Title:
Planar flow melt spinning systems with pressure adjustment and methods thereof
Kind Code:
A1


Abstract:
A system and method for controlling and manipulating solidification of a molten material includes a substrate on which at least a portion of the molten material is dispensed and a first pressure adjustment system at least partially upstream of a location where the molten material is deposited on the substrate. The first pressure adjustment system imposes a first pressure at the upstream location which is different from a second pressure at a location downstream from where the molten material is dispensed.



Inventors:
Byrne, Cormac J. (County Wicklow, IE)
Swan, Glenn (Freeville, NY, US)
Steen, Paul H. (Ithaca, NY, US)
Application Number:
11/413748
Publication Date:
11/01/2007
Filing Date:
04/28/2006
Assignee:
Cornell Research Foundation, Inc. (Ithaca, NY, US)
Primary Class:
Other Classes:
164/423
International Classes:
B22D11/06
View Patent Images:



Primary Examiner:
LIN, KUANG Y
Attorney, Agent or Firm:
Troutman Pepper Hamilton Sanders LLP (Rochester) (Rochester, NY, US)
Claims:
What is claimed is:

1. A system for controlling and manipulating solidification of a molten material, the system comprising: a substrate on which at least a portion of the molten material is dispensed; and a first pressure adjustment system at least partially upstream of a location where the molten material is deposited on the substrate, the first pressure adjustment system imposes a first pressure at the at least partially upstream location which is different from a second pressure at a location downstream from where the molten material is dispensed.

2. The system as set forth in claim 1 wherein the first pressure imposed by the first pressure adjustment system is greater than the second pressure.

3. The system as set forth in claim 1 wherein the first pressure imposed by the first pressure adjustment system is less than the second pressure.

4. The system as set forth in claim 1 further comprising a supply system that dispenses the molten material.

5. The system as set forth in claim 4 wherein the supply system comprises: a nozzle having a passage positioned adjacent to and spaced from the substrate to dispense the molten material; and a second pressure adjustment system that applies a third pressure to the molten material being dispensed from the nozzle on to the substrate.

6. The system as set forth in claim 5 wherein the supply system further comprises a reservoir for the molten material and the nozzle is connected to the reservoir.

7. The system as set forth in claim 1 further comprising a drive system connected to the substrate.

8. The system as set forth in claim 1 wherein the substrate comprises one of a wheel, a belt, or product that is being coated with the molten material.

9. A method for controlling and manipulating solidification of a molten material, the method comprising: dispensing the molten material on to at least a portion of a substrate; and imposing a first pressure at a location at least partially upstream from where the molten material is dispensed which is different from a second pressure at a location downstream from where the molten material is dispensed.

10. The method as set forth in claim 9 wherein the first pressure is greater than the second pressure.

11. The method as set forth in claim 9 wherein the first pressure is less than the second pressure.

12. The method as set forth in claim 9 wherein the dispensing the molten material further comprises: positioning a nozzle having a passage adjacent to and spaced from the substrate to dispense the molten material; and applying a third pressure to the molten material being dispensed from the nozzle on to the substrate.

13. The method as set forth in claim 12 further comprising connecting a reservoir for the molten material to the nozzle.

14. The method as set forth in claim 9 further comprising moving the substrate.

15. The method as set forth in claim 9 wherein the substrate comprises one of a wheel, a belt, or a product that is being coated with the molten material.

16. A method for making a system for controlling and manipulating solidification of a molten material, the method comprising: providing a substrate; and positioning a first pressure adjustment system at least partially upstream of a location where the molten material is deposited on the substrate, wherein the first pressure adjustment system imposes a first pressure at the at least partially upstream location which is different from a second pressure at a location downstream from where the molten material is dispensed.

17. The method as set forth in claim 16 wherein the first pressure imposed by the first pressure adjustment system is greater than the second pressure.

18. The method as set forth in claim 16 wherein the first pressure imposed by the first pressure adjustment system is less than the second pressure.

19. The method as set forth in claim 16 further comprising a supply system that dispenses the molten material.

20. The method as set forth in claim 19 wherein the supply system comprises: a nozzle having a passage positioned adjacent to and spaced from the substrate to dispense the molten material; and a second pressure adjustment system that applies a third pressure to the molten material being dispensed from the nozzle on to the substrate.

21. The method as set forth in claim 20 wherein the supply system further comprises a reservoir for the molten material and the nozzle is connected to the reservoir.

