JPH04214320A - Screw extruder - Google Patents

Abstract

PURPOSE:To measure the melting strength of resin in a barrel simply and accurately without generating a trouble in manufacturing during the extrusion and provide a screw extruder controlling the measurement in the proper range. CONSTITUTION:A plurality of pressure sensors 4 are installed in the axial direction of a barrel 1, and pressure value distribution of molten resin in the barrel is found, and its distribution value is displayed on a display section 6 of a computing function device 5 and also melting length of resin is computed through extrapolation, and when the melting length of said resin deviates from a set range, an alarm is issued or the number of rotations of screw is varied.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw extruder that is capable of measuring the pressure distribution of a molten resin within a barrel during extrusion operation, and thereby calculating the melting length of the resin.

0002

2. Description of the Related Art In a screw extruder, a solid raw material introduced from a hopper is heated by heating from a barrel and by shearing action between the screw and barrel, and is finally melted. The melting length of this resin (hereinafter referred to as resin melting length) is determined by various factors such as heating temperature, screw structure, and screw rotation speed.Also, even if the screw rotation speed and feeder rotation speed are constant, the temperature of the raw material Since the bulk specific gravity changes depending on the degree of kneading, degree of water absorption, etc., the resin melting length changes.

[0003] If the resin melting length is too long, it may put an excessive load on the extruder, overflow into the vent hole and block it, and cause product defects such as poor foaming. On the other hand, if the resin melting length becomes too short, physical properties such as impact strength of the extruded product will deteriorate. In this way, the length of the resin melting length has an important meaning in order to proceed with extrusion operations smoothly and improve the physical properties of extruded products. Therefore, controlling the resin melting length within an appropriate range is important for extrusion This is extremely important. However, conventionally there has been no method for measuring resin melt length during extrusion operation.

Conventionally, in order to observe the resin melt length, the extruder was stopped, the screw or barrel was immediately removed, and the molten resin adhering to the screw was observed. There is also an extruder known that has a barrel that can be opened vertically so that the melted state of the resin can be observed immediately after the extruder has stopped (product name: Co-Kneader, Buss Co., Ltd.). (Switzerland)).
However, with these methods and devices, it is not possible to observe the behavior of the resin inside the barrel during operation.

[0005] Japanese Patent Laid-Open No. 1-295814 discloses that a glass window for observation is provided in the barrel of a screw extruder or screw type injection molding machine, so that the molten state of the resin inside can be observed. However, such a method can only be used for experimental molding machines, and is difficult to apply to production machines. One of the reasons for this is that fragile materials such as glass must be used under harsh conditions of high temperature and pressure, and the second reason is that by providing an observation window, it is possible to heating from the outside may become impossible, leading to uneven heating. Furthermore, there is often a step at the boundary between glass and metal in the observation aperture, and especially when using materials with poor thermal stability such as vinyl chloride resin, material may accumulate in such steps. However, there is a very high possibility that thermal decomposition will occur.

[0006]

[Problems to be Solved by the Invention] The present invention provides a screw extruder that can easily and accurately measure the resin melt length in the barrel during extrusion operation using the production machine without causing production troubles. It is an object of the present invention to provide a screw extruder that can control this within an appropriate range.

[0007]

[Means for Solving the Problems] As a result of various studies in consideration of the above points, the present inventor determined the pressure distribution of the molten resin in the barrel, and determined the point where the pressure becomes zero to the upstream side of the extruder. It was found that the length from this point to the barrel tip corresponds well to the actual resin melting length when calculated by extrapolation of
The invention has been completed.

That is, invention 1 is a screw extruder equipped with a plurality of pressure sensors that output the pressure value of the molten resin in the barrel in the axial direction of the barrel, thereby controlling the pressure value distribution of the molten resin in the axial direction. is measured. Invention 2 adds a calculation function device to the extruder to obtain the resin melt length by extrapolating the pressure distribution value output from the pressure sensor, and the resin melt length calculated from this calculation function device is set. It is characterized by being equipped with an alarm device that sounds when it is out of range.

