US2254809A - Metal melting furnace - Google Patents

Description

Sept 2 1941- F. rf-IARALDSEN 2,254,809

METAL MELTING FURNACE gmc/who@ Ma-KW SePt- 2, 1941- F. THARALDSEN 2,254,809

METAL MELT ING FURNACE Syvum/Mm M @www SePf- 2, 1941 y F. THARALDsE-N 2,254,809

METAL MELTING FURNAGE Filed Deo 15, A1957 4 sheets-sheet s Fla d I @www Sept. 2, 1941. F. THARALDSEN METAL MELTING FURNACE Filed Dec. l5, 1957 4 Sheets-Sheet 4 various types.

Patented Sept. 2, 1941 UNITED METAL MELTING FURNACE Filip Tharaldscn, Oslo, Norway Application December- 13, 1937, Serial No. 179,557 In Norway December 21, 1936 (Cl. Sil-12.5)

2 Claims.

This invention relates to the art of melting zinc and other metals having low melting and ignition temperatures and more particularly to improved apparatus for reducing and maintaining the metals in the fluid state. The invention is especially suitable for application to galvanizing processes and,q by way of example, it Will be described in connection with such use.

Heretofore the general practice has been to place th-e zinc or other metal in iron or steel containers, commonly termed kettles" and apply heat externally to the side walls of the containers. Although this method has the advantage of insuring a sufficiently high rate of heat transfer to keep the zinc or other metal in proper condition, the tendency of the zinc to amalgamate with the iron of the container results in rapid contamination of the pure zinc and premature failure of the kettle. The destructive action is accelerated by the presence of chlorides which are unavoidably introduced in minute quantities into the spelter or dross during `th'e galvanizing process. .Another method of heating and melting the metals utilizes a refractory lined container provided with recesses or grooves in its side walls in which are positioned heating coils of Inasmuch as the coils are not in contact with the metal being heated, the difculty of maintaining the required temperature vvithin desired limits is great and frequent interruptions in the galvanizing process are experienced. Also the efllciency of the heating method is very low and the refractory materials are apt .to fail because of localized high temperature zones and pronounced temperature gradients. In any event the life of the refractory materials is short, necessitating frequent rebuilding of the furnace. A

In the melting of zinc, for example, it is necessary to use a ltemperature of about 930 F. in order to secure a reasonable rate of heat transmission. The heat lostby radiation oi the comparatively large body of metal and by absorption by the sheets or Wire being galvanized must be compensated for to maintain the zinc at the required temperature. At 930 temperature, however, zinc burns and consequently cannot be eX- posed to the air when such temperatures are reached. I overcome the above mentioned difficulties by providing a separate heating charnber above thesurface oi the zinc which chamber is sealed against the admission of air.

The apparatus of my invention utilizes a refractory lined container which increases the length of use of the device and aids in keeping the metals low in impurities.

' properties in the finished product.

Ordinarily, zinc in a galvanizing bath is contaminated by the zinciron alloy formed by the action of the zinc on the iron of the container and lby similar action on the metal being galvanized. The elimination of the first source results in a correspondingly increased purity of the spelter and I have provided novel means and method of operation to alleviate the inherent objections to the contamination by the second'source. In the galvanizing process, when the steel to be galvanized reaches a temperature higher than the fusion temperature of the zinc or spelter, a hard, brittle, ironzinc alloy is formed, portions of which spaW-l oil and mix with the spelter. The presence of this alloy, commonly termed dross, is objectionable and must be removed from the spelter which contacts the material being processed. The dross and other impurities ordinarily of greater specic gravity than zinc will accumulate in the bath and Will gravitate ydownwardly and be found at th lower or bottom `part of the bath. In order to prevent an undue concentration of these impurities and to provide for a more economical operation of the process, I provide means whereby zinc containing a controlled amount of such impurities may be readily Withdrawn from the bath, which zinc will not be below the recognized standard of purity for ordinary commercial zinc.

Pure electrolytic zinc which is produced commercially in large quantities at a price only slightly higher than ordinary commercial zinc, has an iron content of .005% or less and a lead content of .01% or less. Ordinary commercial zinc has an iron content of about .1% and lead content of about 1.5%. The ordinary grades are extensively used for castings and for the production of the poorer quality brasses. It is essential however that the zinc used for galvanizing purposes should be as pure as possible in order to obtain the best physical and chemical The use of my method enables the impurities to be drawn ofi in commercially valuable form, i. e., in zinc having an iron content of approximately .1%

Whereas in the methods customarily employed about 10% of the zinc is lost in dross, which substance has a market value equal to but a fraction of the value of the zinc contained in the dross. Any need for an iron or steel container for the bath is eliminated and hence the usualv lead cushion is not required. Thus the lead content oi the zinc is not increased.

