US841232A - Electric rheostat. - Google Patents

Description

110,841,232. PATENTED JAN. 15, 1907. W. F. DANA & H. W. KNQTT.

ELECTRIC RHEOSTAT. APPLICATION FILED JULY 26', 1905.

WITNESSES: down and bind in the buttons.

UNITED STATES PATENT OFFICE.

WILLIAM DANA AND HENDERSON W. KNOTT, OF NEW YORK, N. Y.

ELECTRIC RHEOSTAT.

Specification of Letters Patent.

Patented Jan. 15, 1907.

Application filed July 26,1905. Serial No- 271388.

To all whom it may concern.-

Be it known that we, WILLIAM F. DA A, a citizen of the United States,'and HENDERSON W. KNOTT, a subject of the King of Great Britain and Ireland, residing at New York city, in the county of New York and State of New York, have invented a new and useful Improvement in Electric Rheostats, of which the following is a specification.

' Our invention relates to rheostats in which the electric current is gradually increased from a desired minimum to a desired maximum by the means of a series of graduated resistances. In such rheostats now in use the contact between the switch and the several resistances is usually effected by intervening wires duly attached and insulated, and the rheostat becomes in consequence cumbrous and complicated. The object of our improvement is to construct a rheostat which shall be simple and compact in form.

Our method is to provide strips or buttons of gradually-increasing degrees of resistance and to arrange them consecutively in 00-.

lumnar form with an alternating series of metallic contact-plates. These resistances are composed of graphite and clay (preferably German claylpowdered and mixed to gether, pressed into the form of buttons of similar design and shape, and baked. The graphite and clay when thus baked is brittle and inclined to crack and break off in case the rheostat sustains a jar or shock. It is therefore essential that the buttons be partially inclosed. This is effected by either bending the projecting edges of the metallic contact-plates over against the resistancebuttons, or preferably by causing their surfaces to be hollowed out or recessed, so that thecontact-plates assume a cup-like shape and are thus adapted to receive, surround,

Because of the brittle character of the baked graphite and clay and of its naturally irregular cleavage it is practically impossible to effect a complete and erfect. contact between the surfaces *of the uttons and the surfaces of the metal plates without some intervening medium. 0 overcome this difficulty, we introduce between them a graphitic aste, whose conductivity is similar to t at of the metal plates, and with it we securely cement those surfaces together in close and uniform contact. The method above describedpermits the arrangement of separate resistances in a simple, secure, and compact form, such as is not possible in rheostats where connections are made by wire, and it thereby dispenses with the use of wire and with the expense of wiring between the resistances and contactpieces.

Our invention is illustrated in the accompanying drawings, in which Figure 1 is a front view of our improvement complete and ready to be inserted in a rheostat-frame. Fig. 2 is a detailed sectional view of'the same, showing the method of connecting the resistance-buttons to the contact-plates, in form of a column and of insulating them from their common support. Figs. 3 and 4 illustrate one of said plates and one of said resistance-buttons, res ectively.

Similar letters refer to simi ar parts throughout the several views.

The buttons A are composed of graphite and clay, as above described. They are similar in design and form and are of different and graduated degrees of resistance, the degree of resistance being'in inverse proportion to the amount of graphite present in the mixture. The'buttons A are consecutively arranged upon and in alternation with the contact-plates B. These plates are made of metal and project beyond the edges of the buttons A. They are similar in form and are preferably flattened at one edge I). The surfaces of the plates B are hollowed out or recessed, so as to receive the buttons A, which fit in them closely. These recesses are of sufficient depth to bind the buttons in and to prevent them from breaking or crumbling in case the rheostat suffers a violent shock or jar.

As above set forth, it is practically impossible without a medium to effect a perfect contact between the surfaces of the buttons and the recessed surfaces of the contact- Elates. To fill up the interstices and spaces etween the adjacent surfaces and to cement them together, we have provided a paste of high conductivity. This paste is composed of powdered graphite, pure carbon-dust, and gum-tragicum mixedtogether in the propor tions of six, three, and one, ,respectively. Sufficient water is added to secure to the mixture the proper consistency of paste. In preparing the above composition the aphite must be first freed fromallgaseous e ements by subjecting it to intense heat.

The buttons A and the plates B are placed one upon the other and cemented to ether in the form of a column and are secure in position by a bolt C passing through them alland fastened into the frame of the rheostat. The bolt C is furnished at its ends With the nuts M and M. The buttons A and the contactlates B are insulated from thebolt C and f r om its said nuts by the'insulating mate rial D. The flattened edges bof the contactplates B are arranged in the sameplane; and thusv present an even contact-surface, -over and upon which any -contact-switch with Which rheostats are commonly furnished may-be swept or mani ulated, thus bringing the (lifferentandrgra uated resistance-buttons consecutively into circuit.

We are aware that-ineither a-lseries of resistances with interposed :metallici contacts .nor aswitchadaptedtowbe manipulated in the patlrof such contectsarenew in themselves, and We .make. no claimhereinafter broad enough to include such-series or such switch.

What We claim as our inventionpand desire tosecure :by Letters Patent;is-

, 1. A rheostat comprising a series of resistances composed ofggraphiteand clay, alternating with interposed metallic contactplates, the surfaces ofl-which-are sufficiently recessed to closely-receive andrigidly hold said resistances in su erficial contact, and to protect them from s oek -ori-other external injury,- substantially as described. 1

2. A rheostat Whose resistances are composed of graphite and clay mixed and formed into buttons ofsimilar form, and cemented in close superficial contact to interposing metallic contact-plates by a graphitic paste of high conductivity, substantially as described.

3. The combination, in a rheostat, of graphiteand clay resistance-buttons and of interposed metallic contact plates, alternating therewith and collrrifpletely united thereto at their respective su aces byz a graphitic paste,

" composed ofzpowderedgraphite pure carbondust -gum-tragicume and water mixed: together, substantially asdescribed.

A. Airheostat com rising the'resistancebuttons A, similar; in crmand ofrgraduated degreesiof resistance, rigidly'heldin alternate ing series with and protected by the recessed contact-plates Bzand united to themdn complete contactat their-respective surfacesby a graphitic .=paste of high conductivity,-= all arranged 'inform of" a column.- andso adapted that a contact-swzitch may be-mani-pulatediin the path of said contact-plates; substantially names to this specification in thepresence of two subscribing-witnesses.

JOHN-M. NOLAN,

WALTER H. Donn.

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