Injection molding device and control method thereof

Abstract

To provide an injection molding device capable of effectively suppressing carbonization of a resin and a control method thereof.SOLUTION: An injection molding device 1 includes a cylinder 31, a heater 34, a screw 35, a nitrogen gas feeder 6, and a controller 55. The screw 35 includes a backflow prevention mechanism including a check ring 35d and a check sheet 35b. The controller 55 heats the cylinder 31 by using the heater 34 during molding operation and supplies nitrogen gas to the cylinder 31 by using the nitrogen gas feeder 6. The controller 55 moves the screw 35 back and forth after completion of molding operations and discharges a resin in the cylinder 31. The controller 55 moves the screw 35 backwardly after discharge of the resin, then heating of the cylinder 31 by the heater 34 is stopped without moving the screw 35 forwardly.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an injection molding machine and a control method thereof. [Background technology]

[0002] An injection molding machine has a cylinder and a screw disposed in the cylinder. The injection molding machine injects plasticized resin in the cylinder into a cavity of a mold to form a molded product. When air enters the heated cylinder of an injection molding machine, the oxygen contained in the air may carbonize or discolor the resin. Carbonization and discoloration of the resin cause defects in the molded product.

[0003] Patent Document 1 discloses a conventional injection molding machine. The injection molding machine of Patent Document 1 has a sealing device for replacing the gas in the cylinder with nitrogen gas. The sealing device has a separator for separating compressed air into nitrogen and oxygen. The injection molding machine of Patent Document 1 suppresses carbonization of the resin by supplying nitrogen gas to the cylinder by the sealing device.

[0004] The sealing device is connected to the cylinder via a hose in which an on-off valve is disposed. The sealing device has two separators and a switching valve for switching the connection between them. The sealing device adjusts the nitrogen concentration and flow rate of the nitrogen gas by connecting the two separators connected in series or in parallel to the hose, or connecting only one separator to the hose, using the switching valve. In a configuration in which two separators are connected in series, the nitrogen concentration of the nitrogen gas is relatively high, but the flow rate of the nitrogen gas is small. In a configuration in which two separators are connected in parallel and a configuration in which only one separator is used, the nitrogen concentration of the nitrogen gas is relatively low, but the flow rate of the nitrogen gas is large. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-113945 Summary of the Invention [Problem to be solved by the invention]

[0006] The injection molding machine of Patent Document 1 heats the cylinder before starting the molding operation, and when the cylinder temperature exceeds the nitrogen gas supply temperature, it opens the on-off valve to start supplying nitrogen gas to the cylinder. When the molding operation is completed, the injection molding machine discharges the resin in the cylinder and stops heating the cylinder. When the cylinder temperature falls below the nitrogen gas stop temperature, the injection molding machine closes the on-off valve to stop supplying nitrogen gas to the cylinder.

[0007] In a configuration in which the screw of the injection molding machine has a backflow prevention mechanism including a check ring and a check sheet, the screw moves forward to discharge the resin from the cylinder, the backflow prevention mechanism divides the space inside the cylinder into a front part and a rear part, and in that state, heating of the cylinder is stopped and the temperature of the cylinder drops. Therefore, even if nitrogen gas is supplied to the cylinder during the next molding operation, it does not spread throughout the entire space inside the cylinder, and there is a risk of carbonization of the resin.

[0008] In addition, the injection device does not switch the connection of the two separators during the operation of the injection molding machine. That is, the injection device supplies nitrogen gas with a constant nitrogen concentration and a constant flow rate to the cylinder. If the nitrogen concentration of the nitrogen gas is low, carbonization of the resin may occur during the molding operation. If the nitrogen concentration of the nitrogen gas is high, carbonization of the resin during the molding operation can be suppressed, but the flow rate of the nitrogen gas is small and the time required to replace the gas in the cylinder with nitrogen gas is long. Therefore, during the temperature rise period of the cylinder before the start of the molding operation, the gas in the cylinder is not properly replaced with nitrogen gas, and carbonization of the resin may occur.

