Abstract:
A mold temperature control system comprises a mold section having a cavity, a fluid circuit to distribute a flow of a conditioning fluid, the fluid circuit being positioned spaced apart from the cavity, a temperature sensor positioned in the mold to generate a signal representative of a temperature in the mold, a controllable supply of the conditioning fluid, and a controller for automatically initiating flow of the conditioning fluid through the fluid circuit in response to an initiation temperature and for automatically terminating flow of the conditioning fluid through the fluid circuit in response to a termination temperature.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to controlling mold temperature in a casting system to produce a cast article. Pressure pouring of molten metal from a furnace to fill a mold cavity has been used for several decades. At room temperature, the metal is solid and becomes fluidic when melted with sufficient heat. 
     It is known to use a low pressure countergravity casting apparatus to cast molten metal into a mold. One example of such an apparatus is described in U.S. Pat. No. 5,215,141. Basically, in a low pressure countergravity casting apparatus, molten metal is supplied to a machine furnace. The machine furnace includes a supply conduit for introducing a gas under pressure into the machine furnace. As the gas is introduced into the machine furnace, the molten metal in the machine furnace is forced through a submerged feed tube, or evacuation conduit, into the mold. The evacuation conduit is commonly referred to as a stalk tube. The mold receives the molten metal through holes in the bottom of the mold. 
     The molten metal must cool in the mold and harden to produce the cast article. Cooling of the molten metal is generally done by cooling the mold using a cooling fluid flowing through cooling channels in the mold. Conventionally, cooling of the mold has been controlled by a skilled human operator who adjusts the flow of the cooling fluid, which has been rather imprecise. Insufficient cooling times can lead to an improperly formed cast article. Excessive cooling time leads to decreased cycle times and economic inefficiency. 
     In order to make a solid cast article with the best possible structural properties in the least amount of time, the mold temperature during metal filling and during cooling must be accurately controlled regardless of environmental conditions (e.g., ambient air temperature, humidity, and temperature and pressure of the cooling fluid). During casting, the heat energy of the molten metal (e.g., aluminum) flows into the mold and then into the cooling fluid. Preferably, a temperature profile is achieved such that a directional solidification of the cast article occurs wherein the article solidifies from the outside and then in towards the filling area (i.e., stalk tube). After a solidified article is removed from the mold, it is prepared as quickly as possible for casting another part. This includes ensuring that the mold starts the next cycle at a predetermined temperature. Thus, it is desired to cool a mold as quickly as possible while maintaining acceptable structural properties of the article and providing directional solidification. 
     SUMMARY OF THE INVENTION 
     The above advantages as well as other advantages not specifically enumerated are achieved by a mold temperature control system comprising a mold section having a cavity, a fluid circuit to distribute a flow of a conditioning fluid, the fluid circuit being positioned spaced apart from the cavity, a temperature sensor positioned in the mold to generate a signal representative of a temperature in the mold, a controllable supply of the conditioning fluid, and a controller for automatically initiating flow of the conditioning fluid through the fluid circuit in response to an initiation temperature and for automatically terminating flow of the conditioning fluid through the fluid circuit in response to a termination temperature. 
     Various advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional schematic of a mold temperature control system according to the invention. 
     FIG. 2 is a plan schematic of a mold temperature control system according to the invention. 
     FIG. 3 is a plan schematic of a zone temperature control system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Terms indicating direction may be used in this application. For example, the terms “upper,” “lower,” and “side”, may be used for the purpose of facilitating discussion of the figures under discussion and are not a limitation on the invention or the use or orientation of the invention. Referring now to the figures, a mold temperature control system, indicated generally at  12 , is illustrated in accordance with the present invention. Although this invention will be described and illustrated in conjunction with the particular mold disclosed herein, it will be appreciated that this invention may be used in conjunction with other molds. The general structure and operation of the mold is conventional in the art. Thus, only those portions of the mold which are necessary for a full understanding of this invention will be explained and illustrated in detail. In the illustrated embodiment, the mold temperature control system  12  includes a mold  16 , at least one fluid circuit  20   a-f , and at least one temperature sensor  24   a-e . 
     The illustrated mold  16  includes a first mold section  28  and a second mold section  32 . The mold  16  may include any suitable number of mold sections. For the illustrated mold  16 , the first mold section  28  and the second mold section  32  are positioned to meet at a part line  36  when the mold  16  is in a closed position, as illustrated. The first mold section  28  and the second mold section  32  cooperate to define a cavity  40 . The illustrated cavity  40  is in the general shape of a wheel. The wheel is a cast article  44 . It should be understood that the mold temperature control system  12  may be used to manufacture other types of the cast article  44  in addition to the wheel and is not limited to the manufacture of wheels. The illustrated first mold section  28  includes an upper surface  48  and a lower surface  52 . The illustrated second mold section  32  includes an upper surface  56  and a lower surface  60 . The illustrated first mold section  28  includes side surfaces  64 ,  68 ,  72 . The illustrated second mold section  32  includes side surfaces  76 ,  80 ,  84 . It will be appreciated that the side surfaces  64 ,  68 ,  72 ,  76 ,  80 ,  84  are external surfaces of the mold  16 . Likewise, the surfaces  48 ,  52 ,  56  and  60  are external surfaces of the mold  16 . 
