Elastomers
Material properties and characteristics relevant to elastomer selection and fabrication in P&O.
Elastomers have synthetic polymer with rubber-like properties. When selecting elastomers in practice, balance the needs for comfort vs stability.
- Thermoset or Thermoplastic
- Mechanical Properties
- Functional incompressibility Elastomers subjected to a compressive stress flow.
- Tensile Strength and Elongation Elastomers have a very large elastic range (often 100-1000%) with moderate tensile strength.
- Hardness Typical ranges span from very soft (Shore A 10-20) to very hard (Shore D 50-80). Hardness affects flexibility, wear resistance, and sealing capability .
- Compression Set Low compression set is critical for sealing applications and long-term performance.
- Tear Resistance Vital for durability in dynamic applications or where sharp edges are present.
- Processing/Fabrication Characteristics
- Viscosity and Flow Properties For liquid injection molding or casting, the uncured material’s viscosity and flow characteristics determine processing parameters and part quality.
- Cure Characteristics Vulcanization or curing behavior, including cure time, humidity, temperature requirements, and the need for catalysts or accelerators. This affects manufacturing efficiency and part properties.
- Some silicone systems use atmospheric moisture during curing, while others cure independently of humidity levels.
- Adhesion Properties Bonding capability to substrates, other elastomers, or during multi-shot molding processes. Surface treatments may be required for optimal adhesion.
- Other
- Thermal Stability Elastomers become brittle and are less capable of large deformations below (colder than) their Glass transition (Tg) temperature. Above Tg, they remain flexible and can handle repeated stretching and deformation. This transition is not a sharp phase change but rather a gradual shift over a range of temperatures.
- Biocompatibility Silicone exhibits low allergenicity compared to other materials. For patients with highly sensitive skin, begin material selection with silicone options.
Elastomers – Key Takeaways
- Synthetic polymers with rubber-like properties
- Maybe be thermoset or thermoplastic
- Large deformation: they have a very large elastic range
- Functional incompressibility. Flow is the result of an incompressible elastomer subjected to a compressive stress
- Viscoelastic: Increases stiffness as loading rate increases
- Temperature Dependent: become brittle and are less capable of large deformations below (colder than) their Glass transition (Tg) temperature
- Selecting elastomers in practice, balance the needs for comfort vs stability
These materials undergo a chemical change, hardening permanently when heated (cured). This curing process creates a cross-linked structure that makes them rigid and strong, but also makes them unable to be reshaped by heating.
These materials soften when heated and can be repeatedly melted and reshaped without significant chemical change.
Under compression, elastomers will bulge outward or flow into available space rather than compress volumetrically, which must be accounted for in seal and gasket design.
ability to withstand stretching forces without breaking
The permanent deformation that remains in a material after it has been compressed and the compressive force is removed. Low Compression Set Better for Long Term. Measured as a percentage of the original thickness that is not recovered after compression.
resistance to crack propagation under stress
Increases stiffness as loading rate increases