JPH0628879B2 - Operating method of injection molding machine - Google Patents

Description

The present invention relates to an injection molding machine, and more particularly to BMC (Bulk Molding).
The present invention relates to an injection molding machine suitably used for a molding material containing a glass fiber such as a compound.

[Prior Art] In the case of an injection molding machine using a pelletized material, the material is supplied into the barrel by a hopper, and in some cases, a screw conveyor is used for the purpose of adjusting the supply amount. On the other hand, in the case of a block-shaped molding material such as BMC, it is difficult to supply the material into the barrel of the injection molding machine only with the hopper, and the molding material is pressurized by the material pressing and supplying device equipped with a stuffer. Supply is done.

In such a material pressing and supplying device, the space between the stuffer cylinder and the stuffer plunger is almost sealed, and the stuffer plunger is moved to pressurize the material. The pressurizing pressure is generally 100 to several kg / cm ² (value converted into resin pressure).

The material is supplied under pressure from the stuffer into the barrel, and after a certain amount is stored in the tip side of the barrel (this process is generally called a metering process), the plunger or screw in the barrel advances to advance the material. Injection molded.

When performing injection, a backflow prevention mechanism such as a check ring is provided on a screw or a plunger in the barrel to prevent backflow of the material and to generate a required injection output. The injection pressure is generally several hundreds to several thousands hundreds kg / cm ² (value converted into resin pressure).

When a check ring system is used as the backflow prevention mechanism, the check ring is located in front of the barrel during weighing (or plasticizing), and the material passes through the check ring part and the screw (or plunger) Is stored in front of. Further, at the time of injection, the screw (or plunger) advances so that the check ring closes the retracted path of the material, and the material pressure in front of the screw (or plunger) rises. It should be noted that closing the material retreat path by a backflow prevention mechanism such as a check ring will be referred to as a seal hereinafter.

[Problems to be Solved by the Invention] However, when the present inventors made various studies on the injection molding machine as described above, the material pressing and supplying device and the molding material in the barrel were compressed during the measuring step. Since it is in the state, after the end of the metering process, it expands and tries to reach a pressure equilibrium state, and as a result, the plunger is further retracted, and the so-called drooling phenomenon in which the molding material flows out from the nozzle is caused. These not only require trouble in selecting the conditions for measuring the required amount, but also cause variations in the measurement between shots.

Further, variations in the measurement result due to a partial difference in viscosity of the molding material, a difference in compression ratio, or a difference in viscosity between lots of the molding material and a difference in compression ratio. Since variations in measurement greatly affect the appearance and physical properties of molded products, it has been difficult to obtain stable molding quality with conventional operating methods.

[Means for Solving the Problems] The present invention provides a barrel having a plunger or a screw for material injection and having a material inlet at the rear side thereof, and a barrel provided rotatably and rotatably in the barrel. An injection molding machine comprising: a plunger or a screw for pressing the material, a backflow prevention mechanism provided on the plunger or the screw, and a material pressing and feeding device connected to the material inlet of the barrel. The operation is performed by a metering process in which the plunger or screw of the pressure supply device is actuated in the material pressing direction to store a predetermined amount of material at the tip of the plunger or screw in the barrel, and a subsequent injection process of the material that advances the plunger or screw. In this case, the pressing force of the material by the plunger or screw of the material pressing and supplying device is reduced before the end of the measuring step. Is.

[Operation] There is a relationship as shown in FIG. 2 between the pressing force of the material and the metering speed in the material pressing and supplying device including the plunger or the screw. That is, when the pressing force is decreased, the measuring speed is also decreased, and when the pressing force is lower than a certain pressing force, the measuring speed becomes 0.

Therefore, in the present invention, the weighing speed is reduced by reducing the pressing force before the end of the weighing process. for that reason,
At the time when the metering process is completed, the pressure of the material in the barrel and the material pressing and feeding device is reduced and equilibrated, and the drooling phenomenon such as the retreat of the plunger and the material outflow is prevented.

Embodiments Embodiments will be described below with reference to the drawings.

