JP2023040635A - Resin changeover method for inline injection molding machine - Google Patents

Abstract

To provide a resin changing method for in-line injection molding machines that can completely discharge retained resin from the inner wall of the tip of the injection cylinder.SOLUTION: In a resin change method for an in-line injection molding machine 100 with a screw 11 having a spiral flight 12 built into the injection cylinder 21, a resin change mode is provided and the screw 11 is held in the resin change position when the resin change mode is activated, the screw 11 is continuously rotated under rotational conditions in which the unmelted resin is mixed, and the molding material mixed with unmelted resin is continuously discharged from the injection cylinder 21 through the gap between the tip of the screw 11 and the inner wall surface BN of the tip of the injection cylinder 21.SELECTED DRAWING: Figure 2

Description

The present invention relates to a resin replacement method for an in-line injection molding machine having a screw with a helical flight inside an injection cylinder.

Injection molding using an in-line injection molding machine is performed according to the following procedure. First, a resin material is supplied into the injection cylinder using a material supply device. The supplied resin material is plasticized and stored in the injection cylinder at the tip of the screw as a molten resin by shearing heat generated by the rotational motion of the screw with helical flights and by the amount of heat generated by the heater or the like provided in the injection cylinder. (weighing process). Next, the screw is moved forward to inject and fill the mold cavity with the molten resin stored in the injection cylinder (injection step). The mold is opened and the molded product is taken out from the mold cavity through holding pressure filling (holding pressure process) that compensates for solidification shrinkage due to cooling and solidification of the molten resin and cooling and holding (cooling process) in the mold cavity. This series of molding operations is repeated until the required number of molded products is obtained.

Here, in injection molding, many resin materials are often used in one injection molding machine. For example, like automobile interior parts, a colorant such as black, red, or blue is added to a thermoplastic resin such as polypropylene (PP) resin or polyethylene (PE) resin to adjust the color tone of the part. In this case, the coloring agent is frequently replaced based on the production plan. Additives such as plasticizers and flame retardants are added to the resin material based on the application of the parts. In addition, thermoplastic resins such as polypropylene (PP) resin and polyethylene (PE) resin are used according to the application of the product, and need to be replaced each time the type of additive or resin material changes. Here, the resin material and the additive are collectively referred to as the molding material, and replacement of the molding material is referred to as resin replacement.

Therefore, it is strongly desired to improve the work efficiency of resin replacement. A study has been reported in which the injection unit is inspected overhaul after the work of replacing the resin, and the part where a large amount of molding material remains is observed. According to this, it was confirmed that a relatively large amount of molding material remained (referred to as retained resin) in two places: the resin flow path in the backflow prevention device arranged at the tip of the screw and the inner wall surface at the tip of the injection cylinder. rice field. This staying resin repeats deposition and peeling, is mixed with the molding material, and is injection-filled. As a result, residual resin with properties different from those of the original molding material is mixed into the molded product, and the physical properties of the molded product change significantly, resulting in molding defects that make the product unusable (resin replacement failure). In order to improve this resin change failure, the number of resin change operations is increased, a large amount of molding material is consumed, and a large amount of expensive cleaning agent is used.

Therefore, many proposals have been made to reduce resin replacement failures, and regarding the resin flow path in the backflow prevention device, it seems that a large improvement effect has been obtained because it is easy to replace with an improved part. However, the inner wall surface of the tip of the injection cylinder, which is not easy to replace parts, is still in the trial and error stage. Among them, for example, as shown in Patent Document 1, a special specification screw tip part with a built-in convex scraping plate is provided, the screw is rotated at the forward position of the screw, and the scraping plate is used to rotate the tip of the injection cylinder. Resin change is proposed to forcibly remove the residual resin on the inner wall surface of the . It should be noted that this scraping plate is housed at the tip of the screw in processes other than resin replacement, so it is said that there is no effect on injection molding.

Further, for example, as shown in Patent Document 2, resin replacement is proposed in which the screw is continuously rotated with a small gap between the inner wall surface of the tip of the injection cylinder and the tip of the screw. Further, a plurality of concave resin flow paths are provided at the tip of the screw, and the molten resin passing through the resin flow paths is used to improve the efficiency of scraping off the stagnant resin.

