Mold Powder Research Articles

A new method for estimating the isothermal devitrification and crystallization of mold powder slags from non-isothermal DSC data

Abstract The rate of formation of crystalline phases from liquid and glassy mold powder slags is of foremost importance in the performance of molds used for continuous casting of steel. This study shows how the Induction Period (of Simon and Kolman) and the Kissinger methods can be combined in a kinetic model to evaluate the isothermal rate of formation of crystalline phases from thermo-analytical data – onset temperature, T i , peak maximum temperature, T m , shape index, S , and conversion at peak maximum, x m – collected at various linear heating and cooling rates. The diagram of the extent of isothermal transformation as a function of time calculated for a commercial mold powder, used for casting low carbon steels, shows good agreement with the degree of transformation observed in photomicrographs of glass disks devitrified isothermally, at several temperatures for different times. Additionally, qualitative and quantitative X-ray diffraction results obtained at room-temperature from glass powder samples treated isothermally and quenched also show good accord with the degree of transformation predicted with the kinetic model developed in this work.

Prediction model for steel/slag interfacial instability in continuous casting process

In a continuous casting process, mould powder is typically adopted to cover molten steel, which prevents liquid steel from oxidation by air, preserves heat for the top layer of liquid steel, lubricates the initial shell and so on. However, mould powder may deteriorate the quality of the final product if the entrapment of mould powder forms, which is usually caused by the instability of the steel/slag interface. In the current work, a model to predict the critical point of interfacial instability for liquid–liquid stratified flow was developed based on the Kelvin–Helmholtz instability. To prove the validity of the prediction model, a water model experiment was carried out in a rectangular container. In this experiment, oil and water were used to simulate slag and molten steel respectively. The results of the water model prove that the prediction model is correct. Applying the prediction model to a steel–slag system, the critical velocity of molten steel for mould powder entrapment is 0.463–0.541 m s− 1. When considering the most severe chemical reaction, the critical velocity decreases to 0.29 m s− 1. The lowest critical velocity of molten steel is 0.264 m s− 1 when the viscosity of the slag and steel/slag interfacial tension is extremely low.

Research on uses plant ashes in processing powders for classical moulding of steel

In this work we examine various possibilities of using plant ashes in processing powders for moulding steel, in order to reduce the consumption of steel. Thus, there have been studied plant ashes which can be used to process powders and then some moulding powder compositions have been analysed.

High Temperature Rheometric Measurements of Mould Powders

Abstract Issues of viscosity and rheological properties of powder moulds are important from the perspective of modelling, along with the control of continuous casting process. Conducted analysis within subject literature indicates that there are many theoretical considerations concerning the effects of viscosity of powder moulds. The objective of this study was to perform rheological measurements of powder moulds, the study contains the results of rheological tests of seven chemical compositions with a carbon content from 5.0 to 10.7% and which were tested with applied shear rates from 10 to 40 s-1, which are similar to those in a real process: the velocity of strand passes/drawing and mould movements.

Analysis of the Equilibrium State of Flux Powders in the Mould During Continuous Casting of Steel

Abstract Mould fluxes in the continuous casting of steel perform a protective function against oxidizing effect of the atmosphere on liquid metal, reduce friction between the solidifying steel shell and the walls of the mould and regulate the transfer of heat to the mould walls. Their chemical composition is crucial as it impacts the determination of the characteristic temperatures. The paper presents calculation results of the equilibrium composition of the selected mould powders in thermodynamic conditions similar to the actual conditions during continuous casting of steel slabs based on FactSage. The calculations were verified by high temperature tests of mould flux powders.

Long-term Properties of Laser Sintered Parts of Polyamide 12 - Influence of Storage Time and Temperature on the Aging Behavior

The key in selective laser sintering (SLS) of polyamide 12 for exceeding the cusp from a prototyping to a serial production technique poses the long-term behavior of such components. The improvement of additive manufacturing technologies is attended by the enlargement of the possible ranges of use. The crucial obstacle for their actual use is the ignorance of the long-term properties and the consequential fact of not given warranty. The aging behavior of polyamide 12 based injection molded parts and powder for the SLS process is largely probed and methods of analysis are well-established. On the basis of several build jobs consisting of vertically build tensile bars, oven storage experiments are realized. Storing for several time periods and temperatures allows a first calculation of the aging behavior in consideration of the building position and process parameters of each bar. First of all the adaptability of two methods of analysis, tensile test und solution viscosimetry, for determining the state of the aging of SLS parts is surveyed. It shows that depending on the used method of analysis the building position of the picked up sample could play a role. Furthermore the influence of the process parameters, the aging processes itself and the necessary storage conditions for the artificial aging of the parts are considered. All in all this article gives a review of the aging mechanisms of oven stored polyamide 12 parts, possible methods of analysis to determinate their state of aging and first results to qualify the adaptability to selective laser sintered parts. In Addition to that a first correlation between mechanical and chemical properties is made. The presented results form a first step for the future to be able to guarantee the requested product quality over its lifetime, but nevertheless other methods of analysis have to be qualified for the determination of the aging behavior of SLS parts.

