Injection molding machine for foam molding and control method of injection molding machine

Abstract

The injection molding machine (1) of the present invention comprises: a heating cylinder (17) having a gas injection port (26); a screw (18); a gas cylinder (30); a pressure reducing valve (34) for reducing the primary pressure of gas from the gas cylinder (30) to a secondary pressure; a gas supply unit (43) for supplying the secondary pressure gas to the gas injection port (26); a secondary pressure detection means (42) for detecting the secondary pressure; and a control means (4). Moreover, the control means (4) detects abnormalities by comparing a preset pressure in the injection molding machine (1) with the secondary pressure.

Description

[Technical Field]

[0001] The present invention relates to an injection molding machine that injects an inert gas into an injection material to form a foamed article, and a control method for such an injection molding machine. [Previous Technology]

[0002] An injection molding machine system for obtaining foamed molded articles using a physical foaming agent, namely an inert gas, is generally configured as follows. That is, the injection molding machine system for foam molding consists of a heating cylinder and a screw. The heating cylinder is divided into multiple sections according to the shape of the screw, including a first compression / metering section, a starvation section, and a second compression / metering section from upstream to downstream. An inert gas injection section is provided in the heating cylinder according to the starvation section. The inert gas system is supplied from a gas supply source such as a gas cylinder. The primary pressure of the gas supplied from the gas supply source is reduced to a secondary pressure using a pressure reducing valve. This secondary pressure inert gas system is connected to the injection section.

[0003] The injection material is conveyed and melted from upstream to downstream in a heating cylinder by a screw, and then mixed in the first compression and metering zone. Next, the pressure of the injection material is reduced in the starvation zone, and a secondary pressurized inert gas is injected. The injection material injected with inert gas is then mixed and compressed in the second compression and metering zone, metered, and then injected into a mold to obtain a foamed molded article. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2014-200937

[0005] In injection molding machines for foaming, there is a situation where the injection section of the inert gas is blocked due to the ejected material pushing it up, which is called vent up. The injection molding machine for foaming described in Patent Document 1 is equipped with an vent up detection mechanism in the injection section. When vent up occurs, it is mechanically detected and the ejected material is pushed back into the heating cylinder. [Summary of the Invention]

[0006] (The problem that the invention aims to solve)

[0007] In injection molding machines used for foam molding, various problems can occur besides overflow. These include backflow of inert gas and poor inert gas supply. The secondary pressure of the inert gas is properly controlled by a pressure reducing valve, and then confirmed to be at the required pressure using a pressure gauge that allows visual confirmation of the secondary pressure. Furthermore, the injection material is also properly supplied. However, it is still impossible to completely prevent these problems; there is a possibility that problems may occur but go unnoticed, resulting in a large number of defective products.

[0008] Other issues and new features will become clear from the description and accompanying drawings in this specification. (Technical means to solve the problem)

[0009] The present invention relates to an injection molding machine having the following configuration: The injection molding machine includes: a heating cylinder having a gas injection port; a screw; a gas cylinder; a pressure adjustment means for adjusting the primary pressure of gas from the gas cylinder to a secondary pressure; a gas injection port for supplying the secondary pressure gas to the heating cylinder; a secondary pressure detection means for detecting the secondary pressure; and a control means. Furthermore, the control means compares a preset pressure in the injection molding machine with the secondary pressure to detect any abnormalities. (Effects compared to prior art)

[0010] According to the present invention, signs of overflow, gas backflow, poor gas supply, etc. can be quickly detected, so as to prevent defective products from occurring.

Implementation Method

[0012] Hereinafter, specific embodiments will be described in detail with reference to the drawings. However, the description is not limited to the following embodiments. To make the explanation clearer, the following descriptions and drawings are appropriately simplified. In each drawing, the same symbol is assigned to the same element, and repeated explanations are omitted as necessary. Furthermore, to avoid making the drawings complicated, omitted parts are indicated by shaded lines.

[0013] This embodiment will be described. <Injection Molding Machine> The injection molding machine 1 of this embodiment, as shown in FIG1, is generally composed of a mold clamping device 2 and an injection device 3 mounted on a base B, and is controlled by a controller 4 as a control means. The mold clamping device 2 may be of the direct-pressure type, but in this embodiment it is of the toggle type. That is, the mold clamping device 2 is composed of a fixed plate 7, a movable plate 8, a mold clamping housing 9, connecting rods 10, 10, ... connecting the mold clamping housing 9 and the fixed plate 7, and a toggle mechanism 11. The mold clamping device 2 mounts molds 13 and 14 on the fixed plate 7 and the movable plate 8. When the toggle mechanism 11 is driven, the molds 13 and 14 are in the mold clamping state.

[0014] <Injection Device> The injection device 3 of this embodiment is an injection device for foaming molding using a physical foaming agent, i.e., gas, as shown in FIG2. The injection device 3 consists of a heating cylinder 17 and a screw 18 installed in the heating cylinder 17. The thread depth of the screw 18 varies from the upstream side to the downstream side, and the heating cylinder 17 is divided into a plurality of sections. That is, the heating cylinder 17 is divided from the upstream side into: a supply section 20, which supplies and melts the injection material; a first compression and metering section 21, which compresses the molten injection material; a starvation section 22, which reduces the pressure of the injection material; and a second compression and metering section 23. In the heating cylinder 17, a gas injection port 26 is opened in the starvation section 22 to inject gas into the injection material. In the second compression and metering section 23, the injection material and gas are mixed.

[0015] <Gas Supply Device> A gas supply device 28 of this embodiment is connected to the gas injection port 26. The gas supply device 28 is composed of the following components: two gas cylinders 30, 30, which are gas supply sources; gas cylinder opening and closing valves 31, 31; a primary gas pipe 33, through which gas from the gas cylinders 30, 30 is supplied; a pressure reducing valve 34, which is a pressure adjusting means for adjusting the gas pressure in the primary gas pipe 33, i.e., the primary pressure; a secondary gas pipe 36, through which gas reduced to secondary pressure by the pressure reducing valve 34 is supplied; a check valve 38, which is provided in the secondary gas pipe 36; and an opening and closing valve 39, which is also provided in the secondary gas pipe 36 as an opening and closing means. A primary pressure gauge 41, which is a primary pressure detection means for detecting the primary pressure, is provided in the primary gas pipe 33, and a secondary pressure gauge 42, which is a secondary pressure detection means for detecting the secondary pressure, is provided in the secondary gas pipe 36. The front end of the secondary gas pipe 36 becomes the gas supply section 43, which is connected to the gas injection port 26.

