US3257709A - Method and apparatus for making a string of molded electrical resistors - Google Patents

Description

June 28, 1966 w. J. FERNAN ET AL METHOD AND APPARATUS FOR MAKING A STRING OF MOLDED ELECTRICAL RESISTORS 6 Sheets-Sheet 1 Filed 001.. 9, 1962 ATTOQ/VEYS.

June 28, 1966 w. J. FERNAN ET AL 3,257,709

METHOD AND APPARATUS FOR MAKING A STRING 0F MOLDED ELECTRICAL RESISTOR-S Filed Oct. 9, 1962 6 Sheets-Sheet 5 5g \o 41 /23 P15. 4

/4 INVENTORS 5 2 I9 WILL/AM J. FER/VAN W/LL 64M J. HEPBST BY 521.5 I. SHOBEQT 11 ATTUR/VfVJ June 28, 1966 w. J. FERNAN ET AL 3,257,709

METHOD AND APPARATUS FOR MAKING A STRING OF MOLDED ELECTRICAL RESISTORS Filed Oct 9, 1962 6 Sheets-Sheet 5 INVENTORS W/lL/AM J. FElQ/VAN IV/LL/JM J. 195E857 BY 245 1'. SHOBEQT 11' ATTORNEYS.

June 28, 1966 w. J. FERNAN ET AL 3,257,709

METHOD AND APPARATUS FOR MAKING A STRING OF MOLDED ELECTRICAL RESISTORS Filed Oct 9, 1962 6 Sheets-Sheet 6 /M /PE SUPPLY SPOOL [MOL DER PULLER TT'ER (UR/N6 Ul/E/V BAY/N6 Ol/EN INVENTORS W/AL/AM J. FERA/A/V mum/u J. #5255?" BY RLE 1. $H08ER7'1Z A 7'TOR/VEX5.

United States Patent 3,257,709 METHOD AND APPARATUS FOR MAKING A STRllgJG 0F MOLDED ELECTRICAL RESIS- TOR William .1. Fern-an, William I. Herbst, and Erle I. Shobert 11, St. Marys, Pa, assignors to Stackpole Carbon Company, St. Marys, Pa, a corporation of Pennsylvania Filed Oct. Q, 1962, Ser. No. 229,363 11 Claims. (l. 29-15562) This invention relates to the making of electrical resistors by molding them around the ends of wire leads, and more particularly to the making of a continuous string of such resistors.

It is among the objects of this invention to provide a method and apparatus for making molded electrical resistors rapidly in such a manner that they can be operated upon and handled in a continuous string of indefinite length which can be fed into an automatic machine for connecting the individual resistors into electric circuits.

In accordance with this invention a long wire is out near its front end to form in front of the out a wirelead. This lead and the long wire are fed forward to a predetermined position where their adjacent ends will be spaced apart. A resist-or body then is molded around and between the spaced ends. Periodically, the foregoing steps are repeated to form additional resistor" bodies, each connected to the preceding one by a wire lead cut from the long wire. As the string of resistor bodies leaves the machine they can be treated or operated upon in various ways and then wound in a coil for further treatment and handling.

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which FIG. 1 is a fragmentary side view of my machine;

FIG. 2 is a view of the front of the machine;

FIG. 3 is a horizontal section taken on the line IIIIII of FIG 1;

FIG. 4 is a fragmentary vertical section taken on the line IVIV of FIG. 1;

FIGS. 5 to 9 are fragmentary vertical sections showing different positions of the movable parts of the machine as astring of resistors is being formed; and

FIG. is a diagram. of various steps in making a string of resistors in accordance with my invention.

Referring to FIGS. 1 to 4 of the drawings, mounted in the bed 1 of a machine are four vertical posts 2 arranged in a rectangle, with their upper ends mounted in the head 3 of the machine. Slidably mounted on the lower portions of the posts is a lower ram 4, from the center of which a bottom punch 5 extends upward. Slidably mounted on the upper portions of the posts is an upper ram 6 that carries a downwardly extending top punch 7 in line with the lower one. The two rams can be moved up and down the posts by rods 8 that may be actuated in any suitable manner, such as by pistons and cylinders, cams or levers.

