US3464483A

US3464483A - Casting of molten metal

Info

Publication number: US3464483A
Application number: US613334A
Authority: US
Inventors: Daniel B Cofer; Thomas L Bray
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1967-02-01
Filing date: 1967-02-01
Publication date: 1969-09-02
Anticipated expiration: 1986-09-02

Description

Se t. 2, 1969 o. B. COFER ETAL' 3,464,483

CASTING OF MOLTEN METAL Filed Feb. 1. 1957 2 Sheets-Sheet 1 PRIOR ART INVENTORS DANIEL B. COFER THOMAS7 BRAY aygxfzm ATTORNEYS Sept. 2, 1969 Filed Feb. 1.. 1967 PRIOR ART D. BCOFER ET AL 3,464,483

CASTING 0F MOIJTEN 2mm,

2 Sheets-Sheet 2 INVENTORS DANIEL B. COFER THOMAS L. BRAY ATTORNEYS 3,464,483 CASTING F MOLTEN METAL Daniel B. Cofer, Carrollton, Ga., and Thomas L. Bray, Birmingham, Ala., assignors to Southwire Company, Carrollton, Ga., a corporation of Georgia 'Continnation-in-part of application Ser. No. 543,644, Apr. 9, 1968. This application Feb. 1, 1967, Ser. No. 613,334

Int. Cl. B22d 11/06, 11/12; B29c 1/02 U.S. Cl. 164278 11 Claims ABSTRACT OF THE DISCLOSURE What is disclosed herein is a casting machine for the continuous casting of a non-ferrous molten metal in the annular mold of a casting wheel. The mold is formed of a metal having iron as the major constituent such as low carbon steel to provide a mold having a rate of heat transfer which is low relative to the rates provided by prior art molds and as a result a non-ferrous molten metal is solidified in the mold in a manner which substantially reduces the non-uniform cooling of the non-ferrous molten metal that is characteristic of prior art molds. In addition, the low carbon steel provides a mold with a rate of temperature propagation or transfer which is low relative to the rates provided by prior art molds and as a result, the thermal fatigue characteristic of prior art molds when used in continuous casting is substantially reduced. The reduction in thermal fatigue and the structural strength of low carbon steel result in the mold having a long useful life relative to prior art molds.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of co-pending US. patent application Ser. No. 543,644, filed Apr. 19, 1966, and entitled Casting of Molten Metal, now United States Patent No. 3,321,007.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to casting machines, and more particularly, to a casting machine in which a casting wheel defines an annular mold for casting a molten metal in a shape With a small surface area relative to the mass of molten metal to be cooled during casting and that is exposed to cyclic temperature conditions during continuous casting.

Description of prior art In the continuous casting of molten metals with prior art casting machines, it is customary to use a continuous casting mold which is substantially closed and in which a molten metal is solidified to obtain a cast metal as the molten metal passes through or travels with the mold. The continuous casting mold may be formed 'by continuously travelling walls, by a combination of continuously travelling and stationary elements, or simply by a stationary tube from which a cast metal passes after solidification of the molten metal. However, regardless of the particular arrangement used to form the continuous casting mold, the solidification of a molten metal in a casting machine to obtain a cast metal is accomplished by the transfer of heat from the molten metal to or through the mold which is itself frequently cooled by the subsequent transfer of heat to a fluid medium such as Water or air.

Moreover, regardless of the particular arrangement used to form the continuous casting mold, it is a requirement of a casting machine that the solidification of a molten metal be achieved within a reasonably short length of time. This requirement exists because desirable high States Patent 6 "ice Patented Sept. 2, 1969 casting rates can be obtained only with reasonably rapid solidification of the molten metal. Such reasonably rapid solidification of the molten metal is particularly difficult to achieve in the continuous casting of a cast metal such as a cast bar having a shape which provides only a small surface relative to the mass of molten metal which must be cooled. This is because a large amount of heat must be transferred through a relatively small surface in a relatively short time. It is for this reason that various elaborate cooling arrangements have been proposed and used in prior art casting machines for casting bars and similar shapes of a cast metal.

