[1]Un.ited States Patent Office Patented Oct. 18, 1960 2,956,320 CASTING OF METAL Verne Pulsifer, La Grange, M., assignor to OHn Mathieson Chemical Corporation, East Alton, Ill., a corporation of Virginia Filed Dec. 28, 1955,, Ser. No. 555,923 10 Clabns. (CI. 22-.:57.4) This invention relates to the art of casting of metals and more particularly to an improved apparatus and method for continuously casting a slab of metal in t-he cross sectional shape approaching that of strip or sheet metal. A typical slab may have cross sectional dimensions in the neighborhood from aroimd 4" x. 1/2 " up to around 30" x 1/2" for example. Heretof,ore, the method of continuously casting metals has met with a substantial degree of success only in casti.hg of ingots of relatively great thickness. For this reason continuously cast circular ingots and rods or nearly square billets of relatively heavy sections are more common than rectangular sections having a width far M excess of the thickness. But it has long been recognized that it would be desirable to continuously cast a flat slab suitable for further processina to commercial sheet metal by just a few additional finish operations instead of the rather extensive rolling reductions, both hot and cold, and annealing steps required to bring a heavy slab or bloom down to the shape and gauge of the wrought strip or sheet metal product desired. Attempts have been made to directly cast thin slabs of metal by continuously pouring molten metal between a pair of cooled rolls, e.g. U.S. 49,053, issued to Bessemer, and U.S. 382,321, issued to Nor-ton et al., or upon the surface of a casting drum, e.g. U.S. 1,531,747, and U.S. 1,611,911, issued to Hazelett, or between cooperatin.- drum and belt, e.g. U.S. 359,348, issued to Daniels, and even between traveling belts, e.g. U.S. 594,583 issued to Wood. But metal produced with the methods and devices of the type represented by this and other prior art and known improvements thereon has been inferior and cornmercially unacceptable except for a few low melting metals, notably lead and zinc. A metal such as cartrdge brass or aluminum, for example, produced on apparatus of this type is found to be entirely too porous in intemal structure and is characterized by a very poor surface having many cold shuts. These surface irre,- ularities may be attributed largely to irregularities and disturbances in movement of the molten nietal as it approaches the mold wall. Therefore, one object of this invention is to provide acontinuous cast@n.@ apparatus and process free from the difficulties and disadvanta-,es encountered with prior devices and novel methods of producing a comparatively thin continuous castingof metal slab. Another object is the obtainrnent in continuous casting of substantial constancy of therinal conditions during the whole of the operation and of re.-ularity of the progress of solidification by having as great and constant as possible a portion of the final cooling affected through the cross section of the ingot itself, with a thermalgradient approaching the horizontal, rather than through the. lateral sijrface of the ingot. Thus internal shrinkage aiid radial cracking are avoided to a considera-ble degree. Another object is to provide a new and improved apparatus for economically and efficiently casting continu2 ous lengths of relatively thin metal metal strip of satisfactory soundness, surface quality and gauge. Another object is the provision of new and superior means for the substantial elimination of mechanical forces and influences which disturb and impair the proper solidification of the molten metal in continuous casting apparatiis of the type described. A still further object is to provide a new and improved control of the molten metal solidification in continuous 10 casting apparatus of the type described. Other objects and advantages of the invention will be apparent from the following description and the accompanying drawing in which: Fig. 1 is an elevational view in cross section of a 15 preferred embodiment of this invention-, Fig. 2 is a view taken on 11-Il of Figure 1; and Fig. 3 is a cross sectio'nal plan view taken on line 111-111 of Figure 1. In accordance with this invention the foregoing objects 20 are accomplished by the provision of novel apparatus having a combination of coacting features together adapted for improved continuous casting of a length of metal slab of a width far in excess of its thickness as will hereinafter more fully appear. 'ne casting appa25 ratus and process of this invention is characterized by an unproved introduction of the metal and by an improved control of the solidification process. One feature of the invention provides a metal shaping member in which substantially no relative motion oc30 curs between the solidifying metal and the mold or die side walls defining the metal congelation regions of the apparatus. This is accomplished by forming the side walls of u nidirectionally traveling surfaces of continuous, spaced apart metal belts or the like which support 35 the molten metal durina, solidification and also by a particular structural arrangement of molten metal feed which prevents premature contact between tbe metal and the belts. This eliminates forces that might otherwise occur between the solidifying metal and the walls 40 of tle niold. By continuing the occurrence of metal solidification in the castin.