Question about post curing molds & parts

General Composites Discussions Composites Talk
#1

So here are my short questions…

Part 1.

I build all of my molds out of red polyester tooling gel coat, (the average stuff most of us use) and Hydrex100 VE resin. All of my molds are .5 inches, (1.25cm) thick and reinforced with 1.5", (3.8cm) thick square steel. If I were to post cure, wouldn’t the factory part I’m making a mold off of, (often times either plastic, fiberglass, or carbon). Or if I build my molds thick enough, let them cure at room temp for a day or two, then reinforce with steel, would that alone prevent the mold from warping even if the part does?

Part 2.

I’ve noticed my flat panel parts have a slight warp to them after a few cycles in and out of the sun. Nothing bad, but the slightest bit of warp in my mind tells me that I wasted time building a perfect mold.

This part in particular is a flat hollow running board. 3 inches wide, 72 inches long, .75 inches high. In CM, 7.6 x 190.5 x 1.2). The two halves are made out of the following.

Top
11.5oz carbon, 19.7oz carbon, 17oz biaxial glass.)

Lower
11.5oz carbon, 19.7oz carbon

Here is a photo.

http://i1278.photobucket.com/albums/y504/ShadowcraftDesign/Lamborghini%20Gallardo/SL%20Side%20Skirts/DSC00891_zps2cdcccdb.jpg~original

I’m infusing using MVR8071 from Resin Research. I believe its Resin Research? Its a VE / PE blend.

On another note can somebody recommend me a better resin?

#2

Also on another note. When the parts are cool and you knock on them you can feel the stiffness and hear it. Its like knocking on a piece of metal. A nice and strong vibration.

However, when the parts are in the sun and you knock on them it sounds like I’m knocking on a door. Very little vibration, dull sound.

#3

How do you reinforce with steel? directlyu on the mould, or on the flanges. Laminated or glued. I would postcure without reinforment anyway, to prevent the steel affecting the mould. Seems more than stiff enough.

Warping will happen with non symmetrical layups. especially when using glass and carbon together.

If they sound dull in the sun, the resin is a bit soft. What is the temperature? Carbon parts can get hot easily, you can get over the max. temperature of your resin.

#4

I epoxy the steel frame to the flanges of the molds and or long flat parts only. All of my molds are built by using one layer of glass at a time. Me and somebody else will wet out a gigantic piece of glass and then work it onto the mold. Areas that are light will get a bit more. The mold in question is 4 layers of 1.5oz matt, 2 layers of 1708 biaxial, then 4 layers of matt.

The temp in direct sun here in Florida sometimes hits 190f.

#5

I agree that the unbalanced laminate schedule is a large part of your problems. Combine that with the high temps of the FL sun and warping is not too surprising. You might need to move to something with a higher Tg to keep the side exposed from to the sun more stable

#6

Just wanted to ad that if you have something that’s border line in terms of balanced layup putting it in non ideal post curing scenario’s may magnify the error in the layup.

Meaning if you put a part from a 70 degrees place and stick it in the direct sunlight that’s beating down and you take the parts tempeture and in 10 minutes it’s 100 degrees, then in 5 minutes it’s reading 120 then that would be an issue. Also take under consideration that it’s only hitting on 1 side as well. I bet if you measure the temperature of the top side of the part vs the bottom side there would be a decent difference. But I could be wrong.

#7

The unbalanced laminates meaning the two halves being made up of different layers? How would that affect the surface? The part isnt warping. The part keeps its shape very well. No bowing, twisting, etc. The only problematic areas are the large flat areas.

I might just have to stick to a better quality resin.

#8

So how about post curing molds on parts that usually tend to give in the sun? For example if I’m making a mold off of an unstable plug, or a plastic plug. How could I post cure a mold with out damaging the plug? I’m not worried about salvaging the plug afterwards, but if the plug changes during post cure, couldn’t the mold follow? OR again, does the thickness of the mold and the evenness of the layup really keeps this from happening and there should be no change if post cured at a slow ramp up rate?

If that’s the case couldn’t I post cure a finished mold with out the plug in it? Then couldn’t I post cure parts the same way or should I keep the parts in the mold?

