I am doing a small quality analysis of a ceramic slip-casting process. I'd like to find out how many percentage of the quality faults, in general, is caused by different phases of the slip casting process starting from the preparation of the slip to its casting, green-state processing, firing and glazing (if that is done).
People usually tell me that appx. 10 % of all the pieces in slip casting go to reject (some can be reprocessed). I assume most of this is caused by fluctuation in the slurry quality due to raw material variation and partly wrong dosing of additives which both cause agglomeration, changes in thixotrophy, etc. that mostly cause problems seen after firing. Maybe second biggest problem is the casting where mold wear is the biggest problem?
Would anyone have any source or research material or even a hunch if I'm right?
Päivää, Matti. I too have heard the 10% reject figure for ceramic processing. Issues revolve around agglomerates causing voids (and thus points of weakness) on firing. There's a balance between making a small well-packed structure for optimum strength and powder and slurry processing (attractive forces causing aggregation; need to keep the particles about before they come together etc). Some basic introduction can be found in:
October 2nd, 2013 The PSD, zeta potential, and rheology of ceramic materials and ceramic slurries/suspensions
https://www.brainshark.com/malvern/vu?pi=97328853&text=M021507
Also see the attached.
Thank you Alan! Those really are the challenges when preparing a slip.
I would also like to find out the rough percentages of what causes the rejects in general. If 10 % is the total amount of reject, then does anyone know what portion of that is caused by the variation in the slip (that Dr. Rawle mentioned) and what comes from the mold wear, etc.?
Dear Matti,
Your 10 % of total amount of reject looks very high comparing with our experiments (3-4 %) in Hungary. So please first prepare a "Pareto diagram" of defective products and give a distribution of the reasons. Using permanent raw material composition wth the same pőlymotph modification and cristalin structure and permanent processing technology, the temperature of slip and the mold wear are playing also very important roll as well as humadity, temperature and air-circulation in the halle of slipcasing and drying.
Regards,
László A. Gömze
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