US3313921A

US3313921A - Infrared heater

Info

Publication number: US3313921A
Application number: US321950A
Authority: US
Inventors: Mohn Heinrich; Horstmann Georg; Muller Eberhard
Original assignee: Heraeus Schott Quarzschmelze GmbH
Current assignee: Heraeus Quarzschmelze GmbH; Heraeus Schott Quarzschmelze GmbH
Priority date: 1962-11-16
Filing date: 1963-11-06
Publication date: 1967-04-11
Anticipated expiration: 1984-04-11

Description

APIil 11, 1967 H. MoHN ETAL 3,313,921

' INFRARED HEATER I Filed Nov. 6, 1965 2 Sheets-Sheet 1 ngz NVEIITOAS! xfs/mm MoH/v, GEORG HoRsrMM/v) Baak/mko Mu'iLR April 1,1 1967 H. MoHN l-:TAL 3,313,921

INFRARED HEATER Filed Nov. 6, 1965 2 Sheets-,Sheet 2 lNVEa/ros:

IIE/#RICH Molina GEORGHoRSrMA/VN) EERIMRD MULJER Treff/vifs United States Patent O 3,313,921 INFRARED HEATER Heinrich Mohn, Hailer, Georg Horstmann, Eruchkohel, near Hanau am Main, and Eberhard Muller, Hanau am Main, Germmy, assignors to Heraeus Quarzschmelze G.m.b.H., Hanau am Main, Germany, a German trm File-'l Nov. 6, 1963, Ser. No. 321,950 Claims priority, application Germany, Nov. 16, 1962, H 47,417; Mar. 12, 1963, H 48,501 3 Claims. (Cl. 2MP- 553) The present invention relates to an electric infrared heater having an electric heating conductor Within a tube of quartz glass, vitre-ous silica ware, refractory glass, or the like, and elect-ric connections for said heating element at one end of said tube.

There are different designs of electric infrared heaters of the above-mentioned type already known. The heating conductor of these known infrared heaters usually consists of a wire or wire coil which is wound on the out-side of a supporting tube from the inlet end thereof, and the other end of the conductor then runs from the other end of the supporting tube through the inside of this tube back to the inlet end where the electric connections for two ends of the conductor are located. These infrared heaters have the disadvanta-ge that the part of the heating conductor which extends along the insi-de of the supporting tube is excessively heated during the operation of the heater which is due to the fact that` aside from its own heat, this inner part also yreceives a considerable additional heat from t-he part which is wound upon the outside of the supporting tube and that the heat of this inner part cannot be freely radiated therefrom. Due t-o the excessive thermal load on this part of the heating conductor extending along the inside of the supporting tube, this part becomes highly incandescent and easily burns through.

There is another type of infrared heaters known which also has it-s electric connections at one end thereof and in which the heating conductor is provided in capillary tubes in a solid body of quartz glass or vitreous silica ware which may also be formed by sintering or melting. Such infrared heaters have the disadvantage that they. are rather bulky and that in the operation of the heater the solid body of quartz glass or the like is not heated uniformly so that thermal stresses occur which may result in fissures and cracks in this body which in serious cases may `even end in bursting and destruction of the entire heater. Due to the relatively large bulk. of the heater, there is also the danger that heat accumulations may form therein which may impair the heating conductor. These infrared heaters with capillary tubes have the further very serious disadvantage that they can beproduced only at a very considerable expense.

It is an object of t-he present invention to provide an infrared heater of the type in which the heating conductor is mounted within an outer tube of quartz glass, vitreous silica ware, refractory glass or the like and the electric connections for the heating conducto-r are provided at one end of this tube, and which is designed so as to overcome all of the above-mentioned disadvantages of similar infrared heaters in an extremely simple manner. According to the invention, this is attained by providing a thin strip of an electrically insulating material, preferably quartz glass, vitreous silica ware, refractory glass or the like, at the inside of the outer tube and spaced at a short distance from the inner wall thereof so as to form a partition in this tube, and by inserting the heating conductor into the chambers which are formed in the tube by this partition. The insulating strip is made of very small thickness in comparison to its length. The heating con- `thickness of only 1 mm.

