My research was dedicated to the process optimization and casting defect prevention of railway steel castings produced by the green molding clay sand method. The work combined systematic laboratory experiments, computational simulation, industrial validation, and microscopic defect analysis. The central goal was to produce high-quality steel castings, such as coupler yokes and knuckles, with low production cost, high efficiency, and a low occurrence of casting defect formation. Green molding clay sand is an energy-saving and recyclable molding medium, but it is also sensitive to raw material quality, environmental conditions, and process control. Therefore, understanding the relationship between sand composition, sand performance, and final casting quality became the foundation of my research.
Fundamental Aspects of Green Molding Clay Sand
Green molding clay sand is composed of silica sand, bentonite, starch-based additives, and water. The sand is not baked or hardened before pouring; it possesses only green strength. This feature makes it highly productive and easy to automate, but it also creates challenges. During pouring, moisture vaporizes and migrates through the mold, and the expansion of silica sand may produce stresses that lead to several typical casting defect categories, including blowholes, scabs, sand burning, and hot tears. In railway steel castings, these defects are particularly dangerous because they can propagate under alternating loads and cause premature fracture or severe wear.
The raw materials must be selected carefully. For steel castings, silica sand should contain at least 94% silicon dioxide, with low clay content and controlled fines. Bentonite should preferably be sodium-activated or natural sodium bentonite because of its high thermal durability and resistance to burn-out. Starch-based additives, such as alpha starch and dextrin, increase toughness, reduce sand brittleness, and create space for quartz expansion during heating. Moisture content must be balanced carefully: too little water gives brittle sand, while too much water leads to low strength and gas-related casting defect problems.
Key Sand Performance Indicators
Several parameters are used to evaluate green sand quality. Moisture content is measured by weight loss after drying:
$$
w = \frac{m_w}{m_s} \times 100\%
$$
where \(w\) is moisture content, \(m_w\) is water mass, and \(m_s\) is dry sand mass. Compactibility indicates the volume reduction of sand under standard ramming:
$$
C = \frac{V_0 – V_f}{V_0} \times 100\%
$$
where \(V_0\) is initial loose volume and \(V_f\) is final compacted volume. Permeability is determined by the flow of air through a standard sand specimen:
$$
P = \frac{V_a H}{p A t}
$$
where \(V_a\) is air volume, \(H\) is specimen height, \(p\) is pressure difference, \(A\) is cross-sectional area, and \(t\) is time. Green compressive strength, hot wet tensile strength, shatter index, and surface stability all help to quantify the ability of the sand mold to resist erosion, cracking, and erosion-related casting defect formation.
| Performance parameter | Typical requirement for steel green sand |
|---|---|
| Compactibility | 45–60% |
| Green compressive strength | 70–120 kPa |
| Hot wet tensile strength | ≥3.0 kPa |
| Permeability | 150–450 |
| Shatter index | 65–75% |
| Surface stability | ≥95% |
Experimental Program for Sand Formulation
In my experiments, the foundry used separate facing sand and backing sand. The facing sand was prepared with new silica sand, while the backing sand mainly used return sand. This approach reduces cost and improves refractoriness on the mold surface. Before designing the formulations, I characterized the new sand and return sand. The return sand had been recycled repeatedly, so its particle size had become finer and its fines content had increased.
| Property | New sand | Return sand |
|---|---|---|
| Main sieve fraction | 40 mesh | 50 mesh |
| Moisture content | <1% | 0.7% |
| Clay content | <1% | 6.8% |
| Effective bentonite content | — | 5.05% |
The methylene blue titration method was used to measure effective bentonite content. A standard calibration curve with known bentonite additions was established, followed by titration of return sand samples. This allowed me to calculate the active clay level and to determine how much bentonite must be replenished in the backing sand. The effective bentonite content is related to the volume of methylene blue solution consumed:
$$
B_{\text{eff}} = \frac{C_{MB} V_{MB}}{m_s} \times k
$$
where \(C_{MB}\) is the concentration of methylene blue solution, \(V_{MB}\) is the volume consumed, \(m_s\) is the sample mass, and \(k\) is a constant derived from the calibration curve. This information was essential because excessive dead clay and fines cause poor refractoriness and increase the risk of mechanical sand burning and other casting defect types.
