US2887763A

US2887763A - Assembly molding process for electrical elements

Info

Publication number: US2887763A
Application number: US525406A
Authority: US
Inventors: Benjamin L Snavely
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-07-07
Filing date: 1955-07-29
Publication date: 1959-05-26
Anticipated expiration: 1976-05-26

Description

May 26, 1959 FlGQl. 9

B. L. SNAVELY ASSEMBLY MOLDING PROCESS FOR ELECTRICAL ELEMENTS Original Filed July 7, 1949 2 Sheets-Sheet 1 39 ,3 I, 35 2o 4 as IH ll 40 37 I3 nnuqw mum: 12 INVENTOR 4 l7 '8 22b 220 B. SNAVELY ATTRNEYS.

" y 1959 B. L. SNAVELY 2,887,763

' ASSEMBLY MOLDING PROCESS FOR ELECTRICAL ELEMENTS Original Filed July 7, 1949 2 Sheets-Sheet 2 v INVENTOR. 45 48 B. L. SN

United States Patent C) I ASSEMBLY MOLDING PROCESS FOR ELECTRICAL ELEMENTS Benjamin L, Snavely, Takoma Park, Md.

Original application July 7,' 1949, Serial No. 103,501, now Patent No. 2,745,083, dated May 8, 1958. Divided and this application July 29, 1955, Serial No.

525,406 v H i t Claims. (Cl. 29- 1ss.s

(Granted under Title 35, U.S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to assembly molding processes for electrical elements and more particularly pertainsto methods of. assembling electromagnetic transducer arrangements of thetype disclosed in my copending application Serial No. 103,501, filed July 7, 1949, now U.S. Patent No. 2,745,083, of which this is a divisional application.

More specifically, the invention is directed to methods of assembling an electromagnet within a suitable apertured supporting structure by energizing the'electromagnet so as to maintain it in a fixed predetermined position within the aperture of the supporting structure while pouring a dimensionally stable mold about the electromagnet in such a manner that the electromagnet is rigidly retained within the aperture andso encased by the-mold as to have a planar face thereof exposed'for electrica communication with an armature.

Ruggedness in construction is of particular importance in transducer devices since these devices are often handled by unskilled persons who are unaware of the delicacy of adjustment so necessary to maintain continued accuracy of these instruments. Furthermore, due to-the design of prior arrangements of devices of this character,

diificulty has been encountered in manufacturing these devices with the small tolerances that are required. Heretofore, it has been necessaryto provide shims for adjusting the air gaps of the individual units to obtain satisfactory operating characteristics.

In order to eliminate the difiiculties in the manufacture of devices of this nature and to provide devices having extremely small manufacturing tolerances, the present invention provides new methods and means of assembly and construction which will not only find application in the hydrophones described herein for purposes of illustrating the methods of the invention but which will also find general application in the construction of other types of transducers and in other kinds of electrical-instruments. Inparticular, theinvention provides novel ICC the supporting structure to fixedly support the assembly within the confines of the hollow section of the supporting structure.

-Wi-th the foregoing in mind, it is an important object ofthe present invention to provide methods of general application for mounting sensitive electrical unitswhich must be protected from shock and at the same time maintained in fixed spatial relationship with associated elements,

- Anotherobject is to provide new and improved methods ofmanufacturing sensitive electrical units which are of rugged and shock-resistant construction.

It is a further object of the invention to provide methods and means for constructing a transducer, particularly of'the hydrophone type, which will result in small manufacturing tolerances, especially in establishment of the air gap between the armature and the core and coil assembly.

. A significant object of theinvention is the provision of methods for mounting sensitive electrical components by means of a dielectric encasement for reducing eddy current effects while simultaneously maintaining the associated components in fixed spatial relationship.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detttiledldescription when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

Fig. '1 is a sectional view of one form of transducer having the sensitive electrical components thereof mounted in accordance with the teachings of the invention;

Fig.2 illustrates one method of the invention employed for supporting a core and coil assembly in the supporting structure of Fig. 1; and

Fig, 3 is a center section of another form of transducer having the-sensitive electrical elements thereof mounted in. accordance with another method of the invention.

