What is the preweld defect of welding

Because of the pre-weld own characteristics, in the back of the welding operations, there often produce tumors, burn, wrong side, solder partial, broken weld (broken arc), weld reinforcement is too low or too high, porosity and slag and other defects. Among them burn, broken weld (broken arc) more likely to be found to take timely repair welding, generally does not have a significant impact on the internal and external welding quality.

Pre-weld defects affecting the quality of internal and external of submerged-arc welding
(1) on the back of weld flash  The back of the weld seam quality internal tumors, tracking stability and the welding process will have a greater impact. Within the welding torch head is generally provided with guide wheels, in order to stabilize the welding head and the guide track. When the guide wheel tumor encountered in the groove weld, the welding head will suddenly rise, the spatial position of the wire (wire extension length and spacing) and arc length will change drastically, which will lead to generation of weld slag, incomplete penetration , the outer surface of weld defects such as bad. Meanwhile guide wheels are also likely to deviate from the groove center, so that the weld side. When welding arc burning to the tumor at the arc will suddenly become shorter, or even a short circuit extinction, affecting the normal welding. Thus, a tumor may often lead to weld two welding defects.

(2) the wrong side 
The wrong side of the geometry will adversely affect the internal and external weld penetration and cross-section, the wrong side of ultra-poor will directly lead pipe downgrade or scrapped.

(3) Partial welding, weld reinforcement is too low or too high 
Partial welding, weld reinforcement is a major factor too low to generate the welding burn, cracks and other defects. Low high bias and residual weld is substantially reduced thickness with or without the back cover back cover weld seam (weld severe migraine), the binding will also cause reduction of strength of the formed seam, which is easy to produce and cracks within the weld burn defects. Weld reinforcement is too high will cause the outer weld penetration and weld ultra reduced.

(4) pores, slag 
Pre-weld porosity, slag is caused by one of the major internal and external SAW blowholes and slag defects. Most pre-weld porosity distribution in internal welds, namely the stomata (pores of the surface pores few). Slag is generally present in the manual welding weld root. When the welding, arc welding can pre-weld toe and lower porosity, slag melting or partial melting away. Since the fused pores, including the root of the weld slag, the slag and non-metallic material gas to escape from the weld surface is relatively far, the time required is relatively long, and the internal welding heat input is generally small , the liquid metal bath shorter residence time at high temperatures, combined with the impact of external factors (welding specifications instability, welding arm shake the tube inequality), it is easy to make gas or nonmetallic slag material is "trapped" in the weld metal, forming the weld slag near surface pores or defects. It also reveals the actual production, the weld point-like defects (pores, slag) more, and most of the near-surface distribution of the reasons for the weld.