10-05-2010, 08:27 PM
E-Paw ...
To defeat air bubbles you must first not introduce any into your casting epoxy. Yeah, I know that sounds like a "duh" statement, but it is critical! When mixing the catalyst into the epoxy, stir gently, slowly and mix thoroughly without any undue "splashing." You needn't stir violently to get a thorough mix.
The next step is to eliminate any air bubbles that have joined the party despite your best efforts to avoid them. Then, when you make your "pour," do so slowly and from a height that allows the liquid being poured to "neck down" to as fine a stream as you can. The premise is that any bubble larger that the stream at the point of contact with the mold will break when the stream gets narrower than the diameter of the bubble.
Next, so as not to capture any air which may manifest itself as a bubble on the actual surface of the mold, start your pour in a corner and keep it there, letting the casting liquid spread out across the surface of the mold. When the mold cavity you are pouring fills, quickly move to the next mold cavity and stay in the corner where you begin the pour.
One last thing. Surface tension. Although the use of petroleum jelly seems like an intuitive choice for a mold release, it has "dimension" and may impart that dimension to the finished part, yielding an imperfect surface on the final production part. When I was in design school (in the mid '60's and then again in the early '70's) and taking the class where we did patterns and molds and master molds from which to cast production molds, and then had to produce a run of "parts," we used a solution found in the pharmacy called "tincture of green soap" as a mold release. It had a very low coefficient of friction and was a marvelous mold release. You may find other substances that will work as well (Pam, maybe) but gently brush it on the surface of the mold, paying attention to a smooth surface and no bubbles.
Hope that helps.
To defeat air bubbles you must first not introduce any into your casting epoxy. Yeah, I know that sounds like a "duh" statement, but it is critical! When mixing the catalyst into the epoxy, stir gently, slowly and mix thoroughly without any undue "splashing." You needn't stir violently to get a thorough mix.
The next step is to eliminate any air bubbles that have joined the party despite your best efforts to avoid them. Then, when you make your "pour," do so slowly and from a height that allows the liquid being poured to "neck down" to as fine a stream as you can. The premise is that any bubble larger that the stream at the point of contact with the mold will break when the stream gets narrower than the diameter of the bubble.
Next, so as not to capture any air which may manifest itself as a bubble on the actual surface of the mold, start your pour in a corner and keep it there, letting the casting liquid spread out across the surface of the mold. When the mold cavity you are pouring fills, quickly move to the next mold cavity and stay in the corner where you begin the pour.
One last thing. Surface tension. Although the use of petroleum jelly seems like an intuitive choice for a mold release, it has "dimension" and may impart that dimension to the finished part, yielding an imperfect surface on the final production part. When I was in design school (in the mid '60's and then again in the early '70's) and taking the class where we did patterns and molds and master molds from which to cast production molds, and then had to produce a run of "parts," we used a solution found in the pharmacy called "tincture of green soap" as a mold release. It had a very low coefficient of friction and was a marvelous mold release. You may find other substances that will work as well (Pam, maybe) but gently brush it on the surface of the mold, paying attention to a smooth surface and no bubbles.
Hope that helps.
biL
Lehigh Susquehanna & WesternÂ
"America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves." ~~Abraham Lincoln
Lehigh Susquehanna & WesternÂ
"America will never be destroyed from the outside. If we falter and lose our freedoms, it will be because we destroyed ourselves." ~~Abraham Lincoln