As the "medium" of heat transfer inside and outside the annealing furnace, the inner cover of bell type annealing furnace directly affects the intensity of heat transfer in the furnace, and then affects the heating quality and output of steel coil. Its safe and stable operation is directly related to the production and product quality of cold rolled sheet. Therefore, the production of inner cover of bell type annealing furnace must have reliable air tightness, stability, cold and hot sudden change resistance and dimensional accuracy. This brings high difficulty to the assembly, welding and rolling of the inner cover in the manufacturing process, and also presents unprecedented challenges to the domestic manufacturers.

Key technology innovation

2.1 self made tooling to ensure the accuracy of cylinder assembly

Make a r1094 mm sample plate, roll out r1094 mm arc at both ends of three steel plates and 1084 arc at both ends of one steel plate with special mould, and inspect while rolling the plate. Three cylinders with outer diameter of 2 200 mm and one cylinder with outer diameter of 2 180 mm are rolled by plate rolling machine.

The cylinder of the plate rolling machine shall be loaded again to ensure that the ovality is not more than ± 2mm, and the misalignment is not more than 2mm when the large-diameter thin-wall corrugated cylinder is assembled.

2.2 rolling corrugation by four step method to improve cylinder strength

The four step rolling method is adopted to ensure the corrugation depth is 10 + 2mm and the width meets the four dimensions as shown in the figure, so as to solve the problem that the inner cover is inclined due to insufficient strength when it works in the environment of high and low temperature, cold and hot sudden change all the year round.

Place the stainless steel cylinder on the platform. After leveling, draw a line with a height ruler according to the drawing size to determine the position of the center line of each wave. Note that the center line of the wave must be vertical to the center line of the cylinder. The finished cylinder should be placed on the corrugator horizontally, and the end face should be close to the retaining roll without deflection.

One step, the center of the rolling die is overlapped with the center line of the ripple, the reduction size is adjusted by 3 mm, and the positioning center is determined.

Step 2: after checking the positioning center, continue to adjust the ruler to move down 5 mm to make the rolling ripple depth reach 8 mm.

Three steps, continue to deepen the reduction size by 2 mm, start the corrugator, and the corrugation depth is 10 mm.

Four steps, continue to run the corrugator, keep the scale depth unchanged, adjust and modify the rolled corrugation to ensure beautiful appearance, accurate size and meet the drawing requirements.

2.3 isometric alignment to ensure the shape and position accuracy of the inner cover

The base flange and cylinder are assembled by equidistant method to ensure that the verticality deviation of 7 554 mm high inner cover is not more than 5 mm.

(1) The 270 mm high stainless steel cylinder is matched with the flange, and the upper opening is fixed with the supporting flange (outer diameter 2180 mm, inner diameter 1980 mm), so as to ensure that the cylindricity of the cylinder does not exceed 2 mm. Inside and outside welding, fillet weld fillet height 10 mm.

(2) The cylindricity of 16Mn cylinder with height of 150 mm should be adjusted by hand, which should not exceed 2 mm. The 16Mn cylinder with 150 mm height is assembled with flange and welded inside and outside, and the height of welding corner is 10 mm.

(3) Make support flange (outer diameter 2 600 mm, inner diameter 2 200 mm) to fix the two cylinders.

2.4 argon arc welding and gas shielded arc welding are combined to carry out cylinder welding

When the cylinder is assembled and welded, argon arc welding is used for backing, CO2 gas shielded welding is used for inner opening, and external submerged arc welding is used for cover. By selecting reasonable welding parameters, the benign welding of large-diameter and thin-walled stainless steel bellows is realized, and the accuracy of X-ray flaw detection is above grade II.

6) Bell type furnace liner-2.jpg

2.4.1 welding conditions

(1) The welding power source uses the direct current reverse connection method, that is, the workpiece is connected to the negative pole of the electric welding machine, and the welding wire is connected to the positive pole.

(2) The temperature difference between welding passes is less than or equal to 60 ℃.

(3) The dry elongation length of welding wire should be 22-35 mm, which should be as short as possible.

(4) The welding environment temperature should not be lower than 0 ℃.

2.4.2 argon arc welding primer

The two corrugated cylinders after spot welding are placed on the rotary tire. The diameter of the rotary wheel is Φ 400 mm, the distance is 2 500 mm, and the speed is 20 R / min.

The welding wire of argon arc welding is S310. Under the condition of ensuring good penetration and fusion, the method of small current, short arc and fast welding is adopted. The thickness of primer shall not exceed 2 mm. After the backing layer is welded, the weld surface shall be inspected carefully, and there shall be no crack, slag inclusion, air hole and other defects. Use an angle grinder to grind the bottom layer to expose the metallic luster, remove the defects such as cracks, slag inclusion and air holes, and smooth the bumps.