[0009] Therefore, an object of the present invention is to provide an injection molding machine and a control method thereof that can effectively suppress carbonization of resin. [Means for solving the problem]

[0010] In order to achieve the above object, an injection molding machine according to one embodiment of the present invention is an injection molding machine having a cylinder, a heater for heating the cylinder, a screw arranged inside the cylinder, a screw drive mechanism for rotating and advancing the screw, a nitrogen gas supply device for supplying nitrogen gas to the cylinder, and a control device, wherein the screw has a backflow prevention mechanism, which forms a resin flow path for moving plasticized resin in the cylinder forward relative to the screw when the screw moves backward, and closes the resin flow path to restrict the resin from moving backward relative to the screw when the screw moves forward, and the control device heats the cylinder with the heater during a molding operation, supplies nitrogen gas to the cylinder with the nitrogen gas supply device, and after the molding operation is completed, moves the screw forward and backward using the screw drive mechanism to discharge the resin in the cylinder, and after the resin is discharged, moves the screw backward using the screw drive mechanism, and then stops heating the cylinder with the heater without moving the screw forward.

[0011] In order to achieve the above-mentioned object, a control method for an injection molding machine according to another aspect of the present invention is a control method for an injection molding machine having a cylinder and a screw arranged inside the cylinder, wherein the screw has a backflow prevention mechanism, which forms a resin flow path for plasticized resin in the cylinder to move forward relative to the screw when the screw moves backward, and closes the resin flow path to restrict the resin from moving backward relative to the screw when the screw moves forward, heats the cylinder and supplies nitrogen gas to the cylinder during a molding operation, and after the molding operation is completed, moves the screw forward and backward to discharge the resin in the cylinder, and after the resin is discharged, moves the screw backward, and then stops heating the cylinder without moving the screw forward. Effect of the Invention

[0012] According to the present invention, after the molding operation is completed, the heating of the cylinder is stopped with the screw retracted. This connects the front and rear parts of the space in the cylinder by the resin flow path formed in the backflow prevention mechanism. Therefore, when nitrogen gas is supplied to the cylinder for the next molding operation, it spreads throughout the entire space in the cylinder, effectively suppressing carbonization of the resin. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic configuration of an injection molding machine according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram showing a schematic configuration of an injection device and a nitrogen gas supply device of an injection molding machine. [Diagram 3] FIG. 2 is a cross-sectional view of the tip of a screw of an injection device and its vicinity. [Figure 4] FIG. 2 is a functional block diagram of the injection molding machine. [Diagram 5] 4 is a graph showing an example of the relationship between the nitrogen concentration and the flow rate of nitrogen gas that can be supplied by the nitrogen gas supply device. [Figure 6] FIG. 11 is a diagram illustrating an example of a nitrogen gas supply operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] An injection molding machine according to one embodiment of the present invention will be described below with reference to Figures 1 to 6. An injection molding machine plasticizes resin, which is a molding material, and injects it into a cavity of a mold to form a molded product.

[0015] FIG. 1 is a diagram showing a schematic configuration of an injection molding machine according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of an injection device and a nitrogen gas supply device of the injection molding machine. FIG. 3 is a cross-sectional view of the tip portion of a screw of the injection device and its vicinity. In FIG. 3, the check head is shown as seen from the front. FIG. 3A shows a state in which the screw moves backward and a resin flow path is formed, and FIG. 3B shows a state in which the screw moves forward and the resin flow path is closed. FIG. 4 is a functional block diagram of the injection molding machine. FIG. 5 is a graph showing an example of the relationship between the nitrogen concentration and the flow rate of nitrogen gas that can be supplied by the nitrogen gas supply device. FIG. 6 is a diagram explaining an example of the supply operation of nitrogen gas.

[0016] As shown in FIG. 1, an injection molding machine 1 according to this embodiment includes a mold clamping device 2, an injection device 3, an ejection device 4, a control unit 5, a nitrogen gas supplying device 6, and a base .

[0017] The mold clamping device 2 is disposed on a base 7. The mold clamping device 2 opens, closes, and clamps a fixed-side mold 81 and a movable-side mold 82. The fixed-side mold 81 and the movable-side mold 82 form a cavity 83.

[0018] The mold clamping device 2 has a fixed die plate 21, a movable die plate 22, and a mold clamping drive mechanism 23. A fixed side mold 81 is attached to the fixed die plate 21. A movable side mold 82 is attached to the movable die plate 22. The mold clamping drive mechanism 23 clamps the fixed side mold 81 and the movable side mold 82 in the front-rear direction (left-right direction in FIG. 1) by the fixed die plate 21 and the movable die plate 22 to generate a mold clamping force.

[0019] The injection device 3 is disposed on a base 7. The injection device 3 includes a cylinder 31, a nozzle 32, a resin supply unit 33, a heater , a screw 35, and a screw drive mechanism .

