US2005175A - Centrifugally-cast circular ingot - Google Patents

Description

June 18, 1935.

Filed Dec.

INVENTOR Patented I June 18,. 1935 UNITED STATES PATENT OFFICE r 2,005,175 CENTRIFUGALLY-OAST CIRCULAR moor James L. Adams, Jr., Youngstown, Ohio Application December as, 1932, Serial No. 649,181

3 Claims.

The presentinvention relates broadly to the art of ingot making, but more particularly to the high-speed centrifugal casting of relatively wider and thinner than usual circular ring ingots, in

. which the successive stages of solidification have been appropriately controlled so as to give great solidity'and density to the resultant mass, with substantially complete elimination of the cus-. tomary pipes, shrinkage cracks, blow-holes, gaspockets, blisters, non-uniformity of carbon-distribution, variations of chemical structure and crystal formations, and slag and other non-metallic inclusions common to the usual ingot of commerce, in which considerable segregation, or

5 separation of the several constituents of the molten mixture, normally occurs during the initial cooling and solidification.

My invention also covers an ingot in which certain surfaces, or at least one surface, has been preferably hot-trimmed after solidification, to better prepare the metal for subsequent belt-mill rolling, and remove un-wanted surface inclusions.

Some of the primary objects of the present invention, therefore, consist inthe provision of a metal ingot which is (1) uniformly dense and solid throughout, within very narrow plus and minus limits, (2) of substantially uniform chemical composition, and if of steel, then of very uniform carbon-content throughout, (3) that is substantially without interior piping and fissures, or

shrinkage cracks, (4) that has been substantially freed of slag, non-metallics, and low-density metallic inclusions, (5) is very low in gas-inclusions, (6) that has been trimmedto remove at least interior surface irregularities and non-desired elements, ('7) which is of the extra wide and the thin walled type, and (8) has substantially all of its coarser, radial-cleavage-plane type of crystal structure located just below the outside diametral surface, where it is readily broken down intofrom one of the broad surface faces toward the other, across its thinnest sectional dimension, under such heat control as to eliminate all interior piping, and inner diameter sub-surfacecrystal slip planes, and avoid the imprisonment of non-desired slag and gases.

A further object of value was to supply an ingot of such shape that the rolling will elongate the entire mass together, and not have to "pull outmetal that is well away from the roll surfaces, as in the usual square orrectangular ingot.

That is, the latter type of ingot has, to begin with, a heavy sub-surface layer all around, of coarse, weak metal crystals with outwardly. directed inter-crystal cleavage envelopes, which will not. stand very much ingot elongation without separation tending to occur between successive crystals, and thus opening up the surface and near surface layers to the entry of air and oxygen. The first pass through the rolls breaks down these crystals into a finer and tougher grained structure, capable of standing far more stretching out abuse thereafter, but in a rectangular straight type ingot the first pass, unfortunately, does not contact with but two faces of the ingot. The metal on the other two main faces must however stretch very considerably-during this first pass, although the crystals there have not yet been worked between the rolls at all, and are, in consequence, still very brittle and weak longitudinally of the ingot, so that a certain amountof opening up of the crystal surface and near-surface elements occurs, very detrimental to the final sur-' face layers here after the rolling. In my ingot, however, the percentage of the total ingot surface that is not directly reached by the first pass through the rolls is almost negligible, and the general thickness of the ingot is so vastly much less than in the customary straight rectangular ingot, that substantially all of the r0ll-to roll metal at any given instant is being extended about equally, and not part being lengthened while the larger bulk holds-back in the piece, and has to r be pulled-out and its crystals separated by the former, by sheer strength and awkwardness.

The net result is that my ingot gives a much better knit final surface structure, and at the same time a far more rapid reduction to the required size in the mill.

greatly cut plate and sheet manufacturing costs, by providing a typeofingot eminently suited for use in connection with a high-speed and highcapacity, continuous belt-mill, such, for example, as that shown and described in my co-pending application, Serial #674,661, filed June 7th, 1933.

One leading object is to substantially eliminate the now usual 15% to 25% end-crop loss, necessitated by the customary interior piping and solidification fissures.

