Material
Gypsum Powder
Answer in brief
Gypsum is a powder that can turn into a solid inside your equipment.
Stucco leaving a calciner is hot, cohesive and chemically thirsty, and any moisture it meets starts a setting reaction that no vibrator will undo.
- Keep conveying and venting air dry.
- Allow for hot material at the silo inlet and for consolidation at the outlet.
- Design for cleanout, because a partial set has to be removed mechanically.
Reviewed October 21, 2026 · Updated October 21, 2026
Handling challenges
Handling calcined gypsum means handling a material that is waiting for water.
Hydration starts in the air
Humid conveying air, a leaking vent filter or condensation on a cold silo wall is enough to begin the reaction.
The first sign is usually not a blocked silo but lumps in the product and a slow loss of setting performance at the board line.
- Dried conveying air and sealed, vented silos.
- Insulation where condensation on the inside wall is credible.
- Filter cleaning that actually removes the cake rather than compacting it.
Temperature
Stucco arrives hot from calcination, and hot powder aerates, then consolidates hard as it cools in the silo.
The design basis has to include the hot inlet condition and the cooled, consolidated outlet condition, because they are not the same material from a flow point of view.
Discharge and feeding
Mass flow geometry with a generous outlet and a mechanical discharge aid gives the most reliable result.
Loss-in-weight feeding into the mixer needs a stable, deaerated inlet; a flooding gypsum feed produces a board thickness problem before anyone sees a flow problem.
Cleanout
Any set material has to come out mechanically, which means access hatches, planned downtime and a safe method statement rather than a person with a bar.
What to establish before buying equipment
- Inlet temperature and the cooling profile inside the silo.
- Flow function for the consolidated, cooled powder.
- Dew point of all air in contact with the product.
- Access for cleanout and the planned frequency.
Material behavior
- Flowability
- Poor to moderate, consolidates quickly
- Abrasiveness
- Moderate
- Cohesiveness
- High after consolidation
- Moisture behavior
- Reacts with water and sets; moist air alone is enough
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