Abstract
As global industrialization accelerates, the foundry industry—particularly sand casting—has become a significant contributor to carbon emissions due to its resource-intensive processes. This study proposes a hybrid carbon emission calculation model for sand casting by integrating the Input-Output (IO) method and Process Analysis (PA) under the Life Cycle Assessment (LCA) framework. The model quantifies emissions across four production stages (molding, melting, recycling, and machining) by analyzing material consumption, energy use, and waste treatment. A case study of an 11 MW locking disk component demonstrates the model’s practicality, revealing that material-related emissions dominate (74.19% of total emissions), with melting stage optimization identified as a key lever for decarbonization. This work provides a granular methodology for calculating per-unit casting emissions and actionable insights for sustainable sand casting practices.
1. Introduction
The sand casting process, a cornerstone of traditional manufacturing, accounts for substantial energy consumption and carbon emissions. In 2019, China’s industrial carbon emissions reached 9.825 billion tons, 29% of the global total, with the foundry sector exhibiting an energy efficiency of only 15–25%—far below international standards. To align with national carbon neutrality goals (e.g., China’s 2030 Carbon Peak Action Plan), decarbonizing sand casting is critical. Existing research often calculates emissions at the process or facility level, neglecting per-unit casting quantification. This study bridges this gap by:
- Developing a stage-specific carbon emission model for sand casting.
- Validating the model through a real-world case study.
- Proposing actionable strategies to reduce emissions in high-impact stages.
2. Methodology
2.1 System Boundaries and Carbon Sources
The sand casting process is divided into four stages (Figure 1):
- Molding: Resin sand consumption, mixer energy use, and dust emissions.
- Melting: Raw material (e.g., scrap steel, pig iron) usage, furnace energy demand, and slag/byproduct treatment.
- Recycling: Sand reclamation energy and waste gas emissions.
- Machining: Grinding/polishing energy and particulate matter disposal.
Carbon emissions are categorized as:
- Material Emissions: Indirect emissions from resource extraction and processing.
- Energy Emissions: Direct emissions from electricity/fuel consumption.
- Waste Emissions: Emissions from treating byproducts (e.g., dust, slag).
2.2 Quantitative Model
2.2.1 Material Emissions
Material emissions (CMdCMd) for a casting (dd) are calculated as:CMd=CMmolding+CMmelting+CMrecycling+CMmachiningCMd=CMmolding+CMmelting+CMrecycling+CMmachining
- Molding Stage:
CMmolding=Md⋅R1⋅(1−η)⋅fb+∑i=1nMd⋅IitQi⋅fcCMmolding=Md⋅R1⋅(1−η)⋅fb+i=1∑nMd⋅QiIit⋅fc
- MdMd: Casting weight.
- R1R1: Sand-to-iron ratio.
- ηη: Resin sand recovery rate.
- fb,fcfb,fc: Emission factors for resin sand and fixed materials.
- Melting Stage:
CMmelting=Md⋅(1+MIR)⋅∑g=1g0Rg2⋅fgCMmelting=Md⋅(1+MIR)⋅g=1∑g0Rg2⋅fg
- MIRMIR: Ratio of excess molten iron to casting weight.
- Rg2Rg2: Proportion of raw material gg in molten iron.
- Recycling/Machining Stages:
Fixed emissions based on shared resource allocation:
CMrecycling/machining=∑c=1c0Md⋅IctQi⋅fcCMrecycling/machining=c=1∑c0Md⋅QiIct⋅fc
2.2.2 Energy Emissions
Energy emissions (CEdCEd) derive from equipment electricity use:CEd=∑a=14(∑k=1k0Pk⋅tk+∑m=1m0Pm⋅smvm⋅60)⋅feCEd=a=1∑4(k=1∑k0Pk⋅tk+m=1∑m0Pm⋅vm⋅60sm)⋅fe
- Pk,PmPk,Pm: Power of processing and handling equipment.
- tk,sm,vmtk,sm,vm: Operating time, distance, and speed.
- fefe: Electricity emission factor.
2.2.3 Waste Emissions
Waste emissions (CUdCUd) include energy for treating dust, slag, and gases:CUd=∑a=14(∑j=1j0Pj⋅Mjavj+∑m=1m0Pm⋅sm⋅Mjavm⋅1000)⋅feCUd=a=1∑4(j=1∑j0Pj⋅vjMja+m=1∑m0Pm⋅vm⋅1000sm⋅Mja)⋅fe
2.3 Key Parameters
Critical parameters for the model are summarized in Table 1.
