US3470304A

US3470304A - Induction furnace with perforated tungsten foil shielding

Info

Publication number: US3470304A
Application number: US617770A
Authority: US
Inventors: Henry J Geringer
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1967-02-16
Filing date: 1967-02-16
Publication date: 1969-09-30
Anticipated expiration: 1986-09-30

Description

Sept. 30, 1969 H. J. GERINGER INDUCTION FURNACE WITH PERFORATED TUNGSTEN FOIL SHIELDING Filed Feb. 16. 1967 FIG. 22 INVENTOR HENRY J. GERINGER 9' 9 FIG.

f I ATTORNEYS United States Patent US. I C]. 13--26 6 Claims ABSTRACT OF THE DISCLOSURE An induction heater having tungsten foil shielding between its coil and the specimen which is to be heated. The foil is perforated to minimize susception, and it is loosely wound into a tubular configuration about the susceptor or specimen.

Origin of the invention The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

Background of the invention This invention is concerned with the induction heating of metallurgical specimens to elevated temperatures in an induction coil furnace. The invention particularly relates to heating such specimens to 5000 to 6000 F. without reactions between refractory materials.

Induction coil furnaces make use of insulating refractory materials in the form of ceramics as well as precision made parts which are very close fitting. It has been found that certain test specimens react with the insulating material at the elevated temperatures to which these specimens are heated. Also, these conventional furnaces are constructed in such a manner that certain gases and atmospheres cannot be added during heating because of the danger of reaction with the ceramics at the very high temperatures which would reduce or volatilize the ceramic materials.

Certain of the ceramic insulators having high temperature capabilities are radioactive or toxic and are dangerous to operating personnel. Also, this material breaks down even when used only in vacuum because of thermal cycling and the accompanying thermal expansion and contraction. The sensitivity of ceramic insulation to damage from thermal gradients prevents use of rapid heating and cooling cycles in the furnace. Shielding present-day induction furnaces is complicated and costly with delays and equipment downtimes being encountered. Also, the ceramic insulators utilized in conventional furnace designs sometimes melt or outgas making attainment of high vacuum impractical when operating at very high temperatures.

Summary of the invention These problems and difficulties have been solved by an induction heater constructed in accordance with the present invention. A split cup containing loosel coiled tungsten foil is utilized in the present invention instead of precision radiation shields and spacers used in prior art furnaces. This split cup forms a holder for either a susceptor cup or a billet which is to be inductively heated.

Objects of the invention It is, therefore, an object of the present invention to provide an induction furnace having a minimum number of component parts which do not require close dimen sional tolerances.

Another object of the invention is to provide a high temperature induction furnace which may be used with various gases or atmospheres.

Still another object of the invention is to provide an induction furnace which is readily adaptable to rapid heating and cooling cycles.

These and other objects of the invention will be apparent from the specification which follows and from the drawings wherein like numerals are used throughout to identify like parts.

Description of the drawings FIG. 1 is a vertical section view of an induction furnace constructed in accordance with the present invention;

FIG. 2 is a plan view of the furnace taken along the line 22 in FIG. 1 showing the novel arrangement of the specimen, susceptor cup, split sleeve, foil shielding and container cup in an induction heater constructed in accordance with the invention;

FIG. 3 is a sectional view taken along the line 3-3 in FIG. 1 showing the manner in which the specimen is shielded in the furnace; and

FIG. 4 is a sectional view taken along the line 44 in FIG. 1 showing the relative positions of the supports and heat shields.

Description of the preferred embodiment Referring now to the drawing, there is shown in FIG. 1 a specimen 10 which is to be inductively heated by a coil 12 of an induction furnace in a manner well known in the art. The specimen 10 is contained in a susceptor cup 14 which, in turn, is positioned in the induction coil 12. The susceptor cup 14 is of tungsten and has a floor 16 upon which the specimen 10 rests. A centrally disposed opening 18 in the floor 16 enables an inert gas to pass through the susceptor cup 14 when the induction furnace is operated in an environment containing such a gas.

