US20060054294A1

US20060054294A1 - Short cycle casting processing

Info

Publication number: US20060054294A1
Application number: US11/225,279
Authority: US
Inventors: Scott Crafton; Paul Crafton; Ian French; Volker Knobloch
Original assignee: Individual
Current assignee: Consolidated Engineering Co Inc
Priority date: 2004-09-15
Filing date: 2005-09-13
Publication date: 2006-03-16
Also published as: WO2006031954B1; WO2006031954A3; WO2006031954A2

Abstract

A conveyance mechanism for transporting a casting is provided. A system and method of processing a metal casting also are provided.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/610,010, filed Sep. 15, 2004, which is incorporated by reference herein in its entirety.

BACKGROUND

Metal casting processes are well known to those in the field of metallurgy. There is a continuing need to develop efficient processes that provide shortened heat treatment times, efficient reclamation of materials, and superior metal properties.

SUMMARY

This invention relates to a system and method of processing a casting that involves various process steps. Some of such steps include mold preparation, including creation of molds with inner cores and chills associated with the molds, pouring of molten metal, at least partial solidification of the metal, chill removal, mold removal, de-coring, sand reclamation, heat treatment, quenching, cooling, removal of remaining sand, and de-burring. The apparatus and system provide for decreased processing times for the casting.

BRIEF DESCRIPTION OF THE DRAWINGS

The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:
FIG. 1 is a schematic representation of an exemplary system according to various aspects of the present invention;
FIG. 2 depicts an exemplary mold that may be used according to various aspects of the present invention, in a pouring position;
FIG. 3 depicts an exemplary bottom portion of the mold of FIG. 2 with a chill being placed therein;
FIGS. 4A and 4B depict the exemplary mold of FIG. 2 being inverted;
FIGS. 5A and 5B depict the chill being removed from the exemplary mold of FIG. 2;
FIG. 6 depicts the exemplary mold of FIG. 2, after the chill is removed;
FIG. 7 depicts an exemplary process for removing the bottom portion of the mold of FIG. 2, according to various aspects of the present invention;
FIG. 8 depicts another exemplary process for removing the bottom portion of the mold of FIG. 2, according to various aspects of the present invention;
FIG. 9 depicts an exemplary conveyance mechanism for conveying a casting according to various aspects of the present invention; and
FIG. 10 depicts another exemplary conveyance mechanism for conveying a casting according to various aspects of the present invention.

