WO1999027345A1 - Device and method for measuring cohesion in fine granular media - Google Patents

Device and method for measuring cohesion in fine granular media Download PDF

Info

Publication number
WO1999027345A1
WO1999027345A1 PCT/ES1998/000325 ES9800325W WO9927345A1 WO 1999027345 A1 WO1999027345 A1 WO 1999027345A1 ES 9800325 W ES9800325 W ES 9800325W WO 9927345 A1 WO9927345 A1 WO 9927345A1
Authority
WO
WIPO (PCT)
Prior art keywords
consolidation
granular
cohesion
consolidated
powder
Prior art date
Application number
PCT/ES1998/000325
Other languages
Spanish (es)
French (fr)
Inventor
Antonio Castellanos Mata
Antonio Ramos Reyes
José Manuel Valverde Millan
Original Assignee
Universidad De Sevilla, Vicerrectorado De Investigacion
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Universidad De Sevilla, Vicerrectorado De Investigacion filed Critical Universidad De Sevilla, Vicerrectorado De Investigacion
Publication of WO1999027345A1 publication Critical patent/WO1999027345A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N7/00—Analysing materials by measuring the pressure or volume of a gas or vapour
    • 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0091—Powders
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/10—Devices for withdrawing samples in the liquid or fluent state
    • G01N2001/1006—Dispersed solids
    • G01N2001/1012—Suspensions
    • G01N2001/1018—Gas suspensions; Fluidised beds

Definitions

  • the object of the present invention is an automated device for measuring the cohesion of fine granular media (powders).
  • the apparatus is based on a procedure that uses the fluid seat in a novel way, where the granular medium is first initialized to a reproducible state; the initial granular medium is consolidated or deconsolidated by means of a controlled gas flow; the consolidated / deconsolidated powder seat is then subjected to a gas flow, directed in such a way that the granular material is under tension;
  • the overpressure that causes the dust seat to rupture then provides a measure of the tensile stress of the granular material, which in turn is a function of the consolidation and the vacuum fraction.
  • the determination of these three interdependent properties constitutes a measure of the fluidity of the material.
  • the invented technique is of great interest to the xerographic industry as a diagnostic method based on fundamental physical properties.
  • One technique is to measure the elapsed time in which a given mass of material is discharged from a hopper (Book of ASTM Standards. Part 9, American Society for Testing and Materials, Philadelphia, 1978, 45). This technique is mostly used to test metallic powders. For powders that flow with difficulty, the hopper is vibrated in order to facilitate flow (DA Hall and JG Cutress. The effect of fines contained, moisture and added oil on the handling of small coal. J Inst. Fuel, 33, 1960, 63-72). In this technique, induced vibrations can cause dust compaction.
  • Another technique is to place a series of disks vertically with a central hole whose diameter is gradually reduced. The procedure consists in downloading the material through the discs.
  • the diameter of the smallest hole through which the sample passes three consecutive times is taken as the index of fluidity of the material.
  • Hosokawa test a technique that is currently used in the xerographic industry to classify the fluidity of experimental toners
  • a series of sieves of variable mesh size are placed vertically. The sieve series is vibrated and the relative amount of dust that passes through each sieve gives a measure of the toner fluency.
  • the techniques described have a serious problem consisting in the initialization of the sample of the material.
  • the granular and cohesive nature of fine powders means that in any situation the internal stresses in the material do not have a uniform distribution. This distribution depends largely on the history of the material, so it is difficult to get the sample to be in an initial reproducible state.
  • the fluidity of fine powders is greatly affected by the humidity of the ambient gas. Another major drawback is that the results depend not only on the physical properties of the material but also on the design and
  • the measurements only provide a relative measure of the fluidity of the powder.
  • the Hosoka test for example, is known to be very sensitive to the person who drives it who needs specific training to be able to operate the device with a certain guarantee. There is therefore a need for a more robust technique independent of the experimenter.
  • the characterization of the fluidity of the powder is more appropriate through the direct measurement of some of its physical properties.
  • a suggested property to characterize the fluidity of the granular material is its angle of repose (ISO 3435-1977 -E- Classification and Symbolization of Bulk Materials).
  • This property is not well defined in cohesive granular materials since it depends on the chosen mass of material (it is well known that very small blocks of cohesive powders can form 90 ° angles).
  • the average particle size of the material is correlated with its degree of cohesion and therefore with the ease with which they flow.
  • the use of additives can substantially alter the fluidity of the material by modifying the mechanical properties of the particles such as their hardness or adhesion energy (JM Valverde, A. Ramos, A.
  • SUBSTITUTE SHEET RULE 26 is in an initial reproducible state. In the separation cell the adhesion of the powder can be measured but it becomes difficult to achieve a homogeneous and controlled consolidation.
  • the present invention relates to a device, and the method used therein, to measure the cohesion of fine granular media.
  • the device uses a gas flow (direct or reverse), computer controlled, as a compacting and de-compacting agent for dust to vary the state of consolidation by means of controlled and coordinated valves.
  • the procedure has several stages: a first one in which the granular medium is initialized to a reproducible state; a second in which the initialized granular medium is consolidated or deconsolidated by means of a controlled gas flow; and finally, the consolidated / deconsolidated powder seat is subjected to a gas flow, directed in such a way that the granular material is under tension.
  • Overpressure causes the dust seat to rupture by providing a measure of tensile stress of the granular material, which, together with the measure of the consolidation effort and the vacuum fraction, allows us to measure the fluidity of the material.
  • Figure 1 Scheme of the device through which the fine powder status diagram can be obtained.
  • - A Mechanical device that is placed at the base of the seat.
  • - C Computer.
  • the device (figure 1) consists of: a fluid gas controller (MFC), a compressed dry nitrogen tank (N), a pressure gauge that measures the pressure difference between the gas passing through the circuit and the atmospheric pressure ( ⁇ p ), a cylindrical asiem (B) where the dust is located on a filter that can be made of ceramic or metal, a valve that remains open in the processes of decompression and rupture (v.), another valve that remains open in the compression processes (v.E2), a valve that remains open during compression (v Cl), a valve that remains open in the decompression and rupture processes (v C2), an ultrasound emitting device that is used to measure the dust seat height (S), a mechanical device that is placed at the base of the seat to shake it in order to favor fluidization (A), a computer (C) that automatically controls the valves, the flow controller, the pressure gauge, e l Ultrasound emitter and mechanical agitator.
  • MFC fluid gas controller
  • N compressed dry nitrogen tank
  • ⁇ p the pressure difference between the gas passing through the circuit and the
  • the novelty of the device is in the use of a fluid seat in a novel sequence of operations as can be seen below:
  • the state of the granular material When fluidized, the state of the granular material is homogeneous, so that it loses all memory of its initial heterogeneous state. If the gas flow and vibrations are cut off, then the fluidized powder is deposited in a reproducible state (the dust is not perfectly uniform since the bottom of the seat is somewhat more consolidated than the material at the top, but this is not important because it is the material at the bottom of the seat to which the measures concern).
  • Cohesive forces in granular materials increase with the consolidation effort.
  • measures of consolidation efforts of a few Paséales are difficult to do.
  • forces are typical of those that exist in the thin layers of dust found in xerographic practice, and in many other processes.
  • a gas flow is directed upwards through the seat.
  • the gas flow increases quasistatically so that the pressure drop across the seat increases linearly with the gas velocity.
  • the gas velocity is such that the pressure drop across the seat balances the weight of the dust sample per unit area, and at this point a non-cohesive granular material would become fluidized (this is known as the minimum fluidization speed point).
  • all granular materials have some degree of cohesion, and thus the pressure drop across the seat continues to grow for a gas flow above U mf .
  • Two ingredients are essential, the use of reverse flow as a means to consolidate dust, and the use of the ultrasonic device to measure the height of the seat.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Medicinal Chemistry (AREA)
  • Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
  • Developing Agents For Electrophotography (AREA)

Abstract

The invention relates to an automated device for measuring cohesion in fine granular media (powders). The device is based on a method which uses a fluid medium in a novel manner enabling a granular medium to be obtained in a first reproductible state. The granular medium is subsequently consolidated or de-consolidated by means of a controlled gas flow. The consolidated/de-consolidated powder medium is subjected to the gas flow which is directed in such a way that the granulated material is placed under pressure. The overpressure causes the powder medium to rupture and provides a measurement of the tensile force of the granular material which is in turn a function of consolidation and vacuum fraction. Determination of these three interdependent properties enables the fluidity of the material to be measured. The technique thus disclosed is particularly applicable to the xerographic industry as a diagnostic method based on the properties of fundamental physics.

Description

Memoria Descriptiva Descriptive memory
TÍTULOTITLE
Dispositivo y procedimiento para medir la cohesión de medios granulares finos.Device and procedure for measuring the cohesion of fine granular media.
OBJETO DE LA INVENCIÓNOBJECT OF THE INVENTION
El objeto de la presente invención es un dispositivo automatizado para la medida de la cohesión de medios granulares finos (polvos). El aparato se basa en un procedimiento que usa de forma novedosa el asiento fluido, donde el medio granular primero se inicializa a un estado reproducible; el medio granular inicializado se consolida o desconsolida por medio de un flujo controlado de gas; el asiento de polvo consolidado/desconsolidado se somete entonces a un flujo de gas, dirigido de tal forma que el material granular se halle bajo tensión; la sobrepresión que causa la ruptura del asiento de polvo proporciona entonces una medida del esfuerzo tensil del material granular, que a su vez es una función de la consolidación y de la fracción de vacío. La determinación de estas tres propiedades interdependientes constituye una medida de la fluidez del material. La técnica inventada es de gran interés para la industria xerográfica como método de diagnóstico basado en las propiedades físicas fundamentales.The object of the present invention is an automated device for measuring the cohesion of fine granular media (powders). The apparatus is based on a procedure that uses the fluid seat in a novel way, where the granular medium is first initialized to a reproducible state; the initial granular medium is consolidated or deconsolidated by means of a controlled gas flow; the consolidated / deconsolidated powder seat is then subjected to a gas flow, directed in such a way that the granular material is under tension; The overpressure that causes the dust seat to rupture then provides a measure of the tensile stress of the granular material, which in turn is a function of the consolidation and the vacuum fraction. The determination of these three interdependent properties constitutes a measure of the fluidity of the material. The invented technique is of great interest to the xerographic industry as a diagnostic method based on fundamental physical properties.
INFORME SOBRE EL ESTADO DE LATÉCNICAREPORT ON THE STATE OF LATÉCNICA
Existen varias técnicas estándar para caracterizar la fluidez de los materiales granulares. Dichas técnicas se dividen en dos grupos. Existen una serie de técnicas en las cuales se evalúa la fluidez del polvo por medio de la facilidad de su transporte aThere are several standard techniques to characterize the fluidity of granular materials. These techniques are divided into two groups. There are a number of techniques in which the fluidity of the powder is evaluated through the ease of transport to
HOJA DE SUSTITUCIÓN (REGLA 26) través de diversos dispositivos estándar (grupo I). En el otro grupo de técnicas se encuentran aquellas en las que se trata de obtener propiedades físicas fundamentales del material en función de las cuales se encuentra el grado de fluidez del polvo (grupo II).SUBSTITUTE SHEET (RULE 26) through various standard devices (group I). In the other group of techniques are those in which it is about obtaining fundamental physical properties of the material based on which is the degree of fluidity of the powder (group II).
Grupo I:Group I:
Una técnica consiste en medir el tiempo transcurrido en el que una determinada masa de material se descarga de una tolva (Book of ASTM Standards. Part 9, American Societyfor Testing and Materials, Philadelphia, 1978, 45). Esta técnica se usa sobre todo para testear polvos metálicos. Para polvos que fluyen con dificultad, se hace vibrar la tolva con el objeto de facilitar el flujo (D. A. Hall y J. G. Cutress. The effect of fines contení, moisture and added oil on the handling of small coal. J Inst. Fuel, 33, 1960, 63-72). En esta técnica, las vibraciones inducidas pueden provocar la compactación del polvo. Otra técnica consiste en colocar en sentido vertical una serie de discos con un agujero central cuyo diámetro se va reduciendo progresivamente. El procedimiento consiste en hacer descargar el material a través de los discos. El diámetro del menor orificio a través del cual pasa la muestra tres veces consecutivas se toma como el índice de fluidez del material. En el test de Hosokawa (técnica que en la actualidad se usa en la industria xerográfica para clasificar la fluidez de los tóners experimentales), se coloca en sentido vertical una serie de cribas de tamaño de malla variable. Se hace vibrar la serie de cribas y la cantidad relativa de polvo que atraviesa cada criba da una medida de la fuidez del tóner. En general, las técnicas descritas tienen un grave problema consistente en la inicialización de la muestra del material. La naturaleza granular y cohesiva de los polvos finos hace que en cualquier situación las tensiones internas en el material no posean una distribución uniforme. Esta distribución depende en gran medida de la historia del material, de manera que es difícil conseguir que la muestra se encuentre en un estado inicial reproducible. Por otro lado, se sabe que la fluidez de los polvos finos se encuentra muy afectada por la humedad del gas ambiente. Otro gran inconveniente es que los resultados no sólo dependen de las propiedades físicas propias del material sino también del diseño y lasOne technique is to measure the elapsed time in which a given mass of material is discharged from a hopper (Book of ASTM Standards. Part 9, American Society for Testing and Materials, Philadelphia, 1978, 45). This technique is mostly used to test metallic powders. For powders that flow with difficulty, the hopper is vibrated in order to facilitate flow (DA Hall and JG Cutress. The effect of fines contained, moisture and added oil on the handling of small coal. J Inst. Fuel, 33, 1960, 63-72). In this technique, induced vibrations can cause dust compaction. Another technique is to place a series of disks vertically with a central hole whose diameter is gradually reduced. The procedure consists in downloading the material through the discs. The diameter of the smallest hole through which the sample passes three consecutive times is taken as the index of fluidity of the material. In the Hosokawa test (a technique that is currently used in the xerographic industry to classify the fluidity of experimental toners), a series of sieves of variable mesh size are placed vertically. The sieve series is vibrated and the relative amount of dust that passes through each sieve gives a measure of the toner fluency. In general, the techniques described have a serious problem consisting in the initialization of the sample of the material. The granular and cohesive nature of fine powders means that in any situation the internal stresses in the material do not have a uniform distribution. This distribution depends largely on the history of the material, so it is difficult to get the sample to be in an initial reproducible state. On the other hand, it is known that the fluidity of fine powders is greatly affected by the humidity of the ambient gas. Another major drawback is that the results depend not only on the physical properties of the material but also on the design and
HOJA DE SUSTITUCIÓN (REGLA 26) -.SUBSTITUTE SHEET (RULE 26) -.
características del dispositivo. De este modo, las medidas sólo proporcionan una medida relativa de la fluidez del polvo. Más aún, el test de Hosoka a, por ejemplo, es conocido por ser muy sensible a la persona que lo maneja que necesita de un entrenamiento específico para poder manejar el aparato con cierta garantía. Existe por tanto necesidad de una técnica más robusta independiente del experimentador. La caracterización de la fluidez del polvo es más apropiada a través de la medida directa de algunas de sus propiedades físicas.device features Thus, the measurements only provide a relative measure of the fluidity of the powder. Moreover, the Hosoka test, for example, is known to be very sensitive to the person who drives it who needs specific training to be able to operate the device with a certain guarantee. There is therefore a need for a more robust technique independent of the experimenter. The characterization of the fluidity of the powder is more appropriate through the direct measurement of some of its physical properties.
Grupo II:Group II:
Una propiedad sugerida para caracterizar la fuidez del material granular es su ángulo de reposo (ISO 3435-1977 -E- Clasification and Symbolization of Bulk Materials). No obstante, esta propiedad no se encuentra bien definida en los materiales granulares cohesivos ya que depende de la masa escogida de material (es bien sabido que bloques muy pequeños de polvos cohesivos pueden formar ángulos de 90°). El tamaño medio de las partículas del material se encuentra correlacionado con su grado de cohesión y por tanto con la facilidad con la que fluyen. Sin embargo, se conoce que el uso de aditivos puede alterar sustancialmente la fluidez del material mediante la modificación de las propiedades mecánicas de las partículas como su dureza o su energía de adhesión (J. M. Valverde, A. Ramos, A. Castellanos y P. K. Watson, Tensile strength and void fraction as functions of consolidation stress for a set of xerographic toners, Powder s and Grains 97, Balkema, Rotterdam, 1997) que juegan un papel decisivo en la fluidez del medio. La razón de Hausner dada por el cociente entre la densidad del polvo compactado (por medio de vibración) y su densidad en el estado de fluidización es una característica muy útil del material relacionada con su fluidez (L. Svarovsky, Powder Testing Guide, Elsevier, New York, 1987). La compresibilidad del material, según Svarovski y Carr (R. L. Carr, Chap. 2, Gas-Solids Handling in Process Industries, Marcel Dekker, NY, 1976), se encuentra también directamente relacionada con la fluidez del material. La celda de Jenike permite estimar el ángulo de fricción del material. Sin embargo no son accesibles los estados de baja consolidación y es un problema el que la muestraA suggested property to characterize the fluidity of the granular material is its angle of repose (ISO 3435-1977 -E- Classification and Symbolization of Bulk Materials). However, this property is not well defined in cohesive granular materials since it depends on the chosen mass of material (it is well known that very small blocks of cohesive powders can form 90 ° angles). The average particle size of the material is correlated with its degree of cohesion and therefore with the ease with which they flow. However, it is known that the use of additives can substantially alter the fluidity of the material by modifying the mechanical properties of the particles such as their hardness or adhesion energy (JM Valverde, A. Ramos, A. Castellanos and PK Watson, Tensile strength and void fraction as functions of consolidation stress for a set of xerographic toners, Powder s and Grains 97, Balkema, Rotterdam, 1997) that play a decisive role in the fluidity of the environment. Hausner's ratio given by the ratio between the density of the compacted powder (by means of vibration) and its density in the fluidization state is a very useful characteristic of the material related to its fluidity (L. Svarovsky, Powder Testing Guide, Elsevier, New York, 1987). The compressibility of the material, according to Svarovski and Carr (R. L. Carr, Chap. 2, Gas-Solids Handling in Process Industries, Marcel Dekker, NY, 1976), is also directly related to the fluidity of the material. Jenike's cell allows estimating the friction angle of the material. However, low consolidation states are not accessible and it is a problem that the sample
HOJA DE SUSTITUCIÓN REGLA 26 se encuentre en un estado inicial reproducible. En la celda de separación puede medirse la adhesión del polvo pero se hace difícil lograr una consolidación homogénea y controlada.SUBSTITUTE SHEET RULE 26 is in an initial reproducible state. In the separation cell the adhesion of the powder can be measured but it becomes difficult to achieve a homogeneous and controlled consolidation.
La fluidez del medio granular está asociada a las fuerzas de cohesión entre partículas, que dependen fuertemente del grado de compactación del material. Nuestro objetivo final es obtener el esfuerzo tensil y la densidad del material en función de su estado de consolidación. De este modo, el logro de un estado de consolidación controlado y reproducible es vital para nuestro propósito. Aunque hasta el momento existen diversas formas de consolidar la muestra, ninguna se ajusta a nuestras necesidades:The fluidity of the granular medium is associated with the cohesion forces between particles, which strongly depend on the degree of compaction of the material. Our ultimate goal is to obtain tensile stress and material density based on its state of consolidation. Thus, the achievement of a controlled and reproducible state of consolidation is vital to our purpose. Although so far there are several ways to consolidate the sample, none fits our needs:
a.- Consolidación por pistón: es difícil controlar el régimen de baja consolidación.a.- Piston consolidation: it is difficult to control the low consolidation regime.
b.- Consolidación por centrifugación (J. M. Valverde, A. Ramos, A. Castellanos y P. K. Watson, Tensile strength and void fraction as functions of consolidation stress for a set of xerographic toners, Powders and Grains 97, Balkema, Rotterdam. 1997): Se ha usado para un rango limitado de esfuerzos de consolidación (pero está restringida a este rango de esfuerzos y no se presta al concepto de automatización que requerimos.b.- Centrifugal consolidation (JM Valverde, A. Ramos, A. Castellanos and PK Watson, Tensile strength and void fraction as functions of consolidation stress for a set of xerographic toners, Powders and Grains 97, Balkema, Rotterdam. 1997): It has been used for a limited range of consolidation efforts (but is restricted to this range of efforts and does not lend itself to the concept of automation that we require.
c- Consolidación por masa variable en el asiento: se ha usado por nosotros en un rango limitado de esfuerzos de consolidación (, pero está restringida a este rango y, además, tampoco se presta a la automatización.c- Consolidation by variable mass in the seat: it has been used by us in a limited range of consolidation efforts (but is restricted to this range and also does not lend itself to automation.
Existe una necesidad urgente de un aparato o una técnica para medir las propiedades cohesivas de los materiales granulares finos tales como los toners xerográficos, cuyas propiedades de fluidez son de importancia tecnológica;There is an urgent need for an apparatus or technique to measure the cohesive properties of fine granular materials such as xerographic toners, whose fluidity properties are of technological importance;
DESCRIPCIÓN GENERAL DE LA INVENCIÓNGENERAL DESCRIPTION OF THE INVENTION
HOJA DE SUSTITUCIÓN (REGLA 26) La presente invención se refiere a un dispositivo, y al procedimiento utilizado en éste, para medir la cohesión de medios granulares finos. El dispositivo usa un flujo de gas (directo o inverso), controlado por ordenador, como agente compactador y descompactador del polvo para variar el estado de consolidación por medio de válvulas controladas y coordinadas.SUBSTITUTE SHEET (RULE 26) The present invention relates to a device, and the method used therein, to measure the cohesion of fine granular media. The device uses a gas flow (direct or reverse), computer controlled, as a compacting and de-compacting agent for dust to vary the state of consolidation by means of controlled and coordinated valves.
El procedimiento tiene varias etapas: una primera en la que se inicializa el medio granular a un estado reproducible; una segunda en la que el medio granular inicializado se consolida o desconsolida por medio de un flujo controlado de gas; y por último, el asiento de polvo consolidado/desconsolidado se somete a un flujo de gas, dirigido de tal forma que el material granular se halle bajo tensión. La sobrepresión causa la ruptura del asiento de polvo proporcionando una medida de esfuerzo tensil del material granular, lo cual, unido a la medida del esfuerzo de consolidación y a la fracción de vacío, nos permite medir la fluidez del material.The procedure has several stages: a first one in which the granular medium is initialized to a reproducible state; a second in which the initialized granular medium is consolidated or deconsolidated by means of a controlled gas flow; and finally, the consolidated / deconsolidated powder seat is subjected to a gas flow, directed in such a way that the granular material is under tension. Overpressure causes the dust seat to rupture by providing a measure of tensile stress of the granular material, which, together with the measure of the consolidation effort and the vacuum fraction, allows us to measure the fluidity of the material.
Explicación de las figurasExplanation of the figures
Figura 1 : Esquema del dispositivo mediante el que puede obtenerse el diagrama de estado de polvos finos.Figure 1: Scheme of the device through which the fine powder status diagram can be obtained.
- MFC: Controlador del gas fluido.- MFC: Fluid gas controller.
- N2: Tanque de nitrógeno seco comprimido.- N 2: Compressed dry nitrogen tank.
- Δp: Manómetro.- Δp: Pressure gauge.
- B: Cilindro donde se encuentra el polvo asentado.- B: Cylinder where the dust is located.
- v.El : Válvula que permanece abierta en los procesos de descompresión y ruptura. - v.E2: Válvula que permanece abierta en los procesos de compresión.- v.: Valve that remains open in the decompression and rupture processes. - v.E2: Valve that remains open in the compression processes.
- v Cl : Válvula que permanece abierta durante la compresión.- v Cl: Valve that remains open during compression.
- v C2: Válvula que permanece abierta en los procesos de descompresión y ruptura.- v C2: Valve that remains open in the decompression and rupture processes.
- S: Aparato emisor de ultrasonido.- S: Ultrasound emitting device.
- A: Aparato mecánico que se coloca en la base del asiento. - C: Ordenador.- A: Mechanical device that is placed at the base of the seat. - C: Computer.
HOJA DE SUSTITUCIÓN (REGLA 26) DESCRIPCIÓN DETALLADA DE LA INVENCIÓNSUBSTITUTE SHEET (RULE 26) DETAILED DESCRIPTION OF THE INVENTION
El dispositivo (figura 1) consta de: un controlador del gas fluido (MFC), un tanque de nitrógeno seco comprimido(N ), un manómetro que mide la diferencia de presión entre el gas que pasa por el circuito y la presión atmosférica (Δp), un asiemto cilindrico (B) donde se encuentra el polvo asentado sobre un filtro que puede ser de cerámica o metal, una válvula que permanece abierta en los procesos de descompresión y ruptura (v.El), otra válvula que permanece abierta en los procesos de compresión (v.E2), una válvula que permanece abierta durante la compresión (v Cl), una válvula que permanece abierta en los procesos de descompresión y ruptura (v C2), un aparato emisor de ultrasonido que se utiliza para medir la altura del asiento de polvo (S), un aparato mecánico que se coloca en la base del asiento para agitarlo con el objetivo de favorecer la fluidización (A), un ordenador (C) que controla automáticamente las válvulas, el controlador de flujo, el medidor de presión, el emisor de ultrasonido y el agitador mecánico . La coordinación de todos estos elementos para llevar a cabo los ciclos de compresión/descompresión se realiza por medio de tarjetas de adquisición de datos y de un programa que ha sido creado al efecto.The device (figure 1) consists of: a fluid gas controller (MFC), a compressed dry nitrogen tank (N), a pressure gauge that measures the pressure difference between the gas passing through the circuit and the atmospheric pressure (Δp ), a cylindrical asiem (B) where the dust is located on a filter that can be made of ceramic or metal, a valve that remains open in the processes of decompression and rupture (v.), another valve that remains open in the compression processes (v.E2), a valve that remains open during compression (v Cl), a valve that remains open in the decompression and rupture processes (v C2), an ultrasound emitting device that is used to measure the dust seat height (S), a mechanical device that is placed at the base of the seat to shake it in order to favor fluidization (A), a computer (C) that automatically controls the valves, the flow controller, the pressure gauge, e l Ultrasound emitter and mechanical agitator. The coordination of all these elements to carry out the compression / decompression cycles is carried out by means of data acquisition cards and a program that has been created for this purpose.
La novedad del dispositivo está en la utilización de un asiento fluido en una secuencia novedosa de operaciones como pueden verse a continuación:The novelty of the device is in the use of a fluid seat in a novel sequence of operations as can be seen below:
1.- Inicialización:1.- Initialization:
Los materiales granulares finos y cohesivos tienden en general a empaquetarse de una forma muy heterogénea con regiones más empaquetadas y otras regiones con estructuras más abiertas; claramente, tales polvos son difíciles de caracterizar. Así pues, nuestro primer paso es llevar el material granular a un estado reproducible de consolidación, y esto se realiza por medio del asiento fluido del siguiente modo: se somete al polvo a un flujo de gas controlado, y alcanzada una velocidad crítica del flujo, el asiento llega a fluidizarse. En el caso de polvos altamente cohesivos es necesario vibrar el asiento para romper los canales, burbujas, etc. La incorporación deFine and cohesive granular materials generally tend to be packaged in a very heterogeneous manner with more packed regions and other regions with more open structures; clearly, such powders are difficult to characterize. Thus, our first step is to bring the granular material to a reproducible state of consolidation, and this is done through the fluid seat as follows: the powder is subjected to a controlled gas flow, and reached a critical flow rate, The seat becomes fluidized. In the case of highly cohesive powders it is necessary to vibrate the seat to break the channels, bubbles, etc. The incorporation of
HOJA DE SUSTITUCIÓN (REGLA 26) un vibrador accionado automáticamente permitirá medir la razón de Hausner del material correlacionada con su fluidez.SUBSTITUTE SHEET (RULE 26) an automatically driven vibrator will allow to measure the Hausner ratio of the material correlated with its fluidity.
Cuando se fluidiza, el estado del material granular es homogéneo, de tal forma que pierde toda memoria de su estado heterogéneo inicial. Si el flujo de gas y las vibraciones se cortan, entonces el polvo fluidizado se deposita en un estado reproducible (el polvo no es perfectamente uniforme ya que el fondo del asiento está algo más consolidado que el material en la parte superior, pero esto no es importante pues es el material en el fondo del asiento al que conciernen las medidas).When fluidized, the state of the granular material is homogeneous, so that it loses all memory of its initial heterogeneous state. If the gas flow and vibrations are cut off, then the fluidized powder is deposited in a reproducible state (the dust is not perfectly uniform since the bottom of the seat is somewhat more consolidated than the material at the top, but this is not important because it is the material at the bottom of the seat to which the measures concern).
2.- Consolidación/ Desconsolidación:2.- Consolidation / Deconsolidation:
Las fuerzas cohesivas en los materiales granulares se incrementan con el esfuerzo de consolidación. En el caso de materiales granulares finos, tales como los toners xerográficos, medidas de esfuezos de consolidación de unos pocos Paséales son difíciles de hacer. Sin embargo, tales fuerzas son típicas de aquéllas que existen en las capas delgadas de polvos que se encuentran en la práctica xerográfica, y en muchos otros procesos.Cohesive forces in granular materials increase with the consolidation effort. In the case of fine granular materials, such as xerographic toners, measures of consolidation efforts of a few Paséales are difficult to do. However, such forces are typical of those that exist in the thin layers of dust found in xerographic practice, and in many other processes.
Después de estas investigaciones, reconociendo la necesidad de automatización, inventamos el siguiente método de consolidar el polvo siguiendo el paso de inicialización descrito anteriormente. En este proceso novedoso, tomamos el lecho fluido e invertimos el flujo de gas. En este paso de consolidación, el esfuerzo de consolidación en el fondo del asiento se obtiene sumando la caída de presión a través de la capa de polvo y el peso por unidad de área del polvo inicializado. Esta técnica de flujo inverso nos permite cubrir un rango de consolidaciones desde unos cientos Paséales hasta 2500 Paséales. Con una instrumentación mejorada se podrían alcanzar más altas consolidaciones.After these investigations, recognizing the need for automation, we invented the following method of consolidating the powder following the initialization step described above. In this novel process, we take the fluid bed and reverse the gas flow. In this consolidation step, the consolidation effort at the bottom of the seat is obtained by adding the pressure drop across the dust layer and the weight per unit area of the initialized powder. This reverse flow technique allows us to cover a range of consolidations from a few hundred Paséales to 2500 Paséales. With improved instrumentation, higher consolidations could be achieved.
Por medio de un flujo de descnsolidación, manteniendo la masa de material granular fija, podemos obtener valores del esfuerzo de consolidación menores que el peso por unidad de área. Por medio de este paso de desconsolidación somos capacesThrough a de-consolidation flow, keeping the mass of granular material fixed, we can obtain values of the consolidation effort lower than the weight per unit area. Through this deconsolidation step we are able
HOJA DE SUSTITUCIÓN REGLA 26) de cubrir un rango de esfuerzos de cien Paséales bajando hasta diez Paséales. Con instrumentos mejorados esperamos poder alcanzar un valor más bajo límite de un Pascal para el esfuerzo de consolidación.SUBSTITUTE SHEET RULE 26) of covering a range of efforts of one hundred Paséales down to ten Paséales. With improved instruments we hope to reach a lower limit value of a Pascal for the consolidation effort.
Por medio de una técnica de pulso acústico podemos medir la altura del asiento fluido correspondiente a un valor dado del esfuerzo de consolidación. Esto nos permite calcular el promedio de la fracción de vacío del polvo consolidado o desconsolidado, lo que es una medida muy útil para caracterizar el polvo: primero, materiales granulares con partículas de gran tamaño y baja cohesión se empaquetan bastante, en realidad pueden alcanzar el límite de apilamiento aleatorio, fracción de vacío del orden de 0.45; por el contrario, materiales granulares con partículas de pequeño tamaño y alta cohesión se empaquetan en estructuras abiertas y pueden acercarse al límite de agregación balístico, donde la fracción de vacío es de 0.85.Through an acoustic pulse technique we can measure the height of the fluid seat corresponding to a given value of the consolidation effort. This allows us to calculate the average of the vacuum fraction of the consolidated or deconsolidated powder, which is a very useful measure to characterize the dust: first, granular materials with large particles and low cohesion are packaged quite a lot, they can actually reach the random stacking limit, vacuum fraction of the order of 0.45; on the contrary, granular materials with particles of small size and high cohesion are packaged in open structures and can approach the ballistic aggregation limit, where the vacuum fraction is 0.85.
3.- Medidas del Esfuerzo Tensil:3.- Measures of Tensile Effort:
Posteriormente a la etapa de consolidación/desconsolidación se dirige un flujo de gas hacia arriba a través del asiento. El flujo de gas se incrementa cuasiestáticamente de tal modo que la caída de presión a través del asiento aumenta linealmente con la velocidad del gas. En el punto donde la velocidad del gas es tal que la caída de presión a través del asiento equilibra el peso de la muestra de polvo por unidad de área, y en este punto un material granular no cohesivo llegaría a fluidizarse (esto se conoce como el punto de mínima velocidad de fluidización). En la práctica, todos los materiales granulares presentan algún grado de cohesión, y así la caída de presión a través del asiento continúa creciendo para un flujo de gas por encima de Umf. Nótese que por encima de este punto el flujo de gas somete al material granular a un estado de tensión, y a medida que la tensión en el polvo crece se alcanza un punto en el cual el polvo se rompe bajo tensión y llega a fluidizarse. Esta velocidad del flujo se conoce como velocidad de comienzo de fluidización, y la tensión máxima a la que el polvo se encuentra a esta velocidad define el esfuerzo tensil del polvo σt. Este esfuerzo tensil es una función creciente del esfuerzo de consolidación. Los materiales granulares deAfter the consolidation / deconsolidation stage, a gas flow is directed upwards through the seat. The gas flow increases quasistatically so that the pressure drop across the seat increases linearly with the gas velocity. At the point where the gas velocity is such that the pressure drop across the seat balances the weight of the dust sample per unit area, and at this point a non-cohesive granular material would become fluidized (this is known as the minimum fluidization speed point). In practice, all granular materials have some degree of cohesion, and thus the pressure drop across the seat continues to grow for a gas flow above U mf . Note that above this point the flow of gas subjects the granular material to a state of tension, and as the tension in the dust grows, a point is reached at which the dust breaks under tension and becomes fluidized. This flow rate is known as the fluidization start rate, and the maximum voltage at which the powder is at this speed defines the tensile stress of the powder σ t . This tensile effort is a growing function of the consolidation effort. The granular materials of
HOJA DE SUSTITUCIÓN (REGLA 26) baja cohesión muestran valores bajos del esfuerzo tensil mientras que materiales granulares de alta cohesión muestran valores relativamente altos del esfuerzo tensil.SUBSTITUTE SHEET (RULE 26) Low cohesion shows low tensile stress values while high cohesion granular materials show relatively high tensile stress values.
Desde el punto de vista de la comprensión del comportamiento del medio granular, es útil combinar los datos del diagrama de consolidación con los datos del esfuerzo tensil. Juntos forman lo que se conoce como el Diagrama de Estado para Cizalla Cero, como se muestra en la figura 2. Este diagrama proporciona las interrelaciones entre el esfuerzo de consolidación, la fracción de vacío, y el esfuerzo tensil; es probablemente el mejor modo de mostrar cómo estas tres variables están relacionadas y así caracterizar el polvo.From the point of view of understanding the behavior of the granular medium, it is useful to combine the data in the consolidation diagram with the tensile stress data. Together they form what is known as the State Diagram for Zero Shear, as shown in Figure 2. This diagram provides the interrelationships between consolidation effort, vacuum fraction, and tensile stress; It is probably the best way to show how these three variables are related and thus characterize the dust.
4.- El medidor automático de la fluidez de polvos finos:4.- The automatic fine powder flow meter:
En vista de la utilidad de estos tipos de medidas es deseable automatizar el proceso, y hacerlo independiente del experimentador. El punto importante a tener en cuenta es que el proceso por nosostros expuesto está determinado por un flujo de gas, y que por medio de una serie de válvulas y controladores de flujo somos capaces de efectuar todo el proceso por medio de un ordenador. Las medidas, como son la velocidad del flujo de gas, la diferencia de presión, y la altura del asiento, son accesibles para el mismo computador, y de estos conjuntos de medidas, los valores del esfuerzo de compresión, de la fracción de vacío, y del esfuerzo tensil, se calculan automáticamente .In view of the usefulness of these types of measures, it is desirable to automate the process, and make it independent of the experimenter. The important point to keep in mind is that the process for us exposed is determined by a gas flow, and that through a series of valves and flow controllers we are able to carry out the entire process through a computer. The measurements, such as the speed of the gas flow, the pressure difference, and the seat height, are accessible to the same computer, and of these sets of measurements, the values of the compression effort, the vacuum fraction, and tensile stress, they are calculated automatically.
Dos ingredientes son esenciales, el uso del flujo inverso como medio para consolidar el polvo, y el uso del aparato de ultrasonidos para medir la altura del asiento.Two ingredients are essential, the use of reverse flow as a means to consolidate dust, and the use of the ultrasonic device to measure the height of the seat.
HOJA DE SUSTITUCIÓN (REGLA 26) SUBSTITUTE SHEET (RULE 26)

Claims

REIVINDICACIONES
1. Dispositivo para medir la cohesión de medios granulares finos, caracterizado por el uso de un flujo de gas (directo o inverso), controlado por ordenador, como agente compactador y descompactador del polvo para variar el estado de consolidación por medio de válvulas controladas y coordinadas.1. Device for measuring the cohesion of fine granular media, characterized by the use of a gas flow (direct or reverse), controlled by a computer, as a compacting and de-compacting agent for dust to vary the state of consolidation by means of controlled valves and coordinated.
2. Dispositivo para medir la cohesión de medios granulares finos, según reivindicación 1 , caracterizado por el uso de un emisor de ultrasonidos controlado por ordenador para medir la fracción de vacío del material.2. Device for measuring the cohesion of fine granular media according to claim 1, characterized by the use of a computer-controlled ultrasonic emitter to measure the vacuum fraction of the material.
3. Dispositivo para medir la cohesión de medios granulares finos según reivindicaciones 1 y 2, caracterizado por el uso de un vibrador o agitador controlado por ordenador para favorecer la fluidización del polvo.3. Device for measuring the cohesion of fine granular media according to claims 1 and 2, characterized by the use of a computer controlled vibrator or agitator to favor the fluidization of the powder.
4. Procedimiento para medir la cohesión de medios granulares finos, utilizado en dispositivo descrito según reivindicaciones 1 a 3, caracterizado por medir la fluidez del material a través de la interdependencia entre la medida del esfuerzo tensil, del esfuerzo de consolidación y la fracción de vacío.4. Procedure for measuring the cohesion of fine granular media, used in a device described according to claims 1 to 3, characterized by measuring the fluidity of the material through the interdependence between the measure of tensile stress, consolidation effort and vacuum fraction .
HOJA DE SUSTITUCIÓN (REGLA 26) SUBSTITUTE SHEET (RULE 26)
PCT/ES1998/000325 1997-11-26 1998-11-26 Device and method for measuring cohesion in fine granular media WO1999027345A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ES009702518A ES2131031B1 (en) 1997-11-26 1997-11-26 DEVICE AND PROCEDURE TO MEASURE COHESION OF FINE GRANULAR MEDIA.
ESP9702518 1997-11-26

Publications (1)

Publication Number Publication Date
WO1999027345A1 true WO1999027345A1 (en) 1999-06-03

Family

ID=8301386

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/ES1998/000325 WO1999027345A1 (en) 1997-11-26 1998-11-26 Device and method for measuring cohesion in fine granular media

Country Status (2)

Country Link
ES (1) ES2131031B1 (en)
WO (1) WO1999027345A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002095364A1 (en) * 2001-05-22 2002-11-28 Ingenieria Energetica Y De Contaminacion, S.A. Automatic system for collecting, weighing and releasing solid particles
WO2007042585A3 (en) * 2005-10-11 2007-06-21 Univ Sevilla Method and device for measuring the angle of friction and the cohesion of granular media
CN102706773A (en) * 2011-03-28 2012-10-03 厦门钨业股份有限公司 Characterization method for powder macroscopic flow during extrusion molding process and used device
CN108776081A (en) * 2018-07-05 2018-11-09 中国石油大学(华东) A kind of dissolved gas crude oil flow behavior experiment circuit device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2695451B2 (en) * 2017-06-29 2019-10-17 Tecn Mecanicas Ilerdenses S L DEVICE FOR COLLAPSE TEST OF A PULVERULENT OR GRANULAR MATERIAL COLUMN

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3701399A1 (en) * 1986-02-24 1987-08-27 Freiberg Brennstoffinst Method and device for determining rheological characteristic values of fine bulk goods
JPH03269340A (en) * 1990-03-20 1991-11-29 Hosokawa Micron Corp Method and instrument for measuring adhesion of granular body
WO1995015213A1 (en) * 1993-12-02 1995-06-08 Rijksuniversiteit Groningen Fluidization of a bed of a cohesive powder
WO1997038297A1 (en) * 1996-04-09 1997-10-16 Amherst Process Instruments, Inc. Apparatus for determining powder flowability

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3701399A1 (en) * 1986-02-24 1987-08-27 Freiberg Brennstoffinst Method and device for determining rheological characteristic values of fine bulk goods
JPH03269340A (en) * 1990-03-20 1991-11-29 Hosokawa Micron Corp Method and instrument for measuring adhesion of granular body
WO1995015213A1 (en) * 1993-12-02 1995-06-08 Rijksuniversiteit Groningen Fluidization of a bed of a cohesive powder
WO1997038297A1 (en) * 1996-04-09 1997-10-16 Amherst Process Instruments, Inc. Apparatus for determining powder flowability

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
IGWE GODWIN JOSEPH I.: "Improved apparatus for measurement of specific surface areas of powders", INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH,, vol. 26, no. 6, June 1987 (1987-06-01), pages 1254 - 1259 *
PATENT ABSTRACTS OF JAPAN vol. 16, no. 85 (P - 1319) 28 February 1992 (1992-02-28) *
VALVERDE JOSE MANUEL ET AL.: "The tensile stregth of cohesive powders and its relationship to consolidation free volume and cohesivity", POWDER TECHNOLOGY,, vol. 97, no. 3, 1 July 1998 (1998-07-01), pages 237 - 245 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002095364A1 (en) * 2001-05-22 2002-11-28 Ingenieria Energetica Y De Contaminacion, S.A. Automatic system for collecting, weighing and releasing solid particles
WO2007042585A3 (en) * 2005-10-11 2007-06-21 Univ Sevilla Method and device for measuring the angle of friction and the cohesion of granular media
CN102706773A (en) * 2011-03-28 2012-10-03 厦门钨业股份有限公司 Characterization method for powder macroscopic flow during extrusion molding process and used device
CN108776081A (en) * 2018-07-05 2018-11-09 中国石油大学(华东) A kind of dissolved gas crude oil flow behavior experiment circuit device
CN108776081B (en) * 2018-07-05 2021-02-09 中国石油大学(华东) An experimental loop device for the flow characteristics of dissolved gas crude oil

Also Published As

Publication number Publication date
ES2131031B1 (en) 2000-03-01
ES2131031A1 (en) 1999-07-01

Similar Documents

Publication Publication Date Title
Ashton et al. Some investigations into the strength and flow properties of powders
Savage et al. Stresses developed by dry cohesionless granular materials sheared in an annular shear cell
De Jong et al. Properly determine powder flowability to maximize plant output
Stahl et al. Discrete element simulation of ballast and gravel under special consideration of grain-shape, grain-size and relative density
Ambroso et al. Penetration depth for shallow impact cratering
Doanh et al. Stick-slip behaviour of model granular materials in drained triaxial compression
Asmar et al. A generalised mixing index in distinct element method simulation of vibrated particulate beds
WO1999027345A1 (en) Device and method for measuring cohesion in fine granular media
Evesque et al. Pile density is a control parameter of sand avalanches
Blanco-Rodríguez et al. Stress distribution in two-dimensional silos
Molenda et al. Airflow resistance of seeds at different bulk densities using Ergun’s equation
Lawrence Jr Ultrasonic shear wave velocities in sand and clay
Williams et al. The preparation of powder specimens for shear cell testing
Ohtsuki et al. Surface level migration in vibrating beds of cohesionless granular materials
Rathbone et al. Aeration, deaeration, and flooding of fine particles
Gu Gravity flowrate of bulk solids from mass flow bins
Lesikar et al. Determination of grain dust explosibility parameters
Rastogi et al. Survey of characterization techniques of dry ultrafine coals and their relationships to transport, handling and storage
Hueso Pore water pressure behaviour and evolution in clays and its influence in the consolidation process
Corriveau et al. Internal friction angles: characterization using biaxial test simulations
Linemann et al. Compaction of Powders due to Vibrations and Shocks
Kumar Fundamental studies on bulk flow characteristics of fine coal
Jiang et al. Undrained cyclic simple shear simulation of liquefiable granular particles subjected to large shear strains up to 100% by 3D DEM
Yanagida et al. Damping characterisation of particulate materials using low intensity vibrations: Methodology for determining damping properties from acceleration transmissibility data and comparison with existing direct experimental techniques
Huber et al. Vibro-viscosity and granular temperature of cylindrical grain skeletons-experiments

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): CA JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
121 Ep: the epo has been informed by wipo that ep was designated in this application
122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: CA