3,313,921 Patented Apr; 11, 1967 lCC ductor which is located in the two chambers may then radiate its heat freely and there is no danger as in the infrared heaters of the known type that the parts of the heating conductor or the supporting part might become excessively heated or that heat accumulations or uneven heating of the heater parts might occur. If the insulating strip as well as the outer tube are made, for example, of opaque quartz glass, a very uniform heating effect will be attained since the insulating strip permits the infrared radiation of the heating conducto-r to pass through it very well up to about 4p because of the good permeability of quartz within the infrared wave ran-ge. By being made of the same material, the outer tube and the insulating strip have the same coefficient of thermal expansion. Quartz glass, vitreous silica ware, or lrefractory glass are especially suitable materials for making the insulating vstrip because of their good elasticity and electric insulating effect. Another advantage of the invention also consists in the fact that the insulating strip with the heating conductor thereon may be inserted in a very simple manner and without danger of breakage into the Outer tube, even if it has a length of, for example, l m. and a The insulating strips may also be easily produced at a low expense,`for example, by extrusion. This if of considerable importance since infrar-ed heaters are articles of which very large amounts are required in industry and which therefore should be m-ade by method-s of mass production. The infra-red heater according to the invention therefore not only overcomes all of the technical disadvantages of the infrared heaters of a simi-lar type which were previously known, but its Iradiation properties are also superior and its manufacture is considerably more simple and inexpensive than that of the known heaters.

The above-mentioned as well as various additional features and advantages of the present invention will becom-e more clear-ly apparent from the following detailed description thereof which is to be read with reference to ,the accompanying drawings, in which FIGURE l shows a perspective view of an infrared heater according to the inventi-on;l

FIGURE 2 shows a cross section which is taken along line II-II of FIGURE 1;

FIGURE 3 shows a similar cross section of an infrared heater according to a modification of the invention;

FIGURE 4 shows a longitudinal section of an infrared heater according to a further modication of the invention; while f FIGUR-E 5 shows a cross section which is taken along line VV of FIGURE 4.

Referring rst to FIGURES 1 and 2 of the drawings, the infrared heater according to the invention consists of an outer tube 1 of quartz glass, vitreous silica ware, refractory glass, or similar material, into the open end of which an insulating strip 2 of a similar material is inserted on which a heating conductor in the form of a wire coil is mounted, the two

parts

5, 5 of which extend along the opposite sides of the insulating strip 2 within two equal chambers 3 and 4 which are formed by strip 2 at the inside of tube 1. This strip 2 preferably has a width only slightly smaller than the inner diameter of tube 1 and its lower end is provided with a slot 6 in which the straight connecting part between the two coiled parts 5 of the heating conductor is held. The lower end of the insulating strip 2 is preferably held in position near the closed end of tube 1 by a wad of quartz wool 7. The free upper ends 8 and 9 of the heating conductor are to be connected to a source of current.

FIGURE 3 shows a modification of the invention, in which the insulating strip has a cross-shaped cross section so as to form four

equal blades

10, 11, 12, and 13.

By the insertion of this insulating strip, four

equal charnbers

14, 15, 16, and 17 are formed at the inside of tube 1 in which two

separate heating conductors

18 and 19 may be located which may be separately connected to a source of current. Of course, it is also possible to employ a single heating conductor which is passed twice back and forth along the insulating strip within the four chambers 14 to 17.

The infrared heater either according to FIGURES 1 and 2 or according to FIGURE 3 may be further improved in the manner as illustrated in FIGURES 4 and 5 by twisting the flat insulating strip 2 or, in a similar manner, the cross-shaped strip to 13 accordin-g to FIGURE 3 about its longitudinal axis. This has the advantage that the heating coil or coils will be held more securely in the proper position so that, even after the heater has Ibeen used for a long time in a perpendicular position and even though it may have a length of 1 m. and more, the coil or coils will be absolutely prevented from sagging or from becoming distorted. Furthermore, the radiation of this infrared heater will be even more uniformly distributed n all directions than that of the heaters according to FIGURES 1 to 3, especially if the heating conductor consists of two equal heating coils which are passed back and forth. yEven in the particular case when the heating conductor consists of two unequal parts, for example, of a heating coil and a straight return wire which are separated from each other -by the twisted insulating strip, a uniform distribution of the radiation in all directions will be atta-ined.

The inventive arrangement of a Hat insulating strip which is either straight or twisted or of an insulating strip with intersecting blades, either straight or twisted, within the tube of an infrared heater has proved especially successful if the tube has an inner diameter of 6 to 16 mm. into which an insulating strip of a thickness of about 0.8 to 1.5 mm. and a width of slightly less than the inner diameter of the tube is inserted. If the insulating strip, either at or with intersecting blades, is twisted, each spire preferably has a len-gth of 3 to 5 cm. The heating conductor preferably consists of a heating coil passing along the chambers which are formed by the insulating strip, and it is preferably made and supplied with current so that the infrared heater has an output of about 4 to 7 mm. into which an insulating strip of a thickness of about A s can be appreciated by the artisan, the advantages of the invention proceed from using a partition member support structure and outer tube container for the electrically energized infrared radiation generating elements which assure a substantially free interchange of radiant `energy emitted by the various generating elements and portions thereof. This results in a uniform omni-directional distribution of the generated radiation which eliminates differential thermal stresses and hot spots that could damage the tube or even the generating elements themselves, as in certain prior art infrared heaters. To achieve such a favorable radiation distribution, the outer tube as well as the partition member and its various blades are made of a material, preferably quartz which is substantially transparent to infrared radiation.

