In the field of heavy machinery manufacturing, the production of large-scale integral cast steel components, such as edger roll mill housings, presents significant challenges due to complex geometries, stringent quality requirements, and the need for advanced foundry technology. This study focuses on the development and implementation of innovative casting techniques to address these challenges, ensuring the production of high-quality components that meet rigorous standards. The integral edger roll mill housing discussed here features a complex structure with multiple crossbeams and columns, requiring meticulous planning in every aspect of the foundry technology process to achieve desired internal integrity, dimensional accuracy, and mechanical properties.
The primary technical requirements for this component include full compliance with ultrasonic testing standards, specific mechanical properties in the normalized and tempered condition, and adherence to dimensional tolerances for non-machined surfaces. Key challenges identified in the foundry technology process involve managing solidification and feeding in sections with varying wall thicknesses, controlling dimensional accuracy amid differential shrinkage, minimizing sand inclusion defects during pouring, and ensuring fine-grained microstructure to avoid ultrasonic testing issues related to coarse grains. Through the application of divisional solidification control, customized gating systems, and micro-alloying techniques, these challenges were effectively mitigated, resulting in a successful casting that exemplifies advanced foundry technology.
The structural complexity of the edger roll mill housing, with its four crossbeams connected by rib plates and columns featuring large-diameter holes, necessitates a holistic approach to foundry technology. Wall thicknesses range from 370 mm to 700 mm, creating hotspots that are prone to shrinkage defects if not properly managed. Ultrasonic testing mandates a high level of internal soundness, with specific criteria for surface and subsurface regions, particularly in critical areas like inner window radii where repairs are prohibited. This underscores the importance of robust foundry technology in preventing defects that could compromise component performance.
To meet the technical requirements, the foundry technology strategy encompassed several key areas: divisional solidification and feeding control, precise calculation of shrinkage allowances and machining margins, design of a fully open gating system for rapid filling, and chemical composition control with micro-alloying. The following sections detail these aspects, supported by tables and mathematical models to illustrate the principles and outcomes. The integration of these elements demonstrates how modern foundry technology can overcome the inherent difficulties in producing large, complex castings.
Technical Requirements and Challenges in Foundry Technology
The edger roll mill housing must satisfy strict criteria based on industry standards, which directly influence the foundry technology employed. Ultrasonic testing is required over the entire casting, with surface regions (up to 50 mm from the finished surface or one-fifth of the wall thickness) assessed against Level 2 criteria, and deeper sections against Level 3. Additionally, inner window radius areas are subject to angle beam testing and must be free of repairs, placing a premium on defect-free production through advanced foundry technology. Mechanically, the material ZG230-450 must achieve a yield strength (ReL) of at least 230 MPa, tensile strength (Rm) of 450 MPa, elongation (A) of 22%, reduction of area (Z) of 32%, and impact energy (AKU) of 35 J at room temperature after normalizing and tempering. Dimensional controls for non-machined surfaces follow CT13 tolerance standards, necessitating precise patternmaking and casting simulation in the foundry technology process.
| Parameter | Requirement |
|---|---|
| Ultrasonic Testing | 100% coverage, Level 2 for surface, Level 3 for interior, no repairs in critical radii |
| Material | ZG230-450 (normalized and tempered) |
| Yield Strength (ReL) | ≥ 230 MPa |
| Tensile Strength (Rm) | ≥ 450 MPa |
| Elongation (A) | ≥ 22% |
| Reduction of Area (Z) | ≥ 32% |
| Impact Energy (AKU) | ≥ 35 J (room temperature) |
| Dimensional Tolerances | CT13 for non-machined surfaces |
The challenges in foundry technology for this component are multifaceted. First, the varying wall thicknesses create differential solidification rates, increasing the risk of shrinkage porosity and voids if feeding is inadequate. Second, the complex geometry leads to non-uniform shrinkage during cooling, requiring tailored contraction allowances to maintain dimensional accuracy. Third, the tall, double-layer structure slows mold filling, exacerbating the risk of sand erosion and inclusions due to prolonged exposure to molten metal. Fourth, the thick sections result in prolonged solidification times, promoting coarse grain growth that can impair mechanical properties and ultrasonic testability. Addressing these issues demanded innovative solutions in foundry technology, such as divisional solidification control, optimized gating, and micro-alloying.
Mathematically, the solidification behavior can be modeled using Chvorinov’s rule, where solidification time (t) is proportional to the square of the volume-to-surface area ratio (modulus): $$ t = k \left( \frac{V}{A} \right)^2 $$ where \( k \) is a constant dependent on mold material and casting conditions. For large castings, this highlights the importance of controlling modulus through chills and risers, a key aspect of foundry technology. Additionally, the feeding distance (L) for risers can be expressed as: $$ L = C \cdot D $$ where \( C \) is a coefficient (typically 3-4 for steel) and \( D \) is the section thickness or hot spot diameter. In this case, values of 3.3 to 3.6 were used, demonstrating the application of empirical models in foundry technology to prevent defects.
