Measuring trace water in argon

Paul Boughton

Rolls-Royce in Barnoldswick, manufactures the Wide–Chord fan blade. The blade design is used on the RB211-535 and RB211-524 and all Trent engines. The latest being Trent 900 for the super jumbo AIRBUS A380.

The wide-chord blade is made from three layers of titanium which are bonded together after being heat treated to a superplastic state, the metal 'sandwich' then being inflated with a gas (in this case argon). This produces a girder structure at the centre of the blade. This makes the blade exceptionally strong, lightweight and durable.

While the blade is in the heat treatment unit, the pipe work to the fused titanium blade is under vacuum to remove air. The argon is supplied into the blade at 0.4 barA and then increased to 0.5barg. At this pressure a MCM moisture meter is looking for water content below 200ppm to ensure integrity of the process.

After this phase, the pressure is greatly increased to 35 BAR to create the balloon shape at the top edge of the blade. There has to be no contamination of air during the fusion and the increased pressure process. Due to the high cost of these blades, destructive testing should be minimised.

Hence Rolls-Royce needed the accurate analysis from the MCM moisture meter to ensure the integrity of the superplastic forming process.

For more information,

Moisture Control & Measurement Ltd is based in Wetherby, West Yorkshire, England.

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