Is there any resins out there that don’t require a detailed post cure to be able to withstand moderate temperatures in the summer?

#9

Guess I misunderstood, you described the parts as warping… If you are ending up with not flat flat areas after cycles in the sun you might be seeing localized shrinkage in your Vinyl Ester. Are we talking visually not flat (not smooth reflections) or physically not flat (not smooth if you run your hand over it)?

#10

I guess now that you mentioned it, it wouldnt be warping… Coincidentally as you made your post I saw my first terribly warped part today. I infused it, then put it in the sun after 40 min, then as I pulled the bag off and went to go work on something else I herd the flanges of the part pop off the mold and I had to lay plywood down to see if it would keep it straight. Not such a big deal because the panel gets bonded with another rigid structure, but I basically wanted to see what would happen if I put the part in the sun for a few hours then pulled the bag off.

But to answer your question. Yes, what was once a straight flat mirror like panel is now a slightly wavy panel that is surely visible, but hardly noticeable when running your hand across the 6 ft board. The slightly visible wave is enough to annoy me though because I spent so much time perfecting the mold. For the part to be anything less than a perfectly flat surface where the reflection doesn’t jump around on you as you walk over it, is not acceptable in my eyes.

#11

I can’t answer any of your other questions but this resim might be suitable http://www.resinservices.com/custom.asp?CustomID=14&Productid=70

#12

Sent them an email. Hopefully they can help. Thanks!

#13

I’ve always had a practice of letting the part-in-mold overnite cure at room temp. Eight hours plus before ramping temps for post cure.

The science behind most ester resins require that linking time or things go wrong in a hurry not to mention surface quality.

#14

I would say that if you are only seeing visual changes to the flat surfaces you should start by changing from vinyl ester to epoxy before you start trying anything too crazy

#15

Changing resin systems at this point before mastering the cure points would seem crazy in my opinion.

You’ll just be starting over to some extent.

#16

My first reaction is to check the datasheet of the current resin, for the ultimate Tg. Then postcure in mould to reach that Tg (I hope the mould has a high Tg)

If the ultimate Tg of the resin used is less than some 200 degrees C, then change the resin system to something better.

#17

That’s the same resin I used to use at another job. It’s actually Interplastic: http://www.interplastic.com/p-rtminfusionresinss.php It’s a coReyzn brand. THey don’t really have good info on post cure but you could ask them what they suggest.

Stuffs a pain… I had tried to postcure parts outside in the sund, some long thin parts similiar to yours. Not a good idea… they completely lost shape and were worthless. That resin should cure for some time before a post cure and I would post cure in the molds before detooling.

This resin shrinks a lot. We were using it to infuse large fusealge parts and the shrinkage was ridiculous if you need tight tolerences. We also had issues with off gassing, thats another story. Was nice and super thin but I’d trade it for epoxy any day. With epoxy you can let it RT cure and the hardness and tensile and whatever measurements will beat that coreyzn. If you have a guage you can check the hardness and see how it develops over time but it in our tests it was something like 2 weeks before you see the proper hardness.

And you add steel to your molds? Really? I usually use light weight stuff, it’s really the core that adds dimension, shape, that increases rigidity.

that’s my 2cents

#18

A lot of thought and development goes into polyester infusion resins. Which is funny, as it is much easier to thin down a polyester than an epoxy. But just adding styrene will kick you in the back, due to shrinkage.

Try sourcing another polyester infusion resin. There must be plenty around.

As for postcuring: as long are there is not even basic info such as HDT or Tg, you are just gambling.

#19

Many people say about heat resistance, but such flat plate is likely deforming in temps below 0. Anyone know why it happen?

#20

by the way… how do you guys understand this? -

" Increase the laminate temperature slowly so the
Heat Deflection Temperature (HDT) is not exceeded.
As the laminate is heated, it will continue to cure,
pushing the HDT above the laminate temperature. If
the post-cure temperature exceeds the HDT of the
room-temperature cured composite, the epoxy will
soften and may cause print through or distortion of
the laminate. "

Its from epoxy instruction of processing

So reading this I cannot understand what will cause the print through?