JP2015227032A - Measuring control method of injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring control method of an injection molding machine capable of preventing backflow of resin from a storage part in an injection stand-by state after completion of a measuring step.SOLUTION: A measuring control method of an injection molding machine is configured so that: in a measuring step, after a screw 21 reaches a measuring completion position and rotation operation of the screw 21 is stopped, with respect to pressure drop of pressure P2 of the resin in a rear side of a check valve 24, the screw 21 is retreated before and after of rotation stop of the screw 21, and pressure P1 of the resin in a front side of the check valve 24 is dropped to almost equal pressure to the pressure P2, namely screw retreat operation is provided.

Description

  The present invention relates to a metering control method for an injection molding machine.

  In the injection device of the inline screw type injection molding machine, the resin material such as resin pellets supplied from the material supply unit of the injection device is rotated between the inner peripheral surface of the heating barrel and the outer peripheral surface of the screw by rotating the screw. In a resin flow path formed between them, plasticized (melted) continuously, and in a space called a reservoir inside the tip of the heating barrel, a quantity of plasticized resin necessary for one injection filling process A metering step for storing the is performed. Then, after completion of the metering step, an injection step is performed in which the screw is advanced to inject and fill the resin in the reservoir into the cavity of the mold through the injection nozzle at the tip of the heating barrel.

  A measuring process and an injection process of an inline screw type injection molding machine will be briefly described with reference to FIG. FIG. 1 is a schematic cross-sectional view of an injection device at the time of switching from a measurement process to an injection process according to a general measurement control method. FIG. 1A shows a measuring process, FIG. 1B shows an injection standby state in which the measuring process is completed, and FIG. 1C shows a state immediately after the injection process starts.

  A screw head 22 having a conical shape and having a plurality of recesses 22a in the longitudinal direction is fixed to the tip of the screw 21 in the heating barrel 10. A ring-shaped check valve 24 (also referred to as a check ring or the like) is arranged in the small diameter portion 22b of the screw head 22 on the tip end side of the screw 21 so as to be movable by a predetermined amount in the longitudinal direction of the screw 21. Has been. The movement amount is a distance S (es) that is restricted by the large-diameter portion 22c (forward limit) of the screw head 22 on the storage unit 11 side and the rear seat 23 (reverse limit) on the tip end side of the screw 21.

  As shown in FIG. 1 (a), the pellet-shaped resin supplied from the material supply unit 13 into the heating barrel 10 during the weighing process is a screw 21 having a spiral flight 21a formed on the outer peripheral surface thereof. By rotation, the resin flow channel 14 formed between the inner peripheral surface of the heating barrel 10 and the outer peripheral surface of the screw 21 flows toward the storage portion 11 (front). In the meantime, it becomes a molten state (plasticization) by the thermal energy of the heating means (not shown) arranged on the outer peripheral surface of the heating barrel 10 and the shear energy (thermal energy) directly applied to the resin by the rotation of the screw 21. . Due to the resin pressure P <b> 2 generated by this resin flow, the check valve 24 is pressed toward the storage unit 11, moved to the storage unit 11 (forward limit), and between the check valve 24 and the rear seat 23 of the screw 21. Is opened by a distance S. Further, in this state, the opened resin flow path 14 and the longitudinal concave portion 22a of the screw head 22 are communicated with each other, and the resin on the rear seat 23 side of the screw 21 is continuously stored in the storage portion 11 in front of the screw head 22. Is done.

Moreover, with the increase in the amount of resin stored in the storage unit 11 during the weighing process, the screw 21 is
The material moves to the material supply unit 13 side (rear) while maintaining the rotation. This screw retreat operation is performed in a state in which a resistance force (back pressure = P1) accompanying the retreat operation is applied to the screw 21 in order to apply a predetermined pressure P1 to the resin stored in the storage unit 11. That is, the relationship between the resin pressure P1 of the resin in the reservoir 11 in front of the check valve 24 and the resin pressure P2 of the resin in the resin flow path 14 behind the check valve 24 in the metering process is P1 <P2. In this relationship, the resin flow to the resin reservoir 11 is maintained.

