JP5666488B2 - Method of flushing injection device - Google Patents

Description

  The present invention relates to a so-called flushing in which molten resin is discharged from a heating cylinder of an injection apparatus for the purpose of changing the color of a material resin or stopping the operation of the apparatus.

  The injection molding machine is composed of a pair of molds, a mold clamping apparatus for clamping these molds, an injection apparatus for melting a resin material and injecting the resin material into the mold as known in the art, and the injection apparatus is a heater. The heating cylinder is heated by the cylinder, the screw is driven in the axial direction and the rotation direction in the heating cylinder, and the hopper for supplying the resin pellets of the material. Accordingly, when the resin pellets are supplied from the hopper and the screw is driven in the rotation direction, the resin pellets are melted by the heat of the heating cylinder and the heat generated by the shearing of the screw, and sent to the front of the screw to measure the molten resin. A pair of molds are clamped by a mold clamping device, the screw is driven in the axial direction, molten resin is injected into the cavity formed in the mold, and after waiting for cooling and solidification, the mold is opened. can get.

  By the way, when the so-called color change for changing the resin of the material is performed, or when the injection molding machine is stopped for a long period of time, it is necessary to discharge the molten resin from the heating cylinder. Such discharge of molten resin is called flushing or purging, and is roughly divided into the following two types depending on whether or not the screw position is fixed. The first flushing method is a method of stopping the supply of resin pellets and rotating the screw so that the screw position is fixed. Since the screw position is fixed, the molten resin is continuously discharged to the outside from the nozzle at the tip of the heating cylinder when sent to the front of the screw. After rotating the screw for a predetermined time, the rotation of the screw is stopped, the screw is driven in the axial direction, and the molten resin accumulated in front of the screw is discharged to complete the flushing. In contrast, the second flushing method is the same in that the supply of resin pellets is stopped, but the molten resin is measured in front of the screw so that the screw position is retracted when the screw is rotated. Like that. At this time, a predetermined back pressure may be applied to the screw and the screw may be retracted by the resin pressure, or so-called suckback may be performed in which the screw is forcibly retracted. In any case, the screw is rotated to send the molten resin to the front of the screw and measure a predetermined amount. When weighed, the rotation of the screw is stopped and the screw is driven in the axial direction to inject the molten resin. That is, it discharges. Such measurement and injection of the molten resin are repeated a predetermined number of times, and the molten resin in the heating cylinder is discharged.

  In both the first flushing method and the second flushing method, the molten resin can be discharged from the heating cylinder. For example, when the flushing is performed in a state where the nozzle of the injection device is separated from the mold, the first flushing method is used. The flushing method of No. 2 is not substantially superior or inferior. However, when flushing with the nozzle of the injection device touching the fixed mold, that is, when the molten resin is discharged from the gate of the fixed mold with the mold open, depending on the size and shape of the gate, the flow of the molten resin Resistance is great. Then, in the first flushing method in which the screw position is stopped and the flushing is performed only by the rotation of the screw, the gate becomes a resistance and the discharge efficiency is slightly lowered. On the other hand, in the second flushing method, the resistance of the gate is not affected during measurement. The resistance of the gate is related only when the screw is driven in the axial direction, and it can be said that the molten resin does not flow back by the backflow prevention device provided in the screw, so that it does not substantially influence. Therefore, the molten resin can be discharged efficiently and in a short time. That is, it can be said that the second flushing method is excellent because flushing can be performed with the same efficiency regardless of whether the nozzle touches the fixed mold or is separated.

  It is a problem if the screw continues to rotate in a so-called starvation state in which almost no molten resin disappears from the heating cylinder during flushing. For example, if the inside of the heating cylinder is starved in the second flushing method, the screw does not retract during measurement. Then, the measurement will not be completed and the screw will run idle. Thus, if the screw is idle in a starved state, the screw is damaged. In order to prevent the idling of the screw in a starvation state, a method of setting a limit on the measuring time by a timer is well known. In other words, when the predetermined time has elapsed, the metering is interrupted and the screw rotation is stopped, so that the screw can be prevented from idling in a starved state.

JP 2006-88557 A

  In Patent Document 1, the driving torque for rotating the screw is monitored, and when the driving torque reaches a torque lower limit value which is a predetermined set value, it is determined that the molten resin in the heating cylinder has been sufficiently discharged. A purge method for stopping the rotation of the screw, that is, a flushing method is described. Since this method fixes the screw position when rotating the screw, it can be said to be the first flushing method described above. In the method described in Patent Document 1, when the driving torque reaches the torque lower limit value, it is determined that the molten resin has been sufficiently discharged, and the rotation of the screw is stopped immediately or after a predetermined time has elapsed, so that the screw is in a starved state. Prevents rotation.

