Method for measuring aperture of sand core filter funnel

Abstract

The invention relates to the technical field of laboratory detection solid-liquid separation, in particular to a sand core filter funnel aperture measuring method, which comprises the following steps: connecting measuring devices of filter plate holes of a sand core filter funnel, and dripping a layer of purified water thin water film with a preset thickness on a filter plate of the sand core filter funnel by using a burette; starting an air pressure device to stably and slowly pressurize the suction flask, observing the surface of the filter plate from above, recording the pressure value of the digital pressure device at the moment when a first bubble appears, and calculating the average pressure value of n tests; when bubbles uniformly appear on the surface of the filter plate, recording the pressure value of the digital pressure device at the moment, calculating the average pressure value of n tests, and calculating the maximum aperture and the average aperture of the filter plate; the uncertainty of the sand core funnel aperture measurement method is evaluated, then the measurement accuracy is calculated and judged, the maximum aperture and the average aperture of the filter plate hole of the filter funnel can be measured, the measurement accuracy is judged, and the accuracy and the reliability of the sand core funnel aperture measurement method are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of laboratory detection solid-liquid separation, and in particular to a method for measuring the aperture of a sand core filter funnel. Background Art

[0002] The sand core filter funnel is a commonly used filtration equipment in laboratories. It is mainly composed of filter plates, filter membranes and sand cores. It is a tool used to separate and filter sediments and microorganisms of different particle sizes to achieve the purpose of clarifying liquids. In recent years, due to the high filtration accuracy, fast filtration speed and easy operation of the sand core filter funnel, it has been widely used in laboratory research and production in the fields of chemistry, biology, and medicine. In many biological, chemical, and highway experiments, it is necessary to measure the pore size of the sand core filter funnel, because the funnel caliber and capacity caliber affect the filtration speed, and the capacity determines the amount of liquid that can be processed at one time. However, depending on the usage scenario, the general pore size specification of the sand core filter funnel is 0.6 ~30 The pore size is small and the structure is special. The minimum measurement size of the standard gauge block circulating in the industry is 0.5mm, so it cannot be measured directly and can only rely on the manufacturer's introduction. However, some tests require knowing the size of the maximum pore size and the average pore size. Otherwise, it will cause significant impacts such as inaccurate test data due to inaccurate manufacturer's nominal pore size. Therefore, a method for accurately measuring the pore size of the sand core filter funnel filter plate is urgently needed. Summary of the invention

[0003] The present invention provides a sand core filter funnel pore diameter measurement method, which is intended to solve the defects of the above-mentioned prior art.

[0004] The present invention adopts the following technical solutions: A method for measuring the pore size of a sand core filter funnel comprises the following steps: S1: The sand core filter funnel is installed on a matching suction filter bottle so as to be in a sealed state, the side wall of the suction filter bottle is sealedly connected to the air pressure device through a pipeline, and a digital pressure device for displaying the pressure value is also connected to the sealed pipeline; an electron microscope for real-time observation of the filter plate inside the sand core filter funnel is installed on the top of the sand core filter funnel, and the electron microscope and the digital pressure device are both connected to a computer; S2: The test environment temperature is set to 20°C ± 1°C, the relative humidity is 50%, and a thin film of pure water with a preset thickness is dripped onto the filter plate of the sand core filter funnel using a burette; S3: Start the air pressure device to steadily and slowly pressurize the suction filtration bottle, observe the surface of the filter plate from above, and record the pressure value P1 of the digital pressure device when the first bubble appears, and calculate the average pressure of n tests as ΔP1; S4: Continue to pressurize, and when bubbles appear evenly on the surface of the filter plate, record the pressure value P2 of the digital pressure device at this time, and calculate the average pressure of n tests as ΔP2; S5: Calculate the maximum pore size and average pore size of the filter plate of the sand core filter funnel; S6: Uncertainty evaluation of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u introduced by the repeatability of the sand core filter funnel aperture measurement 1 , Standard uncertainty u introduced by the resolution of digital pressure gauge 2 The standard uncertainty u introduced by the maximum allowable error of the digital pressure gauge 3 ; Then comprehensively calculate and judge the accuracy of the maximum pore diameter and average pore diameter measurement.

