US2421537A - Electrical resistance annealing device for wire - Google Patents

Description

June 3, 1947. J. 5. BOYERS 2,421,537

ELECTRICAL RESISTANCE ANNEALING DEVICE FOR WIRE Filed Sept. 17, 1945 anaemic 0 JOHN S. BUYERS Patented June 3, 1947 ELECTRICAL RESISTANCE ANN EALING DEVICE FOR WIRE John S. Boyers, Arlington Heights, Mass., assignor to United States of America, as represented by the Secretary of the Navy Application September 17, 1945, Serial No. 616,917

1 Claim. 1

The present invention relates to means for annealin fine steel wire, particularly the type of wire used in the recording and reproducing of sound.

In general my invention relates to a device to anneal wire by means of the passage of an electric current to produce a temperature sufficiently high to anneal the wire but not high enough to cause burning or permanent damage to the wire.

In accordance with my invention an annealing device is produced which is sufliciently small to be mounted directly on the case of the recording or reproducing apparatus.

Further, in accordance with my invention an annealing device is produced which utilizes current at a potential normally available in recording and reproducing equipment.

Also in accordance with my invention, the distribution of equilibrium temperature along the length of the wire may be made to occur in a predetermined gradual manner.

In accordance with one aspect of my invention means are provided for protecting the wire against mechanical damage while it is being heated and further, to protect other objects which may become damaged by coming in contact with the heated wire.

In accordance with other aspects of my invention, means are provided to protect the terminal of the device from the deposition of foreign substances and from making undesirable electrical contact with other objects durin nonuse.

My invention also resides in features of construction, combination and arrangement herein described or disclosed.

The wire commonly used in wire recording apparatus consists of a continuous strand of tempered steel approximately .004 inches in diameter. This wire is easily broken if it is mishandled. To make it usable after breaking, it must be joined by some means. One way which has been found to provide a satisfactory joint easily and quickly made is the joining of the broken end of the wire by means of a knot, for example, a square knot. In order to facilitate the tying of a knot, it is necessary to anneal the wire before tying. After the knot is tied, heat must again be applied to relieve any stresses set up by the tying. Regardless of whether the wires are jointed by tying or by some other means, it is desirable that the section of the wire immediately adjacent the joint be finally annealed in order to prevent breakage at or near the joint which may tend to occur because of the discontinuity of cross section at thepoint of juncture.

To accomplish such annealing, it has been the practice in the past to use any readily available source of heat such as a lighted match, glowing cigarette and the like. While the latter method recesses IS in the base material.

has the advantage of not requiring additional equipment, it suifers from the serious disadvantage that the temperature may be either too low to result in the drawing of the temper of the wire or may be sufiiciently high to cause burning and. consequent weakening of the fine wire.

Referring to the drawings:

Figure 1 is a perspective view showing the external appearance of one embodiment of my device in assembled condition;

Figure 2 is a cross section of the device shown in Figure 1 including the mounting plate and current source;

Figure 3 shows another embodiment of my device using a differently shaped electrode or terminal and protective cap.

Referring to Figures 1 and 2, the body of the device consists of a base In made of some insulating material such as porcelain or an insulating plastic such as Bakelite. This base can be mounted on the case of the recorder by means of screws l2. Terminal studs [4 of copper or other good conducting material are provided to contact the wire. Such terminals are preferably seated in Extensions H! of the studs extend through the case 20, being insulated therefrom by bushings 22 to provide terminals for the electrical connections. A longitudinal slot 24 intersects the recesses I5 and is slightly deeper than the top of the terminal studs l4. Electrical connections are made as indicated in Figure 2 to a winding 26 of the transformer in the associated apparatus. Such Winding may be one of the cathode heater windings having a potential in the neighborhood of 3 volts.

The spacing of the terminals M for a wire having a given resistivity is important. While the spacing may be determined from theoretical considerations of voltage and resistance, other factors may effect the heat balance existing under equilibrium conditions, and it has been found that the spacing between the terminals for a given voltage may be determined very readily by experiment. The spacing should be such that the equilibrium temperature in the wire is sufficientl high to result in the annealing or drawing of the temper, yet not so high as to cause oxidation or burning of the wire. Due to the fine gauge of the wire, an equilibrium temperature is reached almost immediately, and it is not necessary to depend upon the skill of the operator to remove the wire from the annealer at the proper time to avoid damage.