The primary object of the invention is to provide a furnace for melting zinc and other metals having low melting and oxidation points in which the heating chamber-is positioned above the surface of the zinc or other metal, the chamber being sealed against the entrance of air.

A further object of the invention is to provide an apparatus for the purpose specified which facilitates the control of the degree of purity of the bath and the removalof the accumulated impurities.

These and other objects and advantages of the invention will become apparent from a consideration of the drawings and the following detailed specification of practical embodiments of the invention.

In the drawings:

Figure 1 is a top view of a melting furnace i constructed in accordance with my invention;

Figure 2 is a sectional view taken along the line 2-2 of Figure 1;

Figure 3 is a sectional view taken along the line 3 3 of Figure 1;

Figure 4 is a cross-sectional view similar to Figure 3 of a modified furnace in which electrical heating elements are substituted for the radiant tubes of Figures 1 3;

Figures 5 and 6 are detailed Views of the electrical heating means employed in the furnace of Figure 4;

Figure 7 is a cross-sectional view of a modified form of furnace in which gas flame heating means is substituted for the radiant tube or electrical heating means;

Figure 8 is a cross-sectional view of the gas furnace of Figure '7, the viewbeing taken along the line 8 8 of Figure '7; and i Figure 9 is a top view of another modied form of furnace.

Referring to the drawings, II indicates a furnace shell supported in a pit in the concrete. foundation I0 and enclosing the inner and outer refractory linings I4 and I2, respectively. A layer of insulating material I3 is positioned between the linings to reduce the heat losses of the furnace. As shown in Figures 2 and 3 the oor of the melting chamber is concaved longitudinally and sloped transversely and portions of the end `walls of the chamber are extended at I9 and. 2| to provide end walls for a chamber positioned above the surface of the metal being melted or heated. A vertical longitudinally extending wall I8 extends between the walls I9 and 2| adjacent the lowermost section of the floor and divides the metal chamber into a pair of compartments 30 and 3|. The lower edge of wall I8 terminates short of the floor of the melting chamber. or suitable openings 21 are provided in its lower portion whereby passageways are provided from compartment 30 into compartment 3| along the inclined bottom surface of the chamber.

A second wall I1, parallel with wall I8',`xspans the compartment 30 and with walls I8, I9 and 2| and a'roof forms n air tightenclosure above the surface of the' ath of metal in the melting chamber of the surface. The roof consists of a number of refractory plates 22 supported` on shoulders on the walls I1, I8, I9 and 2|, a layer of insulation 23 above the plates, and a suitable cover 20. The lower edge of wall I1 terminates short of the bottom of the melting pot but it will l. normally be immersed a vconsiderable distance below the level of the uid metal. It can thus be seen that the fluid metal itself seals the chamber thus created against the entrance of atmospheric and as shown in Figures 1, 2 and 3 the means may take the-form'of radiant tubes 33, suspended from the roof plates 22 by any suitable means (not shown), and provided with gas burners 39 and 34, in accordance with usual practice. In Figure 4, suitable electrical resistance heating elements 4I are substituted for the radiant tubes 33, which resistance elements are supported from the roof plates 22 on refractory tube carriers 43 suspended from the plates by the rods 42. Bushings 44 are inserted in apertures in the plates to prevent the rods 42 from pulling loose from the plates. Any suitable means maybe employed to conduct current to the elements 4I.

It can thus be seen that the metal of the bath is heated entirely by radiation and since the heating chamber is sealed against the entrance of air, a temperature higher than the ignition point of the metal being heated may safely be maintained in the chamber. This higher temperature results in a higher rate of heat transmission and insures the maintenance of proper conditions in the bath. Since the heat input is readily controlled,.the temperature of the bath may be controlled within narrow limits, a feature of importance in galvanizng and other operations. If desired, the heating chamber may be filled with a non-oxidizing or neutral gas and with a pressure slightly higher than atmospheric pressure. To insure against damage to the metal should air accidently enter the heating chamber and to promote heat conductivity between the chamber and metal, a number of plates 35 of high heat conductivity and impervious to attack by the zinc or other metal being heated are floated on the surface of the metal within the chamber. These plates are preferably of graphite and cover substantially all the surface of the bath within the heating chamber.