DESCRIPTION

The present invention is directed generally to various systems and methods for providing a reduced heat treatment time or cycle. The reduced or “short” cycle may be attributed to various aspects of the present invention, including, for example, removal of at least a portion of the outer mold prior to heat treatment, and the absence of baskets or trays commonly used for conveyance of castings through the heat treatment furnace.
The present invention may be best understood by referring to the figures. For purposes of simplicity, like numerals may be used to describe like features. However, it should be understood that use of like numerals is not to be construed as an acknowledgment or admission that such features are equivalent in any manner. It also will be understood that where similar features are depicted, not all of such identical features may be labeled on the figures.
FIG. 1 presents a schematic overview of an exemplary “short cycle” apparatus or system 100 according to various aspects of the present invention. At a pouring station 200, a molten metal is poured into a mold including an outer mold and various other features, including risers, gate, and/or cores, as is understood by those skilled in the art, to form a casting.
One example of a mold 210 is depicted in FIGS. 2 and 3. In this example, the mold 210 is used to form an engine block. The casting to be formed generally is defined by a metal block with ports and channels defined therein, such as cylinder chambers, oil and air ducts, and a crank shaft cavity. In FIG. 2, the mold 210 is in a pouring position. The mold 210 includes risers 220, gate 230, down sprue 240, and an outer mold 250. Additionally, to form the crank shaft cavity, a chill 260 is placed in the bottom, casting-bearing portion 270 of the mold 210, as is known by those in the art. As illustrated in FIGS. 4A and 4B, after pouring, the mold 210 with the casting 280 therein inverted and allowed to solidify at least partially. The casting 280 typically solidifies in the direction indicated by the arrows.
Returning to FIG. 1, at a chill removal station 300, the chill 260 is removed through the bottom portion 270 of the mold 210 to form a cavity 310, as illustrated schematically in FIGS. SA and 5B.
Next, the outer mold 250 is at least partially removed at a mold removal station 400. In one aspect, the outer mold is substantially removed. In another aspect, the outer mold is completely removed. For purposes of simplicity and unless specified otherwise, as used herein, the terms “remove”, “removal”, and “removed” refer collectively to partial, substantial, and complete removal.
Any suitable means may be used to remove the outer mold. In one aspect, the outer mold is removed using pulse wave processing, in which sound or fluid “pulses” are directed at the mold to shatter it. One example of a pulse wave demolding system is disclosed in U.S. patent Ser. No. 10/616,750, which is incorporated by reference herein in its entirety. However, other pulse wave demolding systems, and other methods, techniques, or processes may be used in accordance with the present invention.
FIG. 6 depicts the casting 280 and remaining mold portions after the removal of the outer mold. In this example, the outer mold portion has been removed, and the bottom mold portion 270, the remaining riser 220, gating 230, sprue 240, and manifold mold portion 410 remain, in some instances, because of the challenges associated with removing such portions.
If desired, the system 100 may include an optional process temperature control system or station (not shown) integral with or separate from the mold removal station 400. At the process temperature control station, the temperature of the casting may be maintained at or above a “process control temperature” (or “process critical temperature”), below which the time required to both raise the castings to the heat treating temperature and perform the heat treatment is significantly increased. In another aspect, the casting may be allowed to reach a temperature below a predetermined process control temperature.
It will be understood by those skilled in the art that the process control temperature for the castings will vary depending upon the particular metal and/or metal alloys used for the castings, the size and shape of the castings, and numerous other factors. The benefits of maintaining the temperature of the casting at or above a process control temperature are described in U.S. patent application Ser. No. 10/051,666, which is incorporated by reference herein in its entirety.
In one aspect, the process control temperature may be about 400° C. for some alloys or metals. In another aspect, the process control temperature may be from about 400° C. to about 600° C. In another aspect, the process control temperature may be from about 600° C. to about 800° C. In yet another aspect, the process control temperature may be from about 800° C. to about 1100° C. In still another aspect, the process control temperature may be from about 1000° C. to about 1300° C. for some alloys or metals, for example, iron. In one particular example, an aluminum/copper alloy may have a process control temperature of from about 400° C. to about 530° C. In this example, the process control temperature generally is below the solution heat treatment temperature for most copper alloys, which typically is from about 475° C. to about 550° C. While particular examples are provided herein, it will be understood that the process control temperature may be any temperature, depending upon the particular metal and/or metal alloys being used for the castings, the size and shape of the castings, and numerous other factors.
