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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
This apparatus allows the mixed potting compound and the objects to be encapsulated to be de-gassed separately before pouring, and for the pouring itself to be done under a vacuum
The mixed potting compound is placed in the centre container - a disposable paper cup - and the objects to be impregnated are placed in the molds round about. Once a suitable vacuum has been developed (550 Torr), the potting compound is then poured into the first mold by turning the external spindle knobs. The remote switch is then pressed to move the inner turntable round to the next mold to be filled.
The chamber is vented to the air, and then pumped down again, a cycle repeated several times, before the molds are taken out and left to cure at atmospheric pressure.
The conical filter flask is charged with Drierite dessicant.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Well I'm confused, and I think I have to say that I was wrong about the hardener boiling in the chamber.
I looked up the chemicals by CAS # from the MSDSs (two for the epoxy resin and one for the hardener), and the vapor pressures were all in the range of 10 to 20 u. And since I know I didn't go that low, I have to say that, as Ash suggested, I must have been looking at entrapped air.
The vigorous bubbling and splattering I experienced is an issue. If I ever vacuum encapsulate anything again in the future, I'll have to do it differently.
Anyway, tomorrow I hope to test the coils and see how the epoxy has affected their frequency response...and if I don't like it, they're going right in the garbage...
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I give up on epoxy...
The second coil that I encapsulated, the layer wound coil, has a problem in that the epoxy is still a little "sticky" after almost two days. Upon being touched, it leaves a fingerprint, yet it's hard in the sense that I cannot gouge it with a fingernail.
And I'm baffled by this because the epoxy left in the mixing cup, from the same batch, seems to have cured perfectly, i.e., it's not "sticky" at all.
And there's a yet a third sample of epoxy from the batch, that I kept, and it too, has no problems, i.e., it's not "sticky".
This makes me think that I really did boil something away in the vacuum chamber, yet when I tested the pump, it pumped right down to the previously measured limit of about 35u, implying to me that no volatile stuff went through it.
Edit:
I just took a rag and wiped it, and now it's not "sticky" anymore, so maybe there's really no problem.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
jpsmith123 wrote ...
I give up on epoxy...
The second coil that I encapsulated, the layer wound coil, has a problem in that the epoxy is still a little "sticky" after almost two days. Upon being touched, it leaves a fingerprint, yet it's hard in the sense that I cannot gouge it with a fingernail.
And I'm baffled by this because the epoxy left in the mixing cup, from the same batch, seems to have cured perfectly, i.e., it's not "sticky" at all.
And there's a yet a third sample of epoxy from the batch, that I kept, and it too, has no problems, i.e., it's not "sticky".
This makes me think that I really did boil something away in the vacuum chamber, yet when I tested the pump, it pumped right down to the previously measured limit of about 35u, implying to me that no volatile stuff went through it.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
jpsmith123 wrote ...
I give up on epoxy...
The second coil that I encapsulated, the layer wound coil, has a problem in that the epoxy is still a little "sticky" after almost two days. Upon being touched, it leaves a fingerprint, yet it's hard in the sense that I cannot gouge it with a fingernail.
And I'm baffled by this because the epoxy left in the mixing cup, from the same batch, seems to have cured perfectly, i.e., it's not "sticky" at all.
And there's a yet a third sample of epoxy from the batch, that I kept, and it too, has no problems, i.e., it's not "sticky".
This makes me think that I really did boil something away in the vacuum chamber, yet when I tested the pump, it pumped right down to the previously measured limit of about 35u, implying to me that no volatile stuff went through it.
This surface tackiness is normal in unwaxed resins.
If yours is a waxless variety, you can prevent surface tackiness by laying a polymer sheet such as PTFE over the surface while it cures OR coat the surface with a PVA release agent spray, which you can wash off in the kitchen sink when the resin has cured. And as a last resort you can always remove the tacky layer with wet-&-dry sandpaper.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Futurama...
The metallic goons have been deployed, with instructions to make an offer JP cannot refuse.
jpsmith123 wrote ...
I won't go willingly Patrick...Never!...they'll have to come and get me...
Proud Mary wrote ...
This surface tackiness is normal in unwaxed resins.
If yours is a waxless variety, you can prevent surface tackiness by laying a polymer sheet such as PTFE over the surface while it cures OR coat the surface with a PVA release agent spray, which you can wash off in the kitchen sink when the resin has cured. And as a last resort you can always remove the tacky layer with wet-&-dry sandpaper.
There are permanent sparys too.
Its good of you to point this out Proud Mary, whan i do my polyester casting (sourced from Michaels) that surface layer is always a problem and we use that spray to make any air exposed surfaces dry, thus eliminating the "stickiness layer". But why did his two other waste cups dry/cure hard with no stickiness, even when exposed to air?
Im very suspicious he volatized a chemical off, in which case its not a surface defect, but a defect throughout the whole epoxy volume.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
Proud Mary wrote ...
This surface tackiness is normal in unwaxed resins.
If yours is a waxless variety, you can prevent surface tackiness by laying a polymer sheet such as PTFE over the surface while it cures OR coat the surface with a PVA release agent spray, which you can wash off in the kitchen sink when the resin has cured. And as a last resort you can always remove the tacky layer with wet-&-dry sandpaper.
There are permanent sparys too.
Its good of you to point this out Proud Mary, whan i do my polyester casting (sourced from Michaels) that surface layer is always a problem and we use that spray to make any air exposed surfaces dry, thus eliminating the "stickiness layer". But why did his two other waste cups dry/cure hard with no stickiness, even when exposed to air?
Im very suspicious he volatized a chemical off, in which case its not a surface defect, but a defect throughout the whole epoxy volume.
Well now, I have no sure answer to that one, Patrick, not knowing much beyond the rudiments of casting - but when air-inhibited waxless resin is cast in a vacuum, using the type of apparatus I described above, then no tacky layer forms because of the relative absence of air to inhibit it. This method is called dry vacuum impregnation. (As I'm sure you know, air-inhibited waxless resins are used in multi-layer casting, as the tacky surface helps the next layer bond in. Waxed resins are used for glossy top coats - the wax floats to the surface during gelling, and so prevents the resin reacting with the air.)
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Grooved Bobbins For Segmented Windings
