Vacuum Furnaces for Metallurgical Applications
With the constant need in the metallurgical field to develop better materials, both lighter and stronger, application of vacuum technology in the manufacturing process has been of paramount importance.
Processes of melting, brazing, welding and casting by first creating vacuum and then backfilling with an inert gas in a chamber has helped produce better materials which have been proved to be stronger, with thinner cross sections, with a long life due to prevention of oxidation and other contaminations. This has brought about various requirements especially in the fields of space, aerospace, atomic energy, defence, medical, lighting, automotive, etc.
A typical vacuum furnace for brazing, annealing, heat treatment, etc. is a leak tight vacuum vessel with insulation for retention of temperature within the chamber and heating elements to internally heat within a defined area called the hot zone. For different levels of temperatures, different methods of insulation and heating elements are provided.
R&D applications.
Design challenges
The challenges involved in designing of these high temperature, high vacuum, high pressure furnaces is that they have to be leak tight, unlike atmospheric furnaces. Therefore a good metal vessel creation is the big challenge and it is achieved by using high quality stainless steel.Heating is usually done by resistive heating. Depending upon the process, it can also be done by induction. Since it is in vacuum, its operating voltage is low to avoid creation of plasma and arcing. Therefore all vacuum furnaces with resistance heating use low voltage, high current power sources to heat the furnaces.Heating elements are made of nichrome, molybdenum, tungsten, tantalum or graphite.
Depending upon the material characteristics, temperatures during hardening vary. Quenching is by gas (high pressure) or by dipping in oil. This requirement is also based upon materials. High pressure gas furnaces can go up to 20 bar.
The SS vessels are high strength steel vessels and are constructed using ASME unfired pressure vessel codes. Good welding practices by TIG welding and qualification of welding and using high quality 0-rings like viton with special flanges and rotary locking arrangement are some of the requisites to make a good quality product.
Processes galore
Currently there are many processes which are being carried out in vacuum such as brazing, annealing, hardening, tempering, stress relieving, passivation, solution ageing and many more applications, where people use different levels of vacuum, different levels of gas pressure and different mediums to achieve the desired results.
Vacuum Furnaces are built in two different configurations:
- Horizontal loading configuration.
- Vertical loading configuration.
If a cylindrical job is there then it is vertically mounted. If it is an odd shape or square or rectangle then it is mounted on a horizontal configuration. Depending upon the job profile either horizontal or vertical furnaces are made use of. Sintering is the other application where it has emerged in processing powder metallurgical components and also to process high temperature ceramics like high alumina, zirconium, beryllium and other refractory materials. Sintering constitutes preparation of powder; compaction with a starting mass and then this is fired to sintering temperatures starting from 1000 deg. C to 2000 deg. C to get the required components.
Rotary brazing furnaces were evolved for double walled inverted nozzles having a circular configuration which need to be brought together for circulation of a fluid within a set path requiring to be brazed. In a static condition it becomes very difficult to provide a uniform braze along the path of the fluid. To overcome this, a rotary motion of the components during the brazing cycle is the answer. During circular motion, the flow of the braze material is uniform and provides the much needed seal to eliminate any short cuts in the path of the flow.
HHV has been making induction melting and casting furnaces for the aerospace industries. These are predominantly harnessed for casting of turbine blades using super alloy materials to provide thin cross sections and good resilient strength.
HHV’s niche
HHV has been in this business for last four decades and have built all varieties of furnaces in the past. Major installation which have been done by HHV are rotary brazing furnace in department of space, vacuum indication melting and casting furnaces to HAL Koraput and vacuum brazing annealing and hardening furnaces in HAL , DMRL, Department of Space, Atomic Energy and many other industries as well. HHV is a leading manufacturer of all of kinds of vacuum furnaces and its strength is to design and build with recipe embedded within the furnaces for customer applications.
For more information
Web: www.hhv.in
