From start to finish, the production of metal products is one of the most energy-intensive industries in the world. As a result, improving both energy and production efficiency, while also ensuring product quality, is likely at the top of any manufacturer’s to-do list.
When it comes to heat treating, however, understanding the way the furnace works is key to optimizing the process. Fortunately, this understanding can be achieved with thermal profiling.
What is temperature profiling?
As mentioned, the first step in understanding and optimizing any heat-treatment process is temperature profiling, which is essentially the continuous reading and recording of product temperature and/or ambient air at a number of points throughout the furnace.
These readings are stored on a datalogger (Figs. 1 and 2), which moves with the product through the furnace while being protected by an insulated enclosure. This enclosure is called a thermal barrier (Figs. 3 and 4) and is designed to repeatedly keep the logger safely within its operating range, even at the most extreme operating temperatures.
Once the data is downloaded from the datalogger or retrieved via radio frequency (RF) telemetry, process engineers are able to analyze an in-depth time-temperature profile that showcases the temperatures the product experienced throughout the entire heating process. This information is the critical piece to any puzzling heating operation because, in its simplest form, it displays how hot the product became and for how long. It also displays at what temperatures it reached and at what point.
Process engineers know exactly what the perfect profile of each product should be because variations in that profile could indicate a potential problem to them. They are also able to verify products are reaching quality standards, increase throughput, improve costs associated with energy used by the furnace and more.
Temperature Profiling vs. Alternatives
While control thermocouples placed throughout the furnace can inform process engineers how the furnace is operating, they do not provide a complete picture of the process. Control thermocouples only provide furnace ambient temperatures and do not allow for direct product-temperature measurement. This is also critical because heating rate is often dictated by the product’s geometry.
Alternatively, direct product-temperature measurement is possible when attaching trailing thermocouples. This approach can be both unsafe and difficult, however, if the furnace is long or is running a lot of product.
The furnace is the heart of any heating operation, and the quality and reliability of the finished product depends on its performance. Because the alternatives do not provide a complete picture, a temperature profiling system is the ideal tool for maximizing the efficiency of the heat-treatment process and getting the most out the furnace. Many temperature profiling systems can be used for such purposes.
For example, there are Datapaq loggers available that feature 10 and 20 channels for maximum data collection, can read temperatures up to 1700°C (3092°F) and operate in temperatures up to 110°C. When paired with a rugged thermal barrier (Fig. 4), heat treaters can sample data throughout the entire process, even though process temperatures may exceed 1000°C (1832°F) all of which is ideal for most high-temperature heat-treatment applications.
Profiling Product in Action
There are a variety of products that require heat treatment. When looking at steel pipes for the oil-and-gas industry, for example, it is vital that each product has been heat treated properly. These pipes are subject to high pressure, and the physical properties of the final product ultimately depend on the heat-treatment cycle.
In this example, each pipe is heat treated at approximately 950°C for 60-90 minutes, which is de-pendent on the thickness and grade of the steel. Because this product is processed in a walking-beam furnace, however, rectangular thermal barriers with conventional thermal protection cannot be in-stalled. A specialized range of cylindrical thermal-barrier solutions was developed that fit inside the pipes so that they pass through the process measuring product temperatures from inside the pipes.
Once the end user was able to implement a Datapaq thermal profiling system and see into their process for the first time, they were able to utilize the datalogger and intuitive software to provide process traceability and product certification. In addition, the manufacturer was able to reduce changeover time for different-sized pipes and quickly identify process faults within the furnace in order to reduce waste.
Because the manufacturer could reduce both production time and waste, less fuel (and therefore less energy) was used. In other applications, such as hot forming, similar thermal profiling techniques can be applied to shorten heating time by up to 15%, which also translates into energy (and cost) savings due to less energy consumption.
Temperature Uniformity Surveys (TUS)
In the aerospace and automotive industry, manufacturers are required to prove that their furnaces are compliant with specifications such as AMS 2750 and CQI-9.
A composites supplier, for example, was required to regularly survey the autoclaves where composites are cured and needed to be audited by Nadcap. Once they introduced a thermal profiling system utilizing RF telemetry, the supplier was able to reduce TUS cycle times by up to 50%, which saved hundreds of hours in time and energy. The dedicated TUS software option available with some thermal profiling systems, such as Datapaq, also helped bring report generation and data collection down from days to hours.
Additionally, another supplier was required to conduct surveys every quarter to ensure each reheat furnace was compliant with AMS 2750 specifications. This supplier chose to implement a Datapaq logger with RF telemetry, which reduced downtime and improved overall furnace performance and energy usage.
Measuring and analyzing what is happening to product as it moves through a furnace or oven is the first step in both understanding and optimizing any heat-treatment process. If heat treaters today regularly use temperature profiling equipment and intuitive software solutions, they have the opportunity to make precise furnace adjustments that can help significantly increase productivity, control product quality, confidently prove process control, and even achieve potential energy and cost savings.
For more information: Contact Fluke Process Instruments, 6920 Seaway Blvd., Everett, Wash. 98203; tel: 425-446-6780; e-mail: firstname.lastname@example.org; web: https://www.flukeprocessinstruments.com. Author Stewart Griffiths is product specialist for Fluke and is located in the U.K.