Calculation method for chain tension of scraper conveyor under coal pile

Abstract

The invention discloses a method for calculating chain tension of a scraper conveyor under a coal pile, which applies rock and soil mechanics knowledge and based on the arching characteristic of coal, that is, after bulk coal particles are piled into the coal pile, stress transfer can occur due to the existence of internal friction force between materials, and the coal pile can be subjected to chain tension calculation. The physical phenomenon that positive pressure borne by the scraper machine buried in the lower center position of a coal pile does not rise all the time along with the height of the coal pile and does not increase after reaching a certain height is avoided, and in combination with experience in actual production, friction resistance generated by coal on side plates and a middle plate of the scraper machine is reduced, so that the positive pressure of the scraper machine is reduced. According to the method, the design is reasonable, calculation is convenient, the blank of the method for calculating the chain tension when the scraper is buried under the coal pile is filled, and the actual production requirement can be met.

Description

Technical Field

[0001] This invention relates to the field of scraper conveyor design technology, specifically a method for calculating the chain tension of a scraper conveyor under a coal pile. Background Technology

[0002] Scraper conveyors are widely used in the transportation and transfer of coal. During operation, due to scraping, truck tipping, or stacker-reclaimer stacking, scraper conveyors often end up buried under coal piles. In this case, the chain tension is completely different from that under continuous material feeding conditions. Since there is currently no method to calculate the chain tension when the scraper conveyor is buried under coal piles, calculations based on existing continuous material feeding methods can lead to insufficient drive power and incorrect chain selection, often resulting in situations where the scraper cannot pull the coal or the chain breaks. Summary of the Invention

[0003] The purpose of this invention is to provide a method for calculating the chain tension of a scraper conveyor when it is buried under a coal pile, based on which the drive power of the scraper conveyor and the chain selection can be further calculated.

[0004] The solution adopted by this invention to solve its technical problem is: a method for calculating the chain tension of a scraper conveyor under a coal pile. Based on the arching characteristics of the soil and rock: the coal transported and transferred by the scraper is in bulk particles. After the coal pile is formed, stress transfer will occur due to the internal friction between the materials. As a result, the normal pressure on the scraper conveyor buried in the center of the coal pile will not increase with the height of the coal pile, but will stop increasing after reaching a certain height.

[0005] The method for calculating the chain tension of a scraper conveyor under a coal pile provided by this invention includes the following steps: ① Draw a schematic diagram and force analysis diagram of the scraper conveyor under the coal pile, such as... Figures 1 to 5 As shown, Figure 1 for Figure 2 A sectional view.

[0006] ② Actual verification shows that the normal pressure exerted on the middle plate of the scraper conveyor by the coal pile is approximately equal to the pressure generated by the coal at a height twice the effective width of the scraper conveyor. The length of the material pile pressing against the scraper conveyor is determined without considering the angle of repose. L, The impact on the calculation results is minimal; the formula is listed below. ···········⑴ In the formula: N 1 The scraper conveyor is subjected to positive pressure from the coal pile. KN; The density of coal, KN / m 3 B1 The effective pressure-bearing width of the scraper conveyor m； L Coal pile length, m。

[0007] ③ The scraper conveyor transports coal by using a chain-driven scraper to push it along the chute. Since static friction is greater than dynamic friction, static friction is sufficient for calculation. Therefore, the maximum static friction generated by the positive pressure of the coal pile that needs to be overcome to move the coal on the scraper plate is: ···········⑵ In the formula, The maximum static friction force that coal must overcome to move on a scraper conveyor. KN µ The static friction coefficient between coal and the scraper conveyor plate, i.e., between coal and steel plate, is dimensionless.

[0008] ④ The scraper conveyor is buried under the coal pile, and its interior will be filled with coal. The coal will exert pressure on the side plates of the scraper conveyor. Furthermore, as described in step ②, the height of the scraper conveyor side plates is [missing information - likely a specific height]. h The coal, under the influence of gravity, will exert a uniformly distributed, downward vertical load on the coal in the scraper conveyor trough, as shown in the schematic diagram. Figure 3 For fill surfaces subjected to continuous uniformly distributed loads according to Rankine's earth pressure theory, the earth pressure calculation type is as follows: The pressure exerted by coal on the scraper conveyor side plate at any depth within the height range of the scraper conveyor side plate is: ······⑶ In the formula: The pressure exerted by coal on the scraper conveyor side plate at any depth within the height range of the side plate. KPa γ The density of coal, KN / m 3 Z Side panel at any depth m Active earth pressure coefficient q The height of the scraper conveyor side plate and above is (2) B 1 - h) refers to the uniformly distributed, downward vertical load exerted by the coal on the coal in the scraper conveyor trough under the action of gravity. KPa.

