Abstract
This article presents an extensive study on the utilization of exothermic pads in the production of duplex stainless steel castings through sand casting processes. The comparison between the traditional metallic pads and the innovative exothermic pads, particularly the EX5 BLEND exothermic material, is thoroughly discussed. The research employs solidification simulation software to predict the performance of the designed exothermic pads, followed by actual pouring tests to validate the findings. The results reveal that the EX5 BLEND exothermic pads can effectively replace metallic pads, thereby reducing metal consumption, energy expenditure during pad removal, and overall production costs. This article delves into the design, production, and quality control of castings using exothermic pads, supported by visual and radiographic inspections.
Keywords: Exothermic material, exothermic pad, cast steel, sand casting, duplex stainless steel, metallic pad, simulation software, quality control
Introduction
In the field of casting, particularly for high-alloy materials such as duplex stainless steel, metallic pads are traditionally used to extend the feeding distance of risers, ensuring sound castings. However, these metallic pads often require removal after solidification, leading to significant waste in metal material and energy consumption. The search for more efficient and cost-effective alternatives has led to the development of exothermic pads, which harness the combustion properties of specific materials to maintain a liquid state for an extended period, fulfilling the feeding function without the need for subsequent removal.
This article explores the application of exothermic pads, specifically the EX5 BLEND material, in the production of duplex stainless steel castings. By analyzing the design, production process, and quality control measures, this study aims to provide insights into the benefits and practical considerations of using exothermic pads in sand casting operations.
1. Background and Literature Review
1.1 Overview of Duplex Stainless Steel
Duplex stainless steel, characterized by a dual-phase microstructure of ferrite and austenite, exhibits exceptional mechanical properties, corrosion resistance, and weldability, making it ideal for various industrial applications. Its high alloy content, however, poses challenges in casting processes, particularly in terms of feeding and shrinkage control.
1.2 Traditional Feeding Methods
Traditional casting methods rely heavily on metallic pads, particularly for high-alloy materials like duplex stainless steel. These metallic pads, while effective in providing feeding channels, necessitate removal after casting, which is both time-consuming and energy-intensive. Moreover, the scrap metal generated from pad removal adds to the overall production costs.
1.3 Exothermic Materials and Their Applications
Exothermic materials, capable of generating heat through a chemical reaction, have found applications in various industries, including casting. In casting, these materials can be used to create exothermic pads that maintain the liquid state of metal in specific regions for an extended period, serving as an alternative to metallic pads. While several exothermic materials exist, their applicability and efficiency in casting operations vary widely.
2. Materials and Methods
2.1 Selection of Exothermic Material
For this study, the EX5 BLEND exothermic material was chosen based on its superior heat generation and insulation properties. Compared to traditional exothermic materials, EX5 BLEND was found to maintain a higher temperature for a longer duration, making it ideal for castings requiring extended feeding periods.
2.2 Design of Exothermic Pads
2.2.1 Preliminary Design
The dimensions of the exothermic pads were designed to match those of the metallic pads used in the traditional process, ensuring consistency in the experimental setup. The outer diameter, inner diameter, and thickness of the pads were set to 270 mm, 175 mm, and 90 mm, respectively.
2.2.2 Solidification Simulation
Solidification simulation software was utilized to predict the performance of the designed exothermic pads. By inputting the thermodynamic properties of the EX5 BLEND material, the software simulated the temperature profile within the casting during solidification, allowing for adjustments to the pad design to optimize feeding performance.
2.3 Production Process
2.3.1 Preparation of Exothermic Pads
The powdered EX5 BLEND material was mixed with a binder in the prescribed ratio and pressed into the desired shape using a custom-made core box. The prefabricated exothermic pads were then coated with a release agent and dried to prevent sticking during casting.
2.3.2 Molding and Pouring
The exothermic pads were placed in the designated positions within the sand mold. Special care was taken to ensure that the exhaust channels were unobstructed,
4. Comparison and Analysis
4.1 Material Consumption and Cost Savings
The primary advantage of using EX5 BLEND exothermic pads over metallic pads lies in the significant reduction of material consumption and associated costs. In the production trial, it was found that the total pouring weight for the casting using exothermic pads was 980 kg, compared to 1050 kg for the casting using metallic pads. This resulted in an increase in the process yield from 51.4% to 55.1%, indicating a more efficient use of materials. Furthermore, the elimination of the need to remove the metallic pads through sawing or plasma cutting reduced labor costs and energy consumption. Although there is an initial cost for the exothermic material, the overall cost savings, taking into account reduced metal consumption and elimination of removal costs, were substantial.
4.2 Thermal Performance and Feeding Effectiveness
The thermal performance of the EX5 BLEND exothermic material, as demonstrated in Figures 1 and 2, shows a clear advantage over conventional exothermic materials. The ability to maintain the metal at 1147°C for 5.70 minutes, compared to 2.25 minutes with standard exothermic materials, ensures a longer and more effective feeding period for the casting. This extended period of liquid metal at the critical feeding points helps prevent defects such as shrinkage porosity, thereby improving the overall quality of the casting.
4.3 Ease of Removal and Surface Quality
As illustrated in Figures 10 and 11, the exothermic pads can be easily removed through vibration and shaking, leaving a clean and smooth casting surface. In contrast, the removal of metallic pads typically requires labor-intensive methods like sawing or plasma cutting, which not only increases costs but also leaves behind surface imperfections that may require additional finishing. The clean removal of exothermic pads, without any need for cutting or grinding, preserves the integrity of the casting surface, resulting in a superior finish.
4.4 Quality Assurance
Both castings produced in the trial, one using metallic pads and the other using exothermic pads, underwent rigorous quality checks, including 100% volume radiographic inspection at the flange positions. The results indicated that neither casting had any internal defects, satisfying the customer’s quality requirements. This confirms that the use of EX5 BLEND exothermic pads does not compromise the quality of the final product while offering significant advantages in terms of cost savings and process efficiency.
In conclusion, the application of EX5 BLEND exothermic pads in the production of duplex stainless steel castings represents a significant improvement over traditional metallic pads. The ability to reduce material consumption, eliminate the need for labor-intensive removal processes, and maintain high-quality standards make exothermic pads an attractive option for casting manufacturers. The successful trial in this study demonstrates the viability.