Humidity-resistant inorganic binder for sand core making in foundry practice

Abstract

The performance of sand core was improved by using the modified water glass as a binder and adding powder additives in the sand hardening process. The optimal proportion of the compound additives was determined by an orthogonal test, with a ratio of microsilica: polyvinyl alcohol solution: borax: B agent = 25: 20: 2: 1. The binder accounted for 2% of the sand by weight, and the compound additives accounted for 0.96%. The core box was heated to 175 °C, and the compressed hot air of 120 °C kept blowing for 40 s. Tensile strength was used as the main indicator to evaluate the humidity-resistance of the sand core. For the sand core, the instant tensile strength reached 0.73 MPa, the tensile strength at room temperature was 1.81 MPa, and that of sand core holding at the condition of 35 °C and 90% RH for 2 h and for 4 h reached 1.61 MPa and 1.19 MPa, respectively. The gas evolution was 7.5 mL•g-1 at 850 °C for 3 min. The residual tensile strength was 0 MPa at 750 °C for 5 min. Fourier-transform infrared spectroscopy analysis showed that the humidity-resistance of the core was greatly improved by the powder additives.

A Comparative Analysis on Organic and Inorganic Core Binders for a Gravity Diecasting Al Alloy Component

“…Compared to earlier product generations, the newest inorganic binder offers an improved humidity resistance, as stated by several research studies. 23,28,43 Specific additives, added to enhance the humidity resistance of cores, enable reaching up to 5 days of storage at 30°C and 70 % relative humidity without any significant impairment of strength. The literature and present findings revealed that inorganic cores exhibit a greater tendency to moisture absorption, as confirmed by the greater HL values resulting from the moisture absorption comparative tests conducted through the climatic chamber.…”

“…It has been proved that additives enhanced the bending strength and long-term stability of cores. 28,44 In addition, it should be pointed out that the storage stability of inorganic cores can be considerably extended by some logistical/practical techniques, such as air-conditioning the core storage areas within the foundry or reducing the core storage time by employing line production. In this regard, this study reveals that long storage in the foundry warehouse, up to 14 days (at 18°C and 32 % relative humidity), does not compromise the tolerances of inorganic cores, as demonstrated by the optical 3D analysis of surfaces.…”

“…[25][26][27] Attention has also been paid to the humidity resistance of sodium silicate bonded sands and to the curing of the binder. [28][29][30][31][32][33][34][35][36] Although extensive research has been devoted to binders systems, few studies have directly investigated their direct employment in the foundry, 37 also considering the effects of moisture absorption on their performances. 38 The present experimental study aims to contribute to this growing research and industrial topic by investigating this moisture absorption effects on the performance of organic and inorganic sand cores employed to produce a gravity diecasting Al alloy component.…”

Limitations and advancements of Sodium Silicate inorganic sand binders; A review

“…Another proposed solution was the utilization of additives that reduce the number of hydrophilic groups within the binder. Sond et al identified that adding micro silica, polyvinyl alcohol solution, borax, and an agent called B agent in the ratio of 25: 20: 2: 1 increased the tensile strength more than four times (1.19 MPa vs 0.27 MPa) when tested after 4 hours in 90% relative humidity [13,14].…”

Technological and Quality Aspects of the Use of Innovative Inorganic Binders in the Production of Castings

“…The curing reaction then runs according to the Equation (1). In contrast to traditional processes, the dehydration curing process of alkaline silicates results in significantly higher mechanical properties of molding mixtures, in this case determined as transverse strength, even at significantly lower binder dosages [8][9][10]. See the differences of transverse strength of molding mixtures using alkaline silicates binders cured by different methods in Figure 1, where the reference value 100% means the strength value for "microwave" curing (marked as MV) of molding mixture with inorganic binder and reaches transverse strength of approximately 4 MPa.…”