Abstract:
A method of controlling a molding system for fabricating a molded article from a settable mixture includes the steps of priming several discharge containers with different components of the settable mixture and evacuating the discharge containers through a conduit into a mixing head. The mixing head combines the components to form the settable mixture that is then injected into the mold. During the priming step, pressure within each of the discharge containers is monitored to detect air being drawn into the system. Pressure of the settable mixture is monitored at the mixing head and at the mold tool to detect any blockages that can cause damaging pressure fluctuations. To prevent built up of residual settable mixture within the settable mixture, all parts of the system that contact the settable mixture are flushed with a solvent and then air-dried to rid the system of the solvent.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a method of controlling a molding system for fabricating a molded article from a settable mixture.  
           [0002]    Many methods of fabricating molded articles include the mixing of at least two fluid materials to form a settable mixture that is discharged into a mold tool. The fluid materials typically include at least two reactive components that harden when mixed. Typically, the settable mixture is injected into the mold tool at a high pressure such that little residual settable mixture remains within the conduits to the mold tool. However, in a low pressure molding system where the settable mixture is not injected at high pressures, a greater amount of settable mixture may remain in the conduits to the mold tool. Residual settable mixture will harden over time and may cause undesirable blockages within the conduits to the mold tool. Such blockages may result in higher pressure within the molding system. The higher pressure can cause damage to the molding system if not properly monitored and diagnosed.  
           [0003]    Accordingly, it is desirable to develop a method of controlling a molding system that can expel residual settable mixture to prevent blockages, and sense pressure build ups to prevent damage to the molding system.  
         SUMMARY OF THE INVENTION  
         [0004]    An embodiment of this invention discloses a method of controlling a low pressure molding system to prevent residual build up and detect pressure fluctuations within the molding system.  
           [0005]    The molding system includes a mold tool supported by a structure, a material delivery system, and material storage containers. Components stored within the material storage containers combine to form a settable mixture that is injected into a cavity of the mold tool to form a molded article. The material delivery system includes at least one discharge container for each component. Each discharge container includes a piston connected by a shaft to a plenum. A drive cylinder drives the plenum vertically. A position sensor is disposed on the plenum to monitor the relative position of the plenum during operation of the material delivery system. Each of the discharge containers is in communication with a material storage container, and the mixing head. An inlet valve and an outlet valve are disposed at each discharge container to control flow of components into and out of each discharge container. Components from the material discharge containers are directed through a conduit to the mixing head. Each of the components travels through a separate conduit to metering valves disposed within the mixing head. The metering valves control the flow of components into the mixing head to maintain a predetermined ratio required to form the settable mixture.  
           [0006]    The mixing head includes an air inlet valve and a solvent inlet valve to control flow of air and solvent used to flush and dry the conduit of the molding system exposed to the settable mixture. Settable mixture that hardens within the mixing head or the conduit to the mold tool may partially block the passage to cause increased pressure with the molding system. Dramatic increases in pressure may cause damage to the molding system, and it is therefore desirable to take precautions to prevent such a blockage. A mold valve is disposed at the mold tool to control the flow of settable mixture into the mold tool. Further, the mold valve includes a setting to vent air pressure supplied to the mix head.  
           [0007]    Pressure of the components and the settable mixture are monitored to safeguard the molding system from undesirable pressure fluctuations. As such, various pressure sensors are disposed throughout the molding system to monitor pressure at different stages of the molding process.  
           [0008]    A first step in the method of molding includes the step of priming each of the discharge containers. The plenum raises upward to move the pistons upward, thereby drawing a specific quantity of component into each discharge container. As the plenum rises, a pressure sensor monitors the pressure inside each of the containers such that the controller may compare the pressure within the discharge containers with a prime pressure value. Deviation from the prime pressure value indicates that air is being drawn into the discharge container. If air is being drawn into the discharge cylinder the molding cycle will be shut down to prevent damage to the system.  
           [0009]    The next step of the method is the injection step and includes actuation of an injection timer. The injection timer sequentially initiates operation of the inlet and outlet valves, the mixing head and the mold valve at specified time values. A first time value signals actuation of the inlet and outlet valves to close the inlet valves and open the outlet valves. A second time value signals actuation of the motor of the mixing head. A third time value signals actuation of the metering valves of the mixing head and starts the plenum downward to expel the components into the mixing head.  
