MXPA99003085A - Apparatus and method for semi-solid material production - Google Patents

Abstract

An apparatus and process is provided for producing semi-solid material suitable for directly casting into a component wherein the semi-solid material is formed from a molten material and the molten material is introduced into a container. Semi-solid is produced therefrom by agitating, shearing, and thermally controlling the molten material. The semi-solid material is maintained in a substantially isothermal state within the container by appropriate thermal control and thorough three-dimensional mixing. Extending from the container is a means for removing the semi-solid material from the container, including a temperature control mechanism to control the temperature of the semi-solid material within the removing means.

Description

APPARATUS AND METHOD FOR THE PRODUCTION OF SOLID SEMI MATERIAL TECHNICAL FIELD The present invention relates generally to the production and supply of a slurry of semi-solid material for use in material-forming processes. In particular, the invention relates to an apparatus for producing a slurry of substantially non-dendritic semi-solid material suitable for use in a molding or casting apparatus.

BACKGROUND OF THE INVENTION The casting or reocolado of grout is a procedure where the molten material is subjected to vigorous agitation as it undergoes solidification. During normal solidification processes (ie, not reocolated), dendritic structures are formed within the material that solidifies. In geometrical terms, a dendritic structure is a solidified particle in the form of a type of an elongated rod that has transverse branches. The vigorous agitation of materials, especially metals, during solidification, eliminates at least some of the dendritic structures. Said agitation cuts the tips of the solidified dendritic structures, thus reducing the dendrite formation. The resultant material slurry is a solid-liquid composition, composed of relatively fine, non-dendrite solid particles in a liquid matrix (hereinafter referred to as a semi-solid material). In the molding step, it is well known that the components made from the semi-solid material have great advantages over the processes of conventional molten metal formation. These benefits are derived, in large part, from the reduced thermal requirements for the handling of semi-solid material. A material in a semi-solid state is at a lower temperature than the same material in a liquid state. In addition, the heat content of the material in the semi-solid form is much lower. In this way, less energy is required, less heat needs to be removed, and the casting equipment or mold used to form the components of semi-solid materials have a longer life. In addition, and perhaps importantly, the casting equipment can process more material in a given amount of time since the cooling cycle is reduced. Other benefits of the use of semi-solid materials include more uniform cooling, a more homogeneous composition, and fewer voids and porosities in the resulting component. The prior art contains many methods of apparatus used in the formation of semi-solid materials. For example, there are two more basic methods for effecting vigorous agitation. One method is mechanical agitation. This method is illustrated in the patent of E.U.A. 3,951,651 to Ehrabian et al, which discloses rotating blades within a rotating crucible. The second method of agitation is achieved with electromagnetic agitation. An example of this method is described in the patent of E.U.A. No. 4,229,210 to Winter et al, which is incorporated herein by reference. Winter and others describe the use of either AC induction or pulsed DC magnetic fields to produce indirect agitation of the semi-solid. Once the semi-solid material is formed, however, virtually all of the methods of the prior art then include a solidification and heating step. This so-called double process causes the solidification of the semi-solid material to an ingot. One of the many examples of the double process is described in the patent of E.U.A. No. 4,771,818 to Kenney. The solid ingot resulting from the double process is easily stored or transported for further processing. After solidification, the ingot must be reheated so that the material gains again the semi-solid properties and advantages discussed above. The reheated ingot is then subjected to manipulation such as casting or molding to form a component. In addition to modifying the properties of the semi-solid material, the double process requires additional steps of cooling and reheating. For efficiency reasons and material handling costs, this could be highly desirable to eliminate the solidification and reheating step that the double process demands. The patent of E.U.A. No. 3,902,544 to Flemings et al., incorporated herein by reference, describes a forming process of semi-solid material integrated with a casting process. This process does not include double processing, and solidification step. There are, however, numerous difficulties with the process described by Flemings and others. First, and very importantly, Fiemings and others require multiple zones including a zone of molten material and a zone of agitation, which are integrally connected and require extremely accurate temperature control. In addition, in order to produce the semi-solid material, there is a flow of material through the integrally connected zones. The semi-solid material is produced through a combination of material flow and temperature gradient in the zone of agitation. In this way, the calibration of the required temperature gradient with the material flowing (possibly in variable form) is exceedingly difficult. Second, the process of Flemings et al. Describes a means of individual agitation. Thorough and thorough agitation is necessary to maximize the semi-solid characteristics described above. Third, the Flemings and others process lacks effective transfer means and flow regulation from the agitation zone to a casting apparatus. Additional difficulties with the Flemings process, and improvements thereto, will be apparent from the following detailed description. A primary object of the present invention is to provide a formation of semi-solid material suitable for molding directly to a component. Another object of the present invention is to provide a more efficient and cost-effective semi-solid material formation process. Still another object of the present invention is to provide an apparatus and a process for forming a semi-solid material and maintaining the semi-solid material under substantially isothermal conditions. A further object of the present invention is to provide the formation of the semi-solid material suitable for the formation of components without a solidification and reheating step. Still another object of the present invention is to provide a process and apparatus for the formation of a semi-solid material with improved cutting and stirring.

