How soon to remove a polyseter part from the mold?

Hi Guys,

I went to a seminar last week on closed molding, and had some questions I wanted to float out there. I do 99% epoxy work, and want to learn more about polyester.

I'm wondering about standard practices, as the gist of the seminar was that a polyester/vinylester part can be pulled from the mold 1 minute after the peak exotherm temperature has been passed, and the part is cooling down, where the mold can be turned more than one time a day.

I've always done a 3 day deal... Layup the skin coat at quitting time, next day layup part in the morning, third day pull part...

I'm wondering about this, say you are going over a male mold or repair and need to fair the outer surface. Has the part done all the shrinking that it is going to do, after it passes peak exotherm? Can the fairing bog go on the minute after it is sandable without chasing shrinkage a few days out?

Is there anything stopping a secondary epoxy bond, on a two piece part like around the flange of a deck the same day the polyester part was laid up?

Thanks,

Zach

 

Problem with pulling a part too soon is it will be green & liable to deformation if not supported correctly.
Back in the 70's a well known 32ft cruiser racer was selling so well that they were ripping hulls from the mould as fast as they could go.
My father in law owned one of these & she had 4 big dents in the hull on each quarter from a very ill fitting cradle, Dents aft were 1" & 3/4" deep respectively.
Port bow was 1 1/2" deep, Stb bow was nearly 3" deep at its deepest point tapering out 3ft long by 2ft vertically. The assemblers had simply scribed the main bulkheads and furniture round the dents & glassed them permanently in place. He had me fill & fair them & it took some gallons of epoxy & filler!

 

It all depends on the exact resin used and the expected finish of the part. 2 and 3 minute gel times for resin aren't uncommon, we also have gel coats that are tack free in about 8 minutes, so the resins are there to do it. Rapidly pulled parts tend to have a poorer surface quality than parts that sit in the mold longer, but for many industrial purposes this is fine. De-molding an under cured part is a reliable method to create problems.

Every type of part, and every combination of resin (and gel coat if it’s used) will be different, also you need to factor in the mold temp and ambient temp, so there is no set time to de-mold, just a rule of thumb that says, let it sit longer in the mold if you want it to look better.

 

I have worked with polyester and VE and according to my experience best is waiting 24 hours, resine is not getting completly hardened after exoterm, postcure is good for better properties

 

Ok lets get back to the begning !! what are you making and how big ??
Poly is nothing like epoxy !! shrinkage will happen for long time but is depended on the max heat used to cure the part !! if its cured at 35c then later exsposed to 45c it will cure even more get the picture so colours of parts id reall important as if it sits in the sun and gets even hotter than it was cured at it will cook even more !! As for epoxy to stick together as soon 4 to 6 hours after its hard is ok !! poly to poly is just as good as epoxy !! specially of its got glass strands mixed with it !! small cats we used the chopper gun to do the wet glass layer beteen deck and hull and were vertually impossible to part the two once they were a day old !! the size and bonding area plays a very important part in joining as you will be aware of !!
i am not a believer in hot brews doing any kind of glassing reguardless what resin you using !! i am a firm believer in Glass reinforcesed fillers and bonding with wet layers of glass !! , micro fibres are ok but the length of glass strands is where its all at for strength even using epoxy resins !! buts that just me !!

Yeah you can pull parts while they still hot but you get what you get !! so if you get distortion and funny shapes who you going to blame ?? WE have mould for a reason not just to make a shape but to hold the part while it going hard and curing !!
Best to let them cool oyt 100% !!
Or use a small bower heater and keep the part and the mould warm for a good couple of hours or so then let to cool 100% !!
Continually using heat is not good for the molds as they to will beging to slowly but surely change shape little by little to !! hot cold, hot cold, and so on !! remember its plastice you playing with !!
In cold weather we used to our advanage to do 4 to 6 layers of glass all at once but had to be very carefull with catalyst levels !! knowing that once exsotherm started it would get hot !! but if you real careful and started with slow resin and did all the layers and the last one bumped the catalyst up a little to make it start to kick off then the layup would get moderately warm and stay warm for quite a long time then when the chemical reaction had ceased it cooled slowly as the mould had warmed also !! this has a two fold effect !! one wet on wet glass used less resin and second the part was much better cured because the thick layer with slow resin didnt shrink as much, even thought it and the mould stayed warm for longer in the mould !! so if you get to know the products you are working with you can play a little to get the best from them !! know what the safe low level of catalyst is of the resin you using before you even attempt any of this The resin manufacture always has a upper and lower catalyst range to work within so never exceed these levels up or down !! They are there for a reason !!

 

Thanks for the replies.

What I am rebuilding: an old wooden 83 foot coast guard cutter... that takes the epoxy work. http://83footernoel.blogspot.com/

I've been looking to do components on it out of polyester so I can get out of the "Putty it today, Sand it tomorrow" deal and bond a polyester and foam core part to the boat. Example, could be something like the decorative skin on the roof overhang I just did out of 3/8th's plywood, resin coated and sprayed in primer before installation.

It could have just as easily built a table with a dead slick top and molded each of the pieces on it out of polyester and core mat, instead of having to fair and sand out slick 15 sheets of 3/8ths marine grade. At 1 a day thats 15 days to get a stack of parts to do the job, vs 1 every few hours... Which is the reason for the question.

I'm curious about polyester, as epoxy I don't have much choice each step has to wait a day to cure to be ready/safe to sand. With polyester I'm wondering if I can layup a part today, and take it all the way through the fairing process to be ready for finish primer by quitting time, instead of having at least a 3 day ordeal with epoxy.

