AU454635B2 - Longlife casting machine - Google Patents

Description

Z4,6 78 MI In a typical systemu for continuously casting metal, such as copper, steel or aluminum, an endless flexible metal band is guided about a portion of the peripheral groove of a rotatable casting wheel, and molten metal is poured into the moving mold formed by the band the peri- pheral groove in the wheel. As the casting wheel rotates, coolant is applied to its external surfaces and to the outside surface of the portion of the band that closes-the peripheral groove of the casting wheel to extract the heat from the molten metal at a rapid rate and to prevent the castind wheel and band from overheating. By the time the metal band is removed from the peripheral groove of the casting wheel by the band wheels, the molten metal will1 have been solidified and can be extracted from the casting wheel and passed on to another stage in the continuous process. The function of the band guide wheels is to guide the band into engagement with the periphery of the casting wheel to form the arcuate mold, and then to remove the band from the periphery of the casting wheel t6 open the mold, and guide the band back to its initial mold forming position. One arrangement is to have a single large tensioning wheel spaced above the casting wheel and have the inner surface of the flexible band extend about both the casting wheel and the tensioning wheel. The other typical arrangement is to have the band pass beneath the casting wheel during its return flights, with the band guide wheels engaging the "outer" surface of the baid, In both arrangements it is desirable to guide the band away from the area above the casting wheel so that the equipnent )-mcessary for pouring the molten metal into the mold and ecxtracting the solidified metal from the mold can be positioned

454.63

24,678m Thus, the tensxoning wheel or band guide in this space. wheels must be sized and positioned to guide the band away from the upper portion of the casting wheels; however, in order that the band be guided away from the upper portion of the casting wheel, it has been found necessary to utilize a relatively small band presser wheel or band positioning wheel to position the band adjacent the casting wheel and urge the band into its initial engagement with the periphery of the casting wheel. The band positioning wheel is of small diameter in order to keep the area above the casting wheel relatively free from encumbrance by the band. In the operation of a continuous casting machine of the types generally set forth above, one of the major maintenance problems is the care and replacement of the band. It is necessary that the band be of relatively small thickness so that it can bend and flex as it passes around the casting wheel and band wheels. Also, a relatively thin band transfers the heat from the molten metal more rapidly than a thicker band and allows the molten metal to solidify more rapidly; however, the relatively thin band is more likely to become overheated from the transfer of heat from the molten' metal and deteriorate more rapidly than a relatively thick band. Thus, the endless flexible metal band utilized with a continuous metal casting machine must be fabricated with a thickness to withstand substantial heat deterioration, and yet be thin enough to flex around the band wheels. The continual bending and flexing of the band about the smaller band positioning wheel has the most damaging effect on the band since the band must undergo a curvature of a shorter radius when passing around this band wheel, and the strain felt by the band from the smaller band wheel

454635

24,678 Mn tends to rapidly deteriorate the band.

In accordance with the present invention, there is

provided in a machine for continuously casting metal wherein

an endless flexible band is guided into closed relationship

with a portion of the peripheral groove of a rotatable casting

'wheel, guided away from the peripheral groove, and returned on

the same side of the casting wheel to the peripheral groove by

a plurality of band guide wheels of substantially the same

diameter and a band positioning wheel of smaller diameter than

the band guide wheels is positioned adjacent the periphery of

the rotatable casting wheel and arranged to press the flexible

band into positive contact with the casting wheel, the

inprovement therein of the ratio between the thickness of the

flexible band and the diameter of the band positioning wheel

being lower than one to ninety. In a preferred form while

S454.635

246 78 m

wheels are sufficiently the diameters of the larger band guide in the band as it passes large to prevent excessive strain positioning wheel next over these guide wheels, the band urges the band into engagement adjacent the casting wheel which spout has been enlarged with the casting wheel at the pouring at this location in no more than so that the strain experienced at the other band wheels. three times the strain experienced invention to provide a Thus, it is an object of this casting metal which includes casting machine for continuously that extends the life of the a band and band wheel arrangement casting machines. band over the previously known is to provide a casting Another object of this invention metal that requires less machine for continuously casting maintenance than the prior art. of the present Other objects, features and advantages upon reading the following invention will become apparent conjunction with the accompanying specification, when taken in drawings. of a casting machine Fig. 1 is a schematic illustration the wherein the inner surface of for continuously casting metal heel, band is passed around the casting wheel and a tensipn 5 635 srae24,6 Ml 78 and the outer sraeof the band Is engaged by a smaller band positioning wheel,, Figs. 2 and 3 are graphs which illustrate band strain of the band of the casting machine of Fig. 1; Fig. 2 illustrating band strain with the use of a relatively small7 band positioning wheel, and Fig. 3 illustrating band strain with the use of a relatively large band positioning wheel. Fig. 4 is a schematic illustration of a casting machine for continuously casting metal wherein the band is guided with its inner surface engaging the casting wheel and its outer surface passing around the band wheels. .Figs. 5 and 6 are graphs similar to those of.Figs. 2 and 3 and illustrate band strain of the band of the casting machine of Fig. 4; Pig. 5 showing band strain when a relatively small band positioning wheel is used, and Fig. 6 illustrating band strain when a larger band positioning wheel is used, Fig. 7 is a schematic detail illustration of the intersection of the band with the casting wheel, Referring now in more detail to the drawings, in which like numerals indicate like parts throughout the several views, Fig. 1 shows a casting machine 10 which includes casting wheel 11, band tension wheel 12, and band positioning wheel 13. Continuous flexible band 14 extends around casting wheel 11 and band tension wheel 12 and forms an arcuate mold with the peripheral groove (not shown) of casting wheel 11. Band positioning Oheel 13 urges band 14 into engagement with the rperip'hery of casting wheel 11. The graphs of Figs. 2 and 3 represent band strain as the continuous flexible band 14 passes through a cycle about 6 454,63