[0005] In some embodiments, in S2, before using a burette to drip a thin film of pure water of a preset thickness onto the filter plate of the sand core filter funnel, the air tightness check of the experimental equipment is performed: close the ventilation valve leading to the suction bottle, start the air pressure device to pass a certain amount of gas, and when the digital pressure count value shows 1.5 kPa ~ 2.5 Pa, close the precision control valve, observe the value change of the digital pressure device, if the pressure change value within 2 minutes is not greater than 1% of the initial pressure value, the air tightness meets the requirements.

[0006] In some embodiments, in S2, a thin water film of pure water having a thickness of 1 cm to 2 cm is dripped onto the filter plate of the sand core filter funnel using a burette.

[0007] In some embodiments, in S3, the air pressure device is started to steadily and slowly pressurize the suction filtration bottle, and the surface of the filter plate is observed from above. When the first bubble appears, the pressure value P1 of the digital pressure device is recorded at this time, and the average pressure of n tests is calculated as ΔP1, which is converted into the average value of the maximum pore size. max Before the test, the effect of ambient temperature on the aperture results is tested: if the ratio of the calculated aperture to the aperture under the same working conditions at the test ambient temperature is less than the preset value, the test ambient temperature meets the test requirements.

[0008] In some embodiments, while detecting the effect of ambient temperature, the effect of liquid column difference is also detected: According to the liquid pressure formula (1): p = ρgh (1) Where: p is pressure, unit is Pa; ρ is the liquid density, in kg / m 3 ; g is the acceleration due to gravity, in N / kg, h is the liquid column difference, in m; Calculate the influence of the preset liquid column difference on the aperture measurement results: If the ratio of the calculated aperture to the aperture under the same working conditions is less than the preset value, the test liquid column difference meets the test requirements.

[0009] In some embodiments, in S5, the maximum pore size and average pore size of the filter plate are calculated by formula (2): (2) Where: ΔP is the additional pressure, unit is Pa; d is the pore size of the bubble, in m; γ is the surface tension of the liquid, in N / m; When ΔP is ΔP1, the bubble pore size is the maximum pore size d max , unit is m; When ΔP is ΔP2, the bubble pore size is the average pore size , unit is m.

[0010] In some embodiments, in S6, the measurement accuracy of the maximum pore size of the sand core filter funnel is determined as follows: Standard uncertainty u introduced by repeatability of pore size measurement of sand core filter funnel 1 : Measure the maximum pore size of the sand core filter funnel, that is, read the pressure value when the first bubble appears. Measure ten times in total and calculate the average pressure value according to formula (3): (3) Where: u 1 The standard uncertainty introduced for the repeatability of the sand core filter funnel aperture measurement, in Pa; n is the total number of measurements; p i is the pressure value measured for the i-th time, in Pa; is the average value of n pressure values, in Pa; Standard uncertainty u introduced by the resolution of the preset grade digital pressure gauge 2 : The standard uncertainty introduced by the preset grade digital pressure gauge resolution is evaluated by Class B, and the preset grade digital pressure gauge resolution is selected as P 3 Pa, obeys uniform distribution, then the pressure is calculated according to formula (4): (4) In the formula, u 2 The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa; P 3 is the resolution of the digital pressure gauge, in Pa; Standard uncertainty u introduced by the maximum allowable error of the preset grade digital pressure gauge 3 : The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge is evaluated by Class B. The error of the preset grade digital pressure gauge is ±P 4 Pa, take the half width as P 4 Pa, the pressure is calculated according to formula (5): (5) In the formula, u 3 The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge, in Pa; P 4 is the error of the digital pressure gauge, in Pa; Calculate the combined standard uncertainty according to formula (6): : (6) According to formula (2), ,length is the maximum pore size uncertainty of the sand core filter funnel, in um; The maximum aperture expansion uncertainty u of the sand core filter funnel is calculated according to formula (7): u (7) Where, u is the uncertainty of the maximum aperture expansion of the sand core filter funnel, in um; K is the sensitivity coefficient; is the maximum pore size uncertainty of the sand core filter funnel, in um; When the ratio of u to the maximum pore size of the sand core filter funnel is less than 1%, the measurement method of the maximum pore size is accurate, otherwise it is inaccurate.

