Novel Ceramic Casting Slips for Step Change Improvement in Performance John Adams
Background - 1 Casting Slip Components Kaolin clay Ball clay Feldspar Quartz Chemical additives (eg dispersants) Products Tableware Earthenware Porcelain Stoneware Sanitaryware Wash basins Shower trays Lavatories Urinals Bidets
Background - 2 Most adjustments to slip compositions aimed at increasing cracking resistance reduce casting rate (which should be high to minimise production times and costs). Adjustments usually alter: -viscosity - thixotropy (time dependent increase in viscosity) - slip density Packing Density of particles in the Green Body Particle Engineering Mineral composition Particle size Particle size distribution Particle shape Particle shape distribution Using: + Chemical Manipulation Salt content Trace elements and ions Organic content Dispersants/deflocculants
Background - 3 Industrial processes operate at casting rates (CR) between 0.5 and 2.5 mm 2 /min (1 mm 2 /min corresponds to 60 min in a mould to form a green body with a thickness of ~ 8 mm (8 mm) 2 /60 min ~ 1 mm 2 /min) Processing speeds and workflow in factory, before and after slip casting, cannot easily be adjusted to meet any substantial change to this rate. SO, we need to improve cracking resistance BUT stay within the practically-possible CR.
A Major Barrier to Progress Traditional methods for testing a slip involve industrial-scale trials. There was no reliable, industry-accepted, (speedy) lab-based testing procedure. SO, if cracking is excessive, adjustments are made to the casting slip, little-by-little, to solve the problem. High production losses result till the problem is solved. Innovation Needed
Discussions with Major Customers Cracking can occur: 1. In the mould (against mechanical resistance) 2. On removal from the mould 3. During cutting or working 4. During drying (moisture gradients) 5. During firing mechanical & temp stresses Concentrate on Stages 1 => 4. The origins of problems in Stage 5 are thought to be different. Innovation Needed
Innovations Required 1. Generation of new predictive methodology 2. Development of ffundamental understanding of how slip properties affect cracking resistance (desire to use locally-sourced materials globally) 3. Development of novel products/formulations Proof of performance in full scale production environment
Predictive Lab Methods - Approaches 1) Tensometer Stress Test 12 10 8 6 4 2 0 0 20 40 60 80 100 120 140 160 180 200-2 Time / Minutes 2) Mud Crack Approach 3) Observation in ESEM 4) Whole Body Characterisation/Analysis 5) Cracking Tolerance Number
Cracking Tolerance Number (CTN) - 1 Resistance to Cracking - wet strength; plasticity Exacerbation of Cracking - shrinkage At a critical moisture content the MoR or Plasticity vs moisture curve goes through a break of slope. At the break of slope a Cracking Tolerance Number gives a measure of the resistance to cracking of the green body. CTN cmc = (MoR cmc x Plasticity cmc ) / (Moisture slip cmc) x 0.33 where: MoR = Modulus of Rupture Plasticity = Deformation of bars Moisture slip = initial moisture content of slip cmc = critical moisture content of bars
Cracking Tolerance Number - 2 2 ) #N/A #N/A #N/A #N/A 12.00 #N/A #N/A #N/A #N/A #N/A #N/A 10.00 #N/A #N/A 14.78 9.85 1.198 14.4 8.00 14.13 10.24 10.384 1.1043 0.986 13.55 10.5091 12.65 6.00 10.842 0.87 0.5475 Bending Strength (kg/cm 4.00 2.00 0.00 5 7 9 11 13 15 17 19 Cast Moisture (wt%) Deformation (mm) 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 5 7 9 11 13 15 17 19 Cast Moisture (wt%) Sample Details: Xtracast Moisture Strength Deflection Weight Length Diameter Bulk Density 16.56 4.93 4.10 1.9173 35.70 6.17 1.80 15.67 8.61 2.17 1.7195 31.58 6.17 1.82 15.40 8.83 1.72 2.1232 39.24 6.18 1.80 15.30 9.45 1.38 1.7769 32.75 6.19 1.80 14.78 9.85 1.20 1.7499 32.52 6.18 1.79 14.40 10.24 1.10 S.G. 2.64 Average 1.80 Slip 14.13 10.38 0.99 13.55 10.51 0.87 Solids CMC MOR DEF CTN 12.65 10.84 0.55 72.4 15.0 9.90 1.28 30.2
Size and Shape of Particles Size Shape Steepness
Particle Size, Shape and Steepness t Size = esd (function of d,t; technique specific) 1980 d 1990 % Finer Than 75% 50% Shape - Aspect Ratio = d/t 2000 25% Steepness ~ d 75 /d 25 (or some such) Size 2010
Particle Characteristics (Source & Engineering) 96 UK Clay 96 US Clay B (ISO) 80 1 AR 80 95%<1μm PSize 40%<2μm B (ISO) AR 80 80 95%<1μm 40%<2μm PSize 1 96 US Delam Clay B (ISO) 1 AR 80 80 95%<1μm 40%<2μm PSize 96 Eng d Clay B (ISO) AR 80 80 95%<1μm 40%<2μm PSize 1
Dewatering /Casting Rate Fast Dewatering Blocky Platey Slow Dewatering Fast Casting Slow Casting Engineered Medium Dewatering Medium Casting
6.0 Comparison of the Pore Sizes of 2 Bodies Demonstrating Different Particle Packing % Relative Volume 5.0 4.0 3.0 2.0 High Density (1860 g/l) Low Density (1800 g/l) 1.0 0.0 0.010 0.10 1.0 10.0 Pore Size (µm)
Cracking Tolerance Number - 3 Relationship between CTN and CR - Conceptual Picture CTN Innovative Slips State-of-the-art Slips 1.0 CR (mm 2 )/min
Cracking Tolerance Number - 4 Relationship between CTN and CR - Real Data 100 90 CTN V Casting Rate 80 Standard Bodies CTN 70 60 50 40 Middle East Bodies NSC Novel data Slips 30 20 y = -8Ln(x) + 23 10 0 0 0.5 1 1.5 2 2.5 Casting Rate (mm2/min) Casting Rate / mm 2 /min
Cracking Tolerance Number - 5 Production Scale Proof of Performance Factory Trials Using a Slip containing a Novel Engineered Clay 5 Trials at Factory 1 losses reduced by 0.9% 2 Trials at Factory 2 losses reduced by 3.7% Phased introduction to Production
Summary 1. Invented novel predictive method 2. Developed fundamental understanding of key parameters 3. Developed novel slip formulations based on particle packing considerations 4. Proved the performance of new products with customers Nigel Glasson Neil Forbes Brian Waters Acknowledgements Tony Hiorns Chris Nutbeem