Guidelines for the manufacture of gypsum plaster in Mechanized pan system
1991 Edition

IS 13001 specifies that gypsum raw materials, whether natural or by-product, must be free from contaminants such as clay or organic matter. The gypsum should be crushed and screened to particle sizes generally ranging from 10 to 20 mm to ensure uniform calcination. Moisture content should be controlled and maintained below 5% to facilitate effective calcination. The prepared gypsum is then uniformly fed into the pan system, which has a diameter of 1.25 meters and a depth of 0.7 meters, with a bulged bottom to aid discharge and heating efficiency.

Temperature control during calcination is achieved by adjusting the fuel feed rate and manipulating furnace dampers to regulate heat input. Thermocouples and pyrometers are installed for each pan to monitor temperature accurately. Operators use this feedback to optimize the operation cycle, calcination temperature, and heating rate, adapting to the quality of gypsum and fuel. This closed-loop control ensures the gypsum is calcined uniformly without overburning, especially important for by-product gypsum.

IS 13001 recommends using steam coal crushed to approximately 50 mm size for furnace fuel. As an alternative, dried firewood can be employed. The furnace is a vertical cylindrical shaft lined internally with fire bricks, with two furnaces serving each calciner set. A chimney at least 6 meters high provides the necessary draft for efficient combustion, ensuring optimal heat transfer to the gypsum pan.

The mechanized pan system ensures uniform gypsum plaster quality by employing a mild steel pan equipped with a vertical rotating shaft, fitted with two levels of churning blades and a sweeping chain at the bottom. This arrangement guarantees continuous mixing, preventing sedimentation and ensuring even heat distribution throughout the gypsum charge. A removable lid reduces dust loss. The furnace provides consistent heat, while the churning mechanism prevents overcalcination or uneven processing, resulting in homogeneous plaster with consistent particle size and moisture content.

Finished gypsum plaster must undergo chemical and physical testing in accordance with IS 1288:1982 and IS 2542 (Part 1):1978. Chemical tests verify the purity and absence of harmful impurities, while physical tests assess parameters such as fineness, setting time, soundness, and mechanical strength. The plaster is expected to have at least 90% passing through a 90-micron sieve and meet the specified setting times and strength limits. These tests ensure compliance with BIS standards for durability and performance.