It is also for this reason that continuous casting molds for cast bars and similar shapes of a cast metal have characteristically been constructed of materials having a high rate of heat transfer. With prior art casting machines, it was felt that such materials were necessary to provide a mold which would quickly and efficiently transfer heat from the molten metal to the particular cooling arrangement selected and which would efficiently cool the molten metal in spite of only a relatively small surface being available for cooling.

A difficulty with using a material having a high rate of heat transfer for a continuous casting mold is that such materials frequently have relatively poor structural strength. In addition, continuous casting molds such as those provided by casting wheels are exposed to cyclic temperature conditions as a molten metal is repeatedly received and cooled, and the relatively large temperature fluctuations which generally occur throughout most materials having a high rate of heat transfer with exposure to these cyclic temperature conditions cause excessive thermal fatigue in such molds. Thus, the useful life of a continuous casting mold constructed of a material having a high rate of heat transfer has characteristically been relatively short because of the formation of large thermal cracks in the mold and often because of the complete structural failure of the mold. Further, in molds provided by casting wheels, the poor structural strength and thermal fatigue encountered in the prior art has frequently resulted in thermal ratcheting and the partial closing of the casting groove.

Moreover, the use of a material having a high rate of heat transfer in a continuous casting mold for cast bars and similar shapes of a cast metal has often adversely affected the properties of the cast metal. This is because the continuous rapid transfer of heat through the mold from the molten metal to a cooling arrangement selected to provide eflicient and rapid cooling of the mold which is characteristic of a prior art mold causes the mold to be simply a heat transfer device to which the peripheral portions of the molten metal continuously transfer heat at a rate which is substantially greater than the rate at which heat is transfered from the central portion of the molten metal to these peripheral portions.

As a result, there is a non-uniform cooling of the molten metal and sometimes a chilling of the peripheral portions of the molten metal. The non-uniform cooling of a molten metal or the chilling of any portion of a molten metal will often adversely affect the properties of many cast metals.

The non-uniform cooling of the molten metal which is characteristic of prior art continuous casting molds constructed of materials having a high rate of heat transfer also resnlts in the early forming of only partially solidified molten metal While substantial heat remains in the central portion of the molten metal. Since the partially solidified molten metal occupies less space in the mold than that occupied by the molten metal initially, a gap is formed between the mold and some of the peripheral portions of the partially solidified molten metal which reduces the continued cooling of the molten metal by contact between the molten metal and the mold.

The heat transferred across this gap generally does not effectively offset the reducing of heat transfer by contact between the molten metal and the mold which occurs because of this gap. Thus, the rapid initial solidification of the peripheral portions of the molten metal which is characteristic of prior art continuous casting molds constructed of materials having a high rate of heat transfer not only results in a non-uniform cooling of the molten metal, but also results in a reduction in the cooling efiiciency with which the molten metal is cooled while there is still substantial heat in the central portion of the molten metal.

In some prior art continuous casting molds, this reduction in the cooling efiiciency of the mold while there is still substantial heat in the central portion of the molten metal causes a reheating of the previously solidified peripheral portions of the molten metal by heat transferred from the central portion to these peripheral portions. This, in turn, causes a partial melting of the peripheral portions of the partially solidified molten metal and the previously formed gap to be in whole or in part eliminated. When this occurs, there is a second rapid cooling of the peripheral portions of the molten metal which further contributes to the non-uniform cooling of the molten metal and may even cause a second chilling of the peripheral portions of the molten metal.

SUMMARY OF THE INVENTION The invention disclosed herein overcomes these and other difficulties encountered in the prior art in that it provides a casting machine for the continuous casting of a molten metal under cyclic temperature conditions at efficient casting rates with substantially uniform cooling of all portions of the molten metal and without signiticant chilling of any portion of the molten metal even though the surface of the molten metal is small relative to the mass of molten metal to be cooled. Thus, the invention provides a cast metal which has little tendency to crack or fail mechanically. Further, the invention provides a continuous casting mold which has a relatively long useful life because of its initial structural strength and because of the small amount of thermal fatigue and the lack of thermal ratcheting in the mold even though the mold is exposed to cyclic temperature conditions.

