Mold Heating Research Articles

Non-uniformity of Mould Heat Transfer and Distortion During Wide and Thick Slab Continuous Casting

Non-uniformity of Mould Heat Transfer and Distortion During Wide and Thick Slab Continuous Casting

Mould Powder Development for Continuous Casting of Steel

Mould powders significantly determine the stability of the continuous casting process of steel at all casting speeds. The main functions of mould powders are to provide strand lubrication and to control the mould heat transfer in the horizontal direction between the steel shell and the copper mould. The composition, properties and operational performance of mould powders were investigated in detail with a focus on high-speed thin slab casting and conventional slab casting. Various advanced characterisation methods were applied, completed with experiments at laboratory scale and full-scale plant trials. It was found that melting of mould powder at the meniscus and crystallisation of the slag film are key processes during continuous casting. Both powder melting and slag crystallisation are primarily based on the composition of the mould powder and the mould slag. Additionally, the operational parameters during continuous casting will affect these processes as well. Results of the work are used for a further and more fundamental understanding of the mould powder functions and to guide mould powder design for various steel grades.

Challenge to control mould heat transfer during thin slab casting

At the thin slab caster of Tata Steel, IJmuiden, mild cooling mould powders were introduced with the aim to control the mould heat transfer during casting. These mild cooling mould powders are characterised by specific values of basicity, solidification point and chemical composition. Application of these mould powders resulted in a redistribution of mould heat transfer during casting, i.e. a reduced and more stable mould heat transfer in the critical upper part of the mould and an increased mould heat transfer in the lower part of the mould. The average mould heat transfer and hence the shell thickness at mould exit are comparable to the standard powder. The application of mild cooling mould powders also resulted in improved solidification behaviour of the steel shell. A thinner chill zone with smaller thickness variations was observed. Furthermore, it was found that the mould taper required optimisation to match the changes in shrinkage behaviour to ensure uniform solidification. The use of mild cooling powders was observed to give an increase in mould friction. Mould thermal monitoring indicated that the solid slag films fractured (sheeting) in the upper part of the mould. However, no operational problems were reported, which indicate that the first 200 mm under the steel meniscus is essential for initial solidification and for the formation of a homogeneous steel shell. All these findings can be understood by considering the crystallisation properties of the mould slag, which include the cooling rate. Mild cooling has been shown to provide uniform heat transfer and adequate lubrication for high speed thin slab casting.

Experimental verification of hematite ingot mould heat capacity and its direct utilisation in simulation of casting process

Heat capacity of alloys (metals) is one of the crucial thermophysical parameters used for process behaviour prediction in many applications. Heat capacity is an input variable for many thermodynamical (e.g. Thermocalc, Pandat, MTData, …) and kinetic programs (e.g. IDS-Solidification analysis package, …). The dependences of heat capacity on common variables (temperature, pressure, ...) are also commonly used as the input data in software packages (e.g. ProCast, Magmasoft, ANSYS Fluent, …) that are applicable in the field of applied research for simulations of technological processes. It follows from the above that the heat capacities of materials, alloys in our case, play a very important role in the field of basic and applied research. Generally speaking, experimental data can be found in the literature, but corresponding (needed) data for the given alloy can very seldom be found or can differ from the tabulated ones. The knowledge of proper values of heat capacities of alloys at the corresponding temperature can be substantially used for addition to and thus towards the precision of the existing database and simulation software. This study presents the values of Cp measured for the hematite ingot mould and comparison of the measured data with the Cp values obtained using the software CompuTherm with respect to simulation of technological casting process.

Investigation on the Rate of Solidification and Mould Heating in the Casting of Commercially Pure Aluminium in Permanent Moulds of varying Thicknesses

The quality of casting in the foundry can be measured by the rate at which solidification of the molten metal takes place, which is consequent upon the rate the mould, is able to dissipate the heat of solidification to the surroundings. The faster or slower the heat removal process during solidification the structure of the grains formed by the casting is either finer of coarser. An experimental investigation was carried out to compare the rate of solidification of commercially pure aluminium in metallic moulds. The rate at which solidification occurred was compared with the rate at which the mould absorbed and dissipates heat. The experiments conducted recorded the temperature fields at different casting location and that of the moulds respectively. The results showed that there is a direct relation of the rate of heat absorption by the mould and the rate of solidification in metallic moulds.

