US 3841920 A
An infrared radiation source comprising a nickel-chromium alloy wire having an oxidized surface and being helically coiled around a stainless steel threaded core which functions as a heat ballast. The source is manufactured by wrapping the wire around the core in a threaded groove to form a helical coil with separated turns; unscrewing the core from the coil; forming an oxide coating on the wire by holding the coil in an oxidizing environment and heating the coil by passing electric current through the wire; and, while forming an oxide coating on the wire, screwing the core onto the coil until all the turns thereof are engaged around the core.
Description (OCR text may contain errors)
United States Patent [191 Martin METHOD OF MANUFACTURING AN INFRARED RADIATION SOURCE  Inventor: James R. Martin, Willesley, Mass.
 Assignee: Block Engineering, Inc., Cambridge,
22 Filed: Jan. 2, 1973 21 Appl. No.: 320,096
Related US. Application Data  Division of Ser, No. 159,686, July 6, 1971, Pat. No.
[451 Oct. 15,1974
Primary ExaminerRalph S. Kendall Attorney, Agent, or Firm-Schiller & Pandiscio [5 7 ABSTRACT An infrared radiation source comprising a nickelchromium alloy wire having an oxidized surface and being helically coiled around a stainless steel threaded core which functions as a heat ballast. The source is manufactured by wrapping the wire around the core in a threaded groove to form a helical coil with separated turns; unscrewing the core from the coil; forming an oxide coating on the wire by holding the coil in an oxidizing environment and heating the coil by passing electric current through the wire; and, while forming an oxide coating on the wire, screwing the core onto the coil until all the turns thereof are engaged around the core.
5 Claims, 2 Drawing Figures METHOD OF MANUFACTURING AN INFRARED RADIATION SOURCE This application is a division of my copending application Ser. No. 159,686 filed July 6, l97l for Infrared Radiation Source and Method of Manufacture, now US. Pat. No. 3,737,625 issued June 5, 1973.
The present invention is concerned with an electrically energized infrared radiation source and method of manufacturing the infrared source.
Sources of infrared radiation, particularly in the shorter wavelengths, find substantial utility in a number of scientific fields. Many applications such as spectroscopy, require a source of substantially constant emission free from fluctuations and subject to control within narrow limits. Conventional infrared radiation sources used for such purposes generally comprise a high resistance electricalconductor formed of metal, ceramic or a combination thereof, through which an electric current is passed to heat the source to infrared emission. Coiled wire sources exhibit good emission in the near infrared, but suffer from thermal instability resulting in fluctuations in the intensity of the radiation. On the other hand, ceramic sources are generally more stable but exhibit relatively low emission in the near infrared.
Objects of the present invention are to provide a novel and improved infrared source formed of wire and characterized by high emission in the near infrared and greatly improved thermal stability; and to provide a simple and inexpensive method of manufacturing the aformentioned source.
These and other objects of the invention are realized by providing a high electrical resistance wire having an oxide coating, coiled around a threaded core adapted to function both as a heat ballast during the operation of the source and as a coil-forming mandrel during the manufacturing process.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
, The invention accordingly comprises the several steps'and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elementswhich are exemplified in the following detailed disclosure,-and the scope of the application of which will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:
FIG. 1 is a perspective view of the infrared source of the invention; and
FIG. 2 is a sectional view taken substantially through the center or axis of the source.
Reference is now made to the drawings wherein there is illustrated a coiled wire, infrared source embodying and manufactured in accordance with the present invention. The basic components of the source are a helical coil 12, with separated turns, of a relatively high electrical resistance wire, and a metal core around which the wire is coiled. The surface of the wire is oxidized to provide a dielectric coating electrically insulating the coil 12 from core 10. As a component of the source, the core performs the dual functions of supporting the wire and more importantly, acting as a heat ballast for preventing fluctuations in the temperature of the wire and infrared emission of the source. The core also performs an important function in the manufacturing process, namely that of a mandrel about which the coil is formed.
