CN102621196A - Online measuring method for mixing uniformity and cooling crystallization uniformity of extruded material - Google Patents

Abstract

The invention discloses an online measurement method for mixing uniformity and cooling crystallization uniformity of extruded materials. At least one plate capacitor is arranged at the outlet of the extruded material on the extruder, and two electrodes of the plate capacitor are respectively located at the extruded On both sides of the material, during the extrusion of the extruded material, measure the capacitance value of the plate capacitor and determine the mixing uniformity or cooling crystallization uniformity of the extruded material from the functional relationship between the capacitance value and the dielectric constant of the mixed extruded material. The method of the present invention utilizes the principle that the variation of the capacitance value reflects the variation of the dielectric constant of the mixed extruded material between the two electrodes of the capacitor, and evaluates the mixing of the extruded material by measuring the variation of the capacitance value of the plate capacitors on both sides of the extruded material of the extruder. Uniformity and cooling crystallization uniformity are conducive to online monitoring of the quality of plastic products.

Description

An online measurement method for mixing uniformity and cooling crystallization uniformity of extruded materials

technical field

The invention relates to an extruder device used for plastic products, in particular to an online measurement method for the mixing uniformity and cooling crystallization uniformity of extruded materials on the extruder.

Background technique

The extruder is a device used to process polymer plastic products. The extrusion process refers to the plasticization of polymer (plastic) particles into a uniform melt through the extrusion system in the barrel, and the pressure established during this process Next, the process of being continuously extruded by the screw head, the extrusion process includes steps such as feeding, melt plasticization, and screw extrusion. Although this process lasts for a short period of time, the state of the melt in the extruder changes greatly. These variations have a decisive influence on the quality of the final product.

In recent years, the quality requirements of plastic products have been increasing, and faster and more reliable online measurement and control methods are needed in the processing process. In the production process, these control methods need to record the changes of various quality parameters as early as possible. In the extrusion production process, the existing technology for measuring the quality of extruded products is mainly off-line point measurement, such as the polymer products that will be produced Take it out for component analysis, mechanical performance experiment, thickness and density measurement experiment, etc. However, although these measurement methods can obtain product quality results, if a problematic product is detected, the information that needs to be fed back to adjust production parameters based on these problems is already several hours later, which is far behind the control of real-time production , At this time, it has already led to the waste of tons of products, causing considerable economic losses.

The current online measurement methods of the extrusion production line mainly include online measurement of the temperature and pressure inside the barrel. However, none of these can directly reflect the final quality of the product, and the amount of information provided is extremely limited. For example, the Chinese patent "Method and device for measuring the temperature of plasticized plastic at the outlet of the extruder" with application number 200910206586.6 discloses a method of measuring the temperature of the plastic by using the propagation velocity of the medium sound wave of the material to be extruded method and device, but only limited to online temperature or pressure testing, and cannot measure quality parameters such as thickness uniformity, density uniformity, mixing uniformity, or cooling crystallization uniformity that reflect the quality of plastic products, and thus cannot directly reflect the final quality of plastic products. quality. In polymer plastic products made of mixed materials, the uniformity of pellets after mixing is the direct quality parameter of polymer extrusion products, while the mechanical properties of polymer materials are mainly determined by the uniformity of crystallization in the cooling crystallization process. Decide. Therefore, in the case of mixing and processing two polymer materials, it is necessary to monitor the mixing uniformity of the extruded material and the cooling crystallization uniformity online.

Contents of the invention

The technical problem to be solved by the present invention is to provide an online measurement method for mixing uniformity of extruded materials on an extruder.