[0016] In the machines constituting the gas supply device 28, the primary pressure gauge 41 and the secondary pressure gauge 42 are connected to the controller 4, and the primary pressure and the secondary pressure are input to the controller 4. Furthermore, the gas cylinder opening and closing valves 31, 31, the pressure reducing valve 34, and the opening and closing valve 39 are connected to the controller 4, and the gas cylinder opening and closing valves 31, 31, the pressure reducing valve 34, and the opening and closing valve 39 are controlled by the controller 4.

[0017] The gas supply device 28 of this embodiment is configured accordingly. However, the gas cylinder 30 can be a single cylinder, or even three or more cylinders, to implement the present invention. In addition, the gas supply device 28 can also be composed of, for example, gas cylinders 30 and a pressurizing device, or a nitrogen generating device and a pressurizing device. The supplied gas is generally an inert gas such as nitrogen or carbon dioxide, but it is not important if it is air, hydrocarbon gas, argon, helium, hydrogen, or any other gas that can dissolve in resin. Furthermore, the on / off valve 39 can be installed in the middle of the gas pipe that supplies secondary pressure gas to the gas injection port, or an on / off mechanism such as a needle valve that is actuated by compressed air can be installed in the gas injection section. In this embodiment, the gas cylinder on / off valves 31 and 31 serve as a means of switching which of the gas cylinders 30 and 30, which are the gas supply sources, is used as the gas supply source. By opening and closing the gas cylinder opening and closing valves 31 and 31, the gas cylinders 30 and 30 that are used can be switched.

[0018] In the gas supply device 28, the gas cylinder opening / closing valve 31, the primary pressure gauge 41, the check valve 38, and the opening / closing valve 39 are not essential, but if these components are provided, various responses can be made when abnormalities occur regarding the supplied gas. Furthermore, multiple machines can be connected to the controller 4, but even if only the secondary pressure gauge 42 is connected, minimal responses can still be made. Abnormalities can be quickly detected by monitoring the secondary pressure online.

[0019] <Feeder> A feeder 44 is installed in the heating cylinder 17 of the injection apparatus 3 in this embodiment. The feeder 44 is also connected to and controlled by the controller 4 to control the amount of injection material supplied to the heating cylinder 17 from the hopper 45. An injection material detection sensor 46, which serves as a means of detecting injection material, is provided in the feeder 44, and the sensor 46 is also connected to the controller 4. The controller 4 can determine whether injection material is being supplied appropriately from the feeder 44 based on the signal from the injection material detection sensor 46. In addition, the injection material detection sensor 46 can also be installed in the feeder 44, or in the injection material supply port of the heating cylinder 17 or in the hopper 45. Furthermore, an automatic material conveying device for supplying injection material can also be installed in the feeder 44 or the hopper 45. When an injection material detection sensor 46 is installed in the hopper 45 or material conveying device, it is sufficient to detect whether there is any residue in the injection material supplied to the feeder 44.

[0020] <Controller> The injection molding machine 1 of this embodiment is described in detail below, which can detect various abnormalities by monitoring the secondary pressure of the gas in the controller 4. Furthermore, when the controller 4 detects an abnormality, it takes various responses according to the nature of the abnormality. To perform abnormality detection and responses, various setpoints or programs are set in the controller 4. The setpoints include a setpoint for the secondary pressure of the gas (set pressure), setpoints for judging abnormalities (1st to 5th threshold values), and 1st to 4th settling times. As programs, the controller 4 is equipped with programs for implementing alarm output, pressure reduction control, pressure increase control, supply quantity reduction control, supply quantity increase control, and gas supply source switching control.

[0021] In the injection molding machine 1 of this embodiment, the amount of gas dissolved in the injection material is controlled by the gas pressure supplied to the heating cylinder 17. Because the screw 18, arranged in the starvation zone 22, has a deeper thread groove and a larger volume between the threads, the resin flowing in from the upstream first compression / metering zone 21 is depressurized, and the injection material pressure becomes approximately zero. Therefore, even with a lower pressure gas that can be supplied from a gas cylinder or the like, it can be supplied stably. The gas supplied to the heating cylinder 17 fills the starvation zone 22 of the heating cylinder 17. Because the gas system acts isotropically as a fluid pressure, the injection material pressure in the starvation zone 22 becomes approximately the same as the secondary pressure. The gas contacts the molten resin in the starvation zone 22 and dissolves an amount corresponding to the gas pressure. That is, the amount of gas dissolved in the molten resin increases proportionally to the secondary pressure.

[0022] On the other hand, if the resin in the starvation zone 22 increases for some reason, thereby increasing the injection material pressure, resin may overflow into the gas inlet 26, potentially preventing gas from being supplied to the heating cylinder 17. In this case, the resin blocking the gas inlet 26 will compress the gas in the secondary gas pipe 36, increasing the secondary pressure. By detecting this situation, poor gas supply caused by overflow can be detected.

[0023] Furthermore, if the primary pressure of the gas supplied from the gas supply source is not sufficiently higher than the secondary pressure, the gas pressure in the starvation zone 22 within the heating cylinder 17 will decrease due to the reduction in the secondary pressure or the decrease in the amount of gas supplied to the heating cylinder 17, thereby reducing the amount of gas dissolved in the molten resin. In this case, by detecting the decrease in primary or secondary pressure, the defect caused by insufficient gas supply from the gas supply source can be detected.

[0024] On the other hand, in this embodiment, a feeder 44 is used to tighten the supply of resin material. Normally, the gas system supplied to the heating cylinder 17 is liquid-tightly sealed between the starvation zone 22 and the first compression / metering zone 21 by the molten resin. However, if the resin supply from the feeder 44 is too low, or if the material disappears even without the feeder 44, there is a risk of temporary or continuous seal rupture and gas backflow to the primary end. In this case, the gas backflow can be detected by detecting a sudden change in the secondary pressure.

[0025] If there is such overflow, gas pressure drop, or gas backflow, molding defects will occur frequently. Therefore, in the injection molding machine 1 of this embodiment, the management of secondary pressure and the detection of abnormalities become important.

