US2728837A - Resistors - Google Patents

Description

Dec. 27, 1955 M. cARuso RESISTORS Filed April 21, 1953 INVENTOR: 4/44/0 m/s0 ATTORNEY:

United States Patent RESISTORS Mario Caruso, New Bedford, Mass. Application April 21, 1953, Serial No. 350,165 3 Claims. (Cl. 201-67) This invention relates to the method of producing an improved type of electric resistors and the article made by this method.

The art of electric resistors is quite complex, and there exist numerous patents and voluminous literature covering various ways of manufacturing resistors of different types.

The present invention contemplates an improved method of producing moisture-impervious, insulated electric resistors which not only have all the requirements of a stable, efiicient and practical resistor, but in addition possess certain very important and advantageous features lacking in heretofore produced resistor structures.

The prime object of the present invention is to employ a relatively simple, inexpensive but very effective method of producing a moistureproof and insulated resistor structure by the formation of a jacket or envelope composed of easily manufacturable and readily assemblable parts made from prefabricated standard stock material always available in the open market, and by compacting within that envelope a resistance compound, which latter, in consequence of its composition and of the method employed, becomes intimately joined or united with the envelope material.

A more specific object of this invention is the provision of a method of producing insulated, moisture-impervious resistors, and which method comprises preparing envelope-forming parts made from prefabricated stock material, such as rods and tubing, and wherein the tubing is cut to required length, to efi'ect tubular members of future envelopes, and wherein end covers for that tubular members are shaped from standard rods, and which end covers are provided with apertures for the reception of prefabricated electrodes, and which method further comprises positioning of the electrodes in a certain way relative the end covers to facilitate their movement within and in outward direction in respect to the future envelope or jacket of the resistor, compacting a resistance composition within the future envelope, the movement of the electrodes being effected by the compacting procedure, and which movement of the electrodes causes them to become firmly imbedded and anchored within the compacted resistance compound, thereby precluding their bodily movement within the finished resistor structure and preventing their disengagement in normal usage from said structure, and which method further includes the steps of heat-sealing with one another all of the elements of the envelope, fusing the end cover material about the electrodes, heat-sealing them within these end covets, thereby preventing moisture from ever penetrating into the interior of the resistor jacket or envelope, thus preserving the resistance compound compacted Within the envelope and precluding its deterioration, whereby the intended resistance value of the device remains constant during extensive use, if not subjected to abuse, and which method includes the step of effecting a firm union be tween the compacted resistance compound and its en- .velope.

A further object of this invention is the provision of an electric resistor, the envelope of which is made of moistureproof dielectric thermoplastic material, and wherein the parts of the envelope are prefabricated and assembled and are heat-sealed with one another after assembly, and wherein the electrodes for the resistor comprise wire structures with broad heads projecting into the envelope, and wherein the heads form conical shapes, the conical faces of which being directed towards the closing elements of the envelope, and wherein the electrode bodies are heat-sealed within the end elements of the envelope, and wherein the resistance compound is firmly compacted within the envelope so that it forms intimate contact and union with the interior of the envelope body and with the heads of the electrodes, and wherein the electrodes are firmly anchored within the compacted resistance compound, thus preventing their movement within and their disengagement from the resistor envelope in ordinary use.

in exemplifying the afore-indicated method, first the different components of the resistor structure are prepared. The envelope comprises three parts, a cylindrical tubular member made from thermoplastic tubing, preferably of a phenol base such as phenobaldehyde resin mixed with a suitable filler and lubricant. For closing the ends of the tube there are provided end covers made of the same or similar material in the form of prefabricated rods. These end covers comprise disc structures with hub-like central enlargements, which latter are adapted to project into the tube member. The periphery of the disc structures are preferably beveled and so are the peripheral faces of the hubs. These end covers are provided with central apertures for the reception of the electrodes, which latter are also prefabricated and consist of wire structures having substantially enlarged termini in the form of conical heads, and which heads are so positioned within the envelope that in the finished resistor structures the conical faces are in adjacency with the hub enlargements of the covers, while the fiat bases of the electrode cones face one another.