Another important object is to provide an ingot which has not only been centrifugally cast at high-speed to assist in densifying and-purifying the metal, but which has been jarred" or shaken also, during its solidification period, if desired. so

Another vital object of my invention is to Y as to better get rid of gas inclusions, through the more or less viscous metal.

Another object is to get'an ingot in which the non-desired inclusions have been delivered substantially in toto, to the smooth interior cylindrical surface, where they are readily hotor coldtrimmed away, to thus leave a clean metal product. I

Another object is to greatly cutthe usual solidification time, and the soaking pit heating period, by supplying a relatively thin walled ingot, of broad expanse. I

An outstanding object is to provide an ingot of such form as to require a minimum number of passes through the mill to roll to required thicknesses.

A further object is to provide an ingot of such shape that it can be quickly and conveniently heated, or evened up in temperature, as required, either by gas or by oil flames, in a reducing'atmosphere, or inert gas envelope, if desired, or

electrically, by peripherally or otherwise circulating currents, preferably. produced directly in the metal by electro-magnetic induction, which can be made to automatically give the greater concentrations of current in the lower temperature belts around the ring, and therefoiffe'the greater heating-up here, to provide (quick evening-up of temperatures therein.'-

A still further object met by a ringingot is that it may be rotated, v'ery readily around-its own axis during the heat-ing, if so desired, and thusfgive greatiuniformi tyi to the resultant temperature, even if some of the burners may be d'ffsizeh' Another object of my invention is toprovide an ingot so thin "ii section as to greatly fore-shorten the solidificationtime', and thus the time :allotted both for segregation of the constituents'of the metal mixtuzfe, and for the growth in size of the metal crystals, thus leading at once toija more general uniformity of the chemical strueture, as wellas to a more refined grain development, preparatory to rolling.

An added object is to provide an ingot so poured centrifugally, as to substantially eliminate the usual surface sliver, and tear, or droplet formations, and laminations, whichnow often carry over into the final rolled surfaces, and cause numerous inspection rejections, with consequent costly scrapping, as a result of splashing in the far corners of the usual mould, during the pourmg. t

A supplementary object is to provide an ingot of such form that it may be very conveniently hot-trimmed on at least one major surface, by water-cooled rotary blade tools, which are the only known type capable of standing up for long periods of regular use, under the very high surface temperatures encountered on a heated ingot, either just before it enters, or as it leaves the soaking pit, preparatory to rolling. Yet another object is to provide a form of ingot which can be rolled into ultra lbngplates, or non-cut bands, as required, and of greater than usual total weight per piece. the utmost advantage in electric pipe welding, to cut down the total end-scrap losses.

Other worthwhile objects will be obvious to anyone versed in the art to which my invention appertains.

With all these and other objects in view, I have provided an ingot which will substantially fill such requirements, it being noted that my apparatus is capable of keeping the interior broad surface of the ingot liquid as long as may be de- Such very long plates are of' sired to assure that the solidification will be progressively from the outer peripheral face inward through the casting, and under such centrifugal and jarring conditions as to assure maximum compacting, but without extending such heating enough to permit the growth of large crystals, and extended segregation of the more easily separated components'of the metal.

'It will be further noted that I preferably hot trim at least one major surface of my ingot, so that the latter is supplied with surface minor inclusions eliminated substantially from this face, and with variations in thickness of ring reduced to a form entirely amenable to later rolling, without introducing side camber in the finished belt. Thus if the ring be somewhat thicker, at one point around the periphery thereof, this willintroduce no especial trouble in the rolling, provided such extra thickness is not to severe, and provided further that it is maintained constant for the full length of the ingot, and does not alter the uniform heating.

Or if the mould be made somewhat conical in its interior, for easier withdrawal of the ingots after solidification, such conicality will not necessarily interfere with the production, nevertheless, of a straightbelt, provided the lesser end of the cone be made proportionately thicker radially, so as to give anequal bulk of metal, and weight, per inch of axial length of ingot, preparatory to the rolling.