Facing Sand Single-Factor Experiments
I first performed single-factor experiments to determine suitable ranges of bentonite, starch additive, and water. A baseline mixture of new sand, bentonite, and water was prepared without additives. Then alpha starch and dextrin were added separately at levels from 0.1% to 0.5%. Both additives improved hot wet tensile strength and surface stability, but their effects were not identical. Alpha starch provided a smooth increase in hot wet strength, while dextrin gave better green surface toughness but reduced flowability slightly.
Based on these experiments, I used a blended additive with an alpha starch-to-dextrin ratio of 3:2. The total additive level was kept between 0.1% and 0.5%. Bentonite content was then varied from 7.0% to 8.5%, and water content from 2.8% to 3.7%. The target performance range given by the factory was green compressive strength 80–100 kPa, hot wet tensile strength at least 3.0 kPa, and compactibility 50% ± 5%.
Orthogonal Experimental Design
After the single-factor stage, I designed orthogonal experiments with three factors and three levels. The facing sand factors were bentonite content, additive content, and water content. The backing sand factors were bentonite replenishment, additive replenishment, and water content. Such an L9 orthogonal design allowed efficient evaluation of main effects and interactions in a limited number of tests.
| Sand type | Level | Bentonite % | Additive % | Water % |
|---|---|---|---|---|
| Facing sand | 1 | 7.5 | 0.1 | 3.0 |
| 2 | 8.0 | 0.3 | 3.3 | |
| 3 | 8.5 | 0.5 | 3.6 | |
| Backing sand | 1 | 0.1 | 0.1 | 3.0 |
| 2 | 0.2 | 0.2 | 3.3 | |
| 3 | 0.3 | 0.3 | 3.6 |
For each orthogonal run, I measured compactibility, permeability, green compressive strength, hot wet tensile strength, shatter index, and surface stability. The resulting data were analyzed by range analysis to find the dominant factor for each performance parameter.
Results and Optimized Sand Recipes
Facing Sand Results
The orthogonal experiments revealed that water content was the dominant factor for compactibility. Permeability was mainly influenced by the amount of fine components, including bentonite and additives. Green compressive strength was most sensitive to bentonite content. Hot wet tensile strength, shatter index, and surface stability were strongly affected by starch-based additives. These relationships were extremely useful for industrial control because they allowed me to adjust the correct component when a certain sand property drifted outside the target range.
| Performance | Dominant factor | Observed trend |
|---|---|---|
| Compactibility | Water | Increases with water |
| Permeability | Fines / additives | Increases with additive, decreases with water |
| Green compressive strength | Bentonite | Increases with bentonite |
| Hot wet tensile strength | Additive | Increases with additive |
| Shatter index | Additive / water | Increases with moisture and additive |
| Surface stability | Additive | Increases with additive |
Based on repeated verification tests, I recommended the following optimized facing sand recipe:
| Component | Content |
|---|---|
| New silica sand | 100% |
| Sodium bentonite | 8.0–8.5% |
| Starch-based additive | 0.3–0.5% |
| Water | 3.0–3.6% |
The optimized facing sand achieved the following properties: compactibility 51–54%, permeability 440–450, green compressive strength 85–95 kPa, hot wet tensile strength 4.1–4.5 kPa, shatter index 70–72%, and surface stability 97.0–97.5%. These values satisfied the factory specification and were considered suitable for high-quality steel casting production.
Backing Sand Results
The backing sand was made from return sand with small replenishments of bentonite and additive. Water content was the most important factor because the return sand already contained substantial fines and dead clay. A small change in water content produced a large change in compactibility, permeability, and green strength. Therefore, precise moisture control is necessary to avoid casting defect issues caused by soft mold surfaces, erosive metal flow, or inadequate venting.
The optimized backing sand recipe is shown below:
| Component | Content |
|---|---|
| Return sand | 100% |
| Bentonite replenishment | 0.2–0.3% |
| Starch-based additive | 0.1–0.3% |
| Water | 3.3–3.6% |
This backing sand produced compactibility of 55–60%, permeability of 200–210, green compressive strength of 90–95 kPa, hot wet tensile strength of 3.8–4.5 kPa, shatter index of 72–75%, and surface stability of 97.5–98.0%. The use of the two-sand system provided a strong and refractory mold surface while allowing the bulk of the mold to be produced from recycled sand at low cost.
Industrial Validation of Sand Recipes
The laboratory formulations were later used in the mass production line. The sand treatment system included online measurement of moisture, compactibility, and green strength. The sand mixer was able to adjust water and additive additions automatically. During a successful production day at an ambient temperature of about 34°C and relative humidity of about 80%, the measured facing sand and backing sand properties matched my laboratory recommendations closely. The production records also showed that the sand properties remained stable during continuous operation. This demonstrated that the experimental recipes and the control rules derived from them were reliable and transferable to industrial practice.
