Organic Binder System Research Articles

Research of the New Laboratory Methodology for Measuring the Disintegration of Mixtures with Inorganic Binders Hardened by Dehydration

The paper deals with the possibilities of using alkali silicate based inorganic binders for automotive industry aluminium castings production. In recent years, inorganic binders are coming back to the foreground and their manufacturers are developing new processes, which are starting to progressively supersede organic binder systems. Paper describes known knowledge about classic alkali silicate binders with focus on hardening processes and on improving their technological properties. Trends from the area of development and the use new alkali silicate based inorganic binders are also shortly described. As part of the experimental work, specific methods of producing samples were developed, with the help of which properties such as disintegration were subsequently evaluated by measuring abrasion and residual strengths. Characteristics such as residual compressive strength or shear strength at different thermal loads were also evaluated. When comparing the laboratory results with the results of de-coring in real conditions, a high degree of correlation was achieved, which makes it possible to determine the optimal recipe/procedure for the production of geometrically complex cores.

A Test Stand for Quantifying the Core Gas Release and the Gas Permeability of Inorganically-Bound Foundry Cores

Environmental and work safety aspects necessitate a radical change in the foundry industry. Organic binder systems for foundry sand cores create toxic combustion products and are, therefore, more and more often substituted by inorganic binder systems. While providing an environmental advantage by mainly releasing water vapor, inorganic binder systems impose new challenges for the casting process. The gas release of inorganically-bound foundry cores can lead to increased gas porosity in the cast parts and thus to high scrap rates. The present work aims to gain more understanding of the gas generation and transport in inorganic sand binder systems. We developed a test stand to measure the temperature-dependent core gas release in inorganically-bound foundry cores and their gas permeability. Samples were prepared in a core blowing process and analyzed using the test stand. The measurement results are in good agreement with validation experiments and existing literature.

A dimensional analysis based model to predict completion of solvent debinding step for Metal Injection Moulded parts

ABSTRACT The objective of this study is to develop a mathematical model to predict, for instance, the time for complete debinding of a metal injection moulded (MIM) part, the extent of solvent debinding (%) at any point of time and the debinding rate (g/min). To this end, two feedstocks, one containing carbonyl iron powder and the other made from irregular-shaped metallic particles from the shopfloor grinding sludge (both mixed with an organic binder system) were used to make by MIM, parts of nine different geometries. Each geometry has its own modulus. The effects of powder material, solid loading (influencing the binder content) and debinding temperature on the debinding characteristics were studied for the moduli of the nine parts. Parts with smaller moduli (thin parts) were found to debind faster than those with higher moduli. Parts, made of carbonyl iron feedstock (CI90), debind faster than that made of irregular-shaped particulates. A generalised solvent debinding model based on dimensional analysis has been proposed and verified experimentally. The root mean square error was found to be approximately 4% between experimentally determined and predicted debinding characteristics. These predictions are used to effectively design and curtail the solvent debinding cycles in MIM process.

The virtual core - modelling and optimization of core manufacturing and application

Development and manufacturing of high quality cast parts with tight dimensional requirements depend to a large extent on the stability and application of the sand cores. The core-sand is based on a complex granular multi-material system, where curing of an organic or inorganic system bond the grains into a porous core. The chosen combination of sand and binder determines the thermo-mechanical properties of the core. The paper provides an overview of current modelling capabilities along the life cycle of sand cores. A detailed analysis of the production steps is presented as well as the resulting properties linked to the application in the casting process. Several questions and some answers are given to the understanding of core related defects and how simulation can bridge the gap between core production and application of cores in the casting process. Today, process simulation of sand core production is an accepted tool for core box design and prediction of robust production conditions. The first modelling step is core shooting where expanding air is the driving force for sand flow from a core shooting machine into the core box. Coupled two phase flow modelling of air and granular material is required to represent the process sufficiently. The final process step in core manufacturing is core curing and moisture transport where porous media gas flow modelling is applied. Phase transformations as well as the relevant transport phenomena and the complete heat balance in case of thermally controlled processes need to be considered. During casting the deformation of the bonded sand material is generally governed by thermal expansion, phase transformation and the location of core prints. For long thin walled cores, buoyancy forces due to density differences between the cast material and the bonded sand material can play an important role due to creep effects in the organic binder systems. For inorganic systems moisture content and moisture transport during casting are affecting the mechanical behaviour, such as bending strength. The paper presents a detailed overview of a recent implemented soil plasticity model which is calibrated for different binder systems and sand types. The data are based on comprehensive mechanical tests to provide temperature, moisture and time dependent input data for the shown examples. This includes new steps and future challenges in modelling the anisotropy of printed sand cores and digitalization of the foundry in general.