These and other improvements in a casting machine for the continuous casting of molten metal are provided by a casting machine having a mold that initially retains sufficient heat from the molten metal in the mold adjacent the molten metal to cause an increase in the temperature of the mold which prevents too rapid cooling of the peripheral portions of the molten metal and that restricts this increase in the temperature of the mold and other extreme temperature changes to only a portion of the mold. More specifically, these improvements are provided by a mold which is constructed or formed of a material such as low carbon steel or another metal having iron as a major constituent and which When used in casting a non-ferrous molten metal such as molten copper results in the mold having a rate of heat transfer and a rate of temperature propagation or transfer which are both low relative to these rates in prior art molds. The rate of heat transfer is such that that portion of the mold adjacent a molten metal increases rapidly in temperature to a temperature which substantially attenuates the initial cooling of the molten metal by the mold while in addition being such that the mold nevertheless transfers heat from the molten metal to a cooling medium. The rate of temperature transfer of the mold is such that the increase in temperature of the mold when the mold initially receives a molten metal and other extreme temperature changes are restricted to that portion of the mold adjacent the molten metal.

The slowing of the initial cooling of a molten metal prevents the rapid initial solidification of the peripheral portions of the molten metal. Thus, the invention pro vides for substantially uniform cooling of all portions of the molten metal.

Moreover, when the solidification of a molten metal does reach that point at which a gap is formed between the partially solidified molten metal and the mold, the

substantially uniform cooling of the molten metal has reduced the heat in the central portion of the molten metal to a degree which avoids that substantial reheating of the peripheral portions of the molten metal that is frequently encountered in prior art molds. However, the rate at which heat is nevertheless transferred from the molten metal to a coolant by the mold results in the complete solidification of the molten metal at casting rates equivalent to those achieved in prior art casting machines. Since the mold is exposed to the cyclic temperature conditions of repeatedly receiving and cooling a molten metal during continuous casting, the restricting of extreme temperature changes to that portion of the mold adjacent the molten metal prevents those extreme fluctuations in temperature throughout the mold which cause substantial thermal fatigue. This and the fact that a mold constructed or formed of a material having relatively low rates of heat transfer and temperature transfer need not have the poor structural strength characteristic of prior art molds constructed or formed of materials having high rates of heat transfer result in the invention providing a casting machine having a mold which is structurally strong and which has a relatively long useful life.

BRIEF DESCRIPTION OF THE DRAWING These and other features and advantages of the invention will be more clearly understood from the following detailed description and the accompanying drawings in which like characters of reference designate corresponding parts throughout and in which:

FIG. 1 is a side elevational view of a continuous casting machine of a type in which the invention disclosed herein may be readily embodied;

FIG. 2 is a partial sectional view of the continuous casting machine shown in FIG. 1 taken substantially in line 2-2 in FIG. 1;

FIG. 3 is a schematic presentation of the solidification of a molten metal in a mold provided by a casting machine such as the casting machine of FIG. 1 which embodies the invention and shows the solidifying molten metal at the four points indicated in FIG. 1;

FIG. 4 is a schematic presentation of the solidification of a molten metal in a mold provided by a prior art casting machine similar to the casting machine of FIG. 1 and shows the solidifying molten metal at the four points indicated in FIG. 1;

FIG. 5 is a schematic presentation of temperature gradients through the mold between the casting cavity and the coolant in the casting machine of FIG. 1 when the casting machine embodies the invention and shows a temperature gradient before a molten metal is received in the mold and a temperature gradient substantially immediately after the molten metal is received in the mold;

FIG. 6 is a schematic presentation of temperature gradients through the mold between the casting cavity and the coolant in a prior art casting machine similar to that shown in FIG. 1 and shows a temperature gradient before a molten metal is received in the mold and a temperature gradient substantially immediately after the molten metal is received in the mold.

DESCRIPION OF AN EMBODIMENT These figures and the following detailed description disclose a specific embodiment of the invention but the invention is not limited to the details disclosed since it may be embodied in other equivalent forms.

