1. ভূমিকা
Sand casting has powered the iron foundry industry for centuries, enabling the production of complex geometries at relatively low cost.
Recently, Compacted Graphite Iron (CGI)—also known as vermicular graphite iron—has emerged as a material bridging the gap between traditional gray cast iron and ductile iron.
By combining desirable properties of both, CGI offers higher tensile strength and thermal conductivity than gray iron, yet retains superior castability and damping compared to ductile grades.
এই নিবন্ধে, we examine “what is sand casting with CGI?” through metallurgical, processing, যান্ত্রিক, and economic lenses.
We aim to present a comprehensive yet practical resource for foundry engineers, design professionals, and materials researchers interested in harnessing CGI’s benefits.
2. Compacted Graphite Iron (CGI): Metallurgy and Properties
Compacted (vermicular) graphite iron (CGI) occupies an intermediate position between gray iron and ductile iron:
its unique graphite morphology yields a combination of strength, stiffness, and thermal properties not attainable in other cast irons.
Graphite Morphologies: From Gray to Ductile to CGI
Graphite in cast iron appears in three primary morphologies. Each influences mechanical and thermal behavior:
- ধূসর লোহা: Flake graphite provides crack‐arresting behavior under vibration but limits tensile properties.
- CGI: Vermicular graphite appears as short, compact “worms” (compactness factor ≥ 60 %), enhancing strength and conductivity while retaining acceptable damping.
- নমনীয় আয়রন: Graphite occurs as nearly perfect nodules; this maximizes ductility but reduces damping and thermal conduction compared to CGI.
Chemical Composition and Alloying Elements
Chemically, CGI resembles ductile iron but requires tighter control of certain elements, especially magnesium and sulfur, to achieve the desired vermicular graphite form.
Typical target composition (EN-GJV-450-12) appears below:
| উপাদান | সাধারণ পরিসীমা (ডাব্লুটি %) | ভূমিকা / Effect |
|---|---|---|
| কার্বন (গ) | 3.4 - 3.8 | Provides graphite-forming potential; excess C can lead to carbides. |
| সিলিকন (এবং) | 2.0 - 3.0 | Promotes graphite precipitation; balances ferrite/pearlite ratio. |
| ম্যাঙ্গানিজ (এমএন) | 0.10 - 0.50 | Controls sulfides and refines grain; excessive Mn ties up C, risking carbide formation. |
| ফসফরাস (পি) | ≤ 0.20 | অপবিত্রতা; can increase fluidity but reduces toughness if > 0.10 %. |
| সালফার (এস) | ≤ 0.01 | Must be minimal to prevent MgS formation, which would inhibit vermicular graphite nucleation. |
ম্যাগনেসিয়াম (মিলিগ্রাম) |
0.03 - 0.06 | Critical for vermicular graphite; too little Mg yields gray iron, too much produces spheroidal graphite (নমনীয় আয়রন). |
| Cerium / RE (Ce) | 0.005 - 0.015 | Acts as a nodulizer/modifier—refines vermicular graphite and stabilizes it against over-inoculation or inconsistent cooling. |
| তামা (কিউ) | 0.2 - 0.8 | Increases strength and hardness; high Cu (> 1 %) can promote carbides. |
নিকেল (মধ্যে) |
≤ 0.5 | Improves toughness and corrosion resistance; often omitted for cost reasons unless specific performance is needed. |
| মলিবডেনাম (মো) | ≤ 0.2 | Inhibits carbide formation; helps maintain a ferritic–pearlitic matrix with uniform graphite distribution. |
| আয়রন (ফে) | ভারসাম্য | Base metal; carries all alloying additions and determines overall metallic properties. |
Key Points:
- Maintaining Mg between 0.035 % এবং 0.055 % (± 0.005 %) অপরিহার্য; falling outside this window shifts graphite morphology.
- সালফার must remain extremely low (< 0.01 %)—even 0.015 % S can tie up Mg as MgS, preventing vermicular graphite formation.
- সিলিকন levels above 2.5 % encourage graphite flake growth and a more ferritic matrix, improving thermal conductivity but potentially reducing strength if excessive.
