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Understanding the Resin Encapsulation Process Part 1
What Happens When You Severely Overheat a Resin Casting
While resin encapsulation seems straightforward, several variables can lead to undesirable results. Incorrect application techniques, use of highly detailed or porous objects, improperly preparing organic materials, inattentive or hurried pouring, or overheating the casting can all lead to unsuitable outcomes.
Overheating a casting is one of the most common and easiest mistakes to make. Overheating occurs when a casting is not able to efficiently shed the heat that is generated from the chemical reaction between part A and B. This heat is called the exotherm. An exotherm can reach higher temperatures when a large amount of material is reacted in a mold that is too deep, or in a shape with a large center of mass that does not allow the reaction to shed the heat produced, like a cube. Exotherms generated on larger scales can reach extremely high temperatures and have the potential be dangerous. Trying this is not recommended. Dangerous exotherms are not a risk if you are using the resin as intended.
Some projects, like encapsulation, may require casting a thicker layer. When this is attempted, there is always the chance of overheating the casting, However, there are safe ways to trial and practise these castings. It is always recommended to try any project on a smaller scale before attempting the final project.
Using a resin outside of the application instructions always comes with risk. However, the limits of a product can make it easier to plan your project to avoid unwanted results. It was for this reason the EcoPoxy R&D team decided to do a trial at a volume and in dimensions that would be guaranteed to overheat.
Below are the details of the trial, and explanations of what occurred, including images and a graph.
This trial was conducted by professionals in a controlled environment and should NOT be attempted or repeated by anyone.
FlowCast SPR Trial – Effects of Severely Overheating Resin
Dimensions of mold:
Width – 6 inches
Height – 6 inches
Depth – 6 inches
Volume of resin (mixed):
3600 millilitres or approximately 122 ounces.
Cedar and pine supports
MDF covered with EcoPoxy Mold Tape
The resin part A and B were measured by volume (2400 mL part A, 1200 mL part B) and mixed for 5 minutes. Once fully mixed, the resin was decanted into the mold. A thermocouple was attached to the mold and centered in the middle of the casting. Just before the resin was added, the datalogger attached to the thermocouple started recording. The resin was poured into the mold and the casting was then allowed to cure under observation.
Approximately four hours after being poured, the casting started to heat up. This was noted, and the team documented the following:
- At 4.5hrs and at 60°C the casting temperature started climbing extremely quickly. This was recorded by the datalogger, and the casting became somewhat cloudy and showed rippling.
- At 140°C significant yellowing was seen in the resin and resin was being pushed out onto the surface of the casting. Yellowing started at approximately 100⁰C but became extremely dark and apparent at this time.
- At approximately 200°C the resin began to blacken in the center. The walls also contracted and bowed inward. There is normally an approximate shrinkage of about 2% when the resin cures. The obvious bowing of the mold walls was a new observation.
- At approximately 230°C the resin began to crack due to heat and stress. Small cracks began at the edges and slowly grew towards the center in feather-like patterns. At this temperature, a crack separated the resin from the thermocouple, creating the dip seen in the graph.
- Within 30 minutes of the temperature starting to climb, it reached the peak recorded temperature of approximately 260°C. It was theorized that the casting could have reached a much higher temperature, potentially 300°C, but this is unconfirmed, as the thermocouple was not in contact with the resin at this time.
- Upon reaching approximately 260°C, the resin cracked further and began to release smoke and black, lava-like resin.
Below is the temperature graph created from the data taken by the thermocouple. Notes have been added at key points.
You can clearly see that once the exotherm started to climb, there was no way to control it. This is why it is recommended to stay within the casting dimensions specified for a resin system and to always follow manufacturer instructions. This was an extreme example of what could happen.
The following images show the casting once it was fully cured, cooled and demolded.
FlowCast SPR is not recommended for encapsulations as it is very reactive, making it incompatible with this process. FlowCast can be used for encapsulations, keeping in mind that at larger volumes and greater casting thicknesses, it can still overheat. If you do want to experiment, always do small-scale trials representative of your project before attempting a full-scale encapsulation.