How does the Front End Loader Work in Open-pit Mines?

Front end loader is the loading equipment which is used to shovel and unload the material with the bucket in the front of the tire or crawler type self-propelled body. Because most of them walk on tires, they are generally called wheel loaders. In large open pit mines, the front end loader can be used with the excavator to pile up blasted ore, clean up the working face and complete the loading operation which is difficult for the excavator at the end of benches. In small and medium mines, front end loaders are often used as combined mining, loading, and transportation equipment.

This article will take you to understand how the front end loader works as mining and loading equipment, loading and transportation equipment and auxiliary equipment.

When the front end loader is used as the main mining and loading equipment in the open pit mine, its efficiency depends on the layout of the front end loader and the automobile and the dimension of the stope working face.

(1) Front End Loader and Automobile Layout

① Front end loader is inclined to the automobile. As shown in Figure 1(a), the automobile and the working surface are at an angle of 30°-45°, and the front end loader and the automobile cross each other obliquely. The front end loader must be turned when moving towards and unloading to the car. This layout scheme is widely used in open-pit mines in various countries.

② Front end loader is at right angles to the automobile. As shown in Figure 1(b), make the automobile to be loaded move in and out parallel to the front of the working surface. This scheme has a longer cycle time. It is mainly suitable for tire type front end loader or crawler type front end loader with rigid frame structure, and working places where the working surface is narrow or the front end loader cannot be turned.

③ Front end loader is parallel to the automobile. As shown in Figure 1 (c), the shoveling direction of the front end loader is parallel to the driving direction of the automobile, and the automobile can be arranged on the main line. This scheme increases the running distance of the pre-installation working process, but it prevents the automobile from running on a bad working surface. Some mines (clay mines) have poor working face conditions and are difficult to drive, so this scheme is often adopted.

(Figure 1. Front End Loader and Automobile Layout)

(2) Stope Working Bench Dimension

After the specification of the front end loader is determined, it is necessary to make the dimension of stope working bench adapt to the equipment. According to information, in open-pit mines, if the bench height is between 2-20m, the front end loader can be used. The most widely used mine bench height is 8-15m.

When the front end loader with a bucket capacity of 3m3 is loaded into a 10t class car, the width of the working bench is generally 25-28m. When the front end loader with a bucket capacity of 5m3 is loaded on a 25t class car, the width of the working bench should be 30-50m. If the front end loader is matched with mobile crusher and belt conveyor, the width of the working surface should be determined according to the layout and the minimum turning radius of the front end loader.

When the front end loader is used as loading and transportation equipment, the main factors affecting its production efficiency are the haul distance and slope. The haul distance and slope parameters should be determined by comprehensive consideration of the mine production site and actual conditions.

(1) Reasonable Haul Distance

When using front end loaders instead of excavators to work with vehicles, the data varies greatly due to different factors used in determining the haul distance in different mines in different countries. For example, the reasonable haul distance of a limestone mine in Japan is recommended to be 100-150m. The Russian mine believes that the reasonable transport distance of the front end loader is related to the mine output, the load capacity of the front end loader and road conditions. When the mine's annual output is 300,000-500,000 tons, the reasonable haul distance determined by the Russian mine is 100-300m. Some companies in the United States believe that this haul distance is reasonable (100 -300m) only when the working cycle time of the front end loaderis not more than 3 minutes.

(2) Transport Scheme

When the front end loader is used as the loading and transportation equipment, it can be directly unloaded to the chute, the receiving hopper of the mobile crusher and other transfer equipment. The layout plan should be within a reasonable range of haul distance. The specific layout of the working face is shown in Figure 2.

(Figure 2. Front End Loader Transport Scheme)

Because of the multiple functions of the front end loader, it has also been widely used in the auxiliary operations of modern large-scale open-pit mines. For example, it is used to clean up the accumulation of blasting rock, carry unqualified large rocks in the working face and funnel, build and maintain roads, transfer stripped rocks, level mining sites and dumps, transport oil and spare parts to open-air equipment, etc. In addition, it can also be used for trenching engineering operations.

The working face layout scheme for the auxiliary work of the front end loader should be determined according to the specific conditions of the site. When the front end loader is used to dig the ditch, the slope of the ditch should be less than 20%, and the width of the ditch can be reduced to 6m (the width of the excavator and the car is generally 18-19m). If the trench is very deep, it can be excavated in layers. Generally, the thickness of each layer is 3-6m.

It can be seen from the above that whether the front end loader is used as the main equipment or as auxiliary equipment, it can not only complete the loading and transportation operation alone, but also work with the automobile. Because the front end loader has many advantages such as flexibility, light weight, convenient operation and low cost, it may gradually replace the excavator as the main mining equipment in small and medium mines.

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