[0009] Invention 3 further includes a control device for returning the resin melting length to the set range by changing the screw rotation speed when the resin melting length calculated by the calculation function device is out of the set range. It is characterized by what it did. Note that the resin pressure inside the barrel measured in a screw extruder differs between the screw groove and the screw flight, and the measured value for the screw groove also differs from the screw groove to the screw flight.
Changes periodically with rotation as a period. Therefore, it is preferable that the pressure of the resin by a certain pressure sensor is always measured at the same point on the screw groove. For this reason, it is preferable to detect the rotational state of the screw using an encoder so that the pressure at the same position in the screw groove can always be measured.

[0010] Furthermore, the extruder to which the present invention can be applied is not limited to the twin screw extruder exemplified in the examples described later, but can also be applied to a single screw extruder. The present invention is applicable regardless of the presence or absence of vent equipment. Furthermore, the raw materials used in the extruder of the present invention include all synthetic resins as long as they can be extruded.

[0011]

[Function] With the above configuration, inventions 1, 2, and 3 exhibit the following effects. That is, in invention 1, the pressure value distribution of the molten resin in the axial direction is measured during operation, and the measured resin pressure value distribution in the axial direction, that is, the measured pressure value vs. the length from the barrel tip to the upstream direction of the extruder. As shown in the examples described later, the relationship between the heights is often a straight line downward to the right in the upstream direction. In such a case, by extrapolating this straight line to the upstream direction of the extruder, that is, to the right, the point of zero pressure can be found. Even if the above relationship is a curve, several points upstream of the extruder can be found. Since the pressure distribution by the pressure sensor is linear, the point of zero pressure can be found by extrapolating this part. The length thus obtained from the point of zero pressure to the tip of the barrel can be taken as the resin melting length.

[0012] In invention 2, abnormality in extrusion can be known by an alarm when the resin melt length is out of the set range during operation, and problems in extrusion operation or defects in quality of extruded products can be detected. Detect outbreaks early and take measures against them.
It becomes possible to take measures such as changing the operating conditions so as to return the resin melting length to within the set range. In addition, in invention 3, it is possible to return the resin melt length to the above-mentioned setting range by directly changing the screw rotation speed using the control device. It is possible to prevent quality defects in advance or as quickly as possible, and even in the case of unmanned operation, stable operation and stable quality can be obtained at all times.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a screw extruder according to the present invention. This extruder is installed in a barrel 2 with two screws 1 meshing with each other, and a vent hole 3 in the middle of the barrel 2.
This is a so-called vent type twin-screw extruder A equipped with a.

A plurality of pressure sensors 4, 4- are provided in the barrel 2 toward the tip of the vent hole 3, so that the pressure of the molten resin can be measured at each point. The pressure values measured by the pressure sensors 4, 4- are input to the control device 5, and a computer (not shown) built in the control device 5 calculates the measured resin pressure from the tip of the barrel to the upstream direction of the extruder. A regression analysis of the length relationship is performed to determine the resin melting length.

[0015] Furthermore, an alarm device is provided that issues an alarm when the resin melting length is out of a set range, or a control device is provided that changes the screw rotation speed when the resin melting length is out of a set range. In addition, 6 is a display part of the control device 5, 7 is a raw material supply part, and 8 is an extrusion mold. Molding Example 1 The above-mentioned screw extruder was used, and a hard vinyl chloride resin compound was used as the molten resin raw material, and the screw feeder 7 was used to supply the compound. The pressure distribution of the molten resin is measured by pressure sensors 4, 4--, and is input to the control device 5,
The pressure value distribution was displayed on the display unit 6 in the form shown in FIG. Note that the screw 1 in the upper part of FIG. 2 and the pressure sensor installed in the barrel 2 show a positional relationship for measuring pressure values.

This pressure value is regression-analyzed by a built-in computer in the control device 5, and the correlation coefficient is 0.98~
A linear relationship was obtained at 1.00, and the extrapolated value to zero pressure was obtained, and the resin melting length was determined. From this measured resin melting length, changes in the state of the raw material, such as changes in the bulk specific gravity of the resin, can be estimated, and more suitable extrusion conditions can be determined.

Molding Example 2 This is a screw extruder in which the shape of the metering part of the screw 1' is divided into two zones and does not have a vent hole, and is equipped with a pressure sensor and a control device like the extruder shown in FIG. Molding was carried out using the same extruder as in Molding Example 1, using hard vinyl chloride resin as the raw material. As shown in Figure 3, the pressures P1 to P6 are measured in each zone, regression analysis is performed using these values, and the pressure distribution on the upstream side is extrapolated in the same manner as in Example 1. We were able to determine the resin melting length.

