CA2305188A1 - An improved continuous casting mold system and related processes - Google Patents

Abstract

An improved mold and process for continuous casting involves the use of a mold surface that is fabricated from a material, such as diamond, that is nonmetallic, an efficient conductor of heat and that is more degradation-resistant than the conventional materials and coatings that are used on mold surfaces. In one embodiment, the nonmetallic material is bonded to a conventional mold liner. In a second embodiment, the entire mold wall can be fabricated from the nonmetallic material. In another aspect of the invention, since materials such as diamond are transparent in the infrared range, the temperature of the outer shell of the casting can be monitored through the nonmetallic material without interfering with the casting process, and this information can be used to control one or more variables in the casting process.

Description

AN IMPROVED CONTINUOUS CASTING MOLD SYSTEM
AND RELATED PROCESSES
BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to the technical field of metal making and processing using the continuous casting process. More specifically, this invention pertains to an improved mold surface for a continuous casting machine, and to a system and method for controlling the casting process by actually monitoring the temperature of the casting at the mold surface while the machine is operating.
2. Description of the Prior Art and the Related Technolo~y Production of metals by use of the continuous casting technique has been increasing since its large-scale introduction about thirty years ago, and now accounts for a large percentage of the volume of steel, among other metals, produced each year worldwide. It is well known that continuous casting machines typically include a mold that has two essentially parallel and opposed wide walls, and two essentially parallel opposed narrow walls that cooperate with the wide walls to define a casting passage of rectangular cross section. Molten metal is supplied continuously into a top end of the casting passage, and the mold is designed to cool the metal so that an outer skin forms before the so-formed slab or strand exits a bottom of the casting passage. In order to efficiently dissipate the heat from the molten steel, the mold casting surfaces are typically lined with copper or have a copper alloy surface layer and contain numerous passages through which water flows, during the molding process for rapid heat exchange. In some instances, the mold is cooled by spraying water directly against the cooler side of the mold liner. The strand is further cooled by spraying as it travels away from the mold. until ii becomes completely solidified. It may then be processed further into an intermediate or finished metal product, such as steel plate, sheeting or coils by traditional techniques such as rolling.
The mold casting surfaces, also known as the "hot faces" of the mold. are exposed to the high temperature molten steel and corrosive mold flux for prolonged periods of time.
Copper is a very efficient thermal conductor. but is relatively soft and is thus susceptible to early wear and other types of degradation. Under normal casting conditions, the hot faces of the mold experience relatively rapid degradation such as wear, cracking and steam and chemical erosion. This effect is exacerbated in high-speed molds, which tend to run at higher temperatures wherein the copper material begins to further soften. The assignee of this S invention, A.G. Industries, Inc., is the largest North American provider of maintenance and repair services for continuous casting machines, and is intimately familiar with the degradation and wear that occurs on mold faces during casting.
In order to prolong the life of the mold surfaces for as long as possible, it is typical to pre-coat the copper mold surface with a friction and corrosion resistant material, such as such as nickel or chromium. Other techniques for protecting the mold wall surfaces have been proposed and/or put into commercial use. For example, U.S. Patent 5,499,672 discloses a process for protecting a copper mold surface by applying a metal carbide protective material onto the mold surface. Another protective coating technique involves applying a Ni-Cr alloy to the copper mold faces by a thermal spraying process.
This process is described in the publication Ni-Cr Allvy Thermal Spraying of the A'arnou~
Face of Continuous Casting Mold, dated May 1989 by Nippon Steel Corporation and Mishima Kosan Co., Ltd. While the coatings that have been developed to date have been able to reduce the rate and severity of mold wear to some extent, it remains a fact of life in the continuous casting industry that the mold faces must be periodically removed and replaced or repaired.
Taking the mold off line~to do this represents a significant cost to a steelmaker, perhaps as much as fifteen thousand dollars per hour.
The strand or slab has a very thin skin when it initially forms in the mold.
Rupture of the skin must be avoided at all costs because it can cause a condition known as a breakout, i.e., where molten metal escapes through the skin beneath the mold. A severe breakout can encase portions of the machine that are in its path in molten metal, rendering those components unusable and requiring them to be replaced and reconditioned. One of the factors that is important in determining whether or not a breakout is likely to occur is the thickness of the skin as the casting moves through the mold. Theoretically, skin thickness could be measured in situ during casting by monitoring the infrared emissions of the slab. but in practice this has not been feasible because the entire slab is surrounded by the mold, making measurement impossible. Some systems exist that attempt to model the casting thickness by sampling temperatures at selected locations in the mold liner, but these systems can be less than accurate because of the varying thickness of the copper material between the sensors and the casting surface.
A need exists in the continuous casting industry for a mold face that is less vulnerable to wear and degradation during casting than conventional mold faces are.
Additionally, a need exists for a continuous casting mold that permits improved monitoring of the casting as it moves through the mold so that breakouts and other unwanted conditions can be prevented.
SUMMAKY OF THE INVENTION
Accordingly, it is an object of the invention to provide a mold face design for continuous casting that is less vulnerable to wear and degradation during casting than conventional mold faces are.
IS It is further an object of the invention to provide a continuous casting mold that permits improved monitoring of the casting as it moves through the mold so that breakouts and other unwanted conditions can be prevented.
In order to achieve the above and other objects of the invention, an improved mold wall assembly for use in a continuous casting machine includes, according to a first aspect of the invention, an inner portion that is constructed and arranged to conduct heat away from the mold liner during operation; and an outer surface that forms a casting surface of the mold, the outer surface including a degradation-resistant nonmetallic material that has high thermal conductivity, whereby the mold liner will exhibit superior wear and heat transfer characteristics during its operation in a continuous casting machine.
According to a second aspect of the invention, a method of making a strand of continuously cast material includes steps of: (a) introducing molten metal into a mold that includes a plurality of mold surfaces, at least one of the mold surfaces having an outer coating comprising a degradation-resistant nonmetallic material that has high thermal conductivity;
(b) cooling the molten metal by conducting heat away from the molten metal through the outer coating; and moving the cast strand out of the mold.