  According to the conventional method in the second flushing method, that is, the method of limiting the measuring time by providing a timer, and the method described in Patent Document 1, the screw is prevented from rotating in the starvation state and the screw is damaged. Can be prevented. However, there is a problem to be solved by either method. First, in the second flushing method, a timer is provided. If the set timer is long, the rotation of the screw may not be stopped even if the inside of the heating cylinder is starved. The timer can generally be changed by the operator. However, since the fluidity of the resin changes depending on the type and temperature of the resin, an optimal timer must be set each time, which is complicated. If the timer is set incorrectly as described above, the screw cannot be prevented from rotating in the starved state, and the screw is damaged. Even if the timer is set properly, if the screw is sucked back during weighing, it will not be detected even if the heating cylinder is starved, and weighing will be performed for the set number of times. If the screw is repeatedly discharged, it may not be possible to prevent the screw from slipping. The method described in Patent Document 1 has the following two problems. The first problem is that the torque lower limit value must be changed every time the type and temperature of the resin are changed, and the work is complicated. If the resin conditions change, the flow resistance will change, so it is necessary to reset the torque lower limit value too. However, if the setting is incorrect, the starvation state cannot be detected and the screw rotates and the screw is damaged. The second problem is that the flow resistance of the molten resin sent forward is included as noise in the measured driving torque of the screw rotation. That is, since the method described in Patent Document 1 is implemented by the first flushing method, not only the rotational resistance of the screw but also the flow resistance when the molten resin is fed forward is added to the driving torque for rotating the screw. It will be done. Then, when the nozzle touches the fixed mold and when the nozzle is separated, the flow resistance for sending the molten resin forward changes, so that the drive torque changes even if the rotational resistance of the screw is equal. In other words, since the flow resistance is excluded and only the rotational resistance of the screw cannot be accurately detected, it is not always possible to detect the state of the molten resin remaining in the heating cylinder, and the rotation of the screw can be stopped. There is no guarantee.

  An object of the present invention is to provide a flushing method for an injection apparatus that solves the above-described problems. Specifically, the molten resin in the heating cylinder can be efficiently and sufficiently discharged, It is another object of the present invention to provide a flushing method for an injection device that can reliably prevent idling of a screw in a starved state in a heating cylinder even when the temperature changes, and that is easy to maintain.

  In order to achieve the above-mentioned object, the present invention provides a material supply from a hopper in an injection device comprising a heating cylinder and a screw that can be driven in the rotation direction and the axial direction in the heating cylinder. It is configured as a flushing method that stops and repeats the metering operation and the injection operation to discharge the molten resin in the heating cylinder to the outside. Then, the torque for rotating the screw is monitored, and when the torque less than a preset ratio with respect to the maximum value of torque after the start of flushing is detected, the metering operation is stopped, the injection operation is performed, and the flushing is finished. Configure. The weighing operation may be performed by applying a back pressure to the screw, or may be performed by sucking back the screw forcibly.

Thus, in order to achieve the above object, the invention according to claim 1 is an injection apparatus comprising a heating cylinder and a screw provided in the heating cylinder so as to be drivable in the rotational direction and the axial direction. Stop the material supply from the hopper behind the heating cylinder, rotate the screw to measure the molten resin in front of the screw, and drive the screw in the axial direction to measure the molten A flushing method for discharging the molten resin in the heating cylinder to the outside by repeating an injection operation for discharging the resin to the outside, and monitoring a torque for rotating the screw in the metering operation ; detecting the maximum torque is the maximum value of torque, the metering operation upon detection of a torque of less than a preset ratio with respect to said maximum torque Stops constructed as flushing method of the injection apparatus, characterized in that by carrying out the injection operation terminating the flushing.
According to a second aspect of the present invention, in the method according to the first aspect, the measuring operation is performed as a flushing method for an injection apparatus, wherein the metering operation is performed by applying a predetermined back pressure to the screw.
According to a third aspect of the present invention, in the method according to the first aspect, the metering operation is performed by sucking back the forcibly retracting the screw in the axial direction. Configured as a method.
According to a fourth aspect of the present invention, in the method according to any one of the first to third aspects, the ratio is 50 to 62%.