[0009] ⑤ The pressure exerted by the coal in the scraper conveyor trough on a single side plate of the scraper conveyor per unit length is given by formula (3). σa Integral over the range of scraper conveyor side plate height h ·······⑷ After sorting, ········⑸ In the formula, The single-sided side plate per unit length of the scraper conveyor is subjected to the pressure of the coal in the trough. KN h Effective height of scraper conveyor side plate m。

[0010] ⑥ The maximum static friction force generated between the coal in the scraper conveyor trough and the two side plates of the scraper conveyor during movement and transportation is: ·····⑹ In the formula, L Coal pile length, m.。

[0011] ⑦ When a scraper conveyor buried under a coal pile is working, it does not move the entire coal pile, but rather removes a certain thickness of coal from under the pile. Shear stress exists between the materials. As the coal flow moves with the scraper, the maximum shear stress occurs on the shear surface at the scraper height. However, since the scraper height is generally only about 10cm, calculating the maximum shear stress surface based on the bottom surface of the coal pile (i.e., the middle plate of the scraper conveyor) has little impact on the overall calculation and is more conservative. According to Coulomb's equation, the maximum shear stress experienced by the coal pushed by the scraper is... ···········⑺ In the formula, The maximum shear stress experienced by coal as it is pushed by the scraper. KPa σ b The scraper conveyor is buried under the coal pile, and the compressive stress generated by the coal pressing against the scraper conveyor's middle plate... KPa ψ The internal friction angle of coal, 。

[0012] c The cohesive force of coal, with a value of 0 for coal, is dimensionless. ⑧ The shear force inside the coal that needs to be overcome when the coal is pushed by the scraper is T = B · L · becauseσ b = N 1 / (B · L), Substituting into equation (1) and rearranging, we obtain equation (2). ···········⑻ In the formula, T The shear force inside the coal that needs to be overcome when it is pushed by the scraper. KN.

[0013] ⑨ The scraper conveyor is driven by a chain, which moves the scraper blades to push the coal along the conveyor. The tension on the chain is the sum of all resistances encountered by the coal during its movement, the sum of frictional resistance encountered by the scraper and chain as they slide between the middle and bottom plates of the conveyor, the resistance encountered by the chain as it passes the sprocket, and the sum of the chain preload. Therefore, the tension on the chain is: ·········⑼ In the formula, f z The sum of the frictional resistance experienced by the scraper and chain as they slide between the middle plate and the bottom plate of the scraper conveyor. KN w represents the resistance experienced by the chain as it passes through the sprocket. KN s Chain preload, KN Substituting equation (1) into equation (2), and then substituting it together with equations (6) and (8) into equation (9) and rearranging, we obtain equation (9). Because q = (2 B 1 - h)· B · L · γ / B · L =(2 B 1 - h)· γ Therefore, the final formula for calculating the chain tension under the coal pile is obtained. ········⑽ In the formula, f z The sum of the frictional resistance experienced by the scraper and chain as they slide between the middle plate and the bottom plate of the scraper conveyor. KN w represents the resistance experienced by the chain as it passes through the sprocket. KN s Chain preload, KN In the formula f z w and s are calculated using the existing conventional calculation methods for scraper conveyors.

[0014] The chain tension under the coal pile is calculated according to formula (10). F 总 This allows for the calculation of the scraper conveyor's drive power and the selection and design of components such as the chain, preventing accidents such as the inability to pull coal or the chain breaking.

[0015] This invention is reasonably designed and easy to calculate. Based on the characteristics of coal piles, it incorporates calculation methods from geotechnical mechanics, filling the gap in the calculation method of chain tension when a scraper conveyor is buried under a coal pile, and can meet the actual production needs.

[0016] The technical solution of the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Figure 1 A cross-sectional view of the scraper conveyor buried under the coal pile; Figure 2 A schematic diagram of a scraper conveyor buried under a coal pile along its length; Figure 3 This is a stress diagram of the scraper conveyor side plate; Figure 4 This is a stress diagram of the scraper conveyor's middle plate subjected to the normal pressure of the coal pile. Figure 5 This diagram illustrates the shear resistance experienced by the scraper blades of a scraper conveyor buried under a coal pile. The arrows in the diagram represent this resistance. v The diagram shows the direction of scraper movement. Detailed Implementation

[0019] The following examples further illustrate the essence of this invention: Taking a 1.2-meter-wide scraper conveyor used in an open-air coal storage yard of a power plant as an example, the coal is dry, loose, and fine coal, and the scraper conveyor trough width... B =1.2 m Effective width B 1 =0.8 m Side panel height h =0.8 m Coal pile length L =15 m Coal pile height H =5 m width of coal pile S =6 m Coal heavy weight γ =8 KN / m 3The static friction coefficient between coal and steel plate µ =0.4, active static pressure coefficient K a =0.21, the internal friction angle of coal ψ =45 。 Substituting into equation (10), the total tensile force that the chain needs to withstand is obtained. F 总 =245.47 KN +f z +w+s, where f z The values ​​of w and s are derived from the total length of the scraper conveyor and the unit length weight of the chain and scraper using existing conventional calculation methods. This invention calculates based on a horizontal arrangement of the scraper conveyor; for both upward and downward conveying scraper conveyors, it is sufficient to consider the gravitational components of the coal, chain, and scraper along the inclined plane.