The resistor compound is made from the usual ingredients such as carbon black, an inert filler and a thermoplastic binder, preferably of the phenol-aldehyde resin base, and which binder, when the compound is subjected to pressure and heat, will effect an intimate union of the compound with the interior surface of the prefabricated jacket or envelope of the resistor structure.

With all of the components of the future resistor structure ready, one of the electrodes is passed through one of the end covers so that the conical end of its head faces the hub enlargement of the cover. The electrode is so positioned that its head is somewhat distanced from the hub. Now the beveled periphery of the cover is pressed into one end of the tubular member while the latter is held Within a heatable die, the cover being supported by a plunger movable within the die. Now the resistance compound in granulated or powder form is poured into the tube and compacted therein to the desired density. During the compacting procedure portions of the compound are first directed into the space between the electrode head and the end cover, and as the compacting procedure progresses, the electrode head is caused to move in the direction towards the cover, whereby the conical surface of the electrode head exerts outward pressure against the compound. This function of the conical head surface causes a firm anchoring of the head within the compound, and, as the compacting of the compound continues, the electrode movement progresses until the apex of its cone engages the hub enlargement of the cover, and the outward movement of the electrode is stopped. Obviously the pressure exerted by the conical surface of the electrode head against the trapped compound is very substantial, whereby an intimate contact between the head and the compound is efiected.

When the tube of the envelope is substantially but not quite completely filled with the compressed compound, there is added loose compound above the tube. Now a second electrode is passed through the other end cover for the tube and is held so that the electrode head extends a distance from the hub enlargement of the cover. .Now the cover is ready to be forced into the still open end of the tube under application of surplus loose compound which latter becomes firmly compacted by the forcible insertion of the second cover. The electrode of that cover first penetrates the already compacted resistance compound Within the tube, and the surplus of resistance compound at the top of the tube is trapped by the second cover as it is being inserted into the tube end and is forced against the already compacted compound. During that period the second electrode recedes toward the hub enlargement of the cover and compresses the surrounding compound with its conical head portion as the beveled edge of the cover enters the cylindrical interior of the tube end. As the inward movementof the cover progresses, the compound in contact with the head is further compressed and more of the compound is compressed by the end cover against the electrode head, whereby the latter becomes firmly anchored.

During the aforedescribed procedure the die holding the tube is heated, and as the second cover is forced into the open tube end, the unused surplus of loose compound is removed by elevating the closed resistor structure, whereupon the now closed resistor is caused to re-entcr the heated die and additional pressure is exerted against the end covers, and the resistor structure is subjected to greater heat. This added heat brings about the fusing of the tube material with the cover material and causes plasticizing or softening of the thermoplastic binder in the compound. As a result a firm, intimate union between the compound and the interior surfaces of the resistor envelope is effected, as well as the sealing of the electrodes in the end covers for the tube; the resistor structure is thus finished and is removed from the die.

The above outline method will be more clearly understood by referring to the accompanying drawings, where- Fig. l is a perspective view of a finished resistor produced by the aforesaid method;

Fig. 2is an enlarged cross section taken approximately along a plane indicated at 2-2 in Fig. 1;

Fig. 3 shows all the elements of the resistor with the exception of the resistance compound;

Fig. 4 is a vertical section through a heatable die hold ing the tube with one attached end cover of a future resistor structure prior to compacting resistance compound within the tube;

Fig. 5 shows a section similar to that of Fig. 4 with the compound partly compacted and with the second cover ready to be inserted into the other tube end;

Fig. 6 shows the electrode structure in its final closed position prior to the removal of unused surplus compound;

Fig. 7 shows the resistor in its elevated position with all surplus compound removed;

Fig. 8 illustrates the resistor within the heated die to effect the fusing of the resistor elements and the sealing of the electrodes; and

Fig. 9 shows the finished resistor on its way to be discharged from the die.

