JP2003011192A - Method for holding pressure of injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the pressure of a molten resin in a heating cylinder constant in a motor-driven injection molding machine. SOLUTION: In the in-line type injection molding machine in which a screw 5 in the heating cylinder 4 is rotated by a screw rotating motor 6, and the screw 5 is advanced by screw thrust generated by rotating a screw member 7 by an injecting motor 8, a brake 9 is provided in the rotation transmission system of the motor 8 and a screw shaft 7, when the packing of the molten resin in a cavity is completed by the rotation of the motor 6, the passage of electricity to the motor 8 is cut off, and the pressure of the cavity is held by preventing the retreat of the screw 5 by working the brake 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor driven in-line type injection molding machine.

[0002]

2. Description of the Related Art A motor driven injection molding machine includes a screw rotation motor for rotating a screw and an injection motor for driving a screw shaft to rotate the screw shaft in the injection direction. It has.

In injection molding, the difference in the injection speed greatly affects the quality of the product, especially the flow mark at the stage of filling the cavity with the molten resin, and the resin in the gate portion solidifies after the completion of the filling of the molten resin. The difference in the injection pressure holding (holding pressure) until the gate seal is completed has a great effect on the quality of the product, especially on sink marks and burrs.

Conventionally, a servomotor capable of highly precise control is used as an injection motor and the rotation of the motor is controlled to deal with the above problem. Concerning the pressure holding, the servomotor cannot be held because the motor shaft becomes free and the screw retracts due to the pressure of the molten resin in the cavity just by cutting off the power supply. For this reason, it is necessary to control and operate the injection motor so that the injection motor is intermittently energized so as to maintain the pressure in the cavity at about ⅔ to ⅓ of the injection pressure. In this case, the load on the injection motor is large,
Further, the control system for the motor becomes complicated.

The present invention clarifies a pressure holding method for an in-line type injection molding machine which can solve the above problems.

[0006]

According to the present invention, a screw member connected to a screw (5) in a heating cylinder (4) is rotated by an injection motor (8), and the screw (5) is moved to the injection side by a screw thrust. In the forward in-line injection molding machine, the brake (9) is provided in the rotation transmission system of the injection motor (8) and the screw member, and the process of filling the molten resin into the cavity by the rotation of the injection motor (8) is started. Switching the pressure holding process in the cavity
Breaks the power to the injection motor (8) and brakes
It is characterized in that the screw (5) is prevented from retreating by making use of (9).

[0007]

[Operation and effect] In the injection step, the screw (5) is advanced by the screw thrust generated by rotating the screw member by the injection motor (8), and the molten resin in the heating cylinder (4) is moved to the nozzle (42) at the tip. ) Into the cavity.

When the injection of the molten resin into the cavity is completed, the pressure holding step is instantaneously switched. This is an injection motor
This is done by cutting off the energization to (8) and using the brake (9) to prevent the screw (5) from retracting. As a result, the inside of the cavity is maintained at an appropriate pressure, and it is possible to prevent sink marks from occurring in the resin product and variations in the product weight. Injection motor as before
By intermittently energizing (8), the control system is simplified as compared with maintaining the pressure inside the cavity, and troubles due to overload on the injection motor can be avoided.

[0009]

1 is a front view of an injection unit (2) which is a main part of an injection molding machine for carrying out the present invention, and FIG. 2 is a plan view thereof. Screw (5) and screw shaft (7)
The slide block (3) with the
(1) It will be slidable on top.

The slide block (3) is slidably supported by four guide shafts (23), both ends of which are supported by support plates (21) and (22), respectively. The screw shaft (7) is projected. A heating tube on the front support plate (21)
A screw (5) is rotatably housed in the heating cylinder (4), and a hopper (41) is connected to the base end of the heating cylinder (4).

A screw rotation motor (6) is mounted on the slide block (3), a pulley (61) provided on the rotating shaft of the motor, and a pulley provided at the rear end of the screw (5).
The belt (62) is connected to the (51).

The screw shaft (7) is a ball screw shaft having a small frictional resistance and is screwed to the slide block (3). A rear part of the screw shaft (7) is a round shaft (70), which is supported by penetrating the rear support plate (22) so as to be freely rotatable and axially immovable. The screw thrust generated by the rotation of the screw shaft (7) causes the slide block (3), that is, the screw.
(5) moves in the axial direction.

An injection motor (8) is provided on a rear support plate (22), and a small pulley (81) provided on the rotating shaft of the motor and a rear end of the round shaft (70) of the screw shaft (7). The timing belt (82) connects the large pulley (71) provided at the end. Injection motor
(8) is a high precision control motor such as a servo motor.

A brake (9) is connected to the rotation transmission system of the injection motor (8) and the screw shaft (7). The brake (9) is an electromagnetic brake in the embodiment, but any brake can be used as long as it can control the brake pressure.

Pressure sensor for molten resin in the heating cylinder (4)
The injection motor (8), the brake (9), and the screw rotation motor (6) (not shown) are connected to the control unit (200). The control unit (200) is a screw that maintains the set injection pressure.
Control the forward speed of (5), and when holding pressure,
The brake (9) can be controlled so as to be effective until it prevents the screw (5) from retracting. Further control unit of the embodiment (200)
Responds to the signal from the pressure sensor when kneading the molten resin by rotating the screw (5) in the heating cylinder (4) and retracting the screw (5) at the time of measurement, to the electromagnetic brake (9). Voltage to control the strength of the brake and to maintain the pressure of the molten resin in the heating cylinder (4) within the allowable range
It can be controlled to give a load to the rotation of (7).