           [0010]    The plenum moves downwardly until reaching a predetermined empty position as indicated by the position sensor. Pressure within the mixing head, the conduit and the mold cavity is monitored to detect pressure fluctuations indicative of a blockage. Pressure detected above a predetermined threshold will cause a controller to shut down the molding system until corrective action can be taken to prevent damage to the molding system.  
           [0011]    During any mold cycle, a quantity of settable mixture remains within the mixing head, the conduit and the mold valve and must be removed before hardening and forming a blockage. A flush cycle includes flowing solvent through the mixing head through to the mold valve and out of the molding system. The flow of solvent is for a predetermined time calculated to fully rid the molding system of residual settable mixture in preparation for the next molding cycle. The solvent is evacuated by a blast of pressurized air introducing into the mixing head.  
           [0012]    The method of this invention prevents damage to a low pressure molding system by monitoring pressure fluctuations and by flushing residual settable mixture from the system after every molding cycle to prevent damage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0014]    [0014]FIG. 1 is a schematic view of the molding system;  
         [0015]    [0015]FIG. 2 is a schematic view of the material delivery system; and  
         [0016]    [0016]FIG. 3 a flow chart illustrating the method steps of this invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring to FIGS. 1 and 2, a disclosed embodiment of this invention is a method of controlling a molding system  10  including a mold tool  12  supported by a structure  18 . The molding system  10  includes a material delivery system  20  in communication with material storage containers  24 ,  26 , and  28 , a mixing head  64  in communication with the material delivery system  20  and a controller  86 . Components stored with the material storage containers  24 ,  26 , and  28  combine to form a settable mixture that is injected into a cavity  14  of the mold tool  12  to form a molded article  16 . The molded article illustrated is a bath tub, however it is within the contemplation of this invention to fabricate any type of molded article with this method.  
         [0018]    The material delivery system  20  includes at least one discharge container for each component. Preferably, the delivery system includes three discharge containers  36 , 38 , and  40 , each of which draws a component of the settable mixture from each one of the material storage containers  24 ,  26 , and  28 . Each discharge container  36 ,  38  and  40 , includes a piston  58  connected by a shaft  59  to a plenum  54 , best shown in FIG. 2. The plenum  54  is driven vertically by a drive cylinder  56 . The drive cylinder  56  is preferably a hydraulically actuated cylinder controlled to drive the plenum  54  upward and downward, thereby driving the attached pistons  58  upward and downward. Although a hydraulic cylinder is illustrated in the preferred embodiment, it is within the contemplation of this invention to use any type of drive as known by one skilled in the art.  
         [0019]    A position sensor  62  is disposed on the plenum  54  to monitor the relative position of the plenum  54  during operation of the material delivery system  20 . The position sensor  62  may be of any type known to one skilled in the art. The position sensor  62  is in communication with the controller  86  such that the controller  86  controls movement of the plenum  54  by way of the drive cylinder  56 . Further, proximity sensors  60  are positioned to sense when the plenum  54  has reached extreme limits of horizontal travel. The proximity sensors  60  are also in communication with the controller  86 .  
         [0020]    The controller  86  is in communication with the material deliver system  20 , the mixing head  64  and the mold tool  12  to control and monitor the entire molding process. Lines  87  schematically illustrate the communication between the controller  86 , the material delivery system  20 , the mixing head  64  and the mold tool  12 .  
         [0021]    Each of the discharge containers  36 , 38  and  40  is in communication with a material storage container  24 ,  26 , and  28  and the mixing head  64 . Preferably, flexible hoses communicate components with each of the discharge containers  36 , 38  and  40 . An inlet valve  48 , 50  and  52  and an outlet valve  42 ,  44 , and  46  are disposed at each discharge container  36 , 38  and  40  to control flow of components into and out of each discharge container  36 , 38  and  40 . Each of the valves  42 - 52  actuate in response to signals from a controller  86 . The inlet and outlet valves  42 - 52  along with the controller  86  are of any type as known to one skilled in the art.  
         [0022]    Components from the discharge containers  36 , 38 , and  40  are directed through a conduit to the mixing head  64 . Each of the components travels through a separate conduit to the mixing head  64 . As should be appreciated, each of the conduits may be a flexible hose, pipe, or any other type of conduit known to one skilled in the art for transporting a fluid medium. Metering valve  68 , 70 , and  72  control the quantity of component that flows into the mixing head  64  to maintain a predetermined relationship between each of the components such that the components are properly combined to form the settable mixture.  
