Welding content of spiral finned tube
1. Welding principle
The high-frequency current is used as the heat source to heat the contact surface and the area to be welded, and at the same time, the upsetting force is applied to the outside of the fin tube to realize the solid phase welding of the contact surface.
2. Preparation before welding
(1) There should be no obvious pits on the surface of the pipe material, and sandblasting should be used to remove oil, rust and other dirt.
(2) The preparation of the upsetting wheel should ensure that the clamping of the steel belt in the circumferential direction is moderately tight and uniform, and the inner parts can rotate flexibly.
(3) The welding between the electrode body and the contact should be firm and reliable, cooling smoothly, and no leakage.
3. Welding parameters
It mainly includes the tensile strength and welding rate of the welded joint.
4. Welding inspection
Visual inspection: Perform visual inspection after welding, and the result of the inspection should meet the standard requirements.
Welding rate inspection: peel off the finned tube for 2 to 3 turns, and check once every 120 degrees. Divide the actual weld width by the nominal thickness of the steel strip to get the welded rate.
Metallographic inspection: From the joint surface, the incomplete normalized structure and the original normalized structure are inspected for inclusions, lack of fusion, cracks and other macro defects.
5. The connotation of high frequency welding
High frequency welding is a kind of welding technology, there are two kinds of induction welding and contact resistance welding.
Solid-phase plastic pressure welding——heat the junction area of the edge of the tube blank to a plastic state of 1300°C-1350°C, and then extrude the oxide film out of the weld under the pressure of the squeeze roller. At the same time, the two edges are made by high temperature When welded together, the extrusion strength is required to be greater than 40-50MPa.
Semi-melting welding-heating the transfer area of the edge of the tube to a semi-melting state, and squeezing the liquid film with oxides out of the weld through the extrusion of the squeeze roller, and the welding is completed at the same time. The extrusion strength is generally 20 —30MPa.
Fusion welding——heat the transfer area at the edge of the tube blank to a molten state, and the welding temperature is above 1400℃. At this time, the molten metal is partially vaporized, and then squeezed by the squeeze roller, periodically in the entire liquid overlap area. Sparks splash, and its extrusion strength is close to that of semi-fusion welding.