  After the resin amount set in advance is stored in the storage unit 11, the material supply to the material supply unit 13 and the rotation operation of the screw 21 are stopped (completion of the metering process). This state is shown in FIG. In this state (immediately after the completion of the metering process), the distance S is opened between the check valve 24 at the forward limit and the rear seat 23 of the screw 21. Then, after the injection standby state, as shown in FIG. 1 (c), the screw 21 is moved at a predetermined speed in a state where the resin flow path on the mold side (not shown) after the injection nozzle 12 at the tip of the heating barrel 10 is opened. -Advance at a predetermined pressure (injection process). The movement stroke (distance S) in the longitudinal direction of the check valve 24 varies depending on the size of the injection device and the like, but is usually 2 to 3 mm, and is about 5 to 6 mm at the longest. Therefore, immediately after the screw 21 starts moving forward, the rear seat 23 of the screw 21 moves forward by a distance S and comes into close contact with the rear end of the check valve 24 (reverse limit). The space between the screw 21 and the rear seat 23 is closed. The resin pressure P1 of the resin in the storage unit 11 is rapidly increased by the closing of the check valve 24 and the forward movement of the screw 21, and the relationship between P1 and P2 is reversed and P1> P2.

  As a result, the check valve 24 receives the resin pressure P <b> 1 that increases from the resin on the storage unit 11 side, and is pressed to the rear seat 23 side of the screw 21, thereby enhancing the close contact state with the rear seat 23. In this way, during the injection process, the close contact state between the check valve 24 and the rear seat 23 (closed state of the resin flow path 14) is maintained, and the resin in the storage portion 11 passes through the check valve 24 to the screw 21 side. Back flow into the resin flow path 14 is prevented.

  In this way, no drive power unit or special control is required, and in the metering process, the opening operation between the resin flow path and the storage part due to the resin flow (resin pressure) to the storage part side is injected. In the process, the same closing operation is performed by the forward movement operation of the screw, thereby switching the opening / closing operation between the resin flow path and the storage part and the back flow of the resin during the injection process from the storage part to the resin flow path side. The check valve that can be prevented has a simple structure and a relatively high backflow prevention capability in the injection process, and is a general configuration in an inline screw type injection molding machine. However, in recent years, there has been a demand for further improvement in weighing accuracy in the weighing process, and while the resin flow path is switched from the open state to the closed state, the resin in the storage portion passes through the check valve to the resin flow path side of the screw. Variation in the amount of metered resin, which is attributed to backflow, is a problem. The actual amount of injected resin is smaller than the estimated measured resin amount by the reverse flow rate of this resin, but if this reverse flow rate is approximately constant for each molding cycle, the estimated resin amount is set in the weighing process. What added the reverse flow rate may be the amount of metered resin. However, the problem is that the aforementioned reverse flow rate of the resin is not always constant for each molding cycle.

  In order to improve the variation in the amount of the metering resin due to the variation in the reverse movement of the check valve after the completion of the metering process, Patent Document 1 discloses an injection screw (with the screw rotating stopped after the metering is completed). An injection method is disclosed in which a screw is sucked back (retracted), a reverse rotation of the injection screw is performed by a predetermined amount at the suck back (retracted) position, and then the injection screw is advanced to shift to an injection process.

  The backward movement of the screw after the completion of the measurement is such that the ring valve (check valve) whose front end is pressed is moved backward together with the screw in an open state (Patent Document 1, paragraph 0008). Furthermore, although not described in the document, it is presumed that the operation is for securing a screw advance distance for bringing the check valve into a completely closed state at the original measurement completion position. In the subsequent reverse rotation operation in the reverse position, the resin pressure P2 of the resin in the resin flow path behind the check valve is decreased by rotating the screw in the direction opposite to the normal rotation in the metering process. The relationship with the resin pressure P1 of the resin in the front reservoir is P1> P2, and the reverse (close) operation of the check valve is promoted. The check valve is completely closed while the screw is advanced from the reverse position to the original measurement completion position by starting the injection process from the reverse position, and from the original measurement completion position, the check valve is However, under the completely closed state, the injection process is performed and the back flow of the resin can be prevented.

