US3614505A - Packaged magnetron - Google Patents

Abstract

A packaged magnetron comprising a cylindrical permanent magnet coaxially disposed on the outer periphery of an anode, a radiator located between said magnet and anode, two circular conjugate yokes positioned on the magnet, facing each other, and a plurality of holes made in said yokes.

Description

United States Patent Akihlro Fukatsu Yokohama;

Masao Kato, Tokyo, both of Japan Appl. No. 52,892

Filed July 7, 1970 Patented Oct. 19, 1971 Assignee Tokyo Shlbaura Electric Co. Ltd.

Kawasaki, Japan July 10, 1969 Japan 1 Inventors Priority PACKAGED MAGNETRON 6 Clalms, 4 Drawlng Figs.

US. Cl 313/153,

313/l1,315/39.71 Int. Cl 1101] 25/50 [50] Field ofSearch 313/153,

' [56] References Cited UNITED STATES PATENTS 3,302,060 1/1967 Blok et a1 315/3911 FOREIGN PATENTS 1,041,518 9/1966 Great Britain 313/153 Primary Examiner-John Kominski Attorney- Flynn & Frishauf ABSTRACT: A-packaged magnetron comprising a cylindrical permanent magnet coaxially disposed on the outer periphery of an anode, a radiator located between said magnet and anode, two circular conjugate yokcs positioned on the mag not, facing each other, and a plurality of holes made in said yokes.

PACKAGED MAGNETRON BACKGROUND OF THE. INVENTION This invention relates to a packaged magnetron, particularly to a packaged magnetron with improved yokes.

The conventional packaged magnetron used for a domestic microwave heating apparatus consisted of two columned magnets disposed across a magnetron tube body, facing each other and two conjugate yokes, each shaped like a square plate, mounted in contact with the upper and lower ends of the magnetron tube body and the magnets, respectively.

There was, however, a fear that the prior art magnetron had the magnets overheated by the heat generated by the magnetron tube body, thus deteriorating its magnetic characteristics. For this reason, a cast magnet of a good temperature characteristic, though expensive, was employed. Since the magnet takes a major portion of the whole cost of the magnetron, use of an inexpensive magnet is desired. Indeed, a ferrite magnet was inexpensive, but was inferior to the cast magnet in temperature characteristic; the magnetic force of the cast magnet decreased by 0.02 percent per unit temperature 1' C. while that of the ferrite magnet decreased by 0.2 percent. That is the reason why the inexpensive ferrite magnet was not so much used.

The magnetical properties of the cast magnet necessitate the elongation of a magnet and thus of a magnetron. For example, when this type of magnetron was mounted in a microwave cooking apparatus, the entire apparatus became too large. The magnetron is mounted on the mounting plate of oven of the cooking apparatus through the gasket. The gasket, however, having a poor heat conduction, is heated in the portions of great field strength because of the ohmic loss due to the skin effect, thus losing the gasket effect and causing a spark in the gasket portion. This phenomenon cripples the magnetron by damaging the output dome glass, perforating the glass-scalable metal and lowering the degree of vacuum by melting the brazing metal. Furthermore, the yoke should not be too wide because of cooling. In order to pass the required flux therefore, it should be thick sufficiently. If the yoke were too thick, however, it would be pressed with difficulty.

SUMMARY OF THE INVENTION Accordingly, an object of this invention is to surmount these disadvantages and provide a packaged magnetron employing an inexpensive ferrite magnet and capable of obtaining a continuously high output by forced gas cooling, comprising a pipe-shaped magnet coaxially disposed with a spacing on the outer periphery of the magnetron tube body, two conjugate yokes mounted in close contact with the two opening ends of the magnet respectively, so as to allow the magnetron tube body and magnet to be interposed therebetween, and a plurality of cooling holes radially disposed on the yokes.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view illustrating a magnetron embodying the present invention;

FIG. 2 is a plan view illustrating the magnetron of FIG. 1;

FIG. 3 is a sectional view illustrating another embodiment of the invention; and

FIG. 4 is a sectional view of FIG. 3 taken along line IV-IV.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. I, a cylindrical ferrite magnet 11 is coaxially disposed with a spacing on the outer periphery of a magnetron tube body 12. Two conjugate disc yokes l3 and 14 are mounted in close contact with the both opening ends of the magnet ll, respectively. Holes 15 and 16 are made in the centers of the disc yokes l3 and 14, respectively. A cathode bushing 17 and an antenna portion 18 of the magnetron tube body 12 are projecting from the holes 15 and 16, respectively. The magnet II and the magnetron tube body 12 are fixedly disposed between the two yokes l3 and i4. Cooling holes l9 and 20 are made at regular intervals in the circular direction in the surface of the yokes l3 and 14 located over the spacing respectively. Cooling gas, such as air, passes through these cooling holes 19 and 20, respectively.

