Pressure measuring device and injection molding machine

Abstract

Provided is a pressure measuring device capable of being attached to an injection molding machine and easily performing a mold switching operation, and an injection molding machine. Provided is a pressure measuring device (5) capable of being attached to an injection unit (1) of an injection molding machine that injects a molding material, the pressure measuring device (5) including: a measuring cylinder (50) attached to the injection unit (1) through which the molding material injected by the injection unit (1) flows; a plurality of molds (62, 63) of different specifications attached to the measuring cylinder (50) through which the molding material flows; a flow path switching pin (64) that selectively switches a discharge destination of the molding material to any one of the plurality of molds (62, 63); and a pressure sensor (61) that measures a pressure of the molding material in the measuring cylinder (50).

Description

Technical Field

[0001] The present invention relates to a pressure measuring device for an injection unit of an injection molding material that can be installed on an injection molding machine, and an injection molding machine equipped with the pressure measuring device. Background Technology

[0002] When performing injection molding, it is necessary to know the melt viscosity of the molding material. For example, knowing the melt viscosity serves as a reference for deriving molding conditions. In particular, for materials such as biodegradable plastics or composite materials containing nanofibers, metal powders, ceramic powders, etc., information about their melting or flow characteristics is often lacking, making prior knowledge of the melt viscosity useful. Alternatively, measuring the melt viscosity can also aid in quality management. For instance, when using a mixture of virgin and recycled materials as molding materials, determining the melt viscosity can help predict the degree of material degradation.

[0003] One device for determining the melt viscosity of molded materials is the capillary rheometer. A capillary rheometer comprises a barrel, a die with a fine opening at the barrel outlet, and a pressure sensor for measuring the pressure inside the barrel. The capillary rheometer uses a piston to extrude a sample filled into the barrel and measures the pressure inside the barrel at that time, thereby determining the viscosity of the sample. In this specification, unless otherwise specified, a die with a cylindrical cross-section and a fine opening is referred to as a capillary die, and a die with a rectangular cross-section and a fine opening is referred to as a slit die.

[0004] General viscosity measuring devices, including capillary rheometers, are relatively expensive and not widely used among injection molding machine users. Furthermore, the manual filling of the molding material into the barrel as a sample is time-consuming and labor-intensive. Therefore, it is worth considering using the injection molding machine's apparatus to measure melt viscosity with a simpler mechanism. For example, Patent Document 1 discloses an injection molding machine in which a pressure sensor is installed in the nozzle adapter with a nozzle, and the melt viscosity is calculated by measuring the resin pressure. The injection molding machine in Patent Document 1 uses the nozzle as a capillary mold to perform the same measurement as a capillary rheometer. Using an injection molding machine also has the advantage of being able to perform the measurement in an environment close to that of actual injection molding.

[0005] [Existing technical documents]

[0006] [Patent Literature]

[0007] Patent Document 1: Chinese Patent CN 104512018 A Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] When performing pressure measurements for viscosity determination, it is sometimes necessary to change the mold to a different size. For example, when implementing Bagley correction to determine the true shear stress by considering the pressure loss generated at the orifice inlet and outlet of the mold, it is necessary to use two or more molds with different effective orifice lengths to measure the pressure when using each mold. In the injection molding machine of Patent Document 1, if Bagley correction is to be implemented, the nozzle used as a capillary mold must be changed midway through the measurement.

[0010] This invention was made in view of this situation, and its object is to provide a pressure measuring device that can be installed on an injection molding machine, which, by being configured to selectively choose the mold to be used from a plurality of molds of different specifications, enables pressure measurement to be performed more easily. Other objects or advantages of the invention will be set forth in the following description.

[0011] [Technical means to solve the problem]

[0012] According to the present invention, a pressure measuring device is provided, which can be installed in the injection unit of an injection molding machine for injection molding material. The pressure measuring device includes: a measuring cylinder installed in the injection unit for the flow of molding material injected by the injection unit; multiple molds of different specifications installed in the measuring cylinder for the flow of molding material; a flow path switching pin for selectively switching the discharge destination of the molding material to any one of the multiple molds; and a pressure sensor for measuring the pressure of the molding material in the measuring cylinder.

[0013] [The effects of the invention]

[0014] The pressure measuring device of the present invention can be installed in an injection molding machine and is configured to selectively select the mold to be used from multiple molds of different specifications via a flow path switching pin. Therefore, even when mold switching is required, mold switching operations can be easily performed. Furthermore, pressure measurement can be performed more simply. Attached Figure Description

[0015] Figure 1 This is a schematic structural diagram of an injection molding machine according to an embodiment of the present invention, with the injection nozzle installed.

[0016] Figure 2 This is a schematic structural diagram of an injection molding machine according to an embodiment of the present invention, with a pressure measuring device installed.

[0017] Figure 3 This is a three-dimensional view of the pressure measuring device from above.

[0018] Figure 4 This is a three-dimensional view of the pressure measuring device from below.

[0019] Figure 5 This is a side cross-sectional view of the pressure measuring device.

[0020] Figure 6 It is a VI-VI arrow diagram of the pressure measuring device, and it is a front cross-sectional view.

[0021] Figure 7 This is a cross-sectional view of the first capillary mold and the second capillary mold.

[0022] Figure 8 This is a block diagram of the control device.

[0023] Figure 9 This is an example of a graphical user interface (GUI) for viscosity measurement in "simple measurement mode".

