Inorganic Binder System Research Articles

Effect of zirconia as inorganic binder on molds for precision casting

AbstractSand‐casting molds suffer from surface defects and low strength. An organic–inorganic binder conversion process, wherein an organic binder is converted to an inorganic binder, has been proposed to increase the application temperature of the sand‐casting mold and simplify the manufacturing process for precision casting. However, the usable temperature of the typical SiO2–Na2O binder system is limited to approximately 1000°C owing to the low liquefaction temperature of the compound. The resulting glass phase (Na2SiO3) exhibits low viscosity, and the casting of large objects results in low strength. Therefore, in this study, we propose a SiO2–Na2O–ZrO2 ternary inorganic binder system; the addition of zirconia (ZrO2) into sodium silicate (Na2SiO3) as an inorganic binder was expected to increase the operating temperature of the mold and improve its mechanical properties. The results confirmed that the addition of ZrO2 improved the mechanical properties by preventing the formation of Na2SiO3. In addition, a higher sintering temperature corresponded to smaller and larger amounts of Na2SiO3 and Na2ZrSiO5, respectively, and thus a higher strength. Therefore, we expect our developed ternary inorganic binder system to be highly advantageous for producing molds for high‐temperature and precision casting.

Condensation and hydrophobicity of the surface hydroxyl groups between organosilane modified water glass and microsilica

As one of the novel green foundry binders, the bonding strength of two-component inorganic binder system (water glass-microsilica) under wet conditions needs to be further improved. In this work, γ-(methacryloxypropyl) trimethoxy silane (MPS) was added to water glass. The effect of MPS on the storage stability of sand core was studied, based on which the mechanisms of condensation and hydrophobicity of water glass-microsilica were discussed. The results showed that the maximum bonding strength of 1.0 wt% MPS modified sand core was increased by 15.5% at 80–85% RH. MPS promoted the dehydration condensation between water glass and microsilica, which will make its three-dimensional network more complex. Moreover, it formed a hydrophobic organosilane layer on the surface of the bonding bridge, which can play a role in shielding hydrophilic Na+ and prevent the destruction of bonding film by forming Si–O–R bonds, preventing the external water from damaging.

Development of Ternary Inorganic Binder System for Manufacturing High-Functional Ceramic Molds and Core

In existing ceramic mold manufacturing processes, inorganic binder systems (Si-Na, two-component system) are applied to ensure the effective firing strength of the ceramic mold and core. These inorganic binder systems makes it possible to manufacture a ceramic mold and core with high dimensional stability and effective strength. However, as in general sand casting processes, when molten metal is injected at room temperature, there is a limit to the production of thin or complex castings due to reduced fluidity caused by the rapid cooling of the molten metal. In addition, because sodium silicate generated through the vitrification reaction of the inorganic binder is converted into a liquid phase at a temperature of 1,000 °C. or higher, it is somewhat difficult to manufacture parts through high-temperature casting. Therefore, in this study, a high-strength ceramic mold and core test piece with effective strength at high temperature was produced by applying a Si-Na-Ti three-component inorganic binder. The starting particles were coated with binary and ternary inorganic binders and mixed with an organic binder to prepare a molded body, and then heat-treated at 1,000/1,350/1,500 °C to prepare a fired body. In the sample where the two-component inorganic binder was applied, the glass was liquefied at a temperature of 1,000 °C or higher, and the strength decreased. However, the firing strength of the ceramic mold sample containing the three-component inorganic binder was improved, and it was confirmed that it was possible to manufacture a ceramic mold and core via high temperature casting.

Fabrication of a ceramic core for an impeller blade using a 3D printing technique and inorganic binder

Ceramic cores for fabricating an impeller blade were prepared by a process using 3D printing and an inorganic binder system. This process is much simpler than precision casting and can produce ceramic cores with strength suitable for casting. The two types of 3D printer, powder bed binder jet printing (BJP) and selective laser sintering (SLS), with different starting materials were used as 3D printers. The core prepared by the SLS showed a higher strength than that by the BJP because of the smaller particle size of the starting powder, which induces a large specific surface area, resulting in the high coating efficiency of the inorganic binder. The core sample prepared using SLS showed a lower coefficient of thermal expansion than that by BJP, indicating that the core made by SLS is more applicable in precision casting. In addition, the core after casting was completely eluted in a NaOH solution. The casting of the real impeller blade casting was very successful and the precision of the product was excellent.

