Introduction to mining and transport in open pit mining

     
                                                      Procurement and installation work

Mining and loading work is the process of using mining equipment to extract ore and rock from a pile of ore and rock that has been crushed by blasting, and then loading it into transport containers to be transported to the receiving bin of the crusher or a certain location.

The mechanical equipment used in mining and loading work includes excavators, electric shovels, loaders, etc. Due to the hardness of the ore rock in metal mines, excavators and electric shovels are mainly used in production.

      The main working parameters of excavators include the following aspects:

(1) Excavation radius: The horizontal distance from the center of rotation of the excavator to the tip of the bucket teeth during excavation.

Maximum excavator radius: the excavation radius when the boom extends horizontally to the maximum extent.

Standing horizontal excavation radius: The excavation radius of a bucket placed flat on a standing horizontal plane.

(2) Excavation height: The vertical distance between the tip of the bucket teeth and the standing level during excavation.

Maximum excavation height: The vertical distance between the tip of the bucket teeth and the standing level when the boom is extended to its maximum and raised to its highest position.

(3) Unloading radius: The horizontal distance from the center of rotation of the excavator to the center of the bucket during unloading.

Maximum unloading radius: The unloading radius when the boom extends horizontally to its maximum extent.

(4) Unloading height: The vertical distance between the lower edge of the bucket and the standing level.

Maximum unloading height: The maximum unloading height at which the boom extends and reaches its highest position.

Excavation depth: The vertical distance between the tip of the bucket teeth and the standing horizontal when digging with a bucket.

      Excavator operation mode

(1) Normal blasting operation mode

In the loading operation of open-pit mines, there are three types of loading methods based on the relative position of transportation equipment and excavators: flat loading, loading, and combined loading.

A   Flat car

Excavators and transportation equipment are located at the same level.

B   Loading the car

The transportation equipment and excavator are located at the upper and lower levels of the steps, respectively.

C   Joint loading

The transportation equipment is located on a flat plate in the middle of the steps.

In actual production, the most commonly used is the flatbed truck.

(2) Special loading operation method

When the structure of the ore body is complex, there are many rock interlayers within the ore body, or there are multiple different grades of ore in the deposit, in order to meet the requirements of product quality and grade, and minimize the loss and impoverishment of ore, special mining and loading methods must be adopted during the loading process to achieve the separation of different grades of ore and interlayer rocks.

A   Partition blasting and loading

When different types and grades of ores are present in the horizontal direction of the steps, or when there is a boundary between ore and rock in the horizontal direction of the steps, they can be divided into small areas according to ore variety, grade, or ore rock boundary for blasting and loading. As shown in the figure below, Zone I is rock and Zone II is ore. First, blast and load Zone II, and then blast and load Zone I to minimize ore loss and impoverishment.

B   Segmented blasting and loading

When there are local ore (or rock) layers in the vertical direction of the steps, the method of segmented blasting can be used according to their depth of occurrence. After blasting, excavators can be used to load and transport this part of the ore (or rock) away.

C   Layered mining and loading

When mining gently inclined or horizontal thin ore bodies, the entire step can be divided into two or several sub steps according to the ore rock contact line for layered mining.

Firstly, blast the upper part of the steps, and then create a flat passage from the lower part of the steps leading to the upper part of the steps for the excavator to travel up and down. When the upper part of the steps is advanced to a certain distance and the lower part of the steps is exposed to a certain area, drilling and blasting can begin on the lower part of the steps. At this point, work is carried out simultaneously by dividing the steps up and down. After blasting the lower part of the steps, the excavator returns and loads the lower part of the steps, while drilling and blasting the upper part of the steps.

This method of operation can minimize ore loss and impoverishment to the greatest extent possible, ensuring the provision of qualified ores of different grades. But it is necessary to set up a smooth channel with steps for the excavator to move up and down frequently, reducing the effective working time.

      Determination of excavator production capacity and quantity

The production capacity of excavators refers to the actual volume or tonnage of ore and rock loaded into transport containers from the working face within a certain calculation unit of time. There are generally two methods for determining production capacity: comparative method and analytical calculation method.

A   Comparison method

The comparative method is often used in formulating mining stripping plans and designing new mines.

For mines in production, when formulating a mining and stripping plan, the excavator production capacity can be determined based on the actual statistical excavator production capacity of the mine in recent years, combined with comparative analysis of specific production conditions, and considering the indicators that may be achieved after taking measures.

