Mold-filling monitoring

Thermocouples are used to track the temperature change in the mold cavity which occurs due to the conductive and convective heat transfer between the mold walls and resin for non-isothermal mold filling applications, and also due to the exothermic heat release of the resin cure. If the temperature of the resin is considerably different than the mold walls, the sensor readings will change when the resin wets the sensor, and the data are used to monitor the flow front position by embedding many sensors in the mold cavity. The response rate of the thermocouples is dependent on the temperature differential between the walls and the resin inlet, and thermal diffusivities of the mold material and resin. These sensors cannot come in contact with the resin if they are to be reused, thus one needs to remove the cured resin on top of the sensor with acetone or some other process. 

Yeniknez, B. and Sozer, E. M., A grid of dielectric sensors to monitor mold filling and resin cure in resin transfer molding . Composites Part A Applied Science and Manufacturing, 40,476-489, 2009. 

Once the prepolymer and catalyst are added together, the chain extension (curing) reactions will commence. The time taken to mix must be carefully monitored. It must be sufficient to allow complete mixing, but there must be enough pot life left to allow pouring into the mold while the material is at the lowest viscosity possible. This is to allow the polyurethane to fill the mold completely and any entrapped bubbles to reach the surface. 

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