JPH0694150B2 - Material Weighing Method in Plunger Type Injection Device with Pressure Hopper - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring a molding material in a plunger-type injection device equipped with a pressure hopper, and particularly to a technique for stabilizing the time required for the measurement of the molding material. It is about.

(Background Art) In a plunger type injection device equipped with a pressure hopper,
The operation (metering operation) for supplying the molding material into the heating cylinder in which the injection plunger is inserted is usually performed according to the procedure shown in FIGS. 4 to 6.

That is, when the measurement start command is issued, first, the injection plunger 2 which has been held at the forward position at the time of completion of the injection molding operation is retracted to a position where the lower opening of the pressure hopper 4 is closed. When the lower opening of the pressure hopper 4 is closed by the injection plunger 2, the piston 6 of the pressure hopper 4 is subsequently lowered and brought into contact with the molding material 8 in the pressure hopper 4. FIG. 4 shows the state at this stage.

In the figure, 10 is a pressure switch connected to the elevating cylinder 12 of the pressure hopper 4, which detects the contact pressure of the piston 6 to the molding material 8 from the operating oil pressure of the elevating cylinder 12, and determines the contact position. It is for detection.

When the piston 6 is lowered to a position where it comes into contact with the molding material 8 with a predetermined contact pressure, and that is detected by the pressure switch 10, a timer (not shown) preset to a predetermined operation time is activated. And at the same time, the fifth
As shown in the drawing, the injection plunger 2 is further retracted from the position where the lower opening of the pressure hopper 4 is closed, and the lower opening of the pressure hopper 4 is opened. 6 is further lowered, and the molding material 8 is extruded and supplied into the heating cylinder 14. Then, when the timer has completed the time counting operation and the scheduled time has elapsed, the backward movement of the injection plunger 2 and the downward movement of the piston 6 are stopped, and the molding material 8 is extruded from the pressure hopper 4 into the heating cylinder 14. After the supply operation is stopped and the extrusion supply operation of the molding material 8 is stopped, the injection plunger 2 is moved forward and the piston 6 is moved upward.

The injection plunger 2 is advanced to a position where the pressing force by the injection cylinder 16 reaches a predetermined amount and the pressure switch 18 is actuated, while the piston 6 moves the molding material 8
It is lifted up to the position where it is not in contact with. Then, in this state, the advance position of the injection plunger 2 is compared with a plunger advance position region that is set in advance by being divided into a plurality of parts, and when it is determined that the advance position is the measurement completion region, the molding material 8 Although the weighing operation is completed as it is,
If not, the operating time of the timer is set to a preset time corresponding to the forward movement position region,
The above operation is repeatedly executed under such a timer setting state, and thereafter, the same operation is repeated until it is determined that the forward movement position of the injection plunger 2 reaches the measurement completion region and the measurement operation is completed. To be executed. After the measurement operation is completed, the injection plunger 2 is further advanced to inject the measured molding material 8.

Thus, in the conventional material measuring method using such a timer, although the descent operation time of the piston 6 required for each extrusion feeding operation of the molding material 8 into the heating cylinder 14 is extremely stable, the pressure hopper is used. Piston down time and heating cylinder 14
The correlation with the amount of material supplied to the inside is extremely low, and the piston 6
Since the amount of the molding material extruded and supplied into the heating cylinder 14 due to the individual descending operations of the piston 6 is extremely large, there is a problem that the number of times the material is extruded and supplied into the heating cylinder 14 due to the descending operation of the piston 6 significantly changes. Therefore, as a result, the required time required for the measurement from the start to the completion of the measuring operation fluctuates greatly, the residence time of the molding material in the heating cylinder 14 greatly varies, and the molding conditions such as the curing time of the molding material vary. There was a problem such as a large variation.

Incidentally, FIG. 7 shows that the plunger advance position region is divided into the measurement completed region III and the two first and second measurement incomplete regions I and II, while the material into the heating cylinder immediately after the start of the measurement operation. Both the timer setting time at the time of extrusion supply and the timer setting time at the time of material extrusion supply into the heating cylinder next time when the forward position of the injection plunger is determined to be the region I are 3.
Set to 3 seconds and set the plunger forward position to Area II.
If it is determined that the next time the material is supplied and extruded, the timer setting time is set to 1.8 seconds, and the displacement of the forward position of the injection plunger is measured when the molding material is metered according to the above conventional method. From the measurement results, it can be seen that the number of times the material is extruded and fed into the heating cylinder due to the descending operation of the piston from the start of measurement to the end of the measurement fluctuates significantly, at 1 to 5 times. is there.

