In our research on the sustainable development of the sand casting foundry industry, we investigated the impact of using different energy sources and equipment on carbon emissions and costs. The sand casting foundry is a critical sector in the national economy, but it consumes substantial energy and generates significant carbon emissions. To promote its transformation towards a low‑carbon future, we established comprehensive models for carbon emissions and production costs based on the characteristics of the sand casting foundry process. We then applied these models to four typical melting furnaces—induction furnaces, coke‑fired cupolas, natural gas‑fired cupolas, and natural gas rotary furnaces—under varying melting capacities and product types. Our findings provide theoretical support for the sand casting foundry to select more environmentally friendly and economically efficient melting methods.
Research Methodology
Carbon Emission Model
In a typical sand casting foundry, the production process includes molding, melting, and post‑treatment stages. The melting stage is the primary source of energy consumption and carbon emissions. We classified carbon emissions into three categories: material‑related, energy‑related, and undesired emissions, following the characteristics of the sand casting foundry process. The carbon emission model is given by:
$$
C = \sum_{m=1}^{M} C_m G_m + \sum_{e=1}^{E} C_e G_e + \sum_{u=1}^{U} C_u H_u
$$
where:
- \(C\) = total carbon emissions during production (kg CO₂)
- \(C_m\) = quantity of the \(m\)-th material used
- \(G_m\) = carbon emission factor of the \(m\)-th material
- \(M\) = total number of materials
- \(C_e\) = quantity of the \(e\)-th energy source used
- \(G_e\) = carbon emission factor of the \(e\)-th energy source
- \(E\) = total number of energy sources
- \(C_u\) = quantity of the \(u\)-th undesired emission (e.g., waste gas treatment)
- \(H_u\) = carbon emission factor of the \(u\)-th undesired emission
- \(U\) = total number of undesired emission sources
Cost Model
The total production cost in a sand casting foundry includes equipment usage cost, energy cost, floor space rental, and labor cost. We formulated the cost model as:
$$
C_L = \left[ \sum_{a=1}^{A} (F_a + S_a P) \right] + T R (1+w) N + \sum_{c=1}^{C} E_c
$$
where:
- \(C_L\) = total production cost (CNY)
- \(F_a\) = usage cost of the \(a\)-th equipment (CNY)
- \(S_a\) = floor space occupied by the \(a\)-th equipment (m²)
- \(P\) = rental cost per unit area (CNY/m²)
- \(A\) = total number of equipment
- \(T\) = labor working time (h)
- \(R\) = labor wage rate (CNY/h)
- \(w\) = welfare and insurance rate (taken as 14% according to Chinese labor law)
- \(N\) = number of workers
- \(E_c\) = total cost of the \(c\)-th energy source (CNY)
- \(C\) = total number of energy sources
Data and Analysis of Melting Furnaces
We analyzed four types of melting furnaces commonly used in the sand casting foundry: induction furnace, coke‑fired cupola, natural gas‑fired cupola, and natural gas rotary furnace. The energy consumption for melting 1 ton of cast iron is presented in Table 1, based on previous studies and industry data.
| Furnace type | Coke (kg) | Electricity (kWh) | Natural gas (m³) |
|---|---|---|---|
| Induction furnace | 0 | 650 | 0 |
| Coke‑fired cupola | 145 | 0 | 0 |
| Natural gas‑fired cupola | 0 | 0 | 65 |
| Natural gas rotary furnace | 0 | 0 | 80 |
Using the carbon emission factors: coke = 2.79 kgCO₂/kg, natural gas = 2.00 kgCO₂/m³, grid electricity (coal‑fired) = 0.749 kgCO₂/kWh, we calculated the carbon emissions per ton of cast iron as shown in Table 2.
| Furnace type | Coke | Electricity | Natural gas | Total |
|---|---|---|---|---|
| Induction furnace | 0.00 | 486.85 | 0.00 | 486.85 |
| Coke‑fired cupola | 404.55 | 0.00 | 0.00 | 404.55 |
| Natural gas‑fired cupola | 0.00 | 0.00 | 130.00 | 130.00 |
| Natural gas rotary furnace | 0.00 | 0.00 | 160.00 | 160.00 |
Carbon Emissions under Different Melting Capacities
We considered melting 80 t and 120 t of molten iron. The furnaces selected were: induction furnace (10 t/h), coke‑fired cupola (20 t/h), natural gas‑fired cupola (10 t/h), and natural gas rotary furnace (10 t/h). For the coke‑fired cupola, an additional electricity consumption of 1.2 kWh per ton was included for the spray tower waste gas treatment. The total carbon emissions are presented in Table 3.
| Melting capacity (t) | Induction furnace (kgCO₂) | Coke‑fired cupola (kgCO₂) | Natural gas‑fired cupola (kgCO₂) | Natural gas rotary furnace (kgCO₂) |
|---|---|---|---|---|
| 80 | 38,948 | 32,364 | 10,400 | 12,800 |
| 120 | 58,422 | 48,546 | 15,600 | 19,200 |
From Table 3, the natural gas‑fired cupola reduced emissions by approximately 67.87% compared to the coke‑fired cupola, and by 73.29% compared to the induction furnace. This demonstrates that adopting natural gas‑fired equipment can significantly lower the carbon footprint of a sand casting foundry.
