TECHNICAL FIELD Non-Limiting embodiments disclosed herein generally relate to the molding arts, and more specifically to a method of operating an injection unit of a molding system.

BACKGROUND OF THE INVENTION With reference to FIGS. 1A - ID there is depicted an operational sequence for a known method of operating an injection unit 10 of a reciprocating screw type. The construction of the injection unit 10 is depicted as a simplified schematic representation thereof. The injection unit 10 broadly includes a barrel 20 within which there is disposed a screw 30 that is free to rotate and reciprocate therein for sake of extruding and subsequently injecting a shot of molding material (e.g. plastic) through a nozzle 40 that is disposed at a downstream end of the barrel 20. The screw 30 is operatively connected to a rotational actuator 50 and a linear actuator 60 that are disposed at an upstream end of the barrel 20. Also depicted is a nozzle shutoff 70 that is disposed in the nozzle 40, the nozzle shutoff 70 is operable to selectively control a flow of the molding material through the nozzle 40. Finally, the injection unit 10 is shown to include a controller 80 that is operatively connected to the rotational actuator 50, the linear actuator 60 and the nozzle shutoff 70 for control thereof. The controller 80 includes instructions being embodied in a controller-usable memory (not shown), the instructions for directing the controller 80 to control the rotational actuator 50, the linear actuator 60 and the nozzle shutoff 70, amongst other controllable devices (not shown) of the injection unit 10, to execute the known method.

The description of the known method of operating the injection unit 10 begins with reference to FIG. 1A wherein the screw 30 is shown in a forward position in the barrel 20 with the nozzle shutoff 70 being open and the pressure in front of the screw is at a value set for hold. This is the state of the injection unit 10 at the end of hold. In the next step, as shown with reference to FIG. IB, the screw 30 is retracted axially, as shown, to reduce the pressure at a tip of the screw 30 and in a melt distribution system 92, such as a hot runner, that is associated with a mold 90 to a low value. This is the state of the injection unit 10 at the beginning recovery. The next step in the known method, as shown with reference to FIG. 1C, is to close the nozzle shutoff 70, and in so doing isolate the melt distribution system 92 from the injection unit 10, and to extrude a shot of molding material in the barrel 20 in front of the screw 30 with rotation of the screw 30. The extrusion of molding material causes the screw 30 to retract to an injection start position with accumulation of the molding material in front thereof (i.e. it is the pressurization of the molding material that causes the screw 30 to retract). The last step of the known method, as shown with reference to FIG. ID, involves opening of the nozzle shutoff 70 and subsequently advancing of the screw 30, as shown, to inject the shot of molding material through the nozzle 40 and into the mold 90.

For parallel operation of a mold clamp (not shown) and the injection unit 10 in a molding system, wherein the mold 90 has a melt distribution system 92 having a hot tip nozzle 94, it is necessary to use a nozzle shutoff 70 in the injection unit 10. This is because during recovery when the screw 30 is plasticizing and feeding plastic forward there is pressure created which would re-pressurize the hot runner and cause drooling into molding cavities 96 of the mold 90 if it were not isolated by a nozzle shutoff 70.

The time taken to open and close this nozzle shutoff 70 directly reduces the time available for recovery. Although the nozzle shutoff 70 actuates quite quickly, in the case of a high speed molding system making closures of the type for capping a container, this time is significant. For example it may take a total of 0.4 seconds to open and close the nozzle shutoff. When this time is compared to the overall molding cycle time of say 2 seconds and an available recovery time 1 second it can be seen that this time is significant. Another action that reduces time for recovery is the screw 30 pullback (not shown) that is required to decompress the hot runner 92. This pullback is done without rotation of the screw 30 to avoid pressure buildup and is done prior to closing the nozzle shutoff 70 in order to avoid trapping residual hold pressure in the hot runner 92 that could lead to drool. Other methods of operating an injection unit of the reciprocating screw type are outlined with reference to the following publications.