[0026] <Control Method of Injection Molding Machine of This Embodiment> The control method of the injection molding machine of this embodiment will now be described. In the control method of the injection molding machine of this embodiment, the secondary pressure of the gas detected by the secondary pressure gauge 42 is input to the controller 4. The controller 4 determines whether the operation is normal or abnormal and takes necessary measures. The basis for the controller 4 to determine whether the secondary pressure is normal or abnormal, and the basis for determining the countermeasures to be taken, is based on the 1st to 5th threshold values. Figure 8 shows the corresponding measures taken based on the secondary pressure in conjunction with the 1st to 5th threshold values ​​to determine whether the operation is normal or abnormal. Referring to this figure, the processing of the controller 4 will now be described.

[0027] <Controller Processing> As shown in Figure 3, controller 4 moves from the start to step S1 to determine whether the secondary pressure is greater than the set value plus the first threshold value. When the secondary pressure is less than the set value plus the first threshold value, controller 4 moves to step S2. In step S2, controller 4 determines whether the secondary pressure of the gas is less than the set value minus the second threshold value. When the secondary pressure is greater than the set value minus the second threshold value, controller 4 determines it to be normal. That is, based on the set value, the range greater than the lower second threshold value and less than the upper first threshold value is taken as the normal pressure range. If the secondary pressure is within the normal pressure range, controller 4 determines it to be normal and returns to the start.

[0028] In step S1, if it is determined that the secondary pressure is greater than the set value and the difference is greater than the first threshold value, then the controller 4 proceeds to step S3. In step S3, the controller 4 checks whether the secondary pressure is greater than the set value and whether the difference is less than the third threshold value. If it exceeds the third threshold value, the possibility of overflow is high. At this time, the controller 4 performs a stop process S3.

[0029] The Stop Processing SS system, as shown in Figure 5, checks whether the opening and closing means, i.e., the opening and closing valve 39, is controllable in step S21. The controller 4, when the opening and closing valve 39 is present, executes step S22 to close the valve and stop the gas supply. Then, regardless of whether the opening and closing valve 39 is present, the controller 4 executes step S23 to stop the forming cycle after it is completed. Furthermore, the Stop Processing SS system can be executed immediately, or after a certain period of hesitation or a certain number of cycles, depending on the reason, urgency, and whether the operation is manned or unmanned. Alternatively, the controller 4 can execute the alarm processing SB (described later) simultaneously with or before the Stop Processing SS system to notify the operator of any abnormalities.

[0030] In step S3, if the controller 4 determines that the difference between the secondary pressure and the set value is less than the third critical limit, it proceeds to step S4. In step S4, it is determined whether the pressure reducing valve 34 can be operated by the controller 4, i.e., whether there is a pressure control means. If there is no pressure control means, the controller 4 proceeds to step S7. Alternatively, if the controller 4 determines that the difference between the secondary pressure and the set value is less than the third critical limit in step S3, then regardless of the determination in step S4, i.e., regardless of whether there is a pressure control means, alarm processing SA is implemented. In alarm processing SA, the controller 4 issues an alarm that there is a risk of overflow at the gas injection port 26. The alarm can be displayed on the monitor attached to the controller 4, or an alarm sound can be output by a speaker. Alternatively, the administrator can be notified via email, etc.

[0031] In step S4, if a pressure control mechanism is confirmed, the controller 4 proceeds to step S5 and implements pressure reduction control. Pressure reduction control involves controlling the pressure reducing valve 34 to lower the secondary pressure to the normal pressure range. Even if the pressure reducing valve 34 is controlled to lower the secondary pressure, the pressure in the secondary pressure gauge 42, located further downstream of the check valve 38, will not immediately decrease. This is because if the gas inlet 26 is not blocked by resin, the gas in the piping will be supplied to the heating cylinder 17 and dissolved in the molten resin, thus gradually reducing the pressure.

[0032] If pressure reduction control is implemented, the controller 4 observes the process via step S6. That is, the controller 4 monitors the secondary pressure and checks whether the secondary pressure returns to the normal pressure range within the first stable time. If it returns to the normal pressure range within the first stable time, the controller 4 determines it is normal. That is, the controller 4 returns the process to the beginning. However, if the secondary pressure does not return to the normal pressure range within the first stable time, and the difference between the secondary pressure and the set pressure does not reach the third threshold value, the controller 4 proceeds to step S7.

[0033] Step S7 is a process that is executed directly from step S4 or from step S6. In step S7, the controller 4 checks whether there is a feeder control means. That is, the controller 4 checks whether a feeder 44 is present and whether it can be controlled by the controller 4. If there is no feeder control means, the controller 4 implements the stop process SS as described above. If there is a feeder control means, the controller 4 implements the supply reduction control of step S8. That is, the controller 4 controls the feeder 44 to reduce the supply of injection material. The reason is that if the supply of injection material is reduced, it is less likely for injection material to bulge at the gas injection port.

[0034] If supply reduction control is implemented, the controller 4 observes the process via step S9. That is, the controller 4 monitors the secondary pressure and checks whether the secondary pressure returns to the normal pressure range within the second stable time. If it returns to the normal pressure range within the second stable time, the controller 4 determines that it is normal. That is, the controller 4 returns the process to the beginning. However, if the secondary pressure does not return to the normal pressure range within the second stable time, the controller 4 implements the previously described stop process SS.

[0035] In step S2, if the controller 4 determines that the secondary pressure of the gas is less than the second threshold value or more than the set value, it proceeds to process A. As shown in Figure 4, the controller 4 proceeds to step S11. In step S11, the controller 4 checks whether the secondary pressure of the gas is lower than the set pressure and whether the difference between the secondary pressure and the set pressure is greater than or equal to the fifth threshold value. If it is greater than or equal to the fifth threshold value, the controller 4 determines that a gas supply abnormality has occurred and implements the previously described stop process SS. On the other hand, if the difference between the secondary pressure and the set pressure is less than or equal to the fifth threshold value, the controller 4 proceeds to step S12.

[0036] In step S12, the controller 4 confirms the rate of decrease in the secondary pressure of the gas. That is, the controller 4 calculates the rate of decrease (the percentage decrease per unit time) of the secondary pressure of the gas, and checks whether the rate of decrease is above the fourth critical limit. When the rate of decrease is above the fourth critical limit, there is a high probability that the gas will momentarily backflow within the heating cylinder 17. In this case, the controller 4 proceeds to step S16.

