US2204623A

US2204623A - Variable resistor

Info

Publication number: US2204623A
Application number: US91027A
Authority: US
Inventors: Ruben Samuel
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-07-17
Filing date: 1936-07-17
Publication date: 1940-06-18
Anticipated expiration: 1957-06-18

Description

June 18, 1940.

S. RUBEN VARIABLE REsIsT'oR I Filed July 17, 1936 INVENTOR SAMUEL RUBEN BY m ATTORNEY Patented June 18, 1940 UNITED STATES PATENT OFFICE Application July 17,

4 Claims.

Another object is the provision of a variable resistor device of the wire-wound type in which a sheath of metal is directly cast upon the resistor element to aord a rapid heat transference.

A further object is the provision of a variable resistor device of the wire-wound type in which the wire is integrally coated with a thin, comparatively flexible inorganic insulating coating thermally bonded to the wire and which has a supporting housing of metal cast directly upon and around the insulated wire.

Another object is to provide a variable resistance element having a high rate of heat dissipation and a negligible temperature gradient between the active resistor and a surrounding intimately-contacting metal body.

Other objects will be apparent from the disclosure and the drawing in which- Fig. 1 represents a plan view of a variable resistor constructed according to the invention;

Fig. 2 is a cross-section taken on the line 2 2 0f Fig. 1;

Figs. 3 and 4 show detailed views at the ends of the resistor coil; and

Figs. 5 and 6 are magnied views of portions of the resistance winding.

This application is a continuation in part of my co-pending applications Ser. No. 67,599, led March 7, 1936, and Ser. No. 71,365, filed March 28, 1936.

Broadly the present invention may be said to comprise a variable resistor of the wire-wound type in which the resistance wire has an insulation of inorganic material integral with its surface, part of said insulation being cut away to permit contact with the wire by a movable contact element, the insulated portion of the wire being embedded in a metal support which is directly cast upon the insulation, thus providing an immediate heat transference from the resistance element to the exterior.

The inorganic insulating coating is best ap- 1936, Serial No. 91,027

plied to the resistance wire by the electro-deposition method described in my co-pending application Ser. No. 67,599. The wire passes through a solution in which finely-divided insulating material, such as colloidal kaolinite is suspended in 'an organic silicate such as ethyl silicate. The resistance wire is positively charged and the container in which the solution is held is negatively charged. As the wire is pulled through the s olution a thin coating of kaolin and silicate is elec- 10 trolytically deposited upon the wire which is then passed through an oven which bakes and hardens the insulation. A continuous process is used, the wire preferably passing through the solution a number of times at a temperature of about 160 15 C., being baked after each immersion to insure a non-porous coating. The repeated passes eiect a self-healing action inasmuch as any weak or porous areas remaining from the previous pass will be covered up. In the electro-deposition 20 process the potential between the wire and the metal container in which the solution is held may be about 6 volts, depending upon 'the speed of wire travel through the solution, the concentration of the colloid, the size of the wire, etc.

e following formula and procedure for coating nickel-chromium Wire of small diameter has given excellent results:

500 g. of ethyl silicate are mixed with 100 g. of alcohol and 9 g. of water. After standing for 24 30 hours g. of water and 130 g. of colloidal kaolin (kaolinite) are added and the entire mixture ballmilled. Should the solution tend to gel, an organic inhibitor in an amount up to 10% of the weight of the kaolin may be added.

Instead of the mixture described above, I may coat the wire with a solution as described in my co-pending application Serial No. 71,365, as follows:

200 g. of Garnett shellac is dissolved and com- 40 bined with 1,000 c.c. of a 10% ammonia solution which is stirred and heated to C. to completely dissolve the shellac and eliminate any excess of free ammonia. This solution is then diluted with 3500 c.c. of` water and 1125 g. of 45 kaolinite added. The mixture is then ball-milled for 10 hours.

The coated wire is flexible, resistant to alkalies and acids and can be heated to high temperatures without leakage. If desirable,'a top coat 50 of ethyl silicate may be applied to the coated wire in order to increase its abrasion resistance.

In order that a flexible coating may be obtained it is practically necessary to limit the thickness of the coating to not more than 3 mils. 55

` heat dissipation.

For most purposes a coating of from 1 to 2 mils is amply suiiicient. The wire so coated, considering its inorganic nature, is remarkably flexible and may be wound upon small or irregularly-shaped metal mandrels or supports without cracking. A

Other suitable finely-divided suspendable inorganic insulating materials may be substituted for the kaolinite, for instance titanium oxide. The metal housing cast around the insulated wire should have a melting point lower than that of the coating used. In general application, I prefer a zinc alloy casting containing aluminum and copper.

