In the realm of industrial consumables, steel casting shots play a pivotal role, particularly in equipment manufacturing sectors where they are extensively used for surface cleaning and strengthening of steel plates, steel materials, and forged castings. As a key component in steel casting processes, these shots are categorized based on composition and performance into cast steel shots, stainless steel shots, and alloy steel shots. Among these, cast steel shots, which include high-carbon, low-carbon, and medium-carbon variants, are characterized by their moderate hardness, high toughness, impact resistance, and ability to be reused multiple times. This makes them ideal for applications in machinery manufacturing, steel structures, automotive, shipbuilding, and container industries. With the rapid advancement of industrialization, the production scale and number of enterprises in the cast steel shot manufacturing industry have been growing steadily. Consequently, there is an increasing demand for higher quality and performance, driving research efforts to focus on varieties, microstructure, and service life of steel casting shots.
The manufacturing process for steel casting shots is continuously optimized. The conventional production workflow involves several stages: sorting and melting of furnace charges, composition adjustment of molten steel, shaping of the cast steel shots through granulation, heat treatment, and final packaging. The granulation methods are diverse, with common techniques including air spraying, water jet impact, and centrifugal atomization. Regardless of the method, process control during shaping is critical for determining the final product quality. In many domestic productions, centrifugal projection of molten steel into a water curtain ring is employed for granulation. However, it has been observed that during this process, elements such as silicon and manganese are prone to oxidation, necessitating the addition of excess alloy materials beyond theoretical calculations to meet chemical composition standards. This not only escalates material costs but also underscores the need for process improvements. Therefore, this study aims to explore the application of a nitrogen protective atmosphere during water curtain granulation to mitigate the oxidation of silicon and manganese, thereby reducing alloy consumption and enhancing the efficiency of steel casting production.
From a first-person perspective, I embarked on this investigation to address the oxidation challenges in steel casting shot production. The core idea revolves around integrating a nitrogen protection system into the water curtain granulation setup. The experimental design involved setting up a nitrogen pipe ring around the centrifugal disc, with uniformly distributed small holes to allow even nitrogen flow, thereby creating an inert atmosphere that shields the molten steel droplets from air exposure during granulation. This approach is expected to lower the oxidation rates of silicon and manganese, which are crucial alloying elements in steel casting compositions. The following sections detail the materials, methods, results, and insights gained from this study, with an emphasis on quantitative analysis through tables and formulas to summarize key findings.
Experimental Materials and Methods
The experimental setup was designed to simulate actual production conditions while allowing controlled variations in nitrogen flow rates. The primary materials and equipment used are listed below:
| Material/Equipment | Specifications |
|---|---|
| Liquid Nitrogen | Purity: 99% |
| Nitrogen Gasifier | Capacity: ≤100 m³/h |
| Glass Rotor Flow Meter | Range: 2.5–40 m³/h; Pressure: ≤0.6 MPa; Temperature: -40 to +120°C |
| Nitrogen Pipe Ring (Custom-made) | Equipped with 10 holes of 3 mm diameter each |
| Valves and Rubber Tubes | For connection and flow control |
The experimental procedure was systematic. Prior to pouring, the nitrogen supply was activated five minutes in advance, with flow rates adjusted via the flow meter to 5, 10, 15, 20, and 25 m³/h. These values were chosen based on practical considerations: too low a flow might not provide adequate protection, while excessively high flows could be cost-prohibitive for large-scale steel casting applications. During pouring, the nitrogen flow was maintained consistently, and samples were collected at early, middle, and late stages for analysis. Key parameters measured included the oxidation rates of silicon and manganese, as well as the hollow and irregular shape rates of the produced steel casting shots. The oxidation rate was calculated using the formula:
$$ \text{Oxidation Rate} (\%) = \frac{C_0 – C_f}{C_0} \times 100 $$
where \( C_0 \) is the initial content of the element in the molten steel, and \( C_f \) is the final content in the granulated shot. This formula helps quantify the extent of elemental loss due to oxidation. Additionally, safety precautions were emphasized, such as ensuring ventilation after nitrogen use to prevent hypoxia risks.
