Method for forming a square-to-round transition section of a flue duct

Abstract

The application discloses a forming method of a square-round transition joint cylinder of a flue, and solves the problem of how to develop a simple and easy-to-operate manufacturing process for the square-round joint transition cylinder with high quality; the forming method comprises a half unfolded body plate (3) of a pre-prepared square-round transition joint cylinder, a channel steel strip (9), a horizontal upper chain hoist (14) and a horizontal lower chain hoist (15); the half unfolded body plate of the pre-prepared square-round transition joint cylinder is obtained according to an unfolded drawing of the pre-prepared square-round transition joint cylinder; the channel steel strip (9) with the same length as the corresponding straight line edge is respectively spot-welded on each straight line edge of the unfolded body plate, and three triangular reinforcing rib frame frameworks of ⊿DEB, △ABC and ⊿FCG are formed; the horizontal upper chain hoist (14) is connected between a first lifting lug (10) and a third lifting lug (12); the horizontal lower chain hoist (15) is connected between a second lifting lug (11) and a fourth lifting lug (13); and the safety risk is reduced, and the construction quality is ensured.

Description

Technical Field

[0001] This invention relates to a steel plate flue or steel plate air duct made of steel plates in a power plant, and particularly to a method for forming a square-round transition section cylinder in a steel plate flue or steel plate air duct in a power plant. Background Technology

[0002] Large thermal power units are equipped with steel plate flues or steel plate air ducts, which are usually made of steel plates with a thickness of 4-5 mm spliced ​​and welded together. Within the flue or air duct, a square-to-round transition section is installed to transition the square flue to a round flue, adapting to the flue's design requirements. During the on-site splicing and assembly of the flue or air duct, the traditional method for manufacturing the square-to-round transition section is as follows: First, a pre-fabricated development diagram of the square-to-round transition section is drawn. Based on this diagram, a steel plate blank is cut out, and the blank is divided into two equal parts. Each part is then made into a half-arc shape of the square-to-round transition section. Finally, the two half-arc shapes are butt-welded together to form the square-to-round transition section. The manufacturing process of the half-arc shape of the square-to-round transition section is as follows: ( 1) Draw a rectangle in the middle of the rectangular steel plate blank. The length of the rectangle is equal to the side length of the square opening of the square-round transition section cylinder, and the height of the rectangle is equal to the height of the square-round transition section cylinder. (2) Starting from the left end point of the top edge of the rectangle and ending from the right end point of the top edge of the rectangle, cut out an arc-shaped notch. Twice the arc length of the arc-shaped notch is equal to the arc length of the round opening of the square-round transition section cylinder. (3) Connect the midpoint of the arc of the arc-shaped notch to the two ends of the bottom edge of the rectangle to form an isosceles triangle and two symmetrical inverted triangles. The top edge of these two inverted triangles is arc-shaped. (4) Draw a left right triangle to the left of the left inverted triangle and a right right triangle to the right of the right inverted triangle. If the left right triangle and the right right triangle are spliced ​​together, they will form an isosceles triangle. The virtual isosceles triangle is exactly the same as the isosceles triangle mentioned above. (4) According to the steps (1) to (3) above, cut each steel plate blank, and then bend the inverted triangle with the top edge of the arc into an arc shape, so that the top edge of each arc-shaped inverted triangle is 90 degrees, thus forming a half square-round transition section with a semi-circular top opening and a half-mouth-shaped bottom opening. Finally, weld the two half square-round transition sections formed together to form a square-round transition section cylinder. However, the above-mentioned bending of the inverted triangle into an arc shape has the problem of operational difficulties. On-site, two solutions are generally adopted: manual hammering and bending using a plate rolling machine. When the diameter of the circular opening of the square-round transition section reaches 5000-10000 mm, the aforementioned bending operations become even more difficult. If manual hammering is used to form the section, there are problems such as excessive labor intensity, poor quality of the curved plate, and poor surface aesthetics. If a plate rolling machine is used to roll the curved plate, the width of the plate rolled by the rolling machine is limited, while the height of the inverted triangle to be bent is relatively large. It is necessary to weld and splice several sections of the bent plate laterally to form the inverted triangular curved shape, resulting in many and concentrated transverse welds. This not only affects the strength of the transition section but also increases the risk of leakage in the cylinder. Therefore, how to develop a simple and easy-to-implement manufacturing process that can complete the square-round transition cylinder with high quality has become an urgent problem to be solved on the construction site. Summary of the Invention

[0003] This invention provides a method for forming a square-round transition section cylinder in a flue gas duct, solving the technical problem of how to develop a simple and easy-to-implement manufacturing process that can produce a high-quality square-round transition section cylinder.