  In Patent Document 2, in order to improve the variation in the amount of the injected resin due to the variation in the closing time of the resin flow path during the injection process, the screw is moved backward by a set distance between the completion of the weighing process and the start of the injection process. An injection molding machine having means for bringing the backflow prevention ring (check valve) into contact with the seal ring (rear seat) by returning to the measurement completion position again is disclosed.

  Similarly to the backward movement operation after the completion of measurement in Patent Document 1, the backward movement operation of the screw in Patent Document 2 is performed so that the injection process is performed from the original measurement completion position in a state where the check valve is completely closed. Therefore, it is performed in order to secure the screw advance distance. That is, Patent Document 1 and Patent Document 2 start the injection process by starting the injection process after the position of the check valve at the start of the injection process is moved (retracted) to the complete closed position (forward limit). This prevents the back flow of the resin that is supposed to occur during the closing (reverse) operation of the check valve.

JP 09-029794 A Japanese Patent Laid-Open No. 04-070316

  In recent years, the resin pressure P1 of the resin in the reservoir in front of the check valve and the resin pressure P2 of the resin in the resin flow path behind the check valve while switching from the metering process to the injection process through the injection standby state. Changes have been verified, and the situation of resin backflow during this period has become increasingly clear. This will be described with reference to FIG. FIG. 2 is a graph showing changes in the resin pressure P1 in front of the check valve and the resin pressure P2 in the rear based on the passage of time during the switching from the metering process to the injection process according to a general metering control method. is there. The horizontal axis represents time t, and the vertical axis represents pressure P.

First, although not shown, the metering process initiated by the resin pressure of the resin flow of the resin flow path 14 that caused by the screw rotation P2 (P _F), a check valve 24 from the closed position (rearmost) It moves to the open position (advance limit), and the resin in the resin flow path 14 flows into the storage part 11. At this time, a back pressure (= resin pressure P1 / P _B ) is applied to the screw 21 itself, but the resin pressure is such that the screw 21 is at the injection advance limit position and the screw 21 is moved backward by the resin in the storage portion 11. Therefore, the start of movement of the check valve 24 to the open position (forward limit) is not due to the differential pressure between the resin pressure P1 and the resin pressure P2, but due to the resin pressure P2. Resin is fluidized in the storage unit 11, even after the resin pressure such as to retract the screw 21 into the resin of the reservoir 11 occurs, the relationship between the resin pressure P1 (P B) _<resin pressure P2 (P _F) is maintained Therefore, the open state of the check valve 24 is continued and the metering process is continued.

Here, the check valve 24 behind the resin pressure P2 is a substantially all of the original the pressure generating limit, the pressure P _F according to the kinetic energy of the given resin resin flow by the screw rotation. Other than that, there is basically no energy source for applying pressure to the molten resin filling the resin flow path 14 behind the check valve 24. The molten resin behind the check valve 24 gradually increases in proportion to the unmelted resin as it approaches the material supply unit 13 side, and the vicinity of the material supply unit 13 is almost completely in a pellet form (solid ) In an atmosphere open state filled only with resin. Thus, the metering process is completed, rotation later time to stop t1 of the screw 21, the resin pressure P2 of the resin in molten state behind the check valve 24 without being maintained, by the time t2, the P _F rapidly drops to the atmospheric pressure P _A neighborhood. The time required from _{P F} of the P2 pressure drop to atmospheric pressure _{P A} proximity (t2-t1) is about 1 second.

Next, as described above, the resin pressure P1 in front of the check valve 24 (reservoir 11) is the pressure P _B applied by the backward resistance (back pressure) of the screw during the measurement process. Here, in the injection standby state after the completion of the weighing process, even if the position of the weighing process of the screw 21 and the back pressure are maintained, the relationship of P1 <P2 is associated with the pressure drop of the resin pressure P2 described above. After the point X (hereinafter referred to as a transition point), the relationship shifts to P1> P2. Moreover, as shown in FIG.1 (b), the check valve 24 is an open state (forward limit) also in the transition point X. As shown in FIG. As a result, after the transition point X, the resin in the storage portion 11 flows backward to the resin flow path 14 on the rear seat 23 side behind the check valve 24.