[0024] Figure 10 This is an example of a GUI used for viscosity measurement in the "Bagley correction mode".

[0025] [Explanation of Symbols]

[0026] 1: Injection Unit

[0027] 451: Nozzle mounting hole

[0028] 5: Pressure measuring device

[0029] 50: Measuring cylinder

[0030] 51: First feed cylinder

[0031] 52: Second feed cylinder

[0032] 524: Mold mounting hole

[0033] 61: Pressure sensor

[0034] 62: First capillary mold

[0035] 621: First capillary

[0036] 63: Second capillary mold

[0037] 631: Second capillary

[0038] 64: Flow path switching pin

[0039] 67: Heater

[0040] 68: Heater

[0041] 7: Control device Detailed Implementation

[0042] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. In each drawing, for the purpose of improving visibility, some constituent elements are sometimes omitted. The various modifications described below can be implemented in any combination.

[0043] The injection molding machine of this embodiment includes: an injection unit 1, injection molding material; a clamping unit (not shown) for opening, closing, and clamping a mold (not shown); and a control device 7 for controlling the injection unit 1 and the clamping unit. During injection molding, the injection unit 1 plasticizes the molding material and, after measuring a predetermined amount, injects it from the injection nozzle 46. The clamping unit is configured to hold the mold and open, close, and clamp it. During injection molding, when the molding material is injected, the clamping unit closes the mold and applies a predetermined clamping force to the mold. After the molding material injected from the injection nozzle 46 into the mold cavity cools and becomes a molded article, the clamping unit opens the mold to discharge the molded article and closes the mold again. The clamping unit can employ well-known structures such as a direct-pressure type or a toggle type.

[0044] In this specification, materials that can be injected using an injection molding machine are broadly referred to as molding materials. Besides materials primarily composed of resin, this includes metal injection molding (MIM) materials obtained by adding resin as a binder to metal powder, and ceramic injection molding (CIM) materials obtained by adding resin as a binder to ceramic powder. Furthermore, the following description uses an injection molding machine using thermoplastic molding materials as an example, but the present invention is also applicable to injection molding machines using thermosetting molding materials. Thermosetting molding materials include liquid injection molding (LIM) materials, which are thermosetting liquid materials.

[0045] The injection molding machine in this embodiment is a so-called screw pre-plasticizing injection molding machine, in which the plasticizing unit 2 and the injection unit 4 are independently configured. Figure 1 As shown, the injection unit 1 includes a plasticizing device 2, a junction 3, and an injection device 4. Figure 1 In the diagram, a portion of the structure is represented as a cross-sectional view. The following will... Figure 1 The left side, i.e., the side of the injection-molded material, is designated as the front side. Furthermore, [the following text appears to be incomplete and requires further context: "will..."] Figure 1 The right side of the middle, that is, the side that supplies the molding material, is designated as the rear side.

[0046] The plasticizing device 2 includes a plasticizing barrel 21, a plasticizing screw 23, a check valve 25, a plasticizing screw drive 27, and a heater 29. The plasticizing barrel 21 is a hollow cylinder heated to a predetermined temperature by a heater 29, such as a band heater. A material inlet 211 for supplying molding material is formed at the rear end of the plasticizing barrel 21. The plasticizing screw 23 is rotatably disposed within the plasticizing barrel 21. The plasticizing screw 23 feeds the molding material supplied from the material inlet 211 into the plasticizing barrel 21, melting it through the heat and shear heat from the heater 29 while simultaneously moving it forward. The check valve 25 is any actuator that advances the plasticizing screw 23, such as a hydraulic cylinder or an electric cylinder. Upon completion of metering, the check valve 25 advances the plasticizing screw 23 to block the flow path, preventing backflow of molding material during injection. The plasticizing screw drive 27 is any actuator that rotates the plasticizing screw 23, such as a hydraulic motor or an electric motor.

[0047] Connector 3 connects plasticizing device 2 and injection device 4. Connector 3 can also be heated to a specified temperature by a heater.

[0048] The injection device 4 includes an injection barrel 41, a plunger 42, a plunger drive device 43, an encoder 44, a nozzle barrel 45, an injection nozzle 46, and heaters 47 and 48.

[0049] The injection barrel 41 is a hollow cylinder heated to a specified temperature by a heater 47, such as a belt heater. The plunger 42 is a generally cylindrical member that can move freely within the injection barrel 41. The plunger drive device 43 is any actuator that moves the plunger 42 forward and backward, such as a hydraulic cylinder or an electric cylinder. The encoder 44 is a sensor that reads the position of the plunger 42. By using the position information of the plunger 42 read by the encoder 44 and a timer (not shown), the moving speed of the plunger 42, i.e., the injection speed, can be calculated.

[0050] The nozzle barrel 45 is a barrel body installed in front of the injection barrel 41 and heated to a specified temperature by a heater 47 such as a belt heater. The nozzle barrel 45 has a supply flow path connecting the connector 3 to the injection barrel 41 and a discharge flow path connecting the injection barrel 41 to the injection nozzle 46. A nozzle mounting hole 451 for mounting the injection nozzle 46 is formed on the front surface of the nozzle barrel 45. More specifically, a female thread is formed on the inner wall of the nozzle mounting hole 451 that engages with the male thread formed at the rear end of the injection nozzle 46. The injection nozzle 46 is installed in the nozzle barrel 45 during injection molding. The injection nozzle 46 is heated to a specified temperature by a heater 48 such as a coil heater.

