Abstract:
Improved method and apparatus for injection molding particularly useful with multiple hot runner valve gates to fill a single large mold cavity. A hot runner injection nozzle is provided having a gate through which melt is injected into a mold cavity, and a valve stem is movable on the injection nozzle between an open position permitting flow of melt through the gate and a closed position blocking the flow of melt through the gate. The valve stem is movable to at least one position between the open and closed positions restricting the flow of melt through the valve gate.

Description:
BACKGROUND OF THE INVENTION 
     It is known to employ multiple hot runner valve gates to fill large mold cavities. It is also known to employ sophisticated automatic control for the opening and closing of the multiple valves in sequence in order to optimize the filling and packing of the large mold cavities and in response to cavity pressure sensor signals. The present invention provides a simple, inexpensive and easily utilized improvement particularly useful with such multiple hot runner valve gates for filling such large cavity molds. 
     U.S. Pat. No. 4,420,452 to van Dalen et al. teaches the sequential feeding of resin through a series of hot runner valves to fill a single large cavity mold. The valves are disclosed as being pneumatically, hydraulically or electrically opened and closed in any desired sequence using a process computer, although the details of how the valves are controlled and the design of the valves themselves are not shown. U.S. Pat. No. 5,556,582 to Kazmer teaches two hot runner valve gates, each with servo-hydraulic controlled valve stems that respond to a closed loop control system sensing melt pressure in the mold cavity for filling a single large mold cavity. During molding, the valves are adjusted based on information from the sensor. However, this automatic system is very expensive to build and requires a computer to be programmed to process sensing data in order to provide control signals to the servo controlled valves. 
     Other references teach various ways for mechanically adjusting the closing or opening position of hot runner valve stems in single or multi-cavity molds. U.S. Pat. No. 3,491,408 to Notkins teaches a manually adjustable threaded stop for setting opening position. U.S. Pat. No. 3,252,184 to Ninneman shows a hot runner injection orifice control with adjustable valve stem control for each nozzle feeding its own cavity using spring closing and fluid pressure opening against a preset stop. U.S. Pat. No. 3,561,062 to Goron teaches an injection molding nozzle with a flow-control mechanism within each nozzle employing a rotatable nozzle which can be progressively turned to regulate the flow of resin into the mold cavity. U.S. Pat. Nos. 5,067,893 and 5,141,696 to Osuna-Diaz show injection molding devices having actuation systems for operation of a shut-off valve stem movably mounted in a valve gate employing a worm/gear drive for controlling the valve stem position. U.S. Pat. No. 5,780,077 to von Holdt teaches a worm/gear drive for adjusting a nozzle opening that does not include a valve stem. U.S. Pat. No. 4,330,258 to Gellert shows a mechanical double acting mechanism for actuating valve stems in valve gated injection molding systems. U.S. Pat. No. 4,088,271 to Flygenring shows a still further embodiment for mechanically adjusting the valve stem position. 
     Individual control of multiple hot runner valve gates each supplying its own mold cavity are taught by U.S. Pat. 4,279,582 to Osuna-Diaz which shows a hydraulic system and U.S. Pat. No. 4,592,711 to Capy which teaches a worm/gear method for rotating the nozzle to block the supply channel flow in combination with a two position actuated valve stem for sequentially feeding multiple mold cavities. 
     None of the foregoing mechanical valve stem position control means contemplate a predetermined intermediate settable position for the valve stem wherein the rate of resin flow filling the mold cavity is altered by moving the valve stem to said predetermined intermediate settable position during filling, particularly to restrict the flow of melt through the valve gate. Such a system would be highly desirable. 
     Japanese Patent 62-41851 teaches a rack/gear driven method for driving a valve stem in a coinjection nozzle to one of three positions to select which of the two melt channels can fill the mold cavity. While this reference teaches an intermediate valve stem position, it is for the purpose of blocking or unblocking a second resin supply channel in a coinjection nozzle and it does not contemplate altering the flow rate of a single resin supply channel during the filling process. 