There are three possible patterns for the change in the resin pressure P1 after the transition point X and the reverse flow of the resin. One is the pattern shown in FIG. This is pattern 1. In this pattern 1, after the transition to the relationship of P1> P2, the check valve 24 in the open position (advance limit) is almost closed by the back flow of the resin generated by the differential pressure between P1 and P2 (P1-P2). The check valve 24 is kept open (forward limit) without moving to the position (reverse limit) side. In this case, in the injection standby state after the completion of the weighing process, even if the position and back pressure of the screw 21 at the completion of the weighing process are maintained, the open state (advance limit) of the check valve 24 is maintained. while the relationship P2 is maintained, the backflow of resin from the reservoir 11 to the resin flow path 14 is continued, as shown in FIG. 2, the resin pressure P1 (P _B) drops to the atmospheric pressure P _a proximity ( Time t3). As a result, P1 = P2 ≒ _{P A,} and the check valve 24 is resin backflow stops left open. The reverse flow rate of the resin from the transition point X to the time t3 is indicated by the area of the region A indicated by hatching in FIG.

The second is not shown in the figure, but after the transition to the relationship of P1> P2, the check is in the open position (advance limit) due to the back flow of the resin generated by the differential pressure between P1 and P2 (P1-P2). Although the valve 24 moves to the closed position (retreat limit) side, the pressure difference between P1 and P2 gradually decreases due to the back flow of the resin, so it does not move to the close position (retreat limit), and the middle of the movement stroke It is a pattern that stops at a position. The opened state of the check valve 24 is maintained in the intermediate position, as a result, backflow of the resin is continued until P1 = P2 ≒ P _A. This is pattern 2. In this pattern 2, since the distance between the check valve 24 and the rear seat 23 where the resin flows back is shorter than the distance S, the cross-sectional area of the flow path through which the resin flows back becomes narrower than the pattern 1 described above. However, since the cross-sectional area of the flow path is narrowed, the pressure drop rate of the resin pressure P1 in the reservoir 11 is smaller than that of the pattern 1, and the differential pressure (P1-P2) between P1 and P2 that causes the resin to flow backward is greater than that of the pattern 1. Also grows. As a result, since the reverse flow speed of the resin is increased in the pattern 2, the timing at which the reverse flow of the resin is stopped is different from that in the pattern 1, and the reverse flow rate of the resin is not significantly different from that in the pattern 1.

Although not shown in the figure, the check valve is in the open position (advance limit) due to the back flow of the resin generated by the pressure difference between P1 and P2 (P1-P2) after the transition to the relationship of P1> P2. 24 is a pattern in which the check valve 24 is kept in the closed state (retreat limit) by moving to the closed position (retreat limit) side. This is pattern 3. In this pattern 3, a possibility that the resin pressure P1 falls to atmospheric pressure P _A vicinity is low, even if the relationship is maintained in P1> P2, the check valve 24 is in the closed state (retreating limit) It is considered that there is almost no back flow of resin from the time point. In other words, the reverse flow rate of the resin in the pattern 3 is an amount from the transition point X to the time when the check valve 24 is in the closed state (retreat limit), and the reverse flow rate is smaller than that of the pattern 1 and the pattern 2. it is conceivable that.

After the injection process, in parallel with the measurement process, a cooling and solidification process, a mold opening process, a product take-out process, a mold closing / clamping process are performed, and the process proceeds to the next injection process. In general, the weighing process is completed first and the injection standby state in FIG. 2 is often obtained in the state of FIG. Thus, in the injection stand-by state, as shown in region A of FIG. 2, the resin pressure P1 and the resin pressure P2 is either resin backflow occurs until the pressure drop together to atmospheric pressure P _A near some cases Since the back flow of the resin occurs until the check valve 24 is closed (retreat limit) due to the differential pressure between the resin pressure P1 and the resin pressure P2, the amount of resin to be injected and filled becomes smaller than the desired amount of resin. There is a problem.