Claims

1. A method for calculating the tension of the chain of a scraper conveyor under a coal pile, characterized in that, Includes the following steps: Step 1: Derive the calculation process for the normal pressure exerted by the coal pile on the scraper conveyor's middle plate; Step 2: Derive the calculation process for the pressure exerted by coal on the scraper conveyor side plate at any depth within the height range of the scraper conveyor side plate: Step 3: Derive the calculation process for the pressure exerted by the coal in the scraper conveyor trough on a single side plate of the scraper conveyor per unit length; Step 4: Derive the calculation process for the shear force inside the coal that needs to be overcome when the coal is pushed by the scraper; Step 5: List the comprehensive derivation process of the calculation method for the chain tension of the scraper conveyor under the coal pile. The method for calculating the chain tension of the scraper conveyor under the coal pile is characterized by the following steps: Step 1: Derive the calculation process for the normal pressure exerted by the coal pile on the scraper conveyor's middle plate; Step 2: Derive the calculation process for the pressure exerted by coal on the scraper conveyor side plate at any depth within the height range of the scraper conveyor side plate: Step 3: Derive the calculation process for the pressure exerted by the coal in the scraper conveyor trough on a single side plate of the scraper conveyor per unit length; Step 4: Derive the calculation process for the shear force inside the coal that needs to be overcome when the coal is pushed by the scraper; Step 5: List the comprehensive derivation process of the calculation method for the chain tension of the scraper conveyor under the coal pile.

2. The method for calculating the tension of the scraper conveyor chain under the coal pile according to claim 1, characterized in that... The normal pressure exerted on the middle plate of the scraper conveyor by the coal pile is approximately equal to the pressure generated by the coal at a height twice the effective width of the scraper conveyor. Step one specifically includes: calculating the normal pressure exerted on the middle plate of the scraper conveyor by the coal pile using the following formula. ···········⑴ In the formula: N 1 The scraper conveyor is subjected to positive pressure from the coal pile. KN; The density of coal, KN / m 3 B 1 The effective pressure-bearing width of the scraper conveyor m； L Coal pile length, m。 3. The method for calculating the tension of the scraper conveyor chain under the coal pile according to claim 1, characterized in that, Step two specifically includes: calculating the pressure exerted by coal on the scraper conveyor side plate at any depth within the height range of the scraper conveyor side plate using the following formula. ·········⑶ In the formula: The pressure exerted by coal on the scraper conveyor side plate at any depth within the height range of the side plate. kPa γ The density of coal, KN / m 3 Z Side panel at any depth m Active earth pressure coefficient q The height of the scraper conveyor side plate and above is (2) B 1 - h) refers to the uniformly distributed, downward vertical load exerted by the coal on the coal in the scraper conveyor trough under the action of gravity. kPa.

4. The method for calculating the tension of the scraper conveyor chain under the coal pile according to claim 1, characterized in that, Step three specifically includes: the pressure generated per unit length of the scraper conveyor side plate by the coal in the scraper conveyor trough. ·······⑸ In the formula, The single-sided side plate per unit length of the scraper conveyor is subjected to the pressure of the coal in the trough. KN h Effective height of scraper conveyor side plate m。 5. The method for calculating the tension of the scraper conveyor chain under the coal pile according to claim 1, characterized in that, Step four specifically includes: overcoming the internal shear force of the coal when it is pushed by the scraper. ············⑻ In the formula, T The shear force inside the coal that needs to be overcome when it is pushed by the scraper. KN.

6. The method for calculating the tension of the scraper conveyor chain under the coal pile according to claim 1, characterized in that, Step five specifically includes: listing a comprehensive formula for calculating the chain tension of the scraper conveyor under the coal pile. ········⑽ In the formula, f z The sum of the frictional resistance experienced by the scraper and chain as they slide between the middle plate and the bottom plate of the scraper conveyor. KN w represents the resistance experienced by the chain as it passes through the sprocket. KN s Chain preload, KN In the formula f z w and s are calculated using the existing conventional calculation methods for scraper conveyors.

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