Abstract:
The injection molding machine has an extruder for providing molding material, a cavity for retaining the molding material prior to injection into a mold, a plunger within the cavity to move the material out of the cavity, and a check valve. The check valve has separate means to permit the material to flow from the extruder to the cavity and from the cavity to an adjacent mold. By having separate flow channels for molding and recharging, the injection molding machine may be recharged on the fly.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed to an apparatus for injection molding. More specifically, the disclosed apparatus allows for reduced injection cycle time when injecting rubber.  
         BACKGROUND OF THE INVENTION  
         [0002]    Injection molding presses for injecting molding materials into molds are well known in the manufacturing industry. Molding materials such as rubber composites must typically be cured within their molds under specific temperature and pressure conditions. Prior to the injection of molding material into the mold, the injection press clamps the mold so that the mold is under pressure during the injection operation.  
           [0003]    The time required for each molding cycle may be six minutes or more. A molding cycle typically includes the steps of clamping the mold, injecting material into the mold, holding the mold in a clamped condition with the injection nozzle still contacting the mold to initiate curing, and recharging the injection unit with material. Such molding cycle times are required, since the molds must remain under pressure within the press to complete the injection operation, initiate curing, and recharge the injection unit with molding material for the next cycle. Recharging of the unit with material occurs during this time in order to prevent any loss of material from the unit and so that when the next mold is presented to the unit for filling, filling may be immediately begin.  
           [0004]    U.S. Pat. No. 5,286,186 discloses an apparatus for injection molding rubber. The apparatus has both a check valve to prevent molding material from passing back into the extruder during injection of the material and a separate shut-off valve to prevent molding material from passing to the injection nozzle during recharging of the internal cavity. The check valve and the shut-off valve do not operate together such that when one is activated the other is automatically operated and material may still pass through one of the valves when not desired.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a new and improved apparatus for performing a molding process. The apparatus is designed to increase the number of molds processed in a specific time period by permitting recharging of the injection molding machine on the fly.  
           [0006]    The injection molding machine has an extruder for providing molding material, a cavity for retaining the molding material prior to injection into a mold, a plunger within the cavity to move the material out of the cavity, and a check valve. The check valve has separate means to permit the material to flow from the extruder to the cavity and from the cavity to an adjacent mold.  
           [0007]    The check valve has an injection outlet port to permit flow from the cavity to an injection nozzle and a transfer column to permit flow from the extruder to the cavity. The injection outlet port and the transfer column are spaced from one another.  
           [0008]    Movement of the check valve from a recharging position to an injecting position is activated by a hydraulic cylinder. The check valve is moved axially along its centerline to move the valve from an injecting position to a recharging position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The invention will be described by way of example and with reference to the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is a cross sectional view of the injection apparatus;  
         [0011]    [0011]FIG. 2 is a cross sectional view of the injection apparatus;  
         [0012]    [0012]FIG. 3 is a cross sectional view of the check valve; and  
         [0013]    [0013]FIG. 4 is a perspective view of the injection apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    An injection apparatus  10  in accordance with the present invention is illustrated in FIGS. 1, 2, and  4 . The injector  10  has an internal cavity  12  with a plunger  14  to which a charge of molding material is supplied by the extruder  16 . Once the internal cavity  12  is filled with material, the plunger  14  is activated to inject the material into an adjacent mold (not shown). To conserve space, the cavity  12  and the extruder  16  are located adjacent to one another, with the extruder  16  inclined at a low angle relative to the cavity  12  to reduce the distance between the exit port  18  of the extruder and the opening of the cavity  20 .  
         [0015]    The extruder  16  includes a barrel  22  with a single extruder screw  24  located within the barrel  22 . An opening (not shown) is provided in the extruder barrel  22  for feeding strips of molding material into the barrel  22 . Preferably, the molding material is rubber. The extruder screw  24  is driven by a reciprocating motor  26 . Since heat is generated within the barrel  22  by mastication of the molding material, coolant flow is provided about the barrel  22  in a coolant flow area  28 . The desired temperature is maintained by a thermal jacket  30  and monitored by thermocouplings located about the barrel  22 .  
         [0016]    The internal cavity  12  is located within a housing  32 . After the cavity  12  is filled with material, the material is pushed out of the cavity  12  by the plunger  14  and to the nozzle  34 . The nozzle  34 , at that time, is engaged in a sealing relationship with a sprue opening of a mold. To maintain the desired temperature in the internal cavity  12 , cooling jacket  36  is provided about the cavity housing  32  and coolant is provided similar to the extruder.  