Process Simulation and Optimization of Railway Steel Castings
The second major part of my research was computational simulation of mold filling and solidification. I used the ProCAST software package, which is based on the finite element method. The objective was to predict potential casting defect locations before making expensive production trials. The parts studied were a large coupler yoke and a smaller coupler knuckle. Both are safety-critical railway components made from high-strength low-alloy steel grade ZG25MnCrNiMo.
The simulation of mold filling is governed by the continuity and Navier–Stokes equations:
$$
\nabla \cdot \mathbf{u} = 0
$$
$$
\rho \left( \frac{\partial \mathbf{u}}{\partial t} + \mathbf{u} \cdot \nabla \mathbf{u} \right) = -\nabla p + \mu \nabla^2 \mathbf{u} + \rho \mathbf{g}
$$
where \(\mathbf{u}\) is velocity, \(p\) is pressure, \(\mu\) is dynamic viscosity, and \(\mathbf{g}\) is gravitational acceleration. The solidification process was modeled with the transient heat conduction equation:
$$
\rho c_p \frac{\partial T}{\partial t} = \nabla \cdot \left( k \nabla T \right) + \dot{q}
$$
where \(T\) is temperature, \(c_p\) is specific heat, \(k\) is thermal conductivity, and \(\dot{q}\) is latent heat release or other volumetric heat sources. The solid fraction was estimated with the lever rule:
$$
f_s = \frac{T_L – T}{T_L – T_S}
$$
where \(T_L\) is liquidus temperature and \(T_S\) is solidus temperature. Shrinkage porosity was evaluated with the Niyama criterion:
$$
N_y = \frac{G}{\sqrt{\dot{T}}}
$$
where \(G\) is the temperature gradient and \(\dot{T}\) is the cooling rate. A low Niyama value indicates a high probability of shrinkage porosity and therefore an increased casting defect risk.
| Parameter | Value |
|---|---|
| Alloy | ZG25MnCrNiMo |
| Liquidus temperature | 1505°C |
| Solidus temperature | 1433°C |
| Latent heat | 65 kJ/kg |
| Pouring temperature | 1585°C |
| Mold material | Green molding clay sand |
| Mold-metal interface coefficient | 500 W/(m²·K) |
| Insulating sleeve coefficient | 100 W/(m²·K) |
Simulation of the Original Coupler Yoke Process
The original yoke process used two castings per mold, horizontal pouring, and three ordinary sand risers on the hook head plus one riser on the hook tail. The simulation showed that the metal velocity near the ingate was high, especially around the hook tail pin hole. This high velocity could erode the mold and produce sand inclusion, slag inclusion, and metal penetration. The large flat surface of the hook body was also identified as a potential location for gas entrapment and blowholes. Shrinkage porosity was predicted in the hook head corners, the pulling lug root, and the transition between head and body. The stress simulation predicted high effective stress in riser roots, the hook neck, and complex inner corners, leading to a high hot-tearing tendency.
| Location in yoke | Predicted casting defect |
|---|---|
| Hook tail pin hole | Erosion, slag entrapment, sand burning |
| Large flat surface of hook body | Blowhole, gas entrapment |
| Hook head inner corners | Shrinkage porosity, hot tearing |
| Hook neck transition | Shrinkage porosity, high stress |
| Riser roots | Hot tearing |
Trial castings produced with the original process confirmed these simulation results. I observed blowholes on the hook body plane, sand burning and rough surfaces in the hook head, and micro-cracks at fillets after magnetic particle inspection. These observations indicated that the model could correctly predict important casting defect mechanisms.
Improved Yoke Process
Based on the simulation results, I proposed the following changes to the yoke process: the ingate was moved to one side of the hook body, shaped refractory runners were used, the three ordinary head risers were replaced with cylindrical insulating risers, an additional top insulating riser was placed on the hook body, a small blind riser was added near the ingate, mold vents were staggered to prevent sand falling into the cavity, and shaped external chills were placed at hot spots.
After the improvement, the simulation showed a much more uniform velocity field around the hook tail pin hole and reduced erosion risk. The solidification pattern was improved because the insulating risers maintained a clear feeding path. Shrinkage porosity was largely confined to the gating and riser system, with only minor porosity in the complex inner corners of the hook head. Stress levels were significantly lower, and the hot-tearing tendency was reduced. Actual trial castings produced with the improved process had better surface quality and far fewer internal and external casting defect problems.