[0020] The cylinder 31 has a cylindrical shape. The cylinder 31 is arranged along the front-rear direction. The nozzle 32 is arranged at the front end of the cylinder 31. The resin supply unit 33 is arranged at the rear end of the cylinder 31. The resin supply unit 33 has a hopper that contains powdered or granular resin. The resin supply unit 33 supplies resin to the cylinder 31. The heater 34 is, for example, a band heater, and is arranged on the outer circumferential surface of the cylinder 31. The heater 34 heats the cylinder 31.

[0021] The screw 35 is accommodated in the cylinder 31 so as to be rotatable and movable forward and backward. The screw 35 has a screw body 35a, a check sheet 35b, a check head 35c, and a check ring 35d. The screw body 35a has a spiral flight. The check head 35c is screwed to the tip of the screw body 35a. The check ring 35d has a cylindrical shape, and the check head 35c is inserted inside it. The check ring 35d can move in the forward and backward directions relative to the check head 35c with its outer circumferential surface in contact with the inner circumferential surface of the cylinder 31. The check sheet 35b is sandwiched between the tip surface of the screw body 35a and the check head 35c. There is a gap through which the resin flows between the outer circumferential surface of the check head 35c and the inner circumferential surface of the check ring 35d.

[0022] As shown in Fig. 3A, when the screw 35 moves backward, the check ring 35d moves forward relative to the check head 35c, and a resin flow path 35e is formed between the check ring 35d and the check sheet 35b. As shown in Fig. 3B, when the screw 35 moves forward, the check ring 35d moves backward relative to the check head 35c, and the resin flow path 35e between the check ring 35d and the check sheet 35b is closed (disappears). The check ring 35d and the check sheet 35b constitute a backflow prevention mechanism.

[0023] The screw drive mechanism 36 has, for example, an electric motor and drives the screw 35 to rotate and move forward and backward.

[0024] The ejection device 4 has an ejection mechanism 41. The ejection mechanism 41 drives an ejector pin (not shown) to eject it into the cavity 83, and ejects the molded product from the movable mold .

[0025] The control unit 5 controls the overall operation of the injection molding machine 1. As shown in FIG 4, the control unit 5 has a display device 51, an input device 52, a storage device 53, a timer 54, and a control device 55.

[0026] The display device 51 is, for example, a liquid crystal display. The input device 52 is, for example, an operation key or a touch panel. The storage device 53 is, for example, a magnetic disk device or a non-volatile memory. The storage device 53 stores molding conditions and the like. The control device 55 has a computer. The control device 55 is communicably connected to the display device 51, the input device 52, the storage device 53, and the timer 54. The control device 55 displays various information on the display device 51 and performs an operation according to an operation input to the input device 52. The display device 51 and the input device 52 may be, for example, a tablet device or a notebook computer connected to the control device 55 by wireless communication. The control device 55 is also communicably connected to the mold clamping drive mechanism 23, the heater 34, the screw drive mechanism 36, the ejection mechanism 41, and the nitrogen gas supply device 6. The control device 55 controls the mold clamping drive mechanism 23, the heater 34, the screw drive mechanism 36, the ejection mechanism 41, the nitrogen gas supply device 6, and the like in the operation of molding a molded product (molding operation).

[0027] The nitrogen gas supplying device 6 is housed in the base 7. The nitrogen gas supplying device 6 separates nitrogen from air to generate nitrogen gas. The nitrogen gas supplying device 6 supplies nitrogen gas to the cylinder 31 through a pipe 68. One end of the pipe 68 is connected to the nitrogen gas supplying device 6, and the other end of the pipe 68 is disposed toward the space in the cylinder 31 where the screw 35 is disposed (the accommodation space 31a). The nitrogen gas supplying device 6 generates nitrogen gas using pressure swing adsorption (PSA).

[0028] The nitrogen gas supply device 6 has an air compressor 61, a filter 62, a first adsorber 63, a second adsorber 64, a buffer 65, a plurality of switching valves 66, and a silencer 67. The first adsorber 63 and the second adsorber 64 contain an adsorbent that adsorbs oxygen contained in the air and allows nitrogen to pass through. The silencer 67 is connected to the switching valve 66 and is used when releasing the oxygen adsorbed in the first adsorber 63 and the second adsorber 64.

