In the context of global industrialization, the emission of greenhouse gases, primarily carbon dioxide, has become a critical environmental concern. As a foundational sector in traditional manufacturing, the sand casting industry is a significant source of resource consumption and pollution, with energy utilization rates as low as 15%–25% and waste emissions substantially higher than in developed regions. This underscores the urgent need for carbon reduction strategies within sand casting services. To address this, we propose a quantitative carbon emission calculation model tailored for individual castings in sand casting processes, integrating input-output and process analysis methods based on life cycle assessment theory. This model aims to provide a detailed framework for quantifying carbon emissions, enabling enterprises to make informed decisions for sustainable production.
The life cycle of a casting product encompasses multiple stages, with the casting process being a focal point for carbon emission analysis. For sand casting services, the process typically includes molding, melting, recycling, and machining phases. Each stage contributes to carbon emissions through material consumption, energy usage, and waste generation. Our approach systematically quantifies these emissions by categorizing them into material carbon emissions, energy carbon emissions, and waste carbon emissions. This granular analysis allows for the allocation of emissions to individual castings in batch production, facilitating targeted carbon reduction efforts.
Carbon emissions in sand casting services are derived from three primary sources: material-related emissions, energy-related emissions, and waste-related emissions. Material emissions arise from the consumption of inputs such as resin sand, steel scrap, and pig iron during the casting process. Energy emissions result from the operation of equipment like mixers, furnaces, and cranes, which consume electricity. Waste emissions are associated with the treatment of by-products such as dust, fumes, and slag. By delineating these sources, we establish a clear system boundary for carbon emission calculation, ensuring comprehensive coverage of all relevant factors in sand casting services.
To quantify material carbon emissions, we distinguish between variable and fixed materials. Variable materials, such as resin sand and molten metal ingredients, have consumption rates directly tied to process parameters, while fixed materials, like refractory coatings and methanol, require allocation based on output. The material carbon emissions for a casting d across different stages are calculated as follows. For the molding stage, the variable carbon emissions due to resin sand consumption are given by:
$$ C^{1}_{VR,d} = M_d R^1 (1 – \eta) f_b $$
where \( M_d \) is the weight of casting d, \( R^1 \) is the sand-to-metal ratio, \( \eta \) is the resin sand recovery rate, and \( f_b \) is the carbon emission factor of resin sand. The sand-to-metal ratio is derived from:
$$ R^1 = \frac{\rho_b (V_x – V_d)}{M_d} $$
with \( \rho_b \) as the density of resin sand, \( V_x \) as the mold box volume, and \( V_d \) as the casting volume. Fixed material carbon emissions in molding are computed by:
$$ C^{1}_{ST,d} = \sum_{c=1}^{c_0} \frac{I^1_c}{O_d} f_c $$
where \( I^1_c \) is the consumption of fixed material c over a period, \( O_d \) is the output of casting d, and \( f_c \) is the carbon emission factor of material c. Thus, the total material carbon emissions in molding are:
$$ CM^1_d = M_d R^1 (1 – \eta) f_b + \sum_{c=1}^{c_0} \frac{I^1_c}{O_d} f_c $$
In the melting stage, material carbon emissions are variable and depend on the molten metal composition. For casting d, this is expressed as:
$$ CM^2_d = M_d (1 + M_{IR}) \sum_{g=1}^{g_0} R^2_g f_g $$
where \( M_{IR} \) is the ratio of pouring surplus to casting weight, \( R^2_g \) is the proportion of raw material g in the molten metal, and \( f_g \) is its carbon emission factor. For recycling and machining stages, material emissions are fixed and calculated similarly to the molding stage:
$$ CM^3_d = \sum_{c=1}^{c_0} \frac{I^3_c}{O_d} f_c $$
$$ CM^4_d = \sum_{c=1}^{c_0} \frac{I^4_c}{O_d} f_c $$
The overall material carbon emissions for casting d in sand casting services are summarized as:
$$ CM_d = M_d R^1 (1 – \eta) f_b + M_d (1 + M_{IR}) \sum_{g=1}^{g_0} R^2_g f_g + \sum_{a=1}^{4} \sum_{c=1}^{c_0} \frac{I^a_c}{O_d} f_c $$
Energy carbon emissions stem from electricity consumption by equipment. In the molding stage, emissions from sand mixers and cranes are calculated using:
$$ CE^1_d = \left( \sum_{l=1}^{l_0} \frac{p_l M_d R^1}{v_l} + \sum_{m_1=1}^{m_1_0} \frac{p_{m_1} s_{m_1}}{v_{m_1}} \right) f_e $$
where \( p_l \) and \( v_l \) are the power and efficiency of mixer l, \( p_{m_1} \), \( s_{m_1} \), and \( v_{m_1} \) are the power, distance, and speed of crane \( m_1 \), and \( f_e \) is the carbon emission factor of electricity. For the melting stage:
$$ CE^2_d = M_d (1 + M_{IR}) E_n f_e + \sum_{m_2=1}^{m_2_0} \frac{p_{m_2} s_{m_2}}{v_{m_2}} f_e $$
with \( E_n \) as the electricity consumption per ton of molten metal. Recycling stage emissions are:
$$ CE^3_d = M_d R^1 E_o f_e + \sum_{m_3=1}^{m_3_0} \frac{p_{m_3} s_{m_3}}{v_{m_3}} f_e $$
where \( E_o \) is the electricity per ton of resin sand processed. Machining stage emissions include contributions from shot blasting machines and cranes:
$$ CE^4_d = \left( \sum_{u=1}^{u_0} p_u t_u + \sum_{m_4=1}^{m_4_0} \frac{p_{m_4} s_{m_4}}{v_{m_4}} \right) f_e $$
The total energy carbon emissions for sand casting services are thus:
$$ CE_d = \left( \sum_{l=1}^{l_0} \frac{p_l M_d R^1}{v_l} + \sum_{m_1=1}^{m_1_0} \frac{p_{m_1} s_{m_1}}{v_{m_1}} \right) f_e + M_d (1 + M_{IR}) E_n f_e + M_d R^1 E_o f_e + \left( \sum_{u=1}^{u_0} p_u t_u + \sum_{m_4=1}^{m_4_0} \frac{p_{m_4} s_{m_4}}{v_{m_4}} \right) f_e $$
Waste carbon emissions arise from the treatment of by-products like dust and slag. For the molding stage, emissions from dust treatment equipment are:
$$ CU^1_d = M_d \frac{M^1_{U1} p_{w1}}{v_{w1}} f_e $$
where \( M^1_{U1} \) is the waste generation per ton of casting, \( p_{w1} \) is the power of treatment equipment \( w1 \), and \( v_{w1} \) is its processing speed. Melting stage emissions include those from fume treatment and slag handling:
$$ CU^2_d = M_d \frac{M^2_{U1} p_{w2}}{v_{w2}} f_e + M_d \frac{M^2_{U2} p_{i2} s_{i2}}{M_{i2} v_{i2}} f_e $$
Recycling and machining stage waste emissions are similarly computed. The total waste carbon emissions for sand casting services are:
$$ CU_d = \sum_{a=1}^{4} M_d \frac{M^a_{U1} p_{wa}}{v_{wa}} f_e + M_d \frac{M^2_{U2} p_{i2} s_{i2}}{M_{i2} v_{i2}} f_e $$
Combining all components, the total carbon emissions for casting d in sand casting services are:
$$ C_d = CM_d + CE_d + CU_d $$
To illustrate the application of this model, we analyze a locking disk component produced via sand casting services for wind turbine applications. The casting weighs 6,932 kg and is made of ductile iron QT500-14. Key parameters include a sand-to-metal ratio \( R^1 = 8.25 \), resin sand recovery rate \( \eta = 0.93 \), pouring surplus ratio \( M_{IR} = 0.1 \), and electricity carbon emission factor \( f_e = 0.93 \, \text{kgCO}_2/\text{kWh} \). The carbon emission factors for materials are summarized in Table 1.
| Material/Energy | Carbon Emission Factor | Unit |
|---|---|---|
| Resin Sand | 0.02543 | kgCO₂/kg |
| Refractory Coating | 6.0232 | kgCO₂/kg |
| Methanol | 2.5 | kgCO₂/kg |
| Steel Scrap | 8.2 | kgCO₂/kg |
| Pig Iron | 2.13 | kgCO₂/kg |
| Return Material | 2.67 | kgCO₂/kg |
| Carbon Additive | 4.2 | kgCO₂/kg |
| Silicon Carbide | 14.68 | kgCO₂/kg |
| Ferrosilicon | 2.3 | kgCO₂/kg |
| Electricity | 0.93 | kgCO₂/kWh |
The composition of molten metal for the locking disk is detailed in Table 2, which influences material carbon emissions in the melting stage of sand casting services.
