Title:
Electrical method of mechanically connecting and mutually insulating spaced metal elements
United States Patent 2419149


Abstract:
2 Claims. (Cl. 219-10) 1 2 This invention relates to a method of making insulated structures and more particularly an improved structure incorporating spaced substantially parallel conductive plates or sheets connected by insulating spacers. Various structures involve the use of spaced parallel...



Inventors:
Erwin, Lodwig
Application Number:
US51673144A
Publication Date:
04/15/1947
Filing Date:
01/01/1944
Assignee:
MOBILE REFRIGERATION INC
Primary Class:
Other Classes:
52/404.1, 337/168, 337/221, 337/232, 337/296
International Classes:
H01J5/28
View Patent Images:
US Patent References:
2140709Constructional element1938-12-20
2111749Electric protective device1938-03-22
1278911N/A1918-09-17



Description:

2 Claims. (Cl. 219-10) 1 2 This invention relates to a method of making insulated structures and more particularly an improved structure incorporating spaced substantially parallel conductive plates or sheets connected by insulating spacers.

Various structures involve the use of spaced parallel sheets or plates of metal or other conductive material with air spaces therebetween.

For example, heat insulated walls or panels for refrigerated or heated enclosures such as rooms, 10 compartments and vehicle bodies have been made of thin steel sheets suitably coated or finished ,to reflect radiant heat energy and spaced apart to form dead air spaces therebetween. Certain electrical condensers are also formed of spaced parallel conducting plates with the air therebetween acting as the dielectric. In these and like structures, it is essential that the adjacent conductive sheets be mechanically connected by suitable means at many points in order to strengthen the structure, to prevent vibration or contact of the plates and for other reasons. It is, however, essential that the connections used be non-conducting so that the plates remain thermally or electrically isolated or both. In all structures of the type described and particularly those comprising relatively closely spaced sheets of considerable area, it is difficult if not impossible by previously known means and methods to permanently secure insulating mechanical connectors between the substantially inaccessible portions of the sheets remote from their edges. This difficulty is aggravated when such connectors are to be simultaneously secured between three or four spaced parallel sheets.

spacWith the above and other considerations in With the above and other considerations in mind, it is proposed in accordance with the present invention to provide a multiple conductive sheet structure of the type described in which the adjacent sheets are permanently mechanical- 40 ly connected in spaced substantially parallel relation by insulating supports or connectors. A particular object of the invention is the provision of an improved method of permanently mechanically connecting metallic plates or sheets in spaced relation while maintaining them trically and thermally isolated. Various other objects, advantages and characteristic features of the invention will be apparent from the following description.

In describing the invention in detail, reference will be made to the accompanying drawing which illustrates certain embodiments thereof. In the drawings: Fig. 1 is a simplified and diagrammatic elevation, taken edgewise of the plates, and showing a connector embodlying the invention in position to' be welded between two metallic plates in accordance with the invention; Fig. 2 is an elevation similar to Fig. 1 showing the connector and plates after the welding operation is completed; Fig. is a elevation of an insulating connector of the type shown in Figs. 1 and 2; Fig. 4 is a side elevation of one of a plurality of sheets interconnected in accordance with the invention; Fig. 5 is an edge view of three sheets connected in accordance with the invention; Figs. 6 and 7 are respectively sectional elevations of two modified forms of my improved insulating connector; and, Figs. 8, 9 and 10 are respectively elevations illustrating three different types of current sepal :rable links used in connection with connectors embodying the invention.

In general, the objects of the invention are carried out by means including a connector formed of material that is relatively non-conh0 ductive of heat or electricity or both and which has secured thereto oppositely disposed end pieces or caps of weldable conductive metal. The metal caps are electrically connected by a conductive link which is capable of carrying a heavy electric current of such magnitude and for a sufficient time interval to weld the caps to metal plates or other parts but which is fusible or otherwise separable in response to the flow of such current for a longer time interval, or in response to a heavier current. Conductive links of this nature will be hereinafter referred to generically as current separable links, this term embracing both links of the nature of conventional slow blowing fuse links that are fusible by heat generated by the passage of current therethrough and links of the type employed in therovroa d cutouts that are separable by heat mal overload cutouts that are separable by heat generated by the flow of current through an eement other than the link itself.

