US1745526A - Method of making electrical heating units - Google Patents

Description

Feb. 4, 1930. w. A. BRAUN ET AL METHOD OF MAKING ELECTRICAL HEATING UNITS Original Filed June 10. 1925 2 Sheets-Sheet 6 INVENTORJ M My mam/Lu, WTWM ATTORNEYS Feb. 4, 1930. w. A. BRAUN El AL 1,745,526

METHOD OF MAKING ELECTRICAL HEATING UNITS Original Filed June 10, 1925 2 Sheets-Sheet 2 Fi .3. j

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Patented Feb. 4, 1930 UNITED STATES PATENT OFFICE WILLIAM A. BRAUN AND CHARLES MAURER, OF DOVER, OHIO, ASSIGNORS TO DOVE MANUFACTURING (30., OF DOVER, OHIO METHOD OF MAKING ELECTRICAL HEATING UNITS Original application filed .Tune 10, 1925, Serial No. 36,128. Divided and this application filed February 10, 1926. Serial No. 87,288.

This invention relates to improvements in methods of'making heating units with particular reference to that class of units in which a resistance wire is embedded in a suitable di-electric material within a shallow container which forms a portion of the unit when completed. Common examples of such heat units are to be found in sad irons, vulcanizers and other articles in which the eontainer is necessarily of highly conductive material and in. which the resistance wire is located in close proximity to the wall of the container but necessarily electrically insulated therefrom in such a manner as to avoid short circuits. The embedding material must not only be highly di-electric but'it must also be capable of holding the resistance wire in place and it must possess maximum heat conductivity whereby the heat generated by the electric current in the wire may be rapidly conveyed and distributed throughout the wall of the container to be heated.

Heretofore the operation of preparing the resistance wire and inserting it in the embedding material has been a diflicult operation requiring considerable time, care and skill on the part of the workmen in order to avoid short circuits between successive loops or portions of the wire and between the wire and the wall of the container. It is the object of this invention to provide a more simple and more expeditious method and one which can be practiced by comparatively unskilled employees and in which uniform results may be attained, the danger of short circuits beiu eliminated and the resistance wire being un ailingly and uniformly embedded and held in the embedding material in a predetermined spaced relation of the various portions to each other and to the wall of the container. I

This application is a division of a case heretofore filed by us on or about J une 10th, 1925, Serial No. 36,128 and relating to apparatus whereby the method herein claimed may conveniently be practiced.

In the drawin s:

Figure 1 is a pan view of the holding form employed in the practice of the improved method as seen from the side at which the resistance wire is applied, and showing a helically coiled resistance wire in position thereon preparatory to the annealing thereof or theinsertion thereof into the embedding material. The form illustrated is used in the manufacture of sad irons.

Figure 2 is a sectional view drawn on line 2-2 of Figure 1.

Figure 3 is a similar view showing the form in the position which it occupies when holding the resistance wire coil in an iron base having a recess partially filled with embedding material.

Figure 4 is a similar view of the sad iron erence characters throughout the several views.

In the practice of the improved method a resistance wire of the required length and cross section is first wound into a helical coil '1 of small diameter. The diameter of .the coil is preferably about half of the thickness of the layer of embedding material which is to receive it. This coil is then looped or turned upon itself into the position which it is to occupy when embedded in the container or recessed base, the form of the loops and their position being such as to obtain a desired heat distribution. Inthe manufacture of sad irons it is desirable to so form the loops that there will be a plurality of portions of the coil extendin along each side in the direction of the point with the ends brought into proximity in the rear portion and extended upwardly for connection with the conducting wires of an electric circuit.

The wire is looped in the desired position The holding form is then used as a carrier to convey the looped coil intoa layer of plastic embedding material, preferably a material which becomes plastic or semi liquid by the addition of water, but which tends to harden when dry and which may be baked in the form of a brick. The holding form is utilized to hold the coil of wire in its embedded position when the wire embedding material is being dried or otherwise hardened sufficiently to retain the wire. The form is then withdrawn and an additional layer of semi-liquid or plastic embedding material applied to fill voids and to completely cover the wire. Thereafter the embedding material is again dried, pressed and baked. In the manufacture of sad irons and similar articles a metallic base is employed which is suitably recessed to receive the layers of embedding material with the wire therein in spaced relation to the walls of the base or container and the wire is so positioned or looped in this recess as to provide the desired heat distribution fiver or throughout the bottom surface of the ase.