@ apparatus of this invention between traveling surfaces of adequate length there is avoided change of metal shape during solidific@iton other than the norr@ial contraction which always follows cool45 ing of the metal. Cracks perpendicular to the longitudinal axis of the ingot are virtually avoided by substan@tially complete elimination of the restraint imposed by the mold. -5( Another feature r,-Iates to the capacity of the aforem-.ntioned particular structural arrangement of means for charging molten metal to the region of solidification not only without premature contact but also in a quiescent state and without exposure to other than a protec55 tive atmosphere. By this means there is avoided undesired heat loss prior to the point of solidfication. To accor-riplish this the molten metal is introduced at the proper temperature from a relatively sha-Ilow pool under sufficient hydrostatic pressure into a region of confinement havin@ a conflauration substantially identical with 60 and in collimation -%vith the cross-section defined by the traveling side walls. This region is positioned to affe@-t the metal immediately prior to entr@ of the molten metal into the metal shaping portion of the apparatus 65 betvreen the traveling side walls. Tbus, rearrangement of the metal volume and the resultin- disturbing flow of metal is substantially eliminated at the point of s.olidification. All distur@bance of the metal both immediately prior to as well as during solidification is avoided in the 70 casting apparatus herein described. Another feature -of this invention relates to interposit,'qn of a continuous coating or layer of mold dressing medi-
[2]3 um of a desired and adjustable thickness and/or composition between the moving metal and the mold surfaces traveling in unison with the metal. The introduction of this medium has a number of functions, but the chief function is the control of the degree of heat transnaission through the metal belts forming the mold side walls and regulation of the cooling rate for the casting process. Another is the provision of a reducing material in the mold about the metal as protection against oxidation. The dressing medium also functions as a seal betnveen stationary and moving parts of the apparatus but not as a lubricant for the cast metal. No lubrication is.. required between the metal being cast and any part of the apparatus. A high degree of r-ontrol of the casting process is obtained by the regulation of the thickness of this mold coating material functionng chiefly as an agency for controlling the heat transmission to the sidewalls. Furthermore, by means of this feature of the invention it is possible to not only adjust the mode of metal crystallization and to influence the metal structure forming between the flat faces of the slab but also to adjust the gauge of the slab within certain limits and from edge to edge. The latter prevents wedge shaped castings which are not desired in the rolling mfll. Cooling of the metal to solidification occurs chiefly through t@ransmission of the heat by way of the solidified section of the casting which is subject to direct fluid cooling. Abstraction of heat longitudinally with respec-t to the molten metal at the point of solidification through the previously solidified cast metal is the essential means of tooling as compared to the heat lost laterally by way of the dressing media surrounding the metal and the metal belts forming the side walls of the die section of the apparatus. Ordinarily no other attempt is made to cool the rolls, belts or other parts of the apparatus at points at which molten metal is to be found in contact with the casting apparatus, except such cooling of the belts as is inherent to the device shown and described. However the plastic dressing tends at first to have a relatively bri@f lateral cooling effect on the metal after which it acts as an insulator. This iijitial effect may be varied by heating or refrigerating the incoming dressing as desired for certain metals. In the preferred embodiment described herein and illustrated in the accompanying drawing, the improved strip casting apparatus of this invention comprises a rigid supp(>rting frame 1, carrying a main or discharge mold section 200 for imparting the desired cross sectional shape of the casting and an entry or upper mold section 100 for giving the molten metal a desired preliminary spatial @arrangement and for feeding the molten metal to the other section under certain desired conditions. Supported on and joumalled in the frame 1 are a first pair of face pinch rolls 2 and 3 and a first pair of side pinch rolls 4 and 5, which together with the face rolls 2 and 3 are the entry rolls. Also rotatably supported on the f-rame are a second pair of face rolls 7 and 8 and a serond pair of side rolls the latter of