[0011] In some embodiments, in S6, the measurement accuracy of the average pore size of the sand core filter funnel is determined as follows: Standard uncertainty introduced by repeatability of average pore size measurement of sand core filter funnel : The average pore size of the sand core filter funnel was measured, that is, the pressure value read when bubbles appeared evenly on the filter plate surface. The pressure was measured ten times in total and the average pressure value was calculated according to formula (8): (8) Where: The standard uncertainty introduced for the repeatability of the average pore size measurement of the sand core filter funnel, in Pa; n is the total number of measurements; is the pressure value measured for the i-th time, in Pa; is the average value of n pressure values, in Pa; Standard uncertainty introduced by the resolution of the preset grade digital pressure gauge : The standard uncertainty introduced by the preset grade digital pressure gauge resolution is evaluated by Class B, and the preset grade digital pressure gauge resolution is selected as Pa, obeys uniform distribution, then the pressure is calculated according to formula (9): (9) In the formula, The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa; is the resolution of the digital pressure gauge, in Pa; Standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge : The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge is evaluated by Class B. The error of the preset grade digital pressure gauge is ± 4 Pa, take the half width as 4 Pa, the pressure is calculated according to formula (10): (10) In the formula, The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge, in Pa; is the error of the digital pressure gauge, in Pa; Calculate the combined standard uncertainty according to formula (11): : (11) According to formula (2), , is the uncertainty of the average pore size of the sand core filter funnel, in um; According to formula (12), the uncertainty of the average pore size expansion of the sand core filter funnel is calculated. : (12) In the formula, is the expanded uncertainty of the average pore size of the sand core filter funnel, in um; k is the sensitivity coefficient; is the uncertainty of the average pore size of the sand core filter funnel, in um; when When the ratio of the average pore size to the sand core filter funnel is less than 1%, the average pore size measurement method is accurate, otherwise it is inaccurate. Beneficial Effects

[0012] The invention discloses a method for measuring the pore size of a sand core filter funnel. Compared with the prior art, the invention has the following advantages: The measuring method of the present invention is based on the principle of liquid surface tension. A thin film of pure water with a preset thickness is dripped onto the filter plate of the sand core filter funnel with a burette, and then the air pressure device is started to steadily and slowly pressurize the suction filtration bottle. The surface of the filter plate is observed through a microscope, and the pressure value P1 of the digital pressure device when the first bubble appears and the pressure value P2 when bubbles appear evenly on the filter plate surface are recorded; according to the maximum bubble pressure method, that is, when the force generated on the aperture end face is slightly greater than the surface tension of the sand core funnel aperture liquid, the bubble escapes from the sand core funnel aperture, and this additional pressure is proportional to the surface tension and inversely proportional to the curvature radius of the bubble. When the additional pressure is maximum, the curvature radius R is equal to the aperture radius r of the sand core funnel. The maximum aperture and average aperture of the sand core funnel can be calculated according to the Laplace formula, and then the standard uncertainty u introduced by calculating the repeatability of the sand core filter funnel aperture measurement is calculated. 1 , Standard uncertainty u introduced by the resolution of digital pressure gauge 2 The standard uncertainty u introduced by the maximum allowable error of the digital pressure gauge 3 The accuracy of the maximum pore size and average pore size measurement is comprehensively calculated and judged to ensure the accuracy of the sand core funnel pore size measurement method. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below, which constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions explain the present invention and do not constitute improper limitations on the present invention. Figure 1 A flow chart of a method for measuring the pore size of a sand core filter funnel provided in an embodiment of the present invention; Figure 2-Figure 11 The pressure image provided by the embodiment of the present invention when the first bubble appears is measured repeatedly ten times; Figure 11-Figure 21 The pressure image provided in the embodiment of the present invention when bubbles appear evenly on the filter plate surface is measured repeatedly ten times. DETAILED DESCRIPTION

