US2939099A - Metal clad heating strip with ribbon element - Google Patents

Description

May 31, 1960 G. H. MOREY 2,939,099

METAL CLAD HEATING STRIP WITH RIBBON ELEMENT Filed Sept 8, 1958 2 Sheets-Sheet l INVENTOR. GLEN H. MUREY BYm/m ATTORNEYS G. H. MOREY May 31, 1960 METAL CLAD HEATING STRIP WITH RIBBON ELEMENT m m Wm H m G 2 Sheets-Sheet 2 BY Z I Z ATTORNEYS Filed Sept. 8, 195a United t tes Pat M METAL CLAD HEATING STRIP WITH RIBBON ELEMENT Glen H. Morey, Terre Hante, Ind., assignor to Linton- Summit Coal Company, Terre Haute, Ind., a corporation of Indiana Filed Sept. s, 1958, Ser. No. 759,652

3 Claims. (Cl. 338-243 This invention relates to electric heating tapes and methods of manufacture thereof and in particular to ribbon-like strip heating tapes.

Electric heating tapes are known and generally consist of relatively fine resistance wires supported on a fabric carrier or the like in a zig-zag pattern so that energization of the heating element will cause heat to be developed over substantially the entire area of the tape. Such heating tapes have certain definite drawbacks and limitations. In the first place the wires are relatively small and are thus fragile and are subject to being broken or pinched off and which occurrence would ruin the heating tape.

Further, since the wires are relatively small the heat is not developed uniformly over the tape and any degree of uniformity of heat development and dissipation can only be approximated by distributing the wire in the tape.

I The use of relatively small wires also imposes a severe limitation on the heating tapes with regard to the length to which the tapes can be made and the total amount of electric power that can be converted into heat energy. Such tapes according to the prior art are also generally limited as to temperature because of the tendency of insulation, usually of quartz, asbestos or a high temperature glass, to disintegrate or crumble or otherwise deteriorate at extremely high temperatures.

In my co-pending application, Serial No. 752,812, filed August 4, 1958, for Electrical Heating Tape and Method of Making there is disclosed a novel electric heating tape having as one particular characterizing feature the provision of a ribbon-like heating element as opposed to the conventional wire type heating elements. The tape disclosed in that application is flexible and has wide utility for heating pipes or for being applied to other surfaces where flexibility of the tape is important. Because the tape must be flexible, however, the sheathing about the ribbon-like heating element must also be flexible and this dictates the use of a fabric or textile material such as knitted, woven, braided material. This in turn, imposes limitations of maximum temperature as well as requiring that the heating tape be protected against physical abuse. Such flexible tapes can be made waterproof by the application to the sheathing of a sealing and waterproofing material, but this in turn imposes a still lower temperature limitation on the heating tape.

Having the foregoing in mind, it is a primary object of the present invention to provide a heating tape utilizing a ribbon-like heating element in which the above drawbacks and limitations are not present.

Another object of this invention is to provide a heating tape utilizing a ribbon-like heating element which is extremely rugged thereby permitting the use of the tape in circumstances that would not permit the use of a more fragiletape.

.. ,;;It is also an object of this invention to provide a heat- 1 8 gpe and a. method of, manufacturing. the same utir 2,939,099 Patented May 31, I960 lizing a ribbon-like heating element which can be made completely weather-proof but in which the usual temperature limitations are eliminated.

Another object of this invention is the provision of a heating strip or heating tape utilizing a ribbon-like heating element in which the character of the electrical insulating material immediataely surrounding the heating element does not impose a temperature limitation on the strip or tape.

Another object of this invention is the provision of a heating strip or tape and the method of manufacturing the same which can be used singly or in combination to provide heating for various structures such as ovens, heating tunnels and the like.

