US2502770A - Induction heater - Google Patents

Description

April 1950 c. H. wATsoN 2,502,770

INDUCTION HEATER Filed NOV. 16, 1945 2 Sheets-Sheet 1 Invent??? (045 14 Wflffia/v,

2 Sheets-Sheet 2 Inventor: (am/MY War-90m awn fi/J flzfa/m g c H WATSON INDUCTION HEATER April 4, 1950 Flled Nov 16 1945 Patented Apr. 4, 1950 UNITED STATES PATENT OFFICE INDUCTION HEATER Coleman H. Watson, Birmingham, Ala., assignor, by mesne assignments, to Carnegie-Illinois Steel Corporation, a corporation of New Jersey Application November 16, 1945, Serial No. 629,152

3' Claims. 1

This invention relates to improvements in electrically heating continuously moving strip, rod, wire or the like, and more particularly to induction heating of such articles.

Heating continuously moving strip, rod, wire, etc. is done for various purposes, such as annealing, or air bluing, and in preparation for continuous hot dip galvanizing or tinning. Another common use of such heating is to melt electrolytically deposited tin coatings to render the same smooth and lustrous. Two methods of fusing such coatings of tin have been commonly used. One method is to pass a heavy electric current through the strip by means of brushes and collector rings which are connected to the rolls carrying the strip. The installation expense for such method is quite high and the operating expense is high, due to current drop in leads and brushes, and leakage to the ground. It is also objectionable due to the bearings being heated by eddy currents making lubrication difficult and inefiective.

Another commonly used method for melting tin coating on continuously moving strip is by high frequency induction. As in the foregoing method, the installation expense is quite high and production expense is high due to the losses inherent in such type of heating.

It is accordingly an object of the present invention to provide an efiicient manner of heating continuously moving strip, wire, rod and the like.

It is another object to provide an electrical heater for continuously moving strip, wire, rod and the like, which is relatively simple in design and low in cost.

-The foregoing and further objects will become apparent from the following specification taken in conjunction with the appended drawings, wherein:

Figure 1 is a diagrammatic view of an electrical induction heater for continuously moving metallic strip embodying my invention;

Figure 2 is a modification;

Figure 3 is a modification particularly adapted to annealing, normalizing or hot dip galvanizing continuously moving metallic strip; and --Figure 4 is a modification of Figure 3, and shows an arrangement particularly adapted to melting an electrolytically deposited tin coating on continuously moving metallic strip.

Referring more particularly to the drawings, the numeral 2 designates a continuously moving strip of electro-conductive material, such as steel, which is passed upwardly around a roll 4 and downwardly around a roll 6 and returned to a generally horizontal plane of movement around a roll 8. The rolls 4 and 6 are mounted with their axes parallel and anelectro-conductive roll l0, having a diameter greater than the distance between the peripheries of rolls 4 and 8, is disposed slightly thereabove so thatithe strip in its upward and downward travel is deflected substantially thereby so as to firmly contact the same throughout its width to make a good electrical contact therewith. This in effect forms a closed loop I2 of conductive material by forming an effective short circuit for the lower ends of the looped strip.

Disposed adjacent the downwardly traveling leg of the loop [2 is a primary l4 connected to a source of low frequency current, such as conventional cycle by leads IS. The primary has a core [8 formed of magnetic material through which the downwardly extending leg of the loop l2 passes, whereby the loop becomes the secondary of the transformer. If the strip has been previously electrolytically coated with tin, the heating can be regulated to bring the tin coating to a state of fusion whereby a bright lustrous coating is produced. Since the loop of the strip is the secondary, there is no loss due to drop in resistance caused by leads, brushes or collector rings. Moreover, since all the current induced by the primary and core in the strip is confined to the short-circuited loop, there is a negligible voltage across the junctions at the connector roll, and therefore, no appreciable current can be cir culated through the ground. Since no current circulates through the bearings, no heat is generated therein by eddy currents. In Figure 2, there is shown a modification wherein the connector roll I 0 is replaced by a fluid connector, such as a lead bath contained in a pot 20. Additional rolls 28 and 3B are provided so that the strip may be directed into and out of the pot. The pot may be divided into two compartments 22 and 24 by a partition 26. Such a partition permits using the pot 20 for tinning or galvanizing the strip. To prevent the spelter or tin being carried up to roll 6, the compartment 22 may contain molten lead, and compartment 24, the liquid coating metal, such as lead or tin. This permits the strip to be brought to the proper temperature before entering the coating bath.

