PvT data describes the way in which the specific volume of a material varies with pressure and temperature. Specific volume can change significantly at the high temperatures and pressures encountered during processes such as the injection moulding of polymers and is a dominating factor in the packing & cooling phase of the moulding cycle. PvT information is essential in flow simulation software for accurate prediction of shrinkage & warpage.

Gammadot measure PvT behaviour using a high pressure dilatometer system developed by Rapra Technology Ltd. The technique employs a stainless steel bellows test cell with Mercury as the containing fluid, Figure 1. Volume changes related to changes in temperature & pressure are monitored via a displacement tranducer. Use of a containing fluid enables samples to be characterised in solid & liquid form. The test cell is surrounded by oil within a sealed pressure vessel, Figure 2. Measurements are made over a range of temperatures (23°C to 380°C) and pressures (5 MPa to 200MPa). The family of curves derived from testing are fitted to mathematical models to provide the coefficients required by flow simulation software packages such as Moldflow and Sigmasoft 3D.
PvT Sample Cells - Complete, loaded cell (Left) and separated cell showing sample containment tube (right) The PvT Apparatus (lower right) & PvT sample cell filling station (left) PvT Sample Cell being loaded into pressure vessel


Guide to PvT Sample Cell Schematic

A: Screen-Pack Steel Mesh
B: Polymer Sample (Moulded Strips)
C: Sample Holder Tube
D: Drilled Plug
E: Containing Fluid (Mercury)


Rapra Technology PvT Apparatus
A: Platinum Resistance Thermometer
B: Bridgeman Seal Assembly
C: Heater Zone 1
D: Pressure Vessel
E: Sample Cell Bellows Assembly
F: Heater Zone 2
G: LVDT Sensor Rod

Example Semi-Crystalline Thermoplastic Trace
Example Amorphous Thermoplastic Trace
Example Elastomer Trace
Example Ceramic Trace
We have experience in characterising a wide variety of materials including many types of semi-crystalline & amorphous thermoplastics, cured elastomer (NR, EPDM, FKM, VMQ, SBR, NBR, etc), detergents, ceramics, and cured epoxy resins to name a few.