Between the two rams, a pair of dies 10 and 11 are slidably mounted on the posts. They may be moved up and down independently of the punches by means of rods 12 actuated in any suitable manner. The two dies are provided at their centers with aligned rectangular passages 13 and 14, each adapted to snugly receive the adjoining punch. When the dies are closed, the two passage-s form a molding cavity. The lower punch may be permanently disposed in the lower passage, but the upper punch is above the upper passage part of the time. The adjacent ends of the punches are concave, as shown in FIG. 4, and when they are together in the center of the molding cavity they form a cylindrical chamber having the size of the resistor that is to be formed.

3,2517% Patented June 28, 1966 "ice The bottom of the upper die 10 in front of and behind its vertical passage 13 is provided with a pair of aligned grooves 16 that are semicircular in cross section and of a size to fit half way around the wire that is fed to this 7 machine to form resistor leads. The grooves are midway between the opposite sides of .passage 13. Another pair of like grooves 17 is provided in the upper face of the lower die in positions to register with the upper grooves when the dies are closed. Each die also is provided with two vertical slots 18, one directly in front of and one behind its vertical passage. The upper and lower slots are aligned. Slidably mounted in the two lower passages are wire guides 19, the lower ends of which are secured to the lower ram 4. The upper portion of each guide projects above the lower die and is forked to provide a V notch :20, the lower end of which opens into a narrow vertical slot 21 in the longitudinal vertical plane of grooves 16 and 17. The slot is about the same width as the grooves. When the guides are in their upper positions, a wire lying in the grooves will extend through slots 21.

Rigidly mounted at the back of the machine is a guide block 23, which is provided with a bore 24 through it in line with the bore formed by the die grooves when the dies are closed. This block receives the front end portion of a long flexible wire 25, from which resistor leads are to be cut. The wire comes from a supply spool shown only in FIG. 10. The block has .a vertical passage 26 through it that intersects bore 24. Slidably mounted in this passage is a cutter blade 27, the lower end of which normally is above the bore. The blade may be moved down through the passage in any suitable manner, preferably by being rigidly connected by an arm 28 to the upper ram so that they will move in unison.

The wire is fed from the supply spool forward through guide block 23 by a reciprocating feeder behind guide block 23. As shown in FIG. 5, the feeder may take the form of a slide 30 mounted on a suitable support 31. The slide may be reciprocated toward and away from the block by any suitable means. There is a vertical longitudinal slot 32 in the slide, through which the wire extends. Disposed in the end of this slot closest to the guide block is a gripper cam 33 pivotally suspended from a pin 34 mounted in the slide. The shape of the cam is such that when the slide is moved forward toward the guide block the lower end of the cam will clamp the wire tightly against the bottom of the slot and thereby feed the wire ahead at distance equal to the length of the stroke.

To charge the molding cavity with resistor-making material M (FIG. 7), such as a mixture of powdered graphite and a thermosetting resin, a charging plate 35 beneath upper punch '7 is slidably mounted on top of the upper die between guides 36 secured to that die. The plate can be moved back and forth across the die at right angles to the wire grooves 16 and 17 by any suitable means, such as by a rod 37 connected to a piston or other actuating means. The charging plate has a vertical opening 38 through it of about the same size and shape as the top of the molding cavity. The opening is large enough to permit the upper punch to move down through the plate when the opening is directly over the molding cavity. At other times, opening 38 is located directly beneath the outlet of a hopper 39 supported by the upper die. The hopper contains the powdered material.

