DE2539066A1 - DETERMINATION OF THE SOLIDIZATION PHASE IN INJECTION MOLDING MACHINES - Google Patents

Description

R. 2829
29.8.1975 Ot

Attachment to

Patent and

Utility model auxiliary registration

ROBERT BOSCH GMBH,
7000 Stuttgart 1

Determination of the solidification phase "in injection molding machines

The invention "relates to an injection molding machine for thermoplastics, one with regulated Screw movement rotating and axially displaceable screw press, which is located axially on a bottom the pressure of a hydraulic fluid supports the piston, plasticizes the plastic and puts it in an injection mold presses.

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After the filling process it is necessary to put it in the injection mold to keep pressed plastic melt under pressure for some time, so that during solidification Occurring volume contraction does not lead to any impermissible changes in the shape of the injection-molded part. For this one usually has a "certain period of time waited after the filling process before the holding pressure phase was ended and the casting mold was opened. The cycle times injection molding machines had to be burdened with 'considerable safety margins.

Proceeding from this, the object of the present invention is the solidification phase of the plastic melt more precisely than before and thus bring about an increase in production without doing that Risk of. To accept insufficiently solidified injection molded parts.

According to the invention, this object is achieved in that a pressure measuring element is arranged in the vicinity of the gate, that a the internal mold pressure proportional signal to a controller, which according to the deviation from the target value the hydraulic pressure changed in the sense of a minimization of this deviation and that the laugh pressure phase at an increase in hydraulic pressure above the regulation limit.

The invention is based on the "knowledge that there is. controlled internal mold pressure curve is possible, the time-dependent change in the hydraulic pressure during the To use solidification phase as a parameter for the extent of solidification of the plastic melt.

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Until the start of the solidification phase is the temporal The course of the internal pressure and the hydraulic pressure is the same, only the absolute level of the two pressures is different, because it is due to the different effective pressure area on the hydraulic piston "ben on the one hand and on the Snail cages on the other hand to a pressure transmission comes. With the start of solidification, however, there is a steady increase in the hydraulic pressure. The cause This increase is due to the increase in viscosity in the runner and the detachment of the solidifying plastic material from the pressure measuring member due to volume contraction. Both processes cause a pressure loss in the mold, whereby the regulator triggers the increase in hydraulic pressure. This point in time is identical to the beginning of the solidification phase; if this is known, the end of the solidification phase can be reached and thus also the high pressure phase with a tolerance can be estimated within a few seconds. The invention thus allows the. Nachdruckzeit and thus also optimize the entire cycle time during injection molding.

The end of the high pressure phase expediently takes place after a period of time depending on the size of the sprue channel from the beginning of the hydraulic pressure increase. This period of time is usually on the order of a few seconds.

For the exact determination of the internal pressure of the mold, it is advisable to place the pressure measuring element in the injection mold in To be attached near the gate, as this area is usually has the longest solidification time of the plastic part. Furthermore, it is in the sense of a simple

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knowing the "increasing at the beginning of the solidification phase Hydraulic pressure increase advantageous to specify a constant setpoint for the internal mold pressure. Of course, the target value for the internal mold pressure can also have any non-constant profile to have.

Finally, it has proven to be beneficial for the controller to generate an electrical signal and thus on a servo valve seated in the pressure line of the hydraulic circuit acts.

Finally, it has been found to be beneficial that the controller is on one in the pressure line of the hydraulic circuit seated servo valve acts.

Further details and features emerge from the following description of an exemplary embodiment based on drawings; it shows:

Fig. 1 shows the course of the mold internal pressure, the hydraulic pressure and the weight of the injection molded part produced as a function of the mold filling and holding pressure time and

2 shows an injection molding machine according to the invention, shown schematically in longitudinal section.