which are not shown in the drawing but which are related to side rolls 4 and 5 as rolls 7 and 8 are to rolls 2 and 3. Movably supported on these rolls are two mold face belts 13 and 14 and two mold side belts 15 and 16. Disposed in the entry side of the bite of the first pairs of rolls but spaced by a predetermined distance, found suitable in practice, from the surfaces of the belts passing over these rolls i@ a hollow pouring block or tundish 17 adjustably supported on the frame saddle 18 mounted on frame 1. Housed in the saddle 18, in close association with the pouring block @17 and each of the first pairs of orifice defming rolls, are supply chambers 19, 20, 21 and 22 for feeding a plastic mold dressing material 23 between each of the belts and the pouring block. Also mounted on the frame saddle 18 is any suitable adjustable means for varying at will the opening between surfaces of the be-Its 13, 14, 15 and 16 and the block 17 4 and thereby controlling the thickness of dressing material fed therefrom in interposed relationship between each of the traveling mold belts and the metal of the casting. 5The sizing pass 26 of mold section 200 is - generally defined by the complementary mold face belts 13 and 14 and the complementary mold side belts 15 and 16. These at pass 26 support the moltea metal in its transition to the solid state without relative motion between the solidi10 fying metal and the surrounding belts and also aid in iniluencing the heat abstraction desirably. A pass length at least adequate to accomplish the foregoing is selected. T'he belts 13,, 14, 15 and 16 are, carried@ about the pair of rolls 2 and 7, pair 1 3 and 8, pair 4 and 9 and 15 pair 5 and 10 respectively. The rolls are driven in unison in any suitable manner. To assure that all belts move at the same speed together, each group of rolls is interconnected as by bevel gears 6. Each belt is preferably a thin continuous band of 20 metal such as stainless steel. The bridging parts of the belts coming from each one of the confronting faces of the first pairs of rolls, and taken up on a corresponding one of the confronting faces of the second pairs of rolls are maintained by any suitable means at sufficient ten25 sion to cause these parts of the belts to travel in straigbt lines between each of the two respective rolls on which each belt is supported and operated. nese straight line portions of the belts adjacent the lateral edges thereof are disposed in a contiguous relationship with respect to 30 each other such that together the belts form the four traveling side walls of a generally rectangular passageway or cavity into which the molten metal is teemed directly from the pouring block 17 and it is in this substantially rectangular cavity that the shaping or molding 35 of the casting occurs. The mold face belts 13 and 14 which correspond to and confine the wide flat faces of the strip to be cast, are broad and flat as compared to the relatively narrow mold ride belts 15 and 16. 40 In order that the side belts may better fit in sealing relationship against the spaced parallel mold face belts 13 and 14, each of the side belts preferably is provided with a concavity by running the relatively narrow side belts around pah-s of concave faced side rolls including rolls 45 4 and 5 each of which has a face width somewhat less than the width of the ffexed mold side belts in order that the edges of the side belts may extend somewhat beyond the side pinch rolls whereby the side belt edges are adapted to be forced into spring pressure contact with the tiO mold face belts. This concave shape of mold side walls gives a desirable convex or rounded edge contour to the casting and tends to reduce severe corner cooling which introduces unequal contraction and may result in splitting of the casting. ti5 Entry mold section 100 is defined by the pouring blor-k 17 of the consti-uction shown and hereinafter more fully described and which isconstrained in aligned but spaced relationship with the belts on the entry side of the fotir roll assembly of first pairs of rolls defining the entry ori60 fice of the sizing pass referred to above. The tundish or block 17 is made of any suitable refractory material such as Carbonmdum, and preferably a dense clay graphite mixture or a suitable metal boride, such as zirconitim. It consists of (1) an upper part or 65 receptacle for holding a relatively sh0ow reservoir 31 of molten metal maintained at a constant temperature near the solidus and at a constant level and also of (2) a second or IoNver part 32 known as the pouring or down spout designed to project in form fitting relatio.nship be70 tween the entry faces of the belts as they pass over the entry bite or orifice defining rolls. This spout part of t e @blo 17 has outer concave surfaces complementary to the contour of the roll surfaces and the surfaces of the belts which ride on the rolls and pass in interposed 75 relationst@ip betwgen the lower form- fitti-Pg part 3Z of
