Ahead of a very difficult and important job I do some test laminates, to practise and test my equipment etc.

Yesterday and today something strange happened (one test per day), I made good bags and had full vacuum,
the pump pulled the bag hard on the mold and carbon and it was the same after a 15minute drop test,
but as soon as I open up the resin inlet the bag goes slack, not all over the bag at ones, only as far as the resin has reached,
so first at the inlet and at then all over the part, but it is worse and the resin inlet, quite ok at the vacuum hose.

There is not leak that I can see or hear, no typical pumping in the vacuum hose or small stream of air bubbles that occurs if there is a leak.
The part gets fully infused but there is extra resin on top is the dist mesh.
If I close the inlet and let the pump work some resin is drawn out, but the bag never goes really tight again.

The vacuum gauge on the pump indicates full vacuum and today I clamped off the hoses and put a 10cm hose with a
brand new vacuum gauge on the inlet to the pump, that also showed full vacuum.
I also tried to have the vacuum hose directly to the pump for a minute, to exclude the catch put, no difference.

The day before yesterday I made a small test without a catch pot, stupid yes I know, I had a 2 meter hose to collect the resin,
but the bag had a leak I did not find before and one mistake led to another and the resin reached the inlet of the pump.
But that was only for a second and the pump has some large diameter plumbing pipes between the inlet and actual pump,
today I took those pipes apart and there was a little hard epoxy there, but now close to the pump, I cleaned that and a mesh-filter
that had some dust and dirt on it, on the underside of that mesh there is a membrane and a spring, that was clean.
But yes this problem occurred after the epoxy reached the pump inlet.

The pump is a German Busch R5 RA0016 single stage pump, all the other parts are from easy comp, the mold is a flat ureol piece
that is sealed with a two comp sanding primer.

I have never experienced this before, usually the bag and vacuum is good and the bag stays firmly sucked down through the whole process,
so what could be the cause of this?
Some problem with the pump even though I cant find dirt of epoxy after the first pipes?

Pulling vacuum on dry carbon stack is ofcourse an easier job for the pump than pulling resin,
but the bag is very tight on the stack before I infuse, then the epoxy fills the slack in the bag and it goes loose.
That tells me the vacuum just isnt good enough, but how can two separate gauges show full vacuum then?
Because they are on the pump side?
I will try again and put a hose and gauge on the inlet side and see what the vacuum is there.

This might play a part in the problem, yesterdays bag was made with the wb160 bag and I didn't have large enough
plets to allow the bag to go down around the silicone connectors, and today's test was made with the
stretch bag, which wants to un-stretch, but would that let the resin to overflow the bag? no..

I also noted that the shut off valve on the pump lets some vacuum through when it is closed,
that shouldn't be a problem since I experience this problem when it is open, but maybe that indicates a malfunction in that valve,
maybe it sucks air through its axle, impossible to hear with the pump running.



Any advice or speculation is welcome.

http://motoform.blogspot.se

Regarding your issue with apparent loss of vacuum once the inlet has been opened, did this result in any imperfections in the finished part?

It is quite normal for the inlet side of an infusion to become a little looser once the port is opened, as there is less pressure being placed on this side of the bag due to the open port and around the inlet and it will become quite loose as resin flows in.

Once the infusion has finished and the inlet is clamped off, the vacuum inside the bag will gradually equalize across the whole bag and the looseness around the inlet side should tighten-up once more.

Thanks for your reply,
but I know that it normally is like you describe, but what I an experiencing now is not normal,
it is much worse, I can grab the bag with two finger and easily lift all the slack, there is lots of resin under and the resin flows slowly through the part.

http://motoform.blogspot.se

If you have the resin mix set too high above the mould it can flow in  too fast and create a loose bag full of resin.

It is at the same level, 15cm hose away.
But yes maybe I let it flow a bit fast, but still, this is different to all my other infusions.

How loose the bag comes in infusion varies depending on viscosity of resin, thickness of laminate, size of part etc.  Height of the resin pot can make some difference.

Certainly with a thicker part, you will find the resin flows into the bag a lot quicker than it will initially be soaked into the laminate, so you can get an excess of resin in the bag at the resin end.  If you clamped the resin feed, as the resin soaks in, the bag would tighten up again and the vacuum level in the bag would even out.

Ideally the bag should tighten up again once the infusion has completed and the resin feed is clamped off, unless there is a lot of excess resin still there. You could suck some of this out into the catch pot but be careful not to go too far.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

How big are the panels and what is the layup? 

Hi Warren

thanks for your reply, I agree, my point is that this has always occurred but at a much lower rate / level, this is significantly more.

However, and this is the reply to Hanaldo as well, these test parts are very small 10*12cm approx, and the stack was 4*220 twill with 2mm soric in the middle,
and yesterday 450+220 2mm soric 220+450.
To be considered a thick laminate with the size in mind?
and if so, is this to be expected?

And to be honest, when I say "all the other infusions I have done" I don´t mean parts of this size, only larger ones.

http://motoform.blogspot.se

Yeh, that will be a large part of the problem. For such a small part, you really need to throttle the resin flow right back. It is definitely something I would expect to happen on a small panel. 

Ok, thanks.
I will do more tests and pay attention to flow rate and resin temp / viscosity.
I will also place another silicone connector with hose and gauge at the inlet side of the part and monitor the vacuum there.

http://motoform.blogspot.se