US2645693A - Molded casing for electrical apparatus - Google Patents

Description

y 1953 T. M. COLE ET AL MOLDED CASING FOR ELECTRICAL. APPARATUS Filed Sept. 15, 1949 IN VEN TOR. THOMAS M COLL a PA UL M. CHR/STf/VSE/V Patented July 14, 1953 MOLDED CASING FOR ELECTRICAL APPARATUS Thomas M. Cole, New York, N. Y., and Paul M. Christensen, West Orange, N. J., assignors' to Federal Electric Products Company, Newark,

N. J a corporation Application September 13, 1949, Serial'No. 115,334

2' Claims. 1

The present invention relates to casings for electrical devices, especially molded insulation casings for automatic circuit breakers and switches. A circuit breaker and its casing, of the type shown by the patent to H. A. Humpage, No. 2,459,427, are represented on the accompanying drawings, primarily because the present invention was developed for such circuit breakers, and also for convenience in describing the invention. It will-be understood, however, that while the invention is particularly applicable to circuit breaker casings of the type referred to, it is not necessarily so limited as concerns its broader aspects.

In thefabrication of casings for circuit breakers or other electrical devices in which arcing occurs or which are provided with are chutes, as in the cited patent for example, for arcs which may be formed when a movable contact is separated from a stationary contact, the general practice, at present, is to use a general purpose resin, such as Bakelite, from which to mold the casing, and in the areas affected by the arc, the casing is provided with liners or other surface coverings of arc-resisting insulation material. While arc-resisting molding compounds are available, they are considerably more expensive than the general purpose molding compounds, and, therefore, it is rather expensive to make the casing entirely from such special purpose molding compounds.

A primary object of the present invention, therefore, is to provide a molded insulation casing which is well adapted to resist the effect of arcs in the region of the casing normally aifected thereby and to accomplish this result without molding the casing entirely of the more expensive arc-resistant insulation material and without requiring the provision of liners or other arc-resistant coverings in the casing.

A further object is the provision of an improved and inexpensive molded casing for an electric circuit breaker, or the like, with an arc-chute or passage molded of arc-resistant insulation material and formed as an integral part of the casing which may be molded mainly of less expensive insulation material.

The above and other objects, features and advantages of the present invention will be fully understood from the following description considered in connection with the accompanying illustrative drawings.

In the drawings:

Fig. 1 is a side view of the inner surface ofone part of a casing for an electric circuit breaker;

Fig. 2 1s a sectional view of the complete casing, taken on the line 2--2 of Fig. 1;

Fig. 2A is a view similar to Fig. 2 and showing another form of the invention;

Fig. 3 is a view similar to Fig. 1 showing the circuit breaker mechanism positioned in the housing;

Fig. 4 is an end View of the complete casing with the circuit breaker mechanism positioned therein; a

Fig. 5 is a view similar to Fig. 2 showing a casing of another form; and

Fig. 6 is a view of a mold illustrative of the method employed in moldin the housing.

Referring to Figs..1 through 4. in detail, the

automatic circuit breaker Ill is, as hereinbefore indicated, of the general type disclosed in the above cited patent to H. A. Humpage. Said circuit breaker has a two part insulation casing or housing I2 formed of two identical or symmetrical casing parts 14, each of said parts being formed of insulation material by a molding operation. In this form oi the casing, each part l4 forms one-half of the housing, each part having a recess It for the mechanism, and the twocasing parts being secured in housing defining relation in any suitable way. Each casing part I4 is provided at one of its ends with an open recessed portion I8 in which a terminal member and the stationary contact of the circuit breaker unit is positioned. An arcing chamber or chute is formed in the ends of the casing parts below said recessed portion It in the companion casing parts M as indicated at 20 in Figs. 2 and 4. The front of each casing is provided with recessed portions which define opening 22 through which the handle 24 projects for manual operation of the circuit breaker mechanism.

