US1914354A - Electric induction furnace - Google Patents

Description

June 20, 1933. w. ADAM, JR

ELECTRIC- INDUCTION FURNACE Filed April 2, 1930 Patented June 20, 1933 UNITED STA TES' WILLIAM ADAM, JR., OF ABINGTON, PENNSYLVANIA ELECTRIC INDUCTION FURNACE Application filed April 2,

My invention relates to an improvement in an electric induction furnace.

A purpose of my invention is to adapt an electric induction furnace to more successful operation in melting low melting point al- A further purpose is to utilize an induction furnace in melting alloys sought to contain definite proportions of one or more easily volatile or readily oxidizable const1tuents 1n the product, particularly zinc alloys containing cadmium, lead, copper, aluminum, magnesium, mercury, or the like, in which a definite percentage of the alloying metal 1s necessary for subsequent mechanical manipulation of the cast bar, or is desired in the prodnot.

A further purpose is to avoid poor crystal structure or other undesirable physical propert ies due to excessive pouring temperatures in inductively heated metals.

A further purpose is to prevent the production of striations in castings made from an induction furnace.

A further purpose-is to avoid the loss of volatile Or oxidizable constituents such as cadmium, aluminum, mercury, magneslum, and the like, from a low melting polnt alloy melted in a furnace by providing the furnace 0 with a heated delivery spout having a heat conducting lining.

A further purpose is to provide an 1nduc' tion furnace with a desirable form of heated delivery spout. I

Further purposes will appear in thespecification and in the claims.

I have elected to show one main form only of my invention, showing however detail 0 modifications and selecting a main form and detail modifications that are practical and efficient in operation and which well illustrate the principles involved.

Figure 1 is a side elevation, half-section,

showing my invention embodied upon a submerged channel type of induction furnace of the character indicated.

Figure 1a is a fragmentary section taken upon the line 1a--1a of Figure 1.

Figure 2 is a reduced scale fragmentary 1 930. Serial No. 440,971.

sectional view illustrating another form of delivery spout and a heater therefor.

Like numerals refer to like parts in all figures.

Describing in illustration and not in limitation and referring to the drawing In the melting and pouring of low melting point alloys considerable difliculty is encountered by reason of the low temperature range between the point at which the metal becomes molten and the temperature at which it is desirable to pour the metal. For example, in the making of photo-engravers zinc sheets an alloy of zinc and a small quantity of cadmium and lead is used which becomes molten at about 800 F. and in which the crystalline character of the metal very considerably and disadvantageously changes as v the pouring temperature rises; so that the crystalline structure is undesirably affected by pouring at 850, and the metal is noticeably injured at 880.

It is desirable to pour the bars from which the sheets are made by a comparatively wide and shallow stream and, if the temperatureof pouring be too low, the casting thus made has longitudinal lines or zones of weakness in it which develop into streaks and fissures in the rolled plate. In this particular illustration therefore there are disadvantages both ways, through unfavorable crystallization if the temperature be much raised, and through physical defects in the casting if the temperature be much lowered.

' Again, in melting zinc base die casting alloys, which usually contain a few percent of aluminum and copper, and a small amount of magnesium, it is important to keep the pouring temperature low, especially for the sake of reducing oxidation.

The above examples are used as illustrations only, but there are various otherlow melting point alloys, such as type metals, lead alloys for storage batteries, zinc alloys for primary cells, etc., in which the same condi-. tions are present, even if to less degree.

These low melting point alloys are very desirably treated in induction electric furnaces of which the most desirable, because the least complicated in manufacture and in use,

are furnaces of two main types, the one having a submerged channel in which the heating takes place, of which the best examples are found in the Wyatt type (see WVyat't Patent No. 1,201,671) and in the Foley type (see Foley Patent No. 1,638,660) and the socalled .coreless furnace, of which the best examples are found in various Northrup patents (beginning with Northrup No. 1,286,394 andNo. 1,286,395).

Along with the marked advantages in mmplicity, efliciency and ease of control embodied in these two forms of induction furnace, both forms have disadvantages from the standpoint of melting these low melting point alloys, in that both have the coolest metal at the surface and the hottest metal at some other point in the body of the pool of the furnace.

The Wyatt and Foley types of furnace present more difiiculty from differences in temperature than the coreless type, s nce the molten metal in the channel comprises rela tively a small part of the total molten metal content. The metal is heated below the body of the pool, and is driven into the pool as a jet, and this does not secure as qu ck and uniform circulation as is obtained in the coreless form where the molten metal circulates upwardly at the center of the pool spreads outwardly at the top and receives its morements of heat largely during the downward movement around the circumference. In both forms the surface is exposed to atmospheric cooling, and pouring takes place from the surface through a pouring spout.

