Coal is the most important mineral resource in the world. According to the estimation of international energy experts, the recoverable reserves of coal in the world are about 687.5 billion tons of standard coal.
The development and utilization of coal resources is an important material basis for developing the national economy and ensuring people’s life. In terms of the varieties of coal production in China, anthracite accounts for about 20% of the total output, bituminous coal accounts for about 75%, and lignite accounts for only 5%. Coal has a wide range of uses. It is not only a fuel, but also an important industrial raw material. Hundreds of chemical raw materials can be produced by decomposing, refining and comprehensive utilization of coal by chemical methods; Coal is also an important means of living for urban and rural people. It can be seen that coal is closely related to modern industry, agriculture and people’s life. Therefore, to do a good job in coal management, we must first understand the basic knowledge of coal.
The formation of coal is the remains of ancient organic matter (mainly plants) formed through biological and chemical metamorphism. It can be roughly divided into two stages. The first stage is peat stage, that is, from plant to peat stage. When the plants die, they accumulate in the swamp full of water. At first, due to the existence of water, there is insufficient oxygen. Later, they are isolated from the air under the water surface. Under the action of bacteria, until all parts of the plants continue to decompose and interact, and finally the remains of the plants turn into brown or dark brown sludge material, which is peat. This process is called Peating process. This stage requires a long period of geological history and millions of years.
In the second stage, peat is transformed into lignite, lignite is transformed into bituminous coal, and bituminous coal is transformed into anthracite. When the peat layer is formed. Water often scours the low-lying areas of the continent, bringing a large number of mud, sand and stones, and gradually forms rock strata (called roof) in the mire layer. Under the pressure of the roof rock layer, the peat layer buried under the roof has undergone a series of changes, such as compaction, water loss, colloidal aging, hardening and so on. At the same time, its chemical composition has also changed slowly, gradually turning into dark brown lignite with large specific gravity and dense density. When the roof is gradually thickened, the static pressure of the roof is gradually increased, and the temperature in the coal seam is also gradually increased, the coal quality changes, and gradually changes from diagenesis to metamorphism dominated by temperature. In this way, lignite gradually becomes bituminous coal and anthracite. If there is a higher temperature, it may eventually become graphite.
Transmission drum
It is the main component that transmits traction to the conveyor belt. The belt conveyor operates by the friction between the belt tensioned around the drum and the drum. Therefore, there must be enough adhesion between the conveyor belt and the drum surface to transfer the traction force to the conveyor belt, otherwise the belt will slip on the transmission drum when the conveyor is running.
1.To prevent the roller from slipping between the belts, the following conditions must be met:
- Increase the wrap angle X of the conveyor belt on the transmission drum. Due to the layout limitation of the belt conveyor, the change direction drum or compression drum can be set to increase the wrap angle, and the wrap angle is required to be 200 ° – 240 °.
- Increase the friction coefficient between the belt and the drum. The friction coefficient of the smooth roller is 0.2-0.25, and the friction coefficient of the rubber roller is 0.25-0.4. In order to increase the friction coefficient, wrap or cast rubber on the surface of the roller.
(3) The belt core needs a certain initial tension to compress the belt on the drum, which is met by the tensioning device.
-
Drum classification:
(1) According to the drum shape, it can be divided into two types: cylindrical and round drum. The drum drum can make the belt run in the center.
(2) According to the classification of drum surface, it is divided into smooth surface and rubber surface. In the case of low power and low ambient temperature, smooth roller can be adopted. When the power is large, the environment is humid and easy to slip, the rubber roller is used.
(3) the rubber surface roller is divided into rubber wrapping and rubber casting. The rubber of the rubber wrapping roller is easy to separate, and the screw head is exposed to scratch the conveyor belt. The advantage is that the rubber surface can be replaced by itself. The rubber casting roller is thick and wear-resistant, with long service life. The disadvantage is that the price is high, and the user cannot cast new rubber by itself.
(4) Herringbone groove rubber surface roller: it is formed by pasting the pre-vulcanized herringbone groove rubber plate on the roller surface with adhesive. It has high friction coefficient, so it can reduce the tension of the tape and prolong the service life of the tape. Because the groove can cut off the water film, it can also obtain good driving performance in particularly humid places. Disadvantages: it can only run in one direction. During installation and operation, the herringbone tip shall be consistent with the running direction of the tape, so as to facilitate the discharge of dirt in the groove. For reversible belt conveyor, prismatic groove rubber surface drive drum shall be adopted.
