Abstract:
An injection valve attached to a mold insert, the injection valve including a valve nose body and the mold insert having a bore for receiving an end of the valve nose body, inserting the valve nose body into the bore of the mold insert and holding in position by means of a releasable locking mechanism.

Description:
PRIOR APPLICATIONS  
       [0001]     This application is a continuation-in-part of International Application No. PCT/GB2004/005178, filed on Dec. 9, 2004, which in turn bases priority on British Application No. 0328467.6, filed on Dec. 9, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     This invention relates to composite production by resin transfer molding.  
         [0004]     2. Description of the Prior Art  
         [0005]     The automation of composite molding production techniques requires control of two basic raw materials, i.e. the resin mix and the fiber pack. Automation of the resin transfer molding process thus involves the control of a two-stage production operation in which the fiber is first loaded into the mold and then, after the mold is closed, resin injection is effected.  
         [0006]     The present invention is concerned with the second stage of the above process and, in particular, with the injection valve that controls the flow of mixed resin into the mold cavity. The injection valve has an inlet port and an outlet port, and it is opened by a control signal from the injection machine so as to allow the resin mix to flow into the mold until a predetermined volume has been injected. Upon completion of the injection cycle, the valve closes isolating the mold from the supply. The valve is then flushed through automatically, ready for the next injection cycle, and the cleaning fluid used for flushing purposes being discharged through a discharge port.  
         [0007]     Installation of the injection valve is typically effected by attaching the outlet or nose of the injection valve to a mold insert fixture and then connecting the nozzle of the injection machine to the inlet port. A form of clamp is typically used to prevent the injection valve becoming separated from the mold insert fixture, the clamp acting on the rear of the injection valve to hold it in place while a seal on the front of the valve seals the valve outlet or nose to the mold fitting.  
         [0008]     It is an object of the present invention to provide improvements in the apparatus and procedures described above.  
         [0009]     A more specific object of the present invention is the provision of an improved method of, and means for, connecting the injection valve to the mold insert fixture.  
         [0010]     A further object of the present invention is the provision of improved sealing means for the injection valve.  
         [0011]     A valve may also be connected to a mold insert fixture for controlling the discharge of resin from a mold, and it is to be understood that, as used herein, the term “injection valve” includes any form of valve which is designed to be connected to a mold insert fixture and which incorporates flow control means.  
       SUMMARY OF THE INVENTION  
       [0012]     According to a first aspect of the present invention, there is provided a method of attaching an injection valve to a mold insert, the injection valve including a valve nose body and the mold insert including a bore for receiving an end of the valve nose body, the method including fitting the end of the valve nose body in the bore of the mold insert by means of a releasable locking mechanism.  
         [0013]     The bore in the mold insert is preferably a stepped bore and the end of the valve nose body preferably includes a peripheral groove to receive a movable element of the locking mechanism.  
         [0014]     The movable element of the locking mechanism may be a U-shaped spring clip, and the mold insert is preferably formed with slots to receive the arms of the U-shaped spring clip.  
         [0015]     The end portion of the nose body may include a chamfered or inclined portion that engages the arms of the U-shaped spring clip to move them away from one another as the end of the nose body is inserted in the bore of the mold insert.  
         [0016]     Possible alternative methods of holding the end of the valve nose body in position include the use of multiple clip fingers entering a plurality of slots, and the use of a cam lock that is rotatable between locking and unlocking positions.  
         [0017]     According to a second aspect of the present invention, there is provided an injection valve that can be used in the method defined above in which the injection valve includes a pneumatic cylinder and a main valve body that has a threaded connection with a valve nose body. The pneumatic cylinder preferably contains a piston having a shaft that, at an end thereof remote from the cylinder, carries a seal. Operation of the piston and cylinder mechanism preferably results in movement of the piston from a position in which the injection valve is closed and the seal is in engagement with an opening in the valve nose body to a position in which the injection valve is closed and the seal is in engagement with an end of a tubular portion of the main valve body.  
         [0018]     The piston is preferably urged by means of a spring into a position in which the injection valve is closed and is movable pneumatically into an open position.  
         [0019]     According to a third aspect of the present invention, there is provided an injection valve that can be used in the method defined above, the valve being operable by means of a piston and cylinder mechanism in which the piston shaft is movable relative to a main valve body and the piston shaft is formed with a groove containing a PTFE sealing ring, and the main valve body included a sleeve that is formed of PTFE and is engaged by the PTFE sealing ring.  