22. The method as set forth in claim 16 further comprising a drive system connected to the substrate.

23. The method as set forth in claim 16 wherein the substrate comprises one of a wheel, a belt, or a product that is being coated with the molten material.

Description:

The subject invention was made with government funding from the National Science Foundation under contract no.: NSF DMI-0423791. The U.S. Government may have certain rights.

FIELD OF THE INVENTION

The present invention generally relates to planar-flow melt spinning systems and methods and, more particularly, to planar flow melt spinning systems with pressure adjustment and methods thereof

BACKGROUND

Single roll planar-flow melt spinning (PFMS), also known as planar-flow melt spinning, single roll planar-flow spin casting, and planar-flow spin casting, is a rapid manufacturing process used to produce thin metallic ribbons or foils. In this process, a planar nozzle is brought into close proximity to a rotating metallic wheel (also known as a substrate). Liquid metal flows through the nozzle into this narrow region where a puddle, constrained by surface tension, is formed. Solidification occurs from the wheel surface, which has a temperature lower than that of the liquid metal, as it translates through the puddle and a solid ribbon is continually ejected from the puddle. Typically, ribbon thicknesses on the order of 100 μm are produced, though this can vary as needed.

This process was first introduced in the 1970's and has been extensively studied since, particularly in relation to the unique microstructural features obtained from the rapid cooling that is on the order of 106 K/s as disclosed in Belden, R. H. “Commercializing a new product”. Chemical Engineering Progress, 81 (5), 27-29, (1985). and Kavesh. S., “Principles of Fabrication”, in: Gilman, J. H. and Leamy, H. J. (Eds), Metallic Glasses, ASM, Metals Park, p. 36, (1978), which are herein incorporated by reference in their entirety. To date only limited scale-up from bench scale devices have been possible due to the difficulty in maintaining good product quality when casting thin ribbon. This difficulty arises because only a limited number of control parameters exist and successful ribbon production occurs only for certain combinations of these parameters. One example of a melt-spinning process that has been used commercially is disclosed in U.S. Pat. No. 4,142,571 to Narasimhan, which is hereby incorporated by reference in its entirety. The need exists for a method or system to produce a wider range of product thicknesses by the addition of an extra control parameter or parameters. The present invention provides such a method and system.

SUMMARY

A system for controlling and manipulating solidification of a molten material in accordance with embodiments of the present invention includes a substrate on which at least a portion of the molten material is dispensed and a first pressure adjustment system at least partially upstream of a location where the molten material is deposited on the substrate. The first pressure adjustment system imposes a first pressure at the at least partially upstream location which is different from a second pressure at a location downstream from where the molten material is dispensed.

A method for controlling and manipulating solidification of a molten material in accordance with other embodiments of the present invention includes dispensing the molten material on to at least a portion of a substrate. A first pressure is imposed at a location which is at least partially upstream from where the molten material is dispensed. The first pressure is different from a second pressure at a location downstream from where the molten material is dispensed.

A method for making a system for controlling and manipulating solidification of a molten material in accordance with other embodiments of the present invention includes providing a substrate and positioning a first pressure adjustment system at least partially upstream of a location where the molten material is deposited on the substrate. The first pressure adjustment system imposes a first pressure at the at least partially upstream location which is different from a second pressure at a location downstream from where the molten material is dispensed.

The present invention provides an improved system and method for controlling and manipulating solidification of a molten material. With the present invention, good quality ribbon product can be maintained for a variety of thin ribbons by generating a pressure differential between the upstream meniscus (USM) and the downstream meniscus (DSM). That is, ribbon product can be cast at settings of the control parameters where, in the absence of this pressure differential, no product or product of poorer quality results.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, perspective view, which is not to scale, of a planar flow melt spinning system with pressure adjustment in accordance with one embodiment of the present invention;

FIG. 2 is a side, cross-sectional view, which is not to scale, of a nozzle for the planar flow melt spinning system shown in FIG. 1 and the PFMS molten metal puddle;

FIG. 3 is a graph of a plurality of cast attempts which vary U, G or Pover, where each point represents a single cast attempt and S=0;

FIG. 4 is a diagram of a successful cast of ribbon product and a failed cast of ribbon product; and

FIG. 5 is a table of data for eleven examples of ribbon product cast attempts.

DETAILED DESCRIPTION

A planar flow melt spinning system 10 in accordance with one embodiment of the present invention is illustrated in FIG. 1. The system 10 includes a wheel 12 on which a molten material is deposited, a driving system 14 that rotates the wheel 12, a pressure adjustment system 16, a reservoir 18, a nozzle 20, and another pressure adjustment system 22, although the system 10 can include other numbers and types of elements in other configurations. The present invention provides a number of advantages including providing an improved system and method for controlling and manipulating solidification of a molten material.