The injection unit (2) is connected to a nozzle touch device (100) by a motor (101) and a screw shaft (102) rotated by the motor, and moves the entire injection unit (2) slightly back and forth. As a result, the nozzle (42) at the tip of the heating cylinder (4) can be brought into contact with and separated from the fixed mold (300).

However, as shown in FIG. 1, the screw (5)
Rotate the screw (5) at the most advanced position to guide the pellets in the hopper (41) into the heating cylinder (4), and perform the plasticizing step of the resin that is sent to the front of the heating cylinder (4) while melting. To do.

When the front portion of the heating cylinder (4) is filled with the molten resin, a force for pushing the screw (5) backward acts on the screw (5) rotating in the direction of feeding the molten resin forward. To do. The injection motor (8) is de-energized, and if there is no brake (9), the slide block (3) can be freely rotated by rotating the screw shaft (7) with the force pushing the screw (5) backward. It will move backward, and the pressure of the molten resin in the heating cylinder (4) will fall below the allowable range.

In the present embodiment, when the screw (5) is retracted, the brake (9) is actuated to move the screw shaft (7) through the pulley (81), the timing belt (82) and the pulley (71). With respect to the rotation, a load can be applied to maintain the pressure of the molten resin in the heating cylinder (4) within an allowable range, and resistance can be given to the backward movement of the slide block (3). Thereby, the pressure of the molten resin in the heating cylinder (4) can be maintained within the set range.

In the next injection step, the brake for the screw shaft (7) is released, and the screw shaft (7) is rotated by the injection motor (8), whereby the screw (5) is advanced and melted as described above. The resin is injected from a nozzle (42) at the tip of the heating cylinder (4) into a cavity (not shown) formed between the fixed mold (300) and the movable mold (301).

When the injection into the cavity is completed, the pressure holding step is immediately switched to. This cuts off the power supply to the injection motor (8) and activates the brake (9) to prevent the screw (5) from retreating and suppress the pressure drop in the cavity. As a result, the inside of the cavity is maintained within an appropriate pressure range, and the sinking of the resin product and the variation of the product weight do not occur.

If the resin in the gate section solidifies, the brake
(9) is released and the injection motor (8) is rotated to move to the next plasticizing step of the resin.

In the pressure-holding step, even if the brake (9) is used to prevent the screw (5) from retreating, the injection pressure is not maintained as it is, and the pressure is naturally lowered to maintain the pressure. If the pressure falls within the desired pressure range, but the pressure drops significantly for some reason, immediately before turning on the brake (9) in the pressure-holding process, rotate the screw (5) about one revolution to raise the pressure in the cavity a little. Therefore, it is possible to use the brake (9).

In the embodiment, the screw shaft (7) is rotated to drive the screw (5) forward, but the screw shaft is projected on the screw, and the nut in a fixed position screwed to the screw shaft is rotated. It is also possible to drive the screw forward, and the point is to rotate the screw member and drive the screw forward by the screw thrust.

The present invention is not limited to the configuration of the above embodiment, and various modifications can be made within the scope of the claims.

[Brief description of drawings]

FIG. 1 is a front view of a main part of an injection molding device.

FIG. 2 is a plan view of the above.

[Explanation of symbols]

(3) Slide block (4) Heating tube (5) Screw (6) Screw rotation motor (7) Screw shaft (8) Injection motor (9) Brake

Claims (3)

[Claims] 1. An in-line type injection molding in which a screw member connected to a screw (5) in a heating cylinder (4) is rotated by an injection motor (8) to advance the screw (5) to an injection side by a screw thrust. In the machine, a brake (9) is provided in the rotation transmission system between the injection motor (8) and the screw member,
The injection motor (8) is used to switch from the process of filling the cavity with the molten resin by the rotation of (8) to the process of holding the pressure in the cavity.
A method for maintaining pressure in an in-line type injection molding machine, characterized in that the retraction of the screw (5) is prevented by shutting off the power supply to the screw and using the brake (9). 2. The screw (5) in the heating cylinder (4) is rotated by a screw rotation motor (6), and the screw (5) is advanced to the injection side by rotating a screw member by the injection motor (8). In an in-line type injection molding machine that uses screw thrust by causing the brakes (9) to be provided in the rotation transmission system between the injection motor (8) and the screw member, the pressure of the molten resin in the heating cylinder (4) When the screw (5) moves backward, brake
By making use of (9), resistance is given to the rotation of the screw member to maintain the pressure of the molten resin in the heating cylinder (4) within an allowable range, and the molten resin to the cavity by the rotation of the injection motor (6). When the filling is completed, the brake (9) is used to prevent the screw (5) from retreating to maintain the pressure in the cavity, which is a pressure maintaining method for an in-line type injection molding machine. 3. The injection motor (8) is a servomotor, the brake (9) is an electromagnetic brake, and the brake
(9), the injection motor (8) and the screw (5) are connected to the control unit (2
The method for holding pressure of an in-line type injection molding machine according to claim 1 or 2, wherein the pressure holding method is linked to 00).