US3109228A

US3109228A - Manufacture of electric radiant heating panels

Info

Publication number: US3109228A
Application number: US832603A
Authority: US
Inventors: Martin T Dyke; Emil W Razlag
Original assignee: Thermway Ind Inc
Current assignee: Thermway Ind Inc
Priority date: 1959-08-10
Filing date: 1959-08-10
Publication date: 1963-11-05
Anticipated expiration: 1980-11-05

Description

Nov. 5, 1963 3,109,228

MANUFACTURE OF ELECTRIC RADIANT HEATING PANELS M T. DYKE 3RD., ETAL Filed Aug. 10

INVENTORS. mazfl/v 7. awn? 3' E/WA w eAzLA ATTOE/VEYS resistor.

United States Patent Filed Aug. 10, 1959, Ser. No. 832,603 Claims. (61. 29155.7)

'I'his invention relates to a process for manufacturing electric radiant heating panels and like elements.

An object of the invention is to provide a better and more economical method of manufacturing such heating panels.

Another object is to simplify and improve the mass production of these panels.

These and other objects will in part be understood from and in part pointed out in the following description.

One of the first commercially available electric radiant heating units consisted of a frame in which was mounted a sheet of tempered glass. On the rear side of the glass sheet theer was applied an electrical resistor in the form of a thin ribbon of metal which was heated by current from a suitable source, such as a 115 volt power line. Most of the heat so generated in the resistor then would radiate from the frontof the panel to provide very clean, comfortable heating.

Recently, to overcome the tendency of glass heating panels to shatter with sudden changes in temperature'or from mechanical shock, panels of porcelainized steel have been developed. The sheet steel center of such a panel provides great mechanical strength while the porcelain coating provides an electric insulating surface on which a heating resistor can be atfixed, and this coating also serves to promote radiation of infra-red heat energy from the panel.

One problem with such a panel is how to apply to the hard, smooth, impervious porcelain surface a resistor element which will cling tightly to it in spite of repeated expansion and contraction during heating and cooling of the unit. It has been found that molten aluminum sprayed onto the panel in a thin layer while the panel is at an elevated temperature of from about 500 F. to about 700 F. will provide such a resistor. Now, a typical panel is designed to be connected directly to the power line (e.g. 115 v.). Thus, even though the aluminum is applied in a very thin layer, to obtain a sufficiently high value of resistance it is necessary that the aluminum be in the form of a narrow zig-zag strip folded back and forth along the panel so that its total length is much greater than that of the panel. Previously, attempts have been made to spray the aluminum directly over such a zig-za'g path, but working at the high temperature required and in view of the limitations of the metal spraying equipment, as a practical matter is is impossible to do this with sufficient accuracy and uniformity. Accordingly, it has been the practice to coat the porcelain surface of the panel with a continuous,'uniforn1 layer of aluminum, and then to etch this aluminum into the desired zig-Zag pattern.

This etching operation required as a first step the applying upon the continuous aluminumlayer of a special heat-and-chemically-resistant material, such as silicone varnish, in the zig-zag pattern desired. Thereafter, the varnish-coated, aluminized panel was treated first in a bath of hot alkali to remove the uncoated portions of the aluminum, and then in a bath of acid to neutralize the alkali, this being followed by a thorough rinse in water to remove the acid. Also either before etching or afterward electrical terminals had to be applied to the ends of the If applied afterward, it was necessary then to remove the varnish coating from the ends of the resistor;

it before, there was the problem of the solder and flux interfering with the etching operation. It is evident, therefore, that this prior procedure involves a number of steps, each of which had to be performed in a given order and some of which were critical as to time and temperature. As a consequence, mass production of these units required an intricate and carefully regulated production line. Moreover, because of the relative slowness in production, a substantial inventory in panels along the line was required. The present invention eliminates these difliculties, and yet the panels manufactured according to the invention are actually better than previous ones.

In accordance with the invention, in one specific embodiment thereof, an electric radiant heating panel is manufactured by first taking a sheet of porcelainized steel, cleaning it thoroughly and then applying to one of its faces a thin coating of kaolin in the negative of the zigzig pattern desired for the resistor. This coating of kaolin is advantageously applied to the panel as a wet paste through a silk screen. Next, without the need for preliminary drying the panel is raised to a temperature from about 500 F. to about 700 F. in the course of which the kaolin is baked to a dry adherent coating. T hen while at this temperature the panel is sprayed with a continuous, uniform thin layer of aluminum and quickly thereafter while still hot it is plunged into plain cold water. Though the metallic coating is continuous and completely covers the kaolin, because the metal was sprayed onto the panel, it is microporous. Thus, Water readily penetrates it to the under coating of kaolin which immediately absorbs the water, expanding and loosening in so doing. This blisters the metal layer loose from the panel in those portions covered by the kaolin, the loosened metal and softened kaolin being then easily washed and brushed off. The aluminum in the remaining'areas where it directly contacted the porcelain SUI? face of the panel adheres tenaciously to'form a resistor in the zig-zag pattern desired. In fact, so tightly does this remaining metal adhere that in cleaning away the blistered metal and kaolin it is possible to scrub forcibly with a wire brush without damaging the electrical continuity of the resistor strip.

