Novel Ceramic Casting Slips for Step Change Improvement in Performance. John Adams

Transcription

1 Novel Ceramic Casting Slips for Step Change Improvement in Performance John Adams

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8 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

9 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

10 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.

11 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

12 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

13 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

14 Predictive Lab Methods - Approaches 1) Tensometer Stress Test Time / Minutes 2) Mud Crack Approach 3) Observation in ESEM 4) Whole Body Characterisation/Analysis 5) Cracking Tolerance Number

15 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

16 Cracking Tolerance Number ) #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A Bending Strength (kg/cm Cast Moisture (wt%) Deformation (mm) Cast Moisture (wt%) Sample Details: Xtracast Moisture Strength Deflection Weight Length Diameter Bulk Density S.G Average 1.80 Slip Solids CMC MOR DEF CTN

17 Size and Shape of Particles Size Shape Steepness

18 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 % Steepness ~ d 75 /d 25 (or some such) Size 2010

19 Particle Characteristics (Source & Engineering) 96 UK Clay 96 US Clay B (ISO) 80 1 AR 80 95%<1μm PSize 40%<2μm B (ISO) AR %<1μm 40%<2μm PSize 1 96 US Delam Clay B (ISO) 1 AR %<1μm 40%<2μm PSize 96 Eng d Clay B (ISO) AR %<1μm 40%<2μm PSize 1

20 Dewatering /Casting Rate Fast Dewatering Blocky Platey Slow Dewatering Fast Casting Slow Casting Engineered Medium Dewatering Medium Casting

21 6.0 Comparison of the Pore Sizes of 2 Bodies Demonstrating Different Particle Packing % Relative Volume High Density (1860 g/l) Low Density (1800 g/l) Pore Size (µm)

22 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

23 Cracking Tolerance Number - 4 Relationship between CTN and CR - Real Data CTN V Casting Rate 80 Standard Bodies CTN Middle East Bodies NSC Novel data Slips y = -8Ln(x) Casting Rate (mm2/min) Casting Rate / mm 2 /min

24 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

25 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