These and other objects and advantages will become more apparent upon reference to the drawings in which:

Figure 1 is a perspective view showing heating tapes according to the present invention applied to a pipe or conduit that is to be heated;

Figure 2 is an enlarged view of one of the tapes with a portion of the outer sheath in section to show the internal construction;

Figure 3 is a sectional view indicated by line 33 on Figure 2;

Figure 4 is a sectional view indicated by line 4-4 on Figure 2;

Figure 5 is a view showing a heating tape or strip according to the present invention mounted adjacent a wall of an oven or tunnel or other enclosure for supplying heat thereto;

Figure 6 is a perspective view showing one manner in which a sheath of electrical insulating material can be applied to a ribbon-like heating element;

Figure 7 is a view showing a preliminary formation of the metallic outer sheath that is mounted about the heating element;

Figure 8 is a view illustrating the insertion of the ribbon-like heating element having a sheath of electrical insulating material thereon into the preliminarily shaped metallic outer sheath;

Figure 9 is a view showing the final operation in connection with compressing the metallic outer sheath about the insulated ribbon-like heating element;

Figure 10 is a fragmentary view showing a heating tape or strip according to the invention in which the electrical insulating material surrounding the heating element includes wire reinforced threads or yarns;

Figure 11 is a view showing a modified form of the heating tape; and

Figure 12 is a sectional view indicated by line 12-12 on Figure 11.

Referring to the drawings somewhat more in detail, in Figure 1 there is a pipe or conduit 10 which it is desired to maintain at a predetermined temperature. For this purpose one or more heating tapes 12 are mounted on the surface of the pipe or conduit and extend axially therealong. These heating elements would normally be clamped to the pipe so as to be in good .thermal contact therewith and insulation would be pro vided about the entire assembly to inhibit heat loss.

Each tape or strip 12 has terminals 14- at the opposite ends thereof by means of which the heating elements of the strip or tape are energized. I Referring now to Figures 2 and 3 it will be observed that the terminals 14 are attached to the ends of a ribbon like heating element 16. Such a ribbon-like heating element might be quite narrow and could be up to 3" in width and the thickness might vary from a few thou sandths of an inch upwardly.

The exact combination of width and thickness of the tape would be determined by the application in which the tape was to be employed and the watts per square inch to be developed thereby, taking into account the available voltage source. Such determinations can be made according to well known practices. In length substantially no limitations exist for the ribbon-like heating element and the heating strip or tape can be made as long as desired to fit any particular job. This is a characteristic of the heating tape of the present invention which is distinctly different from conventional heating tapes which are severely limited as to possible length and Width on account of the use of a fine wire therein as the heating element. The ribbon-like heating element 16 has a sheath 18 of electrical insulating material which is applied thereto in the form of a woven, braided, or knitted sleeve or wrapped strip. The sheath can be a single layer of the textile material or may comprise multiple layers and will generally consist of high temperature quartz, asbestos, or a synthetic material such as the fiber known by the commercial name Fiberfrax.

Surrounding sheath 18 according to the present invention is a metallic sleeve 20 which extends substantially the full length of the heating tape although being terminated inwardly of the terminals thereof to prevent shorting therebetween.

The ends of the heating strip or tape between the ends of the metallic outer sleeve 20 and the terminals could be sealed if desired but in general the temperatures at which the tape or strip according to this invention is adapted for being operated would prevent the use of any sealing material except a ceramic or the like.

As will be seen in Figures '3 and 4, the outer metallic sheath 20 is flattened against the sides of the sheathed ribbon-like heating element thereby to provide the shortest possible path for heat through the flattened sides of the metallic sheath and likewise to compact as much as possible the electrical insulating material between the ribbonlike heating element and the outer metallic sheath to provide for eflicient transfer of heat from the heating element to the sheath thereby permitting operation of the heating element at high temperatures without there being an extremely large temperature lag between the inside and outside of the heating strip or tape. For example, temperatures in excess of 2000 F. can readily be attained by the heating strip or tape according to the present invention and while at this temperature the fabric or textile electrical insulating material tends to crumble, the metallic outer sheath will hold the material in place so that the heating strip or tape will have extremely long life even at these elevated temperatures,

One possible use of a strip or tape according to this invention is illustrated in Figure 5 wherein 22 indicates the Wall of an enclosure such as an oven or the wall of a heating tunnel. Posts 24 may project outwardly from the wall and carry bus bars 26 between which bus bars the heating tape or heating strip 23 according to this invention may extend and with the strips or tapes being arranged at any desired spacing and according to any pattern to provide for the proper supply of heat to the enclosure inside wall 22.

