RTM versus VEC?

[Splint]

Hi folks,
I'm curiuos to find out if the VEC closed mold system as used by www.genmar.com http://www.genmar.com/images/vecImag...l%20viewLR.jpg produces significantly technically superior parts than the RTM system.
The VEC system monitors more than 500 variables but I suspect most of the variables it monitors would make minimal difference, if any to the final part.
Would boat manufacturers chose to run with a closed mold system like VEC if the tooling costs were not an issue, rather than use RTM?
I have also been led to beleive that some manufacturers use a chopper gun to line their molds with glass prior to layup. Would a chopper gun produce a weaker part than that the same part made using a woven cloth? Does it make much difference?

Cheers and thanks in advance for your replies.
Splint

[yokebutt]

I don't know why genmar insists on using that dorky term "Virtual Engineered Composites" when the process already has a perfectly good name since many decades, Resin Transfer Molding.

Yokebutt.

[Splint]

Yes it is essentially the same thing, obviuosly Genmar is trying to use it as a marketing ploy, which probably brings them aditional sales.
My main question is whether there is any real advantage in using a male and female mold as opposed to a female mold with vacuum bag, eg stronger, lighter, better resin fiber ratio.

Cheers
Splint

[John ilett]

I think this is a system I read about a while ago now.

The moulds have a liquid surrounding them so the cure/cycle times are much faster. The article I read said that a 20 something footer could be popped out each hour.

The inner mould also has the liquid and a ram which displaces the liquid to create the laminate pressure from the semi flexible inner mould, this may also be far more than regular vacumm so better resin-fibre ratios etc.

All a very very expensive set up in comparison to basic RTM.

Just speaking from memory so no offence taken if you feel this is BS.

Best boat for your set up costs would be vacuum infused. If you have to skin the boat with chop strand then do it by hand, forget chopper guns.

[yokebutt]

Splint,
There are definitely benefits, the matching tooling allows both surfaces of a part to have a nice finish. Another reason is that the government reclassified styrene from a Volatile Organic Compound (VOC) to Hazardous Air Pollutant, (HAP) a few years ago and have started clamping down on emissions since.

Yet another reason, I suspect, is to reduce the variability in product that is always a factor when things are built by hand. (Designers and engineers have always resented their dependence on the people that actually make things to turn a design into a finished product)

Yokebutt.

[marshmat]

What yoke and john said.

About your chopper guns: The reason chopped-strand is used as the first layer after the gelcoat is that it does not 'print-through' the weave pattern to the gelcoat. Chopped strand is nowhere near as strong as roving or weave. Its use as the first layer adds weight, but gives a smoother hull surface. Chopped strand should not be used for the actual structure. The hand-layup equivalent of chopper-gun (mat cloth or veil), is slightly stronger and more uniform, but takes more work. Neither should be used for structure.

[yokebutt]

Not that I want to be picky, but I think we should reiterate what some of these abbreviations mean, RTM, or Resin Transfer Molding is a technique where you have matching rigid tools, you put the reinforcements in dry, then you pump in the resin.

VARTM, or Vacuum Assisted Resin Transfer Molding uses one rigid tool and a bag, the resin is drawn in with vacuum rather than pumped in, SCRIMP is a type of this method, it's also called RI or Resin Infusion and a few other things, especially when it fails.

I'll leave the rest of the alphabet soup for someone else to decode.

Yokebutt.

[Herman]

Indeed true.

The VEC system is another type of RTM: 2 rigid tools (moulds), fiber in between, and a resin pump pumping resin in.

The tool however, does not need to be that rigid, as it is in a waterbath. This make the tools a lot cheaper. Also, you can use multiple tools, so you can fill the tool with glass, outside of the waterbath. The expensive waterbath is used to its full potential, popping out a boat every hour or so.

Another system is MIT from Plastech, but it is not quite that flexible as VEC. Instead of a waterbath, it uses a very rigid backing mould. Therefore the tool needs to be very smooth on the product side, but also on the outside, which make making the thin moulds quite difficult.

So we can add VEC and MIT to the line:

Sprayup:
Chopper gun sprays resin, hardener and glass into a tool, after which workers compact the laminate with bubble buster rollers. also "no roll" systems are available, usually used in robotised work areas. (bath tubs and the like).

Handlayup:
Mat and/or woven materials layed in a tool, and laminated by hand

Handlayup with vacuum:
Same as above, laminate compacted with a vacuum bag.

Resin infusion under film:
Dry fabric in the tool, vacuumbag over it, and pull resin in by means of vacuum. (also advertised as controlled vacuum infusion, RI, and the like. erroneously advertised as RTM and Resin Injection)
See www.polyworx.com for examples

VARTM:
Vacuum assisted Resin Transfer moulding
A tool will be filled with glass, a semi flexible top mould will close the tool. A vacuum is created in the product cavity. Resin is being pumped in by a machine, under relatively low pressure.
See www.plastech.co.uk

MIT:
Filling the tool with glass keeps the tool occupied for a considerable amount of time. So the MIT (multiple insertion tooling) system was developed:
The tool is split up into a very rigid part, and a thin part. The thin part is filled with glass, then VARTM-ed. A second thin part is being filled during infusion of the first part, so after gel, the thin part and the product can be removed. Immediately the next thin tool can be inserted, so the big tool and the infusion machine can keep working.
See www.plastech.co.uk for details

VEC:
The thick tool is replaced by a water bath. This makes it easier to produce the thin tools, as they do not need to mate exactly with the rigid tool.

RTM:
2 very rigid tools are clamped together, with the glass in the product cavity. Resin is injected under high pressure, and in most times the mould is heated.

There are other ways to produce a part, like prepreg, winding, press moulding, but if you want info on that, contact me or do an Internet search.