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GLASS TO GLASS AND GLASS TO METAL JOINTS
WITH CERROSEAL-35
CERROSEAL-35 is an alloy made of indium and tin that softens at approximately 240 F and is liquid above 260 F. Because of its low vapor pressure, Cerroseal-35 can be used in high vacuum apparatus that require a seal of glass and glass or glass and metal. Besides adhering to glass Cerroseal-35 will also adhere to mica, quartz, thermo-setting plastics and glazed ceramics. Being rich in tin, it will bond to any metal that can be pre-tinned with ordinary lead-tin solder provided tinning is done at same temperature (450 F- 500 F) required for ordinary solder.

Cerroseal-35 has been adapted by firms who use it regularly in production items. An instrument maker can use Cerroseal-35 to replace litharge and glucerine in sealing the glass dome to the metal base of a differential pressure gauge; Fig. 1.
Fig. 1
METAL FITTINGS
GLASS TUBE
CERROSEAL-35
APPLIED
PARTS ASSEMBLED
FIG. 2
Metal fittings are attached to each end of a glass cylinder by a maker of communication equipment. Fig.2.

Glass and quartz windows are sealed in peep holes of processing tank applications and also can be used to solder electrical connectors to glass.

Cerroseal-35 is used for the final sealing of some loaded components by U.S. Ordnance where high temperature solder would be too dangerous to use.

INSTRUCTIONS FOR MAKING GLASS SEALS
GENERAL: The glass cannot be too clean. Wash thoroughly with soap and water and rinse. An additional rinse of acetone or alcohol is beneficial. Heating the glass to about 700 F. followed by cooling to a working temperature prior to applying the Cerroseal-35, has been found to give better adhesion. Also, extra cleaning by a bombardment of the surface of the glass with high tension discharge from a spark coil will inprove the adhesion.

FLUXES: No flux of any kind can come in contact with the glass or alloy during the process of joining. Flux destroys the adhesive quality of Cerroseal-35.

GLASS TO METAL SEALS
  1. Tin metal parts with pure tin or regular tin-lead solder and flux. Thoroughly eliminate all flux. Retin metal parts with Cerroseal-35.

  1. Have a container of molten Cerroseal-35 conveniently located. A laboratory crucible is satisfactory. As an applicator use a small artists paint brush, cotton swab, cheesecloth or lens tissue.

  1. Gradually warm glass to working temperature of Cerroseal-35.

  1. Remove from heat and apply alloy with a wiping motion, using applicator. If either the glass or alloy are too hot the Cerroseal-35 will not adhere. As glass cools to proper temperature and wiping motion is continued adhesion will begin. Continue spreading Cerroseal-35 until the desired area is covered. Rewarm the glass periodically as necessary while coating. A good coating job results in a perfect mirror when viewed from opposite side.

  1. Rewarm both parts so that the alloy surfaces appear "wet" and assemble. When tubing is joined, additional Cerroseal-35 should be flowed into joint to completely fill the space. A fillet will strengthen and improve appearance. When joining flat pieces, clamp lightly until Cerroseal-35 solidifies. Heavy pressure will squeeze out too much metal. Film should be from .003" to .006" thick for glass to glass and .008" or more for glass to metal joints to compensate for differences in coefficients of expansion between the glass and metal.

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