A third aspect of the invention involves an improved mold assembly for a continuous casting machine that includes a plurality of mold walls, each of which mold walls has at least one mold surface that together defines a casting space having an upper opening and a lower opening; and wherein at least one of the mold walls is fabricated from a degradation-resistant nonmetallic material that has high thern~al conductivity, whereby the mold assembly will exhibit superior wear and heat transfer characteristics during its operation in a continuous casting machine.
A fourth aspect of the invention involves a method of making a strand of continuously cast material that includes steps of introducing molten metal into a mold that includes a plurality of mold surfaces; cooling the molten metal by conducting heat away from the molten metal through the mold surfaces by means of conductive heat transfer; and further cooling the molten metal that is within the mold by means of radiation heat transfer that occurs through at least one of said mold surfaces.
According to a fifth aspect of the invention, an improved mold assembly for use in a continuous casting machine includes a surface that fornis a casting surface of the mold, the surface being at least partially transparent to radiation that is within the infrared range, whereby the mold is capable of cooling the molten metal that is within the mold by means of radiation heat transfer that occurs through the surface.
These and various other advantages and features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part hereof However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.
BRIEF DESCRIPTION Oh' THE DRAWINGS
FIGURE 1 is a fragmentary horizontal cross-sectional view taken through a mold wall assembly for a continuous casting machine that is constructed according to a preferred embodiment of the invention;

FIGURE 2 is a vertical cross-sectional view taken through one component of the assembly shown in FIGURE 1;
FIGURE 3 is a diagrammatical view of a preferred feature in the assembly shown in FIGURES 1 and 2;
S FIGURE 4 is a schematic diagram depicting a preferred control system for the assembly shown in FIGURES 1 through 3;
FIGURE 5 is a fragmentary vertical cross-sectional view taken through a mold wall assembly that is constructed according to a second embodiment of the invention; and FIGURE 6 is a fragmentary vertical cross-sectional view taken through a mold wall assembly that is constructed according to a third embodiment of the invention.
DETAILED DESCR1PTION OF THE PREFERRED EMBODINiENT(S) Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIGURE l, an improved mold wall assembly 12 for a continuous casting machine 10 includes a plurality of mold walls, including an opposing pair 14, 16 of narrowface walls and an opposing pair of broadface walls 18,20. Each of the mold walls 14, 16, 18, 20 has at least one mold surface that together define a casting space 26 having an upper opening and a lower opening. The mold wall assembly 12 is designed, as is conventional, so that molten metal can be supplied continuously into the top end of the casting space 26, and so as to cool the metal so that an outer skin forms before the so-formed slab or strand exits a bottom of the casting passage. As is conventional, coolant supply pipes 22, 24 are provided for providing a water coolant to the narrowface walls 14, 16 and the broadface walls 18, 20, respectively.
Referring now to FIGURE 2, which is a vertical cross-sectional view taken through one of the broad face walls 20 in FIGURE 1, it will be seen that wall 20 includes a liner assembly 27 that bears the mold face 28, and a support assembly 32 to which the liner assembly 27 is secured. As may be seen in FIGURE 2. the liner assembly 27 includes an inner portion 29 that is embodied as a copper liner 3U, and an outer layer 44 of degradation-resistant, non-metallic material that forms the mold face 28, and will be discussed in greater detail below. The support assembly 32 includes the coolant supply pipe 24, a coolant return WO 00/0??52 PCT/US99/1?602 pipe 42, an inlet plenum 36 and an outlet plenum 38. Both the inlet and outlet plenums 36, 38 are in communication with a cooling channel 34 that is defined in the copper liner 30 of the liner assembly 27. In operation, as is conventional, the coolant, which is typically water, i introduced from the coolant supply pipe 24 into the inlet plenum 36, where it flows upwardly through the cooling channel 34 and out into the outlet plenum 38. The coolant is then returned to a circulation pump through the return pipe 42.
The layer 44 of degradation-resistant, non-metallic material is preferably a material that is an efficient conductor of heat, that is very hard and degradation-resistant, that can tolerate the high temperatures that exist in a continuous casting mold during operation, that is resistant to the acidic environment in which a continuous casting machine typically functions, and that, for reasons discussed in greater detail below, is preferably transparent in the infrared portion of the spectrum. Two of the known materials that exhibit these characteristics are diamond and crystalline boron nitride.
Diamond is a allotrope of carbon that is metastable at ordinary pressures, having a large activation energy barrier that prevents conversion to graphite, the more stable allotrope at ordinary temperatures and pressures. It has long been sought after not only for its intrinsic beauty and value as a gemstone but also for its many unique and valuable mechanical, electrical, optical and thermal properties. Diamond is the hardest material occurring in nature, has a low co-efficient of friction, is extremely resistant to chemical attack, is optically transparent to much of the electromagnetic spectrum, including being highly transparent to infrared radiation, and has the highest heat conductivity of any material.
Crystalline boron nitride (CBN) has properties that are comparable to diamond in many respects.
One advantageous feature of the invention is depicted diagrammatically in FIGURE

