US3643203A

US3643203A - Wrought steel conduit bushings

Info

Publication number: US3643203A
Application number: US13590A
Authority: US
Inventors: Bernard J Mclaughlin; George W Petri; Raymond J De Moor
Original assignee: Deutsche ITT Industries GmbH
Current assignee: Thomas and Betts Holdings Inc
Priority date: 1970-02-24
Filing date: 1970-02-24
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15

Abstract

A wrought steel conduit bushing is provided. The bushing is formed from a blank by use of bending, stretching, setting, piercing, extruding, flattening, flaring and drawing techniques. Initially, a flat piece of iron is drawn into a cup and a flange is set. The closed end of the cup is reverse drawn to form a double shell or wall. The closed end of the cup is pierced and the resulting opening is extruded. The inner shell is then expanded to form a smooth annular ring with the outer shell to permit the passage of insulated wire without scarring the insulation. The inner shell is flared and flattened to complete the annular ring and to complete an inner cylindrical wall which may be threaded for mounting on rigid conduit. One or more ground lugs are then formed by bending a tang to provide an integral ground connection.

Description

cLauglllin et al.

[ l e. 115, T972 [54] WM'UUGHT STEEL CUNWUTT BlJSllllNGfi [73] Assignee: luternationnl Telephone and Telegraph Cor-ration, New York, NY.

22 Filed: l el.24,197ll [211 App]. No.: 13,591)

3,278,883 10/1966 Lipsey .339/141L FORElGN PATIENTS OlR APP'LlCATlONS 398,571 9/1933 Great Britain ..16/2

Primary Examiner-Marvin A. Champion Assistant Examiner-Robert A. Hafer AttorneyC. Cornell Remsen, Jr., Walter J. lBaum, Percy P. Lantzy, .1. Warren Whitesel, Delbert 1P. Warner and James B. Raden A wrought steel conduit bushing is provided. The bushing is formed from. a blank by use of bending, stretching, setting, piercing, extruding, flattening, flaring and drawing techniques. llnitially, a flat piece of iron is drawn into a cup and a flange is set. The closed end of the cup is reverse drawn to form a double shell or wall. The closed end of the cup is pierced and the resulting opening is extruded. The inner shell is then expanded to form a smooth annular ring with the outer shell to permit the passage of insulated wire without scarring the insulation. The inner shell is flared and flattened to complete the annular ring and to complete an inner cylindrical wall which may be threaded for mounting on rigid conduit, One or more ground lugs are then formed by bending a tang to provide an integral ground connection.

5 Claims, 12 Drawing ll igures SHEET 1 OF 5 lllllllll 'IIIII7TTIII FIG. IA

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WIIIG UGIHIT STIIIEIL CGI IDIUIT FIJSIIIII JGS This invention relates to connectors for terminating rigid conduit at the point where the conduit enters an enclosure. It relates particularly to one-piece connectors that may or may not have an insulated throat coating and which provide smooth orifices through which insulated cable may be drawn without injury to the insulation.

Prior art connectors, or bushings, for use between rigid conduit and an enclosure generally include a metallic conduit bushing for mechanically connecting the conduit and the enclosure. A smooth rounded throat of insulation material is provided in the bushing to prevent damage to conductor insulation. Usually, the rounded throat is formed as a separate element. The metallic conduit bushing is threaded internally so that it may be fastened to the end of a piece of rigid conduit which in turn is secured to the enclosure. If the rounded throat is formed as a separate insulator element, it could be threaded to fit into the conduit bushing. Alternately, a smooth rounded throat may be formed by coating, or other means, directly onto the conduit bushing. Whether the smooth throat is added directly to the conduit bushing or by a separate piece with provisions for connection, the resulting conduit bushing is relatively costly for use as a connector.

It is an object of the present invention to provide an integral conduit bushing having a smooth throat that can perform its function without the necessity of added insulation material in the throat.

It is a further object of this invention to provide a conduit bushing having one or more ground lugs formed integrally with the bushing.

The foregoing objects and others ancillary thereto are preferably realized by various drawing, setting, piercing, extruding, forming and flattening operations performed serially in a multistation progressive die to form a conduit bushing. The part is carried from station to station by means of a scrap train. This method requires a minimum of direct labor cost.

