US 2748187 A
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Description (OCR text may contain errors)
May 29, 1956 J. M. F. CONRAD ELECTRIC TERMINAL Filed June 28, 195] Z g fm I... l n
"EL/ENTOR fit/ as f4 1! [mind ATTORNEY United States Patent F ELECTRIC TERMINAL Julius M. F. Conrad, Warren Township, Somerset County,
N. 1., assignor to llrilhart Research Corporation, Mineola, N. Y, a corporation of Delaware Application June 23, 1951, Serial No. 234,121
8 Claims. (Cl. 174-.453)
The present invention relates to electric terminals and more particularly to an electric terminal adapted to be permanently attached to a transformer casing or the like and to form a hermetic seal bet-Ween the conductor of said terminal and said casing.
In certain types of electrical equipment, it is neces- I sary that a conductor pass through a casing wall and form a hermetic seal with the Wall. Such seal has to be effective under severe atmospheric conditions and at various temperatures. Rigid tests are provided to be sure that the terminals will stand up and maintain the hermetic seal under such conditions. In some tests the terminal is clamped in position and subjected to air press sure while the conductor is forced in opposite directions by as much as of an inch when measured at its end. if there is any leakage under these conditions, the termi: nal is rejected. Further, the terminal is required to withstand as much as 5,000 volts between the tubular at.- taching member and the conductor.
Frequently electric terminals withstanding these tests leak after they have been applied to a transformer casing. The reason for the failure after application to the casing of a properly tested terminal is that heat applied during the soldering operation causes the metal tube torming part of the terminal to expand and contract, which upsets the molding material and weakens the bond between it and the metal parts. This is aggravated by the fact that the heat tends to soften the insulating ma-. terial during the soldering operation. Various attempts have been made to overcome these objections and to provide a more perfect terminal.
The. terminal most generally used comprises a cylindri.- cal insulating body having a conductor extending centrally through it with protuberances thereon to anchor it in position. A tubular member is embedded in the insulating member with a rightaugle. flange protruding outwardly through the insulating body for attachment to a casing. In some cases the flange is at the end of the tubular member and in other cases at the middle. l'n both cases, excessive failures result not only in the testing operation but also as a result of soldering to transformer casings.
The presentinvention provides an improved terminal with an improved tubular memberwhich overcomes the above objections and minimizes the percentage of defective terminals not only in the testing operation but also after the terminalS are applied to. suitable, casings; in fact, terminals which are defective produce improved results when soldered to a casing and in many cases serve perfectly thereafter.
The invention also provides a relatively simple. and inexpensive construction for providing an electric termi'- nal which forms a hermetic seal between the conductor and the casing to, which it is. applied.
An object of the present invention is tov provide a newand improved transformer terminal.
Another object ofthe invention is to provide a new and improved electric terminal for use under condizfl ldd 'l Patented May 29, 1956 ice tions where a hermetic seal is required between the casing and the conductor.
Another object of the invention is to provide an improved electric terminal which may be inexpensively manufactured and installed without impairing the hermetic seal between the parts thereof.
A "further object of the invention is to provide an improved electric terminal which automatically improves the seal between the conductor and the casin wall during the attachment of the terminal to the casing wall.
Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.
A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawings, forming a part of the specification, wherein:
Fig. its a longitudinal sectional view showing a preferred embodiment of the present invention;
Fig. 2 is a longitudinal sectional view of the present invention taken at right angles from the View shown in Fig. 1;
Fig. 3 is a transverse sectional view taken along the line of Fig. 1;
Fig. 4 is a sectional view showing a modified form of the invention;
Fig. 5 is, a perspective view of the generally tubular attachment illustrated in Figs. 1 through 4; and
Fig. 6 is an enlarged fragmentary view showing a portion of the terminal in section.
Referring again to the drawings illustrating a preferred embodiment of the invention, and more particularly to Fig. 1 thereof, there is illustrated a casing it having an aperture 2 therein adapted to receive a transformer terminal indicated generally at 4. The terminal comprises in the preferred embodiment a conductor 7 extending centrally through a generally cylindrical body of insulating material 8. with one end of the conductor 14 protruding at the bottom of the insulating material and the otherend preferably formed into a book 15 at the upper end of the insulating body. For the purpose of securing the terminal to. the wall of the casing, a tubular member 9 is embedded in the insulating material. The interior of the tube 9 is spaced sufiiciently far from the centrally extending conductor 7 to insulate it therefrom. A substantial thickness of insulating material extends about the ends of the tubular member 9 to hermetically seal it within the insulating material. An annular enlargement i2 is provided, preferably at the, middle of the tubular member, and projects abruptly outwardly from the tubular portion 9 beyond the insulating material, as shown in Fig. 1, so that it may be soldered to the casing about the. aperture 2.
