To become an Inspection Engineer

The static volt ampere characteristic of the arc. The external characteristic of the power source.

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The static characteristic of the arc is the dependence of the arc voltage on the current Uд = f(Icв)  at the constant length (lд = сonst).

The numerous studies have established that, although there are differences for different arcs (inessential), the common for all arcs is that the dependence for the arc Uд = f(Icв) – the static characteristic of the arc is nonlinear (Fig. 1). This arc distinguishes from other energy consumers, for example, the resistor that has a linear characteristic (U = f(I) the dependence in accordance with Ohm’s law is linear). This is due to another mechanism of electrical conductivity in the arc than Continue reading →

To become an Inspection Engineer

The fatigue test.

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Another type of mechanical testing, which we will consider in this series of articles, is called the fatigue test. This type of test allows you to determine the fatigue strength of the metal. The loading of the element during fatigue tests is cyclical. The fatigue tests help the constructor to determine the ability of the metal to resist fracture under cyclic load conditions. Usually, to achieve the fatigue limit of metal, the series of fatigue tests should be carried out. The tests are carried out at different stress levels, until the maximum possible voltage level is found, below Continue reading →

Inspection of Welded Seams

The power supply classification features. The potential distribution in the arc. The welding arc properties (Part 1).

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The arc power supply is classified according to the following characteristics:

  1. by the current type: a) alternate current: transformers, elevated-frequencies generators; b) direct current: generators, rectifiers.
  2. by the design features:

The transformers are divided into 3 groups:

  • With the normal magnetic scattering:
  1. a) with the separate throttle;
  2. b) with the combined throttle.
  • With the increased magnetic scattering:

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Metallography and Heat Treatment of Metal

The metal structure basis (Part 3).

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During the welding heat is not transmitted in the uniform manner. The certain part of the metal part is heated to a very high temperature, while the metal temperature on the sections adjacent to the weld zone remains lower. This leads to the fact that in areas located at different distances from the near-weld zone, the expansion occurs at different scales. That part of the metal part that is exposed to the straight will expand, while at other sites the metal that has the lower temperature will resist expansion.

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Metallography and Heat Treatment of Metal

The polymorphic transformations in alloys (Part 3).

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The diffusionless transformation can occur as a result of the disordered atomic transitions (it is called «massive»). It is possible to combine the ordered, cooperative rearrangement of the lattice with the diffusion redistribution of components between the initial and the resulting solid solutions. Which of the indicated mechanisms of polymorphic transformations is realized depends on the magnitude of the change in the thermodynamic potential, on the ratio of cooling rates, the diffusion and lattice rearrangement, and on the structure of the solid Continue reading →