Understanding Materials Flowability (Part I) BSH&E SEMINAR

Transcription

1 Understanding Materials Flowability (Part I)

2 Agenda Session I Corporate Introduction Session II Understanding Materials Flowability I Session III Understanding Materials Flowability II Session IV Pneumatic Conveying Principles Session V Pneumatic Conveying Components Session VI Introduction to Feeding Technology Session VII Feeder Types, Selection & Operation Session VIII Controls Session IX Systems Application Examples

3 Why Plastics?

4 Common Plastic Properties Thermal Properties Melting Point and Other Transitions Heat Deflection Temperature (HDT) Electrical Properties Volume Resistivity Surface Resistivity Tracking Index Electrical Strength Physical Properties Density Water Absorption Vicat Softening Humidity Absorption Thermal Expansion Melt Flow Rate Thermal Conductivity Viscosity Number Flammability Mechanical Properties Tensile & Flexural Compression Impact (Charpy, Izod) Creep Hardness

5 Plastics Compounding Raw Material Receiving Storage Conditioning Conveying Premixing Dosing Extrusion

6 Typical Raw Materials Resin (organic) Fillers (inorganic) Fibers (natural & manmade) Additives (solids & liquids) Rework

7 Pellets Relatively smooth surface Bulk Density 0.4 to 0.6 kg/dm 3 Lens or cylindrical shape approximately 3mm Regular shape Easy to handle Angle of repose < 45

8 Fillers A solid material capable of changing the physical and chemical properties of materials: by surface interaction (or its lack thereof) by its own physical characteristics Classification Chemical composition Mineral, C black, glass, organic, metal Organic vs. Inorganic Wood flour Wollastonite Natural vs. Man-made Glass Aramid Properties

9 Some Industrial Minerals Fillers Mineral ATH Al(OH) 3 Barite BaSO 4 Calcium Carbonate CaCO 3 Kaolin Al 2 O 3.2SiO 2.2H 2 O Mica (muscovite) KAl 2( AlSi 3 O 10 )(OH) 2 Silica SiO 2 Talc Mg 3 Si 4 O 10 (OH) 2 Titanium Dioxide TiO 2 Wollastonite CaSiO 3 Smoke suppressant Use Sound deadening & vibration control Ground vs. precipitated Improves electrical resistivity Reinforcement Filler and reinforcement Increases stiffness and resistance to high temperature creep Weatherability, whiteness, opacity Improves strength, stiffness, scratch resistance

10 Powder Fluidizable to bridge building Free flowing to adhesive or cohesive Very light bulk densities of 0.05 up to 1.5 kg/dm 3 Dry to hygroscopic Non- to very abrasive Typical CaCO 3 & Talc Moist, Sticky Materials Non-Free Flowing Products

11 Plastic Regrind Irregular shapes flakes 3mm thick Large particle size distribution Sharp edges

12 Flowability

13 Flowability Influencers Material Characteristics Physical & chemical properties Particle Interactions With particles, equipment & environment Bulk Properties Compressibility & cohesion Flow Rate Properties Throughput, velocities, flow angles & fluidizability Handling Equipment Geometry, surface finish & abrasion

14 Bulk Powder Behavior Shape/Size Stress Surface Area Packing Porosity Moisture Particle Uniformity Particle Density Powder Flow (powder rheology) Particle Packing (bulk density) Fluid Phase Velocity Aeration Vibration Solid Concentration Shear Angles of Friction Plastic/Elastic Properties Tensile Strength

15 Laboratory Tests Abrasion Particle Shape Sieve Analysis Bulk Density Characteristics Visual Observations Velocities Can Velocity Terminal Velocity Bulk Velocity Flowability Compressibility index or Hausner ratio Flow rate through an orifice Shear cell Flow Angles Angle of external friction Angle of internal friction Angle of repose Angle of slide Conveyor Equipment Manufacturers Association Guidelines CEMA Standard 550, March 26, 2009

16 Scale of Flowability Flow Characteristic Compressibility Index (%) Hausner Ratio Excellent Good Fair Passable Poor Very Poor Very, very poor > 38 > 1.60 Source: Carr. R.L. Evaluating Flow Properties of Solids. Chem. Eng. 1965, 72,