Furthermore, for example, as shown in Patent Document 3, in a state in which the injection cylinder and the mold cavity are communicated, first, the amount of resin that is more than half of the mold filling capacity is plasticized and weighed (the screw is retracted), and the mold is A resin replacement method has been proposed in which high-speed jogging injection is performed into the cavity, then the screw is continuously rotated at the screw forward position, and the remaining amount of resin is extruded into the mold cavity. At this time, in the first plasticization measurement, the screw is retracted by controlling the low pressure back pressure where unmelted pellets are mixed. Let It is believed that this increases the efficiency of scraping off the retained resin.

JP-A-51-6257 JP-A-4-158018 JP-A-11-28753

Here, in Patent Literature 1, a screw tip component of special specifications having a built-in scraping plate that can freely move back and forth is required. In the event of a failure such as the scraping plate moving, injection molding cannot be continued, and production must be immediately interrupted to replace the screw tip parts, requiring major maintenance work, which can lead to production stability. have anxiety about Further, the driving device for the scraping plate is arranged at the rear end of the long screw so as to communicate with the inside of the screw. Since the screw rotates and moves forward and backward, it is required that the driving device also be moved in synchronism with the screw operation. Furthermore, a driving device for the screw is connected to the rear end of the screw, and it is structurally impossible to arrange the two driving devices at the same position, and this cannot be applied to a general in-line injection molding machine.

Further, in Patent Document 2, the gap between the inner wall surface of the tip of the injection cylinder and the tip of the screw is made very small, and the molten resin flowing in the resin flow path scrapes off the stagnant resin. The retained resin has been in a high temperature state for a long time, and the resin component is thermally decomposed, and a part thereof is oxidized or carbonized (referred to as thermal deterioration). When the molding operation is finished, the injection cylinder stops heating temperature control and is cooled, and the heat-degraded stagnant resin is also cooled and solidified, and the stagnant resin becomes a firm solidified layer. When molding is started again, new staying resin is deposited on the solidified layer. By repeating this process, the retained resin becomes very strong and cannot be easily scraped off by the molten resin flowing in the resin channel. In addition, since the flow of the molten resin is extremely small in the range of the tip of the screw other than the resin flow channel, it is conceivable that a new stagnant resin is formed on the tip of the screw. In addition, the plasticized molten resin melted and kneaded on the screw side flows intensively in the resin channel, causing the separation and aggregation of additives with different specific gravities, which induces poor dispersion of the plasticized molten resin. It is also possible.

Moreover, in Patent Document 3, it is said that the unmelted pellets scrape off the stagnant resin, and the scraping efficiency is higher than that of the molten resin. However, the resin replacement operation in which unmelted pellets coexist is limited to the retraction operation of the screw, and the resin replacement efficiency of the inner wall surface at the tip of the injection cylinder where much resin remains is not expected at all. Even if the screw is rotated continuously under the condition that unmelted pellets are mixed at the screw forward position, the injection cylinder and the mold cavity are in a state of communication, so the molding material is continuously discharged into the mold cavity. be. At this time, the mold cavity is already filled with more than half of the injection filling capacity of the molding material. In this state, in order to continuously discharge the molding material into the mold cavity, the filled molding material must be spread out and forced to fill, which requires a high filling pressure. The condition in which unmelted pellets are mixed is to continuously rotate the screw under low pressure control, but this low pressure control cannot force the mold cavity to be filled. If forced filling is possible, high pressure control is required and the unmelted pellets disappear.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a resin replacement method for an in-line injection molding machine that can completely discharge residual resin on the inner wall surface of the tip of an injection cylinder.

In the resin replacement method for the in-line injection molding machine of the present invention,
In a resin replacement method for an in-line injection molding machine having a screw with a helical flight inside an injection cylinder,
A resin replacement mode is provided, and when the resin replacement mode is started, the screw is held at the resin replacement position, and the screw is continuously rotated under a rotation condition in which unmelted resin is mixed, so that the tip of the screw and the injection cylinder are separated from each other. The molding material mixed with unmelted resin is continuously discharged from the injection cylinder through a gap between the front end portion and the inner wall surface.

Further, in the resin replacement method for the in-line injection molding machine of the present invention,
The resin replacement position is a position of the screw where the unmelted resin comes into contact with the inner wall surface of the injection cylinder when the molding material mixed with the unmelted resin passes through the gap. .