[0014] The following is a description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0015] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0016] like Figure 1 - Fig.21 As shown, the technical solution of the present invention: A method for measuring the pore size of a sand core filter funnel comprises the following steps: S1: The sand core filter funnel is mounted on a matching suction filter bottle so as to be in a sealed state, the side wall of the suction filter bottle is sealedly connected to the air pressure device through a pipeline, a digital pressure device for displaying the pressure value is also connected to the sealed pipeline, an electron microscope for real-time observation of the filter plate inside the sand core filter funnel is mounted on the top of the sand core filter funnel, and the electron microscope and the digital pressure device are both connected to a computer; S2: The test environment temperature is set to 20°C ± 1°C, the relative humidity is 50%, and a thin film of pure water with a preset thickness is dripped onto the filter plate of the sand core filter funnel using a burette; S3: Start the air pressure device to steadily and slowly pressurize the suction filtration bottle, observe the surface of the filter plate from above, and record the pressure value P1 of the digital pressure device when the first bubble appears, and calculate the average pressure of n tests as ΔP1; S4: Continue to pressurize, and when bubbles appear evenly on the surface of the filter plate, record the pressure value P2 of the digital pressure device at this time, and calculate the average pressure of n tests as ΔP2; S5: Calculate the maximum pore size and average pore size of the filter plate of the sand core filter funnel; S6: Uncertainty evaluation of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u introduced by the repeatability of the sand core filter funnel aperture measurement 1 , Standard uncertainty u introduced by the resolution of digital pressure gauge 2 The standard uncertainty u introduced by the maximum allowable error of the digital pressure gauge 3; Then comprehensively calculate and judge the accuracy of the maximum pore diameter and average pore diameter measurement.

[0017] The preferred embodiments disclosed in the present invention are as follows: Figure 1-Figure 21 As shown: The invention discloses a method for measuring the pore size of a sand core filter funnel, comprising the following steps: S1: The sand core filter funnel is installed on a matching suction filter bottle so as to be in a sealed state, the side wall of the suction filter bottle is sealed and connected to the air pressure device through a pipeline, and a digital pressure device for displaying the pressure value is also connected to the sealed pipeline; an electron microscope for real-time observation of the filter plate inside the sand core filter funnel is installed on the top of the sand core filter funnel, and the electron microscope and the digital pressure device are both connected by computer control; The digital pressure device of this test uses a digital pressure gauge with a grade of 0.05 and a range of (0-40) Pa. The air pressure device can be a manual pressure pump with a micro-pressure adjustment function or an electric fully automatic pressure calibrator. This test uses a fully automatic pressure calibrator. S2: The test environment temperature is set to (20±1)℃ and the relative humidity is 50%; First, check the air tightness of the experimental equipment: close the ventilation valve leading to the suction bottle, start the air pressure device to pass a certain amount of gas, and when the digital pressure count value shows 1.5kPa~2.5Pa, close the precision control valve and observe the value change of the digital pressure device. If the pressure change value within 2 minutes is not greater than 1% of the initial pressure value, the air tightness meets the requirements; otherwise, it does not meet the requirements and needs to reconnect the system until it is qualified.

[0018] A thin film of pure water is dripped from the upper end of the sand core filter funnel to the filter plate using a burette. The thickness of the thin film of water is set to 1 cm to 2 cm, and 1 cm is selected in this embodiment.

[0019] S3: Start the fully automatic pressure calibrator to steadily and slowly pressurize the suction bottle, observe the surface of the filter plate through a microscope, and record the pressure value P1 of the digital pressure gauge when the first bubble appears. Calculate the average pressure of n tests as ΔP1, and convert it into the average value of the maximum pore size. max .

[0020] This method is based on the maximum bubble pressure method. A special measuring device is designed and manufactured to measure the pore size (including the maximum pore size and the average pore size) of the filter plate of the sand core filter funnel. The outer surface of the sand core filter funnel is dipped in water and sealed and placed on the matching suction bottle. The suction bottle is in a sealed state. Pure water with a known surface tension is dropped into the sand core filter funnel to form a film. The suction bottle is slowly pressurized by a fully automatic pressure calibrator. At this time, a pressure is applied to the surface of the funnel aperture, generating a pressure difference (Δp = p 大气 - p 系统 ), when the force generated on the aperture end face is slightly greater than the surface tension of the sand core funnel aperture liquid, the bubble will escape from the sand core funnel aperture. This additional pressure is proportional to the surface tension and inversely proportional to the radius of curvature of the bubble. The relationship is: Laplace formula (2) : (2) Where: ΔP is the additional pressure, unit is Pa; d is the curvature diameter of the bubble, in m; γ is the surface tension of the liquid, in N / m; If the aperture of the sand core funnel is very small, the bubbles formed are basically spherical. When the bubbles begin to form, the surface is almost flat, and the radius of curvature is the largest at this time. As the bubbles form, the radius of curvature gradually decreases until a hemispherical shape is formed. At this time, the radius of curvature R is equal to the aperture radius r of the sand core funnel filter plate, and the radius of curvature reaches the minimum value. According to formula (2), the additional pressure reaches the maximum value at this time. The additional pressure is the pressure value displayed by the digital pressure gauge. As the bubbles grow further, R increases and the additional pressure decreases until the bubbles escape. That is, the additional pressure is the largest when R=r. The aperture 2r of the sand core funnel filter plate can be calculated.

