Why Bauxite Application Have A High Rework Rate?

Why bauxite application in foundries have a high rework rate? 90% of the problem is that the wrong type of paint was chosen.Specifically as follows:

High impurity content: Bauxite deposits are sedimentary rock deposits of the multi-mineral coexisting type. During the mining of the ore, foreign impurities such as soil lumps, sand, gravel and associated minerals are mixed in. The low-melting substances formed by these impurities during calcination may react with the additives in the coating, affecting the suspension and hanging properties of the coating, and also seriously reducing the refractoriness of the coating, this kind bauxite application in foundries causing defects in castings and increasing the rework rate.

Uneven particle size:Uneven particle size of bauxite can lead to uneven coating, the kind bauxite application in foundries all of which will affect the quality of the castings and subsequently increase the rework rate.

Poor adhesion: When bauxite has poor adhesion, in bauxite application in foundries makes the mold prone to deformation or cracking at high temperatures, thus requiring rework of the casting. cannot form a good bonding force with other materials such as water glass and clay during the casting process, this kind bauxite application in foundries makes the mold prone to deformation or cracking at high temperatures, thus requiring rework of the casting.

Poor fluidity: Bauxite coatings with poor fluidity are difficult to be evenly applied on the mold surface, which cannot effectively protect the surface of the castings. The kind bauxite application in foundries increasing the possibility of rework.

What are the core requirements of the foundry for bauxite?

The core requirements of the foundry for bauxite revolve around three aspects: high aluminum content, low harmful impurities, and stable physical properties, in order to ensure the quality of the castings and the stability of production.

Aluminum content (Al₂O₃): This is a key indicator. The higher the content, the stronger the refractoriness and the greater the strength. The commonly used grades for casting are:
First-grade bauxite: Al₂O₃ content ≥ 85%, used for high-performance refractory bricks and casting materials.
Second-grade bauxite: Al₂O₃ content 70%-85%, used for ordinary refractory products or auxiliary materials.
Impurity content: Low melting point impurities need to be strictly controlled to prevent softening and melting at high temperatures, which would affect performance.
Silicon dioxide (SiO₂): Content should be ≤ 10% (first grade), too high will reduce refractoriness and form low-melting-point silicates.
Iron oxide (Fe₂O₃): Content should be ≤ 2%, too high will cause the refractory material to change color and lose strength at high temperatures, and may also contaminate the castings.
Calcium oxide (CaO):magnesium oxide (MgO): Total content should be ≤ 1%, as they are prone to react with other components to form low-melting-point substances, damaging the structure.

How to ensure the stability of bauxite during the casting process?

To ensure the stability of bauxite during the casting process, it is necessary to start from three key links: source control, processing adaptation, and usage monitoring, covering the entire process from procurement to application, to avoid the quality of castings being affected by material fluctuations.

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