Magnetic bobbin

Application filed. June 21, 1928. Serial No. 287,305.

erably stout woven linen or cotton cloth, which is impregnated with a solution of bakelie varnish or analogous material capable of being hardened by the use of heat and pressure. 55

The mold or dies for preforming the first molding operation comprise a pair of heads 13 and 14, having at their opposed inner faces a pair of recesses as at 15 of suitable diameter to fit snugly over the ends of the eo core 10. The heads 13 and 14 are of such thickness that when they are clamped together with the ends of the core 10 seated in the recesses 15, the outer faces of the heads 13 and 14 are the right distance apart to fit 55 snugly between the inner faces 16 of the ends of a rectangular aperture 17 formed in a rectangular block 18. In order to facilitate assembly of the core in the recesses 15 of the heads, said recesses are flared at their outer 70 ends as well shown in Fig. 3. As shown best in Fig. 3, the heads 13 and 14 are of the same vertical height as the vertical thickness of the apertured block 18.

After the core 10 and heads 13 and 14 have 75 been assembled and inserted in the aperture of the block 18, the assembly of the upper and lower parts of the mold is completed as shown in Fig. 3. The lower part of the mold comprises a bottom plate 19 and a semicircu- go lar block 20 secured to plate 19 by cap screws 21. The ends of the block 20 are counterbored or recessed at their ends as well shown in Fig. 3, in order to form the heads or flanges 22 and 23 of the bobbin. The upper part of 85 the mold is similarly constructed with a top plate 24 and block 25. As well shown in Fig. 3, the blocks 20 and 25 which are mated together with a parting line midway of the mold structure, are of suitable length to fit 90 snugly between the inner surfaces of the heads 13 and 14 of the mold.

The counterbores in the parts 20 and 25 which provide space for the material of the flanges of the bobbin are formed with in- 95 wardly projecting circumferentially extending beads 26 01 substantially semicircular cross-section so that in molding the spool or bobbin there are formed in the outer surfaces of the edges of said flanges, small grooves as 100

The invention relates to improvements in magnetic bobbin and its principal objects are to provide a combined magnetic core and bobbin upon which the electrical winding may be directly -wound without the use of auxiliary ' * supports; to provide a winding hermetically sealed by an enveloping material which will not deteriorate with age or under varying climatic conditions; to provide a coil con₁₀ struction having improved copper efficiency, ^u that is to say, of low resistance with high number of turns for a given winding space; to provide a neat, rugged, efficient and economical construction, and in general, to pro₁₆ vide an improved arrangement of the character specified.

In the drawings which illustrate my invention as applied to the primary of an induction coil or transformer,

2o Fig. 1 is a perspective view of the; completed primary coil unit.

Fig. 2 is a sectional elevation showing the various parts of the mold separated from each other to illustrate the mechanical con25 struction.

Fig. 3 is a sectional elevation of the mold containing the finished spool or bobbin ready to be removed therefrom.

Fig. 4 is a perspective view of the bobbin ₃₀ molded on the core after removal from the mold shown in Fig. 3.

Fig. 5 is an axial section of the core bobbin and primary winding thereon.

• Fig. 6 is a section taken on the line 6—6 of 35 Fig. 5.

Fig. 7 is a plan view of a portion of Fig. 5, and

Fig. 8 is a sectional elevation showing the mold with the completed primary coil con40 tained therein after the final molding operation and ready to be removed from the mold.

Referring to the drawings, it will be seen that in the present instance the core 10 is composed of a bundle of round wires 11 of 45 Norway iron or other suitable highly magnetic material. In order to mold the same in a compact bundle and for another purpose which will hereinafter appear, the bundle of wires, all cut to the same length, is enclosed 50 or wrapped with a sheet of fabric 12, pref2

1,742,018 indicated at 27 in Fig. 4. These grooves are provided for a purpose which will hereinafter appear.

In order to facilitate the leading out of the 5 conductors from the winding which is to be subsequently applied to the spool or bobbin, small notches are provided in the flanges or, in the present .instance, one of the flanges of the bobbin. The outer terminal of the winding will be accommodated in a shallow slot or notch 28 at the upper edge of the flange 29, while the inner terminal is accommodated in an L-shaped notch 30. Said notches 28 and 30 are formed respectively by small pieces 31 15 and 32 inserted in the counterbore at one end of the mold.

The molding operation is effected in a wellknown manner. Preferably, a supply of the plastic material in powdered form is placed 20 in the recesses above the core before the upper half of the mold has been applied and while there is still a small space between the plate 19 of the lower half of the mold and the lower faces or edges of the core supporting 25 elements.

As the parts of the mold have been heated from a previous operation, the material commences to liquefy or become plastic very quickly and after the upper half of the mold to has been applied the mold as a whole is subjected to gradually increasing pressure so that by the time the material is completely liquefied or plasticized the parts have reached the position shown in Fig. 3 of the drawings 35 with the plastic material completely filling all the interstices of the mold cavity. As an incident to the molding operation, the material with which the core wrapping 12 is impregnated also becomes hardened and inti40 mately incorporated with the outer surface of the bundle of wires comprising the core and it also becomes autogenously united with the sleeve or shell 33 of the bobbin. After the molding operation has been completed, the « mold is opened in an obvious manner and the completed core and bobbin unit as shown in Fig. 4 is ready for the winding operation.