  Here, as in the three patterns described above, after shifting to the relationship of P1> P2, the resin is in the open position (forward limit) due to the back flow of the resin generated by the differential pressure between P1 and P2 (P1-P2). The behavior of the check valve 24 depends on whether the magnitude of the pressure difference between P1 and P2 is sufficient to move (retract) the check valve 24, and the check valve. This is the sliding resistance of the check valve 24 when moving (retreating) 24. The former largely depends on the type of resin material used, the size of the injection molding machine, and the specifications of the check valve 24. The latter includes temperature and viscosity of the plasticized resin, contamination mixed in the sliding portion between the small diameter portion 22b of the screw head 22 and the check valve 24, scratches generated in the sliding portion during molding, There are many places due to wear.

  The former can be predicted to some extent in the specification, and is unlikely to cause a variation in the reverse flow rate of the resin shown in the region A for each molding cycle. However, the latter causes a variation in the reverse flow rate of the resin shown in the region A for each molding cycle even when molding is performed with the same resin material under the same molding conditions. Therefore, since the reverse flow rate of the resin in the injection standby state shown in the region A in FIG. 2 is not constant for each molding cycle, it is difficult to measure in advance by an amount corresponding to the reverse flow rate. .

  On the other hand, the reverse flow of the resin to be prevented in Patent Document 1 and Patent Document 2 is a reverse flow rate that is generated during the closing (retreating) operation of the check valve at the start of the injection process. For example, if the moving stroke of the check valve 24 is 10 mm and the forward speed (injection speed) of the screw 21 in the injection process is 30 mm / s, the check valve 24 is almost completely in the injection standby state as in pattern 1. In the open state (forward limit), from the start of the injection process until the screw 21 moves forward and contacts the rear end of the check valve 24, that is, it is necessary for the check valve 24 to be in the closed state (reverse limit). The time (time t5-t4) is as short as about 0.3 seconds. In large thin molding, high cycle molding, and injection foam molding, high speed injection conditions of 100 mm / s or more are often required, and in this case, it is further shortened to 0.1 seconds or less. In the state where the check valve 24 is in the middle of the movement stroke as in the pattern 2, the time (time t5-t4) required for the check valve 24 to be in the closed state (reverse limit) is further shortened. In pattern 3, since the check valve 24 is already in the closed state (retreat limit) at the start of the injection process, the resin backflow itself does not occur.

In fact, as previously described, before reaching the time t4, the resin pressure P1 and the resin pressure P2 is then pressure drop together to atmospheric pressure P _A proximity, during this time t4 to time t5, There is almost no differential pressure that causes a back flow of the resin before and after the check valve 24. During this time, the time required from the start of the injection process until the screw 21 moves forward and comes into contact with the rear end of the check valve 24 (until the check valve 24 is closed) is as described above. Therefore, the reverse flow rate that is supposed to be generated during the check valve closing (retreating) operation at the start of the injection process is indicated by a region B in FIG. On the other hand, the reverse flow rate of the resin from the transition point X to the time t3, that is, the reverse flow rate of the resin in the injection standby state indicated by the region A in FIG. (Time) is clearly longer than region B, and during that time, a differential pressure that causes a back flow of resin occurs before and after the check valve 24, so that it is clearly greater than the back flow rate shown in region B. In view of these, the large influence on the amount of metered resin is that the reverse flow rate that is generated during the check valve closing (retracting) operation at the start of the injection process, indicated by region B in FIG. It is clear that the reverse flow rate of the resin in the injection standby state shown in the region A of FIG.

  The backflow of the resin to be prevented in Patent Document 1 and Patent Document 2 is indicated by the region B, and there is any description or suggestion about preventing the backflow of the resin in the injection standby state indicated by the region A. Absent. Therefore, in the injection method of Patent Document 1 and the injection molding machine of Patent Document 2, it must be said that it is difficult to sufficiently improve the variation in the amount of injected resin.

