US3539972A - Electrical connector for high voltage electrical systems - Google Patents

Description

NOV. 10y 1970 TE ETAL ELECTRICAL CONNECTOR FOR HIGH VDLTAGE ELECTRICAL SYSTEMS Filed "33', 21", 1958 3 Sheets-Sheet 1 ynaNNshgi xx 1 V/muvaroll INVENTORS ROBERT C. RUET'E RUDOLPH P. ALDIGHIERI FRANK A. SILVA ELECTRICAL CONNECTOR FOR HIGH VOLTAGE ELECTRICAL. SYSTEMS F1196 flay 3L. 1968 3 Sheets-Sheet 2 INVENTORS ROBERT C. RUETE RUDOLPH P ALDIGHIER! FRANK A. SILVA wlolld,

THEIR ATTORNEY NOV. 10, 1970 U -r5 EI'AL. 3539,72

ELECTRICAL CONNECTOR FOR HIGH VOLTAGE ELECTRICAL SYSTEMS Filed May 21 1968 5 Sheets-Sheet 5 l 238 FT zsz 244- I I a 240 242 242 27a- I -239 I -27s 23s I I 234 ,274

l am I 3 l' l i IT I I 39 268- I I I I I I \I I I l I INVENTORS 64 ROBERT c. RUETE RUDOLPH P ALDIGHIERI I FRANK A. SILVA THEIR ATTORNEYS United States Patent Ofice 3,539,972 Patented Nov. 10, 1970 3,539,972 ELECTRICAL CONNECTOR FOR HIGH VOLTAGE ELECTRICAL SYSTEMS Robert Ruete and Rudolph P. Aldighieri, Long Valley, and Frank A. Silva, Basking Ridge, N.J., assignors, by mesne assignments, to Amerace Esna Corporation,

New York, N.Y., a corporation of Delaware Filed May 21, 1968, Ser. No. 730,807 Int. Cl. H01r 13/52 US. Cl. 339-111 '18 Claims ABSTRACT OF THE DISCLOSURE An electrical connector element for use in high voltage electrical systems and capable of being connected and disconnected under high voltage load conditions and being safely connected under short circuit conditions by virtue of a structural arrangement which accommodates gases generated by an electric are ordinarily struck during such connection and disconnection, the connector element including a cavity, an electrical contact, a wall dividing the cavity into a first chamber in open communication with the portion of the contact where the electric arc is struck and a second chamber, and a valve interconnecting the first and second chambers such that gases generated by the electric are at the portion of the contact may be relieved from the first chamber into the second chamber. The gases thus passing into the second chamber may be dissipated relatively slowly through a relatively small passage, preferably leading back into the first chamber.

The present invention relates generally to electrical connectors for use in high voltage electrical systems and pertains, more specifically, to electrical connector elements embodying means for accommodating gases generated by an electric arc ordinarily struck during connection and disconnection under high voltage conditions so that such connection and disconnection may be accomplished without failure of the connector structure.

It is now commonplace to find disconnectable electrical connectors employed in a variety of locations in high voltage electrical distribution systems. While it is always best to make or break such disconnectable connections under no-load conditions, it is not always easy or expeditious to determine whether or not high voltage is present in a connection and then assure that no voltage is present before disconnecting a connection or reconnecting the connection. Thus, connections and disconnections are constantly being made under high voltage load conditions.

Such practices ordinarily lead to the formation of an electric are between the contacts of the electrical connectors which are being connected or disconnected. The are will very rapidly generate relatively large quantities of gases. Upon the connection of a pair of complementary electrical connectors under short circuit conditions, these gases have been known to build up sufiicient pressure to preclude completion of the connection or cause failure of one or the other of the connectors, often in such a violent manner as to constitute a hazard to personnel in the vicinity of the connection. These gases actually have been known to cause explosive failure of connector elements with the concomitant danger of flying debris.

It is therefore an important object of the invention to provide an electrical connector construction which enables successful connection under high voltage, short circuit conditions without a disastrous failure of the electrical connector.

Another object of the invention is to provide an electrical connector construction which enables such electrical connector elements to be either connected or disconnected under load in high voltage systems with improved life of the connectors.

Another object of the invention is to provide electrical connector elements having a construction which will accommodate gases ordinarily generated by an electric arc struck during connection under short circuit conditions without a disastrous failure of the electrical connector.

A further object of the invention is to provide a construction for electrical connectors for permitting the making or breaking of a connection under load, the construction having an overall configuration which is compact and compatible with current standards and equipment.