[0029] In the nitrogen gas supply device 6, the destination of compressed air is switched to the first adsorber 63 by the switching valve 66. Compressed air is sent from the air compressor 61 to the first adsorber 63 through the filter 62. The filter 62 removes oil and impurities contained in the compressed air. In the first adsorber 63, oxygen contained in the compressed air is adsorbed, and the nitrogen that has passed through the first adsorber 63 is stored in the buffer 65 as nitrogen gas. When the oxygen adsorbed in the first adsorber 63 becomes saturated, the switching valve 66 connects the first adsorber 63 and the second adsorber 64 to equalize the pressure, and then releases the oxygen adsorbed in the first adsorber 63 from the silencer 67, and at the same time switches the destination of the compressed air to the second adsorber 64. Compressed air is sent from the air compressor 61 to the second adsorber 64 through the filter 62. In the second adsorber 64, oxygen contained in the compressed air is adsorbed, and the nitrogen that has passed through the second adsorber 64 is stored in the buffer 65 as nitrogen gas. When the oxygen adsorbed in the second adsorber 64 becomes saturated, the first adsorber 63 and the second adsorber 64 are connected and pressure-equalized by the switching valve 66, and the oxygen adsorbed in the second adsorber 64 is released from the silencer 67, and at the same time, the destination of the compressed air is switched to the first adsorber 63. Thereafter, the first adsorber 63 and the second adsorber 64 are used alternately in the same manner to store the nitrogen gas in the buffer 65. When the first adsorber 63 and the second adsorber 64 are not being used, they release the adsorbed oxygen. Nitrogen gas with a predetermined nitrogen concentration is stored in the buffer 65. The nitrogen gas supplying device 6 supplies the nitrogen gas from the buffer 65 through the pipe 68 to the cylinder 31. The nitrogen gas supplying device 6 has an oxygen concentration sensor (not shown) and estimates the nitrogen concentration of the nitrogen gas based on the oxygen concentration.

[0030] The nitrogen gas supplying device 6 can supply a large flow rate when the nitrogen concentration of the nitrogen gas to be supplied is low. The nitrogen gas supplying device 6 can supply a small flow rate when the nitrogen concentration of the nitrogen gas to be supplied is high. An example of the relationship between the nitrogen concentration and flow rate of the nitrogen gas that can be supplied by the nitrogen gas supplying device 6 is shown in FIG. 5. The nitrogen gas supplying device 6 can supply a maximum of 20 L / min of nitrogen gas when the nitrogen concentration is 99%, can supply a maximum of 10 L / min of nitrogen gas when the nitrogen concentration is 99.9%, and can supply a maximum of 5 L / min of nitrogen gas when the nitrogen concentration is 99.99%.

[0031] Next, an example of the molding operation executed by the control device 55 will be described.

[0032] Before starting the molding operation, the control device 55 controls the heater 34 to heat the cylinder 31 to a predetermined temperature (molding operation start temperature C2). In preparation for the molding operation, the control device 55 executes a purging operation and measures the amount of resin to be injected initially.

[0033] In the molding operation, the control device 55 controls the mold clamping drive mechanism 23 to press the movable mold 82 against the fixed mold 81 to clamp the mold (mold closing operation). Next, the control device 55 controls the screw drive mechanism 36 to move the screw 35 forward (injection operation (filling)). When the screw 35 moves forward, the check ring 35d abuts against the check sheet 35b to close the resin flow path 35e, restricting the plasticized resin from moving backward. This causes the plasticized resin at the front end of the cylinder 31 to fill the cavity 83. Next, the control device 55 controls the screw drive mechanism 36 to move the screw 35 forward and backward so that a predetermined pressure (holding pressure) is applied to the resin in the cavity 83 (injection operation (holding pressure)).

[0034] Next, the control device 55 controls the screw drive mechanism 36 to rotate and move the screw 35 backward, and supplies (meters) the amount of resin required for one injection to the front end of the cylinder 31 (metering operation). When the screw 35 moves backward, the check ring 35d moves forward relative to the check head 35c to form a resin flow path 35e. The metering operation is also called a plasticizing operation. In parallel with the metering operation, the control device 55 waits until the resin in the cavity 83 cools and hardens (cooling operation).

[0035] Then, when the cooling operation is completed, the control device 55 controls the mold clamping drive mechanism 23 to open the fixed side mold 81 and the movable side mold 82 (mold opening operation), and controls the ejection mechanism 41 to remove the molded product from the cavity 83 with the ejector pin (removal operation).