Simulation of the Original Coupler Knuckle Process
The original knuckle process used eight knuckles per mold, arranged as four pairs with a central blind riser. The simulation showed that the metal entering through the ingate directly hit the core near the knuckle pin hole. This caused high local velocity and a strong risk of erosion and sand inclusion in a critical load-bearing area. The hook wrist and the cast-on projection near the outer arc were identified as hot spots where isolated liquid pools could form. Shrinkage porosity was predicted in the inner wrist surface, the traction projection, and the outer arc near the protection projection. The stress field indicated that hot tearing could occur at the traction lug and the inner wrist corner.
| Location in knuckle | Predicted casting defect |
|---|---|
| Knuckle pin hole | Erosion, slag inclusion, sand burning |
| Inner wrist surface | Shrinkage porosity |
| Traction projection corner | Shrinkage porosity, hot tearing |
| Outer arc near protection projection | Shrinkage porosity |
Trial production with the original knuckle process matched these predictions. More than half of the knuckles showed visible erosion and slag contamination around the pin hole. Magnetic particle inspection revealed micro-cracks near the gate root, the upper part of the inner wrist, the head opening, and the protection projection corner.
Improved Knuckle Process
For the knuckle, I proposed a process with four castings per mold in a symmetrical arrangement. The ingate was moved to the back side of the knuckle, between the pin hole and the tail, to avoid metal impingement on the pin-hole core. The large central riser was replaced by individual top blind insulating risers placed above the pressure plate, which improved feeding efficiency and increased the process yield.
Simulation of the improved process showed that the velocity near the pin hole was much lower and more uniform. The local riser provided a clear feeding path to the thick wrist section, reducing shrinkage porosity in the most critical area. Some shrinkage porosity still appeared, but it moved toward the central part of the knuckle away from the main load-bearing surfaces. Although the overall stress level was slightly higher, the stress in the inner wrist surface remained low. The improved process therefore reduced the probability of casting defect formation and improved the structural integrity of the knuckle.
Production, Quality Control, and Casting Defect Prevention
After the simulation and optimization phase, the foundry began industrial trial production. The production line consisted of sand preparation, molding, core making, melting, pouring, shakeout, primary cleaning, pre-normalizing, inspection, welding repair, heat treatment, machining, and assembly. An automated pouring line with precise stopper control was installed to improve pouring consistency and reduce filling-related casting defect risks.
The automated pouring system helped to maintain a constant pouring temperature and pouring rate. It also reduced oxidation and gas entrapment, which in turn decreased the formation of blowholes and oxides. For railway steel castings, this is particularly important because any casting defect caused by unstable pouring can propagate during service and lead to fatigue failure.
Product Quality Validation
The final trial products were subjected to comprehensive quality checks. These included chemical analysis, mechanical testing, metallographic examination, section density evaluation, dimensional inspection, hardness testing, magnetic particle inspection, dynamic tear testing, and static tensile load testing. The chemical composition of the steel was within specification, with low phosphorus and sulfur contents.
| Element | C | Si | Mn | P | S | Ni | Cr | Mo | Cu | Al |
|---|---|---|---|---|---|---|---|---|---|---|
| Content % | 0.27 | 0.34 | 1.35 | 0.014 | 0.007 | 0.39 | 0.48 | 0.24 | 0.05 | 0.04 |
Mechanical testing results met the requirements for high-strength grade E steel. The hot tearing resistance and ductility were especially important because the components must withstand severe service loads.
| Product | Tensile strength MPa | Yield strength MPa | Elongation % | Reduction of area % | Impact energy at -40°C J |
|---|---|---|---|---|---|
| Coupler yoke | 945 | 855 | 16 | 37 | 50 |
| Coupler knuckle | 940 | 860 | 16 | 35 | 31 |
Section density examinations were performed on prescribed cross-sections. The measured density levels were always better than the maximum permitted levels. For example, the yoke was required to have a maximum level of 3 to 5 depending on the section, while the actual level did not exceed 1 in any section. The knuckle also achieved an actual level of 1, which is excellent for a steel casting. This indicated that the optimized risering system successfully minimized shrinkage-related casting defect occurrence.
