Foundry Sand Additives and Additive
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.
Foundry Sand Additives
Coal Tar Pitch
Additive Level (%)
Green Sand Properties
Dry Sand Properties
Dry Compression (197.2ºC), N/cm²
Principal Applications Foundry Sand Additive Refractaries Ingot Mold Coating Briquette or Pellet Binder
Softening Point (ASTM E28-92)
Ash (ASTM D271-70 M)
Moisture (AGC Method)
Penetration (25ºC, 100 gm, 5 sec.)
Typical Elemental Analysis, Weight %
Typical Particle Sizing
% Retained (Cumulative)
PRODUCT APPLICATION FOR FOUNDRY GRADE GILSONITE
Physical Sand properties with Gilsonite® resin are equal or superior to seacoal at significantly lower additive levels. Gilsonite improves sand density, water requirements and strength (green, dry, baked, and hot). Gas evolution curves show that Gilsonite volatilizes more rapidly than seacoal. Gilsonite has the same total volatiles as seacoal at one-third the additive level.
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.
HEALTH & SAFETY
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.