     It is, therefore, the principal object of the present invention to provide an improved injection method and apparatus employing a hot runner injection nozzle having a gate through which melt is injected into a mold cavity. 
     It is a further object of the present invention to provide a method and apparatus as aforesaid which permits the altering of a single melt supply channel during the mold cavity filling process. 
     It is a still further object of the present invention to provide a method and apparatus as aforesaid which is particularly useful with multiple hot runner valve gates to fill single large mold cavities. 
     Further objects and advantages of the present invention will appear hereinbelow. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the foregoing objects and advantages, as well as others to be described hereinbelow, are readily obtained. 
     The injection molding apparatus of the present invention comprises: a hot runner injection nozzle having a valve gate through which melt is injected into a mold cavity; a valve stem movable in said injection nozzle between an open position permitting the flow of melt through said gate and a closed position blocking flow of melt through said gate; and means for holding the valve stem at least at one position between the open and closed positions restricting the flow of melt through said valve gate. The present invention is particularly applicable to such an apparatus including a large mold cavity which is supplied with melt with at least two of said injection nozzles, valve stems and said means for holding each valve stem, for injecting melt into a single mold cavity. 
     The process of the present invention for injection molding comprises: injecting melt through a valve gate of a hot runner injection nozzle into a mold cavity; moving a valve stem in said injection nozzle between an open position permitting flow of melt through said gate and a closed position blocking flow of melt through said gate; and holding the valve stem at least at one position between the open and closed position to restrict the flow of melt through said valve gate. The present invention is particularly applicable to such a process including injecting melt through gates of at least two of said hot runner injection nozzles into a single mold cavity, moving and holding valve stems in said at least two injection nozzles to at least at said one position to restrict the flow of melt through the valve gates of said at least two injection nozzles. 
     The present invention advantageously provides a low cost, easily settable predetermined intermediate valve stem position so that resin flow rate filling a mold cavity can be changed during the filling/packing step of an injection molding process. The present invention is particularly suitable for use in large molds and therefore the adjustment of the valve stem in accordance with the present invention may advantageously be safely and conveniently performed by a drive means controlled from outside of the molding area. Further features and advantages will appear hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more readily understandable from a consideration of the accompanying, illustrative drawings, wherein: 
     FIG. 1 is a partial sectional view through a large mold cavity with two hot runner injection nozzles of the present invention; 
     FIG. 2 shows a hot runner injection nozzle of the present invention with the valve stem in the fully closed position; 
     FIG. 3 shows the hot runner injection nozzle of FIG. 2 with the valve stem in the fully open position; 
     FIG. 4 shows the hot runner injection nozzle of FIG. 2 with the valve stem at an intermediate position; 
     FIG. 5 shows an alternate embodiment of a hot runner injection nozzle of the present invention with the valve stem in the fully closed position; 
     FIG. 6 shows the hot runner injection nozzle of FIG. 5 with the valve stem fully closed and the stop retracted; 
     FIG. 7 shows the hot runner injection nozzle of FIG. 5 with the valve stem in the fully open position; 
     FIG. 8 shows the hot runner injection nozzle of FIG. 5 with the valve stem at an intermediate position; 
     FIG. 9 shows a still further embodiment of a hot runner injection nozzle of the present invention with the valve stem in the fully closed position; 
     FIG. 10 shows the hot runner injection nozzle of FIG. 9 with the vale stem in the fully open position; 
     FIG. 11 shows the hot runner injection nozzle of FIG. 9 with the valve stem at an intermediate position; 
     FIG. 12 shows a still further embodiment of the hot runner injection nozzle of the present invention with the valve stem in the fully closed position; and 
     FIG. 13 is a detail of the cam plate assembly of FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, FIG. 1 is a partly schematic partial sectional view through large mold cavity  10  with two hot runner injection nozzles  12 , each of which includes valve gates or mold entry  14  and valve stems  16  movable in the direction of arrows  18  to open the valve gates as shown in FIG.  1  and thus permit the flow of melt through the valve gates into the mold, and to close the valve gates and thus block the flow of melt through the valve gates into the mold. The exact number of hot runner injection nozzles  12  employed will generally depend on the size of the mold, but one, two or three or more of said hot runner injection nozzles may be readily employed. Generally, the larger the mold, the more hot runner injection nozzles are employed. 