[0051] Molded material from the plasticizing unit 2 is fed to the injection barrel 41 via the connector 3 and the nozzle barrel 45. In the injection barrel 41, the molding material is stored in front of the plunger 42, and the desired amount of molding material is metered. After metering, when backflow towards the plasticizing unit 2 is prevented by the check device 25, the plunger 42 is advanced, and the molding material is fed to the injection nozzle 46 via the nozzle barrel 45. Thus, the molding material is injected from the injection nozzle 46.

[0052] Here, the pressure measuring device 5 of this embodiment will be described. The pressure measuring device 5 is installed in the injection unit 1 when performing pressure measurements for measuring the viscosity of the molding material. The installation position of the pressure measuring device 5 can be as far forward as possible from the injection barrel 41, but from an operational viewpoint, it is preferable to [position not specified]. Figure 2 As shown, it is installed in place of the injection nozzle 46. That is, simply remove the injection nozzle 46 from the nozzle barrel 45 and install the measuring barrel 50 of the pressure measuring device 5 into the nozzle mounting hole 451 of the nozzle barrel 45. The detailed installation method of the pressure measuring device 5 will be described later.

[0053] like Figures 3 to 6 As shown, the pressure measuring device 5 of this embodiment includes a measuring cylinder 50, a pressure sensor 61, a first capillary mold 62, a second capillary mold 63, a flow path switching pin 64, a fixing plate 65, a positioning rod 66, and heaters 67 and 68.

[0054] The measuring cylinder 50 is installed in the injection unit 1 to allow the molding material injected by the injection unit 1 to flow through. In this embodiment, the measuring cylinder 50 includes a first cylinder 51 and a second cylinder 52, which are detachably configured. The first cylinder 51 and the second cylinder 52 are fastened by a fastening member 53. For example, the fastening member 53 in this embodiment includes a cap nut 531. The first cylinder 51 and the second cylinder 52 are fastened by the cap nut 531. A heater 67, serving as a belt heater, is wound around the cap nut 531.

[0055] The first feed cylinder 51 has a flow path 511, a mounting portion 512, and a flange 513. The flow path 511 is formed axially through the interior of the first feed cylinder 51 and connects to the discharge flow path of the nozzle feed cylinder 45. The mounting portion 512 is provided at the rear end of the first feed cylinder 51 and has a male thread that engages with the female thread formed in the nozzle mounting hole 451. The flange 513 is provided at the front end of the first feed cylinder 51 and abuts against the cap nut 531.

[0056] The second barrel 52 has a flow path 521, a flow path switching pin mounting hole 522, a flow path 523, a mold mounting hole 524, a pressure sensor mounting hole 525, a positioning rod insertion hole 526, and a heater mounting hole 527. Furthermore, at the rear end of the second barrel 52, a male thread is formed that engages with the female thread formed in the inner hole of the cap nut 531.

[0057] Flow path 521 is formed axially inside the second barrel 52 and connects flow path 511 to flow path switching pin mounting hole 522. Flow path switching pin mounting hole 522 is a hole formed on the front surface of the second barrel 52. Flow path switching pin 64 is rotatably inserted into flow path switching pin mounting hole 522. Flow path 523 is formed radially inside the second barrel 52 and connects flow path switching pin mounting hole 522 to mold mounting hole 524. Mold mounting hole 524 is a hole formed on the side of the second barrel 52. A first capillary mold 62 and a second capillary mold 63 are fixed in the mold mounting hole 524. In this embodiment, female threads are formed on the inner wall of the mold mounting hole 524, and male threads are formed on the outer periphery of the first capillary mold 62 and the second capillary mold 63, which can be easily installed and removed by screwing them together. The pressure sensor mounting hole 525 is a hole formed through the side of the second barrel 52 and the flow path 521. A pressure sensor 61 is installed inside the pressure sensor mounting hole 525. The positioning rod insertion hole 526 is a hole formed through the side of the second barrel 52 and the flow path switching pin mounting hole 522. The positioning rod 66 is inserted into the positioning rod insertion hole 526. The heater mounting hole 527 is a hole formed in the second barrel 52 for the heater 68, which serves as a cartridge heater, to pass through.

[0058] The flow path 523, mold mounting hole 524, and positioning rod insertion hole 526 are provided in multiple ways corresponding to the number of molds. In this embodiment, two flow paths 523, mold mounting holes 524, and positioning rod insertion holes 526 are provided respectively. However, it can also be configured to install three or more molds. Multiple molds can also be configured, for example, as... Figure 6 As shown in this embodiment, they are respectively arranged on the same plane perpendicular to the central axis of the second barrel 52.

[0059] The pressure sensor 61 is a pressure transducer that measures the pressure of the molding material inside the measuring cylinder 50. The pressure sensor 61 can be positioned upstream of the first capillary mold 62 and the second capillary mold 63, but ideally it should be close to them. In this embodiment, the pressure sensor 61 is fixed to the pressure sensor mounting hole 525 to measure the pressure of the molding material flowing through the flow path 521 of the second cylinder 52. In this embodiment, the pressure reading is sent to the control device 7, which calculates the viscosity. Alternatively, a display showing the pressure reading can be provided, allowing the operator to read the displayed value for viscosity calculation.

