JPH07276419A - Tandem-type injection molding machine - Google Patents

Abstract

PURPOSE:To provide a tandem type injection molding machine with the capability of preventing scuffing in the bearing part of an injection plunger, staying of resin during the period of changing resin, and the occurrence of voids in an infection cylinder at the time of injection. CONSTITUTION:Shaft-symmetrically opposed inlets 13a, 13b are installed on an injection cylinder 6 at the upstream part of an injection plunger 9 of a second injection device, and a resin flow path 12 from the first step plasticizing device to the second step injection device is divided into two flow paths, to be connected to pouring ports 13a, 13b. In addition, provided on each flow path is flow rate control means that can control the flow rate of resin. During the injection, by employing the rearmost position of the infection plunger as reference, the position change control of injection is conducted in order to prevent the occurrence of voids.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-plastic type tandem type injection molding machine.

[0002]

2. Description of the Related Art Conventional injection molding machines generally employ a single screw for both plasticization and injection.
This system has a problem that the screw L / D effective for plasticization changes due to the screw retracting during plasticization, and the plasticization quality becomes unstable. On the other hand, the pre-plastic injection molding machine adopted in some of them has a problem that the resin leaks from the injection plunger due to the high-pressure resin or the stagnant resin is burnt in the second-stage injection device during injection. In order to solve these problems, Japanese Patent Application No. 5-2
No. 57959 proposes a new type pre-plastic type tandem injection molding machine. The structure is shown in FIG. In the figure, the resin raw material 2 supplied to the raw material hopper 1 is plasticized by the rotation of the screw 3 of the first stage plasticizing device and is discharged to the tip 111 of the screw. The resin is further supplied into the injection cylinder 106 of the second stage injection device through the connection pipe 112 and the inflow port 113. Further, the resin passes through the check valve 7 and is accumulated and measured in the tip 8 of the injection plunger. The injection plunger 9 moves backward, and when the predetermined amount of resin is measured, the first stage screw stops. . The injection into the mold (not shown) is performed by advancing the injection plunger 9 by the hydraulic cylinder 5.

However, in this structure, the resin supplied from the first-stage plasticizer to the second-stage injection device is the resin inlet 113.
Since it flows from above into the injection plunger 9, the injection plunger 9 is pressed downward by the resin pressure from above, and the load increases at the contact portion 120 with the bearing 106a, causing galling at the contact portion. there were. Since the resin flows in from above the injection plunger 9 as described above, the merging portion 1 of the resin flowing around the injection plunger 9
The resin stayed in No. 22 and it took a lot of time to replace the staying resin with a new resin when changing the resin. Further, as described above, in the second-stage injection device, the screw of the first-stage plasticizing device is stopped when a predetermined amount of resin is measured, and the injection is performed after that, so that the injection plunger 9 advances during injection. There is a problem that voids are generated in the resin portion in the cylinder 106, and volatile components in the resin are gasified in the voids, causing bubbles and defective silver strips in the molded product. In addition, the silver strip is a strip of a silver color generated by the gas emerging on the surface of the molded product.

[0004]

As described above, in the pre-plastic type tandem type injection molding machine of Japanese Patent Application No. 5-257959 shown in FIG. 7, in the second stage injection device, the injection from the upper side to the injection plunger is performed. Contact part 1 with bearing due to resin pressure
There was a problem that galling occurred at 20, or the resin stayed in the lower portion of the injection plunger 122 on the side opposite to the upper resin inflow port 113, and it took a long time to change the resin.
Further, there is a problem that voids are generated in the injection cylinder at the time of injection, and the generated gas causes bubbles or defective silver strips in the molded product. Therefore, the present invention significantly reduces the load applied to the bearing by the pressure of the resin that flows into the injection plunger to prevent galling that occurs at the contact portion with the bearing, and when changing the resin, the resin inlet of the plunger To promote the resin replacement of the stagnant resin on the side opposite to, and to eliminate the generation of voids in the injection cylinder during injection,
It is intended to provide a tandem injection molding machine capable of injecting while continuing plasticization, and to solve the above-mentioned conventional problems.