The susceptor cup 14 and specimen 10 must be properly shielded and insulated from the coil 12 and other furnace parts at high operating temperatures between 5000 and 6000 F. to prevent overheating and the resulting damage to the various furnace components. This is accomplished in the present invention by enclosing the specimen 10 and the susceptor cup 14 in a split container cup 20 which is also fabricated from tungsten sheet and then positioning the cup 20 in the coil 12. Susception in the container cup 20 is minimized by a slot 22 extending along its entire length. The cup 20 has a generally cylindrical configuration as shown in the drawing, and its outside diameter is smaller than the inside diameter of the coil 12 to facilitate insertion.

A tungsten plate 24 having a radially extending slot 25 forms the bottom of the container cup 20. A slotted cylindrical support 26 of tungsten is secured to the bottom of the plate 24 as shown in FIG. 1.

The split container cup 20 is removed from the coil 12, and the bottom edge of the support 26 is placed on a flat surface remote from the furnace. A tungsten support 28 having a triangular shape is placed on the plate 24 at the bottom end of the split container cup 20. The triangular support 28 is separated at one corner to inhibit susception.

A tungsten foil disk 30 is placed on the triangular support 28. The disk 30 has a diameter slightly smaller than the inside diameter of the container cup 20 and a thickness of one mil.

An important feature of the invention lies in the fact that the foil disk 30 is perforated to minimize suscep tion. This perforation is accomplished by placing the foil between two abrasive sheets, such as 50D garnet paper,

and passing this assembly through a pair of pressure rolls.

Various specimens which are to be heated will differ in size. Likewise, the susceptors 14 have different lengths to accommodate specimens of various lengths. Each specimen 10 is matched with a susceptor 14 having the proper length.

The susceptor 14 and specimen 10 should be located approximately at the center of the split container cup 20 for optimum heating. Consequently, the number of triangular supports and foil disks required will vary. Also, triangular supports having different widths may be used.

For example, in the embodiment shown in FIG. 1, a second triangular support 32 which is the same as the support 28 is placed in contact with the disk 30. A second foil disk 34 is then placed on the triangular support 32.'

Still another triangular support 36 is placed on the disk 34, and a similar disk 38 is placed on the opposite surface. A smaller triangular support 40 is placed on the foil disk 38. Another perforated foil disk 42 is placed on the triangular support 40.

It will be noted from FIG. 1 that the triangular support 40 is considerably narrower than the other

triangular supports

28, 32 and 36. FIG. 4 shows that the triangular supports are staggered when they are placed on top of one another in order to insure stability. With this arrangement the

foil shields

30, 34, 38 and 42 act as heat barriers while the triangular supports 28, 32, 36 and 40 properly position the susceptor cup 14 and the specimen 10 within the split container cup 20.

A circular tungsten plate 44 having a thickness of about .020 inch and a radially extending slot 45 is then placed over the foil disk 42 for added rigidity. Another triangular support 46 is placed on this plate. The thickness of the triangular support 46 is approximately the same as that of the triangular support 40, and the length of each of its legs is shorter than the lengths of the corresponding legs of the other triangular supports. Another perforated tungsten foil disk 48 having a reduced diameter is placed on the support 46.

A perforated disk 49 of one mil tungsten foil is placed over the opening 18 in the bottom plate 16 of the susceptor cup 14. A specimen 10 is then placed in the susceptor cup 14 on the foil disk 49, and the assembly is ready for positioning in the split container cup 20. A pair of lifting hooks or the like engage opposed holes in the susceptor cup 14 near the uppermost end. The susceptor cup 14 and specimen 10 therein are picked up by the lifting hooks and properly centered in the split container cup 20.

A split sleeve 50 made from a sheet of tungsten having a thickness of about 0.020 inch is then inserted into the container cup 20 around the susceptor cup 14 and triangular support 46. A slit 52 inhibits susception in the split sleeve 50. This slit is produced by separating the opposed edges of the sleeve. 50 when it is formed from tungsten sheet.