가변 금형온도 제어기법을 적용한 사출금형의 냉각성능 고찰

In injection molding, the mold temperature is one of most important process parameters that affect the flow characteristics and part deformation. The mold temperature usually varies periodically owing to the effects of the hot polymer melt and the cold coolant as the molding cycle repeats. In this study, a pulsed mold temperature control was proposed to improve the part quality as well as the productivity by alternatively circulating hot water and cold water before and after the molding stage, respectively. Transient thermal-fluid coupled analyses were performed to investigate the heat transfer characteristics of the proposed pulsed mold heating and cooling system. The simulation results were then compared with those of the conventional mold cooling system in terms of the heating and cooling efficiencies of the proposed pulsed mold temperature control system.

Conformai Cooling through Thin Shell Moulds Produced by 3D Printing

In today’s competitive mould industry, a product’s time-to-market plays an important role in the success of a company by producing quality moulds. For many years mould designers struggled for the improvement of the cooling system performance, due the fact that the cooling system complexity is physically limited by the fabrication capability of the conventional tooling methods. Even conventional cooling performance may not meet the expectations of the mould engineer to maintain uniform mould temperature. Proper thermal control is useful not only for cooling purposes, but also for the preservation of mould heat to increase the part quality and production rate. Conformal cooling is an emerging methodology to control more accurately the temperature of the mould cavity throughout the process. Controlling of the temperature in thin shell moulds is a challenging task, and if successful, will pave way towards increased part quality and production rate. This paper presents the results of experimental investigations carried out casting aluminium in thin shell moulds produced by three-dimensional (3D) printing with and without conformal cooling channels. The freedom to create the internal geometry by the use of the 3D printing process allows for the fabrication of moulds with complex internal cooling passages compared to other rapid prototyping processes.

Overviews of the Behavior of Heat Transfer of Soft-Contact Electromagnetic Continuous Casting Mold

Abstract. Soft-contact electromagnetic continuous casting is a new technology to improve the surface quality of billet. The soft-contact electromagnetic continuous casting mold heat transfer mechanism was discussed through the molten steel heat transfer process in the mold in this paper. The aspect that previous studies have not designed in the heat transfer process has been pointed out in the last. The researchers did not add the flux film as a heat transfer medium,but the slag in the mold is a very important thermal resistance actually.

Research on Solidification Heat Transfer Model of Copper Horizontal Continuous Casting

Study the horizontal continuous casting mold solidification heat transfer process is not only to optimize the structure of the mold so that it has a uniform stress field, to improve the quality of slab, to extend the mold life basis, and improve production efficiency and cost-effective method. Therefore, oxygen-free copper horizontal continuous casting process as the research object, the establishment of a level of TU1 billet continuous casting mold solidification heat transfer model for the simulation of oxygen-free copper horizontal continuous casting mold solidification and heat transfer process has laid a theoretical foundation.

Effects of Process Parameters on Surface Gloss in Rapid Heat Cycle Molding Process

process parameters; surface gloss; Rapid Heat Cycle Molding Abstract: Rapid Heat Cycle Molding is a novel injection molding, which may improve product surface quality effectively. In this paper, one-factor experimental design and Taguchi method were used and the influence of different process parameters (mold heating temperature, melt temperature, injection rate, injection pressure, and packing pressure) on surface gloss of injection product was studied. The results showed that temperature is the significant factor to the surface gloss. Mold heating temperature is principal factor in mold process parameters, while the melt temperature is the secondary factor and injection pressure is the least. The surface gloss increases with increasing mold heating temperature, melt temperature, injection rate through whole processing, while it increases to top then decreases with increasing injecting and packing pressure

