Comparative Studies on the Electrical and Mechanical Behavior of Some Soldering and / or Impregnation Lacquers

Abstract

In order to evaluate the behavior in various electrical applications, the main mechanical and electrical characteristics of three different varieties of specifically chosen lacquers - based on alkyl-epoxy-melamine copolymer, the epoxy polymer and polyurethane were compared. From the mechanical determinations, it was found that at ambient temperature the polyurethane lacquer bending resistance was approximately equal to that of the epoxy lacquer and about 6.5 times higher that of the alkyl-epoxy-melamine copolymer. It has also been shown that at bending force of less than 150 Nm the investigated polyurethane lacquer has relatively large deformations of 0.4 mm / kN, which indicates a high capacity to take over relatively high deformations of the metal support (due to thermal expansion from various applications) without significant increasing mechanical stress. The recorded values for the alkyl-epoxy-melamine-based copolymer lacquer and the pure epoxy lacquer are 0.11 mm / kN and 0.03 mm / kN respectively. Determinations by dielectric spectroscopy have shown that at frequencies below 250 Hz the dielectric losses tgd for the epoxy and polyurethane lacquers are approximately equal and are about 2.9 times lower than for the alkyl-epoxy-melamine copolymer lacquer. It was also found that at frequencies higher than 250 Hz the investigated materials behave differently, respectively at the frequency increase up to 10 kHz, the dielectric loss tgd of the polyurethane lacquer remains constant at about 0.0045 in contrast to the epoxide lacquer at which the dielectric loss tgd increases monotone to 0.0095 at 10 kHz, respectively of the alkyl-epoxy-melamine copolymer at which the dielectric loss tgd is approximately constant 0.012 in the 250 Hz-10 kHz range.

Ageing of Some Lacquers Due to Microbiological Stress

“…For the comparative evaluation of resistance to mould action and influence of microbiological stress on the ageing of some polymeric lacquers, samples of siliceous sheet metal plates for electrical use were prepared as in [1].…”

“…The investigated lacquers polymerization was carried out by heating with 1.5 degrees / min and after 3 h at 155 ± 5 o C, natural cooling in a thermostatic oven with air circulation [1]. The samples were exposed to the moulds action both in a buffered mineral solution type Czapek -Dox, prepared from MERCK p.a.…”

“…Also, based on the insulation resistance values measured at ambient temperature (22 ± 3°C) with a FLUKE 1550B MegaOhmMeter (in DC at 250V with a circular measuring electrode described in [4,25] having a contact surface of 20cm 2 ) the volume resistances [1] of the lakes investigated before and after exposure to microbiological stress were calculated. Fourier transformed infrared spectra were recorded on a Jasco FTIR -4200 (Jasco, JP), coupled with and Attenuated Total Reflectance (ATR) Jasco PRO 470-H module, at resolution of 4 cm -1 .…”

“…The lacquers based on synthetic polymers have many applications in electrical engineering such as layers of corrosion protection, electro-insulating films and / or impregnation of insulating materials, consolidation of magnetic core and windings of transformers and / or electric motors [1], etc. Under the concerted and synergistic action of the stress factors (electrical, thermal, climatic, mechanical -especially vibration, microbiological [2][3][4][5] etc.)…”

The Hydrophily of Some Lacquers for Electrical Use

“…Various polymers are frequently used in electrical applications, both to ensure an adequate level of insulation and to perform anti-corrosion protection layers and / or to strengthen magnetic core and windings of electric transformers and / or motors [9], etc.…”