Does Water Quality Affect Green Sand Properties?

Water-soluble salts or electrolytes are just some of the mineral contaminants found in everyday tap water used by foundries across the U.S for their green sand systems. Bentonite is the main bonding compound of green sand systems, and for it to have quality bonding, it first must be activated with the use of an agent. A good activating agent must fulfill three requirements:

  • Be distinctly soluble in water, having a solubility of at least 1 g/100 g of water.
  • Be composed of anions, which react with cations (Na+) to give insoluble compounds.
  • Supply small, univalent cations for ion exchange.

Previous research studied the effect of these electrolytic salts on the physical characteristics of green sand, in particular wet tensile strength. Wet tensile strength testing helps determine the tensile strength of the green sand’s condensation zone after the mold has been poured. Previous research has shown that an increase in the electrolytic salts, found in well water, led to a decrease in wet tensile strength when compared to samples of green sand containing distilled water, where the wet tensile was not affected.

Past research led to the question of whether these electrolytes are causing the decreasing strength within the clay-water relationship. This possibly could be due to the anionic (positively charged ions) nature of sodium bentonite clay and its necessary cationic (negatively charged ions) exchange between the electrolytic salts within the water. Anions and cations react together to form neutralized compounds. An example of this reaction is that of Sodium (Na+) and Chlorine (Cl-) where the two react together forming your basic table salt (NaCl).

Past research conducted on the effect of individual electrolytic salts on the wet tensile strength of green sand showed salts had an immediate effect on the wet tensile strength, with the wet tensile strength decreasing initially. However, as time went on, the wet tensile strength was determined to increase. This was determined to be due to the presence of the particular electrolytes within the system and not the actual concentration.

Recently, trials were conducted at the University of Northern Iowa Metal Casting Center (Cedar Falls, Iowa) to evaluate the effect of contaminants commonly found in tap and well water in the U.S. on green sand properties. Sixteen water samples were obtained from different regions of the country and a series of experiments were designed to evaluate the effect of the measured contaminants.

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