[0004] The present invention solves the above technical problems through the following technical solutions: A method for forming a square-to-round transition section cylinder of a flue gas duct, characterized by the following steps: The first step is to cut out a rectangular steel plate blank according to the area of ​​the pre-made square-round transition section cylinder development diagram, so that the area of ​​the rectangular steel plate blank is larger than the area of ​​the square-round transition section cylinder development diagram. The second step is to divide the steel plate blank from the first step into two equal parts, each of which is a blank of half an arc shape of the prefabricated square-round transition section. The third step is to draw half of the prefabricated square-round transition section cylinder on the blank and cut out half of the prefabricated square-round transition section cylinder plate. Step 4: Connect the midpoint A of the upper arc of the half-unfolded plate to the left endpoint B and right endpoint C of the lower horizontal line to form an isosceles triangle; connect the left endpoint D of the upper arc of the half-unfolded plate to the left endpoint B of the lower horizontal line to form a left inverted triangle and a left right triangle with an arc at the top; connect the right endpoint F of the upper arc of the half-unfolded plate to the right endpoint C of the lower horizontal line to form a right inverted triangle and a right right triangle with an arc at the top. Step 5: Based on the lengths of the straight sides of the half-expanded body plate drawn in Step 4, make channel steel bars respectively, and spot weld each channel steel bar to its corresponding straight side to form three triangular reinforcing rib frames: ⊿DEB, △ABC and ⊿FCG. Step 6: Weld the first lifting lug to the reinforcing rib at the upper vertex D of the left right triangle, weld the second lifting lug to the reinforcing rib at the left outer vertex E of the left right triangle, weld the third lifting lug to the reinforcing rib at the upper vertex F of the right right triangle, and weld the fourth lifting lug to the reinforcing rib at the right outer vertex G of the right right triangle. Step 7: Connect the horizontal upper chain hoist between the first and third lifting lugs; connect the horizontal lower chain hoist between the second and fourth lifting lugs. Step 8: Based on the circular opening of the pre-made square-round transition section cylinder, fabricate a semi-circular transition plate for spot welding during the bending process. The semi-circular transition plate is composed of a first arc-shaped trapezoidal plate, a second arc-shaped trapezoidal plate, a third arc-shaped trapezoidal plate, a fourth arc-shaped trapezoidal plate, a fifth arc-shaped trapezoidal plate, a sixth arc-shaped trapezoidal plate, a seventh arc-shaped trapezoidal plate, and an eighth arc-shaped trapezoidal plate. The outer radius of the semi-circular transition plate is equal to the radius of half a circular opening of the square-round transition section cylinder. Step 9: Simultaneously operate the horizontal upper and lower chain hoists to bend and deform the left and right inverted triangles. During this process, weld the outer arc edge of the first arc-shaped trapezoidal plate to the left arc edge of the bent left inverted triangle, and position the first arc-shaped trapezoidal plate horizontally. Simultaneously, weld the outer arc edge of the eighth arc-shaped trapezoidal plate to the right arc edge of the bent right inverted triangle, and position the eighth arc-shaped trapezoidal plate horizontally. Step 10: Repeat Step 9 repeatedly, bending and transforming the left and right inverted triangles into arcs in sequence. Then, spot weld the second, third, fourth, fifth, sixth, and seventh arc-shaped trapezoidal plates to the top arc-shaped edges of the left and right inverted triangles in sequence, until the surfaces of the left and right right-angled triangles are perpendicular to the surface of the isosceles triangle, and the top arc-shaped edges of the left and right inverted triangles form a semi-circular opening of the square-round transition section cylinder. Step 11: Repeat steps 3 through 10 to complete the production of the other half of the circular transition section. Step 12: Weld the two square-round transition section semi-cylinders together to complete the forming of the square-round transition section cylinder in the flue gas duct.

