Perda de temperatura em revestimentos odontológicos, após sua remoção do forno

The time elepsed between the removal from the furnace of a castin cylinder and the casting proper, depends on the knowledge and ability of the operator. The heat loss, after removal of a furnace temperature of 700ºC at different time intervals, was mensured in four dental casting investiments, using different volumes of investment, with or without the protection of a casting ring and with or without asbestos liner. The results, presented in the form of tables and graphs, tell us about the importance of this additional technical detail, in the dental casting operation. Temperature losses in the order of from 100º to 200ºC were verified, already two minutes after removal from the furnace.

Properties of alloys in the crystallization interval

In the contribution the high growth of viscosity and initial stress of alloys in the crystallization interval with undercooling against of the liquidus follows from theoretical analysis. At these alloys used in pressure die casting the permissible undercooling that does not endanger pressure die casting operation. The application of the device for die temperature regulation ensures the safe operation.

Six Sigma DMAIC project to improve the performance of an aluminum die casting operation in Portugal

Purpose The purpose of this paper is to illustrate an application of the Six Sigma define, measure, analyze, improve, control (DMAIC) problem-solving methodology in a Portuguese industrial enterprise, aimed at reducing the rejection rate of a specific manufactured product due to defects generated in an aluminum gravity die casting operation. Design/methodology/approach Along the five-stage roadmap, a set of analytical and conceptual tools was systematically employed to better characterize the problem, define the product’s critical to quality characteristics, estimate the process baseline, determine the relevant cause-and-effect relationships, identify the root causes leading to the high rejection rate, implement an improvement plan, determine the effectiveness of the improvement actions, and put in place a control plan. Findings The project team discovered that the high rejection rate was caused by factors inherent to the gravity die casting operation itself and by the mixing of rejected parts made of different types of alloys from other locations within the plant. Another key finding was that the successful execution of the project was only possible due to the belief and support of top management and to the active involvement of the team members. Practical implications This case study illustrates a successful practical application of a Six Sigma project in a small-medium enterprise in Portugal, as well as the operational and financial benefits that derived from it; thus providing a good example for others to follow. Originality/value Few cases of continual improvement initiatives, including Six Sigma projects, developed at a Portuguese company are available in the literature; this paper fills such void by describing a very successful application that demonstrates the advantages that other companies can learn in terms of adopting structured methodologies to improve the quality of their products and the efficiency of their processes. Moreover, the analysis and conclusions herein presented can be of great importance for companies using gravity die casting technology.

Solution Space Exploration of the Process Design for Continuous Casting of Steel

Continuous casting is the process of solidifying molten metal to produce different products such as billet, bloom, or slab. This process can be formulated mathematically in terms of conflicting objectives including productivity, yield, quality and production costs to satisfy sets of constraints such as oscillation mark depth, metallurgical length and center line segregation. The objectives are conflicting in the sense that, if the productivity is increased, there is a reduction in other performance measures. These performance specifications are greatly influenced by operating conditions such as casting speed, superheat, mold oscillation frequency, and secondary cooling conditions. The process of identifying the set points for the continuous casting operation is iterative and expensive. The uncertainties inherent in modeling the phenomena computationally behooves exploration of the solution space to determine the quality of the solution and gain insight. In this paper, a method to explore the solution space is introduced. The method includes weight sensitivity and constraint sensitivity analysis. This analysis allows a designer to ascertain to what extent the solution is insensitive to uncertainties inherent in the modeling of the decision problem. This is a crucial step towards determining robust solutions for performance measures. The utility of the method is illustrated in providing decision support for the continuous casting operation in presence of variability in the operating parameters and conflicting end requirements, such as productivity and quality parameters. This method can be instantiated for exploring the solution space for ladle, tundish, rolling and annealing and thereby facilitating the exploration of the solution space for critical unit operations associated with steel product manufacturing. This development has the potential to reduce the number of plant trials necessary to determine the set points for manufacturing a new product mix with a new grade of steel using the existing equipment in a steel mill. The focus in this paper is on the method and not the results per se.

Toward the Ideal of Automating Production Optimization

The advent of improved factory data collection offers a prime opportunity to continuously study and optimize factory operations. Although manufacturing optimization tools can be considered mainstream technology, most U.S. manufacturers do not take full advantage of such technology because of the time-intensive procedures required to manually develop models, deal with factory data acquisition problems, and resolve the incompatibility of factory and optimization data representations. Therefore, automated data acquisition, automated generation of production models, and the automated integration of data into the production models are required for any optimization analysis to be timely and cost effective. In this paper, we develop a system methodology and software framework for the optimization of production systems in a more efficient manner towards the goal of fully automated optimization. The case study of an automotive casting operation shows that a highly integrated approach enables the modeling and simulation of the complex casting operation in a responsive, cost-effective and exacting nature. Technology gaps and interim strategies will be discussed.

Application of Nb-O Affinity in Clean Steel

This report introduces a new deoxidation process that starts with a vacuum degassing followed by the addition of ferro-niobium in the same vacuum facility. The addition of strong deoxidation substance like aluminum and/or silicon is not adopted. Owing to the degassing in vacuum, which in reality reacts as deoxidation with C in molten steel, the solute oxygen in molten steel (O) is stabilized by niobium, which generates an ample number of fine oxide particles composed of (Nb, Mn)2O3-phase. Provided the carbon-degassing is conducted so as to reach the O prior to the FeNb addition would be around 100ppm and less, these oxide-inclusions do not agglomerate before and during solidification, because of the weak cohesivity of niobium-based oxides in molten steel, which would enable defect-free cast products as well as clogging-less casting operation. Also, the steel containing these fine (Nb, Mn)2O3-particles but no Al, exhibits so-called intra-granular acicular ferrite transformation and good toughness of weld heat affected zone (HAZ).