When the metal of the casting is within the desired process control temperature range, the casting typically will be cooled sufficiently to solidify as desired. However, if the metal of the casting is permitted to cool below its process control temperature, it has been found that the casting may need to be heated for at least about 4 additional minutes for each minute that the metal of the casting is cooled below the process control temperature to reach the desired heat treatment temperature, for example, from about 475° C. to about 550° C. for aluminum/copper alloys, or from about 510° C. to about 570° C. for aluminum/magnesium alloys. Thus, if the castings cool below their process control temperature for even a short time, the time required to heat treat the castings properly and completely may be increased significantly. In addition, it should be recognized that in a batch processing system, where several castings formed from the same metal or metal alloy are processed through the heat treatment station in a single batch, the heat treatment time for the entire batch of castings generally is based on the heat treatment time required for the casting(s) with the lowest temperature in the batch. As a result, if one of the castings in the batch being processed has cooled to a temperature below its process control temperature, for example, for about 10 minutes, the entire batch typically will need to be heat treated, for example, for at least an additional 40 minutes to ensure that all of the castings are heat treated properly and completely.
Accordingly, various aspects of the present invention include systems for monitoring the temperature of the castings to ensure that the castings are maintained substantially at or above the process control temperature. For example, thermocouples or other similar temperature sensing devices or systems can be placed on or adjacent the castings or at spaced locations along the path of travel of the castings from the pouring station to a heat treatment furnace to provide substantially continuous monitoring. Alternatively, periodic monitoring at intervals determined to be sufficiently frequent may be used. Such devices may be in communication with a heat source, such that the temperature measuring or sensing device and the heat source may cooperate to maintain the temperature of the casting substantially at or above the process control temperature for the metal of the casting. It will be understood that the temperature of the casting may be measured at one particular location on or in the casting, may be an average temperature calculated by measuring the temperature at a plurality of locations on or in the casting, or may be measured in any other manner as needed or desired for a particular application. Thus, for example, the temperature of the casting may be measured in multiple locations on or in the casting, and an overall temperature value may be calculated or determined to be the lowest temperature detected, the highest temperature detected, the median temperature detected, the average temperature detected, or any combination or variation thereof.
To maintain the temperature of the casting at or above the process control temperature, the mold removal station (or separate process temperature control station, where applicable) may include one or more various heat sources, such as radiant heaters, infrared, inductive, convection, conduction, or other types of heating elements. The walls and ceiling of the station also may include a radiant material that tends to radiate or direct heat toward the castings and/or molds.
By including such features, cooling of the castings may be arrested at or above a process control temperature. The process control temperature generally is a temperature below the solution heat treatment temperature required for the metal of the castings, such that the castings are cooled to a sufficient amount or extent to enable them to solidify, but below which the time required to raise the castings up to their solution heat treatment temperature and thereafter heat-treat the castings is increased exponentially. The castings are maintained at or above their process control temperature until the castings enter the heat treatment station. By arresting the cooling of the castings and thereafter maintaining the castings at a temperature that is substantially at or above the process control temperature for the metal of the castings, the time required to heat treat the castings can be significantly reduced. Accordingly, the output of the pouring station for the castings can be increased and the overall processing and heat treatment time for the castings can be reduced.
Although maintaining the process control temperature is discussed in the context of the mold removal station, it will be understood that the system may include other features or stations to maintain the temperature of the casting at or above a process control temperature. For example one or more heat sources, including radiant heating elements such as infrared and inductive heating elements, convection, conduction, or other types of heat sources may be used to direct heat at the castings or molds as the castings or molds are transferred from the pouring station to the chill removal station. In addition, a heating element or heat source can be mounted directly to the transfer mechanism to heat the castings and/or the sand molds.