It has been found that the use of the insulating channel member having a groove 24 is accompanied by several important advantages. The heated wire is protected from damage and from drafts of ambient air which might prevent it from reaching annealing temperature. In addition, other objects which may become damaged through contact with the heated wire are protected from touching it. The recessing of the terminals I4 at either end of the slot 24 has the advantage that such terminals are less likely to make undesired electrical contact during the period when the annealer is not in use.

It will be noted that the terminals [4 present a relatively large convex metallic surface. Electrically this is an advantage since it presents a greater area of contact and insures satisfactory contact in spite of localized corrosion or dirt deposits. From a thermal standpoint it has been found that making such terminals of comparatively massive construction as shown results in a very desirable efiect. Because of the high thermal conductivity of the terminal material, the temperature of the wire at point of mechanical contact will be kept to a low value. As the wire leaves the curved surface on a tangent, the proximity oi the metallic terminal will cause the equilibrium temperature to increase gradually from the low value existing at the point oi contact to a maximum value existing in the wire at a point approximately midway between the terminals. On each side of the annealed portion, therefore, there will be a length of wire only partially annealed. Such gradual change of the mechanical properties reduces the likelihood of breakage in the vicinity of the annealed portion.

Figure 3 shows a modified form of my invention. The terminal studs 32 are mounted in spaced relation on mounting plate The terminals are provided with a thread adjacent to the base a rounded tip 35 in which there is provided smooth groove or notch 33 adapted to receive the wire. Caps A of insulating material have holes 42 internally threaded to match the threaded portion 34 of the studs.

By use of the caps the terminals are protected from corrosion and from undesired electrical contact during period of non-use. While I have shown the insulating caps threadedly engaging the studs, such caps may be maintained in place by frictional engaging a bayonet pin or the like.

In order to keep the diameter of the caps to a reasonable value it is necessary to make the studs of slightly less diameter than in the embodiment shown in Figures 1 and 2. Due to the decrease in terminal area, it is advisable to modify the terminal by providing means, for example notch 38, to prevent the wire from slipping off during heating. The use of such a notch has the additional advantage that the wir is urged into more intimate contact with the terminal due to the relatively sharp, wedge-like cross section. If desired, the notch may be slightly inclined in the plane of the terminals so that primary electrical contact is made at the extreme outside vertex. Thus the wire in leaving the stud will be in close thermal relationship to the inside walls of the notch and will not reach as high a temperature as the wire near the center of the heated portion. Thus, as in the embodiment of Figures 1 and 2, there will be a gradual transition between the annealed and non-annealed portion of the wire and the danger of future breakage in this region consequently reduced.

While Figure 3 does not show a slot connecting the two terminals it will be obvious that a slotted insulating member could be placed between terminals 34. It would, of course, be necessary that the slotted member clear the terminals 34 by an amount sufiicient to allow application of the caps 40.

It will be seen from the above that I have produced an annealing device which is small in size, easy to use and inherently accurate. While I have shown and described but two embodiments of my invention, it will appear to those skilled in the art that various changes and modifications may be made without departing from my invention and I therefore aim in the appended claim to cover all such changes and modifications as fall within the true scope of my invention.

What is claimed is:

An electrical resistance annealing device, for a short length of magnetizable wire of the type used in wire recorders, comprising a block of electrical insulating material adapted to be mounted on the case of a wire recorder, a pair of spaced convex terminals countersunk within said block, extensions on said spaced terminals adapted to be connected to a source of low voltage within the wire recorder to cause heating of the wire upon contact therewith to an annealing temperature, said insulating block having a countersunk channel extending from the extremities thereof in a straight line and connecting said pair of spaced countersunk terminals whereby spaced points on the wire to be heated may be placed in said channel to contact said terminals, said channel protecting the wire during heating from short circuiting, and also reducing ambient air effects on the annealing temperature; the voltage, terminal spacing and cross section of said channel being so proportioned that a temperature suflicient for annealing but not high enough to damage the wire is produced and maintained upon and during contact between the wire and said terminals.

JOHN S. BOYERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENT Number Name Date 211,938 Shaw Feb. 4, 1879 1,448,566 Muller et al Mar. 13, 1923 1,647,296 Jefferies Nov. 1, 1927 1,937,420 Wood et a1 Nov. 28, 1933 2,009,647 Brusse et al July 30, 1935

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