Silicone and polyurethane are commonly used materials for making molds. Both materials have their own advantages and disadvantages, and the materials suitable for casting are also different. For the purpose of this article, we will introduce these two mold rubbers in detail.
Silicone Rubber
Silicone rubber has the best mold release properties of all mold rubbers and will not stick to most materials. Therefore, applying a release agent to the surface of your cured silicone rubber mold before casting is often not necessary. In addition, silicone rubber has the best high temperature heat resistance, and you can cast low-temperature molten metal alloys such as tin and pewter into silicone rubber molds. Silicone rubber offers the mold maker the advantage of high tear resistance, and silicone also has very good chemical resistance.
At present, the most popular silicone rubbers for making molds in the market are tin-cured silicone and platinum-cured silicone:
1. Tin-Cure Silicone Rubber: This silicone is also called condensation silicone, which is mainly used in mold making of industrial products, and they are great for casting almost any material. Tin-cured silicone will shrink over time, and with age, they will lose tear strength and eventually become unusable.
2. Platinum-Cured Silicone Rubber: Platinum-cured silicone is also known as addition silicone. This silicone can reach food grade and is more expensive than tin-cured silicone, but this silicone will almost never shrink and has better aging resistance.
Polyurethane Rubber
Polyurethane rubber is available in wide hardness range, from softer than your skin to harder than a car tire and every hardness inbetween. They cost less than silicone rubber.
Compared to the excellent release properties of silicone rubber, urethane rubber can stick to almost any material, so it is often necessary to apply a release agent when casting products with urethane rubber. In addition, urethanes are moisture sensitive, meaning that they may bubble or even foam when exposed to humid air.
Polyurethane rubber is good for casting wax, plaster, concrete and resins.
| Rubber Type | Tin-Cured Silicone Rubber | Platinum-Cured Silicone Rubber | Polyurethane Rubber |
|---|---|---|---|
| AB Ratio | 100:2~100:5 | 1:1 or 10:1 | 1:1 |
| Hardness(Shore A) | 5-50 | 0-60 | 20-70 |
| Process technology | Pour, Brush, Spray. | Pour, Brush, Spray. | Pour, Brush, Spray. |
| Advantages | 1.Excellent mold release. |
1.Excellent mold release. 2.Good temperature resistance and aging resistance. 3.Shrinkage is as low as 0.1%. |
1. Excellent tear resistance. |
| Disadvantages |
1. easy to age 2. The shrinkage rate is relatively large, about 0.3%. |
1.Cured rubber has limited storage life. 2.relatively high cost. |
1. Easy to absorb moisture and generate air bubbles. 2.Poor mold release, need to apply mold release agent |
| Casting Materials |
Epoxy Resins Polyurethane Foam Polyester Resins low-melt metals |
concrete Wax or Plaster |
|