Further, in the resin replacement method for the in-line injection molding machine of the present invention,
The rotation condition is set by a rotation peripheral speed obtained by multiplying the diameter of the screw by the number of revolutions. It is characterized by adjusting within a range.

Furthermore, in the resin replacement method for an in-line injection molding machine of the present invention,
The rotation condition is characterized by further adding adjustment of the heating temperature of the injection cylinder.

Further, in the resin replacement method for the in-line injection molding machine of the present invention,
It is preferable that a preferential flow path through which the unmelted resin passes is provided on the surface of the tip of the screw.

Further, in the resin replacement method for the in-line injection molding machine of the present invention,
It is preferable that the gap narrows continuously with respect to the flow direction of the molding material in which the unmelted resin is mixed.

According to the present invention, it is possible to provide a resin replacement method for an in-line injection molding machine that can completely discharge residual resin on the inner wall surface of the tip of an injection cylinder.

1 is a conceptual diagram of an in-line injection molding machine according to an embodiment of the present invention; FIG. It is a figure which shows typically the resin exchange method which concerns on 1st Embodiment of this invention. It is a figure which shows typically the resin exchange method which concerns on 2nd Embodiment of this invention. It is a figure which shows typically the resin exchange method which concerns on 3rd Embodiment of this invention. FIG. 2 is a flow diagram showing a resin replacement method for an in-line injection molding machine according to the present invention; It is a figure which shows typically the resin exchange method of a prior art.

Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. In addition, the following embodiments do not limit the invention according to each claim. In addition, not all combinations of features described in the embodiments are essential for the solutions of the inventions according to the respective claims. In addition, in this embodiment, the scale and dimensions of each component may be exaggerated, and some components may be omitted.

[Inline injection molding machine]
First, an in-line injection molding machine according to an embodiment of the present invention will be described with reference to FIG. In the following description, the in-line injection molding machine according to the embodiment of the present invention is based on a horizontal in-line injection molding machine, but the present invention is not limited to this. An in-line injection molding machine 100 shown in FIG. 1 includes an injection device 10 , an injection drive section 30 , an injection control section 40 and an injection mold 50 .

In the injection molding die 50, a fixed die 51 and a movable die 52 are supported by a die clamping device (not shown), and the movable die 52 moves forward and backward with respect to the fixed die 51 by the die clamping device. Here, regarding the motion of the movable mold 52, the motion of approaching the fixed mold 51 is defined as the mold closing motion, and the motion of moving away from the fixed mold 51 is defined as the mold opening motion. In addition, the mold touch point is the position where the fixed mold 51 and the movable mold 52 abut during the mold closing operation, the mold clamping operation is the movement in the mold closing operation direction from the mold touch point, and the completion position of the mold clamping operation is The mold clamping limit and the operation from the mold clamping limit to the mold touch point are defined as the step-down operation. A mold cavity 53 is formed within the range of the mold clamping limit from the mold touch point. The stationary mold 51 is also provided with a gate 54 for filling the molding material into the mold cavity 53 .

The injection device 10 includes a cylindrical injection cylinder 21 and a screw 11 that is arranged in the injection cylinder 21 and that rotates about an axis and moves forward and backward in the axial direction. A resin molded product is obtained by injecting and filling the molding material into the mold cavity 53 using the injection device 10 .

A plurality of heaters 24 are arranged on the outer peripheral surface of the injection cylinder 21 at predetermined intervals, and the temperature of the heaters 24 is controlled by a temperature control device (not shown) to manage the injection cylinder 21 at a predetermined temperature. The temperature control by the heater 24 is used for preheating the supplied molding material, applying heat to the molding material during plasticization, and controlling the temperature of the plasticized molten resin in the weighing process, which will be described later. The tip of the injection cylinder 21 is provided with a cylinder head 22 having a conical inner wall surface and a nozzle 23 . When injection-filling the molding material into the mold cavity 53, the nozzle and the gate 54 in the fixed mold 51 are connected. A material hopper 25 is provided behind the injection cylinder 21, and molding material is supplied from the material hopper 25 into the injection cylinder 21 by a material supply device or the like (not shown).

