US1683060A - Resistance device and method of making same - Google Patents

Description

' Sept. 4, 1928.

/ 1,683,060 c. E. VAWTER RESISTANCE DEVICE AND METHOD OF MAKING SAIIE Fil 6d Sept. 18, 1924 INVENTOR MARLES E. 1VAWTR ATTORNEY Patented Sept. 4, 1928.

UNITED STATES PATENT OFFICE.

CHARLES E. VAWTER, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR '.!.O DUBILIER CONDENSER CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

RESISTANCE DEVICE AND METHOD OF MAKING SAME.

Application filed September 18, 1924. Serial No. 738,422.

My invention relates to electrical resistance devices of the type disclosed in my ranging from a few thousand ohms to several megohms are required. These res1stances should have relativelyhigh currentcarryin capacity, and should not change materia y with a rise or fall in temperature.

In other words, the resistances should be substantially constant. It is desirable to provide a simple and easily manufactured resistance device-of this nature, capable of presenting and maintaining a resistance having the required and predetermined value;

also to originate a method by which such devices can be readily and inexpensively produced. The present invention has been made with a view to obtaining these results.

I have found that a very satisfactory resistance device can be made by inserting a quantity of suitable material, preferably in the form of a paste, into an insulating casing, and then subjecting the device to furw ther treatment. Preferably the casing should be porous, to enable it and its contents to bedthoroughly dried and then coated and scale i The nature of my invention will be aps5 parent from the followin detailed description, which is to be considered in conjunction with the accompanying drawings, in which: Figure 1 is a longitudinal elevation, partly in section, of the completed resistance device according to my invention.

The same numerals. identify the same parts throughout.

The numeral 1 on the drawing indicates L5 a tube or spool of some suitable porous insulating material such as wood. This tube may have its ends bored out larger for a purpose to be explained later. The ends of the tube are closed by caps 2 of some conductive s0 material such as metal, and the inside of the tube is filled with :1. treated resistance material 3. Each cap 2 has a projection 4.- which can be thrust into the adjacent enlarged end of the bore of the tube, this proi 5 jection 4 being in the form of a shank or mixture of manganese dioxide, lamp-black boss having threads 5 or being otherwise roughened on its exterior surface.

The resistance material 3 contains a binder which is of such a nature that it not only causes the material 3 to cohere, but also makes it adhere tightly to the metal proections 4 of cap '2, which the material 3 completely surrounds; and to the inside of the tube 1. I

Hence the caps are firmly cemented to the ends of the tube and efficient and permanent electrical contact between the cap and the resistance material 3 is obtained.

The material 3 consists preferably of a and glue. The manganese dioxide is ground to powder and mixed with lamp-black in approximately equal proportions. Le Page liquid glue can then be added, the entire mass being agitated in a stirring vessel to intermix the ingredients thoroughly; while the operation of filling a number of tubes like the tube 1 is performed. After mixing the manganese dioxide and lamp-black in equal'proportions, the glue can be added in such quantity that, for example, for every twenty parts by weight of the manganese dioxide and lamp-black 125145 parts of glue will be present. When the mixture has been made, it is utilized to fill a selected number of tubes or spools 1, by means of a squirt gun or any other apparatus. As each tube or casing lis filled up to both ends, the caps 2 are puton immediately and in this condition, then tube is air dried for about one week.-

While drying, the filled tubes with their caps in place are put in suitable holders to prevent the caps from working off the ends of tubes while the caps are becoming set in the process ofdrying. After drying for about seven days they are heated at 125 to 150 for 2 to 3 hours, and then placed in a paraflin bath under a vacuum for some minutes to remove all air and all traces of 1 remaining moisture. Then air is again admitted under any desired pressure until all interior spaces are thoroughly filled with: paraffin.

Next each of the devices are treated elec- 105 trically by testing at 800 volts and then allowed to lie one week for aging. The resistance devices are-now segregated and classified according to the different values of the resistance which they present, by measure- 110 ment, for example, at 220 volts, and then sired with a given mixture, 'the middle secafter another week these measurements can be checked at a lower voltage, such as six volts. This precaution is taken to detect any changes in the value of the resistance which may have taken place. All of the devices which are satisfactory are then taken and labeled and packed, the other ones which are not satisfactory can be treated further in the same way until they attain the condition required.

When finished, the resistance devices having the structure and character above indi' cated are perfectly dried and entirely mois ture-proof. Their resistance is constant and will not chan e in service, and each device will have su cient mechanical strength to enable it to withstand handling and avoid damage when subjected to the ordinary careless manipulation frequently given to appliances of this sort.

