US3092716A - Electric resistance heating units - Google Patents

Description

June 4, 1963 E. J. LIMPEL ELECTRIC RESISTANCE HEATING UNITS Filed April 3, 1961 3 9 I a T. L L: T1; Mn g I I I I I I I I l J I I 'I \I 1 1| INIfENTOR. 8ugene J. Llmpel BY AndrflsGSibr/p Diffarneys United States Patent 3,092,716 ELECTRIC RESISTANCE HEATING UNITS Eugene J. Limpel, Thiensville, Wis., assignor to O. Smith Corporation, Milwaukee, Wis., a corporation of New York Filed Apr. 3, 1961, Ser. No. 100,289 7 Claims. (Cl. 219-149) This invention relates to electric resistance heating units and particularly to a heating unit for heat treating steel bars, billets or the like by passing a current through the member.

Electric resistance heating units having a pair of spaced electrodes have been employed to heat a steel billet by passing current through the billet. The billet is clamped between the electrodes at 'least one of which is movable to establish a pressure contact with the ends'of the electrodes during the current flow.

The contact between the end of the billet and the adjacent electrode during the initial establishment of current flow has caused particularly diflicult problems. The presence of an uneven end cut or any form of projections on the end of the billet establishes a small concentrated point of contact with the adjacent electrodes With a resultant exceptionally high current density through the contacting points. Burning of the-electrodes and/or the work may occur' and seriously affect the efficiency and operation of the heating unit.

Various suggestions have been made. For example, it has been proposed that an initial low density current be established to soften the rough and irregular end of the member with the applied pressure serving to flatten the member and establishing a smooth intimate contact. Thereafter,- the current is increased to provide the desired work heating ofthe member. The prior art also suggests introducing a granulated or powdered material between the adjacent end of the electrode and the member being heated to eliminate arcing between the two members.

The present invention is directed to a simple and durable electrode construction for producing good electrical contact with the billet or the like.

In accordance with the present invention, the billet engaging end of the contact or electrode is provided with a conical recess adapted to receive the end of the billet and establish a narrow ring contact area therewith. Current and pressure are simultaneously applied between the contact and the billet. The initial high current density through the narrow ring-like area immediately softens any protrusions or contacting members and allows the high pressure to establish firm electrical engagement in a narrow ring area. The softening of the adjacent end of the billet results in an increased contact area which readily and safely carries the current density established for proper heating of the bar or billet.

In accordance with another aspect of the present invention, the cont-act area of the contacts is coated with or formed of a suitable hard material such as carboloy, tantalum, or the like to prevent wearing away of the contact area.

The present invention provides a simple and relatively inexpensive electric resistance heating contact having a long life.

The drawing furnished herewith illustrates the best mode presently contemplated for carrying out the invention.

In the drawing:

FIG. 1 is a side elevational view of an electric heating unit constructed in accordance with the present invention with parts broken away to show details of construction; and

Patented June 4, 1963 vided for supplying power to the electrode units 2 and 3 for establishing suitable current flow through the billet 1. A hydraulic motor 7 is secured to the upper electrode unit 2 and is adapted to apply a pressure through the electrode unit 2 across the billet 1 and establish firm electrical contact between the ends of the billet 1 and the adjacent electrode units 2 and 3.

The illustrated steel billet 1 is provided with coined beveled edges 8 to establish ring-like surfaces for initial engagement with the electrode units 2 and 3, as subsequently described. The billet may be formed of cast or scrap steel or may be any other member adapted to be heated by passing a current through the member.

Each of the electrodes units 2 and 3 is generally similar in construction and the upper electrode unit is described in detail. Corresponding elements in the electrode unit 3 are correspondingly numbered in FIG. 1 to provide similar descriptive explanation.

The electrode unit 2 includes a tubular base 9 of copper or copper alloy mounted within a supporting frame structure 10 of the resistance heating unit 4. The base'9 is supported in a suitable electrical insulating bearing 11 to isolate the base from the frame structure 10. A cooling chamber 12 is formed within the base 9 and connected by an inlet 13 and an outlet 14 to a source of coolant such as water or the like. A contact block 15 is brazed or otherwise intimately secured to the end of the base 9 adjacent the billet 1.

The contact block 15 is formed of a high strength, wear resistant material such as carboloy or tantalum. The outer end of the contact block 15 is provided with a frustoconical recess 16 adapted to receive the adjacent end of the steel billet 1 with the coined beveled edge 8 engaging the wall of the recess.

The hydraulic motor 7 is connected through a suitable supporting bracket 17 to the frame structure 10 and includes a piston rod 18 secured to the outer end of the electrode base 9 of the upper electrode unit 2. The hydraulic motor 7 is adapted to axially move the electrode with respect to the billet 1 for clamping of the billet between the contact blocks 15. The motor 7 establishes a relatively high pressure on the ends of the billet 1 engaging the wall of the respective recesses 16 of the electrode units 2 and 3.