After this water bath and scrub, the panel is dried and electrical terminals applied. This is advantageously done by spraying thin areas of copper at the very end of the aluminum resistor and then soldering the terminals to this copper. There is no problem here of having first to remove from the resistor a varnish coating, or with the solder and flux poisoning a subsequent etching operation. Since no etching and neutralizing chemicals are used in this process, there are absolutely no trace amounts of acid or alkali remaining on the panel. Thus, the insidious problem of failure of the resistor on a panel many years later because of the slow but deadly corrosive action of these chemicals is completely eliminated. The thermal shock of putting the hot, just metallized panels into cold water tends to reveal any defects in their porcelain and metal resistor coatings. Moreover, immediately plunging the hot panels into cold water promotes the blistering action of the kaolin and the removal of the unwanted portions of the aluminum. The time required to make a panel by this new process is less than half that of the previous one. In addition, the hazards of volatile organic solvents and alkali and acid fumes are entirely avoided.

'A better understanding of the invention together with a fuller appreciation of its many advantages will best be gained from the following description given in connec tion with the accompanying drawings wherein:

FIGURE 1 shows a porcelain covered steel panel, on one :face of which has been applied a thin coating of kaolin in the negative of the pattern desired for the metallic resistor to be applied to the panel; a

scrubbing with a brush is desirable.

FIGURE 2 shows the panel with its kaolin coating in the process of being sprayed with aluminum; and

FIGURE 3 shows a completed panel, the metal in the portions covered by the kaolin having been blistered off in a water bath leaving a zig-zag resistor strip firmly anchored to the porcelain surface of the panel.

The panel shown in FIGURE-1 comprises a thin sheet steel core 12 which is covered on its front and rear faces by tightly

adherent porcelain layers

14 and 16. The porcelain layers should preferably be free of pin holes and should completely coat the steel sheet to provide effective electrical insulation. The steel should be freeof contaminants so that the porcelain and the resistor to be applied remain tightly adherent during repeated heating and cooling of the panel. Porcelainized steel sheets. of this quality are available commercially.

Applied to porcelain face 14 of the panel in a negative zig-zag pattern is a thin coating 18 of kaolin. important characteristics of this material are that it withstands the high temperaures encountered; that it'readily mixes and sofens in a safe, cheap solvent (e.g.' water); that it dries to a thin, cohesive, sufficiently adherent coating; and that it readily re-absorbs thesolvent to return to a soft condition. formulated as follows: 1.0 pound of type #964 kaolin manufactured by Whittaker, Clark & Daniels, Inc.,

As an example, this material is screen can easily be washed clean; as a consequence this bronze screening operation gives consistently excellent results. Thus, the coating applied to every panel is uniform and precise.

I vAfter a'panel has been coated with a pattern of kaolin, it is then put ona conveyor and run through an oven where its temperature is raised to a value from about 500 F. to about 700 F. In the course of this heating, any water remaining in the kaolin is evaporated leaving a dry, thin, adherent coating on the panel. While at this elevated temperature the panel isv then sprayed with molten. aluminum in an even uniform layer as illustrated in FIGURE 2. The aluminum is advantageously applied from a stationary spraying unit 20, which can be a model number 24 metallizing .gun'manufactured by Metallizing Engineering Co. of Westbury, L.I., N.Y.,. while the panel one or more guns may be used side-by-side to give a layer of suflicient evenness. The actual metallizing operation on apanel 16 by 24 inches using three of these metallizing guns takes about seconds. After spraying, the still hot panel with its metal coating is plunged into cold water, thekaolin immediately expanding and selectively blistering the aluminum away from the panel as explained above. This blistering action is so effective that most of the kaolin and blistered metal can be wiped off the panel with a soft rag. However, to be sure that all of the loose metal and kaolin are removed a thorough The panel is then dried.

FIGURE '3 shows the panel after it has been washed and this loose material removed. The aluminum which directly contacted porcelain layer 14 remains very tightly adherent to it in the form of a zig-zag resistor 22. The edges of the resistor are'even and correspond closely to the side lines of the kaolin coating. Thus, since this coating was exact in size in the first place, by controlling the uniformity of the. aluminum coating from panel to panel, it is easily posible to produce panels with closely uniform operating currents and temperatures.

