In my extensive experience within the foundry industry, designing effective gating and feeding systems for copper alloy sand casting parts remains a cornerstone of producing sound, high-integrity castings. Among various geometries, complex plate-shaped sand casting parts—such as semi-circular sliders, large T-shaped busbars, and transition plates—present some of the most significant challenges. While their shapes may appear deceptively simple, the inherent difficulties in achieving proper feeding and avoiding defects like shrinkage porosity and oxide inclusions are substantial. For these sand casting parts, after determining the pouring position and riser location, the precise sizing of the riser becomes the most critical step in the process design.
Traditionally, the industry has relied on two primary approaches, each with notable limitations. Handbook-based or purely experiential methods often lack the specificity and accuracy required for these demanding geometries, leading to inconsistent results, lower yield, or costly defects. On the other hand, while computer solidification simulation technology has provided valuable insights over the past decade, it is not a panacea. The software often simplifies complex physical phenomena, and the results may not perfectly align with reality, frequently requiring adjustments based on practical know-how. Furthermore, the process of model preparation, data input, and analysis is time-consuming and demands a high level of operator expertise. There has been a clear gap: the need for a design method that is both sufficiently accurate and highly efficient for daily foundry practice.
This article, based on years of hands-on practice, statistical analysis of production data, and validation through solidification simulation, aims to bridge that gap. I have developed a streamlined and reliable riser design methodology specifically for aluminum bronze and brass complex plate sand casting parts produced via sand casting. This method synthesizes the strengths of empirical knowledge and simulation-based verification into a practical set of guidelines and formulas, enabling rapid yet accurate riser sizing, ensuring casting quality, maximizing process yield, and significantly improving design efficiency.
The Foundational Principles and Methodology
The core of this便捷设计方法 (convenient design method) lies in establishing quantitative relationships between the key geometric parameters of the sand casting part and its corresponding side riser. The method is specifically tailored for a horizontal molding arrangement with the mold tilted at an angle of $10^{\circ}$ to $15^{\circ}$ (a “climbing” pour), utilizing side risers. This configuration offers distinct advantages for complex plate sand casting parts: it facilitates slag and gas flotation towards the riser, allows for easier riser removal, and simplifies mold and core assembly compared to vertical pouring methods.
For an irregular plate sand casting part, we define its primary dimensions as follows:
- L: The maximum length of the casting (mm).
- m: The maximum width or lateral dimension of the casting in the direction perpendicular to the riser attachment face (mm).
- T: The maximum thickness of the casting, accounting for any recesses or depressions (mm).
The corresponding riser is typically designed as an elongated “waist-round” (ellipsoidal or similar) shape, with its key parameters being:
- a: The length of the riser (mm).
- b: The width or diameter of the riser (mm).
- h: The height of the riser (mm).
- n: The number of risers required for the casting.
The design process involves two main stages: Calculation and Verification. The calculation uses proportionality constants derived from empirical and simulated data, while the verification checks the riser’s aspect ratio and the overall process yield.
Stage 1: Riser Parameter Calculation
The primary dimensions of the riser are calculated using the following formulas, where $k_1$, $k_2$, and $k_3$ are empirical coefficients dependent on the casting’s dimensions:
$$
n \cdot a = k_1 \cdot L
$$
$$
b = k_2 \cdot T
$$
$$
h = k_3 \cdot m
$$
The value of $n$ (number of risers) is first estimated based on the casting length $L$ and the desired final riser length $a$, typically aiming for a suitable $a/b$ ratio (verified in Stage 2). For very long castings, $n$ may be 2 or more.
Stage 2: Riser Design Verification
After obtaining initial values for $a$, $b$, and $h$, two critical checks must be performed:
- Aspect Ratio Check: The ratio $a / b$ must fall within a specified range. An ratio that is too low may not provide adequate feeding distance, while one that is too high may make the riser inefficient or difficult to place.
- Process Yield Check: The calculated yield, defined as:
$$
\text{Process Yield} (\%) = \frac{\text{Casting Weight}}{\text{Casting Weight} + \text{Riser(s) Weight} + \text{Gating System Weight}} \times 100\%
$$
must fall within an acceptable range, typically between 55% and 75% for these types of sand casting parts, ensuring economic efficiency without compromising quality.