Figures 7 and 8 illustrate a furnace construct ed in accordance with my invention in which a gas dame is substituted for the radiant tubes or electrical heating elements of the furnaces described above. In this embodiment the heater chamber is enlarged and is provided with checkerwork for the passage of air for combustion and products of combustion. A horizontal wall 5|) divides the heating chamber into upper and lower spaces 53 and 54, respectively, each of said spaces being provided with bales for the circuitous passage of the air and the products. The furnace consists of a refractory vessel 46 -having a dip tank 41 and a shell 45. In an end wall of the heating chamber, a gas inlet 49 is positioned above the surface of the bath and gas issuing therethrough is adapted to be immediately mixed with air coming into the furnace through `a port 51passing through space 53 and lreaching the gas through port 55 in the horizontal wall 50. The products of combustion move across the furnace through space 54 and back again and are exhausted through stack 5B. 'I'he quantity of air furnished is less than that required for com,-

plete combustion of the gas injected so that no air. Suitable heating means are positioned in l' oxygen will be available for combinationwith the metal of the bath. The products of combustion are therefore non-oxidizing and a temperature higher than the ignition point of the metal being heated may be employed. As in theiirst described embodiments, a plurality of graphite plates 35 are oated on the metal within the heating chamber.

Referring again to Figures 2 and 3, it should be noted that the metal of the bath normally comes in contact with no iron or steel other than that being galvanized. The pump 36 is provided solely to empty the tank and it is arranged for ready removal from the apparatus when not required. When the furnace is first started and pure zinc is placed in the pot and melted, pure zinc may vbe tapped out of the compartment 3i by removal of the plug I6, allowing the zinc to flow down the spout l5 into the casting bed 38. After a time, however, the impurities in' the zinc and some additional iron from the steel being galvanized, if galvanizing is being carried on, will accumulate and settle to the bottom of the bath. Due to the slope of the floor of the bath the impurities will gradually move under the baille I8 into chamber 3l. If plug I6 is now removed the mixture or pure zinc and impurities will rise in the comparatively narrow space 3| and be tapped off. By tapping on small quantities at regularly spaced intervals, the pure portion of the bath can be prevented from droppingl below the lower edge'of wall I8, the impure zinc can be removed, and additional pure metal may be added. By varying the frequency and quantity of removals, the bath may be operated in such a manner that the purity of the metal is kept at a certain value for galvanizing operations and at the ysame time the metal tapped off is pure enough to satisfy the requirements for ordinary commercial zinc. The zinc thus tapped o is useful in making castings and for a wide variety of other uses and has a market value only slightly lower than pure electrolytic zinc which is fed to the furnace. It can thus be seen that by reducing metal loss due to oxidation, reducing metal loss due to alloying, and operating the bath in such manner that the impurities may be removed in commercially valuable form, that substantial economies are effected in the operation of the process. Also the heating methods employed result in greater eiciency of the apparatus.

Figure 9 illustrates an` installation embodying the features of the invention in which the tank 5I is substantially longer than the tanks Il of` ing chambers 53 and 54, longitudinally aligned,-

are provided over the surface of the bath and a space is left between them for the convenienti' 50 insertion of the pump 36.` As in Figures 1-3, radiant tubes 33 may be employed inthe heating chambers and suitable openings 56 and 58 may be provided in the top wall of the impure metal compartment. In all installations suitable covers, 51 for example, may be placed over these openings. Figure 9 illustrates that a wide variety of arrangements of the various constituent elements of the apparatus may be made without deviating from the principles of this invention.

As shown more clearly in Figures l and 2, the guide 25, the purpose of which is to direct the travel of the material being galvanized (the rods 26, for example), may conveniently be supported at one end on the wall of the dipping compartment and at its other end in the notch 2d provided in the wall |71.

The above specifically described embodiments of my invention should be considered as illustrative only and not as limiting the invention. Various rearrangements and altered combinations of the'novel features disclosed are readily apparent and should be taken as being within the scope of the invention if so indicated by the appended claims.

What I claim is:

1. Galvanizng apparatus comprising a refractory lined pot for the support and connement of a quantity of molten metal, means to heat said metal by radiation, a plate of high heat conductive material floating on the surface of said material and separating said metal from said heating means, said material being impervious to reaction by the metal, a plurality of compartments in said pot, means to direct the flow of impurities in the metal from one compartment to the other, one of said compartments constituting a vat for the reception of material to be galvanized, and means to tap off the impure metal from the other of said compartments.

2. Galvanizing apparatus comprising refractory surfaces for the support and confinement of a bath of zinc, said surface including an inclined bottom wall and four side walls, a pair of spaced parallel walls extending from above the normal upper surface of said bath toward said bottom.

wall but terminating short thereof, said parallel walls spanning two opposed Walls of said first mentioned walls and spaced from the other two of said rst mentioned walls, a plate of high heat conductive material fioating on the surface of said bath between said parallel walls, said material being impervious to reaction by said zinc, heating means above said plates, means to guide elongated metal shapes through said bath between one of said parallel walls and one of said four walls and means to tap off zinc from the space between the other of said parallel walls and an adjacent one of said four walls.

FILIP THARALDSEN.

Images