The connectdr C shown in Figs. 1, 2 and 3 has a body Ii formed of r olded thermal and electrical insulating material. This material may comprise a thermoplastic or thermosetting resin including the knorw resinous materials such as phenol 45 formaldehyde and urea formaldehyde resins, hard elec- rubber, or insulating compounds of the nature of hard rubber such as are available on the market and known in the electricalart. End caps 12 of iron, steel or other weldable metal are perma50 nently secured to the opposite ends of the insulating body i in any suitable manner as b inwardly crimping the edges 13 of the cap flanges if so that they are imbedded in the material forming the body I u . The end faces of the caps 55 may be provided with one or more raised points or lugs 15 which provide contact points of limited area for spot welding, although the provision of these points is not essential to the invention.

In orderi to form a circuit for the flow of weld60 ing current, a current separable link 16 is connected between the two end caps 12. In the embodiment shown in Figs. 1, 2 and 3, the link IG is a slow blowing fusible link of a type well known in the art. The opposite ends of the link 16 are suitably permanently secured to the flanges 14 of the respective caps 12 by means such as brazing, soldering, welding or the like, and the link is preferably disposed in spaced relation to the body II of the connector, as shown in Fig. 1. The link !2 may be formed of a suitable known fuse I metal such as lead or lead alloys, zinc or zinc alloys, Moneli metal, copper or aluminum. Its minimum cross section is such that it will melt and "blow" or open after currents sufficient to weld the end caps 12 to adjacent metal elements I has flowed therethrough for a time interval somewhat greater than that required to form such welds. Known slow blowing fuse links of appropriate current capacity are suitable for this purpose. In general, such links are formed of fusible 2 metal of considerable mass so that an appreciable time interval is required for current flow therethrough to heat the link to a melting temperature.

In accordance with the known practice, the link I may be provided with spaced reduced sections 2 as shown in Fig. 3 which insure a positive and wide separation of the fused ends thereof.

My improved method of mechanically connecting while thermally and electrically isolating spaced parallel plates or sheets of conducting 3 material will now be described. As shown in Fig. 1, a connector C of the type described is placedc between the wo adacent plates P and P. These plates may be closely spaced substantially parallel thin steel plates of the type having surfaces or surface coatings that reflect a high percentage of the heat rays incident thereon. The invention is of course not limited to the use of this material but embraces the connection of any weldable conductive plates including various structural panels and the plates of electrical condensers.

Two welding electrodes 13 and 19 are brought in contact with the outer surfaces of the plates Pi and PF respectively at points aligned with the ends of the connector C as shown. The structure comprising the plates and the interposed connector is preferably compressively gripped between the electrodes 18 and 18. This has been illustrated by the compressed spring 20 interposed between a fixed support 21 and the electrode !., and insulated from the electrode by the block 21 of insulating material. The other electrode 19I may be held by any suitable fixed insulated support 23. Obviously, other means may be used to clamp the structure between the electrodes. With the electrodes thus disposed, a welding current is caused to flow between them. Such current may be supplied in accordance with known practice from the secondary winding 24' of a welding transformer T, the winding being connected to the electrodes 18 and !0 by heavy low resistance cables 25 and 26. The secondary winding 24 may comprise one or two turns of heavy low resistance wire or cable. The primary winding 27 of the transformer T is energized from a suitable source of alternating current indicated at 28 through a switch 29. If necessary or desirable, a series resistor 30 may be included in the supply circuit of the primary winding 27 and a push button switch 31 may be employed to shunt out the resistor ?0 when it is desired to momentarily increase the current output of the tranformer T for a purpose to be described.