Table 1: Key Parameters for Carbon Emission Calculation
| Parameter | Description | Unit |
|---|---|---|
| MdMd | Casting weight | kg |
| R1R1 | Sand-to-iron ratio | – |
| ηη | Resin sand recovery rate | % |
| fb,fg,fcfb,fg,fc | Emission factors (resin, iron, fixed materials) | kgCO₂/kg or kgCO₂/kWh |
| fefe | Electricity emission factor | kgCO₂/kWh |
| E1,E2E1,E2 | Energy intensity (melting, recycling) | kWh/kg |
3. Case Study: 11 MW Locking Disk Component
3.1 Component Overview
A QT500-14 ductile iron locking disk (6,932 kg) produced via sand casting was analyzed. Key parameters include:
- Sand Molding: Sand-to-iron ratio R1=8.25R1=8.25, resin recovery rate η=93%η=93%.
- Melting: 58.19% scrap steel, 24.69% pig iron, 14.26% returns.
- Energy: Electricity emission factor fe=0.93fe=0.93 kgCO₂/kWh.
3.2 Emission Calculation
3.2.1 Material Emissions
Resin sand, refractory coatings, and raw materials contributed 44,791.79 kgCO₂ (91.3% of total emissions). The melting stage dominated (99% of material emissions), driven by scrap steel and pig iron (Table 2).
Table 2: Material Emissions Breakdown
| Material | Quantity (kg) | Emission Factor (kgCO₂/kg) | Emissions (kgCO₂) | Contribution (%) |
|---|---|---|---|---|
| Resin Sand | 4,001.13 | 0.02543 | 101.75 | 0.21 |
| Scrap Steel | 4,437.10 | 8.20 | 36,384.25 | 74.19 |
| Pig Iron | 1,882.66 | 2.13 | 4,010.07 | 8.18 |
| Returns | 1,087.35 | 2.67 | 2,906.50 | 5.93 |
3.2.2 Energy Emissions
Equipment such as mixers, furnaces, and cranes generated 4,234.82 kgCO₂ (8.6% of total). The melting furnace alone accounted for 83.7% of energy emissions (Table 3).
Table 3: Energy Emissions by Equipment
| Equipment | Energy Use (kWh) | Emissions (kgCO₂) | Contribution (%) |
|---|---|---|---|
| Melting Furnace | 3,812.60 | 3,545.72 | 83.7 |
| Sand Recycler | 680.19 | 632.91 | 14.9 |
| Shot Blaster | 26.67 | 24.80 | 0.6 |
3.2.3 Waste Emissions
Dust treatment and slag handling contributed 247.58 kgCO₂ (0.5% of total), with molding-stage dust being the largest source (Table 4).
Table 4: Waste Emissions by Stage
| Stage | Waste Type | Quantity (kg) | Emissions (kgCO₂) |
|---|---|---|---|
| Molding | Dust | 0.586 | 4.28 |
| Melting | Slag | 0.054 | 0.002 |
| Recycling | Dust | 1.050 | 7.66 |
3.3 Emission Distribution
Material emissions dominated (91.3%), followed by energy (8.6%) and waste (0.5%) (Figure 2). The melting stage accounted for 87.4% of total emissions, highlighting its optimization potential.
4. Discussion: Pathways for Decarbonization
- Material Optimization:
- Increase scrap steel usage (lower emission factor than pig iron).
- Adopt low-carbon additives (e.g., replacing carburizers with bio-based alternatives).
- Energy Efficiency:
- Upgrade furnaces to high-efficiency induction models.
- Implement energy recovery systems for waste heat.
- Waste Minimization:
- Improve resin sand recovery rates (>93%).
- Install advanced dust collectors to reduce particulate emissions.
- Process Reengineering:
- Optimize gating systems to reduce excess molten iron (MIRMIR).
- Digitize process controls to minimize idle equipment time.
5. Conclusion
This study establishes a granular carbon emission model for sand casting, enabling per-unit casting quantification through a hybrid IO-PA approach. The locking disk case study validates the model’s accuracy, with material emissions identified as the primary contributor (91.3%). Future work will expand the model to include upstream (e.g., raw material production) and downstream (e.g., transportation) stages, fostering holistic decarbonization in sand casting. By prioritizing melting-stage optimizations and adopting circular economy principles, foundries can significantly reduce their carbon footprint while maintaining competitiveness.