CN110646326A - Material fluidity test method - Google Patents
Material fluidity test method Download PDFInfo
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- CN110646326A CN110646326A CN201911046233.4A CN201911046233A CN110646326A CN 110646326 A CN110646326 A CN 110646326A CN 201911046233 A CN201911046233 A CN 201911046233A CN 110646326 A CN110646326 A CN 110646326A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N11/00—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
- G01N2203/0003—Steady
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
Abstract
The invention discloses a material fluidity test method, which comprises the following steps: providing a material fluidity testing device, sequentially placing a certain amount of sample particles into a mould and compacting the sample particles to form a sample divided into two or more layers, wherein each layer is a sample unit, compacting the sample unit of the previous layer before placing the sample particles of the sample unit of the next layer to ensure that each layer of the sample unit has uniform density, carrying out a uniaxial compression test on the sample, and calculating the fluidity of the sample. The material fluidity test method provided by the invention overcomes the problems that the existing Jenike direct shear test method is complex and the existing uniaxial compression test result is inaccurate.
Description
Technical Field
The invention relates to the technical field of mechanical tests, in particular to a material fluidity test method
Background
The increase in moisture inherent in mineral flow materials leads to increased bonding and poor flow properties, which can cause difficulties in handling and transporting the material, because some of the particulate material may adhere to the walls of the container or the flow rate may be slow due to moisture content. Therefore, it is an industry standard to monitor the flowability of bulk materials to minimize potential plugging on the transport and handling chains.
The flowability of the bulk material is controlled by the flow function, which is the unconfined yield strength σcAnd principal stress sigma1The Jenike Direct Shear Test (JDST) is widely accepted and used among various test methods for measuring flow functions. However, JDST has several disadvantages: in order to obtain reliable and repeatable results, experienced operators will perform pre-consolidation, pre-shearing and shearing procedures from which flow functions are obtained, with high requirements on the quality of the operators; moreover, JDST is very time consuming, often taking several days to complete; JDST cannot be performed in the field and must be performed in a laboratory setting to obtain accurate results. In addition, measurement errors may also occur because JDST must be performed on multiple samples.
An alternative method of testing flowability is to perform uniaxial compression tests, however, the results of uniaxial compression tests are less accurate than JDST. Uniaxial compression tests, the core of the problem is the friction of the inner walls of the mould, often referred to as the resulting principal consolidation stress σ1A non-uniform Janssen effect that decays exponentially with respect to sample depth. It would be an urgent problem for those skilled in the art to provide a simple and reliable method for testing the flowability of a material.
Disclosure of Invention
The invention aims to provide a material fluidity test method to overcome the problems of complexity and inaccurate test result of the existing material fluidity test method.
In order to achieve the above object, the present invention provides a material fluidity test method, comprising:
providing a material flowability test device;
sequentially placing a certain amount of sample particles into a mould and compacting to form a sample divided into two or more layers, wherein each layer is a sample unit, and compacting the sample unit of the previous layer before placing the sample particles of the sample unit of the next layer to ensure that each layer of the sample unit has uniform density;
the samples were subjected to uniaxial compression testing and the flowability of the samples was calculated.
Optionally, the degree of compaction of each layer sample is:
wherein: u shapenIndicating the n-th layer under-compaction, Un0Represents n0Under-compaction of the layers, n representing the number of layers, n0Denotes the first layer of the insert, nallIndicating the total number of layers.
Optionally, the cumulative mass of the inserted sample particles is:
wherein: u shapen0Representing the percentage of the first layer under-compressed, niRepresenting the number of layers i, nallDenotes the total number of layers, pdDenotes the dry bulk density, m0Indicates the initial water content, D the sample diameter, and H the height of the sample.
Optionally, there is at least one layer of said sample unit having a density value lower than the final density value of the sample.
Optionally, the density values of the sample units of each layer vary in a linear relationship.
Optionally, the density value of the first layer of the sample unit is greater than the density value of the second layer of the sample unit.
Optionally, the height of the sample unit is the same for each layer.
Optionally, the uniaxial compression test specifically includes:
applying an initial load in an axial direction of a mold of a material fluidity testing apparatus to compress the sample;
removing the sample from the mold;
applying a gradual increase in stress to the sample;
and measuring the stress value when the sample collapses.
Optionally, the uniaxial compression test comprises calculating a flow function, the flow function representing the flowability of the sample in dependence on the stress value.
Optionally, the material flowability test method comprises performing the uniaxial compression test on the samples at different initial loads.
Optionally, the uniaxial compression test comprises determining the compressibility of the sample, the compressibility of the sample being represented by a sample compressibility factor Φ:
wherein: phi denotes the sample compression coefficient, epsilon denotes the axial strain in the constrained compression test, sigma1Indicating the prevailing integrated pressure.
Optionally, the sample is iron ore, and when the sample compression coefficient Φ of the iron ore is greater than 0.152, the uniaxial compression test is performed.
The invention provides a material fluidity test method, which comprises the following steps: providing a material flowability test device; sequentially placing a certain amount of sample particles into a mould and compacting to form a sample divided into two or more layers, wherein each layer is a sample unit, and compacting the sample unit of the previous layer before placing the sample particles of the sample unit of the next layer to ensure that each layer of the sample unit has uniform density; the samples were subjected to uniaxial compression testing and the flowability of the samples was calculated. The material fluidity test method provided by the invention overcomes the problems that the existing Jenike direct shear test method is complex and the existing uniaxial compression test result is inaccurate.
Drawings
FIG. 1 is a schematic diagram of a flow function obtained using JDST;
FIG. 2 is a schematic view of a uniaxial compression test;
FIG. 3 is a graph comparing JDST and flow function obtained from a single axis compression test;
FIG. 4 is a graph showing the effect of wall friction on stress state for samples under the uniaxial compression test and JDST using Hvorslev and Roscoe face analysis;
FIG. 5 is a graphical representation of critical porosity for stress state analysis of samples under uniaxial compression test and JDST using Hvorslev and Roscoe surfaces;
FIG. 6 is a schematic diagram of a material flowability testing method according to an embodiment of the present invention;
FIG. 7 is a graphical illustration of the calculation of undercompression rate versus number of layers provided by an embodiment of the present invention;
FIG. 8 is a graph of particle size distribution for a sample provided in accordance with an embodiment of the present invention;
FIG. 9 is a graph showing the results of bulk-weight testing of samples provided in accordance with one embodiment of the present invention;
FIG. 10 is a graph comparing the flow function obtained from the test method provided by one embodiment of the present invention and a conventional uniaxial compression test;
FIG. 11 is a diagram comparing the flow function obtained from JDST contraction and the test method provided by the embodiment of the present invention;
FIG. 12 is a schematic axial stress-axial strain diagram for a uniaxial compression test provided by one embodiment of the present invention;
FIG. 13 is a graph of a flow function distribution obtained by uniaxial compression testing in Jenike flow classification according to an embodiment of the invention;
FIG. 14 is a graph of normal axial stress versus axial strain;
FIG. 15 is a graph of normal axial stress versus axial strain plotted in a quasi-linear fashion;
FIG. 16 is a graph comparing the JDST and flow functions of coal obtained from a single-axis compression test provided in accordance with one embodiment of the present invention;
FIG. 17 is a graph comparing JDST and flow functions of limestone obtained from a uniaxial compression test provided by an embodiment of the present invention;
FIG. 18 is a schematic front view of a first material fluidity testing apparatus according to an embodiment of the present invention;
FIG. 19 is a schematic top view of a first material fluidity testing apparatus according to an embodiment of the present invention;
FIG. 20 is a schematic top view of a second material fluidity testing apparatus according to an embodiment of the present invention;
wherein: 10-mould, 11-split mould, 12-hinge, 30-chassis, 40-load sensor, 50-piston, 60-bracket, 70-sample, 701-sample unit.
Detailed Description
The rapid depletion of near-surface iron ore has led to an increasing demand for deep deposits located near ground water levels and even below ground water. The increase of the inherent moisture of the mining flowing material leads to the improvement of the bonding property and the deterioration of the flowing property. Such materials have poor flow properties and can cause difficulties in handling and transporting the material, since some particulate material may adhere to the walls of the container or flow at a slower rate due to moisture content. Therefore, it is an industry standard to monitor the flowability of bulk materials to minimize potential plugging on the transport and handling chains.
The flowability of the bulk material is controlled by the flow function, FIG. 1 is a schematic flow function obtained using JDST, see FIG. 1, where the flow function is the unconfined yield strength σcAnd consolidation stress sigma1The Jenike Direct Shear Test (JDST) is widely accepted and used among various test methods for measuring flow functions. However, JDST is time consuming, complicated in test procedure and inefficient.
An alternative method of testing flowability is to perform a uniaxial compression test, and FIG. 2 is a schematic of a uniaxial compression test provided by an embodiment of the present invention, as shown in FIG. 2, at a predetermined consolidation pressure σ1Next, the sample preparation material is injected into the circleCylindrical mould and compaction to form a sample, followed by removal and consolidation of the stress sigma1In response to the load, the mold was opened, leaving a free-set cylindrical sample free of lateral restraint, and the compression test was performed. FIG. 3 is a graph comparing JDST with the flow function obtained from the single-axis compression test, which is shown in FIG. 3 and which is simple to operate, but the test results are less accurate than JDST.
The core of the uniaxial compression test problem is the friction of the inner walls of the mold, often referred to as the Janssen effect, which causes the consolidation stress σ 1 to be non-uniform, and which decays exponentially with respect to the sample depth. In uniaxial compression tests, attempts have been made to overcome the effect of wall friction. One attempt to correct the uniaxial flow function by a mathematical method, however, the correction coefficient is often changed according to different material types, and cannot be generally applied. Another attempt used a tri-axial sample preparation method that wrapped a film around the sample and added lubricating oil between the film and the mold walls to minimize wall friction effects. In addition, further attempts were made to eliminate the wall friction effect using infinite layer sample preparation methods. The latter two attempts result in a flow function that approaches the result of JDST. However, the testing procedures for both of these methods are complex and inefficient for commercial or industrial use.
Fig. 4 is a graph for analyzing the effect of wall friction on stress state of the uniaxial compression test and the sample under JDST using Hvorslev and Roscoe planes, from which the result of the uniaxial compression test affected by the wall friction effect can be studied, as shown in fig. 4. The Hvorslev surface is determined by the shear strength of the test piece in three-dimensional space consisting of porosity, normal stress and shear stress. In JDST, the sample is largely unaffected by wall friction effects due to the material being pressed into a relatively thin layer, which results in the sample being at HS(0)Stress state of S(0)On the critical state line of the Roscoe surface, the positive stress is σ(0)Porosity of e(0). In the traditional uniaxial compression test, the effective normal stress acting on the sample is reduced to sigma due to the wall friction effect(1)This is effectively compared to the stress state of the JDST samplesHigh porosity e(0)The yield curve is reduced.
Although the wall friction effect can be minimized by the above experiment, the sample may not reach the critical state if the critical porosity is not reached. For JDST, the limited travel of the top shear ring relative to the fixed base of the shear cell typically requires a series of applied torsions of the cell cover that carry the normal load applied during the initial stages of shear consolidation of the contained sample. The purpose is to ensure that the sample is in the critical state HS(0)To reach a critical porosity e(0). FIG. 5 is a graphical representation of critical porosity for uniaxial compression testing and sample stress conditions under JDST using Hvorslev and Roscoe surfaces, as shown in FIG. 5, for which a higher porosity e would be obtained without such "twisting" induced particle reassembly(1)Result in HS(1)Is low, which occurs in conventional uniaxial compression tests. This phenomenon is also often observed in bulk density compression tests. When the sample is pressed under a "torsional" axial load, the bulk weight of the sample is higher than the bulk weight of the sample under a non-torsional axial load. Therefore, in addition to minimizing the wall friction effect, it is also important to ensure that the critical porosity within the sample is achieved during uniaxial compression testing, otherwise the shear strength of the uniaxial sample is relatively low.
Based on the above analysis, the inventors believe that the critical porosity of the test piece is more critical to the determination of the shear strength of the test piece, which is not addressed in the conventional uniaxial compression test. Therefore, the inventors developed a uniform density sample preparation method to reach the critical state of the sample, thereby improving the accuracy of the uniaxial compression test.
The following describes in more detail embodiments of the present invention with reference to the schematic drawings. Advantages and features of the present invention will become apparent from the following description and claims. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
Fig. 6 is a schematic view of a material fluidity test method provided by an embodiment of the present invention, fig. 7 is a schematic view of a calculation of a compaction under-condition rate with respect to a number of layers provided by an embodiment of the present invention, referring to fig. 6 and 7, the material fluidity test method includes: providing a material flowability test device; sequentially placing a certain amount of sample particles into a mold and compacting the sample particles to form a sample 70 divided into two or more layers, wherein each layer is a sample unit 701, and compacting the sample unit 701 in the previous layer before placing the sample particles in the sample unit 701 in the next layer to ensure that each layer of the sample unit 701 has uniform density; the sample 70 was subjected to a uniaxial compression test, and the flowability of the sample 70 was calculated. The uniaxial compression test specifically comprises: applying an initial load in an axial direction of a mold of a material fluidity testing apparatus to compress the sample; removing the sample 70 from the mold; applying a gradual increase in stress to the sample 70; and measuring the stress value when the sample collapses. The uniaxial compression test involves calculating a flow function that represents the flowability of the sample 70 in terms of the stress values. The material flowability test method includes performing the uniaxial compression test on the sample 70 at different initial loads.
The material flowability test method involves a well-defined pre-consolidation procedure: the "under-compacted" sample preparation method allowed uniaxial samples to reach a state of compaction comparable to the JDST sample. The degree of compaction of each layer sample was:
wherein: u shapenIndicating the n-th layer under-compaction, Un0Represents n0Under-compaction of the layers, n representing the number of layers, n0Denotes the first layer of the insert, nallIndicating the total number of layers. The cumulative mass of the sample particles inserted was:
wherein: u shapen0Representing the percentage of the first layer under-compressed, niPresentation layerA number i, nallDenotes the total number of layers, pdDenotes the dry bulk density, m0Indicates the initial water content, D the sample diameter, and H the height of the sample. In a preferred embodiment, there is at least one layer of the sample unit 701 having a density value lower than the final density value of the sample 70. The density values of the sample units of each layer vary in a linear relationship. The density value of the sample unit in the first layer is larger than that of the sample unit in the second layer. The height of the sample units in each layer is the same. Before preparing the next layer of sample units, the surface of the previous layer of sample units is scratched, so that a plurality of layers of sample units 701 are fused together.
The material fluidity test method is adopted to carry out experimental research on the selected 4 iron ore samples. All samples were obtained by a series of crushing and screening. Subsequently, the material was homogenized and screened to sample particles of less than 4 mm. When the bulk solid is composed of large particles of different sizes, the fine particle solid generally enhances the cohesive strength of the coarse particle solid. The moisture content of each sample was then prepared within the nominal operating range. Table 1 is a table of material properties for selected iron ore samples, all material properties are shown in table 1. Fig. 8 is a graph of a particle size distribution of a sample according to an embodiment of the present invention, the particle size distribution of the sample being shown in fig. 8.
Table 1: material properties of selected iron ore samples
For each sample, the volume weight test was initially performed according to ASTM standards. Fig. 9 is a schematic diagram of volume-weight test results of samples provided by an embodiment of the present invention, and results of four samples with different water contents are shown in fig. 9. Then, a series of JDST tests were performed on each sample having an outer diameter of 101.6mm in accordance with ASTM standards. In the uniaxial compression test, each sample was analyzed by comparison using a conventional sample preparation method (UCT, i.e., conventional uniaxial compression test UCT) and a test method provided by the present invention (UDUCT, i.e., uniform density uniaxial compression test). For reference, in the testing method provided by the invention, 5 different bulk density values corresponding to a large range of normal stresses are selected for testing, and a flow function is deduced.
FIG. 10 is a graph comparing the flow rate function obtained by the conventional uniaxial compression test and the test method provided by one embodiment of the present invention, and the samples IO-B (9.2%) and IO-C (12.1%) collapse under the action of gravity using the conventional uniaxial compression test method as shown in FIG. 10. Therefore, no flow function is obtained. In contrast, all samples using the test method provided by the present invention were able to withstand gravity without collapse. By comparing the flow functions obtained in the two experiments, it was found that the test method provided by the present invention gave a higher ranking in all samples. Therefore, the embodiment of the invention considers that the shear strength is improved when the test method provided by the invention is adopted.
Fig. 11 is a comparison graph of the flow function obtained by JDST reduction and the test method provided by an embodiment of the present invention, and as shown in fig. 11, for a sample with high water content, the flow function ordering between two experiments can be well matched, including: IO-A is respectively 6.5%, 7.9% and 9.9%; IO-B is respectively 13.7% and 16.8%; IO-C is 18.5% and 20.6% respectively; IO-D was 11.6% and 13.6%, respectively.
However, the Uniform Density Uniaxial Compression Test (UDUCT) still resulted in an underestimation of the flow function compared to JDST under lower humidity conditions. Further investigation of the failure behavior of the samples indicated that these mismatch tests failed to reach an unconfined yield stress peak during compressive loading. Fig. 12 is an axial stress-axial strain diagram in a uniaxial compression test provided by an embodiment of the invention, and fig. 12 shows one test case with matched flow function (fig. 12(a)) and one test case with unmatched flow function (fig. 12(b)), with different axial stress-axial strain relationships during compressive loading. In the mating test, the sample exhibited a higher shear strength when a compressive load was initially applied. After the peak stress is reached, the sample exhibits a degree of residual stress upon continued compressive loading. The shear plane was clearly visible after the sample was destroyed. In contrast, in mismatched tests, the sample collapsed rapidly after exhibiting a certain shear strength. No clear shear plane was seen, showing free-flow behavior.
The flow function of bulk solid materials can also be classified according to the Jenike flowability classification, which is expressed as:
wherein: ff (a)cDenotes the Jenike flowability index, σ1The expression is the main integration pressure, σcIndicating an unconfined yield strength.
Jenike flow power index ffcThe following flow behavior was characterized:
ffc>10: free flowing, very low cohesion;
4<ffc<10: easy flowing and low cohesion;
2<ffc<4: cohesiveness;
1<ffc<2: the cohesion is very high;
ffc<1: no flow.
FIG. 13 is a graph of a flow function distribution obtained by uniaxial compression testing in Jenike flow classification according to an embodiment of the invention, and all flow functions from UDUCT are plotted according to Jenike flow classification in FIG. 13. It can be clearly observed thatcAll matching flow functions of (2) are dispersed in viscosity<ffc4) and very viscous (1)<ffc2) area. The unmatched flow function is distributed in free flow, very low cohesion (ff)c>10) And readily flowable, low cohesion (4)<ffc10) zone. Thus, applicants believe that there is a distinct cohesive threshold for iron ore materials beyond which UDUCT can produce a flow function similar to JDST. When the cohesion level is below this threshold, the sample exhibits a lower shear strength, thereby inducing free-flow behavior.
Furthermore, it shows a Jenike flowability index ffcIt is not suitable to define the bulk fluidity of an iron ore material, since the flow function is usually based on consolidation pressure (σ) across two classifications1) And (4) horizontal. From a practical perspective, in the low consolidation stress region where mass flow regime is dominant, Jenike flow regime classification is reasonable. However, under high consolidation stress conditions, linear extrapolation of Jenike flow capacity classification seems to underestimate the difficulty of material handling, since the flow function of viscous iron ore material tends to be steady and funnel flow is common under high consolidation stress conditions.
The volume-weight curves for all iron ore samples are also related to whether the uniform density single axial flow function can be matched to the corresponding JDST flow function. As shown in FIG. 9, compared with unmatched test cases, the volume-weight curves of all the test cases with matched traffic functions have a larger volume-weight range span, which is especially obvious in IO-B and IO-C. The bulk density curve essentially reflects the compressibility of the iron ore sample, defined as:
wherein: Ψ represents the sample compressibility factor, ρB(σ1) Bulk density at normal pressure 1, pB(0)Indicating that the positive stress is zero.
Since the mass of the substance input to the volume-weight test unit is fixed,
ρB(σ1)·V(σ1)＝ρB(0)·V(cell)，
wherein: v (sigma)1) Denotes the positive stress as σ1The sample volume at time, V (cell), represents the sample volume under the volume of the unit for bulk weight testing.
Therefore, the temperature of the molten metal is controlled,
since the same cross-sectional area applies to V (σ)1) And v (cell), the above formula can be represented as:
wherein: h (cell) represents the height of the sample cell, H (σ)1) Is representative of pressure σ1The height of the sample cell, ε, represents the axial strain in the constrained compression test.
Thus, it is feasible to convert all the bulk density curves to an axial strain-axial stress plot, and fig. 14 is a normal axial stress versus axial strain plot, as shown in fig. 14. As is clear from fig. 14, there is a compression threshold above which the UDUCT can generate a flow function similar to JDST.
The change of the compression rate of the iron ore sample under different humidity is mainly caused by the clay mineral such as kaolin contained in the material. An important feature of the clay content in iron ore is the induction of macroscopic shrinkage-expansion behaviour. In the wet state, the sample has a tendency to swell and therefore to undergo a large volume change under normal load. In the dry state, the sample shrinks and the volume change under normal consolidation stress is small.
The applicant believes that the binding behaviour of the iron ore samples is also due to the combined effect of the clay-moisture effect. For an iron ore sample, significant cohesion occurs when the material is wetted to some extent. When more water is added to the sample, it generally results in an increase in overall shear strength. As previously described, UDUCTs are capable of producing a flow function similar to JDST when iron ore samples exhibit cohesive behavior. Thus, based on this analysis applicants believe that compression can use a threshold to represent the behavior of significant viscous flow-an iron ore sample, since the combined effects of clay content and moisture are cohesion and compressibility for both macroscopic iron samples.
The normal axial strain versus axial stress for all samples is shown in FIG. 14. The log-like axial strain-axial stress relationship shown in fig. 14 can be converted to a quasi-linear relationship, and fig. 15 is a quasi-linear relationship of normal axial stress to axial strain, as shown in fig. 15. By this method, the compressibility of the sample can be simply expressed as the slope of the axial strain-log axial stress correlation linear fit, expressed as:
wherein: phi denotes the sample compression coefficient, epsilon denotes the axial strain in the constrained compression test, sigma1Indicating the prevailing integrated pressure.
Table 2 is the quasi-linear parameters of the torsional axial strain-axial stress relationship, and all the fitting function parameters are shown in table 2.
TABLE 2 quasi-linear parameters of the relationship of torsional axial strain to axial stress
The results in Table 2 show that the sample compression coefficient phi (i.e.,. epsilon./log 10(σ.)) obtained when the volume-weight test was conducted1) Over 0.152) UDUCT on iron ore samples can produce a flow function comparable to JDST. In fact, the empirical compressibility index Φ can be used to indicate the viscous flow behavior of iron ore materials, and only a bulk density test is required. Therefore, if quantitative evaluation of the fluidity of the iron ore material is required, a simple and rapid uniaxial compression test of uniform density can be performed. Shorter turnaround times based on this mobility monitoring arrangement can reduce material handling blockages during iron ore mining.
From the foregoing, it can be seen that the present invention has proven to be advantageous over existing methods (e.g., JDST and conventional uniaxial compression testing) by way of example, or at least provides a useful alternative. The present invention provides a sample preparation method that achieves similar results for UDUCT and JDST, but is simpler, less time consuming, field-actionable, and less costly than JDST. The uniform density sample preparation method ensures that the uniform critical compaction of the uniaxial compression test sample can be compared favorably with that of the JDST sample. The flow function of iron ore samples obtained with UDUCT can be compared to the JDST flow function when the material shows a pronounced cohesive flow behaviour, which is determined by the compressibility of the samples obtained by the volume-weight test. Therefore, the invention can quickly evaluate whether the UDUCT can generate the traffic function matched with JDST. Compared with the traditional uniaxial compression test, the invention provides a sample preparation method and a suitable substitute UDUCT test, and the UDUCT can obtain more accurate results. The uniform density samples prepared in the uniaxial compression test of the present invention significantly improve the shear strength of the samples, thereby producing a better flow function than conventional uniaxial compression tests. Therefore, in mining operations, such as iron ore mining, the method can be used to obtain a fast and reliable indicator of fluidity. Once implemented at the bulk material handling facility, this approach can improve efficiency and reduce potential plugging.
The embodiments of the invention have been described in terms of their use in iron ore materials and, in addition, the invention is equally applicable to other flowable materials such as bulk solids, powdered materials such as pharmaceutical powders and limestone, as well as other ores. Using coal as an example, a comparative experiment was performed using UDUCT and JDST, and fig. 16 is a graph comparing the flow functions of coal obtained by JDST and uniaxial compression tests provided in an embodiment of the present invention, the results of which are shown in fig. 16. The figure shows that the applicability of the invention to coal is the same, since the fluidity of the coal samples tested using UDUCT and JDST gave essentially the same results. Similar tests were performed on limestone, and fig. 17 is a graph comparing the JDST provided by an embodiment of the present invention with the flow function of limestone obtained from a uniaxial compression test, and the results are shown in fig. 17, indicating that UDUCT can reproduce the flow function obtained from JDST.
Fig. 18 is a schematic front view of a first material fluidity testing apparatus according to an embodiment of the present invention, and fig. 19 is a schematic top view of the first material fluidity testing apparatus according to an embodiment of the present invention, as shown in fig. 18 and 19, the material fluidity testing apparatus including: the mold comprises a piston 50, a load sensor 40, a moving load disk 20, a mold 10 and a chassis 30, wherein the mold 10 is arranged on the chassis 30, the mold 10 comprises a plurality of split molds 11, the split molds 11 can surround to form an inner cavity of the mold 10, the moving load disk 20 is arranged in the inner cavity and moves along a square direction close to or far away from the chassis 30, a piston rod of the piston 50 is connected with the moving load disk 20, and the load sensor 40 is arranged on the piston rod to detect the load of the moving load disk 20. The inner cavity is a cylindrical inner cavity. The side of the chassis 30 remote from the mobile load tray 20 is also provided with a bracket 60 for providing support.
The mold 10 may be implemented in a variety of structural types. Referring to fig. 18 and 19, the mold 10 includes: the base plate comprises a first mold, a second mold and a third mold, wherein the first mold is arranged on the base plate, the second mold and the third mold are respectively connected to two sides of the first mold through hinges 12, and the first mold, the second mold and the third mold surround to form the inner cavity. Fig. 20 is a schematic top view of a second material fluidity testing apparatus according to an embodiment of the present invention, and referring to fig. 20, the mold in another structure includes: the mold comprises a first mold, a second mold and a third mold, wherein one side face of the first mold, one side face of the second mold and one side face of the third mold are respectively provided with a driving unit, and the driving units drive the first mold, the second mold and the third mold to surround to form the inner cavity. The driving unit comprises a piston, a cylinder, an electric telescopic rod and the like.