In operation, while the dies and punches and guides are retracted as shown in FIGS. 1 and 5, the long wire 25 extending through the feeder slide 30 and into guide block 23 is advanced by the feeder until the front end of the wire projects a short distance into the space between the two vertical die passages 13 and 14. Assuming that a short lead wire 41 is held between the dies at the opposite side of those passages, with its rear end projecting a short distance into the space between them, the upper die is lowered to engage the two wiresas shown in FIG. 6. At the same time, the bottom ram 4 is raised part way to lift wire guides 19 in order to center the wires and make sure that they lie in or directly below grooves 16 in the upper die. The lower die then is raised until it engages the upper one and the wires are enclosed by the two sets of grooves as shown in FIG. 7, whereby the mold cavity is completed. The lower ram is raised further at the same time. Then charging plate 35 is moved to transfer a charge of resistor-making material M from hopper 39 to the mold cavity, into which the material either falls or is pushed by the upper punch when that punch is lowered. The two punches are moved toward each other in the mold cavity to mold the material into a cylindrical resistor body 42 around the ends of the wires projecting into the cavity, as shown in FIG. 8. Preferably, at the same time cutter blade 27 is moved down through the guide block to cut out a section of the wire at that point. The dies are then separated, as shown in FIG. 9, followed by the punches, and then the resistor body and the long wire are moved ahead to locate the rear end of the rear lead near the outlet side of the opened mold cavity and to locate the front end of the long wire between the punches at the inlet side of the cavity. The cycle then is repeated, whereby a string of resistor bodies is formed of any desired length. If the long wire is cut by a thin blade, the string will have to be advanced faster than the long wire in order to space the rear end of the rear lead wire from the front end of the long wire at the mold cavity, so it is preferred to use the thick blade 27 so that the long wire and the string can move forward at the same speed.

The successive resistor bodies and thin connecting leads are moved ahead periodically by a puller formed from a reciprocating slide 44 on a support 45 at the front of the machine. This slide likewise has a vertical longitudinal slot 46 through it, but the slot is wide enough to receive the resistor bodies. The base portion of the slide at the bottom of the slot is short and is inclined downwardly at its opposite ends to permit it to slide backward under each successive resistor body. Each successive wire lead is clamped against the base of the slot by a gripper cam 47 suspended from a pivot pin 48 extended across the upper part of the slot. The feeder and puller may operate in unison. The arrows in FIGS. 5 and 7 show that they are in motion in the directions indicated. In FIGS. 6, 8 and 9 the feeder and puller are stationary.

While a resistor body is still in the mold cavity, it is heated sufficiently to partly cure it so that it will retain its shape and have some strength until it can be completely cured later. The heating may be done by electric heating elements 50 (FIGS. 5 to 9) mounted in chambers 51 in the dies beside vertical passages 13 and 14.

It is desirable to paint the ends of the wire leads with carbon paint before the resistor bodies are molded around them, whereby to form better electrical connections between the leads and bodies. As shown in FIG. 10, the painting can be done by applying the paint to the long wire 25 along short sections about as long as the resistor bodies and spaced apart about the same distance as those bodies. Each successive painted section travels through a dryer and then enters the feeder. When it reaches the guide block the central portion of the painted section is cut out by the cutter blade, leaving the adjacent ends of the wires painted.

After the resistor bodies leave the puller they pass through a curing oven and then may travel through apparatus where the resistors are insulated and color coded. Finally, the string of resistors is wound in a coil on a reel, which then may be immersed in a tank to impregnate the resistors with moisture-resisting material. After that, the coil is placed in an oven to bake the resistors.

As the resistor string is uncoiled for use, the resistors may be separated by cutting each successive wire lead in half by any suitable means.

It will be seen that by this invention resistors can be made rapidly and treated and handled as a string of any desired length. The ability to wind the string on a reel greatly facilitates the storage, shipping, handling and use of these resistors.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. 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.

We claim:

1. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a long wire near its front end to form in front of the cut a wire lead, feeding said lead and long wire forward to a predetermined position where their adjacent ends will be spaced apart, pressure molding a resistor body around and between said spaced ends, and periodically repeating the foregoing steps to form additional resistor bodies each connected to the preceding one by a wire lead cut from said long wire.

2. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a long wire near its front end to form in front of the cut a wire lead, feeding said lead and long wire forward to a predetermined position where their adjacent ends will be spaced apart, pressure molding around and between said spaced ends a resistor body containing a thermo-setting resin and simultaneously heating said body sufiiciently to retain its shape until said resin can be completely cured later, and periodically repeating the foregoing steps to form additional resistor bodies each connected to the preceding one by a wire lead cut from said long wire and ready to be cured.

3. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a long'wire near its front end to form in front of the cut a wire lead, feeding said lead and long wire forward to a predetermined position where their adjacent ends will be spaced apart, pressure molding around and between said spaced ends a resistor body containing a thermo-setting resin, periodically repeating the foregoing steps to form a string of resistor bodies, intermittently moving said string ahead, and curing, insulating and color coding each successive resistor body in the string.

4. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a long wire near its front end to form in front of the cut a wire lead, feeding said lead and long wire forward to a predetermined position where their adjacent ends will be spaced apart, pressure molding a resistor body around and between said spaced ends, periodically repeating the foregoing steps to form a string of resistor bodies, winding said string onto a reel, and impregnating the resistor bodies on the reel with moisture-resisting material.

5. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a section from a long wire near its front end to form in front of the cut a wire lead, feeding said lead and long wire forward a predetermined distance, then pressure molding a resistor body around and between the spaced wire ends produced by said cutting, and periodically repeating the foregoing steps to form additional resistor bodies each connected to the preceding one .by a wire lead.

6. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising painting with carbon paint a short length of a long wire near its front end, allowing the paint to dry, cutting a section of the wire from the middle of said .painted length to form in front of the cut a wire lead having a painted end portion, feeding said lead and long wire forward a predetermined distance, then pressure molding a resistor body around and between the spaced painted wire end portions produced by said cutting, and periodically repeating the foregoing steps to form additional resistor bodies each connected to the preceding one by a wire lead cut from said long wire.

7. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a section from a long wire near its front end to form in front of the cut a wire lead, feeding said lead and long wire forward in unison a predetermined distance and then holding them stationary, pressure molding a resistor body of greater length than said section around and between the spaced wire ends produced by said cutting, and periodically repeating the foregoing steps to form additional resistor bodies each connected to the one in front of it by a wire lead out from said long wire.

8. In the making of a string of electrical resistors in which axially spaced resistor bodies are connected by wire leads, the method comprising cutting a section from a long wire near its front end to form in front of the cut a wire lead, pulling said lead forward a predetermined distance, simultaneously pushing the long wire ahead a predetermined distance while maintaining it spaced from said lead, then pressure molding a resistor body around and. between the spaced wire ends produced by said cutting, and periodically repeating the foregoing steps to form additional resistor bodies each connected to the one ahead of it by a wire lead cut from said long wire.

9. Apparatus for making a string of electrical resistors in which axially spaced resistor bodies are connected by flexible wire leads, comprising upper and lower dies, means for moving the dies into and out of engagement with each other, the dies being provided with a pair of aligned vertical passages therethrough forming a molding cavity when the dies are closed, a vertically reciprocable bottom punch in the lower passage, a vertically reciprocable top punch normally disposed above the upper passage, the closed dies being formed to hold between them at the front and back of said cavity and in axial alignment a short wire lead and the front end portion of a long flexible wire with the adjacent ends thereof projecting into the cavity but spaced apart, means for delivering a charge of powdered resistor material to the top of the molding cavity, means for moving said punches toward and away from each other in said cavity to mold said material into a re sistor body with said wire ends embedded therein, cutting means behind the dies adapted to cut said long Wire to form a second short wire lead projecting from said body, means for pulling said resistor body forward away from the molding cavity when the dies and punches are retracted until the free end of said second lead will project only a short distance into the cavity, and means for feeding the long wire-forward between the retracted dies until its front end will project only a short distance into said cavity, whereby when the dies are closed again the molding cavity will be ready to receive another charge of powdered resistor material.

10. Apparatus according to claim 9, in which said cutting means includes a member provided with a wire-receiving longitudinal bore therethrough for guiding the wire to the dies, said member having a transverse passage therethrough intersecting said bore, and a cutting blade disposed in said transverse passage normally at one side of the longitudinal bore and movable across it to cut a section from a wire in the bore.

11. Apparatus as recited in claim 9, in which said dies are provided with vertically aligned slots at the front and back of said vertical passages, and a pair of vertically reciprocable wire guides are mounted in said slots in the lower die, each guide being provided With a downwardly extending V notch terminating at its lower end in a vertical slit for receiving a wire when the guides are moved up in the upper slots.

