Rate Table Environmental Testing
Devices often require testing under a wide range of environmental conditions. Since many of the components within a table cannot tolerate widely varying conditions, the technique used is to extend the spindle through a thermally insulated tube to place just the platen (and therefore the test package) within the environmental chamber.
The extension tubes are designed to have a high torsional stiffness, low thermal conductivity.
Cranfield Precision uses a custom designed extension tube comprising a stainless steel housing and polymer concrete core (eg Granitan). The result is a highly damped, stiff, stable and thermally insulating extension tube.
The new tube will hold a 200°C differential for over two hours, with a reduction in system bandwidth of only about 30 percent.
For long period soak testing at low temperatures, the lower end of the tube can be fitted with thermostatically controlled heaters.
A zero friction seal between the chamber floor and the rotating tube is achieve using a double labyrinth seal, one at the top and one at the bottom of the tube, with a slight negative pressure on the exhaust between them.