Automated Mold Heating System Using High Frequency Induction with Feedback Temperature Control

Abstract High frequency induction heating is an efficient means of rapidly heating a mold surface by means of electromagnetic induction. It was recently applied to the rapid heating of injection molds for a range of purposes. To implement high frequency induction for rapid mold heating, the heating conditions have to be set appropriately to obtain the desired range of mold temperatures. In the present study, a rapid mold heating system is developed. It consists of a high frequency power supply, induction coils, a robot system, temperature sensors and controllers. The mold surface temperature is measured using the temperature sensors, and this data is then fed back to the controller so as to control the heating time. This fully automated induction heating system with feedback temperature control is then implemented for the injection molding of a transparent part with multiple holes, resulting in great improvement in the surface appearance as well as the optical properties of the molded part.

Determination of heat transfer coefficients at metal–mold interface during horizontal unsteady-state directional solidification of Sn–Pb alloys

This paper presents a theoretical–experimental study of the metal–mold heat transfer coefficients during horizontal directional solidification of Sn–Pb hypoeutectic alloys (5 wt%Pb, 15 wt%Pb, 20 wt%Pb and 25 wt%Pb) in presence of thermo-solutal convection. A water-cooled solidification experimental apparatus has been developed, and specimens have been solidified under unsteady state heat flow conditions. Five computer guided thermocouples have been connected with the metal, and the time–temperature data have been recorded automatically. A numerical technique which compares theoretical and experimental thermal profiles is used for investigating the influence of solute content on h i values. This has permitted the evaluation of the variation of metal–mold heat transfer coefficients along the solidification of Sn–Pb alloys, as well as the analysis of the effects of thermo-solutal convection. The interfacial heat transfer coefficients of alloys studied are represented by equations which show the time dependence during the process. The experimental and calculated values have shown a very good agreement. A comparative analysis between the results of this work and those from the literature proposed to analyze the metal–mold heat transfer coefficients during upward and downward vertical solidification of Sn–Pb hypoeutectic alloys is conducted.

Fabrication of Plastic Micro Features on Microporous Mold by Hot Embossing

The method of using ultrasonic heating to aid high precision moulding of micro features has been studies. The study developed a method of using ultrasonic vibration to heat the polymer and hot embossing high precision micro features. A commercial ultrasonic welding machine is converted to provide the heating of polymer and mold then into precision micro features for study of ultrasonic heating and the microflow of polymer under ultrasonic agitation. A stainless steel microporous mold of 200µm thick with through holes of 50µm and 200µm in diameter were used. Using a frequency of 35kHz, the microflow behavior of PC (Polycarbonate) and PE (Polyethylene) in the microchannels were investigated. The differing properties of microflow for these two types of polymer give indication on the theoretical and practical agreement on prediction of microflow under ultrasonic energy.

New approaches in microcasting: permanent mold casting and composite casting

For several years, microcasting was based on investment casting. New approaches are now the permanent mold casting and composite casting of micro parts. Casting was performed with aluminum bronze of the type CuAl10Ni5Fe4. Permanent mold casting was commenced with steel mold inserts in a lost mold. The development of a band heater enabled the heating of permanent molds inside the casting machine. This shall ensure sufficient form filling of micro cavities. For permanent mold casting micro structured steel molds and graphite molds were used. Composite casting was investigated for surrounding a micro part by melt, and for pouring a metal melt into a micro structured part. In both cases different materials were combined. For metal–ceramic composite casting ZrO2, Al2O3 or Si3N4 were used in connection with Al bronze. For metal–metal composite casting Al bronze was cast around steel. First results for both new approaches are presented.