Referring now to Fig. 1, wherein is shown a hydrophone employing the assembly teachings of the invention, the numeral 4 refers to a backing plate to which the diaphragm 5 is attached. The plate 4 is of an annular con: struction and has mounted within its centrally located aperture 35 the core and coil assembly 22. The backing plate 4'is welded to the front of a cylindrical casing 3 which houses electrical components within a water-tight methods .01": construction for accurately establishing the cally, the invention contemplates methods of magnetizing the core and coil assembly so as to rigidly maintain it in a predetermined position by magnetic traction within ahollow supporting structure while thecore and coil assemblyis beingencased within a poured cast-of plaster 9f Paris whi h, w raha d n digr siq y. tater-leeks w h chamber. 'A circular closure plate 6 seals the rear portioncf casing 3 by means of bolts 62, and a cable 9 is led into the casing 3 through a packing gland formed in a boss 8.v Intermediate backing plate 4 and closure plate 6-, a;bulkhead plate 26 is provided which divides the interior of the hydrophone into two water-tight compartments and which supports electrical components, such as condenser 33 and resistor 34, thereby protecting the electrical components in ,the front compartment from damage in case water enters the hydrophone through cable 9 and its surrounding gaskets.

' Referring now more particularly to the coil and core 22 and to the manner of .its assembly within its supporting elements, it will'be seen that the backing plate 4 is provided, with a centrally located aperture 35. A shoulder 36 is formed-within. the aperture 35, and a hollow cylindrical auxiliary supporting member 24 is provided with a flange 37 which is seated on and supported by shoulder "36. Bolts 138 secure cylindrical member24tto the backing plate 4. A pin 39, fixed to the backing plate, passes through a hole in the flange 37 and serves to dijs-. pose-the coreand coil in a predetermined angular position within. its supporting elements. The core and coil ans1. ti s.. .n n a e supported nand r wndeq by a mass of molded plastic dielectric material 25 which rigidly supports the core and coil assembly within the cylindrical member 24 and insulates it from its surrounding metallic supporting members. Preferably an annular rib 40 is formed within the cylindrical member 24 to more effectively anchor the plastic material 25.

Diaphragm 5 is made up of a central vibrating portion 14 and a peripheral annular section 13 which is thicker than the central portion 14 and which supports the diaphragm on the flat outer sealing surface of the backing plate 4. The central vibrating portion 14 of the diaphragm is slightly thickened at its outer edges, as at 15, in order to prevent the central portion 14 from breaking away from the thick supporting annulus 13 when the diaphragm is subjected to a very large deflection. A boss 16 is formed on the interior face of the diaphragm at the central portion thereof. Cemented to this boss is a disc-shaped permalloy armature 17 which is protected from damage by a Bakelite resin guard ring 18. A metal gasket 21 between the sealing surfaces of the diaphragm and the backing plate provides a watertight seal, and at the same time spaces the armature 17 and the core and coil assembly 22 a predetermined distance from each other. The assembly of the core and coil within its supporting elements forms an important feature of the invention.

The method of manufacturing this assembly, in accordance with the present invention, will now be described and may be understood more readily by reference to Fig. 2. First of all, the flat peripheral sealing surfaces of the diaphragm and the outer face of the armature 17 are simultaneously ground flat and coplanar with one another. Next, the hollow cylindrical member 24 is bolted in place on the backing plate and the sealing surfaces of the backing plate and the circular lip 41 of the cylindrical member 24 are simultaneously ground flat and so as to be coplanar. The cylindrical member 24 is then removed from the backing plate and clamped $91 to flat steel plate 42. Following this, the core and coil assembly 22 including core 22b which has its face ground perfectly flat is positioned within the cylindrical member 24 in face adjacency with the surface of the steel plate as shown in Fig. 2, and precisely centered therein by means of a jig (not shown). A current of one or two amperes is then passed through the coil 22a through leads 43, thus cifectively anchoring the core and coil in a fixed relation to the cylindrical member 24 by means of magnetic traction. Following this, the jig is removed and a suitable liquid dielectric material of a character providing dimensional stability after hardening is cast around the core and coil filling the interior of the cylindrical member 24. Before the dielectric material hardens, terminals 23 are embedded in its surface. A satisfactory dielectric material for casting around the coil and core assembly is a plaster of Paris composition having resinous strengthening binder. This casting composition has been found to have excellent dielectric properties and also to provide a mechanically rugged and shock proof support for the core and coil assembly which thereafter maintains a constant position of this assembly in the cylindrical member. It will be readily apparent that, when the dielectric mass 25 has hardened and the cylindrical member 24 is removed from the supporting surface 42, the outer surfaces of the core 22b will be coplanar with the circular lip 41. When this assembly is bolted in place on the backing plate, the peripheral sealing surfaces of the backing plate, the

