vacuum bag material

[scphantm]

is there any reason why i can't use just regular plastic sheeting from home depot as a vacuum bag for vinylester resin?

[ondarvr]

Can it be used....yes....does it work well....not really.

Its weak and tends to leak, the QC and uniformity of the film thickness can leave a lot to be desired.

[Herman]

Too much thin spots, too much porisity. And it tends to get weak and soft in contact with styrene.

[War Whoop]

#1 there is no safety provided in that cheap Throwaway material like a 400% elongation in for real tough bag material, what I am saying a failure of the worst sort at the worst time is in the making here.

Plus the Nylon bag film loves the tacky tape.

[gonzo]

We use it all the time without any failures. Not from Home Depot, but anyway regular poly sheeting.

[War Whoop]

Originally Posted by gonzo

We use it all the time without any failures. Not from Home Depot, but anyway regular poly sheeting.

This is a infusion job @ 28 HG ,I would use the real material to avoid the "Dairy Cow" look from all the leakage,simple bagging at lower pressures no big deal.

[scphantm]

ok cool. i will use it for practice and testing to develop my technique and then switch to the real stuff for actual parts.

[gonzo]

War Whoop: nowhere does it say it is an infusion job.
scphantm: What specifically are you laminating?

[scphantm]

gonzo, he got that from another post i made. it is for infusion jobs. i need a new skill for the next phase of the boat im building, just trying to get consumables prices down.

im going to start with test panels to get used to the materials and techniques. then i have a few hatch doors i can do to get used to making the molds and infusing in molds. then i have a few other small and not so small things around the boat to practice the techniques and get the practice in. then in spring i have to build a mold and make the bow deck. complete with seating pad and stuff. thats probably going to be my first really big item to make.

[gonzo]

What made you choose infusion? It is possible to vaccum a hand layed laminate to make it denser too. Infusion is complicated, and doesn't really pay unless you are thinking of high volume production. One of the problems with infusion is temperature control. Since all the resin goes in, the thicker parts can overheat and burn or distort. The infusion of resin itself is only part of the technical difficulties. The molds have to be designed with cooling/heating to be able to control the quality of the laminate. With hand layed parts, it is possible to control overheating by slowing the schedule and letting the part cool. Heating can be done with infrared lamps. Next door to our shop they do infusion. The molds are metal and heat controlled.

[scphantm]

we are not doing anything that thick (yet) and when we do the extension to the hull we will have the guys at the composites shop next door helping us because the lower portion of the hull is an inch and a half and they routinely punch out 8 inch thick infusions.

the primary reason for infusion is the unlimited setup time and the ability to take our time, except when we are gel coating something. working in this relentless florida sun, trust me, thats a HUGE plus. otherwise i would vacuum bag a hand layup.

[gonzo]

I have worked in Florida a lot and know what you mean. Infusion molds often have plumbing for temperature control. You could run regular tap water to cool some areas. If you have someone next door to help, things are easier.

[Herman]

The start temperature of the resin does have influence on gel and set times (you can design your infusion strategy for that) but hardly has any influence on peak temperature.

Water cooling a mould is to move away generated heat. I actually just bought a 7,5 kW chiller for cooling. besides moving the heat away, you will need to dump it somewhere too (a chiller or a huge radiator with fan(s).

Choosing the right resins and curing agents can keep temperature down considerably.