         [0023]    The mixing head  64  includes a mixing device  67  driven by a motor  66 . The specific configuration of the mixing head  64  is best described in pending application Ser. No. 09/662,662 titled “Mix Head Assembly for a Molding Material Delivery System” herein incorporated by reference. Although preferably, the mixing head  64  is as disclosed in the described pending application, a worker knowledgeable in the art will understand that the method of this invention can be applied with mixing heads of differing configurations.  
         [0024]    The mixing head  64  includes an air inlet valve  81  and a solvent inlet valve  74  to control flow of air and solvent used to flush and dry components of the molding system  10  exposed to the settable mixture. As appreciated, once the components of the settable mixture are combined, a curing process is initiated that acts to harden the settable mixture to form the molded article  16 . Residual settable mixture remaining within the mixing head  64  along with the conduit  65  from the mixing head  64  to the mold tool  12  may also harden. Settable mixture that hardens within the mixing head  64  or the conduit to the mold tool  12  may block the passage to cause increased pressure with the molding system  10 . Dramatic increases in pressure may cause damage to the molding system  10 , and it is therefore desirable to take precautions to prevent such a blockage.  
         [0025]    The settable mixture evacuated from the mixing head  64  travels through the conduit  65  to a mold valve  84 . The mold valve  84  is disposed at the mold tool  12  to control the flow of settable mixture into the mold tool  12  such that settable mixture does not escape from inside the cavity  14  of the mold tool  12 , and also to control the amount of settable mixture injected into the mold cavity  14 . The mold valve  84  further includes an outlet leading back to a solvent supply  76 . The mold valve  84  includes a setting within which settable mixture is allowed into the mold cavity  14 , another setting closes off flow to the mold cavity  14 , and another setting allowing the flow of solvent out of the conduit  65 . Further, the mold valve  84  includes a setting to vent air pressure supplied to the mix head  64 . Air pressure from an air supply  80  is introduced into the mixing head  64  and conduit to dry and expel any remaining solvent to prevent contamination of the settable mixture during molding operations.  
         [0026]    Pressure of the components and the settable mixture are monitored to safeguard the molding system  10  from undesirable pressure fluctuations. Various pressure sensor are disposed throughout the molding system  10  to monitor pressure at different stages of the molding process. The material delivery system  20  includes pressure sensors  22  to measure pressure within each of the discharge containers  36 , 38 , and  40  as component is drawn from the material supply containers  24 ,  26  and  28 . The mixing head  64 , the conduit  65  and the mold tool  12  include pressure sensors  82  to monitor pressure during injection of the settable mixture into the mold tool  12 .  
         [0027]    Referring to FIG. 3, a flow chart of a process according to the present invention includes the first step of priming each of the discharge containers  36 ,  38 , and  40  as indicated at  90 . The priming step  90  includes the sub steps of opening each of the inlet valves  48 , 50 , 52  and closing each of the outlet valves  42 , 44 , and  46 . This configuration of the inlet and outlet valves is the prime position indicated at  91 .  
         [0028]    The plenum  54  is then raised upward to draw the pistons  58  upward, thereby drawing a specific quantity of component into each discharge container  36 ,  38 , and  40   40 . Note that each discharge container  36 ,  38  and  40  is of a predetermined size such that the size relationship between each of the discharge containers  36 , 38  and  40  provides the ratio of components required to form the settable mixture. Further, although three discharge containers are shown in this embodiment, it is within the contemplation of this invention that several discharge containers may contain the same component to provide the correct ratio to form the settable mixture.  
         [0029]    As the plenum  54  raises, the pressure sensors  22  monitors the pressure inside each of the containers such that the controller  86  may compare the pressure within the discharge containers  36 , 38 , and  40  with a prime pressure value. The prime pressure value is a value that represents optimal filling of the discharge containers  36 , 38 , and  40 . Deviation from the prime pressure value indicates that air is being sucked into the discharge container  36 , 38 , and  40 , and will cause a stoppage of the molding system  10 . As appreciated, air above a predetermined pressure within one of the discharge containers  36 , 38 , and  40  disrupts the proper mixing of components, and may also cause undesirable pressure fluctuations within the molding system  10 .  