Additionally, prior to entry into the heat treatment furnace, the castings may pass through an entry or rejection zone (not shown), where the temperature of each casting is monitored to determine whether the casting has cooled to an extent that would require and an excessive amount of energy to raise the temperature to the heat treatment temperature. The entry zone may be included in the process control temperature station, or may be a separate zone, as desired. The temperature of the casting may be monitored by any suitable temperature sensing or measuring device, such as a thermocouple, to determine whether the temperature of the casting has reached or dropped below a pre-set or predefined rejection temperature. In one aspect, the predefined rejection temperature may be a temperature (for example, from about 10° C. to about 20° C.) below the process control temperature for the metal of the casting. In another aspect, the predefined rejection temperature may be a temperature (for example, from about 10° C. to about 20° C.) below the heat treatment temperature of the heat treatment furnace or oven. If the casting has cooled to a temperature equal to or below the predefined temperature, the control system may send a rejection signal to a transfer or removal mechanism. In response to the detection of a defect condition or signal, the subject casting may be identified for further evaluation or may be removed from the transfer line. The casting may be removed by any suitable mechanism or device including, but not limited to, a robotic arm or other automated device, or the casting may be removed manually by an operator.
As with the above, it will be understood that the temperature of the casting may be measured at one particular location on or in the casting, may be an average temperature calculated by measuring the temperature at a plurality of locations on or in the casting, or may be measured in any other manner as needed or desired for a particular application. Thus, for example, the temperature of the casting may be measured in multiple locations on or in the casting, and an overall value may be calculated or determined to be the lowest temperature detected, the highest temperature detected, the median temperature detected, the average temperature detected, or any combination or variation thereof.
Returning to FIG. 1, the casting then is transferred 500 to a loading station 600 prior to entry into a heat treatment station 700. In one aspect, as the casting 280 is transferred, the bottom mold portion 270 on which the casting rests is removed. Any suitable device or method may be used to remove the bottom mold portion, as desired. For example, as illustrated in FIG. 7, a mold engagement device 510 (presented only in representative fashion) may engage the bottom mold portion 270 with a downward force at the time that the casting is lifted with an upward force, for example, by a robot 520 (representatively presented), as part of the transfer process. This downward force pushes or hits the bottom mold portion 270, dislodging it or at least a portion of it from the casting 280.
As another example, the casting may be lifted during the transfer process with the bottom mold portion still attached. During transfer to the heat treatment station, the casting may strike (or be stricken by) an object that causes the bottom mold portion to dislodge. Alternately or additionally, the bottom mold portion may be impinged with a pulse wave of sound or air or other fluid in a manner similar to that discussed previously, thereby removing the bottom mold portion from the casting. In such an example, the down sprue of the mold is then removed or “knocked-off” and the remaining mold with casting 280, which is shown in FIG. 8 to include the risers 220 and gate 230 with at least some of the manifold-associated mold portion 410, is transferred to the loading station 600 for the heat treatment station 700.
If desired, the risers and at least a portion of the gate may be removed prior to entry into the loading station 600 and/or the heat treatment station 700. The riser and/or gate may be removed using any suitable device or method, for example, a cutting blade, water jet, or other cutting type mechanism. By doing so, the manifold-associated mold portion may be more readily accessed for removal by, for example, pulse wave processing or any other suitable technique.
Still viewing FIG. 1, after the bottom portion of the mold is removed, the casting is placed on a conveyance mechanism (not shown) at a loading station 600. The conveyance mechanism may be any suitable system or device. In one aspect, the conveyance mechanism is designed without the need for the use of trays or baskets to convey the castings. By doing so, any use of thermal energy typically required to heat a basket or tray is avoided. Additionally, such baskets or trays typically would have to be returned from the exit of the furnace to the entrance for reuse, and such process is not required. However, it will be understood that although the use of conveyance mechanisms and systems without baskets or trays is described herein, such mechanisms and systems may be used if desired.
For example, in one aspect illustrated in FIG. 9 (risers and gate remain intact) and FIG. 10 (risers and gate removed), the conveyance mechanism may include a plurality of parallel roller bars 610 arranged transverse to the intended direction of travel of the castings. One or more guide tubes 620 extend perpendicular to the roller bars 610 and parallel to the intended direction of travel of the castings 280, as indicated by arrows A in FIG. 10. As depicted, each casting 280 is placed on the roller bars 610 with its crank shaft cavity 310 straddling one of the guide tubes 620, such that the respective guide tube 620 is received in and extends longitudinally through the crank shaft cavity 310. Thus, the crank shaft cavity 310 receives and cooperates with the guide tube 620. The guide tube 620 is stationary relative to the roller bars 610 and the casting 280 is caused to move along the stationary guide tube 620.
To convey the casting 280, the roller bars 610 are driven by an electrical and/or mechanical device, for example, a motor, to rotate and to move the casting 280 from roller bar to roller bar 610, and the guide tube 620 defines the path of travel of the casting 280 and guides the casting 280 along that path of travel. The guide tubes 620 also help prevent the casting 280 from tipping as it is conveyed, and maintain the spacing between castings 280 aligned side by side across the roller bars 610.
