JPS5840522Y2 - magnetron - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improvement of a magnetron incorporating a ferrite permanent magnet.

With the spread of microwave ovens, there is a constant demand for magnetrons used in microwave ovens to be smaller, lighter, more reliable, and lower in price.

The biggest factors that determine the size and weight of a magnetron are the magnet material and the configuration of the magnetic circuit, and one of the current magnetrons that can be made smaller and lighter is one that incorporates rare earth magnets or alnico magnets inside the vacuum tube. It is of structure.

However, none of these have become mainstream because of the large amount of gas released from the magnet, which raises concerns about reliability, and their high prices.

Next, a magnetron with a structure that allows for reduction in size and weight is a so-called ferrite magnet-in-magnet type in which disc-shaped ferrite magnets are placed above and below an oscillation tube.

A typical example of this structure is shown in FIG.

In the figure, 1 is the oscillation tube body, 2 is the cathode stem part, 3 is the output part, 4 a and 4 b are ferrite magnets, 5 a,
5 b is a magnetic conduction plate for effectively guiding the sulfur flux of the magnet to the magnetic pole piece (not shown) of the main body, 6 is a radiator, 7 is a yoke, and 8
1 is a gasket, 9 is a shield box, 10 is a capacitor, 11 is an insulator, and 12 is a choke coil.

One way to further reduce the size and weight of a magnetron with such a structure is to use the cylindrical ferrite magnet 4a,
4 There is a method to reduce the inner diameter of b.

By reducing the inner diameter of the ferrite magnet, the magnet can be used more effectively. For example, if the distance between the magnetic poles is 14 mm, the diameter of the flat top surface of the magnetic poles is 14 mm, the outer diameter of the magnet is 60 mm, and the thickness of the magnet is 1Q mm, the inner diameter of the magnet is The relationship between Bg and the working space center magnetic field Bg is as shown in FIG.

It can be seen from FIG. 2 that Bg increases if the inner diameter of the magnet is made smaller.

For magnetrons, anode radius, cathode radius, anode voltage,
Once the anode current is determined, the necessary central magnetic field Bg is determined, so
By reducing the inner diameter of the magnet, it is possible to make the entire magnet smaller.

This effect becomes more pronounced as the inner diameter of the magnet becomes smaller;
As can be seen from the figure, since the cathode stem section and the anode output section each pass through the inside of the magnet, it is impossible to make it smaller unnecessarily.

In order to actually make the magnet smaller, there are methods to reduce the outer diameter, thinner thickness, or a combination of the two, but effective use of the magnet, low-temperature demagnetization characteristics,
The permeance coefficient of the Mavnetron magnetic circuit using ferrite magnets is preferably 1 to 1.5 in view of mechanical strength and external dimension constraints of the magnet.

As an example of magnet dimensions for which such consideration was made, 24
50 MHz 600 W output with magnetic pole gap of 1
4mm, magnetic pole top surface diameter 14mm, center magnetic field Bg 17
Assuming 00 G (Gauss), practical magnet dimensions are as shown in the table below.

(Magnetic characteristics Br≧4100 (G), Hc≧2800
(Oe), BHmax > 4 MGOe) One of the drawbacks of ferrite magnets is that their magnetic properties are highly dependent on temperature.

That is, as the temperature rises, the residual magnetic flux density Br decreases,
Normally, in the operating condition range of magnetrons -20 to 100°C, Br changes by about -0.2%/°C.

The basic function of a magnetron is to convert low frequency power (including direct current) into high frequency power, but the power conversion efficiency is usually about 70%, and about 30% is heat loss.

This heat loss is dissipated to the outside by the radiator 6 shown in FIG. 1, but if the anode is used in a normal microwave oven and the operating conditions are poor, the temperature around the anode may reach about 200°C.

The temperature of the magnet near the anode increases along the path shown by the arrow in FIG.

That is, the heat generated at the anode is transferred to the magnet 4 via the radiator 6 and the yoke 7 with which the outer surface of the radiator is in thermal contact.
a, 4b and the magnetic conduction plates 5a, 5b
There are two paths to the magnet through.

The thermal energy that enters from these two paths is balanced with the energy carried away while exchanging heat with the cooling air flowing on the surface of the magnet, and the magnet temperature is determined.

Now, if we consider the temperature of the magnet at the mouth when the magnet becomes smaller,
It has the following disadvantages:

(1) Since the surface area is small, the amount of heat exchanged by cooling is small, and the magnet temperature tends to rise.

(2) Spaces 14a and 14b through which cooling air can easily pass through
increases, and considering the same air volume, the wind speed on the magnet surface decreases and the amount of heat exchange decreases.

(3) Similar to (2) above, the amount of air that effectively cools the radiator 6 also decreases, so the temperature of the entire anode increases.

Making the magnet smaller and lighter by reducing the inner diameter of the magnet in this way is economically very advantageous, but the temperature of the magnet increases, resulting in a decrease in magnetic force and operational stability. .

The present invention has been made in view of the above circumstances, and aims to provide a magnetron that has a smaller and lighter magnet and has performance that satisfies the characteristics of conventional products.

A representative example of the present invention relating to cooling is shown in FIG. 4, a plan view of the main part of the present invention is shown in FIG. 5A, and a side view is shown in FIG. 5B.
The present invention will be explained with reference to FIG. 4, FIG. 5A, and FIG. 5B.