[0037] In step S16, controller 4 checks whether there is a feeder control means. That is, controller 4 checks whether the injection molding machine 1 has a feeder 44 and whether it can be controlled by controller 4. If there is no feeder control means, controller 4 performs the previously described stop process SS. If there is a feeder control means, controller 4 performs the supply increase control in step S17. That is, controller 4 controls the feeder 44 to increase the supply of injection material. The reason is that if the supply of injection material increases, the resin in the sealing part increases, and the backflow of gas can be prevented liquid-tightly.

[0038] If supply increase control is implemented, the controller 4 observes the process in step S18. If the rate of decrease of secondary pressure is lower than the fourth threshold value between the number of molding cycles that become the reference, for example, 5 molding cycles, it is judged to be normal. Alternatively, if the rate of decrease of secondary pressure is lower than the fourth threshold value during the fourth stability time that becomes the reference, it is judged to be normal. At this time, since there may be cases where several injections are required before the effect of supply increase control is achieved, a delay time can be set between the number of reference cycles or the time that becomes the reference to avoid over-observation judgment. If, even with the implementation of supply increase control, the rate of decrease of secondary pressure is still above the fourth threshold value, the controller 4 performs the stop process SS as described above.

[0039] In step S12, when the controller 4 determines that the rate of decrease of the secondary pressure of the gas has not reached the fourth threshold value, it is determined that the supply pressure from the gas supply source, i.e. the primary pressure, is likely to decrease, and the process moves to step S13.

[0040] In step S13, controller 4 checks whether there is a pressure control means. If there is no pressure control means, controller 4 moves to process B. Process B is shown in Figure 6, where controller 4 first executes step S31. That is, controller 4 checks whether there is a gas supply source switching means. In this embodiment, the gas supply source switching means are gas cylinder opening and closing valves 31 and 31, which can switch the gas supply source, i.e., gas cylinders 30 and 30. If it is determined that there is a gas supply source switching means, controller 4 executes step S32, operates gas cylinder opening and closing valves 31 and 31, and implements gas supply source switching control to switch the currently used gas cylinder 30 to another gas cylinder 30.

[0041] When there is no means to switch the gas supply source, or when the secondary pressure does not return to the normal range even after the gas supply source switching control is executed, the controller 4 implements alarm processing SB and issues an alarm urging the replacement of gas cylinder 30. The alarm can be displayed on the monitor, sounded by the speaker, or sent to the administrator via email. Furthermore, a stop process can be executed simultaneously with alarm processing SB.

[0042] In step S14, if it is determined that there is a pressure control means, the controller 4 moves to step S14.

[0043] The controller 4 performs pressure increase control in step S14. That is, it controls the pressure reducing valve 34 to bring the secondary pressure within the normal pressure range.

[0044] If pressure increase control is implemented, the controller 4 observes the process via step S15. That is, the controller 4 monitors the secondary pressure and checks whether the secondary pressure returns to the normal pressure range within the third stable time. If it returns to the normal pressure range within the third stable time, the controller 4 determines it is normal. That is, the controller 4 returns the process to the beginning. However, if the secondary pressure does not return to the normal pressure range within the third stable time, and the difference between the secondary pressure and the set pressure does not reach the fifth threshold value, the controller 4 executes the previously described process B.

[0045] In the injection molding machine 1 of this embodiment, the controller 4 also checks whether the supply of injection material is normal. That is, as shown in FIG7, the controller 4 performs step S41. The injection material detection sensor 46 checks whether the injection material falls into the heating cylinder 17 at predetermined intervals. If the supply of injection material is not normal, there is a possibility that the seal will break due to the interruption of injection material, causing gas to flow back to the feeder side, and therefore the stop process SS described above is performed.

[0046] Furthermore, in S13 and S15 of this embodiment, the controller 4 uses the first, second, fourth, and fifth threshold values, as well as the presence or absence of pressure control means, as the judgment criteria for executing process B, i.e., for executing gas supply source switching control. However, the controller 4 may also more directly use the difference between the set pressure or secondary pressure and the primary pressure as the judgment criteria. In this case, the controller 4 may also use the sixth threshold value as the judgment criteria for the difference between the primary pressure and the set pressure or secondary pressure. If the difference between the primary pressure and the set pressure or secondary pressure does not reach the sixth threshold value, then process B is executed. The sixth threshold value can be appropriately set according to the gas usage amount; for example, 1 MPa can be set as a reference.

[0047] The above describes the control method for the injection molding machine according to this embodiment. It has been explained that first and second threshold values ​​are used to determine the normality / abnormality of the secondary pressure. Although these values ​​vary depending on the size of the molding machine or the configuration of the gas supply device, even within the normal operating range of the molding machine, the secondary pressure will still vary due to the dissolution of the injection material by the gas. In a standard-sized molding machine, the variation range may be around 0~0.5 MPa, while in a large molding machine, the variation range may be around 0.5~1.0 MPa. Therefore, the first and second threshold values ​​are preferably set to 0.1~1.5 MPa, and more preferably to a range of 0.2~1.0 MPa. The third and fifth threshold values ​​must be greater than these; for example, they can be appropriately set within the range of 0.5~3.0 MPa, depending on the variation in gas pressure.

[0048] However, a ratio can also be used in this judgment. For example, the secondary pressure can be defined as 95% to 110% of the set pressure as the normal range. Even if a ratio is used for judgment, it is essentially equivalent to using the first and second threshold values. This is because it is equivalent to setting the first threshold value to 10% of the set pressure and the second threshold value to 5% of the set pressure.

[0049] Furthermore, the upper and lower limits of the normal range can also be used. For example, when the gas pressure setting is set to 10 MPa, the range of 10.5 MPa to 9.5 MPa can be set as the normal range. However, in this case, the value of the normal range must be changed every time the gas pressure setting is changed. Therefore, using the first and second threshold values ​​or using a ratio for judgment can save the user time and effort, and is therefore better.

[0050] This embodiment is described in relation to the use of a secondary pressure gauge 42, but a pressure switch can also be used instead. In this case, the pressure switch can be set with upper and lower limits corresponding to the normal range of the 1st, 2nd, 3rd, and 5th threshold values. When the secondary pressure exceeds the normal range, the controller 4 receives a signal from the pressure switch. The pressure switch can be set manually or through communication with the controller 4. However, in the case of manual setting, the pressure switch setting must be changed every time the gas pressure setting value is changed. Therefore, the method of setting the pressure switch through communication with the controller 4 and in conjunction with the setting value is more efficient and reduces the user's workload.