With this construction the magnetron of the invention has two conjugate yokes l3 and 14 disposed in close contact with the entire opening ends of the magnet 11, respectively. Thus the magnetic flux of the magnet 11 passes in the line of the axis of the magnetron tube body-l2 through almost entire regions of the yokes l3 and 14, respectively. The resultant substantial increase of the flux-passing region causes the corresponding decrease of the yoke thickness, thereby facilitating the pressing of the yoke. The anode of the magnetron tube body 12 is heated by the electrons emitted from the cathode and accelerated. However, this heat escapes outwardly through a plurality of cooling holes 19 and 20 made in the yokes 13 and 14 respectively, thereby preventing the magnetron tube body 12 from being overheated. The cooling effect of the magnetron can be enhanced by forced air cooling, thereby continuously obtaining a high output.

The effective cooling of the magnetron causes the magnet not to overheat, therefore the magnetron permits employment of a ferrite magnet which is inexpensive through it may have bad temperature characteristics. The flattening (i.e., giving a large coercive force) characteristic of the ferrite magnet can contribute to a decrease in the height of the magnet 11 and thus of the entire magnetron. Furthermore, the ferrite magnet, which possesses the aforesaid characteristics is free from any external effect arising during the replacement of a magnetron tube body, and eliminates the necessity of carrying out magnetization as has been required for the prior art magnetron involving a cast magnet, thus permitting the replacement of the tube body to be performed simply by removing one of the conjugate yokes.

When this magnetron is mounted in an apparatus, such as microwave cooking apparatus it is disposed on the mounting plate at the opening end of the cylindrical magnet. The resultant large distance between the antenna portion 18 of the magnetron tube 12 and the mounting plate opposite to the yoke, such as the yoke l3, 14, 24 or 25 can prevent the magnetron tube body from the overheating damage due to plasma sparks, thereby preventing the damage of the antenna dome.

FIG. 3 illustrates another embodiment of the present invention. A radiator 21 is coaxially disposed around the outer portion of the magnetron tube body 12 and a cylindrical magnet 11 is coaxially disposed around the radiator 21. On both opening ends of the cylindrical magnet 11 are respectively settled yokes 24 and 25 each of which has a circular edge portion 26 and a ring-shaped hollow projection 27 projected coaxially from the circular edge. The magnetron tube body 12 is fixedly interposed between the yokes 24 and 25, a cathode bushing 17 and antenna portion 18 projecting respectively from holes 22 and 23 bored in the center of the yokes. A plurality of cooling holes 28 and 29 are bored in the surface of the projection of the yokes at regular intervals and to the extent of both sides thereof.

The magnetron of this construction has a better cooling effect than the previous embodiment due to the mounting of the radiator and a substantial increase in the total areas of the cooling holes 28 and 29. The output can thus be so much increased. The shapes of the yokes 24 and 25 are well adapted for passage of the flux from the magnet. The less the leakage of magnetic flux, the more effective use of the flux.

It will be understood that various changes and modifications may be made without departing from the spirit or scope of the invention herein disclosed. It is intended, therefore, that all matter contained in the foregoing description and in the drawing is to be interpreted as illustrative only and not as limitative of the invention. For example, the cylindrical magnet previv ously described may be replaced by a plurality of curved magnets combined. The use of a magnet need not be restricted to that of a ferrite magnet, but any other type of magnet may be employed.

What we claim is:

l. A packaged magnetron comprising a magnetron tube body, a pipe-shaped magnet coaxially disposed with a spacing on the outer periphery of said magnetron tube body, two yokes closely fixed on the both sides of the magnet respectively, and a plurality of cooling holes radially disposed in those areas of each of said two yokes located over said spacing.

2. The magnetron as claimed in claim 1 wherein the magnet is a ferrite magnet.

3. The magnetron as claimed in claim 1 wherein the pipeshaped magnet is a cylindrical magnet and the two yokes are of the disc type.

4. The magnetron claimed in claim 1 wherein a radiator is coaxially located around the magnetron tube body.

5. The magnetron as claimed in claim 1 wherein each of said two yokes comprises a circular edge portion and a ring-shaped 5 hollow projection projected coaxially from the circular edge portion.

6. The magnetron as claimed in claim 5 wherein each of said yokes has a plurality of cooling holes bored in the surface of the ring-shaped hollow projection at regular intervals and to the extent of both sides thereof.

Claims (6)

1. A packaged magnetron comprising a magnetron tube body, a pipe-shaped magnet coaxially disposed with a spacing on the outer periphery of said magnetron tube body, two yokes closely fixed on the both sides of the magnet respectively, and a plurality of cooling holes radially disposed in those areas of each of said two yokes located over said spacing.

2. The magnetron as claimed in claim 1 wherein the magnet is a ferrite magnet.

3. The magnetron as claimed in claim 1 wherein the pipe-shaped magnet is a cylindrical magnet and the two yokes are of the disc type.

4. The magnetron claimed in claim 1 wherein a radiator is coaxially located around the magnetron tube body.

5. The magnetron as claimed in claim 1 wherein each of said two yokes comprises a circular edge portion and a ring-shaped hollow projection projected coaxially from the circular edge portion.

6. The magnetron as claimed in claim 5 wherein each of said yokes has a plurality of cooling holes bored in the surface of the ring-shaped hollow projection at regular intervals and to the extent of both sides thereof.

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