Coil 12 preferably comprises a wire having a circular cross section and formed of a nickel-chromium alloy of the type conventionally employed for electrical resistance heating and exhibiting high electrical and oxidation resistance. Core 10 may take the form of a conventional cylindrical screw formed with V-shaped threads and a slot or socket 14 adapted to be employed to rotate the screw. Core 10 is preferably formed of a metal having a high specific heat and resistance to corrosion, stainless (chromium alloy) steel being particularly suited for this purpose. By way of example, an infrared source embodying the invention was formed by winding seven turns of a nichrome wire available from The Kanthal Corporation, Bethel, Connecticut under the trademark KANTl-IAL A, size 0253, around a conventional No. 6-32 5/16 inch long stainless steel set screw.
in the preferred method of manufacturing the source, the wire is formed into a coil by winding the desired number of turns around a mandrel conveniently formed by core 10, with the wire engaged in the screw thread and having adjacent turns separated from one another. The core is then removed, by rotation, from the coil, and the latter is then heated in an oxidizing en vironment, that is, an atmosphere containing an oxidizing gas such as oxygen, to oxidize the wire and form a very thin electrically insulating, oxidized coating thereon. Uniform heating is accomplished simply and conveniently by passing an electric current through the wire. The screw is then inserted part way, e.g. one turn, into the coil and both the wire and coil are heated in an oxidizing environment. During this second heating operation, the set screw is rotated to gradually intro duce it into the coil until all the turns thereof are engaged around the screw. The second heating operation is also effected by passing current through the wire with the initial oxide coating providing the initial requisite electrical insulation between the coil and the core.
In the example given above, the coil was first heated in air without the core for a period ten minutes at a temperature of l,OO0C. The 6-32 stainless screw was then inserted one turn and both the coil and screw were maintained at a temperature of l,OO0C for another 5 minutes. The screw was then rotated to gradually insert in completely into the coil while oxidation was continued at the same temperature. Insertion of the screw is gradual in order to permit an oxide layer to form on the wire between it and the screw to prevent short circuiting of the turns of the coil and to assure substantially constant electrical resistance (and temperature) throughout the length of the coil. The engagement of a circular cross section wire in a V-shaped groove provides for contact between the wire and ballast along two lines thus providing for greater thermal coupling. This arrangement also permits oxygen to contact all portions of the wire surface during the concurrent assembly and oxidation operations.
The oxidized coating on coil 12 not only provides a dielectric insulating layer between the wire and core 10 but, importantly functions as a thermal conductor providing excellent thermal coupling between the heated wire infrared radiator and the thermal ballast provided by the core while not interfering with infrared emission.
It is by virtue of this construction and arrangement that temperature fluctuations due, for example, to changes in the heating current, are avoided and the infrared output of the source remains constant. Heating of the coil is more uniform and the coil is well supported throughout its extent so as to-be protected against damage and breakage.
Since certain changesmay be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
What is claimed is:
l. The method of manufacturing an infrared radiation source comprising:
coiling a wire of relatively high electrical resistance around a threaded metal core having a relatively high corrosion resistance to form a coil having a multiplicity of turns engaged in the threaded groove of said core and separated from adjacent turns;
rotating said core relative to said coil to at least partially withdraw said core from said coil and disengage turns thereof from said core;
concurrently heating said core and said coil in an oxidizing environment, and while said coil is being oxidized, rotating said core relative to said coil to progressively engage all of the turns thereof with said threaded groove.
2. The method of claim 1 wherein said core is withdrawn completely from said coil prior to first heating said coil in an oxidizing environment to form an oxide coating thereon.
3. The method of claim 1 wherein said coil is heated by passing electric current through said wire.
4. The method of claim 3 wherein core is rotated relative to said coil to advance said core into said coil to heat said coil and form an oxide coating thereon while electric current is being passed through said wire.
5. The method of claim 4 wherein core is formed of a chromium alloy steel having high corrosion resistance and said wire is a nickel-chromium alloy having relatively high electrical resistance.