Referring to Figure lit will be observed that the helically coiled wire is arranged in loops having portions 1, 2 and 3 extending along one surface of a dielectric form or plate 4 on each side of the longitudinal center of the form. In the rear portion of the form one end of the coil is formed into additional portions 5, 6, 7 and 8 extending back and forth, with the extremity of the coil leading to a tubular stud 9 through which the 'uncoiled extremity of the wire passes. On the other side of the longitudinal center line the other end portion 12 of the r coil extends to'a tubular stud '15; through which'theuncoiled end portion 10 of the'wire passes. L

The portions .1, 2, 3, 5, 6, 7, 8 and 12 of the wire coil are heldin position by positioning pegswhich are secured to the platel and arranged in suitable rows to receive the. coiled wire between them. The pegs of the outer row have semi-cylindrical portions 20 and reduced end portions 21. The wire coil is received upon the shoulder 22 at the outer end of the semi-c lindrical portion 20. The.

flattened sides 0 the semi-cylindrical portion 20 are adapted to fit against the side ,wall 25 of the base or container 26 shown in Figure 3 when the form is inserted therein for the purpose of positioning the wire and holding it in the layer 27 of embedding material. The pegs in the inner rows preferably have cylindrical portions 30 corresponding with the semi-cylindrical portions 20 of the pegs in the outer row and reduced exfrangible and non-combustible under the temperatures to which this material is subjected, a composition of lava or of asbestos and. carbon bein preferably employed. The plate 4: is also formed of similar material, the material commercially known as bakelite being preferred, although any other material possessing the necessary rigidity and which has a low-co-efiicient of expansion and contraction and which will not warp or break in ordinary use, may be used.

To facilitate manipulating the form and also to provide means whereby it may be rigidly secured to the base or container, we preferably provide the plate 4 with a centrally disposed swiveled thumb piece 38' having a screw threaded end portion which projects into the space between the inner rows of coil holding pegs and which is adapted to be screwed into a socketed stud 39 formed in afi the recess.

The form 4 is provided with a set of gauge pins 40 having reduced end portions of greater length than those of the pegs heretofore described. These gauge pins 40 are otherwise preferably formed in the same manner asthe pegs heretofore described, their inner portions being flattened if in the outer row or cylindrical if in the inner row. They preferably constitute a portion of the series of pegs upon which the wire coil is supported.

The use of the form will be readily understood from the above description but will here be briefly reviewed. After forming the resistance wire into a helical coil, except as to the end portions, one end portion is passed through one of the tubular studs 9 or 15 and the coil is then looped over the pegs as shown in Figural until its other unwound end can be passed through the companion tubular stud. These unwound ends project from the rear face of the plate 4, i. e., the upper face when the form is in the position in which it is shown in Figure 3. They are connected with electric circuit terminals and electric current in suficient volume and pressure is passed throu h the wire to heat it to a cherry the current is being passed through the wire. Thereupon the form is adjusted to the container or base as shown inFigure 3, thereby carrying the coil of wire into the recess, said recess having been previously partially filled with semi-liquid or plastic embedding material. The wire will be embedded therein to a depth which is determined by the gauge pins 40, i. e by the length of the reduced end portions of the gauge pins, the shoulders 41 of which are in the same plane with the shoulders 22 and 22' on all of the-pegs above described. These gauge pins co-operate with the pins of the outer row having the flattened side surfaces 20 to secure an accurate positioning of the coil in the container or ase.

After the holding form has been utilized to embed the resistance wire as shown in Figure 3 it is left in position until the embedding material has become suficiently dry and hard to support and retain the wire in the position in which it has been placed by the form. Thereupon the form is withdrawn, the

' slightly tapered extremities of the pegs permitting a withdrawal of the form Without disturbing the wire. The second layer of embedding material is thereupon applied in a suiiiciently fluid condition to allow it to readily fill the voids heft by pegs in the orig inal layer. The second layer is sufficiently thick to properly cover the coils, portions of the latter being exposed the upper surface of the original layer. will be noted that the original layer i such thickness and the reduced ends "e gauge pins are of such .iength that the thicker portions of the pegs wilt not enter the embedding material. This is desirable to avoid the displacement extent when the resistance wire is being insorted After the second. layer of embedding mahas been applied it is allowed to dry irden and then compressed preferably in hydraulic press under a pressure of ap proximately forty tons to the square inch, after which the container with the embedding material therein is baked in any suitable manner.

