Features and requirements of self-protected flux-cored wire
I. Characteristics of self-shielded flux-cored wire
In 1958, the United States and the former Soviet Union developed a flux-cored wire without the need for additional gas protection at the same time, namely the current self-shielded flux-cored wire. In the following 50 years, the self-protected flux-cored wire has been greatly developed due to its unique advantages. In the United States, self-shielded flux-cored wire accounts for 30% of the total flux-cored wire.
At present, self-protecting flux-cored welding wires are widely used in pipeline construction, marine engineering, outdoor large-scale steel structure manufacturing, high-rise steel structure construction, surface surfacing, etc.
Self-protecting flux-cored wire protects molten droplets and molten pools through the slag-generating agent and gas-generating agent in the wire flux core under the high-temperature arc. The self-shielded flux-cored arc welding method has the following advantages:
1. No additional protective air source is needed, the welding torch has a simple structure, light weight and easy operation;
2. Good resistance to wind and air holes. During welding, a protective atmosphere is formed by the metallurgical reaction of the welding wire itself. Welding can be performed under the fourth-level wind. As long as the wind speed does not exceed 8m / s, no protective measures can be taken, especially suitable for Field construction operations;
3. The arc penetrating force should be large, the droplets should be spray-like transition, and the splash should be small;
4. Excellent all-position vertical down welding operation process performance, good operation process performance;
5. Good slag removal performance;
6. Deposited metal can also obtain higher low temperature toughness under various severe conditions such as low temperature and wind.
Second, the use requirements of self-shielded flux-cored wire
Using dedicated DC power supply and inverter power supply.
⒉ Direct current connection (DC-) should be used: the welding piece is connected to the positive pole of the power supply, and the welding torch is connected to the negative pole of the power supply.
The polarity is reversed, it is easy to splash, the penetration is shallow, and it can not be welded.
⒊When the angle of the welding wire is downward welding, it is generally required to maintain the welding wire and the workpiece at 800 to 900 to avoid the slag and molten iron from flowing down when it is close to the vertical position, which affects the smooth operation of the welding operation, and is prone to defects such as slag inclusion and porosity.
4. The dry elongation of self-shielded flux-cored wire should generally be controlled at 6 to 10 times the diameter of the wire. If the dry elongation is too long, the wire will melt too quickly and the arc blowing force will be reduced.
⒌ The surface to be welded shall be uniform and smooth, and shall be free of rust, scum, grease and other harmful substances that affect the quality of welding.
⒍The welding ground wire should be as close to the welding area as possible, and the conductivity should be good.
⒎The quality of welding parameter adjustment directly affects the welding quality.
The current is too small, which is likely to cause defects such as impervious welding and slag inclusion.
If the current is too large, it is easy to cause burn-through and increase the spatter. It will cause slag and iron to flow under the down welding, which can not be used for welding.
If the voltage is too low, the arc will be unstable, the top wire and the molten pool will not open, and slag inclusion will occur.
If the voltage is too high, it is easy to cause the arc to be too far away from the molten pool, air will be drawn into the molten pool, and air holes will appear.