[3]5 the block 17 and the orifice defming rolls. This spout 32 encloses a mold entry passageway 33 having surfaces defined by the parallel straight lines tan.-ent to the aforementioned rectangwar mold sizing pass 26 defined by the belts as they pass over the first set of rolls. This rectangular passageway serves to lead the molten metal under desired conflnement within the block from the reser-voir 31 to the zone of con,-elation between the belts 13, 14, 15 and 16 not only without exposure to the atmosphere but also without premature lateral cooling and freezing with the concomitant unde;sirable formation of a curvilinear metal "skin" that would ordinanly be formed in the absence of mold section 100 and immediately thereafter undergo disruption beyond the roll pass or bite to make a strip having as a consequence an inferior quality. Fur-ther the passa,-eway 33 serves to give the molten metal a prelimenary "shape" like that of the final casting so that subsidence of metal cross fl(>w, counterfloiv and turbulence may occur in the passageway 33. The spout portion 32 of the block 17 extends as close as possible to the sizing pass 26 defined by the closest approach of the surfaces of the four belts riding the entry rolls at the bite of these rolls. By means of this particular block structure there is prevented the inception of freezing or solidification of the molten metal on the converging faces of the mold face and side belts at the rolls before the metal has reached a po@nt at the aforementioned "orifice." The prevention of freezing on the interior walls of an open ended travelin- belt type of continuous casting mold prior to movement of the metal to a place in the mold having the desired constancy of shape is an important factor together with the other features of the invention in securing a high quality continuously cast slab of metal. While the block 17, forced by any suitable means to ride in juxtaposed relationship adjacent the dressing medium on the moving belts, has been described as feeding metal ver-tically downward, it is evident that the appara'Lus may be modified to operate horizontally or even to feed the metal upwardly. The depth of the reservoir 31 is not limited to the radius of the rolls and is made adequate to exert enoi,-gh pressure to resist gas release and the resultant porosity in the metal. At the point of transfer of the quiescent molten metal from the passa,@eway 33 in the block 17 to the main mold section 200 between the traveling mold belts, there is fed by extrusion a thin peripheral layer of semi-solid mold dressing medium 23 of controlled anti-oxidant and preferably thermally insulating composition, of suitable plasticity and of controued thickness between the molten metal and the belts. A suitable medium may consist of one or more of carbon black, graphite, bone ash, magnesium oxide, asbestos, vemiiculite, kieselguhr, or diatomaccous silica or porous silica gel sold under the trademark Sil-O-Cel in any suitable vehicle such as kerosene, lard oil, or a silicone. The medium is compounded to give suitable propert-.es and a smafl but desired amount of inert or at least reducing atmosphere under the various conditions encountered in the castin- operation. The dressing applied to the mold face belt 13 may be identical with the dressing applied to the opposing mold face belt IL4 but also may be of different composition in some cases to facilitate crystallization control in the casting. The dressing applied to the mold side belts 15 and 16 as a rule should be of a more heat insulating nature than the dressing applied to the face belts which may be accomplished in the former by a high content of kieselguhr, bentonite or the like. With appropriate subdivision of each chamber, different dressing may be applied to the same belt. The dressing layers from all supply chambers together form a thin sheath 41 surrounding the periphery of the metal and serves as a conductor of heat of controlled resistivity to the lateral flow of heat from the metal being cast to th.- bands of metal between which solidification takes place. The element of control is effectuated chiefly by varia2,956,320 tion in the thickness of the thin extruded layer 41 of dressin.- compound carried by the belts. While it is preferred that the thickness of the dressing layer 41 be less than or at most not greatly in excess of about 0.005 of an inch, the thickness is to be varied by the mold operator until there is achieved the desired casting quality and thickness as hereinbefore explained. The thickness of dressing will, of course, vary with the composition of the metal cast, viith the composition of the 10 dressing, with the ternperatures of the charging metal and coolant employed and also with other factors such as variations in the thickness, cross sectional area and speed of the strip of metal being cast. As a further means Gf controrably varying the heat 15 transmission via the belts and to improve the dressing carrying capacity thereof the belt surface facing the casting cavity may be provided with an adherent film of oxide or phosphate or the like. The same surfaces of the belts may also be initially scratch brushed to an extent 20 insufficient to increase the heat transmission capacity