Closure of the switch 29 causes heavy current flow through the welding circuit including the secondary winding 24, the cables 25 and 26, the electrodes 18 and 19, the plates Pi and P2, the lugs 15, the caps 12 and the link 16. The points of highest resistance in this circuit are those at which the caps 12 contact the plates Pi and P2, and the temperature at the contacting surfaces quickly rises to a point where the metal of these parts softens and unites, this action being promoted by the pressure exerted by the electrodes .0 on the composite structure. The time interval required to complete the welds is very short, particularly where the velds are of the nature of spot welds due to the raised points or lugs 15 on the connector caps 12. Completion of the welds 5 reduces the resistance of the welding circuit at the points of juncture between the cans 12 and the plates Pi and P2, and this ordinarily results in an increase in current after the welds are made. Immediately after the welds are made, 0 the link 16 blows as shown in Fig. 2. The delay in blowi te ing of the link until after the welds are made results from the above explained slow blowing characteristic of the link, and rapid blowing after completion of the weld may be caused or 5 expedited by the automatic current increase noted above. If it is necessary or desirable to further expedite blowing of the link after the welds are made, the push button shunt switch 31 may be momentarily closed to increase the 0 current through the link.

The blowing cf the link 16 thermally and electrically isolates the connector caps 12, and the disclosed operation thus both mechanically unites the plates and isolates them thermally and electrically. Where electrical insulation alone is desired, the body I of the connector C may be formed of heat conductive- insulating material such as porcelain. glass or the like.

The above described operation may be repeated as desired to secure any number of suitably spaced connectors C bettwen the plates Pi and P2 as generally stra illutrate in ig. 4. The operation may also be employed to simultaneously unite three spaced parallel plates or like members in which case one connector C is disposed between each adjacent pair of plates and the electrodes 18' and !9' are pressed a.ainst the outer surfaces of the outer plates in alignment with the aligned connectors as illustrated in Fig. 5.

The weldable metal end pieces of rmy improved connector may be formed and secured to the insulating body portiion thereof in various ways.

As shown in Fig. 6, weldable metal end pieces 35 having integral locking extensions 36 on the inner faces thereof may be secured to the oppositely disposed surfaces of the insulating body I i' by molding the insulating material about the extensions 36 as shown. A-current separable link such as a fusible link sO' is connected between the end pieces 35 and fuses and onens in the manner described above after welds between the pieces 35 and adjacent metal elements are made.

The current separable link may be enclosed within the insulating body of the connector and one such arrangement is illustrated in Fig. 7. As there shown, a central opening or bore 37 ex. tends through the insulating body 38 between the locking extensions 36' of the two weldable metal end pieces 35'. The current separable link, here shown as a f.sible link 40, is secured at its ends to the locking extensions ?6' and passes through the opening 37. A small lateral vent opening 39 may be provided to permit the escape from the passage 37 of the gases generated when the link blows. The passage 37 may be centrally enlarged as shown so that any portions of the link 40 that may remain unconsumed after it blows cannot form a conductive path between end pieces 35'.

In place of fusible links, I may employ other forms of current separable links or connections to electrically connect the weldable end pieces or caps of my improved connector during the welding operation. One such form is generally similar to the separable connections employed in overload thermal cutouts known in the art. The general arrangement includes a spring biased conductive link secured in current conducting connection between the end pieces by means including a metal or alloy that fuses or melts when heated to a predetermined temperature from some source other than the current passing therethrough, and when so fused or melted releases the spring biased link which then opens the connectione such alternative form of current separa- 2( ble link is illustrated in Fig. 8 where the connector C' is of the same general structure as that disclosed in Figs. 1, 2 and 3 and described above.