মাইক্রোস্ট্রাকচার: Vermicular Graphite in a Ferritic/Pearlitic Matrix
The as‐cast microstructure of CGI depends on solidification rate, ইনোকুলেশন, and final heat treatment. Typical features include:
| Microstructural Feature | বর্ণনা | Control Parameter |
|---|---|---|
| Vermicular Graphite Flakes | Graphite flakes with rounded ends; aspect ratio ~ 2:1–4:1; compactness ≥ 60 %. | Mg/RE content, inoculation intensity, শীতল হার (0.5–2 °C/s) |
| Ferritic Matrix | Predominantly α‐iron with minimal carbide; yields high thermal conductivity. | Slow cooling or post‐cast normalization |
| Pearlitic Matrix | Alternating lamellae of ferrite and cementite (~ 20–40 % মুক্তা); increases strength and hardness. | Faster cooling, moderate Cu/Mo additions |
| Carbides (Fe₃C, M₇C₃) | Undesirable if present in significant volume; reduce ductility and machinability. | Excess Si or overly rapid cooling; insufficient inoculation |
| Inoculation Particles | Added ferrosilicon, ferro-barium-silicon, or rare-earth-based inoculants create nucleation sites for vermicular graphite. | Type and amount of inoculant (0.6–1.0 kg/T) |
- Matrix Control: ক ফেরিটিক ম্যাট্রিক্স (≥ 60 % ফেরাইট) yields thermal conductivity of 40–45 W/m·K,
যখন ferrite–pearlite mixes (30 % - 40 % মুক্তা) push yield strength to 250 - 300 এমপিএ without excessive embrittlement. - Vermicular Graphite Nodule Count: Target 100 - 200 vermicular flakes/mm² in sections ~ 10 মিমি পুরু. Lower counts reduce strength; higher counts risk transitioning to nodularity.
যান্ত্রিক বৈশিষ্ট্য (শক্তি, Stiffness, Fatigue)
CGI’s mechanical properties combine strength, stiffness, and moderate ductility. Representative values (EN-GJV-450-12, normalized) appear below:
| সম্পত্তি | সাধারণ পরিসীমা | Comparative Benchmark |
|---|---|---|
| টেনসিল শক্তি (ইউটিএস) | 400 - 450 এমপিএ | ~ 50 % higher than gray iron (200 - 300 এমপিএ) |
| ফলন শক্তি (0.2 % অফসেট) | 250 - 300 এমপিএ | ~ 60 % higher than gray iron (120 - 200 এমপিএ) |
| বিরতিতে দীর্ঘকরণ (ক %) | 3 - 5 % | Intermediate between gray iron (0 - 2 %) and ductile iron (10 - 18 %) |
| স্থিতিস্থাপকতার মডুলাস (ই) | 170 - 180 জিপিএ | ~ 50 % higher than gray iron (100 - 120 জিপিএ) |
| কঠোরতা (Brinell HB) | 110 - 200 এইচবি (matrix‐dependent) | Ferritic CGI: 110 - 130 এইচবি; Pearlite CGI: 175 - 200 এইচবি |
| ক্লান্তি শক্তি (Rotating Bending) | 175 - 200 এমপিএ | ~ 20 - 30 % higher than gray iron (135 - 150 এমপিএ) |
| প্রভাব কঠোরতা (Charpy V‐Notch @ 20 ° সে) | 6 - 10 জে | Better than gray iron (~ 4–5 J), below ductile iron (10–15 J) |
Observations:
- উচ্চ Young’s modulus (E ≈ 175 জিপিএ) leads to stiffer components—advantageous in engine blocks and structural parts requiring minimal deflection.
- Fatigue resistance (≈ 200 এমপিএ) makes CGI suitable for cyclical loads (যেমন, cylinder heads under thermal cycles).
- কঠোরতা can be tailored via matrix composition: pure ferritic CGI (~ 115 এইচবি) excels in wear applications; pearlitic CGI (~ 180 এইচবি) is chosen for higher strength needs.
Thermal Conductivity and Damping Capacity
CGI’s unique graphite form and matrix produce distinctive thermal and vibrational characteristics:
| সম্পত্তি | CGI Range | Comparison |
|---|---|---|
| তাপ পরিবাহিতা | 40 - 45 ডাব্লু/এম · কে | ধূসর লোহা: 30 - 35 ডাব্লু/এম · কে; নমনীয় আয়রন: 20 - 25 ডাব্লু/এম · কে |
| নির্দিষ্ট তাপ (20 ° সে) | ~ 460 J/kg·K | Similar to other cast irons (~ 460 J/kg·K) |
| তাপ সম্প্রসারণ (20–100 °C) | 11.5 - 12.5 × 10⁻⁶/°C | Slightly higher than gray iron (11.0 × 10⁻⁶/°C) |
| Damping Capacity (Log Decrement) | 0.004 - 0.006 | ধূসর লোহা: ~ 0.010; নমনীয় আয়রন: ~ 0.002 |
- তাপ পরিবাহিতা: High conductivity (40 ডাব্লু/এম · কে) accelerates heat dissipation from hot spots in engine blocks and turbocharger housings, reducing thermal fatigue risk.