Another technical problem to be solved by the present invention is to provide an online measurement method for cooling crystallization uniformity of extruded materials on an extruder.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

An online measurement method for mixing uniformity of extruded materials, which is applied to an extruder. At least one plate capacitor is arranged at the outlet of the extruded material on the extruder, and the two electrodes of the plate capacitor are respectively located on the two sides of the extruded material. On the other hand, the extruded material is a mixed extruded material including two polymer materials, the flat capacitor is located between the extrusion head of the extruder and the cooling water tank, the capacitance value of the flat capacitor is measured and the capacitance value and the mixed The function of the dielectric constant of the extruded material determines the mixing uniformity of the mixed extruded material.

Further as a preferred embodiment, measuring the capacitance value of the plate capacitor comprises the following steps:

The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module;

converting the analog voltage value into a digital quantity through an analog-to-digital conversion module;

Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module;

The capacitance value of the plate capacitor is obtained according to the collected voltage value digital quantity and the linear relationship between the voltage value and the capacitance value.

；上式中C_x为平板电容器的电容值，为挤出物料上部空间的电容值，

为挤出物料下部空间的电容值，δ为挤出物料厚度，ε₀为空气的介电常数，ε₁₂为混合挤出物料介电常数，d为上面电极到挤出物料间的距离，S为两电极的相对面积，D为两电极间的相对距离。 Further as a preferred embodiment, the functional relationship between the capacitance value of the flat panel capacitor and the dielectric constant of the mixed extrusion material is:

; In the above formula, C _x is the capacitance value of the plate capacitor, is the capacitance value of the upper space of the extruded material,

is the capacitance value of the lower space of the extruded material, δ is the thickness of the extruded material, ε ₀ is the dielectric constant of air, ε ₁₂ is the dielectric constant of the mixed extruded material, d is the distance between the upper electrode and the extruded material, S is the relative area of the two electrodes, and D is the relative distance between the two electrodes.

Further as a preferred embodiment, the measuring method comprises the following steps:

The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module;

converting the analog voltage value into a digital quantity through an analog-to-digital conversion module;

Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module;

Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module;

The mixing uniformity of the extruded material is determined according to the digital value of the collected voltage value and the functional relationship between the voltage value obtained by the capacitance-voltage conversion module and the dielectric constant of the mixed extruded material.

As a further preferred embodiment, it also includes the step of feeding back the digital quantity collected by the collection module to the control system of the extruder.

An online measurement method for cooling and crystallization uniformity of extruded materials, which is applied to extruders. At least one flat capacitor is arranged at the outlet of extruded materials on the extruder, and the two electrodes of the flat capacitors are respectively located on the sides of the extruded materials. On both sides, the extruded material is a mixed extruded material including two polymer materials, and the flat capacitor is located between the cooling water tank of the extruder and the tractor. The function of the dielectric constant of the extruded material determines the cooling crystallization uniformity of the mixed extruded material.

Further as a preferred embodiment, measuring the capacitance value of the plate capacitor comprises the following steps:

The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module;

converting the analog voltage value into a digital quantity through an analog-to-digital conversion module;

Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module;

The capacitance value of the plate capacitor is obtained according to the collected voltage value digital quantity and the linear relationship between the voltage value and the capacitance value.

；上式中C_x为平板电容器的电容值，

为挤出物料上部空间的电容值，

为挤出物料下部空间的电容值，δ为挤出物料厚度，ε₀为空气的介电常数，ε₁₂为混合挤出物料介电常数，d为上面电极到挤出物料间的距离，S为两电极的相对面积，D为两电极间的相对距离。 Further as a preferred embodiment, the functional relationship between the capacitance value of the flat panel capacitor and the dielectric constant of the mixed extrusion material is:

; In the above formula, C _x is the capacitance value of the plate capacitor,

is the capacitance value of the upper space of the extruded material,

is the capacitance value of the lower space of the extruded material, δ is the thickness of the extruded material, ε ₀ is the dielectric constant of air, ε ₁₂ is the dielectric constant of the mixed extruded material, d is the distance between the upper electrode and the extruded material, S is the relative area of the two electrodes, and D is the relative distance between the two electrodes.

