US 3025385 A
Description (OCR text may contain errors)
March 13, 1962 YUKIO TANAKA 3,025,385
ELECTRIC HEATING APPARATUS 0F FLUIDIZEID ELECTRO-CONDUCTIVE POWDER RESISTANCE Filed Oct. 19, 1959 INVENTOR- Y YUK/O TA NAKA. W M
United States Patent M Japan Filed Oct. 19, 1959, Ser. No. 847,372 Claims priority, application Japan Apr. 27, 1959 2 Claims. (Cl. 21950) This invention relates to an electric heating apparatus.
For heating apparatuses are conventionally used salt baths, resistance furnaces, arc furnaces, induction heating furnaces and Criptle furnaces and so on. However, these have respectively the following defects:
Salt baths have defects that salt will be consumed and will adhere to the heated piece; that it is necessary to select the kind of salt in accordance with the kind of the piece to be heated and the heating temperature; that, if water is dropped into the bath, there is a danger of causing the explosion of the salt; that therefore the operation and maintenance of the bath are difficult and that the running cost of the bath is high.
Resistance furnaces have defects that, as heat generation by electric resistance is utilized in the furnace; that therefore thermal efiiciency is low and that the maintenance of the furnace is difiicult.
Arc furnaces have not only the same defects as of resistance furnaces but also defects that the operating temperature is too high; that the temperature control is extremely diificult and that the thermal efficiency is low.
Induction heating furnaces have defects that the erection cost or initial cost of the electric source and others is enormous and that the operation is difiicult.
Criptle furnaces wherein heat generation by carbon particles is utilized have defects that it is difficult to insert the piece to be heated into the furnace; that the heating is not performed uniformly, that a reactor device causing the drop of power factor is required in order to compensate the negative resistance characteristic of carbon.
The principal object of the present invention is to provide a heating apparatus wherein relatively high temperature heating is possible, temperature control is easy and the control range of temperature is Wide.
A further object of this invention is to provide a heating apparatus which is easy to operate and can be manufactured at a low cost.
Another object of this invention is to provide a heating apparatus wherein, even if the piece to be heated is irregular in shape, it can be heated uniformly.
According to the present invention, there is provided a heating apparatus comprising a chamber containing an electro-conductive powder and having a micro-porous bottom wall Within, means to fiuidize the electro-conductive powder within said chamber by feeding a gas through said micro-porous bottom wall and electrodes to flow an electric current through said fluidized electro-conductive powder.
The micro-porous bottom wall in the above described invention is such as, for example, a porous tile plate which in nature can pass any gas but can not pass any electro-conductive powder. The electro-conductive powder may be a carbon powder the particle size of which is determined by the specific gravity and otherphysical properties of the powder material but may be, in short, adapted to fluidization. For example, the grain size of about 100-150 meshes is preferable. The gas pressure to be used to fluidize the carbon powder is different depending on the thickness and porosity of the microporous bottom wall but may be of compressed air of about 4-10 kg./crn. As a fiuidizing gas, air is usually 3,025,385 Patented Mar. 13, 1962- used, but nitrogen or other inert gas may be used in case oxidization is to be avoided. The shape of the electrode is preferably such as will make the current density in the chamber as uniform as possible. It is possible to improve the flow of the electric current by using auxiliary electrodes. The electric current to be used is an alternating current of any frequency but may be a direct current.
The present invention shall now be explained with reference to the accompanying drawing so as to be well understood.
The drawing is a longitudinally sectioned elevation of a heating apparatus according to the present invention. 1 is a fluidizing chamber for the heating of piece. 2 is a bed of electroconductive (carbon) powder particles floating in fiuidizing chamber 1. 3 and 4 are electrodes dipped into the bed of carbon powder 2. 5 is an electric source connected to electrodes 3 and 4. 6 is a micro porous bottom wall fitted in the bottom of the fluidizing chamber 1. Micro-porous bottom wall 6 is made of such material as will freely pass air but will not pass the electro-conductive powder. 7 is an air inlet provided in the botom of the fluidizing chamber 1.
