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Hello and welcome to another Easy Composites video tutorial. We're going to be just taking
a quick look at how easy it is to degas RTV silicone rubbers and casting resins using
our complete vacuum degassing system. Degassing is a highly effective process for removing
trapped air from within mixed materials such as RTV silicone rubbers polyurethane casting
resins infusion epoxies; all sorts of materials where air can become entrapped when the two
parts of a material are mixed together and if we have a look at this example here, which
is an RTV silicone rubber which has been mixed with its catalyst and allowed to cure at room
temperature without any degassing and as we can see we've got lots of trapped air within
the silicone, particularly on this example this has not been mixed in a way to reduce
the air entrapments and we can see the effect quite clearly. But compare that to this which
is exactly the same material, same silicone, but this has been degassed in this chamber
and then allowed to cure we can see that this is completely free of any air entrapment whatsoever,
so this would have a far improved tear strength over the undegassed version and also an improved
surface finish as well. Other materials that we might want to degas, this is a polyurethane,
water clear polyurethane. Now in this example again this has been mixed, part a and part
b together, and then allowed to cure without any degassing. Now we have to look a little
closer so if I hold this still you can see very fine air bubbles trapped within the material
and then we compare that to this one, where we've got a perfectly clear material, no trapped
air bubbles whatsoever. A degassing chamber is very commonly used for degassing resins
once they've already been poured into a mould, particularly moulds with fine surface detail,
and especially if they've got undercuts and the reason can be ably demonstrated using
this nitrile glove. If we tie a knot in it, not trying to get any air particularly trapped
within the glove itself but inevitably there'll be a small amount of air in the glove. Tie
a knot drop it into the degassing chamber. We pull a vacuum on this now, what happens
immediately as soon as the air is evacuated from this chamber, so we've got very low pressure
in the chamber, the tiny amount of air that's inside the glove expands hugely so it's volume
increased massively. Now we've sped this footage up slightly, this actually took roundabout
two minutes but it does give you a really good demonstration of why we degas and what
the whole principle of it is which is to expand the air to a bigger volume. So as soon as
we let the air back into the chamber, so the degassing chamber becomes at normal atmospheric
pressure the it crushed that air back down to its original size. I'll try and explain
why we might want to do this by means of a diagram on the board. So if I just draw a
random shape that we're trying to make a casting of. I've got a couple of details that I've
drawn here at different scales. So this is a large significant part of the moulding and
it's a potential, or it is certainly an undercut which is likely to have resin not flow into
it properly resulting in a large air cavity which means a significant part of the casting
of a part would be missing if we didn't do something about this. Now, when we've got
something at this scale, we would generally have a vent hole that we would have put in
at the time when we made the mould using a drinking straw or a dowel or some other means
so that this whole can breath, and that means that as the resin is poured into the mould
it can carry on rising up into this area because this won't become trapped air, because the
air can escape as the resin fills it. Now what we can't do is have vent holes to every
single fine surface detail, a nose, a chin, tiny leaves on a casting, it just isnt pratical
you'd have vent holes everywhere and you'd be forever finishing the part. So that's where
the degassing chamber comes in and it really is the only way to tackle this problem of
fine undercuts, such as this once we've demonstrated or I'm trying to demonstrate here. So what
we would do is pour the resin into the pot and then load the whole part in the mould
into the degassing chamber. When we draw a vacuum on the whole part then trapped air
that's been caused where the resin has filled into these fine surface details would expand
significantly just like it did with the glove that we showed earlier. Now when it does so
those larger air bubbles will come out and rise to the top you'll still be left with
a cavity but there'll be really nothing in that apart from a very minute amount of air
that's expanded significantly. When we put the pressure back on by venting the degassing
chamber to atmosphere then the size of those air pockets, or the size of the air will contract
hugely so would take up a much smaller volume just like the glove did when it shrank back
down. When this happens it sucks resin back up into these cavities so you'll be left with
almost negligible, in fact probably negligible, you probably wouldn't see it on the finished
part, and the resin would be fully occupying what was originally a cavity, and so by doing
the degassing process with the resin already in the mould we can ensure all these fine
surface details and undercuts are filled with resin properly on the finished parts. The
complete vacuum degassing system available from easy composites is as the name suggests
a full turn key solution for degassing. When you buy the product you have a choice between
this large vacuum pump and this smaller one. The way to decide which pump is right for
you is simply to look at the materials you expect to be degassing. If you're working
with highly reactive materials, like fast cast polyurethanes or water clear polyurethanes
and these tend to have quite a short pot life so you need to degas them as quick as possible
so that you can get on with pouring them before then start to cure. If that's the case and
you're working with those materials then the larger pump because that will empty this chamber
in about thirty seconds. Now silicon rubbers tend to have much longer pot lives so if you're
only considering and only want to be able to degas less reactive materials, like the
silicones then this small pump will pull down this chamber in a roundabout three minutes.
