Juhani Orkas

Effect of Heat Treatment on Thermal Conductivity of Aluminum Die Casting Alloys

Thermal conductivity is an important property when high heat dissipation is a requirement during the use of the cast component. This study was carried out to study the effect of heat treatment on thermal conductivity of three common aluminum die casting alloys. Measurement of thermal conductivity was done by the Hot Disk method. A substantial increase in thermal conductivity was measured as a result of heat treatment. Microstructural changes due to heat treatment was examined by optical and scanning electron microscopy.

Studies on Equivalent Viscosity of Particle-Reinforced Flexible Mold Materials Used in Soft Tooling Process

To reduce the cooling time in soft tooling process, one of the possible solutions is the use of composite mold materials, but that may affect melt mold flow properties. Therefore, a study on equivalent viscosity of melt mold material, which primarily influences the flow ability is essential. In this work, we have carried out an experimental study on equivalent viscosity of flexible mold materials (such as polyurethane and silicone rubber, which are of particular type) reinforced with highly thermal conductive filler particles, namely, aluminum and graphite powder. It has been observed that in addition to an increase of equivalent viscosity, different curing behaviors were noticed in mold materials reinforced with different fillers. By analyzing the performances of various equivalent viscosity models reported in literature, it has been observed that for higher particle size, the existing models deviate much from the experimental results. We have proposed an extension of the generalized model of Arefinia and Shojaei by including a factor that depends on particle size. It is found that the extension model provides better explanations compared to other models to the experimental results, especially for suspensions of flexible mold materials with higher particle sizes. Finally, a predictive approach is suggested for the equivalent viscosity of reinforced flexible mold materials, which may be useful to decide the amount of typical filler particles to be considered for mixing with a flexible mold material.

Cast Bonding of Cast Irons to Ferritic Stainless Steel

Composite metal products consisting of two different alloys can be prepared by a few methods. Cast bonding is one of these methods. The bond between the two materials forms primarily in the solid state by diffusion, after casting of a cladding alloy on to the preheated surface of a substrate. In this work, a ferritic stainless steel was used as the substrate, and, gray iron or nodular iron as the cast alloy. It was found that these two alloys can be successfully joined, and under specific casting parameters, a very strong bond develops between the two alloys. Bond strength was found to be greater than that of gray iron. Microstructural zones on both sides of the bond were studied. It was found that diffusion of chromium into iron and diffusion of carbon into steel is significant in bonding. Chemical composition changes due to diffusion was studied by EDS. Fe-Cr-Mn carbides were formed at the bond during the casting. These carbides were largely eliminated by a subsequent high temperature heat treatment.

Studies on effective thermal conductivity of particle-reinforced polymeric flexible mould material composites

Due to poor thermal conductivity of conventional flexible polymeric mould materials, the solidification of (wax/plastic) patterns in soft tooling (ST) process takes a longer time. This problem can be solved by increasing the effective thermal conductivity of mould materials through (high thermal conductive) particle reinforcement. Therefore in this study, the equivalent thermal conductivities (ETCs) of particle-reinforced polymeric mould materials, namely silicone rubber and polyurethane are experimentally observed using hot disc technique. Findings show that not only the amount of filler content and type of filler material, but also particle size has significant influence on the effective thermal conductivity of polymer and it starts increasing drastically at 20–30 per cent volume fraction of filler content. To predict the cooling time in ST process, it is important to have an appropriate model of ETC. In this study, a new method is proposed based on a genetic algorithm fuzzy (GA-fuzzy) approach to model the effective thermal conductivity of a two-phase particle-reinforced polymer composites (PCs). The effectiveness of the model is extensively tested in comparison with various empirical expressions reported in literature based on the experimental measurements. It has been found that the model based on GA-fuzzy approach not only outperforms the existing models, but also possesses a generic one applicable to a wide range of two-phase particle-reinforced PCs.

Morphological Investigation of Foamed Aluminum Parts Produced by Melt Gas Injection

Porous metal materials are a new class of materials with low densities, large specific surface, and novel physical and mechanical properties. Their applications are extremely varied: for light weight structural components, for filters and electrodes, and for shock or sound absorbing products. Recently, interesting foaming technology developments have proposed metallic foams as a valid commercial chance; foam manufacturing techniques include solid, liquid, or vapor state methods. The foams presented in this study are produced by Melt Gas Injection (MGI) process starting from melt aluminum. The aim of this investigation is to obtain complex foamed aluminum parts in order to make the MGI more flexible. This new method, called MGI-mould process, makes possible to produce 3D-shaped parts with complicated shape or configuration using some moulds obtained by traditional investment casting process.