lhe circuit breaker mechanism in addition to the manually operable member 24, includes a movable contact member 26 mounted in the chamber 6 for pivotal movement. Said movable contact member is provided at one end thereof with a-contact 28 which is engageable with and disengageable from a companion stationary contact 30 carried by a terminal member 32 of any suitable type. A thermal-current responsive member 34 which, as here shown, consists of a thermostatic bi-metallic flexible strip, is welded or otherwise secured at one end thereof to a side.

edge of movable contact member 26. The free endof lei-metallic strip 34 is arranged to releasably engage the end of one arm of a lever 36 pivotally mounted on the end of movable contact member 26 opposite the end which carries the contact 28. The other arm of lever 36 is connected to the handle 24 by a resilient link 38. A coil spring 4& is operatively interposed between the movable contact member 26 and the handle 24 for biasing the movable contact member to its open position. A flexible metallic conductor or connector 42 is connected to the thermal element as and to a companion terminal member 44. Said thermal element is operable not only in response to the heating eiTect of the current passing therethrough but is also operable under the control of an electromagnetic member 46 mounted thereon, near the free end thereof, and a companion rigid armature 48 is fixed to the fixed end of thermal member 34. The manner of operation of the circuit breaker mechanism and its various components, is fully described in the above mentioned patent.

As i well understood, arcs are ordinarily formed within casing 12 when the movable contact 28 is separated from its companion stationary contact 38, and said arcs will play against the surfaces of the arc chamber or chute 20 and portions of the housing adjacent to the inner end of said chamber, i. e., in the region of contacts 28 and. 3B.

In accordance with the present invention, the casing I2 is, or ma be, molded mainly or in large part of inexpensive material such a Bakelite which is a suitable general purpose phenolic molding compound. In order, however, that the arcing action may be properly resisted by those casing portions which are in the arc-region, casing 52 is molded, in said region thereof, from a special arc-resisting molding compound such as, for example and not by way of limitation, a melamine-formaldehyde condensation product, or other molding compounds having similar arcresisting qualities or use characteristics. Examples of commercial products having arc-resisting characteristics are those produced by the Monsanto Chemical Company under the trade names Resimene 803A and Melmac 1500. Preferably, the arc-resisting material need only be a thin layer or lining 53 on the inside of walls 52 of the are chamber and on the adjacent casing surfaces against which the arcs play, as illustrated in Fig. 2. However, if desired, substantially the entire thickness of the arc-chamber region of the casing and said adjacent wall portions of the casing may be formed of said arcresisting material, as illustrated at 5 3 in Fig. 2A. In either case, the arc-resisting material is calized preferably only in those portions of the housing that are subjected to the action of the arc, the balance of the housing being formed, as hereinbefore stated, of a less expensive material which is not so highly arc-resistant.

It will be noted, as illustrated in Figs. 1, 2 and 2A, that the separate molding compounds are intermolded at their juncture J and are integrally united into the single mass which forms each casing part l4. It will be understood that each casing part M is provided with the individual use characteristics or qualities associated with each of the separate compounds, said use characteristics being retained by the separate compouncs after the intermolding thereof and being available in those portions of the casing part wherein the associated compound is localized. Specifically, the casing will have superior arcresisting characteristics in their portions 50, 54 containing the arc-resisting compound.

The casing 12A illustrated in Fig. 5 represents the presently preferred form of our invention.

It differs from the casing l2 in that the companion complementary parts [4A and [4B thereof are not symmetrical halves in the manner of the parts [4. Casing part MA is similar to part id is of greater depth than the latter in order to contain the complete circuit breaker apparatus illustrated in Fig. 3. Casing part 14A constitutes the body portion of easing 12A, and casing part [4B constitutes the complementary cover or closure member for said casing. Casing [2A is provided with the arc chamber 28A which is similar to are chamber 20. It will be understood that the arc-resisting material may be provided only as a layer on the inner surfaces of casing EZA in the vicinity of the arcs, as at 59A, or it may form the entire thickness of the arc chamber region and adjacent wall portions of the casing in the same manner as wall portions 54 in Fig. 2A.

