JPH0692086B2 - Pellet size control method and pelletizer using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a pellet size in which a plastic strand is cut into pellets having a desired diameter and / or length, and a pelletizer (also referred to as a strand cutter) using the method.
Regarding

[0002]

2. Description of the Related Art Most of thermoplastic resins are once pelletized and then processed into plastics molded articles. One of the pelletizing methods is the strand cut method. This is a method in which a polymerized molten resin is extruded from a porous die, a string-shaped strand is cooled and solidified, and then cut into short pieces, and a pelletizer is mainly used. By the way, if the cut pellets do not have the same size, the pellets cannot be blended uniformly, and cause accidents such as a bridge of the molding machine hopper and a trouble of the air conveyer. For this reason, in the operation of the pelletizer, a skilled worker must constantly measure the pellet size and adjust the operating conditions.

[0003]

The pellet size has a relation with the stabilization of the polymerization in the previous step, and becomes unstable especially at the start of the operation, which requires frequent adjustments by workers. Conventionally, this was taken as a matter of course, but the present inventor considered that automation of pellet size adjustment was indispensable for rationalizing pelletizing equipment. Japanese Patent Laid-Open No. 2-3100
09 and Japanese Patent Laid-Open No. 3-61507,
A control device and a manufacturing method for making the pellets uniform in size have been proposed. However, the former cannot be applied when using an extruder or a gear pump, and the latter is not realistic because the equipment is complicated by using liquid. Therefore, the present inventor has researched a pellet size control method which can be easily automated, and a pelletizer using the pellet size control method which is simple and easy to use, and has completed the present invention.

[0004]

As a first aspect of the present invention, the present invention comprises a plastic roll obtained by cooling and solidifying molten plastic extruded in a strand form from an extruder, and comprising a rotating roll and a pinch roll for pressing the strand. In a pelletizer that takes out with a take-up roll, sends out to a cutting section consisting of a rotary blade and a fixed blade and cuts, detects the displacement of the pinch roll, and compares this with a desired pellet diameter,
A method for controlling the pellet diameter of the pelletizer, which is characterized by controlling the rotating roll to an optimum rotation speed to eliminate the deviation between the desired pellet diameter and the displacement value of the pinch roll, and controlling the pellets thus cut to the desired diameter. I will provide a.

Further, as a second invention, the pellet diameter is controlled by using the above pellet diameter control method, and further, the rotation of the rotary roll and the rotary blade which is set to cut the strand into a desired length. Calculate the speed ratio, determine the rotation speed of the rotating blade from the calculated rotation speed ratio by measuring the rotation speed of the rotating roll, control the rotation speed of the rotating blade to the obtained rotation speed, the pellets cut by Provided is a method for controlling a pellet size, which is characterized by controlling a desired diameter and length.

Furthermore, as a third invention, a pelletizer utilizing the first invention, that is, a plastic roll obtained by cooling and solidifying molten plastic extruded in a strand form from an extruder is pressed by a rotating roll and a pinch roll. In a pelletizer that takes up with a take-up roll consisting of and feeds to a cutting section consisting of a rotary blade and a fixed blade to cut and pelletizes, a setter A for setting a desired pellet diameter and displacement of a pinch roll are detected. And a control unit A for comparing the input signal from the displacement meter with the set value of the setter A and outputting the optimum rotation speed command signal of the rotating roll for eliminating the deviation, It consists of a rotating roll drive unit that follows the optimum rotation speed command signal, detects the pinch roll displacement, and rotates it by comparing it with the set pellet diameter. Controls Lumpur optimal rotational speed, with the pellet taken to provide a pelletizer characterized in that a control system for controlling the desired diameter.