Referring to FIGS. 1 and 2, the molten material is dispensed on the wheel 12, although other types of substrates can be used, such as a belt or a product that is to be coated with the molten material. In this particular embodiment, the wheel 12 has a diameter of about 1 m, although the particular dimensions of the wheel 12 can vary as needed for the particular application. Although not shown, the wheel 12 may also include a cooling system to actively cool the wheel 12 during the casting process.

The driving system 14 includes a motor 13 and a shaft 15 and is used to rotate the wheel 12, although the driving system 14 can comprise other numbers and types of components in other configurations. Since components and operation of driving systems are well known to one of ordinary skill in the art, they will not be described in detail here. In this particular embodiment, the wheel 12 is seated on the shaft 15 which is rotated by the motor 13.

The pressure adjustment system 16 is a differential pressure device that is designed to seal against the moving wheel 12, nozzle 20, and liquid puddle of molten material. In this particular embodiment, the pressure adjustment system 16 includes a housing 24, a pump system 26, and a tube or hose 28 which are connected together, although the pressure adjustment system 16 could comprise other numbers and types of components in other configurations. The housing 24 of the pressure adjustment system 16 essentially acts like a shoe which is fitted around the moving wheel 12 enclosing the upstream meniscus (USM) of the dispensed molten material while permitting the wheel 12 to rotate through the housing 24. The pump system 26 is a venturi-type vacuum pump system, although other types of pump systems can be used, such as a pump system that delivers an inert gas to the USM of molten material. The hose 28 is connected between the housing 24 and the pump system 26, although other manners for connecting the housing 24 and the pump system 26 could be used. As indicated by the double arrow in FIG. 1, the pump system 26 can be used to both increase the pressure inside the housing 24 by directing a gas or gases to the housing via the hose 28 and decrease the pressure in the housing, eventually creating a vacuum if desired, by withdrawing the gas or gases in the housing 24, although other types of systems, such as just a vacuum system or just an applied pressure system could be used for the pump system 26. In this particular embodiment, the pressure downstream of the location where molten material is deposited is left at atmospheric pressure, although other arrangements could be used, such as incorporating another pressure adjustment system at this location to raise and/or lower the downstream pressure.

The reservoir 18 holds the molten material, although the reservoir 18 for molten material can be comprised of other types of and combinations of elements. The nozzle 20 is connected to the reservoir 18 and has a dispensing end with an opening that has a width B and which is positioned adjacent to and spaced from the wheel 12 by a gap G, although other types of nozzles with other numbers and types of components, with other dimensions and configurations and which are integrally formed with or are connected to the reservoir 18 can be used. The molten material is dispensed out from the reservoir 18 via the nozzle 20.

The pressure adjustment system 22 comprises a tank of pressurized inert gas, such as Argon, which is supplied to the reservoir 18 via a tube or hose 30 or other conduit, although the pressure adjustment system 22 could comprise other numbers and types of components in other configurations. The supplied gas from the pressure adjustment system 22 applies pressure on to the molten material which controls the flow of the molten material out of the reservoir 18 via the nozzle 20 on to the wheel 12, although other types of systems to dispense the molten material could be used.

A method for casting of a molten material in accordance with embodiments of the present invention will now be described with reference to FIGS. 1 and 2. The motor 13 in the driving system 14 is engaged to begin to rotate the wheel 12. In this particular embodiment, the wheel 12 is rotated at a casting speed on the order of about ten m/s (linear velocity) to achieve solidification rates of the molten material on the order of about ten cm/s for aluminum, although the particular speed of rotation of the wheel 12 can vary as needed for the particular application.

Once the desired rotational speed for the wheel 12 is reached, the pump system 26 is used to either direct a gas or gases to the housing 24 via the hose 28 or to draw out the gas or gases in the housing 24 via the hose 28. Accordingly, the pressure adjustment system 16 adjusts the pressure in the housing 24 to generate a pressure difference with the pressure downstream of where the molten material is dispensed onto the wheel 12 which is enough to influence solidification. In this particular example, the pressure adjustment system 16 imposes an increased pressure by directing a gas to the housing 24 via the hose 28, although the pressure adjustment system 16 can impose other types of pressures, such as reducing the pressure in and/or creating a vacuum in the housing 24.