Further as a preferred embodiment, the measuring method comprises the following steps:

The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module;

converting the analog voltage value into a digital quantity through an analog-to-digital conversion module;

Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module;

Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module;

According to the digital value of the collected voltage value and the functional relationship between the voltage value obtained by the capacitance voltage conversion module and the dielectric constant of the mixed extrusion material, the cooling crystallization uniformity of the extruded material is determined.

As a further preferred embodiment, it also includes the step of feeding back the digital quantity collected by the collection module to the control system of the extruder.

The beneficial effects of the present invention are: the online measurement method for the mixing uniformity of extruded materials of the present invention uses the change of the capacitance value of the plate capacitor to reflect the principle of the mixing uniformity of the extruded materials between the two electrodes of the plate capacitor, through the extrusion head of the extruder Set a plate capacitor between the cooling water tank and measure the change of its capacitance value to evaluate the mixing uniformity of the extruded material. This measurement method can realize the online measurement of the mixing uniformity of the mixed extruded material, and the parameters of the mixing uniformity Feedback to the extruder control system is beneficial to improve the quality of plastic products during the production process.

Another beneficial effect of the present invention is: the online measurement method for cooling and crystallization uniformity of extruded materials in the present invention uses the principle that the change of the capacitance value of the plate capacitor reflects the crystallization uniformity of extruded materials in the process of cooling and crystallization. A plate capacitor is installed between the water tank and the tractor to measure the change of its capacitance value to evaluate the uniformity of cooling crystallization of the extruded material, so as to monitor the quality of plastic products; further feedback the parameters reflecting the uniformity of cooling crystallization to the extruder The control system is conducive to improving the quality of plastic products in the production process.

Description of drawings

The specific embodiment of the present invention will be further described below in conjunction with accompanying drawing:

Fig. 1 is the structural principle diagram of plastic product quality online measuring device on extruder of the present invention;

Fig. 2 is the structural representation of plate capacitor in measuring device of the present invention;

Fig. 3 is a schematic diagram of the position of the plate capacitor in the embodiment of the online measurement method for mixing uniformity and cooling crystallization uniformity on the extruder of the present invention;

Fig. 4 is a schematic diagram of the principle of measuring the capacitance value of a plate capacitor in the measuring method of the present invention.

Detailed ways

Before the description of the measurement method of the present invention, the on-line measurement device for the quality of plastic products on the extruder used to implement the measurement method of the present invention will be introduced in detail.

Referring to Fig. 1, a plastic product quality online measuring device on an extruder includes a flat panel capacitor 10 for measuring the extruded material quality parameters on the extruder, and two electrodes of the flat capacitor are positioned at both sides of the extruded material, so The two electrodes of the flat panel capacitor 10 respectively lead a wire 30 to be connected to a capacitance measuring unit 20. The capacitance measuring unit 20 is used to monitor the variation trend of the capacitance value between the two electrodes of the flat panel capacitor 10 in real time. The capacitance value of the extruded material is drawn to draw the capacitance change curve of the extruded material, which provides control parameter data for the closed-loop control system.

Preferably, referring to Fig. 1, the capacitance measuring unit 20 includes a capacitance-voltage conversion module 21 for converting the capacitance value measured by the plate capacitor 10 into an analog voltage value, and the capacitance-voltage module 21 is connected with an analog voltage value The analog-to-digital conversion module 22 for converting to digital quantities is connected to a collection module 23 that continuously collects digital quantities from the analog-to-digital conversion module 22 .

Referring to Fig. 2, the plate capacitor 10 is designed based on the capacitance principle, including two symmetrical electrodes 11 made of metal plates, when the extrusion process did not take place, the dielectric layer between the two electrodes 11 was air 12; When the extrusion process occurs, a dielectric layer composed of extruded materials 13 such as polymer melt is contained between the two electrodes 11 .

