| HS Code | 893583 |
| Color | Off White |
| Shoreahardness | 42 A |
| Tensilestrength | 800 psi |
| Elongationatbreak | 500% |
| Tearstrength | 100 pli |
| Compressionset | 25% |
| Specificgravity | 1.05 |
| Viscosity | 1,500 cps |
| Potlife | 2.5 minutes |
| Demoldtime | 30 minutes |
| Fullcuretime | 24 hours |
| Mixratiobyweight | 1:1 |
| Mixratiobyvolume | 1:1 |
As an accredited 3D Systems QuickPlastic Cast Urethane Material Elastomer 42 A factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
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Low-pressure vacuum casting of 3D Systems QuickPlastic Cast Urethane Material Elastomer 42 A into CNC-machined aluminum footbed molds is encountered in orthotic and midsole prototyping lines where the casting viscosity must remain below 3,000 mPa·s at 25 °C for the first 6 min after mixing to fill 1.2 mm metatarsal dome features without entrapped air. A lot-adjusted prepolymer-to-curative addition ratio of 100:42 by weight is representative for a 5.8 % NCO prepolymer and must be corrected against the certificate of analysis when ambient relative humidity exceeds 40 %; deviation outside ±0.5 % in curative weight fraction shifts measured hardness by 3–5 Shore A and alters hysteresis loops recorded under ASTM D412-16. Hardness is checked after 24 h at 23 °C using ASTM D2240-15e1 on a 6 mm plied specimen. Compliance for finished orthotic components is evaluated under EU MDR 2017/745 for non-invasive surface-contacting devices, with material testing to ISO 10993-5:2009 and ISO 10993-10:2021 for sensitisation. Production-scale equipment includes 20 L stainless steel vacuum mixing tanks, elastomer-specific meter-mix machines with dynamic rotor-stator mixers, and mold preheating stations set to 60 °C; material is degassed at −0.095 MPa for 5 min before pouring, which becomes a bottleneck when batch mass exceeds 5 kg because dissolved gas removal is non-uniform at the vessel walls. Post-cure proceeds at 80 °C for 8 h; skipping post-cure leaves compression set above 30 % under ASTM D395-18 Method B. Terminal finished parts include running shoe midsole prototypes, full-contact orthotic insoles, heel wedges, and cast foam replacement pads.
In automotive NVH components, cast urethane with 42 Shore A hardness is substituted for injection-molded EPDM when annual volumes remain below 5,000 units and tooling life beyond 10,000 cycles is not required. The formulation addition ratio is typically 100:58 by weight of prepolymer to curative at an NCO index of 1.03, with 0.2 wt% hydrophobic fumed silica added as a thixotrope and 0.1 wt% molecular sieve moisture scavenger to counter residual water in recycled rubber tooling. Automotive compliance is driven by IATF 16949:2016 production control, REACH EC 1907/2006 Article 33 communication obligations for SVHCs above 0.1 wt%, RoHS 2011/65/EU Annex II restricted substances, and end-of-life requirements under ELV 2000/53/EC; relevant material testing includes ASTM D2000-18 M4AA 42 A for classification and ASTM D395-18 Method B compression set after 22 h at 70 °C. On low-pressure meter-mix dispensing lines, the material is injected into preheated steel molds at 65–70 °C, with a 3–5 min gel time and demold at 30 min; premature demold at 20 min creates tear at the mold parting line because green strength has not exceeded 0.8 MPa. A process conflict exists between rapid demold and post-cure densification: post-cure at 100 °C for 16 h lowers compression set below 12 %, but residual internal stresses from urethane shrinkage can warp thin 2 mm flanges. Silicone-free internal mold release is permitted at 0.5–1.0 wt% addition only when validated for post-casting adhesive bonding. Terminal products include steering rack isolators, HVAC actuator grommets, body plug seals, and battery cooling line isolators.
