I approached the large cold heading machine body as a heavy-section ductile iron casting that demanded more than ordinary foundry practice. The component weighed approximately 50 t, was made of QT500-7, and measured 4 550 mm × 2 250 mm × 1 820 mm. Its average wall thickness was 200 mm, with a minimum wall thickness of 100 mm and a maximum wall thickness of 500 mm. The shape itself was not geometrically complex, but the massive wall thickness, multiple shaft holes, and the requirement for zero gas porosity, slag inclusion, shrinkage cavity, and shrinkage porosity made this ductile iron casting a serious technical challenge. A local region measuring 800 mm × 1 850 mm contained a 500 mm thick section, and eight straight and inclined holes of ϕ100 mm × 800 mm had to be machined from that thick section. Therefore, the design of the pouring system, riser feeding system, chiller layout, and venting system was critical for internal soundness in this ductile iron casting.
I treated the operating-side cantilever half-shaft hole as the main reason to avoid traditional wooden pattern practice. A conventional wooden pattern would have required complicated core prints, loose pieces, and core box combinations. It would also have made core setting, mold closing, and shaft-hole spacing measurement difficult. For this large ductile iron casting, I selected an EPS foam pattern with furan no-bake resin sand molding. That choice reduced core prints and loose pieces, improved dimensional chain control, limited flash and fins, and raised the external dimensional accuracy of the ductile iron casting.
Structural features and technical difficulties
I summarized the main geometric and quality parameters of this ductile iron casting in Table 1. The table shows why the casting belongs to the ultra-heavy-section ductile iron casting category. The combination of large mass, thick sections, and machined holes created a high risk of shrinkage porosity, graphite degeneration, and slag entrapment.
| Parameter | Value | Process significance for ductile iron casting |
|---|---|---|
| Casting mass | 50 t | Requires high pouring capacity and synchronized ladle operation |
| Material | QT500-7 | Ferritic-pearlitic ductile iron with strength and elongation balance |
| Overall size | 4 550 mm × 2 250 mm × 1 820 mm | Large mold and core dimensions increase handling and venting difficulty |
| Average wall thickness | 200 mm | Slow cooling promotes coarse graphite and shrinkage defects |
| Minimum wall thickness | 100 mm | Still heavy compared with common ductile iron castings |
| Maximum wall thickness | 500 mm | Severe thermal center and graphite degeneration risk |
| Local thick section | 800 mm × 1 850 mm × 500 mm | Needs strong chilling and feeding |
| Machined holes | 8 × ϕ100 mm × 800 mm | Internal defects are unacceptable |
| Quality requirement | No gas porosity, slag inclusion, shrinkage cavity, or shrinkage porosity | Demands balanced solidification and clean filling |
The technical difficulties in this ductile iron casting were not limited to shrinkage. I had to control unstable pouring that could cause slag inclusion, solidification contraction that could produce shrinkage cavity and shrinkage porosity, poor nodularization in the heavy section, and graphite distortion. These issues are typical barriers in the localization and scaling-up of large cold heading machines. For a ductile iron casting of this size, every process decision had to support calm filling, directional or simultaneous solidification, and reliable feeding.
Molding process selection
I used furan no-bake resin sand molding with an EPS foam pattern removal process. This route was energy-saving, environmentally favorable, and cost-effective. It also shortened the production cycle. Because the EPS pattern remained in the mold until pouring, I could avoid many loose pieces and external core prints in difficult-to-clean areas. The result was fewer fins and flash and better dimensional consistency. For a large ductile iron casting with multiple shaft holes, this was a major advantage.
The casting mass was large enough to require two ladles pouring simultaneously. I arranged two bottom-pouring open pouring systems. One side used a 30 t electric ladle, and the other side was connected through a bridge runner to another 30 t electric ladle. The foam pattern and ceramic tube runners were assembled before sand filling. This arrangement allowed me to fill the heavy ductile iron casting quickly and smoothly without excessive turbulence.