24, 6 78 ni The numbered casting wheel 11 and band tension wheel 12. points along the abscissas of the graphs illustrate the corresponding numbered positions about the casting machine, and the ordinates of the graphs illustrate the amount of strain felt by the band. The difference between Figs. 2 and 3 is the amount of strain felt by the band at point 3 in the band cycle, where a larger band positioning wheel 13 is used for the cycle of the graph of Fig. 3, and a smaller band

positioning wheel 13 was used for the cycle of the graph of Fig. 2. Fig. 4 shows casting machine 20 which includes casting wheel 21, band guide wheels 22, 23, 24, and 25, band

positioning wheel 26, and endless flexible metal band 27. The inner surface of band 27 extends about casting wheel 21 and defines a mold with the peripheral groove (not shown) of the casting wheel. The outer surface of band 27 extends about band guide wheels 22-25, and about band positioning wheel 26. Figs. 5 and 6 are graphs of the..strain felt by band 27 as it passes through a cycle about casting machine 20. As

with Figs. 2 and 3, the positions indicated along the abscissas

of the graphs of Figs. 5 and 6 indicate the various corresponding positions noted in Fig. 4 in a single band cycle, with the difference in Figs. 5 and 6 being that a larger band positioning wheel 26 was used for the cycle of the graph of Fig. 6 while a smaller band positioning wheel was used for the cycle of the graph of Fig. In both Figs. 1 and 4 the illustrations are schematic and the relative sizes of the elements of the casting machines are not to scale, particularly the sizes of band positioning ,heels 13 and 26. Furthermore, it will be apparent from S454

24.6 78 /1 Figs. 2, 3, 5, and 6 that the sizes of band positioning wheels 13 and 26 are variable for the purpose of illustrating the disclosed invention. The continuous metal bands 14 and 27 are flexible, and as with any material they are subject to. failure due to fatigue from continuous flexing as the bands pass around the various band wheels and due to the thermal shock experienced in each cycle of the band from the heat exchange f rom the molten metal poured into the arcuate mold foraed between the band and the casting wheel, When the bands are bent about the casting wheel or one of the guide wheels, the theoretical strain set-up in the band surface is e t

where t is the band thickness and D is the wheel diameter. The strain is in the tension on the outside or convex surface of the band and the compression on the inside or concave surface of the band next to the wheel about which it is passing. Of course, there is also some band strain experienced continuously by the band due to initial tightening of the band about all of the wheels; however, this portion of the band strain is slight and can be ignored for the purposes of this disclosure since a similar strain is present in all casting machines of similar construction. When the molten metal is poured into the arcuate mold formed betwveen the band and the casting wheel, the bending strain due to the heat gradient across the thickness of the band will depend on the rate of heat transfer through the handl, and on the ability of the band to deform. As is shown in Fig. 7, the moltcan rotai 30 initially conte'cte band J14 wharm 8 454,63 immediatel et ad1 the band is relativelY cool and causing a substantial to its highest temperature, thus at thermal shock. The temperature gradient is illustrated the band to 31. of course, the indreased temperature causes in expand lengthwtise, and since the surface of the band the outer direct contact with the molten metal is hotter than will tend to expand surface of the band, the inner surface the band were not under more than the outer surface. If casting wheel, it would normally tension and extended about the Thus, in order to extend bend away from the casting wheel. the casting wheel a substantial the band around the curvature of band. The bending strain will bending strain is exerted in the in band surface temperature be proportional to the difference To illustrate the conditions and band average temperature. wheel with its inner of a band extending about a casting metal and its outer surface surface in contact with molten thermal strain can bO having coolant applied to it, the of a band of twice the thickness assumed to be the same as that sides and cool in the of band 14, thermal shocked on both would not bend and would center. A band under these conditions surface and center temperatures have the same difference between temperatures of band 14. as the inner and'outer surface of the band, the maximuml To determine the bending strain thermal stress at the surface is* 1 3.25