The pressure adjustment system 22 applies a gas pressure to the molten material in the reservoir 18 which causes the molten material to be forced out through the nozzle 20. The nozzle 20 dispenses the molten material on to a portion of the wheel 12 to form a puddle of molten material which solidifies or freezes to form the ribbon product 32. Typically, the puddle length is one hundred times a thickness T of the ribbon product 32 and twenty times the gap G, although these dimensions can vary as needed. In addition to the overpressure Pover and a velocity U of the wheel 12, parameters which affect the dimensions of the resulting ribbon product 32 include the dimensions of gap G and of slot breadth B. Solidification takes place on contact with the substrate at a rate Vthat varies along the front. A ribbon product of thickness T is spun or carried off from the substrate at a velocity U. The stabilizing influence of suction (due to solidification) maintains a substantially laminar flow in the gap. By way of example only, if the molten material is aluminum, it has a melting temperature of about θm=660° C. The principal thermal control parameters are the temperature of the nozzle 20 which in this particular example is (θh˜720° C.), the temperature of the wheel 12 which in this particular example is (θc˜30° C.), and the contact heat-transfer coefficient H which in this particular example is about (˜105 W/m2 K).

Set forth below is an examination and discussion of the parameters involved in casting and also examples of casts of ribbon product 32 produced without and with a pressure adjustment upstream of where the molten material is dispensed on the substrate 12. With the present invention, an extra degree of freedom is added to the process of planar flow melt spinning by adjusting the pressure outside the upstream meniscus (USM) relative to the pressure outside the downstream meniscus (DSM), PU−PD as shown in FIG. 2. In this example, PD will remain at atmospheric pressure, though this pressure may also be adjusted as needed.

In a typical PFMS operation, four parameters are used to control the thickness of the final ribbon product, T˜O(100 μm). The parameters are the rotation speed U˜O(101) ms−1 of the wheel 12, the distance of gap G˜O(1) mm between the wheel 12 and the nozzle 20, the overpressure Pover and the width or breadth B of the opening at the dispensing end of the nozzle 20 as shown in FIG. 2. Typically, the length of the puddle of molten material>>G. The overpressure Pover is the pressure at the point where the fluid is injected into the gap region. This is controlled during experiments. It is known empirically that there exists a window, i.e. a range of operating conditions, within the many combinations of these parameters where casting of ribbon product can occur successfully as disclosed in Carpenter, J. K. and Steen, P. H., “Planar-Flow Spin-Casting Of Molten Metals: Process Behaviour,” Journal of Materials Science, 27 (1), 215-225 (1992) and Praisner, T. J., Chen, J. S.-J., Tseng, A. A., “An Experimental Study Of Process Behavior In Planar Flow Melt Spinning,” Metallurgical and Materials Transactions B, 26B, 1199-1208, (1995), which are herein incorporated by reference in their entirety.

Typically, this window is presented as a plot of the Weber number, We=ρU2/(2σ/G), against the pressure index, PI=(Pover−PD)/(2σ/G), where σ is the surface tension and ρ is the liquid metal density. Failure is defined by the presence of holes or cast-wise striations in the solidified product. Even with successful casts of ribbon product, imperfections may be present on the product. These imperfections may be associated with instabilities less ‘fatal’ as disclosed in Praisner, T. J., Chen, J. S. -J., Tseng, A. A., “An Experimental Study Of Process Behavior In Planar Flow Melt Spinning,” Metallurgical and Materials Transactions B, 26B, 1199-1208, (1995), which is herein incorporated by reference in their entirety, than those that define the boundaries of the window; these are not the focus, however.

The total pressure drop from the gas or gases outside the USM to the gas or gases outside the DSM, PU−PD, can be evaluated by summation of the pressure drops across the puddle, which are shown in simplified fashion in FIG. 2. This summation is given by Eqn. 1,
PU−PD=(PU−Pu0)+(Pu0−Pover)+(Pover−PD) (1)

Eqn. 1 is simplified by scaling each pressure drop by the inertial pressure ρU2, rearranging and introducing a new dimensionless parameter for the pressure drop from USM to DSM, S=(PU−PD)/(2σ/G) SWe=(PU-Pu 0ρ U2)+(Pu 0-Poverρ U2)+(PIWe).(2)

In Eqn. 2, (Pu0−Pover)/ρU2 accounts for pressure gains/losses as flow enters and travels in the upstream portion of the puddle.

