Drum mix plants

 Technical requirement of Drum Mix Plants

yogendra borse

    The drum mix plant should be of reputed make and proven design, sturdy in structure and capable of producing desired quality of mix as per specification for laying bituminous road surface and should have following essential arrangements:

1) Cold Aggregate Feeder:-

     The cold aggregate feeder arrangement should have minimum 3 bins of sufficient capacity capable of storing different sizes of aggregates and fines to ensure continuous uninterrupted supply of aggregates matching the capacity of the plant. Each bin should have independent belt feeder system driven by a variable speed motor and a control gate to ensure accurate aggregate feed to meet design mix formula. It is pre-requisite that only properly screened and graded materials are fed to the bins.

    There should be a gathering conveyor to receive and transport material discharged from bins with separate drive arrangement.

    There should be a screen or a suitable arrangement like baffle plate at the discharge end of gathering conveyor for rejection of any oversize metal above the permissible limit. The conveyor should be fitted with suitable electronic weigh bridge device for weighing quantity of cold aggregate being fed to dryer drum.

    The plant should have a mineral filler arrangement with suitable control device to accurately proportion the flow of filler material into dryer drum at appropriate stage.

2) Dryer Drum :-

    It should be thermo drum type with smooth rotation arrangement to give rated output and capable to reducing the moisture content of the aggregate to desirable limit of 2% to 6% and achieving hot mix temperature (up to 160°C as per requirement) with such design that no blue smoke is emitted from the exhaust. The drum may have optional arrangement for feeding reclaimed material. There should be arrangement to restrict burner flame up to certain length in the drum before bitumen is injected.

    It should be fitted with positive displacement bitumen pump driven by variable speed motor automatically controlled from control cabin, capable of feeding desired quantity of bitumen synchronised with aggregate feed system. Thermic fluid system or hot oil circulation system should be an in built feature to keep bitumen pump and pipes sufficiently hot to avoid clogging of pipes.

3) Burner :-

    The Burner used should be capable of burning the fuel efficiently and develop the requirement temperature. It should be fitted with remote control system to detect flame failure and also electric spark ignition system or some other suitable arrangement. Burner operation should have thermostatic control of flame within the specified temperature range.

4) Bitumen Heater:-

    It should consist of an insulated tank of adequate capacity fitted with effective and positive control of temperature for allowing continuous circulation of bitumen between Bitumen Heater & proportioning units. Suitable arrangements should be provided for recording the temperature at the tank and in circulating system.

5) Fuel System :-

    Fuel tanks should be of sufficient capacity and fitted with suitable type of fuel pump to receive the fuel from storage tank and supply to line heater burner.

6) Cyclone System :-

    Cyclone unit is required to control dust discharging within the admissible standard of pollution level.

7) Operating control Unit :-

    The drum mix plant must have centralised system with operation from a control cabin located adjacent to the drum mix plant. The central system should be capable of following:

i) Automatic control of speed of each bin feeder conveyor and gate so as to control and regulate the flow of various grades of material to ensure constant and accurate proportion of aggregates.

ii) Pre-set and control the percentage of flow of aggregate and asphalt required as per design mix.

iii) Automatic detection of plant operation, failure, display of aggregate temperature, asphalt and mix temperature aggregate flow etc. Fully automatic aggregate blending, bitumen/ aggregate ratio control and burner control system.

iv) Control for presenting the moisture content. of aggregate displayed digitally.

v) Entire control system should be such that. if desired it would be operated manually also.

8) Surge Silo :-

     The plant may have optional arrangement to store hot mix material for at least equivalent to 30% of rated capacity to cater for any delay in loading the tippers. Temporary storage silo should have adequate automotive hydraulic unloading arrangement operated either from the control cabin or manually with necessary safety Control.