  Further, in Patent Document 1, after weighing, the screw is sucked back (retracted by a screw), the screw is reversely rotated at that position, and the resin pressure P2 is lowered to relatively increase P1, and P1> P2 In this relationship, the pressure difference is increased, and a positive closing operation of the check valve is induced. However, as described above, since the resin pressure P2 drops to near atmospheric pressure in about one second after the screw rotation is stopped, the reverse rotation of the screw does not contribute to the closing operation of the check valve. . As in pattern 3 described above, the check valve P1> P2 generated in this way can completely move the check valve in the open position (forward limit) to the closed position (reverse limit). Whether it is possible depends on the type of resin material to be used, the size of the injection molding machine, and the specifications of the check valve 24, so that there are many restrictions on implementation. Further, increasing the difference in the resin pressure of P1> P2 causes an increase in the back flow rate of the resin when the check valve is not completely closed as in pattern 1 or pattern 2, and the amount of metered resin There is a possibility of further increasing the variation.

  The present invention has been made in view of the above-described problems, and specifically, an injection molding machine capable of preventing a back flow of resin from a storage portion in an injection standby state after completion of a weighing process. An object is to provide a weighing control method.

  In order to achieve the above object, the metering control method for an injection molding machine according to the present invention is based on a check valve after the screw reaches the metering completion position and stops the screw rotating operation in the metering step. In response to the pressure drop of the resin pressure P2 on the rear side, after the screw stops rotating, the screw is moved backward to reduce the pressure P1 of the resin from the check valve to substantially the same pressure as the pressure P2. Have.

  In the metering control method for an injection molding machine according to the present invention, the pressure drop rate of the pressure P1 may be interlocked with the pressure drop rate of the pressure P2 in the screw retreat operation.

  Furthermore, it is preferable that the metering control method for an injection molding machine according to the present invention completes the screw retreat operation within one second.

  On the other hand, in the metering control method for an injection molding machine according to the present invention, when the outer diameter of the screw is D (dee) and the correction coefficient is α (alpha), the screw retraction distance ΔL (delta L) in the screw retraction operation. Is expressed by ΔL = αD, and the correction coefficient α is preferably in the range of 0.025 to 0.25.

  In the metering control method for an injection molding machine according to the present invention, the pressure of the resin pressure P2 behind the check valve after the screw reaches the metering completion position and stops the screw rotation operation in the metering step. In response to the descent, the screw is retracted after stopping the rotation of the screw, and the screw retracting operation is performed to lower the pressure P1 of the resin ahead of the check valve to substantially the same pressure as the pressure P2. It is possible to prevent the back flow of the resin from the storage part in the injection standby state.

It is a schematic sectional drawing of the injection device during a change from a measurement process to an injection process concerning a general measurement control method. It is the graph which displayed the change of the resin pressure P1 of the front of a non-return valve and the resin pressure P2 of back based on time passage during the switching from a measurement process to an injection process concerning a general measurement control method. The graph which displayed the change of the resin pressure P1 of the front of a non-return valve and the resin pressure P2 of the back based on progress of the time of switching from the measurement process to the injection process of Example 1 which concerns on the measurement control method of this invention. It is.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

  With reference to FIG. 3, a measurement control method for an injection molding machine according to the first embodiment of the present invention will be described. FIG. 3 is a graph showing changes in the resin pressure P1 in front of the check valve and the resin pressure P2 in the rear based on the passage of time while switching from the metering process to the injection process in the first embodiment. Further, the present invention is a metering control method for an injection molding machine, and the injection molding machine to be used does not have a special configuration, so that FIGS. 1 and 2 are also referred to as necessary.

  The metering control method of the injection molding machine according to the first embodiment of the present invention is different from the general metering control method in that after the screw 21 stops rotating, the screw 21 is retracted to the front of the check valve. This is the point of having a screw retraction operation that lowers the resin pressure P1 to approximately the same pressure as the resin pressure P2. Except for this point, the method is basically the same as a general measurement control method, and therefore, detailed description thereof will be omitted or will be described with reference to FIGS. 1 and 2, and only differences will be described in detail. Therefore, in FIG. 3, the same reference numerals are used for the same components as those in FIG. 2, and the configurations different from those in FIG. 2 are distinguished by adding “′ (apostrophe)” to the corresponding symbols.