As described above, according to the present invention, in an injection apparatus including a heating cylinder and a screw that can be driven in the rotation direction and the axial direction in the heating cylinder, the supply of the material from the hopper is stopped. The flushing method in which the molten resin in the heating cylinder is discharged to the outside by repeating the metering operation and the injection operation. That is, the screw is rotated to measure the molten resin in front of the screw, the screw is driven in the axial direction, the measured molten resin is injected, discharged to the outside, and flushed by repeating these operations. When the flushing is performed by such a method, at the time of measurement, it is not affected by the flow resistance of the molten resin that is generated when the molten resin is discharged to the outside. Therefore, regardless of whether the nozzle at the tip of the heating cylinder touches the fixed mold, and regardless of the flow resistance of the molten resin, the molten resin can be efficiently metered, resulting in injection. The molten resin can be efficiently discharged by the operation. Then, the present invention monitors the torque that rotates the screw in the weighing operation, detects the maximum torque that is the maximum value of the torque after the start of flushing, and detects a torque that is equal to or less than a preset ratio with respect to the maximum torque. The metering operation is stopped, the injection operation is performed, and the flushing is finished. Therefore, the amount of molten resin remaining in the heating cylinder can be estimated relatively accurately regardless of the type and temperature of the resin, and the molten resin can be sufficiently discharged from the heating cylinder, and the heating cylinder can be starved. The rotation of the screw in the state can be reliably prevented. In this way, the amount of molten resin in the heating cylinder can be estimated relatively accurately regardless of the type and temperature of the resin because the torque required to rotate the screw is interposed between the heating cylinder and the screw. This is because it can be considered to be due to the viscous resistance of the molten resin. This is because it is not necessary to consider that the flow resistance for feeding the molten resin forward and discharging it to the outside is mixed into the torque as noise. Actually, torque due to friction of machine parts also exists, but most of the torque can be regarded as due to the viscous resistance of the molten resin interposed between the heating cylinder and the screw. When the molten resin is sufficiently filled in between, the torque becomes the maximum value, and by evaluating the ratio of the torque to the maximum value, it is possible to estimate how much the molten resin remains. . Since the evaluation is based on the torque ratio, it is relatively unaffected by the magnitude of the resin viscosity. In other words, it is less affected by the type and temperature of the resin. Therefore, according to the present invention, when a torque equal to or less than a preset ratio with respect to the maximum value of torque after the start of flushing is detected and the measuring operation is stopped, the molten resin can be sufficiently discharged regardless of the type and temperature of the resin. In addition, the screw can be reliably prevented from being damaged. According to another invention, the ratio is configured to be 50-62%. If the metering operation is stopped when a torque of 50% to 62% or less is detected with respect to the maximum value of the torque, a sufficient amount of molten resin can be discharged and the heating cylinder cannot be starved. Can be guaranteed.

It is a figure which shows typically the injection device which concerns on embodiment of this invention. It is a graph explaining the flushing method which concerns on embodiment of this invention, and is each a graph which shows each of the rotation speed of the screw in flushing, the torque required for rotation of a screw, and a screw position.

  An embodiment of the present invention will be described. An injection molding machine that performs a flushing method according to an embodiment of the present invention is also configured in the same manner as a conventional injection molding machine, and includes a pair of molds, a mold clamping device that clamps the molds, and a resin material. The injection apparatus 1 etc. which melt | dissolve and inject | pour into the metal mold | die clamped are comprised. Although only the injection device 1 is shown in FIG. 1, the injection device 1 includes a heating cylinder 2, a screw 3 provided in the heating cylinder 2 so as to be driven in a rotational direction and an axial direction, A nozzle 5 provided at the tip of the cylinder 2, a hopper 6 provided near the rear end of the heating cylinder 2 for supplying resin of the material into the heating cylinder 2, and the screw 3 are driven in the rotational direction and the axial direction. And a drive mechanism 8 to be operated. A conventionally known backflow prevention device 9 is provided at the tip of the screw 3, and does not interfere with the metering when the screw 3 is rotated to meter the molten resin, but when the screw 3 is driven in the axial direction for injection. The reverse flow of the molten resin is prevented. Since the drive mechanism 8 can be composed of various known mechanisms, it is simply shown in FIG. 1, but the motor 11 that drives the screw 3 in the rotational direction and the screw 3 is driven in the axial direction. It is comprised from the drive device 12. FIG. The motor 11 and the drive mechanism 12 are connected to the controller 13 of the injection molding machine by signal lines S1 and S2, and can be driven by a signal from the controller 13. The rotational torque of the screw 3 can be accurately measured from the current value supplied to the motor 11, and is input to the controller 13 through the signal line S1.