3. As may be seen in FIGURES 2 and 3, a passage 46 may be formed in the copper liner plate 30 of the liner assembly 27. An optical fiber 48 is situated in the passage 46, and is optically coupled to the transparent layer 34 of degradation-resistant, non-metallic material on a side thereof that is opposite to the casting surface or mold face 28 of the layer 44. A sensor 50 is then coupled to a second, opposite end of the optical fiber 48. The purpose of the sensor 50 is to monitor a property of the continuous casting process by examining the spectral characteristics of the light that is carried through the optical fiber 48. In its preferred embodiment, sensor 50 is constructed and arranged to monitor the infrared profile of the transmitted light, so as to monitor the temperature of the exterior of the cast strand as it moves downwardly along the casting surface within the mold. By monitoring this temperature, the thickness of the skin of the casting can be determined, which is a useful indicator for many things, including the susceptibility of the strand to breakouts after it exits the bottom of the mold, the optimal withdrawal speed of the strand from the machine, the optimal rate at which coolant is circulated through the mold walls. and the uniformity of shell growth. Referring now to FIGURE 4, it will be seen that a number of such sensors SO are provided in the mold assembly, and that each of those sensors provides information to a CPU
52 that serves as a local control system for the mold wall assembly 12. CPU 52 is in two-way communication with a main control system 54 of the continuous casting machine 10, and is further in communication with different subsystems for modif~~ing different performance variables of the continuous casting process. FIGURE 4 depicts four such subsystems 56, 58, 60 , 62, but the number could be more or less, depending upon the number of performance variables that are desired to be controlled in response to the optical monitoring that is performed by the sensor 50. For example, one of the subsystems may permit adjustment of the withdrawal speed of the continuous casting machine. Another subsystem may permit adjustment of the taper of the mold. Third and fourth subsystems for adjusting the rate of cooling the mold may constitute a control system for adjusting the volumetric flow of coolant through one or more of the mold walls, or changing the composition of mold flux for changing the heat conduction properties of the mold.
In order to analyze the data that is gathered by the sensors 50, a commercially available thermal imaging system may be used. One such imaging system that could be used is available from Mikron Instruments of Oakland, New Jersey and is sold as an "Imaging Pyrometer." This system is disclosed in part in IJ.S. Patent 4.687,344, the disclosure of which is hereby incorporated as if set forth fully herein.
Looking now to FIGURE 5, a mold assembly 64 that is constructed according to a second embodiment of the invention includes a casting surface 66, and a body 68 that is fabricated entirely of the non-metallic. degradation-resistant material of the type that is discussed in detail above. A cooling channel 70 is defined in the body 68 of material. and a sensor 72, which is similar in construction to the sensor 50 discussed above, is coupled to a rear side of the body 68. In this embodiment of the invention, the entire mold wall is made of the diamond or CBN material. It is believed that this embodiment holds great potential for the future, because such a mold wall would be expected to substantially outperform any mold wall that is in service today. Fabricated entirely of a material such as diamond, it would be much more efficient at conducting heat away from the strand during casting than a metallic mold wall would, it would exhibit lower friction than any metallic mold wall would, and it would be virtually indestructible in terms of wear.
FIGURE 6 depicts yet another embodiment of the invention. In this embodiment, as in the embodiment that is described above in reference to FIGURE S, the entire mold liner 80 is fabricated from a degradation-resistant nonmetallic material that has high thermal conductivity, whereby the mold liner will exhibit superior wear and heat transfer characteristics during its operation in a continuous casting machine. As in the embodiment of FIGURE 5, the preferred materials arc diamond or CBN, and the mold liner can be constructed according to any of the fabrication processes disclosed below, or by any other process that will be effective. A sensor 72, which is similar in construction to the sensor 50 discussed above, is coupled to a rear side of the mold liner 80. In this embodiment, the mold liner 80 does not have an internal cooling passage, but is constructed as a "spray-type" mold in which the side 86 of the liner that is opposite the casting 82 is subjected to cooling spray from one or more spray nozzles 88. The high thernial conductivity of this type of mold liner will contribute to the effective cooling of the casting and the formation of casting that has a uniform solidified shell 84. In addition, a significant amount of heat will also be transferred away from the casting by means of radiation as a result of the transparency of the mold in the infrared range. This stands in favorable contrast to a conventional continuous casting mold, where there is no heat transfer through the mold wall by means of radiation.
There are a number of known techniques for artificially building coatings and masses of materials such as diamond and crystalline boron nitride, and the inventors recognize that any one of those known techniques could be used within the purview of the invention. The inventors further appreciate that this technology is advancing at a rapid rate, and expect io be able to utilize other. more efficient techniques for creating the necessary structure when such new technology becomes available. The following U.S.
Patents and PCT
Publications disclose techniques for artificially building coatings and masses of materials such as diamond and crystalline boron nitride, and are to be considered exemplary for purposes of this disclosure. Each of the documents listed below are hereby incorporated into this disclosure as if set forth fully herein:
U.S. Patent No. Name Publication Date 4,490,229 Mirtich et al. 12/25/94 4,504,519 Zelez 3/ I 2/85 4,770,940 Ovshinsky et al. 9/13/88 4,830,702 Singh et al. 3/16/89 4,910,041 Yanagihara et al. 3/20/90 4,939,763 Pinneo et al. 7/3/90 4,948,629 Hacker et al. 8/14/90 4,954,365 Neifeld 9/4/90 4,981,717 Thaler 1/1/91 4,987,007 Wagal et al. 1/22/91 5,015,528 Pinneo 5/14/91 5,071,677 Patterson et al. 12/10/91 5,080,753 Doli et al. 1/14/92 5,082,359 Kirkpatrick 1 /21 /92 5,096.740 Nakagama et al. 3/17/92 5.154,945 Baldwin et aI. 10/13/92 U.S. Patent No. Name Publication Date 5,221,411 Narayan 6/22/93 5,221,501 Feldman et al. 6/22/93 5,230,931 Yamazaki et al. 7/27/93 5,236,740 Peters et al. 8/17/93 5,243,170 Maruyama et al. 9/7/93 5,260,106 Kawarada et al. 11 /9/93 5,264,071 Anthony et al. 11 /23/93 5,271,890 Shimura et al. 11/21/93 5,273,731 Anthony et al. 12/28/93 5,273,788 Yu 12/28/93 5,302,231 Bovenkerk et al. 4/12/94 S,S 16,500 Liu et al. 5/14/96 5,525,815 Einset 6/11 /96 PCT App. No. Namc Publication Date PCT/CJS95/05941 Mistry 11 /23/95 PCT/US95/00782 Mistry ???