In Eqn. 2 (PU−Pu0) represents the pressure jump across the USM. For a given upstream liquid-substrate contact angle θ, and fixed nozzle 20-meniscus contact line, the radius of curvature of the USM has limiting values when the meniscus is assumed to be an arc of a circle. These limits occur at conditions of pull-under, indicated by the position of the meniscus at L2 in FIG. 3 and at the blow-out condition, indicated by the position of the meniscus at L1 in FIG. 3. These extreme meniscus shapes lead to pressure bounds. Casting flows are typically self-metered (fixed pressure drop), though this is not limiting, and concave menisci are never seen. Image analysis in PFMS shows that the meniscus at the pull under position L2 has a similar shape to the meniscus at blow-out position L1, but the positions L1 and L2 are different as indicated in FIG. 3.

Blow-out occurs at the nozzle 20 edge, L1. At any other position, when the limiting shape is being approached, the meniscus position would change, advancing along the nozzle 20 face until it reaches L1. In this case pressure changes in the up-stream section of the puddle must be taken account of, (Pu0−Pover)/ρU2≠0. Likewise, the case of pull-under can only occur at position L2. If the meniscus were anywhere else, it would retreat along the face of the nozzle 20 to the edge of the nozzle 20 at the injection point, before it would be dragged under the slot of the nozzle 20. At such a position the upstream region has vanished and there is no upstream pressure change, (Pu0)−Pover)/ρU2˜0.

In summary, blow-out occurs at the end of the nozzle 20 face when a maximum pressure jump across the meniscus is exceeded. (Pu 0-PUρ U2)(1-cos θ2We)L1(3)

On the other hand, pull-under happens at the other end of the nozzle 20 face when the pressure falls below a minimum value. This pressure is the least for the liquid metal to bridge to the wheel 12 and to have sufficient contact for solidification. Otherwise, the cast of the ribbon product fails. The appropriate inequality is then: (1-cos θ2We)L2(Pover-PUρ U2).(4)

Combining Eqns. 2, 3 and 4 yields the operating window, -(1-cos θ2We)L1+Pu 0-Poverρ U2+PIWeSWe-(1-cos θ2We)L2+PIWe(5)

By way of example, a simplification is made to equation. 5. The pressure change in the upstream region is accounted for by a generic ‘loss coefficient’ K. This yields, Pu 0-Poverρ U2=-12K(uU)2=-12K(TG)2.(6)

Here u is average velocity of the fluid in the puddle and u<<U, as disclosed in Steen, P. H., Karcher, C., “Fluid Mechanics of Spin Casting,” Annual Review of Fluid Mechanic, 29, 373-397 (1997), which is herein incorporated by reference in its entirety. Pover≧Pu0 is required to drive flow into the upstream section. The second equality follows from a steady state mass balance, uG=TU, that relates the fluid velocity to the thickness of the product (neglecting the nearly 20% density change upon solidification for aluminum). One can finally write the semi-empirical model for the operating window as: -(1-cos θ2)L1-12K(TG)2We+PIS-(1-cos θ2)L2+PI.(7)

Here K is a free fitting parameter for the data. Eqn. 7 represents an operating window where an extra degree of freedom S, has been added to the system. S≠0 represents an adjustment to the pressure at least partially upstream of where the molten material is dispensed on the substrate 12, relative to the pressure downstream from where the molten material is dispensed on the substrate.

By way of example only, the case where S=0, or in other words conventional processing conditions when both menisci are exposed to equal pressure (atmospheric pressure in this case, though this can vary as needed), is examined. This is the We vs. PI window described previously in Carpenter, J. K. and Steen, P. H., “Planar-Flow Spin-Casting Of Molten Metals: Process Behaviour,” Journal of Materials Science, 27 (1), 215-225 (1992) which has been incorporated by reference in its entirety. Included in FIG. 3 are experimental We-PI data points, representing both successful and failed casts determined by the quality of the ribbon product. Each data point represents a single experiment. Average values of PI and We are plotted. A one meter diameter Cu—Be wheel 12 and the nozzle 20 geometry indicated in FIG. 2 were used in all these experiments. By way of example only, an image is shown in FIG. 4 of a successful cast or ribbon product 40(1), which corresponds to ribbon #7 in the table in FIG. 5, and a failed cast of ribbon product 40(2), which corresponds to ribbon #3 in the table in FIG. 5. Holes, cast-wise striations and bad edges characterize the failed cast of ribbon product 40(2).

