question is how much vacuum is required ??

I come from the engine side of the business but after years of working in the industry, I know who to ask!

 

tunnels, same as in your other thread its not that professionals or home builders don't have answers. Builders with answers have not replied because they know you are not asking for advice. I am sure you have the knowledge so why not just share it as a starting point.

 

Tunnels,

You are the one who claims to be in the industry for ages!

You nearly never forget to tell novices and "old salts" about your 8 racers you have built (or have been part of the construction).

Now you argue about getting no simple answers.

There are no simple answers in our industry!!!

There is a rule engraved in stone:

if you have not encountered a compromise today, you are not in boatbuilding business.

Professional answers are easiest to get when the enquiry is professional.

You must not wonder why Hoyts reply was as valid as all the rest! The question was amateurish.

Not to hammer on you again (I did enough), but to get a clear picture of yourself, I would recommend, you sit back and ask yourself why?

And stop promoting VE resin as the solution for every problem in GRP building please!!! It is not so much better than all the other ...esthers. And too close, pricewise, to EP, to be a real choice for a homebuilder. And on top of that it is the most finicky of all the resins we have.

Straight questions, straight answers, when you skimp on promoting your CV.

Regards
Richard

 

Like the other post lots of people answered but it seems that basic things are a little of guess work unless you are someone that does the same job quite a few times .
There are so many variables , so many differant ways of doing the same job . Each one ends with the same results just we have differant ways to get there .
Anyway i hope some one will learn something from whats been posted .

 

I think this is a very good thread. I know I learned from it.

 

Hi
Me to ! I had hoped to get more responce but yes there were some good points . Thank you !

 

Tunnels, I think that it is worth while to keep this discussion going. Initially I was suspicious of your motives, please accept my apologies.

A lot of builders only use 30 – 60% vacuum for bagging wet laminates main reason stated for this is that higher vacuum will lead to resin starved parts.
I don't think this is the case only a symptom of ill-fitting bags, laminate degradation from air leaks, entrapped air and dissolved gases.

Typical stitched glass fabric has ~31% volume fraction glass content, this only increases to ~50% with 1 atmosphere of pressure (eg infusing at 100% vacuum. This is still far short from the upper limit of around 75% volume fraction.
When ever I decide to go to the trouble and expense of bagging something I like to get the maximum benefit which means high vacuum.
I use epoxy resin for which a number of manufacturers recommend 80% max vacuum.
For bagging I use a small diaphragm pump that achieves 85% vacuum, at this level I notice some degradation which I attribute to entrapped micro bubbles expanding and possibly some dissolved gas as well.
Take a cored panel made on a laminating table as an example, to overcome;-
1.resin starvation; eliminate bridging by having enough pleats appropriately located and bring on the vacuum slowly in stages so that all bridging can be eliminated. Match your bleeder/breather volume to the excess resin volume in the laminate, for thin laminates 70 – 100gsm polyester wadding is all that is required.
2.Air leaks; use an ultrasonic leak detector to eliminate these. I also run all jobs at the 85% pump capacity as this allows a simple visual check for micro leaks by fitting a hose to the pump outlet and placing this into a container of water. If there are no leaks there will be no bubbles. Where possible run a air channel (rope, spiral wrap, hessian web, shade cloth) just inside around the perimeter of the bag to catch any leaks through the seal before they get to the part.
3.Entrapped air; do not overwork your laminates as micro bubbles are hard to expel, larger ones are easily removed at the start as the vacuum is brought on. Pre wet the core by roller or squeegee before wetting out the bottom laminate, this allows time for the micro bubbles that form on the surface (foam especially) to collapse. Some epoxy resin formulations contain air release additives that help with this.
4.Dissolved gases; I think this is the only true enemy of high vacuum and unlike for infusion degassing first usually is not an option due to time constraint. Using a slow bleed release film will help as it will slow the excess resin migration from the laminate into the bleeder and allow more time for any dissolved gas bubbles that do form to come out first.

How high a vacuum do you all use? any differences in approach?

Cheers
Andrew

 

Can one degas the resin before mixing and then mix in a vacuum chamber?

 

Thank you ANDREWK !!
I totally agree it takes time for people to front up and put on paper there own exsperiances !
I hope as people read through they glean ideas and information that can help and give a little better understanding of the problems others have had and how they were overcome .
This is a good place to store this info for others to be able to refer to at a later stage .
Keep the info coming ,good work and thank you every one !! DONT STOP !!

 

jonr, I guess most of us choose to use lower vacuum rather than bother with de gassing.
I do de gas the resin for the smaller infusion jobs, now I also infuse far more often than bag a wet lay up.

 

You can heat the resin and or your job to help remove the out gassing
The older the resin the worse the problem

 

degassing

Degassing is a must if you are infusing. As tunnels has stated in his post, a small trapped bubble in an atmospheric pressure will enlarge when subjected to vacuum.

When mixing resin, bubbles is enivitable. You can degass the mixed resin after by placing the pail in a vacuum chamber, not before. 2 to 5 mins will do.

 

resin infusion

There are two types of resin infusion.
One is to force the resin by pressure and second is to use vacuum to pull in the resin (vacuum assisted resin transfer VARTM)

VARTM can be low pressure or high pressure depending on the process.

If you are resin infusing with a closed mold (male and female) or if you are making a laminate with CSM on it, you use Low Vacuum.

If you are making a laminate that is intended to have as little resin as possible, you use high vacuum.

Look at it this way. CSM needs a lot of resin to look nice and its function is to be impermeable. Under high vacuum, there will be very little resin left and even leave you with dry patches of CSM.

With denser fabic such as WR and UNI's you are aiming for 50% or less resin. High vacuum is needed. This makes for a very solid laminate.

You cannot mix the two process at the same time as it is counter intuitive.

 

Tunnels,
Got carried away with resin infusion in the last post.

First, it is not a good idea to suck (bond a core to a wet laminate). It will disturbed the initial layup.

It is always a good idea to bond the core when the laminate is still tacky. Wheen it is dry, it is too late. You have to sand (scour) the ist set with 120 grit, The same goes through if you are applying the 2nd set of laminate. It is supposed to be a contnous process. If you stop, you sand.

Bonding core can be of several method. Using a wet mat, resin slurry, corebond. even epoxy glue.

To remove the trapped air, you can press on it, walk on it (core permitting) use an industrial vibrator, sandbagged it, or use whatever weight available. Place a layer of scrap laminate on top to even outh the pressure.

Personally, I like the above kind of mess but if you are bonding core to a vertical/inclined surface, then bag it.

How much pressure? It depends on what bonding agent you are using. Assuming the core is perforated. You will be looking at the holes getting filled up with the glue as you apply vac. Stop vac as soon as you are satisfied it has bonded properly.

Ballpark figures, resin and wet glue about 10 to 12" mercury. With corebond a little higher. I have been succesful up to 20" Hg. Careful placement of release film and bleeder cloth though,

Whatever you do, make sure you do not exceed the manufacturers recommendation. You need a minimum thickness of bond material to be effective. If I remenber correctly, about 1/32"for corebond. Resin will not cure properly in the 20 to 25 mil range. You have to bump up the cobalt or catalyst.

Last, you are bonding the core, not sucking the resin/glue out. Watch out for the placement of bleeder cloth so that in does not form a bridge to the glue or resin. It will suck the resin/glue out before it bonds.

 

I find that it's 5 minutes minimum to de-gas, more like 10 minutes to get complete de-gassing.
Also found that heating the job has only made it worse as it increases the out gassing.

rxcomposite, I disagree with what you are saying about infusion, there is a thread on infusion that we can take this up in if you like.