1) Title of the invention
"Development of Mold Coat and Process of Mold Coat Application for Sand (Silica/Zircon) Mold/Core to Cast Magnesium Alloys without Adding Inhibitors (Sulfur, Boric Acid, KBF„ etc.) in Sand Mix"
2) Field of invention
The present invention is development of mold coat and process of the applying the same on sand mold/core. Mold coat material is developed to avoid the usage of inhibitors in sand mix for making sand (silica/zircon) molds to cast Magnesium alloy castings through sand casting process.
3) Use of invention
The invented mold coat and process of the applying it on molds are intended to use for casting Magnesium alloy castings. They significantly reduce Foundry Defects such as gas holes, blow, and cracks( induced due to hardness of mold/core) due to addition of inhibitors in Magnesium alloy castings.
Also, commonly used inhibitors are very corrosive in nature and may form borates during thermal reclamation resulting in chocking/corrosion of reclamation plant. The developed mold coat and it's application process enables mold/core sand thermally reclaimable due to reduced application of inhibitors (around 0.1% or less of the sand weight, against 2 to 10% commonly used worldwide).
4) Prior art
Inhibitors (Sulfur, Boric acid, KBF4) were being used around 2 to 10% of the sand depending on various factors in the sand mix to make mold/core to cast magnesium alloy castings. Silica or Zircon based mold coat readily available in market was being used to coat mold/core. These inhibitors are considered necessary during casting process since they avoid metal mold reaction and'thereby related casting defects. However, the inhibitors also lead to various casting defects, health and environmental issues.

5) Draw backs of prior art
a) Foundry defects: Foundry defects like gas holes, blow, and cracks( induced due to high
hardness of mold/core) result from addition of inhibitors.
b) Difficult to knock out: Inhibitor addition causes increased hardness of mold/core after
pouring molten alloy in mold cavity. It results in difficulty in knock out process.
c) Health Issues: Burning of inhibitor in mold/core forms toxic fumes which are hazardous to heath.
d) Environmental Issues: It is not possible to reclaim mold/core sand consisting of inhibitors. Sand has to be scrapped after single usage, which causes environmental issues due to dumping of highly contaminated sand.
e) Though Zircon/Silica based mold coats are readily available in market and are in use for magnesium alloy casting, they are ineffective in preventing metal mold reaction without addition of inhibitors in sand mix.
6) Comparison between prior art and present invention
Conventional method results in higher foundry defects, leading to difficulty in knock out process of mold/core, causes higher health hazard and environmental issues due to dumping of sand contaminated with inhibitors and help only partially in protecting mold from metal mold reaction. However, present method results in significantly reducing foundry defects by avoiding inhibitors in sand mix, ease the knock out process and reduce health and environmental hazards. These benefits are apart from excellent protection from metal mold reaction as more stable compound than Magnesium Oxides is used as protective coat.
7) Aim of the invention
Aim of the invention is to develop mold coat and process for the application of the same it on sand mold/core , which can avoid necessity of inhibitor addition in sand mix and simultaneously provide excellent protection from metal mold reaction, reduce foundry defects ( pertaining to inhibitor additions), leading to reduce health hazard and enable mold/core sand reclaimable.
8) Summary of the present invention
The present invention is development of Mold coat and process for applying it on sand mold/core to cast Magnesium alloy castings through sand casting process.

The invented mold coat has primary and secondary mold coatings.
Primary mold coating is water based mold coat, which is solution of chalk powder (100 mesh size or finer) with sodium silicate. Application of the same is to be done through spraying method on heated mold/core.
Secondary mold coating is any commonly used zircon/silica based mold coat where inhibitor to be added in sprit solvent. Mold/core to be dried completely in the oven before pouring the molten metal in mold cavity. Direct flame shall not be used on mold/core for drying the mold/core as it results in detrimental effect on properties of mold coat to avoid metal mold reaction.
9) Brief description of mix
Two types of mold coating materials are used with additives and different suspension mediums.
Primary mold coat is chalk powder with sodium silicate where suspension medium/solvent is water. Application of mold coat has to be carried out by spraying the same on mold/core. Preheating of Mold/core is necessary before applying mold coat.
Secondary mold coat is commonly used zircon/silica based mold coat. Inhibitor (K8F4) to be added around 12-13% of mold coat paste weight in second mold coat. Suspension/solvent medium shall be sprit. Mold coat shall be completely dried before pouring molten alloy. Heating shall be done in the oven and direct flame is not recommended.
10) Statement of invention
Development of Mold coat and process of application of the same on sand mold/core to cast Magnesium Alloy through sand casting process, without adding inhibitors in sand mix.


The present invention is best suited for all Magnesium alloys {Mg-Zn-Zr-RE; Mg-Zn-RE; Mg-Ag-NdRE; Mg- Al-Zn-Mn) when poduced through sand casting process.
By using the invented mold coat and new process to apply it, the acceptance rate on a magnesium casting {Figure A) lead to improvement of acceptance rate from 50% to 90% in a sample size of 50 numbers.

"I claim"
1. The invented Mold Coat and application Process for Sand Molds to cast Magnesium Alloy Castings developed at Foundry & Forge Division, Hindustan Aeronautics Limited is a new material and process development for sand casting , the details of which are not available in open literature.
2. The process has been optimised for all Magensium alloys castings produced through sand casting process.
3. The use of developed mold coat and application process of the same for sand molds is to reduce foundry defects pertaining to inhibitors, reduce environmental and health hazard related issues and enable sand molds thermally reclaimable.
4. The composition of mold coat and application process is optimized.
5. The developed mold coat is effective for all Magnesium Alloys (Mg-Zn-Zr-Rare Earths or Mg-AI-Zn-Mn or Mg-Zr-Ag based alloy).