It is not obligatory that my ingot be hottrimmed to meet the above mentioned conditions, as it might be conceivably so cast as not to need it, but I prefer trimming, and in my copending application, ,Serial #680,570, filed July 15th, 1933, I have illustrated and described apparatus, and a method of producing the ingot of my present invention, while a further co-pending application, Serial #652,142, filed January 17th, 1933, shows an ingot-buggy suitable for the quick and expeditious transport of my ingot from soaking pit, and its delivery direct into my belt-mill previously referred to, while under slow, continued rotation so as to not receive a chill in localized spots therearound.

While my improved ingot is particularly adapted for use in the belt-mill of my invention, be-

fore referred to, it might conceivably be applied to other uses, where compacted, clean, pure metal, substantially 'free from slag inclusions, is required.

In the drawing, Figure 1 is a perspective elevation of my improved ingot, showing the approximate desired proportions thereof.

Figure 2, in similar perspective, shows a modified form, also amenable to easy rolling, it being noted that there may be a plurality of either or both of the types of general surface alteration shown, if desired for easier ingot moulding purposes, without serious eifect on the final shape 7 of the crystal structure over these latter or nontudinally into=an ultra-long narrow strip, or a square. Y

In all these figures, similar parts are designated by the same reference-numbers, successive letter subscripts being added to distinguish between the successive figures.

" Referring now more particularly to Figure 1, my ingot is shown at I, .while 2 and 3 indicate interior and exterior general surfaces thereof, respectively.

-In Figure 2, similar elements are indicated by 2a and 3a respectively, while at 4 and 5 are shown full length radial projections and depressions, re-

spectively, the normal extent thereof being exaggerated considerably for the sake of cleamess. In Figure 3, a coned ingot is shown, in which 6-6 and 1-1 indicate the major and minor diameters, respectively, while 8 and 9 refer to the respective wall thicknesses at these same ends, it being noted 9 is made substantially as much thicker than 8, as the major diameter is to the minor, so that inch-by-inch of axial length of ingot, the same total weight will be presented. But these proportions may be altered slightly to correspond with actual behavior of the ingot upon first rolling tests, to give a straight, non-cambered belt.

In Figure 4, at the left, progressive surfaces of inner solidification are presented at 3c, l0 thru l5, and finally 20, while at the right I have shown roughly the general form of the resultant crystal lization of my ingot, in which at It is illustrated the substantially radially placed, coarse, and initially weak outwardly directed, but sub-surface dendritic structure, and at H the much smaller grained and tougher, free crystal inner structure, while it shows the thin surface layer of non-metallic inclusions carried to the extreme interior position by the strong centrifugal effect and the active shaking introduced during the solidification period. Later on these latter are usually removed, as'indicated at 2'0 here. I make sure that the freezing of the ingot occurs progressively as shown, by addinginterior .dis'tributed heat,-as and if required during the solidification interval.

These sub-surface dendritic, or tree-trunk like crystals show radially positioned and relatively very weak envelopes, or cleavage shells, which,.

however, if not opened up to oxidation by pulling apart, very largely disappear during the first and second passes through the mill, becoming more finely grained and tougher under the actual working. It will be especially noted that the total amount of free edge surface, at the two axial ends of my ingot, and which is not directly contacted by the rolls even during'the very first pass there- .through, is very small indeed, so that practically all of the near-surface .dendritlc structure of my I ingot is broken down and toughened immediately, while very little of it must be stretched out by the elongating ingot, without direct rolling thereover, or so as to pull apart and open-up the cleavage shells, or planes, and thereby give a porous, 'oxidized, and materially weakened nearsurface layer.

It'will, however, be equally noted that in the ordinary straight rectangular ingot of commerce, certainly not over about 60% to 65% of the total outer dendritic surface ,layer can possibly be reached during the first pass through the rolls. But the ingot .as a whole, and therefore its remaining two major faces along therewith, must stretch or elongate nevertheless, thus breaking open for the free entry ofair and oxygen, much worked faces, which'it is then hoped will weld together properly again during the next pass, after a 90 degree turn. of the ingot.

' But such welding may, or may not, actually ocour to the full value desired.

