US 3904850 A
A flexible heating panel and method for making such a heating panel, the panel having an insulated flexible heating element bonded to an overlying insulated flexible electrical ground and having the electrical connections mounted on the top surface therewith. The method further including the steps of securing the connections thereto, and protectively sealing the electrical connections from the surrounding influences.
Description (OCR text may contain errors)
United States Patent [191 Johnson FLEXIBLE HEATER PANEL  inventor: Ben Q. Johnson, San Marcos, Tex.  Assignee: Thermon Manufacturing Company  Filed: Mar. 11, 11974 21 Appl. No.: 449,772
52 U.S.Cl. .219/s2s;219/535;219/541;
219/549;171/51 51 int. (11. ..u0sa 3 34 58 Fieldofsearch ..219/212, 345,528,529,
 References Cited UNITED STATES PATENTS 2,844,696 7/1958 Custer, Jr. 219/345 2,845,519 7/1958 Willat..... 219/528 2,938,992 5/1960 Crump.... 219/528 3,178,560 4/1965 Mapp ct a1 1 219/528 3,209,128 9/1965 Chapman ct al 219/528 jut J64! 2936 2& 4
e a I "fifft'f'ff'ff'ffifflfi' ,5- 'siiiiiwi nwkiwikfi- 3 A9,: 9 4
[ 51 Sept. 9, 1975 3,454,746 7/1969 Duoois 219/549 3,584,198 6/1971 Doi ct a1. 219/549 3,627,981 12/1971 Kuhn 219/212 3,657,517 4/1973 Hoyt 219/535 3,780,262 12/1973 Rudd 219/530 3,790,753 2/1974 Miller 219/528 Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or FirmPravel & Wilson [5 7 1 ABSTRACT 2 Claims, 3 Drawing Figures I 1? a! a 2 FLEXIBLE HEATER PANEL BACKGROUND OF INVENTION l. Field of Invention This invention relates to flexible heating panels.
2. Description of the Prior Art Prior art heater panels disclose the value of having protective grounding features to prevent inadvertent electrical shocks. Some of the prior art heater panels utilize a ground layer such as those devices disclosed in US. Pat. Nos. 3,454,746; 2,971,073; and 3,627,98l.
However, numerous practical problems are incumbent with the use of such a heater panel. For example, it is desirable to protect the edges of the various layers from the effects of environmental deterioration. Furthermore, it is desirable to secure the electrical connections located at different layers within the heater panel firmly to the panel to avoid inadventent electrical disconnection which would render the panel inoperative. The ground layer must further be effectively insulated from both the heater elements and any electrical connections thereto to prevent internal shorts under normal operating conditions.
SUMMARY OF THE INVENTION The present invention provides a new and improved flexible heater panel assembly having a flexible, fullyinsulated heater element bonded to a flexible, fullyinsulated electrical ground overlying the heater element such that, if the panel assembly is inadvertently pierced by an electrical conductive object, the ground layer is pierced in such a manner that a subsequent contacting of the heater element will ground out the heater element circuit through the ground layer thus preventing electrical shocks. The heater panel assembly includes electrical lead-in Wires securely mounted on this fully-insulated assembly and all electrical elements therewith are protectively sealed to prevent environrnental deterioration.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an oblique view of the apparatus in the preferred embodiment of this invention as used for heating a pipe;
FIG. 2 is a plan view of the present invention, showing the multiple layer construction; and
FllG, 3 is a sectional view taken along the lines -13 of FTC:v 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings the letter H designates the flexible heater panel assembly of the preferred embodiment of thisinvention mounted onto a pipe P for heat ing the same, the heater panel assembly H having a heater element layer E and a flexible ground layer G.
The heater panel assembly H includes a heater element layer E having a base insulation layer 10 having a bottom face 101; and an upper face 10a of a suitable electrical insulation material, such as silicon rubber. For strength, glass fibers (not shown) can be embedded within the insulation materials to reinforce the insulation layer 10. Alternatively, other electrical insulation materials such as Teflon, butyl rubber or polyamides can be used.
Overlying the base insulation layer 10 on face 10a is a series of electrically resistive heating elements or strips 12 which are symmetrically arranged in a known manner about the face 10a of the base insulation layer 10. The elements 12 in the preferred embodiment of this invention are formed of an electrically resistive flat foil tape made of a nickel-steel alloy. The heating elements 12 have appropriate electrical connection points 12a and 12b for making electrical connections, to electric line 22, which is powered by a suitable power source (not shown). Overlying the heater element 12 is an electrical insulation layer 14 having a bottom face 14b and an upper face 14a formed of insulating material such as silicon rubber as discussed above. The base insulation layer 10 and the electrical insulation layer 14 are of reinforced silicon rubber with the opposite faces 10a and 14b of the layers 10, I4 bonded about the heating element 12 by an appropriate vulcanizing process utilizing proper heat and pressure to form the heater element layer E. A void 11 (FIG. 3) may be formed between the faces 10a and 14b or it may be filled by vulcanizing in such a fashion that faces 10a and 14b are bonded together leaving no voids.
The flexible ground layer G includes an electrical insulation layer 16 having a bottom face 16b and an upper face 16a of suitable insulation material. The upper face 16u provides a mounting surface for a finely woven wire screen 18 of aluminum, copper, or steel, or any other suitably electrically conductive material that will serve a grounding function. Such electrically conductive material is also flexible and of minimal thickness. Overlying the wire screen 18 is a top insulation layer 20 having a bottom face 20b and an upper face 20a. The electrical insulation layer 16 and the top insulation layer 20 are formed of preferably a reinforced silicon rubber vulcanized about the wire screen 18 to produce the ground material layer G.