- Damping: CGI’s damping factor (0.004 - 0.006) absorbs vibrational energy better than ductile iron, aiding noise, কম্পন, and harshness (NVH) control—especially in diesel engines.
- তাপ -প্রসারণের সহগ: CGI’s expansion (≈ 11.5 × 10⁻⁶/°C) matches steel engine liners closely, minimizing thermal stresses at the liner/block interface.
3. What Is Sand Casting Compacted Graphite Iron (CGI)?
বালি ing ালাই with compacted graphite iron (CGI) follows the same overall steps as conventional iron sand casting,
mold preparation, melting, ঢালা, দৃঢ়ীকরণ, and cleaning—but modifies key parameters to produce CGI’s unique “vermicular” graphite morphology.
Defining the Process
Pattern and Mold Construction
- প্যাটার্ন ডিজাইন: Foundries create patterns (often from wood, ইপোক্সি, or aluminum) that include allowances for 3–6 % shrinkage typical of CGI alloys (solidus ~ 1 150 ° সে, liquidus ~ 1 320 ° সে).
- Sand Selection: Standard silica‐sand molds (ব্যাপ্তিযোগ্যতা > 200, AFS grain fineness ~ 200) work well,
but enhanced binders—phenolic–urethane or furan—help resist CGI’s higher pouring temperature (~ 1 350–1 420 ° সে). - Cope and Drag Assembly: Technicians pack the drag around the lower half of the pattern, then remove the pattern and place cores (প্রয়োজন হলে) before ramming the cope.
Careful vent placement ensures gas escape when high‐temperature CGI fills the cavity.
Melting and Metal Treatment
- Charge Composition: Typical melts use 70–80 % recycled scrap, 10–20 % pig iron or hot‐metal,
and master alloys to fine-tune chemistry. Foundries aim for C 3.5 ± 0.1 %, এবং 2.5 ± 0.2 %, and S < 0.01 %. - Magnesium and Rare-Earth Additions: Right before pouring, operators add 0.035–0.055 % মিলিগ্রাম (alongside 0.005–0.015 % RE/Ce) in a covered ladle to form vermicular graphite rather than flakes or spheroids.
They stir gently to distribute modifiers uniformly. - Inoculation and De-Oxidation: Foundries inoculate with ~ 0.6–1.0 kg/T of ferrosilicon or barium-silicon inoculant to provide graphite nucleation sites.
Simultaneously, de-oxidants—such as FeSi—scavenge dissolved oxygen and minimize oxide inclusions.
Pouring and Mold Filling
- Superheat Management: Pouring temperature for CGI sits around 1 350–1 420 ° সে (2 462–2 588 ° F), roughly 30–70 °C above the liquidus.
This extra superheat ensures complete filling of thin wall sections (নিচে 4 মিমি) but also increases the risk of sand erosion. - গেটিং ডিজাইন: Foundries use a tapered sprue and generous runner cross-sections, sized for a Reynolds number (Re) এর 2 000–3 000—to minimize turbulence.
Ceramic foam filters (30–40 ppi) often intercept any inclusions carried into the mold. - Mold Venting: Because CGI fluidity rivals gray iron, proper venting—through bottom vents under risers and controlled permeability—prevents gas entrapment.
Specialized risers (exothermic or insulated) feed molten metal into the last-to-solidify hot spots.
Solidification and Microstructure Control
- Graphite Nucleation: As the molten CGI cools from ~ 1 350 ° C থেকে 900 ° সে, vermicular graphite nucleates on inoculant sites.
Foundries target a cooling rate of 0.5–2.0 °C/s in sections between 10–15 mm thick to develop 100–200 vermicular flakes per mm². - Matrix Formation: নীচে 900 ° সে, the austenite-to-ferrite transition begins.
Rapid cooling yields more pearlite (higher strength but lower thermal conductivity), while moderate cooling produces a primarily ferritic matrix (better heat dissipation).
Foundries often normalize at 900 °C after shakeout to achieve a 60 % ferrite–40 % pearlite balance. - Shrinkage Feeding: CGI shrinks by approximately 3.5 % upon solidification. Risers sized at 10–15 % of casting mass—positioned at strategic hot spots—mitigate shrinkage porosity.
