US3322184A

US3322184A - Thermal barrier for casting metals

Info

Publication number: US3322184A
Application number: US394631A
Authority: US
Inventors: Daniel B Cofer; Dale D Proctor; George C Ward
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1964-09-04
Filing date: 1964-09-04
Publication date: 1967-05-30
Anticipated expiration: 1984-05-30
Also published as: GB1067921A; BE669194A; DE1508715A1; CH448395A

Description

1967 D. B. COFER ETAL 3,322,184

THERMAL BARRIER FOR CASTING METALS Filed Sept. 4, 1964 INVENTORS DANIEL B. COFER DALE D. PROCTOR BY GEORGE C.WARD

JMKWMW ATTORN EYS I Daniel B. Cofer,

United States Patent Ofifice 3,322,l4- Patented May Kill, 196'? 3,322,184 THERMAL BARBER, F011: (JAFJHNG METALS Dale D. Proctor, and George C. Ward, tCarrollton, Ga, assignors to Sonthwire tl'ompany, Carrollton, Ga, a corporation of Georgia Filed Sept. 4, 1964, Ser. No. 394,631 Claims. (Cl. l64-72) This invention relates to the casting of metals and is more particularly concerned wtih a method of providing a thermal barrier between cast metals and casting molds.

The efficient and economical casting of metals requires that the physical separation of a cast metal from a casting mold be easily and conveniently accomplished, that the continuous or repeated casting of a metal in a casting mold not cause the rapid deterioration or destruction of the casting mold, and that the cooling of the cast metal in a casting mold does not occur in such a manner as to cause a substantial segregation in the cast metal of alloy constituents. These three requirements are difiicult to meet in the casting of metal and are particularly diflicult to meet in the continuous casting of metal where elaborate and time consuming preparation of a casting mold each time it is used is not possible.

Accordingly, it has been customary in the continuous casting of metal and in most other casting techniques to tolerate undesirable deterioration of casting molds and the undesirable segregation of alloy constituents in the cast metal and to meet the requirement for the physical separation of the cast metal from a casting mold by using various parting and releasing agents. However, even this last requirement has not always been successfully met. This is because previous parting and releasing agents have rarely been applied to casting molds in a uniform manner.

The invention disclosed herein meets the three requirements for the efiicient and cast. The thermal barrier serves to physically separate the cast metal from the casting mold so that the cast metal peripheral portions of the cast metal.

The thermal barrier of the invention may be formed from any of many well known materials having the physical characteristic of being a relatively poor conductor of heat, of having a melting point well above that of the cast metal, and of being relatively easy to apply in a metals having a lower melting point, and which is also relatively inexpensive and easy to obtain. Accordingly, the present invention is described herein in terms of a thermal barrier formed of soot.

It is also described in terms of applying a thermal barrier to the casting wheel and belt of a casting machine used in the continuous casing of metal. This is because the application of previous parting and releasing agents in a uniform manner to the continuously moving casting wheels and belts of casting machines has not been previously accomplished in a satisfactory manner and because the present invention is particularly well adapted to use in the continuous casting of metals. However, it will be understood that the thermal barrier of the present inven- 2? tion may be formed of materials other than soot and may be applied to casting molds other than those formed by a casting wheel and belt.

From the foregoing, it will be understood that it is an object of the present invention to provide a method of forming an improved parting or releasing agent for easting molds. Another object is to provide a novel, simple and improved method of retarding the transfer of heat from cast metal to casting molds. A further object of the present invention is to provide a method of preventing the deterioration of casting molds by the heat from cast metal. In addition, it is an object of the invention to provide a method of reducing the segregation of alloy constituents in cast metal so as to improve the characteristics of the cast metal. It is also among the objects of the invention to provide a method of conveniently applying a uniform coating of material to a continuously moving mold surface.

These and other features, advantages and objects of the present invention will become apparent from consideration of the following specification taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a fragmentary side elevational view of the casting wheel and belt of a casting machine and of appsratus adapted for applying a thermal barrier to the continuously moving mold surfaces.

FIG. 2 is an enlarged sectional view taken along the line 22 in FIG. 1 showing the burner arrangement for applying a thermal barrier to the belt.

FIG. 3 is an enlarged fragmentary side elevational view of the burner arrangement for applying a thermal barrier to the casting wheel groove.

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3.