Pouring position and parting surface
I followed the principle that the heavy section should face upward to improve feeding and encourage sequential solidification. At the same time, the internal sand core was enormous and heavy, so core lifting and closing carried high risk. Therefore, I adopted a seated-core process and placed the heavy section upward. That was the most reliable configuration for this ductile iron casting.
Because the casting was tall, I designed a bottom-pouring system. The goal was stable metal flow, reduced mold wall erosion, and smooth gas evacuation. I combined edge risers with chiller cooling to build a balanced solidification system and move toward no-riser or small-riser casting. The parting surface was set on the reverse side of the body. This decision simplified pattern assembly and helped control the heavy section during solidification.
Pouring system and venting system
I applied the principle of large flow rate, low flow velocity, and stable dispersion. I designed two bottom-pouring open systems with the front face of the body as the bottom. Two ladles poured synchronously. The ingates were distributed evenly on the front face to balance the temperature field, suppress turbulence, and reduce oxidation slag generation and entrapment.
I calculated the pouring system according to rapid pouring practice for ductile iron castings and the large-orifice outflow theory. The cross-sectional area ratio was set as follows:
$$ \sum S_{\text{spruce}} : \sum S_{\text{runner}} : \sum S_{\text{ingate}} = 1 : 1.5 : 1.8 $$
For a pouring mass of 53 500 kg, I calculated a pouring time of 180 s. The process yield reached 93.5%. The total sprue cross-sectional area was 307.7 cm², and I used two ϕ140 mm ceramic tubes placed on both sides. The total runner cross-sectional area was 452.2 cm², and I used ϕ120 mm ceramic tubes. The total ingate cross-sectional area was 549.5 cm², and I used 28 ϕ50 mm ceramic tubes. The pouring basin was a 1 200 mm × 800 mm × 750 mm slag-retaining type to achieve effective slag entrapment, stable flow buffering, and increased metallostatic head.
| Pouring system item | Value | Implementation |
|---|---|---|
| Area ratio | 1 : 1.5 : 1.8 | Sprue : runner : ingate |
| Pouring mass | 53 500 kg | Including risers and running system |
| Pouring time | 180 s | Rapid and stable filling |
| Process yield | 93.5% | High yield for heavy ductile iron casting |
| Total sprue area | 307.7 cm² | 2 × ϕ140 mm ceramic tubes |
| Total runner area | 452.2 cm² | ϕ120 mm ceramic tubes |
| Total ingate area | 549.5 cm² | 28 × ϕ50 mm ceramic tubes |
| Pouring basin | 1 200 mm × 800 mm × 750 mm | Slag-retaining, buffering, pressurizing |
| Ingate velocity target | ≤ 0.8 m/s | Prevent turbulence and secondary oxidation |
For the large sand core, high gas generation, and seated-core process, I arranged 16 edge risers that also served as gas vent passages. I fixed the sand core to the lower mold through four fastening through-holes. To ensure downward venting from the internal cavity, I designed four ϕ100 mm steel pipe core skeletons connected to a mesh core skeleton. The steel pipe inner walls were evenly distributed with ϕ18 mm vent holes and connected to four ϕ80 mm outlet holes in the lower mold. During mold closing, I raised the lower mold, ignited the gas at pouring, and ensured the sand core and chillers were fully dried before closing. This reduced gas generation and prevented flashing or violent gas eruption.
The bottom-pouring open system allowed liquid iron to pass through two ceramic sprues, runners, and 28 ceramic ingates and fill vertically from the front face. This achieved rapid and stable flow, suppressed turbulence and splashing, and limited secondary oxidation. Based on the large-orifice outflow theory and MAGMA simulation, I set the pouring time to 180 s ± 20 s and controlled the ingate velocity below 0.8 m/s. Because the large-orifice system had a large ingate area, I placed shaped chillers at the ingates on the front face to eliminate contact hot spots and reduce the tendency for shrinkage porosity. I also optimized the ingate distribution to ensure a uniform temperature field.
The flow velocity can be estimated as:
$$ v = \frac{G}{\rho A t} $$
where \( G \) is the pouring mass, \( \rho \) is the density of liquid iron, \( A \) is the total ingate area, and \( t \) is the pouring time. This relation helped me confirm that the selected ingate area and pouring time kept the flow within the desired low-velocity range for this ductile iron casting.