Evaluation of the color durability of acrylic resin veneer materials after immersion in common beverages at different time intervals: A spectrophotometric study.

Proper function, esthetics, and cost are the prime factors to be considered while selecting bridge veneering materials. The purpose of the study is to evaluate color durability of acrylic veneer materials after immersion in common beverages at different time intervals. Spectrophotometer was used for taking color measurements based on the transmission of light through the specimens made of the selected materials which were Tooth moulding powder (DPI) and Acrylux (Ruthinium). Thirty specimens of standardized dimensions were prepared from each material. The specimens were divided into three groups of 10 each. One group of each material was immersed in tea (TajMahal) and another group of each material in cola (Pepsi) as the staining solutions. The remaining group of 10 from each material served as control and was stored in distilled water. Color measurements were obtained pre-immersion, and after 1, 15, and 30 days of immersion. Tooth moulding powder displayed better color durability than Acrylux over the 1 month immersion period in both staining solutions. Tea resulted in more discoloration compared to cola (Pepsi). The difference in the color durability of Acrylux and Tooth moulding powder may be attributed to the differences in the composition of tested resin veneering materials, i.e. their polar properties, which contribute to the absorption of staining solution, and the different brands and the strengths of the solutions.

Microstructural Characteristics of Mold Fluxes Associated to their Thermal Behavior

During continuous casting process of steels, several problems can arise when an inadequate heat removal in the mold is produced. This heat extraction occurs through mold powder layers formed between the cooled mold and the solidifying steel. At operating temperatures, the mold flux forms glassy and crystalline phases that affect the heat transfer from the steel to the mold.In this paper, thermal conductivity results, obtained at 900° C, on two commercial mold powders are presented. From these essays, the interfacial thermal resistances: mold/flux and flux/steel were determined. On longitudinal sections of the samples taken from essays, glassy and crystalline phases were characterized. The thermal behavior of these layers is correlated with the proportion of observed phases and chemical composition of each material.

A comparative evaluation of the marginal accuracy of crowns fabricated from four commercially available provisional materials: An in vitrostudy

Purpose:The purpose of this in vitro study was to evaluate and compare the primary marginal accuracy of four commercially available provisional materials (Protemp 4, Luxatemp Star, Visalys Temp and DPI tooth moulding powder and liquid) at 2 time intervals (10 and 30 min).Materials and Methods:A customized stainless steel master model containing two interchangeable dies was used for fabrication of provisional crowns. Forty crowns (n = 10) were fabricated, and each crown was evaluated under a stereomicroscope. Vertical marginal discrepancies were noted and compared at 10 min since the start of mixing and then at 30 min.Observations and Results:Protemp 4 showed the least vertical marginal discrepancy (71.59 μ), followed by Luxatemp Star (91.93 μ) at 10 min. DPI showed a marginal discrepancy of 95.94 μ while Visalys Temp crowns had vertical marginal discrepancy of 106.81 μ. There was a significant difference in the marginal discrepancy values of Protemp 4 and Visalys Temp. At 30 min, there was a significant difference between the marginal discrepancy of Protemp 4 crowns (83.11 μ) and Visalys Temp crowns (128.97 μ) and between Protemp 4 and DPI (118.88 μ). No significant differences were observed between Protemp 4 and Luxatemp Star.Conclusion:The vertical marginal discrepancy of temporary crowns fabricated from the four commercially available provisional materials ranged from 71 to 106 μ immediately after fabrication (at 10 min from the start of mix) to 83–128 μ (30 min from the start of mix). The time elapsed after mixing had a significant influence on the marginal accuracy of the crowns.

