Metal fusion bonding – Process – Metal to nonmetal with separate metallic filler
Patent
1981-03-12
1983-07-26
Ramsey, Kenneth J.
Metal fusion bonding
Process
Metal to nonmetal with separate metallic filler
228165, 228168, 228263A, B23K 120, H01J 3510, B23K 119
Patent
active
043949533
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of joining individual parts of an X-ray anode, in particular of a rotating anode, by which a part composed of high-melting metal or its alloys is joined by soldering with one or a plurality of graphite parts.
In commercial X-ray apparatuses, the X-rays are normally induced by bombarding high-melting metals with electrons. Since only about 1% of the electron energy is converted by this method into X-radiation and the remaining 99% of the electron energy is converted into heat, it is necessary in the design and construction of X-ray anodes to take measures in order to remove or radiate from the X-ray anode the heat generated at the point hit by the electrons. Graphite is known to be a good heat radiator. It has thus been proposed already in the past to provide X-ray anodes, in particular rotating X-ray anodes made of high-melting metals for heavy duty tubes, with graphite parts joined therewith by soldering, in order to enhance the dissipation of heat. A number of solders with low vapor pressure and good wettability have been proposed for such soldered joints, in particular the metals titanium, zirconium, platinum and paladium-nickel alloys. The soldering operation is carried out in a high vacuum.
Until now, such soldered joints were often the cause of operational failures. The adhesion between the parts joined by soldering was not satisfactory, and the soldered joints could be produced only with a quality that was insufficiently reproducible. The layer of solder was generally too thick and the thickness of the layer was disadvantageously uneven even within one soldered combination. The surfaces to be joined showed hollow spaces with no solder and shrinkage cavities caused by or in the course of solidification which, furthermore, could not be detected with sufficient reliability by test methods which do not cause damage.
The cause for layers of solder with uneven thickness are mainly the problems in connection with the exact adjustment of the parts to be combined during the soldering process and the necessity related thereto of having to use rather too much than too little solder in order to largely avoid in this way zones having no solder. Voids are caused, among other things, by the fact that the metals used as solder are oxidized on their surfaces, so that reaction with graphite during the soldering action causes the formation of carbon oxide gases which cannot sufficiently well escape from the layer of solder.
Safely obtaining a homogeneous soldered joint with the lowest possible thickness of the layer of solder is a basic requirement for the increased thermal capacity and increased heat radiation by the graphite parts desired for such types of X-ray anodes. If these requirements are not satisfied, the results are in many cases overheating of individual zones of the rotating anode, the formation of cracks and distortions in the anode, and ripping of the soldered joint. Moreover, the above-mentioned inclusions of gas within the layer of solder may slowly escape from the anode through the pores of the graphite while the X-ray unit is in operation and subsequently lead within the highly evacuated X-ray tube to highly undesirable electrical instabilities, discharges and shorts.
It is, therefore, the problem of the present invention to provide a method of joining high-melting metal parts and graphite parts in X-ray anodes by soldering, in particular in rotating anodes, and to avoid by said method the above shortcomings of the methods known to date.
According to the present invention said problem is solved by providing the graphite surface to be soldered with grooves which are mainly semicircular in cross section and which do not intersect the edges of said graphite surface, and by through-drilling the graphite parts approximately vertically to the graphite surface to be combined by soldering, with the boreholes feeding into the grooves, so that excessive solder can leak off and gases formed during the soldering operation may escape.
The grooves are normally milled int
REFERENCES:
patent: 3710170 (1973-01-01), Friedel
patent: 3751702 (1973-08-01), Dietz
patent: 3887723 (1975-06-01), Kaplan
patent: 4061263 (1977-12-01), Ohlstein
Bildstein Hubert
Egger Lambert
Sonnweber Alfred
Hodak Marc
Ramsey Kenneth J.
Schwarzkopf Development Corporation
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