Most Preferred Processes for Applying the Non Metallic $ Wear Resistant Layer In one embodiment, which utilizes the process that is taught in U.S. Pat. No.
4,490,229, a diamond-like carbon film can be deposited in the surface of a substrate by exposing the surface to an argon ion beam containing a hydrocarbon. The current density in the ion beam is low during initial deposition of the film. Subsequent to this initial low current condition, the ion beam is increased to full power. At the same time a second argon ion beam is directed toward the surface of the substrate. The second ion beam has an energy level much greater than that of the ion beam containing the hydrocarbon. This addition of energy to the system increases mobility of the condensing atoms and serves to remove Lesser-bound atoms, increasing the percentage of diamond bonds.
In a second embodiment, which utilizes the process that is taught in U.S. Pat.
No.
4,504,519, an amorphous. carbonaceous, diamond-like film is produced by a hybrid process in a deposition chamber using a radio frequency plasma decomposition from an aikane, such as n-butane, using a pair of spaced, generally parallel, carbon electrodes, preferably ultra pure carbon electrodes. While most films of this invention were deposited using normal butane, other alkanes, such as methane, ethane, propane, pentane, and hexane can be substituted in the process of this invention to produce the improved carbonaceous, diamond-like film thereof. The deposition chamber, such as a stainless steel chamber, includes a pair of generally parallel and horizontal, vertically spaced, pure carbon electrodes with the substrate to be coated positioned on the lower carbon electrode. The electrodes are typically positioned about 2 up to about 8 centimeters apart from each other, with the preferred electrode spacing being approximately 2.5 centimeters: The chamber is evacuated to its ultimate pressure, generally in the region of about 10< - 7 > torr, and then backfilled with an alkane, such as n-butane, to a pressure of approximately 8 x 10< - 4 > torr. Thereafter, the vacuum system is throttled to a pressure in the range of approximately 25 to I00 millitorr.
After stabilization of the pressure, the radio frequency power is applied to the pair of pure carbon electrodes with the lower electrode (substrate target) being biased in the range of about 0 to about - 100 volts, and the upper electrode being biased in the range of about - 200 to about -3500 volts. Radio frequency plasma decomposition is begun, and an amorphous. carbonaceous, diamond-like film is deposited onto the substrate at rates varying between about 8 up to 35 angstroms per minute, to produce a film of up to about 5 micrometers in thickness.

In a third embodiment, which utilizes the process that is taught in U.S. Pat.
No.
4,770,940. a hard carbonaceous film is formed by decomposing a gaseous hydrocarbon having carbon atoms tetrahedrally coordinated to its nearest neighbors through carbon-carbon single bonds. The gaseous hydrocarbon is decomposed in a radio frequency maintained plasma and the plasma decomposition products are deposited on a cathodic substrate.
Optionally, fluorocarbons may be present in a decomposition gas.
In a fourth embodiment, which utilizes the process that is taught in LJ.S.
Pat. No.
4,830,702, a hydrocarbon/hydrogen gas mixture is passed through a refractory metal hollow cathode which is self heated to a high temperature. The gas mixture is dissociated by a combination of thermal and plasma effects. The plasma plume emanating from the hollow cathode heats the substrate, which is positioned on a surface of the anode.
Growth of the diamond film is enhanced by bombardment of electrons.
In a fifth embodiment, which utilizes the process that is taught in U.S. Pat.
No.
4,910,041, a film is formed on a substrate through a process of bringing a substrate into 1 S contact with a plasma zone formed by generating, by use of a discharge electrode or discharge electrodes, high temperature or quasi-high temperature plasma of a gas containing at least one carbon-containing compound. The electrodes include a sheet-like electrode provided with a slit having a linear portion and connected to a microwave electric source.
Alternatively, the plasma zone is formed by forcing a high temperature or quasi-high temperature plasma generated in an arc between the electrodes to move by applying a magnetic field. The process enables energy efficient formation of films on substrate surfaces.
In a sixth embodiment, which utilizes the process that is taught in U.S. Pat.
No.
4,939,763, a synthetic diamond film may be formed by a D.C. plasma-assisted deposition at 0.5 to 1.5 amperes plasma current at a temperature of 600 to 800 degrees C
using methane/
hydrogen (0.8-1 : 99.5-1 volume ratio) at a total pressure of 20-30 torn.
In a seventh embodiment, which utilizes the process that is taught in U.S.
Pat. No.
4,948,629, diamond films are deposited at substrates below temperatures of 400 degrees C. by chemical vapor deposition using a high powered pulsed laser and a vapor which is an aliphatic carboxylic acid or an aromatic carboxylic anhydride.