When a compressed air source is connected to the air inlet 7, air will flow in the direction indicated by the arrows and the carbon powder will be fluidized in the fluidizing chamber. A piece to be heated not illustrated is dipped in the bed of carbon powder by being inserted between the electrodes 3 and 4 in the fiuidizing chamber. In such state, the carbon powder will be fluidized and move so that the particles may come into and out of contact with each other as if in the case of molecular motions.
In such case, if the electric source 5 is connected to the electrodes 3 and 4 and an electric power is fed, an electric current will flow through the carbon powder. Therefore, the carbon powder will generate heat due to said electric current and the piece to be heated located between the electrodes will be heated by the heat thus generated.
The exothermic mechanism in this case can be considered to be as explained in the following:
Such Ioules heat as is caused by the resistance of the carbon powder itself and the contact resistance between the powder particles will be the element of heat generation. When the powder is fluidized with air at a high temperature, heat will be generated even by the exothermic reaction caused. by chemical reaction between carbon and oxygen in the air. In such case, carbon will be consumed but heat will be generated instead. Therefore, even though a carbon powder is used, it will present no negative resistance characteristic, and will act as a pure resistance load.
As seen from the above explanation, a piece to be heated is dipped in the fluidized powder in the chamber. Therefore, the resistance of dipping and removal into and from the heating space is very low and the operation is quite easy. Further, even if the shape of the piece to be heated is irregular, the contact of the piece with the fine carbon powder in the fluidized state will be uniform. Therefore, the piece can be uniformly heated irrespective of its shape.
The carbon will remain stable at high temperatures and therefore the piece to be heated will be able to be heated from a low temperature to a high temperature above 1000 C. If the chamber is filled with an inert gas to be used to fluidize the fine electro-conductive powder, the piece to be heated will be able to be heated up to about 1800 C.
The apparatus of the present invention can be used for a carbon sintering device. It can be used for a steel nitriding furnace by the use of ammonia gas as the fluidizing medium. The temperature control is so easy that the apparatus can be used also for a thermostatic bath.
According to my experiments, when a carbon powder of about 150 meshes was used, a copper plate of a surface area of 50 cm. was used for each electrical, the distance between the electrodes was made 5 cm., a porous tile plate was used for the micro-porous bottom wall, the plate was 30 mm. thick though its porosity could hardly be numerically defined and an alternating current of 100 volts, 50 cycles was impressed between electrodes and intensity of current flowed between the electrodes was 100 amperes, and gas pressure of air was 7 kg./cm. heat was generated up to the temperature of the electro-con iuctive powder of about 1300 C. The state of the fluidized powder at that time Was 40% higher compared with the case when the fluidization is not occurred.
By inserting a crucible, for example a carbon crucible, in such fiuidizing chamber, it is possible to melt even billets in this carbon crucible.
The above described example is merely for illustration and should not be construed to limit the present invention set forth in the appended claims.
What is claimed is:
1. A heating apparatus comprising a chamber having a micro-porous bottom wall within, a bed of electroconductive powder particles supported on said microporous bottom wall, means for fluidizing the bed of powder particles within said chamber by feeding a gas upwardly through said micro-porous bottom wall, and electrodes to flow an electric current through said fluidized bed of powder particles.
2. A heating apparatus comprising a chamber having a mirco-porous bottom wall within, a bed of electroconductive carbon powder particles supported on said micro-porous bottom wall, means to fiuidize the powder within said chamber by feeding a gas upwardly through said micro-porous bottom wall and electrodes to flow an electric current through said fluidized powder.
References Cited in the file of this patent UNITED STATES PATENTS 441,401 Dewey Nov. 25, 1890 749,418 Acheson June 12, 1904 FOREIGN PATENTS 689,165 France May 26, 1930 801,653 Great Britain Sept. 17, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,025,385 March 13, 1962 Yukio Tan'aka It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 4, lines 11 and 14, before "powder", each occurrence insert bed of carbon Signed and sealed this 19th day of June 1962.
ERNEST w. SWIDER DAVID L- LADD Commissioner of Patents Attesting Officer