One of the novel features of the invention is the utilization of tungsten foil 54 for shielding and insulating the susceptor cup 14. This foil 54 has a thickness of one mil and is perforated in the manner previously described to inhibit suseeption. The foil 54 is loosely wound to a cylindrical configuration and placed about the split sleeve 50 which maintains the foil out of contact with the susceptor cup 14.

A pair of

chevron spacers

56 and 58 in the form of bent strips of tungsten are positioned between the foil shield 54 and the inside surface of the split cup container 20 on diametrically opposed sides of the specimen 10 as shown in FIGS. 2 and 3. These spacers prevent the foil shield 54 from unwrapping and contacting the split container cup 20. The contact between the foil shield 54 and the inner surface of the split container cup 20 is further minimized by providing an inwardly turned flange 4 I on one edge of the slit 22 in the split container cup 2 as shown in FIGS. 2 to 4.

A split ring =60 of tungsten is placed about the periphery of the upper edge of the sleeve 50 to cover the space between the sleeve and the split container cup 20 containing the foil shield 54. The split ring 60 is maintained in position by another split ring 62 which engages the upper surface of the split ring 60.

After all the components are assembled in the manner shown in FIG. 1, the entire assembly is positioned in the center of the coil 12. This is accomplished by utilizing a pair of lifting hooks 64 shown in FIG. '1. The legs of the hooks engage suitable holes which extend through the split container cup 20 adjacent the upper surface.

The assembly is accurately positioned within a coil 12 by utilizing a three-legged base plate 66 which rests on the bottom or floor of the furnace. A tapered upper surface on the base plate 66 engages the bottom edge of the support 26. The upper end of the split container cup 20 is then covered by a perforated foil disk which is preferably attached to the furnace cover which encloses the coil 12. The base plate 66 is preferably stainless steel while all of the other components of the furnace are tungsten. The majority of the tungsten structural elemens have a thickness of .020 inch. The foil has a thickness of one mil as pointed out above.

While a preferred embodiment of the improved furnace shielding has been shown and described, it will be appreciated that various structural modifications may be made without departing from the spirit of the invention or the scope of the subjoined claims. For example, the entire assembly can be suspended within the coil 12 by providing a suitable support for the hooks 64. Also, when the specimen 10 is in the form of a billet it may be heated directly without the use of the susceptor cup 14. In this case the split sleeve is placed around the billet, and the foil shield 54- encircles the sleeve as shown in the drawings.

What is claimed is:

1. In a high temperature induction furnace having a coil for receiving a specimen to be heated, the improvement comprising layers of perforated tungsten foil adjacent the specimen for heat shielding the same, and

means for supporting said foil layers when the specimen is positioned in the coil.

2. Apparatus as claimed in claim 1 including a susceptor cup for supporting the specimen in the coil.

3. Apparatus as claimed in claim 2 wherein the susceptor cup and thin foil are of the same material to prevent contamination of the specimen.

4. In a high temperature induction furnace having a coil for receiving a specimen to be heated, the improvement comprising layers of thin foil adjacent the specimen for heat shielding the same, and

' means for supporting said foil layers when the specimen is positioned in the coil comprising a split container cup having a slot extending along the entire length. 1

5. Apparatus as claimed in claim 4 including heat shields at one end of the split container cup.

6. In a high temperature induction furnace having a coil for receiving a specimen to be heated, the improvement comprising a susceptor cup for supporting the specimen in the coil,

layers of perforated foil adjacent the specimen for heat shielding the same, both said susceptor cup and said perforated foil being of the same material to prevent contamination of the specimen, and means for supporting said perforated foil layers when the specimen is positioned in the coil.

(References on following page) 3,470,304 5 6 References Cited J. SPENCER OVERHOLSER, Primary Examiner UNITED TA E PATENTS ROBERT D. BALDWIN, Assistant Examiner 3,036,888 5/1962 LoWe 219--10.49

3,162,710 12/1964 Anderson 13 27 CL 3,409,730 11/1968 Ebihara 13-30 X 5 219-4049