Feeding and chilling system design
Because the wall thickness was large, I used the balanced solidification concept and combined external chillers with risers. The objective was small-riser or no-riser casting. To compensate for fluctuations in liquid iron composition and variations in molding compaction, I placed 16 edge risers on the top of the casting. Each riser measured 120 mm × 100 mm × 400 mm, with an edge of 120 mm × 15 mm. These risers provided local feeding and acted as gas vents.
To prevent shrinkage cavity and shrinkage porosity in heavy sections, hot spots, and important machined surfaces, I placed multiple ϕ160 mm × 150 mm round chillers on both the front and back faces of the casting. I also placed several 250 mm × 120 mm × 120 mm rectangular chillers in the internal cavity and on the external surface in heavy and hot-spot regions. The intensified chilling promoted balanced solidification and ensured density in the ductile iron casting.
| Feeding and chilling item | Size or quantity | Function in ductile iron casting |
|---|---|---|
| Edge risers | 16 pieces, 120 mm × 100 mm × 400 mm | Feeding and gas venting |
| Riser edge | 120 mm × 15 mm | Controlled feeding channel |
| Round chillers | ϕ160 mm × 150 mm, multiple | Chilling hot spots on front and back faces |
| Rectangular chillers | 250 mm × 120 mm × 120 mm, several | Chilling internal cavity and heavy external regions |
| Shaped ingate chillers | At ingates on front face | Eliminate contact hot spots |
| Venting pipes | 4 × ϕ100 mm steel pipes | Downward gas evacuation from sand core |
| Vent holes in pipes | ϕ18 mm evenly distributed | Collect gas from core interior |
| Lower mold outlets | 4 × ϕ80 mm | Discharge gas to atmosphere |
The modulus of a hot spot can be written as:
$$ M = \frac{V}{A} $$
where \( V \) is the volume and \( A \) is the cooling surface area. For the 500 mm thick section, the modulus was large, so the chilling and feeding system had to reduce the local modulus and shift the final solidification location toward the risers. This was a key step in producing a sound ductile iron casting.
Molding, core making, and mold closing
I used resin sand molding. Because the casting was tall, I adopted split-box molding. I first used a middle flask for sand filling and then added the lower flask. When making the lower mold and middle mold, I placed the foam pattern and three locating pin patterns on the molding floor, arranged external chillers according to the process, and assembled the pouring system with straight pipes, elbows, and tees. Then I placed the middle flask and used a continuous elevator resin sand mixer to fill sand. I compacted the areas around shaft holes, chillers, and ceramic tubes and scraped the sand surface. Next, I placed the lower flask, embedded four ϕ80 mm gas outlets and four fastening hooks at the core print area, filled and compacted sand, and scraped the surface. I fastened the middle flask and lower flask with multiple bolts. After the resin sand hardened, I turned the whole assembly over, so the middle and lower flasks became one unit.
For the upper mold, I placed the upper flask on the middle flask, positioned chillers, edge riser foam patterns, and sprue ceramic tubes, then filled, compacted, scraped, and hardened the sand. I lifted the pattern and turned the flask. I removed the foam pattern from the upper and lower molds, repaired the mold, and applied coating. This completed the lower and upper molds.
During core making, I placed a long rectangular mesh steel bar core skeleton wrapped with vent rope inside the foam core box to build an internal vent network. I installed four ϕ100 mm steel pipe core skeletons as lower gas outlets to ensure smooth venting. I reserved four ϕ60 mm ceramic tubes on the core skeleton to form upper and lower fastening through-holes, allowing rigid fastening of the sand core to the lower flask. I installed multiple screw clamps on the outside of the core box to prevent deformation. In the width direction, I evenly embedded three ϕ80 mm ceramic tubes as reinforcing ribs to suppress opening deformation caused by casting contraction.