Influence of albumin and methylcellulose additives on the mechanical behaviour of mullite-based cellular green bodies

In this work, the influence of bovine serum albumin (BSA) and methylcellulose (MC) as processing additives on the mechanical behaviour of the mullite-based cellular green bodies determined by diametral compression was studied. Two different forming routes were used to prepare compacts, which are based on the thermal treatment of aqueous suspensions foamed by mechanical stirring. The cellular microstructure of the green bodies was characterized in detail, by the use of 3D-stereological analysis. Parameters obtained relative to the cells’ features (amount, size, type, morphology, etc.) were related to the forming route and the composition of each system. Stress-strain curves were obtained from load-displacement data, and which, together with those calculated mechanical parameters, were ranalyzed in order to get information about the role of the organic binder system.

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.

Process Parameter Optimization of Extrusion-Based 3D Metal Printing Utilizing PW-LDPE-SA Binder System.

Recently, with a broadening range of available materials and alteration of feeding processes, several extrusion-based 3D printing processes for metal materials have been developed. An emerging process is applicable for the fabrication of metal parts into electronics and composites. In this paper, some critical parameters of extrusion-based 3D printing processes were optimized by a series of experiments with a melting extrusion printer. The raw materials were copper powder and a thermoplastic organic binder system and the system included paraffin wax, low density polyethylene, and stearic acid (PW–LDPE–SA). The homogeneity and rheological behaviour of the raw materials, the strength of the green samples, and the hardness of the sintered samples were investigated. Moreover, the printing and sintering parameters were optimized with an orthogonal design method. The influence factors in regard to the ultimate tensile strength of the green samples can be described as follows: infill degree > raster angle > layer thickness. As for the sintering process, the major factor on hardness is sintering temperature, followed by holding time and heating rate. The highest hardness of the sintered samples was very close to the average hardness of commercially pure copper material. Generally, the extrusion-based printing process for producing metal materials is a promising strategy because it has some advantages over traditional approaches for cost, efficiency, and simplicity.

Foundry sand core property assessment by 3-point bending test evaluation

Improved understanding of foundry sand core properties is a key requirement for high precision casting process development. The present work demonstrates the potential to evaluate mechanical and functional sand core properties using precisely acquired 3-point bending test load curve data applying standard bending test geometries.Four organic binder systems have been investigated. Further to bending strength and the elastic modulus, which can be directly derived from the load curves, a load curve pre-treatment to eliminate sample settlement effects was applied for a corrected deflection and stiffness analysis. The consumed mechanical work shows characteristic elastic and plastic work portions until fracture, which are specific for different sand cores, respectively their condition. Dimensionless indicators to quantify core brittleness have been developed based on curve and on work parameters.In general for mechanical evaluations of resin bonded sand cores, visco-plastic effects need to be considered, as for not fully hardened binder systems decreased strength, deflection and work of fracture were observed at lower load speeds.The benchmark results show that the load curve evaluation concept is a suitable tool to analyse foundry sand core properties more sensitively.

Application of cores and binders in metalcasting

This paper offers an overview of fundamentals and recent global developments of cores and binders used in metalcasting operations. The basic technical characteristics of salt and sand cores are provided along with organic and inorganic binder systems. A particular attention is paid to inorganic binders, receiving recently a renewed interest. The description of research and development efforts is accompanied by history and present status of commercial solutions used by the casting industry. The new development directions, aimed at meeting the growing complexity of the component design requirements and ever-more stringent environmental regulations, are emphasised.

Synthesis and characterization of terbium-doped SrSnO3 pigments

Present work contains results related to the synthesis of new ceramic pigments based on strontium stannate in which a part of tin ions was substituted by terbium ions. The pigments of general formula SrSn1−xTbxO3, where x=0–0.5, were synthesized by solid state reaction and by suspension mixing of initial reagents. The samples were characterized by X-ray diffraction analysis, colouristic analysis, lightfastness, scanning electron microscopy and particle size analysis. Single phase powders which were prepared by solid state reaction at the temperature of 1400°C have a perovskite orthorhombic crystal structure and an increasing content of terbium causes a shift of the diffraction lines and an expansion of the unit cell. Mechanoactivation and the subsequent calcination at the temperature 1500°C can be suggested as the preferable method for obtaining the pigments with the most interesting colour properties and with the highest light stability. Strontium stannate pigments doped by terbium were characterized with interesting light yellow colour. Formula SrSn0.5Tb0.5O3 presents a composition of the sample with the best colour properties. A technological use of the pigments was tested by application into an organic binder system and high temperature ceramic glazes.