A genetic fuzzy based modeling of effective thermal conductivity for polymer composites

Evaluation of equivalent thermal conductivity ETC of particle reinforced polymer composites PRPCs is a complex process since some of the influencing parameters are associated with uncertainties and ambiguities e.g., dispersion state of filler in the matrix, uniformity of filler particle size and shape, etc. By realizing it, an attempt has been made to model the ETC of 2-phase PRPCs based on a genetic fuzzy approach. The model performance is rigorously tested in three stages to establish its practical applicability: based on experimental data not used in model development cited in literature, new measured thermal conductivities of flexible mould composites and finally by assessing the feasibility of values of missing data in the reported in-complete data set based on the developed model. Estimations of ETC by the proposed model are shown reasonable, even better compare to existing models and suggesting a generic model applicable to a wide range of 2-phase PRPCs.

Experimental studies on equivalent thermal properties of particle-reinforced flexible mould materials

The investment casting process uses wax patterns which may be produced using the soft tooling process where the common flexible (polymer) mould materials used are polyurethane rubber, silicone rubber, etc. of a typical kind. However, due to poor thermal conductivity of these materials, solidification time of (wax) patterns takes longer leading to reduced rapidity of the process to a great extent. This problem may be overcome by increasing thermal conductivity of mould material that can be achieved either by molecular orientation of polymer itself or by addition of conductive fillers into polymer. The method of controlled addition of thermal conductive (particulate) fillers into mould material may be adopted by realizing it as the simplest and easiest to implement technique in industry. In this article, an experimental study has been carried out to find the effects on equivalent thermal properties of flexible mould materials reinforced with conductive filler particles. Two different types of particles (aluminium and graphite) with different morphological characteristics are considered as fillers. The measurement of thermal properties is carried out by a transient plane heat source technique. As much as 10-fold increases in thermal conductivity and thermal diffusivity values of mould materials reinforced with conductive fillers are found. In explaining the experimental results by several empirical/semiempirical models, it is observed that the Lewis–Nielsen model provides a good estimation, while the Agari–Uno model (fitted with experimental data) shows better agreement than other models.

Elevated temperature thermal conductivities of some as-cast and austempered cast irons

ABSTRACT The aim of this study was to provide insight on thermal conductivity of three cast iron groups, namely lamellar, compacted and spheroidal graphite irons at elevated temperatures up to 673 K (400°C) in as-cast and austempered states. Austempering treatments increased mechanical properties of all the studied materials while decreasing thermal conductivity across the line. The effects of austempering on conductivity were lower for grey and compacted graphite iron than for spheroidal graphite irons. The results indicate that heat treating can be a viable option in increasing cast iron performance in thermally stressed applications. One ferritic low-silicon spheroidal graphite iron surpassed lamellar graphite iron in conductivity at elevated temperatures, while high-silicon spheroidal graphite irons exhibited low conductivities.

Assessment of environmental impacts of foundary waste in utilisation and disposal

In this work the harmful compounds of most commonly used foundry sands in Finland, i.e. green sand, furan sand, ester hardened phenolic sand and sodium silicate sand together with respective dusts were identified. Their environmental impact was evaluated mainly by comparing the content of harmful compounds against target values given for non-contaminated soil. Additionally, an interlaboratory comparison study was arranged in order to get information on the comparability of the metal and polycyclic aromatic hydrocarbons (PAHs) analysis results. The total Chromium contents of studied foundry sand and dust types generally exceeded significantly the target values given for the evaluation of contaminated soil. However, the leaching of Chromium was as a whole very low. Additionally, foundry sands contained only small amounts of organic compounds compared to the target values given for the contaminated soils. On the other hand in case of foundry dusts phenol concentrations correlated with PAH-concentrations resulting in significant phenol and PAH-concentrations in some dust types. For detailed environmental evaluation further information on the leaching behaviour of different metals from foundry dusts is required, especially when the waste masses are relative big. Results of the interlaboratory comparison, especially for some metals as aluminium and chromium, varied significantly addressing the need for further discussions on advantages and disadvantages of different test methods.