         [0030]    The plenum  54  is raised until reaching a filled position as indicated by the position sensor  62 . Further, if the top limit proximity sensor  60  is tripped this will also cause the plenum  54  to stop. Once the plenum  54  has reached the filled position, each of the discharge containers  36 ,  38  and  40  contain the predetermined amount of component. The molding system then moves to the injection step as indicated at  92 .  
         [0031]    The controller  86  initiates the beginning of an injection timer  85 . The injection timer  85  is used to sequentially initiate operation of the inlet and outlet valves  42 - 52 , the mixing head  64  and the mold valve  84 . These times include a start delay to allow the inlet and outlet valves to shift to a injection position and to allow the motor  66  of the mixing head  64  to reach a predetermined level of operation.  
         [0032]    A first time value, T1 (indicated at  94 ) signals actuation of the inlet and outlet valves  42 - 52  to close the inlet valves  48 - 52  and open the outlet valves  42 - 46 . A second time value, T2 (indicated at  96 ), signals actuation of the motor  66  of the mixing head  64 . A third time value, T3 (indicated at  98 ), signals actuation of the metering valves  68 , 70 , and  72  of the mixing head  64 . The plenum  54  starts downward to expel each of the components to the mixing head  64 . During movement of the plenum  54  and flow of component material to the mixing head  64 , the metering valves  68 ,  70  and  72  open proportionally to balance incoming flow of component material to ensure that the relationship is correct to form the settable mixture.  
         [0033]    The specific ratio of component material used to form the settable mixture is provided for by the sizing of the discharge containers  36 , 38 , and  40  in relation to each other. The metering valves  68 ,  70  and  72  provide a second means of providing the proper quantity of component material to form the settable mixture. As should be appreciated, as the component materials are flowing to the mixing head  64 , instances may occur where the proper ratio of component material is improper to form the settable mixture. The metering valves  68 , 70  and  72  control the flow of component material such that all times during he combination and mixing a proper ratio of component material is present within the mixing head  64 .  
         [0034]    The plenum  54  moves downwardly until reaching a predetermined empty position as indicated by the position sensor  62 . The lower proximity switch  60  will signal the controller  86  to stop downward movement if the plenum  54  does not stop in response to signals from the position sensor  62 .  
         [0035]    During the injection cycle, components are mixed to form the settable mixture by the mixing head  64  and further injected through the conduit  65  and mold valve  84  into the mold cavity  14 . Pressure within the mixing head  64 , the conduit  65  and the mold cavity  14  is monitored to detect pressure fluctuations that would indicate a blockage. As discussed above, a blockage in the conduit  65  may cause damage to the molding system  10 . For that reason, a pressure detected above a predetermined threshold will cause the controller  86  to shut down the molding system  10 .  
         [0036]    During a normal molding cycle settable mixture is injected into the mold cavity  14  and the mold valve  84  closed. A quantity of component material will remain in the conduit  65  between the mixing head  64  and the material delivery system  20 . The component material in these conduits is not mixed and therefore does not immediately harden and can remain within each of the conduits until the next molding cycle. Settable mixture remains within the mixing head  64 , the conduit  65  and the mold valve  84  and must be removed before hardening to prevent a blockage.  
         [0037]    The flush cycle (indicated at  100 ) proceeds by closing the mold valve  84  to isolate the mold cavity  14  and allow flow of solvent. The mixer head  64  solvent valve  74  is opened and solvent flows through the mixing head  64 , the conduit  65 , and the mold valve  84  to evacuate any residual settable mixture. The flow of solvent is for a predetermined time calculated to fully rid the molding system  10  of residual settable mixture in preparation for the next molding cycle. After the solvent has flowed for a predetermined time, the solvent itself must also be evacuated from the mixing head  64 , the conduit  65  and the mold valve  85 , because the solvent may contaminate the settable mixture during subsequent molding cycles. For this reason, pressurized air is introduced into the mixing head  64  to drive out any remaining solvent from the mixing head  64 , the conduit  65  and the mold valve  84 . Again air is flowed from the mixing head to the mold valve  84  for a predetermine amount of time calculated to remove all remnants of solvent in preparation for the next molding cycle.  
         [0038]    The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason, the following claims should be studied to determine the true scope and content of this invention.