[0036] The operations from the mold closing operation to the removal operation constitute one molding operation. The control device 55 repeatedly executes the molding operation to mold a molded product. The execution of one molding operation is called one cycle. The molding operation includes a mold closing process for executing a mold closing operation, an injection process for executing an injection operation, a cooling process for executing a cooling operation, a mold opening process for executing a mold opening operation, and a removal process for executing a removal operation. The injection process includes a process related to filling in the injection operation and a process related to pressure holding in the injection operation.

[0037] Next, an example of the nitrogen gas supply operation executed by the control device 55 will be described with reference to FIG.

[0038] FIG. 6 shows an example of an operation in which nitrogen gas is supplied to the cylinder 31 at a constant flow rate during a molding operation.

[0039] After the injection molding machine 1 is started (powered on), an operation related to the molding operation is input to the input device 52. In response to the input of the operation, the control device 55 controls the heater 34 to start heating the cylinder 31 (time T0). At this time, air is retained in the accommodation space 31a of the cylinder 31. The control device 55 obtains the temperature of the cylinder 31 by a temperature sensor (not shown). The control device 55 also controls the nitrogen gas supply device 6 to start generating nitrogen gas.

[0040] When the temperature of the cylinder 31 rises and reaches the supply start temperature C1 (time T1), the control device 55 controls the nitrogen gas supply device 6 to supply nitrogen gas (first nitrogen gas N1) to the cylinder 31 at a nitrogen concentration D1 and a flow rate F1. The nitrogen concentration D1 is, for example, 99.9%, and the flow rate F1 is, for example, 10 L / min. It is preferable that the flow rate F1 of the first nitrogen gas N1 is the maximum flow rate that can be supplied when the nitrogen concentration is D1. By supplying the first nitrogen gas N1 to the cylinder 31, the replacement of the air in the accommodation space 31a with the first nitrogen gas N1 proceeds.

[0041] When a predetermined replacement reference time Tx has elapsed since the start of the supply of the first nitrogen gas N1 (time T2), the control device 55 controls the nitrogen gas supply device 6 to supply nitrogen gas (second nitrogen gas N2) with a nitrogen concentration D2 and a flow rate F2 to the cylinder 31. The nitrogen concentration D2 is higher than the nitrogen concentration D1, for example, 99.99%. The flow rate F2 is lower than the flow rate F1, for example, 5 L / min. The flow rate F2 of the second nitrogen gas N2 is preferably the maximum flow rate that can be supplied when the nitrogen concentration is D2. The replacement reference time Tx is set, for example, according to the volume of the accommodation space 31a so that the air in the accommodation space 31a is appropriately replaced with the first nitrogen gas N1.

[0042] Alternatively, when the supply amount of the first nitrogen gas N1 exceeds a predetermined replacement reference amount Vx (time T2), the control device 55 may control the nitrogen gas supply device 6 to supply the second nitrogen gas N2 to the cylinder 31. The replacement reference amount Vx is set, for example, according to the volume of the accommodation space 31a so that the air in the accommodation space 31a is appropriately replaced with the first nitrogen gas N1.

[0043] When the temperature of the cylinder 31 rises and reaches the molding operation start temperature C2 (time T3), the control device 55 starts the molding operation. Even during the molding operation, the control device 55 controls the nitrogen gas supply device 6 to supply nitrogen gas to the cylinder 31. Also, even during the molding operation, the control device 55 controls the heater 34 to heat (control the temperature) the cylinder 31 to a temperature appropriate for the molding operation.

[0044] When the molding operation ends (time T4) and an operation for ending the operation (shutdown) of the injection molding machine 1 is input to the input device 52, the control device 55 controls the nitrogen gas supply device 6 to supply nitrogen gas (second nitrogen gas N2) with a nitrogen concentration D2 and a flow rate F2 to the cylinder 31, and executes a purge operation to discharge the resin inside the cylinder 31. In the purge operation, the control device 55 controls the screw drive mechanism 36 to rotate and move the screw 35 forward and backward, and discharge the resin inside the cylinder 31 from the nozzle 32.