circular lip 41, and the outer surfaces of the core 22b I bled on the backing plate without a gasket therebetween, the outer face of the armature would directly abut the outer face of the core 22b. An air gap of any desired size between the face of the armature and the face of the core may be established by inserting a gasket of proper thickness between the sealing surfaces of the diaphragm and the backing plate. The characteristics and elficiency of the transducer of the invention depend very heavily on the accuracy with which the air gap between the armature and the core is established. The construction described above permits this air gap to be established of any predetermined size depending on the choice of the thickness of the gasket, and with an accuracy limited only by the accuracy with which the coplanar surfaces are ground.

Referring now to Fig. 3, wherein is shown another diaphragm arrangement in a hydrophone, there is provided a diaphragm 45 having a thick peripheral portion 54 which is bolted to the fiat peripheral portion of backing plate 46. An armature 47, similar in all respects to the armature 17 described above, is afiixed to the center of the perfectly flat interior face of the diaphragm. The outer surface of the diaphragm, opposite the armature 47, is thickened as at 48. When the diaphragm is subjected to extreme deflections, the thickened center portion of the diaphragm will tend to remain flat, and this will prevent stresses between the armature and the diaphragm which might break them apart.

The backing plate 46 is provided with a centrally located aperture 49 in which a coil and core assembly 22, similar in all respects to that described above, is rigidly fixed by a mass of molded plastic dielectric 50 which supports assembly 22 and the terminals 51 in the same manner as casting 25 above. The core and coil assembly 22 is directly opposite the armature and is spaced therefrom by an air gap of predetermined size. It is to be noted that the face of the core and coil assembly is not coplanar with the peripheral sealing surfaces of the backing plate as is the case in Fig. l and there is no gasket between the backing plate of the diaphragm to establish the air gap between the armature and the core and coil assembly as in the arrangement of Fig. 1.

The method of mounting the core and coil assembly of Fig. 3 is similar to the method described in connection with the hydrophone of Fig. 1 with a slight variation in procedure in order to compensate for the recessed core and coil assembly and to establish the air gap with the desired accuracy.

In order to establish the air gap and to fixedly recess the core and coil assembly, the following procedure is followed. The diaphragm 45 with the armature 47 affixed thereto is bolted to the backing plate 46. The diaphragm and backing plate are then laid in a horizontal position with the armature 47 facing upward. A circular metallic disc of diameter just slightly smaller than the hole in the back plate and of thickness equal to the required air gap is then laid on the armature, and the core and coil assembly is placed in position against the disc. The core and coil assembly is centered with a suitable jig and held in place by magnetic traction as previously explained. A plastic dielectric is then cast around the core and coil assembly filling the aperture in the backing plate and is then allowed to harden. The diaphragm is then disassembled from the backing plate and the circular spacing disc removed. Upon reassembling the hydrophone, an air gap of the desired magnitude will have been established with great accuracy.

The advantages of the above described method and means for mounting a core and coil within its supporting members are many. The

cast dielectric material

25 and 50 which encases the coil and core assemblies in Figs. 1 and 3, respectively, prevent any displacement of the core and coil with reference to the armature or its surrounding supporting members. The core and coil of Fig. 1 is held in strict coplanar relationship with the sealing/surfaces of the backing plate and therefore is held'strictly parallel to the armature. In Fig. 3, the core and coil are recessed within the backing plate a distance equal to the desired air gap. The dielectric material in addition prevents the flow of eddy currents which might be set up in the surrounding metallic, supporting elements."v In a simple and rapid manner the core and coil is accurately centered within the member 24 and the outer surface of the core aligned in perfect coplanar relationship with the annular lip 41 in the arrangement of Fig. l and perfectly recessed in the arrangement of Fig; 3. While the

dielectric composition

25 and 50 are cast orotherwise formed around the corel-and coil and within the cylindrical member 24 and backing plate 46, respectively, the core and coil is rigidly held in this predetermined position by means of magnetic traction. Thus there is no possibility of displacement of the core and coil assembly while plastic material is formed, around it. The foregoing construction and method of assembly of th'ecore and coil element within its supporting membersmay obviously be applied to the construction and assemblyof any desired type of transducer element where high accuracy and ruggedness of construction are particularly desirable. t