Integrated numerical analysis to evaluate replication characteristics of micro channels in a locally heated mold by selective induction

High-frequency induction heating is an efficient way to heat mold surfaces by electromagnetic induction using a non-contact procedure. Due to its ability to rapidly heat and cool mold surfaces, this method has been applied recently to the injection molding of micro/nano structures. The present study investigates a localized heating method involving the selective use of mold materials to enhance the heating efficiency of high-frequency induction heating. A composite injection mold consisting of ferromagnetic material and paramagnetic material was used for localized induction heating. The feasibility of this localized heating method was investigated through numerical analyses in terms of its heating efficiency for localized mold surfaces and the resulting flow characteristics in micro channels. To take into account the effects of thermal boundary conditions of localized induction heating, a fully integrated numerical analysis effectively connecting electromagnetic field calculation, heat transfer analysis, and injection molding simulation was carried out. The proposed integrated simulation was applied to the injection molding of a rectangular strip containing micro channels, and the resulting mold heating capacity and replication characteristics of the micro channels were compared with experimental findings in order to verify the validity of the proposed simulation.

Surface carburization of steel castings

Shaping methods based on sand-resin mixtures have undoubted benefits and accordingly are increas� ingly used in the manufacture of highperformance iron, steel, and nonferrousalloy castings. However, they cannot be unconditionally recommended for lowcarbon steel castings. This is because heat from the molten metal destroys the organic components present in such molds. At low temperatures (150 °C), these mixtures mainly emit water vapor and complex hydrocarbons. At high tem� peratures (700°C), however, the gas emitted consists predominantly of carbon monoxide (84-85%), hydro� gen H2 (3-6%), carbon dioxide CO2 (around 5%), and methane CH4 (around 2%) (1). In the mold cavity, this gas mixture is partially oxidized by oxygen and is diluted by atmospheric nitrogen but retains a high reducing (carburizing) potential. Consequently, on casting low� carbon steel in a mold made of sand-tar mixture, sur� face carburization of the castings occurs as they solidify (2). In casting carbon steel and some alloy steels, this is somewhat compensated by subsequent surface decar� burization in cooling of the castings in the mold and subsequent heat treatment. However, in castings of highchromium alloy steel, the carburized surface layer is retained, since there is practically no decarburization in view of the formation of a protective chromium� oxide film on the casting surface. With increase in carbon content, the corrosion resistance of the highchromium steel falls sharply (3). Therefore, the retention of carburizing layer at the sur� face of such castings significantly impairs their perfor� mance. In the present work, we study the influence of the gas formed at the metal-mold interface on the surface carburization of 10X18H9 Л steel castings, in the case of molds made from mixtures with different binders. We assume here that the destruction products of the organic components in the mixture are transformed to CH4, CO, H2, and CO2 at high temperatures. Corre� spondingly, the basic carburization potential of the gas medium is mainly due to the presence of hydrocarbons (primarily CH4) and carbon monoxide in the gas phase. Accordingly, surface carburization of the cast� ing may be regarded as mainly the result of the reaction of steel with these components of the gas mixture (1) 2CO = (C) + CO 2 ;( 1 )

Influence of Mould Heat Storage Capacity on Properties of Grey Iron

Grey cast iron is characterized by presence of a large portion of its carbon in the form of graphite flakes which are observable in their microstructures. Their properties are significantly dependent on the micro-constituents of the, cast iron components. A way of controlling the microstructure of cast iron is through the controlled cooling rates during solidification. To control cooling rate, the heat storage capacity of the mould is important. This paper presents the characteristic effects of graphite flake sizes on some mechanical properties of grey cast iron. Six mould materials with heat storage capacities ranging from 1.52 kJ.m-2.K-1.s-1/2 to 2.16 kJ.m-2.K-1.s-1/2 were prepared and used to cast some grey cast iron samples whose microstructures were observed by optical microscopy. Mechanical properties of the grey iron were evaluated. The results show that the properties increased with the heat storage capacity of the mould. Also, the microstructures show a dependence on heat storage capacity of the mould.