An important feature, of the present invention is the pr sio t th annular e largem nt 2 which Provides a groove, 16 on the interior of the, tubular member 9. As will; be pointed out hereinafter, this groove traps air, which is compressed during the. molding operation and provides an annular air chamber about the insulating material. When the solder is applied for attaching the. tubular member 9; to the casing, the heat expands the annular enlargement 12 away from the conductor 7, expands the air trapped therein, and to some extent softens and expands the insulating material. The expanded air and insulating material puts the softened insulating material under compression and thus forces it firmly against the centrally extending conductor '7, as well as against adjacent walls of the tubular member 9; As the annular enlargement 12 cools, it contracts inwardly against the plastic material and holds or even increases the compression applied by the now cooling air, to retain and improve the hermetic seal and likewise to retain and improve the hermetic seal between the tubular member and the insulating material.
The plastic material is preferably injected under high pressure into and around the tubular member 9, the injec' tion molding pressure being anywhere from about 5,000 to 20,000 pounds per square inch; As a result, the size of the air space in the groove 16 of a terminal may appear quite small in some instances due to the fact that the trapped air is highly compressed in the space. As this highly compressed trapped air is heated during soldering of the enlargement 12 to a casing, its pressure is further increased and the softened plastic is forced firmly against the adjacent conductor and tube surfaces.
Even though in some instances the air might be trapped at only one side of the annular enlargement 12, the soldering heat softens the plastic entirely around the annular groove and the compressed air finds its way around the entire inner portion of the groove 16 to force the softened plastic inwardly throughout the circumference of the groove.
I have discovered that the groove shown at 16 herein not only reduces the percentage of terminals which will not stand up under the rigid tests imposed upon them to a negligible number but also improves the hermetic seal between the parts during the soldering of the terminal in place. I have found that the diflerence between utilizing a sleeve with an annular groove 16, as shown, and one in which a solid flange is used is unbelievable. The rejects are numerous and high percentagewise with the solid flange; in addition, the hermetic seals are impaired during the soldering operation. With a tubular member having a groove 16 therein, the rejects during the tests are negligible and the soldering operation actually improves the seal and never impairs it.
An enlarged section of the terminal is illustrated in Fig. 6 in which the principles described above are illustrated as they are understood. The air pressure and the expanding insulating material tend to force the softened insulating material inwardly toward the centrally extending conductor '7 and against the enlargement shown. This pressure also tends to force the insulating material more rigidly against the inside of the tubular member. While the theory given above is believed to be correct, the construction is known to produce improved results; hence applicant has described and claimed the construction and if by any chance the results should flow from a different theory, there is no intention of limiting the invention or the patent to be issued on. it to any precise theory, as applicant is not required either to know or to. embody the exact theory of operation in his patent.
In the preferred embodiment illustrated in Figs. 1 and 2, the conductor '7 is anchored in position by means of three protuberances 21 which may be formed by flattening the cylindrical conductor at these portions. Preferably one of the flattened portions is in line with the annular groove 16 of the tubular member 9 so that the air pressure will be effective at the enlarged portion of the conductor 7. However, it is not desired to limit the inven tion to this particular construction as a pair of protuberances can be used, as illustrated in Fig. 4, and good results can be obtained without any protuberances.
The insulating body 8 may be formed of any suitable material but is preferably formed of a synthetic resin. l have found that a polymer of trifluoroehloroethylene gives excellent results and better results than any other known material. This synthetic resin comprises two halogens, fluorine and chlorine, and is an exceptionally stable hightemperature, non-inflammable thermoplastic. The M. W. Kellogg Company, located at Jersey City, New Jersey,
sells the material under the trade name KEL-F, Grade 300.
The tubular member 9 is preferably a copper and tin electroplated brass. The tin on the exterior facilitates the soldering operation between the enlargement and the casing about the aperture 2.