As shown in FIG. 3, the resin pressure P2 of the molten resin behind the check valve 24 is not maintained until the time t2 after the time t1 when the measuring process is completed and the rotation operation of the screw 21 is stopped. to rapidly drop to atmospheric pressure _{P a} near from _{P F.} Here, in the metering control method of the injection molding machine according to the first embodiment of the present invention, after the rotation operation of the screw 21 is stopped, the screw 21 is moved backward by a distance ΔL (screw backward movement operation).

This screw retreat operation is to lower the resin pressure P1 of the storage portion 11 in front of the check valve 24 by expanding the volume of the storage portion 11. The screw retreat operation, until slightly later time t3 'in the time t2, the resin pressure P1, if ask substantially the pressure drop to the same atmospheric pressure P _A from the check valve 24 and the resin pressure P2 behind the rear seat side , P1 <P2 shifts to a relationship of P1> P2 at the transition point X ′, and the amount of resin flowing backward from the storage portion in the injection standby state after the completion of the metering process is shown in the area A ′ indicated by hatching in FIG. Shown in area.

  It is obvious that this area A ′ is sufficiently small with respect to the area A in FIG. 2, and the amount of resin flowing back from the storage portion in the injection standby state after the completion of the weighing process is reduced with respect to a general weighing control method. Can be greatly reduced. That is, since the amount of resin flowing back from the storage portion in the injection standby state is small, the reverse flow rate of the resin indicated in this region A ′ varies in any of the patterns 1 to 3 described above. However, the amount of variation can be significantly reduced with respect to the amount of variation in the reverse flow rate of the resin indicated in the previous region A. In the injection standby state from time t3 ′ onward to time t4 when the injection process starts, the pressure difference between the resin pressures P1 and P2 is substantially zero, so the check valve 24 is in the open state (forward limit). However, it goes without saying that the amount of resin flowing backward is substantially zero even at the midway position of the movement stroke toward the closed position (retreat limit).

In the first embodiment, for ease of explanation, the time t3 ′ is set to a time slightly delayed from the time t2, but the resin pressure P1 can be set by appropriately setting the reverse speed to the distance ΔL of the screw 21. By linking the pressure drop rate with the pressure drop rate of the resin pressure P2, or by completing the backward movement to the distance ΔL of the screw 21 within one second, the time t3 ′ is substantially matched with the time t2, that is, by the resin pressure P1 is the pressure drop substantially to atmospheric pressure P _a proximity at the same time the resin pressure P2, 'without generating an area a' transition point X can be substantially zero. Note that within one second, as described above, in which the resin pressure P2 is taken as a reference time, which is the required for pressure drop to atmospheric pressure P _A neighborhood.

  In this manner, the reverse flow rate of the resin from the storage portion during the switching from the metering process to the injection process through the injection standby state can be set to the resin amount indicated by the areas A ′ and B in FIG. 3. As described above, the reverse flow rate indicated by the region A ′ can be further reduced by appropriately setting the reverse speed of the screw 21 up to the distance ΔL, and the reverse flow rate indicated by the region B is negligible. Therefore, the measurement control method for the injection molding machine according to the present invention can sufficiently satisfy the high measurement accuracy required for the measurement process in recent years.

  Further, since the relationship between the resin pressure P1 and the resin pressure P2 is P1 <P2 from the completion of the weighing process (when the screw rotation operation is stopped) to the transition point X ′, the relationship from the resin flow path 14 to the storage unit 11 is satisfied. The resin flow does not stop completely, and the resin overflows to the reservoir 11 until the transition point X ′ is reached. Therefore, by appropriately setting the reverse speed up to the distance ΔL of the screw 21, not only the area A ′ is reduced, but also the amount of overflow of the first half of the resin into the reservoir 11 at the transition point X ′ It is also possible to cancel the reverse flow rate (region A ′) from the storage unit 11 in the latter half, and to keep the reverse flow rate of the resin in the injection standby state substantially only in the amount shown in the region B.

