Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Molding pressure control means responsive to pressure at...
Reexamination Certificate
2000-02-22
2002-12-03
Silbaugh, Jan H. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Molding pressure control means responsive to pressure at...
C425S207000, C425S208000, C425S557000, C425S564000
Reexamination Certificate
active
06488490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermoplastic resin injection molding machine, and more particularly to an injection molding machine of which the plasticating unit and the injecting unit are provided so as to be independent of each other.
2. Description of the Related Art
Conventionally, as an injection molding machine of which the plasticating unit for plasticating a thermoplastic resin and the injecting unit for injecting the plasticated resin into a metallic mold are provided so as to be independent of each other, screw replasticating type injection molding machines have been known. In the front of the injecting plunger of the injecting unit, a chamber, called a reservoir, for reserving a resin in an amount corresponding to one shot is formed. The resin plasticated by means of the plasticating unit is fed into the chamber, and injected into the mold by moving the injecting plunger forward.
In the case of such an injection molding machine, as the molding cycle, injection, dwelling, cooling, and mold-opening-closing are repeated in that order as shown in FIG.
1
A. The plasticating unit is stopped during the injection, the dwelling, and the mold opening-closing. At the same time when the cooling process is started, the screw of the plasticating unit is driven so that the resin plasticated in the reservoir is fed, and synchronously, the injecting plunger is moved backward whereby the weighing is carried out.
The term “margin” means an excess time-period till the mold opening-closing is started after the cooling is completed, and is provided for the stabilization of the molding cycle. The time-period is changed correspondingly to the shot capacity.
As seen in the above-description, in the case of injection molding machines using an injecting plunger, it is required to determine optimal values with respect to the weighing and a molding pressure for each injecting molding machine and moreover, each of the molds if they are different from each other. Accordingly, the optimal values are determined by repeating the trial shot. Thus, these injection molding machines have the fault that it takes a long time to carry out the work for determining the optimal values.
Moreover, for a conventional injection molding machine, it is necessary to provide a space for a reservoir and a plunger-stroke. Thus, there has been the fault that the size of the injection molding machine is large as a whole.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a thermoplastic resin injection molding machine of which the weighing process is obviated, with which simplified, high precision injection molding is enabled, and which can be reduced in size.
To achieve the above-described object, according to the present invention, there is provided a thermoplastic resin injection molding machine which comprises a plasticating unit for plasticating a thermoplastic resin, and an injecting unit connected to the plasticating unit through a connecting passage to inject the plasticated resin into a mold through an injection port, the injecting unit including a rotary pump of which the suction side is connected to the plasticating unit through the connecting passage and the discharge side is connected to the injection port, whereby the plasticated resin is intermittently injected through the injection port by means of the rotary pump.
According to the present invention, as the injecting unit, the rotary pump is used. Therefore, the plasticated resin is discharged in one direction only, and it is unnecessary to provide the process of moving-backward, that is, the weighing process. In particular, it is unnecessary to determine an optimal value with respect to the weighing before hand, in contrast to a conventional injection molding machine. The weighing can be adjusted so as to have an optimal value only by controlling the rotation of the rotary pump. Thus, the work for repeating the trial shot to determine the optimal value can be obviated.
Further, in the case of the rotary pump, a motor, a rotary actuator, or the like may be used as a driving source. Accordingly, the driving source can be reduced in size as compared with a plunger which is reciprocated, and the necessary space can be decreased. Therefore, as a whole, the injection molding machine can be reduced in size.
As the rotary pump of the present invention, different types of rotary pumps such as a circumscribing gear pump, an inscribing gear pump, a trochoid pump, a vane pump, a screw pump, or the like can be employed. For example, when a circumscribing gear pump is used, desirably, a relatively high injection pressure can be attained, and moreover, an injection-performance is stable even at a high temperature.
For the purpose of attaining molding products of high quality, it is necessary to control the shot capacity and the injection pressure at a high precision. Conventionally, it has been necessary to determined optimal values with respect to the weighing and the injection pressure by trial shot. According to the present invention, the shot capacity can be continuously adjusted by the rotation of the rotary pump. Accordingly, molding products of high quality can be obtained by stopping the pump when the injection pressure reaches a predetermined value.
Thus, preferably, a pressure sensor is provided to detect an injection pressure in the mold, and the rotary pump is stopped when the injection pressure reaches a predetermined value. By controlling like this, the injection pressure in the mold can be controlled at a high precision, and molding products stable in qualities can be obtained.
Further, it is possible to control the injection pressure so as to have a predetermined value by no use of a pressure sensor. That is, a torque limiter may be provided on a driving shaft for driving the rotary pump to provide a slide when the torque exceeds a predetermined value. In this case, when the injection pressure exceeds a predetermined value, the torque limiter provides a slide. Therefore, even if the driving shaft of the rotary pump continues to be rotated, the injection pressure can be kept at a predetermined value. Hereupon, desirably, when the torque limiter provides a slide, the injection pressure is prevented from decreasing. As the torque limiter, means having the same function as a sliding clutch or the like are included.
When the plastication is carried out intermittently as in a conventional thermoplastic resin injection molding machine (FIG.
1
A), the plastication efficiency is ready to be reduced. Especially, for a resin having low engaging properties such as LCP, the reduction of the efficiency is remarkable.
On the other hand, according to the present invention, the weighing process is unnecessary. Therefore, it is not needed that the plastication process is synchronized with the weighing process. The plastication process can be converted to be an off-line as shown in FIG.
1
B. That is, the plastication unit can be driven continuously during all the period of the molding cycle, and the plastication efficiency can be considerably enhanced. When the plastication is converted to be an off-line like this, the margin after the cooling process is completed is unnecessary. Thus, the molding cycle can be significantly shortened as compared with the conventional one.
As described above, when the plastication unit is continuously driven, the pulsation of a resin is generated, caused by the intermittent injection of the rotary pump and the continuous supply by the plastication unit, so that stable injection can not be achieved. Accordingly, preferably, the connecting passage has the volume at which the pulsation of the resin, caused by the intermittent injection by the rotary pump and the continuous supply by the plasticating unit, can be absorbed. For example, stable injection is enabled by setting the volume of the connecting passage to be at least 100 times of the volume of the shot capacity. The qualities of molding products are enhanced.
For the purpose of absorbi
Seta Kunihito
Takeda Takeshi
Burns Doane , Swecker, Mathis LLP
Luk Emmanuel
Murata Manufacturing Co. Ltd.
Silbaugh Jan H.
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