Next, the predictions of puddle stability on the data are overlaid. The right-hand-side of Eqn. 7 gives PI independent of We. Plotted for θ150° (the approximate contact angle measured in experiments), this appears as the vertical line at PI˜0.9 seen in FIG. 3. The left-hand-side of Eqn. 7 gives a linear relationship between We and PI, whose slope depends on parameters T/G and K. Parameter T/G is evaluated from experiment (T/G)=0.16 (average for data ±0.05) while K is treated as a fitting parameter. Two lines, corresponding to K=1.8, 2.8, are plotted in FIG. 3, giving an indication of the sensitivity of the fit to K.

Most of the successful casts fall between the pull-under and blow-out lines predicted by the semi-empirical analysis. The predicted shape of the window is consistent with previous empirical results (Carpenter and Steen 1992).

That none of the data fall outside the K=2.8 window suggests that the puddle limits are upper bounds on the stability. That is, there may be other instabilities that come into play for any particular cast, but the blow-out vs. pull-under window is an absolute window. Hence there exists a limit on the number of combinations of parameters which produce ribbon product or good quality ribbon product when S=0. The upper boundary (We≧200 in FIG. 3) has been attributed to too high a wheel-speed to allow sufficient solidification to occur.

By examining the predicted window in FIG. 4 it is apparent that the left boundary occurs when PI is too low and the puddle is very small, typically pinned at L2 (FIG. 3) with the contact line unstable enough to lead to air-entrainment which disrupts solidification. Pulling a vacuum on the USM can ensure that the meniscus is not pinned at L2 and therefore return to a regime of successful casting. On the other hand, the blow-out boundary occurs when the overpressure is too high relative to the wheel-speed resulting in a long puddle. This results in a location where the meniscus is positioned at L1 or beyond in FIG. 3, with the meniscus blowing out from underneath the nozzle 20. Applying a pressure to the USM can lead to a smaller and more stable puddle.

With the present invention as described herein and illustrated in FIGS. 1 and 2, it is possible to probe S≠0. That is, the first pressure upstream of the location where the molten material is deposited on the substrate 12 can be altered, relative to the second pressure downstream from where the material is deposited. A series of casts at S≠0 were carried out and are listed in Table 1 shown in FIG. 5, with S=0 for a baseline. S<0 indicates that a vacuum has been pulled on the USM in the housing 24, while S>0 indicates that a pressure has been applied to the USM in the housing 24. Most casts are in the We˜110±17 range. For S=0 and We˜110, using Eqn. 7, or by inspection of FIG. 3, the window of stable PI values is given by 0.9≦PI≦3.4 for the K=1.8 boundary.

Ribbons #1 through #4 in Table 1 shown in FIG. 5 represent failed casts produced near the pull-under condition (these casts correspond to 0.84≦PI ≦1.16). This happened when trying to cast very thin ribbon product 32 using a low Pover. This is because overpressure is the primary control parameter for ribbon thickness, with Pover˜T2. Controlling the overpressure delivers a flow-rate according to the resistance to flow. In these cases the puddle was very small, with the USM pinned at the right edge of the nozzle 20 face (i.e. L2 in FIG. 3). These conditions are close to the failure boundary and lead to ribbon product with holes which tear and shred during casting. It is also readily observed that failed ribbons near this condition almost always have very poor edges.

On the other-hand ribbons #5 through #8 in Table 1 shown in FIG. 5 correspond to 0.78≦PI≦1.16, with a vacuum being pulled on the USM. The resulting ribbon product 32 from the vacuum cast was of superior quality and was much longer than when the product 32 was cast without the device. That is, the cast was moved away from the edge of the stability window back into a region of successful casting. Hence, the vacuum (pulled via the pump system 26) allowed a ribbon product 32 to be produced under conditions that would normally fail.

On the right side of the window, it is expected that failed casts should occur when PI˜3.4, or greater. Cast #9 in Table 1 shown in FIG. 5 was carried out at a high Pover in order to produce a relatively thick ribbon product 32. The puddle in this experiment blew out from underneath the nozzle 20 and was unstable, resulting in a poor quality ribbon that showed striation patterns. In contrast, ribbons #10 and #11 in Table 1 shown in FIG. 5 were produced with an applied pressure on the USM. This resulted in a better quality product.

Accordingly, as illustrated by the discussion and examples provided herein the present invention provides an improved system and method for controlling and manipulating solidification of a molten material. With the present invention, good quality ribbon product can be maintained for a range of thin ribbons by generating a pressure differential between the USM and the DSM.

Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Accordingly, the invention is limited only by the following claims and equivalents thereto.