Before demolding pneumatic gripper bladders, the 42 A elastomer must achieve a tear strength above 10 kN/m under ASTM D624-00(2020) die C to survive repeated flexing at 40 kPa actuation pressure. The formulation addition ratio for this low-viscosity work window is 100:36 by weight, yielding a mixed viscosity of 1,400 mPa·s at 25 °C and a pot life of 7 min, which requires continuous degassed flow into mold channels under −0.09 MPa. Compliance for industrial robot end-effectors is evaluated under ISO 10218-1:2011 for physical interfaces and ISO 8573-1:2010 class 3.4.4 compressed air purity; food-contact variants require FDA 21 CFR 177.1680 and EU EC 1935/2004 migration testing. The production process uses a 2-component benchtop meter-mix dispenser with static mixing nozzle, pouring into silicone molds produced from polyvinyl alcohol prints; after curing at 70 °C for 2 h and post-curing at 80 °C for 12 h, bladders are inspected for wall thickness at 0.8 mm using ultrasonic gauging. Bottlenecks occur when tooling channels narrow below 0.4 mm, where the static mixer produces visible anisotropy in tensile tear; ASTM D624-00(2020) die C tear strength then drops below 12 kN/m. Terminal parts include flexible gripper bladders, vacuum cup skirts, adaptive jaws for fragile glass handling, and pneumatic finger pads.
In medical training replication, anatomical models fabricated from the 42 A cast urethane require dual validation: mechanical hardness similar to subcutaneous tissue and chemical compliance for repeated skin contact. The formulation is mixed at 100:30 by weight with a 0.5 wt% aliphatic colorant and 0.05 wt% silicone-based air release agent; the low curative ratio keeps the Shore A hardness at 42 but extends gel time to 12 min, enabling multi-layer casting without visible knit lines. Biocompatibility anchors to ISO 10993-5:2009 clause 8.3 MTT extraction, ISO 10993-10:2021 sensitisation, and ISO 10993-23:2021 irritation, though the material is not supplied as an implantable grade; long-term tissue contact beyond 24 h requires device-specific validation. Production uses vacuum-assisted casting into epoxy molds derived from segmented CT scans, followed by 65 °C cure for 4 h and 80 °C post-cure for 8 h; the longer post-cure reduces unreacted isocyanate extractables below the analytical threshold used in ISO 10993-18:2020 chemical characterisation. Manufacturing constraints include batch-to-batch tint stratification if pigments are added above 0.8 wt%, causing visually detectable density gradients in ultrasound phantoms. Terminal products are venipuncture training pads, surgical suture trainers, dental mandible gingival inserts, breast examination phantoms, and ultrasound needle guidance phantoms. Published data for acoustic attenuation of this specific formulation is limited; if phantom acoustic velocity must match 1,540 m/s, independent verification under relevant phantom performance standards is required.
When low-pressure encapsulation of consumer electronics and hand-held devices is specified, the 42 A urethane is used where rigid potting compounds create stress cracking in solder joints during thermal cycling. The conditional operating window is 55–60 °C mold temperature and −0.095 MPa vacuum; below this temperature, mixed viscosity exceeds 4,500 mPa·s, preventing fill of 0.3 mm connector strain-relief ribs. Formulation addition for these parts is 100:24 by weight of curative at an NCO index of 1.05, with 0.7 wt% hydrophobic fumed silica added for sag resistance and 0.05 wt% silicone air release agent; altering the curative ratio outside ±0.3 wt% produces hardness drift above 46 Shore A. Amine-based adhesion promoters are excluded because residual primary amines accelerate crosslinking in the static mixer and reduce pot life below 30 s. Compliance testing includes RoHS 2011/65/EU Annex II homogeneous material limits, REACH EC 1907/2006, IEC 62368-1:2018, and UL 94 HB flammability per IEC 60695-11-10; dielectric strength is tested under ASTM D149-20 at 12 kV/mm only after 24 h conditioning at 23 °C and 50 % RH. Production lines use a 2-component low-pressure dispensing robot with planetary mixer and heated feed lines, casting directly into polypropylene or aluminum tooling over populated PCB substrates; pot life in the static mix head is 90 s, so purge cycles are timed every 2 min to avoid crosslinking in the nozzle. The main failure mode is amine blush from ambient humidity above 60 % RH, causing visible surface haze and reduced adhesion to metals; substrates are preconditioned at 50 °C for 1 h before casting. Terminal parts include handheld scanner edge bumpers, battery pack sealing gaskets, USB connector strain reliefs, and AR/VR headset cushion gaskets.