J Obviously many modifications and variations of the presentinvention are possible in the light of the above teachings. ,It is therefore to be understood that within the. scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured, by Letters Patent of the United States is:

l. The method of mounting a magnetizable electrical assembly in a predetermined position within the concavity of a supporting member, said electrical assmebly including an electrically conductive path terminated by a pair of terminal elements: said method comprising the steps of supporting said member on a planar magnetizable surface, positioning said assembly within the concavity of said member in said predetermined position and supported in said position by said magnetic surface, magnetizing said assembly by applying electrical potential across said pair of terminal elements to pass current through said conductive path whereby said assembly is retained in said predetermined position within said concavity by magnetic traction with said magnetizable surface, pouring a hardenable fluid mixture of plastic material into said concavity and around said assembly, whereby said assembly is fixedly supported within said concavity uponvhardening of said plastic material, and embedding a portion, of each. of said terminal "elements in said plastic material prior .to the hardening thereof. 2. The method of mounting a magnetizable electrical assembly in a predetermined position within a supporting member .having .an aperture in a flat face thereof,,.said electrical assembly including an electrically conductive path terminated by a pair of terminal elements: said method comprising the steps of supporting said flat face in face-adjacency on a flat magnetizable surface, positioning said assembly within the aperture in said member in said predetermined position and in abutting faceadjacency to said flat magnetizable surface, magnetizing said assembly by applying electrical potential 'cross said pair of terminal elements to pass current through said conductive path whereby said assembly is held in said predetermined position by magnetic traction with said magnetizable surface, pouring a hardenable fluid dielectric into said aperture and around said assembly, whereby said assembly is insulatably supported in said apertured member upon hardening of said dielectric, and embedding a portion of each of said terminal elements in said dielectric material prior to the hardening thereof. 3. The method of mounting a magnetizable electrical assembly in a predetermined position within a supporting member having an aperture in a flat face thereof, said electrical assembly including an electrically conductive sembly is held in said predetermined position by magnetic traction with said spacing member pouring a hardenable'fiuid mixture of dielectric material into said aperture and around said 'assembly,*whereby said assembly is rigidly supported in and insulated from said apertured member upon hardening of said material and embedding a portion of each of said terminal elements in said dielectric material prior to the hardening thereof.

4. The method of mounting a magnetizable electrical assembly in a predetermined position within a supporting member havingwan; aperture in a flat face thereof and simultaneouslyv establishing an air gap between said assembly and an armature. coacting therewith, said electrical assembly including an electrically conductive path terminated by a pair of terminal elements: said method comprising the steps of detachably mounting said flat face in abutting face adjacency on the fiat portion of a supporting framework having said armature affixed thereto and positioned thereon to extend Within said aperture, placing a flat magnetizable spacing member on said arma: ture, supporting a flat surface of said assembly on said flat spacing member in face-adjacency therewith, magnetizing said assembly by applying an electrical potential across said terminal elements to pass current through said conductive path whereby said assembly is held in said predetermined position by magnetic tractionwith said spacing member, pouring a hardenable slurry of dielectric material into said aperture and around said assembly, embedding a portion of each of said terminal elements in said slurry, permitting said slurry to harden, separating said supporting member from said supporting framework, removing said flat spacing member, and securely' remounting said supporting member on said frame,- work whereby said assembly is supported in and insulated from said supporting member and spaced a predetermined distance from saidarrnature in accordance with the thickness of said flat spacing member.

5. The method of mounting a magnetizable electrical assembly in a predetermined position within the con? cavity of a supporting structure, said electrical assembly including an electrically conductive path terminated by a pair. of terminal elements: said method comprising the steps of supporting said assembly within said concavity and in said predetermined position by means of:a magnetizablemember, magnetizing said assembly by applying an electrical potential across said terminals to pass current through said conductive path whereby said assembly is held in said predetermined position within said concavity by magnetic traction with said magnetizable member, casting a hardenable fluid plastic mixture around said assembly, whereby said assembly is fixedly supported within said concavity upon hardening of said mixture and embedding a portion of each of said terminal elements in said mixture prior to the hardening thereof.