In making the heating strip or tape according to this invention an elongated strip of the heating element material may be provided as at 30 and this material is fed through a station 32 where sheathing material 34 is supplied either by braiding, knitting, weaving or wrapping the sheathing material about the heating element.

As to the metallic sheathing, in Figure 7 it will be seen that relatively thin walled tubing 36 is passed between forming rollers 38 to provide for a generally elliptically shaped tube 40. Tube 40 then has the sheathed ribbonlike heating element 34 inserted therein. Thereafter, the tube with the heating element therein is passed through a second set of forming rollers 42 and this comprises the metal sheathing about the heating element. The heating tape or strip can either be manufactured in the lengths desired, in which case no cutting off of the metallic sheathing is necessary, or it can be made in strips as long as the metallic tubing and the ends of the heating element thereafter exposed. It is also possible when making extremely long heating strips or tapes according to this invention to weld lengths of the metal tubing together end to end and thereby provide a metallic sheathing of any desired length.

It has been mentioned before that the ribbon-like heating element of the present invention can be insulated by means of threads or yarns which are reinforced with fine wires and which wires tend to add strength to the assembly and also tend to hold individual fibers of the threads or yarns of the insulating textile material in place which is advantageous when the heating strip or tape is operated at extremely high temperatures. Such wires are quite small, usually being only a few thousandths thick so that they are highly flexible. By making the wires of stainless steel, Inconel, Nichrome or Kanthal the wires are made resistant to corrosion or deterioration at high temperatures.

In Figure 10 the metallic sheathing is indicated at 44, the ribbon-like heating element at 46 and the fabric or textile sleeving at 48 with the reinforcing wires of some of the threads or yarns indicated at 50. These reinforcing wires are completely covered by the fibers of the individual yarns or threads of textile material and thus are kept from coming into contact with the metallic outer sheath or the inner ribbon-like heating element. If desired, of course, more than one sheath could be provided and for example in Figure 10 the wire reinforced sheath could be mounted about an unreinforced innermost sheath thereby further insuring that the wires would not touch the heating element while at the same time the Wires would serve to support the insulating fibers of both the outer and inner fabric sheaths.

It will also be understood that a heating strip or tape of the present invention need not necessarily be operated at extremely high temperatures and that it would form an advantageous construction because of its great ruggedness and resistance to physical abuse in relatively low temperature installations. The advantages would still obtain that large radiating surfaces Would be heated that would permit operation of the heating element at lower temperatures than is the case with heating tapes having fine wires therein. With low temperature operation it would be possible to sealingly impregnate or coat at least the exposed ends of the fabric sheath and the ribbon-like heating element with a plastic material such as silicone rubber thereby to make the entire tape Weather-proof thereby permitting use of the heating tape or strip in exposed locations where heating elements having a fabric body might be unsatisfactory.

Similarly as with the fine wires that support the fibers of electrical insulating material, the metallic outer sheath, particularly where it is to be employed with a high temperature tape, could advantageously be made of heat and corrosion resistant material, of which class of metallic substances, stainless steel, Inconel, Nichrome or Kanthal are examples.

The heating tapes described in detail above include an outer metallic sheath which is relatively thin walled and which is made of material sufliciently lacking in ductility so that the tapes have only limited flexibility. This degree of flexibility is suificient to enable the tapes to conform to configurations that do not depart substantially from planar but it is not possible to wind the tapes about pipes or to bend them to fit curvatures of any great degree.