A still further object of the invention is to provide an electrical connector having a relatively simple construction capable of economical fabrication.

The above objects, as well as further objects and advantages, are attained by the invention which may be described briefly as an electrical connector element for use in high voltage electrical systems and capable of being connected and disconnected under high voltage conditions, the connector element including means for accommodating gases generated by an electric arc ordinarily struck during such connection and disconnection, the gas accommodating means comprising means providing a cavity within the electrical connector element, means dividing the cavity into a first chamber and a second chamber, an electrical contact having at least that portion where the electric arc is struck in open communication with the first chamber, and valve means interconnecting the first and second chambers and operable between a first position wherein the first chamber and the second chamber are in communication with one another and a second position wherein the first chamber and the second chamber are closed to one another, the valve means being responsive to the relative gas pressures in the chambers such that a pressure in the first chamber greater than the pressure in the second chamber will open the valve means to vent gas from the first chamber to the second chamber and a pressure in the first chamber no greater than the pressure in the second chamber will allow the valve means to remain closed.

The invention will be more fully understood and further objects and advantages thereof will become apparent in the following detailed description of preferred embodiments of the invention illustrated in the accompanying drawing, in which:

FIG. 1 illustrates complementary electrical connectors with a connector element constructed in accordance with the invention shown in a longitudinal cross-sectional VIEW;

FIG. 2 is an enlarged fragmentary cross-sectional view of portions of the connectors of FIG. 1 as the connectors are being connected;

FIG. 3 is a cross-sectional view of another connector element illustrating another embodiment of the invention;

FIG. 4 is a longitudinal cross-sectional view illustrating a connector element in the form of a bushing constructed in accordance with the invention; and

FIG. 5 is a reduced fragmentary cross-sectional view illustrating an alternate construction for a portion of the connector element shown in FIG. 4.

Referring now to the drawing, and particularly to FIG. 1, an electrical connection is to be made between a high voltage cable 10 and a transformer 12 in a high voltage electrical distribution system. The high voltage cable 10 has a central conductor 14, which is covered with an insulating jacket 16 which, in turn, is sheathed within a conductive shield 18. The cable 10 is terminated within an electrical connector element 20 shown in the form of an elbow having a body 21 which includes an inner member 22 of insulating elastomeric material and an outer member 24 of conductive elastomeric material. A central electrical contact is shown in the form of a pin 26 of conductive metal projecting axially through a receptacle 28 in the body 21 of the connector element 20. A tip 30 of nonconductive plastic material is afiixed to the end of the pin 26 for purposes which will be described hereinafter.

Affixed to the transformer 12, and projecting outwardly of the casing 32 thereof, is an electrical connector element constructed in accordance with the invention and shown in the form of a transformer bushing 34. Bushing 34 is provided with a housing 36, preferably fabricated of an elastomeric material and having an axially projecting outer body portion 38 constructed of a dielectric material, preferably an insulating elastomer. Within the housing 36 is an electrical contact 39 shown in the form of a metallic socket 40 having a plurality of segments 42 which are biased radially inwardly by an annular spring member 44 which encircles segments 42 adjacent the mouth 46 of the socket 40. A plastic sleeve 48 is juxtaposed with the socket 40 within the housing 36 and has an axially directed cylindrical bore 50 therein for receiving the plastic tip 30 of the corresponding connector element 20 as the connector elements 20 and 34 are connected.

Both the electrical contact 39 and the plastic sleeve 48 are actually affixed to a first tubular member 52 adjacent one end 54 thereof. The first tubular member 52 extendsaxially to the other end 56 thereof where the tubular member 52 is terminated by a base 58. The base 58 has a threaded aperture 59 so that the bushing 34 may be removably secured to a threaded stud 60 carried by a well member 62 which is permanently secured to the transformer casing 32. The threaded stud 60 is mechanically fixed and electrically connected to a lead 64 of the transformer 12. The first tubular member 52 and the base 58 are electrically conductive and are constructed of metal. The first tubular member 52 and the base 58 thus establish a cavity 66 within the bushing 34. A second tubular member 68, which is actually an integral portion of the electrical contact 39, extends axially into the cavity 66 and has an annular wall 70 spaced radially from the first tubular member 52 and closed off by an end wall 72 secured thereto, thus establishing dividing means for dividing the cavity 66 into a first chamber 74 and a second chamber 76. The first chamber 74 is in open communication with passages 78, established between the segments 42 of the socket 40, and with the interior of the socket, while the second chamber 76 is sealed off from the housing 36 by the first tubular member 52 and the base 58. An opening 80 in the end wall 72 communicates with both the first chamber and the second chamber and a valve means 81 is provided in the form of a ball valve having a ball 82 resiliently biased by a helical spring 84 which engages a shoulder 86 on the base 58 and which urges the ball 82 toward the first chamber 74 and into engagement with a seat 88 provided for the ball at the opening in the end wall member to close the opening 80.

