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Particle Size and Distribution: Theory and Application

Particle Size and Distribution: Theory and Application A primary objective of any powder coating application is to achieve the highest possible First Pass Transfer Efficiency for the powder. Maximizing FPTE requires utilizing powder that has a PSD paired to that specific application.

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Particle Size and Distribution: Theory and Application

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  1. Particle Size and Distribution: Theory and Application A primary objective of any powder coating application is to achieve the highest possible First Pass Transfer Efficiency for the powder. Maximizing FPTE requires utilizing powder that has a PSD paired to that specificapplication. A correct understanding of how PSD relates to an application is essential to selecting the best target forachieving that FPTE goal and maintaining System Balance. The heart of PSD analysis resides with knowing the attributes of particle size. Stephen Larson Bigfork Research Bigfork Research

  2. Particle Size and Distribution: Theory and Application SURFACE AREA Charge to Mass Ratio Forces! - Electrical, Inertial, and Gravitational PSD Values – Quick Overview PSD – Preferential Deposition, Adjusting for Application Case Study 1 – Out of Control – Virgin to Reclaim Ratio Case Study 2 - PSD too Narrow? PSD Specifications – Examples Papers and Articles Bigfork Research

  3. Surface Area / Volume “When a cell grows, its volume increases at a greater rate than it’s surface area, therefore it’s SA:V ratio decreases.” “When an object/cell is very small, it has a large surface area to volume ratio, while a large object/cell has a small surface area to volume ratio.” - No Brain Too Small*Biology, NZ 1um = A 3.14 / V .52 SA/V Ratio: 6 : 1 10 um = A 314.16 / V 523.6 SA/V Ratio: .6 : 1 50um = A 5026.55 / V 33,510 SA/V Ratio: .15 : 1 100um = A 31,415 / V 52.4MM SA/V Ratio: 6.0e -4 : 1 Surface Area plays a key role in determining electrostatic properties of a particle, as expressed by Charge (Q) to Mass (M) ratio. Bigfork Research

  4. Q/M - Charge to Mass Ratio • “particle charge to mass ratio is inversely proportional to the particle diameter” • “Charge to mass ratio is a critical parameter that needs to be determined in • order to accurately predict behavior of a charged particle exposed to inertial, electrical, and gravitational forces. The effectiveness of various electrostatic applications depends directly on this parameter. “ • - Toljic, Adamiak, Castle, University of Western Ontario • Factors • Particle Volume • Density • Surface Charge Density • Take-Away • Smaller Particles > Surface Area • Increased Surface Area = Increased Charge • Smaller Particles = Increased Q/M • Increased Density = Decreased Q/M Bigfork Research

  5. FORCES! • Electrical • Small Particles are more affected by the Charge Field versus Larger Particles. • Attracted to Edges • Increased Wrap • Ion Wind • “the interaction between the movement of charged particles and ions and the electrically neutral air in which they are suspended which in • turn gives rise to an additional component of forward velocity.” • - Hughes, U of Southhampton, 1995 Bigfork Research

  6. FORCES! • Inertial • “Whencompared with fine particles, large particles tend to • have more straight-line motion.” • - Paul R. Horinka, Morton International, Powder Coatings • Therefore larger particles: • Increase Throw into Racking Depth • Increase Penetration into Faraday Areas • Gravitational • “As particle size increases, gravitational force increases while electrostatic force declines” -Toljic, Adamiak, Castle • Coarse Particles on Booth Floor • Powder Cascade from Top to Bottom of Racks Bigfork Research

  7. Particle Size Distribution: Primary Values d(0.1) - Fines Value decreases, % of Fines Increase Increases with Reclaim Poor Fluidization - Storage Stability Surging and Spitting Limitation of Film Thickness (Back Ionization) Increased Powder Delivery Pressures Impact Fusion Reduces Filter Life Particle Breakdown in System d(0.5) - Average Primary Mfg. QC Value for PSD 40um – Default for GI Smooth Focus for Adjusting to Applications D(0.9) – Coarse Value Increases, % Coarse Particles Increase Important for Faraday Penetration Gravity and Booth Floor Sweeping Bigfork Research

  8. PSD – Preferential Deposition, Adjusting for Application, and Other Factors • One PSD Does Not Fit All • Preferential Deposition of Optimal • Powder Particle size will change with • Application • Each Application Is Unique • Part Geometry • Racking and Hanging Efficiency • Type, Age, and Condition of Equipment • Line Speed • Powder Formulation • Coating Requirements Bigfork Research

  9. Case Study: PSD Adjustment for System Balance Application: Utility Vehicles Powder Platform: Polyester TGIC Part Types: Frames, Suspension Parts, Utility Beds, Tubing Quality Issues: Inconsistent application properties, light\zero faraday penetration, poor fluidization, excessive air pressure settings, impact fusion, and …. … Going through wear parts very quickly. Bigfork Research

  10. Case Study: PSD Adjustment for System Balance Top PSD Curve - Virgin Bottom PSD Curve - Hopper Bigfork Research

  11. PSD and Adjustment – System Balance Virgin to Reclaim Analysis – d(0.5) Average Bigfork Research

  12. PSD and Adjustment – System Balance Virgin to Reclaim Analysis – d(0.1) Fines Bigfork Research

  13. PSD and Adjustment – System Balance Virgin to Reclaim Analysis – d(0.9) Coarse Bigfork Research

  14. Case Study: Poor Faraday Coverage – Powder Manufacturing Plant 1 vs 2 Application: Riding Lawn Mowers Powder Platform: Polyester Primid Part Types: Frames, Brackets, Mower Decks, Fenders Quality Issues: Inconsistent application properties - reducedfaraday coverage with specific lots Bigfork Research

  15. Case Study: Poor Faraday Coverage – • Powder Manufacturing Plant 1 vs 2 • Applicator Observation: Certain lots of incoming powder exhibited reduced Faraday Coverage. • Investigation: • Fluidization properties between the two lots were very similar, with a slight increase in fluidization from Plant 2. • All other properties similar, i.e., reactivity and flow • PSD of Plant 2 significantly tighter, in theory, better • Adjustments were made to the PSD of Plant 2 powder, problem is resolved Bigfork Research

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  17. Articles: “Surface Area to Volume” - No Brain too Small, Biology Group, NZ “Determination of Particle Charge to Mass Ratio Distribution in Electrostatic Applications: A Brief Review” - Toljic, Adamiak, Castle Dept. of Electrical and Computer Engineering, University of Western Ontario, 2008 “Electrostatic Powder Coating” - Dr. J.F. Hughes Department of Electrical Engineering University of Southampton England, 1984 “Powder Particle Size: It’s Effects on Coating Line Performance” - Paul R. Horinka Morton International Powder Coatings 1995 Bigfork Research

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