The invention in the continuous casting of metals disclosed herein may be most easily understood in terms of a continuous casting machine such as that shown in FIG. 1. However, it should be understood that the continuous casting machine 10 shown in FIG. 1 is representative of many casting machines having a mold which substantially encloses molten metal as it is solidified to obtain cast metal and with which efiicient casting rates can be obtained only by relatively rapid solidification of the molten metal. Moreover, it should also be understood that the continuous casting machine 10 is representative of many casting machines which cast a bar 30 or other shape having a small surface relative to the mass of a molten metal to be cooled during casting and in which a mold is exposed to cyclic temperature conditions as it continuously receives a molten metal to be cooled and removed as a cast metal.

The continuous casting machine 10 selected to illustrate an embodiment of the invention comprises a casting wheel 11 rotatably mounted on a support member 12 for rotation by a motor (not shown) or other power source. Rotatably carried by the support member 12 on opposite sides of and adjacent the casting wheel 11 are two

idler pulleys

14 and 15. These idler pulleys 14 and 15 cooperate with an idler pulley 16 carried by the support member 12 below the casting wheeel 11 to support a continuous band 17 which engages the lower periphery of the casting wheel 11 between the idler pulley 14 and the idler pulley 15.

The casting wheel 11 has a peripheral groove 18 which is closed by the band 17 and which is formed by the mold members or walls 20 of an annular continuous casting mold M that cooperates with the band 17 to define a casting cavity V into one end of which a molten metal 21 is poured from a crucible 22 and from the other end of which the completely solidified molten metal passes as a bar 30. The mold M is cooled by the passage of coolant 23 in three channels 24 adjacent the walls 20 and by the spraying of coolant 23 on the band 17 with nozzles 27 extending from an arcuate duct 28. It will be understood that the coolant 23 is fed to the three channels 24 and to the arcuate duct 28 from a coolant supply (not shown) and that after passing through the channels 24 and over the band 17, the coolant 23 is either discharged from the system or recirculated.

It will also be understood by those skilled in the art that the cooling arrangement described provides an effective means for removing heat from the mold M by the transfer of heat from the mold M to the coolant 23. More importantly, it will be understood by those skilled in the art that in a continuous casting machine 10 having an effective cooling arrangement, the removal of heat from the molten metal 21 for solidification of the molten metal 21 is primarily determined by the transfer of heat between the molten metal 21 and the mold M, by the transfer of heat through the mold M, and by the transfer of heat between the mold M and the coolant 23.

Thus, the continuous casting machine 10 used herein for the purpose of illustrating the invention is a conventional casting machine to the extent that the solidifying of the molten metal 21 is a function of the heat transferred between the molten metal 21 and the coolant 23. It is for this reason and because the structural arrangement of the continuous casting machine 10 in general resembles prior art casting machines that the structural arrangement of the continuous casting machine 10 is not described in greater detail.

However, unlike continuous casting machines used in the prior art, in a casting machine 10 embodying the invention disclosed herein, both the band 17 and that portion of the casting wheel 11 forming the mold M between the coolant 23 and the molten metal 21 are formed of a mold metal or other material having a rate of heat transfer which results in that portion of the mold M adjacent the molten metal 21 rapidly increasing in temperature to an attenuating temperature which substantially attenuates the initial cooling of the molten metal 21 immediately after the molten metal 21 is poured from the crucible 22 into the casting cavity V while at the same time providing for the transfer of heat through the mold M from the molten metal 21 to the coolant 23. The material from which the band 17 and that portion of the casting wheel 11 forming the mold M between the coolant 23 and the molten metal 21 are formed also has a rate of temperature transfer which prevents the rapid propagation or transfer of this attenuating temperature throughout the mold M. Those skilled in the art will understand that these heat transfer and temperature transfer rates can also be provided by a mold construction using several materials to form a composite mold M. Thus, the mold M formed of a single mold metal is only representative of apparatus embodying the invention disclosed.

