Increasing in the amount of coal dust has some special effects :

Prevent Sand burning

Produce reduction environment: CO2 and H2

Prevent surface Oxidation

Sand not clinging to pieces

Prevent expansion of sand

Good. Thank you so much dear Masoud. I liked of the last one of the parameters. 

The prevent expansion of sand.

Thank you.

Taken from:

Principles of Foundry Technology

By P. L. Jain

Coal Dust – It is commonly used in green sand and dry sand moulding for protecting mould surfaces against the action of molten metal and improving surface finish of cast iron castings. When the moulten metal come in contact with mould surfaces containing coal dust, a gaseous envelope is formed which resists the fusion of sand to metal. Use of coal dust increases both green and dry strength, reduces expansion, tendency to scabbing and metal penetration.  It, however, tends to reduce the permeability of sand. Good quality coal dust suitable for foundry use should consist of finely crushed bituminous coal  free from foreign material, and should have fineness about 150 mesh BS sieve, equivalent to 106 micron IS sieve. It should have a minimum 30% volatile matter, maximum 20% ash, 3% moisture, 1% sulpher and 0.2% phosphorus content. Specifications of coal dust for use in foundry are covered by IS: 1752-1973.  Pitch and fuel oil are used as reducing agents and have similar effect as coal dust. IS13100-1991 give the specification of pitch powder for use in foundries.  

Hope this helps. 

Best Regards 

Martin 

Apologies I only initially read the title. 

I am interested in this topic. I think you are right and the iron can take carbon from the coal dust, that seems logical. I am interested to see how the increase in coal dust affects the gas produced during the casting process. Both from an environmental point of view within the foundry i.e. air quality and from a perspective of addition gas within the sand mould and how that affects the integrity of the cast component.  

From a die cast point of view producing cores with a 2 part resin system with an amine catalyst. I found that increasing the resin content beyond a certain point was detrimental from a point of view of producing too much gas during the casting process. Obviously understand that is a different process all together. Interested in reading your findings. 

Ok thank you so much for your interest and your answer to this topic.

You notice to gas production by coal dust. We have two parameters in green sand: Volatile (V.O.L) and L.O.I   Now, tow parameters are effective in gas produce in the produced casting parts . V.O.L formation by Bentonite and L.O.I formation by coal dust. Bentonite is increased moisture. when the Bentonite is increase in the green sand it means the moisture is high level in the sand so it possible to product gas in the casting parts. And besides about L.O.I (coal dust). when the coal dust is at a high level in the mixture of the green sand, we have a high percent ash and combustible materials in the green sand. So, when the molten metal is contact with the wall of the mold, then the combustible materials start burning and they product gas in the molten metal. the permability was reduced because we have amount of coal dust (L.O.I) in the green sand and so the gases can not be exit of the mold, so they remind as gas in the casting parts. Because when the combustible materials start burning, they produce free carbon and the carbon will reaction with Oxygen and then produce blowhole with base Co or Co2 in the casting parts.

I hope so you achieve your answer to this descriptions. If there were any vague point told me if I have been the knowledge I do not hesitate to answering.

Regards,

Hi Azim, 

Thanks for your answer. 

How does the Loss Of Ignition test of standard green sand compare to the LOI produced from the increased coal dust green sand. As a comparison in terms of the specific value?

Regards 

Martin