In hydraulic manifold mock-ups where mineral oil resistance is the controlling variable, Huntsman Iroprint™ F 90116 is used to print temporary lip seals, flange gaskets, and wiper rings that must survive contact with ISO 1817 reference fluids. Polyester-based TPU grades of comparable 95 Shore A hardness exhibit lower equilibrium volume swell in IRM 902 and IRM 903 oils than polyether TPU, a property attributed to ester segment polarity; however, published data for this specific filament in long-term mineral oil service is limited, and prototype validation should include 70 h immersion at 100 °C with tensile retention measured per ISO 527-2. Leakage through printed seal interfaces is governed less by bulk material permeability than by interlayer fusion defects: a 0.4 mm nozzle printing 0.2 mm layer heights at 225 °C on a direct-drive all-metal hot end produces a void population along layer lines that can be minimized by increasing bead overlap to 30 % and orienting the seal cross-section perpendicular to the printing bed. Compression set remains the operational boundary; ISO 815-1 and ASTM D395-18 Method B data for polyester TPU at 70 °C typically show lower recovery than thermoset polyurethane elastomers. Prototype gaskets should therefore be compressed only within the 10 % to 15 % strain range and subjected to a 0.2 MPa pneumatic holding test for 5 min to verify leakage before the assembly enters a hydraulic test bench.

Does Interlayer Fusion Limit Fatigue Life in Corrugated Bellows Prototypes?

The limiting failure mode in corrugated bellows is not ultimate tensile rupture but crack initiation at interlayer boundaries during repeated flexure. When F 90116 is printed with a 0.4 mm nozzle and 0.15 mm layer height, the extrusional shear history is insufficient to erase the weld line between the previously deposited bead and the fresh melt; the result is strength anisotropy measured by ISO 527-2 that can reach 40 % between XY and Z orientations. That anisotropy matters in convoluted bellows because each folding cycle imposes tensile strain perpendicular to the layer plane at the inner radius. Fatigue testing on polyester TPU bellows prototypes is typically executed with a displacement-controlled pneumatic actuator at 2 Hz and 20 mm stroke; the test is stopped when a through-crack reduces internal pressure below 0.1 bar. Pre-drying at 80 °C for 4 h in a desiccant dryer with a dew point below -30 °C is non-negotiable above 60 % ambient relative humidity because hydrolysis at the ester linkages during extrusion reduces molecular weight and lowers tear resistance. The narrow processing window of 90–95 Shore A polyester TPU is further tightened in thin-wall bellows; a ±5 °C drift in melt temperature around 225 °C changes apparent viscosity enough to produce over-extrusion at the convolution roots or under-extrusion at the crests. Operators on desktop extrusion platforms report that a hardened steel nozzle with a 0.4 mm orifice and a direct-drive extruder set to 2.5 mm³/s volumetric speed maintains stable bead width if the spool diameter is verified at three angular positions before each build. When idle time exceeds 10 min at temperature, a purge of at least 20 mm should be extruded because the residence time in the hot end shifts the melt flow index and creates surface roughness on the first printed perimeter.

A vacuum gripper lip manufactured from F 90116 requires a tear-resistant sealing face that maintains conformability under repeated pick-and-place cycles. ASTM D624-00 die C tear strength and ISO 34-1 trouser tear are the controlling test methods; the value obtained on printed specimens depends on raster angle, with ±45° rasters distributing strain more evenly across the lip contact area than 0° rasters. In practice, the lip is printed as a three-perimeter shell with 20 % triangular infill and a 0.12 mm final layer height, then annealed at 100 °C for 2 h to relax orientation stresses; annealing temperatures above 110 °C for polyester TPU can induce tackiness, oxidation, and dimensional warping unless the part is fixture-supported. The seal contact width is designed at 2.5 mm to 3.0 mm because narrower contacts under 0.6 bar vacuum leak at layer-boundary microchannels. The Shore A durometer is mounted on a calibrated stand with a 1 kg load and read after 15 s per ISO 7619-1; printed lips below 93 Shore A after conditioning frequently indicate insufficient drying or over-annealing. Field observations on end-of-arm tooling vary; when edge tick formation appears, it is usually at the transition between the lip sealing land and the sidewall rather than in the bulk material. The failure signature is a small fold crack that propagates along a perimeter weld after a period of cyclic compression, indicating that toolpath design, not base polymer choice, is the primary reliability variable in high-speed handling cells.

