CN101762639A - Mixed state ultrasound on-line monitoring method in polymer production process - Google Patents

Abstract

The invention discloses an ultrasonic on-line monitoring method for a mixed state in a polymer production process, belonging to the technical field of industrial detection. The present invention obtains the amplitude of the ultrasonic echo signal reflecting the mixing state of the polymer in real time through the ultrasonic sensor installed on the single-screw or twin-screw extruder; the temperature and temperature of the molten polymer in the barrel obtained by using the temperature and pressure sensor at the corresponding position Pressure is used as a reference quantity, and the echo amplitude is corrected and normalized by rank filtering and low-pass filtering methods; the correlation coefficient matching method is used to complete the position matching of the amplitude curve in different periods; the ultrasonic echo amplitude deviation of the corresponding position in different periods is calculated, Through the relationship between the amplitude and the polymer content, the mixing state of the polymer can be identified; this method can monitor the mixing state of the polymer in the process of extrusion in real time, and provide state parameters for the product quality and process adjustment of the polymer.

Description

Ultrasonic on-line monitoring method of mixing state in polymer production process

Technical field: the invention belongs to the technical field of industrial detection, and specifically relates to an ultrasonic on-line monitoring method of the mixing state in the polymer production process.

Background technique:

Polymer blends are a mixture of two or more homopolymers or copolymers. Due to their superior performance, they have become an indispensable class of important materials in the fields of national economy and national defense. The blending processing method of the polymer is mainly to mix through a single (twin) screw extruder. The solid polymer enters from the feed port, changes from solid to molten state in the barrel of the screw extruder, and is extruded from the discharge port of the extruder into the molding tool. The quality of the final extruded product is related to the performance ratio of raw materials, the temperature and pressure in the barrel, the screw speed of the extruder, the screw structure and other factors, and it is also reflected in the different parts of the mixture in the screw extruder barrel during the production process mixed state. Therefore, in the production process, the online detection of the state of the polymer mixing process is of great significance. The detection results can be used to adjust the production process in time, reduce product waste and waste pollution, and speed up the product production cycle.

At present, the polymer production line mainly guides the production by monitoring the temperature and pressure in the barrel, and the methods of obtaining the mixing state information are offline, such as performing physical and chemical analysis on the mixed samples obtained through special sample collectors installed in different parts. analysis, observation of the mixing process through glass windows installed on the extruder, etc. None of these methods can give real-time and accurate mixing information, and cannot meet the needs of production, which seriously restricts the development of my country's polymer processing industry.

Ultrasonic testing technology uses ultrasonic waves to penetrate the blended polymer melt, and its echo amplitude, sound velocity, attenuation coefficient and acoustic impedance will change with the melting state of the blend. This principle can be used for polymers in screw extrusion. Mixed state detection at different locations in the process. When polymers are mixed, their molten state temperature in the extruder is generally above 100°C, while general ultrasonic probes can only work at room temperature, which affects the application of ultrasonic technology in this area.

Invention content:

The purpose of the present invention is to provide an ultrasonic on-line monitoring method of the mixing state in the polymer production process, which can realize real-time monitoring and state identification of the mixing state of the polymer in different parts of the extruder on the polymer extrusion production line and production analysis.

The ultrasonic on-line monitoring method of the mixing state in the polymer production process provided by the present invention is characterized in that: the amplitude of the ultrasonic echo signal reflecting the mixing state of the polymer is obtained in real time through an ultrasonic sensor installed on a single-screw or twin-screw extruder; The temperature and pressure of the molten polymer in the barrel obtained by the temperature and pressure sensor at the corresponding position are taken as a reference, and the echo amplitude is corrected and normalized by using the rank filtering and low-pass filtering methods; Position matching during the period; calculate the amplitude deviation of the ultrasonic echo at the corresponding position during different periods, and identify the mixing state of the polymer through the relationship between the amplitude and the polymer content.

According to on-site monitoring requirements, temperature and pressure sensors and ultrasonic sensors can be installed on different parts of the screw extruder to monitor the polymer mixing status of multiple parts at the same time, so as to realize the monitoring of the polymer mixing process.