In my ingot, however, substantially all of this detrimental effect is obviated, it being noted, from my co-pendlng application above referred to, that I even provide means whereby the narrow end faces of my ring ingot may be rolled down likewise during the very first pass through the'mill, if so desired.

In Figure 5, I have shown axially-directed -ofl"-. set and elements, exaggerated for the sake of cleamess, and which would normally give an unstraight and camberless belts were required, but which, in the helical spiral or screw form shown at l9 and 20, might conceivably roll out into a desirable type of belt, provided the latter were to be spirally slitted into an ultra long final strip,

in which case the offsets would permit a' material shaped final form, so that the forward end of one can he slipped just within the trailing axial end of the preceding, and so on indefinitely. v

In such cases, the conical ingot of Figure 3, or the straight sided product of Figure l, may be supplied to the mill with one axial-end very desirable form of ring-ingot,. where precisely slightly thickened up radially, beyond the value originally intended in the respective figures.

This will then produce a slightly coned belt, or one which, if later cut across, will develop an edgecurved or cambered plate; if such were desired.

From my co-pending ring-ingot producing apparatus application, above cited, it will be noted. that I centrifugally rotate such ingot during preferably the entire pouring and solidification period, and that as, and if desired,'I may also jar the said ingot during all, or selected portions of such period, as determined.

Certain very definite advantages accrue to an ingot produced in this manner. 'I'hejarring very radically accentuates the elimination of gases, particularly, over what is possible under a straight centrifugal process.

Other very decided advantages accrue from the fact that I hot-trim the interior surface thereof,

at least, and thus deliver an ingot substantially free from slag, and non-metallic inclusions.

Further definite advantages accrue in my ingot from the control of the solidification so as to restrict it to a single inwardly progressively cylinder of solidification at any one instant, whereby all interior piping and fissures are avoided.

Other important advantages accrue thereto because of its high percentage of actual rolling surface, compared to the idle areas within the ingot,

whereby high percentages of reduction per pass become possible; thus greatly expediting the rolling, enabling the latter to be completed during higher than normal temperatures and therefore with less destructive work on the metal structure, so that a much greater than usual total reduction and elongation can be readily reached.

Other advantages arise from my ingot requiring a ,far less time than usual in the temperature equalizing furnace or the soaking pit, because of its thin wall, and shape which is very favorable forItemperature equalization in a short period.

Very decided advantages accrue from the fact that my ingot has been produced under conditions which give it a far' greater uniformity of carbon-content, in case the metal used is steel, than has heretofore been customary in the usual straight ingot of commerce, wherein the carbon may be very decidedly different at the top than at or near the bottom, and also with local spots of divergent carbon percentages.

Other advantages accrue from my ingot being of a form which can be slowly rotated during transport hot to and from the soaking pits, thus eliminating the customary cooler spots dueto the usual prolonged contacts with cold metal parts, before reaching the rolling-mill rolls.

Yet other advantages accrue from my ingot having been so cast as to avoid substantially all splashing of the molten metal from the farthermost points of the mould, as is customary for the straight-ingot mould, with consequent formation of surface defects of numerous types in the resultant ingot of commerce.

An added advantage accrues from the combination of all the above mentioned advantages in one and the same product.

Still further advantages will be evident to anyone versed in the art of ingot making, and although I have shown several preferredembodiments of my invention, it will be understood that moderate changes in the form and construction thereof, may be made without departing either from the spirit of my invention, or the scope of my broader claims.

I claim:

1. A cast ring-ingot with substantially helically directed end-faces, on its axially disposed ends. said end-faces forming offset elements with respect to main body of ring-ingot, but included between inner and outer radii of latter.

2. An exteriorly straight-line coned ring-ingot with constant weight per running inch along its generating axis, and with a helical offset located on'each end thereof, as taken in axial direction.

3. A cast ring-ingot with straight-line coned outside generated surface, with constant weight of metal per axlalrunning inch therealong, andmade of a steel'characterized by all the qualities imparted. by concomitant centrifugal casting, and jarring, during the pre-solidification period thereof.

JAMES L. ADAMS. 'JR.

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