The screw 11 is disposed in the injection cylinder 21 so as to be movable back and forth, and the injection drive section 30 and the rear end portion of the screw 11 are connected. The injection drive unit 30 is operated based on the control command from the injection control unit 40 to adjust the rotation and forward/backward movement of the screw 11 . Here, regarding the motion of the screw 11, the direction closer to the mold cavity 53 is defined as forward F, the forward motion F is forward motion, the direction away from the mold cavity 53 is backward B, and the backward motion B is backward motion. .

Further, the screw 11 is provided with a helical flight 12 extending from the rear B to the front F. The helical direction and angle of the flight 12 are set so that the molding material supplied from the material hopper 25 can be rotationally transported forward F with respect to the rotational direction of the rotational movement of the screw 11 by the injection drive unit 30 . As shown in FIG. 1, the flights 12 are arranged in a single row at a constant interval and at a constant angle, but the arrangement is not limited to this. It can also be an array of Alternatively, a plurality of flights 12 may be arranged only in a partial range of the screw 11 .

Further, the screw 11 has a cylindrical shape whose diameter increases stepwise from the rear B to the front F. That is, the volume of the gap between the screw 11 and the injection cylinder 21 is set so as to gradually decrease from the rear B to the front F, for example, the transport zone, the compression zone, and the melting zone. As a result, the molding material supplied from the material hopper 25 is transported forward by the rotational motion of the screw 11 and the flight 12, and the reduction in volume causes compression and shear heat generation to act on the molding material. Due to the synergistic effect, the melted resin is gradually melted (referred to as plasticization), the molten resin is generated toward the front F of the screw 11, and the molten resin is stored in the front F of the screw 11 (referred to as a weighing process). As the molten resin is stored, the screw 11 retreats to the rear B side. The melt-kneadability of the molding material is adjusted by restricting the backward movement of the screw 11 (referred to as back pressure adjustment). After that, the stored molten resin is injected and filled into the mold cavity 53 (referred to as an injection step).

A rear seat 13 , a non-return ring 14 , and a screw head 15 are provided at the tip of the screw 11 on the front F side. During the metering process, the resin flow path within the non-return ring 14 is opened to allow forward transportation of the molten resin. Also, in the injection process, the resin flow path in the non-return ring 14 is closed, and the stored molten resin can be accurately injected and filled into the mold cavity 53 .

Here, in injection molding, one injection molding machine uses many types of molding materials according to the application and required characteristics of the product. For example, like automobile interior parts, it is common to add colorants such as black, red, and blue to thermoplastic resins such as polypropylene (PP) resin and polyethylene (PE) resin to adjust the color tone of the parts. and the resin is changed frequently. In addition, plasticizers that give flexibility to resin materials, nucleating agents and clarifying agents that control the crystallinity of crystalline resins, flame retardants that suppress combustion, antistatic agents that suppress static electricity, resins Various additives such as lubricants that improve the fluidity and releasability of materials, weathering agents that suppress deterioration due to ultraviolet rays, ultraviolet deterioration inhibitors, and reinforcing agents such as glass fiber and carbon fiber are selected as appropriate. , the resin is changed. In addition, general-purpose resins such as polypropylene (PP) resin and polyethylene (PE) resin, engineering resins such as polyamide (PA) resin and polycarbonate (PC) resin, polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin, etc. A thermoplastic resin such as a super engineering resin is selected as appropriate. Therefore, there is a strong demand for an efficient resin replacement method for a molding material in which a resin material and an additive are combined.

For this reason, we identified locations where the molding material tends to stay. First, a visualization device capable of observing the inside of the injection cylinder 21 was manufactured, and the flow state of the molding material was observed using this visualization device. Next, the actual in-line injection device was operated under the same observation conditions as those of the visualization device, and an overhaul inspection was conducted to investigate the stagnation points of the molding material. Finally, using the mass-produced in-line injection molding machine 100, an overhaul inspection was conducted to investigate in detail the locations where the molding material was accumulated and the state of the accumulated molding material (referred to as "accumulated resin"). From these investigation results, the tip of the injection cylinder 21, more specifically, the inner wall surface of the cylinder head 22 was found to have the largest amount of retained resin.