[0060] In this embodiment, a first capillary mold 62 and a second capillary mold 63, which are molds of different specifications for supplying molding materials, are installed in the measuring cylinder 50. For example... Figure 7 As shown, in the first capillary mold 62, a first capillary 621 with a predetermined inflow angle, diameter, and effective length, and a cylindrical cross-section, is formed. Furthermore, in the second capillary mold 63, a second capillary 631 with the same inflow angle and diameter as the first capillary 621, but with a shorter effective length, is formed. Molding material conveyed via the flow path switching pin 64 flows through the first capillary 621 and the second capillary 631. Here, the inflow angle refers to the cone angle of the tapered portion that may also be formed at the inlet of the orifice. When a tapered portion is not provided as in the first capillary mold 62 and the second capillary mold 63 of this embodiment, the inflow angle is treated as 180°. The flow paths in the first capillary mold 62 and the second capillary mold 63, other than the first capillary 621 and the second capillary 631, only need to have a flow path diameter that allows for negligible pressure loss. Furthermore, tool holes 622 and 632, which can be fitted with tools of any shape, can be formed at the flow path outlets of the first capillary mold 62 and the second capillary mold 63, respectively. In this embodiment, hexagonal holes that fit with a hexagonal wrench are formed as tool holes 622 and 632. In this way, the installation operation of the first capillary mold 62 and the second capillary mold 63 into the mold mounting hole 524 becomes easier.

[0061] The flow path switching pin 64 selects the mold to be used from multiple molds, specifically from the first capillary mold 62 and the second capillary mold 63 in this embodiment. In other words, the destination of the molding material supplied from flow path 511 and flow path 521 is selectively switched to any one of the multiple molds. The flow path switching pin 64 in this embodiment is a cylindrical member that rotatably fits into the flow path switching pin mounting hole 522, and has a flow path 641, a tool hole 642, and a recess 643. The flow path 641 is bent 90° in the middle, with its inlet side connected to flow path 521 and its outlet side connected to one of flow paths 523. By rotating the flow path switching pin 64, the flow path 523 connected to flow path 641 can be switched, and even the mold to be used can be selected. The tool hole 642 is a hole formed on the front surface of the flow path switching pin 64 and fitted with a tool of any shape. In this embodiment, a hexagonal hole fitted with a hexagonal wrench is formed as the tool hole 642. By fitting the tool into the tool hole 642, the flow path switching pin 64 can be rotated. The recess 643 is a hole formed on the side of the flow path switching pin 64, and is located at a position where it connects to the positioning rod insertion hole 526 when one of the flow paths 641 and 523 is connected. That is, in this embodiment, the flow path switching pin 64 is provided on the central axis of the second barrel 52, and when the outlet side of the flow path 641 is connected to the flow path 523, the recess 643 and the positioning rod insertion hole 526 are located on opposite sides, sandwiching the central axis.

[0062] The fixing plate 65 is a plate-shaped component that is fixed to the front surface of the second barrel 52 by bolts or the like, and abuts against the flow path switching pin 64 to prevent the flow path switching pin 64 from falling off. An opening is formed in the center of the fixing plate 65 in a manner that does not cover the tool hole 642.

[0063] The positioning rod 66 has a rod-shaped member that inserts into the positioning rod insertion hole 526. After the flow path switching pin 64 is rotated to select the mold to be used, the positioning rod 66 is inserted into the positioning rod insertion hole 526. As a result, the front end of the positioning rod 66 is engaged with the recess 643, the flow path switching pin 64 is accurately positioned, and accidental rotation is prevented.

[0064] In this embodiment, the flow path switching pin 64 is configured to be manually rotated using a tool, but it can also be configured to be automatically rotated by any actuator such as a fluid pressure cylinder or an electric motor. In this case, the mold switching performed by means of the flow path switching pin 64 can also be controlled by the control device 7.

[0065] The pressure of the molten molding material is measured using the pressure measuring device 5 as described above. With the pressure measuring device 5 installed in the injection unit 1, the melting, metering, and injection of the molding material are performed in the same manner as during injection molding. The molding material extruded by the plunger 42 passes through the nozzle barrel 45 and sequentially through flow paths 511, 521, 641, and 523, exiting from one of the multiple molds selected by the flow path switching pin 64. At this time, the pressure sensor 61 measures the pressure of the molding material flowing in the flow path 521. With a pressure measuring device 5 like this embodiment, the mold to be used can be easily switched using the flow path switching pin 64, thus improving workability.

[0066] To prevent the molding material ejected from the first capillary mold 62 or the second capillary mold 63 from scattering, it is preferable to install the measuring cylinder 50 in the injection unit 1 with the first capillary mold 62 or the second capillary mold 63, or even the mold mounting hole 524, facing downwards. Specifically, the measuring cylinder 50 is installed according to the following procedure. First, the cap nut 531 is inserted into the first cylinder 51, so that the mounting part 512 of the first cylinder 51 is screwed into the nozzle mounting hole of the nozzle cylinder 45. Next, the first cylinder 51 is engaged with the second cylinder 52, and positioned with the mold mounting hole 524 of the second cylinder 52 facing downwards. In this state, the cap nut 531 is screwed into the second cylinder 52, and the cap nut 531 is rotated until the wall surface 531a of the cap nut 531 abuts against the flange 513 of the first cylinder 51. In this way, the first cylinder 51 and the second cylinder 52 are secured.