[0045] When the purge operation is completed (time T5), the control device 55 controls the screw drive mechanism 36 to move the screw 35 backward. As a result, the check ring 35d and the check sheet 35b (backflow prevention mechanism) form a resin flow path 35e. The resin flow path 35e connects the front part (front part 31a1) and the rear part (rear part 31a2) of the backflow prevention mechanism in the accommodation space 31a of the cylinder 31. When the purge operation is completed (time T5), the control device 55 controls the heater 34 to stop heating the cylinder 31. The temperature of the cylinder 31 drops. In this way, the cylinder 31 from which the resin has been discharged by the purge operation is in a state where there is no resin in the accommodation space 31a, and when the first nitrogen gas N1 is supplied to the cylinder 31 in this state after the next start of the injection molding machine 1, the first nitrogen gas N1 can be distributed throughout the entire accommodation space 31a.

[0046] When the temperature of the cylinder 31 reaches the supply stop temperature C6 (time T6), the control device 55 controls the nitrogen gas supply device 6 to stop the supply of nitrogen gas to the cylinder 31. The supply stop temperature C6 may be lower than the supply start temperature C1, may be higher than the supply start temperature C1, or may be the same as the supply start temperature C1.

[0047] Then, the control device 55 shuts down (powers off) the injection molding machine 1. Alternatively, the control device 55 performs the above operation (times T0 to T6) again, for example, after the resin or the mold is replaced. The time periods T0 to T3 are a temperature rise period for the cylinder 31. The time periods T3 to T4 are a molding operation period. The time periods T4 to T6 are a termination operation period.

[0048] As described above, the injection molding machine 1 has the cylinder 31, the screw 35 arranged inside the cylinder 31, and the nitrogen gas supplying device 6 that supplies nitrogen gas to the cylinder 31. The nitrogen gas supplying device 6 separates nitrogen from air to generate nitrogen gas. During a temperature rise period of the cylinder 31, the nitrogen gas supplying device 6 supplies nitrogen gas (first nitrogen gas N1) having a low nitrogen concentration and a high flow rate to the cylinder 31, and then supplies nitrogen gas (second nitrogen gas N2) having a high nitrogen concentration and a low flow rate to the cylinder 31.

[0049] As a result, during the temperature rise period of the cylinder 31, the first nitrogen gas N1 with a high flow rate is supplied first, so that the air inside the cylinder 31 is replaced with nitrogen gas in a short time, and then nitrogen gas with a high nitrogen concentration is supplied to the cylinder 31. This makes it possible to suppress carbonization of the resin during the temperature rise period of the cylinder 31 before the molding operation, and also suppress carbonization of the resin during the molding operation.

[0050] Furthermore, the nitrogen gas supplying device 6 starts supplying the first nitrogen gas N1 when the temperature of the cylinder 31 becomes equal to or higher than the supply start temperature C1. Then, the nitrogen gas supplying device 6 starts supplying the second nitrogen gas N2 when a predetermined replacement reference time Tx has elapsed since the start of the supply of the first nitrogen gas N1. Thus, by appropriately setting the replacement reference time Tx, the air in the cylinder 31 can be appropriately replaced with the first nitrogen gas N1 during the temperature rise period of the cylinder 31.

[0051] Furthermore, the nitrogen gas supplying device 6 starts supplying the first nitrogen gas N1 when the temperature of the cylinder 31 becomes equal to or higher than the supply start temperature C1. Then, the nitrogen gas supplying device 6 starts supplying the second nitrogen gas N2 when the supply amount of the first nitrogen gas N1 exceeds a predetermined replacement reference amount Vx. By appropriately setting the replacement reference amount Vx, the air in the cylinder 31 can be appropriately replaced with the first nitrogen gas N1 during the temperature rise period of the cylinder 31.

[0052] The injection molding machine 1 also includes a heater 34, a screw drive mechanism 36, and a control device 55 that controls the screw drive mechanism 36. The screw 35 includes a backflow prevention mechanism including a check ring 35d and a check sheet 35b. When the screw 35 moves backward, the backflow prevention mechanism forms a resin flow path 35e through which the plasticized resin in the cylinder 31 moves forward relative to the screw 35. When the screw 35 moves forward, the backflow prevention mechanism closes the resin flow path 35e to restrict the resin from moving backward relative to the screw. During the molding operation, the control device 55 heats the cylinder 31 with the heater 34 and supplies nitrogen gas to the cylinder 31 with the nitrogen gas supply device 6. After the molding operation is completed, the control device 55 causes the screw 35 to move forward and backward with the screw drive mechanism 36 to discharge the resin in the cylinder 31. After the resin in the cylinder 31 is discharged, the control device 55 causes the screw 35 to move backward by the screw drive mechanism 36, and then stops heating the cylinder 31 by the heater 34 without moving the screw 35 forward. As a result, the front part 31a1 and the rear part 31a2 of the accommodation space 31a of the cylinder 31 are in a state of communication with each other through the resin flow path 35e, and the temperature of the cylinder 31 drops in this state. Therefore, at the time of the next molding operation, the front part 31a1 and the rear part 31a2 of the accommodation space 31a are in communication with each other through the resin flow path 35e, and the first nitrogen gas N1 supplied to the cylinder 31 spreads throughout the entire accommodation space 31a. As a result, carbonization of the resin remaining in the cylinder 31 can be effectively suppressed.