In disclosing the embodiment of the present invention here chosen by way of illustration, FIG. 1 shows a portion of a casting machine of known type. The periphery of the wheel 10 is provided with the conventional circumferential groovell in its rim 41 into which molten metal is poured for casting. A continuous belt 12 which moves with the wheel 16 engages a fixed sector of the periphery of the continuously moving wheel 10 to form a closed mold between the groove 11 and the belt 12. The belt 12 passes from and to the wheel 10 over an idler pulley 14 and in the direction indicated by the arrow 9' in FIG. 1. Thus, it will be understood that the belt 12 is tangent to the casting wheel 163 at two points so as to provide an entrance for the molten metal and an exit for the cast bar. Molten metal is fed into the groove 11 from a conventional pouring pot 15 through a spout 16, the spout 16 having its discharge end substantially at the point of tangency of the belt 12 as it first engages the wheel 10.

For removal of the cast bar from the groove ll, an ex tractor shoe 18 is mounted at a point somewhat removed from the departing tangent point of the belt 12 with the wheel 10. The extractor shoe 13 is rigidly secured to a fixed block 19 supported by a portion of the machine frame (not shown).

In the operation of the foregoing conventional and Well known equipment, as the wheel 10 :is rotated in the direction shown by the arrow 9' in FIG. 1, carrying with it the belt 112, molten metal is poured into the groove 11 enclosed by the belt 12. The metal cools as it is carried betwen the wheel and belt to emerge as a solid cast bar or rod. Since the continuously moving inner face 12a of the belt 12 and the continuously moving inner faces Illa of the groove 11 constitute mold surfaces, it will be understood that the thermal barrier of the invention must be continuously applied thereto.

For applying a thermal barrier of soot to the belt 12, there is provided a burner arrangement having a burner 20 mounted within a shield 21 supported by an arm 22 secured to the block 19. The burner 20 is of elongated tubular construction and is disposed transversely of the belt 12. One end of the burner 24) is closed while the opposite end receives gas from a gas tube 24. A valve 23 is provided for varying the rate of gas flow to the burner 20? from any convenient source of gas (not shown). It will be understood that varying gas flow rate permits the rate of soot production to be varied with the rate of travel of the belt 12 and to provide soot coatings of various selected thicknesses. Facing the belt 12, the burner 20 is provided with a uniformly spaced row of gas emission ports 25.

The shield 21 includes a fiat mid-portion 26 disposed parallel with the axis of the burner 20 and side edges 28 which extend toward the belt 12 to provide a transversely disposed open ended channel. The edges 28 act to confine the soot for uniform transverse deposit on the belt 12 while water vapor and gaseous products resulting fro-m the combustion of a gas escape from the open ends of the channel.

For coating the groove 11 of the wheel 10, a burner arrangement having a burner 30 is provided. The burner 30 is similar to the burner 20 and extends transversely of the groove 11. Burner 3%) is supplied with gas from any convenient source of gas (not shown) through a gas tube 34. The gas is emitted through burner perforations 35 for combustion and a valve 33 in the tube provides control of the gas so that the rate of soot production may be varied with the rate of travel of the groove 11 and with the thickness of soot coating desired. The burner 3t? is provided with a. shield 31, and an arm 32 attached to the block 19 supports the burner 36) and the shield 31. The shield '31 includes a central flat portion 36 positioned tangential to the wheel adjacent its periphery. Soot resulting from the combustion of a gas in the burner 30 is confined by shield flanges 38 disposed within the groove 11 and shaped to conform with the cross-sectional configuration of the groove Ill. The shield 31 defines an openended transverse channel outwardly of the wheel 16 and water vapor and gaseous products resulting from the combustion of a gas escape from the open ends of the channel.

It has been found that the application of a thermal barrier such as a thermal coating of soot is facilitated if the surface to which it is applied is relatively cool. Thus, a nozzle 40 is provided to supply coolant water to the inner surface of the wheel rim 41. The nozzle 40 is mounted on a stationary ring 42 which is positioned in known manner within the wheel 10 and water from any convenient source (not shown) is fed to the nozzle 4% by tubing of known type and arrangement (not shown). In this connection it will be noted that the free flight of the belt 112 over the pulley 14 provides for adequate cooling of the belt 12.