ঝাঁকুনি, ক্লিনিং, and Final Processing
- ঝাঁকুনি: After 30–45 minutes of cooling, foundries break away mold sand using vibrating tables or pneumatic rams. Reclaimed sand undergoes screening and reclamation for reuse.
- ক্লিনিং: শট ব্লাস্টিং (for ferrous) or air-carbon arc cutting removes residual sand, sprues, and risers. Technicians inspect for surface cracks or fins before heat treatment.
- তাপ চিকিত্সা (Normalization): CGI castings typically normalize at 900 ° সে (1 652 ° F) for 1–2 hours, then air or oil quench.
This step refines grain size and ensures consistent ferrite–pearlite distribution. - Machining and Inspection: After normalization, castings reach final hardness (ferritic CGI ~ 115 এইচবি; pearlitic CGI ~ 180 এইচবি).
CNC centers machine critical surfaces (tolerances ± 0.10 মিমি) and inspectors verify graphite morphology (vermicularity ≥ 60 %) via metallography.
Key Differences from Gray Iron Sand Casting
| প্যারামিটার | ধূসর লোহা | CGI |
|---|---|---|
| তাপমাত্রা ing ালা | 1 260–1 300 ° সে (2 300–2 372 ° F) | 1 350–1 420 ° সে (2 462–2 588 ° F) |
| Graphite Morphology | ফ্লেক গ্রাফাইট (length 50–100 µm) | Vermicular graphite (compact flakes, length 25–50 µm) |
| Melt Treatment | Inoculation only (FeSi) | Mg/RE addition + ইনোকুলেশন |
| Mold Binder Requirements | Standard phenolic or sodium silicate | Higher-strength phenolic/urethane due to erosion risk |
| Cooling Rate Sensitivity | Less critical—flakes form over wide range | More critical—cooling 0.5–2 °C/s needed for vermicular |
| সঙ্কুচিত | ~ 4.0 % | ~ 3.5 % |
| Matrix Control | Primarily pearlitic or mixed ferrite | Tailored ferrite–pearlite balance via heat treatment |
4. Advantages and Challenges of Sand Casting Compacted Graphite Iron (CGI)
Advantages of Sand Casting CGI
Enhanced Strength and Stiffness
CGI’s tensile strength (400–450 MPa) exceeds gray iron by 50 %, while its modulus of elasticity (170–180 GPa) surpasses gray iron by 50 %.
ফলস্বরূপ, CGI castings exhibit less deflection under load—particularly valuable for engine blocks and structural components.
Improved Thermal Conductivity
With thermal conductivity of 40–45 W/m·K, CGI transfers heat 20–30 % faster than gray iron.
This allows quicker engine warm-up, reduced hot spots, and better resistance to thermal fatigue in cylinder heads and liners.
Balanced Damping
CGI’s damping factor (~ 0.005) falls midway between gray (~ 0.010) and ductile (~ 0.002) irons.
ফলস্বরূপ, CGI absorbs vibration effectively—reducing NVH (noise, কম্পন, harshness)—while avoiding the high brittleness of gray iron.
ব্যয়বহুল উত্পাদন
Although CGI adds ~ 5–10 % material cost due to Mg/RE additions and tighter process control, it costs 20–30 % less than ductile iron for equivalent performance.
Lower machining allowances—thanks to improved dimensional stability—further trim casting costs.
Challenges of Sand Casting Compacted Graphite Iron
- Tight Melt Chemistry Control: Maintaining Mg within ±0.005 % is critical. A slight deviation can revert graphite morphology to flake or spheroidal, necessitating full‐scale scrapping.
- Higher Pouring Temperatures: CGI’s 1 350–1 420 ° সে (2 462–2 588 ° F) melt demands more robust mold binders and coatings to prevent sand erosion and scabbing.
- Risk of Carbide Formation: Excess silicon or rapid cooling can produce cementite networks, embrittling CGIs; inoculation and controlled cooling are mandatory.
- Porosity Management: CGI’s higher fluidity leads to greater aspiration of gases unless mold venting and degassing practices are exemplary.
- Limited Global Foundry Expertise: Although CGI’s market share has grown (especially in automotive), only 20–25 % of iron foundries worldwide have mastered the specialized procedures, raising lead times.