     The remaining Figures show the present invention, with a single hot runner injection nozzle being shown; however, it should be understood more than one nozzle may be used and that the other hot runner injection nozzles for a single system where used would generally have the same construction. 
     Referring to the embodiment of FIGS. 2-4, FIG. 2 shows hot runner injection nozzle  12  with the valve stem  16  thereof in the fully closed position blocking valve gate  14  and thus preventing melt from flowing past the valve gate into the mold cavity. Double acting air piston  20  is affixed to upper end  22  of valve stem  16  and is operative to move the valve stem, but naturally other means may be provided to move the valve stem. Air is supplied through air channel  24  to the upper end  26  of air piston  20  to advance valve stem  16  and thus close valve gate  14  as shown in FIG.  2 . Air is supplied through air channel  28  to the lower end  30  of air piston  20  to cause the valve stem  16  to retract as shown in FIG.  3  and thus fully open the valve gate permitting flow of melt therethrough. 
     In accordance with the present invention, a motor means, such as a small, digitally controlled servo-electric linear actuator motor  32  is used to adjust stop means  34  in relation to the valve stem. Thus, valve stem  16  includes upper extension  36  which is spaced from stop  34  in the fully closed position shown in FIG.  2 . FIG. 3 shows air supplied through air channel  28  causes valve stem  16  to retract until upper extension  36  contacts stop  34  which is set by actuator  32  in the fully open position, thus fully opening valve gate  14 . In FIG. 4, after the resin delivery is almost complete through valve gate  16 , actuator motor  32  is activated to advance stop arm  38  to advance stop  34  causing valve stem  16  to advance as shown to a position between the open and closed position. This results in a partial closing of the valve gate as shown in FIG. 4, thereby restricting the flow rate of resin into the mold cavity during the final stage of filling and packing the mold cavity, which is quite advantageous. Each stop means and stop arm is equipped with its own motor as shown in FIGS. 2-4 so that individual control can be used to set the exact desired position of the partially closed valve stem. This position may be determined empirically by examining the results of the molding produced as a result of the complete cycle. Each valve stem may be adjusted individually with motor settings based on the molding results obtained. Once a good molded part has been produced, the motors are controlled so as to repeat these optimum settings for all subsequent molding cycles in synchronism with the air valve controls and the molding cycle. 
     Another operating method would be to use the motor to adjust the full open position of the valve stem so that initially melt flow rate can also be altered in addition to the intermediate adjustment for controlling a second flow rate, i.e., a second intermediate position can be readily be provided. 
     The present invention is simple, convenient and low cost. Moreover, the valve stem position can be controlled to within + or −0.001 inch, which is accurate enough for most applications. 
     FIGS. 5-8 show an alternate embodiment of the present invention, with like reference numerals referring to like components. 
     FIG. 5, similar to FIG. 2, shows hot runner  12  with the valve stem  16  thereof in the fully closed position. Double acting air piston  20  is operative to move the valve stem between the open and closed positions, with FIG. 5 showing the fully closed position. Air is supplied through air channel  24  to advance valve stem  16  and thus close valve gate  14 , and through air channel  28  to retract valve stem  16 , as in the embodiment of FIGS. 2-4. 
     FIG. 5 also employs stop arm  38  with movable stop means  34  at the end thereof facing the upper end  22  of valve stem  16 , as in FIGS. 2-4. However, stop arm  38  has a splined upper end  40  that engages gear  42  which in turn is driven by worm  44 . Stop arm  38  is also threaded into piston  46  that is prevented from rotating by pin  48  or the like means. Turning the worm  44  by a motor (not shown) in a known fashion moves the stop arm and thus causes piston  46  and stop  34  to move, thereby setting the intermediate stop position. 