The significance of using a material for the mold M having the rate of heat transfer described above is best understood by comparing the casting of molten metal 21 in the mold M and in a mold M formed of a prior art material having a rate of heat transfer which results in. the continuous rapid transfer of heat from the molten metal 21 to the coolant 23 as the molten metal 21 is received in the cavity V. FIG. 3 schematically shows the progressive solidification of a segment of the molten metal 21 in the mold M at various arbitrarily selected points a, b, c, and d during the rotation of the casting wheel 11. Similarly, FIG. 4 schematically shows the progressive solidification of the molten metal 21 in the mold M at the same arbitrarily selected points a, b, c and 0! during the rotation of the casting wheel 11.

Thus, FIGS. 3 and 4 schematically show the solidification of the molten metal 21 at corresponding points in its passage through a mold M and a mold M with rotation of the casting wheel 11. However, it should be understood that FIGS. 3 and 4 are merely representative of the solidification of the molten metal 21 and that they are not intended to show the actual state or degree of solidification of the molten metal 21 at any specific point in its passage through a mold M or M.

From both FIGS. 3a and 4a, it will be seen that the initial cooling of the molten metal 21 in the mold M or M occurs as a result of contact between the molten metal 21 and the mold M or M. This is because the molten metal 21 completely fills the mold M or M as it is poured into the mold M or M from the crucible 22 and because this places the peripheral portions P of the molten metal 21 in direct contact with the mold M or M. Thus, in both the mold M and the mold M there is an initial contact transfer of heat between the molten metal 21 and the mold M or M at an initial rate determined largely by the initial difference in temperature between the molten metal 21 and the mold M or M.

However, since the prior art mold M is constructed or formed of a material having a high rate of heat transfer, the initial heat transferred to the mold M from the molten metal 21 passes almost as rapidly through the mold M to the coolant 23 as it is received from the molten metal 21 by the mold M. Thus, the transfer of heat from the molten metal 21 to the mold M continues at a rate of heat transfer which causes the peripheral portions P of the molten metal 21 to solidify rapidly.

As a result, the peripheral portions P of the molten metal 21 are quickly cooled by the mold M and before there has been a significant transfer of heat from the central portion C of the molten metal 21 to these peripheral portions P. This causes a substantially non-uniform cooling of the molten metal 21 which adversely affects the properties of the cast bar 30. In many prior art molds such as the mold M, the cooling of the peripheral portions P is so excessive as to cause chilling of the peripheral portions P of the molten metal 21 which further adversely affects the properties of the cast bar 30.

Further, even when the non-uniform cooling of the cast bar 30 by the mold M does not chill the peripheral portions P of the molten metal 21 the continuous rapid cooling of the molten metal 21 by the mold M causes a substantial shrinking of the partially solidified molten metal 21 and the early forming of a gap G between the mold M and the molten metal 21 as indicated in FIG. 4b. This gap G reduces the continued transfer of heat from the solidifying molten metal 21 to the mold M since it reduces contact between the molten metal 21 and the mold M. As a result, there is reduced cooling of the molten metal 21 by the mold M while there is still substantial heat in the central portion C of the partially solidified molten metal 21. This substantial heat remaining in the central portion C of the partially solidified molten metal 21 is frequently adequate to cause a partial remelting of the previously solidified peripheral portions P of the molten metal 21 and an expansion of the partially solidified molten metal 21 which substantially eliminates the gap G as indicated in FIG. 40.

When this occurs, there is a second rapid cooling of the peripheral portions P of the molten metal 21 before the molten metal 21 finally solidifies completely into the bar 30 as indicated in FIG. 4d. This second rapid cooling serves to further augment the non-uniform cooling of the molten metal 21 by the mold M and may even result in a second chilling of the peripheral portions P of the molten metal 21. However, even in the absence of any second chilling of the partially solidified molten metal 21, it will be understood that the mold M has solidified the portions C and P of the molten metal 21 in a substantially nonuniform manner.