FIG. 1 is a schematic vertical sectional view showing an embodiment of an injection molding machine according to the present invention. In the figure, a cylindrical barrel 22 having a nozzle 21 at its tip and a heater at a relatively low temperature on its outer periphery is a fixed mold 61 attached to a stationary plate 60.
It is arranged so that the nozzle 21 can face the material injection port. 62 is a column, 63 is a column nut, 64
Is a machine base on the mold clamping device side, 65 is a machine base on the injection device side, 66 is a block slidably provided on the machine base 65 in the axial direction, and on the block 66,
The barrel 22 is fixed to the front, and the motor holding member 67 is slidably attached to the rear. 68 is a cylinder for moving the block 66 fixed to the fixed plate 60, 6
Reference numeral 9 is a piston rod, and the tip end of the piston rod 69 is fixed to the central portion of the outer surface of the block 66, and the nozzle 21 is brought into contact with the fixed mold 61 or retracted to the illustrated state by the operation of the cylinder 68. I made it possible.

In the barrel 22, a plunger 24 having an outer diameter smaller than the inner diameter of the barrel 22 and having a backflow prevention mechanism including a check ring 23, a ball and the like near the tip is provided so as to be able to move forward and backward and to rotate. . The material passage 70 is provided between the inner peripheral surface of the barrel 22 and the outer peripheral surface of the plunger 24.
Was set up. A shaft of a rotary drive device such as a hydraulic motor 35 fixed to the motor holding member 67 is connected to the rear of the plunger 24 via a bearing 71 in the motor holding member 67. An injection cylinder 72 and a piston rod 73 are attached between the barrel 22 and the lower side of the motor holding member 67.

At the center of the plunger 24, a convex portion 25 that is in contact with the inner peripheral surface of the barrel 22 is provided. In addition, the convex portion 2 of the plunger 24
On the rear side of No. 5, a screw 29 for discharging the leak material was provided. The screw 29 includes the outer peripheral surface of the convex portion 25 and the barrel 2
The leak material leaked rearward from the clearance between the inner peripheral surfaces of the two is smoothly discharged rearward of the barrel 22, and is provided in a direction opposite to the rotational direction of the plunger 24.

Reference numeral 27 denotes a stuffer vertically provided at a material inlet portion 28 on the rear side of the barrel 22, and a stuffer plunger 30 for pushing down the material is provided therein. Reference numeral 31 is a material supply inlet provided on the side surface of the stuffer 27. 74
Is a cylinder for the stuffer plunger 30, which has a built-in piston 74a and is vertically attached to a part of the barrel 22 in an upward direction. 75 is a piston rod, and 76 is a connecting member.

In the apparatus shown in FIG. 1, the material such as BMC is loaded into the stuffer 27 while the plunger 24 is positioned at the forward limit and is rotated at 25 to 150 rpm, and the material is fed by the stuffer plunger 30. Push down. Then, the material is sent forward through the outer peripheral portion of the plunger 24, and passes through the check ring 23 portion to make the plunger 2
4 are sequentially accumulated in the barrel 22. Of course, in this measuring process, the plunger 24 is gradually retracted.
When using BMC as the material, the temperature of the material is, for example, 40 to 60 ° C., and the temperature of the die for injection is about 160 ° C.
And then, it is preferable to pressure and, for example, several ^kg / cm ^{2 ~140kg} / cm 2 to depress at stuffer plunger 30.

At this time, the back pressure can be applied to the material by controlling the hydraulic pressure in the rod end side chamber of the injection cylinder 72 connected to the rear of the plunger 24. Note that the back pressure can be applied to the material by friction between the outer peripheral surface of the convex portion 25 of the plunger 24 and the inner peripheral surface of the barrel 22, which retracts.

Due to the rotation of the plunger 24, the resin material around the plunger 24 is homogenized and a short circuit of the flow path of the material is prevented. Further, the pressing action of the stuffer plunger 30 and the rotating action of the plunger 24 cause the material to be
4, the material is pushed in such a manner that it does not pass only through the upper material passage 70 of the plunger 24 but also around the lower material passage 70 of the plunger 24, and the material is pushed from the lower side to the upper side of the plunger 24 or the upper side. Since it is sent while also wrapping around from the bottom to the lower side, the entire circumference of the barrel 22 can be smoothly transferred without staying in the barrel 22 even if the material is difficult to flow or the material is hard to flow.

Thus, prior to the completion of the weighing process in which the desired amount of material is stored at the tip of the barrel 22, the stuffer plunger 3
The pressing force of the material by 0 is reduced. This pressing force may be continuously and gradually reduced, or may be gradually reduced. When the stuffer plunger descends to a predetermined position and reaches the weighing point, the weighing process is completed, the stuffer plunger 30 is stopped, and the rotation of the plunger 24 in the barrel 22 is stopped.

