MANUFACTURING PROCESS FOR CHRYSOTILE ASBESTOS CEMENT CORRUGATED SHEETS
The manufacture of A.C. Sheets is based on the principle of famous “Hatschek” process and is well established in India. In brief the manufacturing process shall involve the following stages :-
Pretreatment of Chrysotile Fibre :
Chrysotile fibre bags of different grades are put in fully enclosed full automatic PLC controlled Bag Opening Device. To minimize the exposure risk of Chrysotile Fibre to the worker, manual handling of Chrysotile Fibre is completely avoided by using a fully enclosed fully automatic PLC Controlled Bag Opening Device with bag shredder through which compressed fibre bags are automatically cut.
Chrysotile fibre passes through the enclosed lump breaker and closely connected screw conveyor to be automatically discharged in the mill and the empty bags are automatically fed in the connected Bag shredder where these are shredded and fed to the Edge runner Mill through a duct 25% to 30% water is added in the mill. The fully automatic Bag opening Device, Lump Breaker, Screw Conveyor, Bag Shredder and mill are completely closed integrated unit. The wet chrysotile fibre along with shredded bag particles are discharged from the mill to a closely connected bucket elevator which discharges the wet chrysotile fibre along with shredded bag articles to a storage in which has a screw conveyor attached at the bottom for discharging the wet chrysotile fibre into a batch weighing Hopper placed on electronic load cells which in turn discharge the pre-determined weighed wet chrysotile fibre into the Hydro-disintegrater where he wet chrysotile fibre is mixed with 2000% of water to form asbestos slurry. The whole system of mill, Bucket, Elevator, Storage Bin, Batch weighing Hopper and Hydro-disintegrater is closely connected and integrated unit as a whole. The automatic Bag Opening Device, Edge runner mill and Cement-fly Ash feeding points are provided with suction hoods. These hoods are connected to a pulse jet bag filter unit through a duct. The entire system is designed keeping in mind zero dust generation and no manual handling of chrysotile fibre is done either dry or wet.
Preparation of slurry :
The treated fibre along with predetermined quantities of fly-ash, cement and pulp are charged into a mixing vessel to form slurry.
Sheet making :
The slurry is then fed into the vat from where layers of slurry are deposited on rotating sieve cylinders inside the vat. This is then transferred to a moving end loss polyester felt which deposits the layer on a rotating drum. The required thickness is achieved by successive transfer of slurry films and the sheets so formed are cut and picked up by the conveyor.
The sheets from the conveyor are automatically cut at the ends to the desired size and conveyed to the atmospheric corrugators� machine where the sheets are corrugated and placed in the steel template. The wet edge trimming and cutting including damaged sheets are automatically fed to waste pulped through waste conveyor where the green sheets are re- pulped and returned back to the machine continuously in a closed circuit.
Drying and Curing :
50 corrugated sheets along with templates are loaded on to a trolley and transported to a drying chamber. After drying for 10 � 12 hrs, the sheets are striped from the templates. Thereafter, the sheets are air cured for 28 days.