V- max by: where o- is a dimensionless stress and is given o-0'

E a (L TT0 4 4,6 3

24,678 MI ors e 0- a(TL T0

where B is the Biot number, E is the modulus of elasticity,. a is the thermal expansion coefficient, (TL T0 is the

temperature difference between the molten metal and the band, h is the surface heat transfer coefficient, k is the band thermal condctivity, t is the band thickness. B h (2t)

For an example of a steel band and molten copper: 1 B (2000) (4 x i2)

Therefore s o- 0.29 max Taking a as 6.5 x 10-6 in/in. -OF and (TL TO as 20000F, we

have:

max max a (TL' TO

emax 0.0038 in/in.

This is a compressive thermal strain set up in the band surface adjacent the molten copper and is assumed to be approximately the same for all casting machines. To estimate band life on a casting machine, reference is made to Figs. 1 and 2 of the drawing where a band cycle is Plotted. Point 0 is the beginning point on the graph of Fig. 2 and the point on the band after it has left the casting wheel. As the band travels around the machine, it undergoes other various bending strain conditions as illustrated at the t points of the figures. At point 1, the strain is given by 15, where t 1/8 inches and D 55 inches, and as illustrated on 454.635 the graph of Fig. 1, 1 6. 23 nches per inch. The remaining portion of the graph of Fig. 2 plots the strain experienced by the band as it travels through one band cycle back toward-the 0 position. It will be noted that a relatively small strain is felt by the band at position 1, while a relatively large strain is felt at position 3. Positions 1 and 3 are located in the middle of the curvature of the band as it passes about tension wheel 12 and band positioning w~heel 13, and a graphic presentation is made-of band strain at these positions. Position 4 on the graph indicates strain of the band due to the thermal gradient across the band added to band bending strain due to bending the band around the curvature of the casting wheel; the band strain due to its curvature being illustrated by the dashed lifle. Theoretically, each band can pass around the wheels of a casting machine a certain number of times before it fails.-

This is called band life, and a relationship has been establish- ed between the strain felt by a band~during each cycle and its life. If nj represents the number of times a certain strain occurs in a band cycle, and Ni is the life associated with this strain range, we can determine the number of band cycles, N, to failures niN

For example, in casting machine 10 of Fig. 1 the strain of 0.0023 occurs once, the strain of 0.021 occurs once, and the strain of 0.006 occurs once. The band life associated with each of these strains is, respectively: 2 x 105 cycles, 7.5 x 10 2 cycles, 10 cycl.es, '1 .1 45 63

24,678/11 are: Therefore, the number of band cycles to failure 4.48 x 10 2 for complete Since band failure as calculated above is that visible fracture of the material and it is expected the band fractures, cracks in the band will appear long before removed fromt the under normal situations the band will be casting machine before its fracture. other parameters It is acknowledged that there are various accurate determination that should be considered f or an absolutely of the molten metal of band life. -For instance, the temperature wheel and band is will vary, the rate'of cooling of the casting and will vary, the determined by coolant volume and temperature the length of the band tension applied to the band material and portion of the band Will vary, the width of the band and the molten metal may vary, that does not come into contact with the of the band. These and there will be variations in the thickness to be present in and other varying parameters are likely we have merely every casting machine,- but for our purposes, life and the bending established a relationship between band of the band. 3, when band As illustrated by *the data in Figs. 2 and and the band positioning wheel 13 is 6 inches in diameter t of strain, e thickness is 1/8 inches, the coefficient wheel 13 has a is 0.021 whereas, when band positioning of band strain is only diameter of 20 inches, the coefficient since the reduction .0062 when using the same 1/811 band. Thus, band life, the use of of band strain in each band cycle extends 13 functions to extend a larger diameter band positioning wheel thickness of band 14 was the life of band 14. Similarly, if the Thus, to extend. band reduced, band life wqould also be extended. 45I4.G 3