In the preferred method of making the electric terminal described herein, the tubular member 9 is held in spaced relation to the conductor 7 in a suitable mold. The insulating material may be injection molded under relatively high pressure, as previously referred to, aboutthese two members spaced in their proper relationship. The hot molding material flows about the conductor and through and about the tubular member 9. Air is trapped in the annular groove 16 of the tubular member, as shown in Figs. 1, 2, 4 and 6. In this way the parts may be inexpensively assembled and the seal formed under molding conditions to give the best results. The enlargement 12 may fit into a suitable groove in the mold which serves not only to hold the tubular member accurately in position but also to prevent the molding material from flowing about the outer portion of the enlargement which is to be soldered to the casing 1 by the solder 13, in order to form a hermetic seal therewith.
It will be seen that the present invention provides a new and improved electric terminal particularly suitable for transformer casings and the like. The terminal conductor is hermetically sealed to the casing and is adapted to withstand the rough usage to which it may be subjected without impairing the hermetic seal. The terminal is adapted to be soldered to the casing. The soldering operation does not impair but actually improves the hermetic seal between the parts. The construction is simple and easy to manufacture from readily obtainable parts at a minimum expense.
As various changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantage, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.
Having thus described my invention, I claim:
1. An electric terminal comprising in combination a thermoplastic insulating body, a conductor extending through the body and forming a hermetic seal therewith, a metal member having a tubular portion embedded beneath the surface of the insulating body surrounding said conductor in spaced relation therewith and having an annular bulge intermediate the ends of the tubular portion forming an annular groove on the interior thereof and protruding radially beyond the surface of the insulating body for soldering to a casing, with portions of the material of said insulating body extending into said groove whereby said last named portions will expand during the soldering operation and thereby be com pressed between the conductor and the metal member with the portions of the insulating body which overlie the tubular portion being of substantial thickness and abutting the annular bulge so as to assist in preventing enlargement of said bulge in an axial. direction during said expansion.
2. An electric terminal comprising in combination a thermoplastic insulating body, a conductor extending through the body, a metal tubular member surrounding said conductor and spaced therefrom and surrounding at least a portion of said insulating body, an annular enlargement on said tubular member having substantially parallel radially directed side walls spaced axially forming an annular groove on the interior of said enlargement and protruding from the insulating body for soldering to a casing, said insulating body entering only a portion of the annular groove and forming a gastight pocket in the base of the groove, and a gas under pressure in the gastight pocket.
3. The electric terminal as claimed in claim 2 in which said conductor has an enlargement adjacent to the annular groove.
4. The electric terminal as claimed in claim 2 in which said conductor has a plurality on enlargements thereon anchoring it in said insulating body.
5. The electric terminal as claimed in claim 4 in which at least one of said enlargements is adjacent to the annular enlargement.
6. An electric terminal comprising in combination an insulating body of thermoplastic material, a conductor extending through the body, a tubular metal member surrounding said conductor, an annular enlargement on said tubular metal member having substantially parallel radially directed side Walls spaced axially forming an annular groove on the interior of said enlargement, said tubular member being embedded in the insulating body with said annular enlargement protruding beyond the surface of the insulating body for soldering to a casing, said insulating body only partially filling said annular groove whereby a pocket is provided for trapped gas in the base of the groove, a compressed gas in said pocket whereby said compressed gas will expand during the soldering of the annular enlargement to a casing to form a more perfect seal between said insulating body and said tubular member and said conductor, and the portions of the insulating body which overlie the tubular member being of substantial thickness and abutting the annular enlargement so as to assist in preventing deformation of said enlargement in an axial direction during the expansion of the trapped gas.
7. The electric terminal as claimed in claim 6 in which said compressed gas is air.
8. The electric terminal as claimed in claim 7 in which said conductor has an enlargement adjacent to the annular bulge.
References Cited in the file of this patent UNITED STATES PATENTS 1,604,111 Bingay Oct. 26, 1926 2,299,750 Hull et a1. Oct. 27, 1942 2,383,018 Shere Aug. 21, 1945 2,429,955 Goldsmith Oct. 28, 1947 2,548,353 Cunningham Apr. 10, 1951 2,559,141 Williams July 3, 1951 2,678,963 Everhart May 18, 1954 FOREIGN PATENTS 284,897 Great Britain Feb. 9, 1928