[0005] Annular reinforcing ribs and lower annular reinforcing ribs are welded onto the outer surface of the formed square-round transition section cylinder. Then, the channel steel bars and the first, second, third, fourth, fifth, sixth, seventh, and eighth arc-shaped trapezoidal plates that were spot-welded are removed to obtain the prefabricated square-round transition section.

[0006] A forming fixture for a square-round transition section cylinder of a flue gas duct includes a prefabricated half-developed plate of the square-round transition section cylinder, channel steel bars, a horizontal upper hand chain hoist, and a horizontal lower hand chain hoist. The prefabricated half-developed plate of the square-round transition section cylinder is obtained based on a prefabricated development drawing of the square-round transition section cylinder. An isosceles triangle is drawn by connecting the midpoint A of the upper arc of the half-developed plate to the left endpoint B and right endpoint C of the lower horizontal line. An inverted left triangle and a right-angled left triangle with arc-shaped top edges are drawn by connecting the left endpoint D of the upper arc of the half-developed plate to the left endpoint B of the lower horizontal line. The right endpoint F of the upper arc of the developed plate is drawn by connecting the right endpoint C of the lower horizontal line. The top edge is an arc-shaped right-angled triangle and a right-angled triangle. On each straight side of the drawn half-developed plate, channel steel strips of equal length to the corresponding straight side are spot-welded, forming three triangular reinforcing rib frames: ΔDEB, △ABC, and ΔFCG. A first lifting lug is welded to the reinforcing rib at the upper vertex D of the left right-angled triangle; a second lifting lug is welded to the reinforcing rib at the left outer vertex E of the left right-angled triangle; a third lifting lug is welded to the reinforcing rib at the upper vertex F of the right right-angled triangle; and a fourth lifting lug is welded to the reinforcing rib at the right outer vertex G of the right right-angled triangle. A horizontal upper chain hoist connects the first and third lifting lugs; a horizontal lower chain hoist connects the second and fourth lifting lugs.

[0007] Based on the pre-fabricated semi-circular opening at the top of the square-round transition section cylinder, a splicing transition semi-annular plate is fabricated. The splicing transition semi-annular plate is composed of a first, second, third, fourth, fifth, sixth, seventh, and eighth arc-shaped trapezoidal plates, forming a semi-circular shape. The outer radius of this splicing transition semi-annular plate is equal to the radius of the semi-circular opening at the top of the square-round transition section cylinder. The splicing transition semi-annular plate is spot-welded into the semi-circular opening at the top of the formed square-round transition section cylinder, and the annular surface where the splicing forms the semi-annular shape is perpendicular to the central axis of the square-round transition section cylinder.

[0008] The square-round transition section cylinder is composed of two semi-arc cylinders that have been formed and then welded together; an upper annular reinforcing rib and a lower annular reinforcing rib are respectively provided on the outer side of the completed square-round transition section cylinder.

[0009] The beneficial effects of the present invention are as follows: (1) In order to avoid the phenomenon that all welds are vertical during the welding process, a two-section cutting method is adopted for the layout and cutting of the square-round transition section cylinder instead of four or eight sections, which reduces the welds between the flat plate and the arc plate, and turns the vertical welds into flat welds, which improves the weld quality and saves welding materials; (2) In order to avoid the phenomenon that the arc plate is hammered by a sledgehammer and the surface of the arc plate is not smooth during the production of the arc plate, the chain hoisting technology is used instead of hammering or rolling technology, which achieves the goal of saving labor and saving machinery costs, and also solves the problem of the part not being smooth; (3) In order to avoid the phenomenon that the straight section of the square-round section is a high-altitude weld, the straight section of the round section adopts the ground-to-ground method, which reduces the high-altitude welds, reduces the safety risk, and ensures the construction quality. Attached Figure Description

