Optical Profilometry Metrology Protocols for Indirect Tool Cavity Topography Verification
Calibrated silicone replicas combined with optical profilometry yield sub-micron tool cavity topography metrics without destructive sectioning.
Elastomeric Set
Meaning
Permanent deformation remaining in a rubber or thermoplastic elastomer after the removal of a specific compressive or tensile load defines the stability of a seal. The elastomeric set represents the percentage of the original displacement that the material fails to recover once the stress is released. In gasket design, this value determines the long term sealing force available to prevent leaks.
High values indicate a loss of elasticity, which typically results from chain scission or crosslink degradation at elevated temperatures.
Recovery Variable
Compression testing at 70 degrees Celsius or 100 degrees Celsius for 22 hours provides a measure of performance. A material with a high elastomeric set will flattened out under a bolt load and fail to spring back when the assembly undergoes thermal cycling. This loss of memory is dangerous in automotive cooling systems where pressure varies significantly.
Choosing a grade with better recovery ensures that the seal maintains contact with both mating surfaces throughout the part life.
Molecular Structure
Crosslink density and the type of curing agent used in the formulation dictate how well the chains return to their original position. Sulfur cured systems often exhibit different elastomeric set characteristics compared to peroxide cured or platinum cured alternatives.
Moulding Impact
Processing conditions such as cure time and temperature directly influence the final state of the network. Under-cured parts show poor elastomeric set because the polymer network is not fully established to resist permanent flow. Over-curing can also be detrimental by making the material brittle and prone to micro-cracking under load.
Adjusting the cycle time in the injection or compression mould is the primary way a producer optimizes this property for the application.