As best seen in FIG. 2, as the complementary connector elements 20 and 34 are brought together, the plastic tip 30 will cooperate with the plastic sleeve 48 to serve as a pilot for aligning the respective electrical contacts prior to the making of any electrical contact between these contacts. As the connector element 20 is pushed toward full engagement with the bushing 34, the metallic pin 26 will approach the socket 40 and an electric arc may be struck between portions A and B, immediately causing a rapid generation of a relatively large volume of gas C which could, if not relieved, either preclude a full engagement of the connector elements by establishing a back pressure or could cause an explosive failure of the bushing 34. However, since the socket 40 provides an internal path between the arc and the interior of the socket in the form of passages 78, which. path is in open communication with the first chamber 74, the gas C can flow into the first chamber and, as the volume available in the first chamber for the gas decreases by virtue of the penetration of the contact pin 26 and tip 30 and the pressure of the gas builds up in the first chamber 74, the first chamber will be vented through valve means 81 into the second chamber '76. Thus, the cavity 66 provides the volume necessary to relieve the internal pressure which would otherwise build up to an intolerable level so as to permit completion of the connection between the metallic pin 26 and the socket 40 before the uncontrolled generation of very large volumes of gas can take place with concomitant deleterious effects. Immediately upon the completion of such a connection the electric arc is extinguished and no further gas is generated. Completion of the connection enables the axially projecting body portion 38 of the housing 36 to be seated within the receptacle 28 of the complementary connector element 20 to esablish a watertight connection.

It is noted that bushing 34 provides an extra measure of protection against violent explosive failure and flying debris when the housing 36 is constructed of an elastomeric material. Should the volume of gases generated by an electric arc become so great as to cause the bushing to burst, such a failure would merely rupture and tear the elastomeric material and would not tend to throw harmful fragments which could injure persons in the vicinity of the connector.

Upon disconnecting the complementary connector 20 from the bushing 34 under high voltage load conditions,

an electric arc may again be struck as the metallic pin 26 is withdrawn from the socket 40 and again approaches the position shown in FIG. 2. It is desirable to extinguish this arc as quickly as possible and to restrain any gases which may be generated by the arc so that the arc will cause no damage and ionized gases do not escape and restrike an arc to ground which could injure personnel in the vicinity of the connection. As the contact pin 26 and the plastic tip 30 are withdrawn from the socket 40 and the first chamber 74, a partial vacuum is established in the first chamber 74 by virtue of the withdrawal of the elements formerly occupying the socket 40 and chamber 74 and the closing of the valve means 81 to maintain the available volume of the chamber 74 relatively small. Since the ambient pressure will now be greater than the pressure within the first chamber, the gases generated by the electric arc will be drawn into the first chamber 74 and held there by the higher ambient pressure outside the bushing 34 until the contact pin 26 is withdrawn far enough for the arc to be extinguished. Hence, the combination of the first and second chamber 74 and 76, respectively, with a valve means 81 between the chambers provides adequate volume for accommodating gases generated upon connection of the complementary connector elements to enable complete connection without back pressure and provides a more limited volume upon disconnection of the connector elements to restrain gases generated upon disconnection of the elements.

Since the second chamber is of limited volume by virtue of cavity 66 being wholly within the bushing 34, it will be seen that dissipation of enough of the gases entrapped within the second chamber should take place prior to making another connection at load so that any further gases generated during such a subsequent connection can be accommodated. Hence, the gases which have been trapped within the second chamber 76 may be allowed to dissipate slowly and preferably back into the first chamber 74 and thence out of the connection by passing through passages 78 between the segments 42 of the socket 40 and the cylindrical bore 50 of the plastic sleeve 48. To this end, clearance may be provided between the seat 88 and the ball 82 so that even when the ball is seated in the seat and opening 80 is essentially closed to the rapid passage of large volumes of gas from one chamber to the other, a

relatively slow leakage of gas is permitted from the second chamber 76 to the first chamber 74.

