Adjusting The Foam Density:
By combining equal parts of A and B, the foam expands to about 10 times itâ€™s original liquid volume. The result is a 6 lb. density (per cubic foot) rigid foam that is extremely strong and still relatively light weight. This is perfect for filling small spaces where the highest strength is required and weight is not a real issue.
However, as the volumes increase, a lower density (higher expansion ratio) may be desirable. With the increase of volume, surface area also increases so strength and adhesion are less of a factor. In larger volumes, weight may be the over riding concern. Rather than stock several hard to get foam densities, it is much easier to lower the density of a high density foam as needed.
This type of polyurethane foam is highly reactive to small amounts of water. Even the humidity in the air can slightly alter the expansion ratios. The more moisture introduced into the mix, the higher the expansion ratio. By purposefully adding small amount of water to the mixture, we can adjust the expansion (and density).
The difference of just adding one drop of water is dramatic. Keep in mind that if you double the batch size, you will need to double the water amount to achieve the same expansion ratio. A little experimentation is highly recommended before actual use in your project.
Most other brands of commercially available 2 part liquid foam expand to about 20 times their original volume and are already near the limit of usefulness. The foam is near itâ€™s lowest density and strength. It cannot be adjusted down. Our new Adjustable Density Foam starts as a denser foam that can easily be adjust up using just a few drops of water.
WARNING: Do not burn or use hot-wire cutting methods on this or any other urethane based foam product because toxic fumes will be released. (However, the heat of a motor casing next to the foam is not a concern.)
"We have epoxy for most rocket building applications. Our Adjustable Density Foam is excellent for fin root potting."
Public Missiles, Ltd. carries a complete line of Epoxy adhesives selected for their excellent bonding with PML materials.
Also, take a close look at our adjustable density, expanding urethane foam. It`s perfect for encapsulating fin roots for nearly indestructable fin attachment!