Practical tip: For completely bubble-free potting
Material preparation is key
For completely bubble-free potting results, make sure that the entire potting material preparation and feeding process is carried out in a vacuum. A high-end processing system (Inline Vacuum Potting System FAC-950) removes the dissolved air through thin-film degassing. An agitator provides degassing support in a vacuum tank by circulating the potting material. This lets the dissolved air rise to the surface of the potting material where it comes in contact with the surrounding vacuum. The degassing effect starts at the uppermost surface layers of the material. This much is true: The lower the viscosity of the material, the easier it is for the trapped air bubbles to rise.
The degassing effect starts as soon as the system is being filled with potting material – as shown in the picture – or later during circulation of the material via the tank cover. This is particularly true when the material flows over a wide-stretched discharge plate and the tank wall – as in the case of FAC-950.
Picture at right: Efficient thin-film degassing through conical tank and large discharge plate Picture at right: The right material temperature control is important for potting productivity
Adequate heating in many cases further reduces the viscosity of a material and accelerates the degassing process. In addition to faster and easier processing, air bubbles in the material rise faster, making any required evacuation easier. However, keep in mind that filled media tend to settle faster in the form of sediment in this case.
This process can be counteracted by appropriate agitation and circulation of the potting material. To achieve a continuous and constant temperature, all process components, including storage tanks, material feed lines, pumps and dispensers, etc., should be heated. Caution is advised in the case of potting compounds that cure when heated. Conducting a series of experiments with such potting media is recommended before using them in production.
To prevent introducing more air during the feeding process, all screw connections, material feed lines, pumps and valves must be hermetically or vacuum sealed.
The material preparation requirements depend on the potting material used. Particularly with 2C materials, there are resin systems that cure by moisture. To trigger a reaction, all it takes is to expose the potting medium to the ambient air (air humidity) for an extended period. On the other hand, moisture can lead to undesired secondary reactions in certain resin systems. When the resin is mixed with the hardener in 1C materials, the hardener reacts with the moisture absorbed by the resin. This leads to the formation of CO2, and the material starts to foam.
The unmixed hardener also absorbs moisture, enabling the formation of crystals. In the worst case, these crystals clog the machine filter. Adequate storage, completely emptying the drum and preparing the material in a vacuum can minimize such risks. If possible, moisture-sensitive resin compositions should be kept under vacuum in a preparation system after opening. Contact with moisture can thus be completely prevented.
Gentle preparation of the potting material in a vacuum is important in order to prevent damaging the material. For example, an excessively high vacuum value during preparation can cause outgassing of the material components. Make sure that the vacuum value is not below the permissible vapor pressure shown on the material data sheet.
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