The rate at which gases may leak from the second chamber must be limited to a rate slow enough so as to maintain the partial vacuum established in the first chamber upon disconnection, as set forth above. In addition, the leak rate must be slow enough so that combustion of the gases leaking from the second chamber to the first chamber will not be supported. On the other hand, the leak rate must be great enough to dissipate a sufficient volume of gases from the second chamber for accommodating a subsequent connection after a disconnection.

Turning now to FIG. 3, a connector element is illustrated in connection with a bus bar assembly 110 having a central conductor 114 and a covering of insulating material 116 sheathed with a conductive shield 118 and is shown in the form of a bushing 134 projecting from the bus bar assembly 110. The bushing 134 is provided with a housing 136 having an outer sleeve 137 of electrically conductive elastomeric material in electrical contact with the conductive sheath 118 of the bus bar assembly 110 and an externally tapered portion 138 and within which is atfixed an electrical contact 139 shown in the form of a socket 140 having a plurality of segments 142 biased radially inwardly by a circular spring 144. Juxtaposed with the socket 140 is a plastic sleeve 148 having a bore 150 and both the plastic sleeve 1'48 and the socket 140 are aflixed to a tubular member 152 adjacent one end 154 thereof. Adjacent the other end 156 of the tubular member 152 there is afiixed a valve assembly 160 which is threaded into a further tubular member 162 extending into the bus bar at 163. A still further tubular member 164 of slightly smaller diameter is affixed at one end thereof to the lower end of the valve assembly 160 and carries a plug 165 closing the other end thereof. Thus, the tubular member 152 and the smaller tubular member 164 establish a cavity 166 which is divided into a first chamber 174 and a second chamber 176 by the valve assembly 160. A plurality of passages 178, which lie between the segments 142 of the electrical contact 139, assure that the portions of the electrical contact in the vicinity of the electric are are in open communication with the interior of the socket 140 and the first chamber 174 of cavity 166.

The valve assembly 160 has an opening 180 communicating with the first and second chambers and includes valve means 181 in the form of a ball valve comprised of a ball 182 and a helical spring 184 which urges the ball against a seat 188. The ball valve is thus operable between a first position wherein the ball 182 is away from the seat 188 and the first and second chambers are in open communication with one another through opening 180 and a second position wherein the ball 182 is seated upon the seat 188, opening 180 is closed and the chambers 174 and 176 are essentially closed to one another in that the chambers are closed to the rapid passage of large volumes of gas from one chamber to the other.

Thus, as in the embodiment of FIGS. 1 and 2, gases generated by an electric arc struck at portion A during the making of a connection can enter the first chamber 174 and then pass through opening 180 into the second chamber 176. Upon breaking the connection, as described in connection with the embodiment of FIGS. 1 and 2, the valve means 181 will remain closed and a partial vacuum will be formed in the first chamber 174 to restrain those gases generated by an arc struck at portion A as the connection is broken.

As in the earlier described embodiment, means are preferably provided for enabling any gases entrapped within the second chamber to be dissipated slowly through the first chamber 174, the socket 140 and the sleeve 148 when the ball 182 closes opening 180. In this instance, such means take the form of a passage 189 of very small diameter communicating with the first and second chambers.

As in the embodiment of FIGS. 1 and 2, the bushing 134 shown in FIG. 3 may be removed from the bus bar assembly and replaced by merely disengaging the threaded connection between the valve assembly and the tubular member 162.

Turning now to the embodiments of the invention illustrated in FIGS. 4 and 5, a transformer bushing 234 is shown having a configuration very similar to that described in connection with bushing 34 of FIGS. 1 and 2. Thus, the bushing 234 is provided with a housing 236 having an externally tapered portion 238 and within which there is fixed an electrical contact 239 in the form of a metallic socket 240 having a plurality of segments 242 biased radially inwardly by an annular spring 244 surrounding the segments. Juxtaposed with the month 246 of the socket is a plastic sleeve 248 having a cylindrical bore 250 axially aligned with the opening of the socket. Both the electrical contact 239 and the plastic sleeve 248 are afiixed to a tubular member 252 adjacent one end 254 thereof. The tubular member 252 extends axially to the other end 256 which is closed by means of a base 258 having an aperture 259 into which may be threaded the stud 60 carried by the well member 62 of transformer 12 and connected to a transformer lead 64 as in the embodiment of FIGS. 1 and 2.