In a eighth embodiment, which utilizes the process that is taught in U.S. Pat.
No 4954365, a thin diamond film is prepared by immersing a substrate in a liquid containing carbon and hydrogen and then subjecting the substrate to at least one laser pulse.
In an ninth embodiment, which utilizes the process that is taught in U.S. Pat.
No.
4,981,717, a method of depositing diamond-like films produces depositing species from a plasma of a hydrocarbon gas precursor. The plasma is generated by a laser pulse, which is fired into the gas and is absorbed in an initiater mixed with the gas. The resulting detonation produces a plasma of ions. radicals, molecular fragments and electrons which is propelled by the detonation pressure wave to a substrate and deposited thereon.
i0 In a tenth embodiment, which utilizes the process that is taught in U.S.
Pat. No 4,987,007 a method and apparatus is provided which produces a layer of material on a substrate by extracting ions from a laser ablation plume in a vacuum environment. In a basic embodiment, the apparatus includes a vacuum chamber containing a target material and a laser focused on the target to ablate the material and ionize a portion of the ablation plume.
1 S An accelerating grid within the vacuum chamber is charged to extract the ions from the plume and direct the ions onto a substrate to grow the layer. The basic embodiment has produced diamond-like carbon films on a clean, unseeded silicon substrate at deposition rates approaching 20 microns per hour. The diamond-like carbon films produced were of exceptional quality: uniform thickness with a surface roughness about 1 Angstrom; uniform 20 index of refraction within the range of 1.5-2.5; resistivity greater than 40 melts ohms per centimeter; and a hard surface resistant to physical abuse. An enhanced embodiment includes multiple targets within the vacuum chamber and mechanisms to selectively produce ions from each target. Thus. layers of different materials or doped materials can be made on the substrate. Additionally, the enhanced embodiment includes a mechanism for making patterns 25 or circuits within each layer. One version incorporates a mask within the ion fluence and ion optics to magnify the mask pattern onto the substrate. Another version uses ion optics to form an ion beam and deflection plates controlling the ion beam to write the desired pattern on the substrate.
In an eleventh embodiment. which utilizes the process that is taught in U.S.
Pat. No.
30 5,015,528, a process for forming synthetic diamond is utilized which involves vapor deposition of a carbon gas source in the presence of atomic hydrogen on a substrate contained in a fluidized bed. The diamond may be overcoated by vapor deposition of a non-diamond material.
In a twelfth embodiment, which utilizes the process that is taught in U.S.
Pat. No.
S 5,071,677, a method for depositing diamond films and particles on a variety of substrates by flowing a gas or gas mixture capable of supplying (1) carbon, (2) hydrogen and (3) a halogen through a reactor over the substrate material. The reactant gases may be pre-mixed with an inert gas in order to keep the overall gas mixture composition low in volume percent of carbon and rich in hydrogen. Pre-treatment of the reactant gases to a high energy state is not required as it is in most prior art processes for chemical vapor deposition of diamond. Since pre-treatment is not required, the may be applied to substrates of virtually any desired size, shape or configuration. The reactant gas mixture preferably is passed through a reactor, a first portion of which is heated to a temperature of from about 400 degrees C. to about 920 degrees C. and more preferably from about 800 degrees C. to about 920 degrees C. The substrate on which the diamond is to be grown is placed in the reactor in a zone that is maintained at a lower temperature of from about 250 degrees C. to about 750 degrees C., which is the preferred diamond growth temperature range. The process preferably is practiced at ambient pressures, although lower or higher pressures may be used.
Significant amounts of pure diamond films and particles have been obtained in as little as eight hours. The purity of the diamond films and particles has been verified by Raman spectroscopy and powder x-ray diffraction techniques.
In a thirteenth embodiment, which utilizes the process that is taught in U.S.
Pat. No.
5,080,753, thin films of single crystal, cubic phase boron nitride that is epitaxialiy oriented upon a silicon substrate are formed using laser ablation techniques.
In a fourteenth embodiment, which utilizes the process that is taught in U.S.
Pat.
5,082,359, a method of forming a polycrystalline film, such as a diamond, on a foreign substrate involves preparing the substrate before film deposition to define discrete nucleation sites. The substrate is prepared for film deposition by forming a pattern of irregularities in the surface thereof. The irregularities, typically craters, are arranged in a predetermined pattern, which corresponds to that desired for the location of film cn~stals. The craters preferably are l4 of uniform, predetermined dimensions (in the sub-micron and micron size range) and are uniformly spaced apart by a predetermined distance. The craters may be formed by a number of techniques, including focused ion beam milling, laser vaporization, and chemical or plasma etching using a patterned photoresist. Once the substrate has been prepared the film may be deposited by a number of known techniques. Films prepared by this method are characterized by a regular surface pattern of crystals, which may be arranged in virtually any desired pattern.
In a fifteenth embodiment, which utilizes the process that is taught in U.S.
Pat.
5,096,740, a highly pure cubic boron nitride film is formed on a substrate by a method which involves irradiating an excimer laser on a target comprising boron atoms and optionally nitrogen atom and depositing cubic boron nitride on a substrate which is placed to face the target.
In a sixteenth embodiment, which utilizes the process that is taught in U.S.
Pat.
5,154,945, infrared lasers are used to deposit diamond thin films onto a substrate. In one embodiment, the deposition of the film is from a gas mixture of CH4 and H2 that is introduced into a chemical vapor deposition chamber and caused to flow over the surface of the substrate to be coated while the laser is directed onto the surface. In another embodiment, pure carbon in the form of soot is delivered onto the surface to be coated and the laser beam is directed onto the surface in an atmosphere that prevents the carbon from being burned to C02.
In a seventeenth embodiment, which utilizes the process that is taught in U.S.
Pat.
5,221,411, a method for developing diamond thin films on a non-diamond substrate involves implanting carbon ions in a lattice-plane matched or lattice matched substrate. The implanted region of the substrate is then annealed to produce a diamond chin film on the non-diamond substrate. Also disclosed are the diamond thin films on non-diamond lattice-plane matched substrates produced by this method. Preferred substrates are lattice and plane matched to diamond such as copper, a preferred implanting method is ion implantation, and a preferred annealing method is pulsed laser annealing.
In a eighteenth embodiment, which utilizes the process that is taught in U.S.
Pat.
5,221,501, a method of producing transparent diamond laminates is used which employs a substrate which is removed once a second layer is deposited over the diamond coating, thereby exposing a smooth diamond surface. The second coating should have a refractive index substantially identical to diamond, with zinc selenide and titanium dioxide being particularly preferred. Diamond films having two smooth surfaces may be produced by simultaneous deposition on parallel. opposed substrates until the two diamond films merge together to form a single film or plate, followed by removal of at least a portion of the two substrates.
In a nineteenth embodiment. which utilizes the process that is taught in U.S.
Pat.
5,230,931, a diamond film or an I-Carbon film is formed on a surface of an object by virtue of plasma-assisted chemical vapor deposition. The hardness of the films can be enhanced by applying a bias voltage to the object during deposition.
In a twentieth embodiment, which utilizes the process that is taught in U.S.
Pat.
5,236,740, a cemented tungsten carbide substrate is prepared for coating with a layer of diamond film by subjecting the substrate surface to be coated to a process which first removes a small amount of the tungsten carbide at the surface of the substrate while leaving the cobalt binder substantially intact. Murakami's reagent is presently preferred. The substrate is then subjected to a process, which removes any residue remaining on the surface as a result of the performance of the process, which removes the tungsten carbide. A solution of sulfuric acid and hydrogen peroxide is presently preferred. A diamond coated cemented tungsten carbide tool is formed using an unpolished substrate, which may be prepared by etching as described above or by etching in nitric acid prior to diamond film deposition.
Deposition of a substantially continuous diamond film may be accomplished by reactive vapor deposition, thermally assisted (hot filament) CVD, plasma-enhanced CVD, or other techniques.
In a twenty-first embodiment, which utilizes the process that is taught in U.S. Pat.
5,243, i 70, a method for providing a coating film of diamond on a substrate involves the plasma jet deposition method, in wlzich the deposited diamond film has, different from the cubic crystalline structure formed under conventional conditions, a predominantly hexagonal crystalline structure so as to greatly enhance the advantages obtained by the diamond coating of the tool in respect of the hardness and smoothness of the coated surface.
The improvement comprises: using hydrogen alone as the plasma-generating gas; controlling the pressure of the plasma atmosphere not to exceed 300 Torr; keeping the substrate surface at a temperature of 800 degrees-1200 degrees C.; and making a temperature gradient of at least 13,000 degrees C./cm within the boundary layer on the substrate surface.
In a twenty-second embodiment, which utilizes the process that is taught in U.S. Pat.
5,260,106, a diamond film is attached securely to the substrate by forming a first layer on the surface comprising a mixture of a main component of the substrate and a sintering reinforcement agent for diamond, then forming a second layer comprising a mixture of said agent and diamond on said first layer, and finally forming the diamond film on the second layer.
In a twenty-third embodiment, which utilizes the process that is taught in U.S. Pat.
5,264,071, the bond strength between a diamond and the substrate onto which it is deposited by the chemical vaporization method is decreased to the point where the diamond can be removed from the substrate as a free standing monolithic sheet. The bond strength can be decreased by polishing the substrate, removing corners from the substrate, slow cooling of the substrate after deposition, an intermediate temperature delay in cooling or the application or formation of an intermediate layer between the diamond and the substrate. The freestanding sheet of diamond is envisioned as being of particular use for the embodiment of FIGURE 5.
In a twenty-fourth embodiment, which utilizes the process that is taught in U.S. Pat.
5,271,890, a coating film of a carbon allotrope is formed on a substrate by continuously supplying a fine carbon powder onto the substrate and simultaneously irradiating the fine carbon powder with a laser beam of a high output level thereby inducing sublimation of the fine carbon powder, and quenching the sublimated fine carbon powder to cause deposition thereof on the substrate.
In a twenty-fifth embodiment, which utilizes the process that is taught in U.S. Pat.
5,273,731, a substantially transparent polycrystalline diamond film is made having a thickness greater than 50 microns. A mixture of hydrogen and methane is conveyed into a heat filament reaction zone, which is adjacent to an appropriate substrate, such as a molybdenum substrate to produce non-adherent polycrystalline substantially transparent diamond film.