  The injection molding machine according to the present embodiment is also operated in the same manner as a conventional injection molding machine. That is, in the injection apparatus 1, the heating cylinder 2 is heated by a heater (not shown), the resin pellets of the material are supplied from the hopper 6, and the motor 11 is driven to rotate the screw 3. Then, the material resin is melted by the heat of the heating cylinder 2 and the heat generated by the shearing force of the screw 3. The molten resin is filled during the flight of the screw 3 and sent to the front of the screw 3 while being kneaded by the flight. When a predetermined back pressure is applied to the screw 3 so that the screw 3 can move in the axial direction, the molten resin is sent to the front of the screw 3 in the heating cylinder 2 and the screw 3 moves backward. That is, the molten resin is weighed. Alternatively, a so-called suckback is performed in which the screw 3 is rotated and the screw 3 is gradually retracted in the axial direction by the driving device 12. Even in this way, the molten resin can be measured. The mold clamping device is driven to clamp the pair of molds. The drive device 12 is driven, and the screw 3 is driven in the axial direction for injection. When the mold is opened by driving the clamping device after cooling and solidification, a molded product is obtained. Thereafter, the molded product can be molded in the same manner.

  The flushing method according to the present embodiment will be described with reference to the graph of FIG. In FIG. 2, the three graphs represent the number of rotations of the screw 3, the torque of the rotation of the screw 3, and the screw position of the screw 3 from the top. It is assumed that a normal injection molding cycle is performed before a certain time.

  When flushing, the supply of resin pellets of material from the hopper 6 is stopped. Next, when a predetermined operation for requesting flushing is performed in the controller 13, flushing is started under the control of the controller 13. The start time of flushing is indicated by reference numeral 15 in the graph of FIG. The controller 13 first performs a weighing operation. That is, the screw 3 is rotated to measure a predetermined amount of molten resin at the tip of the screw 3. Even if the resin pellets of the material are not supplied from the hopper 6, the molten resin remains sufficiently during the flight of the screw 3, so that such a molten resin is measured. The metering operation may be such that a predetermined back pressure is applied to the screw 3 so that the screw is retracted by the resin pressure of the molten resin, or a suck back for forcibly retracting the screw 3 may be performed. When a predetermined amount is measured by the measuring operation, the controller 13 executes an injection operation. That is, the rotation of the screw 3 is stopped, the screw 3 is driven in the axial direction, and the molten resin measured in front of the screw 3 is discharged to the outside. The controller 13 repeats such metering operation and injection operation for a preset number of times. In the graph, reference numeral 15 is the start time of the weighing operation, reference numeral 16 is the end time of the weighing operation, the start time of the injection operation, reference numeral 17 is the end time of the injection operation, and the start time of the next measurement operation. Yes. Since the torque is detected as the screw 3 rotates, the torque instantaneously becomes a large value immediately after the start of the weighing operation, then changes slightly, and at the end of the weighing operation, it suddenly drops to a small value. In the injection operation, it becomes substantially zero. On the other hand, when the injection position is set to 0 and the rightward direction in FIG. 1 is positive, the screw position increases linearly by the metering operation and becomes 0 in the injection operation in a short time.

  In the flushing method according to the present embodiment, the rotation of the screw 3 is stopped before the inside of the heating cylinder 2 becomes starved. This actually ends the flushing before repeating the metering and injection operations a set number of times. Specifically: When the controller 13 starts flushing, the torque of the rotation of the screw 3 is monitored immediately after that. Then, the maximum torque 19 at which this torque becomes the maximum value is stored. In the graph of FIG. 2, the maximum torque 19 is detected at 20. The controller 13 continues to monitor the torque, but the torque monitoring is limited to when the screw 3 is rotated. That is, monitoring is performed only during the weighing operation. When the torque monitored in this way becomes equal to or less than a preset ratio with respect to the maximum torque 19, that is, equal to or less than the torque lower limit coefficient, the measuring operation is interrupted. That is, the rotation of the screw 3 is stopped. In the graph of FIG. 2, the timing at which the monitored torque becomes equal to or less than the ratio of the torque lower limit coefficient to the maximum torque 19 is indicated by reference numeral 22. The torque at this time is indicated by reference numeral 23. Since the metering operation is interrupted at this timing, the rotation of the screw 3 can be stopped before the inside of the heating cylinder 2 becomes starved. Finally, the injection operation is performed to complete the flushing.