Cheers,

Zach

 

Yes it possible to make a part in one day and have it ready for sticking to or on the boat
I have made a simple hatch mould 24"x24" with a 2" turn over edge and gel coated and used pigment in the resin so didnt have to double coat and completely glassed with 3/4" thick balsa core and when it was hard cut and sanded the edges , taken the moulding out and sanded and painted with reaction 2 part paint and sat in place in just 6 hours and fitter hinges and catchs next morning
Just got to understand the products you using and what there limitaions are thats all !! quite simple really !!

 

If you are building to class, you will be required to let it sit in the mold for at least 24 hours or until the it has reached the required barcoll hardness test. If the part does not have to be dimensionally sensitive, or if the form itself makes it dimensionally stable, then you can bump up the curing time by upping the catalyst or heating the mold.

Be carefull though. Our next door neighbor was doing fiberglass/polyester commercial parts and was doing a cycle time of 3 hours per mold. Their factory burned THRICE in a row. The culprit was traced to the work process. The laminators were bumping up the catalyst and would leave the unused resin in the work table during coffee breaks. When the conditions are right, the excess resin would heat up, go to spontaneous combustion when nobody is around, and burn down the whole plant. It always ignite when work has started and following a coffee break. It is no joke. I myself have witnessed spontaneous combustion in the yard I have worked on.

 

Thanks for the replies guys.

Polyester has a way of melting plastic buckets if the leftovers aren't dealt with, I can only imagine catalyzing it to the extreme.

I appreciate the advice, it sounds like something production speed is something that requires playing with the materials until quality drops, and then backing up a step or two.

Do you guys have any suggestions for resins that you've used that allow for a quicker turn around time coming off the mold?

Right now I'm using CCP Stypol Low Profile (Composites One C1-1001-30) the "30" in the back is for a "30" minute gel time.

I have a pail of Advance Coatings GP200 summer mix waiting to play with that comes from another supplier, as I can get it most days of the week where the composites one only shows up once a week.

I've got 10 window frames to make out of an MDF mold, and I'm thinking to try the GP200 for it.

Cheers,

Zach

 

I know you looking for quicker turn around times but there are limitations to the materials and the process you are using !!

BUT by change the whole process the turn round times can be halved because use heated aluminium two piece moulds!! faster gell/cure pigmented resins and differant glass!! but whats the point ??

The resin you buy has specifics to it!! , a lower and upper catalyst level if you take it in to you head to exceed these recomended levels then you will get a weaker product at the end of it !! to much catalyst and it turns to rubber and is soft and floppy and no strength at all or the resin turns brittle and crumbles like sugar toffee totally useless !!
All we are saying is live with it ,do what you have to do and do it properly . why so much rush rush rush ??
The world is not going to end tomorrow and if you have a time limits and penalties on your project then shame on you for not doing you home work properly and pricing accordingly !!
There are 24 hours in a day and if you work effecently for 18 of those hours you can move mountains !!
Its all about planning and forseeing how to do things and using you head and whats inside it !!
Here you are trying to learn a whole new and differant process in the middle of a job !! why ??
You make a plan and work back from the finished by date and set times and goals to have work to and jobs done by !! If you start in slow motion and have to finish at breakneck pace then you are a poor planner and thats your problem !!
me i work the other way round start fast and get the jobs done and have time to slow down near the end and take a look at whats been done !!

 

I'd like to learn more about new and different processes because I went to a class and saw gelcoat go into a mold, reinforcement, and core... and a finished part get pulled in less than 2 hours. There is no Rush, Rush, Rush... but there is a thought of trying to learn something new to see if it applies to what I'm doing. If it doesn't, then I'll know something new and still keep doing things the same way I've been doing them.

Three weeks ago I would have made the parts out of epoxy, one a day in a mold. Three weeks ago it would have taken me two days out of polyester, the first for the gelcoat and skin coat... the next for the structural lamination... After having been to an infusion seminar and seen a glossy slick gelcoated part pulled not 2 hours after the gelcoat was laid out of an unheated fiberglass mold... I'm enticed by the idea.

There is no point in working faster than you can think, as it normally makes more work on the finishing end to correct for the things that didn't get thought through... So I'm asking the question, trying to get the majority of the thinking out of the way and know where the pot holes and road blocks are before I get much past enticed.

The hard to do stuff is manageable, once sorted... and asking folks who have been there and got the T-shirt about the perils along the way, goes a long way towards getting things sorted!

Cheers,

Zach

 

The thing with making plugs and moulds is to do the hard yards first and make good moulds so all th ebog and fairing dosent have to be done over and over with each part thats made !! this is why we make moulds to make repeatedly good parts !! 2 hours extra spent making a shiney surface on a plug will save hours and hours later down the track !!
Yes infusion is surely a good way to go but its not the complete answer to all the questions !!as you could and will find out when and if you get involved !!

 

"I went to a class and saw gelcoat go into a mold, reinforcement, and core... and a finished part get pulled in less than 2 hours."....yes of course that can be done, but how many layers and how big was it, bikini fairings for a motorbike, or small boat parts can pop out fast if need be, but serious builds of solid glass boats, say 1/2 to 1" thick take TIME......and patience.

 

Both resins you have are very slow and formulated for either higher amdient temps, or larger parts. 30 minutes is a long gel time, and the other one is a a "summer mix" meaning long working time too.

They should carry 15 and 20 minute gel time resins too.

If you want a faster resin for infusing simple panels or small parts try some 040 8085, they should be able to get you some easily. It will infuse rapidly and gel quickly with a very good surface profile.

 

Thank you,

They made three parts all about a 1/4 inch thick.

One was a 2 foot by 2 foot catamaran hull, one was a 1/4 inch thick RTM hatch cover and the other was a 2 foot by 3 foot decorative cover of some sort.

Cheers,

Zach