Next, as shown in FIG. 6, a research was conducted on a conventional resin replacement method that enables the inner wall surface of the cylinder head 22 to be cleaned intensively. FIG. 6 is an enlarged view of area A shown in FIG. Conventional resin replacement methods are classified into a pattern X in which the weighing process and the injection process are performed multiple times, a pattern Y in which the screw is continuously rotated at the forward position, and a pattern Z in which the patterns X and Y are combined. 6(a) shows pattern X, and FIG. 6(b) shows pattern Y. FIG.

First, for the pattern X, the metering process is started from the advance limit position S1 of the screw 11 . Molding material is transported forward by the rotational movement of the screw 11 and stored in front F of the screw head 15 . The screw 11 retreats to the rear B side as the molding material is stored. If turbulence such as turbulence occurs in the flow of the molding material during the forward transportation of the molding material, air or gas is involved, resulting in molding defects such as silver, gas entrained voids, burrs (fine irregularities), and product shorts. provoke. For this reason, the screw head 15 has a narrow conical shape on the front side F, so that the flow of the molding material can be calmed down and a stable flow can be obtained. The inner wall surface BN of the cylinder head 22 also has a conical shape in accordance with the conical shape of the screw head 15 . Further, as shown in FIG. 6, the inner wall surface BN of the nozzle 23 may also have a conical shape continuous from the cylinder head 22 . It should be noted that the inner wall surface BN will be described as provided in the cylinder head 22 .

When the screw 11 is retracted to a predetermined storage amount, the metering process is finished, and the screw 11 is moved forward to perform an injection process in which the stored plasticized material is discharged from the nozzle 23 . The nozzle 23 is closed in the metering process, and the nozzle 23 is opened in the injection process. In the injection process, due to the conical shape of the screw head 15 and the conical shape of the inner wall surface BN of the cylinder head 22, a preferential flow MF occurs and the molding material on the inner wall surface BN of the cylinder head 22 is left behind. This remaining molding material becomes the retained resin RZ. In other words, in the resin replacement method of pattern X, the staying resin cannot be scraped off, and on the contrary, the staying resin is deposited. It should be noted that the effect of scraping off the stagnant resin cannot be expected at all with the stored molding material that has stopped flowing. In mass production molding in which the weighing process and the injection process are repeated, the generation and deposition of this retained resin are repeated in the same manner.

Pattern Y is a resin replacement method focusing on the retained resin RZ on the inner wall surface BN of the cylinder head 22 . Specifically, the screw 11 is fixed at the forward limit position S1 and continuously rotated, the molding material is continuously discharged from the opened nozzle 23, and the remaining resin RZ is scraped off by the continuous flow MF of the molding material. is. The advance limit position S1 is set at a position where the screw head 15 and the cylinder head 22 never collide. Therefore, the gap between the screw head 15 and the inner wall surface BN of the cylinder head 22 is relatively wide. In addition, the conical shape of the screw head 15 keeps the flow MF in a calm state, so the effect of scraping off the stagnant resin RZ cannot be expected. As a result, a large amount of molding material is consumed for resin replacement. Alternatively, an expensive cleaning agent for resin replacement will be used frequently, resulting in high costs associated with resin replacement.

[Resin replacement method of the first embodiment]
Next, a resin replacement method according to the first embodiment of the present invention will be described with reference to FIG. FIG. 2(a) is an enlarged view of the region A shown in FIG. 1, and FIG. 2(b) is a cross section BB shown in FIG. 2(a).

As shown in FIG. 2(a), the resin replacement method of the first embodiment has a resin replacement mode, and when the resin replacement mode is activated, the screw 11 is held at the resin replacement position S2, and the unmelted resin MZ is mixed. It is characterized in that the screw 11 is continuously rotated under rotation conditions, and the molding material mixed with the unmelted resin MZ is continuously discharged from the opened nozzle 23 . With the aim of increasing the efficiency of scraping off the retained resin RZ, the gap between the screw head 15 and the inner wall surface BN of the cylinder head 22 is made as narrow as possible so that the resin replacement position S2<advance limit position S1. This gap is the position of the screw 11 through which the unmelted resin MZ can pass, preferably the position of the screw 11 where the passing unmelted resin MZ comes into contact with the inner wall surface BN. Further, as shown in FIG. 2(b), due to the rotational motion of the screw head 15, a rotational flow RF is applied to the unmelted resin MZ in the gap, and the unmelted resin MZ moves over the entire inner wall surface BN. .
As a result, when the continuous flow MF and the rotating flow RF of the molding material mixed with the unmelted resin MZ pass through this gap, the unmelted resin MZ acts as an abrasive and strongly scrapes the stagnant resin RZ. can be removed completely to remove the retained resin RZ. As a result, the consumption of the molding material required for resin replacement can be greatly suppressed, and the cost and time required for resin replacement can be reduced.