| Molding and core item | Design detail | Purpose |
|---|---|---|
| Molding method | Furan no-bake resin sand | High strength and good dimensional control |
| Pattern | EPS foam pattern | Reduce loose pieces and core prints |
| Flask arrangement | Middle flask plus lower flask, then upper flask | Handle tall casting geometry |
| Locating pins | 3 locating pin patterns | Maintain mold alignment |
| Core skeleton | Mesh steel bar with vent rope | Internal vent network |
| Downward vent pipes | 4 × ϕ100 mm steel pipes | Connect core gas to lower mold outlets |
| Fastening through-holes | 4 × ϕ60 mm ceramic tubes | Rigid core fixation |
| Anti-deformation ribs | 3 × ϕ80 mm ceramic tubes in width direction | Suppress opening deformation |
| Core supports | 4 × ϕ80 mm × 120 mm and 4 × ϕ80 mm × 200 mm | Prevent core floating |
I positioned the internal sand core precisely through the core print and lowered it steadily into the lower mold core seat. Using the fastening through-holes, I connected long hooked screws to the lower flask hooks. The upper ends of the screws were fitted with backing plates and nuts and embedded with sealing sand in the core. This achieved rigid fixation of the sand core and construction of the vent path.
To prevent core floating, I placed four ϕ80 mm × 120 mm and four ϕ80 mm × 200 mm ductile iron core supports on the core plane. During mold closing, I guided the upper mold smoothly with locating pins and installed multiple box clamps. I set 16 overflow open risers on the upper mold and added two slag-retaining pouring basins. At one pouring basin, I installed a 6 m long bridge ceramic tube mold and pouring basin. This allowed two metallurgical double-girder casting cranes to work with two 30 t ladles for synchronous pouring. The entire arrangement was designed to keep the large ductile iron casting filling process stable and repeatable.
Simulation analysis
I used MAGMA software for filling and solidification simulation. I selected a verified chemical composition, HT250 shaped chillers, furan resin sand mold, mold temperature of 25 °C, good inoculation effect, and general shrinkage tendency. The simulation showed that the filling process was stable, without splashing or jetting. The runner remained full of liquid iron throughout filling, preventing gas and slag from entering and avoiding slag inclusion defects. Therefore, the bottom-pouring open system was reasonable and could ensure casting quality. At 30 s of pouring, the filling state was smooth and progressive.
The simulation also showed that from the end of filling to complete solidification, when the temperature dropped to 1 167 °C, the ductile iron casting took 23 h to solidify completely. After complete solidification, only a small amount of shrinkage cavity and shrinkage porosity appeared at shaft hole locations and in the ultra-heavy section. The distribution was scattered, and the sizes were smaller than the specified defect size. The overall quality was good, with only a small amount of porosity. The porosity rate could visually present the location and size of shrinkage cavity and shrinkage porosity.
According to the MAGMA simulation results, the shrinkage cavity and shrinkage porosity positions were scattered and small in volume. The larger defects were located inside the ultra-heavy section. To avoid the casting defects predicted by simulation, I placed chillers on the inner and outer sides of the shaft hole positions and the ultra-heavy section in actual production. This accelerated metal cooling and reduced hot spot formation. The simulation therefore served as a verification tool for this ductile iron casting and helped me refine the chiller layout before production.
| Simulation item | Result | Process response |
|---|---|---|
| Filling behavior | Stable, no splashing or jetting | Keep bottom-pouring open system |
| Runner condition | Full of liquid iron throughout filling | Prevent gas and slag entrapment |
| Filling time check | 30 s filling state smooth | Confirm ingate distribution |
| Complete solidification time | 23 h to 1 167 °C | Plan cooling and shakeout |
| Defect locations | Shaft holes and ultra-heavy section | Add chillers inside and outside |
| Defect size | Scattered, smaller than specified limit | Acceptable with process control |
| Porosity rate | Low and localized | Improve local chilling |
Melting and pouring process
The chemical composition of the ultra-heavy-section ferritic-pearlitic ductile iron QT500-7 body was the core of quality control. I controlled carbon content moderately to avoid graphite flotation and reduced mechanical properties. I balanced silicon content for strength and room-temperature elongation while limiting the upper value to prevent an increase in the ductile-to-brittle transition temperature. Manganese was controlled as a pearlite-promoting element. Sulfur and phosphorus were strictly limited because sulfur is a nodularization-inhibiting element and phosphorus tends to form hard and brittle phosphide eutectic. I set ω(Mn) ≤ 0.5%, ω(S) ≤ 0.015%, and ω(P) ≤ 0.06% to prevent a decrease in nodularity, slag inclusion, and grain-boundary embrittlement. I also strictly controlled trace anti-nodularization elements and carbide-forming elements in raw materials to avoid segregation in the last solidification zone and the formation of intergranular carbides and inclusions.