[0051] Furthermore, the pressure drop rate of the fourth critical limit can be detected not by the pressure drop rate of the secondary pressure gauge 42, but by using a flow meter or differential pressure gauge to detect the backflow of gas in the heating cylinder from the gas flow rate. The reason is that the secondary pressure drop caused by the backflow is equivalent to the increase in gas flow rate. When using a flow meter or differential pressure gauge, the flow rate of the gas used within the normal operating range can be predetermined, and the range exceeding this can be used as a substitute indicator for the fourth critical limit.

[0052] Furthermore, the control method of the injection molding machine in this embodiment can also be applied to situations where a plurality of gas pressure setpoints are provided and the pressure is controlled to change in stages. In this case, the first and second threshold values ​​are set according to the maximum and minimum values ​​of the plurality of gas pressure setpoints, or the setpoints corresponding to the first and second threshold values ​​can be set one by one for each gas pressure setpoint.

[0053] The invention described above has been specifically explained according to various embodiments, but the invention is not limited to the embodiments described. For example, various changes can be made without departing from the main idea, such as changing the order of each step, or only implementing alarm processing SA or stop processing SS when the secondary pressure exceeds the normal range. Furthermore, the response can be changed depending on whether the machine is in operation or not. For example, when the machine is in operation, the feed rate increase control or feed rate decrease control of the feeder 44 can be replaced by a guided display of indicators indicating changes in forming conditions. When the urgency is low, the stop processing SS can be omitted, and the alarm processing can be left in place for the operator to handle. The various examples described above can also be appropriately combined and implemented.

[0054] Here, the features of the above-mentioned injection molding machine for foaming and the control method of the injection molding machine are briefly summarized as follows [1] to

[28] . [1] An injection molding machine (1) includes: a heating cylinder (17) having a gas injection port (26); a screw (18) drivably disposed in the heating cylinder (17); a gas supply device (28) supplying gas to the gas injection port (26); and a control means (4); wherein the gas supply device (28) includes: a gas supply source (30) supplying gas; a pressure adjustment means (34) adjusting the primary pressure of the gas from the gas supply source (30) to a secondary pressure; and a secondary pressure detection means (42) detecting the secondary pressure; supplying the gas at the secondary pressure to the gas injection port (26); and the control means (4) detecting an abnormality by comparing the set pressure with the secondary pressure. [2] In the injection molding machine (1) described in [1], the control means (4) sets the normal pressure range of the secondary pressure to be greater than the value of the set pressure minus the second threshold value and less than the value of the set pressure plus the first threshold value, and detects the abnormality of the secondary pressure based on the normal pressure range. [3] In the injection molding machine (1) described in [2], the control means (4) issues an alarm that there is a risk of overflow at the gas injection port (26) when the secondary pressure is greater than the normal pressure range and less than the value of the set pressure plus the third threshold value. [4] In the injection molding machine (1) described in [2], the control means (4) stops the molding cycle after it is completed when the secondary pressure is greater than or equal to the value of the set pressure plus the third threshold value. [5] In the injection molding machine (1) described in [2], the gas supply device (28) is provided with a gas pipe for supplying the gas at the gas injection port (26) or with an opening and closing means (39) at the gas injection section. The control means (4) closes the opening and closing means (39) when the secondary pressure is greater than or equal to the set pressure plus a third threshold value, and stops the molding cycle after the molding cycle is completed. [6] In the injection molding machine (1) described in [2], the control means (4) includes a pressure control means that controls the pressure adjustment means (34). When the secondary pressure is greater than the normal pressure range and the secondary pressure is less than or equal to the set pressure plus a third threshold value, the pressure control means performs pressure reduction control so that the secondary pressure becomes the normal pressure range.[7] In the injection molding machine (1) described in [6], the control means (4) stops the molding cycle after it is completed when the secondary pressure is continuously greater than the normal pressure range during the period from the start of the pressure reduction control to the first stable time. [8] In the injection molding machine (1) described in [6], the gas supply device (28) is provided with a gas pipe for supplying the gas under the secondary pressure at the gas injection port (26), or with an opening and closing means (39) at the gas injection section. The control means (4) closes the opening and closing means (39) and stops the molding cycle after it is completed when the secondary pressure is continuously greater than the normal pressure range during the period from the start of the pressure reduction control to the first stable time. [9] As described in [6], the injection molding machine (1) is equipped with a feeder (44) for adjusting the supply of injection material in the heating cylinder (17). The control means (4) controls the feeder (44) to reduce the supply of injection material during the period from the start of the pressure reduction control to the first stable time, when the secondary pressure is continuously greater than the normal pressure range.

[10] As described in [2], the injection molding machine (1) is equipped with a feeder (44) for adjusting the supply of injection material in the heating cylinder (17). The control means (4) controls the feeder (44) to reduce the supply of injection material when the secondary pressure is greater than the normal pressure range and the secondary pressure is less than the value of the set pressure plus the third threshold value.

[11] In the injection molding machine (1) described in [9] or

[10] , the control means (4) stops the molding cycle after it is completed when the secondary pressure continues to be greater than the normal pressure range during the period from the start of the supply reduction control to the second stabilization time.

[12] In the injection molding machine (1) described in [9] or

[10] , the gas supply device (28) is provided with a gas pipe for supplying the gas under the secondary pressure at the gas injection port (26), or with an opening and closing means (39) at the gas injection section. The control means (4) closes the opening and closing means (39) and stops the molding cycle after it is completed when the secondary pressure continues to be greater than the normal pressure range during the period from the start of the supply reduction control to the second stabilization time.

[13] As described in [2], the injection molding machine (1) wherein the control means (4) is to stop the molding cycle after the molding cycle is completed when the secondary pressure is less than the normal pressure range and the rate of decrease of the secondary pressure is above the fourth critical limit.

[14] In the injection molding machine (1) described in [2], the gas supply device (28) is provided with a gas pipe for supplying the secondary pressure gas at the gas injection port (26), or with an opening and closing means (39) at the gas injection section. The control means (4) closes the opening and closing means (39) when the secondary pressure is less than the normal pressure range and the rate of decrease of the secondary pressure is greater than or equal to the fourth threshold value, and stops the molding cycle after the molding cycle is completed.

