What about the high content of stone powder in dry-type machine-made sand? After years of experience, Fodamon engineers have summarized six practical stone powder control methods.
There are four forms of stone powder in manufactured sand:
(1) Free powder: stone powder particles do not bond with each other and are not adsorbed on the sand surface, and can move freely under the action of wind and gravity.
(2) Agglomerate powder: the stone powder particles are tightly agglomerated to form stone powder agglomerates with large particle size, and the particles adhere to and polymerize with each other. This kind of stone powder polymer is difficult to remove by traditional powder separation equipment due to its large particle size and quality.
(3) Attached powder: there are stone powder particles attached to the surface of sand particles with larger particle size. When the surface of sand particles is smooth, stone powder particles are easy to be removed under mechanical force. When the surface of sand particles is uneven, stone powder particles and sand particles adhere to each other tightly, which is difficult to be separated by general mechanical methods.
(4) Crevice powder: there are often some natural or hundreds of micron wide crevices on the sand surface due to mechanical crushing. These crevices are often filled with a large number of stone powder particles. This is one of the most compact methods of stone powder adhesion.
6 kinds of stone powder control technologies and equipment are as follows:
- Feeding vibrating grate screen
The increase of argillaceous content in manufactured sand will increase the water demand, affect the strength of concrete, and thus have a certain impact on its compressive capacity. Therefore, before the raw material enters the sand making process, it is necessary to remove the sludge screen waste and treat it as waste material, which can significantly reduce the moisture content of the raw material at the same time.
According to different material conditions, select the appropriate screen spacing to achieve different desilting effects; Under the condition that the mountain is thick, the vegetation is difficult to be removed, the mountain is seriously weathered, the clay content in the interlayer is large, and it is easy to mix with the soil, increasing the spacing between the sieve strips can effectively reduce the silt content.
- Aggregate chute powder removing device
After screening, the aggregate of a certain specification of the screening machine enters the aggregate unloading chute. An overall removable diffusion air distribution chamber is arranged at a suitable place, and the blower is connected with it. In this way, when the free dust on the aggregate surface passes through the chute, it is blown up by the blower, and then collected into the dust collector under the suction of the dust collector.
In addition, the suction air volume of the dust collector can be controlled by adjusting the pipe regulating valve. Under the condition that the blower is in the form of frequency conversion, the ratio of blowing and suction can be adjusted through the frequency conversion control of the blower and the adjustment of the regulating valve, so as to realize the continuous control of the powder content of the finished sand and gravel aggregate within a certain range.
- High frequency vibration screening pretreatment
Basic principle: the machine-made sand is pretreated by high-frequency vibration for powder dispersion, powder sand separation and coarse and fine classification, and then the stone powder is removed by wind.
Specific method: after the materials are crushed by the sand making machine, when entering the screening module, they can be dispersed through the disperser or the screw rod, which has a preliminary dispersion effect on the agglomerated and adhered stone powder and improves the uniformity of material distribution. At this time, the stone powder can be preliminarily selected through the air separation device. After the primary selection, the materials enter the high-frequency vibrating screen with vibration frequency of 60-80hz and amplitude of 0.15-2.4mm for screening. The vibration intensity of this equipment is 3.5-5 times that of ordinary equipment, which can produce large mechanical force, and has a good dispersion and separation effect on agglomerated stone powder and surface adhesive stone powder. At the same time, the coarse and fine classification of machine-made sand can be realized efficiently.
Compared with ordinary vibrating screen, the powder removal efficiency of machine-made sand after screening by high-frequency vibrating screen is significantly increased by about 40%, and the required air volume is reduced by 45%.
- Centrifugal separator
A powder concentrator is used in the sand making process. Its main function is to separate the excess stone powder and useful particles and recycle them respectively.
Its working principle is: the gas and powder are mixed to form a gas-solid two-phase flow. The rotating distributor and high-speed air flow make the powder containing air flow obtain centrifugal force during rotation. The centrifugal force obtained by different particle sizes is different, so as to realize the separation of coarse and fine powder particles. At the same time, the coarse and fine powders were recovered by corresponding methods. The useful particles are the finished sand, and the useless fine powder is the waste material.
From the installation position of the powder concentrator in the building station, it can be divided into raw material powder concentrator and finished material powder concentrator process layout. The separator has strict requirements on moisture content. When the feed moisture content is higher than 5%, the powder removal efficiency of the separator will be seriously reduced. When the feed water content is 2%, the powder concentrator can give full play to its efficiency, and the sand formation rate is between 60%-70%.
- V-type static Classifier + dynamic high-efficiency powder concentrator
The raw materials enter the sand making machine, after vibration screening, the coarse powder is returned to the sand making machine, and the fine powder is sent to the combined classifier of V-type static Classifier + dynamic high-efficiency powder concentrator. After homogenization by the material distributor, it enters the classification system. The coarse particles enter the finished product warehouse. The fine particles and powder enter the dynamic classifier with the air flow. The sand and stone classification is adjusted by adjusting the rotating speed of the dynamic classifier. The qualified products are discharged into the finished product warehouse through the coarse powder pipe. Adjust the particle grading of the finished product. The fine powder will be collected with the gas through the cyclone dust collector and enter the stone powder silo. The air flow will enter the V-shaped air inlet through the circulating fan.
- Air screen
On the basis of vibrating screening, the air screen combines the wind separation technology to realize the three functions of particle size adjustment, classification and screening.
Its working principle: the materials are evenly spread under the action of the air screen dispersion device and blown to different positions in the air separation room by the blower. The lighter the materials (the smaller the particle size), the farther away the positions are blown, and the longer the screening distance is; The lightest stone powder will be blown to the powder outlet, absorbed by the induced draft fan of the dust collector, and finally concentrated in the powder tank. At the same time, the particle size adjustment board automatically adjusts the proportion of returned materials to fine tune the fineness modulus of finished sand, so as to ensure the stability of the fineness modulus of finished sand.
For the dry sand making system using air screen, the moisture content of raw materials shall be controlled below 1.6% (surface moisture content 0.6%), without mud, the feeding particle size shall be 0-25mm and the grading shall be continuous. If the raw materials are changed, the system capacity will change. If the raw materials contain too much mud or stone powder, the separation process such as powder concentrator or powder removal equipment shall be adopted in the front section.