[0021] Calculate the average pressure of n tests as ΔP1, and convert it into the average value of the maximum pore diameter max Before, first conduct the environmental temperature impact test: Since the experiment was conducted at an ambient temperature of (20±1)℃, the relationship between temperature and pure water tension is: at 19℃, =0.07290 N / m; at 20°C, =0.07275 N / m; at 21°C, =0.07259 N / m; The maximum tension difference Δγ=0.07290 N / m -0.07259 N / m =0.00031N / m, the additional pressure is P1, P1=3.10 Pa, converted to the aperture by Laplace formula, it is about 0.4 , accounting for 0.426% of the aperture under the same working conditions, which is less than the preset limit of 1%. Therefore, the influence of ambient temperature can be ignored and this environment meets the test requirements.

[0022] This embodiment is tested three times, and the additional pressure value P1 is shown in Table 1: Table 1

[0023] Calculate the average additional pressure ΔP1, ΔP1=(3.13+3.10+3.07) / 3=3.1(kPa)=3100Pa, According to formula (2), =0.073 N / m, which is the surface tension of pure water, and we get max =94

[0024] While testing the impact of ambient temperature, we also tested the impact of liquid column difference: According to the liquid pressure formula (1): P = ρgh (1) Where: P is pressure, unit is Pa; ρ is the liquid density, in kg / m 3 ; g is the acceleration due to gravity, in N / kg, h is the liquid column difference, in m; In this test, the sand core funnel liquid column difference h is taken as 0.01m, g is 9.8 N / kg, and ρ is 1kg / m 3 , P is calculated to be 0.1Pa, which is about 0.003 after conversion to pore diameter It accounts for 0.003% of the pore diameter under the same working conditions, which is less than the preset limit of 1%, that is, 0.003%<1%. Therefore, the influence of the liquid column difference meets the test requirements.

[0025] S4: Continue to pressurize, and when bubbles appear evenly on the filter plate surface, record the pressure value P2 of the digital pressure gauge at this time, and calculate the average pressure of n tests as ΔP2; convert it into the average value of uniform pore size 平均 .

[0026] This embodiment is tested three times, and the additional pressure value P2 is shown in Table 1: S5: Calculate the average additional pressure ΔP2, ΔP2=(4.00+4.10+4.18) / 3=4.09 (Pa), According to formula (2), =0.073 N / m, which is the surface tension of pure water, and we get 平均 =71

[0027] S6: Uncertainty assessment of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u introduced by the repeatability of the sand core filter funnel aperture measurement 1 , Standard uncertainty u introduced by the resolution of digital pressure gauge 2The standard uncertainty u introduced by the maximum allowable error of the digital pressure gauge 3 ; Then comprehensively calculate and judge the accuracy of the maximum pore diameter and average pore diameter measurement.

[0028] Standard uncertainty u introduced by repeatability of pore size measurement of sand core filter funnel 1 : The maximum pore size of the sand core filter funnel was measured, that is, the maximum pressure value read when the microscope showed the first bubble, and a total of ten measurements were made, see Table 2 and Figure 2-Figure 11 , Point A in the figure is the pressure value corresponding to the digital pressure gauge when the first bubble appears: Table 2

[0029] Calculate the average pressure according to formula (3): (3) Where: u 1 The standard uncertainty introduced for the repeatability of the sand core filter funnel aperture measurement, in Pa; n is the total number of measurements; p i is the pressure value measured for the i-th time, in Pa; is the average value of n pressure values, in Pa; After calculation, u 1 =63 Pa.