US patent 7,291,297 to Weatherall et al., published on November 6, 2007 discloses in a reciprocating screw (RS) injection unit environment a controller of the injection unit that is arranged to continuously rotate the screw during both conventional plasticizing operation and shot injection. In this way the RS unit is more efficient, utilizing less energy and producing greater resin output. The injection unit includes a non-return valve adjacent a nozzle, which non-return valve is either configured to rotate with the screw to reduce wear or presented as a ball check style non-return valve. In an injection molding environment, the rotating screw includes flights that allow granules of resin to melt and mix in spaces between adjacent flights, but the flights are arranged substantially to inhibit excessive displacement of resin around the flights. PCT patent application publication 2011/103676 to Weatherall, published on September I, 2011 discloses a method of controlling an injection unit for use in an injection molding system. The method includes releasing a rotation control signal to a first actuator to execute rotation of an injection screw to extrude a shot of a molding material within a melt channel therein and cause a retraction of the injection screw, along an axis thereof, to a resultant injection start position with accumulation of the molding material in front of the injection screw. In the method the rotation control signal causes the first actuator to execute rotation of the injection screw through a predetermined number of screw rotations to extrude the shot of the molding material. The method further includes releasing an injection control signal to a second actuator to execute advancing of the injection screw, along the axis thereof, to inject the shot of the molding material. In the method the injection control signal transitions from a first injection control regime to a second injection control regime at a pre-determined injection transition distance from the resultant injection start position. SUMMARY OF THE INVENTION

In accordance with a first aspect disclosed herein is a method of operating an injection unit in a molding system. The method includes the steps of extruding a shot of a molding material with rotation of a screw within a barrel of the injection unit and retracting the screw within the barrel such that during the extruding of the shot of the molding material a melt pressure therein is kept below a predetermined pressure.

In accordance with a second aspect disclosed herein is a controller including instructions being embodied in a controller-usable memory, the instructions for directing the controller to execute a method of operating an injection unit in a molding system. The method includes the steps of extruding a shot of a molding material with rotation of a screw within a barrel of the injection unit and retracting the screw within the barrel such that during the extruding of the shot of the molding material a melt pressure therein is kept below a predetermined pressure. In accordance with another aspect disclosed herein is a related method of operating an injection unit in a molding system. The method includes the steps of retracting a screw within a barrel of the injection unit while the injection unit is in fluid communication with a melt distribution system of a mold, extruding a shot of molding material within the barrel with rotation of the screw therein, closing fluid communication between the injection unit and the melt distribution system, applying back pressure to the screw during the extruding of the molding material and with the closing of the fluid communication between the injection unit and the melt distribution system, opening fluid communication between the injection unit and the melt distribution system, and advancing the screw to inject the shot of the molding material into the mold.

In accordance with a further aspect disclosed herein is a controller including instructions being embodied in a controller-usable memory, the instructions for directing the controller to execute a method of operating an injection unit in a molding system. The method includes the steps of retracting a screw within a barrel of the injection unit while the injection unit is in fluid communication with a melt distribution system of a mold, extruding a shot of molding material within the barrel with rotation of the screw therein, closing fluid communication between the injection unit and the melt distribution system, applying back pressure to the screw during the extruding of the molding material and with the closing of the fluid communication between the injection unit and the melt distribution system, opening fluid communication between the injection unit and the melt distribution system, and advancing the screw to inject the shot of the molding material into the mold.

These and other aspects and features of non-limiting embodiments will now become apparent to those skilled in the art upon review of the following description of specific non-limiting embodiments of the invention in conjunction with the accompanying drawings. DETAILED DESCRIPTION OF THE DRAWINGS

The non-limiting embodiments will be more fully appreciated by reference to the accompanying drawings, in which: FIGS. 1A - ID depict an operational sequence for a known method of operating an injection unit of the reciprocating screw type.