[0067] The components installed on the second barrel 52 can be installed either before or after the first barrel 51 and the second barrel 52 are tightened. In this embodiment, the first barrel 51 and the second barrel 52 are tightened by the cap nut 531, but other fastening components 53 such as bolts can also be used.

[0068] After fastening the first barrel 51 and the second barrel 52 according to the process described above, when the first barrel 51 is screwed into the nozzle mounting hole 451, it is aligned with the mold mounting hole 524 facing downwards. Therefore, if the first barrel 51 and the second barrel 52 are fastened through the above process, they can be installed on the nozzle barrel 45 in the assembled state later. However, if the injection molding machine being installed is changed, the same alignment process must be repeated.

[0069] To ensure that all mold mounting holes 524 face downwards, the mold mounting holes 524 must be formed on one side of the side of the second barrel 52. Ideally, when viewed from the front, the angle between the vertical line passing through the central axis of the second barrel 52 and the straight line passing through the center of the mold mounting hole 524 should be less than 40°. The vertical line passing through the central axis of the second barrel 52 is a straight line representing the direction of gravity.

[0070] Here, the control device 7 of this embodiment will be described. The control device 7 controls the injection unit 1 and the mold clamping unit, and calculates the viscosity based on the pressure value of the molding material measured by the pressure measuring device 5.

[0071] Control device 7 can be constructed by arbitrarily combining hardware and software, for example, Figure 8 As shown, the device includes an arithmetic unit 71, a storage unit 72, an input unit 73, and a display unit 74. The arithmetic unit 71 is any arithmetic circuit such as a central processing unit (CPU) that performs various calculations to control the various devices and performs calculations related to viscosity measurement. The storage unit 72 can be configured by arbitrarily combining random access memory (RAM), read-only memory (ROM), and auxiliary storage devices to store data required for the calculations performed by the arithmetic unit 71. The input unit 73 and the display unit 74 can be independent devices or devices that combine both functions, such as a touch panel. In this embodiment, the input unit 73 and the display unit 74 are provided with an operation panel including a touch panel and input keys.

[0072] During injection molding and viscosity measurement, the control device 7 controls the plasticizing screw drive device 27, check device 25 and plunger drive device 43 of the injection unit 1 to melt, meter and inject the molding material.

[0073] Control device 7 controls heaters 29, 47, 48, 67, and 68 to heat the plasticizing barrel 21, injection barrel 41, nozzle barrel 45, injection nozzle 46, and measuring barrel 50 to the desired temperature. However, heaters 67 and 68 are not used during injection molding. Furthermore, heater 48 is not used for viscosity measurement. Temperature sensors such as thermocouples are installed in heaters 29, 47, 48, 67, and 68, allowing them to be controlled based on the measured temperature.

[0074] The control device 7 calculates the viscosity based on the pressure of the molding material measured by the pressure sensor 61 of the pressure measuring device 5. When calculating the viscosity, the control device 7 can implement a Bagley correction. The Bagley correction is a correction to determine the true shear stress by taking into account the pressure loss generated at the orifice inlet and outlet of the mold. When implementing the Bagley correction, two pressure measurements are required for each viscosity calculation, thus necessitating mold switching. Therefore, it can also be configured such that the user can arbitrarily switch between implementing and not implementing the Bagley correction, implementing it when a more accurate viscosity measurement is desired, and not implementing it if a simple measurement is sufficient. Furthermore, the control device 7 can implement a Rabinowitsch correction when calculating the viscosity. The Rabinowitsch correction is a correction to determine the true shear rate by taking into account the non-Newtonian nature of the molding material as a fluid. The Rabinowitsch correction can be implemented continuously, or it can be configured such that the user can arbitrarily switch between implementing and not implementing the Rabinowitsch correction. If simplifying the computation is the priority, the Rabinovich correction may be omitted.

[0075] In viscosity calculations, the pressure of the molding material within the barrel 50 is measured. The measured pressure may fluctuate during the injection process, but the pressure at the point where it becomes approximately stable can be used as the detection pressure. Alternatively, the average of the measured values ​​during the latter half of the injection process, presumably indicating that the pressure has become approximately stable, can be used as the detection pressure. Furthermore, the injection speed is also used in viscosity calculations. The injection speed used in the calculation can be either a set value or a measured value calculated based on encoder 44, but using the measured value allows for more accurate viscosity calculations. In the case of measured values, either the value at the point where the injection speed becomes approximately stable or the average of the injection speed during the latter half of the injection process can be used.

[0076] Figure 9 and Figure 10 This illustrates an example of a graphical user interface (GUI) 8 for viscosity measurement displayed on the display device 74. Users can navigate from a typical injection molding GUI to the viscosity measurement GUI 8. The GUI 8 includes, for example, a measurement condition input form 811, a measurement result display table 812, a read result display table 813, a mode switch button 82, a measurement start button 83, a data read button 841, a data clear button 842, a selection button 851, a selection deselection button 852, a graph drawing button 86, a save button 87, a setting button 88, and a close button 89.

[0077] The measurement condition input form 811 has input fields for the data required for viscosity calculation and setting values ​​related to viscosity measurement. Specifically, the user inputs the mold specifications (capillary diameter and effective length in the case of a capillary mold), the injection speed setting, and a arbitrarily set measurement name via the input device 73. In this embodiment, the injection speed is configured to allow multiple input values. When multiple injection speeds are input, the control device 7 changes the injection speed in a predetermined order to perform multiple viscosity measurements.