References Cited by the Examiner UNITED STATES PATENTS 2,500,258 4/1950 Mazzoni l8-36 2,577,584 12/1951 Hofreiter 18--16 2,608,633 8/1952 Bol 201-63 2,669,770 2/1954 Brewer 29155.5 2,885,524 5/1959 Eisler 29155.62 2,924,850 2/ 1960 Schultz 1836 3,083,445 4/1963 Hill 29155.62 3,110,088 11/1963 Blom 29-1555 JOHN F. CAMPBELL, Primary Examiner.

r 1W. BOCK, I. M. ROMANCHIK, IR.,

Assistant Examiners.

Claims (2)

1. IN THE MAKING OF A STRING OF ELECTRICAL RESISTORS IN WHICH AXIALLY SPACED RESISTOR BODIES ARE CONNECTED BY WIRE LEADS, THE METHOD COMPRISING CUTTING A LONG WIRE NEAR ITS FRONT END TO FORM IN FRONT OF THE CUT A WIRE LEAD, FEEDING SAID LEAD AND LONG WIRE FORWARD TO A PREDETERMINED POSITION WHERE THEIR ADJACENT ENS WILL BE SPACED APART, PRESSURE MOLDING A RESISTOIR BODY AROUND AND BETWEEN SAID SPACED ENDS, AND PERIODICALLY REPEATING THE FOREGOING STEPS TO FORM ADDITIONAL RESISTOR BODIES EACH CONNECTED TO THE PRECEDIONG ONE BY A WIRE LEAD CUT FROM SAID LONG WIRE.

9. APPARATUS FOR MAKING A STRING OF ELECTRICAL RESISTORS IN WHICH AXIALLY SPACED RESISTOR BODIES ARE CONNECTED BY FLEXIBLE WIRE LEADS, COMPRISING UPPER AND LOWER DIES, MANS FOR MOVING THE DIES INTO AND OUT OF ENGAGEMENT WITH EACH OTHER, THE DIES BEING PROVIDED WITH A PAIR OF ALIGNED VERTICAL PASSAGES THERETHROUGH FORMING A MOLDING CAVITY WHEN THE DIES ARE CLOSED, A VERTICALLY RECIPROCABLE BOTTOM PUNCH IN THE LOWER PASSAGE, A VERTICALLY RECIPROCABLE TOP PUNCH NORMALLY DISPOSED ABOVE THE UPPER PASSAGE, THE CLOSED DIES BEING FORMED TO HOLD BETWEEN THEM AT THE FRONT AND BACK OF SAID CAVITY AND IN AXIAL ALIGNMENT A SHOT WIRE LEAD AND THE FRONT END PORTION OF A LONG FLEXIBLE WIRE WITH THE ADJACENT ENDS THEREOF PROJECTING INTO THE CAVITY BUT SPACED APART, MEANS FOR DELIVERING A CHARGE OF POWDERED RESISTOR MATERIAL TO THE TOP OF THE MOLDING CAVITY, MEANS FOR MOVING SAID PUNCHES TOWARD AND AWAY FROM EACH OTHER IN SAID CAVITY TO MOLD SAID MATERIAL INTO A RESISTOR BODY WITH SAID WIRES ENDS EMBEDDED THEREIN, CUTTING MEANS BEHIND THE DIES ADAPTED TO CUT SAID LONG WIRE TO FORM A SECOND SHORT WIRE LEAD PROJECTIONG FROM SAID BODY MEANS FOR PULLING SAID RESISTOR BODY FORWARD AWAY FROM THE MOLDING CAVITY WHEN THE DIES AND PUNCHES ARE RETRACTED UNTIL THE FREE END OF SAID SECOND LEAD WILL PROJECT ONLY A SHORT DISTANCE INTO THE CAVITY, AND MEANS FOR FEEDING THE LONG WIRE FORWARD BETWEEN THE RETRACTED DIES UNTIL ITS FRONT END WILL PROJECT ONLY A SHORT DISTANCE INTO SAID CAVITY, WHEREBY WHEN THE DIES ARE CLOSED AGAIN THE MOLDING CAVITY WILL BE READY TO RECEIVE ANOTHER CHARGE OF POWDERED RESISTOR MATERIAL.

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