In a twenty-sixth embodiment, which utilizes the process that is taught in U.S. Pat.
5,273,788. a layer of a hydrocarbon molecule is applied to a substrate by the Langmuir-Blodgett technique, and the surface is irradiated with a laser to decompose the layer of molecules at the surface without influencing the substrate. After decomposition the carbon atoms rearrange on the surface of the substrate to form a DLC film.
In a twenty-seventh embodiment, which utilizes the process that is taught in U.S.
Pat. 5.302,231, a method for growing diamond on a diamond substrate by chemical vapor deposition involves alternatingly contacting at elevated temperature said diamond substrate with a gas having the formula C n X m and then with a gas having the formula C
1 Z p . X and Z each form single bonds with carbon. X and Z also are readable to form ZX or a derivative thereof. The Z-X bond is stronger than the C-X bond and also is stronger than the C-Z bond.
In the formulas, n, m, l, and p are integers.
In a twenty-eighth embodiment, which utilizes the process that is taught in U.S. Pat.
5,516,500, diamond materials are formed by sandwiching a carbon-containing material in a gap between two electrodes. A high-amperage electric current is applied between the two electrode plates so as cause rapid heating of the carbon-containing material.
The current is sufficient to cause heating of the carbon-containing material at a rate of at least approximately 5,000 degrees C./sec, and need only be applied for a fraction of a second to elevate the temperature of the carbon-containing material at least approximately 1000 degrees C. Upon terminating the current, the carbon-containing material is subjected to rapid-quenching (cooling}. This may take the form of placing one or more of the electrodes in contact with a heat sink, such as a large steel table. The carbon-containing material may be rapidly-heated and rapidly-quenched (RHRQ) repeatedly (e.g., in cycles), until a diamond material is fabricated from the carbon-containing material. The process is advantageously performed in an environment of a "shielding" (inert or non-oxidizing) gas. such as Argon (At), Helium (He), or Nitrogen (N2). In an embodiment of the invention. the carbon-containing material is polystyrene (e.g., a film) or glassy carbon (e.g., film or powder). In another embodiment of the invention, the carbon-containing material is a polymer. fullerene, amorphous carbon, graphite, or the like. One of the electrodes is preferably a substrate upon which it is desired to form a diamond coating, and the substrate itself is used as one of the two electrodes.