モールドパウダー巻込みに及ぼす粘度の影響に関する水モデル実験

モールドパウダー巻込みに及ぼす粘度の影響に関する水モデル実験

Reduction of slivers by the use of an electromagnetic actuator

The submeniscus velocity has a big influence on the surface quality of slabs. Slabs casted with a low casting speed result in a low submeniscus velocity and suffer more from Al-inclusions, while slabs casted with a higher casting speed have a higher submeniscus velocity and suffer more from mould powder inclusions. If the submeniscus velocity can be controlled, the amount of slivers has to be reduced. ArcelorMittal Ghent decided to install an ElectroMagnetic Actuator (EMA) to control this submeniscus velocity. This topic shows what the impact of the EMA can be on slivers.

Characteristics of subsurface inclusions in deep-drawing steel slabs at high casting speed

Deep-drawing steels are widely used in the automobile industry and macro-inclusions in continuous casting slabs should be strictly controlled because they cause surface defects in the final products. In this paper, industrial tests with different casting speeds from 1.0 m.min-1 to 2.5 m.min-1 and different tundish superheats were carried out, then subsurface inclusions in high-speed casting slabs were investigated with a large detection area by the ASPEX automatic inclusion analysis system, and the effect of the casting speed and tundish superheat was studied. The results show that there are six different types of macro-inclusions found beneath the slab surface, named cluster alumina, bubble plus cluster alumina, lump alumina, cluster TiOx-Al2O3, entrapped mold powder and CaO-Al2O3-MgO, respectively. The above first three types account for about 98% of total inclusions in the slabs cast with the mold fluctuation within ±3 mm. The size of more than 80% of such inclusions ranges from 20 to 50 μm. The number density of inclusions larger than 50 μm decreases with the increase in the casting speed and tundish superheat. The subsurface macro-inclusions in deep-drawing steel slabs are closely related to the hook structure. Increasing the casting speed and superheat is effective for reducing the hook depth and large-sized inclusions on the subsurface of slabs.

Thermal conductivity of powders used in continuous casting of steelPart 2 – Powders

Measurements of the thermal conductivity of casting powders are needed to determine the magnitude of the vertical heat flux in the powder bed of a continuous casting mould. The thermal conductivities and thermal diffusivities of four mould powders have been determined using the transient plane source (TPS) and the transient hot wire (THW) methods. The values reported in this investigation are in good agreement with the results of earlier studies which used the THW method. However, the results were significantly different from λeff values obtained in thermal insulation tests. This was attributed to the large contribution to λeff from gaseous conduction which arises from the large temperature gradient across the sample. It was found that the thermal conductivity (λpowd) of the powders had a mean value of 0.125±0.025 W m−1 K−1 for the four powders studied; this value is in good agreement with two other studies; it increased as the temperature increased with a mean temperature coefficient of (dλ/dT = 9×10−5 W m−1 K−2 for the range 295–1100 K and increased as the bulk density increased (λ295 = 0.010+1.69×10−4ρbulk W m−1 K−1).

Investigation into Formation of Metallic Beads on Wheel Ingots

This paper discusses the results of investigation into the formation of metallic beads on the bottom-poured ingots manufactured in Durgapur Steel Plant. These beads were very hard and offered extreme resistance to the sawing operation. Frequently, the saw blades broke on encountering these beads. A metallographic investigation revealed formation of hard white iron material due to the interactions of the mould powder and the liquid steel in the feeder head. As a result of these findings the mould powder quantity could be rationalized.

Change of Mold Slag Composition during Slab Casting of Steel with High Al Content

Three different mold slags have been sampled in dependence of time during slab casting of TRIP steel, and compositional changes have been analyzed. Mass transfer coefficients governing the decrease of silica and increase of alumina have been determined. Moreover change of manganese content was investigated in dependence of the initial manganese content of the mold powder which was close to zero for one of the powders investigated. The following findings have been revealed: Mass transfer coefficients are rising with increasing elapsed time or decreasing silica content, respectively. An initial increase of manganese content by oxidation from the steel followed by later reduction has been observed for the manganese free mold powder. For interpretation of these findings, further simulation according to an effective equilibrium reaction zone model was performed. It was revealed that the primary impact of the steel flow at the steel/slag interface close to the mold wall followed by a stratified flow is of major importance for the phenomena observed. Further results make it possible to predict the steady state composition and show that steady state silica content is nonzero in any case. Moreover, for the mold powders investigated here, it was concluded that manganese content does not decrease silica reduction.

