One of the main application relevant parameters of a resin is its flow characteristics, which need to be adjusted as closely as possible to the intended use and installation conditions.
Optimised flow characteristics are particularly important e.g. for the encapsulation of complex geometries, narrow spaces and coil windings and for reducing the risk of potential problems, such as air inclusions and voids. On the other hand, high steadfast stability may be required, for example when used as a thixotropic bead with a low flowability.
WEVOPUR 67210 FL
- Low viscosity despite high filler content
- UL 94 V-0 in 1.5 mm
- WLF 1.0 W/m·K
- High mechanical strength
WEVOPUR 801 FL
- Good adhesion to various materials
- Good chemical resistance
- Operating temperature range -40 °C to 140 °C
WEVOPOX 2505 / WEVODUR HC 1002
- Insulation class H (155 °C)
- Excellent impregnation characteristics
- Hot curing
- Good electrical properties
Optimised flow properties reduce the risk e.g. of air inclusions and voids.
Quantifying flow properties
The flow characteristics of a resin can be quantified by rheological parameters, with viscosity playing a major role. The unit of dynamic viscosity is mPa·s. The lower this value, the better in general the flowability. The viscosity of water is defined as 1 mPa·s and the viscosity of engine oil, for example, is 500–1000 mPa·s.
The temperature of the material has an influence on the viscosity, which is reduced when the temperature increases. In this case, temperatures of 40 °C to 50 °C yield optimum flow characteristics at low viscosities. Increasing the temperature beyond this range does not significantly improve the flow characteristics, but it increases the tendency of fillers to settle and shortens the pot life. The flow characteristics depend not only on the rheological parameters mentioned, such as viscosity and thixotropy, but also on the wetting characteristic of the encapsulant on the substrate surface.
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