[0010] Figure 1 A schematic diagram of the blank 1 of the prefabricated square-round transition section of the present invention; Figure 2 The development of the prefabricated square-round transition section cylinder, which is half marked on blank 1. Figure 2 Structural diagram; Figure 3 A schematic diagram of the structure of half of the unfolded body plate 3 of the prefabricated square-round transition section cylinder of the present invention; Figure 4 This is a schematic diagram of the structure of the present invention, in which one half of the unfolded body plate is decomposed into five triangles; Figure 5 This is a schematic diagram of the reinforcing ribs on the half-expanded plate 3 of the present invention; Figure 6 This is a diagram showing the connection relationship between the two-hand chain hoist and the half-expanded plate 3 of the present invention; Figure 7 This is a schematic diagram of the splicing transition semi-circular plate of the present invention; Figure 8 This is a schematic diagram of the structure of the present invention in the initial stage of tension deformation; Figure 9 This is a schematic diagram of the structure of the present invention during the tension deformation process; Figure 10 This is a schematic diagram of the structure of the square-round transition section semi-cylinder after molding according to the present invention; Figure 11 yes Figure 10 Top view; Figure 12 This is a schematic diagram of the structure of the square-round transition section cylinder after molding according to the present invention. Detailed Implementation

[0011] The present invention will now be described in detail with reference to the accompanying drawings: A method for forming a square-to-round transition section cylinder of a flue gas duct, characterized by the following steps: The first step is to cut out a rectangular steel plate blank according to the area of ​​the pre-made square-round transition section cylinder development diagram, so that the area of ​​the rectangular steel plate blank is larger than the area of ​​the square-round transition section cylinder development diagram. The second step is to divide the steel plate blank from the first step into two equal parts, each of which is a blank 1 of half of the arc shape of the prefabricated square-round transition section. Step 3: Draw lines on blank 1 to mark half of the pre-made square-round transition section cylinder and unfold it. Figure 2 Cut out half of the prefabricated square-round transition section cylinder and bend the half of the prefabricated square-round transition section cylinder to form half of the cylinder. Step 4: Connect the midpoint A of the upper arc of half the unfolded plate 3 to the left endpoint B and right endpoint C of the lower horizontal line to form an isosceles triangle 6; connect the left endpoint D of the upper arc of half the unfolded plate 3 to the left endpoint B of the lower horizontal line to form a left inverted triangle 5 with an arc at the top and a left right triangle 4; connect the right endpoint F of the upper arc of half the unfolded plate 3 to the right endpoint C of the lower horizontal line to form a right inverted triangle 7 with an arc at the top and a right right triangle 8. Step 5: Based on the lengths of the straight sides of the half-expanded body plate 3 drawn in step 4, make channel steel strips 9 respectively, and spot weld each channel steel strip 9 to its corresponding straight side to form three triangular reinforcing rib frames: ⊿DEB, △ABC and ⊿FCG; during the subsequent bending process, ⊿DEB, △ABC and ⊿FCG remain straight and do not bend. Step 6: Weld the first lifting lug 10 to the reinforcing rib of the upper vertex D of the left right triangle 4; weld the second lifting lug 11 to the reinforcing rib of the left outer vertex E of the left right triangle 4; weld the third lifting lug 12 to the reinforcing rib of the upper vertex F of the right right triangle 8; and weld the fourth lifting lug 13 to the reinforcing rib of the right outer vertex G of the right right triangle 8. Step 7: Connect the horizontal upper chain hoist 14 between the first lifting lug 10 and the third lifting lug 12; connect the horizontal lower chain hoist 15 between the second lifting lug 11 and the fourth lifting lug 13. Step 8: Based on the circular opening of the pre-made square-round transition section cylinder, fabricate a splicing transition semi-circular plate that is spot-welded during the bending process. The splicing transition semi-circular plate is composed of a first arc-shaped trapezoidal plate 16, a second arc-shaped trapezoidal plate 17, a third arc-shaped trapezoidal plate 18, a fourth arc-shaped trapezoidal plate 19, a fifth arc-shaped trapezoidal plate 20, a sixth arc-shaped trapezoidal plate 21, a seventh arc-shaped trapezoidal plate 22, and an eighth arc-shaped trapezoidal plate 23. The outer arc of this splicing transition semi-circular plate is equal to the arc of half a circular opening of the square-round transition section cylinder. Step 9: Simultaneously operate the horizontal upper chain hoist 14 and the horizontal lower chain hoist 15 to bend the left inverted triangle 5 and the right inverted triangle 7 into arc shapes, while ΔDEB and ΔFCG remain straight. The whole structure follows the bending of the left inverted triangle 5 and the right inverted triangle 7 in a flat plate form. During this process, the outer arc edge of the first arc-shaped trapezoidal plate 16 is welded to the left arc edge of the top of the bent and deformed left inverted triangle 5, and the plate surface of the first arc-shaped trapezoidal plate 16 is set in the horizontal direction. At the same time, the outer arc edge of the eighth arc-shaped trapezoidal plate 23 is welded to the right arc edge of the top of the bent and deformed right inverted triangle 7, and the plate surface of the eighth arc-shaped trapezoidal plate 23 is set in the horizontal direction. Step 10: Repeat step 9, continuously bending and transforming the left inverted triangle 5 and the right inverted triangle 7 into arc shapes. Then, spot weld the second, third, fourth, fifth, sixth, and seventh arc-shaped trapezoidal plates 17, 18, 19, 20, 21, and 22 to the top arc-shaped edges of the left and right inverted triangles 5 and 7 respectively, until the surfaces of the left right-angled triangle 4 and right right-angled triangle 8 are perpendicular to the surface of the isosceles triangle 6. The arc-shaped edges at the top of the left inverted triangle 5 and the right inverted triangle 7 form a semi-circular opening in the square-round transition section cylinder. Under the simultaneous action of the horizontal upper hand chain hoist 14 and the horizontal lower hand chain hoist 15, the arc-shaped edges at the top of the left inverted triangle 5 and the right inverted triangle 7 follow the outer arc of the splicing transition semi-circular plate to form a semi-circle. After the formation, the left right-angled triangle 4, the isosceles triangle 6, and the right right-angled triangle 8 of the square-round transition section semi-cylinder are flat surfaces, while the left inverted triangle 5 and the right inverted triangle 7 are arc surfaces. Step 11: Repeat steps 3 through 10 to complete the production of the other half of the circular transition section. Step 12: Weld the two square-round transition section semi-cylinders together to complete the forming of the square-round transition section cylinder in the flue gas duct.

