Brazing Chamber - November 2008
Brazing is defined by Wikipedia as:
|"a metal-joining process whereby a filler metal is heated above and distributed between two or more close fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled to join the two workpieces together. It is similar to soldering, except the temperatures used to melt the filler metal is above 450C, or, as traditionally defined in the United States, above 800F."|
This application required brazing because the use of SST tube heaters in a vacuum could easily cause the heaters to burn themselves out at the operating temperatures required by this particular customer. In order to prevent this from happening, the heaters were brazed to a thick plate of copper in order to dissipate heat evenly over the surface. A powdered nickel alloy was used as the brazing material.
- Each assembly weighs 800lb and the brazing chamber must process two at the same time.
- Both assemblies must remain flat to prevent liquid nickel from flowing off the copper at temp.
- The heaters in the copper were NOT used to heat the hot box. Instead graphite heaters were suspended both above and below each assembly.
- The electrical connection for each of the graphite heaters had to pass through the vacuum chamber door so electrical connections can be made at atmosphere.
- Each assembly must be loaded into the cart from the side to protect each of the graphite heaters.
- Heater ends must be protected from the heat of the hot box because the internal soldered connections will melt rendering the entire assembly useless.
- Entire hot box and both brazing assemblies had to be cantilevered off the vacuum chamber door and put on a rolling cart.
- I had to incorporate two vieport doors that would line up with one another in it's process configuration. One viewport through a side door in the chamber and the other had to move insulation out of way to see inside the brazing process.
- The thick copper plate had to be precisely machined so that the heaters would fit very tightly in the grooves
- Heaters had to be staked into the bottom of the grooves so they could not move during brazing.
- Copper plate is then orientated so that the nickel powder can be applied to the surface without falling off.
- Assembly is loaded into the brazing chamber via the cart.
- Brazing chamber is pumped down to zero atmosphere.
- Heaters are turned on for approximately one hour until thermocouples read 1800F.
- To prevent oxidation, the hot box needs to cool for approximately 10 hours before the vacuum can be released.
PICTURES & VIDEO:
BACK TO PORTFOLIO