FIG. 2 depicts a flow chart of a method of operating an injection unit of a molding system. FIGS. 3 A - 3D depict an operational sequence for operating an injection unit in accordance with a first non-limiting embodiment of the method of FIG. 2.

FIGS. 4A - 4D depict an operational sequence for operating an injection unit in accordance with a second non-limiting embodiment of the method of FIG. 2. FIGS. 5 A - 5C depict an operational sequence for operating an injection unit in accordance with a third non-limiting embodiment of the method of FIG. 2.

FIGS. 6A - 6C depict an operational sequence for operating an injection unit in accordance with a fourth non- limiting embodiment of the method of FIG. 2.

FIG. 7 depicts a flow chart of a further method of operating an injection unit of a molding system.

FIGS. 8 A - 8E depict an operational sequence for operating an injection unit in accordance with a non-limiting embodiment of the method of FIG. 7.

The drawings are not necessarily to scale and may be illustrated by phantom lines, diagrammatic representations and fragmentary views. In certain instances, details that are not necessary for an understanding of the embodiments or that render other details difficult to perceive may have been omitted.

DETAILED DESCRIPTION OF THE EMBODIMENT(S

With the nozzle 94 of the melt distribution system 92 being configured to include a hot tip gate it is necessary to decompress the melt distribution system 92 in order to prevent drool into the molding cavity 96 and that this is most preferably accomplished through retraction (i.e. pullback) of the screw 30, creating an increased volume. It has been discovered that if the screw 30 were retracted at a higher speed during this pullback motion, the pressure built up by feeding the resin forward could be eliminated thereby allowing recovery during this pullback stage. It has further been found that if the nozzle shutoff 70 (FIG. 1A) were removed, or simply disabled, pressure built up by the screw 30 (FIG. 1A) during recovery could be reduced by retracting the screw 30 either before or during extrusion to counteract the pressure increase caused by the forward pumping of the molding material by rotation of the screw 30. In this way both the time used for pullback of the screw 30 and the opening and closing of the nozzle shutoff 70 could be added to the time available for recovery. Put another way, the underlying strategy that will be illustrated with reference to several non-limiting embodiments of a method 100 (FIG. 2) of operating an injection unit that follow is that recovery (i.e. extrusion of a shot of a molding material) may be performed by the overlapping of screw rotation with other injection unit functions not previously done. This could be useful in high throughput and short cycle applications such as the molding of closures of the type for capping containers (e.g. beverage containers). Accordingly, and as illustrated with reference to the flow chart of FIG. 2, a method 100 of operating an injection unit 110, 210 (FIGS. 3A-3D, 4A-4D, 5A-5C, and 6A-6C) in a molding system (not shown) is proposed, the method 100 broadly includes the steps of: Step 102

The method 100 begins with the step of extruding a shot of a molding material with rotation of a screw 30 within a barrel 20 of the injection unit 110, 210.

Step 104

The method 100 further includes the step of retracting the screw 30 such that during the extruding 102 of the shot of the molding material a melt pressure therein is kept below a predetermined pressure. The predetermined pressure may be selected such as to substantially avoid drooling of the molding material through a nozzle 94 of a melt distribution system 92 that is associated with a mold 90.

The method 100 then ends, or repeats with a step of advancing the screw 30 to inject the shot of the molding material into the mold 90 that is in fluid communication therewith.