As a fourth invention, a pelletizer for cutting pellets of uniform length, that is, a molten plastic extruded in a strand form from an extruder is cooled and solidified, and a plastic roll is pressed against a rotating roll and the strand. In a pelletizer for picking up with a take-up roll consisting of a pinch roll, feeding to a cutting section consisting of a rotary blade and a fixed blade for cutting, and pelletizing, a setting device B for setting a desired pellet length and a rotary roll A rotation speed meter that measures and transmits the rotation speed and the rotation speed ratio between the rotating roll and the rotating blade is calculated from the set value of the pellet length, and the rotating speed signal of the rotating roll is input to determine the rotating speed of the rotating blade. Control unit B for calculating and outputting a rotation speed command signal of the rotary blade
And a drive unit for the rotary blade that follows the optimum rotation speed command signal from the control unit B, calculates the rotation speed ratio between the rotary roll and the rotary blade from the set value of the pellet length, and inputs this rotation speed ratio. A pelletizer is provided which is provided with a control system for controlling the rotation speed of a rotary blade according to the rotation speed signal of the rotating roll and controlling the cut pellets to a desired length.

Furthermore, as a fifth invention, in the pelletizer of the second invention, that is, in the pelletizer of the third invention, a setter C for setting a desired pellet length and a rotation speed of a rotating roll are further provided. The rotation speed of the rotating roll is calculated by calculating the rotating speed of the rotating roll and blade from the receiving terminal of the rotating speed meter and / or the receiving terminal of the optimum rotating speed command signal of the rotating roll and the set value of the pellet length. A control unit C that inputs a speed signal and / or an optimum rotation speed command signal, calculates the rotation speed of the rotary blade and outputs the rotation speed command signal of the rotary blade, and follows the optimum rotation speed command signal of the control unit C. It consists of the rotary blade drive unit, calculates the rotation speed ratio between the rotary roll and rotary blade from the set value of the pellet length, and uses this rotation speed ratio and the input rotation speed signal of the rotary roll. It controls the rotation speed of the rotary blade, with the cut pellet to provide a pelletizer according to the third invention which is characterized in that a control system for controlling to a desired length.

[0009]

FUNCTION AND EXAMPLE OF EMBODIMENT The present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an example of an embodiment of a pelletizer of the third invention which embodies the first invention. Figure 4 is the fourth
FIG. 3 is a schematic view of an embodiment example of a pelletizer of the invention of FIG. 3, and FIG. 3 is a schematic view of an embodiment example of a pelletizer of the fifth invention which embodies the second invention.

First, the outline of the pelletizer according to the present invention will be described. The molten plastic extruded in a strand form from the extruder 1, a gear pump or the like is cooled and solidified in a cooling tank 2, a spray or the like. The solidified plastic strand 3 is taken up by the take-up roll of the pelletizer 4, which is composed of the pinch roll 5 and the rotary roll 6. The drawn strands 3 are sent on the running surface 7 toward the cutting portion composed of the fixed blade 8 and the rotary blade 9. The sent strand 3 is cut by a rotary blade 9 having a gear-shaped blade and a fixed blade 8 to form a pellet 10.

Now, as an embodiment example of the first invention, a pelletizer of the third invention utilizing the same will be described. The first and third inventions aim to control the pellet diameter, which is the most variable and difficult to control. In these inventions, the pellet diameter is controlled by detecting the diameter of the strand before cutting and feeding it back to the rotation speed of the rotating roll to control the take-up speed of the strand. Usually 20
It is not easy to measure the diameter of a large number of strands traveling at a take-up speed of -100 m / min, and the present inventor has tried several direct measurement methods, but this method is complicated and costly. It was neither accurate nor economically feasible. As a result of various studies, it has been found that the diameter of the strand can be easily measured with practically sufficient accuracy by measuring the displacement of the pinch roller. Therefore, this displacement amount signal is input to the control unit A, and the rotation speed of the rotating roll is controlled separately by comparing with the desired pellet diameter that has been set. Since the amount of molten plastic discharged from an extruder or gear pump is quantitative, basically the strand diameter can be changed by changing the take-up speed. Particularly preferable control is possible when the strand diameter is 1 to 4 mm.