COMPENDIUM OF THE INVENTION The present invention provides a method and apparatus for producing a suitable semi-solid material to directly form a component comprising a source of molten material, a container for receiving the molten material, thermal control means mounted to the container for controlling the temperature of the container , and a means of agitation submerged in the material. The stirring means and the thermal control means act together to produce a substantially isothermal semi-solid material in the container. Thermally controlled means are provided to remove the semi-solid material from the container.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic front section view of a semi-solid material production apparatus acing to the present invention. Figure 2 is a schematic side sectional view of the apparatus of Figure 1. Figure 3 is a schematic side sectional view of the apparatus of Figure 2 showing an alternative embodiment of the present invention. Figure 4 is a schematic side sectional view of the apparatus of Figure 2 showing another alternative embodiment of the present invention.

DESCRIPTION OF THE PREFERRED MODALITY In Figure 1, there is shown an apparatus for producing semi-solid material generally with the reference number 10 Separated from the apparatus 10, there is a source of molten material 11 Generally, any material that can be processed to a semi-solid material 50 is suitable for use with this apparatus 10 Suitable molten materials 11 include pure metals such as aluminum or magnesium, metal alloys such as steel alloy or aluminum A356, and mixtures of metal-ceramic particles such as aluminum and silicon carbide. The apparatus 10 includes a cylindrical chamber 12, a primary motor 14, a secondary rotor 16, and a chamber cover 18 The chamber 12 has an internal bottom wall 20 and a cylindrical internal side wall 22, both of which are made of a material refractory The chamber 12 has an outer support layer 24 preferably made of steel The upper part of the chamber 12 is covered by a cover The chamber cover 18 similarly has a layer of refractory material. The thermal control system 30 comprises heating segments 32 and cooling segments 34. The heating and cooling segments 32, 34 are mounted to, or embedded within, the layer. external 24 of the chamber 12 The heating and cooling segments 32, 34 may be oriented in different ways, but as shown, the heating and cooling segments 32, 34 are interleaved around the circumference of the chamber 12 The heating segments and cooling 32, 34 are also mounted to the chamber cover 18. The individual heating and cooling segments 32, 34 can independently add and / or remove the heat, thereby improving the temperature control capability of the contents of the chamber 12. The primary rotor 14 has a rotor end 42 and an arrow 44, which extends upwardly from the ext. rotor rotor 42. The primary rotor shaft 44 extends through the chamber lid 18. The rotor end 42 is immersed in and completely surrounded by the chamber 12. As shown in FIG. rotor 42 has L-shaped blades 43, preferably two of these blades 180 ° apart, extending from the bottom of rotor end 42. L-shaped blades 43 have two portions, one of which is parallel to the side wall internal 22 and the other being parallel to the internal lower wall 20. The L-shaped blades 43, when they rotate, cut the dendrites that tend to form on the inner side wall 22 and the lower wall 20 of the chamber 12. In addition, the rotation of the blades 43 promotes the mixing of material within the horizontal planes. Other knife geometries 43 (for example, T-shaped) should be effective as long as the gap between the inner side wall of chamber 22 and the blades 43 is small. It is desirable that this gap be less than 5.08 cm. In addition, to promote further cutting, the gap between the bottom of the chamber 20 and the blades 43 must also be less than 5.08 cm. A typical rotation speed of the cutting rotor 14 is about 30 rpm. The secondary rotor 16 has a rotor end 48 and an w 46 extending from the rotor end 48. The shape of the rotor end 48 must be designed to promote vertical mixing of the semi-solid material 50 and improve the cutting of the semi material -solid 50. The rotor end 48 preferably has an auger or screw shape, but many other shapes, such as blades inclined relative to a horizontal plane, will work similarly. The w 46 extends upwardly from the bit-shaped rotor end 48. Depending on the rotational direction of the secondary rotor 16, the material in the chamber 12 is forced to move either in an upward or downward direction. A typical rotation speed of the secondary rotor 16 is 300 rpm. The primary rotor 14 and the secondary rotor 16 are oriented relative to the chamber 12 and to each other to improve both cutting and three-dimensional agitation of a semi-solid material 50. In Figure 1, it can be seen that the primary rotor 14 rotates around the secondary rotor 16. The secondary rotor 16 rotates within the predominantly horizontal mixing action of the primary rotor 14. This configuration promotes a three-dimensional and conscientious mixing of the semi-solid material 50. Although Figure 1 illustrates a plurality of rotors, An individual rotor that provides the proper cutting and mixing properties can be used. Said single rotor should offer both cutting and mixing, the mixing being three dimensional so that the semi-solid material 50 in the container 12 can be maintained at a substantially uniform temperature. The environment of the semi-solid material in which the rotors 14, 16 are submerged, is quite hard. The rotors 14, 16 are exposed to very high temperatures, usually corrosive conditions, and considerable physical force. To combat these conditions, the preferred composition of the rotors 14, 16 is a heat and corrosion resistant alloy such as a stainless steel with a ceramic coating of MgZr03, high temperature. Other materials resistant to high temperature, such as a superalloy coated with Al203, are also suitable. A frame 56 is mounted to the chamber lid 18. The frame 56 supports a primary drive motor 58 and a secondary drive motor 60. The respective motors 58, 60 are mechanically coupled to the ws 44, 46 of the respective rotors. , 16. As shown in Figure 1, the primary motor 58 is coupled to the primary rotor shaft 44 through a pair of reduction gears 62 and 64. The primary rotor shaft 44 is supported on the frame 56 a through bearing bushes 66. Similarly, the secondary rotor w 46 is supported on the frame 56 by bearing bushes 68. Both motors 58, 60 can be connected to the rotors via reduction or lifting gear to improve the transmission of energy and / or torque. An alternative to the mechanical agitation described above is electromagnetic agitation. An example of electromagnetic stirring is found in the U.S.A. No. 4,229,210 of Winter and others. Electromagnetic stirring can effect the desired three-dimensional isotropic cutting and mixing properties of the present invention. The molten material 11 can be supplied to the chamber 12 in a number of different ways. In one embodiment, the molten material 11 is supplied through a hole 70 in the chamber cover 18. Alternatively, the molten metal 11 can be supplied through a hole in the side wall 22 (not shown) and / or through a hole in the bottom wall 20 (not shown). The semi-solid material 50 is formed from the molten material 11 after agitation through the primary rotor 14 and the secondary rotor 16, and an appropriate cooling of the thermal control system 30. After an initial start cycle, ei The process is semicontinuous, so that as the semi-solid material 50 is removed from the chamber 12, molten material 11 is added. However, the rotors 14, 16 and the thermal control system 30 maintain the semi-solid material. in a substantially isothermal state.

