Читать книгу Welding Metallurgy - Sindo Kou - Страница 107

1 3.1 Experimental results show that the depth/width ratio of stainless‐steel welds increases with increasing electrode tip angle. How does the angle affect the effective radius of the electric current at the pool surface (the anode spot)? How does this radius in turn affect weld pool convection and the weld depth/width ratio?

2 3.2 It has been suggested that the weldability of stainless steels can be improved by oxidizing the surface by subjecting it to an elevated temperature in an oxidizing environment. From the penetration point of view, do you agree or disagree, and why?

3 3.3 Consider Marangoni convection in a simulated weld pool of NaNO3 such as that shown in Figure 3.22a. As the laser beam diameter is reduced at the same power from 5.9 mm to 1.5 mm, does Marangoni convection in the pool become faster or slower and shallower or deeper, and why?

4 3.4 In electron beam welding with the surface melting mode, which driving force for flow is expected to dominate?

5 3.5Name the four different driving forces for weld pool convection.In GMAW with spray metal transfer, is there an additional driving force for weld pool convection besides the four in (a)? If so, explain what it is and sketch the flow pattern in the pool caused by this force alone.

6 3.6 Paraffin has been used to study weld pool Marangoni convection. The surface tension of molten paraffin decreases with increasing temperature, and convection is dominated by the surface‐tension effect. A thin slice of paraffin is sandwiched between two vertical pieces of glass, and its top surface is in contact with the tips of two hot soldering irons to produce a weld pool that penetrates downward into the thin slice, as shown in Figure P3.6. Sketch and explain the flow pattern and the shape of the pool.Figure P3.6 Paraffin sandwiched between two vertical pieces of glass. Top surface is in contact with the tips of two hot soldering irons to produce a weld pool that penetrates into the thin slice.