[0012] Annular reinforcing ribs 24 and lower annular reinforcing ribs 25 are welded onto the outer surface of the formed square-round transition section cylinder. Then, the spot-welded channel steel strips 9 and the first arc-shaped trapezoidal plate 16, the second arc-shaped trapezoidal plate 17, the third arc-shaped trapezoidal plate 18, the fourth arc-shaped trapezoidal plate 19, the fifth arc-shaped trapezoidal plate 20, the sixth arc-shaped trapezoidal plate 21, the seventh arc-shaped trapezoidal plate 22 and the eighth arc-shaped trapezoidal plate 23 are removed to obtain the pre-fabricated square-round transition section.

[0013] A forming fixture for a square-round transition section cylinder of a flue gas duct includes a pre-fabricated half-expanded plate 3 of the square-round transition section cylinder, channel steel bars 9, a horizontal upper hand chain hoist 14, and a horizontal lower hand chain hoist 15; the pre-fabricated half-expanded plate 3 of the square-round transition section cylinder is obtained according to a pre-fabricated unfolded diagram of the square-round transition section cylinder; characterized in that, the midpoint A of the upper arc of the half-expanded plate 3 is connected to the left endpoint B and the right endpoint C of the lower horizontal straight line respectively, and an isosceles triangle 6 is drawn; the left endpoint D of the upper arc of the half-expanded plate 3 is connected to the left endpoint B of the lower horizontal straight line, and a left inverted triangle 5 and a left right triangle 4 with an arc at the top edge are drawn; the right endpoint F of the upper arc of the unfolded plate 3 is connected to the right endpoint C of the lower horizontal straight line, and a top edge is drawn. The right inverted triangle 7 and right right triangle 8 have arc-shaped ends; channel steel strips 9 of the same length as the corresponding straight side are spot-welded to each straight side of the drawn unfolded plate 3, forming three triangular reinforcing rib frames: ΔDEB, △ABC, and ΔFCG; a first lifting lug 10 is welded to the reinforcing rib at the upper vertex D of the left right triangle 4, a second lifting lug 11 is welded to the reinforcing rib at the left outer vertex E of the left right triangle 4, a third lifting lug 12 is welded to the reinforcing rib at the upper vertex F of the right right triangle 8, and a fourth lifting lug 13 is welded to the reinforcing rib at the right outer vertex G of the right right triangle 8; a horizontal upper hand chain hoist 14 is connected between the first lifting lug 10 and the third lifting lug 1; a horizontal lower hand chain hoist 15 is connected between the second lifting lug 11 and the fourth lifting lug 13.