| Raw Material | Proportion \( R^2_g \) (%) |
|---|---|
| Steel Scrap | 58.19 |
| Pig Iron | 24.69 |
| Return Material | 14.26 |
| Carbon Additive | 2.20 |
| Silicon Carbide | 0.49 |
| Ferrosilicon | 0.17 |
Using the model, we calculate the material, energy, and waste carbon emissions for the locking disk. The material carbon emissions are derived as follows:
$$ CM_d = 6932 \times 8.25 \times (1 – 0.93) \times 0.02543 + 6932 \times (1 + 0.1) \times \sum_{g} R^2_g f_g + \text{fixed material contributions} $$
This results in \( CM_d = 44,791.79 \, \text{kgCO}_2 \). Energy carbon emissions are computed based on equipment parameters, yielding \( CE_d = 4,234.82 \, \text{kgCO}_2 \). Waste carbon emissions, considering dust and slag treatment, amount to \( CU_d = 14.552 \, \text{kgCO}_2 \). Thus, the total carbon emissions for the locking disk via sand casting services are:
$$ C_d = 44,791.79 + 4,234.82 + 14.552 = 49,041.162 \, \text{kgCO}_2 $$
A detailed breakdown of carbon emissions by source is provided in Table 3, highlighting the contributions from each stage and material in sand casting services.
| Emission Type | Material/Energy Source | Consumption | CO₂ Emission (kg) | Percentage (%) |
|---|---|---|---|---|
| Material Emissions | Resin Sand | 4,001.13 kg | 101.75 | 0.21 |
| Refractory Coating | 10.87 kg | 65.46 | 0.13 | |
| Methanol | 16.3 kg | 40.76 | 0.08 | |
| Steel Scrap | 4,437.1 kg | 36,384.25 | 74.19 | |
| Pig Iron | 1,882.66 kg | 4,010.07 | 8.18 | |
| Return Material | 1,087.35 kg | 2,906.5 | 5.93 | |
| Carbon Additive | 167.75 kg | 704.57 | 1.44 | |
| Silicon Carbide | 37.36 kg | 548.5 | 1.12 | |
| Ferrosilicon | 12.96 kg | 29.81 | 0.06 | |
| Steel Shot | 0.01 kg | 0.12 | 0.00 | |
| Energy Emissions | Sand Mixer | 29.05 kWh | 27.03 | 0.06 |
| Crane (Molding) | 1.49 kWh | 1.39 | 0.00 | |
| Crane (Melting) | 3,812.6 kWh | 3,545.72 | 7.23 | |
| Crane (Recycling) | 0.85 kWh | 0.79 | 0.00 | |
| Crane (Machining) | 680.19 kWh | 632.91 | 1.29 | |
| Furnace | 4,102.8 kWh | 3,815.60 | 7.78 | |
| Sand Recycling Line | 2.35 kWh | 2.18 | 0.00 | |
| Shot Blasting Machine | 26.67 kWh | 24.80 | 0.05 | |
| Waste Emissions | Dust Treatment (Molding) | 4.28 kWh | 3.97 | 0.01 |
| Dust Treatment (Melting) | 3.65 kWh | 3.39 | 0.01 | |
| Dust Treatment (Recycling) | 7.66 kWh | 7.12 | 0.00 | |
| Dust Treatment (Machining) | 0.08 kWh | 0.07 | 0.00 | |
| Slag Handling | 0.002 kWh | 0.002 | 0.00 |
The analysis reveals that material carbon emissions dominate the total, accounting for over 91% of emissions in this sand casting services example. Within material emissions, the melting stage contributes the most, primarily due to the high carbon emission factors of raw materials like steel scrap. This indicates that optimizing molten metal composition and reducing pouring surplus can significantly lower carbon footprints in sand casting services. Energy emissions, while smaller, still offer reduction opportunities through equipment efficiency improvements. Waste emissions are minimal but should not be overlooked in comprehensive carbon management strategies for sand casting services.
Our model provides a practical tool for quantifying carbon emissions in sand casting services, enabling enterprises to identify key emission sources and implement targeted reduction measures. For instance, adjusting the sand-to-metal ratio, enhancing resin sand recovery rates, and selecting low-carbon raw materials can mitigate material emissions. Additionally, adopting energy-efficient equipment and optimizing logistics can reduce energy-related emissions. By integrating this model into production planning, sand casting services can advance towards greener manufacturing practices, aligning with global carbon reduction goals.
In conclusion, we have developed a quantitative carbon emission calculation model for sand casting services, combining input-output and process analysis methods based on life cycle assessment. The model effectively breaks down emissions into material, energy, and waste categories, allowing for precise allocation to individual castings. Applied to a locking disk component, it demonstrates the significant impact of material choices and process parameters on carbon footprints. This work offers a foundational framework for carbon emission management in sand casting services, supporting the industry’s transition to sustainable production. Future research could expand this model to include other environmental impacts or integrate it with digital twins for real-time carbon monitoring in sand casting services.