The ultrasonic sensor is composed of an ultrasonic probe, an acoustic coupling rod and a water cooling device; the center frequency of the ultrasonic probe is 2.5 MHz, and the excitation pulse width is 1 μs; the acoustic coupling rod is made of polyether ether ketone, and the main part is a cylindrical structure. The thread structure is closely connected with the screw extruder barrel, the top end is in adhesive contact with the ultrasonic probe, and the bottom end is tangent to the inner wall of the extruder barrel; the constant temperature water in the water cooling device is fully in contact with the acoustic wave coupling rod.

Beneficial effects of the present invention:

(1) Use the ultrasonic echo amplitude, the pressure and temperature of the polymer in the barrel to monitor the mixing state of the polymer in different parts of the barrel online, without being affected by human subjective factors, and play a role in timely guiding and adjusting the production process It can effectively improve production efficiency and shorten the research and development cycle of new products.

(2) The ultrasonic sensor has a water cooling device and a threaded installation structure, which is suitable for working in a high temperature and high pressure environment during the production and extrusion of polymers;

(3) The acoustic wave coupling rod is made of polyether ether ketone, which improves the transmittance of the sound wave at the interface between the coupling rod and the polymer, effectively suppresses the trailing noise of the ultrasonic wave propagating in the cylindrical rod, and improves the signal-to-noise of the characteristic echo Compare;

(4) The bottom end of the acoustic wave coupling rod is tangent to the inner wall of the barrel, which can accurately monitor the mixing state of the polymer without affecting the normal operation of the polymer extruder;

(5) Using the ultrasonic echo deviation at the same position in different cycles as the characteristic quantity, effectively avoiding the influence caused by the screw structure;

(6) Using the temperature and pressure of the molten polymer as a reference, the rank filtering and low-pass filtering methods are used to correct and normalize the ultrasonic echo amplitude, so as to avoid the influence of the temperature and pressure of the molten polymer on the ultrasonic echo signal. Influence;

(7) Use the correlation coefficient matching method to complete the position matching during different periods of the amplitude curve, avoiding the accurate comparison of the corresponding position due to the deviation of the sampling point and the screw position caused by the uneven screw speed;

(8) Combined with signal processing technology and industrial control technology, it can achieve real-time monitoring of the mixing state of multiple different parts of the polymer mixing process, which is easy to expand; it can save, display and analyze the monitoring data, which is suitable for the development of new polymer products. application.

Description of drawings:

Figure 1 is a diagram of the sensor installation location;

In Fig. 1, (1a) sensor installation front view, (1b) circumferential sectional view of sensor installation place;

Fig. 2 is the propagation and echo schematic diagram of ultrasonic wave in polymer;

In Fig. 2, (2a) schematic diagram of propagation principle, (2b) schematic diagram of ultrasonic echo;

Fig. 3 is the B-scan diagram of ultrasonic sensor characteristic echo signal;

In Fig. 3, (3a) position I, (3b) position II, (3c) position III, (3d) position IV;

Fig. 4 is a histogram of characteristic signal amplitude deviation;

The specific implementation method:

The present invention uses ultrasonic echo feature quantity to characterize polymer mixing state information, combined with temperature and pressure in extruder barrel, through signal processing method, adopts computer processing technology, realizes real-time on-line monitoring of polymer in production extrusion process mixed state in .

The ultrasonic on-line monitoring method of the mixing state in the polymer production process obtains the amplitude of the ultrasonic echo signal reflecting the mixing state of the polymer in real time through the ultrasonic sensor installed on the single-screw or twin-screw extruder; the temperature and pressure sensor obtained by using the corresponding position The temperature and pressure of the molten polymer in the barrel are used as reference quantities, and the echo amplitude is corrected and normalized by rank filtering and low-pass filtering methods; the correlation coefficient matching method is used to complete the position matching of the amplitude curve in different periods; During the period, the ultrasonic echo amplitude deviation at the corresponding position can be used to identify the mixing state of the polymer through the relationship between the amplitude and the polymer content.

According to on-site monitoring requirements, temperature and pressure sensors and ultrasonic sensors are installed on different parts of the screw extruder to monitor the polymer mixing status of multiple parts at the same time, so as to realize the monitoring of the polymer mixing process.

The ultrasonic sensor is composed of an ultrasonic probe, an acoustic coupling rod and a water cooling device; the center frequency of the ultrasonic probe is 2.5 MHz, and the excitation pulse width is 1 μs; the acoustic coupling rod is made of polyether ether ketone, and the main part is a cylindrical structure. The thread structure is closely connected with the screw extruder barrel, the top end is in adhesive contact with the ultrasonic probe, and the bottom end is tangent to the inner wall of the extruder barrel; the constant temperature water in the water cooling device is fully in contact with the acoustic wave coupling rod.