Here, the rotation condition under which the unmelted resin MZ is mixed is set by the rotation peripheral speed DN obtained by multiplying the diameter D of the screw 11 by the number of rotations N of the screw 11 . Specifically, if the unit of the diameter D of the screw 11 is mm and the unit of the number of rotations N of the screw 11 is rpm, it is preferable to adjust the rotational peripheral speed DN=6000 to 18000. When the rotational peripheral speed DN is less than 6000, the amount of heat generated by shear generated by rotational motion is insufficient, and unmelted resin is less likely to coexist. In addition, when the rotational peripheral speed DN>18000, the rotational transportation of the screw 11 is too strong, and a large amount of the molding material supplied from the material hopper 25 is forwardly transported without being plasticized. As a result, the screw 11 is clogged with a large amount of unmelted resin MZ, causing rotational vibration of the screw 11 and causing serious troubles such as wear and breakage of the screw 11 . It should be noted that within the range of rotational peripheral speed DN=6000 to 18000, safe operation of the injection device 10 and continuous supply of the molding material mixed with an appropriate amount of unmelted resin MZ can be achieved.

In addition, although the rotation peripheral speed DN is adjusted within the range of 6000 to 18000, depending on the type and size of the molding material, the placement and heat capacity of the heater 24, etc., the unmelted resin MZ is mixed appropriately. may be difficult. In this case, it is preferable to increase the unmelted resin MZ by adjusting the temperature setting of the heater 24 . Specifically, the temperature setting of the heater 24 is lowered to adjust the amount of heat supplied from the heater 24 to be reduced. After replacing the resin, the temperature setting of the heater 24 is returned to the production conditions. Moreover, existing parts can be used as they are for the screw head 15 and the cylinder head 22 . Furthermore, the screw head 15 can also be kept clean due to the cleaning effect of scraping by the unmelted resin MZ.

[Resin replacement method of the second embodiment]
Next, a resin replacement method according to a second embodiment of the present invention will be described with reference to FIG. 3(a) is an enlarged view of the region A shown in FIG. 1, and FIG. 3(b) is a cross section CC shown in FIG. 3(a). A description of the same configuration as in the first embodiment will be omitted, and a different configuration will be described in detail.

In the first embodiment, two positions of the advance limit position S1 and the resin replacement position S2 of the screw 11 can be set, and the advance limit position S1>the resin replacement position S2. On the other hand, as shown in FIG. 3(a), when the gap between the screw head 15 and the inner wall surface BN of the cylinder head 22 is already narrow and it is difficult to advance the screw 11 further, this second 2 embodiment. In the second embodiment, a resin replacement mode is provided, and as shown in FIG. 3A, the advance limit position S1 of the screw 11 is set to the resin replacement position S2. At this resin replacement position S2, it is difficult for the unmelted resin MZ to pass through because the inner wall surfaces BN of the screw head 15 and the cylinder head 22 are narrow. Therefore, as shown in FIG. 3B, a preferential passage 15M is provided through which the unmelted resin MZ passes through the surface of the screw head 15 and contacts the inner wall surface BN. In this state, the resin replacement mode is activated, and while the screw 11 is held at the resin replacement position S2, the screw 11 is continuously rotated under a rotation condition in which the unmelted resin MZ is mixed. It is characterized in that the molding material mixed with is continuously discharged. The molding material mixed with the unmelted resin MZ passes forward F through the preferential flow path 15M while being accompanied by the rotational flow RF caused by the rotational motion of the screw head 15 . At this time, the remaining resin RZ is scraped off with the unmelted resin MZ.

