Composite Mold behavior / Thermodynamics

[Sinope]

Dear All,

Currently we have changed from our epoxy tooling (molds) to aluminium tooling to obtain more accuracy in the dimensions of our final product.

Our resin is preheated to 50 degrees Celsius before injection and our epoxy tooling have similar temperature levels. At these levels the viscosity is adequate to fill the mould and there doesn't seems any undesirable (runaway) exothermic reaction of the curing resin.

Changing to aluminium molds seems currently creating an almost immediate exothermic reaction which prevent us from making products. Lowering down the mould temperature seems not to help and will affect the viscosity in a negative way.

Although the thermal conductivity of Aluminium (+/-250) is much higher than from Epoxy (+/-0.35), and its heat capacity around 50% higher, the temperatures of the Epoxy mould and the Aluminium mould are the same during the injection.

Could it be that the Aluminium mold gives more heat at the same temperature as the epoxy mold and will accelerate the exothermic reaction? Our there any Physical Properties that will described these effects in a better way?

Thanks!

 

[Achy47]

Thank you for sharing your experience with changing from epoxy tooling to aluminium tooling. It is interesting to hear that you have observed a difference in the exothermic reaction between the two types of molds.

Firstly, it is important to note that the exothermic reaction of a curing resin is dependent on a variety of factors, including the type of resin, the curing agent used, and the environmental conditions. Therefore, it is possible that the change in molds is not the sole factor contributing to the observed difference in the exothermic reaction.

That being said, there are some physical properties that may help explain why the aluminium mold is causing a more immediate exothermic reaction. As you mentioned, aluminium has a much higher thermal conductivity and heat capacity compared to epoxy. This means that the aluminium mold is able to transfer heat more efficiently and can hold more heat, resulting in a higher temperature and potentially a faster curing process. Additionally, aluminium is also a better conductor of electricity, which may play a role in the exothermic reaction of certain resins.

In order to better understand and control the exothermic reaction, it may be helpful to conduct some experiments with varying mold temperatures and resin formulations. This will allow you to determine the optimal conditions for your specific resin and mold combination.

I hope this information helps and good luck with your continued research and development.

 

[oswaler]

I would first suggest conducting further experiments to determine the cause of the immediate exothermic reaction when using aluminium molds. This could involve varying the temperature of the aluminum mold and observing the reaction, as well as testing different types of resin and their compatibility with aluminum molds.

In terms of understanding the behavior of composite molds and thermodynamics, it is important to consider the thermal conductivity and heat capacity of the materials involved. As mentioned, the thermal conductivity of aluminum is much higher than epoxy, meaning that it will transfer heat more quickly. This could potentially lead to a faster reaction of the curing resin, as it is exposed to higher temperatures. Additionally, the higher heat capacity of aluminum means that it can absorb and retain more heat, which could also contribute to the exothermic reaction.

Furthermore, the physical properties of the resin itself should also be considered. Different resins may have varying levels of reactivity and heat generation during the curing process, which could be affected by the use of aluminum molds.

In order to fully understand and control the behavior of composite molds and thermodynamics in this situation, it may be necessary to consult with a materials engineer or conduct further research on the specific materials and processes involved. It may also be helpful to analyze the data and observations obtained from experiments to identify any patterns or correlations that could provide insight into the cause of the exothermic reaction.