For newly built mines, theoretical calculations should generally be conducted first, and then the production capacity of excavators from other mines with similar conditions should be selected. Due to the fact that the natural conditions of each mine cannot be exactly the same, when selecting other mine indicators, attention should be paid to analyzing the specific situation, such as slope open-pit, deep pit open-pit, transportation mode, ore and rock properties, equipment maintenance, driver operation technology level, production organization and management level, etc.

B   Analytical calculation method

a   Technical production capacity

Technical production capacity refers to the production capacity that can be achieved by excavators during uninterrupted mining and loading under specific mining technical conditions (such as working face size, rock properties, loading conditions, etc.). After considering the degree of bucket filling, the coefficient of rock loosening, and the working cycle time, the production capacity of continuous work is the maximum production capacity that can be achieved after taking measures.

Technical production capacity Qj (m³/h)=3600 * excavator bucket volume E * real square full bucket coefficient K÷ Excavator cycle time t (s)

Among them, the full bucket coefficient K of the real ore is equal to the volume V÷ of the real ore rock; (Total number of buckets N * bucket volume E)

b   Work productivity

The work production capacity takes into account the impact of various aspects such as blasting, transportation, and equipment maintenance in actual mining work, that is, the time utilization coefficient is considered.

Excavator single shift production capacity Qb (m³/set·); Class)

=Technical production capacity Qj * shift working time T * shovel loading working time as a percentage of shift workη

  The number of excavators required for the mine N=annual stripping volume A÷ Annual efficiency of excavator platform Qa

The number of excavators equipped for open-pit mining production does not consider the spare quantity. If the working system, equipment model, and production efficiency of mining and stripping operations are different, the number of excavators required for mining and stripping operations can be calculated separately. In addition, if there are other projects in the mine, such as road construction, road consolidation, slope and dumping, it is also possible to consider equipping loaders, graders, bulldozers, etc.

      Ways to increase the production potential of excavators

The total capacity of excavators in the entire mine is the total amount of mining stripping, therefore, the production capacity of excavators is an important technical and economic indicator. Fully utilizing the capabilities of excavators is directly related to ensuring or exceeding the stripping volume of the mining plan.

There are many factors that affect the production capacity of excavators. This article mainly discusses the technical influencing factors and ways to improve the capacity of excavators after selection.

A   Shorten the loading cycle time

The time required for one operation cycle of an excavator is the sum of the four steps of excavation loading t1, full bucket rotation t2, unloading t3, and empty bucket rotation t4 to the working face. Namely:

Loading cycle time T=excavation loading t1+full bucket rotation t2+unloading t3+empty bucket rotation t4

The working cycle time is related to the properties of the ore and rock being shoveled, the quality of the ore and rock being blasted and crushed, the parking position of the vehicle, the rotation angle of the loading, and the operator's technical level. Among them, increasing the rotation speed and reducing the rotation time are of great significance in shortening the working cycle time. Drivers can reduce shoveling resistance by adopting a reasonable shoveling sequence, that is, from outside to inside and from bottom to top. In addition, drivers can use waiting time to clean the working face and dump the ore and rock near the parking position of the car, so that the rotation angle of the excavator is not greater than 90 degrees; It can also effectively shorten the work cycle time.

B   Improve the digging full bucket coefficient K

The excavation coefficient is calculated through the full bucket coefficient and the loose bucket coefficient. The full bucket coefficient is the ratio of the volume of loose ore and rock excavated into the bucket to the bucket capacity, which is related to the properties of the ore and rock, blasting fragmentation, and operational techniques, with the most important being blasting fragmentation. When the explosive pile is scattered and there are many large blocks and foundations, the working cycle time of the excavator increases and the full bucket coefficient decreases.

Reducing the large block rate mainly involves two aspects: improving the quality of blasting and selecting large-sized digging buckets. By adjusting blasting parameters, selecting a reasonable charge structure, adopting multi row hole micro difference blasting, and appropriately increasing explosive consumption, measures are taken to reduce unqualified large blocks and foundations, making the shape and size of the explosive pile after blasting conducive to safe and efficient operation of excavators.
C   Improve the utilization coefficient of class working timeη

D   Timely supply empty vehicles to the work area

A smart vehicle scheduling system can be adopted to organize and allocate transportation routes reasonably, improve vehicle replacement conditions, and reduce the time for excavators and other vehicles.