[0078] In this embodiment, the heater temperature is set in the standard injection molding GUI, but an input field related to the heater temperature can also be set in the measurement condition input form 811. The heater temperatures associated with heaters 29, 47, 67, and 68 are typically set to the same temperature. Ideally, the temperature of each part should be stable before viscosity measurement. For example, a limit can be set so that viscosity measurement cannot begin after transferring from the injection molding GUI to the viscosity measurement GUI 8 until an arbitrarily set heating waiting time has elapsed, thereby ensuring temperature stability.

[0079] When the mode switch button 82 is pressed, the system switches between implementing Bagley correction and not implementing Bagley correction. Specifically, the mode switch button 82 allows switching between a "simple measurement mode" without Bagley correction and a "Bagley correction mode" with Bagley correction. As described above, when configured to implement Rabinovich correction, the presence or absence of Rabinovich correction can be selected.

[0080] When the measurement start button 83 is pressed, molding material is injected from the pressure measuring device 5 based on the input data and set values ​​to measure the viscosity of the molten molding material. As described above, multiple measurements are performed continuously when multiple injection speeds are input. Furthermore, when the "Baggley correction mode" is selected, after the measurement using one mold, such as the first capillary mold 62, is completed, a message urging mold switching is displayed. The operator operates the flow path switching pin 64 to switch to another mold, such as the second capillary mold 63, and inputs the intention that the mold switching is complete to the control device 7. Upon receiving this intention, the measurement using the second capillary mold 63 is performed at the same injection speed. However, as mentioned earlier, mold switching using the flow path switching pin 64 can also be performed automatically by controlling the actuator using the control device 7. In this case, since manual operation related to mold switching by the operator is not required during the measurement, viscosity measurement can be performed more efficiently.

[0081] In this embodiment, the viscosity measurement value is the maximum value that can be measured using the injection unit 1. That is, the molding material is measured until the plunger 42 reaches its retraction limit. However, within a range where stable measurement can be performed, the measurement value can also be other values, and can be configured to be arbitrarily set.

[0082] The measurement result display table 812 displays the data obtained from the current viscosity measurement at a glance during each measurement. Furthermore, the readout result display table 813 displays the data obtained from past viscosity measurements at a glance during each measurement. When the data readout button 841 is pressed, data related to the measurement results stored in an external storage medium 75, such as an auxiliary storage device or flash memory, stored in the storage device 72 is displayed on the readout result display table 813. When the data clear button 842 is pressed, the data displayed on the measurement result display table 812 and the readout result display table 813 is reset. The data displayed on the measurement result display table 812 and the readout result display table 813 may also be part of the data related to the measurement results. The data displayed on the measurement result display table 812 and the readout result display table 813 may include, for example, data on injection speed, shear rate, test pressure, viscosity, temperature, and measurement name. The displayed data can be arbitrarily selected by the user. By comparing the data on the measurement result display table 812 and the readout result display table 813, the user can easily understand the characteristics of the molding material. The injection rate and temperature data in the measurement results can be set values, measured values, or both. Especially when the estimated measured values ​​are roughly the same as the set values, only the set values ​​can be saved as data.

[0083] By tapping the data, the user temporarily selects one or more rows of data displayed in the measurement result display table 812 or the reading result display table 813. In this state, when the selection button 851 is pressed, the row that has been temporarily selected is selected. Alternatively, the system can be configured so that a row can be directly selected by tapping the data, without inserting a temporary selection. In this case, the selection button 851 can be omitted. When the selection deselection button 852 is pressed, the row selection is reset. Here, when the graph drawing button 86 is pressed, a graph is displayed on the display device 74 based on the data of the selected row. That is, the control device 7 is configured to draw a graph based on data obtained through viscosity calculation. The displayed graph can be a so-called flow curve, that is, a logarithmic graph with shear rate as the x-axis and viscosity as the y-axis. By configuring the system to display graphs, the characteristics of the molding material can be understood visually. Alternatively, the graph data can be saved as image data to an auxiliary storage device of the storage device 72 or an external storage medium 75 such as a flash memory.

[0084] When the save button 87 is pressed, the data related to the measurement results is output in any format, such as Comma Separated Values ​​(CSV), and saved to an auxiliary storage device of storage device 72 or an external storage medium 75 such as flash memory. The output data may include the specifications of the mold for each measurement (capillary diameter and effective length in the case of a capillary mold), injection speed, shear rate, detection pressure, viscosity, temperature, and measurement name. If corrections have been applied, both the viscosity before and after correction may be included.

[0085] When the setting button 88 is pressed, the prescribed setting screen is displayed. In this embodiment, setting information that does not need to be changed for each viscosity measurement is typically displayed on a setting screen different from the measurement condition input form 811. On the setting screen, for example, the diameter of the plunger 42, the minimum and maximum injection speed that can be set during viscosity measurement, and the heating waiting time can be set. These settings may require authentication such as a password when changed. Furthermore, the diameter of the plunger 42 can be set according to the data of the injection molding machine model, in which case the input field related to the diameter of the plunger 42 can be omitted.

[0086] When the off button 89 is pressed, the viscosity measurement GUI 8 is closed, and the interface moves to the normal injection molding GUI.

