The buried scraper conveyor is widely used in the transportation of various bulk materials in ports, grain depots, oil, flour, alcohol, brewing, feed, chemical industry and other industries. It is a continuous conveying equipment for conveying powder, small particles and small pieces of bulk materials in a closed shell with the help of a moving scraper chain and the characteristics of internal friction and lateral pressure of bulk materials. It can be transported horizontally, obliquely and vertically. During operation, the scraper chain is buried in the materials, so it is called buried scraper conveyor.
Cognition of conveying principle and characteristics of buried scraper
Bulk materials have the characteristics of internal friction and lateral pressure. During horizontal conveying, the material is pushed by the scraper chain in the moving direction and the gravity of the material itself, resulting in internal friction between the material layers. When the internal friction between the material layers is greater than the external friction between the material and the groove wall, the material will form a continuous whole material flow with the scraper chain and be transported. When the ratio of material layer height to slot width is certain, the material flow is stable. During vertical conveying, it mainly depends on the arching characteristics of the materials. When the materials in the closed machine slot are pushed by the scraper chain in the moving direction, they will produce transverse side pressure. When the internal friction caused by the transverse side pressure and the pushing force on the upper materials caused by the continuous feeding of the lower part are greater than the external friction between the materials and the groove wall and the gravity of the materials themselves, the materials will be transported upward with the scraper chain. Due to the vibration of the scraper chain in motion, the material arch of some materials is damaged, resulting in the lag of materials relative to the scraper chain, so the material speed is lower than the chain speed.
The buried scraper conveyor is mainly composed of closed shell (slot), scraper chain, driving device, tensioning device and other components. The utility model has the advantages of simple structure, small volume, good tightness and convenient installation and maintenance; The process layout is flexible, which can be transported horizontally, obliquely or vertically, and can be fed or unloaded at multiple points; Because the shell is closed, it has outstanding advantages in improving working conditions and preventing environmental pollution when transporting materials that are easy to raise dust, toxic, flammable, explosive and high temperature.
2. Type selection, basic design and calculation
2.1. First of all, we should understand the basic characteristics of the transported materials and confirm the feasibility of using the buried scraper conveyor to transport materials.
The buried scraper conveyor has a great relationship with the performance of materials, and generally has the following requirements for the transported materials:
① Material bulk density ρ< 1.8t/m3, recommended for vertical transportation ρ< 1.0t/m3。
② The cohesiveness of materials requires that they can still be loose after being kneaded into a ball by hand.
③ See Table 1 for material particle size requirements.
Table 1 applicable material particle size
Conveying method fragile material non fragile material
Suitable particle size maximum particle size (≤ 10%) suitable particle size maximum particle size (≤ 10%)
Horizontal conveying < B / 20 < B / 10 < B / 40 < B / 20
Vertical conveying < B / 30 < B / 15 < B / 60 < B / 30
Note: B in the table is the effective width of the slot, mm.
④ The applicable temperature of the general model shall be less than 100 ℃. For the special materials with high temperature, toxicity and explosion, high grinding and polishing, strong corrosivity, too large block, too large compressibility, high viscosity, extremely strong fluidity, especially hard and fragile to avoid being broken during transportation, the corresponding special model shall not be selected or adopted.
⑤ Buried scraper conveyor is widely used. There are nearly 1000 kinds of materials that can be transported, such as wheat, soybean, corn, rapeseed, rice, bran, starch, grain powder, malt, grain shell, wood chip, sawdust, cement, clay powder, yellow sand, quartz sand, crushed coal, pulverized coal, carbon black, etc.
2.2. Selection of layout form of buried scraper conveyor
According to the position of the feed inlet and discharge outlet, select a reasonable layout form of the buried scraper conveyor, determine the length and inclination of the buried scraper conveyor, and meet the restrictions and requirements of the length of a single equipment in different layout forms.
2.3. Determination of main technical parameters (including slot width, bearing slot height, scraper chain speed and installation inclination, etc.)
Calculate and select the type according to the output requirements, and determine the specific model width, the height of the bearing machine slot and the speed of the scraper chain.
Calculation formula: Q0 = 3600 * b * h* ν*η
Q0 -- calculated conveying capacity, m3 / h;
B - slot width, m;
H -- height of bearing machine slot, m;
ν—— Speed of scraper chain, M / S;
η—— Conveying efficiency,%;
At the same time, the calculated Q0 value is required to meet Q0 ≥ Qmax
Where Qmax - Maximum conveying capacity required for use, m3 / h;
① The slot width and the height of the bearing slot are selected in combination with the particle size characteristics and output requirements of materials.
② The operating speed of scraper chain shall be selected according to material characteristics, conveying principle, structural characteristics, power consumption, service life and process requirements. Generally, the speed of scraper chain is between 0.08-1.00 M / s. For materials with high suspension and abrasion (such as phosphorite powder, cement, quartz sand, etc.) and materials with certain requirements on crushing rate (such as rice, granulated urea, etc.), it is recommended to select a lower operation speed; For cereals (such as wheat, corn, soybean, etc.) and light materials (such as wood chips, bamboo chips, sawdust, etc.), it is recommended to select a higher running speed; For other materials, the running speed of scraper chain is generally selected between 0.2-0.25 M / s.