In addition to controlling the temperature of the chamber 12 thus maintaining the semi-solid material 50 in a substantially sotropic state, the thermal control system 30 is also instrumental in starting and stopping the apparatus 10. During the start, the thermal control system it must carry the chamber 12 and its contents to the appropriate temperature to receive the molten material 11. The chamber 12 may have a large amount of solidified semi-solid material or solidified material (previously cast) remaining therein from an operation previous. The thermal control system 30 must be capable of supplying sufficient energy to remelter the solidified material. Similarly, when the apparatus 10 is stopped, it may be desirable for the thermal control system 30 to heat the semi-solid material 50 in order to completely drain the chamber 12. Another detection process may cause careful cooling of the semi-solid material. 50 to the melted state. As shown in Figure 2, the removal of the semi-solid material 50 formed in the chamber 12 is preferably through a removal port 72, which extends through a hole 71 in the cover 18. One end of the Removal port 72 should be below the surface of the semi-solid material 50. Removal port 72 is insulated and protects the semi-solid material 50 from becoming contaminated by the ambient atmosphere. Without such protection, it could be more easily that oxidation occurs on the outside of the semi-solid material and any of the components made therefrom are interspersed. Provided around the removal port 72 is a heater 80 for keeping the semi-solid material 50 at the desired temperature. In Figure 2, the removal port 72 extends from the apparatus 10 through the camera of the camera cover 18. In an alternative preferred embodiment, the removal port 72 extends from the side wall chamber 22, which it has an outlet hole 112 as shown in Figure 3. Alternatively, Figure 3 also shows a removal port 73 extending from the bottom wall 20, in which it has an exit hole 113. In any case, as described above, the removal port includes a heater 80 to maintain the isotropic state of the semi-solid material 50 that is being removed. The flow of semi-solid material 50 through port 72 can be achieved through any number of methods. A vacuum can be applied to the removal port 72, thereby sucking the semi-solid material out of the chamber 12. Gravity can be used as illustrated in Figure 3, at port 73. Other transfer methods using mechanical means , such as submerged pistons, helical rotors, or other positive displacement actuators, which produce a controlled rate of transfer of the semi-solid material 50, are also effective. To further regulate the flow of the semi-solid material 50 out of the chamber 12 through any of the removal ports described above, a valve 83 is provided on the port 72. The valve 83 may be a single gate valve or other liquid flow regulation device. It may be desirable to heat the valve 80 so that the semi-solid 50 is maintained at the desired temperature and plugging is prevented. The regulation of the flow can also be crudely effected through local solidification. Instead of a valve 83, a heater / cooler (not shown) can locally solidify the semi-solid material 50 in port 72, thus stopping the flow. Subsequently, the heater / cooler can reheat the material to resume the flow. This procedure could be part of a start and stop cycle, and is not necessarily part of the isothermal semi-solid material production process described above. Another way to transfer semi-solid material 50, while inherent flow control is provided, use a bucket 114 as illustrated in Figure 4. Bucket 114 removes semi-solid material 50 from chamber 12, while heater 82, which is mounted to bucket 114, maintains the temperature of the semi-solid material 50 that is being removed. A bucket cup 115 of the bucket 114 is attached to a bucket driver 116. The cup 115 can rotate to empty its contents, and the actuator 116 moves the bucket in the horizontal and vertical directions.