[0005]

For this reason, the present invention mainly uses a rotating action, and mainly includes a first-stage plasticizing device having a screw for plasticizing a resin and an injection process of axial movement. In a tandem injection molding machine having a second-stage injection device, axially symmetrical opposed inlets are installed upstream of the injection plunger of the second-stage injection device, and the first-stage plasticizing device changes to the second-stage injection device. The resin flow path is divided into two and connected to the counter inlet of the second-stage injection device, and this is a means for solving the problem.
Further, a heater is provided in each of the two connection flow paths, the load of the heater is changed to make the resin temperatures of the two flow paths different, and thereby the resin flow rates of the two connection flow paths are made different, so that the second stage injection device is provided. Of the resin inflow port, the accumulated resin can be eliminated, and a flow rate adjusting valve that can change the flow rate is provided in each of the two connection flow paths, and the opening degree of the valve can be adjusted. By changing the resin flow rates of the two connection flow paths, it is possible to eliminate the stagnant resin at the merging portion of the resin inlet of the second stage injection device. In a tandem injection molding machine having a first-stage plasticizing device having a screw for plasticizing and a second-stage injection device having an axial movement injection process as a main function, injection of the second-stage injection device during the injection process The last position of the plunger Means for output, made of a control means for performing an injection position switching control by the relative position of the origin of the same position, and a means for this problem solution.

[0006]

In the present invention, the axially symmetrical opposed resin inlets are provided in the upstream portion of the injection plunger of the second stage injection device,
Two resin flow paths from the first-stage plasticizer to the second-stage injection device
By branching into two and connecting to the resin inlet, the pressure of the resin flowing from the resin inlet is symmetrical with respect to the injection plunger. As a result, the forces acting on the injection plunger are balanced and the load on the bearing portion of the plunger is eliminated, so that galling at the bearing portion is prevented. Further, when changing the resin, the load of each heater arranged in the two connecting flow paths that face the second-stage injection device and are changed to change the resin temperature (and thus the resin viscosity) of the two flow paths, By making the resin flow rates of the two connection flow paths different, it is possible to form the resin merging portion at a position different from the resin merging portion when the two resin flow rates at the time of normal molding are the same.

As a result, the resin retained in the resin merging portion at the time of normal molding is pushed away and the replacement of the resin is promoted. Further, instead of the above-mentioned heater load, the opening degree of each flow rate adjusting valve is changed in the two connection flow paths to make the resin flow rates in the two connection flow paths different, thereby different from the normal molding time as described above. It is also possible to form a resin merging portion at a place. As a result, the resin retained in the resin merging portion at the time of normal molding is pushed away and the resin replacement is promoted. Further, by detecting the last retracted position of the injection plunger during the injection process and performing the injection position switching control by the relative position with the same position as the origin, even if the injection is performed during plasticization, the injection position switching control can be performed. It is performed at an accurate position from the last retracted position.
As a result, it is possible to continue plasticization for the purpose of eliminating voids in the injection cylinder at the time of injection and prevent variations in injection. Further, when the generation of the voids is eliminated, bubbles and silver molding defects due to the voids are also eliminated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. FIG. 1 is a side sectional view of a tandem type injection molding machine according to one embodiment of the present invention. In the figure, the resin raw material 2 supplied to the raw material hopper 1 is the screw 3 of the first stage plasticizer.
Is plasticized by the rotation of and is discharged to the other end 11 of the screw as in the conventional example of FIG. The other end 11 of the screw is connected to a connecting pipe 12 branched into two, and the resin in the other end 11 is connected into a connecting pipe 12 branched into two.
Flows into the inlets 13a and 13b of the second-stage injection device and is supplied into the injection cylinder 6. Further, the resin passes through the check valve 7 and is accumulated and supplied to the tip 8 of the injection plunger, and the injection plunger 9 retracts. While the injection plunger continues to retreat by the resin supplied to the tip 8,
After the injection step, the injection plunger 9 is advanced by the hydraulic cylinder 5 without stopping the rotation of the first-stage screw, and the resin is injected into a mold (not shown). The stroke position of the injection plunger is detected by the position sensor 15 as a position detecting means.

