US1344406A - Electrical-resistance wire - Google Patents

Description

A H. JOHNSON.

ELECTRICAL RESISTANCE WIRE.

APPLICATION FILED DEC. 19. 1919.

1 ,3 14 A OG, Patented June 22. 1920 loops and intermediate,

bent or crimped to UNITED STATES NATIONAL ELECTRICAL SUPPLY COMPANY, OF COLUMBIA, AIJORPORATION OF VIRGINIA.

OF COLUMBIA, ASSIGNOR TO WASHINGTON, DISTRICT OF ELECTRICAL-RESISTANCE WIRE.

Specification of Lettersratent. Patented J 11113 22, 1920.

Application filed December 19, 1919. Serial No. 345,972.

To all '10 from it may concern:

Be it known that I, Annnnr I'I. JorrNsoN, a citizen of the United States, residing at \Vashington, in the District of Columbia, have invented certain new and useful Improvements in lllectrical-licsistance \Vire, of which the following is a specification.

This invention relates to electrical resistance elements, and it comprises a resistance element made of substantially circular wire, said wire being bent or crimped to form connecting sections between said loops, the connecting sections being flattened on opposite sides, and said flattened surfaces being corrugated or roughened; all as more fully hereinafter set forth and as claimed. I

In the manufacture of electric heating appliances wire having a high degree of resistance is employed. This wire is generally form loops and connecting sections between the loops, producing substantially U-shaped portions, with inverted Ushaped portions therebetween, the legs of the U-shaped portions being connected to the adjacent inverted U-shaped portions. The units are generally arranged in a substantially circular form by bending the unit near the center to produce substantially parallel sections, and then forming the unit into a spiral, with the bent portion at the center of the spiral, and the two ends at the periphery thereof. When a plurality of these coils are employed, they are arranged on top of each other with a strip or sheet of mica, or other insulating material, separating them.

W hen: wire of substantially circular cross section is crimped in this manner, and is then bent in any particular manner to give it a certain external shape, there is a strong possibility of the individual loops coming in contact with each other on the inside of the bend. In electrical resistance elements and especially where the-loops are arranged in a flat spiral, this tendency is noted and it is necessary to avoid it. If two sections of the wire touch each other, one of the loops is short circuited and the current does not pass through it. The result is that the amount of heat that the loop is estimated to furnish is not obtained.

I have found that where the-sides of a loop are first flattened to produce elongated sections, that this ditliculty of short circuiting is avoided and that the rounded ends of the loops 'are kept spaced from each other.

Another important advantage of my invention is obtained where a number of heating elements are employed, arranged one above the other and separated from each other by thin strips of mica or other insulating material. \Vith a unit of wire in which the cross section of the individual loops is substantially circular, there is a tendency of the mica plates to move relative to the units and thus permit the units to come in contact with each other. If the in sulation on the wiring becomes worn at any point, short circuiting occurs from one unit to the other. 1

Where the sides of the loops are flattened to produce elongated sections, this tendency of the insulating strip to work out of position is greatly diminished. Furthermore,

I have found that roughening the sides forming the elongated sections, practically eliminates the tendency of the insulating strips to move. hen a heating element consisting of several units is assembled, a

slight amount of pressure may be applied as each strip of mica or other insulating material is being put in place, causing the roughened portions of the resistance element to embed a slight distance in the mica and thus eliminate any tendency to relative movement.

In the accompanying drawings, I have shown one embodiment of this invention.

In this showing,

Figure 1 is a plan view of an electrical resistance element wherein the sides of the individual loops have been flattened.

Fig. 2 is a sectional view on the line 2-2 of Fig. 1.

Fig. 3 is a sectional view on the line 33 of Fig. 1, and

Fig. 4 is a plan View of a resistance element formed of flattened and roughened resistance wire.

Referring to the drawings, the reference numeral 1 designates a strip of wire that has been bent back and forth to produce 100 s 2. These loops are connected by interme l tened on the two outer sides, as shown at 4 and 5. The sections 3 maybe flattened by passing the wire between two rolls and ap plying pressure thereto, or by any other desired method. After the sides have been flattened, they may be passed between two other rollers having roughened surfaces for the purpose of crimping or roughening the surface of these sections, or the surfaces of the first mentioned rolls may be roughened, in which case the flattening and rough'ening of the wire are brought about in a simple operation. In practice,l prefer to follow the latter practice. The roughened portion is designated by the reference numeral 6 and is more clearly shown in Fig. 3 of the drawings.

In Fig. 4 of the drawings, I have shown for the purpose of illustration the ordinary form ofa resistance unit wherein the strip of wire is first bent at a point 7 near its mid- -dle to produce two substantially parallel sections. These parallel sections are then formed into a spiral 8 with the ends 9 and 10 arranged at the outside of the spiral. By reference to this figure, it will be noted that there is a tendency in a heating unit of this character for the loops 2 to contact with each other at the inside of a bend, such .as at the points 11 and 12. I have found that the flattening of the connecting portions 3 prevents contact of adjacent loops when the device is bent into the form of a spiral.

When it is desired to produce a heating unit of greater capacity than can be obtained from a single resistance element, it is customary to arrange several of the heating elements shown in Fig. 4 upon each other and to separate them by strips of mica or other insulating material. WVhen the wire employed in constructing the elements is of substantially circular cross section, there is a tendency of the mica strips to become displaced and to permit contact of one element with the element next above it. I have found that flattening the connecting sections of the wire employed in constructing such resistance elements, as at 4 and 5 in the drawings, greatly reduces this tendency of the mica plates to become displaced. When these flattening portions are roughened, the tendency of the insulation to become displaced can be entirely overcome. When the heating unit is assembled, the mica; plates are placed on the top of a unit and a sli ht amount of pressure applied thereto. his pressure causes the roughened surface 6 to engage the surface of the mica and hold it firmly. Under such condition, the mica is held in its proper position and relative movement is entirely eliminated.

In the description and drawings, I have shown one advantageous embodiment of my invention, but it is apparent that the invention is not necessarily limited to the exact form shown and described, and that changes may be made without departing from the spirit of the invention or the claims.

\V hat I claim is:

1. An electrical resistance element comprising loops of wire of substantially circular cross section and connecting sections, the connecting sections being flattened to produce oppositely disposed elongated sections.

2. An electrical resistance element comprising loops of wire of substantially circular cross section and connecting sections, tire connecting sections being flattened to pi'roduce oppositely disposed elongated sect ons, said elongated sections being roughened.

3. An electrical resistance element comprising loops of wire, substantially circular in cross section, and connecting sections, said loops being arranged to produce a re- .sistance element of any desired shape, said connecting sections being flattened on the top and bottom.

4. An electrical resistance element comprising loops of wire, substantially circular in cross section, and connecting sections, said loops being arranged to produce a resistance element of any desired shape, said connecting sections being flattened on the top and bottom, and said sections being roughened.

5. The method of constructing electrical resistance elements which com rises arranging a resistance wire in the fbrmof loops and connecting sections, of substantially circular cross section, and flattening two sides of said connecting sections to produce oppositely disposed elongated sections.

6. The method of constructing electrical resistance elements which comprises arranging a resistance wire in the form of loops and connecti g sections, of substantially circular cross I ction, flattening two sides of said connect ng sections to produce oppositely disposed elongated sections, and roughening said elongated sections.

In testimo'n whereof I afiix my signature in presence (5 two witnesses.

ALBERT H. JOHNSON.

Witnesses:

I CHAS. O. REED,

CORNELIA KLUETER.

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