Sand and gravel aggregates are different grades of rock aggregates produced by different types of rock or ore through crushing, sieving and other processing processes. The quality of gravel aggregate directly affects the strength level of concrete, which in turn affects the quality and durability of the entire project, which is related to the safety of engineering construction. Therefore, it is extremely important to ensure the quality of gravel aggregates. So, what determines the quality of aggregates?
On the one hand, the quality of the gravel aggregate is directly related to the equipment and processing technology; on the other hand, it is related to the physical properties of the rock, chemical stability, and the content of harmful substances. This requires sand and aggregate producers to consider various characteristics of rock in addition to high-quality equipment and scientific process technology.
In the production of gravel aggregates, rocks with various characteristics are encountered. Different lithologies have different abrasiveness and crushability for the crusher. It is necessary to select reasonable processing technology and crushing equipment according to the lithology of different rocks to produce high-quality aggregates.
Rock is a naturally produced mineral or glass aggregate with a stable appearance, combined in a certain way. It is the material basis of the crust and upper mantle. According to the genesis, it is divided into magmatic rocks, sedimentary rocks and metamorphic rocks.
Magmatic rock, also known as magmatic rock. The molten material from the inside of the earth is condensed and consolidated under different geological conditions. When the molten slurry is sprayed from the volcanic channel, the rock formed by the surface solidification is called spouted rock or volcanic rock. Common volcanic rocks are basalt, andesite and rhyolite. Rocks formed when lava rises below the surface and condenses at a certain depth in the earth's crust are called intrusive rocks, and are divided into deep diagenesis and shallow diagenesis according to the intrusion site. Granite, gabbro, and diorite are typical deep-seated rocks.
Sedimentary rock: layered rock formed by weathering material, pyroclastic material, organic matter and a small amount of cosmic material through transportation, deposition and diagenesis under normal surface temperature and pressure conditions. According to the origin, it can be divided into clastic rock, clay rock and chemical rock (including biochemical rock). Common sedimentary rocks are sandstone, tuffaceous sandstone, conglomerate, clay rock, shale, limestone, dolomite, siliceous rock, iron rock, phosphorite rock, etc.
Metamorphic rock: Rock formed by metamorphism of the original rock. According to the different types of metamorphism, metamorphic rocks can be divided into 5 categories: dynamic metamorphic rocks, contact metamorphic rocks, regional metamorphic rocks, mixed rocks and metamorphic rocks. Common metamorphic rocks include mylonite, fractured rock, hornstone, slate, phyllite, schist, gneiss, marble, quartzite, mixed rock, etc.
Different rocks have specific physical properties such as specific gravity, porosity, compressive strength and tensile strength, which are all factors that need to be considered in construction projects. The production of sand and gravel aggregates may encounter various types of rocks, whose composition, phase composition, crystalline granularity, density, mineral content and hardness are different, which requires the characteristics of the rock Analysis, and then choose a reasonable crushing process.
3. Crushing equipment
The crushing process is the most important link in the production of gravel aggregates. Therefore, the choice of crusher is particularly important. At present, there are many types of crushers: jaw crusher, hammer crusher, impact crusher, cone crusher, roller crusher, sand making machine and so on. The structure and specifications of various types of crushers are different, and the adapted materials are also different. Therefore, the crushing equipment must be selected according to the characteristics of the material.
Although different types of crushing equipment apply mechanical force to the material to achieve crushing, the method of crushing is different. Such as extrusion crushing, splitting crushing, breaking or bending crushing, impact crushing, etc. Formally because of the different ways of crushing, it makes the applicable materials and the resulting effects different. For example, because the jaw crusher is crushed by crushing, the crushed material has a large amount of flaky particles. The following is a brief introduction to several common crushing equipment:
Jaw crusher: It is composed of fixed jaw plate and movable jaw plate. It uses two jaw plates to squeeze and bend the material to achieve crushing. It is suitable for coarse or medium crushing of various hardness materials. Although this crusher has poor granular shape after crushing and a large amount of needles, it is favored by users because of its simple structure, convenient maintenance and easy replacement of crushing plates.
Hammer crusher: Hammer crusher has the advantages of large crushing ratio, uniform discharge particle size and low energy consumption. However, due to the rapid wear of the hammer head, the application of crushing hard materials is limited; in addition, because the grate is afraid of clogging, it is not suitable for crushing materials with high humidity and clay. This crusher is usually used to crush brittle materials below medium hardness.
Impact crusher: It is a machine that uses the high-speed impact of the hammer and the rebound effect of the impact plate to crush the material by repeated impacts. The machine has a large crushing ratio and can make full use of the high-speed impact energy of the entire rotor. However, because the hammer is very easy to wear, it is also limited in the application of hard material crushing, usually used for coarse, medium or fine crushing of brittle materials below medium hard.
Cone crusher: crusher suitable for medium or fine crushing operations. Due to the improvement of the crushing chamber, the particle shape of the product of the multi-cylinder cone crusher is greatly changed, and the needle shape is also reduced.
Sand making machine: also known as impact crusher, there are generally two kinds of stone stone and stone iron. Among them, the stone-on-stone impact crusher uses stone-on-stone technology to achieve the mutual impact of stone and stone to complete the crushing, effectively protecting the working parts from wear. The vertical shaft impact crusher has a light structure and easy installation; the finished product has stable grain shape and extremely low needle content; the wear is low and the operating cost is low; during the crushing process, an internal circulating air flow is formed in the crushing chamber, and no dust overflow will occur. With large processing capacity and high sand-forming rate, it is an ideal model for artificial sand making and coarse aggregate shaping.
4. The relationship between rock and broken
Sand and gravel aggregates are made from rocks by crushers and other equipment. There are many kinds of rocks. Due to different types and contents of minerals, hardness, size of crystal particles, and density of crystals, their physical and chemical indicators are also different, especially The abrasion of rocks varies greatly. In the selection of crushing equipment, the equipment type should be selected according to the specific rock physical and chemical indicators. The crushability (grinding) of rock mainly depends on its impact strength, and the abrasiveness of rock on equipment mainly depends on its quartz content. For example, the crushability index of granite is lower than that of basalt, and its abrasiveness is much stronger than that of basalt.
Therefore, after the mine is determined, the rock of the mine must be analyzed and tested to detect the crushability (abrasion) and abrasiveness of the rock, so as to select the appropriate crushing equipment and production process. This is of great significance to ensure the quality of gravel aggregates.
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