Next, the structure of the connecting pipe 12 will be described with reference to FIG. 2. The resin discharged by the first-stage plasticizing device passes from the screw tip 11 through the connecting pipe 12 to the symmetrical connecting pipes 14a,
It branches to 14b and flows into the inlets 13a and 13b provided on both sides of the injection cylinder 6. Therefore, the flow of the resin with respect to the injection plunger 9 becomes symmetrical, and the pressure of the flowing resin applied to the plunger is balanced on the left and right. As a result, only a slight radial load acts on the bearing portion 20 of the plunger, and the bearing portion is not galled. By the way, when the resin is supplied into the injection cylinder 6 from the connecting pipes 14a and 14b having the above-described structure, the resin flows symmetrically as shown in FIG. After that, the flow on the left and right is the central part 22
At c and 22d, they merge and the flow velocity disappears, and the resin stays.
When changing the molded product or changing the color of the molded product,
It is necessary to change the resin used until then to another resin, and for that purpose, the resin is changed from the previous resin to the subsequent resin. At that time, it is necessary to push away the accumulated resin in the central portions 22c and 22d. Therefore, in this embodiment, heaters 31a, 32a, 33a are provided on the left connecting pipe 14a, and heaters 31b, 32b, 33b are provided on the right connecting pipe 14d. With these heaters, the same temperature control is performed on the left and right during normal molding, but the temperature control on the left and right is different when changing the resin. For example, when changing resin, the connecting pipe 1 on the left in FIG.
The heater temperature of 4a is made higher than the heater temperature of the right connecting pipe 14b, and the left resin flow rate Qa is made larger than the right resin flow rate Qb. As a result, the resin merging portion in the injection cylinder 6 is located at the right side 23c, 2d from the original central portion 22c, 22d.
It shifts to 3d. As a result, the resin staying in the central portions 22c and 22d is pushed to the right and is replaced by the subsequent resin. That is, the amount of resin and the time required for resin replacement are greatly reduced.

Next, the sequence of the embodiment of the present invention is shown in FIG.
FIG. 4 shows the flow of the plunger position switching control during injection, and FIG. 5 shows the relationship graph of the plunger position. First, in FIG. 3, the screw rotation of the first-stage plasticizer continues during injection and filling. This is to prevent the generation of voids in the injection cylinder 6 of FIG. 1 when the injection plunger 9 advances to inject the resin of the plunger tip 8 into the mold during injection. That is, in FIG. 1, when the inner diameter of the injection cylinder is D, the root diameter of the injection plunger 9 is d, and the injection stroke is L, if the resin is not replenished from the first-stage plasticizer at the time of injection, a void of the following formula is generated. .

[Number 1] void ^{= 4 / π (D 2 -d} 2) which occurs when no resin supply L (1) Therefore, even a screw rotation of the first stage plasticizing unit in the injection filling as described above in this embodiment Second by continuing
The resin supply to the step injection device is continued, and it is possible to avoid the generation of the void of the formula (1). Further, thereby, it is possible to prevent defective products such as bubbles and silver strips due to the voids. The plasticizing conditions during the injection may be different from those during the cooling process, such as increasing the screw rotation speed only during injection filling, depending on the forward speed of the injection plunger.

On the other hand, if the plasticization is continued during the injection filling as described above, while the injection plunger 9 of the second stage moves backward by the resin supply from the first stage, the injection of the plunger advance is performed. The operation will start. However, since the plasticizing time for measuring the predetermined amount of resin varies a little each time, the plunger position at the start of injection also varies from shot to shot, and the injection position is switched depending on the absolute position of the forward stroke of the plunger as in the conventional case. If control is carried out, the actual injection stroke will vary, and therefore short-circuiting (insufficient filling) and burrs (excessive filling) will occur in the molded product. In order to solve the problem, in this embodiment, FIG.
The injection position switching control shown in the flow is performed. In the figure, when the injection start signal is issued, the position detecting means detects the position X1 at which the plunger is most retracted. Next, the control means injects for a predetermined stroke LX with reference to the position X1, and thereafter switches to injection holding pressure and holds for a certain period of time. Thus, the injection is completed.

To explain this with reference to FIG. 5, since the resin is supplied to the second stage by the plasticization of the first stage, the injection plunger retreats from point E to point G. When the injection start signal is output at time SA, the plunger retracts to the position X1 at the point P due to the time delay of the actual injection operation, and the predetermined amount LX is set with reference to X1.
Only by moving the plunger forward to the position X2 and reaching the position X2, the injection pressure holding process starts from the point S. The graph is bent at points Q and R on the way from point P to point S. This is because the injection speed is changed at points Q and R, and the positions of these points Q and R are changed. It depends on the relative position of a predetermined amount of movement from the reference point X1. According to the above-described control, even if the plunger rearmost retreat position X1 varies from shot to shot, the injection position switching control is performed at a relative position with respect to the same position X1. Therefore, a stable resin amount that is not affected by variations in X1 Can be injected and short-circuit and burr defects can be prevented. As the position detecting means, various position sensors such as an ultrasonic sensor including the position sensor as shown in FIG. 1 can be used, and the control means can also be a computer, a dedicated control circuit or the like. You can

FIG. 6 shows another embodiment which replaces the above resin changing method. In the figure, flow rate adjusting valves 18a and 18b are provided respectively between the left and right connections 14a and 14b, and the resin flow rates Qa and Qb can be changed by changing the opening degree of the resin passage with the flow rate adjusting valves. . As in the case of FIG. 2, the same resin flow rate is used on the left and right during normal molding, but the resin flow rates on the left and right are changed when changing the resin. For example, when changing the resin, the resin flow rate Qa of the left connecting pipe 14a in FIG. 6 is made smaller than the resin flow rate Qb of the right connecting pipe 14b. As a result, the resin merging portion in the injection cylinder 6 is displaced from the original central portions 22c and 22d to the left portions 24c and 24d. As a result, the resin retained in the central portions 22c and 22d is swept to the left and replaced with new resin. That is, also in this embodiment, the amount of resin and the time required for resin replacement can be greatly reduced.