The present invention has a cylindrical ferrite magnet 2 on the oscillation tube body 13.
1a and 21b are arranged coaxially, and the outside is covered with a ferromagnetic yoke 7.
In the magnetron, the outer surface of the radiator 6 attached to the outer periphery of the tube body 13 is in heat conductive contact with the inner surface of the yoke 7. A metal plate 15, 16 made of a ferromagnetic material having an area larger than the area of the pole face of this magnet is interposed between the flat plate part of the yoke 7 coupled to the magnet and the outer circumferential side of the magnet and the yoke. A wind shield plate 19 is installed so as to block the space through which the cooling air between the inside surface and the inside surface is going to pass through.
a , 19 b , 20 a , and 20 b are integrally provided around the periphery of the metal plate.

In the embodiment shown in the figure, wind shielding plates 19 a , 19 b , 20 a , 20 provided in a screen-like manner on the metal plates 15 and 16 are further provided.
b is provided diagonally so that the cooling air does not easily pass through the space, and the cooling air that hits the wind shield plate hits the magnet and efficiently cools the magnet.

In this embodiment, small protrusions 17 and 18 are provided on the side of the metal plate facing the yoke.

In this way, by interposing a metal plate made of a ferromagnetic material with a wind shield between the magnet and the yoke, the heat that is about to be transmitted from the radiator to the magnet via the yoke and the heat that has been transmitted to the magnet is guided outside, and the heat that has been transmitted to the magnet is guided to the outside. The temperature rise of the magnet can be suppressed by dissipating heat through the cooling air introduced into the inner space of the magnet.

Moreover, by interposing the metal plate made of a ferromagnetic material with a large area, the magnetic resistance from the yoke to the magnet does not increase undesirably.

In the magnetron of the present invention having the above structure, even if the ferrite magnet is made small, the temperature rise of the magnet can be suppressed and the characteristics stabilized with a simple structure for the following reason.

(1) The heat conducted from the radiator through the yoke in contact with the radiator is dissipated by the metal plate interposed between the flat plate part of the yoke and the magnet, and the wind shield plate integrally provided around the yoke. temperature rise is suppressed.

(2) Since the wind shield plate is integrally provided on the metal plate and is placed in the space between the outer circumferential side of the magnet and the inner side of the yoke, it blocks the cooling air that tries to pass through the space.
The amount of wind that does not contribute to cooling is reduced, and cooling of the oscillation tube body and magnet is facilitated.

In addition to this function, this wind shield plate also has the function (1) above, so that the number of parts can be reduced.

(3) Since the wind shield plate is integrally provided around the metal plate, it is relatively easy to manufacture and easy to assemble.

(4) The wind shield plate is provided on a metal plate interposed between the outer magnetic pole surface of the magnet and the yoke flat plate, and has a thin plate shape and faces the outer circumferential side of the magnet with its narrow end face. Therefore, there is almost no increase in magnetic leakage from the magnet to the yoke.

In addition, in the present invention, since the outer diameter of the magnet can be made small, the inner end magnetic pole surface of the magnet can be attached to the magnetic pole pieces 13 provided at both ends of the main body 13.
It can be arranged so that it directly flows into a.

Note that in these figures, the resonance cavity, cathode, cathode stem, or output section that constitutes the main body 13 is omitted.

The metal plates 15 and 16 in the present invention are made of thin plates of ferromagnetic material such as iron in order to guide and dissipate the heat of the magnet to the outside and to prevent the magnetic resistance between the yoke and the magnet from increasing. There is.

Furthermore, by providing the metal plate of the present invention with other functions, it is possible to provide a magnetron with good characteristics.

That is, as shown in FIGS. 6 and 7, a part of the metal plate 15 protruding from the magnet 21b is bent, and the bent piece 24 is bent to a size large enough to prevent leakage of radio waves to the yoke and shield box near the bent piece 24. Drill the holes 26 and 27.

The magnetron's cooling air (arrow 23) hits the metal plate bent piece 24 and the hole 26.2 in the yoke and shield box.
7 into the shield box and flows as shown by the arrow in Figure 6, the cathode stem inside the shield box,
It is very effective for cooling filter elements, insulators (none of which are shown), etc.

The four wind shielding plates 19a and 19b are formed by bending the periphery of the metal plate 15 itself.

Although the metal plates of the present invention are respectively disposed between two magnets and a yoke in FIG. 4, it goes without saying that either one of them may be effective depending on the overall structure and purpose of the magnetron.

[Brief explanation of drawings]

Figure 1 is a partial cross-sectional view of a conventional magnetron with a ferrite magnet, Figure 2 is a characteristic diagram showing the relationship between the magnet inner diameter and Bg, and Figure 3 is a diagram schematically showing the path of thermal energy reaching the magnet. 4 shows an embodiment of the present invention, and is a schematic cross-sectional view of the main parts related to cooling. FIGS. 5A and 5B are plan and side views thereof, and FIG. A schematic partial cross-sectional view, and FIG. 7 is a perspective view of a metal plate shape. 6...Radiator, 7,25...Yoke, 13...Pipe body, 15,16...
Metal plate, 19a, 19b, 20a, 20
b ・−・−・・Wind shielding plate, 21a, 21b・・・・・・
magnet.

Claims (1)

[Scope of utility model registration request] A cylindrical ferrite permanent magnet is coaxially arranged on the oscillation tube body, which has a radiator attached to its outer periphery.
A magnetron having a radiator-shaped yoke surrounding a radiator and a magnet to form a magnetic circuit, the outer surface of the radiator being thermally connected to the inner surface of the yoke, the outer end magnetic pole of the magnet between the surface and the yoke flat plate,
A metal plate made of a ferromagnetic material having an area larger than the magnetic pole surface area of the magnet is interposed, and a wind shield plate is integrally provided around the periphery of the metal plate, so that the wind shield plate is connected to the outer peripheral side surface of the magnet. A magnetron is characterized by a protruding structure that blocks the passage of cooling air in the space between the inner surface of the yoke.