To help maintain appropriate temperature conditions within the chamber 12, the transfer of semi-solid material 50 can occur in successive cycles. During each cycle, the flow regulation described above allows a described amount of semi-solid material 50 to be removed. The amount of semi-solid material removed during each cycle should be small relative to the material remaining in chamber 12. In this way, the change in thermal mass inside chamber 12 during the removal cycles is small. In a typical cycle, less than 10 percent of the semi-solid material 50 is removed within the chamber. Once the semi-solid material is removed, it can be transferred directly to a casting device to form a component. Said casting device includes that described in "Apparatus and Method for Integrated Semi-Solid Material Production and Casting", an interim application filed on October 4, 1996, which is incorporated herein by reference. Other examples of suitable casting devices include a mold, a die die assembly as described in the U.S. patent specification. 5,287,719, or other commonly known die casting mechanisms. Although not required, it may be desirable to keep the entire apparatus 10 in a controlled environment (not shown). Oxides are easily formed on the outer layers of molten materials and semi-solid materials. Also contaminants other than oxides can enter the molten and semi-solid material. In an inert environment, such as one of nitrogen or argon, the formation of oxide could be reduced or eliminated. The inert environment can also result in some contaminants in the semi-solid material. However, it may be economical to limit the controlled environment to discrete portions of the apparatus 10, such as the supply of the molten material 11 to the chamber 12. Another discrete and economical portion for environmental control may be the removal port 72 (or the bucket). 114). In the removal port 72, the semi-solid material 50 no longer undergoes agitation and the material will soon be cast to a component. In this way, any oxide cover that is formed in this stage will not be dispersed through the material through mixing in the container 12. Rather, the oxides will be concentrated on the outer layers of the semi-solid material. Therefore, to reduce both oxide formation and to reduce high concentration oxide cavities, a controlled nitrogen environment (or other suitable and economical environment) could be advantageous in the removal port 72 stage. The following is an example of the process and apparatus described above after completing the start cycle. The molten aluminum at a temperature of about 677 ° C is drained from the chamber 12 which already contains a large amount of semi-solid material. The primary rotor 14 rotates at approximately 30 rpm and shakes and cuts the aluminum in a clockwise direction. The secondary rotor 16 rotates at approximately 300 rpm and forces the aluminum up and / or down, while cutting the aluminum as well. . The combined effect of the two rotors 14, 16 conscientiously shakes and cuts the aluminum in three dimensions. The thermal control system 30 maintains the temperature of the aluminum at approximately 600 ° C, so that dendritic structures are formed. The rotors 14, 16 cut the dendritic structures as they are formed. Although the thermal control system maintains the temperature of the semi-solid aluminum at about 600 ° C, the rotors 14, 16 continuously mix the semi-solid aluminum keeping the temperature within the material substantially uniform. The solid particle size produced by this particular process is typically in the range of 50 to 200 microns, and the volume percentage of suspended solids in the semi-solid aluminum is approximately 20 percent. The semi-solid aluminum is transferred from the chamber 12 through the removal port 72. The removal port heater 80 also keeps the semi-solid aluminum at 600 ° C. A component can be formed directly from the semi-solid aluminum removed, without any of the additional solidification or reheating steps. Although what are considered to be the preferred embodiments of the present invention have been described herein, other modifications of the invention will be apparent to those skilled in the art from teaching herein. Therefore, it is desired to ensure in the appended claims that all these modifications fall within the true spirit and scope of the invention. Therefore, what is desired is to ensure through the granted patent of the United States is the invention as defined and differentiated in the following claims.

