Compressor fluids under pressure: unexpected effects

WHY

Air conditioner compressor fluids have to prevent friction and wear under elevated gas pressure.  Standard Pin&Vee Block tests with gas 'bubbling' through the lubricant do not correlate with field behaviour, especially with CO2 as the cooling medium.  Another simulation with pressurized gas is needed.  We selected the Falex Block on Ring configuration, as it also recreates the line contacts and is able to work at higher speed than the Pin&Vee block machine.

HOW

Our Falex Block on Ring machine allows pressurizing the lubricant chamber with a gas, up to 10 bar.  Standard block-on-ring tests are done with and without pressure on the dissolved gas.  Tests with increasing contact loads (EP) and tests with constant load (Anti-wear) are done.

 

RESULT

• A sudden loss of lubricity in the CO2 pressurized oil bath can be measured.  Block temperature increases suddenly at 70°C, while lubricant temperature decreases, which indicates that CO2 bubbles are forming in the interface between block and ring. This phenomenon is only seen when the gas is dissolved under pressure in the lubricant.

 

• This leads to poor lubrication and increased wear.  Thanks to right additives, this bifurcation can be eliminated and wear prevention can be significantly improved under pressurized conditions.

 A full text on the presentation, given at the TAE Esslingen Conference of 2014, can be found in our presentation download area or click here for direct access.