[0014]

As described in detail above, according to the present invention, the second-stage injection device is provided with axially symmetrical opposite resin inlets, and the resin pressure flowing from the first-stage plasticizer is injected. Since the two sides of the plunger are balanced, the load on the bearing of the plunger is eliminated, and as a result, the galling at the bearing contact portion, which has been a problem with conventional tandem injection molding machines, can be eliminated. When changing the resin, the second
In the left and right resin passages to the multi-stage injection device, by changing the left and right resin flow rates by operating the heater or the flow rate adjustment valve, the resin that has accumulated in the resin confluence in the injection cylinder during molding is pushed away and resin replacement is promoted. The amount of resin and time required for resin change can be greatly reduced. Furthermore, during injection filling so as not to generate voids in the injection cylinder during injection,
When the plasticization of the first stage is continued and the resin is replenished to the second stage, the injection position switching control is performed by the relative position from the last retracted position of the injection plunger as a reference for each shot of injection. As a result, the resin amount for each shot is stabilized, and excellent effects such as short-circuit and burr defect can be prevented. As a result, it can be put to practical use as a tandem type injection molding machine with no problems.

[Brief description of drawings]

FIG. 1 is a side sectional view of a tandem injection molding machine showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sequence diagram of the tandem type injection molding machine in the embodiment of the present invention.

4 is a flow chart of injection position switching control for implementing the sequence of FIG.

5 is a plunger position explanatory diagram for explaining in detail the injection position switching control of FIG. 4; FIG.

FIG. 6 is a cross-sectional view showing another embodiment in which resin flow rate control is performed with a symmetrical resin flow path equivalent to that in FIG.

FIG. 7 is a side sectional view showing a conventional tandem injection molding machine.

[Explanation of symbols]

1 Raw Material Hopper 2 Resin Raw Material 3 Screw 4 Plasticizing Cylinder 5 Hydraulic Cylinder 5 Injection Cylinder 6a Bearing 7 Backflow Prevention Valve 8 Injection Plunger Tip 9 Injection Plunger 12, 14a, 14b Connection Pipe 13a, 13b Resin Inlet 15 Plunger Position Detecting means 18a, 18b Flow rate adjusting valve 20 Bearing contact portion 22c, 22d, 23c, 23d, 24c, 24d Resin merging (retaining) portion 31a, 31b, 32a, 32b, 33a, 33b Heater Qa, Qb Resin flow rate

Claims (4)

[Claims] 1. A tandem type injection having a first-stage plasticizing device having a screw as a main action of rotation and a plasticizing resin and a second-stage injection device having an axial movement injection process as a main action. In the molding machine, axially symmetrical facing inlets are installed upstream of the injection plunger of the second-stage injection device,
Two resin flow paths from the stage plasticizer to the second stage plasticizer
A tandem type injection molding machine, characterized in that the tandem injection molding machine is divided into two parts and is connected to the counter inlet of the second-stage injection device. 2. A heater is provided in each of the two connection channels, the load of the heater is changed to make the resin temperatures of the two channels different, and thereby the resin flow rates of the two connection channels are made different. 2. The tandem injection molding machine according to claim 1, wherein the stagnant resin at the joining portion of the resin inflow port of the two-stage injection device can be eliminated. 3. A flow rate adjusting valve capable of changing the flow rate is provided in each of the two connection flow paths, and the opening degree of the valve is changed to make the resin flow rates of the two connection flow paths different from each other. 2. The tandem type injection molding machine according to claim 1, wherein the accumulated resin at the joining portion of the resin inflow port of the injection device can be eliminated. 4. A tandem type injection having a first-stage plasticizing device having a screw as a main action of rotation and having a screw for plasticizing a resin, and a second-stage injection device having a main action of an injection process of axial movement. The molding machine is provided with a means for detecting the last retracted position of the injection plunger of the second stage injection device during the injection process, and a control means for controlling the injection position switching by the relative position with the same position as the origin. Characteristic tandem injection molding machine.