Casting: 88 Mesh (90% SiC) vs. 90 Mesh (88% SiC): Which Better for Cast Iron Inoculation? Why?
In cast iron production, late inoculation - adding nucleating agents just before pouring - refines graphite structure, reduces chill, and improves mechanical properties. Silicon carbide (SiC) is sometimes used as an inoculant or adjuvant, but its effectiveness hinges on mesh size (particle size) and purity (SiC content).
A common comparison arises between 88 mesh (≈90% SiC) and 90 mesh (≈88% SiC). While they appear similar numerically, the mesh-number vs. purity difference changes how they behave in the melt.
At ZhenAn, with 30 years of experience supplying SiC for foundry applications, we explain which works better for cast iron inoculation and why.
1. Inoculation Mechanism & Time Window
Inoculation works by introducing nuclei for graphite precipitation during solidification. Key points:
Must occur shortly before pouring (typically 1–3 min for gray iron) so nuclei survive to solidification.
Dissolution rate of the inoculant determines how long active Si and C are available.
Too fast dissolution → short-lived effect; too slow → insufficient Si pickup before solid starts.
Thus, particle size controls dissolution speed, and purity controls how much effective Si and C is released per unit mass.
2. Mesh Size: 88 vs. 90 - What's the Difference?
Mesh number = number of openings per inch.
88 mesh ≈ 180 µm particle diameter
90 mesh ≈ 170 µm particle diameter
Difference seems small, but in foundry practice:
88 mesh particles are marginally larger → slightly slower dissolution
90 mesh particles are marginally smaller → slightly faster dissolution
In inoculation, slower dissolution can be advantageous because it stretches the effective nucleation period within the limited pouring window.
3. Purity: 90% SiC vs. 88% SiC - Impact on Inoculation
88 mesh (90% SiC): Higher SiC content means more Si + C per gram available for nucleation. Fewer impurities (silica, free C) that could interfere with graphite formation or form low-melting compounds.
90 mesh (88% SiC): Lower SiC content → less effective Si+C per gram; more silica means some Si may be tied up in SiO₂, reducing available free Si for graphite nucleation. Also, higher impurity phases may alter melt fluidity or cause inclusions.
Result: 90% SiC releases more active Si and C, enhancing nucleation potential.
4. Combined Effect: Which Is Better for Cast Iron Inoculation?
|
Factor |
88 Mesh (90% SiC) |
90 Mesh (88% SiC) |
|---|---|---|
|
Particle Size |
Slightly larger → slower dissolution |
Slightly smaller → faster dissolution |
|
SiC Purity |
Higher → more effective Si+C per mass |
Lower → less effective, more impurities |
|
Nucleation Duration |
Longer-acting in melt |
Shorter-acting |
|
Risk of Undissolved Residue |
Slightly higher (but can act as solid nuclei) |
Lower dissolution residue |
|
Inoculation Efficiency |
Higher (better Si uptake, longer action) |
Lower (faster burn-off, less Si available) |
Conclusion: 88 mesh (90% SiC) is generally better for cast iron inoculation because:
Slower dissolution fits the narrow inoculation time window.
Higher SiC purity provides more usable Si and C, improving graphite refinement.
Solid particles that don't fully dissolve can remain as heterogeneous nucleation sites, reinforcing the effect.
5. Practical Considerations
Pour Timing: If holding time after inoculation is very short (<1 min), faster-dissolving 90 mesh might seem advantageous, but you sacrifice Si content and risk incomplete inoculation.
Iron Type: In ductile iron with Mg treatment, slower Si release from 88 mesh (90% SiC) helps avoid Mg loss from turbulence.
Blend Approach: Some foundries use a mix (e.g., majority 88 mesh 90% SiC + minority finer) to tune dissolution curve.
Cost vs. Performance: 88 mesh 90% SiC may cost slightly more per kg, but improved inoculation efficiency can reduce rejects and increase mechanical properties, giving better overall economics.
6. Industry Example
A gray iron foundry producing hydraulic valve bodies switched from 90 mesh (88% SiC) to 88 mesh (90% SiC):
Observed finer, more uniform graphite flakes
Reduced section sensitivity in thick-to-thin transitions
Increased machinability and tensile strength
Lower incidence of hard spots in thin sections
7. Why Choose ZhenAn for Foundry SiC
30 years of experience in SiC for inoculation and nodularization processes
Precise control of mesh size and SiC content (88 mesh 90% SiC, 90 mesh 88% SiC, custom blends)
ISO & SGS certified for consistent chemistry and sizing
Packaging suited for automatic ladle dosing systems
Global supply ensuring reliable foundry support
Conclusion
Between 88 mesh (90% SiC) and 90 mesh (88% SiC) for cast iron inoculation, 88 mesh (90% SiC) is the better choice because its slightly larger particle size prolongs dissolution within the critical inoculation window, and its higher SiC purity delivers more effective silicon and carbon for graphite nucleation. This combination improves inoculation efficiency, refines graphite structure, and enhances mechanical properties of the cast iron.
For expert advice on SiC mesh and purity selection for your inoculation process, contact our foundry specialists at:
FAQ
Q1: Does mesh size alone determine inoculation performance?
A: No - purity (SiC content) is equally important because it affects how much active Si and C is available.
Q2: Can I use 90 mesh (88% SiC) if my pour time is very short?
A: Possible, but you may lose inoculation effectiveness due to lower SiC purity and faster dissolution.
Q3: Will undissolved 88 mesh particles harm the casting?
A: Usually not - they can act as extra nucleation sites; excessive amounts might cause inclusions, so dosing must be controlled.
Q4: Does ZhenAn supply 88 mesh with 90% SiC?
A: Yes, we produce both standard and custom mesh/purity combinations for foundry inoculation.
Q5: Should inoculation SiC be used alone or with FeSi?
A: Often blended with FeSi or other inoculants to optimize nucleation and adjust chemistry economically.
Why Choose ZhenAn
Stable, Verified Quality – Controlled sourcing and batch inspection ensure consistent metallurgical performance.
One-Stop Product Range – Silicon carbide, ferro alloys, silicon metal, cored wire, zinc wire, Electrolytic Manganese Metal Flakes.
Custom Specifications – Flexible grades, sizes, and packaging to fit different production processes.
Proven Export Experience – Professional handling of inspection, documents, and international shipping.
Reliable Supply – Stable factory partnerships and dependable delivery schedules.
Fast Support – Quick quotations and practical technical guidance.
Strong Cost–Performance – Balanced pricing with real process value.