The setting of the rotation peripheral speed DN and the heating temperature of the heater 24 is the same as in the first embodiment. In addition, by replacing parts of the screw head 15, efficient resin replacement can be ensured. The priority flow path 15M provided on the surface of the screw head 15 through which the unmelted resin MZ passes has extremely small unevenness. In addition, due to the cleaning effect of scraping by the unmelted resin MZ, the preferential flow path 15M can be kept clean.

[Resin replacement method of the third embodiment]
Next, a resin replacement method according to a third embodiment of the present invention will be described with reference to FIG. FIG. 4(a) is an enlarged view of the region A shown in FIG. 1, and FIG. 4(b) is a cross section DE shown in FIG. 4(a). The description of the same configuration as that of the first embodiment or the second embodiment will be omitted, and the different configuration will be described in detail.

If the advance limit position S1 of the screw 11 cannot be changed (the resin replacement position S2 cannot be set separately), this third embodiment is employed. In the third embodiment, a resin replacement mode is provided, and as shown in FIG. 4A, the advance limit position S1 of the screw 11 is set to the resin replacement position S2. At this resin replacement position S2, the gap between the screw head 15 and the inner wall surface BN of the barrel head 22 is too wide, the unmelted resin MZ and the stagnant resin RZ are separated, and the stagnant resin RZ is scraped off by the unmelted resin MZ. Low efficiency.

Therefore, as shown in FIG. 4A, the conical shape of the screw head 15 and the conical shape of the inner wall surface BN of the cylinder head 22 are changed, specifically, the conical angles of the two conical shapes are changed, The gap between the screw head 15 and the inner wall surface BN is set so as to continuously narrow toward the front F. As a result, as shown in FIG. 4(b), the unmelted resin MZ passing through the gap is captured at the front F, and gradually filled up to the rear B side with the unmelted resin MZ. RZ scraping efficiency can be increased. The setting of the rotation peripheral speed DN and the heating temperature of the heater 24 is the same as in the first embodiment. Moreover, the screw head 15 can also be kept clean due to the effect of scraping off the unmelted resin MZ.

[Resin replacement method for in-line injection molding machine]
Next, a resin replacement method for an in-line injection molding machine according to the present invention will be described with reference to the flowchart of FIG. In FIG. 5, the mass production operation is finished, and the switching of the molding material to be supplied to the material hopper 25 is completed by operating the material supply device (not shown) and the like. In other words, it is assumed that the previous molding material remains in the injection device 10 and the next molding material is put into the material hopper 25 . By doing so, the molding material is continuously supplied without interruption, and continuous rotation of the screw 11 to continuously discharge the molding material, which is a feature of the present invention, is realized. For example, the previous molding material may be continuously discharged, and after the previous molding material is emptied, the next molding material may be supplied and similarly discharged continuously. Alternatively, the discharge may be continuous to either the previous molding material or the subsequent molding material.

First, the injection device 10 is retracted to the rear B side to release the connection with the injection molding die 50 and open the nozzle 23 . Thereby, the molding material is continuously discharged from the nozzle 23 . The discharged molding material is placed in, for example, a heat-resistant container. Therefore, the injection device 10 is retracted to a position where the molding material can be continuously discharged from the nozzle 23 .

Next, the resin replacement mode is activated. The injection control unit 40 operates the injection driving unit 30 to advance the screw 11 without rotating it. When the position of the screw 11 detects the preset resin replacement position S2, the injection control unit 40 operates the injection drive unit 30 to hold the screw 11 at the resin replacement position S2. After that, the injection control unit 40 operates the injection driving unit 30 to continuously rotate the screw 11 based on the rotational speed N adjusted within the range of the rotation peripheral speed DN=6000 to 18000. Due to the continuous rotation of the screw 11, the molding material mixed with the unmelted resin MZ is transported forward. At this time, a change in the state of the molding material, such as a color change, is observed due to the scraped residual resin MZ.

When the remaining resin RZ is completely scraped off and removed, the remaining resin MZ disappears from the molding material discharged from the nozzle 23, and completion of resin replacement to the next molding material is confirmed, and the resin replacement mode is stopped. Completion of resin replacement is confirmed visually by the operator. For example, an image camera may be used to continuously capture images of the discharged molding material, and an image analysis technique such as color difference may be used to automatically determine confirmation of completion of resin replacement. After stopping the resin replacement mode, injection molding is started using the next molding material.