By the method above described, I can make resistance devices from 1200 to 100,000 ohms or in higher resistance values from 100,000 to 20'megohms. The devices are particularly useful as grid leaks for radio sets and their resistance remains constant. They are not subject to the gradual increase of resistance values so marked in most types of highresistances, usually due to poorcontact between resistance material and metal ends. The resistance of the manganese dioxide is always high; while that of the carbon which is referably in the form of lamp-black is reliitively low and by intermixing these with the adhesive or glue and treating as described, the finished device is given the value of resistance which is required and this resistance is maintained.

The end caps 2 do not fit the exterior of the tube 1 tightly, but have a slight clearance (about 1/100 of an inch) to enable resistance material 3 after being inserted in the tube 1' to escape when caps 2 are pushed on; and at the same time give better electrical contact. The resistance material after drying becomes stony yet somewhat resilient, like hardened glue.

Glue is used advisedly rather than shellac, l uer, etc., as-it'has a better conductivity.

e attainment of good and lasting electrical contact by the adhesion of the resistance material 3 to the metal caps 2 is an important feature of this invention.

The same constant resistance can be obtained with different aging eriods but I find that the seven day perio s give the desired results and permit a systematic and eas method to be employed.

he projections require an enlarged recess 6 at each end of the bore of the tube 1 of a certain diameter to allows space around the projections 4 for the resistance material to cement the projections 4 to the inside of the tube 1. If higher resistances are detion of the tube can be bored out to any required smaller diameter.

Having described my invention, what I believe to be new and desire to secure and protect by Letters Patent of the United States is 1. A resistance device comprising a porous insulating casing, electrically conductive caps on the casing, conductive material in the casing connecting the caps and capable of presenting a constant resistance to a current flowing therethrough, and a coating on said casing, the device being dried and airtight.

2. A resistance device comprising a casing in the form of an open-ended tube of'porous insulating material, electrically conductive caps engaging the ends of said tube, a conductive substance in said tube comprising manganese dioxide mixed with carbon capable of offering a constant resistance to the passage of current flowing therethrough, the device and contents being thoroughly dried, and thoroughly impregnated with a waterproof and insulating material.

3. A resistance device comprising an openended tube of insulating material filled with an electrically conductive substance, and end caps aflixed to the tube, each of said caps having a roughened projection which extends into the tube and adheres to the resisgance material which surrounds it in the tu e.

4. A conductive substance of constant resistance, consisting of manganese dioxide and carbon in equal parts by weight, and containing a'binder or adhesive, mingled to aiford a uniform plastic mixture.

5. A conductive substance capable of maintaining a uniform resistance, said substance containing equal parts by weight of manganese dioxide and powdered carbon mixed with an adhesive in the proportion of twenty parts of the manganese dioxide and carbon to 125 or more parts of the adhesive, mingled to afiord a uniform mixture.

6. The process of manufacturing resistance devices which consists in making a mixture of a conductive substancewith an adhesive, forcing said mixture into a tube, closing the ends of said tube with caps of electrically conductive material, subjecting said tube and contents to the action of heat and then coating the entire device to render it impervious to moisture and at the same time, extracting all of the air and moisture therefrom.

"7. The process of manufacturing electrical resistance devices which consists in making a mixture of manganese dioxide and lampblack with the addition of an adhesive, forein said mixture into a porous insulating tu e, capping the ends of said tube, drying said device, subjecting the device to the action of heat and then impregnating the device to make it water-tight; while at the same time, extracting all of the air and mois-' ture therein, and finally aging the device.

8. The process of manufacturing resistance devices which consists in the making of.

a mixture of manganese dioxide and lampblack in owdered form, in equal parts by weight, a ding a relatively large quantity of an adhesive and thoroughly intermingling the adhesive with the lamp-black and manganese dioxide, forcing said mixture into'a porous insulating casing, closing the ends of said casing with electrically conductive caps, subjecting it to the action of heat, and then extracting the air in the casing and contents, impregnating said device with meltedv wax, to make the same air-tight and water-proof.

9. A resistance device comprising a cas-' ing, resistance material capable of being forced in the form of a paste into'the casing, and terminals on the ends of the casing to be engaged by said material to cause the terminals to adhere to the casin upon the drying of said material to make e cient electrical contact with said material.

10. A resistance device comprising a casing, plastic resistance material filling said casing and terminals on the ends of the cas ing connected to said material by adhesive enga ment therewith, to cause said termina s to be maintained upon the casing and make eilicient electrical contacts with said material.

Signed at Philadelphia in the county of Philadelphia and State of Pennsylvania this 29th day of August A. D. 1924.

CHARLES E. VAWTER. I

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