Real-Time, Model-Based Spray-Cooling Control System for Steel Continuous Casting

This article presents a new system to control secondary cooling water sprays in continuous casting of thin steel slabs (CONONLINE). It uses real-time numerical simulation of heat transfer and solidification within the strand as a software sensor in place of unreliable temperature measurements. The one-dimensional finite-difference model, CON1D, is adapted to create the real-time predictor of the slab temperature and solidification state. During operation, the model is updated with data collected by the caster automation systems. A decentralized controller configuration based on a bank of proportional-integral controllers with antiwindup is developed to maintain the shell surface-temperature profile at a desired set point. A new method of set-point generation is proposed to account for measured mold heat flux variations. A user-friendly monitor visualizes the results and accepts set-point changes from the caster operator. Example simulations demonstrate how a significantly better shell surface-temperature control is achieved.

Rapid patterning of spin-on-glass using ultrasonic nanoimprint

The authors succeeded in room-temperature patterning on a spin-on-glass (SOG) coated Si substrate by an ultrasonic nanoimprinting in a short duration of 1 min. Typically, at a room-temperature it takes a large press pressure and a long contact time to nanoimprint without a thermal pretreatment. In our ultrasonic nanoimprinting, a mold is attached directly to an ultrasonic generator, and mold patterns are set in motion at a high-speed in a direction aligned with the direction of the contact force applied. By this movement of mold patterns, plastic deformation and thermal deformation caused by the initial pressure and frictional heat generated by the ultrasonic vibration are combined to achieve precise structures. The authors had already confirmed the assisting effect of ultrasonic vibration at room-temperature nanoimprinting on various engineering plastics and baked SOG without any heating of mold. They then experimented to apply the ultrasonic nanoimprint method on nonbaked SOG coated substrates. They prepared an organic SOG and an inorganic SOG as molding materials, and executed ultrasonic nanoimprinting under various experimental conditions based on the optimized conditions for polyethylene terephthalate (frequency of ultrasonic vibration=10 kHz, contact force=500 N, and contact time=60 s). Moreover, the relationship between the amplitude of ultrasonic vibration and the imprinted depth was investigated, and the influence that the ultrasonic vibration exerted on the transfer accuracy of mold patterns was also determined.

Mathematical Modeling of Hot Tearing in the Solidification of Continuously Cast Round Billets

Billets produced by continuous casting sometimes show the presence of subsurface cracks that can compromise the quality of the final product. The presence of these cracks is revealed by Baumann prints of billet cross sections in which the chill zone is visible and the short radial cracks are located only where the chill zone thickness is thinner. This experimental finding induces the hypothesis that cracks are formed as a result of the presence of unevenness in the mold heat extraction around the billet perimeter. Cracks start to open in the dendritic front in regions where the shell growth in the mold is slower. The study presented in this article focused on steels with a sulfur content of about 300 ppm. The Baumann prints taken from billet samples of numerous different heats allowed detecting the presence of subsurface cracks and their location nearby visible chill zone thinning areas. To understand the mechanisms of crack formation and to define the possible corrections, a modeling activity has been carried out using the finite element technique on 148-mm diameter billets continuously cast at TenarisDalmine (Dalmine, Italy). The model performs a two-dimensional thermomechanical analysis of the solidification in the mold and within about 4 cm below the mold exit, along which the shell surface is cooled only by radiation to the environment, before the sprays of the first ring impact on the strand. The model includes the contact of the shell with the mold inner surface, which moves according to taper and distortion (this last part is calculated by means of a separate mold model); the steel creep behavior; the calculation of the heat transfer through the gap depending on the local mutual distance between the two surfaces; the effect of the liquid steel fluid dynamics on the solidification growth as a result of the temperature distribution; and the calculation of a hot tearing indicator represented by the porosity fraction caused by mechanical strains applied at the dendrite roots. From the simulation results, it is concluded that subsurface cracks are generated in the space between the mold exit and the first cooling ring; the involved mechanisms of formation also are withdrawn. Nucleation of MnS precipitates of large dimensions is an additional cause of defectiveness in controlled sulfur steels. As a final conclusion of this work, the most important actions to eliminate subsurface cracks are derived.