In addition, in the figure, indicates the forward position of the injection plunger at the start of the metering operation (at the completion of the injection molding operation), and ~ are the injection plungers after the first to fifth times of material extrusion supply, respectively. Shows the forward position of
Shows the plunger position after suck back operation.

(Problem to be Solved) Here, the present invention has been made in view of the above circumstances, and the problem is to provide a plunger-type injection device having a pressure hopper, in which the pistons of the pressure hopper are individually By stabilizing the extrusion feed amount of the molding material into the heating cylinder by the lowering operation of the, the number of extrusion feed times of the molding material into the heating cylinder is stabilized, and thus the required time for the measurement of the molding material. To provide a measuring method capable of stabilizing the molding conditions such as the residence time of the molding material in the heating cylinder, and thus the curing time of the molding material, and the individual pistons of the pressure hopper. By stabilizing the amount of extrusion feed of the molding material into the heating cylinder due to the descending operation of, the residence time of the molding material in the heating cylinder is stabilized,
Consequently, it is an object of the present invention to provide a measuring method capable of effectively shortening the time required for measurement, and eventually the injection molding cycle, while stabilizing the molding conditions such as the curing time of the molding material.

(Solution Means) In order to solve such a problem, the first method of the present invention is (A) closing the lower opening of the pressure hopper at the time of measuring the molding material in the plunger type injection device equipped with the pressure hopper. A hopper closing step of retracting the injection plunger to the closing position; and (B) a position where the injection material is brought into contact with the molding material contained in the pressure hopper with a predetermined contact pressure under the closed state of the lower opening of the pressure hopper. Up to the piston contact step of lowering the piston of the pressure hopper, and (C) after the piston contact step, the injection plunger is retracted to open the lower opening of the pressure hopper, and the piston is Heating by inserting the injection plunger by lowering it from the contact position with the material by a preset lowering amount. After the material supplying step of extruding the molding material in the pressure hopper into the cylinder, and (D) after the material supplying step, until the pressing force with respect to the molding material supplied into the heating cylinder reaches a predetermined magnitude. Comparing the advance position of the injection plunger by the plunger advancing step of advancing the injection plunger and (E) the plunger advancing step with a plunger advancing position region set in advance by dividing the injection plunger into a plurality of positions. Is not reaching the metering completion region, the descending amount of the piston in the material supply process is set to the descending amount set in advance corresponding to the plunger advancing process region in which the injection plunger is located, and While repeating the hopper closing process, piston contacting process, material supplying process and plunger advancing process,
When it reaches the measurement completion area, it includes a plunger forward position determination step for completing the measurement operation.

In addition, the second method of the present invention, when measuring the molding material in a plunger type injection device equipped with a pressure hopper,
(A) Supply into the heating cylinder from the residual amount of the molding material in the heating cylinder at the start of the measuring operation and the preset amount of molding material that is preferably present in the heating cylinder at the completion of the measuring operation A feed material amount calculating step for obtaining a molding material amount to be performed, and (b) a hopper closing step for retracting the injection plunger to a closing position for closing the lower opening of the pressure hopper,
(C) A piston contact step of lowering the piston of the pressure hopper to a position where the molding material housed in the pressure hopper is brought into contact with a predetermined contact pressure under the closed state of the lower opening of the pressure hopper by the injection plunger. When,
(D) After the piston contact step, the injection plunger is retracted to open the lower opening of the pressure hopper, and the piston is calculated in the feed material amount calculation step from the contact position with the molding material. The material supply step of extruding the molding material in the pressure hopper into the heating cylinder by lowering it by an amount corresponding to the supplied material supply quantity, and (e) after the material supply step, into the heating cylinder. A plunger advancing step of advancing the injection plunger until the pressing force against the supplied molding material reaches a predetermined amount.

