Vacuum Annealing

Annealing heat treatment is a procedure in which pieces are heated and then slowly cooled in order to achieve a softer structure and enhance material structure for subsequent shaping operations.

Compared to treating under atmosphere, annealing under vacuum offers the following advantages:

• avoiding inter granular oxidation (IGO) and surface oxidation
• avoiding de-carburized areas
• metallic, blank surfaces
• clean surfaces of parts after heat treatment, no washing of parts necessary

Vacuum Annealing Furnaces:

The Horizontal Vacuum Annealing Furnace is designed to heat treat reactive metal tubes and bars and their alloys under vacuum. The vertical annealing vacuum furnace is mostly used for lengthy components, such as overweight rod shaft parts, that need to undergo vacuum heat treatment, recrystallization of non-ferrous metals, or annealing ageing treatment. It is a hot, side-loading, cylindrical wall furnace with a task temperature consistency that is positioned horizontally. The furnace has three chambers: a central hot chamber, cooling chambers on either side, and a loading station and platforms with pulling/pushing mechanisms on either side.

After due cooling, charge basket is pulled back to loading platform and annealed charge is unloaded. Schematic of this furnace is given below:

Fig: Schematic of Vacuum Annealing Furnace.

Why Thermal Profiling is required?

How can process engineers verify that vacuum annealing used to prepare materials is suitable for its intended use? Before processing the components, they must determine whether the treatment of the metal for productivity and internal consistency of the material, production efficiency was effective in order to avoid unnecessary scrap and rework. The pieces will be tested "post procedure" to determine whether or not the treatment was successful.

Major Problems in Vacuum Annealing Furnaces:

The actual temperature of the parts on the conveyor can fluctuate due to radiation, and a few heat losses, so it is incorrect to assume that the heat zone controls component temperature. The annealing process will be improperly handled as a result, and the quality of the manufactured part will be improperly monitored. One area of the metal may expand more quickly than another if it is heated unevenly, resulting in a twisted or fractured piece of metal.

The more common and basic method has been to apply the "trailing thermocouples" method. A very long Thermocouple is attached to the furnace while the product is manually fed into the furnace. The datalogger that is utilised to keep track of the current temperature is kept out of reach of the furnace. Although useful, this approach is challenging to apply and offers a limited amount of information. Trailing thermocouples can be replaced by "thru-process temperature profiling." Instead of thermocouples trailing, a datalogger travels through the furnace with the product. The datalogger is protected by a structure called a thermal barrier, which keeps the temperature of the logger at a safe operating level.

For example, just because a vacuum furnace is set to 500 °C does not mean that the entire chamber is at 500 °C. As a result, a furnace temperature uniformity survey is required. For temperature uniformity testing, we'll need a Thermal Profiling System, thermocouple, and sample bucket. In order to maintain furnace temperature uniformity, a point-to-point temperature monitoring survey of a sample bucket is required.

Solution Provided by Tempsens:

If we closely monitor the curing temperature for a predetermined amount of time, we can solve these issues. Here, the Smartack 10 data logger and Thermal barriers, which were designed and created completely in India, play an important role. One may carefully monitor and adjust the temperature and length of their heat treatment process with these temperature profiling systems. By connecting a thermocouple to the components and bucket, it is possible to obtain the temperature profile of the annealing procedure.

The data logger must be shielded from the furnace ambient temperature, which is accomplished by keeping the data logger inside the thermal barrier.

After the procedure is finished, one can download the data from the data logger and convert it into helpful data using TEMPSENS' SmartLog Software. One can make immediate and precise judgements to address issues with the annealing process after monitoring and statistically evaluating the data, which will improve quality and productivity. Data can be obtained using a simplified data logging process in graphical mode, numerical data, and report formats.

Further Reading

• Thermal Profiling System
• Thermal Profiling - Importance in Reflow Ovens
• Thermal Profiling Importance in Ink Printing