates, and venting mufflers in pneumatic lines. Chemical exposure is limited to pH-neutral and mild alkaline media; concentrated sulfuric acid, nitric acid, and chlorine dioxide at temperatures above 60°C cause oxidative embrittlement. Halogenated solvents such as methylene chloride and trichloroethylene swell the amorphous phase and should be avoided at temperatures above 40°C.

When GUR 4022 Is Used as the PE Skeleton in Gel-Extracted Microporous Separators

When GUR 4022 is used as the high-melting backbone in gel-extracted microporous battery separators, the resin is dissolved in paraffin oil at 150–180°C in a vertical kneader or twin-screw gel extruder. The polymer concentration is controlled between 15 wt% and 30 wt%; at higher concentrations the gel stiffness increases and die pressure becomes limiting, while at lower concentrations the biaxial film draw cannot sustain uniform thickness. The gel is cast through a flat T-die at 180–210°C onto a quenching roll cooled below 40°C to trap the phase-separated gel structure. Sequential biaxial stretching is performed at 90–110°C with machine-direction draw of 4–6× and transverse-direction draw of 5–8×. The pore-forming paraffin oil is then extracted in a countercurrent solvent bath, commonly using methylene chloride or n-heptane; residual extractables are measured according to ISO 6427 and controlled below 500 ppm for electrolyte compatibility. The stretched membrane is heat-set at 120–130°C with 2–5% relaxation to control free shrinkage. Final separator thickness is 12–25 µm, porosity is 35–45%, and Gurley permeability is typically 200–400 s/100 mL. The shutdown onset occurs near 130–135°C and membrane integrity is retained to approximately 155–165°C; published data for the specific GUR 4022 grade in full cell cycling is limited, so end-users should validate the extracted-film properties under their own electrolyte and calendar aging protocols.

Fine bubble diffusion plates in municipal activated sludge basins are machined from sintered GUR 4022 sheet with a nominal pore-size band of 100–200 µm. The plates are mounted in stainless steel headers at 4–8 m water depth and operate at air fluxes of 2–4 Nm³/h per m². The low surface energy of the polyolefin reduces mineral scaling, but the plates require periodic cleaning with dilute hydrochloric acid at pH 2–3 or citric acid at 60°C. Continuous exposure to free chlorine above 500 ppm at 40°C causes surface oxidation and reduces impact resistance; ozone at concentrations above 5 mg/L is not recommended because the amorphous tie-chain population degrades rapidly.

Direct food-contact star wheels and guide strips machined from GUR 4022 are used in dairy, meat, and bakery conveyance lines where the material is covered by FDA 21 CFR 177.1520 for olefin polymers and the migration limits of EU 10/2011. The finished surfaces are burnished to Ra 0.8–1.6 µm as measured by ISO 4287 to reduce biofilm retention. The material tolerates cleaning-in-place with 2 wt% sodium hypochlorite at 60°C for contact times up to 20 min, but repeated exposure at higher concentration increases carbonyl index and lowers notched Izod impact; replacement intervals should be established by the plant under ASTM D256 or ISO 180 impact testing. The absence of plasticizers and slip agents in the base resin simplifies organoleptic compliance, although final compliance is determined on the finished article under the applicable migration test conditions.