[0014] Based on the pre-fabricated semi-circular opening at the top of the square-round transition section cylinder, a splicing transition semi-annular plate is fabricated. The splicing transition semi-annular plate is formed by splicing together a first arc-shaped trapezoidal plate 16, a second arc-shaped trapezoidal plate 17, a third arc-shaped trapezoidal plate 18, a fourth arc-shaped trapezoidal plate 19, a fifth arc-shaped trapezoidal plate 20, a sixth arc-shaped trapezoidal plate 21, a seventh arc-shaped trapezoidal plate 22, and an eighth arc-shaped trapezoidal plate 23 to form a semi-circular shape. The outer arc of the splicing transition semi-annular plate is equal to the arc of the semi-circular opening at the top of the square-round transition section cylinder. The splicing transition semi-annular plate is spot-welded into the semi-circular opening at the top of the formed square-round transition section cylinder, and the annular surface where the splicing forms the semi-circular shape is perpendicular to the central axis of the square-round transition section cylinder.

[0015] The square-round transition section cylinder is composed of two semi-arc cylinders that have been formed and then welded together; an upper annular reinforcing rib 24 and a lower annular reinforcing rib 25 are respectively provided on the outer side of the completed square-round transition section cylinder.

[0016] The aforementioned square-round transition section cylinder is a centrally symmetrical cylinder. If the square-round transition section cylinder is an eccentric cylinder, the bending method is the same as that of the centrally symmetrical cylinder, and the unfolded diagram of the cylinder shall prevail.

