Two Major Technical Pain Points of Insufficient Strength in Foundry Coatings
2026-08-10 09:11Coating spalling, metal erosion and sand adhesion on castings are common quality defects in steel casting production. Many enterprises fall into misunderstandings during process debugging by confusing two key indicators: normal drying strength and high‑temperature scour resistance strength. Such confusion may lead to batch casting rejection.
Ⅰ. Main Causes of Insufficient Normal Drying Strength
Poor additive performance: The quality of binders and functional additives fails to meet requirements and cannot provide sufficient bonding strength for the coating layer.
Insufficient additive dosage: Improper on‑site proportioning with low additive loading results in poor bonding of aggregate powder and loose coating structure.
Quality defects of aggregate powder (easily overlooked)
Particle size: Both excessively coarse and excessively fine aggregate powder weaken dried coating strength. The optimal particle‑size range is 180‑250 mesh.
Specific gravity: Coatings formed by lightweight aggregates feature low compactness. At equal weight, they deliver larger volume and coverage yet lower dry strength compared with high‑specific‑gravity aggregates.
Impurities: Harmful elements such as CaO and MgO in aggregates reduce coating dry strength. Higher impurity content and longer storage time of coating slurry bring more severe strength degradation.
Ⅱ. Core Issues of Insufficient High‑Temperature Scour Resistance Strength
Common drawbacks of conventional foundry coatings: Most ordinary foundry coatings cannot withstand long‑term erosion by molten metal. Coating failure occurs after more than 40‑second scour at 1600 ℃, which explains the wide application of ceramic runner tubes in the industry.
Root cause lies in high‑temperature additive performance rather than aggregate refractoriness: Simply adopting high‑refractoriness aggregates brings limited improvement. High‑temperature functional additives enabling high‑temperature ceramization are critical. High‑quality coatings with merely 1‑2 mm thickness can sustain long‑term scour above 1600 ℃. Within pouring‑temperature range, higher temperature brings higher coating hardness and strength, delivering better high‑temperature performance than ceramic runner tubes.
Ⅲ. Summary of Troubleshooting & Adjustment Measures
| Failure Type | Troubleshooting Items | Adjustment Measures |
|---|---|---|
| Low drying strength | Additives, additive dosage, aggregate (particle size / specific gravity / CaO/MgO impurities) | Select aggregate of 180‑250 mesh; strictly control Ca‑Mg impurities; adjust binder dosage appropriately; replace with higher‑quality additives |
| Low high‑temperature scour resistance | High‑temperature ceramization additives | Replacing with high‑refractoriness aggregate alone has limited effect. Prioritize upgrading high‑temperature bonding / ceramization functional additives to achieve high‑temperature sintering reinforcement of coatings |
Ⅳ. Selection & Process Recommendations
Verify normal drying strength and high‑temperature scour resistance separately. Do not evaluate overall coating performance only by dried appearance.
Comprehensively control aggregate particle size, harmful impurities and high‑temperature ceramization additives to fundamentally avoid defects such as metal erosion, sand adhesion and coating peeling.
Xinda foundry coatings feature excellent drying strength and high‑temperature ceramization anti‑scour performance. Aggregate particle size and calcium‑magnesium harmful impurities are strictly controlled. A full portfolio of water‑based and alcohol‑based products is available for steel casting, iron casting and non‑ferrous alloy casting. Our coatings effectively mitigate coating powdering, high‑temperature erosion and sand adhesion, cutting rejection rate and grinding cost. We also provide formula optimization and on‑site technical support to support stable and efficient production for foundries worldwide.