By the start of the above-mentioned decrease of the pressing force, the material in the barrel 22 and the stuffer 27 expands and its pressure decreases and the pressure is balanced, and in particular, the plunger 24 retracts and the material flows out from the nozzle 21. The ring phenomenon is prevented. In particular, when the plunger 24 is rotated as in the present embodiment, pressure equilibration occurs quickly and with good reproducibility, so that the weighing accuracy is improved. It should be noted that the overrun stroke exceeding the metering point can be minimized by appropriately selecting the time point of starting the pressing force reduction.

When a desired amount of material is collected at the tip of the barrel 22, the rotation of the plunger 24 is stopped, the injection cylinder 72 is actuated to move the plunger 24 forward, and the material is injected into the mold (injection step).

In the apparatus of the above-described embodiment, when BMC, which is the material, is pushed into the barrel 22 only by the pressing action of the stuffer plunger 30 without rotating the plunger 24, the material remains in a part of the barrel 22. , It was not sent smoothly, and the weighing condition was extremely poor. Further, even if the pressing pressure by the stuffer plunger 30 is made extremely large, the BMC weighing ability was still poor, but the staff 24 was rotated at a relatively low speed, for example, 25 to 150 rpm. If the BMC is pushed in with the flanger 30, the BMC is sent all over the barrel 22,
The weighing action was smooth, reliable and easy.

In the present invention, the amount of expansion of the forming material after the pressing force is reduced differs depending on the value of the pressing force before the start of the reduction. Therefore, when the pressing force is large, it is preferable to automatically suppress the pressing force to start before the measuring point, and conversely, when the pressing force is small, start the pressing force decrease near the measuring point. is there.

Further, in the present invention, the weighing speed from the start of the pressing force decrease to the completion of the weighing is smaller than the weighing speed before the pressing force decrease. Therefore, if the pressing force starts to decrease excessively early in an attempt to reduce the overrun stroke from the measuring point, the time of the entire measuring process may become long.
In such a case, the start time of the pressing force reduction is left as it is, and instead, at the same time as the measurement is completed, the stuffer plunger 30 is raised by, for example, several to several tens of mm, and the stuffer 27 and the barrel 22 are urged. The method of eliminating the residual pressure of the molding material is effective.

It is also effective to prevent the overrun stroke of the sluffer plunger 30 and improve the measuring accuracy by decreasing the rotation speed of the plunger 24 before the end of the measuring process or increasing the back pressure of the plunger 24 before the end of the measuring process. is there.

In the above embodiment, the plunger is inserted in the barrel, but the present invention can be applied to an injection molding machine in which a screw or the like is inserted.

Further, in the above-mentioned embodiment, the pressing supply device by the stuffer plunger is shown, but other pressing supply device such as one provided with a screw may be used.

[Effects] As described above, according to the present invention, the pressing force of the material by the plunger or the screw of the material pressing and supplying device attached to the injection molding machine is reduced before the end of the measuring process. Can be prevented, and measurement accuracy and molding quality can be improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the pressing force of the material pressing and supplying device and the measuring speed. 22 ... Barrel, 23 ... Check ring, 24 ... Plunger, 27 ... Staffer, 30 ... Staffer plunger, 70 ... Material passage.

Claims (4)

[Claims] 1. A barrel having a material injection plunger or screw and having a material inlet on its rear side, and a material pressing plunger or screw provided in the barrel so as to be able to move forward and backward and rotatably. An injection molding machine comprising: a backflow prevention mechanism provided on the plunger or screw; and a material pressing and supplying device connected to the material inlet of the barrel, wherein the plunger or screw of the material pressing and supplying device is made of a material. When the operation is performed by a metering step of operating in the pressing direction to store a predetermined amount of material in the tip of the plunger or screw in the barrel and a subsequent material injection step of advancing the plunger or screw, before the end of the metering step. An injection molding machine characterized by reducing the pressing force of a material by a plunger or a screw of the material pressing and supplying device. The rolling method. 2. The method for operating an injection molding machine according to claim 1, wherein the plunger or the screw of the material pressing and supplying device is raised immediately after the end of the measuring step. 3. The plunger or screw in the barrel is rotated at a predetermined speed during the measuring process, and the rotation speed is reduced before the end of the measuring process. The method for operating the injection molding machine according to item 2. 4. A back pressure is applied to a plunger or a screw in the barrel during a measuring process, and the back pressure is increased before the end of the measuring process. The method for operating the injection molding machine according to any one of 3 above.