The power lines 5 are connected to the bases 9 of electrode units 2 and 3 to establish an electrical connection through the base 9 and block 15 to the billet 1.

The operation of the illustrated embodiment of the invention is described as follows.

A billet 1 is inserted between the electrode units 2 and 3 and the hydraulic motor 7' operated to clamp the billet between the electrode units 2 and 3. The opposite ends of the billet 1 project into the adjacent recesses 16 and establish firm electrical contact between the coined edges 8 and the corresponding surfaces of recesses 16. The control switch 6 is closed to apply current to the electrode units 2 and 3 and the billet 1.

The initial current between each of the contact blocks 15 and the adjacent coined edges of the billet 1 rapidly softens the adjacent coined edges. The motor 7, which is a very rapid response motor, quickly moves the upper electrode unit 2 to maintain a pressure engagement between the electrode contact blocks 15 and the ends of the billet 1 and removes any uneveness which may have occurred as a result of the coining or the like. Any slight arcing which may occur does not adversely affect the adjacent wear resistant carboloy blocks 15.

The heat applied across the narrow contact area or band as a result of the concentrated current in the band continues to soften the adjacent edge portion of the billet 1 and the softened edge of the billet 1 is compressed and displaced with a continuously increasing contact area, such as shown in phantom in FIG. 1.

Although the contact blocks 15 are shown as separate solid blocks brazed or otherwise secured to the base 9, the wear resistant surfaces can be provided in any other suitable manner. For example, the base 9 can be extended and provided with suitable conical recesses for receiving the end of the billet. A carboloy or other hard, wear resistant material can be sprayed, evaporated or otherwise applied to the contact area to provide a longlife contact.

The present invention thus provides an improved electric resistance heating electrode having a highly Wear resistant contact face and an improved contact with the member being heated.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim: 1

1. In a contact in a heat treating unit for resistance heating of a billet having the edges beveled to produce a ring contact area without substantial deformation thereof, a contact base, and a contact block of wear resistant material intimately attached to the contact base, said block having a recess with tapered walls and with an opening diameter greater than the end of the billet and a final diameter less than the billet to define a contact area receiving the beveled edge of the billet and establishing an initial narrow ring contact with the billet.

2. In a contact in a heat treating unit for resistance heating of a billet having coined beveled edges without substantial deformation thereof, a cont act base, and a contact block of carboloy attached to the contact base, said block having a recess with tapered walls and with an opening diameter greater than the end of the billet and a final diameter less. than the billet to define a contact area receiving the end of the billet and establishing an initial narrow ring contact with the billet.

3. The method of resistance heating for heat treating of a steel billet, comprising the steps of coining the end edges of the steel billet, securing the billet between a pair of electrodes having tapered openings receiving the ends of the billet, applying pressure to at least one of the elec trodes, applying power to the electrodes to heat the billet, and said pressure establishing a ring-like contact area without substantial deformation of the billet while maintaining firm electrical engagement therebetween.

4. In a contact unit in a heat treating unit for resistance heating of a workpiece having a planar end without ubstantial deformation thereof, an electrode including a contact end having a recess with tapered side walls for receiving the end of the workpiece and engaging the outer edge of said end, and control means adapted to establish limited relative movement of the workpiece and the contact end for establishing limited deformation of the outer edge of the workpiece engaging the contact end and thereby establishing an initial narrow ring contact with the workpiece.

5. The contact unit of claim 4 having cooling means associated with the contact end to cool the tapered side walls.

6. The contact unit of claim 4 wherein said recess is a frusto-conical recess.

7. The contact unit of claim 6 wherein said recess includes a carboloy contact surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,731,858 Grist Oct. 15, 1929 1,756,857 Gilson Apr. 29, 1930 2,178,032 Clausen Oct. 31, 1939 2,890,324 Havlik June 9, 1959

Claims (1)

1. IN A CONTACT IN A HEAT TREATING UNIT FOR RESISTANCE HEATING OF A BILLET HAVING THE EDGES BEVELED TO PRODUCE A RING CONTACT AREA WITHOUT SUBSTANTIAL DEFORMATION THEREOF, A CONTACT BASE, AND A CONTACT BLOCK OF WEAR RESISTANT MATERIAL INTIMATELY ATTACHED TO THE CONTACT BASE, SAID BLOCK HAVING A RECESS WITH TAPERED WALLS AND WITH AN OPENING DIAMETER GREATER THAN THE END OF THE BILLET AND A FINAL DIAMETER LESS THAN THE BILLET TO DEFINE A CONTACT AREA RECEIVING THE BEVELED EDGE OF THE BILLET AND ESTABLISHING AN INITIAL NARROW RING CONTACT WITH THE BILLET.

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