Reference will now be made in detail to various non-limiting embodiment(s) of the method 100 of operating the injection unit 110, 210. It should be understood that other non-limiting embodiment(s), modifications and equivalents will be evident to one of ordinary skill in the art in view of the non- limiting embodiment(s) disclosed herein and that these variants should be considered to be within scope of the appended claims. Furthermore, it will be recognized by one of ordinary skill in the art that certain structural and operational details of the non-limiting embodiment(s) discussed hereafter may be modified or omitted (i.e. non-essential) altogether. In other instances, well known methods, procedures, and components have not been described in detail. With reference to FIGS. 3A - 3D there is depicted an operational sequence for a first non-limiting embodiment of the method 100 (FIG. 2) of operating the injection unit 110 of a reciprocating screw type. The construction of the injection unit 110 is similar to the injection unit 10 and as such identical components thereof have been given identical reference numerals. In fact, the only difference between the injection units is that the injection unit 110 includes a nozzle 140 at the downstream end of the barrel 20 that does not have a nozzle shutoff 70 associated therewith. The description of the first non- limiting embodiment of the method 100 of operating the injection unit 110 begins with reference to FIG. 3 A wherein the screw 30 is shown in a forward position in the barrel 20. This is the state of the injection unit 110 at the beginning of recovery. In this non-limiting embodiment of the method 100, the step of retracting (step 104) of the screw 30 is performed prior to the step of extruding 102 of the shot of the molding material. This can be seen with reference to FIG. 3B, wherein the next step in the method 100 is to retract the screw 30 to a predetermined position. The predetermined position may be, for example, a full shot position (i.e. the position that the screw 30 is known to achieve once a full shot of molding material has accumulated in front thereof). The next step in this non- limiting embodiment of the method 100, as shown with reference to FIG. 3C, involves rotating the screw 30, as shown, through a predetermined number of revolutions that are required to extrude the shot of the molding material. The foregoing is made possible because it has been previously recognized, reference the teachings of commonly assigned PCT patent application publication 2011/103676 to Weatherall, as summarized previously, that for a given set of operating conditions the screw 30 behaves like a constant volume pump and displaces a consistent quantity of molding material per revolution, with only minor variations. The last step in this non-limiting embodiment of the method 100 involves advancing the screw 30, as shown with reference to FIG. 3D, to inject the shot of the molding material into the mold 90 that is in fluid communication therewith. With reference to FIGS. 4A - 4D there is depicted an operational sequence for a second non-limiting embodiment of the method 100 (FIG. 2) of operating the injection unit 110.

The description of the second non-limiting embodiment of the method 100 of operating the injection unit 110 begins with reference to FIG. 4A wherein the screw 30 is shown in a forward position in the barrel 20. This is the state of the injection unit 110 at the beginning of recovery. In this non-limiting embodiment of the method 100, the step of retracting (step 104) of the screw 30 is performed prior to the step of extruding 102 of the shot of the molding material. This can be seen with reference to FIG. 4B, wherein the next step in the method 100 is to retract the screw 30 to a predetermined position. The predetermined position may be, for example, a position that is slightly less than a full shot position by an amount required to decelerate the screw 30 to a stop at the full shot position, wherein linear deceleration of the screw 30 begins once rearward movement of the screw 30 past the predetermined position is detected. The detection of screw 30 movement may be provided, for example, by means of feedback from the linear actuator 60 to the controller 80. The next step in this non-limiting embodiment of the method 100, as shown with reference to FIG. 4C, involves rotating the screw 30, as shown, to extrude the shot of molding material in front thereof. The screw 30 is to be rotated until it has been rearwardly displaced from the predetermined position to the full shot position as shown by contrasting FIGS. 4B and 4C. The last step in this non-limiting embodiment of the method 100 involves advancing the screw 30, as shown with reference to FIG. 4D, to inject the shot of the molding material into the mold 90 that is in fluid communication therewith. With reference to FIGS. 5A - 5C there is depicted an operational sequence for a third non-limiting embodiment of the method 100 (FIG. 2) of operating the injection unit 110.

