Polymer melt viscosity correction method and device based on variable diameter capillary flow channel

Abstract

The application discloses a polymer melt viscosity correction method and device based on a variable-diameter capillary flow channel, and comprises a layout device, wherein polymer melt is uniformly and continuously fed into the device, an inlet pressure P1 and an outlet pressure P2 of a measuring channel are measured by a sensing assembly, and an inlet-outlet pressure difference is calculated after the outlet pressure is corrected; a shear stress τ borne by the material at the pipe wall is calculated by the inlet-outlet pressure difference w and an apparent shear rate changes the average flow rate of the polymer melt and the inlet inner diameter of the measuring channel, a relationship curve obtained by repeated measurement is obtained, so that the real shear rate of the polymer melt at the pipe wall is obtained, and the apparent viscosity of the polymer melt is obtained as the ratio of the shear stress τ w of the pipe wall and the shear rate. The application expands the apparent viscosity measurement function to the variable-diameter structure channel, realizes the measurement and correction of the polymer viscosity in the flow channel with an inclination angle, is convenient and practical, simple in method, stronger in universality, and higher in measurement precision.

Description

Technical Field

[0001] This invention relates to the field of polymer viscosity characterization, and more particularly to a method and apparatus for polymer melt viscosity correction based on a variable diameter capillary channel. Background Technology

[0002] In polymer molding processes, online detection models for melt viscosity are mainly divided into slit and capillary structures. Both structures can characterize the rheological state of materials during molding and processing, encompassing the actual processing history. The former restricts the structure's thickness, simplifying it into a quasi-two-dimensional model. The latter uses the Hagen-Poiseuille principle for calculations in cylindrical coordinates. In practical applications, especially in injection molding, slit structures are uncommon. The size and function of such structures are contradictory, leading to numerous inconveniences in structural design and limiting their application scenarios. Ultimately, offline detection methods relying on slit structures cannot meet the portable requirements for integrated material performance testing in the manufacture of precision microstructured plastic products.

[0003] Therefore, polymer viscosity measurement methods based on capillary structures have become the preferred approach. Researchers have leveraged this advantage to measure the rheological properties of polymers within the fine structures of injection molding machine nozzles or molds, integrating online viscosity characterization functions and driving the development of online polymer rheological characterization technology. However, to facilitate demolding, the runner is designed with a variable diameter structure and a certain draft angle (<3°). This angle interferes with polymer viscosity characterization, limiting the versatility of capillary viscosity detection methods. Current technology still cannot directly measure the rheological properties of polymers using the variable diameter runner structure within the mold during actual production. The application capability of online viscosity detection for polymer processing and molding based on the capillary principle still requires significant adjustments. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a polymer melt viscosity correction method and apparatus based on a variable diameter capillary channel. In a variable diameter channel with a draft angle, no other structure needs to be redesigned, normal product demolding is not affected, and no additional volume is occupied. Size effect correction is performed on the pressure at the outlet of the apparatus. By combining the variable diameter channel with the constant diameter channel, the flow state of the polymer melt can be measured.

[0005] The specific technical solution is as follows:

[0006] A method for correcting polymer melt viscosity based on a variable diameter capillary channel includes the following steps:

[0007] Step 1: Select a variable diameter capillary channel as the measurement channel, with the maximum inner diameter of the measurement channel as the reference, and the length-to-diameter ratio of the measurement channel is greater than 10;

[0008] Step 2: Introduce polymer melt into the measuring channel at a constant speed. Measure the pressure of the polymer melt on the pipe wall at the inlet of the measuring channel as P1, and the pressure of the polymer melt on the pipe wall at the outlet as P2. Correct the outlet pressure using the following expression:

[0009]

[0010] In the formula, P′2 is the corrected outlet pressure, ρ is the density of the polymer melt, v is the average flow velocity of the polymer melt at the inlet, d1 is the inlet inner diameter of the measuring channel, and d2 is the outlet inner diameter of the measuring channel.

[0011] The inlet and outlet pressure difference ΔP is calculated based on the corrected outlet pressure P′2, as shown in the following expression:

[0012]

[0013] Step 3: Treating the obtained polymer melt as a Newtonian fluid, calculate the shear stress τ borne by the material at the pipe wall using the pressure difference between the inlet and outlet. w and apparent shear rate

[0014] Step 4: Change the average flow velocity of the polymer melt and the inlet inner diameter of the measuring channel, and repeat steps 1 to 3 to obtain the average flow velocity v_lnτ of the polymer melt at different inlets. w - Relationship curve;

[0015] Step 5: Based on lnτ w - The relationship curve is used to obtain the true shear rate at the capillary wall when the polymer melt flows through the measurement channel at a fixed velocity in the variable diameter capillary channel under test.

