38 They must be mixed and dosed precisely in accordance with the manufacturer’s instructions and the technical data sheet in the specified mixing ratio. As polyaddition adhesives, epoxies and polyurethanes are very sensitive to fluctuations in the mixture. The A component usually corresponds to the epoxy resin, while the B component contains the hardener, which is often based on amine or thiol. The B component is usually significantly lower in viscosity than A. After mixing the resin and hardener, the reactive volume is subject to a time-limited processing time, as the chemical reaction of hardening begins from the first contact between the resin and hardener, leading to a more or less rapid increase in viscosity. This time interval is called the pot life. One property of epoxy casting resins is the high exothermicity of the curing reaction, where larger amounts of the reactive mixture can give off a considerable amount of heat during the cross-linking reaction. This can lead to components being damaged, particularly with high-volume applications. An appropriate potting strategy with sequential application can control this effect. With the material preparation system (MPS), the material is permanently recirculated in the pipe system, tempered and processed under vacuum without gas voids. The pressure-sensor control at critical points in the processing system guarantees complete command throughout every production cycle. In addition, refilling is possible during operation, so machine availability is not lost due to unnecessary downtime. With the exception of a few examples, pasty adhesive systems based on epoxy resin are formulated as 1K, which means the resin and hardener are present side by side. To ensure the reaction does not occur during shipping, storage and processing, the hardener component is often finely distributed as solid particles in the resin or chemically immobilised. The processing time of these materials – the pot life – is therefore often very long. If the component is heated using an oven, infrared lamp or microwave after application, the hardener component melts, or the immobilisation of the hardener is removed and the chemical reaction takes place at a very high temperature in a matter of minutes until it reaches handling strength. Since it is not necessary to mix resin and hardener, it is often possible to apply the 1K epoxy resin directly from the dosing pump. Sealing is an effective dosing process to protect components from external influences through a barrier. A usually highly viscous sealing material is applied to the components, according to a defined 2D or 3D sealing contour. The most common area of application is the sealing of housings and their covers, and it is also used to connect components to one another. This is used to eliminate dust, temperaturerelated influences, moisture, and protect sensitive components and other external influences. To achieve the optimal sealing contour, a continuous, precise dosing application is essential. CIPG vs FIPG Two dosing methods are typically used: cured-in-place gasket (CIPG) or formed-in-place gasket (FIPG). With CIPG, liquid seals are applied to a housing and the cover is then joined. This process is a soluble compound and allows the lid to be opened to repair the component. The FIPG is an inseparable connection that sticks to both the housing and the lid. Liquid seals are especially useful for sealing complex 3D geometries that cannot be reliably sealed with conventional seals, gaskets, punched parts or weather seals. Using adhesives as FIPG or CIPG has an advantage over silicone in that they have much shorter curing times. In addition, FIPGs and CIPGs can be released from the components, so they are reusable. Liquid seals also have a restoring capability, so they partly or fully return to their original shape. May/June 2024 | E-Mobility Engineering Structural adhesives can seal and provide strength (Image courtesy of PPG)
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