Claims

1. A method for forming a square-to-round transition section cylinder of a flue gas duct, characterized by the following steps: The first step is to cut out a rectangular steel plate blank according to the area of ​​the pre-made square-round transition section cylinder development diagram, so that the area of ​​the rectangular steel plate blank is larger than the area of ​​the square-round transition section cylinder development diagram. The second step is to divide the steel plate blank from the first step into two equal parts, each of which is a blank of half an arc shape of the prefabricated square-round transition section (1). The third step is to draw half of the prefabricated square-round transition section cylinder (2) on the blank (1), and cut out half of the prefabricated square-round transition section cylinder plate. After bending the half of the plate (3), half of the prefabricated square-round transition section cylinder is formed. Step 4: Connect the midpoint A of the upper arc of the half-unfolded plate (3) to the left endpoint B and right endpoint C of the lower horizontal line to form an isosceles triangle (6); connect the left endpoint D of the upper arc of the half-unfolded plate (3) to the left endpoint B of the lower horizontal line to form a left inverted triangle (5) with an arc at the top edge and a left right triangle (4); connect the right endpoint F of the upper arc of the half-unfolded plate (3) to the right endpoint C of the lower horizontal line to form a right inverted triangle (7) with an arc at the top edge and a right right triangle (8). Fifth step: Based on the length of each straight side of the half-expanded body plate (3) drawn in the fourth step, make channel steel strips (9) respectively, and spot weld each channel steel strip (9) to its corresponding straight side to form three triangular reinforcing rib frames: ⊿DEB, △ABC and ⊿FCG; in the subsequent bending process, ⊿DEB, △ABC and ⊿FCG maintain the straight plate status and do not bend. Step 6: Weld the first lifting lug 10 to the reinforcing rib of the upper vertex D of the left right triangle (4), weld the second lifting lug (11) to the reinforcing rib of the left outer vertex E of the left right triangle (4), weld the third lifting lug (12) to the reinforcing rib of the upper vertex F of the right right triangle (8), and weld the fourth lifting lug (13) to the reinforcing rib of the right outer vertex G of the right right triangle (8). Step 7: Connect the horizontal upper chain hoist (14) between the first lifting lug (10) and the third lifting lug (12); connect the horizontal lower chain hoist (15) between the second lifting lug (11) and the fourth lifting lug (13); Step 8: Based on the circular opening of the pre-made square-round transition section cylinder, make a splicing transition semi-circular plate that is spot-welded during the bending process. The splicing transition semi-circular plate is composed of a first arc-shaped trapezoidal plate (16), a second arc-shaped trapezoidal plate (17), a third arc-shaped trapezoidal plate (18), a fourth arc-shaped trapezoidal plate (19), a fifth arc-shaped trapezoidal plate (20), a sixth arc-shaped trapezoidal plate (21), a seventh arc-shaped trapezoidal plate (22), and an eighth arc-shaped trapezoidal plate (23). The outer arc of the splicing transition semi-circular plate is equal to the arc of half a circular opening of the square-round transition section cylinder. Step 9: Simultaneously operate the horizontal upper hand chain hoist (14) and the horizontal lower hand chain hoist (15) to bend the left inverted triangle (5) and the right inverted triangle (7) into an arc shape, while ⊿DEB and ⊿FCG remain straight. The whole structure follows the left inverted triangle (5) and the right inverted triangle (7) and bends in a flat plate form. During this process, the outer arc edge of the first arc-shaped trapezoidal plate (16) is welded to the left arc edge of the top of the bent and deformed left inverted triangle (5), and the plate surface of the first arc-shaped trapezoidal plate (16) is set in the horizontal direction. At the same time, the outer arc edge of the eighth arc-shaped trapezoidal plate (23) is welded to the right arc edge of the top of the bent and deformed right inverted triangle (7), and the plate surface of the eighth arc-shaped trapezoidal plate (23) is set in the horizontal direction. Step 10: Repeat Step 9, bending the left inverted triangle (5) and the right inverted triangle (7) into arc shapes in sequence. Then, spot weld the second arc-shaped trapezoidal plate (17), the third arc-shaped trapezoidal plate (18), the fourth arc-shaped trapezoidal plate (19), the fifth arc-shaped trapezoidal plate (20), the sixth arc-shaped trapezoidal plate (21), and the seventh arc-shaped trapezoidal plate (22) to the top arc-shaped edge of the left inverted triangle (5) and the top arc-shaped edge of the right inverted triangle (7) in sequence, until the plate surfaces of the left right triangle (4) and the right right triangle (8) are perpendicular to the plate surface of the isosceles triangle (6). And the arc-shaped edge at the top of the left inverted triangle (5) and the arc-shaped edge at the top of the right inverted triangle (7) form a semi-circular opening of the square-round transition section cylinder; under the synchronous action of the horizontal upper hand chain hoist (14) and the horizontal lower hand chain hoist (15), the arc-shaped edge at the top of the left inverted triangle (5) and the arc-shaped edge at the top of the right inverted triangle (7) follow the outer arc of the splicing transition semi-circular plate to form a semi-circle; the left right triangle (4), the isosceles triangle (6) and the right right triangle (8) of the formed square-round transition section semi-cylinder are flat surfaces, while the left inverted triangle (5) and the right inverted triangle (7) are arc surfaces; Step 11: Repeat steps 3 through 10 to complete the production of the other half of the circular transition section. Step 12: Weld the two square-round transition section half-cylinders together to complete the forming of the square-round transition section cylinder in the flue gas duct; On the outer side of the formed square-round transition section cylinder, annular reinforcing ribs (24) and lower annular reinforcing ribs (25) are welded respectively. Then, the channel steel strips (9) and the first arc-shaped trapezoidal plate (16), the second arc-shaped trapezoidal plate (17), the third arc-shaped trapezoidal plate (18), the fourth arc-shaped trapezoidal plate (19), the fifth arc-shaped trapezoidal plate (20), the sixth arc-shaped trapezoidal plate (21), the seventh arc-shaped trapezoidal plate (22) and the eighth arc-shaped trapezoidal plate (23) are removed respectively to obtain the pre-made square-round transition section.

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