I have discovered that the temperature of the mass of the pool of either pf these furnacesneed not be raised nearly as high as would otherwise be the case if this surfacepoured molten metal be heated at this point.

Part of the difiiculty lies in the fact that attempts to pour the molten metal at a low temperature result in the metal being chilled by the cooler pouring spout, resultlng in reduction of the cross section of the pouring opening and in corresponding reduction in the width of the bar as poured or in defects within the bar as poured. The pouring temperature for the metal has in the past been excessively high in order to overcome the chilling effect of the unheated spout, and the metal as poured has been of poorer crystalline structure than is desirable for the best uses. Much of the zinc base alloy poured has been intended for photo-engravers Zinc sheets in which the character of crystalline structure is highly important.

I illustrate in Figure 1 a typical induction furnace, the illustration being intended for a conventional one of any furnace to which my invention is adapted to be applied.

In the illustration the furnace comprises an upper portion 5 that contains the molten bath, a vertical V channel 6 having spaced ends opening into the bottom of the bath, the apex of the V at 7 being usually a considerable distance below the bottom 8 of the bath, and an inductor heater looping the V channel.

A voltage impressed on a primary coil 9 causes flux to traverse the furnace core 10,

thereby inducing current in the molten alloy within the V-shaped channel 6, this metal acting as the secondary of the transformer.

A current of relatively high value flows through the metal in the V-shaped channel, heating the metal by resistance, and at the same time the alternating magnetic field threading the channel sets up electrodynamic forces which eject the hot metal out of the as my best form in compliance with the statute.

When the molten bath in this type of furnace has comprised alloys containing volatile substances as for example mercury, the volatile constituent has in the past been largely eliminated due to its materially lower boiling point.

When in the past the induction furnace has been operated at a temperature sufficiently low to produce castings of the best physical characteristics, the melt has frozen when poured, and as a result it has been thought that the induction furnace was not well suited to the use indicated.

I have found that the mere addition of a heater upon the delivery spout of the induc tion furnace adapts the furnace to pour at a temperature at which good crystal structure will result and the metal will be free from defects.

The heater 11 upon the delivery spout permits the furnace to be operated at a somewhat lower temperature which I find prevents the undesirable features which have in the past made the furnace unsuited for use with this type of alloy.

In Figure 1, 12 represents an outer metallic shell of the spout, used for support only. A suitable thickness 13 of good insulating material, such as asbestos or diatomaceous earth, should be placedbetween the shell and heater.

An interior space 14 is provided for the nichrome.

The material 15 between the heater and the inside of the spout is made of a good heat conductor such as graphite or chromite.

For instance, in pouring zinc slabs into an open mould the stream of molten metal may desirably be a sheet eight or nine inches wide, while where the metal is to be poured into a crucible or into a die casting machine around stream of metal of one or two inches in diameter is preferable, and I shape the spout according to the needs of service.

In the reduced scale view shown in Figure 2, I show a delivery spout very similar to Figure 1 except thatthe angle from the body of the furnace into the spout is much steeper than that shown in Figure 1 and the heating element ll'is placed outside the supportingshell 12, instead of inside as in Figure 1.

Where mechanical difficulties are not such as to overbalance the desire for a greater heating efiiciency, the heating elements are desirably inside the shell.

In Figure 2 the shell 12 flares outwardly to form the spout, and the heating elements are-placed substantial 1y against the shell and covered with good heat insulation material 13 such as asbestos or diatomaceous earth. The inside of the shell is lined with a good heat conductor at 1 6, such as graphite or. chromite.

My invention is most desirably applied to a submerged channel type induction furnace, but it will offer certain advantages in connection with any induction furnace, and I Wish to protect any embodiment in an i11 duction furnace.

In View of my inventionand disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus describedmy invention, what I claim as new and desire to secure by Letters Patent is 1. An electric induction furnace for melting volatile alloys, the furnace being formed of material having poor heat conductivity, a delivery spout on the furnace, a heat-conducting lining for the spout and a heater adjacent the lining.

2. In an electric induction furnace, an inductor coil, a furnace body of poor heat conductivity holding a volatile charge adapted to be inductively'heated by, the coil, a delivery spout on the furnace body, a heat conducting lining for the spoutand a resistance heater adjacent the lining.

3. In an electric induction furnace, an inductor coil, a furnace body of poor heat con ductivity holding a volatile charge adapted to be inductively heated by the coil, a delivery spout for the furnace body, a heat conducting lining for the spout, a heater for the lining applying the heat to the lining and a heat insulator beneath the lining and insulating both the-lining and the heater.

WILLIAM ADAM, JR.

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