Foundry Technology Approach: Divisional Solidification and Feeding Control
The core of the foundry technology strategy involved dividing the casting into ten distinct solidification and feeding zones—two for each column and two for each of the four crossbeams—to manage the varying thermal conditions. This divisional approach, based on riser feeding distances and structural hotspots, ensured sequential solidification from the extremities toward the risers, minimizing the risk of shrinkage defects. Thick, sand-insulated chills were placed between zones to create artificial end zones, isolating each region and enabling concentrated feeding via large risers. The riser sizes were determined using the thermal modulus method, ensuring that the riser modulus exceeded that of the feeding sections by at least 1.1 times, a standard practice in foundry technology to guarantee adequate liquid metal supply during solidification.
For the crossbeams, which exhibit rod-like structures with lengths up to 6,400 mm after machining allowances, the maximum hot spot diameters ranged from 490 mm to 550 mm. Each upper crossbeam was equipped with two open top risers of 650 mm × 850 mm cross-section and a height of 1,350 mm, providing a feeding distance of 3.3 times the hot spot diameter. Similarly, lower crossbeams featured two blind risers of 700 mm × 900 mm cross-section and 1,050 mm height, with a feeding distance of 3.6 times the hot spot diameter. The modulus (M) for risers and cast sections was calculated as: $$ M = \frac{V}{A} $$ where \( V \) is volume and \( A \) is cooling surface area. Verification confirmed that riser moduli were sufficient, a critical step in foundry technology to avoid subsurface porosity.
| Component | Hot Spot Diameter (mm) | Riser Type | Riser Dimensions (mm) | Feeding Distance Multiplier |
|---|---|---|---|---|
| Upper Crossbeams | 550 | Open Top | 650 × 850 × 1350 | 3.3 |
| Lower Crossbeams | 490 | Blind | 700 × 900 × 1050 | 3.6 |
| Columns | 760 | Open Top | 1200 × 1600 × 1350 | 3.0 |
At the column ends, the presence of two large-diameter holes (642 mm) created isolated hot spots that could hinder feeding. To address this, one hole near the base was cast solid to maintain a continuous feeding path, enabling bottom-up sequential solidification. Each column end was served by a large open top riser of 1,200 mm × 1,600 mm cross-section and 1,350 mm height, with a vertical feeding distance of three times the hot spot diameter. This decision, validated through simulation, highlights the iterative nature of foundry technology, where design modifications are made based on predictive models. The total casting weight was 110 tons, with a poured weight of 185 tons, emphasizing the scale of foundry technology operations for such components.
Chill design played a vital role in this foundry technology. Insulated chills of 600 mm × 600 mm cross-section and thicknesses of 400 mm (for upper sections) and 500 mm (for lower sections) were used, with thicknesses relative to wall thickness (0.8 to 1.0 times) to ensure effective heat extraction. A 20 mm sand layer between chills and the casting prevented fusion and promoted controlled cooling. Additionally, specialized “radius chills” were applied at inner window radii to prevent cracking and ensure soundness in no-weld zones, a nuanced aspect of foundry technology for stress-prone areas. Computational solidification simulations using software like Magma confirmed the effectiveness of this approach, showing progressive solidification from chills toward risers and no predicted shrinkage defects based on feeding criteria.
Patternmaking, Shrinkage Allowances, and Machining Margins in Foundry Technology
Accurate dimensioning in foundry technology relies on appropriate shrinkage allowances and machining margins, which compensate for volumetric changes during solidification and cooling. For the edger roll mill housing, the complex geometry resulted in varying degrees of restraint, necessitating differential shrinkage rates. In length and height directions, where contraction was relatively free, a shrinkage allowance of 2.0% was applied. In the width direction, however, the interconnection of crossbeams increased restraint, so the allowance was raised to 1.4% to account for the higher effective contraction. This tailored approach in foundry technology helps achieve dimensional precision without over-sizing.
Machining margins were adjusted to harmonize these differential shrinkages in foundry technology. For instance, end faces, inner cylindrical surfaces, and width-direction inner sides were given 30 mm margins, length-direction inner sides received 35 mm, and all outer surfaces had 25 mm margins (all single-sided). This not only accommodated shrinkage inconsistencies but also provided sufficient material for finishing, a common practice in foundry technology to ensure final dimensions meet specifications. The pattern was split into three parts—bottom mold (solid pattern), middle mold (core assembly), and top mold (cover)—facilitating riser placement and minimizing distortion risks by orienting connection ribs horizontally to act as stiffeners.