(Operation) The descending speed of the piston of the pressure hopper when the molding material is extruded and supplied into the heating cylinder is likely to vary, and thus the time required for the piston to descend by a certain amount is also likely to vary. Therefore, as in the method of the present invention, when the molding material is extruded and supplied into the heating cylinder by the downward movement of the piston of the pressure hopper, if the extruded and supplied amount of the molding material is regulated by the descending amount of the piston, heating can be performed. One of the pistons when pushing the material into the cylinder
The time required for each descent operation fluctuates significantly compared with the conventional method using a timer, and the stability is remarkably lacking.

However, the amount of molding material extruded and supplied into the heating cylinder by the descent operation of the piston of the pressure hopper corresponds to the amount of descent of the piston of the pressure hopper extremely well according to the experiments by the present inventors. The number of times the material is extruded and supplied into the heating cylinder due to the downward movement of the piston is much more stable than the conventional method that uses a timer. Since the time required is sufficiently longer than the time required for one downward movement of the piston for extruding and supplying the molding material into the heating cylinder, the variation in the piston downward time required for each downward movement of the piston is due to the material extruding and feeding. By stabilizing the number of operations, it will be sufficiently absorbed.

That is, as in the first method of the present invention, when it is premised that the material extruding and supplying operation into the heating cylinder by the descending operation of the piston is performed a plurality of times, the number of material extruding and supplying operations itself is stabilized. In addition, the time required for the measurement from the start to the completion of the measurement operation can be significantly stabilized, and therefore the molding conditions such as the residence time of the molding material in the heating cylinder and the hardening time of the molding material can be significantly stabilized. It becomes possible to stably form a molded product of excellent quality.

Further, when the material is extruded and supplied into the heating cylinder by the descending operation of the hopper piston, if the extrusion supply amount of the molding material is regulated by the descending amount of the piston, as described above, the molding material into the heating cylinder is Since the amount of extrusion supply of is significantly stabilized, the amount of molding material to be supplied into the heating cylinder is calculated in advance and the calculated amount of molding material is calculated once as in the second method of the present invention. Even if it is supplied into the heating cylinder by the descending operation of the piston, the molding material is not excessively supplied into the heating cylinder excessively. Therefore, the second method of the present invention is used. By adopting it, the required time for measurement, while satisfactorily stabilizing the molding conditions such as the residence time of the molding material in the heating cylinder, and thus the curing time of the molding material,
As a result, the injection molding cycle can be effectively shortened.

Even in the conventional measuring method using a timer, similarly to the second method of the present invention, the operation of supplying the molding material into the heating cylinder is always completed by only one downward movement of the piston. However, in that case, it is necessary to set the timer setting time corresponding to the case where the amount of material extruded and supplied into the heating cylinder is small. In case of large quantity,
The molding material was extremely excessively supplied into the heating cylinder,
As a result, the residence time of the molding material in the heating cylinder varies greatly, which may cause a serious problem.

(Examples) In order to more specifically clarify the present invention,
Some embodiments will be described in detail with reference to the drawings.

Here, the method of the embodiment of the present invention will be described using the plunger type injection device having the structure shown in FIG. 1. The plunger type injection device shown in FIG. The conventional plunger-type injection device shown in FIG. 2 is basically provided with a position sensor 24 including a rack 20 and a pinion 22 for detecting the ascending / descending position of the piston 6 of the pressure hopper 4 instead of the timer. Only different,
Since the other structure is the same as that of the conventional plunger type injection device, the same reference numerals as those of the conventional plunger type injection device are given to the respective constituent members, and detailed description thereof will be omitted.

Further, here, first, an embodiment corresponding to the first method of the present invention will be described according to the flow chart shown in FIG. 2, and thereafter, the second method of the present invention will be described according to the flow chart shown in FIG. A corresponding example will be described.

That is, in the embodiment of the flowchart shown in FIG. 2, when the injection molding operation is completed and a command to start the measurement operation of the molding material 8 is issued, first, the injection plunger 2
However, it is retracted from the advanced position at the time of completion of the injection molding operation, and is retracted to the position where the lower opening of the pressure hopper 4 is closed. Then, when the lower opening of the pressure hopper 4 is closed by the injection plunger 2, the piston 6 of the pressure hopper 4 is subsequently lowered, and is lowered to the position where the pressure switch 10 is activated, and the molding material in the pressure hopper 4 is lowered. 8 is touched. The piston 6 is lowered to a position where it comes into contact with the molding material 8 housed in the hopper 4 with a preset contact pressure.

