US2282398A

US2282398A - Method of making insulated resistors

Info

Publication number: US2282398A
Application number: US362519A
Authority: US
Inventors: Sidney B Ehrlich
Original assignee: Stackpole Carbon Co
Current assignee: Stackpole Carbon Co
Priority date: 1940-10-24
Filing date: 1940-10-24
Publication date: 1942-05-12
Anticipated expiration: 1959-05-12

Description

May 12, 1942. s. B. EHRLICH METHOD OF MAKING INSULATED RESISTORS Filed Oct. 24, 1940 INVENTOR.

WITNEJSE.

BY ffl; ATTO/mms.

Patented May 12, 1942 METHOD 0F MAKING INSULATED Y RESISTORS Sidney B. Ehrlich, St. Marys, Pa., signor to Stackpole Carbon Company, St. Marys, Pa., a

corporation oi.' Pennsylvania Application october 24, 1940, semi No. 362,519

(ci. zal-s3) 3 Claims.

This invention relates to electrical resistance elements, and more particularly to molded iixed resistors that are insulated. y

Resistors of this character are made by molding a mixture' of powdered carbon and a binder, such as Bakelite, into the form of small cylindrical slugs the diameter and length of which depend upon the wattage dissipation desired. At the same time that the slug is molded, wire leads are embedded or molded in its ends so that the resistor can be connected in an electric circuit. The slug is then baked to set the binder and thereby form a strong and hard resistor body. The general manner of insulating these resistors has been to place them in forms and then to mold resinous insulating coatings around them. 'Ihis yIlowing through it.

Another type of insulation that has been proposed is an insulating tube that is slipped over the resistor body and then secured in place. It is diillcult to obtain a tight lit with such a tube because it must be loose enough to slide over the resistor`body. It has also been proposed to wrap the resistor body with a narrow insulating tape wound spirally around the body, but this produces a long undesirable seam that may let in moisture,- and the completed element is not neat in appearance. The ends of the resistor are especially difficult to take'care of with such a tape.

It is among the objects of this invention to provide an electrical resistor with inexpensive insulation which satisfactorily adheres to and -encloses the resistor body, which will. not admit of the tape it can be increased by Wrapping thev tape two or more times upon itself. The tape is held in place by an adhesive, and any tendency for the outer end of the tape to loosen can be avoided by coating the wrapped resistor with a liquid sealing material which is then hardened.

If the colored bands used in color coding the resistor are applied to thetape, the sealing nlm should be transparent so that they can be seen through it. The ends of the resistor can be in sulated by projecting the tape beyond the ends oi the resistor body in order to form cups that are then filled with an insulating composition. To still more securely unite the tape tothe resistor body pressure is applied to the tape at spaced points so that it has a corrugated appearance. In pressing the tape in this manner it is stretched sideways and the portions adjacent its sides caused to rmly adhere to the resistor body throughout its length.

'I'he invention is illustrated in the accompanying drawing in which Fig. l is a side view of one form of my invention; Fig. 2 is an enlarged end view thereof; Fig. 3 is a still further enlarged fragmentary sectional view of the resistor: Fig. 4 is a side view, partly in section, of a modification of this invention; Fig. 5 is an end view of this modiiication; and Fig. 6 is a fragmentary section through a third embodiment of the invention.

Referring to Figs. l, 2 and 3 of the drawing, a cylindrical resistor body l, that has been molded from a mixture of powdered carbon and a binder. hasembedded in its ends theheads of pin-like wireleads 2 by which the resistor can be connected in an electric circuit. According to this invention the resistor body is insulated by a tape 3 that is wound straight around the body one or more timesdepending upon the amount oi insulation desired. The tape is made of a suitable insulating material that has the necessary ilexibility and mechanical strength and that is not aiiected by humidity conditions. The tape is caused to tightly adhere to the resistor body by adhesive 4 previously applied to one of them, but preferably to the tape so that `successive layers of the tape will adhere to one another.

The tape is of a width at least as great as the length of the resistor body, and may be drawn from. a roll as it is wound around the resistor. After the tape has been wrapped around the resistor body, a plurality of axially spaced annular grooves are pressed into the tape. This presses the layers of tape still more tightly together and against the body and stretches them laterally beyond the ends of the body. Proper adhesion between the tape and the resistor body from end to end is thus assured. After the tape wrapping has been subjected to the heat dissipated by the resistor, it becomes hard and practically inseparable from the resistor body.

The tape is protected, and its outer end further prevented from starting to unwind, by a coating film 5 of resinous material or the like which is sprayed or painted on or otherwise applied to the wrapped resistor. Preferably, this material is air drying. The coating film is thicker in the grooves in the tape than between them, and therefore forms a plurality of spaced reinforcing rings. When the resistor heats up in use the tape yields sufficiently to avoid cracking of itself or the coating lrn which also improves the electrical and humidity characteristics of the resistor.

In the modification shown in Figs. 4.and 5 the vtape 6 is wound only once around the restistor body l to which it is secured by an adhesive 1, although it can extend around it more times if desired. Also, the tape wrapping is uncorrugated and of a width substantially the same as the length of the resistor body. To aid in preventing the outer end of the tape from peeling away from the resistor it is feathered, as shown in Fig. 5,

-and the entire wrapping is covered by a sealing film 8 similar to coating 5 of the rst embodiment.

The color coding bands that indicate the resistance value of the resistor may be applied to the outer sealing lm in the usual manner. Or, they may be painted or printed on the tape before it is formed into a roll or as it leaves the roll, in which case the sealing film should be transparent, as shown in Fig. 4, such as methacrylic resin, so that the code'bands 9 can be seen through the film. This method of applying the color bands is considerably cheaper than racking and then painting each individual resistor. It also eliminates the necessity of subjecting the resistor leads 2 to the undesirable atmosphere of a paint room in which paint and oxides resulting therefrom deposit on the leads and prevent easy soldering.

Fig. 6 -shows an embodiment of my invention in which, like in Fig. 3, the insulating tape Il extends beyond the end of the resistor body I and forms therewith a cup. This cup is filled with insulating material l2, -preferably a thermoplastic resin, whereby the ends of the resistor are sealed and insulated.

By using a tape which is wide enough to cover the resistor body from end to end, the tape can be wound straight around the body so that the wrapping is of substantially uniform thickness and a straight seam of minimum length is provided. Also, the tape can be wound around the body a plurality of times, if desired, which could not be done if it were Wound spirally as heretofore. The resistor body is thus most eiectively insulated at a small cost, and its appearance is trim and neat.

According to the provisions of the patent statutes, I have explained the principle and construetion of my invention and have illustrated and described what I now consider to represent its best embodiments. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

l. The method of making a resistor in which a molded body member is enclosed by an insulating tape member, comprising applying an adhesive to one of said members, wrapping said tape member tightly and substantially straight around said body member, and then pressing a plurality of body member surrounding grooves in the tape member whereby it is caused to rmly adhere to said body member.

2. The method of making a resistor in which a 4molded body member is enclosed by an insulating tape member, comprising applying an adhesive to one of said members, Wrapping said tape member tightly and substantially 'straight around said body member, then pressing a plurality of body member surrounding groovesy in the tape member whereby it is caused to firmly adhere to said body member, and coating the tape with ya sealing material which lls said grooves.

i... edge portions caused to firmly adhere to said body.

SIDNEY B. EHRLICH.