resin infusion and surface quality

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#1

Yesterday I did a test of resin infusion for test quality surface.
Tests are 20x 20 cm, one infused on a inox surface, one on a poliester gel coat mold. Gel coat is sanded with 2000 water paper, then with polish. The surface isn’t the best, has undulations but for the test is ok. Molds are treated with meguiars hi temp 87.
Test on gel coat is with 3 layers of 200 gr twill carbon. Test on inox is 2 different thicknesses: 1 with 2 layers of 200 gr twill carbon, the other 1x 200 twill carbon + 2x 650 twill carbon.
Resin is MGS RIM235, hardener are RIMH 233 + RIMH 235.
http://www.momentive.com/Products/ShowTechnicalDataSheet.aspx?id=8257&Rev
pag 99 data sheet of hardener RIMH 233
http://www.gazechim.be/uploads/downloads/Hexion.epoxy.resins..pdf
Total resin (not fully used) 300gr…
part A : RIM 235 = 224 gr
part B : RIMH 233 = 67 gr (fast hardener)
RIMH 235 = 9 gr (slow hardener)

Room temperature 20°C

My vacuum pump is 1 stage 70 L pump
DATI TECNICI:

MODELLO MONOSTADIO
CAPACITA’ DI ASPIRAZIONE IN LITRI AL MINUTO 70 - 2.5 CFM
POTENZA MOTORE 1/4 HP
ALIMENTAZIONE 220 V - 50Hz
VUOTO FINALE: 5 Pa
I put molds under vacuum for about 1 hour, no leaks
Degass resin 15 min.
I do a very solw infusion, about 10 min from start to finish. In photo there are some times. In the second mold infusion starts at 0.46 min, time on cel is from the star of first mold infusion.

cure cycle:

hour 15.39, oven on, set to 30°C
16.20 set to 45°C, piece temperature 36°C
16.42 --------------- " " 40°C
17.13 --------------- " " 46°C
17.31 resin is still rubbery
18.45 resin is hardened but not completely (I control bending the inlet infusion tube when there is resin, it isn’t completely rigid)
20.48 oven off, resin is all rigid, turn off vacuum and demol

some pics

  1. final pieces, with specs
    2, 3, 4) detail surface on inox mold
  2. infusion on inox
#2

other pics
1, 2) infusion on poliestr mold
4, 5, 6) results on inox
7, 8) results on vtr mold

#3

others pics

  1. poliester mold surface
  2. vacuum. My pump is 5 Pa pump, this is what gauge marks. On full vacuum pump change noise, I’m confused with Pa, millibar, mmHg ecc.
#4

results:
pieces are without pinholes, I have to pass the polish to be absolutely sure of this, but I don’t see any pinholes.
surface is ok

today I put a piece in the sun, it reached 43°C, it has little tecture waves.
I put other 2 pieces in oven, without temperature ramp.

hour 11.10 oven set 45°C piece temp 28°C
11.12 oven set 80°C " " 30°C
11.14 ------------- " " 37°C
11.21 ------------- 54°C
11.36 oven reaches 80°C " " 75°C
pieces are soft
11.37 oven set 90°C 75°C
11.44 oven reaches 90°C 84°C
12.04 86°C
12.15 oven set 95°C
12.29 92/93°C
12.45 oven off
cooling, 14 o’clock out of oven

pieces are more texture waves.
I have tried so, next week I post cure the other pieces with a gradual ramp temperature

I tried to make pictures but it’s difficult to see the differences…it’s like if before pieces has clearcoat, and after post cure they are without it…fiber are more in surface

#5

You haven’t heat treated the laminate long enough to fully cure the resin. You are going to see the fabric print-thru over the next days even if they aren’t heated. If you want to reduce the fabric texture you need to fully cure the resin before it’s demolded. This will require a dwell time of at least 15 hours at elevated temps. You will notice that the MGS test samples were cured for 24 hours at room temp and then cured for 15 hours at 80C. You don’t want to just start out at 80C. The typical rule to ramp the temp up 10*C per hour.

#6

yes ok, I tried to do this for see the differences to a ramp cure and a non ramp cure. My current temperature controller doesn’t do a 10 °C/min ramp…too fast to do a ramp like this. I want to see the differences with different cured temperature, if the ramp is so crucial for fabric print-thru, with a post cure in mold and a free postcure. Unfortunately when I unplugged flow mat and peelply, pieces demold. On inox mold I do 2 piece under the same peelply, I wanted to unplugged one and keep the other piece in mold for postcure both without ramp, for see if there are differences with the same temperature developement, with or without mold

#7

question…pag 104 and 105, how I can read these graphics?
http://www.gazechim.be/uploads/downloads/Hexion.epoxy.resins..pdf

pag 104…heat treatment 15h 50°C, ok
E’, storage modulus I suppose is the “rigidity”
what is “onset 69,3 °C”? the point of decline of E’?
what is “tan d (tan delta)”? peak 84,2 °C is the upper point of tan d curve, right?

pag 105…how I can read? If I do heat treatment @50°C (the lower curve), after 5 h it has a Tg of 60°C? after 10 h = Tg of 70°C?
Then whit a heat treatment @ 80°C, after 5 h I have a TG of about 90°C? I don’t understand this, if the operational temperature of the resin is 80°C max

#8

You are right in all your assumptions.

The last line in your post: The resin is suitable for -60 to +80 degrees. (as on page 99, probably where you refer to). Keep in mind that this is the temperature allowed by LBA (Luftfahrt Bundes Amt). The Tg of the resin is higher.

See it like this: The tyres of your car are probably allowed to do 180 km/h. But they will not explode at 181 km/h…

#9

ok thanks herman. But what is “tan delta”?

If I look pag 105, with a 5 h curing @ 50°C I have then a TG of about 60°C. This part is not fully cured, but if I use it under 60°C it is ok, or next days I’m going to going to see the fabric print-thru, as said wyowindworks?

ok, I understand for operational temperature and TG, thanks

#10

Just so I make sure I’m understanding correctly… is “inox” a brand name stainless steel? Why did you use that - just out of curiosity or are you going to be making a stainless steel mould?

#11

yes, correct…in italy stainless steel is usually call inox.
I use it and another composite mold to compare the surfaces…sometimes with composite mold, with resin infusion and the cured in oven pieces, happened to me that fabric print-thru of pieces marks the mold. I don’t know if it can be because I heat too fast and too hot (about 80°C), if is the mold surface that softens with vacuum and hot…so I do a simple test with 2 differents materials. Curing @ 46°C the composite mold is ok without any fabric print-thru. I suppose that heating too fast @80°C, the resin in contact with the mold has a temperature higher than 80°C and can distort gel coat of the mold.
I’m not going to make a stainless mold, but I’m thinking how I can do a mold for flat panels…I have a glass, I don’t know if is better a glass, a stainless panel or a composite mold

#12

question…post cure composites need a heating ramp and a cooling ramp… Cooling ramp is necessary the first time during post curing, right? because in the real use of piece, it hasn’t a cooling ramp

#13

Cooling ramp is important to reduce stress from uneven cooling.