The following engineering quality considerations need to be taken into account:
◾ Does the part have to be completely bubble free? − Normal pouring with doubles degassing
− Centrifugal casting − Vacuum casting
◾ Limits on dimensions − Typical commercial castings*
• 0 to 25 mm ±0.1 mm • 25 to 915 mm ±0.5% • 915 mm plus ±0.7%
◾ Is the profile the most suited to polyurethane? − Shape factor − Heat buildup and dissipation
The smoother the surface finish, the more expensive the mold. Polyurethane reproduces the finish of the mold. A very fine finish requires a hard scratch-resistant mold with no mold release buildup. Polyurethane makes a good mold material as it does not scratch or tear easily.