I. Purpose of a Carbonaceous Additive
A. Reduce imperfections due to the rapid reaction between the silica sand mold and the oxidized surface of molten iron.
B. Improve sand peel from casting at shakeout.
C. Produce smoother, cleaner casting surface.
D. Minimize imperfections, casting losses, scrap.
II. Additive Theories
A. Gaseous Cushion Theory
During pouring, the gases given off from the carbonaceous additives form a gaseous film which prevents the molten metal from making direct contact with the clay-coated sand grains, reducing sand-metal contact and consequently burn-on.
B. Lustrous Carbon Theory
When heated, the carbonaceous materials provide volatile, hydrocarbon gases which then pyrolize to deposit a lustrous carbon graphitic layer in the metal-mold interface region. This deposition acts as a physical barrier to iron silicate formation as well as not being readily wetted by molten iron. The combination effect is to inhibit burn-on and penetration.
C. Reducing Atmosphere Theory
When the carbonaceous materials are heated they create a mold atmosphere of reducing gases. This atmosphere keeps the surface of molten iron at the interface free from oxidation, thus preventing formation of the iron silicate necessary for penetration and burn-on.
A. Burn-on: Sand grains firmly bonded to casting.
B. Burn-off: Casting surface has rough, sandy appearance.
C. Metal penetration: Metal penetrates into voids between sand grains forming fused
mass of metal and sand, casting difficult to remove.
D. Pin holes, caused by high nitrogen content.
A. Highly volatile bituminous coal.
B. Most popular carbonaceous additive to gray iron castings.
C. Additive level about 1.0 – 3.0% of total sand.
D. Add about 0.1 – 0.8% new seacoal to total sand mixture with each recycle.
E. Mold Effects
1. Increased green strength.
1. Low lustrous carbon content, 8-10%.
A. Supplement/substitute to seacoal.
B. Lower ash, lower sulfur.
C. Faster volatile release.
D. Higher lustrous carbon content, 35-38%.
E. 1 part Gilsonite replaces 3 parts seacoal with same or better performance.
Gilsonite Foundry Grade is available in 50 lb. and 25 kilo net multi-ply paper bags which may be palletized and stretch wrapped. It is also available in bulk loaded trucks, containers, and a variety of bulk bag sizes.
Gilsonite is a naturally occurring hydrocarbon. There is no known history of dermatitis, lung disease or other health problems associated with handling of Gilsonite as supplied. Dusts are subject to combustion. Normal precautions used with flammable materials apply.