The Smooth-Cast® Semi-Rigid line of low-cost semi-rigid urethane casting resins cure quickly to semi-rigid plastics that offer exceptional strength and impact resistance. New Formulations – New Look! Smooth-Cast® 61D is newly reformulated with a translucent white appearance and improved physical properties. All Smooth-Cast semi rigids are now mercury free and phthalate free. These plastics are easy-to-use (mix ratio is 1A:1B by volume) and have low viscosities for minimal bubble entrapment. Vibrant colors are possible by adding SO-Strong™, UVO™ or Ignite™ colorants.
These semi-rigid plastics are good for making impact resistant prototypes, models, toys, props, climbing holds, etc.
Safety - Materials should be stored and used in a warm environment (73°F / 23°C). These products have a limited shelf life and should be used as soon as possible. All liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass or plastic.
Mixing should be done in a well-ventilated area. Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk.
Applying A Release Agent - A release agent is necessary to facilitate demolding when casting into or over most surfaces. Use a release agent made specifically for mold making (Universal® Mold Release or Mann’s Ease Release® 200 available from Smooth-On or your Smooth-On distributor). A liberal coat of release agent should be applied onto all surfaces that will contact the plastic.
IMPORTANT: To ensure thorough coverage, apply release and brush with a soft brush over all surfaces. Follow with a light mist coating and let the release agent dry for 30 minutes. Smooth-On silicone rubber molds usually do not require a release agent unless casting silicone into the mold. Applying a release agent will prolong the life of the mold.
MEASURING & MIXING...
Liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass or plastic. Materials should be stored and used in a warm environment (73°F / 23°C).
The components (Parts A and B) should be at room temperature (73°F / 23°C). Combine equal amounts of Parts A & B by volume in a mixing container. Make sure that you scrape the bottom and sides of your container several times. Do not delay between mixing and pouring. Also, the higher the mass concentration, the faster the material gels and cures.
IMPORTANT: Shelf life of product is reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT® Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life of unused liquid urethane products.
Pouring - For best results, pour your mixture in a single spot at the lowest point of the containment field and let the mixture seek its level. This will help minimize air entrapment.
For Best Results - Best results are obtained using a pressure casting technique. After pouring the mixed compound, the entire casting assembly (mold, dam structure, etc.) is placed in a pressure chamber and subjected to 60 PSI (4.2 kg/cm2) air pressure for the full cure time of the material.
Curing - Important: Use this product with at least room size ventilation or in proximity to a forced outlet air vent and do not inhale/breath fumes. Fumes, which may be visible with a significant mass concentration, will quickly dissipate with adequate ventilation. Castings with significant mass may be hot to the touch and irritate skin immediately following cure. Let casting cool to room temperature before handling.
Demold time of the finished casting depends on mass and mold configuration. Low mass or thin-walled castings will take longer to cure than castings with higher mass concentration.
If making rotational or hollow castings, backfilling with a rigid foam (Foam-iT! 5 or other) will provide lightweight reinforcement. Foam backfilling is recommended if castings will be subjected to temperatures above 85°F / 30°C.
Performance - Cured castings are semi-rigid and impact resistant. They resist moisture, mild heat, solvents (intermittent contact) and can be primed/painted or bonded to other surfaces (any release agent must be removed) using Urebond or similar flexible adhesive. If machining material, wear breathing protection. Unpainted castings may discolor in proportion to duration and intensity of exposure to UV light.
If suitability of any Smooth-On material is in question for your application, a small scale test is recommended before using for an important project.
Because no two applications are quite the same, a small test application to determine suitability is recommended if performance of this material is in question.
This moldmaking video shows the process of molding an actual trout for taxidermy or propmaking purposes.
Justin Jotso of Jester Productions and FX's replica Captain America helmet.