5. Common Compacted Graphite Iron Applications via Sand Casting
- Automotive diesel engine blocks
- Cylinder heads and liners
- Exhaust manifolds and turbocharger housings
- Pump and compressor housings
- Gearbox and transmission housings
- Industrial engine components (যেমন, genset blocks)
- Hydraulic valve bodies and pump blocks
6. Comparisons to Alternate Casting Materials
| উপাদান | টেনসিল শক্তি (এমপিএ) | তাপ পরিবাহিতা (ডাব্লু/এম · কে) | ঘনত্ব (জি/সেমি³) | Damping Capacity | জারা প্রতিরোধের | মেশিনিবিলিটি | আপেক্ষিক খরচ | সাধারণ অ্যাপ্লিকেশন |
|---|---|---|---|---|---|---|---|---|
| CGI (Compacted Graphite Iron) | 400–450 | 40–45 | ~7.1 | মাঝারি (~0.005) | মাঝারি | মাঝারি | মাধ্যম (~ 5-10% > ধূসর লোহা) | Diesel engine blocks, সিলিন্ডার মাথা |
| ধূসর cast ালাই লোহা | 200-300 | 30-35 | ~7.2 | উচ্চ (~0.01) | মাঝারি | ভাল | কম | Brake discs, machine beds |
| নমনীয় আয়রন | 550–700 | 20–25 | ~7.2 | কম (~0.002) | মাঝারি | মাঝারি | উচ্চ (~20–30% > CGI) | Crankshafts, ভারী শুল্ক গিয়ার |
| অ্যালুমিনিয়াম অ্যালয় | 150–350 | 120-180 | ~2.7 | কম | উচ্চ | দুর্দান্ত | Medium–High | মহাকাশ, automotive casings |
| কার্বন ইস্পাত (কাস্ট) | 400–800 | 35-50 | ~7.8 | খুব কম | কম | দরিদ্র | উচ্চ | Structural, চাপ জাহাজ |
| স্টেইনলেস স্টিল (কাস্ট) | 500-900 | 15–25 | ~7.7–8.0 | খুব কম | দুর্দান্ত | Poor–Moderate | খুব উচ্চ (~2× CGI) | রাসায়নিক, খাদ্য, এবং সামুদ্রিক সরঞ্জাম |
| ম্যাগনেসিয়াম অ্যালয় | 150-300 | 70–100 | ~1.8 | কম | মাঝারি | ভাল | উচ্চ | Lightweight aerospace and electronics |
| Brass/Bronze Alloys | 300–500 | 50–100 | ~8.4–8.9 | মাঝারি | উচ্চ | মাঝারি | উচ্চ | ভালভ, সামুদ্রিক হার্ডওয়্যার, বুশিংস |
7. উপসংহার
Compacted Graphite Iron (CGI) delivers better strength, stiffness, and thermal performance than gray iron—without the cost of ductile iron.
It requires tight control of chemistry, high pouring temperatures, and proper mold design to ensure vermicular graphite formation.
Already used in engine blocks and cylinder heads, CGI reduces weight by up to 10% and improves thermal fatigue life by 30%.
Advances in simulation and process control are expanding its use to turbochargers, exhausts, and pumps.
With ongoing improvements in alloys and sustainable manufacturing, CGI is becoming a key material in modern, efficient engineering.
এ এই, আমরা আপনার উপাদান ডিজাইনগুলি অনুকূল করতে এই উন্নত কৌশলগুলি উপকারে আপনার সাথে অংশীদার হওয়ার জন্য প্রস্তুত, উপাদান নির্বাচন, এবং উত্পাদন কর্মপ্রবাহ.
আপনার পরবর্তী প্রকল্পটি প্রতিটি পারফরম্যান্স এবং টেকসইযোগ্যতা বেঞ্চমার্কের চেয়ে বেশি হয়েছে তা নিশ্চিত করে.
FAQS
Why is sand casting used for CGI?
Sand casting is cost-effective for complex, বড়, and medium-to-high volume parts.
It accommodates CGI’s specific thermal and mechanical properties, especially in automotive and industrial components.
What are common applications of CGI sand castings?
Typical applications include diesel engine blocks, সিলিন্ডার মাথা, ব্রেক উপাদান,
turbocharger housings, and structural machine parts—where strength and thermal stability are critical.
What are the key advantages of Sand Casting Compacted Graphite Iron?
CGI provides excellent strength-to-weight ratio, improved fatigue resistance, better heat dissipation, and lower cost than ductile iron in similar roles.
How does CGI affect machinability?
CGI is moderately machinable—harder and more abrasive than gray iron but easier than ductile iron. Advanced tooling and cutting strategies are recommended.
Is CGI suitable for high-temperature applications?
হ্যাঁ. Its microstructure resists thermal fatigue and distortion, making it well-suited for components exposed to cyclic thermal loads, such as exhaust manifolds and cylinder heads.