When Polyester TPU Replaces Molded Polyurethane in Cable Harness Prototypes

Cable harness grommets printed in polyester TPU are evaluated for installation abuse before the material is accepted as a surrogate for injection-molded polyurethane. The replacement is driven by the need to iterate grommet, split loom, and cable cleat geometry without waiting for injection mold tooling. Abrasion resistance is measured with DIN 53516 or ISO 4649, and polyester TPU of this Shore band typically shows volume loss in the range of 30 mm³ to 50 mm³ depending on print orientation; specimens with 100 % rectilinear infill and walls perpendicular to the abrasion surface produce lower volume loss than low-density lattices. The operational boundary is clip retention force: printed cable cleats subjected to repeated snap-fit loading show stress whitening at layer interfaces after fewer than 20 insertion cycles if the clip hinge is printed parallel to the build plane. A practical mitigation is to print the hinge axis vertically and use a 0.1 mm layer height; this raises the number of fused polymer welds resisting flexure. Because polyester TPU absorbs moisture faster than polyether TPU at processing humidity above 60 % RH, spools should be fed directly from a dry box at 50 °C to prevent intermittent extrusion and surface pitting in thin-walled split looms. Pull-out force for a 12.5 mm outside diameter grommet in a 10 mm panel hole is measured at 25 mm/min crosshead speed, but the results are only useful when the grommet is conditioned at 23 °C and 50 % relative humidity for 48 h after printing.

Footwear Outsole Traction Lug Trials and Shore Hardness Boundary Conditions

Because outsole traction lugs experience repeated shear at the elastomer-to-floor interface, the printed prototypes are evaluated for tear initiation, abrasion, and hardness drift after simulated wear. F 90116 lands within the 95 Shore A band, placing it at the upper flexibility limit for many running-shoe outsole designs and at the lower stiffness threshold for rigid cleat plates; its polyester backbone contributes better oil and fuel resistance than polyether TPU but less resistance to moist heat aging. Test plaques printed per ASTM D638-14 and aged at 70 °C and 95 % relative humidity for 168 h show a decline in tensile strength that is characteristic of ester hydrolysis; the exact loss for F 90116 should be taken from the supplier data, but similar polyester TPU grades are not recommended for prolonged wet-service footwear without a hydrolysis stabilizer. Wear simulation on a rotary abrasion tester under ISO 4649 is complicated by the anisotropic void network left by the filament deposition path; screening runs are most reproducible when the traction lug is printed with five perimeters, 40 % gyroid infill, and a 0.2 mm layer height, then subjected to a 20 m test path. Hardness recheck with ASTM D2240-15 after 5,000 flex cycles on a ASTM D1052 Ross-flex machine frequently shows a 2 to 4 Shore A increase as the polymer undergoes strain-induced orientation, which changes traction lug deformation behavior and must be modeled before final geometry freeze.

Tear propagation follows fused-layer boundaries before any bulk Shore-A limit is reached.

Printed orthotic pads in F 90116 exhibit layer-boundary tear sensitivity when loaded in shear by gait-cycle ground reaction forces. The relevant mechanical test is ISO 34-1 for tear strength, conducted on specimens cut from a 2.0 mm thick printed sheet in both longitudinal and transverse directions; the ratio of transverse to longitudinal tear strength is a more useful predictor of pad delamination than bulk Shore hardness alone. The functional requirement is not peak tear strength but resistance to crack propagation from the free edge where the heel strike concentrates stress. For prototype pads intended for a human subject evaluation, the surface is sealed with a thin TPU coating only after the pad has been annealed at 100 °C for 1 h to reduce trapped filament stresses. The clinical boundary is skin contact and sensitization potential; raw F 90116 filament is not marketed as a medical-grade thermoplastic, and ISO 10993-1 cytotoxic, sensitization, and irritation testing must be completed before any prolonged skin-contact clinical study. Polishing or solvent smoothing of polyester TPU is less effective than on amorphous thermoplastics and can introduce microcracks at layer boundaries, so the surface finish is controlled mechanically through a 0.1 mm layer height and post-print abrasion with 320-grit cloth. Field feedback from orthotic fitting labs indicates that the primary print failure is delamination at the first heel-strike impact point after approximately 10,000 gait cycles; this is a prototype durability threshold rather than a clinical performance claim.