  Next, the setting of the screw retraction amount ΔL in the screw retraction operation will be described. The resin in the reservoir 11 in front of the check valve 24 is a viscoelastic body having both viscous and elastic characteristics, and it is difficult to accurately obtain the volume modulus and Young's modulus of such a viscoelastic body. . However, as a result of verification by the applicant, it has been found that an appropriate ΔL can be obtained when the screw retraction amount ΔL is expressed by the equation ΔL = αD and the correction coefficient α is in the range of 0.025 to 0.25. D is the outer diameter of the screw 21 on the rear seat 23 side (metering zone).

  Specifically, first, in the test molding, ΔL = 0.1D, that is, α = 0.1, and the screw retraction amount is temporarily set to 1/10 of the outer diameter D of the screw 21 on the rear seat 23 side, Injection molding is performed by the metering control method according to the present invention (screw retraction amount temporary setting step). Comparison between the assumed measured resin amount obtained in this test molding and the weight of the molded product and data collection of variations are performed. Next, the correction value of α in a single setting change is set to 0.025, for example, ΔL = 0.125D (or ΔL = 0.075D), test molding is performed, data is taken similarly, and α Check the direction and degree of increase / decrease. While correcting this in the range of 0.025 ≦ α ≦ 0.25, ΔL with the smallest difference between the assumed measured resin amount and the molded product weight and the variation is obtained.

  As described above, the applicant verifies the range of the correction coefficient α for obtaining the screw retraction amount ΔL from the outer diameter D on the rear seat side of the screw, that is, the lower limit value 0.025 and the upper limit value 0.25. Sought by. As a result of verification by the applicant, when the screw retraction amount ΔL <0.025D, the pressure drop of the resin pressure P1 is insufficient, so the pressure difference of P1> P2 is maintained, and the storage in the injection standby state is performed. The backflow of the resin from the portion 11 to the resin flow path 14 side could not be sufficiently prevented, and the variation in the direction in which the amount of the metered resin decreased could not be solved.

In the case of screw retracting amount [Delta] L> 0.25, the pressure drop across the resin pressure P1 becomes excessive, the resin pressure P1 was pressure drops to a negative pressure lower than the atmospheric pressure P _A. Therefore, in most of the injection standby state, the pressure difference of P1 <P2 is maintained, an overflow phenomenon occurs in which the resin behind the check valve 24 flows toward the storage unit 11, and conversely, the amount of metered resin increases. The direction was uneven. If the above ΔL data is accumulated based on the resin type and molding conditions, α can be corrected in a single setting change in order to obtain higher weighing accuracy or shorten the test molding time. The value may be arbitrarily selected regardless of 0.025.

  Example 1 is an example for easily explaining the measurement control method of an injection molding machine according to the present invention, and the present invention is not limited to the above-described embodiment, and can be implemented in various forms. Needless to say.

DESCRIPTION OF SYMBOLS 10 Heating barrel 11 Storage part 12 Injection nozzle 13 Material supply part 14 Resin flow path 21 Screw 21a Flight 22 Screw head 22a Recessed part 22b Small diameter part 22c Large diameter part 23 Rear seat 24 Check valve

Claims (4)

  In the measuring step, after the screw reaches the measuring completion position and stops the rotational operation of the screw, after the screw rotation stops, the pressure drop of the resin pressure P2 behind the check valve A metering control method for an injection molding machine having a screw retraction operation in which the screw is retracted and the pressure P1 of the resin in front of the check valve is lowered to substantially the same pressure as the pressure P2. 2. The metering control method for an injection molding machine according to claim 1, wherein in the screw retreat operation, the pressure drop rate of the pressure P <b> 1 is interlocked with the pressure drop rate of the pressure P <b> 2.   The weighing control method for an electric injection molding machine according to any one of claims 1 and 2, wherein the screw retreating operation is completed within one second.   When the outer diameter of the screw is D and the correction coefficient is α, the retraction distance ΔL of the screw in the screw retraction operation is expressed as ΔL = αD, and the correction coefficient α is in the range of 0.025 to 0.25. The metering control method for an injection molding machine according to any one of claims 1 to 3.

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