Silicone and Resin Technical Information
Below we have included:
- Definitions for technical terms and characteristics relating to silicone and resins
- Silicone and resin guides and how-to articles
- Tips & hints relating to silicone and resin moldmaking and casting
Term definitions:
Here are some references to qualities or characteristics of these materials, which give different properties to the products. Some common comparisons might be helpful in determining how these properties relate to your selection of materials.
Durometer
A durometer is the device used for measuring the hardness of plastics,synthetics and natural rubber materials. Both scales measure hardness
on a table from 0 to 100.
The higher the measured value, the harder the material. Ratings are always
qualified to plus or minus 5 points due to variations of test results from operator to
operator.
The Shore A scale is most commonly used as a measurement for the more
“rubber-like” materials, including most silicone RTV materials and Flexible urethanes.
Silicone rubbers generally run between 12 and 60 on the Shore A scale.
Flexible Urethanes generally run between 15 and 90 Shore A.
The Shore D scale will measure harder elastomeric products, and rigid materials.
Mid-range Shore D, ie 50-60D will overlap high Shore A, 80-90A with many characteristics.
As well as hardness, other factors of the characteristics of Shore D materials can include brittleness, tensile strength, flexural strength, impact resistance, and surface qualities.
Viscosity
Viscosity is the measurement of a fluid’s internal resistance to flow. This is normallydesignated in units of centipoise or poise.
Approximate Viscosities of Common Materials at room temperature:
| Water | 1cps |
| Machine Oil | 100cps |
| #30 Motor Oil | 250cps |
| Olive Oil | 500cps |
| Castor Oil | 1,000cps |
| Karo Syrup | 5,000cps |
| Honey | 10,000cps |
| Molasses | 100,000cps |
| Peanut Butter | paste |
Thixotropic
Materials reduce their viscosity as agitation or pressure is increased at aconstant rate. Ketchup and mayonnaise are considered thixotropic materials. They
appear thick or viscous but actually pump quite easily. Additives are available for some materials, to turn normally liquid materials, into 'non-sag' materials. This may be particularly relevant when applying a skinlike layer to a substrate.