24,6 78 171 life, the ratio between band thickness and wheel diameter-must be as low as practical in keeping with heat deterioration problems previously discussed. A comparison of the graphs of Figs. 5 and 6 also dis- closes that the use of a larger band positioning 'wheel 26 in casting machine 20 reduces band strain, and increases band life. Fig. 5 illustrates data for a band positioning wheel 26 of a diameter of 6 inches and a band thickness of 1/8"1. Fig. 6

illustrates data for the same casting machine but with a band positioning wheel 26 having a diameter of 12 inches and a band thickness of While the strain at position 9 in the band cycle is 0.021 for the smaller band positioning wheel 26, the strain is only .0104 for the larger band positioning wheel. Obviously, the band life will be prolonged with the use of the larger band positioning wheel 26. To extend band life, it would be desirable to form band positioning wheels 13 and 26 with diameters as large as the band tensioning wheel 12 or band guide wheels 22-25; however, the space requiremlents above casting wheels 11 and 21 require that smaller diameter band positioning wheels be utilized. Thus, while the strain encountered in the banc~at positions 3 (Fig. 1) and 9(Fig. must necessarily be in excess of the

strains in the band as the band passes around band guide wheels 22-25 and band tensioning wheel 12, it is desirable to hold the strain encountered in the band to a level no greater than the strain in the band as the band contacts the molten metal, so the band thickness and materials can be selected and gauged for only the highest necessary strain in a single cycle of the. band. Since band strain virtually cannot be reduced through a level below that encountered in positions 4 (Fig. 1) and '454.63

24,687 9 1M (Fig. it is unnecessary to enlarge the diameters of band positioning wheels 13 and 26 to hold the strain below the necessarily high strain level since further enlargement of the band positioning wheels would cause the wheel to occupy an excessive amount of space above the casting wheel. This band strain limits for the band positioning wheels for the examples shown are calculated*a

The band thicknesses are between approximately 0,0747 inches and 0.125 inches, and the band positioning UAeels are 12 inches and larger for casting machines of the type illustrated in Fig. 4 and 20 inches and larger for the casting machines of the type illustrated in Fig. 1. The diameter of the guide wheels of the Fig. 4 casting machines were 36 inches and the diameter of the tensioning wheel of the Fig. 1 casting machine was inches. Thus, the ratio between positioning wheel diameter and guide wheel diameter and guide wheel or tensioning wheel diameter is maintained at one to three. This ratio is suitable since approximately three times the amount of band strain is experienced when the band first encounters the molten metal as is experienced when extending about a guide wheel. While this invention has been described in detail with particular reference to preferred emibodiments thereof it will be understood that variations and modifications can be effected withi.n the spirit arel scope of the Inven~tion as described berS4 inbefore and as defined in the appended claims.

454.63

Claims (9)

1. 24,6 78 m The claims defining the invention are as follows:- 1. In a machine for continuously casting ndetal wherein an endless flexible band is guided into closed relationship with a portion of the peripheral groove of a rotatable casting wheel, guided away from the peripheral groove, and returned on by the same side of the casting wheel to the peripheral groove a plurality of band guide wheels of substantially the same diameter and a band positioning wheel of smaller diameter than the band guide wheels is positioned adjacent the periphery of

   the rotatable casting wheel and arranged to press the flexible band into positive contact with the casting wheel, the improve- flexible ment therein of the ratio between the thickness of the lover band and the diameter of the band positioning wheel being than one in ato ninety. -o -c ine
2. 2. The =crbn;ti n4claimed in Claim wherein the thickness to of the flexible band is in the range of from .0747 inches is .125 inches, and the diameter of the band positioning wheel greater than 12 inches.
3. 3. Vrhj eclaimed in Claim 1, wherein the diameter of as the band positioning wheel is at least one-third as large the diameter of the band guide wheels, 4. ieeenbi iiclaimed in Claim 1, wherein the diameter of than three the band positioning wheel is sized to impart no more times the bending strain to the flexible band than the band guide wheels. The--eefrAnatieuclaimed in Claim 1, wherein the diameter of more bending the band positioning wheel is sized to impart no the band as strain to the flexible band than the strain felt by contact it passes about the casting vIeal and is in direct With molten metal. 5 46 3

   24.678M 6. In a machine for continuously casting metal wherein the inner surface of an endless flexible band extends partially about the peripheral groove of a casting wheel and about a ten- sioning wheel spaced from the casting wheel and a band position- ing wheel is placed adjacent the casting wheel and engages the outer surface of the band and urges the inner surface of the band into engagement with the casting wheel, the improvement therein of the ratio of band thickness to band positioning wheel diameter being smaller a than 1 to In a r ri--e'-e d 7. The combi nati on claimed 1 in Claim 6, wherein the band

   tensioning wheel diameter is greater than 3 times the positioning wheel diameter. lIn a itnX^A/'hR- '14 8. Th Goabinatin/claimed in Claim 6, wherein the band positioning wheel is sized and arranged to impart no more than 3 times the bending strain to the flexible band than the tensioning wheel. 9. The conibirmtinclaimed in Claim 6, wherein the diameter of the band positioning wheel is sized to impart no more strain to the flexibleband than the strain felt by the band as it passes about the casting wheel and is in direct contact

   with molten metal. DATED this 25th day of January, 1971 SOUTI IRE COMPANY Patent Attorneys for the Applicants P.B. RICE CO.

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