      Transportation work

Open pit mining transportation is one of the main production processes in mining technology, which involves transporting extracted ore out of the mining area and to designated unloading points, transporting stripped materials to the waste dump, and delivering production personnel, equipment, and materials to the work site. The investment in transportation system accounts for about 40% to 60% of the total investment in the mine, and the transportation cost accounts for about 30% to 40% of the ore cost. Therefore, the transportation mode and system rationality of open-pit mines directly affect the economic benefits of open-pit mining production.

Due to space limitations, this article only discusses the calculation of transportation capacity and vehicle selection using dump truck transportation.

      Calculation of transportation capacity

The main factors affecting the production capacity of car shifts are load capacity, transportation cycle, and shift working time.

Vehicle shift production capacity A (tons/shift)=60 * Vehicle load capacity q (tons) * Shift working time T (hours) * Vehicle load coefficient K1 * Vehicle working utilization time coefficientη ÷ Automobile transportation cycle t (minutes)

Number of registered cars N=coefficient of uneven transportation of cars K2 * mining production Qb÷ (Automobile production capacity A * output rate K3)

      Ways to improve vehicle efficiency

A   Improve road conditions

According to statistics, increasing the speed by 1km/h can improve vehicle efficiency by about 4% to 8%.

B   Strengthen production management, reduce auxiliary and non operational time

According to statistics, under normal circumstances, the time required for shift handover and personal necessities is 8% to 10%, about 3% for travel between warehouses and mines, 3% to 5% for car refueling, and 82% to 86% for work time.

To reduce the idle time and non operational time of production vehicles, gas stations should be located at locations where mining and rock transport vehicles pass back and forth; The temporary inspection and maintenance site should be close to the transportation trunk line of the mining site; In the cold northern regions, maintenance vehicles (first maintenance, temporary inspection) should have maintenance warehouses. Regular maintenance and repair of automobiles should be strengthened to improve the vehicle's integrity rate.

C   Strengthen cooperation with shovel loading equipment and improve vehicle supply conditions

D   Strengthen automobile dispatch

      Car selection

After determining the tonnage of the car, it is necessary to choose a specific vehicle model. There are many factors that affect the selection of dump trucks for open-pit mines, among which the most important are the annual transportation volume, distance, road technical conditions, and bucket capacity specifications of the loading equipment.

When choosing a car model, consideration should be given to the quality of the vehicle, reliable operation, reasonable structure, advanced technology, stable quality, low energy consumption, and the suitability of the cabin strength for the impact of large ores. When there are multiple vehicle models to choose from, a technical and economic comparison should be made to recommend the optimal model. For the same open-pit mine, the same model of vehicle should be selected as much as possible. In terms of cost, not only should the purchase price of the new car be considered, but also the operating costs, warranty costs, spare parts prices, and supply of spare parts after production.

For mines with large annual transportation capacity and short transportation distance, it is generally recommended to choose heavy-duty vehicles with an annual transportation capacity of 80 million to 100 million tons. Using vehicles with a load capacity of 150 tons can basically complete the task; On the contrary, vehicles with lower load capacity should be chosen, while larger models must be equipped with larger loading and unloading equipment, increasing excessive investment.

      Selection of new energy vehicle models

The mine has sufficient power supply, and most of it is used for heavy-duty downhill transportation. It is recommended to consider using wide body dump trucks for charging mines.

There is natural gas supply near the mining area, and natural gas extended range mining wide body dump trucks can be considered.

      The application prospects of unmanned mining wide body dump trucks

In accordance with the overall design requirements in the Guidelines for the Construction of Intelligent Mines in the Nonferrous Metal Industry (for trial implementation) issued by the Ministry of Industry and Information Technology, mines are encouraged to adopt cloud, edge and end architecture based on the industrial Internet platform, and establish a platform oriented“ Ore flow; The full process intelligent production control system will gradually promote the construction of intelligent mines in enterprises, and ultimately achieve unmanned production with fewer people throughout the entire mining process.

For existing mines, digitize and intelligentize equipment, carry out complete sets of intelligent equipment applications, achieve intelligent diagnosis of equipment faults, optimization of process parameters, optimization of production processes, optimization of digital simulations, and optimization of business decisions; At the same time, we will carry out the construction of intelligent production systems in mines to achieve digitalization of resources, intelligent control of production processes, and integration of safety management.