US 1909982 A
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May 23, 1933. H.,w. PARKER 1 32 INDUCTION FURNACE Filed Juiy 9, 1950 1 IINVENTIOR Henry W. Parker.
ATTORNEY Patented May 23, 1933 UNITED STATES PATENT OFFICE HENRY W. PARKER, OF TORONTO, ONTARIO, CANADA, ASSIGNOR TO ROGERS RADIO TUBES, LIMITED, 01 TORONTO, CANADA, A CORPORATION OF ONTARIO, CANADA INDUCTION FURNACE Application filed July 9, 1930. Seria1 N0. 466,867.
charge devices such as thermionic tubes, an
induction furnace in the form of an inductance coil forming part of a tuned circuit supplied with radio frequency current encloses the tube being exhausted and is used to heat, by induction, the metallic elements within the tube envelope to assist the process of removing the gases within the tube.
The potential gradient across the ends of the inductance coil of such a furnace, when excited by radio frequency energy and the potential gradient from the coil to ground, reach very high values and produce a glow discharge in the low pressure gases within the tube being exhausted. Positively charged particles of gas moving under a voltage gradient have an equivalent kinetic energy temperature which is relatively very high and thus cause electrochemical activity known in the art as cleanup which prevents the gas from being conducted out of the tube by the pumps. This unduly prolongs the pumpin interval. My invention is directed towar preventing such electrochemical cleanup while the tube is being baked in the furnace and pumped and thus permits of a larger amount of the gas being handled and removed during the pumping operation to reduce the time interval occupied by such pumping.
One of the objects of my invention consists in providing an improved form of induction furnace, by means of which the time interval required for pumping the tube is decreased.
Another object contemplated by my invention comprises providing means by which the aging process is greatly reduced intime.
A further object of my invention consists in providing a. furnace by the use of which the final vacuum achieved in the tube is greatl increased.
another object contemplated by my invention is the production of a higher and more uniform quality of product by the use thereof.
I accomplish all of the above and other desirable features which will hereinafter be pointed out and discussed, b the introduction of an electrostatic shield between the inductance coil and the tube orother object being heated in the furnace, as shown in the drawing accompanying and forming a part of the specification and in which:
Fig. 1 illustrates diagrammatically in section an elevation of my improved furnace.
Fig. 2 is a perspective view of the electrostatic shield used.
Referring now particularly to the figures. My invention comprises an inductance coil 2, preferably constructed of hollow copper tubing, through which a cooling fluid is circulated and to which is connected a variable tuning condenser 8, terminals 9 and 10 being provided for the tuned circuit thus formed to which is attached a source of radio frequency or other energizing high frequency current.
Within the coil or inductance 2 there is provided a cylinder 3 of insulating material and concentric therewith there is inserted an electrostatic shield 4 between which and the tube or other object being heated there is provided a further cylinder of insulating material 7. The electrostatic shield 4. is provided with an integral lug 5 affording a means for grounding the shield as shown. The shield 4 comprises a slotted cylinder provided with teeth in the form of a comb as shown. An other accepted form of. electrostatic shiel may of course be employed, the object of the shield being to prevent electrostatic coupling between the tube being baked and pumped and the inductance coil 2, and at the same time to permit of electromagnetic coupling between the coil and the elements within the tube.
When electrostatic coupling between the coil and the tube is thus prevented the potential gradient of the radio frequency voltage across the ends of the coil 2 and between the coil and ground is prevented from exciting a glow discharge in the gases with in the tube and consequently electrochemical cleanup is eliminated and it is'possible to reserve such cleanup by a glow discharge to a later step in the process which preferably takes place after the pumping 15 completed and after the tube is sealed off. This process is known to the art as aging and the function of this aging process is to produce an adsorption or cleanu of the gases by electrochemical means an at such time the low discharge is desirable to rapidly prod lce a high vacuum after the pumping operation has been completed.
By the use of an electrostatic shield such as just described, a larger amount of gas is removed from the tube by the pump during the interval reserved for pumping the tube and after sealing off a relatively uncontaminated adsorption surface is provided for electrochemical cleanu of the gas. I have found by experiment t at the aging process is reduced from one hour to two minutes by the use of an electrostatic shield and that the final vacuum is thus increased tenfold. I have found that the roduct, that is, thermionic tubes, produced by the use of such a shield are of a hi her quality and more uniform and that it is possible to more rapidly pump the tubes than hitherto.
While I have thus completely described one embodiment of my device, it is of course to be clearly understood that I may modify the details thereof without departing-from the spirit or narrowing the scope of my invention.
Having thus described my invention, what I claim as new and desire to secure by United States Letters Patent is as follows:
1. An inductance furnace comprising, a member formed of insulating material and open at both extremities thereof to receive an object to be heated, a single water-cooled inductance coil enclosing said member, and an electrostatic shield comprising a slotted member, the non-slotted rtion of which is maintained out of the eld of said induc- Y tanoe coil disposed between said inductance coil and the object to be heated and main tained at ground potential.
2. An inductance furnace comprising, an open ended member of insulating material, an inductance coil formed of metallic tubing through which, a cooling fluid is circulated disposed about one surface of said member, an electrostatic shield in the form of an open ended slotted metallic c linder, maintained at ground potential, the non-slotted portion of which is maintained out of the eld of said inductance coil and disposed about the op to surface of said member and a secon open ended member of insulating material disposed between said shield and the object to be heated.
HENRY W. PARKER.