17 Material Characteristics

18 Material Characteristics & Tests Test Property Measured Affects Particle Shape Particle geometry Discharge from hoppers Particle Size & PSD Aspect ratio (L/D) Flowability & Compressibility Particle Hardness Scratch-ability, hardness, abrasion Abrasiveness on equipment. Type of metal and surface treatment used for pipes, bins, hoppers, screws. Particle fragility. Bulk Density Loose & Compact ρ = Weight per unit of volume Storage vessels size & material s compressibility Moisture Content % of water in the material Cohesive strength & arching ability of bulk materials Permeability Ability of the air to pass through bulk material Ability to flood Compressibility Sensitivity of the material to pressure Tendency to pack in a feeder hopper Cohesiveness Tendency of material to adhere to itself Minimum outlet diameter for bins, hoppers, and outlets

19 Circular Glass Silicate BS SE H & M E IN AR Particle Shape Cube Pellets Block Platelets Fiber CaCO3 Feldspar Resin Wood SiO2 BaSO4 Mica Talc Glass Wollastonite Aspect Ratio

20 Particle Size Code A > #35 sieve Code B Code C < #60 sieve

21 Increase of Particle Size

22 Increase of Particle Size

23 Particle Size Distribution Sieve Analysis 100 grams Sample Open inch Micron U.S. No. Wt. grams Note BA BA BA, BL 0 0 PAN 5.9 BA = Balling, BL = Material Blinded Sieve

24 Particle Size & PSD % Passing Sieve Number 1/4 3 1/ Narrow Distribution Top Cut d Particle Size (mm) Broad Distribution

25 Particle Hardness TiO Kaolin CaCO Talc SiO 2 6-7

26 Hardness Methods Mohs Indentation Tabor Brinell Vickers Knoop Rockwell Nanotests Micro Materials Diamond C Corundum Al 2 O 3 Topaz Al 2 SiO 4 (OH - F - ) Quartz SiO 2 Calcite CaCO 3 Gypsum CaSO 4 2H 2 O Talc Mg 3 Si 4 O 10 (OH) Feldspar KAlSi 3 O 8 72 Apatite Ca 5 (PO 4 ) 3 (OH,Cl,F ) 48 Fluorite CaF

27 Particle Interactions

28 Particle Interactions Particle Particle Van de Waals Forces Electrostatic Forces Capillary Forces Sintering Forces Collisions Particle Equipment Friction Shear Strength Particle Environment Humidity Temperature Permeability Vibration Time

29 Particle Particle Interactions Capillary Forces Liquid Bridges! F c = 2πRγ Sintering Process Solid Bridges! R n = kt

30 Particle Particle Interactions van der Waals Forces Hamaker Equation Lifshitz Equation

31 Particle Equipment Interaction Friction Internal Wall Solid particles flowing against each other Angle of internal friction Solid particles sliding along a surface Wall friction angle ΔФ F R ζa A σa V = K

32 Particle Equipment Interactions

33 Particle Environment Interactions

34 Particle Environment Interactions Time Consolidation Increase in strength when stored at rest under compressive stress for a long time interval Sintering Plastic deformation at particle contacts Interactive Forces! σ v A σ c A

35 Summary: Theory to Practice Calculations vs. Observations Flow Types Easy flowing Difficult flowing Adhesive and cohesive Degradable Floodable Prone to segregation

36 Flow Types Easy flowing The material has uniform particle size and shape The material does not absorb air/gas and become fluidized

37 Flow types Difficult flowing The material contains long strands or stringy particles (Fibrous) The material interlocks together and is not easily separate The material has a tendency to grow larger particles because particle surface attraction The material has non-uniform particle size and shape The material is coarse or abrasive The material is fragile of

38 Flow Types Adhesive & Cohesive The material sticks to utensils (Adhesive) The material forms lumps, when compressed, which do not easily fall apart (Cohesive) The material seems to adsorb moisture from the air or your hands during testing (Hygroscopic) The material feels wet or oily (Moist/Oily) CuSO 4 + 5H 2 O CuSO 4. 5H 2 O

39 Flow types Floodable The material contains fine particles that have a tendency to float in the air when disturbed? (Dusty) The material is extremely light weight, easily moved by mild air disturbance? (Fluffy) The material flows across conveyor belts and screws faster than the speed of the conveyor or the screws The material becomes highly charged like a fluid when mixed with air/gas The material is difficult to handle because it flows freely It does not stick together

40 Flow Types Other Difficulties The material particles easily broken or altered from their original state during handling (Degradable) The material has a tendency for different particles sizes to separate during handling (Segregates) The material coat the test lines during terminal & bulk velocity testing (Blinds test tube) The material has irritating characteristics? (Irritant)

41 End of Session II