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The drum body of the drum dryer is heated on the inside by steam. A special composition of cast iron gives the drum a combination of favourable properties: very accurate shape retention even at high steam pressure and temperature, and excellent "scraping properties", which are utilised by the scraping knife.

Steam heating gives a uniform temperature distribution over the drum surface and this results in consistent product quality. The steam condenses on the inside of the drying drum. The condensate is continuously removed from the drum, so that the largest possible surface area remains available on the inside of the drum for condensation of the steam. The steam system is a closed system, which means that the product cannot come into contact with the steam or condensate.

Depending on the design of the drum dryer, the product is applied continuously as a thin film on the underside or top of the main drum. As the drum turns and is heated on the inside, the product dries on the outside of the drum dryer.

The short exposure to a high temperature reduces the risk of damage to the product. The water or solvent evaporates and leaves the process at the top. If necessary, the vapour can also be suctioned off locally around the drum. The dried product layer finally reaches the knife and is scraped off.