Hainan welded steel construction and causes of common defects

Hainan welded steel construction and causes of common defects

First, there is no penetration.
     When the welding electrode arc melting under the force drops to weld, but also part of the base material is heated and melted molten metal electrodes together. Heat melting the base material is called the depth of penetration depth, it is an important factor in maintaining the strength of the weld. Between the base metal and the molten metal if no partial fusion will form no penetration phenomenon. No weld penetration is a serious welding defects, which weaken the strength of the welded connections of up to 60% -80%. No penetration defects frequently occur in construction. Several no penetration phenomenon as shown:

Hainan Steel usually cause no penetration because:

1, I welders or technical difference between the open-groove welding is not open groove.
2, edge weld repair bad cut assembled incorrectly or when welding. Groove slope is not enough, the gap is too small, pure groove edges stay too thick or too thin, or inconsistent thickness on both sides.
3, when the welding speed is too fast or welding current is too small.
4, before welding seam not clean, rust, slag or gas cutting residue have no clean and clear. So that the edge of the base material adverse melted.
5, when the steering rod wrong angle, so that the pool one side of the base material.

Second, the slag.
     Within the weld slag contains impurities called slag. Slag will weaken the weld section, the strength of the weld is greatly reduced. Slag may be due to impurities in the molten metal got into the other foreign particles are formed, it may be in and around molten metal atmospheric chemical reaction or a chemical reaction within the molten metal itself formed. The former produce impurity is usually caused by dirty edge welding. After the oxygen cutting residues such as rust or iron oxide on the base metal and the weld after a former slag did not clean out other causes. Slag impurities generated in the latter category is due to the molten metal when the solution is cooled and solidified precipitate certain compounds and impurities formed by oxidation. Under normal circumstances slag welding rod coating formation should be fully floating form a protective skin on the surface of the weld. If the welding current is too small or when the surrounding environment temperature is too low, which may cause the solidification of the molten metal welds fast, too late to the slag floating molten metal caused by a part in causing the weld slag left in the clip slag.

Slag resulting weld stress concentration, greatly reducing the impact strength of welded joints, particularly in the weld toe harmful impurities greater the larger particles.

Third, crack.
    Cracks in welded joints hazards seriously flawed. It reduces the cross-sectional area of ​​the weld force while causing stress concentration, so that the crack caused by expansion of joint damage.

Crack is generally divided into longitudinal and transverse cracks crack. The most common longitudinal cracks in the weld puddle recess due to the recess does not fill the bath, sink and accumulate harmful impurities easily make local plasticity is reduced. And at the recess and at the last weld solidification cooling, cooling shrinkage stress is concentrated here. Transverse cracks usually during steel welding. Gang carbon upon cooling too fast or uneven cooling may also have transverse cracks.

Welding crack formation is usually due to the following five reasons:

1, the chemical composition of the base material, crystal structure, method of smelting and so on. The higher the carbon content, such as steel or alloy higher the amount, the higher the hardness of steel is usually more prone to cracking during welding.

2, the cooling rate is high when welding cracks easily. Therefore, welding should avoid the draft and avoid rain water. In welding, high carbon steel or alloy steel, according to the composition or properties of the base material, and some measures to be taken after heating insulation before welding.

3, the inner electrode containing sulfur, phosphorus, carbon, high weld cracks easily. Parathion is harmful elements, sulfur high heat weld brittle, high phosphorus weld cold brittleness, electrode containing parathion amount must be at 0.0035 or less.

4, improper welding sequence member also easy to crack. When the knot is not the time to arrange the order of the formation of welding shrinking force, impede the free shrinkage of the weld, resulting in a greater shrinkage stresses generated weld cracking.

5, welding around the low ambient temperature, or in the air cooling conditions have a good result in excessive heat can cause cracks.

Fourth, the overflow.
    There is excessive overflow of molten metal flowing phenomenon four weeks weld without melting the base metal during welding. Overflow is not a major weld defects, but the surface of the base material over more than 3mm should shovel to overflow, then polishing wheel. Overflow is due to the rapid melting of the welding electrodes, along which molten metal flows pool solidified on the base material. Overflow shape as shown in FIG three. When the overflow is often formed when the welding current is too large or choose to manipulate the arc overstretched generated. It is relatively easy to place in vertical or overhead welding when welding. Phenomenon may be less than the base metal penetration occurs in the event of concomitant flooding phenomenon. Supervision found behind the flooding phenomenon is to pay attention to check whether the overflow slit no penetration defects.

Fifth, eating side.
     Eating side edge welded seam refers pillow melting recess. Eating side of the phenomenon as follows Triple Image. Cause eating side when welding current, welding voltage is too high or inappropriate spatial location caused by the uneven distribution of molten metal. Eating side external weld defects in the inspection when the naked eye can see. Eating side of the phenomenon will weaken the cross sectional area of ​​the base metal and the formation of local stress concentration caused damage when member force.

Six pores.
     When welding in a molten metal solution to the gas to be discharged, but met resistance and solidification of liquid metal to remain in the metal forming the pores. Pores while reducing the strength of the weld joints may cause the leakage. Pores formed by welding a uniform, flocks, chain or several individual cases, the weld inspection found a uniform groups of chain-shaped pores must shovel to re-weld welding this paragraph, for a single vent according to the importance of location to decide whether to deal with the main causes of porosity are:

1, the base material surface dirt, rust, paint, grease and other welding.
2, there is no drying electrodes, electrode coating too moist.
3, the welding speed is too fast, rapid solidification of the molten metal leaving no time to exhaust gas to the solution.
4, welding improper operation, arcing pull too long, so there are more gas to dissolve in the metal solution.
5, the base metal electrode material is poor or wrong. (Different from the base material to be used with different electrodes).

More than six kinds of welding defects are relatively common, Hainan steel factory inspection supervision in steel member can serve as a reference. In the actual work, we must first figure out the design requirements, and in strict accordance with the "steel construction and acceptance of norms" and "construction steel welding procedures" and other regulations. Katsukuni Steel specializes in the production of steel plants, warehouses, logistics centers, stadiums, hangars, steel supermarket, high-rise steel buildings, steel container housing and other buildings. Katsukuni Steel currently has a large steel structure production equipment and automatic spraying production line to meet the different needs of customers. Product sales to the Middle East, Africa, Southeast Asia, Europe, South America more than 30 countries and regions.