thereof seriously but sufficient to aid initial adherence of the &essing mediiim to the belts. With a suitable dressing a network of scratches in the belt surfaces may provide a repiica surface on the casting responsible for more 25 rapid removal iof heat by way of the emerging casting. For varying and holding the spacing of the pouring block 17 from the surfaces of the mold face and side belts and thus for varying the dressing charging opening or gate circumscribing the casting metal at the Points: 30 where passagewiy 33 in mold section 100 terminates and main mold section 200 be,-ins, there is provided on each side any suitable m--ans such as screw-down rods 35, the internally threaded helical gear 36, the equalizer rod 37 with screws 38, the intemally threaded helical gear 35 39 with hand wheel 34, and compression springs 40. Alternately, there may be provided a riumber of wedge cams carried bv the frame 18 for adjustably suppor' ing the block 17, it being yieldably urge-d toward the bite of the first pairs of pinch rolls by suitable means such as 40 springs. Such wedge cams would be adapted to coact with corresponding cam following surfaces formed in block 17 as the cams ar@- operated by suitable manually controlled means such as lead screws. However, it is to be understood that other means equivalent to the screw45 down means sho,@vn or the cam means referred to may be substituted therefor. In any event such means for one side may be operated either at substantially equal or different rates with respect to the means for the other side. 50 Dressing material 2,3 is carried in arcuately shaped supp@ly chambers having walls e7- tending from the saddle 18. Each chainber has opposing lateral walls contiguous with one of the -belts and is open on an arcuate side at the belt with Nvhich it is associated. Although one cham55 ber is shown for each belt, it will be appreciated that there may be a plurality. As a means for urging the plastic dressing medium from the supply chambers 19, 20, 21, land 22 into the space bet%veen the convex surfaces of the mold belts and the compleme-.ltary concave surface 60 of the blo--k 17 and for injecting the dressing as a thin sheath on the beits about the molten metal from the circumscribing orifice at the poin-t Nvhere the molten metal leaves passageway 33 in the block 17 and enters the sizing pass 26 and straight walled portion of tne traveling 65 belt mold sect,-'on 290, there is provided in association with each dressing supply chamber a fluid pressure operated ram 50 pivotally supported at o-iie end on the frame I[ and connected at the other end to pistons 51 haning suitable arcuate sides to ride the belt and fit the roll sur7o face em-bracing chambers. Tl-.is constr-uction is especially advantageous for the belt-overrolls type of casting machine of this invention. Congelation of the metal occurs in the moving sheath of dressing material bome by the belts traveling -in 75 unison with ea(-,h other and the metal being cast.
[4]7 Cooling of the metal to solidification in the final stage of latent heat abstraction is accomplished primaxily by drastic longitudinal heat transmission through the solidified ingot 42. This is preferably done by means of jets of cooling water issuing from a plurality of nozzles 45 positioned adjacent the delivery end of mold section 200 @immediately opposite the belts passing over the second or discharge sets of rolls 7, 8, 9 and 10. High pressure cooling water directed between the emergin- casting 42 and the coated belts results in a profuse and turbulent ffow of the coolant over the casting surface wbich is large for a rectangular slab shape case as compared to the volwne of the casting, thus effecting a comparatively rapid abstraction of heat therefrom. Furthermore, impingement of the high pressure jets of water serves to cleanse both the belts and the ingot of adhering spent dressing material, and to replenish the inimersion bath 46 @vith a stream of cooler liquid replacin- the warmed liquid discharged. The resulting longitudinal abstraction of heat is propoT-tio-.qed as needed in the early stages Of metal cooling with a variable portion of lateral heat abstraction which rapidly become-s nunor as the metal progresses th,rough section 200. In the device of this invention, collimation of all parts of the molten and solidified metal undergoing casting is achie7ved as is the;avoidanee of any disruption of the crystallization process from disturbances caused by bending or vibratory forces, %vbich would be set up by lateral rriisaegnment. This is done by supportin-, both the entry and the dischar.-e Tolls of mold section 200 in the rigid frame I and by nesting the pouring block 17, of the partictilar structure shov@,n and deecribed, in form fitt-ing relationshir) just ahead of the bite 6f the entry rolls. By the supporting system here disclosed alignmerit between sections 100 and 200 of the castin. apparatus is maintained and undesired movement and bending between the solid casting 41 and the molten metal at the zone of congelat.on in siv,ng pass 26 is prevented. T'he general operatio-.i of the casting apparatus and method of this invention should be readily understood in vienv of the fore.