The flexible heater panel H may be defined as including protected side portions 30, 31, 32 and 33. Each side portion is formed by the bottom insulation layer 10, which is formed slightly larger in length L and width W so as to include overlapping, protective portions 10s. The overlapping portions 10s of the bottom insulation layer 10 are folded over each of the sides 30, 31, 32, 33 of the entire panel H and include portions 10! which are vulcanized to the top insulation layer face 2014. These overlapping, protective portions 10s of the bottom insulation layer 10 serve to insulate and protect the otherwise exposed edges of the heater element 12, insulation layers 14, 16 and 20 and the ground screen 18. Furthermore, the overlapping portions 10s help to prevent any portion of the heating element 12 from being exposed thus preventing inadvertent electrical shock.
A lead-in cable 22 carrying heater wires 24, 25 and a ground wire 26 connected to a suitable electrical ground 34 is Securely mounted with the upper face 20a of the top insulation layer 20 by a clamp 28. The clamp 28 is mounted to the heater panel assembly H by a pin 35 having a backing plate 36 mounted beneath the base insulation layer 10, to distribute thereon the load exerted on thepin 35, and prevent the pin 35 from inadvertently being torn therefrom. In order to connect the wires 24, 25, 26 to their appropriate connections, a portion (not shown) of the heater panel assembly I-I must be removed to expose the connection points 1211 and 12b of the heater element 12 and a ground connection point 27 of the wire screen 18. This removal operation may be accomplished by etching with a suitable acidic or basic solution, or by cutting with a knife, or
the like. Thus, a small portion (not shown) of the top insulation layer 20, the wire screen 18, and layers l4, 16 must be removed by the above operations to allow electrical connections to be made. With this portion (not shown) removed, the wires 24, 25 are connected to the heater element 12 at connection points 12a and 12b, respectively, to provide power from a suitable source (not shown) for the heater element 12. Furthermore, the ground wire 26 isconnected to the screen 18 at the connection point 27. The wires 24, 25 and 26 can be secured to the connection points 12a, l2b and 27 by any suitable means such as bradding or riveting.
A sealing block 37 of silicon rubber is formed about the wires 24, 25, 26 and a portion of the lead-in cable 22 as well as any evacuated portion laid bare during the removal operation to enclose and secure the wires 24, 25 and 26. The sealing block 37 is molded under heat and pressure and vulcanized to the heater panel assembly H by using an appropriate mold (not shown) such that the evacuated portion is filled with silicon rubber and the wires 24, 25, 26 are separated and suspended within the sealing block 37 in a locked, non-touching positon. The sealing block 37 helps to insure a watertight connection, electrically insulate the wires 24, 25, 26 as well as help to protect and prevent inadvertent disconnection of the wires 24, 25, 26.
In the operation and use of the formof the invention illustrated in FIGS. 13, the heater panel assembly H can be used on a flat surface, or as shown in FIG. 1, on a curved surface of pipe P, or the like. If wrapped about the pipe P, it is preferred that the bottom face b of the base insulation layer 10 be adhesively mounted to the pipe P to prevent relative motion therebetween and insure proper surface area contact with the pipe P to maximize heating efficiency. Due to the particular laminated configuration of the elements of the heater panel assembly H, if the panel assembly H is pierced by an electrically conductive object (not shown) such as a nail or screwdriver, the direction of the puncture is such that the object will first pierce the top insulation layer 20, contact the wire screen 18, and then pierce the electrical insulation layers 16, 14 and finally contact the heating element 12. As such, any electrical surge resultant to contacting the heating element 12 by the conductive object will ground through the conductive object contacting the wire screen 18, which is connected to the wire 26 and the ground 33, thus preventing inadvertent electrical shocks to one so piercing the heating element 12. Of course, if the piercing object 13 is not of a conductive material, no risk is encountered by one who accidentally pierces the heating element The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, materials, components, circuit elements, wiring connections and contacts as well as in the details of the illustrated circuitry and construction may be made without departing from the spirit of the invention.
1. A flexible heating panel comprising:
a first electrical insulating layer serving as the base of I the panel;
a flexible heating tape for heating, overlying said first layer;
a second electrical insulating layer, overlying said flexible heating tape;
a flexible, electrically grounding material for electrically grounding the heating tape in case of accidental penetration of the panel, said grounding material overlying said second layer;
a third electrical insulating layer overlying said grounding material and having a bottom face and an upper face, said upper face serving as the top of the panel;
said second electrical insulating layer includes:
a heater element insulating layer mounted with said flexible heating tape, said heater element insulating layer being formed with said first electrical insulating layer into a heater element layer; and
a ground insulating layer mounted with said grounding material, said ground insulating layer being formed with said third electrical insulating layer into a ground layer, said heater element insulating layer and said ground insulating layer being laminated together;
said first electrical insulating layer includes overlapping, protective portions folded about and adjacent to the end portions of the panel to protect and enclose all of said layers, said overlapping, protective portions being attached to said upper face of said third electrical insulating layer;
electrical leads of an electrical power line and means connecting said leads to said heating element and said grounding material; and
clamp means mounted with the panel to fasten said electrical power line to said upper face of said third electrical insulating layer to prevent said electrical connection means and said electrical leads from becoming inadvertently detached from said heating tape and said grounding material.
2. The structure of claim 1, wherein: said first, second, and third electrical insulating layers are made of glass reinforced silicon rubber.