[0030] Standard uncertainty u introduced by the resolution of the preset grade digital pressure gauge 2 : In this embodiment, a 0.05-level digital pressure gauge is selected. The standard uncertainty introduced by the resolution is evaluated using Class B. The resolution P3 of the 0.05-level digital pressure gauge is 0.001 Pa, which is uniformly distributed. According to JJF 1059 "Evaluation and Expression of Measurement Uncertainty", the pressure is calculated according to formula (4): (4) In the formula, u 2 The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa; P 3 is the resolution of the digital pressure gauge, in Pa; After calculation, u 2 =0.6 Pa.

[0031] Standard uncertainty u introduced by the maximum allowable error of the preset grade digital pressure gauge 3 : In this embodiment, a 0.05-level digital pressure gauge is selected, and the standard uncertainty introduced by the maximum allowable error adopts Class B assessment. The error of the 0.05-level digital pressure gauge is ±P 4 Pa, MPE ± 20Pa, take the half width as P 4 Pa is calculated according to formula (5): (5) In the formula, u 3 The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge, in Pa; P 4 is the error of the digital pressure gauge, in Pa; In this embodiment, the 0.05-level digital pressure gauge MPE±20Pa takes the half-width as 20Pa. After calculation, u 3 =12 Pa.

[0032] Calculate the combined standard uncertainty according to formula (6): : (6) but =64 Pa.

[0033] According to formula (2), ,length is the maximum pore size uncertainty of the sand core filter funnel, in um; after calculation, the maximum pore size uncertainty of the sand core filter funnel is 2um.

[0034] The maximum aperture expansion uncertainty u of the sand core filter funnel is calculated according to formula (7): u (7) Where, u is the uncertainty of the maximum aperture expansion of the sand core filter funnel, in um; K is the sensitivity coefficient; is the maximum pore size uncertainty of the sand core filter funnel, in um; According to the requirements of JJF1059.1 "Determination and Expression of Measurement Uncertainty", k=2, the uncertainty of the maximum aperture calibration result is: u =2×2=4 (μm) u / d 最大 =0.043, that is, when the ratio of the uncertainty of the maximum aperture calibration result to the maximum aperture of the sand core filter funnel is less than the preset value 1, the maximum aperture measurement method is accurate.

[0035] Determination of the measurement accuracy of the average pore size of the sand core filter funnel: Standard uncertainty introduced by repeatability of average pore size measurement of sand core filter funnel : The average pore size of the sand core filter funnel was measured, that is, the pressure value read when bubbles appeared evenly on the filter plate surface. A total of ten measurements were made, see Table 3 and Figure 12-Figure 21 : Table 3

[0036] Calculate the average pressure according to formula (8): (8) Where: The standard uncertainty introduced for the repeatability of the average pore size measurement of the sand core filter funnel, in Pa; n is the total number of measurements; is the pressure value measured for the i-th time, in Pa; is the average value of n pressure values, in Pa; After calculation, Pa.

[0037] Standard uncertainty introduced by the resolution of the preset grade digital pressure gauge : In this embodiment, a 0.05-level digital pressure gauge is selected. The standard uncertainty introduced by the resolution of the digital pressure gauge is evaluated by Class B. The resolution of the 0.05-level digital pressure gauge is selected as Pa, obeys uniform distribution, then the pressure is calculated according to formula (9): (9) In the formula, The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa; is the resolution of the digital pressure gauge, in Pa; The resolution of a 0.05-level digital pressure gauge is 1Pa. After calculation, =0.6 Pa.

[0038] Standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge : In this embodiment, a 0.05-level digital pressure gauge is selected. The standard uncertainty introduced by the maximum allowable error of the digital pressure gauge adopts Class B assessment. The error of the preset level digital pressure gauge is ± 4 Pa, take the half width as 4 Pa, the pressure is calculated according to formula (10): (10) In the formula, The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge, in Pa; is the error of the digital pressure gauge, in Pa; 0.05 grade digital pressure gauge MPE ± 20 Pa, take the half width as 20 Pa, then =12 Pa.

[0039] Calculate the combined standard uncertainty according to formula (11): : (11) but =58 Pa.