[0016] Step 6: Obtain the apparent viscosity of the polymer melt as the shear stress τ of the pipe wall. w and shear rate The ratio of .

[0017] Furthermore, step three is specifically implemented through the following operations:

[0018] Shear stress τ borne by the material at the pipe wall w The expression is:

[0019]

[0020] In the formula, r = d1 / 2 is the inlet radius of the measurement channel; L is the length of the measurement channel;

[0021] Apparent shear rate The expression is:

[0022]

[0023]

[0024] In the formula, Here, Q represents the apparent shear rate, and Q represents the volumetric flow rate of the melt.

[0025] Furthermore, in step four, the shear rate The expression is as follows:

[0026]

[0027] In the formula, According to τ w - The relationship curve was obtained.

[0028] A polymer melt viscosity correction device based on a variable diameter capillary channel, used to implement the polymer melt viscosity correction method based on a variable diameter capillary channel, includes: a sensing component, a temperature control component, and a basic component.

[0029] The basic components include: an insulation sleeve, an outer edge layer, and a measuring channel; the measuring channel is a capillary channel with its maximum inner diameter as a reference and a length-to-diameter ratio greater than 10; the outer edge layer is arranged outside the measuring channel; the insulation sleeve is arranged outside the outer edge layer; the insulation sleeve, the outer edge layer, and the measuring channel are arranged coaxially.

[0030] The temperature control component includes a heating coil and a cooling water circuit; the heating coil is arranged on the outside of the outer edge layer, and the insulation sleeve is wrapped around the outside of the heating coil for heating the inside of the measuring channel; the flow direction of the cooling water circuit is parallel to the axis of the measuring channel, and the cooling water circuit is arranged circumferentially in the outer edge layer;

[0031] The sensing components include: an inlet temperature sensor, an inlet pressure sensor, an outlet temperature sensor, and an outlet pressure sensor; the inlet temperature sensor and the inlet pressure sensor are arranged at the inlet of the measurement channel to detect the temperature and pressure of the polymer melt flowing into the measurement channel; the outlet temperature sensor and the outlet pressure sensor are arranged at the outlet of the measurement channel to detect the temperature and pressure of the polymer melt flowing out of the measurement channel.

[0032] Furthermore, the heating coils are evenly arranged along the axial direction on the outer side of the outer edge layer to ensure uniform heating.

[0033] Furthermore, the cooling water channels are circumferentially and uniformly arranged in the outer edge layer.

[0034] The beneficial effects of this invention are:

[0035] This invention extends the apparent viscosity measurement function to variable diameter channels, enabling the measurement and correction of polymer viscosity in inclined channels. It is convenient, practical, simple, more versatile, and has higher measurement accuracy. Attached Figure Description

[0036] Figure 1 This is a front cross-sectional view of the polymer melt viscosity measuring device based on a variable diameter capillary channel according to the present invention.

[0037] Figure 2 This is a side cross-sectional view of the polymer melt viscosity measuring device based on the variable diameter capillary channel of the present invention.

[0038] Figure 3 This is a schematic diagram of the variable diameter capillary channel involved in the present invention, wherein (a) is a structure in which the inner diameter of the channel gradually increases along the flow direction, and (b) is a structure in which the inner diameter of the channel gradually decreases along the flow direction.

[0039] Figure 4 This is a schematic diagram of the polymer melt viscosity measurement and correction method based on a variable diameter capillary channel according to the present invention.

[0040] Figure 5 The average flow rate of the polymer melt at different inlets in this invention is lnτ w - The relationship curve.

[0041] In the figure, there are sensing components 1, temperature control components 2, basic components 3, inlet temperature sensor 101, inlet pressure sensor 102, outlet temperature sensor 103, outlet pressure sensor 104, heating coil 201, cooling water circuit 202, insulation jacket 301, outer edge layer 302, and measurement channel 303. Detailed Implementation

[0042] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The objectives and effects of the present invention will become clearer as a result. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0043] like Figure 1 , Figure 2 As shown, the polymer melt viscosity correction device based on variable diameter capillary channel includes: sensing component 1, temperature control component 2, and basic component 3.

[0044] Basic component 3 includes: an insulation jacket 301, an outer rim layer 302, and a measuring channel 303. The measuring channel 303 is a capillary channel; if it is of constant diameter, its length-to-diameter ratio must be greater than 10. Figure 3 As shown, if the measuring channel 303 has a variable diameter, its maximum inner diameter should be used as the reference, and the length-to-diameter ratio must be greater than 10. The outer edge layer 302 is arranged on the outside of the measuring channel 303. The heat insulation sleeve 301 is arranged on the outside of the outer edge layer 302 to isolate interference from external heat sources and to avoid the influence of the temperature control component 2 on the external environment. The heat insulation sleeve 301, the outer edge layer 302, and the measuring channel 303 are arranged coaxially.