In Figure 3 there is shown a modification which is particularly adapted to annealing, normalizing or hot dip galvanizing continuously moving metallic strip. In this modification the strip 2 is taken from a reel 32 having a brake 34 thereon and led around the conductor roll 6, which may be formed of copper, and over a power driven pinch roll 36. Tension on the strip 2 resulting from action of the brake 34 keeps the strip in good electrical contact with conductor roll 6. Pinch roll 36, in addition to drawing the strip from the reel, performs the function of feeding or driving the strip. The strip is withdrawn from tank 20, which may contain molten lead or zinc, after passing around roll 8 upwardly over r011 30 and onto a reel 38. The reel 38 is driven by a suitable torque motor (not shown) which is adjusted with just enough torque to take up the slack in the strip but not to material- 1y tension the heated strip. The loop I2 is shortcircuited by connecting the pot 2t and roll 6 to the grounded frame 40 or they may be directly connected. R011 6 is connected to the ground by brushes 42 contacting a neck or extension of the roll.

If desired, tubes 44 and 46 may encase the strip as it enters and leaves the pot 20. These are sealed at the bottom by extending into the molten metal 124 and by baffies 48 and 50 at the top. These tubes can be provided with a suitable atmosphere, such as reducing to prevent the formation of asides, or the tube 44 can hold a gas suitable for cleaning or pickling the strip.

Since the strip Z is cold as it passes over roll 6 and is not heated appreciably until after it has passed over the power driven pinch roll .36, the pinch roll can be formed of any insulating material, such as rubber, which has good tractive properties.

In Figure 4,1 have shown a modified form of the arrangement shown in Figure 3, which is particularly adapted for melting an electrolytically deposited tin-coating on continuously moving strip. Inthis arrangement, the strip 2 is received from the electrolytic coating line and goes after treatment to a conventional drive bridle and shears. The roll 8 in the tank is preferably a copper conducting roll which is connected to the brushes of the upper roll by brushes 52 through the grounded frame. The pot contains a'quenching bath 25, such as Waten'inste'ad of a molten metallic bath. The bath should be deep enough to ensure the coating being frozenbefore the roll 8 is contacted. The tube or muffle 44 in this case is used to conserve the heat though it may contain a controlled-atmosphere.

If desired, the arrangements of Figures 3 and '4 could be used to blue the strip by maintaining steam or air in the muffle 44 and heating the strip to the correct bluing temperature. the arrangements of Figures 1 and "2 could be used by providing a suitable muiile therefor.

While I have shown and described four specific embodiments of my invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised within the scope of my invention, as defined in the appended claims.

I'claim:

1. Apparatus for heating and coating continuously moving metallic strip comprising means for establishing an alternating electro-magnetic field, means for continuously passing strip through said fieldysaid means comprising entry and exit rolls Likewise,

on either side of said first mentioned means, a power-driven pinch roll disposed adjacent said entry roll for maintaining the strip in close con-' tact with the entry roll and for advancing said strip, the exit roll being disposed in a conductive container, a bath of molten coating metal in said container, and means electrically connecting the entry roll and the container to form a conductive loop including the portion of the strip between the entry and exit rolls and said means connecting the entry roll and the container.

2. Apparatus for heat treating continuously moving magnetic metallic strip comprising means for establishing an alternating electro-magnetic field, means for continuously passing strip through said field, said means comprising entry and exit rolls on either side of said first-mentioned means, a power-driven pinch roll disposed adj acent said entry roll for maintaining the strip in close contact with the entry roll and for advancing the-strip, atheexiting roll being disposed in an electrically conductive container, .a bath oi molten metal in said container, tubes :surrounding said strip on the entry andexit side of said bath and extending into said bath to maintain the heated strip in a controlled atmosphere and means electrically connecting the entry roll and the container 'to form a conductive loop in cluding the portion of the strip between the entry and exit rolls and said means connecting the entry roll and the container.

3. Apparatus for heat treating continuously moving magnetic metallic strip comprising means for establishing an alternating electro-magneti'c field, means for continuously passing strip through said field, said means comprising entry and exit rolls on either side of said first-mentioned means, a power-driven pinch roll disposed adjacent said-entry roll for-maintaining the'strip in close contact therewith and for advancing the strip, the exit-roll being disposed inan electrically conductive container, a bath of molten metal in said container'and means electrically connecting the entry roll and the container'to'form an electrically conductive loop including the portion of the strip between the entry and said container and said means connectingthe entry roll and said container.

COLEMAN WATSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Denham Jan. 18, 1949

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