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If your slurry control charts look more like shark teeth than an Iowa cornfield, perhaps you have some opportunity to control your process better.  If you don’t have slurry control charts, do you know what is happening in your slurry over time?  Charting your key parameters provides a visual indication of variability in your process.  The easiest way to reduce variability is to control what is being added to the slurry.OLYMPUS DIGITAL CAMERA

By spending some time reviewing slurry additions, you can minimize variability of key parameters during the shell building process.  Here are a few tips to consider:

  • SiO2 will climb over time so, have your target SiO2 for your make-up slurry about 1 to 2 percentage points below the center point of the dip tank range.
  • Viscosity will also climb, so, target the make-up tank to be about 2 seconds below the dip tank.
  • If pre-wet is being used, target a higher viscosity for the make-up tank.  Do some experimentation to determine the optimal viscosity range of the make-up slurry to maintain the dip tank viscosity through slurry additions.  The goal is to avoid making flour additions directly into the dip tank.
  • Make sure that the pre-wet is being monitored and controlled for key metrics including SiO2, % polymer and bacteria.
  • Educate your operators on when they should use water, binder or a binder-polymer “cocktail” when adjusting viscosity of both the make-up slurry and the dip tank.
  • Monitor and control the make-up slurry as closely as the dip tank.  Optimize the make-up slurry formulation so adjustments to the dip tank are minimal.

Steven Covey might not be an expert on precision investment casting, but he was correct when he said, “Begin with the End in Mind. ” Following these few simple steps will go a long way towards minimizing process variability while saving time and money.