The heart of this method is the determination of the coefficients $k_1$, $k_2$, and $k_3$, along with the acceptable ranges for $a/b$ and process yield. These have been codified into a comprehensive table based on analysis of numerous successful production cases and simulation studies for aluminum bronze and brass sand casting parts with $L < 1800$ mm, $m < 1400$ mm, and $T < 120$ mm.
| Casting Length L (mm) | Coefficient k1 | Coefficient k2 (based on T) | Coefficient k3 (based on m) | Verification a/b | Target Process Yield (%) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| T < 70 mm | T = 70–120 mm | T = 120–160 mm | m < 400 mm | m = 400–700 mm | m = 700–900 mm | m = 900–1100 mm | m = 1100–1300 mm | L ≤ 800 mm | L > 800 mm | |||
| 1600–1800 | 0.35 | 1.40–1.55 | 1.30–1.40 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | 0.30–0.40 | 0.25–0.30 | 0.20–0.25 | 2.2–3.0 | 2.2–3.0 | 65–75 |
| 1400–1600 | 0.35 | 1.40–1.55 | 1.30–1.40 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | 0.30–0.40 | 0.25–0.30 | 0.20–0.25 | 2.2–3.0 | 2.2–3.0 | 65–75 |
| 1200–1400 | 0.35 | 1.40–1.50 | 1.30–1.40 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | 0.30–0.40 | 0.25–0.30 | 0.20–0.25 | 1.8–2.5 | 1.8–2.5 | 60–70 |
| 1000–1200 | 0.35 | 1.40–1.50 | 1.30–1.40 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | 0.30–0.40 | 0.25–0.30 | 0.20–0.25 | 1.8–2.5 | 1.8–2.5 | 60–65 |
| 800–1000 | 0.35 | 1.35–1.45 | 1.25–1.35 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | 0.30–0.40 | 0.25–0.30 | — | 1.5–2.2 | 1.5–2.2 | 60–65 |
| 600–800 | 0.35 | 1.30–1.40 | 1.25–1.35 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | 0.30–0.40 | — | — | 1.5–2.2 | — | 55–60 |
| < 600 | 0.35 | 1.30–1.40 | 1.25–1.35 | 1.20–1.30 | 0.50–0.60 | 0.40–0.50 | — | — | — | 1.0–1.8 | — | 50–60 |
Practical Application and Case Studies
The true test of any foundry methodology is its application to real-world sand casting parts. The following case studies demonstrate the use of this design process, from initial calculation through verification and, where applicable, comparison with solidification simulation results.
Case Study 1: Large Semi-Circular Slider (Aluminum Bronze)
Casting Data: Material: High-Manganese Aluminum Bronze (e.g., ZCuAl8Mn12Fe3Ni2). Dimensions: $L = 1214$ mm, $m = 345$ mm, $T = 150$ mm.
Process Selection: Horizontal molding with a single side riser, mold tilted $10^{\circ}$-$15^{\circ}$. This configuration is favorable for this type of sand casting part as it aids in feeding the central thick section and allows for easy riser removal.
Riser Design:
- Determine Coefficients: From Table 1 for $L=1214$ mm: $k_1=0.35$, $k_2=1.20$–$1.30$ (for $T=150$ mm), $k_3=0.50$–$0.60$ (for $m=345$ mm).
- Calculate Parameters: Assuming $n=1$.
$$ a = k_1 \cdot L = 0.35 \times 1214 \approx 425 \text{ mm (Round to 430 mm)} $$
$$ b = k_2 \cdot T = (1.20 \text{ to } 1.30) \times 150 = 180 \text{–} 195 \text{ mm (Take 190 mm)} $$
$$ h = k_3 \cdot m = (0.50 \text{ to } 0.60) \times 345 = 172.5 \text{–} 207 \text{ mm (Take 190 mm)} $$ - Verify Design:
Aspect Ratio: $a / b = 430 / 190 \approx 2.26$. This falls within the required range of 1.8–2.5 for $L>800$ mm (Table 1). ✅
Process Yield: Casting weight ~300 kg, Riser weight ~152 kg, Gating weight ~20 kg.
$$ \text{Yield} = \frac{300}{300+152+20} \times 100\% \approx 63.6\% $$
This is within the target range of 60–70% for this size. ✅
This design was successfully implemented in production, yielding sound sand casting parts.
Case Study 2: Large T-Shaped Busbar (Brass)
Casting Data: Material: Brass (e.g., ZCuZn38). Dimensions: $L = 1630$ mm, $m = 1262$ mm, $T = 77$ mm.
Process Selection: Horizontal tilted pour with two side risers. Due to the large width ($m > 800$ mm), a large chill (1065 mm long, full width) is necessary to create a directional solidification gradient towards the risers. This is a critical consideration for wide plate sand casting parts.
Riser Design:
- Determine Coefficients: For $L=1630$ mm: $k_1=0.35$, $k_2=1.30$–$1.40$ (for $T=77$ mm), $k_3=0.20$–$0.25$ (for $m=1262$ mm).