Residual magnesium and rare earth content had to match the heavy-section requirement. I controlled Mg at 0.040%–0.055%. If it was too low, nodularization would be insufficient. I kept RE ≤ 0.015%, mainly Ce, because excessive RE can form chunky graphite. I used a combined trace-element control strategy. Sb at ≤0.005% suppressed graphite distortion in heavy sections, prevented chunky graphite, and improved nodularization resistance. Excessive Sb would worsen graphite morphology and promote white iron. Bi at ≤0.02% promoted graphite nucleation and growth and optimized nodularity. The addition amount strictly followed the process limit of ≤0.02%.
Based on the technical requirements and structural features, I determined the chemical composition of the large cold heading machine body ductile iron casting as shown in Table 4.
| Element | Target range or limit | Role in ductile iron casting |
|---|---|---|
| C | 3.50%–3.60% | Balance graphite expansion and prevent flotation |
| Si | 2.3%–2.4% | Promote ferrite and control transition temperature |
| Mn | 0.4%–0.5% | Pearlite promoter, controlled for toughness |
| P | ≤ 0.06% | Limit brittle phosphide eutectic |
| S | ≤ 0.015% | Avoid nodularization inhibition and slag |
| Mg | 0.040%–0.055% | Essential for nodularization |
| Cu | 0.5%–0.6% | Promote pearlite and strength |
| Sb | 0.004%–0.005% | Suppress graphite distortion and chunky graphite |
| Bi | 0.015%–0.02% | Improve graphite nucleation and nodularity |
| Cr | ≤ 0.05% | Limit carbide formation |
| Ti | < 0.04% | Avoid harmful carbide and graphite morphology effects |
| RE | ≤ 0.015% | Control nodularization and avoid chunky graphite |
| Al | ≤ 0.04% | Limit dross and graphite degeneration |
The carbon equivalent was controlled at 4.35%–4.45%. If it was too high, graphite flotation could occur. If it was too low, graphitization expansion would decrease and self-feeding would be less favorable. I used the following carbon equivalent relation:
$$ CE = C + \frac{Si}{3} + \frac{P}{3} $$
For this ductile iron casting, the carbon equivalent window was narrow because the heavy section cooled slowly and the graphite morphology was sensitive to composition. I therefore linked chemical composition control directly to the chilling and feeding design.
Nodularization, inoculation, and melting treatment
I adopted a four-wire feeding nodularization and inoculation process with low-temperature wire feeding nodularization and low-temperature pouring. The nodularization cored wire was a ϕ13 mm high-magnesium type containing light rare earth and calcium. Its composition was ω(Mg) 29.0%–31.0%, ω(RE) 1.5%–2.0%, ω(Ca) 2.0%–3.0%, ω(Si) 42%–44%, and the balance Fe. This wire was used to resist nodularization fading. The inoculation cored wire was a ϕ13 mm ferrosilicon heavy rare earth yttrium and barium inoculation wire. Its composition was ω(RE) 2.5%–3.0%, ω(Ba) 2.0%–3.0%, ω(Ca) 2.0%–3.0%, ω(Si) 46%–48%, and the balance Fe. This wire was used to suppress inoculation fading. The nodularization wire addition was 0.75%–0.85%, and the inoculation wire addition was 0.65%–0.75%.