Since resistor 22 is aluminum, it is desirable to spray over the

areas

24 and 26 at its ends, a thin coating of copper which can, unlike aluminum, readily be tinned.

Thereafter, electrical terminals can be soldered onto the copper by conventional techniques. If desired, resistor 22 can be covered with a suitable layer of, insulation, such as silicone varnish. v

In actual practice, a completed panel is mounted in a suitable frame with resistor 22 on the inside and porcelain face 16 exposed and serving as the heat radiating surface of the unit. The relative thickness of steel sheet 12, porcelain layers 14 and :16, kaolin coating 18, and

metal coating 22 are not shown to scale in the drawings. In an actual panel, 16 by 24 inches, steel sheet 12 had a thickness of 0.049 inch; porcelain layers 14 and .16, 0.0 12 inch; kaolin layer 18, 0.006 inch; and aluminum layer I 22, 0.002 inch. Such a panel typically has an electrical input of 1000 Watts andoperates with a surface temperature of about 350F. The operatingtemperature of this porcelainized steel panel, however, is not critical" and it can without damage to the panel fluctuate widely up or down; In the case of a heating panel using tempered glass as its base, sudden changes in temperature,

or an increase in operating temperature aftera period of years operating at .a lower temperature can cause it to shatter. I r

The above description of the invention is intended in illustration and not in limitation. Various changes may occur to those skilled in the art and these may be made without departing from the spirit or scope of the inven tion as set forth. y

We claim:

1. An improved method of applying a tightly" adherent resistor element having a desired pattern and resistance toa supporting surface comprising the steps of coating a and said panel is .subjectedto thermal shock to reveal" possible defects.

3. A process for manufacturing high quality electric radiant heating panels and the like at lower cost, said process comprising the steps of applying to a base panel 'by' silk screen printing a paste-like mixture consisting principally of kaolin and water in a zig-zag pattern and in a thin layer, heating said coated panel to a substantially ele;

vat'ed temperature, spraying said heated panel with aluminurn-like metal in a thin continuous layer, thereafter putting Water on said metallized panel to remove the kaolin and the metal immediately covering it, and then applying electrical terminals to end portions of the remaining metal on said panel, whereby said panel is free of traces of corrosive chemicals and said remaining metal remains tightly adherent during repeated heating and cooling.

4. An improved method of making aresistance unit suitable for radiant heating and the like, said method com prising the steps of taking a base member having an insulating surface and coating it With a cohesive adherent patterned layer at least several mils thick of a paste-like mixture consisting primarily of kaolin and water, heating said member and layer to an elevated temperature, spraying with a generally uniform layer of aluminum-like metal to a thickness of several mils, and finally washing said metallized member in water to cause said mixture to blister off undersired portions of the sprayed metal.

5. An improved method of making an electrical radiantv heating panel comprising taking a clean base sheet having References Cited in the file of this patent a smooth insulating surface, coating it with a patterned UNITED STATES PATENTS layer of Wet clay material which is driable into a thin J cohesive adherent layer, heating said coated sheet to a f g i substantially elevated temperature above the drying point 5 of said clay material, applying to said heated sheet a FOREIGN PATENTS thin continuous uniform porous layer of conductive metal,

and Washing said metallized sheet in Water to remove ungfgif gi x 5 a d 1. 1 1 wanted metal an sad clay material to cave on said 150,890 swltzefland Feb. 16) 1932 base sheet a tightly adherent resistor having a desired 10 shape and resistance.

Claims

3. A PROCESS FOR MANUFACTURING HIGH QUALITY ELECTRIC RADIANT HEATING PANELS AND THE LIKE AT LOWER COST, SAID PROCESS COMPRISING THE STEPS OF APPLYING TO A BASE PANEL BY SILK SCREEN PRINTING A PASTE-LIKE MIXTURE CONSISTING PRINCIPALLY OF KAOLIN AND WATER IN A ZIG-ZAG PATTERN AND IN A THIN LAYER, HEATING SAID COATED PANEL TO A SUBSTANTIALLY ELEVATED TEMPERATURE, SPRAYING SAID HEATED PANEL WITH ALUMINUM-LIKE METAL IN A THIN CONTINUOUS LAYER, THEREAFTER PUTTING WATER ON SAID METALLIZED PANEL TO REMOVE THE KAOLIN AND THE METAL IMMEDIATELY COVERING IT, AND THEN APPLYING ELECTRICAL TERMINALS TO END PORTIONS OF THE REMIANING METAL ON SAID PANEL, WHEREBY SAID PANEL IS FREE OF TRACES OF CORROSIVE CHEMICALS AND SAID REMAINING METAL REMAINS TIGHTLY ADHERENT DURING REPEATED HEATING AND COOLING.