The embedding material used preferably consists of material similar to that described in Letters Patent of the United States No. 1,530,228, dated March 17, 1925 forga composite pack for electrical heating elements. This material when mixed with water may be poured into the containers and when dried may be baked in brick form by passing an electric current through v the wire. The above described pressure is applied in order to eliminate voids, force the binding material into the interstices between the grains of fused aluminum oxide to cause said grains to form intimate contacts-with the wire and also by shifting the grains, and pressing them upon each other, to break up the coating films o bonding material which would otherwise tend to envelope the grains. The binding material has less di.-electric strength than the fused aluminum oxide grains, and also has less heat conductivity. Therefore, by breaking-up the films of bondin material which would otherwise envelope t e grains, the dielectric strength and the heat conductivity of the units is increased.

The pegs are preferably arranged in rows transverse to the portions of the coil which they support, and in such proximity that they act in pairs to support associated portions of the coil upon the shoulders 22- and between their reduced extremities, each. of the intermediate pegs supporting two portions of the coil, one on each side of said reduced extremity. The coils are therefore supported in much the same manner that they would be supported if mounted in channels or grooves in the face of the supporting form but not as continuously, the transverse rows of pegs being located in sufiicient proximity to keep the coil substantially parallel to the face of the form while allowing a free flow of the material into the coil from all sides and while causing minimum displacement of embedding material when the projecting portions of the form or reduced extremities of the pegs enter such material.

It will, of course, be understood that in Figure 5, the press plate as indicated at 45 and the head or platen of the press is indicated at 46, while in Figure 6 the base of the sad iron with the completed heating unit in the recess thereof is assembled with a cover plate 47 and an outer casing or shell 48 connected by bolts or screws 49 and 50, respecthe embedding material to an unnecessary tively in the ordinary manner.

lVe claim 1. The improvement in the method of forming heating units, which consists in placing in a container a semi-fluid mixture of di-electric material of insufiicient solidity to support and retain a resistance wire in set position, positioning a coil of resistance wire upon a suitable form retaining support within said mixture and supporting it therein by said suport in predetermined spaced relation to the walls of the container, solidifying said mixture to a wire supporting condition and then releasing the wire from said support.

2. The improvement in the method of forming heating units, which consists in placing in a container a semialuid mixture of di electric material, positioning a coil of re sistance wire Within said mixture upon a suitable support for maintaining the wire in set position'and in predetermined spaced relation to the walls of the container in said material, solidifying said mixture to a wire supporting condition and thereafter releasing the wire from said support, and applying a cover- (ii-electric material, hardening the material, and thereafter releasing the element from the form.

13. In the art of forming electrical heating units having a resistance element embedded in a body of di-electric material, the improved method which consists in winding the element upon a form in substantially the shape it will be positioned in di-electric material, heating the element by electrification to eliminate internal strains and permanently fix the loop contours, utilizing said form to embed the wound element in semi-fluid di-electric material, and thereafter releasing the element from the form.

14. In the art of forming electrical heating units having a resistance element embedded in a body of di-electric material, the improved method which consists in Winding the element upon a form in substantially the sha e it will be positioned in di-electric materia heating the element byelectrification to eliminate internal strains and permanently fix the loop contours, embedding said element upon a form in semi-fluid di-electric material, hardening the material, and thereafter releasing theelement from the form.

15. In theart of forming electrical heating unitshaving a resistance element embedded in a body of di-electric material, the improved method Which consists of the following steps in suitable order: (1) winding a resistance element upon a form having insulating supports to substantially the shape it will be 85 positioned in di-electric material, (2) utilizing the form to embed the wound element in di-electric material, (3) electrifying the element, and subsequently removing the supports from the element. WILLIAM A. BRAUN.

CHARLES MAURER.

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