I have found, however, that a tape can be constructed according to the present invention and be relatively flexible while at the same time embodying all of the advantages that obtain from the metallic outer sheath. This is accomplished by forming the outer sheath of a material which is relatively ductile and so shaping tho 5 sheath that the tape can be bent without in any way damaging the tape with regard to its operating characteristics.

Figure 11 shows a member 60 which may be a pipe or conduit or vessel of some sort about which is wrapped a heating tape 62 which, like the tapes previously described includes a ribbon-like heating element 64, an inner sheath of electrical insulating material 66 which may be wire reinforced, and an outer metallic sheath 68.

As will be seen in Figure 12 the outer metallic sheath 68 has a substantial Wall thickness, say, and is formed so that the edge portions as at 70 are somewhat tubular whereas the central portion of the metallic sheath at 72 is pressed tightly against the sides of the ribbon like heating element 64. The material of the outer sheath is ductile aluminum and this, together with the cross sectional configuration of the sheath permits the heating tape to be wrapped around relatively small cylindrical shapes. One tape that was tested was an inch wide when flattened out, and the tubular aluminum sheath had a wall thickness of 0.035". This tape was wrapped around an 8" pipe and heated to red hot (600 C.) for several hours.

Materials other than aluminum could be employed, for example, high temperature alloys having a soft annealed form could be utilized and this would permit operation of the tape at higher temperatures than would be possible with aluminum.

By utilizing the modification of Figures 11 and 12 the advantages of the metal clad tape can be obtained while still gaining the advantage of a certain degree of flexibility of the tape.

It will be understood that this invention is susceptible to modification in order to adapt it to diflerent usages and conditions; and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. In an electrical resistance heating tape or strip; an elongated thin flat ribbon-like heating element, terminals on the ends of the said element for the energization thereof, a first inner sheath of textile material made of fibers of electrical insulating material closely surrounding the said element extending substantially from one terminal to the other, and a thin walled metallic tubular element mounted about the textile sheath and flattened thereagainst and terminating short of the ends of the textile sheath, said textile material being made up of threads or yarns consisting of fibers of electrial insulating material twisted together and fine wire embedded in the twisted together fibers, said tape or strip being sufficiently flexible to conform to the surfaces other than fiat.

2. In an electrical resistance heating tape or strip; an elongated thin fiat ribbon-like heating element, terminals on the ends of the said element for the energization thereof, a first inner sheath of textile material made of fibers of electrical insulating material closely surrounding the said element extending substantially from one terminal to the other, and a thin walled metallic tubular element mounted about the textile sheath and flattened thereagainst and terminating short of the ends of the textile sheath, said textile material being made up of threads or yarns consisting of fibers of electrical insulating material twisted together and fine wires of corrosion resistant material embedded in the twisted together fibers, said tape or strip being bendable to conform to surfaces other than fiat. 3. In an electrical resistance heating tape or strip; a straight piece of relatively thin wide flat ribbon-like resistance wire forming a heating element, a sleeve like sheath of textile material formed of fibers of heat resistant electrical insulating material surrounding the heating element and extending substantially from end to end thereof, a straight metallic sheath surrounding the said textile sheath and extending substantially from end to end of said textile sheath receiving the sheath and wire straight and free of bends, and said metallic sheath being flattened against the said textile sheath along the wide sides of the heating element, said metallic sheath being so flattened as to have arcuate portions connecting the portions thereof that are flattened against the heating element, and the material of said metallic sheath being ductile whereby the tape can be bent to conform to a nonplanar surface to which it is to transmit heat.

References Cited in the file of this patent UNITED STATES PATENTS 1,005,360 Taylor Oct. 10, 1911 1,075,517 Taylor Oct. 14, 1913 1,093,792 Madsen Apr. 21, 1914 1,403,231 Churchward Jan. 10, 1922 1,555,953 Simon Oct. 6, 1925 2,357,241 Wagner Aug. 29, 1944

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