③ The selection of conveying efficiency is mainly related to material characteristics, but the influence of scraper chain speed, scraper chain type, slot size and service conditions, inclination coefficient and other factors should also be considered.
2.4. Selection of conveyor chain and scraper
According to the requirements of conveying length and output, select the appropriate scraper chain to calculate the tension, check the allowable load of the chain, select the appropriate pitch, the structural form of the chain, the width and thickness of the chain plate, and calculate the length of the scraper chain. Scraper chain is the main working part of buried scraper conveyor. The conveying effect of materials has a great relationship with its type. It is the bearing component of buried scraper conveyor. The selection of chain is mainly based on the maximum tension of the conveying chain, and the performance of materials should also be considered. For example, roller chain should not be used for dusty materials, while roller chain should be preferred for materials prone to floating chain. The selection of scraper type is mainly based on the performance of materials, but also limited by the structure of the conveyor itself. For conveying general materials, the type with simple structure can be selected; For conveying materials with high adhesion, the type with simple structure should also be selected to reduce the adhesion of materials on the scraper and facilitate unloading and cleaning; For materials with high suspension and fluidity, the scraper type with complex structure shall be selected; When transporting materials with high density and large slot width, the scraper type with diagonal bracing shall be selected to ensure the strength and rigidity of the scraper; When transporting grain, in order to reduce its crushing rate, improve the wear resistance of the scraper, reduce quality and reduce noise, the scraper made of engineering plastics can be used; In the horizontal transportation of fine powder or dust materials with high bulk density, high proportion of large particle size and high moisture content, and the conveyor is too long, there will be "jamming", which often makes the scraper chain float above the materials, that is, the phenomenon of "floating chain", which can tilt the scraper in the opposite direction of the chain
70 ° - 80 ° is welded on the chain to produce a vertical component of downward pressure on the movement resistance, so that the scraper chain can run close to the groove bottom and avoid the phenomenon of "floating chain".
2.5. Calculation and selection of driving device and motor power
The calculation and determination of motor power shall be based on the speed of scraper chain, the circumferential force of driving wheel, the transmission efficiency of driving device and the calculated power P0 of motor power reserve coefficient, and the rated power of motor PM ≥ P0.
2.6. The selection and determination of the head, tail, feeding section, middle section, inlet and outlet of the buried scraper conveyor are mainly determined according to the structure of the model, the layout form and position of the site and the actual operability.
3. Design improvement stage
After completing the above basic data design calculation and component selection, the general assembly construction drawing can be drawn, but to make a more rigorous design scheme and drawings, we must determine some specific problems in the actual use of the buried scraper conveyor in order to complete the more ideal design scheme.
3.1. Influence of installation position on Design: for example, the buried scraper conveyor is installed outdoors or indoors. When it is arranged in the open air, rainproof measures shall be taken at the driving device at the head of the buried scraper conveyor to prevent the motor from being affected by moisture, and all interfaces shall be closed to prevent rainwater from penetrating into the trough; If it is placed in the pit, attention shall be paid to the waterproof, drainage and lighting measures of the pit, and an appropriate position shall be reserved for cleaning and maintenance; In combination with the actual installation situation on site, design reasonable installation support, maintenance channel or platform, installation foundation and fixing mode, etc.
3.2. The general design driving device of the buried scraper conveyor is not provided with mechanical safety protection measures, and only the motor overcurrent protection device is used to prevent equipment overload or failure, while the electrical control part is generally designed by the selection unit, so the monitoring and protection devices of the equipment (such as anti blocking sensor, speed monitoring, stall and chain breaking protection device, shaft temperature sensor, etc.) should be considered in the design.
3.3. Purchase and purchase of standard parts and components: ① try to choose commonly used and easy to buy in the market, so as to reduce the purchase cost and the source of goods during replacement; ② Professional manufacturers shall be selected as far as possible to ensure stable product quality and improve the operation life of the equipment.
3.4. Cost awareness: the cost factors of buried scraper conveyor mainly include manufacturing cost and purchased parts cost. At present, the price competition of buried scraper conveyor is very fierce. On the premise of ensuring product quality, it is very important to reduce the cost. An excellent designer must fully consider this in the design.
4. Later stage of design
The theoretical research of buried scraper conveyor has a history of nearly one hundred years. Many people at home and abroad have done a lot of work to make its design more scientific. However, there are still some deficiencies in some aspects, the design and calculation methods are not unified, some important parameters still need to be selected based on experience, and there are still many problems to be solved in use. Therefore, after the success of a new product design scheme, it is very necessary to summarize the work. From the manufacturing of the equipment in the factory to the on-site installation, commissioning, operation and maintenance of the equipment, the designer should practice it, listen to the opinions and suggestions of the manufacturing and installation workers, respect the opinions of the owner and experts, improve the design, and summarize a set of effective design methods and experience. Only in this way can the equipment structure become more reasonable and the performance become more perfect.