  Thus, in the present embodiment, the stop of the rotation of the screw 3 is determined based on the torque ratio. The torque of the screw 3 is mainly caused by the friction in the drive mechanism 8 that drives the screw 3 and the friction of the molten resin flowing between the heating cylinder 2 and the screw 3, but the former friction is It is relatively small compared to the latter friction. The maximum torque 19 is detected in a state where the molten resin is sufficiently filled between the flights of the screw 3, and the torque decreases as the molten resin decreases. Since the behavior of the molten resin in the heating cylinder 2 is complicated, the relationship between the torque reduction rate and the molten resin reduction rate is not necessarily linear, but has a sufficient correlation. Since the viscosity of the molten resin varies depending on the type and temperature of the resin, the torque affected by the viscosity should also vary greatly depending on the type and temperature of the resin, but in this embodiment, the torque ratio is thus increased. Since the stop of the rotation of the screw 3 is determined based on this, the remaining amount of the molten resin in the heating cylinder 2 can be estimated with relatively stable accuracy even if the type and temperature of the resin are different. That is, the rotation of the screw 3 can be stopped before the inside of the heating cylinder 2 is starved. The appropriate range of the torque lower limit coefficient is 40 to 70%, preferably 50 to 62%.

By the flushing method according to the present embodiment, a test was performed to confirm that the molten resin can be sufficiently discharged from the heating cylinder 2 and that the rotation of the screw 3 can be stopped before the inside of the heating cylinder 2 becomes starved.
(1) Test method Using the injection apparatus 1 shown in FIG. 1, the amount of the molten resin in the heating cylinder 2 in the state where the flushing was not performed first was examined. That is, the resin pellets of the material were supplied from the hopper 6 and the weighing operation and the injection operation were repeated, so that the molten resin was sufficiently filled between the flights of the screw 3. When the amount of the molten resin in the heating cylinder 2 was examined in this state, it was 82.7 g.
The torque lower limit coefficient was set to 90%, 80%, 70%, 62%, 60%, 50%, and 40%, and the flushing method according to the present embodiment was performed for each torque lower limit coefficient. Then, the amount of the molten resin in the heating cylinder 2 at the end of flushing was examined. The metering operation was performed by a method A in which the screw 3 was subjected to a predetermined back pressure and the screw was retracted by the resin pressure of the molten resin, and a method B by a suckback in which the screw 3 was forcibly retracted. Table 1 shows the amount of the molten resin in the heating cylinder 2 measured in each test. It can be said that when the torque lower limit coefficient is 50 to 62%, the molten resin is sufficiently discharged and the rotation of the screw 3 in the starved state can be prevented.

  The flushing method according to the present embodiment can be variously modified. For example, torque monitoring may be performed with an instantaneous value or may be performed with a moving average. Further, although the torque monitoring is described to be limited to when the screw 3 is rotated, it may be excluded from the monitoring target immediately after the start of the weighing operation. As described above, immediately after the start of the metering operation, the torque instantaneously becomes a large value because this includes the torque necessary to rotate the screw 3 against the moment of inertia. If the immediately after the start of the weighing operation is excluded from the monitoring target, the maximum torque can be determined by excluding the torque that increases instantaneously, so that the remaining amount of the molten resin can be more accurately evaluated.

DESCRIPTION OF SYMBOLS 1 Injection device 2 Heating cylinder 3 Screw 5 Nozzle 6 Hopper 9 Backflow prevention device 11 Motor 13 Controller

Claims (4)

In an injection device comprising a heating cylinder and a screw provided in the heating cylinder so as to be able to be driven in the rotational direction and the axial direction, the supply of material from the hopper behind the heating cylinder is stopped, and the screw And repeating the weighing operation for weighing the molten resin in front of the screw and the injection operation for driving the screw in the axial direction to discharge the measured molten resin to the outside. A flushing method for discharging molten resin to the outside,
The torque for rotating the screw in the weighing operation is monitored , the maximum torque that is the maximum value of the torque after the start of the flushing is detected, and the torque is detected when a torque equal to or less than a preset ratio with respect to the maximum torque is detected. A flushing method for an injection apparatus, wherein operation is stopped, the injection operation is performed, and the flushing is terminated.   The method according to claim 1, wherein the weighing operation is performed by applying a predetermined back pressure to the screw.   The method according to claim 1, wherein the weighing operation is performed by sucking back the screw forcibly retracting in the axial direction.   4. The method for flushing an injection apparatus according to claim 1, wherein the ratio is 50 to 62%.

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