[0087] The following describes in detail the formula for calculating viscosity using control device 7 based on the pressure of the molten molding material. Here, it is set as:

[0088] η ap [Pa·s]: Apparent viscosity

[0089] η[Pa·s]: True viscosity

[0090] τ ap [Pa]: Apparent shear stress

[0091] τ[Pa]: Actual shear stress

[0092] γ ap [s -1 Apparent shear rate

[0093] γ[s -1 ]: Actual shear rate

[0094] P L [Pa]: Detection pressure when using the first capillary mold 62

[0095] P S [Pa]: Detection pressure when using the second capillary mold 63

[0096] P0[Pa]: Estimated pressure when the effective length is 0 mm

[0097] D C [mm]: Diameter of the first capillary 621 and the second capillary 631

[0098] L C [mm]: Effective length of the first capillary tube 621

[0099] S C [mm]: Effective length of the second capillary tube 631

[0100] Q[mm 3 / s]: Volumetric flow rate

[0101] D P [mm]: Diameter of plunger 42

[0102] V[mm / s]: Injection speed

[0103] n: Structural viscosity index.

[0104] Apparent viscosity η ap As shown in the following formula, the apparent shear stress τ is... ap Divide by the apparent shear rate γ ap The obtained value.

[0105] [Number 1]

[0106]

[0107] Here, the apparent shear stress τ ap It is obtained through the following formula. Without Bagley correction, the apparent shear stress τ ap In the calculation, either the first capillary mold 62 or the second capillary mold 63 can be used, but the measurement error is smaller when using the first capillary mold 62. The following formula is the calculation formula when using the first capillary mold 62. When using the second capillary mold 63, the measured pressure P is replaced. L and effective length L C And using the detection pressure P S and effective length S C .

[0108] [Number 2]

[0109]

[0110] Moreover, the apparent shear rate γ ap It can be obtained using the following formula.

[0111] [Number 3]

[0112]

[0113] Based on the above calculation formula, the apparent shear stress τ ap and apparent shear rate γ ap To determine the apparent viscosity η ap In the case of a simple viscosity measurement, the apparent viscosity η can be calculated using the above formula. ap That is sufficient. For more accurate viscosity measurements, at least one of Bagley correction and Rabinovich correction should be performed, preferably both.

[0114] The Bagley correction is a correction to determine the true shear stress τ by considering the pressure losses generated at the orifice inlet and outlet. Pressure losses occur at the orifice inlet, inside the orifice, and at the orifice outlet as the molding material passes through the orifice. The pressure P is measured using the first capillary mold 62. L Subtracting the estimated pressure P0 when the effective length of the orifice (capillary) is 0 mm, we can estimate the pressure (P) when no pressure loss occurs at the orifice inlet and outlet, using the first capillary mold 62. L -P0). The true shear stress τ after Bagley correction is obtained by the following equation.

[0115] [Number 4]

[0116]

[0117] Here, it is assumed that the pressure P0 is obtained by the following formula. As is clear from the formula, when performing Bagley correction, the mold used must be switched and two pressure measurements must be performed to determine the test pressure P when using the first capillary mold 62. L The detection pressure P when using the second capillary mold 63 S .

[0118] [Number 5]

[0119]

[0120] Apparent shear rate γ ap This refers to the shear rate when the structural viscosity index n of the molding material being measured is 1, i.e., when the molding material is a Newtonian fluid. However, in reality, molding materials are generally non-Newtonian fluids, therefore the actual shear rate γa differs from the apparent shear rate γb. ap This will cause a deviation. The Rabinovich correction is to adjust the apparent shear rate γ. apThe true shear rate γ is obtained by multiplying by a specified coefficient defined by the structural viscosity index n. The true shear rate γ after the Rabinovich correction is obtained by the following formula.

[0121] [Number 6]

[0122]

[0123] Here, the structural viscosity index n is the apparent shear rate γ. ap The slope of the logarithm of the actual shear stress τ is given by the following formula. Therefore, the structural viscosity index n is obtained by the following formula. However, in the case of Rabinovich correction only, without Bagley correction, the apparent shear stress τ is replaced by the actual shear stress τ. ap Used for calculations.

[0124] [Number 7]

[0125]

[0126] Using Bagley correction and Rabinovich correction, the true shear stress τ and true shear rate γ are calculated, respectively. The true viscosity η is then given by the following formula, which is the value obtained by dividing the true shear stress τ by the true shear rate γ.

[0127] [Number 8]

[0128]

[0129] As illustrated in several examples, the present invention is not limited to the structure of the embodiments shown in the accompanying drawings, and various modifications or applications can be made without departing from the technical spirit of the invention.

[0130] For example, in this embodiment, a calculation formula related to viscosity calculation when using a capillary mold is described. The capillary mold has a capillary tube with a cylindrical orifice in cross-section, but a slit mold with a rectangular orifice in cross-section can also be used instead. That is, when testing the viscosity of the molding material, a first slit mold can be used, forming a first slit with a specified inflow angle, width, gap, and effective length; and a second slit mold, forming a second slit with the same inflow angle, width, and gap as the first slit but with a shorter effective length than the first slit.

[0131] When using a slit mold, the apparent shear stress τ ap Apparent shear rate γ ap The true shear stress τ and the true shear rate γ are obtained by the following formula, replacing the formula used with the capillary model. Where, let be:

[0132] ηap [Pa·s]: Apparent viscosity

[0133] η[Pa·s]: True viscosity

[0134] τ ap [Pa]: Apparent shear stress

[0135] τ[Pa]: Actual shear stress

[0136] γ ap [s -1 Apparent shear rate

[0137] γ[s -1 ]: Actual shear rate

[0138] P L [Pa]: Detection pressure when using the first slit mold.