Before starting the application of the winding 34, the end of the latter is brought 60 out at the end of the spool. Although this may be accomplished in various ways, I have illustrated in the present instance a leading in wire 35 formed of tubular braided copper wire flattened as best shown by comparison of 65 Figs. 5 and 7. The inner end of said lead conductor 35 is connected to the end of the coil winding by slipping the bared end of the latter into the expanded end of the lead conductor 35 and preferably soldered. It will 60 be understood that tape or other suitable insulating material is applied to the splices so as to prevent improper contact with other portions of the winding.

It will be observed that the braided con65 ductor 35 is suitably bent so as to fit within the L-shaped slot or notch 30 formed in the flange 29 of the spool as previously described.

After the inner lead wire has been connected to the end of the winding and suitably insulated, the winding is completed in the customary manner and it may be observed here that it is not necessary to provide any other insulating material to prevent improper electrical contacts nor is it necessary to provide any further support for the turns of the Avinding. This is due to the fact that the ‘ heads or flanges of the bobbin are integrally united to the ends of the sleeve or shell 33 which itself is thoroughly incorporated with or united to the outer surface of the core ₈₀structure. After the required number of layers or turns has been applied, the outer end of the winding is connected to the other leading in wire 36 as in the case of the inner leading in wire 35, the conductor 36 being laid ₈₅in the notch 28 of flange 29. In order to anchor properly the end of the leading in wire 36, the insulating tape 37 is preferably inserted under the last few turns of the winding which thus hold the end of the terminal _eowire rigidly in proper position.

After the Avinding has been completed in the form shown in Figs. 5, 6, and 7, the structure is inserted in the finishing mold shown in Figi 8, the parts of this mold being construct- ₈₆ed in substantially the same manner as in the case of the first step shown in Fig. 3. However, in the finishing mold, provision is made for bringing out the leading in wires from the right hand head 38 of the mold cavity. ₁₀₀This is effected by forming apertures 39 and 40 extending in a direction parallel with the axis, the wires 35 and 36 being threaded through said apertures 39 and 40 as an incident to the assembly of the head 38 on the end _J05of the bobbin. Also, the end wall of the rectangular apertured portion 41 of the finishing mold structure is notched out as shown at 42 and 43 to accommodate the ends of said leading in wires. _no

The heads 38 and 44 are suitably recessed on their inner faces to fit the outer ends of the composite structure and the inner faces of the upper and lower mold parts 45 and 46 are suitably shaped to form a mold for the ₁₁₅shell on the outside of the winding 34. The second molding operation does not materially differ from the procedure outlined in describing the first step of the molding process.

After the completion of the second mold- ₁₂₀ing operation the outer shell or jacket 47 will be found to be intimately united to the outer edges of the heads or flanges 29 of the spool. An improved result is obtained if the grooves and flanges of the bobbin, be- 125 fore insertion in the mold, are coated with bakelite varnish or cement, thereby insuring perfect union between the new material and that previously molded. Efficiency of such union is further increased by reason of the 130

1,742,018 3 fact that the material of the second molding operation interlocks in the grooves 27 of the flanges and also by shrinkage of the outer shell 33.

₅ The completed coil structure as shown in Fig. 1 of the drawings will be found to be thoroughly sealed, permanently waterproof. The winding has a high copper efficiency because the inner shell 33 can be of compar₁₀ atively slight thickness and the flanges of the spool are rigidly enough united to said shell 33 to require no further reinforcing which might result in loss of valuable winding space. The shell 33 may be made relatively thin as ₁₅ compared with the thickness of a separately molded bobbin by reason of the fact that the shell and the bundle of core wires each contribute to support each other mutually. In this connection, it may be observed that part of the plastic material penetrates the outer layer or layers of the bundle of core wires, thus cementing the same rigidly together and in effect, increasing the effective thickness and strength of the core shell.

Furthermore, by reason of the very heavy pressure incident to the first molding operation, the bundle of core wires is very highly - compressed, in fact the pressure is so great that the wires will be found to have arranged themselves in a honeycomb or geometric pattern of minimum area so that loss of efficiency due to unnecessary air space in the core is reduced to a minimum. Also, by reason of such heavy pressure the wires of the core are so clamped together that thereafter there can be no looseness or rattling of the individual wires. This is an important consideration where the core is to be used in connection with an armature or in a location where it is subject to excessive vibration. Where the coil is to be used in connection with a secondary winding or must be inserted into a space of predetermined size, this construe-< tion is highly advantageous in view of the 45 fact that the 'surface of the coil structure is cylindrical, of accurate size and free from objectionable exterior projecting portions.

The described details of manipulation and construction being illustrative of only one ap50 plication of my invention, the scope of same should be determined by reference to the appended claims, said claims being construed as broadly as possible, consistent with the state of the art.'