Gilsonite vs. Sea Coal in Green Sand
Sea coal (finely ground bituminous coal) has been the traditional carbon additive in green sand for over a century. Gilsonite offers several advantages.
Comparison
| Property | Gilsonite | Sea coal |
|---|---|---|
| Volatile matter | High (55–75%) | Moderate (30–40%) |
| Lustrous carbon | High | Moderate |
| Ash | Low | Higher |
| Sulfur | Low to moderate | Variable |
| Typical dosage | Lower | Higher |
Practical benefits of switching
- Lower additive consumption
- Less ash build-up in the sand system
- Reduced fines and better permeability
- Less smoke and odour in many cases
How to switch
Replace sea coal gradually, for example 25% at a time, and monitor casting finish, sand properties and loss on ignition (LOI).
Blends
Some foundries use gilsonite blended with sea coal or other carbons to balance cost and performance.
Why foundries consider switching
- Lower additive consumption per tonne of sand
- Fewer fines and ash building up in the system
- More consistent lustrous carbon formation
- Possible reduction in smoke at pouring and shake-out
A sample trial plan
| Week | Additive mix | What to watch |
|---|---|---|
| 1 | 75 % sea coal / 25 % gilsonite | LOI, casting finish |
| 2 | 50 / 50 | Compactability, gas defects |
| 3 | 25 / 75 | Shake-out, cleaning time |
| 4 | 100 % gilsonite at reduced dosage | Total cost |
Watch-outs
Because gilsonite is more active, using the same weight as sea coal can create too much gas. Reduce total dosage and monitor results.
See our foundry grade gilsonite. Related: lustrous carbon explained.
Recommended product
Foundry Grade Gilsonite
| Property | Typical value | Test method |
|---|---|---|
| Appearance | Black powder | Visual |
| Particle size | 100 – 300 mesh | Sieve |
| Volatile matter | 55 – 75 % | ASTM D3175 |
| Ash content, max | 5 % | ASTM D3174 |
| Moisture, max | 1 % | ASTM D95 |
| Softening point (R&B) | 150 – 200 °C | ASTM D36 |
| Typical dosage | 0.3 – 1.0 % (iron) | |
| Packing | 25 kg bags palletized; 1 MT jumbo bags for blending plants. | |
Typical values. The final specification is confirmed in the COA of each shipment.
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