SynChem – Resins & Varnishes WEVOPUR 390 PU encapsulating system

• Respect first in – first out principle.
• Transfer daily consumption close to the potting area well in advance to allow them to adjust to production hall temperature. Cold material has higher viscosity and flows slower/differently. This can lead to different material pressure on the mix meter machine and thus to inaccurate mix ratio.
• The filler of WEVOPUR 390 may sediment. Therefore WEVOPUR 390 needs to be homogenized (stirred) prior to use. Homogenize by using e.g. special stir gears (cup stir is better than blade mixing), a drilling machine with top-fitted stir piece or manually with a rod or spatula (no rough-textured wood, splints could get into the resin). Avoid air entrapment during stirring which may lead to humidity (drilling machine with top-fitted stir piece with 100 – 300 rpm). The sedimented filler needs to be completely homogenized (incl. possible bottom sediments).
  Without sufficient homogenization the top part of the container will contain too much resin (reactive component) and in the lower part too much filler. This leads to over/ under cross-linking. The resulting cured polyurethane will be too hard or too soft and shows different mechanical, thermal and electrical properties as indicated in the technical data sheet.
• Protect both resin and hardener against humidity.
• After homogenization the incorporated air can be removed by using vacuum. Place WEVOPUR 390 in the tank and apply vacuum (50 bar) for approx. 30 min while stirring.
• The mixing ratio should be checked and documented daily prior to start of production. Even after short breaks in production it might be useful to check the mixing ratio. Also, the density (dosage of WEVOPUR 390 through mixing head) should be checked. The mixing ratio indicated in the technical data sheets has to be adhered to. Deviations must not be more than 3 % referring to the hardener component.
• Excess hardener can react with humidity leading to formation of carbon dioxide and therefore to air entrapments. Furthermore excess hardener usually leads to harder material. Excess resin acts as a softener. However, a minor low dosage of hardener is usually less critical than an overdosage. It is not recommended to deviate from the ideal mixing ratio to change the material properties.

Preparation of components

Humidity adheres to every metal or plastic surface. Because humidity may lead to air entrapment during curing it might be necessary to dry components prior to encapsulating. It is sufficient to dry components for 1 - 2 hours at 60 – 80 °C in the oven. Pre-drying is particularly important for coilable materials.

The sensitivity of encapsulating systems and hardeners against humidity and the humidity content of various plastic surfaces varies. Please consult with Synflex regarding isolated cases.

Pre-heating of components has a positive influence on the flow behaviour of the resin. The warm component heats up the resin thus lowering viscosity. The resin penetrates the component faster and displaced air can ascent faster. The higher the component’s temperature, the better the resin flows. Component temperatures of up to 80 °C do not affect the uncured resin.

Pre-heated components do also accelerate curing.