How To Improve The Quality Of Machine Sand

In the past two years, with the increasing efforts of environmental protection, sand mining in many rivers has been banned. The machined sand made by crushing and then grinding the stone is gradually replacing the natural sand and gravel, and the application of machined sand has also become a global trend. However, in actual production and application, there are also some problems with the quality of the machined sand, such as excessive needle-like content, high fineness modulus, and stone powder content.

The quality of the finished sand and gravel aggregate depends first on the quality of the sand and gravel raw materials, but the processing quality also has a significant impact on the performance of the concrete, and to a certain extent, it affects the amount of cement used in the concrete, so it must be strictly controlled in the production process. control. In particular, the quality of artificial sand and gravel raw materials, weak particle content, mud content, needle-like content, stone powder content, fineness modulus, and water content have a large impact on concrete performance, and it is difficult to control during the production of sand and gravel. As far as possible to prevent the occurrence of various quality problems, improve the quality of the final product of sand aggregate to ensure the quality of concrete. This article shares several elements of quality control in artificial sand and gravel production.

Quality Control of Raw Materials

Before mining wool, it is necessary to remove the covering layer on the top of the stockyard, and ensure that the surface of the mining layer is free of grass roots and covering soil. When cleaning the cover, try to ensure that it is completed in one go, and leave a certain width of the protective area to avoid the vibration generated during the mining of the wool from causing the boundary soil to slip off and mix into the wool again. In view of the varying depths of mudstone burial and high groundwater levels, it is necessary to excavate drainage channels before mining to reduce groundwater levels. During mining, mining should be performed in order from low to high. For the cover layer, the stripping boundary should be ensured. The width is more than 0.8m than the planned mining area. The mining depth must be strictly controlled to ensure that the thickness of the reserved layer is> 0.2m.

Control of Weak Particle Content

The content of weak particles should not exceed 15% for general and internal concrete, and should not exceed 5% for external and wear-resistant concrete. Excessive weak particles have a significant impact on the strength, abrasion resistance and durability of concrete. Due to the complex processing of the weak particles and the high cost, manual control is usually adopted at the source of the source, mainly by visual analysis and judgment. In general engineering, the lower part of the weak weathering zone is used as the boundary between the useless layer and the useful layer of the stockyard, and the useless layer of the stockyard is used as the waste. In addition, the quarry construction shall be organized reasonably, and the mining procedure of stripping the useless layer first and then mining the useful rocks is adopted to achieve the purpose of reducing the content of weak particles. For rocks with weak and weak weathering layers, multi-dissolved ditch, and multi-dissolved caves, they are first discerned by the naked eye and discarded beforehand. There is also a method of high-pressure water washing to make the content of weak particles meet the quality requirements of sand and gravel.

Control of mud content

The artificial sand and stone production process generally does not produce mud, mainly for controlling the mud content of sand and stone. The control of the mud content of the finished sand and gravel is divided into source control, system processing technology control and production organization measures.

The source control process is mainly to reasonably organize the construction of the stock yard, strictly distinguish the boundary between weak weathering and strong weathering, and use strong weathering materials as waste.

System processing process control program: In dry production, the trace amount of mud in the coarsely crushed rock is separated and processed, and 0-200mm particles are sieved. In wet production, a multi-stage washing machine is generally designed and special cleaning equipment is set up for processing. That is, all 0-40mm rocks are put into a mud washer. In order to remove mud blocks, a washing and dewatering process is specially set to carry out the finished coarse aggregate. Cleaning, effectively ensuring that the mud content of the aggregate reaches the standard.

Production organization measures mainly prohibit irrelevant equipment and personnel from entering the finished material storage yard; the ground of the storage yard should be flat and have appropriate slopes and interception and drainage facilities; for large storage yards, the ground should have clean materials with a particle diameter of 40-150mm The compacted stone cushion is used as the surface protection; the storage time of the finished materials should not be too long, and it should be used in a timely manner as possible. If there is no secondary screening facility in the system and the coarse aggregate pollution is more serious, it should also be used. Flushing and dewatering facilities should be set up before entering the mixing building (station).

Quality control of needle-like content

The quality control measures for the needle-like content of artificial coarse aggregate mainly through the selection of equipment, followed by adjusting the block size of the feed in the production process.Due to the different mineral composition, structure and structure of various rocks, the grain shape and gradation of the rocks after breaking are also different. The hard-grained quartz sandstone and various intrusive igneous rocks have the worst grain shape, with a large needle-like content, while the medium-hardness limestone and dolomite limestone have a small needle-like content. A large number of tests have proved that different crushers produce different pin-shaped content effects. The jaw crusher has a slightly higher needle-like content than the coarse aggregate produced by the rotary and cone crushers, while the needle-like content of the coarse aggregate produced by the impact type, especially the mash crusher, is significantly reduced.

The content of coarsely broken needle flakes is larger than that of medium crushed, and the content of medium broken needle flakes is greater than fine crushed. It indicates that the larger the crushing ratio, the larger the pin-like content. In order to improve the aggregate shape, the block size before coarse crushing should be minimized in the production process, and the small and medium crushed small stones and sand are used as much as possible. , Using finely divided small and medium stones as the finished product of coarse aggregate, this can also strictly control the needle-like content.

