|
1. |
Brazing is accomplished using active alloy braze techniques. The active alloys
generally contain titanium. |
| 2. |
Brazing can
be accomplished with titanium doped braze preforms available from Wesgo and
Degussa. These are typical silver bearing braze alloys containing a few percent
titanium. The other alternative is to paint the ceramic surface with an active
metal hydride film followed by brazing using a standard commercially available
braze alloy. |
 |
|
Surface Preparation
|
|
MACOR® |
| 1. |
Grind
surface to .8 micron (30 microinch) average roughness then lap to .1 micron (5
microinch) average roughness for best braze strength. |
|
2. |
Degrease
surface with organic degreasing agent. Isopropanol and acetone are acceptable. |
| 3. |
Wash
ultrasonically a minimum of 5 minutes in deionized water heated to at least 65°
C (150° F) |
| 4. |
Dry 2 hours
at 100° C (212° F) |
| 5. |
Handle with
gloves to ensure cleanliness |
| 6. |
Use as soon
as possible to prevent contamination of cleaned surfaces. |
|
Metal |
| 1. |
Degrease
using isopropanol and acetone. |
|
2. |
Lightly etch
the metal surface using standard etching solutions. The objective is to remove
any contamination from the surface, lightly roughen the surface and provide a
virgin metal surface for braze alloy flow. |
| 3. |
Rinse in
deionized water. (See MACOR® preparation above) |
| 4. |
Dry at 100°
C. (See MACOR® preparation above) |
| 5. |
Handle with
gloves. |
| 6. |
Use as soon
as possible. |
|
|
Fixturing the MACOR® MGC to
Metal Assembly
|
|
Active Alloy Preforms |
| 1. |
Place a 14
to 75 micron (.001" to .003") thick preform on the area to be brazed. |
|
2. |
Place the
metal part over the preform. |
| 3. |
Fixture to
maintain alignment during firing. |
| 4. |
Apply
approximately 34 kPa (5psi) load on the assembly to facilitate braze alloy
flow-out. |
| Hydride
Process |
|
1. |
Prepare a
slurry of 2 cc ethylene glycol with 1 gram titanium hydride powder. Keep the
mixture agitated. |
| 2. |
Apply a thin
layer of the slurry to the surface of the MACOR® to be brazed. The
hydride must completely cover the area to be brazed. Thickness should be less
than 15 microns (.0007"). |
|
3. |
Allow the
hydride layer to air dry. |
| 4. |
Place a 14
to 75 micron (.001" to .003") thick braze preform over the hydride layer. |
| 5. |
Place the
metal part over the preform. |
| 6. |
Fixture to
maintain alignment during firing. |
| 7. |
Apply
approximately 34 kPa (5psi) load on the assembly to facilitate braze alloy
flow-out. |
|
|
Firing the MACOR® MGC to
Metal Assembly
|
|
1. |
Apply a
minimum vacuum of 10–5
Torr or lower in the furnace and be sure to maintaim throughout the firing
cycle. If using the hydride process, a pressure increase near 350° C (660° F)
can be expected as the hydride decomposes. It is important to maintain the
minimum vacuum level even during the pressure rise. |
| 2. |
Heat at 50°
to 200° C (90° to 360° F) per hour. Maintain equalized heating of both MACOR®
and metal components. |
|
3. |
Hold for 1
minute 20° to 30° C (65° to 85° F) over the braze alloy liquidus temperature. |
| 4. |
Cool at a
rate of 50° to 200° C (90° to 360° F) per hour. Maintain equalized temperatures
on both the MACOR® and metal components. |
|
|
Hints for MACOR® MGC to Metal Brazing
|
|
1. |
Maintain an
oxygen free environment in the vicinity of the components being brazed. If
necessary, titanium getters can be placed in close proximity to the braze joint. |
| 2. |
Use a soft
fixturing material such as boron nitride or graphite. It will help facilitate
removal of the brazed assembly should the alloy flow onto the fixture supports.
A brazing stop-off of liquid boron nitride can be applied to help keep braze
alloy from flowing onto critical surfaces. |
|
3. |
If using the
hydride process, a fresh slurry should be prepared before each brazing operation
due to the short shelf life of the hydride slurry. |
| 4. |
Braze alloy
preforms are recommended for consistent and uniform joint thicknesses. |
| |
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