Now for a typical silicone rubber that's plenty of time to degas it fully and then use it
before it's anywhere near the end of its pot life, so if you're only working with slow
materials the small pump's fine if you're working with a mixture of those materials
or generally fast then go with the large pump. Setting up the system is as easy as can be.
It would be the same whether you were using the large or the small pump, so we'll pop
the small one away and we'll demonstrate the system using the large pump. So taking the
silicone hose that's included in the kit push one end onto the pump and the other end onto
the degassing chamber itself. If you're using the system for the first time like we are
here today then it's very important to remove this dust cap from the vacuum pump and also
ensure that the pump has got it's all filled up to the correct point the oil filler point
is here on the vacuum pump. So with that done we're ready to go and I can mix up some silicone
to show you the degassing process. It's the high viscosity of the silicone itself which
makes it inevitable that we're going to mix in air at the same time we're trying to mix
in the catalyst. Now it is so essential that the catalyst is thoroughly dispersed that
we don't concern ourselves too much with the air entrapment that will be happening while
we're doing it, particularly as the catalysts tend to be a very low viscosity material so
they'll always sit on top of the silicone rubber but that's not a problem and we'll
just carry on mixing and let the degassing chamber do its work. Now if we just get close
up on this mix silicone we can see that is it absolutely full of trapped air bubbles
within the rubber itself so this will be an interesting comparison to take a look at that
and compare it when it comes out of the degassing chamber. With the silicone inside, put the
lid on the chamber and that's just a push fit onto this silicone seal. So looking at
the valves that we've got here, this is the vent valve which lets air back into the chamber
so we want to ensure that's closed. So a valve is closed when it's at right angles to the
alignment of the hose or the fitting, so that's closed. We've got the valve that connects
the chamber to the vacuum pump we want that to be in the open position. We've got a valve
on the vacuum pump we'll leave that closed for now, we'll switch on the vacuum pump,
as soon as we do we can open this valve which will start pulling air out of the chamber
and then immediately we're going to see the silicone start to degas and this vacuum gage
registering very quickly the vacuum level we've got. So let's do that, vacuum pump on.
Open the valve. So you can see the needle start to rise very quickly and then if we
have a look inside you can see that very quickly the silicone starts to expand and froth and
foam as it begins to degas. So we've sped this footage up slightly, we're roundabout
the minute mark here and this will contain to expand until we get to a point which we
call the self collapse this particularly happens with silicones where the walls ahve got so
big that it will then collapse in on itself. So we wait for that to happen, this is the
self collapse coming up now, roundabout the two minute mark and then once that's happened
we can switch off the vacuum pump and then let the air back into the chamber and that's
when you see the true extent of the degassing effect. Now it's depressurised we can remove
the lid easily. Then inside of course we have our perfectly degassed silicone. You can see
a marked contrast here if you look closely at the silicone the difference between this
completely clear rubber and the aerated silicone that went into the degassing chamber. So what
we're doing here is pouring that degassed silicone around a pot as though we were making
a silicone mould and then quite importantly we're performing a second degassing step where
having poured the silicone around the pot, load it back into the degassing chamber, we've
sped this footage up considerably because there's much less silicone and much less air
entrapped in the silicone at this second stage so again. So again having degassed it for
roundabout five minutes this time let the air back into the chamber and this could then
be allowed to cure fully having done so we can demould the parts so take the original
part out and because of that original degassing and the second degassing procedure we're left
with a perfect silicone mould. I hope you've enjoyed our brief introduction to vacuum degassing.
The exact same process that we've used today on the RTV silicone rubber can also be applied
to a wide range of material such as polyurethanes, epoxys in fact just about any material where
you get air entrapment following mixing. The system that we've used today is our complete
vacuum degassing system which is available from our website easycomposites.co.uk. Thank
you.