     The illustrated mold temperature control system  12  includes six fluid circuits  20   a-f , although any suitable number of the fluid circuits may be employed. It should be noted that the fluid circuits  20   a-f  may be positioned within the mold temperature control system  12  other than as illustrated. The type, number and positioning of the fluid circuits can vary with a number of factors, including but not limited to the configuration of the mold  16 , the cavity  40  and the cast article  44  to be produced. FIGS. 1 and 2 illustrate one potential positioning of the fluid circuits. The fluid circuits may be of the bubbler type or of the galley type, for example. Depending upon the needs of a particular application (e.g., temperature profiles desired in a particular mold), the conditioning fluid may be either cooled or heated in order to control the temperature of mold  16 . Different temperature zones within the mold can also be established with different controlled temperatures to assist in directional solidification, and with selective application of heating or cooling fluid within different zones. 
     It will be appreciated that the fluid circuit  20   a  is positioned for fluid flow between the upper surface  48  of the first mold section  28  and the upper surface  56  of the second mold section  32 , although the fluid circuit  20   a  need not be so positioned. For example, the fluid circuit  20   a  might be positioned for fluid flow between two portions of the upper surface  48  of the first mold section  28  or two portions of the upper surface  56  of the second mold section  32 . It will also be appreciated that the fluid circuit  20   b  is positioned for fluid flow between the lower surface  52  of the first mold section  28  and the lower surface  60  of the second mold section  32 , although the fluid circuit  20   b  need not be so positioned. For example, the fluid circuit  20   b  might be positioned for fluid flow between two portions of the lower surface  52  of the first mold section  28  or two portions of the lower surface  60  of the second mold section  32 . 
     It will be appreciated that the fluid circuit  20   c  is positioned for fluid flow between the side surface  64  and the side surface  68  of the first mold section  28 . It will also be appreciated that the fluid circuit  20   d  is positioned for fluid flow between the side surface  72  and the side surface  68  of the first mold section  28 . It will be appreciated that the fluid circuit  20   e  is positioned for fluid flow between the side surface  84  and the side surface  80  of the second mold section  32 . It will also be appreciated that the fluid circuit  20   f  is positioned for fluid flow between the side surface  76  and the side surface  80  of the second mold section  32 . The illustrated positioning of the fluid circuits is not intended to be limiting on the invention, but merely illustrative of one possible positioning of the fluid circuits. 
     The fluid circuits  20   a-f  preferably include first openings  88   a-f . The fluid circuits  20   a-f  also preferably include second openings  92   a-f  . The first openings  88   a-f  may be fluid inlets or fluid outlets as desired. The second openings  92   a-f  may also be fluid inlets or fluid outlets as desired. The first openings  88   a-f  and the second openings  92   a-f  permit fluid flow. A pump  104  may be employed to distribute a conditioning fluid through the fluid circuits  20   a-f . The conditioning fluid may be any suitable fluid, such as for example water, oil, liquid or the like. The conditioning fluid may be also be any suitable gas. The conditioning fluid may be also be any suitable solid having fluidic characteristics. The conditioning fluid may move through the fluid circuits  20   a-f  from the first openings  88   a-f  to the second openings  92   a-f , as indicated by the arrows  96   a-f . The conditioning fluid may also move through the fluid circuits  20   a-f  from the second openings  92   a-f  to the first openings  88   a-f , as indicated by the arrows  96   a-f . Any fluid circuits may be positioned for fluid communication with any other one or more fluid circuits. The fluid circuits distribute a flow of the conditioning fluid. Although the illustrated fluid circuits  20   a-f  are generally arc shaped, they may include one or more straight portions, serpentine portions or may have any other suitable shape. 
     The mold temperature control system  12  may include any suitable number of the one or more temperature sensors  24   a-e . The temperature sensor may be a thermocouple, a resistance temperature device (RTDs), a thermistor, an infrared thermometer or the like. The temperature sensor is preferably a K-type thermocouple. In a preferred embodiment, one or more of the temperature sensor generates a signal representative of the temperature at respective locations within the mold  16 . For purposes of clarity, the mold temperature control system  12  will be discussed concerning an embodiment which includes five temperature sensors  24   a-e . The type, number and positioning of the temperature sensors can vary with a number of factors, including but not limited to the configuration of the mold  16 , the cavity  40  and the cast article  44  to be produced. FIGS. 1 and 2 illustrate one potential positioning of the temperature sensors  24   a-e . 