In Figs. 2 and 3 the components of the resistor are clearly illustrated. Numeral 10 denotes a cylindrical thermoplastic tube preferably made of a phenol base. This tube is cylindrical throughout including its interior surface. Adapted to engage the ends of the tube are covers 11 and 12, each comprising a stepped, disc-shaped structure having a peripheral beveled surface 13, adapted for press fit with the tube ends, and a hub-like enlarge- 4 ment 14 also provided with a beveled peripheral face, and which end covers for the tube have central apertures 15 for the reception of electrodes 16. These electrodes comprise wire shanks 17 with relatively large heads 13 which are acutely cone-shaped, the apices of their conical bodies being adapted to assume final positions adjacent hubs 14, while their flat bases are disposed opposite one another in the finished product, as clearly observable from Fig. 2.

It will become presently evident from the detail description of the method, that the beveled faces 13 of the end covers are forcibly inserted in the cylindrical ends of tube 10, whereby these tube ends are somewhat deformed interiorly but are kept cylindrical exteriorly. Within the envelope or jacket formed by tube 1%} and the two end covers 11 and 12 there is held a resistance cornpound 19 which is compacted to the required density corresponding to the electric resistance requirement of the device.

In Figs. 4 to 9 there is illustrated a die 2% comprising a lower stationary member 21 and an upper movable member 22. The lower member 21 is either heatable or may be heated internally by high frequency current. in the upper movable member 22 there is provided a funnelshaped depression 23 with a cylindrical continuation 24.

At the beginning of the procedure of making the instant resistance structure die member 22 rests against die member 21, as shown in Figs. 4 and 5. Registering with cylindrical extension 24 of upper die member 22 is a cylindrical passage 25 within member 21, and in which passage is operatively mounted a plunger or piston 26 provided with a central passage 27 for the reception of the wire body of an electrode. In the position of piston 26 shown in Fig. 4, the upper piston end supports one end of dielectric cylinder 1t) and the outer face of end cover 11. End cover 11 and tube 10 are partly assembled before they are placed into the passage 25 of die 20. The preassembly of the two elements is preceded by first inserting an electrode 16 into end cover 11 so that the wire portion thereof passes through aperture 15 provided in that cover and so that head 18 is positioned a substantial distance away from hub 14. Then the preassembled tube and end cover 11 are placed into passage 25 so that cover 11 rests against the top of plunger 26, whereupon a second plunger 27, indicated in broken lines in Fig. 4, is forced against the upper end of tube 10, and causes the penetration of end cover 11 into the lower tube end. Now plunger 27 is removed and substituted by a compound-compacting plunger 28 provided with an interior bottom recess 29, adapted for clearing the inserted electrode head. Plunger 27 is so dimensioned that it can pass through funnel extension 24 of upper die member 22 to engage the upper face of tube It), and plunger 28 has a diameter approximating the interior diameter of that tube.

In the diagram illustrated in Fig. 4 compound material 19' in powdered or granulated form is introduced through funnel 23 into the tube. The supply of loose compound into the funnel preferably continues as plunger 28 repeatedly decends into and moves out from cylinder 16, to compact the compound within the tube to its required density and to fill the latter approximately That procedure can be modified in providing a relatively tall column of loose compound above tube 10 and a longer stroke for plunger 28, so that a single inward movement of the plunger will compact the required amount of compound within the tube.

During the compacting procedure the loose particles of the compound are driven by the circumferential face of the lower end of piston 28 about head 18 of the electrode, and toward end cover 11. At the same time head 13 is caused to gradually move toward hub 14 until it is stopped when the head reaches that hub. During the downward movement of head 18 the compacted com pound adjacent the conical head portion is very firmly compressed and exerts pressure against cover 11 and the wall of cylinder 10, whereby the head becomes firmly anchored within the compound.

When the tube is filled with the required amount of compacted compound, the following next step in the method comprises the introduction of end cover 12 into the upper tube end. First an electrode is passed through the cover so that its head 18 extends a distance from hub 14. A plunger 30, provided with an interior passage 31 for accommodating the wire end of the electrode, now brings end cover 12 towards the upper tube end. As will be seen in Fig. the compacted compound within the tube terminates along line 32. It will be also observed from that figure that an ample supply of loose compound is retained Within funnel 23 and its cylindrical extensions 24. As now plunger 30 moves toward the upper end of tube 10, head 18 of the electrode penetrates the central upwardly extending portion of the compacted compound and forces that portion towards the cylinder wall, While cover 12 presses additional compound into the cylinder. By the movement of cover 12 into the tube end the compressed compound within the tube will stop further movement of electrode head 18, and at the same time compressed compound is forced against the conical face of the head. At the time cover 12 first engages the inner edge of tube and as the cover progresses into the upper tube portion, additional compression of the compound is effected. Thus the electrode head becomes firmly anchored within the compound.

When plunger 30 reaches the position shown in Fig. 6, tube 10 is now completely closed by the two covers 11 and 12 and heads 18 of the electrodes assume their intended position adjacent the hubs of the covers. At the position of the resistor shown in Fig. 6 the upper movable member 22 of the die is lifted and surplus compound 19' formerly held in funnel 23 is permitted to gather upon the upper face of die member 21 and about plunger 30. Now both plungers 26 and 30 are moved upwardly while holding tube 10 between them; at that position of the tube, shown in Fig. 7, all of the loose compound is removed from the die by either suction or air pressure.

Now the plungers and the tube are moved back into the lower die member 21 to the position shown in Fig. 8, at which position the resistance structure is subjected to pressure from both ends by plungers 26 and 30 and to sufficiently increased heat, supplied either by way of the die or by diathermically heating the resistor structure, to effect fusing of the tube material with the material of the end covers, to promote sealing of the electrodes in passages of the covers, and to plasticize the thermoplastic binder of the compound so that the latter is caused to intimately contact or even fuse with the interior surface of the resistor envelope. Now the finished resistor is elevated and removed from the die as indicated in Fi 9.

lieferring again to Fig. 2, the fusing effects between tube 10 and end covers 11 and 12 is exaggeratedly indicated at 33, as well as the sealing 34 of the electrodes within the cover apertures. In the finished product, however, the fusing of the cover and tube materials and the sealing of the electrodes is not readily perceivable.

While the foregoing description appears to cover a rather slow-moving production process, actually all the operations involved are very rapid and extremely effective. Thus an ideal resistor structure is produced, which is impervious to moisture infiltration, securely protects and electrically insulates the resistance material within the structure, thereby precluding variations or failure of the intended or desired resistance value of the device. Due to its extreme simplicity and compactness the resistor produced by the present method is very sturdy, withstands rough handling, endures easily the heat usually prevailing in electronic devices, and resists even relatively high pressure when applied against its walls without changing its resistance value or otherwise deteriorating it.

In addition to the above advantages, the electrode construction and their secure anchorage within the resistor structure assures perfect contact between the resistance compound and the electrodes and prevents their disengagement from the ends of the resistor, except when extreme force is applied. Tests conducted show that the wire ends of the electrodes will break before the electrode heads can be pulled from the tube. That feature, in addition to the aforestated advantages, renders the resistor produced by the present method an invaluable, eificient and practically indestructible element for the electronic field, and can be depended on to retain unchanged its resistance value.

Obviously the density of the resistance compound and its composition governs the resistance value of the future resistor. Resistance compounds are well known in the art and need not be further explained. By the same token the degree of density of the compound within tube 10 can be and had been determined by experiments and subsequent tests. It seems evident therefore that resistors of any desired resistance values may be readily produced by the present method Without any difiiculty.

Throughout the specification and the annexed claims the term thermoplastic is being employed to denote generally the type of material used in both the prefabricated resistor envelope, that is the tubing and its end covers, as well as for the binder added to resistance compound, and it is to be understood that that term is meant to include also any plastic materials known as thermosetting, that is substances which become rigid by application of heat as they undergo a chemical reaction of polymerization. The aforesaid binder for the resistance compound, for instance, can be thermosetting plastic, whereas the envelope material is preferably made from thermoplastic substances.

While in the foregoing a specific structure of a resistor is described as well as a specific method of producing the same, it is obvious that the drawings serve merely for explanatory purposes and that changes both in the structure of the device and in the method of producing it are subject to changes and improvements, such variations being deemed to reside within the broad scope of the present invention as defined in the annexed claims.

What is claimed as new is:

l. The method of producing a moistureproof, insulated resistor structure which consists of cutting to a desired length a cylindrical tube made from thermoplastic, dielectric material, providing end covers for said tube also made from thermoplastic and dielectric material and having beveled outer edges, adapted for press fit engagement with the interior end surface portions of the tube, each cover having a conical extension adapted to project into the tube interior, each of said covers also having a central aperture for receiving an electrode, providing wire electrodes having at one of their ends a conical head or enlargement; inserting an electrode through the central aperture of one cover so that its conical head projects a substantial distance from the future interior face of the cover extension, placing the tube into a heated die and forcing a cover holding the electrode into one end of the tube, placing resistance compound, including a thermoplastic binder, into the tube while the latter is held within the heated die, supplying for and compressing into the tube additional compound until it practically but not completely fills the tube and moves the electrode head against its end cover extension, retaining some of the compound above the filled tube, inserting an electrode into another end cover so that the conical head of the electrode extends a distance from the future inner face of that other end cover extension, moving the cover toward the other tube end, thereby causing the head of its electrode to first partly penetrate into the compressed compound with in the tube and then to move toward the inner face of the cover extension, continuing the movement of that other end cover, thereby additionally compressing and directing against the conical face of the electrode head and against the conus of its cover extension the now trapped, retained compound, forcing the beveled edge of that other end cover into the tube end, thereby causing the portions of the trapped compound located between the conical faces of the electrodes and the conical faces of the cover extensions to be forced against the interior wall face of the tube, thus effecting firm anchorage of the electrode heads within the resistance compound and an intimate contact between the electrode heads and the compound, removing the surplus of that additional compound, compressing and heating the now closed tube within the die until the cover and tube material fuses and the cover material seals the electrodes in the cover apertures, and the thermoplastic binder of the compound is plasticized and effects intimate union between the compressed compound and the interior surfaces of the tube and covers.

2. In a moisturedmpervious electric resistor, a dielectric thermoplastic envelope comprising a cylindrical tube filled with compressed resistance compound and sealed at its ends by like-shaped dielectric, thermoplastic covers having beveled peripheral edges and inwardly projecting hub-like enlargements having beveled peripheral faces, electrodes having relatively thin-bodied portions which extend through the covers, said electrodes having relatively large acutely tapered conical heads, the apices of which abut the interior faces of the cover enlargements, said beveled peripheral cover edges engaging the interior end portion of the tube and being fused and heat-sealed with the latter, the thin-bodied portions of said electrodes being fuse-sealed within the cover material; the acutely tapered conical surfaces of the heads serving not only to firmly compress said resistance compound, but also causing the latter to press against the covers and the wall of the tube, whereby these heads are securely anchored within the compound so that they prevent disengagement of the electrodes from the resistor structure.

3. In a moisture-impervious electric resistor, an envelope or jacket formed from a dielectric, thermoplastic tube with forced-in dielectric, thermoplastic end covers, said tube being cylindrical, compressed resistance compound filling the tube, said end covers forming discs with hub-like, interior enlargements having beveled peripheral portions and central apertures, the annular faces of said discs being also beveled, electrodes comprising wire conductors having relatively large and broad acutely coneshaped heads, said wire conductors passing through and being sealed within said apertures, the heads of the conductors projecting into the tube interior with their apices adjacent said hub-like cover enlargements, the beveled faces of the cover discs forcibly engaging and being heatsealed within the interior end portions of the tube; the beveled peripheral portions of said cover enlargements cooperating with the acutely cone-shaped heads in that they trap and firmly compress the resistance compound between them and force the latter against the wall of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,244,548 Benkelman June 3, 1941 2,271,774 Megow et al. Feb. 3, 1942 2,282,398 Ehrlich May 12, 1942

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