Physical and Electrical Characteristics of Silver-Copper Nanopaste as Alternative Die-Attach

A silver-copper (Ag-Cu) nanopaste that formulated by mixing Ag and Cu nanoparticles with an organic binder and solvent system for high-temperature die-attach application has been reported. Various weight percent of Cu nanoparticles (20-80 wt%) was loaded in the nanopaste, in order to investigate its effect on physical and electrical properties of the sintered nanopaste at 380 °C without application of external pressure. X-ray diffraction results showed that Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">97</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">99</sub> , and CuO phases were formed in sintered nanopaste. Porosity of the sintered nanopaste was increased as the loading of Cu increased. A reversed trend has been recorded in the density of the sintered samples. Surface micrographs and topographs were examined by scanning electron microscope and atomic force microscope, respectively. The structural properties obtained from both characterizations were in agreement. Electrical study showed that the sintered nanopaste has electrical conductivity ranging between 2.27×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and 0.81×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> (Ω-cm) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with a reducing value as the loading of Cu increases. These values, supported by other complementary characterizations results, have demonstrated that this nanopaste is able to be considered as the alternative die-attach material for high-temperature applications.

Effect of Sintering Temperature on Silver-Copper Nanopaste as High Temperature Die Attach Material

A novel stencil-printable silver-copper (Ag-Cu) nanopaste that serves as an alternative high temperature die attach material was introduced in this study. The nanopaste was made by mixing 50 nm-sized of Ag and Cu particles with an organic binder system. Sintering temperatures, up to 450°C, were used to sinter nanopaste in air and its post sintered properties were investigated. The viscosity of nanopaste was 350,000 cps and it demonstrated a shear thinning behavior. Scanning electron microscope revealed the change of grain structure with the change in the sintering temperature. Formations of Ag97Cu3 and Ag1Cu99 compounds after sintering were confirmed with X-ray diffraction; and the electrical conductivity of the sintered nanopaste was increased with the increase of the sintering temperature. The study concluded 380°C was the optimum sintering temperature to form a well sintered nanopaste.

Core Viability Simulation for Salt Core Technology in High-Pressure Die Casting

In high-pressure die casting (HPDC) undercuts can only be fabricated by using complex high-maintenance sliders. Until now, this technology has not been used for large-scale and cost-sensitive serial applications. Sand cores from sand-and low-pressure die casting with organic and inorganic binder systems are not suitable for application in HPDC. Using lost cores made from sodium chloride may be a solution for HPDC. Due to the high dynamic forces during the casting process, core failure is still a problem, especially with high ingate velocities.

Characterization of metal oxide-doped lutetium orthoferrite powders from the pigmentary point of view

This thesis deals with the preparation and characterization of inorganic pigments based on perovskite structure of metal oxide-doped LuFeO3. Powder samples were prepared by the conventional ceramic method, i.e., solid-state reaction. Heating temperature was chosen according to results of TG/DTA. Prepared pigments were incorporated into an organic binder system, and their color properties were evaluated by measuring the reflectance in the visible region of light. The most interesting color properties were obtained by preparation of sample Lu0.98Ca0.02FeO3−δ with mineralizer LiF at the temperature 900 °C. Mean size of its particles is 4 μm. X-ray diffraction analysis confirmed a single-phase orthorhombic structure with lattice parameters a = 0.521310 nm, b = 0.55535 nm, and c = 0.75626 nm. Thermal stability of the sample is limited by the temperature of 1,150 °C. Further, the effectiveness of other metal oxide (CoO-, ZnO-, Bi2O3-, and Sb2O3)-doped Lu0.98Ca0.02FeO3−δ system was evaluated with respect to their phase composition, thermal stability, particle size distribution, and color properties. The conclusions of the research showed that a sample containing antimony oxide is the mixture with the best pigmentary-application properties. The powder has a clear orange color, high thermal stability up to 1,340 °C, and mean particle size 4 μm.