In contrast to the mold M, the mold M attenuates the rapid initial cooling of the peripheral portions P of the molten metal 21 before there is excessive cooling of the peripheral portions P of the molten metal 21 and the gap G is formed. This is because the relatively low rate of heat transfer of the material from which the mold M is formed causes a substantial amount of the heat initially transferred from the molten metal 21 to the mold M to be retained by the portion S of the mold M adjacent the molten metal 21 so as to cause a rapid and substantial increase in the temperature of the portion S of the mold M to a temperature which substantially reduces the temperature difference between the molten metal 21 and the mold M. Thus, the transfer of heat from the molten metal 21 to the mold M is attenuated before excssive cooling of the peripheral portions P of the molten metal 21 and suflicient solidification of the molten metal 21 to form the gap G occur. However, the material from which the mold M is constructed has a rate of heat transfer which provides for the heat from the molten metal 21 to be continuously transferred through the mold M to the coolant 23 at a rate which results in the heat transferred to the coolant 23 alone or the heat transferred to the coolant 23 and the heat retained in the mold M together being equal to that amount of heat which must be removed from the molten metal 21 in order to completely solidify the molten metal 21 in a predetermined interval of time.

Thus, the invention provides controlled cooling of the molten metal 21 in a manner which causes the heat transferred from the peripheral portions P of the molten metal 21 to the mold M subsequent to the initial heat transferred to the portion S to not substantially exceed the heat transferred from the central portion C of the molten metal 21 to the peripheral portions P. As a result, substantially uniform cooling of the molten metal 21 occurs until that point in the solidification of the molten metal 21 indicated in FIG. 30 is reached at which the gap G is formed between the molten metal 21 and the mold M because of the solidification of the molten metal 21.

The forming of the gap G in the mold M reduces the transfer of heat from the molten metal 21 to the mold M because it reduces the contact between the molten metal 21 and the mold M. However, unlike the mold M, in the mold M, the gap G is formed later and after a longor period of substantially uniform cooling. Thus, there is less heat in the central portion C of the molten metal 21 when the gap G is formed in the mold M and less tendency than with the mold M for the heat of the central portion C to reheat the peripheral portions P of the molten metal 21. As a result, the cooling and solidification of the molten metal 21 continues in a substantially uniform manner without that non-uniform cooling or chilling of the peripheral portions P of the molten metal 21 which is frequently encountered in the prior art because of the heat remaining in the central portion C of the molten metal 21 when the gap G is formed.

It will now be understood that the mold M is both a means for retaining heat adjacent the molten metal 21 to provide an initial temperature increase which prevents too rapid initial cooling of the molten metal 21 and a means for transferring heat from the molten metal 21 to a coolant 23. It will also be understood that the solidification of the molten metal 21 to obtain the cast bar 30 between the points a and d in FIG. 1 requires the transfer from the molten metal 21 to the mold M of a particular amount of heat between the points a and d and that the casting rate is dependent upon the length of time required to transfer this particular amount of heat from the molten metal 21 to the mold M.

In both the mold M and the mold M, the length of time required to transfer this particular amount of heat from the molten metal 21 to the mold M or M' is dependent not only upon the rate at which heat is transferred by the material of the mold M or the mold M and the degree of cooling provided by the coolant 23 but also upon the distance through the mold M or M between the molten metal 21 and the coolant 23. It is because of this and because many materials having a relatively low rate of heat transfer also have great structural strength that the mold M provides casting rates equivalent to those achieved in the prior art by simply reducing the distance through the mold M between the molten metal 21 and the coolant 23 to a degree not possible with prior art materials without seriously impairing the strength of the mold M.

Moreover, since the mold M, unlike the mold M, initially retains a substantial amount of heat to provide a temperature of the portion S of the mold M which attenuates the initial cooling of the molten metal 21, the total amount of heat transferred to the mold M from the molten metal 21 between the points a and d in FIG. 1 is the sum of the amount of heat retained in the mold M which remains in the mold M at point d and of the heat transferred by the mold M to the coolant 23 between the points a and d in FIG. 1. Thus, the mold M will also provides casting rates equivalent to those of prior art mold M even if the distance between the molten metal 21 and the coolant 23 is the same in the mold M and the mold M' by allowing some or most of the amount of heat initially and subsequently retained in the mold M to remain in the mold M at point d in FIG. 1 and by removing this heat from the mold M between points d and a with the coolant 23 in the channels 24 while the mold M is empty.