For prosthetic socket liners and wearable cushioning interfaces, the 42 A cast urethane is tested for compression set after exposure to −20 °C and subsequent cyclic loading, because stiffening at low temperature causes skin shear at the residual limb. The production formulation uses 100:42 by weight resin-to-curative at an NCO index of 1.00; no external plasticizer is added, because plasticizer migration under 50 °C wear conditions would reduce Shore A hardness below 38 after 72 h. Compliance for skin-contact prosthetic components falls under EU MDR 2017/745 Annex I, Chapter II, Part 10.2, with ISO 10993-5:2009 and ISO 10993-10:2021; mechanical performance is characterized using ASTM D2240-15e1, ASTM D412-16 tensile set, and ASTM D395-18 Method B compression set at 70 °C for 22 h. The process for gel-like urethane liners uses vacuum casting into polished aluminum or glass-filled nylon tools at 55 °C, with 4 h gel and 12 h post-cure at 80 °C; the latter is critical because under-cured parts exhibit compression set above 25 % and tacky exudate. On production scale, batch-to-batch variance is controlled by resin preheating to 35 °C for 24 h before metering, and by testing a 2 mm slab from each batch for ASTM D624-00(2020) die C tear before release. Terminal products include transtibial socket liners, off-loading heel pads, prosthetic knee cushioning, and metatarsal pads. Published data for this specific cast urethane in prolonged skin-wear under high humidity is limited; moisture vapor transmission must be separately verified for each wall thickness.
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Designated for vacuum-assisted casting into silicone tools, the 3D Systems QuickPlastic Cast Urethane Material Elastomer 42 A is a two-component thermosetting polyurethane elastomer. The “42 A” model designation identifies a nominal Shore Type A durometer of 42 when measured under ASTM D2240; this places the cured solid in the low- to mid-durometer elastomer segment rather than the semi-rigid or rigid QuickPlastic polyurethane grades. The liquid resin and isocyanate hardener are metered, mixed, degassed, and poured into soft tooling where the polyaddition cure converts them into a crosslinked network that cannot be re-melted. The material is therefore classified as a thermoset and is not interchangeable with melt-reprocessed thermoplastic polyurethanes.
The crosslinked network forms by reaction of an isocyanate-functional hardener with a polyol and chain-extender blend. Because cure development is stoichiometric rather than evaporative, metering accuracy and homogenization influence final hardness more than ambient humidity under normal dry conditions. Volumetric metering without mass verification is not recommended for production batches. A deviation of ±1 part by weight in the hardener-to-resin ratio can shift durometer, residual extractables, and cure shrinkage; the manufacturer’s batch documentation should be used to set the mix ratio and allowable variation.
On the Shore Type A scale defined by ASTM D2240, a 42 A durometer reading is lower than production elastomers specified at 60 A or 70 A and higher than ultra-soft gels below 30 A. The practical consequence is a combination of low indentation resistance and increased conformability under clamp or bolt load. Compared with a 70 A cast urethane from the same family, the 42 A grade generally requires lower closure force to seal a mating surface and can absorb larger deflection before generating high contact stress. In assemblies where rigid QuickPlastic grades are tested under ASTM D638, failure is typically associated with tensile yield or brittle fracture; the 42 A elastomer is instead evaluated under ASTM D412, which reports elongation-at-break and tensile values relevant to elastomeric behavior.
Tooling for this cast urethane grade is commonly produced from addition-cure platinum silicone. Condensation-cure tin-catalyzed silicones are avoided because residual tin compounds can inhibit polyurethane cure at the mold surface and produce a tacky skin. Before casting, the tool is heated to a uniform temperature of 60 °C to 70 °C in a forced-air oven. The liquid components are degassed separately under vacuum, generally below 2 kPa residual pressure, until visible bubble evolution stops. They are then metered by mass, combined, and mixed under vacuum so that air incorporation is minimized. The mixed material is poured into the cavity in a continuous stream to avoid folding air into the tool. Gel time shortens as shot mass increases because the exothermic urethane reaction accelerates the isocyanate-hydroxyl cure.
Vacuum-assisted casting is the controlling process route because the material cures as a thermoset and cannot be injection molded after gelation. The maximum practical shot size is governed by machine cup volume and exotherm. When total mixed mass exceeds 1.5 kg, pot life may drop below 5 min in a 25 °C environment; operators can extend handling time by pre-cooling the polyol side to 18 °C before metering and by dividing large pours into staged shots. Demold time is a function of temperature history rather than wall-clock time alone. Parts removed before reaching demolding hardness can exhibit permanent deformation and elevated compression set. A post-cure cycle, often 4 h to 8 h at 80 °C, is used to complete secondary crosslinking and stabilize mechanical properties. The post-cure oven should be vented because low-molecular-weight volatiles may be released during final cure.