A cavity 266 is thus established within tubular member 252. Both the tubular member 252 and the base 258 are electrically conductive, and are fabricated of metal, to complete an electrical path between the contact 239 and the stud 60 which will be threaded into aperture 259. The electrical contact 239 has an axial extension shown in the form of a second tubular member 268 having a smaller diameter than the first tubular member 252 so that the annular wall 270 thereof is spaced radially from the wall of the first tubular member. An end wall 272 seals off the end of the second tubular member 268 to divide the cavity 266 into a first chamber 274 and a second chamber 276. The first chamber 274 is in open communication with passages 278 established between the segment 242 of the socket 240 and with the interior of the socket. A plurality of apertures 280 are spaced circumferentially around and extend radially through the annular wall 270 of the second tubular member and valve means 281 shown in the form of an annular band 282 of elastomeric material normally closes the apertures 280 by virtue of the resilience of the elastomeric material of the band. The annular band 282 is seated within an annular recess 283 in the annular wall 270 so as to be positively retained against axial movement along the second tubular member 268.

In response to a greater gas pressure in the first chamber 274 than in the second chamber 276 the annular band 282 will dilate resiliently to allow such pressure to be relieved so that the construction illustrated in FIG. 4 will operate in a manner similar to that described in connection with FIGS. 1 and 2.

As in the earlier described embodiments, slow leakage of gas is permitted from the second chamber 276 to the first chamber 274 by virtue of a relatively small passage established by a screw 284 loosely fitted in a threaded aperture 286 in the end Wall 272.

As seen in FIG. 5, the screw 284 of the bushing 234 of FIG. 4 may be replaced by a plug 288 of porous ma terial such as a porous member of sintered metal which will allow slow leakage of gas from the second chamber 276 to the first chamber 274 when the valve provided by the annular elastomeric band 282 is closed over apertures 280.

It is to be understood that the above detailed description of embodiments of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention which is set forth in the appended claims.

The embodiments of the invention in which an ex- 7 clusive property or privilege is claimed are defined as follows:

1. An electrical connector element for use in high voltage electrical systems and capable of being connected and disconnected under high voltage load conditions, said connector element having a construction including means for accommodating gases generated by an electric arc struck during such connection and disconnection, said gas-accommodating means comprising:

means providing a cavity within said electrical connector element;

means dividing said cavity into a first chamber and a second chamber;

an electrical contact having at least that portion where the electric arc is struck in open communication with the first chamber;

means providing at least one opening communicating with the first and second chambers such that rapid passage of gas from one said chamber into the other said chamber is permitted through said opening-providing means; and

valve means associated with the opening-providing means and operable between a first position wherein the opening is open and the first and second chambers are in open communication and a second position wherein the opening is closed, the valve means being responsive to the relative gas pressures in the chambers such that a pressure in the first chamber greater than the pressure in the second chamber will open the valve means to vent gas through the opening from the first chamber to the second chamber and a pressure in the first chamber no greater than the pressure in the second chamber will allow the valve means to maintain the opening closed.

2. The electrical connector element of claim 1 including means for permitting relatively slow dissipation of gas from the second chamber when the valve means is in the second position.

3. The electrical connector element of claim 2 wherein said means for permitting relatively slow dissipation of gas communicates with the first chamber such that gas is dissipated from the second chamber into the first chamber.

4. The electrical connector element of claim 1 wherein the dividing means includes a wall separating the first and second chambers and wherein the valve means includes a valve member resiliently biased against said open in the direction toward the first chamber.

5. The electrical connector element of claim 4 wherein:

the valve member is a ball;

the opening includes a seat for the ball; and

the valve means includes a spring biasing the ball against the seat in the second position and permitting displacement of 'the ball away from the seat in the first position.

6. The electrical connector element of claim 5 wherein sufficient clearance is provided between the ball and the seat to permit relatively slow leakage of gas from the second chamber to the first chamber when the ball is against the seat.

7. The electrical connector element of claim 4 wherein the valve member includes a resilient band biased against the opening by the resilience of the band in the second position and resiliently displaceable away from the opening in the first position.

8. The electrical connector element of claim 7 including a relatively small passage in the wall and communicating with each of the first and second chambers for permitting relatively slow leakage of gas from the second chamber to the first chamber when the band is against the opening.

9. The electrical connector element of claim 1 wherein:

the cavity-providing means includes a housing having an outer body portion of dielectric material and an inner generally tubular member fixed within the outer portion and Within which the cavity extends axially with respect to the electrical connector element; and the electrical contact is fixed within the tubular member and includes a passage communicating with said portion of the electrical contact and the cavity.