GEOPOL®. The Innovated Environment Friendly Inorganic Binder System

GEOPOL®. The Innovated Environment Friendly Inorganic Binder System

Effects of South African Silica Sand Properties on the Strength Development and Collapsibility of Single Component Sodium Silicate Binders

Abstract This study shows the results of the investigation of the strength performance, and residual strength of a single component inorganic binder system Cast Clean S27®. The study was conducted using three different foundry sand sources in South Africa. Sample A is an alluvial coastal sample, sample B is an alluvial riverbed sample and Sample C is a blasted sample from a consolidated quartzite rock. The binder was also cured using three different curing mechanisms. The aim of the investigation was to determine the variation of strength performance and residual strength between the different South African sand sources based upon the physical and chemical properties of the sand sources. The moulding sand was prepared using three possible curing mechanisms which are carbon dioxide curing, ester curing and heat curing. The strength measurements were determined by bending strength. Sample A and sample C sand had good strength development. Sample B sand had inferior strength development and excellent high temperature residual strength. The study showed that the single component inorganic binders have good strength development and low residual strength. The silica sand properties have major contributing factors on both strength development and residual strength. The degree of influence of silica sand properties on strength performance and residual strength is dependent on the time of curing and method of curing.

Reliability studies of gelcast fused silica between organic and inorganic binder systems

AbstractFused silica ceramics was prepared by using conventional organic binder, mathacrylamide‐N,N′‐methylenebisacrylamide (MAM‐MBAM) system by gelcasting process. Mechanical properties of green bodies were studied as a function of solid loading varying from 60 to 72 vol%. After evaluating the green body mechanical properties, the samples were densified at different sintering temperature from 1200 to 1450°C with definite intervals of 50°C and subjected to flexural strength analysis. Variation in flexural strength with sintering temperature was observed and correlated with the quantity of devitrification of fused silica during sintering. Quantification of devitrified cristobalite was carried out by using 20 wt% rutile (TiO2) as an internal standard by X‐ray diffraction. It was found that, as the cristobalite content increased, flexural strength decreased. Reliability studies were carried out for the samples having maximum flexural strength with and without crystalline content. Reliability studies have shown that for this organic binder system the sample sintered at 1300°C is crystalline free and most reliable product. The mechanical properties and reliability of this product processed with organic binder are compared with inorganic binder system. Results indicate that the sample fabricated using inorganic binder system is exhibiting high Weibull modulus and thus better reliability.

3D Printing of Inorganic Sand Moulds for Casting Applications

The paper at hand introduces a 3D printing (3DP) process for additive manufacturing of inorganically bound sand moulds. The fundamental differences to 3DP with organic binders (which is state of the art) are explained and the quality relevant process parameters of the inorganic process are introduced. Since the inorganic binder system is thermally activated during the printing process the main focus lies on the heating procedure. The properties of printed specimens are measured by the quality features fluid migration and strength for which novel methods of moulding sand testing are used. Results show that the identified process parameters have a significant influence on specimen properties. The interaction of the attributes fluid migration and strength are also shown. By understanding the relationship between process parameters and quality features the properties of printed inorganic sand moulds can be tailored to fit casting specific requirements.

Granulation processing parameters on the mechanical properties of diatomite-based porous granulates

Abstract The development of cheap natural porous diatomite into catalyst supporting materials has obvious technical interests. High-intensity granulation process in the presence of clay-based inorganic binder system can be used to preserve the porous network of the diatomite structure and enhance mechanical stability of achieved granulates. In this work, via tuning the granulation parameters, such as pan rotation speed, rotation modes between the pan and the impeller, as well as the factor of granulation time, the size distribution and the mechanical stability of formed granulates were adjusted. Specifically, the pan rotation speed can assist the change of granulate growth mechanism and thus affect their mechanical attrition resistant ability; the rotation mode between impeller and pan has an influence on the powder distribution inside of the pan and the modification of granulate growth rate can be observed; and a certain prolongation of granulation time has no influence on granulates mechanical stability but only increases the granulate size.