Claims (21)

1. An apparatus for producing a semi-solid material suitable for directly forming a component, comprising: a source of molten material; a container for receiving the molten material; thermal control means for controlling the temperature of the container; a stirring medium immersed in the material and acting together with the thermal control means to produce a substantially isothermal semi-solid material; and means for removing the semi-solid material from the container, said removal means having a temperature control mechanism for controlling the temperature of the semi-solid material within the removal means.

The apparatus according to claim 1, wherein the removal means further comprises a flow control mechanism for regulating the flow of said semi-solid material out of the chamber.

The apparatus according to claim 2, wherein the source of the molten material includes a flow regulator operating with the flow control device to maintain a substantially constant level of semi-solid material in the container.

4. The apparatus according to claim 2, wherein the flow control device regulates the flow of the semi-solid material out of the chamber, so that no more than one-tenth of the semi-solid material is removed per cycle of removal.

The apparatus according to claim 1, wherein the agitating means comprises a mechanical agitation device.

The apparatus according to claim 5, wherein the mechanical stirring device comprises a primary rotor and a secondary rotor.

The apparatus according to claim 5, wherein the mechanical stirring device is made of a high temperature alloy coated with a ceramic.

The apparatus according to claim 6, wherein the primary rotor includes an arrow from which extends an arm having a first portion that is substantially parallel to the side wall of the container.

The apparatus according to claim 8, wherein said arm includes a second portion that is substantially parallel to the bottom wall of the container.

The apparatus according to claim 9, wherein the first and second portions of the arm are not more than 5.08 cm from the walls of the container.

The apparatus according to claim 8, wherein the secondary rotor is auger-shaped and promotes mixing of the semi-solid material along a secondary rotor axis.

12. The apparatus according to claim 1, wherein the stirring means comprises an electromagnetic stirring device.

The apparatus according to claim 1, wherein the semi-solid material comprises aluminum or an alloy thereof.

14. The apparatus according to claim 1, wherein the semi-solid material comprises magnesium or an alloy thereof.

15. The apparatus according to claim 1, wherein the semi-solid material comprises steel or an alloy thereof.

16. The apparatus according to claim 1, wherein the removal means comprise a removal port.

The apparatus according to claim 16, wherein the removal port extends through a cover in said chamber.

18. The apparatus according to claim 16, wherein the removal port extends through a side wall in the chamber.

19. The apparatus according to claim 16, wherein the removal port extends through a bottom wall in the chamber.

20. An apparatus for directly producing a component from a semi-solid material, comprising: a source of semi-solid material; a container for receiving the semi-solid material; agitation means acting with the container for stirring the semi-solid material in the container; the agitation means include a primary rotor and a secondary rotor operating as well to provide three-dimensional mixing and cutting; and thermal control means for controlling the temperature of said container, the thermal control means and the agitation means serving to produce a semi-solid material and maintaining said material in a substantially isothermal condition.

21. A method for directly producing a component from a semi-solid material, comprising: obtaining a molten material; receive the molten material in a container; cutting the molten material in the container with stirring means; mixing the molten material in the container with the stirring means; thermally controlling the molten material, together with said agitation, to form a semi-solid material maintained in a substantially isothermal condition; and transferring the semi-solid material from said chamber through a removal port.