Here a link strip 41 formed of low resistance resilient metal such as high brass, spring steel 2 or the like is welded or otherwise fixed at one end to one end cap 42 of the connector C' and is bent in U-formation as shown so that its other end 43 is adjacent the opposite end cap 44. The material forming the link 41 is sufficiently resilient so that it will spring from the bent position shown in full lines to that shown in dotted lines in Fig. 8 unless its end 43 is fixed to the cap 44. A plate 45 of low resistance metal such as copper may be welded or otherwise fixed to the cap 44 to form a seat at which the link end 43 may be secured. The link end 43 is fixed to the plate 45 by a thin layer 46 of low resistance low melting point metal or alloy. When welding current passes between the plates Pi' and P2', considerable heat is quickly generated at the end face of the cap 44 where the weld is formed, and this heat is conducted through the plate 45 to the metal layer 46 during the time interval required to complete the weld. When sufficient heat has been thus conducted to raise the temperature of the layer 46 to its melting or fusing point, the end 43 is released and the strip 41 springs away from the cap 44 to approximately the position shown in broken lines in Fig. 8, thus opening the electrical and thermal connection between the end caps 42 and 44.

As illustrated in Fig. 9, two spring strips 47 and 48 may be employed, each being fixed at one end to one of the weldable end caps 49 and 50, and being spring biased to move to the open positions illustrated by broken lines. The strips 47 and 48 are connected by a layer 51 of low resistance low melting point metal or alloy.

When the welds between adjacent plates and the end caps 52 and 53 of the connector C" are made, heat from the welds travels along the strips 47 and 48 to the fusible layer 51 and melts or fuses this layer, releasing the strips and so opening the link.

In the modification of Fig. 10, a heating unit in the form of a small grid or coil 54 of resistance wire is employed to furnish heat which melts the metal or alloy layer 55 that secures the free end of the outwardly biased spring strip 56 in the closed position shown. One end of the grid 54 is welded or otherwise fixed in electrical coritact with the end cap 58 of the connector C"' and the other end thereof bears the layer 55 which secures and electrically connects the free end of the spring strip 56 in place. Upon the flow of welding current between the end caps 59 and 58, heat is generated in the grid 54 by the flow of this current therethrough, and after a time interval sufficient to complete the welds between the caps and the adjacent plates or other metal parts, the heat so generated raises the temperature of the layer 55 to the melting or fusing point thereof and the strip 56 springs open.

The heating grid or coil 54 may be readily modified by changes in its dimensions or composition or both to provide a heating interval sufficient to permit completion of the welds before the link separates.

The metals or alloys employed to form the layers 46, 51 and 55 of the modifications disclosed Sin Figs. 8, 9 and 10 may comprise any metals or alloys of sufficient conductivity to carry the welding current without melting due to current flow through the layers themselves and of sufficient- ly low melting point to fuse and release the spring link or links at the temperature at which the layers are heated by heat from the weld or from the heating unit shortly after the welds are made. Suitable low fusing alloys of this nature 0are well known in the electrical art and are used 0for example in overload thermal cutouts.

I claim: 1. A method of mechanically connecting and mutually insulating a pair of spaced conductive metal elements which comprises interposing between the said elements a connector of electrical insulating material having spaced metal end pieces thereon respectively contacting said elements and a current separable link electrically 40 connecting said end pieces, passing an electric current between said elements whereby said end pieces are respectively welded to said respective elements and passing additional current between said elements to open said current separable link :. after said end pieces are welded to said elements.

2. A method of mechanically connecting and mutually insulating a pair of spaced substantially parallel metal plates which comprises interposing between the adjacent surfaces of said plates -, a connector of electrical insulating material having spaced metal plate engaging end pieces electrically connected by a current separable link, passing electrical energy between the outer surfaces of said plates adjacent said connector where-, by said end pieces are respectively welded to said adjacent plate surfaces by energy flowing through said link, and then passing additional energy between the outer surfaces of said plates to open said current separable link.

60 ERWIN LODWIG.

REFERENCES CITED The following references are of record in the file of this patent: 65 UNITED STATES PATENTS Number 2,111,749 1,278,911 2,140,709 Name Date Bussmann -------- Mar. 22, 1938 Griffith ----------- Sept. 17, 1918 Mauser ----------- Dec. 20, 1938