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Steelworks

In welding design what are the different applications of square-groove, V-groove, U-groove and J-groove?

When the base metal is thin (i.e. 0.125” to 0.25”), square-groove can be adopted. Where welding is carried out from one side of the joint, a temporary backup strip can be used to ensure proper joint penetration and to avoid excessive leakage of metal though the joint.

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Convex fillet welds are sometimes used in welding. Why?

There are three types of fillet weld cross section profile, namely, flat, convex and concave. The convexity in convex fillet welds serve as reinforcement, which is believed to provide additional strength. However, care should be taken in not introducing excessive convexity to fillet welds.

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There is a general rule in fillet weld that “the leg should be equal to the thickness of metals.” Why?

Let’s take an example of 6mm thick plates to illustrate the rule. In case 12mm leg is adopted in the fillet weld, the weld volume would be 3-4 times more than required. It would result in waste of weld metal and welder’s time. Worse still, over-welding may weaken the structure and result in distortion owing to the formation of residue stress. As such, the resulting weld could support less stress than fillet weld with “the leg equal to the thickness of metals.”

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Why are insulating washers installed between steel bolts and connecting aluminium plates?

Corrosion of aluminium can be triggered by putting it in contact with another metal in the presence of water. This is known as bimetallic corrosion or galvanic corrosion. The mechanism of such corrosion is the formation of a cell in moist condition so that an electric current is generated to flow between the two metals in direct contact. The degree of corrosion is influenced by the nature of connecting metals, their electrode potential, their areas, conductivity of fluid etc.

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What is the behaviour of internal force in preloaded fasteners?

The force in a bolt in a bolted joint depends on the preloading force applied to it during the tightening operation. For instance, when the preloaded bolt is tightened with a certain force, the bolts’ internal force will not increase significantly if the external applied force on the bolted joint does not exceed the preloading force.

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