Typically, in forming a conduit bushing according to the invention, a blank formed from a thin sheet of malleable steel, or other metal, is first punched to form a cup having a narrow flange. In a succeeding step, the flange is set. The cup is then reverse drawn to form a double wall, or a double shell. The bottom of the cup is pierced and the inner shell is extruded to form a smooth inner cylinder. The inner shell is then expanded to touch the inside of the outer sheil and form a hollow ring along the boundary of the two shells. The inner shell is then flared and flattened to form an annular rigid conduit bushing. In subsequent stages, a flat tang or tangs are formed as a part of the original blank and are bent to provide a ground lug or lugs integral to the conduit bushing. Threads are then cut within the bushing to accept threaded conduit. Suitable holes are drilled in the grounding lug for use in fastening ground connections.

Attention is directed to the copending patent application of B. I. McLaughlin and A. L. Colvis entitled Deep Draw Electrical Connector Lugs" for further disclosures of this general subject matter. The McLaughlin-Colvis application was filed on Oct. 31, 1969, as US. Pat. application No. 872,918. This prior application is hereby incorporated by reference.

The above-mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent, and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

FIGS. IA and IE illustrate a preferred form for a flat blank of metal of use in the practice of this invention,

FIG. 2 shows a step invoived informing a cup from the blank of FIG. ll,

FIG. 3 illustrates the manner of setting a flange for the cup of FIG. 2,

FIG. d shows a reverse drawing step causing a new cup to be formed with a double wall,

FIG. 5 shows the step of piercing the closed end, or bottom, of the cup,

FIG. ti illustrates the step of extruding the bottom,

FIG. '7 is a view in partial section of a step involving expand ing the outer shell,

FIG. II shows the use of an anvil and dies to flare and flatten the inner shell,

FIG. II illustrates, in a crosssectional view, the result of a first bend in the flange of FIG. I to form a ground lug attached to the shell of FIG. 8,

FIG. III shows the form of the ground lug following succeeding bending operations, and

FIG. ll I is a perspective view of a conduit bushing according to the invention.

Turning now to FIGS. IA and IB there is shown a blank 2, formed from sheet metal in a generally circular shape. The blank includes a flat tang at d which has been cut for use later in the formation of a ground lug. A blank with additional tangs may be used if additional grounding lugs are required.

The flat blank is profile cut in a scrap train to be carried from station to station of a multistage progressive die. In the first condition, the blank 2 is drawn between anvils shown in section at A2 and Ad, of FIG. 2, and dies shown at D2 and D4 to form a cup, as indicated in section at C. Reference may be made to the Metals Handbook" 8th edition, Vol. 1, published by American Society for Metals, Novelty, Ohio, and particularly to pages 709-717 for further details relating to the formation of cup-shaped metal parts by the use of deep drawing dies in a press.

The flange F of the cup C, shown in FIG. 3, is set by action of the anvils Ab and A8 concurrently with action of the dies D6 and Dh.

As shown in FIG. 15, in the following station, the cup C is reverse drawn by the joint action of anvils shown in section at AMI, A12, Aid and Allb and dies shown at DII) and DIZ.

After the cup has been reverse drawn in the manner indicated in FIG. 4, the cup is advanced to the next station where the bottom is pierced. Piercing of the bottom is indicated in FIG. 5, where the bottom portion Cl is severed and removed through the opening lid in the anvil Aid. In the station represented by FIG. 5 the workpiece is held in position by anvils A18, A20 and A22 while the die, or punch, Did is used to remove the portion CI of the bottom.

After the bottom has been pierced and a portion C I has been removed, the workpiece is advanced to another station, indicated in FIG. 6, where the bottom is extruded. The extru sion is carried out, as indicated in FIG. 6, between anvils at AZ I, A26 and A28 and a die at Dllo.

Following extrusion of the bottom, the workpiece is advanced to the next station where the inner shell is expanded. The manner of producing this expansion is indicated in FIG. 7 where the workpiece is drawn between the dies Dlh and D20 in cooperation with the anvils at A30 and. A32. As will be clear from the sectional view of FIG. 7, a hollow loop, or ring R, is formed in the workpiece by this step.