New Approach for the Application of Functional Ceramic Material in Carbon Bonded Doloma Refractories to Reduce Emissions

AbstractDoloma carbon bricks with graphite contents of approximately 2 wt% are widely used in the production of stainless steels in argon oxygen decarburisation (AOD) or in vacuum oxygen decarburisation (VOD) vessels as lining material. The application of doloma refractories is connected with metallurgical benefits such as high oxidic stability of its oxides, and the ability to bond sulphur from the hot metal. The production and application of carbon bonded refractories is linked with environmental harmful emissions in the broadest sense. Amongst the aspect of environmental friendly refractory systems this work has observed and shown the interaction of functional ceramic material TiO2 with the organic binder system. In the centre of this work is the aspect of increased residual carbon content of the binder resin due to TiO2 addition. The increased residual carbon content of the binder resin connected with improved mechanical, physical and thermomechanical properties due to sub‐micro scaled TiO2 addition offers the feasibility to reduce the total carbon content without downgrading the brick properties. This aspect has not been observed yet and is of high interest with respect to reduced emissions and environmental friendly refractories. Previous works have investigated the influence of TiO2 on other carbon bonded refractory systems such as alumina carbon and magnesia carbon. As illustrated in this work and previous work, TiO2 is working completely different in the Doloma Carbon system from other systems.

Rheological properties of alumina feedstocks for the low-pressure injection moulding process

The low-pressure injection moulding process (LPIM) allows near-net shape manufacturing of ceramic microcomponents. Feedstocks used in this process have to fulfil different requirements. They have to show good flowability for the machining but they also need to have high solids content to reduce shrinkage during sintering. This work focuses on the flow behaviour of alumina feedstocks with high solids content, based on two different binder systems and two different alumina powders. By varying particle size, organic binder system, and solids content, the rheological properties of the feedstocks were modified significantly. The material parameters such as viscosity, the derived relative viscosity, and yield stress were investigated systematically. The Herschel–Bulkley model turned out to be suitable for the description of the rheological behaviour of these ceramic feedstocks. The dependency of the relative viscosity on solids content could be well described by models like Krieger–Dougherty, the Eilers, and the Quemada models, while the best results for the maximum packing factors were obtained with the Janardhana Reddy et al. model.

Processing of YSZ screen printing pastes and the characterization of the electrolyte layers for anode supported SOFC

Screen printing pastes based on organic binder systems were developed for the production of dense electrolyte layers of Y 0.16Zr 0.84O 1.92(8YSZ) on Ni/YSZ anode substrates for anode supported solid oxide fuel cells (SOFCs). Pastes with a solid loading up to 50 vol.% (86 wt.%) of YSZ powder and the adequate thixotropic behaviour for screen printing could be produced. Dense layers were obtained by sintering at 1430 °C and were shown to be gas tight by window and He leakage test. The electrical conductivity of the dense layers and the resulting activation energy (96–99 kJ mol −1) were obtained from impedance spectra in the temperature range from 250 °C to 900 °C. The agreement with literature values indicates that performing layers have been obtained.

Control of nanosilver sintering attained through organic binder burnout

Control of the low-temperature sintering of nanosilver particles was attained by dispersing and stabilizing nanosilver particles into a paste form using the selected organic binder systems. As demonstrated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), with the existing binder systems, undesirable premature coalescence of nanosilver particles was prevented and the metastable structure was retained until the binder burned out at relatively higher temperatures. Enhanced densification was achieved upon the binder burnout because at the relatively higher temperatures the densification mechanisms, e.g., grain-boundary or lattice diffusion, become more dominant. We propose that the onset of sintering, extent of densification, and final grain size can be controlled by either the size of the initial nanosilver particles or the binder systems with different burnout characteristics.

Effects of Binder and Compaction Pressure on Strength and Fracture Origins in Bodies Pressed from Granules

Granules containing weak, medium and strong organic binder systems were spray dried and the effects of binder and forming pressure on pressed bars' green and sintered strength were investigated. Green strengths were found to improve with increasing compaction pressure for all granules. Higher compaction pressure increased the sintered strength for the strong case but did not increase the sintered strengths of the medium case and lowered the sintered strengths for the weak case. SEM observations revealed that the fracture origins in the strong case originated primarily from unlaminated intergranular flaws which can be improved by higher compaction pressure. The fracture origins in the medium and weak cases are mixtures of unlaminated intergranular flaws and pressing damages, in which case increased compaction pressure can lower strength. Higher compaction pressure would only increase sintered strength if the dominant flaw population is intergranular flaws. In cases where the granules are relatively weak, sintered strength may be increased by decreasing compaction pressure.