[0053] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples. Any addition, deletion, or design change of components by a person skilled in the art to the above-mentioned embodiments, or any combination of features of the embodiments, is also included in the scope of the present invention as long as it does not deviate from the spirit of the present invention. [Explanation of symbols]

[0054] 1...Injection molding machine 4...Ejecting device 2...Mold clamping device 41...Ejection mechanism 21...Fixed die plate 5...Control unit 22... Movable die plate 51... Display device 23... Mold clamping drive mechanism 52... Input device 3...Injection device 53...Storage device 31...Cylinder 54...Timer 31a... Storage space 55... Control device 31a1...Front portion 6...Nitrogen gas supply device 31a2...Rear section 61...Air compressor 32…Nozzle 62…Filter 33...Resin supply section 63...First adsorption device 34...Heater 64...Second adsorber 35…Screw 65…Buffer 35a...Screw body 66...Switching valve 35b...Check sheet 68...Pipe 35c...Check head 7...Base 35d...Check ring 81...Fixed side mold 35e...Resin flow path 82...Movable side mold 36...Screw drive mechanism 83...Cavity

Claims

1. An injection molding machine having a cylinder, a heater for heating the cylinder, a screw disposed inside the cylinder, a screw drive mechanism for rotating and advancing the screw, a nitrogen gas supply device for supplying nitrogen gas to the cylinder, and a control device, The screw has a backflow prevention mechanism, the backflow prevention mechanism forms a resin flow path through which the plasticized resin in the cylinder moves forward relative to the screw when the screw moves backward, and closes the resin flow path when the screw moves forward to restrict the resin from moving backward relative to the screw, The control device, During a molding operation, the heater heats the cylinder and the nitrogen gas supply device supplies nitrogen gas to the cylinder; After the molding operation is completed, the screw is moved forward and backward by the screw drive mechanism to discharge the resin in the cylinder; and after the resin is discharged, the screw is moved backward by the screw drive mechanism, and then heating of the cylinder by the heater is stopped without moving the screw forward.

2. The nitrogen gas supply device, Separates nitrogen from air to produce nitrogen gas, 2. The injection molding machine according to claim 1, wherein during a temperature rise period of the cylinder, nitrogen gas having a low nitrogen concentration and a high flow rate (hereinafter referred to as "first nitrogen gas") is supplied to the cylinder, and subsequently, nitrogen gas having a high nitrogen concentration and a low flow rate (hereinafter referred to as "second nitrogen gas") is supplied to the cylinder.

3. The nitrogen gas supply device, When the temperature of the cylinder reaches or exceeds the supply start temperature, the supply of the first nitrogen gas is started.

3. The injection molding machine according to claim 2, wherein the supply of the second nitrogen gas is started when a predetermined replacement reference time has elapsed since the start of the supply of the first nitrogen gas.

4. The nitrogen gas supply device, When the temperature of the cylinder reaches or exceeds the supply start temperature, the supply of the first nitrogen gas is started.

3. The injection molding machine according to claim 2, wherein the supply of the second nitrogen gas is started when the supply amount of the first nitrogen gas exceeds a predetermined replacement reference amount.

5. A method for controlling an injection molding machine having a cylinder and a screw disposed inside the cylinder, comprising the steps of: The screw has a backflow prevention mechanism, the backflow prevention mechanism forms a resin flow path through which the plasticized resin in the cylinder moves forward relative to the screw when the screw moves backward, and closes the resin flow path when the screw moves forward to restrict the resin from moving backward relative to the screw, During the molding operation, the cylinder is heated and nitrogen gas is supplied to the cylinder; After the molding operation is completed, the screw is moved forward and backward to discharge the resin from the cylinder. a control method for an injection molding machine, comprising: after the resin is discharged, moving the screw backward, and then stopping heating of the cylinder without moving the screw forward.

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