         [0020]     According to a further aspect of the present invention, there is provided an injection valve that can be used in the method defined above in which means are provided for flushing the interior of the valve after a resin injection operation using a cleaning fluid, and in which the cleaning fluid is caused to impinge on the rear of a seal that closed the port through which the resin is injected into the mold. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Further features and advantages of the present invention can be gathered from the following descriptions of the preferred embodiment with reference to the attached drawings, wherein:  
         [0022]      FIG. 1  illustrates a sectional view of an injection valve of the present invention with the valve shown in its open position.  
         [0023]      FIG. 2  illustrates a sectional view of the injection valve of the present invention with the valve in its closed position.  
         [0024]      FIG. 3  illustrates a sectional view connecting the nose of the injection valve to a mold insert.  
         [0025]      FIG. 4  illustrates a sectional view of  FIG. 3  shown at right angles with one form of a clip that can be used for connecting the nose of the injection valve to the mold insert, the clip being in the locked position.  
         [0026]      FIG. 4A  illustrates a sectional view of  FIG. 4  with the clip being in the unlocked position.  
         [0027]      FIG. 5  illustrates a cross-sectional view of the clip of  FIG. 4  shown in its locked position.  
         [0028]      FIG. 5A  illustrates a cross-sectional view of the clip of  FIG. 4  shown in its unlocked position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     The injection valve shown in the drawings includes a pneumatically operated piston  10  having an elongated shaft  11 . The piston  10  has a head  12  acted upon by a spring  13 , and the piston head  12  is contained within a cylinder  14  into which air is introduced by an inlet  15  to displace the piston  10  upwardly from the closed position as shown in  FIG. 2 , and into the open position as shown in  FIG. 1 . At the upper end of the shaft  11  of the piston  10 , there is a colored ring  16  that is readily visible when the valve is in its open position. The position of the colored ring  16  thus provides a visual indication of the open condition of the valve.  
         [0030]     Limit switches may also be provided and, in such case, the shaft  11  will be extended so that it can operate both open and closed limit switches, thus providing remote position sensing.  
         [0031]     The spring  13  provides for automatic closing of the injection valve when the supply of air power to the cylinder  14  is removed. The piston and cylinder mechanism is not double-acting and does not require a separate pilot valve to control its operation.  
         [0032]     The cylinder  14  is typically a compact proprietary air cylinder and enables the dimensions of the valve as a whole to be small such that the valve can be fitted more easily to confined mold rear locations. The entire valve can be about half the size of currently available injection valves.  
         [0033]     The shaft  11  is formed with a groove into which is fitted a sealing ring  17  being of PTFE and arranged for sliding engagement with a PTFE sleeve  18 . The engagement of the sealing ring  17  with the sleeve  18  is such as to prevent the materials used for flushing out the resin mix and for cleaning purposes from passing upwardly into the cylinder  14 .  
         [0034]     This sealing arrangement is superior to those that have previously been employed for this purpose. Previous sealing arrangements have typically included two elastomeric “O” rings with grease filling the space between the two rings. The use of a PTFE sealing ring  17  that engages a PTFE sleeve  18  produces a lower coefficient of sliding friction and ensures that there is no progressive build-up of resin mix on the seal.  
         [0035]     The base  19  of the cylinder  14  forms part of a main valve body  21  that has a downwardly extending threaded boss  22  and fits into a threaded socket of a valve nose body  23 . The threaded connection of the main valve body  21  to the valve nose body  23  permits simple assembly of the components of the injection valve and facilitates disassembly for service purposes. This specific design has practical advantages as compared to existing injection valve designs that include four bolts for attaching the air cylinder to the main valve body and four further bolts for fixing the valve bodies together.  
         [0036]     The valve nose body  23  includes a resin inlet  24  and resin flows, in operation, through the inlet  24  into an annular chamber  25  that surrounds a tubular portion  26  of the main valve body  21 . A seal  27  is provided at the lower end of the shaft  11  and, when the injection valve is in its open position as shown in  FIG. 1 , the seal  27  engages the lower end of the tubular portion  26  to prevent the flow of resin into the interior of the tubular portion  26  while permitting the flow of resin through an opening  28  at the lower end of the valve nose body  23  into the mold cavity.  
         [0037]     After the introduction of the resin mix into the mold cavity has been completed and the flow of resin through the resin inlet  24  has stopped, the injection valve is closed and, under the action of the spring  13  and the seal  27 , is moved from the position shown in  FIG. 1  into the position shown in  FIG. 2  in which it closes the opening  28  leading to the mold cavity. When the valve is closed, a cleaning fluid is introduced into the annular chamber  25  through the resin inlet  24  so as to pass downwardly around the tubular portion  26 , and then upwardly through the interior of the tubular portion  26  to a flush outlet  29  extending from the main valve body  21 . The flow of cleaning fluid is directed over the rear of the main nose seal  27  so as to clean the seal  27  very efficiently and to ensure that there can be no sediment collection afforded by mixed resin against the rear of the seal  27 . This extends the service life of the nose seal as compared to previous nose and seal designs.  