- Calculate Parameters: Using $n=2$.
$$ n \cdot a = k_1 \cdot L = 0.35 \times 1630 \approx 570.5 \text{ mm} $$
$$ a = 570.5 / 2 \approx 285.25 \text{ mm (Round to 270 mm for standard practice)} $$
$$ b = k_2 \cdot T = (1.30 \text{ to } 1.40) \times 77 = 100.1 \text{–} 107.8 \text{ mm (Take 105 mm)} $$
$$ h = k_3 \cdot m = (0.20 \text{ to } 0.25) \times 1262 = 252.4 \text{–} 315.5 \text{ mm (Take 270 mm)} $$ - Verify Design:
Aspect Ratio: $a / b = 270 / 105 \approx 2.57$. This meets the 2.2–3.0 requirement. ✅
Process Yield: Casting weight ~840 kg, Riser weight ~195 kg, Gating weight ~50 kg.
$$ \text{Yield} = \frac{840}{840+195+50} \times 100\% \approx 77.4\% $$
This is an excellent yield, indicating highly efficient feeding. - Solidification Simulation Check: A simulation model was run using these riser dimensions and the chill. The results confirmed perfect feeding with no isolated hot spots or shrinkage porosity in the critical sections of the sand casting part, validating the empirical design. The simulation also predicted the slight surface depression (5-6 mm) on the large top plane due to the chill’s effect, which was accounted for in the pattern design.
Case Study 3: Thick Rectangular Plate (Aluminum Bronze)
Casting Data: Material: Aluminum Bronze (e.g., ZCuAl10Fe3). Dimensions: $L = 1050$ mm, $m = 850$ mm, $T = 60$ mm. This represents a more regular plate-shaped sand casting part.
Process Selection: Horizontal tilted pour with two side risers. A chill (500 mm long, full width) is used due to $m > 800$ mm.
Riser Design:
- Determine Coefficients: For $L=1050$ mm: $k_1=0.35$, $k_2=1.40$–$1.50$ (for $T=60$ mm), $k_3=0.30$–$0.40$ (for $m=850$ mm).
- Calculate Parameters: Using $n=2$.
$$ n \cdot a = k_1 \cdot L = 0.35 \times 1050 = 367.5 \text{ mm} $$
$$ a = 367.5 / 2 \approx 183.75 \text{ mm (Round to 180 mm)} $$
$$ b = k_2 \cdot T = (1.40 \text{ to } 1.50) \times 60 = 84 \text{–} 90 \text{ mm (Take 90 mm)} $$
$$ h = k_3 \cdot m = (0.30 \text{ to } 0.40) \times 850 = 255 \text{–} 340 \text{ mm (Take 300 mm)} $$ - Verify Design:
Aspect Ratio: $a / b = 180 / 90 = 2.0$. This is within the 1.8–2.5 range. ✅
Process Yield: Casting weight ~407 kg, Riser weight ~90 kg, Gating weight ~45 kg.
$$ \text{Yield} = \frac{407}{407+90+45} \times 100\% \approx 75.1\% $$
This higher yield compared to more complex shapes with similar dimensions highlights the efficiency achievable with simpler plate sand casting parts using this method.
Critical Considerations and Best Practices
While the provided methodology offers a robust framework, successful implementation for these demanding sand casting parts requires attention to several ancillary factors:
- Chill Application for Wide Plates: For sand casting parts where the width $m \geq 800$ mm, the use of chills (preferably cast iron or steel) is almost mandatory to establish a strong thermal gradient towards the riser(s). The chill length is typically 50-70% of the casting length from the end opposite the riser. It is crucial to preheat and dry the chill surface (to ~150–190°C) before molding to prevent gas evolution and improve metal-chill contact.
- Managing Top Surface Dishes: A significant, predictable dish (concave depression) often forms on the top surface of thick plate sand casting parts due to the chilling action. This must be anticipated during pattern design by adding sufficient machining allowance or, if possible, incorporating a slight convex camber on the pattern.
- Gating Orientation Relative to Chills: A critical practical lesson: When chills are used near the ingates, the gate geometry should be designed so that the metal flow is directed perpendicular to the chill’s face. If the metal flows parallel to the chill face (e.g., from a wide, flat gate), a cold shut or oxide layer can become trapped at the leading edge of the flow, creating a severe defect. Using a narrower, deeper ingate oriented correctly solves this issue.
- Extended Mold Cooling: To minimize distortion and internal stresses in these large, often asymmetric plate sand casting parts, the mold should not be broken too early. A holding time of at least 6 hours post-pouring before shakeout is recommended.
Conclusion
The development and application of this integrated riser design methodology have demonstrated its significant value in the production of high-quality aluminum bronze and brass complex plate sand casting parts. By establishing clear, quantitative relationships between casting geometry and riser parameters—encapsulated in practical formulas and Table 1—this approach effectively bridges the gap between oversimplified experience and computationally intensive simulation. It provides foundry engineers with a tool that is both accurate, as it is rooted in statistical success and simulation-validated data, and efficient, enabling rapid and reliable process design.
The case studies confirm that the method reliably achieves the dual objectives of ensuring soundness (full feeding, minimal shrinkage) and optimizing economic efficiency (high process yield). Furthermore, it systematizes the application of critical complementary techniques like strategic chilling and proper gating design. For foundries specializing in or encountering challenging copper alloy sand casting parts with plate-like geometries, adopting this structured yet flexible design framework can lead to more consistent results, reduced scrap rates, and improved overall productivity.