From the foregoing, it as a hydrocarbon gas, e.g.

will be seen that as a fuel such acetylene (CH H or the like, is supplied through the tubes 24 and 34- to the burners and 30 respectively, the ignition of the gas will produce a uniform adherent soot coating Ed on the inner face 12a of the belt 12 just prior to contact of the belt with the periphery of the groove 11. Concurrently, a soot coating 51 is deposited on the inner faces 11a of the groove 11 just prior to the application of molten metal to the groove 11. Thus, the burners lit and 3t continuously produce a coating of soot in the casting mold formed by the groove and belt just prior to the reception of molten metal between the wheel 1t and belt 12.

The coating of soot is applied to the sides Mia and 11a of this casting mold in a uniform manner since adjustment of the

valves

23 and 33 permits the gas to be burned at various substantially constant rates selected to provide for the constant and uniform application of soot coatings 5t and 51. It will be understood that by adjusting the

valves

23 and 33, the uniform application of the

soot coatings

50 and 51 can be maintained regardless of the rotational speed of the wheel 10.

It will also be understood that by adjusting the

valves

23 and 33, the thickness of the

soot coating

50 and 51 applied to the walls 10a and 11a may be varied. Moreover, it will be understood that by adjusting the positions of the side edges 28 of the shield 21 and of the shield flanges 38 of the shield 31, excessive soot or foreign matter may be scraped from the surfaces 10a and 11a to which the soot coatings 59 and 51 are applied. Thus, the apparatus permits a thermal barrier B of soot to be applied to a casting mold in a uniform manner and to a selected thickness.

It has been found that when a thermal barrier B is formed by coatings of

soot

50 and 51 applied in a uniform manner to a thickness of approximately two thousandths of an inch, copper having small traces of iron, zinc and other alloy constituents which will segregate as alloy constituents under certain known cooling conditions can be continuously cast at an initial pouring temperature of approximately 2150 degrees Fahrenheit using a casting wheel if) of a metal such as copper which will deteriorate at a temperature of approximately 1800 degrees Fahrenheit without deterioration of the casting wheel 10 or substantial segregation of alloy constituents. These results are obtained with the casting wheel having a diameter of approximately fifty inches and a rotational speed of approximately three revolutions per minute and being cooled by action of the nozzle 40 to a temperature of approximately 300 degrees Fahrenheit when the coating of soot 51 is applied. It will be understood that the belt 12 has a speed related to the rotational speed of the wheel 10 and is cooled by travel to and from the pulley 14 to a similar temperature when the coating of soot 50 is applied.

It will also be understood that regardless of thickness, the soot coatings Stl and 51 serve as a parting and releasing agent to permit the easy removal of cast metal from the groove ill and that the thickness of the thermal barrier B required to prevent deterioration or damage to a casting mold and substantial segregation of alloy constituents will vary in accordance with certain conditions. These conditions are the thermal conductivity of the material applied as the thermal barrier, the temperature at which the casting mold deteriorates or is otherwise damaged by heat, the temperature at which the cast metal is poured into the casting mold, the temperature of the casting mold at the time the cast metal is poured, and the cooling rate of the cast metal at which segregation of alloy constituents occurs.

These conditions determine the thickness of the thermal barrier B because they relate to the transfer of heat from the cast metal to the casting mold, and to the transfer of heat which is permissible without deterioration of the casting mold and segregation of alloy constituents, and because it is the control of this transfer of heat by the thermal barrier B which prevents the deterioration of a casting mold and the substantial segregation of alloy constituents. Thus, if the casting mold is relatively cool and the cast metal is relatively hot when the cast metal is poured, the thermal barrier B must be sufficiently thick to retard that initial transfer of heat resulting from the initial difference in temperature between the casting mold and the cast metal which would raise the temperature of the casting mold to a temperature at which the casting mold deteriorates and which would cause the P pheral surfaces of the cast metal to cool so rapidly that those temperature gradients in the cast metal known to cause segregation of alloy constituents occur.

The greater the thermal conductivity of the material used as a thermal barrier B, the thicker the material must be applied in order to retard this initial transfer of heat. On the other hand, for any given material used as a thermal barrier B, the thermal barrier B may be of dea fl g thickness as the difference in temperature between the casting mold and cast metal when poured decreases, as the temperature at which the casting mold deteriorates or is otherwise damaged increases, or as the rate of cooling of the cast metal at or above which segregatiOn of alloy constituents occurs increases.

Moreover, regardless of the material selected, for application as a thermal barrier B to a casting mold, when an enclosed casting mold such as that provided by the wheel 10 and belt 12 is used, the material must have sufiicient thermal conductivity to allow that substantially constant continuous transfer of heat to the casting mold which Will cause the cast metal to solidify within the time allowed therefor. It has been found that this continuous transfer of heat will occur without the rate of cooling of the cast metal reaching that rate which causes a temperature gradient in the cast metal which Will result in the segregation of alloy constituents.