Estimation of Time–Temperature-Transformation Diagrams of Mold Powder Slags from Thermo-analysis of Non-isothermal Crystallization

The temperature range across the mold powder slag in the interfacial gap between the continuous casting mold and strand leads through different transformation behavior into crystalline phases. The transformation rates play a key role in determining the proportion of glassy and crystalline phases present, and thus greatly influence mold heat transfer and lubrication. Although thermal analysis has held great promise to quantify the crystallization of mold slags, so far the information it has provided is scarce. This work shows how differential scanning calorimetry, DSC, data allow evaluation of Time–Temperature-Transformation, TTT, diagrams of mold powder slags, when analyzed with the induction period and the Kissinger methods. The data required for estimating this important tool for the analysis and design of mold powders are onset temperature, T i, peak maximum temperature, T m, shape index, S, and conversion at peak maximum, x m, of the crystallization peaks appearing on thermograms obtained at various heating and cooling rates, ϕ or −ϕ, respectively. Industrial mold powders for casting low- and medium-carbon steels were analyzed to obtain TTT diagrams which correctly portray their different crystallization behavior. The diagrams reveal the start and end curves of the crystalline phases forming at each DSC crystallization peak. The estimated TTT curves present a correct picture of the degree of transformation observed in glass disks (~3 mm thick) treated isothermally for specified time intervals, quenched and examined with a scanning electron microscope. Additionally, the procedure developed for DSC-based TTT diagram calculation is supported by the good agreement between expected transformations and qualitative or quantitative X-ray diffraction results obtained from mold glass-powdered samples treated isothermally in a muffle furnace.

Analysis of Large Inclusions in Q195 Steel

Aimed at the Q195 steel strip inclusion defects in a steel mill, using tracer analysis make system analysis to casting of large inclusions content. Large inclusions in casting containing ladle slag accounted for about 39% of the total number of test, containing tundish covering agent accounts for about 42.2%, while containing protection slag accounted for 45%. Shows that large inclusions in the billet is mainly comes from the crystallizer mold powder entrapment, secondly is the tundish slag and the ladle slag powder entrapment. When transient casting large inclusions content is steady casting several times, increasing the stability of operation on transient casting, controlling the stability of cast-on and ladle changing, stabilizing the liquid level of tundish and mould can improve the quality of the steel.

Mathematical Modeling of Multi-sized Argon Gas Bubbles Motion and Its Impact on Melt Flow in Continuous Casting Mold of Steel

The 3D turbulence k-ε model flow of the steel melt (continuous phase) and the trajectories of individual gas bubbles (dispersed phase) in a continuous casting mold were simulated using an Eulerian-Lagrangian approach. In order to investigate the effect of bubble size distribution, the radii of bubbles are set with an initial value of 0. 1 — 2. 5 mm which follows the normal distribution. The presented results indicate that, in the submerged entry nozzle (SEN), the distribution of void fraction is only near the wall. Due to the fact that the bubbles motion is only limited to the wall, the deoxidization products have no access to contacting the wall, which prevents clogging. In the mold, the bubbles with a radius of 0. 25 – 2. 5 mm will move to the top surface. Larger bubbles issuing out of the ports will attack the meniscus and induce the fluid flows upwards in the top surface near the nozzle. It may induce mold powder entrapment into the mold. The bubbles with a radius of 0. 1 – 0. 25 mm will move to the zone near the narrow surface and the wide surface. These small bubbles will probably be trapped by the solidification front. Most of the bubbles moving to the narrow surface will flow with the ascending flow, while others will flow with the descending flow.

Measures for Reducing the Rate of Breakout of Slab Casters

In order to reduce the rate of breakout of slab caster, improve the operating rate and ensure the stability of the caster, measures including the tundish casting auto-start, the mold level automatic control system optimization, the SEN one-button automatic quick-change technology, the mold breakout forecast system optimization, the mold oscillation parameters optimization, the mold taper measurement optimization and the mold powder management have been adopted by a steel plant of WISCO. As a result, the breakout rate of slab caster was significantly reduced to be zero level in the first 3 years, which is a new record for all steelmaking plant in China.

Application of High Speed Continuous Casting on Low Carbon Conventional Slab in SGJT

Based on the achievement of high speed continuous casting in SGJT, fluid flow, heat transfer, and lubrication behavior were analyzed elaborately. The results indicated that well-bottom SEN with the angle of −20° together with FC mold could reduce the level fluctuation effectively. When FC mold was applied at 1.9 m min−1, there was an increase of average heat flux about 0.06–0.1 MW m−2. During heat transfer analysis, the empirical equation of heat flux was proposed and solidification crater end was validated by pin shooting method. Furthermore, a kind of mold powder employed in high speed casting was described and a new criterion of the consumption rate for high speed casting was put forward.