If desired, the guide tubes may be hollow and provided with apertures (not shown) defined along the length of the guide tubes by which air may escape from the inner cavity of the hollow guide tubes. Thus, in one aspect, pressurized air (or other fluids) can be delivered through the guide tubes and out the apertures to impinge the castings as they pass along the guide tubes. Thus, the guide tubes may perform both a casting guidance function and a fluid guidance/delivery function. The type of fluid, placement of the apertures, temperature of the fluid and selected pressure of the escaping fluid can be coordinated to aid in the heat treatment of the castings, and/or to blow out some of the sand accessible from inside the crank shaft cavity.
If desired, the orientation of the apertures about the guide tube may be selected to attempt to isolate the impingement of certain areas. For example, it may be desirable to attempt to clear bearing surfaces within the crank shaft cavity to improve heat treatment and/or core removal. Alternatively, selected areas may be impinged with cold pressurized air (or other fluids) to quench the casting or regions to achieve the desired properties.
While the use of turning roller bars is described in detail herein, it will be understood that other conveying or transferring systems may be used with the present invention. Such other systems may include walking beams, rotary hearths, circular conveyance mechanisms, chains, pushers, overhead monorails, and others. Further, if desired, the same conveyance mechanism may, if desired, convey the castings to subsequent quenching and cooling.
Returning to FIG. 1, the castings then are conveyed to the solution heat treatment station 700, which includes a heat treatment furnace (not shown). The casting remains within the furnace for an appropriate time and at an appropriate temperature to achieve the desired result. Typical heat treatment times and temperatures are known by those of skill in the art. In one aspect, at the time the casting enters the heat treatment furnace, only the internal cores remain in the casting (for example, an engine block). In another aspect, one or more risers, gate, and cores remain at the time of entry to the heat treatment furnace.
During heat treatment, the sand cores may be removed and collected for later reclamation and reuse, or may be transferred to a sand reclamation system 800, if desired. One example of such a system is described in U.S. Provisional Patent Application No. 60/554,502, which is incorporated by reference herein in its entirety. However, it will be understood that any sand removal, collection, and/or reclamation device or system may be used in accordance with the present invention.
Further, the molds removed during other stages of the process may be placed into a supplemental sand reclamation unit, such as that described in U.S. Pat. No. 5,354,038, incorporated by reference herein in its entirety. Alternatively, the molds may be placed directly into the furnace for processing, for example, within the first couple of zones of the heat treatment furnace, in the manner described in U.S. Provisional Patent Application No. 60/554,502 or in U.S. Pat. No. 5,354,038, both of which are incorporated by reference herein in their entirety.
Still viewing FIG. 1, after heat treatment, the casting may be transferred to a quench station 900 for cooling to a suitable handling temperature. In one aspect, the quenching equipment may include a guide tube conveyance system similar to that described above including, for example, fluid guidance/delivery features. As such, during conveyance, the quenching equipment may immediately begin quenching, for example, the bearing surfaces or features of the casting by spraying a fluid (air, water, oil, etc.) at such surfaces or features in the crankshaft cavity. By doing so, the time required to quench the casting may be reduced.
Where risers, gating, and sprues have not been removed prior to or during heat treatment, such components may be removed after heat treatment, for example, by vibrating, at a riser removal station 1000. The removal of these components and any loose sand trapped in crevices and cavities of the casting results in collection of additional sand that was not previously emptied into the heat treatment furnace. This sand may be returned to the sand reclamation system within the heat treatment furnace.
Finally, whether the risers, gate, and sprues were removed prior to heat treatment, during heat treatment, or after heat treatment, the castings are transferred to a de-burring station 1100.
The final casting then is unloaded from the system 100.
Accordingly, it will be readily understood by those persons skilled in the art that, in view of the above detailed description of the invention, the present invention is susceptible of broad utility and application. Many adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the above detailed description thereof, without departing from the substance or scope of the present invention.
Although numerous embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the embodiments of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention unless specifically set forth in the claims. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other.
It will be recognized by those skilled in the art, that various elements discussed with reference to the various embodiments may be interchanged to create entirely new embodiments coming within the scope of the present invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims. The detailed description set forth herein is not intended nor is to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications, and equivalent arrangements of the present invention.

