|
1. |
Capable of producing hermetic seals on MACOR®,
forsterite and metals such as Sylvania #4, Dumet, 52% nickel
alloys, chrome-iron stainless steel, platinum and Sealmet. |
| 2. |
Surface finish should be 200 (US mesh) grit. Where
feedthroughs will be installed, holes should be drilled 76
to127 microns (.003" to .005") oversize. |
| 3. |
Ensure
that the sealing surfaces are absolutely clean. (see
Cleaning.) |
| 4. |
Glass
frit can be applied by dipping, spraying, painting, screen
printing or extrusion. |
| 5. |
Frit
should be mixed between 5:1 and 15:1 frit to vehicle depending
upon application method. Make only as much slurry as needed to
produce a seal. The slurries have a short shelf life. |
| 6. |
Vehicle can be obtained commercially from suppliers such as
Ferro and Drakenfeld. |
| 7. |
You
can produce your own vehicle using amyl acetate or denatured
alcohol with about 1.2% nitrocellulose or equivalent added as
an organic binder. |
| 8. |
After
applying the frit, it must be thoroughly dried. Oven drying is
recommended but heat lamps can also be used. Keep drying
temperature below 350°C (660°F). Suggested drying cycle is
heat at 200°C (360°F) per hour to 200°C (390°F), hold for 15
minutes and then cool at the same rate. |
| 9. |
To
fuse the frit to the MACOR® to improve handling,
heat at 150° to 200°C (270° to 360°F) per hour to the
softening point of the frit. Hold for 5 to 10 minutes and cool
at the same rate. |
| 10. |
Sealing cycles will depend upon seal geometry and sizes. A
starting point for experimentation is a heating rate of 150°
to 300°C (depending upon size) to the sealing temperature and
then holding at temperature for the time specified by the frit
supplier. |
| 11. |
Maintain an oxidizing environment in the furnace at all times. |
| 12. |
Adhere to all health and safety recommendations from the frit
supplier. |
| 13. |
Seals
may be of either vitreous or devitrified glass. The
devitrified seals are generally mechanically stronger and many
can be machined however, they cannot be reworked if the seal
leaks. A vitreous seal can be reworked if it leaks or is
misaligned. |