10. The electrical connector element of claim 9 wherethe outer body portion is constructed of an insulating elastomcric material and the inner generally tubular member is a metallic sleeve having opposite ends, the electrical contact being fixed within the sleeve adjacent one of said opposite ends; and

the connector element includes means closing the sleeve at the other of the opposite ends.

11. The electrical connector element of claim 10 wherein: v

the electrical contact includes a socket extending axially with the generally tubular member and having an interior for receiving a complementary electrical contact of a complementary connector;

the dividing means includes a second generally tubular member fixed within the first generally tubular member, extending axially and having an annular wall spaced radially inwardly of said first generally tubular member, the interior of the second generally tubular member communicating with the interior of the socket, and the second generally tubular member being closed at one end thereof to establish the first chamber;

said opening of the opening-providing means extends radially through the annular wall of the second generally tubular member; and

the valve means includes an annular band of elastomeric material encircling said annular wall and normally closing said opening.

12. The electrical connector element of claim 11 wherein the means closing the end of the second generally tubular member includes a porous member for permitting relatively slow leakage of gas from the second chamber to the first chamber when the elastomeric band is in the closed position.

13. In an electrical connector for use in high voltage electrical systems and capable of being connected and disconnected under high voltage conditions, a connector construction including means for accommodating gases generated by an electric arc struck during such connection and disconnection, said connector construction comprismg:

a tubular member of electrically conductive metal and including an axially extending cavity therein; means dividing said cavity into a first chamber and a second chamber; an electrical contact affixed to the tubular member and having at least that portion where the electric arc ist struck in open communication with the first chamber;

means providing at least one opening communicating with the first and second chambers such that rapid passage of gas from one said chamber into the other said chamber is permitting through said openingproviding means; and

valve means associated with the opening-providing means and operable between a first position wherein the opening is open and the first and second chambers are in open communication and a second position wherein the opening is closed, the valve means being responsive to the relative gas pressures in the chambers such that a pressure in the first chamber greater than the pressure in the second chamber will open the valve means to vent gas through the opening from the first chamber to the second chamber and a pressure in the first chamber no greater than the pressure in the second chamber will allow the valve means to maintain the opening closed.

14. The electrical connector construction of claim 13 including means for permitting relatively slow dissipation of gas from the second chamber when the valve means is in the second position.

15. The electrical connector construction of claim 14 wherein said means for permitting relatively slow dissipation of gas communicates with the first chamber such that gas is dissipated from the second chamber into the first chamber.

16. The electrical connector construction of claim 13 wherein:

the electrical contact includes a socket extending axially within the tubular member and having an interior for receiving a complementary electrical contact; the dividing means includes a further tubular member fixed within the first said tubular member, extending axially and having an annular wall spaced radially inwardly of the first said tubular member, the interior of the further tubular member communicating with the interior of the socket, and the further tubular member being closed at one end thereof to establish the first chamber;

said opening of the opening-providing means extends radially through the annular wall of the further tubular member; and

the valve means includes an annular band of elastomeric material encircling said annular wall and normally closing said opening.

17. The electrical connector construction of claim 16 wherein the means closing the end of the further tubular member includes means for permitting relatively slow leakage of gas from the second chamber to the first chamber when the elastomeric band is in the closed position.

18. The electrical connector construction of claim 17 wherein the means for permitting relatively slow leakage includes a porous member.

References Cited UNITED STATES PATENTS 2,140,149 12/1938 Arutunoff 200149 X 2,223,975 12/ 1940 Traver 200149 3,413,592 11/1968 Link 339- 11 FOREIGN PATENTS 917,190 8/1954 Germany. 9,827 12/ 1956 Germany.

RICHARD E. MOORE, Primary Examiner "R. Column Column Column Column Column (SEAL) Attest:

Patent No.

Robert C.

ET AL line line line line line UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Ruete should read R. C.

EDWARD M.FLETCHER,JR. Attesting Officer Dated fl g Q 1219 Ruete et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of column 1, "Robert Ruete" should read Robert RUETE In the heading of each sheet of drav RUETE ET AL "esablish" should read establish "open" should read -'opening "with" should read within "ist" should read is should not begin a new paragraph Signed and sealed this 23rd day of January 1973 ROBERT GOTTSCHALK Commissioner of Paten F ORM PO-1050 [IO-69) USCOMM-DC 60376.:

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