[15] In the injection molding machine (1) described in [2], a feeder (44) for adjusting the supply amount of injection material is installed in the heating cylinder (17). The control means (4) controls the feeder (44) to increase the supply amount of injection material when the secondary pressure is greater than the set pressure minus the fifth threshold value and the rate of decrease of the secondary pressure is greater than or equal to the fourth threshold value.

[16] In the injection molding machine (1) described in

[15] , the control means (4) stops the molding cycle after it is completed when the rate of decrease of the secondary pressure temporarily exceeds the fourth threshold value during the period from the start of the supply increase control to the predetermined cycle, or during the period from the start of the supply increase control to the fourth stable time.

[17] In the injection molding machine (1) described in

[15] , the gas supply device (28) is provided with a gas pipe for supplying the gas of the secondary pressure at the gas injection port (26), or with an opening and closing means (39) at the gas injection section. The control means (4) closes the opening and closing means (39) when the rate of decrease of the secondary pressure temporarily exceeds the fourth threshold value during the period from the start of the supply increase control to the predetermined cycle, or during the period from the start of the supply increase control to the fourth stable time, and stops the molding cycle after it is completed.

[18] In the injection molding machine (1) described in [2], the control means (4) stops the molding cycle after it is completed when the secondary pressure is less than or equal to the set pressure minus the fifth threshold value.

[19] In the injection molding machine (1) described in [2], the gas supply device (28) is provided with a gas pipe for supplying the gas at the gas injection port (26), or with an opening and closing means (39) at the gas injection section. The control means (4) closes the opening and closing means (39) when the secondary pressure is less than or equal to the set pressure minus the fifth threshold value, and stops the molding cycle after it is completed.

[20] As described in [2], the injection molding machine (1) wherein the control means (4) is to issue an alarm urging the replacement of the gas supply source (30) when the secondary pressure is lower than the normal pressure range but greater than the set pressure minus the 5th threshold value and the rate of decrease of the secondary pressure is less than the 4th threshold value.

[21] As described in [2], the injection molding machine (1) includes a gas supply device (28) comprising: a plurality of gas supply sources (30); and a gas supply source switching means (31) that selects and switches one gas supply source (30) from the plurality of gas supply sources (30) as the target of use; the control means (4) switches the currently used gas supply source (30) to another gas supply source (30) by the gas supply source switching means (31) when the secondary pressure is lower than the normal pressure range but greater than the set pressure minus the fifth threshold value and the rate of decrease of the secondary pressure is less than the fourth threshold value.

[22] In the injection molding machine (1) described in [2], the control means (4) includes: a pressure control means that controls the pressure adjustment means (34); when the secondary pressure is lower than the normal pressure range but greater than the set pressure minus the 5th threshold value, and the rate of decrease of the secondary pressure is less than the 4th threshold value, the pressure control means implements pressure increase control to bring the secondary pressure into the normal pressure range.

[23] In the injection molding machine (1) described in

[22] , the control means (4) issues an alarm urging the replacement of the gas supply source (30) when the value of the secondary pressure remains lower than the normal pressure range and greater than the set pressure minus the 5th threshold value during the period from the start of the pressure increase control to the 3rd stable time.

[24] As described in

[22] , the injection molding machine (1) includes a plurality of gas supply sources (30) and a gas supply source switching means (31) that selects and switches one gas supply source (30) from the plurality of gas supply sources (30) as the target of use. The control means (4) switches the currently used gas supply source (30) to another gas supply source (30) by the gas supply source switching means (31) during the period from the start of the pressure increase control to the third stable time. When the value of the secondary pressure is maintained below the normal pressure range and above the set pressure minus the fifth threshold value, the gas supply source switching means (31) switches the gas supply source (30) to another gas supply source (30).

[25] The injection molding machine (1) described in any of [1] to

[24] includes the following gas supply device (28): a plurality of gas supply sources (30); a gas supply source switching means (31) that selects and switches one gas supply source (30) from the plurality of gas supply sources (30) as the target of use; and a primary pressure detection means (41) that detects the primary pressure of the gas from the gas supply source (30); the control means (4) compares the primary pressure with the difference between the set pressure or the secondary pressure and detects a decrease in the pressure of the gas supply source (30). When a decrease in the pressure of the gas supply source (30) is detected, the gas supply source switching means (31) switches the currently used gas supply source (30) to another gas supply source (30).

[26] As described in [2], the injection molding machine (1) is equipped with: an injection material detection means (46) that confirms the supply of injection material to the heating cylinder (17); the injection material detection means (46) stops the molding cycle after the molding cycle is completed when the injection material is interrupted and the injection material is detected to be cut off.

[27] As described in [2], the injection molding machine (1) is equipped with: an injection material detection means (46) that confirms the supply of injection material to the heating cylinder (17); a gas supply device (28) that has a gas pipe for supplying the secondary pressure gas at the gas injection port (26) or an opening and closing means (39) at the gas injection section; the injection material detection means (46) that closes the opening and closing means (39) when the injection material is interrupted and the injection material is detected to be cut off, and stops the molding cycle after the molding cycle is completed.

[28] A control method for an injection molding machine, the injection molding machine comprising: a heating cylinder (17) having a gas injection port (26); a screw (18) drivably disposed within the heating cylinder (17); and a gas supply device (28) supplying gas to the gas injection port (26); the gas supply device (28) comprising: a gas supply source (30) supplying gas; a pressure adjustment means (34) adjusting the primary pressure of the gas from the gas supply source (30) to a secondary pressure; and a secondary pressure detection means (42) detecting the secondary pressure; supplying the gas at the secondary pressure to the gas injection port (26), in the control method of the injection molding machine, comparing the set pressure with the secondary pressure to detect an abnormality.

[0055] This application is based on and incorporates the contents of Japanese Patent Application No. 2020-204664, filed on December 10, 2020. (Industrial Applicability)

[0056] According to the present invention, signs of overflow, gas backflow, or poor gas supply can be quickly detected, thereby preventing defective products from occurring. The present invention, which achieves this effect, is useful with respect to an injection molding machine for foam molding and a method for controlling the injection molding machine. [Simplified Explanation of the Diagram]

[0011] Figure 1 is a front view of the injection molding machine of this embodiment. Figure 2 is a front sectional view of the injection apparatus of this embodiment. Figure 3 is a flowchart of the control method implemented in the injection molding machine of this embodiment. Figure 4 is a flowchart of the control method implemented in the injection molding machine of this embodiment. Figure 5 is a flowchart of the control method implemented in the injection molding machine of this embodiment. Figure 6 is a flowchart of the control method implemented in the injection molding machine of this embodiment. Figure 7 is a flowchart of the control method implemented in the injection molding machine of this embodiment. Figure 8 is a diagram showing the control method of the injection molding machine of this embodiment implemented by the secondary pressure of the mixing gas.