Quality Control of Stone Powder Content

The content of artificial sand stone powder refers to the content of particles less than 0.16mm in artificial sand. The particles less than 0.08mm in artificial sand stone powder can be regarded as an inert admixture. The appropriate stone powder content can improve the workability of concrete and increase the density of concrete. It is beneficial to improve the performance of concrete.

The content of stone powder in artificial sand in the dry sand making process is generally high, which can meet the requirements of quality standards. There are also cases where the stone powder content is greater than the standard. At this time, some wet production should be considered, part of the stone powder is washed away or the fan and vacuum equipment is selected to suck out part of the stone powder to meet the standard requirements.

The content of stone powder in artificial sand is generally low in the wet sand making process, and most projects require the recovery of some stone powder to meet the needs of the project. There are two main types of stone powder recovery in artificial sand for hydropower projects: mechanical recovery and manual recovery. In the production of large-scale artificial sand and stone or in a project with a narrow site, it is necessary to design a stone powder recovery workshop (or fine sand recovery workshop) in the process. Pool for recycling. In small-scale artificial sand and stone production or in projects with spacious sites, manual recycling is also used to control the content of stone powder in artificial sand. That is, the overflow water discharged from the sand washer during the production process is naturally stored and dewatered. Sand can be added using a loader in conjunction with dump truck transportation. In order to effectively control the stone powder content, the following measures are often taken:

  • 1. Through continuous testing, the amount of stone powder added can be effectively controlled.
  • 2. A vibrator is attached to the bucket wall of the stone powder adding bucket, and a spiral classifier is installed under the bucket, and the screw classifier is evenly added to the finished sand man silo tape machine to uniformly mix the stone powder.
  • 3. The wastewater treatment workshop should be as close as possible to the finished sand belt machine, which can be smoothly transferred by the belt machine. The dry stone powder cake dried by the filter press is processed into a loose powder by a double roll crusher to prevent the stone powder from forming agglomerates.
  • 4. A stone powder storage yard should be considered in the general construction layout. The storage yard can adjust the amount of addition and reduce the water content through natural dehydration, and to a certain extent, adjust the water content of the finished sand.

Quality Control of Fineness Modulus

The finished sand should meet the requirements of hard texture, cleanness and good gradation. For example, the fineness modulus of concrete sand should be in the range of 2.7-3.2. The general control is within the range of 2.8 ± 0.1, and the sand fineness modulus of dry-mixed mortar can be controlled within the range of 2.3 ± 0.1. More production experience usually adopts the following technical measures to control and adjust the fineness modulus of the finished sand:

  • 1. Screening equipment Select large manufacturers to produce products with stable quality and performance to ensure effective screening and classification;
  • 2. The sand making equipment selects vertical shaft impact crusher and screening machine to form closed-loop production mechanism sand. In the hydropower industry, it was supplemented by rod mills to adjust the fineness modulus of the mechanism sand.
  • 3. Reduce the fineness modulus of the finished sand by reducing the feed amount, feed particle size and steel rod installation amount of the rod mill, or reduce the feed amount or particle size of the vertical shaft impact crusher, Fineness modulus of small finished sand;
  • 4. Adopt the combined sand making technology of vertical shaft impact crusher and rod mill and correctly set the operating parameters of each vertical shaft impact crusher rotor, such as line speed, to control the fine particles of finished sand, increase the content of intermediate grade particles, adjust Finished sand grading;
  • 5. When finished sand is stacked, try to slow down the slope of the stockpile to avoid gradation changes due to segregation.

Quality Control of Moisture Content

In order to reduce the moisture content to within the specified range and to be stable, large-scale projects currently adopt mechanical dehydration methods, while small and medium-sized projects mainly use natural dehydration. In addition, it is necessary to strictly abide by the operating rules during production, and reasonable transformation and storage of the silt storage can also effectively control the moisture content of artificial sand.

The following measures are generally taken:

  • 1. In the general system process, firstly, most of the water in the sand should be mechanically removed. At present, the most commonly used is the vibrating screen dewatering process. The sand after dewatering by the linear dewatering screen can remove the sand with the original water content of 20% -23% to 14% -17%. There is also a vacuum with a correspondingly large investment cost. Dehydration and centrifugation.
  • 2. If artificial sand is unloaded, stockpiled dewatered, and artificial sand reclaimed separately, generally 3-5 days after storage and dewatering, the moisture content can be reduced to less than 6% and stable.
  • 3. The dry artificial sand and the artificial sand of the dewatering screen are mixed into the finished product silo, which can reduce the water content of the sand.
  • 4. Set up a rainproof shed on the top of the finished sand silo, pour a concrete floor on the bottom of the sand silo, and set up blind ditch drainage facilities. The blind ditch will be cleaned once after each bin is put in place to speed up the natural dehydration time and also effectively reduce the water content of the finished sand.

Machine sand processing can use high-performance crushing processing equipment, which has a large crushing ratio, high processing capacity, and good product shape. On the other hand, it can use equipment to improve screening efficiency, improve the quality of finished materials, and protect the environment to improve work efficiency , Not only to achieve the purpose of improving the quality of finished products, but also to reduce production costs.

Relate Project

* Standardized Design Of Artificial Sand Production Line

* Difference Between Natural Sand And Artificial Sand

* Dry Sand Production And Processing Technology

* Factors Of Low Sand Production Of Sand Making Machine

* Improve the Performance of Sand Making Machine

* Application Of Large Sand Making Machine

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