As shown in Figure 1a, temperature and pressure sensors and ultrasonic sensors are installed on different parts of the barrel of the screw extruder, and the relative positions of the temperature, pressure sensor and ultrasonic sensor in the circumferential direction are shown in Figure 1b. In Figure 1b, TPT and UT are respectively Indicates temperature pressure sensor and ultrasonic sensor. The computer control system simultaneously collects the temperature and pressure of multiple temperature and pressure sensors and the ultrasonic signals of ultrasonic sensors, and extracts the characteristic echo amplitude reflecting the mixing state of the polymer; The ultrasonic echo amplitude within a period of time, and then perform rank filtering to filter out the amplitude jump due to the change of the screw structure, and then use the low-pass filtering method to extract the trend of the amplitude change, normalize the echo amplitude, and convert this period of time The amplitude curves of multiple periods within the cycle are matched by using the correlation coefficient matching method; according to the results of the position matching, the amplitude deviation of the ultrasonic echo at the same position is calculated, and the comprehensive deviation is obtained; finally, through the relationship between the amplitude and the polymer content, The mixed state of the polymer is identified using the integrated deviation and displayed. In practical applications, a control module can be added to realize feedback control of the polymer extrusion process as required.

The extraction of ultrasonic characteristic echoes is based on the principle of ultrasonic propagation in Figure 2. The sound wave propagates through the acoustic coupling rod and molten polymer, and generates echoes L1 and L2 at the coupling rod/polymer interface and polymer/screw interface. The typical echo signal received by the probe is shown in Figure 3, and A2 in Figure 3 is the ultrasonic characteristic echo amplitude.

Applications:

Mixing trials of 90% low density polyethylene (LDPE) and 10% calcium carbonate were performed in a single screw extruder. The inner diameter of the barrel is φ90mm, the screw length is 1600mm, and the screw speed is 10r/min; the pressure and temperature sensors are PT124B/PT124G; the same ultrasonic sensors are installed at the four positions in Figure 1 for detection, and Figure 4 shows the characteristic cycles of the four positions Wave signal B scan diagram, it can be seen from the figure that the amplitude of the characteristic echo detected at position I fluctuates greatly, while the characteristic echo signal at position IV is the most stable. Figure 5 lists the four position detection features The comparison of the relative variance of the echo amplitude (the ratio of the variance to the mean value, indicating the relative deviation) shows that the more stable the characteristic echo signal is, the smaller the amplitude variance will be as the mixing progresses. According to this feature, two kinds of Mixed state of the polymer.

Claims (3)

1. mixed state ultrasound on-line monitoring method in the production processes of polyalcohol is characterized in that: by being installed in the amplitude that sonac on single screw rod or the double screw extrusion machine obtains the ultrasound echo signal of reflection polymer mixed state in real time; The temperature and pressure of melt polymkeric substance adopts correction of order filtering and low-pass filtering method and normalization echo amplitude as with reference to amount in the machine barrel that the temperature and pressure transmitter of use correspondence position obtains; Utilization related coefficient matching process is finished the location matches between the amplitude curve different cycles; Calculate the ultrasonic echo amplitude deviation of correspondence position between different cycles, by the relation of amplitude and polymer content, the admixture of identification polymkeric substance.

2. mixed state ultrasound on-line monitoring method in the production processes of polyalcohol according to claim 1, it is characterized in that: according to the monitoring requirements at scene, different parts is installed temperature and pressure transmitter and sonac on screw extruder respectively, monitor the polymer mixed state at a plurality of positions simultaneously, realize the monitoring of polymer mixed process.

3. mixed state ultrasound on-line monitoring method in the production processes of polyalcohol according to claim 1 is characterized in that: said sonac is made up of ultrasonic probe, sound wave coupling bar and water cooling plant; The centre frequency of ultrasonic probe is 2.5MHz, and excitation pulse is 1 μ s; The sound wave coupling bar is material with the polyetheretherketone, and main part is a column structure, adopts helicitic texture closely to be connected with screw extruder barrel, and the top contacts with ultrasonic probe is bonding, and bottom and extruder barrel inwall are tangent; Thermostatted water in the water cooling plant fully contacts with the sound wave coupling bar.

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