The operation up to this point is the same as the conventional method using a timer.

When the piston 6 is lowered to a position where it comes into contact with the molding material 8 with a predetermined contact pressure, the contact position is detected by the position sensor 24, and the contact position detected by the position sensor 24 is used as a reference from the contact position. Also, the lower limit position of the piston 6 is set lower by a predetermined first set amount. Simultaneously with the setting of the lower limit position of the piston 6, the injection plunger 2 is retracted, the lower opening of the pressure hopper 4 is opened, and the piston 6 is lowered from the contact position with the molding material 8. The molding material 8 in the pressure hopper 4 is extruded and supplied into the heating cylinder 14 through the lower opening of the hopper 4. When it is detected that the piston 6 has descended to the lower limit position from the detection value of the position sensor 24 while the piston 6 is descending,
The lowering operation of the piston 6 and the retreating operation of the injection plunger 2 are stopped, the extrusion supply operation of the molding material 8 from the pressure hopper 4 into the heating cylinder 14 is stopped, and after the material extrusion supply operation is stopped, the injection is performed. The plunger 2 is moved forward and the piston 6 is moved upward.

The lower limit position of the piston 6 may be set after the start of the backward movement of the injection plunger 2 and the downward movement of the piston 6 as long as there is time.

The piston 6 is lifted up to a height position where it is not in contact with the molding material 8 by the above-mentioned lifting operation. On the other hand, the injection plunger 2 is advanced to a position where the pressure switch 18 is actuated when the pressing force of the drive cylinder 16 reaches a certain level, as in the case of the conventional method using the timer. Then, the advance position of the injection plunger 2 is compared with a plunger advance position region that is set in advance by dividing into a plurality of parts, and when it is determined that the advance position is the measurement completion region, the measuring operation of the molding material 8 is performed. The process is completed as it is, but if not, the piston 6 corresponds to the plunger advance position region in which the injection plunger 2 is located.
Is set, and the above-mentioned operation is repeated again under the condition that the descending amount of the piston 6 at the time of material extrusion supply from the pressure hopper 4 into the heating cylinder 14 is set to the set descending amount.
Hereinafter, the same operation is repeated until it is determined that the advance position of the injection plunger 2 becomes the measurement completion area and the molding material 8 necessary for the injection operation is supplied into the heating cylinder 14.

In this case, the plunger advance position region is adjacent to the weighing completed region III, the second weighing unfinished region II having a predetermined width adjacent to the weighing finished region III, and the second weighing unfinished region II. The first weighing incomplete area I having a width larger than the second weighing incomplete area II (for example, about 2 to 4 times wider)
As is clear from the flowchart of FIG. 2, when the forward position of the injection plunger 2 is in the first measurement incomplete region I, the next time the material is extruded and supplied into the heating cylinder 14. The lower limit position of the piston 6 is set on the basis of the first set amount, while the forward position of the injection plunger 2 is set to the second measurement incomplete region.
In the case of II, the lower limit position of the piston 6 at the time of material extrusion supply into the heating cylinder 14 next time is smaller than the first set amount thereof (for example, the first and second measurement incomplete regions I, II
Based on the second set amount (of a small ratio of the width dimension ratio) of
It is set.

Therefore, according to such a method, the extrusion supply amount of the molding material 8 into the heating cylinder 14 is defined by the descending amount of the piston 6, and the heating cylinder 14 by the individual descending operation of the piston 6 is performed.
Since the amount of material extruded and supplied into the heating cylinder 14 is extremely stable, the number of times of material extruded and supplied into the heating cylinder 14 due to the descending operation of the piston 6 is remarkably stable. Therefore, each descending operation of the piston 6 is performed. Although the time required for the molding is not constant, the time required for the measurement from the start to the completion of the measuring operation is significantly stable, and the residence time of the molding material 8 in the heating cylinder 10 and thus the molding time of the molding material 8 etc. Conditions are favorably stabilized, so that a molded product of excellent quality can be stably molded.

Next, an embodiment corresponding to the second method of the present invention will be described with reference to the flowchart shown in FIG.