The relationship between shrinkage and restraint can be conceptually modeled as: $$ \epsilon = \alpha \cdot \Delta T \cdot (1 – R) $$ where \( \epsilon \) is the strain, \( \alpha \) is the thermal expansion coefficient, \( \Delta T \) is the temperature drop, and \( R \) is the restraint factor (0 for free contraction, 1 for fully restrained). In foundry technology, empirical data often guides allowance selection, but this formula underscores the need for customization based on geometry. For this casting, the choices resulted in as-cast dimensions within CT13 tolerances, demonstrating the efficacy of the foundry technology approach.
| Direction | Shrinkage Allowance (%) | Machining Margin (mm, single-sided) | Notes |
|---|---|---|---|
| Length and Height | 2.0 | 30-35 | Free contraction |
| Width | 1.4 | 25-30 | Restrained due to crossbeams |
Gating System and Pouring Methodology in Foundry Technology
The gating system design is crucial in foundry technology to ensure smooth, rapid mold filling while minimizing turbulence and sand erosion. For this tall, double-layer casting, a fully open gating system was adopted, meaning the cross-sectional areas increased progressively from the ladle nozzle to the sprue, runners, and ingates—ensuring no flow restriction and reducing velocity to prevent sand wash. The system comprised two levels of ingates to accommodate the height, with absolute openness at each stage to avoid premature filling of upper sections, which could lead to defects.
Pouring was conducted using three ladles (two crane ladles and one stationary ladle) to achieve the required flow rate, with a total metal weight of 185 tons. The ladle nozzles included four of 100 mm diameter and two of 80 mm diameter, connected to six sprue of 140 mm diameter, runners of 120 mm diameter, and 20 ingates of 80 mm diameter per level. The area ratios were calculated as: $$ S_{\text{nozzle}} : S_{\text{sprue}} : S_{\text{runner}} : S_{\text{ingate (lower)}} = 1 : 2.2 : 2.2 : 2.4 $$ This fully open configuration is a hallmark of advanced foundry technology for heavy castings, promoting laminar flow and reducing inclusions.
The pouring temperature was controlled between 1,530 °C and 1,550 °C, with a “slow-fast-slow” sequence: initial slow pouring with one nozzle per ladle to minimize impact, switching to full flow after 10-20 seconds for rapid filling, and reducing flow near the top to allow slag flotation into risers. This methodology in foundry technology significantly curtailed sand inclusion defects, as evidenced by reduced repair welds in the final casting. The emphasis on controlled pouring parameters underscores how foundry technology balances speed and quality to achieve sound components.
Chemical Composition Control and Heat Treatment in Foundry Technology
Material properties in foundry technology are heavily influenced by chemical composition and heat treatment. For ZG230-450, internal controls were implemented to enhance mechanical properties and ultrasonic testability: carbon content was limited to 0.20-0.25%, manganese to 0.9-1.1%, and sulfur and phosphorus to below 0.02% each. Titanium was added at 0.1% (accounting for melting losses) for micro-alloying, which refines grain structure by forming carbonitrides that pin grain boundaries during heat treatment. This approach in foundry technology mitigates coarse grain issues that can impair both mechanical performance and ultrasonic wave transmission.
| Element | Standard Range | Internal Control |
|---|---|---|
| C | ≤ 0.30 | 0.20-0.25 |
| Mn | 0.8-1.1 | 0.9-1.1 |
| Si | 0.3-0.5 | 0.3-0.5 |
| S | ≤ 0.03 | ≤ 0.02 |
| P | ≤ 0.02 | ≤ 0.02 |
| Ti | – | 0.1 |
Heat treatment consisted of normalizing at 890-920 °C followed by tempering at 580-620 °C. To enhance properties, forced air cooling was used after normalizing, accelerating the cooling rate compared to standard air cooling. This foundry technology practice refines the as-cast structure, improves grain size, and yields a better combination of strength and toughness. The cooling rate can be approximated by Newton’s law of cooling: $$ \frac{dT}{dt} = -h (T – T_{\text{env}}) $$ where \( h \) is the heat transfer coefficient, higher for forced convection, leading to finer microstructures. The resulting mechanical properties exceeded requirements, with yield strength at 318 MPa, tensile strength at 506 MPa, elongation at 35%, reduction of area at 66%, and impact energies over 120 J, demonstrating the success of the foundry technology measures.
| Property | Requirement | Actual Value |
|---|---|---|
| Yield Strength (ReL, MPa) | ≥ 230 | 318 |
| Tensile Strength (Rm, MPa) | ≥ 450 | 506 |
| Elongation (A, %) | ≥ 22 | 35 |
| Reduction of Area (Z, %) | ≥ 32 | 66 |
| Impact Energy (AKU, J) | ≥ 35 | 124.1, 141.1, 122.4 |
Production Implementation and Validation of Foundry Technology
The casting was produced according to the described foundry technology, with cooling in the pit to 300-350 °C before shakeout. Riser removal was performed using the casting’s residual heat, requiring continuous cutting to avoid thermal stresses. After heat treatment, the component underwent thorough inspection: dimensional checks confirmed compliance with CT13 tolerances, ultrasonic testing revealed no coarse grain issues or defects in critical areas, and mechanical tests showed ample margins. The minimal repair needs and customer acceptance validate the foundry technology approach, highlighting its applicability to similar large-scale castings.
In conclusion, this study demonstrates how integrated foundry technology—spanning divisional solidification control, customized allowances, open gating, and micro-alloying—can overcome the challenges of producing complex integral castings. The edger roll mill housing achieved all technical requirements, underscoring the importance of a systematic foundry technology framework. Future work could explore automation in molding or real-time monitoring to further enhance foundry technology for such applications, paving the way for more efficient and reliable manufacturing of heavy machinery components.