Posted: 7/28/2008 8:05:46 AM EDT
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Lets say you have a little blob of 5 minute epoxy, Will it float in water? -Jared |
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as long as it is less dense than water. Epoxy in general has a specific gravity ranges from .75-1 water absorption over time may make it sink. |
Why would it absorb water? It seems to be a pretty non porous material. MNJ, How are your physics related to neutral buoyancy? 
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In order for anything to float, it has to displace (by volume) its weight in water. In other words, the amount of water it pushes out of the way (displaces) weighs exactly what the object does. Look into: Archimedes Principle. |
HF, This I understand... I am trying to make something that is 1/16th of an oz, neutrally buoyant... |
The 5 minute epoxies are rarely waterproof. The longer setting ones often are. |
What shape is it? It needs to displace 1/16 of an oz. (.0039lbf) of water. So you need a shape that has a volume of .0000625 ft^3 of volume, or .108 in^3. If it were in the shape of a sphere, its radius would be .295 inches. |
Now you've completely lost me as to what you're trying to accomplish. Where does this piece of sheet metal work into all this? In order for something to be neutrally buoyant, it has to displace an amount of water equal to its own weight. Assuming that you are submerging this thing in fresh water (density = 62.4 lbf/ft^3): Weight (in lbf) = density (lbf/ft^3) * Volume (ft^3) Rearrange the above equation since you are looking for a certain volume for a given weight. |
Epoxy is well known for water absorption. Companies that know the hell what they're doing in design of composite structures incorporate the reduction of strength into their material allowables. |
Go to a hobby store that deals in radio controlled aircraft. They will have microspheres, a powder that has almost no weight. Get some long set epoxy, more than one hour set time. Mix the epoxy according to the instructions, then add in the microspheres until a stiff putty is made. This will have a density of about 1/4-1/2 gram per cubic centimeter. It will adhere to metals better if the surface of the metal is rough and coated with a thin layer of mixed epoxy. Press firmly and let set. Because of the microspheres, water absorption is limited. |