US 2694273 A
Description (OCR text may contain errors)
Nov. 16, 1954 s u 2,694,273
METHOD OF TIPLESS SEALING OF VITREOUS ENVELOPES Filed June 20, 1951 INVENTDR ALBERT B. SPYUT ATTORNEY United States Patent cc METHOD OF TIPLESS SEALING OF VITREOUS ENVELOPES Albert B. Spyut, Waltham, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application June 20, 1951, Serial No. 232,557
2 Claims. (Cl. 49-78) This invention relates to methods of and apparatus for sealing glass envelopes, such as those for miniature and sub-miniature vacuum tubes, without leaving a tip.
The blanks for some types of miniature and subminiature tubes are formed with an exhaust tubulation that serves to support the envelope and connect it to the pumping system of the processing machine during processing. After final exhaust, the efiaust tubulation is sealed off by the application of heat near the junction of the tubulation with the envelope. The glass of the nvelope is usually of a type having a high melting point.
In heating such a hard glass to its melting point in the sealing operation the mount structure is also heated. The result may be the emission of gases from the materials of the mount to contaminate the high vacuum of the envelope, and possibly to poison the cathode and to corrode other elements of the tube structure. It would thus be advantageous if the envelope could be sealed without the use of a hi h enough temperature to produce these undesirable effects.
By present methods of sealing, a tip is formed that protrudes from the envelope at the point where the seal is made. This increases the length of the envelope to no useful purpose, and increases the chances of breakage. It is thus apparent that a method of sealing such envelopes that would not leave a tip would be advantageous.
By the present invention, the envelope is sealed at low temperatures and without leaving an undesirable tip. This is accomplished by supporting a piece of low melting point glass within the envelope in such a position that when it is heated it flows into the opening from the envelope to the exhaust tubulation to form a vacuum tight seal that may be cut off without leaving a tip.
Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawin s. wherein:
Fig. 1 is an enlarged side elevation partially in section and partially broken away of a preferred embodiment of the invention showing an envelope in processing osition before sealing;
Fig. 2 is a detailed isometric view of a part of a modified support for the sealing lass;
Fig. 3 is a vertical section of the envelope shown in Fitz. 1 after sealing;
Fig. 4 is an enlarged view in a vertical section of an envelope showing another method of applying the soft sealing glass;
Fig. 5 is a horizontal section view of an envelope in processin osition showing another method of applying the sealing glass; and
Fig. 6 is a vertical section of a sealed and finished envelo e partially br ken away.
In Fig. 1, the reference numeral 10 represents the envelope to be sealed by the method of the invention. A mount 11 is sup orted in the envelope 10. There is an exhaust tubulation 12 extending from the bottom of the envelope 10 for the purpose of supporting the envelope during processing and of connecting the envelope to the vacuum system of the processing equipment. A lump of soft or low melting point glass 13 is fastened to the under side of a bracket 14 attached to the mount 11. This lump of glass 13 may be firmly atfixed on the bracket 14 by heating either the glass, or the bracket, or both, and afiixing the piece of glass 13 to the bracket 14. The mount 11 is then inserted in the envelope 10 in the usual manner and the assembly is subjected to the usual processing. When the stage in the processing is reached at which the envelope is to be sealed oif, an
2,694,273 Patented Nov. 16, 1954 inductive heating coil 15 is positioned about the envelope 10 and arranged to heat only the bracket 14. When the bracket 14 heats, it transmits its heat to the glass lump 13 which softens and falls down into the opening from the envelope 10 into the exhaust tubulation 12 to form a seal for the exhaust opening, as shown in Fig. 3.
The bracket 14a, as shown in Fig. 2, may also be formed with two prongs 16 and 17 to support the piece of soft glass. When the support is heated by induction from the coil 15, the softened glass 13 falls between the prongs 16 and 17 into the opening in the exhaust tubulation 12 to form a seal as before.
If the lump of soft glass is given a special form so as not to interfere with the fiow of gases into the exhaust tubulation 12, the glass may be rested on the bottom of the envelope 10, and the bracket 14 of Figs. 1 and 3 may be dispensed with. Appropriate shapes for the glass for this purpose are shown in Figs. 4 and 5. In Fig. 4, the glass is shaped like a doughnut 18 and rests on the bottom of the envelope 10 with its opening 20 positioned directly over the opening 21 into the exhaust tubulation 12. Heat is then applied to this glass doughnut 18 and the envelope 10 at its junction with the tubulation 11, preferably by gas jets 22 and 23. As the doughnut melts, it falls into the opening 21 to seal it, as shown in Fig. 6. The exhaust tubulation can then be cut off flush with the end of the envelope 10, as shown in Fig. 6, to form a tipless seal.
An irregularly-shaped piece of glass, such as the triangularly-shaped piece 24 shown in Fig. 5, may be positioned over the opening 21 so that the gases may flow about its edges into the exhaust tube 12. Such a piece, like the doughnut 18, is then heated by open flames, such as the jets 22 and 23 of Fig. 4, or any other convenient heating source, and as before, the lump 24 forms a seal 18 in the exhaust opening 21.
The precise shape of the piece of soft glass is not important. It sufiices that it be of such shape that when it is positioned over the opening 21 there is sufficient remaining space for exhausting the gases into the exhaust tubulation 12.
This invention is not limited to the particular details of construction, materials and processes described. as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.
at is claimed is:
1. A method of sealing an envelope having a mount and formed with an exhaust tubulation, comprising the steps of positioning a piece of vitreous material of a lower melting point than the material of the envelope within the envelope above the tubulation upon a bracket attached to the mount, and heating the said piece of low melting point material until said material drops into the entrance to the exhaust tubulation to form a sealing plug therein.
2. A method of sealing an envelope formed with an exhaust tubulation, comprising the steps of positioning upon a support a piece of vitreous material of a lower melting point than the material of the envelope within the envelope above the tubulation, and heating the said piece of low melting point material by applying induction heating to said support until said material drops into the elptrance to the exhaust tubulation to form a sealing plug t erein.
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