In the embodiment shown in the flowchart of FIG. 3, when the injection operation of the molding material 8 by the forward movement of the injection plunger 2 is completed and a command to start the measurement operation of the molding material 8 is issued, first, the injection plunger 2 The residual amount (cushion amount) A of the molding material 8 remaining in the heating cylinder 14 is obtained based on the current position of the From the preset amount of molding material that is preferably present: C, the amount of molding material that should be supplied into the heating cylinder 14 by the weighing operation:
(C-A) is obtained, and the descending amount of the piston 6 in the pressure hopper 4 corresponding to the amount of molding material is obtained. Then, following the calculation operation, the injection plunger 2 is retracted to a position where the lower opening of the pressure hopper 4 is closed.

It should be noted that, more practically, the lowering amount of the piston 6 in the pressure hopper 4 is the position of the injection plunger 2 corresponding to the residual amount: A (current position of the injection plunger 2): a, and the preset molding material amount. It is calculated based on the measurement completion setting position: c which is the moving position of the injection plunger 2 corresponding to: C.

When the injection plunger 2 is retracted to a position that closes the lower opening of the pressure hopper 4, the piston 6 of the pressure hopper 4 is lowered to a position where it contacts the molding material 8 in the pressure hopper 4, as in the above-described embodiment. The contact position is detected. The contact position and the calculated piston 6
The lower limit position of the piston 6 is set based on the lowering amount of.

When the piston 6 is lowered to the contact position with the molding material 8 and the lower limit position of the piston 6 is set, subsequently, the backward movement operation of the injection plunger 2 is started, and
The piston 6 is further lowered from the contact position with respect to the molding material 8, and the I molding material 8 in the heating cylinder 14 is extruded and supplied. Then, the piston 6 is moved to the set lower limit position.
Is lowered, the lowering operation of the piston 6 is stopped, the backward movement of the injection plunger 2 is stopped, and the material extrusion supply operation into the heating cylinder 14 is stopped.

It should be noted that the setting of the lower limit position of the piston 6 during the material extruding / supplying operation may be performed by the time the material extruding / supplying operation is completed. It does not need to be obtained at the same time as the start of the operation, and may be obtained until the material extrusion feeding operation is completed.

When the downward movement of the piston 6 and the backward movement of the injection plunger 2 are stopped to stop the material extruding and feeding operation, then the piston 6 rises to the non-contact position with the molding material 8 as in the above-described embodiment. At the same time, the injection plunger 2 is advanced to a position where the pressing force on the molding material 8 supplied into the heating cylinder 14 reaches a predetermined amount.
Then, when the pressure switch 18 detects that the pressing force against the molding material 8 has reached the predetermined amount, the forward movement of the injection plunger 2 is stopped, and the measuring operation is completed.

According to such a method, the amount of the molding material 8 accurately corresponding to the descending amount of the piston 6 during the material extruding and feeding operation into the heating cylinder 14 is supplied into the heating cylinder 14, As described above, the amount of lowering of the piston 6 during the material extruding and feeding operation into the inside is performed by the heating cylinder 14 at the completion of the measurement.
It is set corresponding to the difference (C-A) between the preset amount of molding material C, which is desirable to be present in the inside, and the residual amount of molding material in the heating cylinder 14 at the start of the metering operation: A. Therefore, at the time of completion of the measuring operation, the amount of the molding material 8 that accurately matches the preset molding material amount C in the heating cylinder 14 is always present.

According to such a method, as described above, at the time of the completion of the weighing operation, the amount of the molding material 8 that accurately matches the amount C that is desirable to be present in the heating cylinder 14 at all times is high.
In addition to the presence of the molding material 8 in the heating cylinder 14, the extrusion operation of the molding material extruding into the heating cylinder 14 by the downward movement of the piston 6 can be performed only once at all times. The molding conditions such as the curing time of 8 can be satisfactorily made constant, and molding of a molded product of excellent quality can be stably carried out, while the measuring time required for the measuring operation is greatly shortened. That is, the injection molding cycle can be significantly shortened.

Although some embodiments of the present invention have been described in detail above, the present invention is not limited to these specific examples, and the above-mentioned examples are used as a position sensor for detecting the ascending / descending position of the piston 6. The present invention, such as employing something other than the position sensor 24, within a range not departing from its gist,
Based on the knowledge of those skilled in the art, various changes, modifications,
It goes without saying that the invention can be carried out in an improved manner.

