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APPROXIMATIONS
S.Narayana Moorthy

APPROXIMATIONS

THUMB RULES are a great help and are available from various sources in the net. Here some indicators  to arrive at approximations  are given. The geological formations, working conditions, requirements and local set up are widely varying and though a generalization cannot be made, the working parameters calculated after several trials and experience can be of a guiding factor, These are mainly useful for the site personnel to make a start and check on their performance, These are culled and found reasonably realistic.

Though the parameters keep on increasing with the current awareness and changing priorities the basic operational functions remain the same and play a major role in determining the performance.

EQUIPMENT

1.       Review operations

2.       Determine the required payload and cycle times

3.       Review key requirements for loading and hauling units

4.       Compare individual specifications

Influencing factors (what matters most in %)

Maintenance                     48
Production                       23
Engineering                      11
Safety                              03
Personnel                         04

EXCAVATORS:

Considerations                                  Model 1               Model 2               Model3                Model 4

Operating  weight in kgs
Engine output in kws
Bucket capacity in cu.meters
Digging depth in meters
Digging height in meters
Digging reach in meters

SIZE REDUCTION:

1.  Cost of reduction by drilling and blasting       relative index    100

2.  Cost of reduction by hydraulic breaking                                  32

Use of hydraulic breaking/by terminators is no longer restricted to locations where blasting constraints exist and find increasing applications with improvements and the above indices need to be reviewed for a particular application and site 

RIPPING:

Check when considering surface miners or hydraulic impactors:

¨       Seismic velocity less than 2500 m/s                  Rip able

¨       Seismic velocity 2551 to 3200 m/s                    Marginal

¨       Seismic velocity above 3200                            Not rip able*

Ø  *check manufacturer for capabilities

LOADING:

For calculating cycle times:
The speed of a loaded vehicle and empty vehicle isto be considered as recommended by the manufactures.

Cycle time is fixed time + haul time

Fixed Time
Loading time + Lost time in pit acceleration, dump, turn and acceleration at the dump.

Haul Time
Travel time to the dump
Travel time for the empty vehicle from the dump

Provide for MAT factor
It is prudent to provide for maintenance and standby equipment while operating several blocks simultaneously. Provide allowances for the machine availability factor and average availability.

DRILLING:

Consider:

¨       Scheduled working hours

¨       % uptime

¨       Rotation speed and bit weight

¨       Source of each downtime

¨       Weather/Shifting/Maintenance/Equipment failure/Bit changing/Bit failures

¨       Pressure and volume of compressed air

¨       Total production per drill (per hour/per shift)

¨       Maintenance of drill records cost/hour, cost/meter of drilling, cost per metric tone of    the product. % utilization etc)

¨       Drill steel, Fuel, and Salaries not to exceed 26% of the total cost( this should be worked out to local conditions)

¨       Maintenance cost not to exceed 6% of the total cost (this should also be determined to local conditions)

BLASTING:

Parameters for each location:

¨       Diameter in meters

¨       Burden in meters

¨       Spacing in meters

¨       Charge per hole in kgs

¨       Holes per delay

¨       Maximum charge per delay in kgs

¨       Number of rows

¨       Yield per meter in tones

¨       Safety distance in meters

¨       Additional precautions dictated by local conditions

APPROXIMATE COST PER UNIT OF RUN-OFF-MINE

 This combined figure indicates the cost at the pit head/mine and this approximation helps to keep in check the performance. The owning costs consider a repair cost equivalent to the purchase value over the useful life in hours. The cost of all equipment added as a whole and divided by the production target should indicate an approximate cost pertonne of the run-off-mine and from there, detailing can be carried further.

It is worth remembering:

¨       Actual production time  is the standard operating delay per cycle multiplied by the number of cycles per shift

¨       Fuel consumption can be approximately 10%of the engine horse power in litres per hour (check the engine specifications and further improvements)

 NOTE:

Mine managements do a detailed study and come out with the budgets scaled down to a practical level for day to day or even hour to hour monitoring. Automation take away most chores and bring in effective controls giving an edge for site personnel.

Where the deposit is intricate and structurally deformed, exploration data is inadequate or only carried out in stages and multiple recoveries become a must for survival and successful mining, the requirements of the site personnel get focused and it becomes necessary to have a basic grasp to function effectively. This approximations are provided in that perspective.

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