The resistance wire used in the device of this invention can be of unusually small diameter because of the immediate and intimate contact between the coated wire and the metal cast or compressed about it. Due to the absence of heatinsulating substances such as enamel, asbestos or other materials commonly used in the prior art, the variable resistor of this invention is capable of much higher power dissipation than the devices previously used.

In order to more particularly describe the invention reference is made to the drawing in which the insulated wire 2 comprising a metal core having a thin integral kaolinite deposit thermally bonded thereto, as hereinabove described, is wound upon arc-shaped aluminum form i. The ends 3 of the resistance wire are brought out and held in contact with bronze terminals 4 by folded mica sheets 5 which insulate terminals I from the extensions of the aluminum form I in which they are held. The bronze terminals l are bent to provide a contact washer at la for securing to binding posts Ilia. A flat basemetal alloy frame I is case around and in direct contact with the coated wire winding 2, said frame having integral flanges 6a to aid in the Extending through and at right angles to thn base of the frame 6 is metal control shaft l held within bushings I2 and I6 and carrying a metal control arm 8, insulated therefrom by insulating bushing I2 and insulating washer I3. Contact 9, carried by arm 8,

makes direct surface contact with the top of resistance wire winding 2, the coating 30a of which has been removed over the area of contact so as to expose metal core 30 as seen more particularly in Figures 5 and 6. Flat spring I0 serves to hold contact 9 under pressure against the wire surface. Nut l5 secures bushing I6 in the frame S. Sleeve 32, secured to the shaft by pin 3l, holds insulating bushing I2 onto shaft 'I and nut I4 holds insulating washer I3 in place. The shaft 'I carries a knob II, preferably of insulating material. Arm 8 at its end opposite the contact is soldered or welded to a pigtail conducting wire II, the other end of which is secured by center binding post ISa comprising the threaded end of screw I9 which is insulated by insulating washer I8 and insulating sleeve 2U from the frame 6. Screw I9 carries nuts 2I for securing the terminals of the circuit.

The resistant wire winding connects with terminal posts Isa which are designed for having connected therewith terminals for the circuit to be controlled. 0n posts Ila are mounted bronze washers la. and nuts 2 Ia.

I claim:

l. A resistance element for a variable resistor adapted to operate at high temperatures com- Saugen prislng a coil of resistance wire having over substantially its entire surface and bonded thereto by a silicate binder, a thin, hard, uniform, nonsoftening adherent coating comprising a plurality of layers of extremely finely divided high heat resistant particles of inorganic insulating materials of the group comprising high heat resistant silicates and oxides. said resistance element coil being closely wound and the turns thereof being unseparated other than by the insulating coating on the wire, a portion of the insulation being cut away so as to leave a bare section across said coil whereon a movable conductor may make electrical contact with said coil, and a cast metal housing in direct contact with said coil and covering a substantial part thereof.

2. A resistancel element for a variable resistor adapted to operate at high temperatures comprising a coil of resistance wire having over substantially its entire surface and bonded thereto, a thin, hard, uniform, non-softening adherent coating comprising a plurality of layers of extremely finely divided high heat resistant particles of inorganic insulating materials of the group comprising high heat resistant silicates and oxides, said resistance element coil being closely wound and the turns thereof being unseparated `other than by the insulating coating on the wire, a portion oi' the insulation being cut away so as to leave a bare section across said coil whereon a movable conductor may make electrical contact with said coil, and a cast metal housing in direct contact with said coil and covering a substantial part thereof.

3. A resistance element for a variable resistor adapted to operate at high temperatures comprising a coil of resistance wire having over substantially its entire surface and bonded thereto, a thin, hard, uniform, non-softening .adherent coating comprising a plurality of layers of ex tremely finely divided high heat resistant particles of inorganic insulating materials of the group comprising high heat resistant silicates and oxides, said resistance element coil being closely wound and the turns thereof being unseparated other than by the insulating coating on the wire, a portion of the insulation being cut away so as to leave a bare section across said coil whereon a movable conductor may make electrical contact with said coil, and an aluminum metal housing cast directly in contact with said coil and covering a substantial portion of the coated section thereof.

4. A resistance element for a variable resistor adapted to operate at high temperatures comprising a coil of resistance wire having over substantially its entire surface and bonded thereto, a thin, hard, uniform, non-softening adherent coating comprising a layer of extremely finely divided high heat resistant particles of inorganic insulating materials of the group comprising high heat resistant silicates and oxides, said resistance element coil being closely wound and the turns thereof being unseparated other than by the insulating coating on the wire, a portion of the insulation being cut away so as to leave a bare section across said coil whereon a movable conductor may make electrical contact with said coil, and a cast metal housing in direct contact with the insulated portion of said coil and covering a substantial part thereof.

SAMUEL RUBEN.