Molding Example 3 The screw, barrel, and pressure sensor are the same as in Example 1, and the control device is equipped with an alarm device to issue an alarm when the resin melting length deviates from a specified range. Molding was carried out using the same extruder as in Molding Example 1. The falling weight impact value of this extruded hard PVC pipe decreases as the resin melting length becomes shorter;
If it is less than 00mm, it will be less than the standard value of 400mm. Furthermore, the vent hole was located 525 mm from the tip of the barrel, and in order to prevent the vent hole from clogging, the resin melting length had to be 500 mm or less. Therefore, the appropriate range of resin melting length is 400 to 500 mm. These relationships were as shown in FIG.

In order to carry out extrusion molding in such an operating range, operation was carried out with the lower limit of the warning device of the control box set to 400 mm and the upper limit to 500 mm. By adopting such a system, there was no clogging of the vent holes during extrusion operations, and the problem of falling weight impact values falling outside the specifications was also resolved. Molding Example 4 The extruder used in Molding Example 3 is equipped with a control mechanism that changes the screw rotation speed by sending a signal from this control device to the screw drive motor when the resin melt length deviates from the operating range for a certain period of time. Molding was carried out using the same extruder as in Molding Example 1.

[0020] The resin melt length was able to be maintained within the operating range. The correlation between the screw rotation speed and the resin melting length has a correlation coefficient of 0.0 as shown in FIG. This is an inverse correlation of 95 to 1.00, and in this case, a change in the screw rotation speed of 1 rpm can change the resin melting length by 30 mm. The step of changing the screw rotation speed was set to 0.5 rpm, and the speed of change was set to 1 rpm/min.

By employing the above-mentioned control device, it was possible to stably produce hard vinyl chloride pipes of excellent quality without any operational troubles.

[0022]

According to the present invention, the pressure of the molten resin at each position of the barrel can be measured during the operation of the production extruder without interfering with production, and the resin melt length can be measured from the measurement results. As a result, it has become possible to know first of all fluctuations in the amount of raw materials supplied, and it has become possible to take countermeasures early on.

Furthermore, in the second aspect of the invention, even if the resin melting length becomes long and the vent hole is about to be clogged, it is possible to know this in advance and take appropriate measures. Furthermore, if the correlation between the resin melting length and a certain quality is known, the resin melting length corresponding to the value that the specific quality divides the standard value is set as the limit value, and an alarm is issued to prevent quality defects. It will be possible to prevent it from happening.

Furthermore, in invention 3, the resin melting length corresponding to the limit value for quality and operation is inputted to the control device as a set value, and this control device is connected to the screw drive device to control the screw rotation speed. By changing the length, the resin melting length can be controlled within the set range, and even in unmanned operation, stable operation and extruded products of stable quality can be obtained.

As described above, the present invention has clarified the melting behavior of the resin inside the extruder barrel, which was previously unknown, and the knowledge obtained as a result can be used to stabilize the operation of the extruder and improve the quality of extruded products. This greatly contributes to quality improvement. As described above, the industrial value of the present invention is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a screw extruder of the present invention.

FIG. 2 shows resin pressure distribution values of the molten resin in the barrel of the extruder.

FIG. 3 is a resin pressure distribution diagram when the screw shape of the measuring section of the extruder is different between the first half and the second half.

FIG. 4 is a graph showing the relationship between falling weight impact value and resin melting length of an extruded product.

FIG. 5 is a graph showing the relationship between changes in screw rotation speed and resin melting length.

[Explanation of symbols]

1, 1’ screw 2 Barrel 3 Bend hole 4 Pressure sensor 5 Control device 6 Display section A. Extruder.

Claims (3)

[Claims] 1. A screw extruder characterized in that a plurality of pressure sensors are provided in the axial direction of the barrel to output pressure values of molten resin within the barrel. [Claim 2] A calculation function device that extrapolates the pressure value distribution of the molten resin in the barrel to determine the resin melting length in the barrel, and that issues an alarm when the resin melting length is out of a set range. Claim 1, characterized in that it is equipped with an alarm device.
Screw extruder as described in section. 3. A calculation function device for calculating the resin melting length in the barrel by extrapolating the pressure value distribution of the molten resin in the barrel; The screw extruder according to claim 1, further comprising a control device for returning the resin melt length to a set range by changing the resin melt length.