Vacuum Switching Tube

The present invention relates to a vacuum switching tube comprising a housing which is composed of at least one ceramic portion and of metal portions, whereby at least one metal portion contains a thick-walled and a thin-walled cylindrical region, whereby a step preceding out in the radial direction is formed in the inner wall at the transition of the thick-walled to the thin-walled cylindrical region, whereby the thin-walled cylindrical region is connected to the end face of a ceramic element, and whereby a vapor screen is provided, and whereby the vapor screen is soldered to the step of the metal portion. Such a vacuum switching tube of the type generally set forth above is disclosed in U.S. Pat. No. 3,766,345, fully incorporated herein by this reference. The vacuum switching tube disclosed therein is constructed in a relatively complicated manner; it contains a plurality of solder locations and other metal-to-ceramic junctions. The shield design alone requires a plurality of retaining arms which must be soldered, first of all, to the shield and, secondly, to the thick-wall metal portion.

In comparison thereto, the object of the present invention is to provide, in this simplified manner, a simple structure and a simplification of the manufacturing method for the structure.

This object is achieved, in a device of the type set forth above, which is particularly characterized in that at least one metal portion is fashioned as a cap-like structure and is soldered blunt to the end face of the ceramic portion, in that the vapor screen comprises an edge region expanded in the radial direction, and in that the expanded edge region is matched to the diameter of the thin-wall cylindrical region, lies against the step, and is soldered at that location.

The metal portions are thereby advantageously composed of a material whose temperature coefficient is not matched to the temperature coefficient of the ceramic portion. For example, the metal portions can be composed of copper or of a stainless steel and the ceramic portion can be composed of aluminum oxide ceramic.

Assembly advantageously occurs in a method in which the metal portions, the ceramic portion and the shield or screen are soldered to one another in a single work step. Particularly small tolerances can be observed in that the shield and the metal portions are composed of the same material. Only one shield is thereby advantageously provided, this covering the entire ceramic portion in the axial direction.

The structure can easily be assembled and without special requirements made of an assembly form and can be soldered in a soldering process. The shield can thereby be held in a position illustrated on the drawing by the force of gravity until the soldering has been carried out.

Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description, taken in conjunction with the accompanying drawing, on which:

FIG. 1 is a sectional view taken through a vacuum switching tube constructed in accordance with the present invention.

A switching tube comprises a housing 1 and switch contacts 2 and 3 arranged coaxially relative to one another. The housing 1 comprises metal caps 4 and 5 and a ceramic ring 6. The metal caps 4 and 5 comprise thin-walled cylindrical regions 7, whereby at least one metal portion 5 comprises a step 8 at its inner wall at the transition from the thick-walled portion 11 to the thin-walled cylindrical section 7, the step 8 extending outwardly in the radial direction.

A vapor shield 9 comprises an edge region 10 which expands toward the exterior of the device. The edge region 10 lies against the thin-walled cylindrical region 7 and against the step 8 of the cap 5 and is hard-soldered to the cap 5.

The thin-walled cylindrical regions 7 are soldered blunt to the ceramic ring 6 and their wall thickness is dimensioned such that the warping occurring during soldering and due to the different thermal expansion between the ceramic ring 6 and the thin-walled cylindrical region 7 is intercepted by the solder location and does not lead to an untightness of the tube.

The shield 9 covers the ceramic portion 6 in the axial direction, so that one shield 9 suffices for vapor shielding. As a result thereof, the shield 9 can be inserted, during manufacture, and can be applied to the step 8 and remains there merely as a consequence of the force of gravity when the tube is held in the position illustrated during soldering. The other portions can also be held stacked on top of one another for soldering without involved holding devices and can be soldered in one work step.

In this embodiment, the single-solder arrangement of the contacts in the region of the lower metal cap 5 is advantageous, since a relatively large switching space is available here and the metal vapor which occurs can be kept away from the ceramic portion 6 in a particularly suitable manner.

Although I have described my invention by reference to particular illustrative embodiments thereof many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. I therefore intend to include within the patent warranted herein all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.