Defect Statistics in Trial and Batch Production
During initial inspection after shakeout, the primary severe casting defect that could cause rejection was sand penetration extending completely through the casting wall. This defect was caused by loose sand at the ingate or complex curved corners during molding, insufficient mold strength, or improper closing of the mold. Once loose sand was trapped, the flowing steel swept it into the metal and formed a continuous scab or sand inclusion that could penetrate the wall.
| Part | Inspected quantity | Rejected quantity | Rejection rate % | Main reason |
|---|---|---|---|---|
| Yoke | 154 | 8 | 5.2 | Sand penetration / continuous scab |
| Knuckle | 223 | 6 | 2.7 | Sand penetration / continuous scab |
Magnetic particle inspection was performed in the foundry workshop after pre-normalizing and welding repair. The main casting defect detected at this stage was surface cracking. In the yoke, cracks were concentrated at the riser and ingate roots, with a smaller number at the hook neck and hook shoulder. In the knuckle, cracks were concentrated on the inner wrist surface. These cracks were mostly shallow hot tears, typically less than 20 mm in length and less than 10 mm in depth, and they could be repaired by air-arc gouging and welding.
| Yoke inspection location | Crack count |
|---|---|
| Hook front “C” face | 5 |
| Marked side face | 31 |
| Unmarked side face | 1 |
| Hook neck | 9 |
| Hook tail | 21 |
| Riser and gate roots | 112 |
| Total | 179 |
| Knuckle inspection location | Crack count |
|---|---|
| Inner wrist surface | 21 |
| Other locations | 8 |
| Total | 29 |
After full heat treatment, finishing, welding repair, and low-temperature tempering, the number of crack-related casting defect occurrences decreased substantially. Among 690 inspected yokes, only 77, or 11.2%, showed some crack indications. Among 500 inspected knuckles, only 15, or 3.0%, showed crack indications. These cracks appeared mainly at previous weld repair locations and in areas of high residual stress. This demonstrates that post-casting operations such as cutting, welding, heat treatment, and handling play a major role in the final quality of railway steel castings.
Root Cause Analysis and Prevention of Key Casting Defects
Through macro observation and micro-analysis, I classified the observed casting defect problems into four major groups: hot tearing, cold cracking, blowholes, and scabs or sand burning. Each group has a distinct mechanism and requires a distinct prevention strategy.
Hot Tearing
Hot tearing is one of the most severe casting defect problems in green sand steel castings. It occurs at the end of solidification when the casting has low strength and ductility. The solidifying metal cannot accommodate contraction stress and opens up along grain boundaries. In the yoke and knuckle, hot tears appeared mainly at riser roots, sharp corners, and thick-to-thin transitions. The primary causes include poor riser design, inadequate fillet radii, excessive pouring temperature, high sulfur and phosphorus levels, and insufficient mold collapsibility.
To prevent hot tearing, I recommended increasing fillet radii at all riser and gate roots, adding anti-cracking ribs in critical areas, placing shaped chills to create uniform cooling, and controlling pouring temperature. The casting should not be shaken out too early. In addition, the contents of low-melting-point elements such as sulfur and phosphorus must be controlled to avoid grain-boundary embrittlement. Because green sand contains moisture, the cooling rate is relatively fast, so careful control of opening time is essential to reduce the risk of tearing.
Cold Cracking
Cold cracking occurs after solidification when the casting is in an elastic state. It is caused by residual stresses from uneven cooling, mold resistance, or external forces during handling and cutting. Cold cracks are usually straight and have a bright or slightly oxidized fracture surface. In my production study, many such cracks appeared at gate and riser roots due to improper oxygen cutting. The high local heat input from cutting combined with pre-existing residual stress caused the metal to crack.
The recommended prevention methods included preheating the cutting zone before oxygen cutting, cutting in steps rather than from the root directly, avoiding mechanical shock, and moving the casting to a warm location immediately after cutting. The casting should not be placed in a strong draft or wetted with water. If possible, the cutting process should be replaced or supplemented by a safer technique such as band sawing or arc-air gouging followed by grinding.
Blowholes
Blowholes are caused by gas entrapment during mold filling or by gas dissolved in the steel. In green sand molds, water vapor is the main source of gas. If the mold permeability is low, if venting is insufficient, or if the pouring stream is turbulent, gas can become trapped near the upper surface of the casting. In my trials, blowholes were found on the large flat surface of the hook body. These blowholes were often hidden below the surface and only became visible after heat treatment or machining.
To prevent blowholes, I focused on controlling the moisture content of the facing sand and ensuring proper venting. Starch-based additives helped to reduce water sensitivity and improve mold permeability. The pouring process was changed to a smooth bottom-gating style to avoid entrapment of air. In addition, the placement of vents was optimized so that gas could escape through risers and specially positioned vent holes rather than becoming trapped in the casting body.