Results and Discussion
The data collected from the experiments were averaged across sampling stages for each nitrogen flow rate. The results are summarized in the following tables, which highlight the effects on oxidation rates and morphological characteristics of the steel casting shots.
| Nitrogen Flow Rate (m³/h) | Silicon Oxidation Rate (%) | Manganese Oxidation Rate (%) | ||||
|---|---|---|---|---|---|---|
| 1.4 mm Grade | 1.4–0.3 mm Grade | 钢水–0.3 mm Grade | 1.4 mm Grade | 1.4–0.3 mm Grade | 钢水–0.3 mm Grade | |
| 0 (No N₂) | 59.70 | 23.65 | 61.72 | 42.65 | 43.40 | 64.08 |
| 5 | 58.44 | 19.42 | 65.63 | 40.23 | 40.71 | 63.59 |
| 10 | 56.44 | 17.42 | 63.24 | 39.66 | 38.65 | 62.87 |
| 15 | 53.22 | 16.04 | 64.18 | 36.77 | 32.61 | 61.50 |
| 20 | 47.43 | 10.97 | 63.42 | 34.01 | 22.67 | 63.56 |
| 25 | 46.74 | 11.95 | 61.06 | 35.19 | 21.94 | 62.32 |
The data reveal a clear trend: as the nitrogen flow rate increases, the oxidation rates of silicon and manganese generally decrease for the coarser grain grades (1.4 mm and 1.4–0.3 mm). For instance, at 20 m³/h, the silicon oxidation rate for the 1.4 mm grade drops to 47.43%, compared to 59.70% without nitrogen protection. Similarly, manganese oxidation reduces from 42.65% to 34.01%. This can be mathematically represented by a linear approximation for the 1.4 mm grade over the flow range of 0–20 m³/h:
$$ \text{Si Oxidation Rate} \approx -0.65 \times \text{Flow Rate} + 60.5 $$
$$ \text{Mn Oxidation Rate} \approx -0.43 \times \text{Flow Rate} + 42.5 $$
These equations underscore the protective efficacy of nitrogen in steel casting processes. However, for the finest grade (钢水–0.3 mm), the oxidation rates remain relatively high and stable, around 60–65%, indicating that nitrogen protection has minimal impact on very fine particles due to their larger surface area-to-volume ratio and rapid cooling dynamics.
| Nitrogen Flow Rate (m³/h) | 2.36 mm Grade | 2.0 mm Grade | 1.4 mm Grade | |||
|---|---|---|---|---|---|---|
| Hollow Rate (%) | Irregular Rate (%) | Hollow Rate (%) | Irregular Rate (%) | Hollow Rate (%) | Irregular Rate (%) | |
| 0 (No N₂) | 12.0 | 8.3 | 10.0 | 7.5 | 8.6 | 8.0 |
| 5 | 11.8 | 10.7 | 9.8 | 10.2 | 8.5 | 7.5 |
| 10 | 12.5 | 9.6 | 10.2 | 10.6 | 8.2 | 8.6 |
| 15 | 11.2 | 8.0 | 8.9 | 8.7 | 8.1 | 7.2 |
| 20 | 10.8 | 10.7 | 8.1 | 9.3 | 7.9 | 8.8 |
| 25 | 15.2 | 18.2 | 13.8 | 14.3 | 12.5 | 11.2 |
The morphological analysis shows that for nitrogen flow rates up to 20 m³/h, the hollow and irregular shape rates remain relatively stable, with averages around 10% for hollow rates and 9% for irregular rates across grades. This suggests that the nitrogen atmosphere does not significantly disrupt the granulation process within this range. However, at 25 m³/h, there is a marked deterioration in shape quality, with hollow rates increasing to 15.2% for the 2.36 mm grade and irregular rates rising to 18.2%. This can be attributed to excessive nitrogen flow causing turbulence or gas entrapment in the molten steel during steel casting shot formation, leading to defective structures. The relationship can be modeled as a threshold effect:
$$ \text{Quality Deterioration} = \begin{cases}
\text{Negligible} & \text{if Flow Rate} \leq 20 \text{ m³/h} \\
\text{Significant} & \text{if Flow Rate} > 20 \text{ m³/h}
\end{cases} $$
In discussing these results, I consider the underlying mechanisms. The reduction in oxidation rates with increasing nitrogen flow is due to the displacement of oxygen in the surrounding atmosphere, which minimizes contact between molten steel droplets and air. This is particularly beneficial for steel casting shots, as it preserves alloy content and reduces the need for compensatory alloy additions. For coarse grades, the larger droplet size allows for more effective nitrogen coverage, whereas fine grades cool too quickly for the protection to be substantial. The deterioration in shape at high flow rates may result from nitrogen bubbles being incorporated into the droplets or from altered cooling patterns, highlighting the need for optimized flow control in steel casting processes.