The description of the third non-limiting embodiment of the method 100 of operating the injection unit 110 begins with reference to FIG. 5 A wherein the screw 30 is shown in a forward position in the barrel 20. This is the state of the injection unit 110 at the beginning of recovery. In this non-limiting embodiment of the method 100, the steps of extruding (step 102) the shot of the molding material and the retracting (step 104) the screw 30 are performed substantially simultaneously. More particularly, and as shown with reference to FIG. 5B, the screw 30 is being retracted by the linear actuator 60 at a predetermined speed that is known to keep the melt pressure in front thereof below the predetermined pressure. That is, the predetermined speed is selected to counteract a pressure increase caused by the forward pumping of the molding material that is caused by the rotation of the screw 30. The last step in this non-limiting embodiment of the method 100 involves advancing the screw 30, as shown with reference to FIG. 5C, to inject the shot of the molding material into the mold 90 that is in fluid communication therewith.

With reference to FIGS. 6A - 6C there is depicted an operational sequence for a fourth non-limiting embodiment of the method 100 (FIG. 2) of operating an injection unit 210. The construction of the injection unit 210 is similar to the injection unit 110 and as such identical components thereof have been given identical reference numerals. In fact, the only difference between the injection units is that the injection unit 210 includes a linear actuator 260 at the upstream end of the barrel 20 for reciprocating the screw 30 that is equipped with a first sensor 262 and a second sensor 264 that are located to provide feedback to the controller 80 for sake of evaluating a net force acting on a piston 266 thereof. The description of the fourth non- limiting embodiment of the method 100 of operating the injection unit 110 begins with reference to FIG. 6A wherein the screw 30 is shown in a forward position in the barrel 20. This is the state of the injection unit 210 at the beginning of recovery. In this non-limiting embodiment of the method 100, the steps of extruding (step 102) the shot of the molding material and the retracting (step 104) the screw 30 are performed substantially simultaneously. More particularly, and as shown with reference to FIG. 6B, the screw 30 is being retracted by the linear actuator 60 at a rate that has been selected by the controller 80 to keep the melt pressure in front thereof below the predetermined pressure. More particularly, the non-limiting embodiment of the method 100 further includes the step of monitoring the net force being applied to the screw 30 by the linear actuator 260, which is indicative of the melt pressure in front of the screw 30, and wherein the retracting the screw 30 involves retracting the screw 30 fast enough to maintain the net force being applied below a predetermined force. The last step in this non-limiting embodiment of the method 100 involves advancing the screw 30, as shown with reference to FIG. 5C, to inject the shot of the molding material into the mold 90 that is in fluid communication therewith.

The focus of the description shall now turn to a similar method that is implementable on an injection unit having a shutoff valve or other such device for selectively opening or closing a fluid connection with the melt distribution system of the mold. The method includes the unique sequence of steps of retracting the screw to depressurize the melt distribution system whereafter with closing of the shutoff valve (during or after) back pressure is applied to the screw during recovery (i.e. extruding a shot of molding material). In this way the pullback and recovery may be overlapped, at least in part, and the pullback could be done to any arbitrary position less than the shot size. A technical effect of the foregoing may include the ability to extend the utility of an injection unit across a wider range of shot sizes (big and small). That is, by applying back pressure to the screw during recovery, the screw is advanced in the barrel such that additional rearward distance is provided through which control of linear screw motion may be performed (i.e. deceleration) for more accurate shot size control.

The foregoing is set forth in more detail in method 200 as depicted in the flow chart of FIG. 7. The method 200 may be performed, for example, using the injection unit 10 shown in FIGS. 8A-8E which is the same as that shown in FIGS. 1A-1D that was described earlier. The description of the method 200 picks up at a point of completion of a step of injection of molding material into the mold 90.

Step 202

The method 200 begins with the step of retracting the screw 30 within the barrel 20 of the injection unit 10 while the injection unit 10 is in fluid communication with the melt distribution system 92 of the mold 90 for sake of a depressurization thereof. The foregoing may be appreciated by contrasting FIGS. 8A and 8B. FIG. 8A depicts the injection unit 10 at the end of the step of the prior step of injection wherein the screw 30 is at a forward position within the barrel 20. FIG. 8B depicts the injection unit 10 at the end of the step of retracting of the screw 30 to an arbitrary position that may be less (although not necessarily) than a shot position S (FIG. 8E) of the screw 30 (i.e. the position of the screw at the end of recovery). It may be noted that in performing the foregoing that the nozzle shutoff 70 remains open to maintain fluid communication between the injection unit 10 and the mold 90 such that with retraction of the screw 30 the melt distribution system 92 is depressurized to an extent required to prevent further expression of molding material from the nozzle 94 with opening of the mold 90.