1 shows that, apart from a few pressure peaks at the beginning of the filling process, the hydraulic pressure p ™ and the internal mold pressure p _w remain constant until the solidification phase begins. This is indicated by the hatched area. Due to the increase in viscosity in the sprue channel associated with solidification and the volume contraction in the casting mold, the regulator generates an increasing hydraulic pressure so that the internal pressure of the mold can be kept at a constant level. Point I shows the increase in the hydraulic pressure curve and thus the beginning of the solidification phase. 7098 11/0379

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Connected by the volume contraction in the injection mold With the increasing hydraulic pressure, plastic melt is still pressed into the injection mold, see above that the weight G of the injection-molded part increases in accordance with the curve shown. The total freeze of the injection-molded part and the runner is complete at the time the weight is constant. Since from the point in time the constant weight, which is designated in Fig. 1 with II, the material transport from the plasticizing cylinder is interrupted in the mold, the laughing phase can be switched off at this point at the latest will. It is true that this point in time cannot be measured by measurement; but he can with sufficient accuracy can be determined on the basis of the measured point in time I, which signals the start of the solidification phase, because the time difference between I and II is only a few seconds. One can therefore determine the timing Use I as the initial value and after a few seconds time credit the reprint phase automatically abort.

Fig. 2 shows the injection molding machine shown schematically in longitudinal section. In a screw cylinder 1 a screw piston 2 is mounted rotatably and axially displaceably, which is pointed towards the injection end runs out, while it has a longitudinal groove profile 3 at the other end, over which it is axially displaceable with a drive wheel that is stationary with respect to its axial plane 4 is engaged. The twisting of the drive wheel 4 and thus of the worm piston 2 is effected by the worm 5 engaging on the drive wheel.

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In extension of the longitudinal groove profile is on Worm piston 2 has a hydraulic piston 6 attached, which can be acted upon in a known manner on one or both sides and is responsible for the axial displacement of the screw piston.

The goods to be processed are added to the screw piston 2 supplied via the hopper 7 and by the rotary movement of the screw piston and the heating δ of the screw cylinder gradually plasticized. The viscosity can be determined by the processing parameters: back pressure, Screw speed and cylinder wall temperature can be influenced.

If the entered plastic material is sufficiently prepared, the injection mold 9 is filled by placing the cylinder space 10 under pressure via a servo valve 11 is set so that the screw piston 2 moves axially in the direction of the injection nozzle and the upstream plastic melt into the injection mold 9 pushes in. In this case, a certain internal mold pressure p ^ - is established in the injection mold 9, which through a pressure measuring element H is measured and fed to a controller 13 will. The controller 13 compares the actual value with the internal pressure target value given to it and influences it thereupon the servo valve 11 in the sense of minimizing the detected deviation. The internal pressure of the mold is thereby always kept at the constant height shown in FIG.

In addition, the cylinder chamber 10 is connected to the controller 13 via a line 12. If the hydraulic pressure increases

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in the cylinder chamber by an amount above the control tolerance, a signal is triggered in the controller, which signals the passing of point I in FIG. That is, the solidification of the standard part begins and the reprint phase can be switched off within a few seconds.

In summary, the advantage of the invention is that instead of the previous experience values, a clear information about the beginning of the solidification phase and thus one with a few seconds tolerance affected time for switching off the holding pressure phase. You can adjust the reprint time and record the cycle time much more precisely and optimize it compared to the previous injection molding machines.

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Claims (5)

- 8 ~ R ^{20 2} Expectations- Cl. yInjection molding machine for thermoplastics Plastics, one with regulated. Tendon movement rotating and axially displaceable screw press, which is axially attached to a hydraulic fluid under the pressure supports standing piston, plasticizes the plastic and presses it into an injection mold, characterized, that a pressure measuring element (14) is arranged in the vicinity of the gate, which gives a signal proportional to the internal pressure of the mold a controller (13) feeds the hydraulic pressure in the sense of a Minimizing this deviation changes and that the Eachdruckphase with a lying above the control tolerance Increases in hydraulic pressure switches off. 2. Injection molding machine according to claim 1, characterized in that the shutdown according to one of the size of the runner depending on the period from the beginning of the hydraulic pressure increase. 3. Injection molding machine according to claim 1 or 2, characterized characterized in that the pressure measuring element (H) is mounted in the injection mold (9). 4 «Injection molding machine according to one of the preceding claims, characterized in that the setpoint for the internal mold pressure is constant. -9- 709811/0379 - 9 - R 28 2 9 5. Injection molding machine according to one of the preceding claims, characterized in that the controller (13) an electrical signal is generated and thus on a seated in the pressure line of the hydraulic circuit Servo valve (11) acts. 709811/0379 -IAD ORiaiNA!