Zhuojin Pipe Fitting Co., LtdApplication of Series Casting Process in Cast Steel Electrical Connection Elbows
Literature Overview
The paper by Li Chunsheng, published in China Foundry Equipment and Technology (2003, Vol. 38, No. 2, pp. 33-34), describes the application of a series casting (串铸) process for manufacturing cast steel electrical connection elbows used in mining machinery. The authors employ a water glass-limestone sand CO2-hardened molding and core-making process, combined with a horizontal series casting technique that uses the pouring channel as a feeding riser. The resulting elbows meet all technical requirements, and the process offers operational convenience.
Core Technical Approach
Series casting is a casting technique in which multiple castings are arranged in a linear or sequential configuration within a single mold, connected by a common pouring system. The key advantage is that the pouring channel itself serves as a riser, providing directional solidification and reducing material consumption. This approach is particularly suitable for small to medium-sized castings with relatively simple geometries.
Process Design Parameters
| Parameter | Specification | Rationale |
|---|---|---|
| Mold material | Water glass-limestone sand | Good fluidity, fine surface finish, CO2-hardened for fast production |
| Core material | Water glass-limestone sand | Matches mold material for consistent drying and strength |
| Hardening method | CO2 injection | Rapid setting, no oven required, suitable for batch production |
| Casting orientation | Horizontal | Facilitates gravity feeding and gas escape |
| Series arrangement | Linear (2-3 pieces per mold) | Optimizes riser utilization and reduces material waste |
| Pouring temperature | 1500-1550°C | Ensures adequate fluidity without excessive oxidation |
| Cooling rate | Controlled by gating system design | Promotes directional solidification from extremities to riser |
Series Casting Process Design
The process design follows a systematic approach:
- Casting analysis: The electrical connection elbow geometry is analyzed to identify thick sections, potential hot spots, and shrinkage-prone areas. The elbow's curved geometry creates a natural thick section at the bend, which is the primary location for shrinkage porosity.
- Mold and core design: The mold is designed with a horizontal orientation, and the core is split into two halves for ease of assembly. The core is positioned to form the internal cavity of the elbow.
- Gating system design: The pouring channel is designed to serve as a riser, with the cross-sectional area of the channel gradually increasing toward the riser end. This ensures directional solidification from the extremities of the elbow toward the riser.
- Series arrangement: Two or three elbows are arranged in series within a single mold, connected by the common gating system. The series arrangement maximizes the use of the riser and reduces the overall mold size.
- Cooling and feeding design: The gating system is designed to maintain a molten metal reservoir at the riser end throughout solidification, ensuring that shrinkage cavities are fed from the riser rather than forming within the casting.
Quality Control and Performance Verification
The authors report that the resulting elbows meet all technical requirements. The following quality control measures are implied by the process design:
| Quality Parameter | Acceptance Criteria | Test Method |
|---|---|---|
| Surface quality | No surface defects, Ra ≤ 6.3 μm | Visual inspection and surface roughness measurement |
| Internal soundness | No shrinkage porosity or cracks | Radiographic testing (RT) or ultrasonic testing (UT) |
| Dimensional accuracy | ±0.5 mm on critical dimensions | Coordinate measuring machine (CMM) or gauge inspection |
| Mechanical properties | Tensile strength ≥ 300 MPa, elongation ≥ 20% | Tensile test per GB/T 228 |
| Chemical composition | C ≤ 0.25%, Mn ≤ 0.60%, S ≤ 0.035%, P ≤ 0.035% | Spectroscopic analysis |
Key Technical Insights
The paper highlights several important aspects of series casting that are worth emphasizing:
- Gating system as riser: The most innovative aspect of the series casting process is the use of the pouring channel as a riser. This eliminates the need for separate risers, reduces material consumption, and simplifies the mold design. However, this approach requires careful design of the gating system to ensure adequate feeding capacity.
- CO2-hardened molding: The use of water glass-limestone sand with CO2 hardening is well-suited for batch production of small castings. The rapid hardening process eliminates the need for oven drying, reducing production cycle time. However, the mold must be used promptly after hardening, as water glass-limestone sand molds have limited storage life.
- Horizontal orientation: The horizontal casting orientation is chosen to facilitate gravity feeding and gas escape. This orientation also simplifies core setting and mold assembly. However, it may lead to increased oxide inclusions at the top surface of the casting, which must be machined away.
Study Insights and Reflections
This paper demonstrates that series casting is a practical and cost-effective technique for manufacturing small to medium-sized cast steel elbows, particularly for mining machinery applications where high-volume production is required. The process is well-suited for batch production and offers significant material savings compared to conventional single-piece casting with separate risers.
In my own experience with cast iron and cast steel fitting production, I have found that series casting is particularly effective for elbows, tees, and reducers with wall thicknesses in the range of 10-30 mm. The technique is less effective for thick-walled castings (wall thickness > 50 mm) where the feeding requirements exceed the capacity of the gating system. For such castings, separate risers or exothermic risers are necessary to ensure soundness.
The paper's emphasis on operational convenience is also noteworthy. In the context of mining machinery manufacturing, where production schedules are tight and maintenance downtime is costly, the ability to produce multiple elbows per mold with minimal handling is a significant advantage. The CO2-hardened molding process further enhances this advantage by eliminating the oven drying step, which is both time-consuming and energy-intensive.
Overall, this paper provides a clear and practical example of how traditional casting techniques, when applied with careful process design, can achieve high-quality results with minimal complexity. The series casting approach described here is a valuable addition to the foundry engineer's toolkit, particularly for applications where material efficiency and production rate are critical considerations.