Fast Set Urethane

Put Your Fast Set Urethane Knowledge to the Test

4113 Fast Set Tooling/Prototyping Urethane Resin can be cast and de-molded quickly to make durable prototypes, molds and tools. During production, the 2,600-cps liquid, about as viscous as honey, is easy to handle and reproduces fine details well. It shrinks minimally while curing, and the finished parts are dimensionally stable and very heat resistant.

The fast cure time, generally around 30-40 minutes, is ideal for small- and medium-sized parts.

Watch the video and read our directions below for general instructions and key tips for using the Fast Set Tooling/Prototyping Urethane Resin.

Step One: Apply mold release and let dry.

Mold Release

(Option 1) Use six coats of 4120 Easy Clean Mold Release for Urethanes. The 4120 is a low-viscosity liquid that evaporates quickly, with minimal time needed between coats. It can be wiped on with a rag or applied with a sprayer. After the final coat, wait 15-20 minutes for the release to dry completely.

(Option 2) The 4121 Non-Silicone High Temp Paste Wax is a solid that can be wiped on and buffed with a terrycloth rag; the surface of the wax should be broken before each layer dries. Build three layers of wax. Video: We used a 2320 Preval Sprayer and 2321 Glass Reservoir to apply the Easy Clean Mold Release. We used a funnel to fill the reservoir, attached the power unit and applied light coats of the release, wiping excess spray and pooled areas with a clean rag.

Tech Tip

Do not use PVA Release Film with urethanes. PVA Release Film contains water and can leave pitted or cratered surfaces.

Step Two: Shake cans of Fast Set Urethane Resin well.

Each part settles over time and must be mixed well to ensure the filler is evenly distributed. If the filler is not evenly distributed throughout the resin parts, it may change the mix ratio and compromise or change the qualities of the cured part. Video: Off camera, we used a paint mixer to speed up the shaking process.

Tech Tip

To make mixing easier, turn the cans upside down one day before use to help release the filler settled on the bottom of the can.

Step Three: Measure Fast Set Urethane Resin Parts A and B at a 1:1 ratio by weight or volume.

Mix Ratio

It is easier to control the exact amount of each side out of a plastic container, rather than a round can. Video: We measured Part A into a container on the scale, then we poured a little more of Part B than we needed into a separate container. We carefully poured the Part B container into Part A and watched the scale until we had a 1:1 ratio by weight.

Tech Tip

Before resealing the cans of urethane, spray in a dry gas blanket, like 2332 Poly Purge. The dry air displaces ambient moist air and extends the life of open urethanes.

Step Four: Mix Parts A and B well with a plastic stir stick.

Stir Stick

Plastic stir sticks are necessary, as wooden sticks can add moisture to the mixture. Be sure to scrape the sides and bottom of the container for a homogenous mix. The urethane is hygroscopic and can absorb water, affecting the cure. The pot life of the Fast Set Urethane is just 6 minutes, so ensuring a quick, but thorough mix is critical. Video: We used a 2333 Plastic Paint Stirrer for Urethanes as a rigid and reliable mixing tool. Before we poured the urethane, we ensured there was an even coloration throughout the mixture.

Step Five: Pour Fast Set Urethane into the mold.

Pouring the 4113 into the mold

The pot life of the urethane is 6 minutes, depending on the amount mixed and environmental factors. After brushing the surface detail, pour the rest of the urethane slowly to break interior air bubbles that may compromise the strength of the part. Over-fill the mold slightly to avoid sharp edges from a concave part, but do not let the urethane spill onto the mold flange. Video: We poured a small amount of the urethane into the mold over the words and carefully brushed them to remove air bubbles. The rest of the fill took about two minutes.

Tech Tip

Use the disposable 2330 Acid Brushes to go over fine surface detail and help break air bubbles on the surface of the mold.

Step Six: Wait 30-40 minutes for urethane to cure to de-mold stage.

The part will cure faster depending on its thickness; thicker pieces cure faster than thin parts and areas. The curing speed is also dependent on the material and ambient temperatures -- The estimate of 30-40 minutes for de-mold time was measured at 77°F; parts may take longer to cure in colder temperatures. Video: Cooler temperatures in the warehouse, around 65°F, and the relatively small part took around 40 minutes to cure to the demold stage.

Tech Tip

Before demolding, be sure to check thin areas for a hard cure, especially at lower ambient temperatures. Tap the surface with a fingernail or coin.

Step Seven: Release the part from the mold.

Molded Car

Small parts in rigid molds can be tapped on a table to release; pliable molds can be bent slightly to help release suction. For larger rigid molds, a mallet may be used to tap the mold flanges and underside. Video: Our mold and part were small enough to turn over and tap on the table to release. The mold we used was made of the same rigid Fast Set Urethane, so we could not bend it away to start the release.

The Fast Set Tooling/Prototyping Urethane Resin cures to 84 Shore D hardness at 77° (80 Shore D at 150°F) and can be put into service soon after. The finished material can be finished and shaped with machine tools.