Дослідження морфології поверхонь контактування з використанням електронної мікроскопії

Анотація

INVESTIGATION OF SURFACE MORPHOLOGY CONTACT

USING ELECTRONIC MICROSCOPY

V. Korobsky, V. Gural

Metallographic analysis of composite work surfaces contact helps detect patterns of electrical wear, establishing the reasons that cause a particular type of erosive destruction of the contacting surfaces. Erosive wear discontinuous contacts can be caused by the presence of bridged erosion effect of a short arc (mass transfer from the anode to the cathode), the emergence of a plasma arc (mainly mass transfer from the cathode to the anode). The distinctive morphological features impressions plasma arc is a significant difference in the size of the cathode (a_к) and anode spots (a_а) remaining on the surface of contact and it should be noted that  a_а= a_к., while for short arc characteristic a_а< a_к.

The purpose of the study - metallographic and X-ray spectral analysis of contact surfaces and identify the impact energy parameters of the electric arc on the value of electrical wear.

Materials and methods of research. To study were taken contact details starters made of contact materials: copper-based metals with impurities and other thermodynamically stable compounds.

Morphological study of contact surfaces were conducted using scanning electron microscope «Cambridge Stereoscan» S4-10 of attachment for X-ray analysis Link System - 290 and X-ray microanalyzer "Camebax SX - 50".

Research results. X-ray analysis conducted contacts enables investigate the impact energy distribution curves of phase components of the material in the surface layers.

The pictures of contacts still have a large current density, which leads to the formation of flare streams that lead to the destruction of the other electrode. Since the current variable, we have a picture of the destruction of two electrodes similar to one another, melted material plus the transfer of material in the vapor phase.

Basically there are spots cathode type (small dots). In some cases there are connection spots cathode and anode types (large oval interspersed with small dots). The destruction of the electrodes occurs when exposed anode and cathode spots and the action of jets of plasma arc. The contact material is melted, the liquid phase is transferred (corrugated surface irregularities and bumps) appear cathode plasma torches and they lead to significant destruction of movable contacts (bridge). In moving contacts there are few places out plasma jets, but given the fact that switching occurs in alternating current, the losses and the transfer of material occurring both movable and immovable of contacts.

The increase of Nb and 5% or more leads to increased evaporation of copper by an electric arc discharge due to the large difference in thermal properties of components. As a result, the working surface is enriched with Nb, and copper is found in small amounts in the form of small spherical particles that settled vapor mainly in the peripheral areas.

Conclusions

1. The cathode torches with real contact actively destroy rolling contact, so we can recommend to contact a mobile erosion resistant material.

2. Significant volume content of graphite in standard formulations Cu-C prevents welding contact surfaces under the influence as arc discharge, and by the film, which is deposited from the vapor phase on the working surface contacts. This damages the already weak adhesion areas of copper frame, leading to a large copper local overheating and therefore to a significant destruction contact details.

3. Erosive wear contacts starters there is the action of jets of plasma arc AC morphologically confirmed photographs of the working surface contacts.