A method of producing a housing formed of both a general purpose molding compound and an arc-resisting molding compound is illustrated schematically in Fig. 6. As there shown, there is provided a mold 56 for forming a casing part 14. Said mold is provided with a cavity 58 of the required casing shape. A disk or pellet of the general purpose molding compound, indicated in phantom at E0, is positioned in the cavity 58, and a smaller disk or pellet of the arc-resisting molding compound, indicated in phantom at 62, is positioned on top of pellet 80, both pellets being disposed the part of the mold cavity 58 where the arc-resistant layer 50 or arc-resistant portion of easing I4 is to be formed. Pressure is then applied against both pellets, for example a mold plunger may be forced against said pellets, and, as a result, the pellets are intermolded and the casing I4 is formed having the layer 50 or the portion 54 in the region where the arcing occurs. It will be apparent that whether only the layer 50 or the complete wall portion 54 is formed of the arc-resisting compound will depend upon the relative quantities of each of the separate compounds in the mold.

While we have illustrated and described our invention in connection with casings provided with are chamber, it will be understood that it i not limited thereto and that the arc-resistant material can be used in any casing where arcing occurs.

While we have shown and described the preferred embodiment of our invention, it will be understood that the latter may be embodied otherwise than as herein specifically illustrated or described, and that in the illustrated embodiment certain changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principles of the invention within the scope of the appended claims.

l-laving thus described our invention, what we claim and desire to secure by Letters Patent, is:

1. In a circuit breaker having mechanism including companion relatively movable contacts, actuating means for operatively efiecting the engagement thereof and means for effecting the disengagement thereof in response to predetermined current in the circuit; a casing for enclos ing said mechanism, said casing comprising panion complementary parts mutually secured in housing-defining relation for enclosing said mechanism, a separate casing portion defined by said companion complementary parts in the region adjacent said contacts, said separate casing portion defining an arc chute within said casing and being in integral relation with said compileseparate casing portion to resist the arcing of said contacts.

2. Ina circuit breaker having mechanism. including companion relatively movable contacts, actuating means for operatively effecting the engagement thereof and means for effecting the disengagement thereof in response to predetermined current in the circuit; a casing for enclosing said mechanism, said casing comprising companion complementary parts mutually secured in housing-defining relation for enclosing said mechanism, a separate casing portion defined by said companion complementary parts in the region adjacent said contacts, said separate casing portion defining an arc chute within said casing and being in integral relation with said complementary parts, each of the latter being formed of two insulation materials in integral relation, one of said materials having a higher arc-resistant characteristic than the other of said materials, said one material being formed in said separate casing portion to resist the arcing of said contacts, said one material being formed as an inner lining layer on said other material.

THOMAS M. COLE. PAUL M. CHRISTENSEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 777,653 Foster Dec. 13, 1904 1,346,877 Burroughs July 20, 1920 1,431,961 Kempton Oct. 17, 1922 1,593,525 Copeland July 20, 1926 1,599,085 Gibson Sept. 7, 1926 1,709,648 Aalborg Apr. 16, 1929 2,005,684 Sachs June 18, 1935 2,089,050 Burmeister Aug. 3, 1937 2,240,007 Power Apr. 29, 1941 2,240,654 Jochem et al May 6, 1941 2,270,723 Boehne Jan. 20, 1942 2,352,517 Christensen June 27, 1944 2,416,266 Landmeier Feb. 18, 1947 2,439,929 Hill et a1 Apr. 20, 1948 2,474,676 Kelly June 28, 1949 2,551,822 Bingenheimer et a1. May 8, 1951 FOREIGN PATENTS Number Country Date 610,562 Great Britain Feb. 19, 1947

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