When the extrusion process occurs, referring to Figure 4, set δ as the thickness of the extruded material, d as the distance between the upper electrode of the plate capacitor and the extruded material, S as the relative area of the two electrodes of the plate capacitor, and D as the plate capacitor The relative distance between the two electrodes, C ₁ is the capacitance value of the upper space of the extruded material, C ₂ is the capacitance value of the extruded material, C ₃ is the capacitance value of the lower space of the extruded material; the capacitance value of the plate capacitor is C _x . When the extrusion process occurs, the capacitance value C _x is calculated as:

 

为挤出物料上部空间的电容值，其中ε₀为挤出物料的介电常数；

为挤出物料的电容值，其中为挤出物料的介电常数，δ为挤出物料的厚度；

为挤出物料下部空间的电容值。 In Equation 1 above,

is the capacitance value of the upper space of the extruded material, where _ε0 is the dielectric constant of the extruded material;

is the capacitance value of the extruded material, where is the dielectric constant of the extruded material, and δ is the thickness of the extruded material;

It is the capacitance value of the space under the extruded material.

When the extruded material is a mixed extruded material including two polymer materials, the uniformity of the mixing of the two polymer material particles is a direct quality parameter of the extruded polymer product. Assuming that the dielectric constants of the two mixed extrusion materials are ε ₁ and ε ₂ respectively, and the dielectric constant of the mixed extrusion material is ε ₁₂ , then the capacitance value C _x of the plate capacitor is related to the dielectric constant of the mixed extrusion material ε ₁₂ The functional relationship is:

It can be seen from formula 2 that when the influence of other quality parameters on the capacitance value _Cx is negligible, when the two materials are mixed evenly, the dielectric constant ε ₁₂ of the mixed extrusion material should not change much, so the capacitance value _Cx should be becoming steady.

Referring to Fig. 3, in a preferred embodiment of the present invention, a flat plate capacitor is arranged at a first position 41 between the extrusion head 43 and the cooling water tank 44 of the extruder, and the first position 41 between the cooling water tank 44 and the tractor 45 Another flat capacitor is provided at the second position 42 . During the extrusion process, the capacitance value of the plate capacitor at the first position 41 reflects whether the extruded material is heated and mixed in the extrusion process in the barrel:

，对于一个对固定的系统来说，上式中m、n均为定值，因此经转换后的电压值V_x与电容值C_x成线性关系； Capacitance-to-voltage conversion module 21 measures the capacitance value of the flat panel capacitor 10 at the first position 41 and converts it into an analog voltage output, the output analog voltage and the capacitance value are in a linear relationship, and the voltage value output by the capacitance-to-voltage conversion module 21 is set to V _x , capacitance value

, for a fixed system, both m and n in the above formula are fixed values, so the converted voltage value V _x is linearly related to the capacitance value C _x ;

The analog-to-digital conversion module 22 converts the received analog voltage value into a digital quantity;

Acquisition module 23 carries out real-time acquisition to described voltage value digital quantity;

The capacitance value of the plate capacitor is obtained according to the collected voltage value digital quantity and the linear relationship between the voltage value and the capacitance value.

According to the functional relationship between the capacitance value C _x determined in formula 2 and the dielectric constant ε ₁₂ of the mixed extrusion material, the change of ε ₁₂ is calculated, which reflects the change of the corresponding mixing uniformity of the extruded material.

Since the converted voltage value _Vx has a linear relationship with the capacitance value _Cx , the thickness measurement method of the present invention can also directly measure the mixing uniformity of the extruded material from the voltage value _Vx . The steps of the measurement method include:

Convert the capacitance value detected by the plate capacitor into an analog voltage value through a capacitance voltage conversion module 21;

The analog voltage value is converted into a digital quantity through an analog-to-digital conversion module 22;

Collect the digital quantity output by the analog-to-digital conversion module 22 in real time through a collection module 23;

According to the digital value of the collected voltage value and the functional relationship between the voltage value V _x and the dielectric constant ε ₁₂ of the mixed extrusion material, the change of ε ₁₂ is calculated, thus reflecting the change of the mixing uniformity of the corresponding extruded material .