[0040] According to formula (2), , is the uncertainty of the average pore size of the sand core filter funnel, in um; converted to the uncertainty of the average pore size of the sand core filter funnel is 2um; According to formula (12), the uncertainty of the average pore size expansion of the sand core filter funnel is calculated. : (12) In the formula, is the expanded uncertainty of the average pore size of the sand core filter funnel, in um; K is the coefficient; is the uncertainty of the average pore size of the sand core filter funnel, in um; According to the requirements of JJF1059.1 "Determination and Expression of Uncertainty in Measurement", k=2, the uncertainty of the average pore size of the sand core filter funnel is: =2×2=4 (μm) / d 平均 =0.056, that is, when the ratio of the uncertainty of the maximum pore size calibration result to the average pore size of the sand core filter funnel is less than the preset value 1, the average pore size measurement method is accurate.

[0041] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for measuring the pore size of a sand core filter funnel, characterized in that: The steps include: S1: The sand core filter funnel is mounted on a matching suction filter bottle so as to be in a sealed state, the side wall of the suction filter bottle is sealedly connected to the air pressure device through a pipeline, a digital pressure device for displaying the pressure value is also connected to the sealed pipeline, an electron microscope for real-time observation of the filter plate inside the sand core filter funnel is mounted on the top of the sand core filter funnel, and the electron microscope and the digital pressure device are both connected to a computer; S2: The test environment temperature is set to 20°C ± 1°C, the relative humidity is 50%, and a thin film of pure water with a preset thickness is dripped onto the filter plate of the sand core filter funnel using a burette; S3: Start the air pressure device to steadily and slowly pressurize the suction filtration bottle, observe the surface of the filter plate from above, and record the pressure value P1 of the digital pressure device when the first bubble appears, and calculate the average pressure of n tests as ΔP1; S4: Continue to pressurize, and when bubbles appear evenly on the surface of the filter plate, record the pressure value P2 of the digital pressure device at this time, and calculate the average pressure of n tests as ΔP2; S5: Calculate the maximum pore size and average pore size of the filter plate of the sand core filter funnel; S6: Uncertainty assessment of the sand core funnel aperture measurement method: First, calculate the standard uncertainty u1 introduced by the repeatability of the sand core filter funnel aperture measurement, the standard uncertainty u2 introduced by the digital pressure gauge resolution, and the standard uncertainty u3 introduced by the maximum allowable error of the digital pressure gauge; then comprehensively calculate and judge the accuracy of the maximum aperture and average aperture measurement.

2. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: Before dripping a thin film of pure water of preset thickness onto the filter plate of the sand core filter funnel with a burette in S2, perform an air tightness check on the experimental equipment: close the vent valve leading to the suction bottle, start the air pressure device to pass a certain amount of gas, and when the digital pressure count value shows 1.5kPa~2.5Pa, close the precision control valve, observe the value change of the digital pressure device, and if the pressure change value within 2 minutes is not greater than 1% of the initial pressure value, the air tightness meets the requirements.

3. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: In S2, a burette is used to drip pure water onto the filter plate of the sand core filter funnel until the thickness of the thin water film is 1 cm to 2 cm.

4. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: In S3, the air pressure device is started to steadily and slowly pressurize the suction bottle, and the surface of the filter plate is observed from above. When the first bubble appears, the pressure value P1 of the digital pressure device is recorded at this time. The average pressure of n tests is calculated as ΔP1, which is converted into the average value of the maximum pore size. max Before the test, the effect of ambient temperature on the aperture results is tested: if the ratio of the calculated aperture to the aperture under the same working conditions under the test ambient temperature is less than the preset value, the ambient temperature meets the test requirements.

5. The method for measuring the pore size of a sand core filter funnel according to claim 4, characterized in that: While testing the impact of ambient temperature, we also tested the impact of liquid column difference: According to the liquid pressure formula (1): p = ρgh (1) Where: p is pressure, unit is Pa; ρ is the liquid density, in kg / m 3 ; g is the acceleration due to gravity, in N / kg, h is the liquid column difference, in m; Calculate the influence of the preset liquid column difference on the aperture measurement results: If the ratio of the calculated aperture to the aperture under the same working conditions is less than the preset value, the test liquid column difference meets the test requirements.

6. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: In S5, the maximum pore size and average pore size of the filter plate are calculated using formula (2): (2) Where: ΔP is the additional pressure, unit is Pa; d is the pore size of the bubble, in m; γ is the surface tension of the liquid, in N / m; When ΔP is ΔP1, the bubble pore size is the maximum pore size d max , unit is m; When ΔP is ΔP2, the bubble pore size is the average pore size , unit is m.