Claims

1. An injection molding machine comprising: a heating cylinder having a gas injection port; a screw drivably disposed within the heating cylinder; a gas supply device for supplying gas to the gas injection port; and a control means; wherein, The heating cylinder is divided into multiple sections based on the thread shape of the screw, at least from the upstream side to the downstream side. It includes: a first compression metering section for compressing the molten injection material; a starvation section for reducing the pressure of the injection material; and a second compression metering section for further compressing the injection material. The gas injection port is located in the starvation section. The gas supply device includes: a gas supply source for supplying gas; a pressure adjustment means for adjusting the primary pressure of the gas from the gas supply source to a secondary pressure; a check valve located downstream of the pressure adjustment means; and a secondary pressure detection means configured to detect the secondary pressure downstream of the check valve. The gas at the secondary pressure is supplied to the gas injection port. The aforementioned control measures include: a first critical limit value, which is greater than 0.1 MPa and less than 1.5 MPa; and a second critical limit value, which is also greater than 0.1 MPa and less than 1.5 MPa; and a pressure range that is greater than the value of the secondary pressure minus the second critical limit value and less than the value of the secondary pressure plus the first critical limit value is defined as the normal pressure range, and an abnormality in the secondary pressure is detected based on whether the secondary pressure detected by the aforementioned secondary pressure detection measures falls within the aforementioned normal pressure range.

2. As in request item 1, the injection molding machine, wherein, The aforementioned control measure is to issue an alarm that there is a risk of gas overflow at the gas injection port when the secondary pressure is greater than the normal pressure range and the secondary pressure is less than the value of the set pressure plus the third critical limit.

3. As in request item 1, the injection molding machine, wherein, The aforementioned control method is to stop the forming cycle after it is completed when the secondary pressure is greater than or equal to the set pressure plus the third threshold value.

4. As in request item 1, the injection molding machine, wherein, The gas supply device is equipped with a gas pipe for supplying the gas under the secondary pressure at the gas injection port, or with an opening and closing means at the gas injection section. The control means is to close the opening and closing means when the secondary pressure is above or equal to the set pressure plus a third threshold value, and to stop the forming cycle after the forming cycle is completed.

5. As in request item 1, the injection molding machine, wherein, The aforementioned control means includes: a pressure control means that controls the aforementioned pressure adjustment means; when the aforementioned secondary pressure is greater than the aforementioned normal pressure range and the aforementioned secondary pressure is less than the value of the aforementioned set pressure plus the third threshold value, the aforementioned pressure control means implements pressure reduction control so that the aforementioned secondary pressure becomes the aforementioned normal pressure range.

6. The injection molding machine as described in claim 5, wherein, The aforementioned control method is to stop the forming cycle after it is completed when the secondary pressure continues to exceed the normal pressure range during the period from the start of the pressure reduction control to the first stabilization time.

7. The injection molding machine as described in claim 5, wherein, The gas supply device is provided with a gas pipe for supplying the gas under the secondary pressure at the gas injection port, or with an opening and closing means at the gas injection section. The control means is to close the opening and closing means when the secondary pressure is continuously greater than the normal pressure range during the period from the start of the pressure reduction control to the first stable time, and to stop the molding cycle after the molding cycle is completed.

8. The injection molding machine as described in claim 5, wherein, A feeder for adjusting the supply of injection material is installed in the heating cylinder. The control means is that, during the period from the start of the pressure reduction control to the first stable time, when the secondary pressure is continuously greater than the normal pressure range, the feeder is controlled to implement a supply reduction control that reduces the supply of injection material.

9. The injection molding machine as described in claim 1, wherein, A feeder for adjusting the supply of injection material is installed in the heating cylinder. The control means is to control the feeder to reduce the supply of injection material when the secondary pressure is greater than the normal pressure range and the secondary pressure is less than the value of the set pressure plus the third threshold value.

10. The injection molding machine as requested in item 8 or 9, wherein, The aforementioned control measure is to stop the forming cycle after it is completed when the secondary pressure continues to exceed the normal pressure range during the period from the start of the aforementioned supply reduction control to the second stabilization time.

11. The injection molding machine as requested in item 8 or 9, wherein, The gas supply device is equipped with a gas pipe for supplying the gas under the secondary pressure at the gas injection port, or with an opening and closing means at the gas injection section. The control means is to close the opening and closing means when the secondary pressure is continuously greater than the normal pressure range during the period from the start of the supply reduction control to the second stable time, and to stop the forming cycle after the forming cycle is completed.

12. The injection molding machine as described in claim 1, wherein, The aforementioned control method is to stop the forming cycle after it is completed when the secondary pressure is less than the normal pressure range and the rate of decrease of the secondary pressure reaches or exceeds the fourth critical limit.

13. The injection molding machine as described in claim 1, wherein, The gas supply device is equipped with a gas pipe for supplying the gas under the secondary pressure at the gas injection port, or with an opening and closing means at the gas injection section. The control means is to close the opening and closing means when the secondary pressure is less than the normal pressure range and the rate of decrease of the secondary pressure reaches or exceeds the fourth critical limit, and to stop the forming cycle after the forming cycle is completed.

14. The injection molding machine as described in claim 1, wherein, A feeder for adjusting the supply of injection material is installed in the heating cylinder. The control means is to control the feeder to increase the supply of injection material when the secondary pressure is greater than the set pressure minus the fifth threshold value and the rate of decrease of the secondary pressure is greater than the fourth threshold value.

15. The injection molding machine as claimed in claim 14, wherein, The aforementioned control measure is to stop the forming cycle after it is completed, during the period from the start of the aforementioned supply increase control to the predetermined cycle, or during the period from the start of the aforementioned supply increase control to the fourth stable time, when the rate of decrease of the aforementioned secondary pressure temporarily exceeds the aforementioned fourth threshold value.