It will also occur Without the temperature of the casting mold reaching that temperature at which it deteriorates. This can be insured by using any of the various well known arrangements (not shown) for cooling casting molds with a cast metal therein. Thus, it will be seen that the present invention provides a thermal barrier B which retards initial transfer of heat and permits the easy physical separation of a cast metal from a casting mold While at the same time permitting the cast metal to be cooled in the time allotted therefor. It will also be seen that the material selected for the thermal barrier B and the thickness of the thermal barrier B can be readily calculated by those skilled in the art once the conditions defined herein are established and considered in each specific application of the invention.

It will, of course, be understood that the specific apparatus herein presented is by Way of illustration only, and is meant to be in no way restrictive; therefore, numerous changes and modifications may be made and the full use of equivalents resorted to without departing from the spirit or scope of the invention as outlined in the appended claims.

What is claimed as invention is:

1. In a process of substantially complete mold defined by the peripheral groove in a casting wheel steps of applying a thermal coating to a surface of said 4 mold and of subsequently pouring said metal into said mold, cooling said metal in said mold to obtain the substantially complete solidification of said metal and removing said metal from said mold; the thickness of said thermal coating being controlled. during the step of applying said thermal coating to a surface of said mold so that said thermal coating retards that initial transfer of heat from said metal to said mold which is a result of the initial difference in temperature between said metal and said mold and so that said thermal coating does not substantially increase the time required for the substantially complete solidification of said metal in said mold relative to the time required for the substantially complete solidification of said metal in said mold in the absence of said thermal coating.

2. The process of claim 1 in which said thermal coating is selected and controlled during the step of applying a thermal coating so that said thermal coating is a parting means for aiding in removing said metal from said mold.

3. The process of claim 1 in which said initial transfer of heat is limited to a rate which is less than that rate at which substantial segregation of alloy constituents in said metal occurs.

4. The process of claim it including the step of cooling said mold by the transfer of heat from said mold to a coolant and in which said initial transfer of heat from said metal to said mold does not exceed said transfer of complete combustion of a hydrocarbon fuel toward said surface.

References Cited UNITED STATES PATENTS 1,963,149 6/1934 Russell et a1 2265 1,982,762 12/1934 Russell et al. 22-65 2,206,930 7/1940 Webster 22-57.3 2,714,235 8/1955 Brennan 22200.1 X

J. SPENCER OVERHOLSER, Primary Examiner. R. S. ANNEAR, Assistant Examiner.

Claims

1. IN A PROCESS OF CONTINUOUSLY CASTING METAL BY THE SUBSTANTIALLY COMPLETE SOLIDIFICATION OF SAID METAL IN A MOLD DEFINED BY THE PERIPHERAL GROOVE IN A CASTING WHEEL AND BY A BELT WHICH CLOSES A LENGTH OF SAID GROOVE, THE STEPS OF APPLYNG A THERMAL COATING TO A SURFACE OF SAID MOLD AND OF SUBSEQUENTLY POURING SAID METAL INTO SAID MOLD, COOLING SAID METAL IN SAID MOLD TO OBTAIN THE SUBSTANTIALLY COMPLETE SOLIDIFICATION OF SAID METAL AND REMOVING SAID METAL FROM SAID MOLD; THE THICKNESS OF SAID THERMAL COATING BEING CONTROLLED DURING THE STEP OF APPLYING SAID THERMAL COATING TO A SURFACE OF SAID MOLD SO THAT SAID THERMAL COATING RETARDS THAT INITIAL TRANNSFER OF HEAT FROM SAID METAL TO SAID MOLD WHICH IS A RESULT OF THE INITIAL DIFFERENCE IN TEMPERATURE BETWEEN SAID METAL AND SAID MOLD AND SO THAT SAID THERMAL COATING DOES NOT SUBSTANTIALLY INCREASE THE TIME REQUIRED FOR THE SUBSTANTIALLY COMPLETE SOLIDIFICATION OF SAID METAL IN SAID MOLD RELATIVE TO THE TIME REQUIRED FOR THE SUBSTANTIALLY COMPLETE SOLIDIFICATION OF SAID METAL IN SAID MOLD IN THE ABSENCE OF SAID THERMAL COATING.