Of the various other materials which can be used for makin-g the partition member and outer tube are vitreous silica wear, refractory glasses and similar materials. These materials can be, and in certain applications preferably are opaque to visible light radiation, as for example, opaque quartz glass, since in a infrared heater, it is the infrared radiation transmission characteristics which are impogtant. Therefore, it is most advantageous to,

make the partition member and outer tube from a material such as opaque quartz glass which is substantially transparent to infrared radiation up to a wave length of approximately 4 microns. By excluding transmission of visible light radiation generated incidentally by the heater elements, the radiation output of the heater can be made substantially pure infrared.

Although our invention has been illustrated and described with reference to the preferred embodiments thereof, we wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed our invention, what we claim is:

1. An infrared heater comprising an elongated outer tube of quartz having an open end and a closed end, an electrically insulating partition member substantially transparent to infrared radiation and define-d by an elongated strip twisted about its longitudinal axis to divide the interior of said tube into two adjacent convoluted chambers, an electrical resistance heating element disposed within V each of said convoluted chambers for extension along the length thereof and containment thereby, said resistance heating elements being electrically connected in series at the close-d end portion of said tube and disposed for connection at the open end portion of said tube to an eX- ternal source of electrical energy for heating thereby to generate infrared radiant energy for transmission from and through said tube, and support means disposed within said tube at the closed end portion thereof to support said twisted strip partition member in an endwise separated relation to the closed end of the tube.

2. The infrared heater according to claim 1 wherein said support means includes a wad of quartz wool disposed within said tube at the closed end thereof to define a support cushion for the end of the twisted strip partition member adjacent thereto.

3. The infrared heater according to claim 1 wherein said outer tube and twisted strip partition member are made of opaque quartz glass which is substantially transparent to infrared radiation of wave length up to approximately 4 microns.

References Cited by the Examiner UNITED STATES PATENTS 1,437,481 12/1922 Armstrong 219--523 1,894,887 1/1933 Pingrey 219-335 X 1,918,078 7/1933 Apple 3'38-235 1,995,000 3/1935 Hyatt 219-335 X 2,224,422 12/ 1940 Ballman 3318-241 X 2,554,745 5/1951 `Kapsch 219-523 X 2,703,833 3/1955 Vanvor 338--33 2,715,675 8/1955 Macksoud 338-268 X 2,824,199 2/1958 Browne 338-241 X 2,844,694 7/ 1958 Lefebvre 338-236 3,107,290 10/1963 Willinger 219-523 X FOREIGN PATENTS 498,254 10/ 1919 France. 1,143,605 4/ 1957 France.

714,436 8/ 1954 `Great Britain. 838,101 7/ 1960 Great Britain.

ANTHONY BARTIS, Primary Examiner.

RICHARD M. WOOD, Examiner. Y. Y. MAYEWSKY, Assistant Examiner.`

Claims

1. AN INFRARED HEATER COMPRISING AN ELONGATED OUTER TUBE OF QUARTZ HAVING AN OPEN END AND A CLOSED END, AN ELECTRICALLY INSULATING PARTITION MEMBER SUBSTANTIALLY TRANSPARENT TO INFRARED RADIATION AND DEFINED BY AN ELONGATED STRIP TWISTED ABOUT ITS LONGITUDINAL AXIS TO DIVIDE THE INTERIOR OF SAID TUBE INTO TWO ADJACENT CONVOLUTED CHAMBERS, AN ELECTRICAL RESISTANCE HEATING ELEMENT DISPOSED WITHIN EACH OF SAID CONVOLUTED CHAMBERS FOR EXTENSION ALONG THE LENGTH THEREOF AND CONTAINMENT THEREBY, SAID RESISTANCE HEATING ELEMENTS BEING ELECTRICALLY CONNECTED IN SERIES AT THE CLOSED END PORTION OF SAID TUBE AND DISPOSED FOR CON-A NECTION AT THE OPEN END PORTION OF SAID TUBE TO AN EXTERNAL SOURCE OF ELECTRICAL ENERGY FOR HEATING THEREBY TO GENERATE INFRARED RADIANT ENERGY FOR TRANSMISSION FROM AND THROUGH SAID TUBE, AND SUPPORT MEANS DISPOSED WITHIN SAID TUBE AT THE CLOSED END PORTION THEREOF TO SUPPORT SAID TWISTED STRIP PARTITION MEMBER IN AN ENDWISE SEPARATED RELATION TO THE CLOSED END OF THE TUBE.