Extended Analysis and Implications for Steel Casting
To further elucidate the impact of nitrogen protection, I delve into the thermodynamic aspects. The oxidation of silicon and manganese in steel casting can be described by reactions such as:
$$ \text{Si} + \text{O}_2 \rightarrow \text{SiO}_2 $$
$$ 2\text{Mn} + \text{O}_2 \rightarrow 2\text{MnO} $$
The equilibrium constants for these reactions depend on temperature and partial pressure of oxygen. By introducing nitrogen, the partial pressure of oxygen is reduced, shifting the equilibrium towards reduced oxidation. This principle is central to many steel casting techniques aimed at improving material purity. The effectiveness can be quantified using the ratio of oxidation rates with and without protection:
$$ \text{Protection Efficiency} = 1 – \frac{\text{Oxidation Rate with N}_2}{\text{Oxidation Rate without N}_2} $$
For example, at 20 m³/h for the 1.4 mm grade, the protection efficiency for silicon is approximately 20.5%, and for manganese, it is 20.2%. These values underscore the tangible benefits of nitrogen integration in steel casting shot production.
Moreover, the economic implications are significant. By reducing silicon and manganese oxidation, the required alloy additions can be lowered, leading to cost savings. Assuming an initial alloy cost factor \( C_0 \), the reduced oxidation allows for a new cost factor \( C_f \) given by:
$$ C_f = C_0 \times (1 – \text{Reduction in Oxidation Rate}) $$
For large-scale steel casting operations, even marginal reductions translate to substantial financial benefits, making nitrogen protection a viable strategy for enhancing competitiveness.
In terms of process optimization, the study suggests that a nitrogen flow rate of around 20 m³/h strikes a balance between oxidation reduction and shape integrity. This flow rate ensures that for the 1.4 mm grade, silicon and manganese oxidation rates are kept at 47.43% and 34.01%, respectively, while for the 1.4–0.3 mm grade, they are 10.97% and 22.67%. Concurrently, the hollow and irregular rates for key grades remain acceptable: 10.8% and 10.7% for 2.36 mm, 8.1% and 9.3% for 2.0 mm, and 7.9% and 8.8% for 1.4 mm. These outcomes affirm the potential for nitrogen protection to be standardized in steel casting shot manufacturing, particularly in water curtain granulation systems.
Conclusion
In conclusion, this study demonstrates that incorporating a nitrogen protective atmosphere during water curtain granulation in steel casting shot production effectively mitigates the oxidation of silicon and manganese, thereby reducing alloy consumption. The experiments show that within a flow rate range of 0–20 m³/h, increasing nitrogen flow progressively lowers oxidation rates for coarse and medium grain sizes, without adversely affecting the morphological quality of the shots. However, exceeding 20 m³/h leads to deterioration in shape, characterized by increased hollow and irregular rates. Therefore, an optimal nitrogen flow rate of approximately 20 m³/h is recommended for practical applications in steel casting processes. This optimization not only enhances material efficiency but also aligns with the broader goals of sustainable and cost-effective manufacturing in the steel casting industry. Future work could explore the integration of real-time monitoring systems to dynamically adjust nitrogen flow based on process variables, further refining the protection mechanism for steel casting shots.
Throughout this investigation, the focus on steel casting has been paramount, as the techniques and findings are directly applicable to improving the quality and economy of cast steel products. The use of nitrogen protection represents a forward step in the evolution of steel casting technologies, offering a simple yet effective solution to a longstanding production challenge. As the demand for high-performance steel casting shots continues to grow, such innovations will play a crucial role in meeting industry standards and driving technological advancement.