The article are hanged on the Overhead Conveyor which takes vertical up & down bends inside the pretreatment tanks. The tanks are made sloping at entry and exit. Generally the conveyor speed is fixed and tank lengths vary according th chemical specifications (Dipping type). This system is suitable for small and medium articles having low weights, few chemical requirements.
The dip phosphating plant consists of a number of tanks arranged sequentially. The article to be phosphated are loaded in suitable cages abd are transported by an overhead hoist from tank to tank manually or automatically. In Twin hoist system two hoists lift the cage.
For complete automation of handling of cages in pretreatment system transporters are provided. Semiautomatic version is also available. It has wide load carrying capacity (200 to 1000 kg.) P.L.C. based control are provided for integrated plant management system.
Online spray pretreatment is designed based on conveyor speeds and article geometry. It is generally used in conveyorized plants where article types are few, geometry is similar and quantities are large. Articles move over the conveyor through modular spray tunnel where the chemicals are sprayed. The chemical tanks with pumps are placed below or on the side of the tunnel. Due to continuous spray the interaction between article surface and chemical is very fast. For elevated temperature zones insulated tunnel tank modules are provided.