In vacuum brazing, materials are joined by a thermal process in a high-purity vacuum atmosphere. Vacuum brazing allow even metals that are highly reactive to oxygen to be joined. Surfaces must be prepared properly. Also, chemically-active alloys may be used for brazing of dissimilar materials. Large-area brazed joints and complicated geometries can be joined, but uniform heating and cool down are critical for success. Typically, brazing is the last step in assembly and no post-processing operation is required.
In this process, different precious metal, Ni, or Cu-based alloys are used. The choice of solder depends on the base materials and the desired properties of the joint. For example, if copper components are to be brazed, Ag-based brazing alloys are suitable. When joining stainless steel or high-strength superalloys, Ni-based solders are the ideal choice. Ceramic materials such as Al203 or Si3N4 can also be brazed without metallization of the surfaces, though one has to use an “active” braze alloy to wet the surface of the ceramic.
PVA TePla's vacuum brazing systems, electrically heated batch systems for brazing and high-temperature brazing processes, are designed for temperatures of 800 °C to 1.300 °C, in individual cases also up to 1.700 °C. All plants of this type have active gas cooling units in order to be able to cool the brazing batches to room temperature as fast as possible.
Plants for large series with steel or copper materials
The COV system type is generally used for robust high-volume brazing applications in which steel or copper materials are joined. Characteristic of this product line is a robust heating element with heating conductors made of graphite, a graphite soft felt insulation, as well as an oil diffusion pumping station. COV brazing systems can also be used for brazing superalloys or other materials that require increased purity of the furnace atmosphere.
Equipment for extremely reaction-sensitive materials
The MOV type vacuum brazing systems, mostly high vacuum systems, are fully metal lined and have heating inserts constructed of molybdenum or tungsten. The atmosphere is low, to zero hydrocarbon, and therefore ideal for use with reaction-sensitive materials such as titanium, niobium, zirconium or tantalum. Work is carried out in high or ultra-high vacuum, thus meeting the most stringent requirements for brazing atmosphere quality, e.g. in the manufacture of vacuum interrupters. Typically, the MOV systems have turbomolecular or cryogenic vacuum pumping units integrated into the plant.
Vacuum brazing processes have a wide range of applications in a wide variety of industries such as aerospace, energy technology, electromobility and others. Thermal applications in these industries often require high-purity process atmospheres.
Typical workpieces created in this way include:
- Heat exchangers and cold plates (heating, cooling)
- EGR cooler
- Diamond and carbide tools
- Turbine parts (gas turbines, aircraft turbines)
- Vacuum interrupters
- Electron tubes
- Feedthroughs (power feeds, etc.)
- Rotary anodes for X-ray apparatus
- Instruments (pressure probes, thermocouples, sensors)
- Machine parts (pistons, housings, burner parts)
- Components in mold making (near-contour cooled molds)