It is also because the cooling of the molten metal 21 by the mold M is a function both of the cooling between the points a and d in FIG. 1 by the coolant 23 and of the amount of heat retained by the mold M at point d in FIG. 1 that the mold M provides convenient control of casting rates. This is because the cooling of molten metal 21 between the points a and a in FIG. 1 in a particular length of time can be varied by varying the cooling of the mold M between points a and d, by varying the temperature of the mold M just prior to point a in FIG. 1 so as to vary the amount of heat initially transferred to and retained by the portion S of the mold M, or by varying the amount of the heat retained by the mold M at the point a' in FIG. 1 and which is removed between points a and a.

That the use of a material for the mold M which not only has the rate of heat transfer described above but also a rate of temperature transfer which prevents temperature changes of the portion S of the mold M from being rapidly transferred throughout the mold M provides a mold M which resists thermal fatigue is best shown by FIG. 5. In FIG. it will be seen that in a mold M having a relatively low rate of temperature transfer, the substantial change in the temperature of the portion S of the mold M which attenuates the initial cooling of the molten metal 21 and which occurs because of the relatively low rate of heat transfer does not pass through the mold M because of the relatively low rate of temperature transfer.

This is particularly important in the mold M provided by the casting wheel 11 since the mold M is exposed to cyclic temperature conditions as the molten metal 21 is alternately received in the mold M, cooled, and removed as a cast bar 30. The substantial restricting of the resulting temperature fluctuations in the mold M to the portion S of the mold M prevents that thermal fatigue throughout the mold M which would impair its structural strength even though the mold M is formed of a material having great initial structural strength. It is because of this and because many materials having both a rate of heat transfer and a rate of temperature transfer suitable to the invention also have great structural strength that the invention disclosed herein provides a mold M which has a rela tively long useful life and which resists the thermal ratcheting and the closing of the casting groove V frequently encountered with prior art casting wheels similar to the casting wheel 11.

OPERATION A comparison in the casting of molten copper of the operation of the continuous casting machine having the mold M formed of low carbon steel with the operation of a similar casting machine 10 having the mold M formed of copper will further clarify the invention. This is because the copper of the mold M is typical of prior art materials having a high rate of heat transfer, a high rate of temperature transfer, and relatively low structural strength and because low carbon steel is representative of metals such as metals in which iron is a major constituent and which provide a mold metal for the mold M which has a relatively low rate of heat transfer, a relatively low rate of temperature transfer, and relatively great structural strength. It is also because molten copper as the molten metal 21 is generally representative of the non-ferrous molten metals such as copper and aluminum which are generally cast in a casting machine 10.

In describing the operation of both the mold M and the mold M it will be assumed that both the mold M and M are used to cast molten copper at the same temperature A as shown in FIGS. 5 and 6 and that both the mold M and the mold M are at approximately the same temperature B as shown in FIGS. 5 and 6 just prior to point a in FIG. 1. This is because regardless of the particular temperature of the mold M or M or of the molten metal 21, it will be understood by those skilled in the art that a temperature gradient in the mold M just prior to point a in FIG. 1 may be generally represented by the line Y in FIG. 5 and that a temperature gradient in the mold M just prior to point a in FIG. 1 may be generally represented by the line Y in FIG. 6.

It will also be understood by those skilled in the art that because of the relatively low rate of heat transfer in low carbon steel, the pouring of the molten metal 21 into the mold M causes the temperature of the mold M adjacent the molten metal 21 to increase by approximately nine-tenths of the difference between the temperature B of the mold M and the temperature A of the molten metal 21 to a temperature C generally indicated in FIG. 5 and that because of the relatively low rate of temperature transfer in low carbon steel, this increase to the temperature C of the mold M causes the temperature gradient in the mold M to be generally represented by the line Z in FIG. 5. Similarly, it will be understood by those skilled in the art that because of the relatively high rate of heat transfer in copper, the pouring of the molten metal 21 into the mold M causes the temperature of the mold M adjacent the molten metal 21 to increase only by approximately two-thirds of the difference between the temperature B of the mold M and the temperature A of the molten metal 21 to a temperature C generally indicated in FIG. 6 and that because of the relatively high rate of temperature transfer in copper, this relatively small increase to the temperature C of the mold M nevertheless causes the temperature gradient in the mold M to be generally represented by the line Z in FIG. 6.