Cost Analysis under Different Melting Capacities
We used actual industrial prices: electricity = 1.08 CNY/kWh, coke = 1.1 CNY/kg, natural gas = 3.25 CNY/m³, industrial land rent = 100 CNY/m². The floor space and labor requirements for each furnace are given in Table 4.
| Furnace type | Floor area (m²) | Number of workers |
|---|---|---|
| Induction furnace | 30 | 2 |
| Coke‑fired cupola | 70 | 5 |
| Natural gas‑fired cupola | 50 | 5 |
| Natural gas rotary furnace | 60 | 4 |
Applying the cost model, we computed the total cost for melting 80 t and 120 t of cast iron. The results are shown in Table 5.
| Melting capacity (t) | Induction furnace | Coke‑fired cupola | Natural gas‑fired cupola | Natural gas rotary furnace |
|---|---|---|---|---|
| 80 | 59,760 | 20,260 | 22,900 | 27,600 |
| 120 | 73,800 | 26,890 | 31,850 | 38,400 |
On a per‑ton basis, the cost for the natural gas‑fired cupola was about 265 CNY/t for 120 t, whereas the induction furnace cost 615 CNY/t. This represents a cost reduction of approximately 56.84% at 120 t and 61.68% at 80 t, averaging 59.26%. Notably, the coke‑fired cupola had the lowest cost per ton (224 CNY/t at 120 t), but its severe environmental impact has led to its gradual phase‑out in many regions. Therefore, the natural gas‑fired cupola presents an optimal balance between cost and environmental performance for a modern sand casting foundry.
Analysis for Different Product Types
We also simulated the production of three types of cylinder heads (Type A, B, and C) with different weights: 50 kg, 100 kg, and 200 kg, respectively, all with a wall thickness of 10 mm. The pouring time was calculated using the empirical formula:
$$
t = B \, \delta^{P} \, G^{n}
$$
where \(t\) is pouring time (s), \(G\) is casting weight (kg), \(\delta\) is wall thickness (mm), and the coefficients are \(B = 2.00\), \(P = 0.33\), \(n = 0.33\). The calculated pouring times were:
- Type A (50 kg): 16 s
- Type B (100 kg): 20 s
- Type C (200 kg): 25 s
For each product type, we considered melting 10 t of cast iron (producing 200, 100, or 50 units respectively). Table 6 shows the carbon emissions and costs for each furnace–product combination.
| Product | Furnace | Total carbon (kgCO₂) | Total cost (CNY) | Cost per unit (CNY) |
|---|---|---|---|---|
| Type A (200 units) | Induction | 4,868.5 | 7,398 | 36.99 |
| Coke‑cupola | 4,045.5 | 2,920 | 14.60 | |
| NG cupola | 1,300 | 3,058 | 15.29 | |
| NG rotary | 1,600 | 3,560 | 17.80 | |
| Type B (100 units) | Induction | 4,868.5 | 7,176 | 71.76 |
| Coke‑cupola | 4,045.5 | 2,771 | 27.71 | |
| NG cupola | 1,300 | 2,503 | 25.03 | |
| NG rotary | 1,600 | 3,000 | 30.00 | |
| Type C (50 units) | Induction | 4,868.5 | 7,088 | 141.76 |
| Coke‑cupola | 4,045.5 | 2,687 | 53.74 | |
| NG cupola | 1,300 | 2,281 | 45.62 | |
| NG rotary | 1,600 | 2,800 | 56.00 |
Across all product types, the natural gas‑fired cupola achieved a 73.29% reduction in carbon emissions and a 59.26% reduction in cost compared to the induction furnace. While the coke‑fired cupola had slightly lower cost, its high emissions make it unsuitable for sustainable sand casting foundry operations. The natural gas rotary furnace also performed well, though with slightly higher costs and emissions than the natural gas‑fired cupola.
Conclusion and Recommendations
Our comprehensive analysis of energy sources, equipment, and costs in the sand casting foundry clearly shows that the choice of melting furnace has a significant impact on both environmental and economic performance. The natural gas‑fired cupola stands out as the most balanced solution, offering substantial reductions in carbon emissions (up to 73.29%) and cost (up to 59.26%) compared to the traditional induction furnace. Although the coke‑fired cupola has the lowest cost, its severe pollution and non‑compliance with modern emission standards make it an obsolete choice. The natural gas rotary furnace is a viable alternative, but its cost and emissions are slightly higher than those of the natural gas cupola.
We recommend that sand casting foundries transitioning toward sustainability prioritize the adoption of natural gas‑fired cupolas or rotary furnaces. This shift not only reduces the carbon footprint of the sand casting foundry but also improves economic competitiveness. Furthermore, the application of low‑carbon energy and advanced melting technologies should be coupled with process optimization to achieve the dual goals of carbon peak and carbon neutrality in the sand casting foundry industry.
In summary, our study provides a theoretical and practical reference for the transformation and sustainable development of the sand casting foundry. By systematically evaluating carbon emissions and costs under different melting conditions and product types, we have demonstrated that natural gas‑based melting is a key enabler for a greener and more profitable sand casting foundry.