     Various positions for the temperature sensors are contemplated with the mold temperature control system  12 . It will be noted that the temperature sensors  24   a ,  24   c ,  24   e  may be positioned between an external surface of the mold  16  and one or more fluid circuits  20   a-f  of the mold  16 . It will also be noted that the temperature sensor  24   d  may be positioned between one or more of the external surfaces of the mold  16  and the cavity  40  of the mold  16 . It will likewise be noted that the temperature sensor  24   b  may be positioned between the cavity  40  of the mold  16  and one or more fluid circuits  20   a-f  of the mold  16 . In a preferred embodiment, the temperature sensors are spaced apart from one or more of the external surfaces of the mold  16  by a distance within the range of from about 17 mm to about 21 mm, more preferably a distance of about 19 mm. Likewise, in a preferred embodiment the temperature sensors are spaced apart from the one or more fluid circuits  20   a-f  by a distance within the range of from about 17 mm to about 21 mm, more preferably a distance of about 19 mm. Similarly, in a preferred embodiment the temperature sensors are spaced apart from the cavity  40  by a distance within the range of from about 17 mm to about 21 mm, more preferably a distance of about 19 mm. 
     Due to the spacing of a temperature sensor from a mold surface heated by molten metal and a fluid circuit cooled by the fluid, temperature changes at those surfaces are not sensed until after a time lag of up to about 10 seconds. A highly preferred location for one or more temperature sensors is a location approximately equidistant between the cavity  40  and a fluid circuit  20 , such that the temperature sensor is equally affected by such temperature changes. 
     The mold temperature control system  12  may include a controller  100 . In a preferred embodiment, the controller  100  is operative to detect when a portion of the mold  16  reaches an initiation temperature and a termination temperature. The initiation temperature and the termination temperature are temperatures that are approximately proportional to the signal representative of the temperature in the mold  16  being generated by one or more of the temperature sensors  24   a-e  . The initiation temperature is a predetermined temperature at which the conditioning fluid preferably begins to flow through at least one of the fluid circuits  20   a-f . It should be noted that each of the fluid circuits  20   a-f  may be positioned to coincide with the same or a different initiation temperature. The termination temperature is a predetermined temperature at which the conditioning fluid preferably ceases to flow through at least one of the fluid circuits  20   a-f . It should be noted that each of the fluid circuits  20   a-f  may be positioned to coincide with the same or a different termination temperature. 
     It should be noted that each of the temperature sensors  24   a-e  may be positioned to coincide with the same or a different initiation temperature. Likewise, it should be noted that each of the temperature sensors  24   a-e  may be positioned to coincide with the same or a different termination temperature. It will be appreciated that at least one of the temperature sensors  24   a-e  preferably generates a signal representative of the initiation temperature. Likewise, it will be appreciated that at least one of the temperature sensors  24   a-e  preferably generates a signal representative of the termination temperature. 
     The temperature sensor is operative to cooperate with the fluid circuits to provide cooling of the mold  16 . Likewise, the temperature sensor is operative to cooperate with the fluid circuits to control directional solidification of the cast article  44 . Further, the temperature sensor is operative to cooperate with the fluid circuits to bring the mold  16  to an acceptable temperature for the addition of the molten metal to the cavity  40 . 
     The controller  100  is preferably operatively connected to a pump  104  and a motor  108 . The pump  104  and the motor  108  are operative to provide the conditioning fluid to the fluid circuits  20   a-f  in the mold  16 . One or more automatically-controlled valves may also be provided that can be adjusted by controller  100  in order to direct fluid flow to individual fluid circuits. In operation of a preferred embodiment, the signal representative of a temperature in the mold  16  controls the flow of the conditioning fluid in one or more of the fluid circuits  20   a-f . Thus, when the initiation temperature is achieved, the conditioning fluid begins to flows through one or more of the fluid circuits  20   a-f  in the mold  16 . Likewise, when the termination temperature is achieved, the conditioning fluid ceases to flow through one or more of the fluid circuits  20   a-f  in the mold  16 . The controller  100  may also be employed to synchronize the flow of the conditioning fluid through the one or more of fluid circuits  20   a-f . 
     FIG. 3 shows an embodiment of the invention wherein automatically-controlled valves  110  selectively direct conditioning fluid to respective temperature zones established within the mold. Each zone  112 ,  114 ,  116 ,  118 , and  120  has a respective fluid circuit and a respective thermocouple. Each zone has a respective initiation and termination temperature used by controller  100  to maintain each temperature zone within a desired temperature range. Controller  100  separately controls each individual cooling/heating circuit by individually adjusting (e.g., turning on and off) each respective valve  110 . The temperature ranges in each zone may change at different times within a manufacturing cycle (e.g., one temperature range used during article solidification and another temperature range used during mold preparation for molten metal pouring). Furthermore, different zones may be controlled at different temperatures simultaneously to provide a desired temperature profile. During solidification of a cast article in cavity  40 , for example, the preferred directional solidification takes place so that solidification at portions within cavity  40  that are the most remote from stalk tube  41  occurs first. Thus, zones  112  and  116  are controlled to a lower temperature than zone  114 , for example. The configuration of cooling/heating zones can be adapted to each specific mold design and can achieve substantially any desired directional solidification pattern. Since a respective temperature sensor is used to control each respective zone created in the mold by the respective fluid circuits, a controlled temperature environment is provided so that consistently high quality cast articles can be produced with optimum cycle times. 
     The principle and mode of operation of this invention have been described in its preferred embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope.