What is Powder Analysis (1)

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BROOKFIELD _ POWDER FLOW TESTER

What are the industrial issues with powders?

The classic problem with powders is their failure to discharge reliably from bins, hoppers, silos, etc., and poor or unpredictable flow in feeders, dosing machines, packing machines, etc. This causes unwanted interruptions in the production process, leading at times to complete plant shutdown in order to correct the flow restrictions and stoppages. It also leads to variations in pack weight, mixture, performance and sensory properties of powder products.

Quality Control Departments are constantly dealing with raw materials in powder form, which come from multiple suppliers. The variability in particle size and distribution, moisture content, and basic ingredients requires a battery of incoming inspection tests, none of which assure that proper flow will take place when loaded into the plant equipment. The Brookfield Powder Flow Tester is a single-solution instrument which can resolve this uncertainty.

R&D Departments are constantly adjusting formulations of powder products to satisfy customer demand for improved properties: better coating action for paints, enhanced taste for spices, rapid dissolving of chemicals when put into solution. New formulations do not necessarily have the same flow properties, thereby leading to production problems when the process is scaled up to high volume. The Brookfield Powder Flow Tester can predict those problems so they can be prevented.

How can flow problems with powders be eliminated?

There is a proven scientific method, called the Flow Function test, which can analyze powders for flow behavior. ASTM D6128 describes this procedure for compressing and shearing powder samples in a defined annular shear cell, using a well-defined methodology established years ago.

Test algorithm for powder flow analysis requires compression of the sample contained in an annular cell to a defined axial load followed by torsional shearing. Raw data output shows torsional load values in red. Compression of sample is shown as axial load values in green.

Particulate materials constitute a large group of solids that can range in size from sub micron particles to large rocks and minerals. Brookfields Powder Flow Tester measures the flow behavior of bulk solid materials that have a top particle size of 2mm. At least 90% of the sample should consist of particles less than 1mm in diameter. In many instances, powders with larger particles can still be characterized effectively by sieving the material at 1mm and testing the fines (the fines control the flow properties of a material with a wide size range). The generic term used by Brookfield to name these materials is powder, therefore the name of our instrument is Powder Flow Tester.

Unlike liquids which, under the influence of gravity, tend to have a horizontal surface, powders exhibit a structure, due to internal friction and cohesion, which allows them to form piles with angles relative to the surface on which they are placed. At ambient conditions, powders do not change flow behavior when subjected to variable shear rates, whereas most liquids do. However, pressure controls the strength of a powder (i.e., increases the resistance to flow) whereas a liquid will show limited change in rheology under pressure. In other words, the consequence of subjecting a powder to a compressive force is that the powder will flow less easily; the relationship between the compressive stress applied to consolidate the powder and the strength it obtains is the measurement of the powder flowability, or its Flow Function.

There is a need throughout industry to characterize powder flow properties and flow behavior. The Brookfield Model PFT Powder Flow Tester is a precision instrument of robust design that satisfies this need and more.

What is powder analysis?

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Why Choose Brookfield?

Brookfield has over 75 years experience in providing reliable, low cost viscosity and texture measurement instruments while offering high quality product support. We are now using this recipe for success to expand our line of physical testing products to include the Powder Flow Tester.

THE NEW BROOKFIELD POWDER FLOW TESTER IS THE SIMPLE ANSWER TO INDUSTRY NEEDS:

The purchase price is a small fraction of current devices on the market.

A competent lab technician can run tests and collect data within minutes, eliminating the need for a powder specialist.

The automated analysis provided by the Powder Flow Pro software calculates various properties of the powder, including the critical dimensions for reliable powder flow out of the hoppers, feeders, bins and silos.

The Wolfson Center for Bulk Solids Handling Technology at the University of Greenwich, England, has worked closely with Brookfield to design the Powder Flow Tester, thereby, ensuring its suitability for practical industrial use.

ApplicationsR&D, Incoming Materials Inspection, New Product Formulation, Quality Control, Process Plant Design

The resulting data produces a Flow Function, much like what is obtained for liquids when testing with a viscometer to create a flow curve.

Flow Function for powder sample shows non-flowing to very cohesive behavior at low consolidation stresses and cohesive behavior at higher consolidation stresses.

Analysis of the Flow Function leads to calculation of the critical outlet dimensions of feeders, hoppers, etc., through which the powder will flow. Comparing the Flow Function, or these critical dimensions, allows powders to be benchmarked, ranked and compared against one another for flowability. The dimensions can also be used to determine whether a particular powder will flow through an existing plant or process, or to determine what the geometry should be if purchasing new solids handling equipment.

Data output from Flow Function test provides Arching Dimension and Rathole diameter. Data output from additional Wall Friction test provides Hopper Half Angle.

Although ASTM D6128 has existed for many years, the instrumentation used to accomplish the test has been expensive to purchase, requires an experienced operator, and may need a technical expert to interpret the results.

The Brookfield Powder Testing Lab

Adhesives

Cosmetics

Chemicals

Construction: Cement

Fly Ash

Gypsum

Hydrated Lime

Detergents

Equipment Manufacturing: Silos

Bins

Feeders

Hoppers

Energy: Biomass

Coal

Fluxes

Food: Beverages

Biscuits

Cereal

Chocolate

Cocoa/Milk Powder

Cookies

Crackers

Flavorings

Flour

Seasonings

Spices

Gunpowder/Ammunition

Healthcare Products: Tablets

Minerals

Personal Care Products: Talcom Powder

Pharmaceuticals

Starch

Properties MeasuredFlow function relation between consolidation stress and powder strength

Angle of internal frictionAngle of wall frictionCohesive strength

Bulk densityArching dimensionRat-hole diameterNormalized flow function



Small Volume Vane Lid.795-13.252 kPa

Standard Volume Vane Lid.289-4.819 kPa

PFT Powder Flow Tester ...affordable testing for powder characterization

The PFT Powder Flow Tester brings quick and easy analysis of powder flow behavior in industrial processing equipment. Evaluate powder discharge from storage containers. Use as QC check for incoming materials. Rapidly characterize new formulations for flowability and adjust composition to match flow behavior of established products.

Choice of Test Options:- Flow Function- Time Consolidated Test with Flow Function- Wall Friction- Bulk Density

Choice of Flow Function Tests:- Demo (8 minutes)- Standard (38 minutes)- Time Consolidation (user-defined)

Real Time Clock Displays: - Test Step- Remaining Time to Completion

Shearing Algorithm Captures:- Peak Stress Value- Subsequent Stable Stress Value- Recognizes Slip Stick Materials

Data Output:- Flow Index for Powder Flowability- Arching Dimension (Index)- Rat-hole Diameter- Hopper Half Angle- Gravity Chute Angle (Wall Friction Angle)- Bulk Density Curve

Compact design with small footprint Tester fits conveniently on workbenchDepth: 15inches / 38cmWidth: 14inches / 36cmHeight: 27inches / 69cm

Developed in association with The Wolfson Centre

for Bulk Solids Handling Technology at the University of Greenwich, England.

Whats Included?

Instrument

Powder Flow Pro Software with USB Cable

Choose one or both:

- Standard Volume Accessory Kit 230cc Trough & 33cc Vane Lid

- Small Volume Accessory Kit 38cc Trough & 5cc Vane Lid

Wall Friction Lid 304 s/s simulated 2B finish

Outer Catch Tray

Inner Catch Tray with Scraper Tool

Powder Scoop

Cleaning Brush

Optional Accessories

Wall Friction Lids in Mild Steel 22-28RA, Tivar 88 or special order

Temperature Probe

Humidity Sensor

Sieve Kit Standard or Small Volume

Carrying Case for easy transport

Sand Castle Demonstration Kit

Powder Flow Demonstration Kit

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Load for Vertical Axis Compression: 7 kg Accuracy 0.6% FSRAxial Speeds: 0.1mm/second up to 5mm/secondDistance: Accuracy 0.3mmTorque: 7.0 Nm Accuracy 1.2% FSRTrough Rotational Speeds: 1 revolution/hour (RPH) up to 5 RPHTemperature Sensing: -20C to 120C*Humidity Sensing: 10% to 95% RH 5%Dimensions (wxdxh): (cm) 36.2 x 39.7 x 67.6 (in) 141/4 x 155/8 x 265/8Weight: 34 kg (75 lb)

PFT POWDER FLOW TESTER SPECIFICATIONS

* Requires Part No. DVP-94Y Requires Part No. PFT-607Y

2GHz processor with 1 GB of RAM and 30 MB hard drive space available 1024x768 video resolution with 128 MB of graphics memory Windows XP, Vista or Windows 7 (32 and 64 bit) with one USB or RS-232 port

MINIMUM COMPUTER SPECIFICATIONS FOR POWDER FLOW PRO SOFTWARE

Outer Catch Tray

ReversibleScraper Tool

Trough

Inner Catch Tray

Outer and Inner Catch Trays with Scraper Tool for Sample Preparation in Trough

Close-up View of Vane Lid used for Flow Function Test.

Close-up View of Wall Friction Lid for wall friction test and density test

Main screen provides choice of basic tests:- Flow Function- Wall Friction- Time Consolidated Flow Function- Bulk Density

Stress data output screen captures normal stress and shear stress values and plots data in graphical format (calculates Mohr Circle Failure Loci).

Flow Function test produces graphs of powder flow behavior which show: Unconfined Failure Strength vs. Major Principal Consolidating

StressArching Dimension vs. Principal Consolidation StressRat-hole Diameter vs. Powder Fill Level

Powder Flow Pro Software Included

Operation and control of the Powder Flow Tester is accomplished with Powder Flow Pro Software.



To assist you in the evaluation of your powder for flow behavior, Brookfield offers a testing service prior to purchase. Provide Brookfield with samples of your product to obtain a complete test report. Data is presented in both graphical and tabular format for easy analysis and interpretation. The following example shows the report format and type of information that is presented. In the concluding section, calculations for critical arching dimension, rat-hole diameter and hopper half angle assess the potential for stoppages due to the powder flow behavior or equipment limitations.

Customer Test ReportDATA COLLECTED BY: BROOKFIELD POWDER FLOW TESTER

STANDARD TESTS

This report follows four samples sent to our lab for evaluation. The specific graph for each sample is color coded for easy identification. Up to eight data sets can be shown on the same graph.

Flow Function Graph (230cc Trough)

This flow function graph illustrates the flowability of the samples over different consolidating stresses. The x-axis parameter is the consolidating stress used to compress the sample; the y-axis parameter is the strength of the powder. Sample (Data Set) #2 is the most cohesive material of all, falling into the very cohesive range throughout all consolidating stresses. Sample (Data Set) #3 powder also falls into this category. Sample (Data Set) #4 is very cohesive at low consolidating stresses (below 1.5 kPa), cohesive at medium stresses (1.5 - 4.5 kPa), and easy flowing at high consolidating stresses (above 4.5 kPa). Sample (Data Set) #1 material is cohesive at consolidating stresses from 0 4.0 kPa, and easy flowing at consolidating stresses above 4 kPa. Sample 2 clearly exhibits the greatest difficulty for reliable flow behavior.

Bulk Density Graph (230cc Trough)

This bulk density graph illustrates the density of the samples over different consolidating stresses. Samples #1 and #4 have almost identical loose fill densities of 900 kg/m. At 9 kPa of consolidating stress, the density of Sample #1 rises to 1150 kg/m and Sample #4 rises to 1200 kg/m. Samples #2 and #3 have similar loose fill densities ranging from 450-500 kg/m. At 9 kPa of consolidating stress, the density of Sample #2 rises to 770 kg/m and Sample #3 rises to 590 kg/m at 12 kPa of consolidating stress. In general a free flowing powder shows a relatively small change in density with more consolidating stress, while a cohesive powder shows a large change in density.

Wall Friction Angle Graph (230cc Trough)

This graph illustrates the angles of wall friction for each powder over different consolidating stresses. At low normal stress (0.5 kPa) all materials had extremely high wall friction angles ranging from 40 to 65. At a higher normal stress (4.75 kPa), the wall friction angles dropped to a range of 20 to 35. Wall friction angles above 30 are considered very high and below 10 are very minimal. This indicates that Sample #2, and perhaps Sample #1, will have difficulty with reliable flow on the hopper wall surface.

Testing Servicefor powder applications

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Internal Friction Angle Graph (230cc Trough)

This graph illustrates the angles of internal friction at different levels of normal stress. The angle of internal friction is a measure of the friction between the powder particles as they slide against each other. Sample #1 and Sample #4 have the lowest angles of internal friction and will therefore flow more readily than the other two powders. The angle of internal friction for Sample #2 and Sample #3 is approximately 50 which is relatively high and indicative of potential flow problems.

Types of Flow Patterns

Mass-FlowCritical Rat-HoleDiameter

StaticMaterial

FlowingCore

Core-Flow

TIME CONSOLIDATION TEST

Additional testing on these samples would investigate the effect of time consolidation, which addresses how powders increase their internal strength when left in bins/hoppers for longer than planned.

Test duration could be as short as 30 minutes or as long as several days. The former represents a\ temporary work stoppage, the latter an extended plant shutdown. Long term time consolidation tests also predict strength buildup in powders stacked on pallets in storage or in transport over long distance.

SummaryCRITICAL ARCHING DIMENSIONS

SAMPLE (DATA SET) #1 21 mm (0.85 in) SAMPLE (DATA SET) #2 480 mm (19 in)SAMPLE (DATA SET) #3 80 mm (3.1 in) SAMPLE (DATA SET) #4 100 mm (3.9 in)

The critical arching dimension is a conservative calculation of the powders potential in mass flow behavior to build a stable bridge over the hopper outlet, thereby restricting flow. The arching values above indicate that the hopper opening must be greater than 480 mm (18.9 in) to ensure reliable discharge of all powders. The critical arching dimension for Sample #2 is much greater than the other three powders due to its very cohesive and sticky nature, thereby having a much greater tendency to form a stable arch. This calculation also applies to the design of any conveyance device directly downstream of the hopper, such as the spacing between flutes on a screw feeder.

The Powder Flow Tester can also be used to calculate the critical rat-hole dimension which relates to a behavioral problem that may occur under core flow conditions. This calculation requires user input on bin shape, cross section dimension(s), and hopper type (wedge, conical). When this information is provided, the Powder Flow Pro software is able to automatically calculate the rat-hole diameter, as well as the hopper half angle.

1 = c 1 = c3 = 0

B.g.Vol

Conical Hopper:

DRH

Dc

RAT-HOLE ARCHING DIMENSIONS

Types of Flow Obstructions

G() x crit __________DRH = B x g

2 x c x 1000 _____________Dc = B x g

Plane Hopper: c x 1000 ___________Dp = B x g

(where 3dp

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What is Powder Analysis (1)