The mold 10 is surrounded by the split molds 11, and in the closed position, 3 of the split molds 11 form a cylindrical cavity, and the movable load plate 20 compacts the sample material to form the sample 70 when the sample material is filled in the cavity. In the open position, the split mold 11 is away from the sample 70 so as not to interfere with the compacted sample 70.
The material flowability test apparatus provided by the present invention eliminates the effect of the mold 10 on the sample 70 after preparation, relative to current uniaxial flow test apparatus (e.g., Jenike direct shear test apparatus, Freeman technology uniaxial test apparatus, and the uniaxial test apparatus of the university of edinburgh). In contrast, Freeman's uniaxial instrument and the uniaxial instrument of the university of edinburgh require that the sample be prepared in a separate mold and then transferred to the test system, which can affect the consistency of the sample, resulting in inaccurate results.
In summary, in a material fluidity test method provided by an embodiment of the present invention, the material fluidity test method includes: providing a material flowability test device; sequentially placing a certain amount of sample particles into a mould and compacting to form a sample divided into two or more layers, wherein each layer is a sample unit, and compacting the sample unit of the previous layer before placing the sample particles of the sample unit of the next layer to ensure that each layer of the sample unit has uniform density; the samples were subjected to uniaxial compression testing and the flowability of the samples was calculated. The material fluidity test method provided by the invention overcomes the problems that the existing Jenike direct shear test method is complex and the existing uniaxial compression test result is inaccurate.
The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. It will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (12)
1. A material flowability test method, comprising:
providing a material flowability test device;
sequentially placing a certain amount of sample particles into a mould and compacting to form a sample divided into two or more layers, wherein each layer is a sample unit, and compacting the sample unit of the previous layer before placing the sample particles of the sample unit of the next layer to ensure that each layer of the sample unit has uniform density;
the samples were subjected to uniaxial compression testing and the flowability of the samples was calculated.
2. The material flowability test method of claim 1, wherein the degree of compaction of each layer sample is:
wherein: u shapenIndicating the n-th layer under-compaction, Un0Represents n0Under-compaction of the layers, n representing the number of layers, n0Denotes the first layer of the insert, nallIndicating the total number of layers.
3. The material flowability test method of claim 2, wherein the cumulative mass of the inserted sample particles is:
wherein: u shapen0Representing the percentage of the first layer under-compressed, niRepresenting the number of layers i, nallDenotes the total number of layers, pdDenotes the dry bulk density, m0Indicates the initial water content, D the sample diameter, and H the height of the sample.
4. The material flowability test method of claim 3, wherein there is at least one layer of said sample units having a density value lower than the final density value of the sample.
5. The material flowability test method of claim 3, wherein the density values of the sample units of each layer vary in a linear relationship.
6. The material fluidity test method according to claim 5, wherein the density value of the sample unit of the first layer placed in advance is larger than the density value of the sample unit of the second layer placed in the latter.
7. The material flowability test method of claim 6, wherein the height of each layer of the sample units is the same.
8. A material flowability test method according to claim 3, wherein the uniaxial compression test specifically comprises:
applying an initial load in an axial direction of a mold of a material fluidity testing apparatus to compress the sample;
removing the sample from the mold;
applying a gradual increase in stress to the sample;
and measuring the stress value when the sample collapses.
9. A material flowability test method as in claim 8, wherein said uniaxial compression test comprises calculating a flow function representing the flowability of said sample based on said stress value.
10. The material flowability test method of claim 8, comprising performing the uniaxial compression test on the samples at different initial loads.
11. The material flowability test method of claim 8, wherein the uniaxial compression test comprises determining the compressibility of the sample, the compressibility of the sample being represented by a sample compressibility coefficient Φ:
wherein: phi denotes the sample compression coefficient, epsilon denotes the axial strain in the constrained compression test, sigma1Indicating the prevailing integrated pressure.
12. The material fluidity test method according to claim 11, wherein the sample is iron ore, and the uniaxial compression test is performed when a sample compression coefficient Φ of the iron ore is greater than 0.152.
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