1 Products Description
For a heat exchanger ‚ The number of joints between heat exchange tube and Copper clad steel bimetallic plate tube sheet is large. During heat exchanger operation ‚ Connection joint between pipe and tube sheet ‚ Is the most accident-prone part ‚ Therefore, the connection process of heat exchange tube and tube sheet is one of the key processes of the whole heat exchanger manufacturing. Current connection of heat exchanger tubes and tube sheet ‚ It mainly includes expansion joint, welding, expansion joint plus welding, inner hole welding and explosive welding. For copper heat exchanger ‚ Most of the original copper or brass tube sheets ‚ The heat exchange tube shall be made of red copper or other materials.
2 DC argon arc welding
In DC state, the welding current must be large enough to form a good welding pool. During the welding process, with the accumulation of input heat, the welding speed or welding current should be adjusted at any time according to the change of weld pool size. Practice has proved that when the welding current I=280~320A, the weld formation is good; When I>330A, it is easy to blow the liquid metal in the molten pool to the outside of the molten pool due to the large arc blowing force, so the weld cannot be formed; When I ≤ 280A, the melting speed is too slow and the welding process is unstable. When I=300A, manual welding is adopted, and the welding speed is adjusted at any time, and the weld formation is good. However, if automatic welding is adopted, the control of welding speed is complicated and the weld formation is not uniform. Therefore, DC is not suitable for automatic welding, and the operability of manual welding is relatively poor.
3Square wave DC pulse argon arc welding
To overcome the disadvantages of DC welding ‚ Square wave pulsed argon arc welding is adopted (Fig. 2a). Within peak current time ‚ If the peak current is large enough ‚ The molten pool can be formed directly on the joint ‚ After the molten pool reaches the required size, friction welding technology has been widely used in the welding of dissimilar metal materials ‚ However, the friction welder of electromagnetic pure iron and brass.
Art research has not been reported yet. This study passes the test and analysis ‚ The friction welding process of DT4A electromagnetic pure iron and H62 brass was optimized ‚ The characteristics and joint formation mechanism of friction welding of these two friction pair materials are captured and analyzed ‚ The friction welded joint which is stronger than the base metal of pure iron is obtained.
4 Features
(1) The Copper clad steel bimetallic plate tube sheet can be directly welded without preheating.
(2) Square wave pulse welding and triangular wave pulse welding are two effective welding methods. Because the weld metal is melted instantaneously, the arc stays at the starting position during DC welding is avoided, so the welding efficiency is high, the weld seam is uniform, and the shape is good.
(3) The reasonable process parameters of square wave pulse welding are: Ia=350~380A, ta=500ms, Ib=220~250A, tb=250m; The reasonable process parameters of triangular wave pulse welding are: Imx=360~400A, t A 500m, Imn=200~280A, td=500ms. These processes are applicable to both automatic welding and manual welding.
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