It is necessary to clearly understand the difference between the terms «attestation» and «certification» relating to testing for welders. When we say that the welder was certified, it means that this welder demonstrated the sufficient skills to perform the weld. At the same time, the concept of «certification» belongs to the documents which confirm this certification. The welder who has successfully passed the test for the certification program can be called the «attested welder» Continue reading →
The current density distribution, temperature and gas flow velocity in the real welding arc (Part 2).
Therefore, the drop which is in an arch column because power lines of current can’t sharply change the direction, has to make noticeable change to distribution of density of current in it (see Fig. 1), the section I–I under the drop.
As temperature of the arch column is defined by current density in it, under the drop the arch column temperature has to decrease (see Fig. 1).
The lack of side fusion.
The lack of side fusion arises because of small current, high welding speed, low-quality deseaming after the performance of the previous layer.
The lack of side fusion is admissible defect. The repair is regulated by regulating documents on welding.
On the figure, the lack of side fusion is visible in the form of the black dash Continue reading →
The hardness measurement. The Rockwell hardness test method (Part 1).
The method of determining the Rockwell hardness includes numerous embodiments of the same principle as the Brinell, but using indenters with several diameters. In the method the following indenters are used: the conical diamond and the balls of hardened steel with diameter of 1/16, 1/8, 1/4 and 1/2 inch. The prints obtained by the Rockwell hardness test are less than Brinell test. It allows you to make tests on rather small area of metal.
Using one of this indentor, it is possible to put different loadings to the majority of Continue reading →
The polymorphic transformations in metals (Part 4).
The growth rate Up of the new modification crystals depends on overcooling. With increase in overcooling ΔT the difference of chemical potentials Δμ grows and Uр increases. However with the temperature falls the diffusive mobility of atoms decreases. In case of large overcooling this reduction blocks influence of overcooling on Δμ and the crystals growth is slowed down; on the curve dependences of Uр from ΔT there is a falling branch (see Fig. 1) which isn’t on curves of metals crystallization.