(Effects of the Invention) As is clear from the above description, if the first method of the present invention is adopted, the extrusion feed operation of the molding material into the heating cylinder by the lowering operation of the piston of the pressure hopper is performed a plurality of times. In this case, the number of extrusion feed operations of the molding material into the heating cylinder by the downward movement of the piston of the pressure hopper is significantly stabilized, and Since the molding conditions such as the residence time of the molding material and the curing time of the molding material can be remarkably stabilized, a molded product of excellent quality can be remarkably stably produced as compared with the conventional method. .

Further, if the second method of the present invention is adopted, the operation of extruding and supplying the molding material into the heating cylinder by the downward movement of the piston of the pressure hopper can be performed only once, and the molding material can be stably metered accurately. In order to be able to do, like the first method,
The molding conditions such as the residence time of the molding material in the heating cylinder, and thus the curing time of the molding material, can be made stable and good quality molded products can be produced more stably than before, and the weighing operation can be performed. It is possible to significantly reduce the time required for the injection molding cycle and significantly shorten the injection molding cycle.

Incidentally, the first method is advantageously adopted particularly when the amount of the molding material supplied is extremely large or when the molding material having poor fluidity is targeted, and the second method is the molding method. It will be advantageously used when the amount of material supplied is not more than a normal level or when a molding material having good fluidity is targeted.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a main part of an example of a plunger type injection device provided with a pressure hopper to which the method of the present invention is applied, and FIGS. 2 and 3 are respectively the method of the present invention. 4 is a flowchart for explaining an example of the embodiment.
FIG. 4, FIG. 5 and FIG. 6 are schematic cross-sectional views showing different operating states of the plunger type injection device for explaining the conventional method, and FIG. 7 shows the molding material according to the conventional method. It is a graph which shows the example of measurement of the displacement situation of the advance position of the injection plunger at the time of performing a measurement operation. 2: Injection plunger, 4: Pressure hopper 6: Piston, 8: Molding material 14: Heating cylinder, 24: Position sensor

Claims (2)

[Claims] 1. A hopper closing step of retracting an injection plunger to a closing position for closing a lower opening of a pressure hopper, and a molding housed in the pressure hopper under a closed state of the lower opening of the pressure hopper by the injection plunger. A piston contact step of lowering the piston of the pressure hopper to a position where the material comes into contact with a predetermined contact pressure, and after the piston contact step, the injection plunger is retracted to open the lower opening of the pressure hopper. A material supplying step of lowering the piston from a contact position with respect to the molding material by a preset descending amount, and extruding and supplying the molding material in the pressure hopper into a heating cylinder in which the injection plunger is inserted, After the material supply step, the pressing force against the molding material supplied into the heating cylinder is The plunger advance step of advancing the injection plunger until reaching a certain degree, and the advance position of the injection plunger by the plunger advance step are compared with a plunger advance position region that is set by dividing the injection plunger in advance, When the advance position has not reached the metering completion region, the descending amount of the piston in the material supplying step is set to the descending amount set in advance corresponding to the plunger advancing position region in which the injection plunger is located. While repeating the hopper closing step, the piston contacting step, the material supplying step and the plunger advancing step, when the metering completion area is reached,
And a plunger forward position determining step for completing the weighing operation, the method for weighing a material in a plunger type injection device having a pressure hopper. 2. The inside of the heating cylinder based on the residual amount of the molding material in the heating cylinder at the start of the weighing operation and the preset amount of molding material which is preferably present in the heating cylinder at the completion of the weighing operation. To calculate the amount of molding material to be supplied to the pressure hopper, the hopper closing step of retracting the injection plunger to the closing position where the lower opening of the pressure hopper is closed, and the closing state of the lower opening of the pressure hopper by the injection plunger. A piston contact step of lowering the piston of the pressure hopper to a position at which the molding material contained in the pressure hopper comes into contact with a predetermined contact pressure; and after the piston contact step, the injection plunger is retracted. , The lower opening of the pressure hopper is opened, and the piston is fed from the contact position with the molding material. A material supply step of lowering the material supply quantity obtained in the material amount calculation step by an amount corresponding to the material supply quantity and extruding the molding material in the pressure hopper into the heating cylinder, and after the material supply step, A plunger advancing step of advancing the injection plunger until the pressing force with respect to the molding material supplied into the heating cylinder reaches a predetermined amount, and the material in the plunger type injection device with a pressure hopper, Weighing method.