|
Vacuum brazing
PVA-LWT offers vacuum brazing technology in all its varieties.
With PVA-LWT vacuum brazing technology, we make possible almost
all materials combinations with highest quality requirements.
As vacuum brazing can be applied for many different materials,
the potential of application is nearly infinite.
The multitude of applications for vacuum brazing will be
outlined by the following examples:
1. Vacuum brazing for heat-exchangers
2. Vacuum brazing for electronic/power
supply industry
3.Vacuum brazing in hydraulic/pneumatic
industry and in measuring
technology
4. Vacuum brazing for special materials
5. Vacuum brazing in series production
1.Vacuum Brazing for heat-exchangers
Heat exchangers and water-cooled parts are standard products
for vacuum brazing technology. With vacuum brazing large interfaces
can be bonded, which have very good heat transfer properties.
As vacuum brazing is an integral heating process, parts with
a complex joint design can be brazed without any problems.
The plate heat-exchanger made of copper for gas-water applications
is an example for this:
plate heat-exchanger
- Number of joints: approx.750
- Materials: Copper, stainless steel
- Braze: Silver-alloy
- Brazing temperature: 830°C
|
|
 |
Main requirements for the part is gas-tightness and a high
gap-filling level, to insure best heat transfer by maintaining
high corrosion resistance of the joints.
Another design variation is the so called tube heat-exchanger,
which is used for exhaust-cooling in automotives.
tube
heat-exchanger
- Number of joints: approx.100
- Materials: Stainless steel
- Braze: Nickel-alloy
- Brazing temperature: 1190°C
|
|
|
Beside tightness requirements the brazing joints of this
part have to withstand high temperatures and hot gas corrosion
attacks. This can be achieved with a high-temperature nickel-base
filler metal with an extraordinary high chromium content.
top
2.Vacuum brazing for electronic/power
supply industry
In the electronic/power supply industry high voltage components
with ceramic insulators, such as vacuum chamber switches,
high power vacuum tubes and high current feed-throughs are
used.
With PVA-LWT vacuum brazing technology ceramic materials can
reliably be joined to metal parts to achieve gas tight joints.
One constructed part developed and fabricated by PVA-LWT
is the high vacuum current feed-through. This part consists
of four different materials and is made in a two-step joining
process. A Silver-Palladium alloy is used as filler metal.
Beside selection of suited filler metals and process parameters,
assembly of the parts with adequate jigs requires special
know-how.
top
3.Vacuum brazing in hydraulic/pneumatic
industry and in measuring technology
In hydraulic and pneumatic parts the joints are normally
under high mechanical stress. For application of brazing technology
therefore filler metals have to be chosen, that allow fabrication
of high strength joints which are reliable especially under
alternating stress conditions.
The diaphragm separator, a pressure seal for measuring pressure
in liquids is a high performance part. The membrane material
is a very thin and corrosion resistant refractory metal foil,
such as tantalum or titanium. With PVA-LWT brazing technology
the membrane is brazed to a stainless steel flange.
diaphragm
separator
- Materials: Stainless steel (1.4571), refractory
metal foil
- Braze: Silver-alloy
- high strength
- brazing seam free of pores
- leak tightness: <10-9 mbar*l/s
|
|
|
top
4.Vacuum brazing for special
materials
The so called divertor element, which can be found in the
neutral element injection of a fusion research reactor consists
of very special materials. Basically, this part is a special
kind of heat-exchanger. With PVA-LWT vacuum brazing technology
the molybdenum tubes are brazed to the graphite heat shield.
A wetting level of nearly 100% is necessary to achieve extraordinary
heat transfer rates of 700 W/cm2.
cooling-finger
- Materials: Fine grain graphite, molybdenum alloy
- Braze: Silver active braze
- brazing seam free of pores
|
|
|
top |