-Oin.- description, but may be described to.- ethe.r briefly as follows: In operation, first of all, molten metal. is teemed into block 17 of mold section 0 to maintain the desired level of the reservoir 31 from which liquid metal at a desired ten@ perature is fed to passagen,iay 3@3 of do,,vn spout 3.2. I-lere, the molten metal under hydrostatic pressure :arranges itself to the des;red spatial shape, and t-arbule-iice in the flov,-ing stream has an opportunity to subside. From passage 33 the metal enters tle sizing pass 26 b--tween the belts of mold section 2.00 where the metal encounters the refractory &essing material 23@ being extruded in a layer 4.1 of desired thickness, composition and temperature for the metal being cast. In this tr,- .veling lateral sheath, the heat of the metal is abstracted at first laterally over a small portic,n of travel of metal, belts and 'Lhe dressing layer. As the lateral cooling effect dir-iinishes rapidly, the longitudinal cooling effect of cooling sprays 45 and coolant bath 46 becomes stroqger. At this point in the Pr oc,ess, dressing layer 41 operates as a heat insulatin,- sheath. ThO TeSultant cooling in ingot 42 is manifested by gently clirved isothertrs approaching the horizontal instead of the deeply cui-ved isotherms which @are accompanied by an extremely high gradient especially at the lateral surfaces of many heretofore continuously cast in.-ots. Thus, while the metal is in sizirg pass 26 of mold section 22, an excessively rapid successon of isotherms is avoided. In sizing pass 26 the metal is sitppo@-ted adequately in its transition to th@ solid state during which it is subjected to no change of shape as occurs o-i prior casting machi.ie with rolls or dnuns. Fu.-tnermore, there is no relative motion between metal and the m-old so that frictionaj restrairt cold shuts and cracking perpendicular to the ingot axis @re avoided. As the solid metal 42 with desirable external shape and internal strurture emerges from pass 26 substantially 2,956,320 8 all of its surface is subected to strong coohn- by sprays 45 and quench bath 46. At this point the casting process has progressed sufficiently so that there is no danger of impairment of the metal by the quenching. At the same time tb-e bflts 13, 14, 15 and 16 of the apparalus are cleaned off in co-.ldit,:on for @another cycle through dressing supply chambers 19, 20, 21 and 22. The apparatus and process are adniirably adapted to automatic con'trol@ The speed of the casting, feed of 10 the d@ressing medium, and both the temperature and impingement of quI.,iching liqui-d ;at 45 and 46 may be interlock-ingly contro@lled I>y any suitable sensory control equipment which may be associated with the apparatus described. 15 From the foregoing description it is obvious that one advantage secured by means of the apparatus and process of the @present invention is that the moving metal begins solid,;Jying at points substantially all e4ually remote from the poipt at v,,hich the molte@n metal is charged to the 20 mold and solidification proceeds directionally in a controlled manner toward the charging point with a miiu'mum of hindrance by lateral solidification whereby sbrinkage voids and serious bridging are virtually eliminated even in the case of alloys having a Nvide freezing range. 25 Further, by means of t@he present invention, although an extremely shallow freezin-, crater is obtained, uncontrolled penetration by the incoming stream of molten metal from the charging point is prevented since the momentum and tiixbulence of the stream is eliminated 30 and as a conseqiience the solidifying metal has a minimum of gas carried dow.@l into it and washi-iig contact with liqllid metal is prevented. Especially tWs invention is directed to producin@@ ingots reaso@nably free from surface cracks, segregation, and internal disruptions all of which are 35 kn,w, to occur when metal is ch@ill-cast on and subject,-d to squeezin- acton between the converging surfaces encotintered in prior casting devices oj' the roll type. While the invention has been described without reference to any particular metal, ally suitable metals such as 40 copper, aluminum, magnesium and steel and their alloys may be continuously cast with advantage by means of the apparatus and process described herein. Although with some modification liriked sections may be used in lieu of the belts, endless belts of either solid, stranded or woven construction are preferred because of the smooth surface obtainable on the ingot, the reduction possible in the bulk of the appaxatus, as well as the unique suitability Df belts to the entire design. Since other embodiments may occur to those skilled in the art, it is to be understood that various modifica 50 tions may be made in the invention described without departing from the spirit thereof and that the forego . ing is intended to illustrate a preferred embodiment and not to limit the scope of the present invention except as set forth in the appended claims. 55 W I hat is
