Easy-to-mix Shore A and Shore D hardness polyurethane resin systems are widely used for hand pouring and mass casting to produce thin-walled prototypes as well as parts up to four inches thick. The polyurethanes are ideal for producing 10 to 100 durable prototypes and initial parts with a smooth, blemish-free surface finish. For hand and mass casting, resin and hardener are weighed on a precision scale and combined in a mixing container. System components and any fillers or pigments being added are then stirred for about three minutes until a uniform, completely blended mixture is obtained. The resin system is then degassed and poured into a prepared mold and allowed to cure fully.

Polyurethanes feature a number of handling benefits for hand- and mass casting:

• Easy to mix. Many systems have 1:1 or 2:1 resin to hardener mix ratios and low viscosities to facilitate weighing out and mixing of components.
• Ideal for pigmenting and color matching
• Hand pourable with gel times as long as 60 minutes at room temperature
• Fast and slower cure materials available, depending on project requirements
• Permit casting of parts from 0.5 in. to 4 in. thick in a single pour
• Simulate injection-molded thermoplastics including ABS, TPO, and polycarbonate