Claims

1. A conveyance mechanism for transporting a casting having a cavity, comprising:

a plurality of roller bars arranged transverse to an intended direction of travel of the casting;

at least one guide tube extending perpendicular to the roller bars, the at least one guide tube capable of being received within the cavity of the casting; and

a driving device in engagement with the roller bars.

2. The conveyance mechanism of claim 1, wherein the guide tube includes an exterior surface and an interior, the interior including a bore extending along a length of the guide tube.

3. The conveyance mechanism of claim 2, wherein the guide tube comprises a plurality of apertures extending from the bore to the exterior surface of the guide tube.

4. The conveyance mechanism of claim 3, further comprising a source of pressurized air in communication with the bore of the guide tube.

5. The conveyance mechanism of claim 4, wherein the apertures are positioned to impinge the casting selectively with pressurized air.

6. A system for reduced-cycle heat treatment of a metal casting, comprising:

a pouring station for pouring a molten metal into a mold to form a casting, the mold comprising an outer mold including a casting-bearing portion;

a mold removal station comprising a pulse wave demolding system downstream from the pouring station, the demolding system capable of at least partially removing the outer mold from the casting;

a loading station comprising a conveyance mechanism that receives the demolded casting, the conveyance mechanism lacking a basket or tray for receiving the casting; and

a heat treatment station downstream from the loading station.

7. The system of claim 6, further comprising a mold engagement device capable of engaging the casting-bearing portion of the mold.

8. The system of claim 6, wherein the conveyance mechanism comprises:

at least one guide tube extending perpendicular to the roller bars, the at least one guide tube capable of releasably engaging the casting; and

a driving device in engagement with the roller bars.

9. The system of claim 8, wherein the guide tube includes an exterior surface and an interior, the interior including a bore extending along a length of the guide tube, and a plurality of apertures extending from the bore to the exterior surface of the guide tube.

10. The system of claim 8, further comprising a source of pressurized air in communication with the bore of the guide tube.

11. The system of claim 10, wherein the apertures are positioned to impinge the casting selectively with pressurized air.

12. The system of claim 6, further comprising a process temperature control station upstream from the heat treatment station, the process temperature control station comprising a temperature sensing device in communication with a heat source, wherein the temperature sensing device and the heat source communicate to maintain the temperature of the casting at or above a process control temperature for the metal of the casting.

13. The system of claim 5, wherein the heat treatment station comprises:

a heat treatment furnace having an entry zone;

a temperature measuring device within the entry zone; and

a transfer mechanism in communication with the temperature measuring device,

wherein upon detection of a rejection temperature by the temperature measuring device, the transfer mechanism removes the casting prior to entry into said furnace.

14. A method for reducing the heat treatment time of a metal casting, comprising:

pouring a molten metal into a mold to form a casting, the mold comprising an outer mold including a casting-bearing portion;

removing at least a portion of the outer mold using a pulse demolding system;

placing the casting on a conveyance mechanism, the conveyance mechanism capable of conveying the casting without using a basket or tray; and

heat treating the casting.

15. The method of claim 14, further comprising removing any remaining portion of the mold prior to placing the casting on the conveyance mechanism.

16. The method of claim 14, further comprising removing the casting-bearing portion of the mold while transferring the casting to the conveyance mechanism.

17. The method of claim 14, further comprising maintaining the temperature of the casting at or above a process control temperature for the metal of the casting when the casting is formed until the casting is heat treated.

18. A method of processing a metal casting, comprising:

pouring a molten metal into a mold to form a casting;

removing at least a portion of mold;

transferring the casting on a conveyance mechanism comprising:

at least one guide tube extending perpendicular to the roller bars, the at least one guide tube releasably engaging the casting; and

a driving device in engagement with the roller bars; and

heat treating the casting.

19. The method of claim 18, wherein at least a portion of the mold is removed using a pulse demolding system.

20. The method of claim 18, wherein at least a portion of the mold is removed as the casting is transferred to the conveyance mechanism.