Development of a New Coating System for the High Functional Mold in Thin-wall Casting

A new inorganic binder system has been developed to prepare the mold having a high strength for the thin-walled casting. To increase the fracture strength at high temperature, a large amount of inorganic binder should be converted into glass phase and the generated glass phase has to be homogeneously coated on the surface of starting particles. In this work, two types of process were employed to investigate the coating and glassification efficiencies of inorganic precursor. In the first process (process I), the green body consisting of starting powder and organic binder was dipped in the inorganic precursor solution. In the second process (process II), the starting powder was coated by inorganic precursor, and then the organic binder was used to form the green body. The mold sample prepared using process II showed the higher strength value than that using process I, owing to the inclement effect on the glassfication efficiency by the loss of inorganic precursor in process I. The prepared real mold was perfectly produced and the casted product showed a clean surface without defects such as dross, nonmetallic inclusions, and crack. Consequently, the new inorganic binder system could be applied for preparing the mold for the thin-wall casting having high mechanical properties.

Powder preparation for a shell mold using a new coating process

A new coating process in the powder preparation for a shell mold has been developed to increase the fracture strength of the shell mold. It is due to the homogeneous formation of a glass phase on the starting particles and the increase in the glassification efficiency by the reduction in the loss of inorganic precursors. The inorganic binder system used for the new coating process is composed of tetraethyl orthosilicate (TEOS) and sodium methoxide (NaOMe) as the silica (SiO2) and sodium oxide (Na2O) precursors, respectively. Three different coating processes are employed for the powder preparation with a high glassification efficiency. In process I, the starting particles are coated with NaOMe, and then TEOS are coated on the particles treated with NaOMe. Process II is the reverse sequence of process I. Process III involves coating of the particles with a mixture of TEOS and NaOMe. The particles coated with an individual or mixture precursor were fixed with an organic binder and then heated at 1000°C for 1h. Molds prepared through the new coating processes, especially process III, show a higher fracture strength value compared with that of the conventional convert mold process, which may be caused by the increase in the glassification efficiency of the precursors. Powder prepared by process III shows a more uniform coating of the glass phase than those by other processes, resulting from an enhancement in the phase mixing between SiO2 and NaOH molecules.

A new in situ process in precision casting for mold fabrication

A new in situ process for mold fabrication in precision casting has been developed to decrease processing time and production costs, and produce an environmentally friendly mold, compared with the conventional process. In the new process, the starting powder is fastened by an inorganic binder, whereas the mold in the conventional process takes its form by using an organic binder. The fixing of powders by the inorganic binder is caused by a sol–gel reaction of precursor materials. Therefore, the new mold process is more environmentally friendly and simpler than the conventional process. The inorganic binder system for the in situ process was prepared from a mixture of tetraethyl orthosilicate and poly(dimethyl siloxane) as SiO 2 precursor, and sodium methoxide as Na 2O precursor. The prepared samples show a fracture strength of about 5 MPa, indicating that the in situ process can be applied to the fabrication of molds having high mechanical properties.

Sol-Gel Derived Binder for Inorganic Composites

A new low cost inorganic binder system for large volume products like fiber insulation, building materials, etc. has been developed based on sol-gel technology. The precursor for the binder system is an amorphous mineral raw material containing silica as the major component. The sol was prepared by dissolving the amorphous mineral material in formic acid and the mineral was dissolved in a few hours dependent on the molarity of the formic acid. The sol stability was dependent on the solids content and the pH. The gel formation was studied using light scattering and NMR. The results show a growing particle size of particles mainly consisting of silica while the other cations were dissolved in the pore liquid. During the drying of the wet gels, salts of these cations were crystallized in the pores and further decomposed during heating. The derived binder shows good wetting properties to mineral fiber surfaces and a good strength of paper-binder composites. The new binder system applicable to approximately 800°C has a great potential as a substitute for some traditional organic systems.