Temperature profiling in aluminium heat treatment

Many high volume production foundries use continuous furnaces for the heat treatment of castings. Cylinder heads, wheels, suspension components and many other aluminium alloy products are placed in wire product baskets and treated in pusher or roller hearth furnaces. Temperature has to be carefully controlled in the various heat treatment cycle stages in order to make sure the end product complies with design requirements.

The typical heat treatment process parameters are temperature, the time the castings remain in the furnace, and the time from when they leave the solution treatment stage until they enter the quench tank. Typical heat treatment processes, known as T6 and T7, involve a solution treatment followed by air or water quench, and lastly an accelerated age hardening phase.

Age hardening is a very important and delicate stage as it defines mechanical properties of the processed material such as breaking load, limit of proportionality, extension and strength. Accurate temperature monitoring is therefore vital in order to make sure the client’s product specifications are met.

Automatic management of continuous furnaces is normally based on the forced circulating air temperature, which is only indirectly related to the actual temperature of the processed product. Alternatively, the temperature may be measured by trailing thermocouples appropriately placed in the castings. However, this is only feasible for monitoring semi-continuous furnaces, not for continuous furnaces, particularly if they are divided into several stages. In such cases, which are very frequent in actual foundries, in-process control is the only feasible method for monitoring product temperature.

These are measurement systems like the Datapaq system, which are placed in the product baskets carrying the castings in the furnace. They can read and store analog signals from up to ten temperature sensors (thermocouples) placed at strategic points in the baskets/castings. The Datapaq system has a battery which provides enough energy to profile a complete process cycle with a minimum three second sampling rate.

The logger, which stores the data in the memory after analog to digital conversion, is protected by a thermal barrier. This barrier is made of a highly efficient insulating material that can withstand high temperatures for long periods of time and submersion in the water quench. When the heat treatment cycle is over, the stored temperature data may be retrieved and displayed by simply transferring them from the logger memory to any personal computer. Data analysis is made easy with Datapaq’s user friendly Insight analysis software.

If the process requires real-time temperature monitoring, a telemetry option is available which remotely transfers data through radio frequency transmission.

To summarise, the Datapaq system allows you to:

• Guarantee that heat treatment specifications are adhered to.

• Check thermal consistency during the various cycle stages.

• Prevent defects attributable to the way heat treatment is performed.

• Meet all the requirements laid down in the EN ISO 9001 and ISO/TS 16969 standards.

• Streamline the heat treatment process to achieve relative quality which can be sustained in the long term (cost/benefit trade-off), rather than quality at any price.

Datapaq offers complete user friendly and reliable solutions for most heat treatment processes. A Datapaq system enables in-process parameter monitoring and streamlining of the manufacturing process with the end customer in mind.

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