[0045] The temperature control component 2 includes a heating coil 201 and a cooling water channel 202. The heating coil 201 is evenly arranged axially on the outside of the outer edge layer 302, and then covered with an insulation sleeve 301 to uniformly heat the inside of the measuring channel 303. The cooling water channel 202 flows parallel to the axis of the measuring channel 303 and is evenly arranged circumferentially within the outer edge layer 302. The temperature control component 2 is used to constantly regulate the temperature inside the measuring channel 303 and ensure temperature uniformity.

[0046] The sensing component 1 includes: an inlet temperature sensor 101, an inlet pressure sensor 102, an outlet temperature sensor 103, and an outlet pressure sensor 104. The inlet temperature sensor 101 and the inlet pressure sensor 102 are arranged at both ends upstream (i.e., at the inlet) of the measuring channel 303 to detect the state (i.e., temperature and pressure) of the polymer melt flowing into the measuring channel 303; the outlet temperature sensor 103 and the outlet pressure sensor 104 are arranged at both ends downstream (i.e., at the outlet) of the measuring channel 303 to detect the state of the polymer melt flowing out of the measuring channel 303.

[0047] like Figure 4 As shown, the polymer melt viscosity correction method based on variable diameter capillary channels specifically includes the following steps:

[0048] Step 1: Select a section of variable diameter capillary channel as the measurement channel 303. With the maximum inner diameter as the reference, strictly control the length-to-diameter ratio of the measurement channel 303 to be greater than 10, and arrange the sensing component 1, temperature control component 2, and basic component 3 according to the above measurement device.

[0049] Step 2: The polymer melt is accelerated from upstream of the measuring channel 303 and flows through the measuring channel 303 at a constant speed. The inlet pressure sensor 102 detects the pressure of the polymer melt on the pipe wall at the inlet of the measuring channel 303 as P1, and the outlet pressure sensor 104 detects the pressure of the polymer melt on the pipe wall at the outlet of the measuring channel 303 as P2. Using the inner diameter d1 of the inlet channel as a reference, the pressure at the outlet diameter change of the measuring channel 303 is corrected as follows:

[0050]

[0051] In the formula, P2′ is the corrected outlet pressure in MPa; ρ is the density of the polymer melt in N / m³.3 v is the average flow velocity of the polymer melt at the inlet, in m / s; d1 is the inlet inner diameter of the measuring channel 303, in m; d2 is the outlet inner diameter of the measuring channel 303, in m.

[0052] The pressure difference ΔP between the inlet and outlet (i.e., the pressure drop between the measuring channels) is calculated based on the corrected outlet pressure P2′, and the expression is as follows:

[0053]

[0054] Step 3: Calculate the rheological state of the polymer inside the micro-injection mold using the formula for calculating the shear stress of a circular tube and the Weissenberg-Rabinowtsich shear rate formula.

[0055] In this study, any polymer melt flowing through the measuring channel 303 is considered a Newtonian fluid, and the shear stress τ borne by the material at the pipe wall is calculated by measuring the pressure drop ΔP obtained by the pressure sensor. w The expression is as follows:

[0056]

[0057] In the formula, r = d1 / 2 is the inlet radius of the measurement channel 303, in meters; L is the length of the measurement channel 303, in meters.

[0058] Apparent shear rate at the tube wall It can be obtained from the volumetric flow rate Q of the polymer melt or the average flow velocity v of the polymer melt at the inlet, as shown in the following expression:

[0059]

[0060] In the formula, Apparent shear rate, in seconds. -1 Q is the volumetric flow rate of the melt, in cubic meters per second (m³). 3 / s.

[0061] The relationship between the average flow velocity v and the volumetric flow rate Q of the polymer melt at the inlet is as follows:

[0062]

[0063] Step Four: As Figure 5 As shown, based on the specific properties of the polymer melt, the flow rate of the polymer melt and the inlet inner diameter d1 of the measuring channel 303 are changed, and multiple measurements are taken (i.e., steps one to three are repeated) to obtain the average flow rate v of the polymer melt at different inlets, and lnτ w - The relationship curve.

[0064] Step 5: Based on lnτ w - The relationship curve yields the true shear rate at the capillary wall when the polymer melt flows through the measuring channel 303 at a fixed velocity within the variable-diameter capillary channel under test. The expression is as follows:

[0065]

[0066] In the formula, According to lnτ w - The relationship curve was obtained.

[0067] Step Six: Based on the shear stress τ of the pipe wall w and shear rate The apparent viscosity of a polymer melt in the mold used in measuring channel 303 is obtained.

