ABSTRACT
In this paper, the parameters of composite modifiers composed of polyvinylpyrrolidone (PVP), lithium tetraborate and disodium hydrogen phosphate for ester-hardened sodium silicate bonded sand (SSBS) were optimized by orthogonal experiment. The results of orthogonal experiment showed the optimal parameters of PVP, lithium tetraborate and disodium hydrogen phosphate were 8%, 0.15% and 0.2% of sodium silicate binder, and the1 h tensile strength (σ1 h) and the 24 tensile strength (σ24 h) of modified sand samples increased by 44% and 66% and the residual strength (σ950°C) decreased by 49%. The experimental results indicated that the modifiers promoted the bonding bridges of sand sample smoother and tighter at room temperature, which improved the 1 h and 24 tensile strength, and facilitated the formation of Na2Si2O5, Na3PO4, Na4B2O5 and Li2B8O13 and the volatilization of PVP in the process of heating and cooling at 950°C, resulting in the formation of cracks and blow holes on bonding bridges, thereby improving the collapsibility of SSBS.
Highlights
The polyvinylpyrrolidone was the most dominant parameter for the properties of SSBS.
The 1 h and 24 h tensile strength of modified sand samples increased by 44% and 66% and the residual strength decreased by 49%.
The composite modifiers promoted the bonding bridges of sand samples smoother and tighter at room temperature.
Cracks and blow holes emerged on the bonding bridges of modified sand samples in the process of heating and cooling at 950°C.