Scabs and Sand Burning
Scabs are expansion-related casting defect phenomena. When molten steel heats the sand surface, the quartz sand expands while the moisture migrates into the deeper layers. This creates shear stress and weakens the surface layer. If the strength of the sand surface is insufficient, it may buckle and allow molten metal to penetrate beneath it, forming a scab. In the tested castings, scabs appeared on upper surfaces and complex core prints, where thermal radiation time was long.
Sand burning, also called metal penetration, occurs when molten steel enters the spaces between sand grains. It is influenced by the thermal and chemical properties of the sand, coating quality, pouring temperature, and metal static pressure. For the coupler components, mechanical sand burning was observed on the inner wrist surface and around the hook tail pin hole. The surface of the core was strongly attacked, and the coating quality or thickness was insufficient.
To prevent scabs, I increased the starch additive content in the sand to provide additional volume for quartz expansion. I also ensured that the mold compactness was uniform and not excessively high. For sand burning, the most effective solution was to apply a high-performance refractory coating on the core surface, especially in highly stressed areas. The coating thickness was increased moderately, and refractory sand such as chromite sand was used locally where thermal attack was severe. Lowering pouring temperature and reducing the effective pouring height also decreased the tendency for metal penetration.
Statistical Evaluation of Batch Production
The defect rate can be evaluated as:
$$
R_d = \frac{N_{\text{defective}}}{N_{\text{inspected}}} \times 100\%
$$
During stable batch production, the initial surface rejection rate was about 5.2% for the yoke and 2.7% for the knuckle. Most of these rejections were caused by sand penetration that completely bridged the casting wall. After improving molding discipline and core setting accuracy, the rejection rate decreased. In the final inspection, the majority of castings were accepted after minor grinding or localized welding. The only remaining casting defect issue was crack indications, mainly in weld repair zones. These cracks could be controlled within the capability of the foundry without causing structural rejection.
I also calculated the percentage of cracks at each location relative to the total number of cracks:
$$
P_i = \frac{n_i}{N_{\text{cracks}}} \times 100\%
$$
For the yoke, riser and gate roots accounted for about 63% of all cracks found in the foundry workshop. This clearly showed that cutting and grinding operations at the riser contact area were a major source of casting defect formation. For the knuckle, the inner wrist surface accounted for about 72% of all cracks. This area is thick and changes cross-section abruptly, making it prone to thermal contraction stress. A more generous fillet radius and a local chill could reduce this tendency in future production.
Conclusions and Future Direction
My research demonstrated that green molding clay sand is a viable and economical process for producing high-quality railway steel castings, provided that the sand formulation is optimized and the casting process is carefully controlled. The laboratory-designed facing sand and backing sand recipes satisfied the requirements of industrial production and produced stable mold properties during continuous operation. The orthogonal experiments identified the dominant factors for each sand property, allowing the foundry to make fast corrections when needed.
The numerical simulations performed with ProCAST successfully predicted the locations and types of casting defect that would occur in the original process. By changing the ingate position, riser type, chill arrangement, and pouring method, I was able to reduce the probability of erosion, slag inclusion, blowhole, shrinkage porosity, and hot tearing. The improved process was validated by trial production and product quality testing. The final castings met all chemical, mechanical, and metallurgical requirements, including section density and dynamic tear performance.
The most persistent casting defect in batch production was cracking. Cracks appeared primarily at riser roots, welding seams, and abrupt cross-section transitions. Some of these cracks originated from solidification contraction, while others were induced by cutting, welding, and heat treatment operations. Therefore, I concluded that further reductions in casting defect risk should focus not only on mold design but also on the post-casting operations. Standardizing the preheating, cutting, welding, and heat treatment procedures is essential for improving productivity and reducing repair cost.
In the future, I would like to develop an online system that automatically relates sand properties to raw material additions and environmental conditions. This would make green sand control even more reliable. I would also like to continue optimizing the automated pouring line and integrate real-time process data with simulation-based casting defect prediction. Such a system would allow the foundry to correct process deviations before defects are formed, increasing yield and reducing scrap.
In conclusion, the combination of green molding clay sand, systematic sand testing, computational process simulation, and disciplined production management allowed me to produce high-integrity railway steel castings with minimal casting defect occurrence. The low cost, short production cycle, low environmental burden, and recyclability of green sand make it an excellent choice for modern steel foundries, as long as the process is fully understood and controlled.