After the loop has been formed in the workpiece, it is advanced to the next station where the inner shell is flared and flattened in the manner indicated in FIG. Flaring and flattening is performed between the anvil shown in cross section at Add and the dies D22 and D24. This completes the formation of the basic conduit bushing. The following steps relate to the formation of an integral ground lug or lugs for the bushing, providing threads and punching holes in the ground lug.

In succeeding stations of the progressive die the flat tang A of FIG. IA is bent, m shown in FIGS. 9 and III. The bending procedures produce a compact and convenient ground lug which is integral to the conduit bushing and which may be fastened in any known way to grounded elements to assure a good ground for the conduit bushing.

Following the formation of the ground lug, a hole may be drilled as shown at 22 in FIG. III. Suitable threads are then cut, as at 2d, to enable the bushing to be fastened to suitable threaded conduit or other components. The smooth annular loop will provide a surface at as which will enable insulated wires to be passed through the conduit bushing without damage to the insulation.

A perspective view of a conduit bushing according to the invention is shown in partial section in FIG. 11. In this view, the flange is shown to have been trimmed to provide extensions such as that at 28, of use in turning the conduit bushing to thread onto rigid conduit. Internal threads are shown at T and T1. As is more clearly brought out in this view, the annular loop or ring R provides a continuous smooth surface at 26 against which insulated wires may rub without damage to the insulation. lf conductors of No. 4 or larger are pulled through the bushing and insulation is required as specified by section 373-66 of the National Electrical Code, 1968 Edition, a coating of thermoplastic or thermoset material such as nylons, fluorocarbons, polypropylenes may be added by spraying, fluidized bed or dipping processes. it is clear also from this view that the ground lug L, formed from the tang at 4, (FIG. 11) is integral to the bushing and provides a ready means from which the bushing may be connected to ground. In this view also, it will be noted that the lug L may be bent another time to provide a further side L1. The addition of this side Lll strengthens the structure of the lug and prevents it from being bent open by pressure of a setscrew in the hole 22 against a grounding wire. This construction prevents the mechanical advantage of the setscrew from acting as a moment arm to open the lug, and instead presents a closed kinetic loop that reacts against this pressure.

Briefly, in review, it will be seen that the present invention relates to a conduit bushing. The conduit bushing typically is formed from a piece of sheet metal which is bent to form an inner shell and an outer shell. The inner shell forms a cylinder of constant diameter over a part of its length. The bend in the piece of metal forms a hollow annular loop joining the inner shell and the outer shell. The hollow annular loop provides an opening of substantially smaller diameter than that of the cylinder and provides a surface over which an insulated wire may be pulled without injury to the insulation.

The conduit bushing is fonned by a plurality of operations.

These operations include drawing a cup from a sheet of metal, setting a flange on the cup, reverse drawing the cup to form a double wall, piercing the bottom of the cup, extruding the bottom of the cup, expanding the inner wall of the cup to form an annular loop, and flaring and flattening the inner wall of the cup.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

We claim:

1. A conduit bushing formed from sheet metal comprising, a piece of metal, a bend in the piece of metal, the bend shaping the piece of metal to form an inner shell and an outer shell, the inner shell forming a cylinder of constant internal diameter over a part of its length, the outer shell forming a cylinder of constant external diameter over substantially its full length, and the bend in the piece of metal forming a hollow annular loop joining the inner shell and the outer shell, said hollow annular loop providing an opening of substantially smaller diameter than that of the cylinder and providing a surface over which an insulated wire may be pulled without injury to the insulation.

2. A conduit bushing as claimed in claim 1, including a ground lug integral with the conduit bushing.

3. A conduit bushing as claimed in claim I, in which the outer shell includes a ground lug integral therewith.

4. A conduit bushing as claimed in claim 1, in which the outer shell includes a ground lug integral therewith and the ground lug includes an opening to which a ground connection may be made.

5. A conduit bushing as claimed in claim I, in which a portion of the inner shell is threaded internally to permit fastening the conduit bushing to suitably threaded conduit.

Claims

3. A conduit bushing as claimed in claim 1, in which the outer shell includes a ground lug integral therewith.

5. A conduit bushing as claimed in claim 1, in which a portion of the inner shell is threaded internally to permit fastening the conduit bushing to suitably threaded conduit.