[effect]
In the resin change method of an in-line injection molding machine, the screw is held at the resin change position, and the screw is continuously rotated under the conditions where unmelted resin is mixed, and the molding material mixed with unmelted resin is discharged from the nozzle in front of the injection cylinder. is discharged continuously. The resin replacement position should ensure a gap where the unmelted resin contacts the inner wall surface of the cylinder head, and the unmelted resin should scrape off the stagnant resin accumulated on the inner wall surface of the cylinder head. As a result, the retained resin acts as an abrasive, the efficiency of scraping off the retained resin is increased, and the resin change time can be shortened. At the same time, the amount of consumption of the molding material required for resin replacement can be reduced, and the cost required for resin replacement can be reduced. In addition, existing parts such as screws and cylinder heads can be used as they are, leading to easy maintenance and cost reduction of in-line injection molding machines.

Further, the rotation condition is set by the rotation peripheral speed obtained by multiplying the screw diameter by the screw rotation speed. This makes it possible to easily obtain efficient production of unmelted resin. In addition, excessive high-speed rotation of the screw is suppressed to prevent wear and damage to screw parts, etc., contributing to the extension of the life of the in-line injection molding machine. In addition, adjustment of the heating temperature of the injection cylinder was added. As a result, even if the screw part rotates at a safe low speed, it is possible to ensure the generation of unmelted resin, improve the resin replacement efficiency, and assist in extending the life of the in-line injection molding machine.

Also, a preferential flow path through which the unmelted resin passes is provided on the surface of the screw head. Alternatively, the gap through which the unmelted resin passes is continuously narrowed. As a result, for example, even when the advance position of the screw cannot be changed, the unmelted resin can be used to reliably scrape off the stagnant resin. In addition, by replacing only the screw head, efficient resin replacement is possible. Since the screw head may be treated as a consumable item like the non-return ring, the screw head may also be replaced when the consumable item is replaced.

Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the ranges described in the above-described embodiments. Various modifications or improvements can be added to the above embodiments.

REFERENCE SIGNS LIST 100 in-line injection molding machine 10 injection device 11 screw 12 flight 13 rear seat 14 non-return ring 15 screw head 15M priority flow path F front B rear 21 injection cylinder 22 cylinder head 23 nozzle 24 heater 25 material hopper 30 injection drive 40 injection control Portion 50 Injection mold 51 Fixed mold 52 Movable mold 53 Mold cavity 54 Gate A Area X, Y, Z Resin replacement method pattern of conventional technology S1 Advance limit position S2 Resin replacement position BN Inner wall surface MF Flow RF Rotational flow RZ Retained resin MZ Unmelted resin D Diameter N Number of rotations DN Peripheral speed of rotation BB, CC, DE Cross section

Claims (6)

In a resin replacement method for an in-line injection molding machine having a screw with a helical flight inside an injection cylinder,
A resin replacement mode is provided, and when the resin replacement mode is started, the screw is held at the resin replacement position, and the screw is continuously rotated under a rotation condition in which unmelted resin is mixed, so that the tip of the screw and the injection cylinder are separated from each other. A resin replacement method for an in-line injection molding machine, characterized in that the molding material mixed with unmelted resin is continuously discharged from the injection cylinder through a gap between the tip and the inner wall surface. 2. The resin replacement position according to claim 1, wherein the position of the screw is such that the unmelted resin comes into contact with the inner wall surface of the injection cylinder when the molding material mixed with the unmelted resin passes through the gap. Resin replacement method for in-line injection molding machines. The rotation condition is set by a rotation peripheral speed obtained by multiplying the diameter of the screw by the number of revolutions. 3. The resin replacement method for an in-line injection molding machine according to claim 1, wherein adjustment is made within a range. 4. The resin replacement method for an in-line injection apparatus according to claim 3, wherein said rotation condition further includes adjusting a heating temperature of said injection cylinder. 5. The resin replacement method for an in-line injection molding machine according to any one of claims 1 to 4, wherein a preferential flow path through which said unmelted resin passes is provided on the surface of said screw tip. 5. The resin replacement method for an in-line injection molding machine according to any one of claims 1 to 4, wherein said gap continuously narrows in the direction of flow of molding material in which unmelted resin is mixed.

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