[0068] The correction method and apparatus employed in this invention can be applied to flow channel structures with draft angles, extending viscosity measurement capabilities to variable diameter channels. It enables online characterization of the apparent viscosity of the flowing polymer melt, size effect correction for the pressure at the outlet, and correction for the polymer shear rate at the wall surface, making the measurement method more versatile. This invention eliminates the need for expensive traditional rheometers, allowing the measurement structure to be directly integrated into the polymer molding and processing equipment, making the entire testing process more efficient and concise. This invention can be used not only for the fine-structure design of injection molding molds and the study of melt flow at the barrel and nozzle, but also for viscosity measurement in industries such as materials, chemicals, pharmaceuticals, coatings, and food.

[0069] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for correcting polymer melt viscosity based on a variable diameter capillary flow channel, characterized by, The method comprises the following steps: Step one: selecting a variable-diameter capillary flow channel as a measuring channel, taking the maximum inner diameter of the measuring channel as a reference, and the length-diameter ratio of the measuring channel is greater than 10; Step two: uniformly feeding the polymer melt into the measuring channel, measuring the pressure of the polymer melt at the inlet of the measuring channel as P1, and the pressure of the polymer melt at the outlet of the measuring channel as P2; correcting the outlet pressure, and the expression is as follows: ； wherein Pout is the corrected outlet pressure, p is the density of the polymer melt, V is the average flow velocity of the polymer melt at the inlet, Din is the inner diameter of the inlet of the measuring channel, Dout is the inner diameter of the outlet of the measuring channel; According to the modified outlet pressure The pressure difference ΔP between the inlet and outlet is calculated, and is expressed by the following expression: ； Step three: The polymer melt is considered as a Newtonian fluid and the shear stress the material is subjected to at the pipe wall is calculated from the pressure difference over the inlet and outlet and the apparent shear rate ; Step four: change the average flow rate of the polymer melt and the inlet inner diameter of the measuring channel, repeat steps one to three to obtain the average flow rate of the polymer melt at different inlets The relationship curve between the average flow rate of the polymer melt and the inlet inner diameter of the measuring channel is as shown in FIG.

2. The relationship curve between the average flow rate of the polymer melt and the inlet inner diameter of the measuring channel is as shown in FIG.

2. Step five: According to the relationship curve of , the real shear rate at the wall of the pipe when the polymer melt flows through the measuring channel at a fixed flow rate is obtained. In step five, the shear rate The expression for the shear rate is as follows: ； wherein According to obtained from the relationship curve of Step six: the apparent viscosity of the polymer melt is the ratio of the shear stress of the pipe wall and the shear rate .

2. The method for correcting polymer melt viscosity based on a variable diameter capillary flow channel according to claim 1, wherein, The step three is specifically realized by the following operation: shear stress of the material at the tube wall The expression for this is: ； wherein is the entrance radius of the measurement channel; is the length of the measurement channel; apparent shear rate The expression for the apparent shear rate is: ； ； wherein is the apparent shear rate and Q is the volumetric flow rate of the melt.

3. A polymer melt viscosity correction device based on a variable diameter capillary flow channel for implementing the correction method of any one of claims 1-2, characterized in that, It comprises: a sensing assembly, a temperature control assembly, and a basic assembly; The basic assembly comprises an adiabatic sleeve, an outer edge layer, and a measuring channel; the measuring channel is a capillary channel, taking the maximum inner diameter as a reference, and the length-diameter ratio is greater than 10; the outer edge layer is arranged outside the measuring channel; the adiabatic sleeve is arranged outside the outer edge layer; the adiabatic sleeve, the outer edge layer, and the measuring channel are coaxially arranged; The temperature control assembly comprises a heating coil and a cooling water channel; the heating coil is arranged outside the outer edge layer, and the adiabatic sleeve is wrapped outside the heating coil, for heating the inside of the measuring channel; the cooling water channel is parallel to the axis of the measuring channel in flow direction, and the cooling water channel is circumferentially arranged in the outer edge layer; The sensing assembly comprises an inlet temperature sensor, an inlet pressure sensor, an outlet temperature sensor, and an outlet pressure sensor; the inlet temperature sensor and the inlet pressure sensor are arranged at the inlet of the measuring channel, for detecting the temperature and pressure of the polymer melt flowing into the measuring channel; the outlet temperature sensor and the outlet pressure sensor are arranged at the outlet of the measuring channel, for detecting the temperature and pressure of the polymer melt flowing out of the measuring channel.

4. The variable diameter capillary flow passage based polymer melt viscosity correction device of claim 3, wherein, The heating coil is uniformly arranged outside the outer edge layer in the axial direction, so that the heating is uniform.

5. The variable diameter capillary flow passage based polymer melt viscosity correction device of claim 3, wherein, The cooling water channel is uniformly arranged in the outer edge layer in the circumferential direction.

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