         [0038]     As shown in  FIGS. 1-3 , the resin inlet  24  has its port entry so arranged that the flow of resin is inclined downwardly and at a slight tangent to the outer flow annulus. This provides a spiral feed that aids self-purging as the resin passes to the outlet mold port or when the valve is closed, spirals downwards and then upwards to the drain port or outlet  29 . This increases cleaning efficiency after injection.  
         [0039]     It is to be noted that the valve main seal  27  can be serviced from the mold face without a requirement to remove the valve nose body  23  from the mold  31 . This facility is achieved by unscrewing the main valve body  21  and then holding the seal  27  with a small hexagon slotted fixing screw on the external nose face that centrally clamps the sleeve  18  on the piston shaft  11 . Removal and replacement of the seal  27  involves un-tightening the screw with a hexagon key and sliding the seal off the screw, followed by replacement with a new seal and re-tightening of the screw. Removal and replacement of a seal  27  will take, at most, ninety seconds, and this represents a major service improvement as compared to previous injection valve designs.  
         [0040]     It is also to be noted that the details of the seal  27  and its fixing screw are such that when installed they present a surface that is flush with the end face of the valve nose body  23 , and do not impede the creation of a flush molding surface in the mold cavity at the valve inlet when the injection valve is closed.  
         [0041]     Fitting of the lower end of the valve nose body  23  in a mold insert  30  of a mold  31  is illustrated in  FIG. 3 . The lower end portion of the valve nose body  23  typically has an external diameter of 20 mm, and an adjacent portion  32  of the valve nose body has an external diameter of 25 mm. A peripheral groove  33  (see  FIG. 4 ) is formed in the adjacent portion  32  of the valve nose body  23 . The base of the groove  33  typically has a diameter of 20 mm, and the groove  33  is located 20 mm from the lower face of the valve nose body  23 . The insert  30  is made of metal, has a length of 25 mm, and has a stepped bore with internal diameters of 20 mm and 25 mm. At a rear position of the insert  30  and 20 mm from the lower face of the insert, two horizontal slots  34  are machined in the insert  30 , the slots  34  having a depth of 2 mm and being positioned in register with the peripheral groove  33 .  
         [0042]     When the valve nose body  23  of the injection valve is inserted fully in the stepped bore of the insert  30 , the groove  33  is aligned with the slots  34 . A close-fitting 2 mm, generally U-shaped, spring clip  35  is positioned in the slots  34  and enters the groove  33  so that the clip  35  is positioned in the slots  34 , and enters the groove  33  so that the clip  35  occupies the position shown in  FIG. 4 . The valve nose body  23  is locked releasably in position within the bore of the mold insert  30  by means of the spring clip  35 , which as a base  36  and a pair of arms  37  that extend into turned-in end portions  38 . The base  36  of the spring clip  35  includes a ring portion  39 . To remove the valve nose body  23  from the insert  30 , the user moves the spring clip  35  by engaging the ring portion  39  by means of a suitable tool (not shown) displacing the clip  35  from the closed position shown in  FIG. 4  into the open position shown in  FIG. 4A . The injection valve is then moved upwardly to move the valve nose body  23  from the position shown in  FIG. 5  into the position shown in  FIG. 5A . It is noted that removal of the spring clip  35  is not necessary, but merely to move it from the closed position (see  FIG. 4 ) to the open position (see  FIG. 4A ).  
         [0043]     Engagement of the arms  37  of the U-shaped clip  35  in the groove  33  at positions either side of the axis of the valve nose body  23  ensures that the valve nose body  23 , and the injection valve as a whole, is held securely in engagement with the mold insert  30  and mold  31  by means of a locking mechanism that is able to withstand injection mold pressures well above any that are likely to be experienced in practice.  
         [0044]     As shown in  FIGS. 5 and 5 A, the end portion of the nose body  23  includes a chamfered or inclined portion that engages the arms  37  of the U-shaped spring clip  35  to move them away from one another as the end of the nose body  23  is inserted in the bore of the mold insert  30 , until a position is reached in which the arms  37  of the clip  35  are in register with the groove  33  and move resiliently inwardly into locking engagement in the groove  33 .  
         [0045]     Other possible methods of holding the end of the valve nose body  23  in position within the mold insert  30  include, but are not limited to, the use of multiple clip fingers entering a plurality of slots and the use of a cam lock that is rotatable between locking and unlocking positions.