The extruded material enters the cooling water tank 44 after coming out of the extrusion head 43. After the extruded material is cooled and crystallized, when it flows through the plate capacitor at the second position 42 between the cooling water tank 44 and the tractor 45, it is connected with the measuring barrel In the same principle as the uniformity of internal mixing, the cooling and crystallization uniformity of the extruded material can be evaluated by measuring the capacitance value of the plate capacitor at the second position 42. If the cooling crystallization is uniformly mixed, the capacitance value tends to be stable.

Those skilled in the art can understand that the metal plates of the two electrodes 11 of the flat panel capacitor 10 are electrically isolated from each other to form a capacitor. Therefore, in this embodiment, the two electrodes 11 of a flat capacitor are fixed to the first position 41 by an insulating material. On both sides in the radial direction, two electrodes 11 of another plate capacitor are fixed to both sides in the radial direction of the second position 42 through insulating materials. Of course, in addition to fixing the two electrodes 11 of the flat panel capacitor 10 on the extruder through insulating materials, the electrodes 11 can also be fixed and placed on the corresponding positions on both sides of the extruder by means of an external support, as described in the first embodiment in this embodiment. The radial both sides of the first position 41 and the radial both sides of the second position 42; Further, the position of the two electrodes 11 of the plate capacitor 10 can also be adjusted by the external support, thereby adjusting the relative distance between the two electrodes 11 of the plate capacitor 10 or adapting Different heights of the extruder.

In order to realize the monitoring of the capacitance value of the plate capacitor 10, a lead 30 is respectively drawn out on the two electrodes 10 of the plate capacitor 10, and the lead 30 is welded on the back of the electrode 10, and a lead 30 is extended and connected to the capacitance measurement One pole of the capacitive voltage conversion module 21 in the unit 20 is extended and connected to the other pole of the capacitive voltage conversion module 21 by another wire 30 .

Preferably, in addition to displaying the mixing uniformity and cooling crystallization uniformity index of the extruded material through the display device, the present invention can also feed back the digital value of the voltage value obtained by the acquisition module 23 to the extruder control system 50 .

The extruder control system 50 continuously collects and records the digital feedback voltage value. According to the capacitance value detected at the first position 41, the control of the mixing uniformity of the extruded material in the barrel can be realized. When the change of the capacitance value exceeds When the preset threshold value is set, it means that the mixing uniformity of the extruded material is not up to standard, and the production parameters need to be adjusted; according to the capacitance value detected at the second position 42, the control of the uniformity of cooling crystallization in the cooling water tank can be realized. When the capacitance value at the second position fluctuates greatly, it means that the uniformity of the cooling and crystallization process of the extruded material is not up to standard, and the extrusion control system 50 can control the cooling and crystallization of the extruded material in real time by adjusting parameters such as water tank temperature and cooling time. sex.

The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the described embodiments, and those skilled in the art can also make various equivalent deformations or replacements without violating the spirit of the present invention. These equivalent modifications or replacements are all within the scope defined by the claims of the present application.

Claims (10)

1. An online measurement method for mixing uniformity of extruded materials, which is applied to an extruder, and at least one flat capacitor is arranged at the outlet of the extruded materials on the extruder, and two electrodes of the flat capacitor are located at the extruded materials respectively. on both sides, it is characterized in that the extruded material is a mixed extruded material comprising two polymer materials, the flat capacitor is located between the extrusion head of the extruder and the cooling water tank, and the capacitance value of the flat capacitor is measured And the mixing uniformity of the mixed extruded material is determined by the functional relationship between the capacitance value and the dielectric constant of the mixed extruded material. 2. a kind of extrusion material mixing uniformity online measurement method according to claim 1 is characterized in that, measuring the capacitance value of described flat capacitor comprises the following steps: The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module; converting the analog voltage value into a digital quantity through an analog-to-digital conversion module; Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module; The capacitance value of the plate capacitor is obtained according to the collected voltage value digital quantity and the linear relationship between the voltage value and the capacitance value. 3. a kind of extruded material mixing homogeneity online measurement method according to claim 1, is characterized in that: the function relation of the electric capacity value of described plate capacitor and mixed extruded material dielectric constant is:

; In the above formula, C _x is the capacitance value of the plate capacitor,

is the capacitance value of the upper space of the extruded material,

is the capacitance value of the lower space of the extruded material, δ is the thickness of the extruded material, ε ₀ is the dielectric constant of air, ε ₁₂ is the dielectric constant of the mixed extruded material, d is the distance between the upper electrode and the extruded material, S is the relative area of the two electrodes, and D is the relative distance between the two electrodes. 4. A method for online measurement of mixing uniformity of extruded materials according to claim 1, characterized in that: the measurement method comprises the following steps: The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module; converting the analog voltage value into a digital quantity through an analog-to-digital conversion module; Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module; Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module; The mixing uniformity of the extruded material is determined according to the digital value of the collected voltage value and the functional relationship between the voltage value obtained by the capacitance-voltage conversion module and the dielectric constant of the mixed extruded material. 5. The online measurement method for mixing uniformity of extruded materials according to claim 4, further comprising the step of feeding back the digital quantity collected by the collection module to the extruder control system. 6. An online measurement method for cooling and crystallization uniformity of extruded materials, which is applied to extruders. At least one flat capacitor is arranged at the outlet of extruded materials on the extruder, and the two electrodes of the flat capacitors are respectively located at the extruded Both sides of the material, characterized in that the extruded material is a mixed extruded material comprising two polymer materials, the flat capacitor is located between the cooling water tank of the extruder and the tractor, and the capacitance value of the flat capacitor is measured And the cooling crystallization uniformity of the mixed extruded material is determined by the functional relationship between the capacitance value and the dielectric constant of the mixed extruded material. 7. a kind of extruded material cooling crystallization homogeneity online measurement method according to claim 6 is characterized in that, measuring the capacitance value of described flat capacitor comprises the following steps: The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module; converting the analog voltage value into a digital quantity through an analog-to-digital conversion module; Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module; The capacitance value of the plate capacitor is obtained according to the collected voltage value digital quantity and the linear relationship between the voltage value and the capacitance value. 8. A method for online measurement of cooling and crystallization uniformity of extruded materials according to claim 6, characterized in that: the functional relationship between the capacitance value of the flat panel capacitor and the dielectric constant of the mixed extruded materials is:

; In the above formula, C _x is the capacitance value of the plate capacitor,

is the capacitance value of the upper space of the extruded material,

is the capacitance value of the lower space of the extruded material, δ is the thickness of the extruded material, ε ₀ is the dielectric constant of air, ε ₁₂ is the dielectric constant of the mixed extruded material, d is the distance between the upper electrode and the extruded material, S is the relative area of the two electrodes, and D is the relative distance between the two electrodes. 9. A method for online measurement of cooling crystallization uniformity of extruded material according to claim 6, characterized in that: the measurement method comprises the following steps: The capacitance value detected by the plate capacitor is converted into an analog voltage value through a capacitance voltage conversion module; converting the analog voltage value into a digital quantity through an analog-to-digital conversion module; Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module; Collecting the digital quantity output by the analog-to-digital conversion module in real time through a collection module; According to the digital value of the collected voltage value and the functional relationship between the voltage value obtained by the capacitance voltage conversion module and the dielectric constant of the mixed extrusion material, the cooling crystallization uniformity of the extruded material is determined. 10 . The online measurement method for cooling and crystallization uniformity of extruded materials according to claim 9 , further comprising the step of feeding back the digital quantities collected by the collection module to the extruder control system. 11 .

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