[0139] P S [Pa]: Detection pressure when using the second slit mold.

[0140] P0[Pa]: Estimated pressure when the effective length is 0 mm

[0141] B[mm]: Width of the slit

[0142] H[mm]: The gap between the slits

[0143] L S [mm]: Effective length of the first slit

[0144] S S [mm]: Effective length of the second slit

[0145] D P [mm]: Diameter of plunger 42

[0146] V[mm / s]: Injection speed

[0147] n: Structural viscosity index.

[0148] [Number 9]

[0149]

[0150] However, this formula applies when using the first slit mold. When using the second slit mold, the detection pressure P is replaced. L and effective length L S And using the detection pressure P S and effective length S S .

[0151] [Number 10]

[0152]

[0153] [Number 11]

[0154]

[0155] in,

[0156] [Number 12]

[0157]

[0158] [Number 13]

[0159]

[0160] in,

[0161] [Number 14]

[0162]

[0163] The pressure measuring device 5 of this embodiment is particularly effective when switching between multiple molds for viscosity measurement. In this embodiment, two molds differing only in their effective length are installed in the measuring cylinder 50 in a manner that allows for Bagley correction, but the specifications other than the effective length can also be different. Besides Bagley correction, consider the following situation as an example of changing to a mold with different specifications during viscosity measurement. When investigating the relationship between shear rate and viscosity for a certain molding material, multiple viscosity measurements are performed by changing the injection speed. However, injection speeds in injection molding machines have upper and lower limits, so depending on the specifications of the injection molding machine, the desired shear rate may not be obtained. In this case, by switching to a mold with a different diameter in the case of a capillary mold, or switching to a mold with a different width and gap in the case of a slot mold, the viscosity at the desired shear rate can be measured.

[0164] An injection molding machine capable of mounting the pressure measuring device 5 can also be a so-called coaxial screw injection molding machine, which integrates the plasticizing device and the injection device. However, if it is a screw pre-plasticizing injection molding machine, like the one in this embodiment, which includes a check valve 25 to prevent backflow by advancing the plasticizing screw 23, then compared to a coaxial screw injection molding machine, the metering / injection stability is superior, and therefore the viscosity of the molding material can be measured more accurately. The embodiments were chosen to illustrate the principles of the invention and its practical applications. Various modifications can be made with reference to the description. The scope of the invention is defined by the appended claims.

Claims

1. A pressure measuring device, capable of being installed in the injection unit of an injection molding machine for injection molding materials, the pressure measuring device comprising: A measuring cylinder is installed in the injection unit to allow the molding material injected by the injection unit to flow through; Multiple molds of different specifications are installed in the measuring cylinder to allow the molding material to flow through; The flow path switching pin selectively switches the discharge destination of the molding material to any one of the plurality of molds; as well as A pressure sensor measures the pressure of the molding material inside the measuring cylinder. The flow path switching pin is a cylindrical component with an internal flow path. The internal flow path is bent at 90° in the middle. The inlet side is connected to the flow path through which the molding material flows, and the outlet side is connected to the flow path through which the molding material flows to any one of the plurality of molds.

2. The pressure measuring device according to claim 1, wherein... The plurality of modules includes: A first capillary mold, forming a first capillary tube with a cross-sectional cylindrical shape; and The second capillary mold forms a second capillary with a cross-sectional cylindrical shape. The first capillary has a specified inflow angle, diameter, and effective length. The second capillary has the same inflow angle and diameter as the first capillary, but has a shorter effective length than the first capillary.

3. The pressure measuring device according to claim 1, wherein... The plurality of modules includes: A first slit mold, forming a first slit with a rectangular cross-sectional shape; and The second slit mold forms a second slit with a rectangular cross-section. The first slit has a specified inflow angle, width, gap, and effective length. The second slit has the same inflow angle, width and gap as the first slit, but has a shorter effective length than the first slit.

4. The pressure measuring device according to claim 1, wherein... The measuring cylinder comprises: A first barrel, screwed into the nozzle mounting hole of the injection unit; and The second material cylinder has mold mounting holes formed on its side for mounting the plurality of molds. When viewed directly, the angle between the vertical line passing through the central axis of the second barrel and the straight line passing through the center of the mold mounting hole is less than 40°.

5. The pressure measuring device according to claim 4, comprising a fastening component, The fastening component fastens the first material cylinder and the second material cylinder.

6. The pressure measuring device according to claim 5, wherein... The fastening component is a cap nut that abuts against the flange formed on the first cylinder and is screwed into the second cylinder.

7. The pressure measuring device according to claim 1, further comprising: A heater is used to heat the measuring cylinder to the desired temperature.

8. An injection molding machine, equipped with a pressure measuring device as described in any one of claims 1 to 7, the injection molding machine comprising: The control device calculates the viscosity of the molding material based on the pressure of the molding material measured by the pressure sensor. The control device is configured to perform Bagley correction during viscosity calculation and to switch between performing Bagley correction and not performing Bagley correction.

9. The injection molding machine according to claim 8, wherein The control device is configured to generate a graph based on data obtained through the calculation of the viscosity.

10. The injection molding machine according to claim 9, wherein The graph is a logarithmic graph of shear rate and viscosity.

Images