7. The method for measuring the pore size of a sand core filter funnel according to claim 1, characterized in that: In S6, the accuracy of the measurement of the maximum aperture of the sand core filter funnel is determined as follows: The standard uncertainty u1 introduced by the repeatability of the sand core filter funnel aperture measurement is: Measure the maximum pore size of the sand core filter funnel, that is, read the pressure value when the first bubble appears. Measure ten times in total and calculate the average pressure value according to formula (3): (3) Where: u1 is the standard uncertainty introduced by the repeatability of the sand core filter funnel aperture measurement, the unit is Pa; n is the total number of measurements; p i is the pressure value measured for the i-th time, in Pa; is the average value of n pressure values, in Pa; The standard uncertainty u2 introduced by the resolution of the preset grade digital pressure gauge is: The standard uncertainty introduced by the preset grade digital pressure gauge resolution is evaluated by Class B. The preset grade digital pressure gauge resolution is selected as P3Pa, which obeys the uniform distribution. The pressure is calculated according to formula (4): （4） Where, u2 is the standard uncertainty introduced by the resolution of the digital pressure gauge, in Pa; P3 is the resolution of the digital pressure gauge, in Pa; The standard uncertainty u3 introduced by the maximum allowable error of the preset grade digital pressure gauge is: The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge is evaluated by Class B. The error of the preset grade digital pressure gauge is ±P4 Pa. The half width is taken as P4 Pa. The pressure is calculated according to formula (5): (5) Where, u3 is the standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge, in Pa; P4 is the digital pressure gauge error, in Pa; Calculate the combined standard uncertainty according to formula (6): : (6) According to formula (2), ,length is the uncertainty of the maximum pore size of the sand core filter funnel, in um; The maximum aperture expansion uncertainty u of the sand core filter funnel is calculated according to formula (7): u （7） Where, u is the uncertainty of the maximum aperture expansion of the sand core filter funnel, in um; k is the sensitivity coefficient; is the maximum pore size uncertainty of the sand core filter funnel, in um; When the ratio of u to the maximum pore size of the sand core filter funnel is less than 1%, the measurement method of the maximum pore size is accurate, otherwise it is inaccurate.

8. The method for measuring the pore size of a sand core filter funnel according to claim 7, characterized in that: In S6, the accuracy of the measurement of the average pore size of the sand core filter funnel is determined as follows: Standard uncertainty introduced by repeatability of average pore size measurement of sand core filter funnel : The average pore size of the sand core filter funnel was measured, that is, the pressure value read when bubbles appeared evenly on the filter plate surface. The pressure was measured ten times in total and the average pressure value was calculated according to formula (8): (8) Where: The standard uncertainty introduced for the repeatability of the average pore size measurement of the sand core filter funnel, in Pa; n is the total number of measurements; is the pressure value measured for the i-th time, in Pa; is the average value of n pressure values, in Pa; Standard uncertainty introduced by the resolution of the preset grade digital pressure gauge : The standard uncertainty introduced by the preset grade digital pressure gauge resolution is evaluated by Class B, and the preset grade digital pressure gauge resolution is selected as Pa, obeys uniform distribution, then the pressure is calculated according to formula (9): (9) In the formula, The standard uncertainty introduced for the resolution of the digital pressure gauge, in Pa; is the resolution of the digital pressure gauge, in Pa; Standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge : The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge is evaluated by Class B. The error of the preset grade digital pressure gauge is ± 4 Pa, take the half width as 4 Pa, then calculate according to formula (10): (10) In the formula, The standard uncertainty introduced by the maximum allowable error of the preset grade digital pressure gauge, in Pa; is the error of the digital pressure gauge, in Pa; Calculate the combined standard uncertainty according to formula (11): : (11) According to formula (2), , is the uncertainty of the average pore size of the sand core filter funnel, in um; According to formula (12), the uncertainty of the average pore size expansion of the sand core filter funnel is calculated. : （12） In the formula, is the expanded uncertainty of the average pore size of the sand core filter funnel, in um; k is the sensitivity coefficient; is the uncertainty of the average pore size of the sand core filter funnel, in um; when When the ratio of the average pore size to the sand core filter funnel is less than 1%, the average pore size measurement method is accurate, otherwise it is inaccurate.

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