For melting and pouring, I used a silicon carbide graphitization pretreatment plus stream inoculation process. Before tapping, I added 0.5% silicon carbide into the furnace for graphitization pretreatment. During pouring, I added 0.2–0.7 mm BaSi inoculant at 0.15% for stream inoculation. This effectively prevented nodularization and inoculation fading, refined graphite nodules, increased the number of graphite nodules, and improved the comprehensive mechanical properties of the ductile iron casting.
| Treatment item | Material or parameter | Amount or condition |
|---|---|---|
| Nodularization wire | ϕ13 mm high-Mg light RE and Ca wire | 0.75%–0.85% |
| Nodularization wire Mg | 29.0%–31.0% | Resist nodularization fading |
| Nodularization wire RE | 1.5%–2.0% | Support nodularization |
| Nodularization wire Ca | 2.0%–3.0% | Improve reaction control |
| Inoculation wire | ϕ13 mm SiFe heavy RE Y and Ba wire | 0.65%–0.75% |
| Inoculation wire RE | 2.5%–3.0% | Suppress inoculation fading |
| Inoculation wire Ba | 2.0%–3.0% | Promote graphite nucleation |
| Inoculation wire Ca | 2.0%–3.0% | Improve inoculation response |
| Pretreatment | 0.5% silicon carbide | Graphitization pretreatment before tapping |
| Stream inoculation | 0.2–0.7 mm BaSi, 0.15% | During pouring |
Pouring and cooling control
Before pouring, I used a hot air blower to bake the mold for 7–8 h to ensure that the riser outlet air temperature reached 60 °C. I used a low-temperature rapid pouring process. The tapping and wire feeding nodularization temperature was controlled at 1 340–1 350 °C, and the pouring temperature was 1 310–1 320 °C. The pouring time was 180 s ± 20 s, and the pouring mass was 54 t. The time from the end of nodularization treatment to the end of pouring was ≤15 min. After pouring, I spotted the pouring gate three times until the riser no longer overflowed with liquid iron. After solidification, I waited until the casting temperature dropped to ≤300 °C before shakeout and sand removal. The holding and cooling time was not less than 240 h to ensure uniform microstructure and stress release.
$$ t_{\text{cool}} \ge 240 \ \text{h} $$
This cooling requirement was important for the heavy ductile iron casting because rapid cooling after solidification could introduce thermal stress and distort the microstructure. By combining low-temperature rapid pouring with prolonged cooling, I aimed to obtain a uniform matrix, stable graphite morphology, and low residual stress.
| Pouring and cooling parameter | Value | Purpose |
|---|---|---|
| Mold baking time | 7–8 h | Reduce moisture and gas generation |
| Riser outlet air temperature | 60 °C | Confirm drying |
| Nodularization temperature | 1 340–1 350 °C | Low-temperature wire feeding |
| Pouring temperature | 1 310–1 320 °C | Low-temperature rapid pouring |
| Pouring time | 180 s ± 20 s | Stable filling and low turbulence |
| Pouring mass | 54 t | Two-ladle synchronized pouring |
| Nodularization to pouring end | ≤ 15 min | Limit nodularization fading |
| Gate spotting | Three times | Ensure riser feeding |
| Shakeout temperature | ≤ 300 °C | Control stress and microstructure |
| Holding and cooling time | ≥ 240 h | Uniform structure and stress release |
Actual production results
The optimized process produced qualified castings. The rough casting after cleaning showed no unacceptable defects. I tested a 70 mm attached test block of QT500-7 material. The actual results were: tensile strength 480 MPa, yield strength 305 MPa, elongation after fracture 9.5%, nodularity grade 2, graphite grade 5, Brinell hardness 172 HBW, and pearlite content 30%. All mechanical properties and metallographic indicators met the design standard. The ductile iron casting therefore satisfied the required strength, ductility, and microstructure balance.
| Property | Measured value | Requirement or assessment |
|---|---|---|
| Tensile strength | 480 MPa | Meets QT500-7 requirement |
| Yield strength | 305 MPa | Meets design requirement |
| Elongation after fracture | 9.5% | Meets ductility requirement |
| Nodularity grade | 2 | Good nodularization |
| Graphite grade | 5 | Acceptable graphite morphology |
| Brinell hardness | 172 HBW | Within expected range |
| Pearlite content | 30% | Balanced ferrite-pearlite matrix |
| Test block size | 70 mm attached block | Representative of heavy section |
At present, various models of this body have been put into batch production. After customer machining and assembly verification, the castings showed no shrinkage porosity, gas porosity, slag inclusion, or leakage. They fully met the technical quality requirements and satisfied the actual service needs. This confirmed that the process route was stable for this large ductile iron casting.