Thus, by retaining substantial heat in the portion S adjacent the molten metal 21, the mold M provides a temperature difference between the temperature C of the mold M and the temperature A of the molten metal 21 which is substantially less than the temperature difference between the temperature C of the mold M and the temperature A of the molten metal 21 but which nevertheless is sufficiently large for the cooling of the molten metal 21 to continue and be achieved. It is this relatively small temperature difference between the temperature C of the mold M and the temperature A of the molten metal 21 which attenuates the cooling of the peripheral portions P of the molten metal 21 in the mold M and it is the relatively large temperature difference between the temperature C of the mold M and the temperature A of the molten metal 21 which causes the excessive and non-uniform cooling of the molten metal 21 in the mold M.

It is by preventing large temperature changes throughout the mold M as indicated by the line Z in FIG. 5 that the mold M reduces the thermal fatigue which the large temperature changes throughout the mold M as indicated by the line Z in FIG. 6 characteristically cause in a mold M. This lack of thermal fatigue in the mold M and the great structural strength of mold metals such as low carbon steel result in the mold M having a useful life substantially longer and a resistance to thermal ratcheting substantially greater than that of a mold M of copper.

It will be obvious to those skilled in the art that many variations may be made in the embodiments chosen for the purpose of illustrating the present invention without departing from the scope thereof as defined by the appended claims.

We claim:

1. In a casting machine for the continuous casting of a non-ferrous molten metal, a rotatable casting wheel having an annular mold with a peripheral groove in which a non-ferrous molten metal is solidified by cooling, said groove being shaped so that the surface of said molten metal through which heat is transferred to said annular mold is small relative to the mass of said molten metal being solidified by cooling in said annular mold, and said annular mold being made of a material characterized by a rate of heat transfer which is substantially less than the rate of heat transfer of molten copper when said molten metal enters said peripheral groove.

2. The casting machine of claim 1 which includes means for cooling said annular mold prior to said molten metal entering said peripheral groove to a mold temperature less than the initial temperature of said molten metal in said peripheral groove, and in which said annular mold is further characterized by a rate of heat transfer at said mold temperature which is sufficiently less than the rate of heat transfer of said molten metal at said initial temperature for the temperature of those portions of said annular mold adjacent said molten metal in said peripheral groove to increase rapidly to a temperature which is substantially the same as the temperature of said molten metal when said molten metal is received in said peripheral groove and thereby retard the transfer of heat from said molten metal to said annular mold.

3. The casting machine of claim 1 in which said material is further characterized by a rate of temperature propagation which is substantially less than that of solid copper.

4. The casting machine of claim 1 in which said rate of heat transfer of said material is such that it attenuates that initial cooling of said molten metal which occurs by transfer of heat from said molten metal to said annular mold when said molten metal enters said peripheral groove.

5. The casting machine of claim 2 in which said material has a rate of heat transfer which is adequate to trans- -fer heat from said molten metal to said means for cooling said annular mold subsequent to said molten metal being received in said peripheral groove.

6. The casting machine of claim 2 in which said means for cooling said annular mold is a coolant spaced from said peripheral groove by said annular mold.

7. The casting machine of claim 3 in which said rate of temperature propagation is such that it substantially restricts the transfer of a temperature change through said annular mold.

References Cited UNITED STATES PATENTS 3,311,955 4/ 1967 Richards 164-278 49,053 7/ 1865 Bessemer 164-87 315,045 4/1885 Lyman 164-278 883,312 3/1908 Holley 164-278 3,322,184 5/1967 Cofer et al. 164-278 X 3,346,038 10/ 1967 Properzi 164-278 J. SPENCER OVERHOLSER, Primary Examiner R. SPENCER ANNEAR, Assistant Examiner U.S. Cl. X.R. 164-283; 249-135