US3093720A - Electrical pad heaters - Google Patents

Description

June 1l, 1963 M. W. PATRICKl ELECTRICAL PAD HEATERS Filed Aug. 22, 1961 BY M y ATTORNEYS United States Patent O 3,093,720 ELECTRICAL PAD HEATERS h/lalcolm W. Patrick, Bedford, Ohio, assignor to Hupp Corporation, Cleveland, Ohio, a corporation 'of Virginia Filed Aug. 22, 1961, Ser. No. 133,242 1 Claim. (Cl. 213-19) This invention relates to electrical pad-type heating devices and more particularly to such devices for use out Vof doors or in other exposed environments where they are subjected to the effects of moisture, dirt and temperature variationu.

While heaters of the present invention are of general application, it has been found that they are particularly well-suited for use in connection with lheat pumps. As is well known in the art, heat pumps comprise indoor and outdoor coils reversibly connected by a closed refrigerant system to permit operation of the unit for heating or cooling.

When a heat pump is used on the heating cycle, the outdoor coil assembly functions as the evaporator. When, as is often the case, the outdoor ambient temperature is below freezing, there is a tendency for frost to form on the outdoor coils at an accelerated rate and for condensate to freeze in the sump of the unit. In one application the pad-type heaters of the present invention are installed in the condensate sump and are effective to prevent freezing of the water in the sump and the other objectionable conditions which arise upon operation of such units under low ambient temperatures. The pad beaters of the present invention are particularly suited for such application since they are structurally rugged, completely water-proof and impervious to environmental factors which heretofore prevented the trouble free operation of such `units under comparable Severe service conditions.

With these considerations in mind it is the principal purpose and object of the present invention to provide novel electrical pad heaters which have an extended trouble-free service life even yunder the most unfavorable service conditions.

It is a further object of the present invention to provide improved electrical pad heaters which are completely impervious to the effects of moisture, ice or dirt, and thus are particularly well-.suited for operating in exposed outdoor locations.

It is an additional object of the present invention to provide improved electrical pad heaters which have suiiicient mechanical strength to resist damage by impact.

It is a further object of the present invention to provide electrical pad heaters which have an unusually large heating capacity yfor given :size and which are inexpensive to manufacture.

In attaining lthese land other objects, the heaters of the present invention include a length of resistance wire imbedded in an insulating plastic envelope and enclosed in an outer sealed metal envelope of novel configuration which imparts structural rigidity to the entire assembly, and novel means for connecting the interior resistance wires to the exterior of the device to positively seal the entire heater assembly and to prevent mechanical damage to the wires.

Additional objects and advantages will become apparent yas the description proceeds in connection with accompanying `drawings in which:

FIGURE 1 is a top plan view of the heater of the present invention;

FIGURE 2 is an elevation of -the unit of FIGURE 1;

FIGURE 3 is a section taken along line 3--3` of FIGURE l;

FIGURE 4 is an enlarged fragmentary view of the ice inner plastic envelope as it appears before it is enclosed in the outer metal housing and;

FIGURE 5 is an enlarged fragmentary section taken along line S-S of FIGURE 4. Y

Referring now more particularly to the drawings, the heater of the present invention has been illustrated in a rectangular configuration particularly suited for use as a sump heater for a heat pump unit. However, it is to be understood that the pad can assume other configurations as required by the needs of a particular installation.

Two principal components of the heater assembly are the outer th-in metal envelope, indicated generally at 20, and the inner plastic heater assembly, indicated generally at 22, shown separately in FIGURES 4 and 5 to which detailed reference will now be made.

The assembly 22 comprises upper .and lower sheets 24 and 26 of neoprene or a similar exible insulating material, between which is received a continuous length of insulated wire 28. As shown in FIGURE 4 the terminal ends 30 and `32. of the wire 28 are positioned adjacent one corner of the unit and project laterally of the unit. The portion of the wire extending away from the terminal 30 proceeds across the end of the unit and then is formed into a series of reverse U-bends 34 and 36 adjacent the ends of the unit to yform a plurality of parallel lengths extending between the ends of the unit. The wire leading from the terminal 3-2 is provided with a reverse U-bend 38 from which it extends to the front edge of the assembly. Preferably the wire 28 has suiicient stiffness so that once it is bent into the configuration shown in FIGURE 4, it tends to remain in this conguration thus avoiding the imposition of elastic stress on the flexible insulating sheets 24 and 26'.