Process summary and conclusions
I can summarize the successful measures for this large ductile iron casting as follows. First, I used a bottom-pouring open pouring system, optimized chiller chilling, edge riser feeding, anti-deformation ribs, and enhanced mold and core venting. These combined measures effectively solved shrinkage cavity, shrinkage porosity, gas porosity, slag inclusion, and deformation. Second, I optimized the chemical composition, used wire feeding nodularization and inoculation plus stream inoculation, and matched low-temperature rapid pouring. This suppressed nodularization fading and graphite distortion, ensured comprehensive mechanical properties, reduced smoke and dust emissions, and lowered worker labor intensity compared with traditional ladle treatment. Third, for multi-variety, single-piece, small-batch, and non-finalized medium and large castings, the EPS foam pattern removal process simplified pattern making and molding, shortened the product development cycle, and reduced production cost.
The most important lesson I drew from this ductile iron casting practice was that heavy-section solidification cannot be solved by a single measure. The pouring system, riser, chiller, sand core, venting, chemical composition, nodularization, inoculation, pouring temperature, and cooling time must all be coordinated. The heavy section must be placed upward for feeding, but the sand core must also be fixed and vented reliably. The pouring system must fill quickly, but the ingate velocity must remain low. The risers must feed, but the chillers must reduce hot spots. The composition must promote nodularity, but trace elements must suppress graphite distortion. When these factors are balanced, a large ductile iron casting can be produced with stable quality.
In this ductile iron casting project, I used simulation to verify filling and solidification before production. The simulation predicted stable filling, full runners, a 23 h solidification time to 1 167 °C, and only scattered small shrinkage defects at shaft holes and the ultra-heavy section. I responded by adding chillers inside and outside those regions. The final production results confirmed that the simulation-guided process was effective. The 70 mm attached test block reached 480 MPa tensile strength, 305 MPa yield strength, 9.5% elongation, nodularity grade 2, graphite grade 5, 172 HBW hardness, and 30% pearlite. These values met the QT500-7 requirements and demonstrated that the ductile iron casting process was robust.
For future heavy-section ductile iron casting work, I would keep the following priorities. I would maintain the carbon equivalent in the range of 4.35%–4.45% and avoid both graphite flotation and insufficient graphitization expansion. I would keep Mg at 0.040%–0.055% and RE at ≤0.015% to balance nodularization and chunky graphite risk. I would continue to use Sb at 0.004%–0.005% and Bi at 0.015%–0.02% within the strict limits. I would keep the pouring temperature at 1 310–1 320 °C and the pouring time at 180 s ± 20 s for this 54 t pouring mass. I would maintain the holding and cooling time at no less than 240 h and shakeout at ≤300 °C. These parameters were not arbitrary; they were linked to the heavy-section behavior of this ductile iron casting.
The production practice also showed that EPS foam pattern removal with furan resin sand was suitable for this large ductile iron casting. It reduced core prints, loose pieces, and flash, and it improved dimensional accuracy. The seated-core process with rigid fastening and multiple vent paths prevented core floating and gas-related defects. The two-ladle synchronized pouring through two bottom-pouring open systems provided the required filling rate without excessive turbulence. The edge risers and chillers created a balanced solidification condition. The anti-deformation ribs controlled opening deformation during cooling. Each of these measures contributed to the final soundness of the ductile iron casting.
I conclude that the process route is repeatable and suitable for industrial production. The large cold heading machine body ductile iron casting achieved the required internal quality and mechanical properties. The batch production results confirmed that the castings met customer requirements after machining and assembly. The combination of process design, simulation, melting control, nodularization, inoculation, pouring, and cooling formed a complete and reliable solution for this heavy-section ductile iron casting.