         [0017]    Connecting the extruder  16  and the internal cavity  12  and connecting the internal cavity  12  and the nozzle  34  is the check valve  40 . The check valve  40  has a block configuration, see FIG. 3. The check valve  40  has an injection outlet port  42  and a transfer column  44 . The injection outlet port  42  permits material to flow from the internal cavity  12  to the nozzle  34  and the transfer column  44  permits material to flow from the extruder  16  to the cavity  12 .  
         [0018]    The injection outlet port  42  is located at one end of the check valve  40 . The injection outlet port  42  has an internal diameter D v  equivalent to the diameter D I  of the nozzle tube  46 . If desired, for the purpose of altering the material flow pressure, the port diameter D v  may be greater than the diameter D I  of the nozzle tube  46 . When aligned for use, the injection outlet port  42  connects the nozzle  34  to the internal cavity  12  to allow the molding material to pass from the cavity  12  to the nozzle  34  and into a mold.  
         [0019]    Distanced from the injection outlet port  42  is the transfer column  44 . The transfer column  44  connects the extruder  16  and the cavity  12 , permitting material to flow from the extruder  16  to the cavity  12  when the injector  10  is being recharged with molding material. The column  44  has an entrance port  48  and an exit port  50 . When aligned for use, the entrance port  48  connects to the extruder  16  and the exit port  50  connects to the internal cavity  12 . The illustrated column is shown with two bends  52  in the column. For material flow purposes, any bends  52  in the column  44  are preferably constructed to reduce material build up in the bends  52  and the creation of dead zones.  
         [0020]    Below the check valve  40  is a hydraulic cylinder  54  for moving the check valve  40  between the injection and the recharging position. The hydraulic cylinder  54  has a position sensor for indicating what position the cylinder  54  is in, and thus, what position the check valve  40  is in. The check-valve  40  is in injection position when the injection outlet port  42  is aligned with the nozzle  34  and the internal cavity  12 , as seen in FIG. 1.  
         [0021]    The check valve  40  is in recharging position when the transfer column  44  permits the flow of material from the extruder  16  to the cavity  12 , as seen in FIG. 2.  
         [0022]    As noted, the check valve  40  has a block configuration. The configuration may have an overall circular, square, triangular, or polygonal shape. When the check valve  40  is formed in a non-circular block configuration, it reduces any accidental or incidental radial rotation of the check valve  40  within the apparatus, reducing the possibility of misalignment of the injection outlet port  42  and the transfer column  44 .  
         [0023]    The main portion of the transfer column  44 , and the associated portion of the hydraulic cylinder  54 , is illustrated as axially off-center in the check valve  40 . By axially offsetting the column  44 , rotation of the check valve  40  is precluded and prevents misalignment of the check valve  40 . If the configuration of the check valve  40  is non-circular, than the transfer column  44  may also be located along the central axis of the block and rotation of the check valve  40  is precluded by the check valve configuration. Other means of preventing radial rotation of the check valve  40  may be used in addition to or instead of these specific means.  
         [0024]    Operation of the apparatus occurs in the following manner. The hydraulic cylinder  54  is activated to move the transfer column  44  to the recharging position, as seen in FIG. 2. Molding material has been feed into the extruder screw  24 . The material is masticated and conditioned by the screw  24 . The material flows from the screw  24  into the column  44  and then into the internal cavity  12 . As the material flows into the cavity  12 , the plunger  14  is pushed back by the material to a position so that the volume in the cavity  12  is approximately equivalent to the volume of rubber to be injected into the mold.  
         [0025]    After the required volume of material is in the internal cavity  12 , the hydraulic cylinder  54  is activated to move the check valve  40  into the injecting position, as seen in FIG. 1. The plunger  14  is then moved forward to shoot the material into the injection outlet port  42  and then into the nozzle  34 . At this time, the nozzle  34  is in contact with the mold sprue port, and the material passes from the nozzle  34  into the mold.  
         [0026]    After all of the material is transferred to the mold, the hydraulic cylinder  54  is activated to return the check valve  40  to the recharging position, closing off any means for further material to continue to flow into the mold. Material that has already been prepared by the screw  24  now flows, via the transfer column  44 , to the internal cavity  12 , recharging the injector  10  and preparing for the next molding operation.  
         [0027]    By forming the check valve  40  with two different mechanisms  42 ,  44  for injecting the material into the mold and for recharging the cavity  12 , while the injector  10  is recharging, material cannot flow out of the nozzle  34 , and during molding, excess material cannot flow from the screw  24  and into the nozzle  34 . Because material cannot flow out the injector  10  during recharging, it makes it possible to recharge the injector  10  while “on the fly;” that is, the injector  10  may be recharged as either the injector  10  is moved to the next mold or as a new mold is being positioned adjacent to the injector  10  for filling. The disclosed check valve provides the injector  10  with a consistency and reliability that is not present with conventional check valves and shut-off valves.  
         [0028]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the fill intended scope of the invention as defined by the following appended claims.