In a twenty-ninth embodiment, which utilizes the process that is taught in U.S. Pat.
5,525,815, a continuous diamond structure deposited by chemical vapor deposition is disclosed having at least two thermal conductivity diamond layers controlled by the diamond growth rate where one thermal conductivity diamond layer is grown at a high growth rate of at least one micron per hour for hot filament chemical vapor deposition and at least 2-3 microns per hour for microwave plasma assisted chemical vapor deposition, on a substrate such as molybdenum in a chemical vapor deposition chamber and at a substrate temperature that promotes the high growth rate, and the other thermal conductivity diamond layer is grown at a growth rate and substrate temperature lower than the high growth rate diamond layer. High growth rate and low growth rate diamond layers can be deposited in any sequence to obtain a continuous diamond structure that does not show distinguishable, separate, crystalline columnar layers, having improved thermal conductivity.
In a thirtieth embodiment, which utilizes the process that is taught in PCT
Publication WO 95/31584 (Corresponding to International Application No.
PCT/LJS95/05941 ), energy, such as from a UV excimer laser, an infrared Nd:YAG
laser and an infrared COZ laser is directed through a nozzle at the surface of a substrate to mobilize and vaporize a carbon constituent (e.g. carbide) within the substrate (e.g, steel). An additional secondary source (e.g. a carbon-containing gas, such as COZ) and an inert shielding gas (e.g.
N2) are also delivered through the nozzle. The vaporized constituent element is reacted by the enerlry to alter its physical structure (e.g. from carbon to diamond) to that of a composite material, which is diffused into the back of the substrate as a composite material.
In a thirty-first embodiment, which utilizes the process that is taught in PCT
Publication WO 95/20253 (Corresponding to International Application No.
PCT/IJS95/00782), laser energy is directed at a substrate to mobilize, vaporize and react a constituent (primary) element (e.g. carbon} contained within the substrate, so as to modify the composition (e.g. crystalline structure j of the constituent element, and to diffuse the modified constituent back into the substrate. as an adjunct to fabricating a coating (e.g. diamond or diamond-like carbon) on the surface of the substrate. This creates a conversion zone immediately beneath the substrate. which transitions metallurgically from the composition of the underlying substrate to the composition of the coating being fabricated on the surface of the substrate, which results in diffusion bonding of the coating to the substrate. Additional (secondary) similar (e.g. carbon) or dissimilar elements may be introduced in a reaction zone on and above the surface of the substrate to augment the fabrication of and to determine the composition of the coating. The laser energy is provided by a combination of an excimer S laser, an Nd: YAG laser and a C02 laser, the output beams of which are preferably directed through a nozzle delivering the secondary element to the reaction zone. The reaction zone is shielded by an inert (non-reactive) shielding gas (e.g. N2) delivered through the nozzle. A flat plasma is created by the lasers, constituent element and secondary element on the surface of the substrate and the flat plasma optionally extends around the edges of the substrate to fabricate a coating thereon. Pre-treatment and coating fabrication can be preformed in conjunction with one another (in-situ). Alternatively, a substrate can be pre-treated to characterize its surface for subsequent coating. In either case, certain advantageous metallurgical changes are induced in the substrate due to the pre-treatment.
The processes (pre-treatment and coating fabrication) are suitably performed in ambient, without preheating the substrate and without a vacuum. The lasers are directed at any suitable angle (including coaxial) relative to the substrate and/or the plasma.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention. the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims (32)

WHAT IS CLAIMED IS:

1. An improved mold wall assembly for use in a continuous casting machine, comprising:
an inner portion that is constructed and arranged to conduct heat away from the mold liner during operation; and an outer surface that forms a casting surface of the mold, said outer surface comprising a degradation-resistant nonmetallic material that has high thermal conductivity, whereby the mold liner will exhibit superior degradation and teat transfer characteristics during its operation in a continuous casting machine.

2. A mold wall assembly according to claim 1, wherein said degradation-resistant nonmetallic material that has high thermal conductivity is selected from the group consisting of diamond and crystalline boron nitride.

3. A mold wall assembly according to claim 1, wherein said degradation-resistant nonmetallic material that has high thermal conductivity comprises a carbonaceous material.