16. The injection molding machine as described in claim 14, wherein, The aforementioned gas supply device is equipped with a gas pipe for supplying the gas under the aforementioned secondary pressure at the aforementioned gas injection port, or with an opening and closing means at the gas injection section. The aforementioned control means is to close the opening and closing means when the rate of decrease of the aforementioned secondary pressure temporarily exceeds the aforementioned fourth threshold value during the period from the start of the aforementioned supply increase control to a predetermined cycle, or during the period from the start of the aforementioned supply increase control to the fourth stable time, and to stop the forming cycle after the forming cycle in progress is completed.

17. The injection molding machine as claimed in claim 1, wherein, The aforementioned control method involves stopping the forming cycle after it is completed when the secondary pressure is below the set pressure minus the fifth threshold value.

18. The injection molding machine as described in claim 1, wherein, The gas supply device is provided with a gas pipe for supplying the gas under the secondary pressure at the gas injection port, or with an opening and closing means at the gas injection part. The control means is to close the opening and closing means when the secondary pressure is below the value of the set pressure minus the 5th threshold value, and to stop the forming cycle after the forming cycle is completed.

19. The injection molding machine as claimed in claim 1, wherein, The aforementioned control method is to issue an alarm urging the replacement of the gas supply source when the secondary pressure is lower than the normal pressure range but greater than the set pressure minus the 5th threshold value, and the rate of decrease of the secondary pressure does not reach the 4th threshold value.

20. The injection molding machine as claimed in claim 1, wherein, The aforementioned gas supply device includes: a plurality of gas supply sources; and a gas supply source switching means, which selects and switches one gas supply source from the plurality of gas supply sources as the target of use; the aforementioned control means switches the currently used gas supply source to another gas supply source when the secondary pressure is lower than the normal pressure range but greater than the set pressure minus the fifth threshold value, and the rate of decrease of the secondary pressure does not reach the fourth threshold value.

21. The injection molding machine as claimed in claim 1, wherein, The aforementioned control means includes: a pressure control means that controls the aforementioned pressure adjustment means; when the aforementioned secondary pressure is lower than the aforementioned normal pressure range but greater than the value of the aforementioned set pressure minus the 5th threshold value, and the rate of decrease of the aforementioned secondary pressure does not reach the 4th threshold value, the aforementioned pressure control means implements pressure increase control to bring the aforementioned secondary pressure into the aforementioned normal pressure range.

22. The injection molding machine as claimed in claim 21, wherein, The aforementioned control measure is that, during the period from the start of the aforementioned pressure increase control to the third stabilization time, when the value of the aforementioned secondary pressure remains below the aforementioned normal pressure range and greater than the value of the aforementioned set pressure minus the aforementioned fifth critical limit, an alarm is issued urging the replacement of the aforementioned gas supply source.

23. The injection molding machine as claimed in claim 21, wherein, The aforementioned gas supply device includes: a plurality of gas supply sources; and a gas supply source switching means, which selects and switches one gas supply source from the plurality of gas supply sources as the target of use; the aforementioned control means, during the period from the start of the aforementioned pressure increase control to the third stabilization time, when the value of the aforementioned secondary pressure remains below the aforementioned normal pressure range and above the value of the aforementioned set pressure minus the aforementioned fifth threshold value, switches the currently used gas supply source to another gas supply source by the aforementioned gas supply source switching means.

24. An injection molding machine as described in any of claims 1 to 9, wherein, The aforementioned gas supply device includes: a plurality of gas supply sources; a gas supply source switching means that selects and switches one gas supply source from the plurality of gas supply sources as the target gas supply source; and a primary pressure detection means that detects the primary pressure of the gas from the aforementioned gas supply source; the aforementioned control means compares the primary pressure with the difference between the aforementioned set pressure or the aforementioned secondary pressure, and detects a decrease in the pressure of the aforementioned gas supply source; when a decrease in the pressure of the aforementioned gas supply source is detected, the gas supply source switching means switches the currently used gas supply source to another gas supply source.

25. The injection molding machine as claimed in claim 1, wherein, The aforementioned injection molding machine is equipped with: an injection material detection means that confirms the supply of injection material to the aforementioned heating cylinder; the aforementioned injection material detection means that, when the injection material is interrupted and a material breakage is detected, stops the molding cycle after the ongoing molding cycle is completed.

26. The injection molding machine as described in claim 1, wherein, The aforementioned injection molding machine is equipped with: an injection material detection means that confirms the supply of injection material to the aforementioned heating cylinder; the aforementioned gas supply device is equipped with a gas pipe for supplying the aforementioned secondary pressure gas at the aforementioned gas injection port, or with an opening and closing means at the gas injection section; the aforementioned injection material detection means is equipped with closing the aforementioned opening and closing means when the aforementioned injection material is interrupted and the injection material is detected to be cut off, and stopping the molding cycle after the ongoing molding cycle is completed.

27. A control method for an injection molding machine, the injection molding machine comprising: a heating cylinder having a gas injection port; a screw drivably disposed within the heating cylinder; and a gas supply device supplying gas to the gas injection port; wherein the heating cylinder is divided into a plurality of intervals according to the thread shape of the screw, at least from an upstream side toward a downstream side, and includes: a first compression metering interval for compressing molten injection material; a starvation interval for reducing the pressure of the injection material; and a second compression metering interval for further compressing the injection material; wherein the gas injection port is disposed in the starvation interval; and the gas supply device comprising: a gas supply source for supplying gas; a pressure adjustment means for adjusting a primary pressure of the gas from the gas supply source to a secondary pressure; a check valve disposed downstream of the pressure adjustment means; and a secondary pressure detection means configured to detect the secondary pressure downstream of the check valve. The gas under the aforementioned secondary pressure is supplied to the aforementioned gas injection port. In the aforementioned control method of the injection molding machine, a first threshold value greater than 0.1 MPa and less than 1.5 MPa and a second threshold value also greater than 0.1 MPa and less than 1.5 MPa are set. The pressure range that is greater than the value of the aforementioned secondary pressure minus the aforementioned second threshold value and less than the value of the aforementioned secondary pressure plus the aforementioned first threshold value is set as the normal pressure range. The abnormality of the aforementioned secondary pressure is detected based on whether the secondary pressure detected by the aforementioned secondary pressure detection means has entered the aforementioned normal pressure range.

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