In the manufacture of the unit the entire length of wire is iirst bent to the final coniguration shown in FIG- URE 4, the insulation is removed from the terminal portions of the wire and the ends of the power supply lines 4@ and 42 are wrapped securely around these terminal portions. The wires are silver soldered and wrapped with electrical tape. The upper surface of the lower insulating sheet 26 and the entire wire grid are coated with a suitable cement such as cement sold under the trademark Pliobond, and the Wire grid lis positioned on the lower sheet 26. After the main power cables 40 and `42 are passed through .a slit 44 in the upper sheet 24, the upper sheet is carefully pressed onto the lower sheet and the wire grid with the edges of the sheets matched. As shown in FIGURE 5, the sheets are pressed together between the lengths of wire 28 to form a permanent bond between the upper and lower sheets which extends over substantial surface area. To insure adhesion of the upper and lower insulating sheets 24 and 26, short pieces of electrical tape 48 are rmly pressed into place at the corners of the unit and along the edges of the unit. An additional piece of tape 56i is installed between the sheets 24 and 26 in -the region of the terminal portions of the wire 28. To provide further insulation in the region of the connection between the wire 28 and the main power leads 40 and `42, a piece of electrical tape 51 is installed in this area.

The outer metal housing of envelope 20 is formed from a single thin sheet of metal, preferably thin gauge steel. After the sheet is cut to size which is approximately the same length as the nal assembly and twice the width, the sheet is stamped to form a central dish-shaped embossment SZ surrounded by a flat marginal -iiange '54. A cup-shaped embossment 56 is also lformed at this time adjacent one corner of the sheet. A tube 58 is then brazed to the embossment S6. The housing is then partially folded over on itself, the fold 60 forming one iinished edge of the completed assembly, the other three edges being open to permit the insertion of the heating assembly :shown in FIGURE 4. The two power leads 40 and 42 are drawn through the tube 5S, and the subassembly is inserted between the `folded portions of the metal housing and is secured in place with dobs of Pliobond cement. The assembly is then spotwelded as at 62 with the flanges 54 `of the folded sections `of the rnetal housing carefully aligned. The assembly is then com pleted by seam welding the three open edges along the lianges 54 to `form a hermetically sealed container. Final sealing of the assembly is effected by forcing a plastic substance 64 such las that sold under the trademark Permagum into the outer end of the tube 53 in surrounding relation with the cables 40 and 42. The assembly is then tested for leaks with air under water and the iinish is applied. Finally the assembly is readied for use by bending the tube 5S to the configuration shown or any other configuration required to permit convenient installation of the unit. When the tube is bent, it is allowed to iiatten to provide a strain relief.

While the unit may have any desired `dimensions in a typical case, it is approximately 31 inches long, 9 inches wide and inch thick. The inner heating assembly is approximately 11/2 inches shorter and l3A inch narrower than the youter metal envelope to permit the edges of the latter to be tightly sealed together by seam welding without adversely affecting the inner plastic assembly. In a unit of this size the spacing and distribution of the wires will be such that the total of length of wire accommodated in the unit is almost 50 feet, thus giving the unit large capacity and providing for uniform distribution of heat over the entire area of the unit.

The invention may be embodied in `other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claim rather than by the foregoing description, and all changes which come Within the meaning and range of equivalency of the claim are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

A weatherproof electrical pad heater comprising a flat grid of resistance Wire arranged in a series of side-byside lengths connected by U-bends, a pair of plastic sheets adhesively secured together to enclose said grid, an outer rigid metal housing comprising a metal sheet having a central flat section surrounded by marginal flanges offset from the plane of said central section, said central flat section being slightly more than twice the Width of said plastic sheets and slightly longer than said plastic sheets, said metal sheet being folded double in surrounding relation with said plastic sheets to form a rigid envelope, said flanges being disposed outwardly beyond the marginal edges of said plastic `sheets and being sealingly secured together in waterproof relation, electrical leads extending through one of said plastic sheets and a portion of said flat section connecting said resistance wire to the exterior of said envelope, a tube rigid with said envelope enclosing said electrical leads and means sealing said leads at the entrance to said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,018,512 De Laney et al Oct. 22, 1935 2,112,060 Atchison Mar. 22, 1938 2,490,111 Whitehead Dec. 6, -1949 2,513,733 Morris July 4, 1950 2,716,181 Ritter Aug. 23, 1955 2,845,519 Willat July 29, 1958 2,951,929 Fox Sept. 6, 1960 2,971,073 Eisler Feb. 7, 1961

Images