6. A casting method of rigidly and insulatably encasing a magnetizable electrical unit within a hollow housing structure, said unit including an electrically conductive path terminated by a pair of terminal elements: said method comprising the steps of assembling the housing structure on a supporting assembly of which at least a portion thereof is magnetizable, supporting the electrical unit within the hollow housing structure by means of said assembly and positioned in abutting relation with 7 the magnetizable portion thereof, applying an electrical potential across said pair of terminals to pass electric current through said conductive path thereby to magnetically anchor the electrical unit on the magnetizable portion of said assembly, casting a hardenable liquid dielectric within said housing structure and around said electrical unit whereby said unit is rigidly and insulatably retained by said housing structure upon hardening of said dielectric, and embedding a portion of each of said terminals in said dielectric prior to the hardening thereof.

7. The method of mounting a magnetizable electrical unit in a predetermined position within a supporting member having a reference face of predetermined configuration with a bore entering said face and extending at least part way into said supporting member, an irregular concavity forming a portion of said bore, and said electrical unit including an electrically conductive path terminated by a pair of terminal elements: said method comprising the steps of assembling said supporting member on a structural assembly with said reference face in abutting engagement with a similarly configured face of said structural assembly of which'at least a portion is magnetizable, supporting the electrical unit in said predetermined position within said irregular concavity by means of said magnetizable portion of said structural assembly, applying electrical potential across said pair of terminals to pass electric current through said conductive path thereby to magnetically anchor the electrical unit on the magnetizable portion of said assembly, filling said concavity with a hardenable liquid material of a character providing dimensional stability after hardening, embedding a portion of each of said terminal elements in said material, and allowing said material to harden whereby the irregularities of said concavity rigidly interlock said hardened material to thereby fixedly support said electrical unit within said concavity in said predetermined position with said terminal elements having exposed portions for electrical connection.

8. In the method of claim 7, the hardening step being promoted by the utilization of a slurry of plaster of Paris as the hardenable liquid material.

9. The method of rigidly mounting an electromagnet formed by a core with a coil terminated by a pair of terminal elements, in a predetermined position within a casing having a reference face of predetermined configuration with a bore entering said face and extending at least part way into said casing, an irregular concavity forming a portion of said bore, comprising the steps of supporting said casing on a magnetizable member with said reference face resting on a similarly configured face of said member, positioning the electromagnet within said concavity with a face of the electromagnet resting on a similarly configured face of said member, magnetizing said electromagnet by applying an electrical potential across said terminals to pass current through said coil whereby said electromagnet is securely retained within 0 said concavity by magnetic traction with said member, filling said concavity with a quick-drying liquid dielectric of a character providing dimensional stability after hardening, embedding a portion of each of said terminal elements in said dielectric, and allowing said liquid dielectric to dry and harde'n whereby the irregularities of said concavity rigidly interlock said hardened material to thereby fixedly support said electromagnet within said concavity with said terminal elements having exposed portions for electrical connection.

10. The method of rigidly mounting an electromagnet formed by a core with a coil terminating in a pair of terminal elements, in a predetermined position within a casing having a reference face of predetermined configuration with a bore entering said face and extending at least part way into said casing, an irregular concavity forming a portion of said bore, and simultaneously establishing an air gap between said electromagnet and an armature operatively associated therewith comprising the steps of detachably assembling said reference face of said casing on a similarly configured face of a supporting framework having said armature affixed thereto and positioned to extend into said concavity, placing a flat magnetizable spacing member on said armature, supporting a flat surface of said electromagnet on said spacing member in said predetermined position within said concavity, magnetizing said electromagnet by applying electrical potential across said pair of terminals to pass current through said coil to thereby retain said electromagnet in said predetermined position by magnetic traction with said spacing member, filling said concavity with a hardenable slurry of dielectric material, embedding a portion of each of said terminal elements in said slurry, allowing said materials to harden wherebythe irregularities of said concavity rigidly interlock said hardened material to thereby fixedly support said electromagnet in said predetermined position within said concavity, disassemblying said casing and supporting framework, removing said spacing member, and securely reassembling said casing and framework whereby said electromagnet is supported in and insulated from said casing and spaced a predetermined distance from said armature in accordance with the thickness of said spacing member.

References Cited in the file of this patent UNITED STATES PATENTS