     Thus, in operation, FIGS. 5-6 show the valve stem  16  in the fully closed position. FIG. 5 shows stop  34  in the advanced position and FIG. 6 shows stop  34  in the retracted position. In operation, referring to FIG. 6, air is supplied through air channel  24  that acts on both pistons  46  and  20  causing the pistons to separate from each other as far as possible and causing valve stem  16  to fully close valve gate  14 . FIG. 7 shows air being supplied to air channel  28  causing piston  20  to retract and fully open valve gate  14 . FIG. 8 shows air supplied to both air channels  28  and  50 , causing piston  46  to advance so as to engage stop  34  with piston  20 , which is in turn urged back into contact with stop  34  by air supplied through channel  28 . This results in control of the intermediate position of valve stem  16  as shown in FIG.  8 . 
     The advantage of this approach is that once the intermediate stop position has been set by means of the worm/gear arrangement, this mechanism is not needed for operation during molding. The positions of the valve stem are all actuated by means of the two air pistons. 
     FIGS. 9-11 show a still further embodiment of the present invention, with like reference numerals showing like components. 
     FIG. 9, similar to FIGS. 2 and 5, shows hot runner  12  with the valve stem  16  thereof in the fully closed position. Double acting air piston  20  is operative to move the valve stem between the open and closed positions, with FIG. 9 showing the fully closed position. Air is supplied through air channel  24  to advance valve stem  16  and thus close valve gate  14 , and through air channel  28  to retract valve stem  16 , as in the previous embodiments. 
     However, FIG. 9 employs a wedge for effecting the intermediate position of the valve stem. 
     Referring to FIG. 9, valve stem  16  includes arm  52  extending above air piston  20  and connected to first wedge  54 . Second wedge  56  driven by piston  58  contacts first wedge  54  as shown in FIG. 9 in the mold closed position. In the fully open position shown in FIG. 10, air through air channel  28  moves valve stem  16  to the fully open position and also moves first wedge  54  upwardly away from valve gate  14 . In the intermediate position shown in FIG. 11, second wedge  56  is moved laterally, air through air channel  24  moves valve stem  16  downwardly towards valve gate  14  and also moves valve stem arm  52  and first wedge  54  in the same direction. However, the second wedge  56  controls the downward movement of valve stem and positions the valve stem in the intermediate position. 
     FIGS. 12-13 show a still further embodiment of the present invention using a cam approach for controlling the intermediate position of the valve stem. 
     Referring to FIG. 12, hot runner injection nozzle  112  includes valve stem  116  and valve gate  114 . Air piston  120  controls the movement of the valve stem between the open and closed position via air channels  124  and  128 , with FIG. 12 showing the closed position. Stop means  134  is provided by stop arm  138  which is controlled by cam plate  160 . Stop arm  138  and therefore stop means  134  is movable via roller  162  in roller guide  164 , shown in more detail in FIG. 13, by motor means not shown, as for example by an air cylinder. Thus, stop means  134  engages air piston  120  to prevent complete opening of valve gate  114  and set the intermediate position. Naturally, several intermediate positions may be set by this embodiment as by stopping the roller in various positions in the roller guide in order to adjust the setting of the stop means. One can also conveniently provide steps in the roller guide to conveniently locate the roller at various locations in the roller guide. 
     The present invention obtains significant advantages. In addition to providing means to inexpensively and simply and effectively control the intermediate position or positions of a hot runner valve stem, the present invention also has the advantage of closing the valve stem by using an air piston. If stem closing was driven directly by a motor or mechanical gear drive, there is a risk of over stroking the stem and deforming the fragile gate area. By completing the closing motion solely by using the air piston, this danger is avoided because the comparatively low force of the air piston allows the stem to stall when it contacts the gate area. 
     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.