Step 204

The method 200 further includes the step of extruding a shot of molding material within the barrel 20 with rotation of the screw 30 therein. The extruding may begin with, during or after the retracting 202 of the screw 30. In keeping with the method 100, the steps of extruding and retraction may be coordinated such that a melt pressure of the molding material in the barrel 20 is kept below a predetermined pressure while the injection unit 10 remains in fluid communication with the melt distribution system 92. The foregoing step may be appreciated with reference to the non-limiting operating sequence shown in FIGS. 8A-8E, specifically FIG. 8B wherein it may be appreciated that extrusion commences with retraction of the screw 30 and prior to closing of the nozzle shutoff 70.

Step 206

The method 200 further includes closing fluid communication between the injection unit 10 and the melt distribution system 92. The closing of fluid communication may occur before, during or after commencement of the extruding of the shot of molding material bearing in mind, as previously discussed, that if extrusion is begun prior to the closing of fluid communication that steps may need to be taken to limit the pressurization of the molding material. As may be appreciated with reference to FIG. 8C, the closing of fluid communication may include selectively positioning (i.e. rotating) the nozzle shutoff 70 that is disposed in the nozzle 40 at an end of the barrel 20. The closing of the fluid communication will be further discussed in conjunction with the next step in the method 200.

Step 208

The method 200 further includes applying back pressure to the screw 30 during the extruding 204 of the molding material and with the closing of the fluid communication between the injection unit 10 and the melt distribution system 92. The foregoing is illustrated with reference to FIG. 8C wherein a back pressure is applied to the screw in the direction of the arrow thereby urging the screw 30 to move forward towards the nozzle 40. Doing so may cause the screw 30 to advance during a part of the extruding of the shot of molding material as can be appreciated by contrasting FIGS. 8B and 8C. In so doing additional rearward distance is provided through which linear motion of the screw 30 may be controlled. A technical effect of the foregoing may include improved shot size control. As may be appreciated, the closing of fluid communication may occur prior to or during the applying of the back pressure to the screw 30 to substantially prevent the re-pressurization of the melt distribution system 92 during this operation. Steps 211/212

The method 200 concludes with the opening 211 of fluid communication between the injection unit 10 and the melt distribution system 92 and advancing 212 of the screw 30 to inject the accumulated shot of the molding material into the mold 90 (via the melt distribution system 92 that is in fluid communication therewith). The opening 211 of fluid communication between the injection unit 10 and the melt distribution system 92 may occur during or after completion of the extruding 204 of the shot of molding material bearing in mind that if the nozzle shutoff 70 is opened early that steps will be required to maintain the pressure in the molding material below a pre-determined pressure as described previously.

It is noted that the foregoing has outlined some of the more pertinent non-limiting embodiments. It will be clear to those skilled in the art that modifications to the disclosed non-embodiment(s) can be effected without departing from the spirit and scope thereof. As such, the described non-limiting embodiment(s) ought to be considered to be merely illustrative of some of the more prominent features and applications. Other beneficial results can be realized by applying the non-limiting embodiments in a different manner or modifying the invention in ways known to those familiar with the art. This includes the mixing and matching of features, elements and/or functions between various non-limiting embodiment(s) is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one embodiment may be incorporated into another embodiment as skill in the art would appreciate from this disclosure that features, elements and/or functions of one embodiment may be incorporated into another embodiment as appropriate, unless described otherwise, above. Although the description is made for particular arrangements and methods, the intent and concept thereof may be suitable and applicable to other arrangements and applications.