Special Furnaces Simulate Aero-Engine Conditions

Five specially designed Carbolite furnaces are enabling Vibro-Meter UK to perform long-term thermal test programmes that simulate conditions experienced by thermocouples in gas turbine aero-engines.

Vibro-Meter UK is part of Meggitt plc and one of the leading manufacturers of sensors for the aerospace sector.  The furnaces were bought to enable the company to carry out research into the stability and accuracy of thermocouples as a result of long-term exposure to temperatures up to 1100°C in aero-engines.  An important aspect of the equipment is the ability to simulate working conditions by cycling the thermocouples for long periods between typical operating temperatures and ambient temperatures.

In order to achieve this, the Carbolite furnaces have an automatic loading mechanism that push and pulls bundles of thermocouples in and out of the heating zone of a horizontal tube furnace.  The five furnaces built for Vibro-Meter have a maximum temperature of 1200°C and three heated zones in order to ensure precise temperature control at the centre of the 38mm diameter tube where the thermocouples are heated.

Each thermocouple is typically 2mm in diameter, and about 15 are usually tested at a time.  Test programmes typically involve holding the samples in the furnace for 30 minutes at a temperature between 700°C and 1050°C, extracting them and exposing them to ambient air for five minutes and then re-inserting them into the furnace again for 30 minutes.  This sequence is generally repeated 4000 times before the samples are analysed and calibrated to determine the effects.

The furnace design allows entire cyclic programmes lasting over 2000 hours to be carried out automatically once the temperature and time data has been input into the control system.  The five furnaces allow Vibro-Meter to carry out several programmes in parallel at the same time.

The equipment has been designed to be compact and convenient to use in a laboratory situation, with double skin construction helping to keep the outer case cool and high-quality insulation optimising thermal efficiency.  A high-precision PID temperature controller, timer and associated power control equipment are housed within an integral control box.