Among the devices provided in this control system, the pellet diameter setting device is, for example, a digital switch type device, and is normally provided with an indicator thereof (in the drawings and below,
Although it does not describe the indicator, it can be provided where necessary for operation). A known capacitor / coil, differential transformer, eddy current sensor, laser displacement meter, optical displacement meter, potentiometer, or the like may be used as the displacement meter that detects and transmits the displacement of the pinch roll. The signal from the displacement meter is input to the control unit A, but if necessary,
Smooth it through an integrator. In the control unit A, the signal from the displacement gauge is compared with the set value of the setter, and the deviation is passed through a PID element, for example, and a delay element between the extrusion section and the pelletizer is added to eliminate the deviation. Output as the optimum rotation speed command signal for the rotating roll. However, this deviation does not mean the obtained primitive data. The displacement of the pinch roll is not necessarily the same as the pellet diameter, depending on the number of strands, the material of the roll, the type of strand (e.g., elastomer), and appropriate correction is added as necessary. In addition, during operation, in order to add fine corrections by actually measuring the processed pellets,
It is convenient to provide the correction setting device A. The optimum rotation speed command signal of the rotating roll is output to the driving unit of the rotating roll directly or via an amplifier. Examples of the drive unit include a combination of a DC servo driver and a DC servo motor, an AC servo driver and an AC servo motor, and an inverter and an induction motor. When the induction motor is used, the actual rotation speed may deviate from the rotation speed command. If there is a possibility of this, the rotation speed of the rotating roll may be detected and calibrated by the control unit A.

In the pelletizer of the second aspect of the invention and the fifth aspect of the invention embodying the same, the pellet length is controlled in addition to the above-mentioned control of the pellet diameter. The pelletizer of the fourth aspect of the invention controls the length of pellets, and the apparatus is similar to the pelletizer of the fifth aspect of the invention. The pellet length is determined by the rotation speed ratio between the rotating roll and the rotating blade. However, the rotation speed of the rotating roll is
It varies depending on the control of the pellet diameter. Therefore, in the pelletizers of the fourth and fifth inventions, the rotation speed ratio between the rotating roll and the rotating blade is calculated from the set value of the pellet length, and an appropriate rotating speed signal of the rotating roll is input,
A control system for controlling the rotation speed of the rotary blade based on this and the rotation speed ratio and controlling the pellet length was additionally provided.

The setter B or C for setting the desired pellet length may be of the same type as the pellet diameter setter A. The rotation speed of the rotating roll is detected by a known rotary encoder, proximity switch, photoelectric switch, micro switch, tacho generator, or the like, and is output to the control unit B or C as a pulse or an analog signal. Further, instead of the rotation speed of the rotation roll, the optimum rotation speed command signal of the rotation roll for controlling the pellet diameter may be directly input from the control unit A to the control unit C via the receiving terminal. The latter does not require measurement of the rotation speed of the rotating roll,
Economical, but generally less accurate than the former. In the control unit B or C, the rotation speed ratio between the rotating roll and the rotating blade is calculated from the set value of the pellet length, and the rotating speed of the rotating blade is calculated from the rotating speed of the rotating roll and / or the command optimum rotating speed. Then, the rotation speed command signal of the rotary blade is output. Further, it is convenient for operation to provide a correction setting device B or C for minute dimension correction during operation. The configuration of the drive unit of the rotary blade conforms to that of the drive unit of the rotary roll. Depending on the configuration of the drive unit for the rotary blade, it is also possible to attach a tachometer to the rotary blade and read the rotational speed with the control unit B or C to perform speed calibration.

[0015]

EFFECTS OF THE INVENTION By adopting the pellet size control method for a pelletizer of the present invention or a pelletizer using the pellet size control method, a desired pellet diameter and / or pellet length can be obtained without requiring a skilled operator as in the prior art. The pellets can be cut. In particular, it is effective for size control and labor saving at the start or end of the operation, and the pellet manufacturing process can be automated and unmanned. That is, if a desired pellet diameter and / or pellet length is set in the setting device of the pelletizer of the present invention, pellets having a desired size can be manufactured. The equipment required for this is mainly a control system that does not require special equipment, and does not require a large cost. If necessary, minute dimension correction can be easily performed without stopping the operation. It contributes to increase the yield of normal pellets.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an example of an embodiment of a pelletizer of a third invention that embodies the first invention.

FIG. 2 is a schematic diagram of an embodiment example of a pelletizer of the fourth invention.

FIG. 3 is a schematic diagram of an example of an embodiment of a pelletizer of the fifth invention that embodies the second invention.