Because isocyanate groups are moisture-sensitive, processing at relative humidity above 60 % can generate carbon dioxide gas, microvoids, and reduced tear strength. For humid production environments, a dry air or nitrogen shroud across the mixing vessel and mold filling station is used. The polyol component should be stored sealed at 15 °C to 30 °C and equilibrated to processing temperature before opening; condensation on cold containers must be prevented. Addition of incompatible amine-based mold release or certain sulfur-containing clays can alter cure stoichiometry and produce a soft, weak surface. Dimensional tolerance is influenced by linear cure shrinkage and by the coefficient of thermal expansion of the silicone tool; critical dimensions should be qualified with first-article inspection using production tooling rather than master pattern data.
Selection of this material in place of a peroxide-cured or platinum-cured silicone often occurs when higher tensile and tear properties are required at equivalent hardness, or when the part must be painted, bonded with polyurethane adhesives, or machined after cure. However, the operational boundary differs from silicone. Silicone typically retains flexibility at temperatures where urethanes soften or undergo thermo-oxidative embrittlement; continuous exposure above 80 °C, or intermittent excursions above 100 °C, should be validated for the specific service environment. In sealing applications, leakage performance is controlled by compression set, surface finish, and fluid swell. Testing under ASTM D395 Method B, ISO 815-1, or ASTM D471 is advisable before substitution. Published data for this specific 42 A product under all these conditions is limited; qualification should use coupons produced from the same batch and post-cure schedule as the production run.
Qualification testing for the material should be structured around elastic material standard designations rather than rigid plastic methods.
| Property | Test method | Unit | Qualification note |
|---|---|---|---|
| Durometer hardness | ASTM D2240 | Shore A | Nominal 42 |
| Tensile strength | ASTM D412 | MPa | Elastomer tensile specimen |
| Ultimate elongation | ASTM D412 | % | Elastomer tensile specimen |
| Tear strength | ASTM D624 | kN/m | Die C geometry |
| Density | ASTM D792 | g/cm³ | Method A recommended |
| Compression set | ASTM D395 Method B | % | Validate time and temperature |
| Fluid resistance | ASTM D471 | % | Mass and volume change |
The substitution of 42 A cast urethane for a liquid silicone rubber or injection-molded TPE affects tooling cost, cycle time, and part geometry. Vacuum casting has lower tooling cost because silicone molds are poured from a master, but the process is limited to lower throughput and tighter part-size constraints than injection molding. The cast urethane surface reproduces the master texture, including machined or textured finish; however, trapped air can create internal voids in thick sections if venting and gating are not adjusted. Published data for the specific heat transfer, viscosity, and gel-time profiles of this 42 A grade under high-humidity or cold environments is limited; process windows should be confirmed with production-scale trials.
Post-cure stabilization is required before final inspection of tensile and compression set properties. The first 24 h after demolding show the largest property drift; hardness and tensile strength generally increase as residual isocyanate reacts. Dimensional measurements taken immediately after demolding can shift by 0.3 % to 0.8 % based on equivalent cast urethane grades due to thermal contraction and continued crosslinking. Parts should be conditioned for a minimum of 3 days at 23 °C and 50 % relative humidity before final metrology. In severe service, hydrolytic stability is a known limitation of polyurethane elastomers; prolonged immersion in hot water above 60 °C can reduce tensile strength. For dry environments, the material class generally exhibits greater abrasion resistance than a silicone of similar durometer.
An application using this material for impact-isolating feet in automated guided vehicles illustrates the interaction among hardness, operating frequency, and temperature. A 42 A durometer value is low enough to permit deflection during normal travel but high enough to retain shape under repeated clamping. The design must account for cyclic fatigue, frictional wear, and possible exposure to lithium-based greases. Cast urethane can swell in high-polarity fluids, and no substitution should be accepted without immersion testing. Since fatigue crack initiation in cast elastomers is sensitive to internal voids, radiography or sectioning of first articles is used to confirm that the vacuum casting cycle removes entrapped air.