4. A mold wall assembly according to claim 1, wherein said degradation-resistant nonmetallic material that has high thermal conductivity comprises an allotrope of carbon.

5. A mold wall assembly according to claim 2, wherein said degradation-resistant nonmetallic material that has high thermal conductivity is substantially transparent in the infrared range.

6. A mold wall assembly according to claim 5, further comprising optical monitoring means for optically monitoring a property of the continuous casting process through said material.

7. A mold wall assembly according to claim 6, wherein said optical monitoring means comprises an optical fiber that is optically coupled to said transparent material at a side thereof that is opposite the casting surface of the mold.

8. A mold wall assembly according to claim 6, wherein said optical monitoring means comprises spectral measurement means for measuring the spectral characteristics of light that is transmitted through said material.

9. A mold wall assembly according to claim 6, wherein said optical monitoring means further comprises means for analyzing the spectral characteristics of light that is measured by said spectral measurement means.

10. A mold wall assembly according to claim 9, wherein said optical monitoring means further comprises means for modifying at least one performance variable of the continuous casting process in response to the analysis that is performed by said means for analyzing the spectral characteristics of light that is measured by said spectral measurement means.

11. A mold wall assembly according to claim 9, wherein said means for analyzing the spectral characteristics of light that is measured by said spectral measurement means comprises means for sensing the temperature of an outer surface of a cast strand that is positioned adjacent the mold wall assembly.

12. A mold wall assembly according to claim 10, wherein said means for modifying at least one performance variable of the continuous casting process in response to the analysis that is performed by said means for analyzing the spectral characteristics of light that is measured by said spectral measurement means comprises means for adjusting the withdrawal speed of a continuous casting machine.

13. A mold wall assembly according to claim 10, wherein said means for modifying at least one performance variable of the continuous casting process in response to the analysis that is performed by said means for analyzing the spectral characteristics of light that is measured by said spectral measurement means comprises means for adjusting the rate at which heat is transferred away from said inner portion.

14. A method of making a strand of continuously cast material, comprising steps of:
(a) introducing molten metal into a mold that includes a plurality of mold surfaces, at least one of the mold surfaces having an outer coating comprising a degradation-resistant nonmetallic material that has high thermal conductivity;
(b) cooling the molten metal by conducting heat away from the molten metal through the outer coating; and (c) moving the cast strand out of the mold.

15. A method according to claim 14, wherein step (a) is performed with said degradation-resistant nonmetallic material that has high thermal conductivity being selected from the group consisting of diamond and crystalline boron nitride.

16. A method according to claim 14, wherein step (a) is performed with said degradation-resistant nonmetallic material that has high thermal conductivity comprising a carbonaceous material.

17. A method according to claim 14, wherein step (a) is performed with said degradation-resistant nonmetallic material that has high thermal conductivity comprising an allotrope of carbon.

18. A method according to claim 14, wherein step (a) is performed with said degradation-resistant nonmetallic material that has high thermal conductivity being substantially transparent in the infrared range.

19. A method according to claim 18, further comprising a step of optically monitoring a property of the continuous casting process through said transparent material.

20. A method according to claim 19, wherein said step of optically monitoring a property of the continuous casting process through said layer of crystallized, transparent diamond material involves the use of an optical fiber that is optically coupled to said material at a side thereof that is opposite the casting surface of the mold.

21. A method according to claim 19, wherein said step of optically monitoring a property of the continuous casting process through said transparent material comprises measuring the spectral characteristics of light that is transmitted through said material.

22. A method according to claim 21, wherein said optical monitoring step further comprises a step of analyzing the spectral characteristics of light that is measured by said spectral measurement means.

23. A method according to claim 22, further comprising a step of modifying at least one performance variable of the continuous casting process in response to the step of analyzing the spectral characteristics of light that is measured by said spectral measurement means.

24. A method according to claim 22, further wherein said step of analyzing the spectral characteristics of light that is measured by said spectral measurement means includes sensing the temperature of an outer surface of a cast strand that is positioned adjacent the mold.

25. A method according to claim 23, wherein said seep of modifying at least one performance variable of the continuous casting process comprises adjusting the withdrawal speed of a continuous casting machine.

26. A method according to claim 23, wherein said step of modifying at least one performance variable of the continuous casting process comprises adjusting the rate at which heat is transferred away from said inner portion.

27. An improved mold assembly for a continuous casting machine, comprising:
a plurality of mold walls, each of said mold walls having at least one mold surface that together define a casting space having an upper opening and a lower opening; and wherein at least one of said mold walls is fabricated from a degradation-resistant nonmetallic material that has high thermal conductivity, whereby the mold assembly will exhibit superior wear and heat transfer characteristics during its operation in a continuous casting machine.

28. A method of making a strand of continuously cast material, comprising steps of:
(a) introducing molten metal into a mold that includes a plurality of mold surfaces;
(b) cooling the molten metal by conducting heat away from the molten metal through the mold surfaces by means of conductive heat transfer; and (c) further cooling the molten metal that is within the mold by means of radiation heat transfer that occurs through at least one of said mold surfaces.

29. A method according to claim 38, wherein at least one of the mold surfaces comprises a material that is substantially transparent in the infrared range.

30. A method according to claim 39, wherein said material is selected from the group consisting of diamond and crystalline boron nitride.

31. An improved mold assembly for use in a continuous casting machine, comprising:

a surface that forms a casting surface of the mold, said surface being at least partially transparent to radiation that is within the infrared range, whereby the mold is capable of cooling the molten metal that is within the mold by means of radiation heat transfer that occurs through said surface.

32. A mold assembly according to claim 31, wherein said material is selected from the group consisting of diamond and crystalline boron nitride.