[Explanation of symbols]

1: Extruder 2: Cooling tank 3: Plastic strand 4: Pelletizer 5: Pinch roll 6: Rotating roll 7: Running surface 8: Fixed blade 9: Rotating blade 10: Pellet

Claims (5)

[Claims] 1. A molten plastic extruded in a strand form from an extruder is cooled and solidified, and the plastic strand is taken up by a take-up roll consisting of a rotating roll and a pinch roll for pressing the strand, and comprises a rotary blade and a fixed blade. In a pelletizer that feeds to the cutting section and cuts, detects the displacement of the pinch roll, compares it with the desired pellet diameter, and optimizes the rotating roll to eliminate the deviation between the desired pellet diameter and the displacement value of the pinch roll. A pellet diameter control method for a pelletizer, which comprises controlling the rotation speed to control the pellets cut to a desired diameter. 2. The pellet diameter control method according to claim 1 is used to control the pellet diameter, and the rotational speed ratio between the rotary roll and the rotary blade to be set in order to cut the strand into a desired length. To calculate the rotational speed of the rotary blade from the calculated rotational speed ratio by measuring the rotational speed of the rotary roll, controlling the rotational speed of the rotary blade to the obtained rotational speed, the desired pellets cut A pellet size control method for a pelletizer, characterized by controlling the diameter and length. 3. A molten plastic extruded in a strand form from an extruder is cooled and solidified, and the plastic strand is taken up by a take-up roll consisting of a rotating roll and a pinch roll for pressing the strand, and comprises a rotary blade and a fixed blade. In a pelletizer that sends to the cutting part, cuts and pelletizes, a setter A that sets the desired pellet diameter, a displacement meter that detects and transmits the displacement of the pinch roll, and a setter that inputs the signal from the displacement meter. Comprising a control unit A for comparing the set value of A and outputting an optimum rotation speed command signal of the rotation roll for eliminating the deviation, and a drive unit for the rotation roll that follows the optimum rotation speed command signal, The displacement of the pinch roll is detected, the rotating roll is controlled to the optimum rotation speed by comparing with the set pellet diameter, and the cut pellets are controlled to the desired diameter. Pelletizer, characterized in that a control system is provided for. 4. A molten plastic extruded in a strand form from an extruder is cooled and solidified, and a plastic strand is taken up by a take-up roll consisting of a rotating roll and a pinch roll for pressing the strand, and comprises a rotary blade and a fixed blade. In a pelletizer that sends to the cutting unit, cuts and pelletizes, a setter B that sets the desired pellet length, a tachometer that measures and sends the rotation speed of the rotating roll, and a set value of the pellet length. Calculate the rotation speed ratio of the rotating roll and the rotating blade from, input the rotation speed signal of the rotating roll,
It consists of a control unit B that calculates the rotation speed of the rotary blade and outputs a rotation speed command signal for the rotary blade, and a drive unit for the rotary blade that follows the optimum rotation speed command signal from the control unit B. Setting the pellet length Calculate the rotation speed ratio of the rotating roll and the rotating blade from the value, and control the rotating speed of the rotating blade by this rotating speed ratio and the input rotating speed signal of the rotating roll,
A pelletizer characterized by having a control system for controlling the pellets cut to a desired length. 5. The pelletizer according to claim 3, wherein a setter C for setting a desired pellet length, a tachometer for measuring and transmitting the rotation speed of the rotating roll, and / or the pelletizer according to claim 3. The rotation speed ratio between the rotating roll and the rotary blade is calculated from the receiving terminal of the optimum rotation speed command signal and the setting value of the pellet length, and the rotation speed signal of the rotating roll and / or the optimum rotation speed command signal is input to rotate. It consists of a control unit C that calculates the rotation speed of the blade and outputs a rotation speed command signal for the rotary blade, and a drive unit for the rotary blade that follows the optimum rotation speed command signal from the control unit C. Calculate the rotation speed ratio between the rotating roll and the rotary blade from, and control the rotation speed of the rotating blade by this rotation speed ratio and the input rotation speed signal of the rotating roll,
4. The pelletizer according to claim 3, further comprising a control system for controlling the pellets cut to have a desired length.