Infusion technique question - height of resin reservoir

Just by accident, I wandered into a quite good series of RTM ( Resin Transfer Moulding ) videos



This particular one on the series discusses the process of infusing the FG, using vacuum of course..

He points out that the process is not really 'sucking' resin with a pump, but more creating a pressure differential to 'push' the resin from the reservoir, through the glass.

In his lightweight parts process, he has only one 'exhaust' manifold, and multiple inlet manifolds, to increase the backpressure on the resin, over and above what the vacuum pump can do.

The thought that occurred to me was that, all the infusion videos I have seen have the resin Receptacle on the floor, below the actual job.

From this video, it seems there might be a lot of advantage to placing the resin reservoir higher up than the job, to increase the back pressure on the resin, even more than the vacuum pump can do.

Has anyone had any experience with this ?

 

Im pretty sure scrimp methods always have the barrels of resin elivated to the higher points of a big project. Ive only done hatch doors, and the tool was a two piece that did not have inlet hoses and a resivor. Ionstead it was a floppy lid that sealed around the edges, We just skin coated the parts traditionally (the molds were already gelcoated) and the layup was continuous strand mat instead of chopped. We just poured the pre weighed amount of resin right in the middle of the part on the CS mat and then placed the floppy lid on and applied the vaccum.

 

Thanks for that info CC. It looks like at least some people are aware for the technique then.

 

vacuum vs gravity

If you elevate the reservoir, then you have gravity flow.
If you rely entirely on vacuum, you are ensured a more uniform distribution of the resin. With gravity flow, there can be pooling in lower regions.
Depending on the part shape, part size, the viscosity of resin, and the quality of vacuum, you may find it useful to assist the vacuum flow with gravity flow.

I sometimes place the reservoir about a foot above a relatively flat uniform part. This gives a little gravity assistance, but not a lot. I don't think I'd ever use more than a foot. Also, must be ready to shut off the resin supply.

 

Thanks MC. It sounds like its a viable option. I know that the gravity pressure increase dramatically with height.

It sounds like it may be possible to get away with quite low vacuum pressure in some cases.

 

It seems you have a reservoir -with excess, catilized excess ( wasted) when you should ONLY have enough to make the part--EXACTLY and no more-except perhaps in the inlet media lines-that are sacrificial from projects I have seen done. That way extra -puddling in the lower areas would not be a concern because there is very little or no wasted resin.

 

I've watched a few infusion demonstrations and there is a small amount of resin left in the reservoir. It is much better to have resin left in the reservoir than risk sucking air into the part.

 

For something like a one off hull obviously, a half gallon or a gallon is no matter. But for outfits cranking out parts like hatch doors they dont have any waste - they do it every day- all day so they cant afford wasted material.

 

yes. His later posts make the point that he programs his system with really precise amounts.

I guess supervision would be critical

 

There are so many different nuances in infusion methods it can make your head spin. None of them are really right or wrong, most have situations and/or parts where they work very well, and others where they are a poor choice, or at least not the best one.

The choice of tooling makes a big difference, rigid, or semi rigid tools at times can benefit from pressure feeding, bagged infusion is less tolerant, but done correctly it is workable in some situations.

 

Good point. It sounds like a lot of practical experimentation is the secret. Nice to be aware of another option I guess.

 

How about you experiment by making my rudder? Spring arrives tomorrow...

PDW

 

yep, an easy task... heres the one i did for masalai;

You can do all manner of things, infuse uphill, downhill, bucket above or below, its all doable... if you wanna learn whats possible, just start playing around with it...

 

Yeah - you're right. I have decided I cant possibly borrow your boat if it has a marine ply rudder blade, so I am going up to Island Speciality Timbers to get a couple of planks of Celery Top Pine for the blade.

I have my standards you know ( and if you don't like them, I have others )

 

When making boats a gallon or so wasted material is not that critical. When doing high output smaller parts, usually the complete system is changed to VARTM / RTMLight, and resin waste is dealt with by using RTM machines, which limit wasted resin to some 100 gram / 4 ounces at maximum, no matter of the size of the job (that said, job size is limited when doing RTMLight)

On placing reservoirs higher than the part: never do it unattended, or you are in for a nice surprise at times.

However, the point is, that the size of the inlets combined make a huge difference in infusion speed. Which is what the push-pull story is about.