heating tape for bladder mold?

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#1

i have a question about introducing heat to an aluminum bladder mold. For now, my composites shop is the corporate apartment i am living in, so i am limited in my project space. i would like to initiate some heat to my mold to help the resin kick. i am less interested in high cure temps, but in my apartment, at ambient - it takes upwards of 24 hours for the resin to fully harden. if i could make the mold even 30 degrees warmer it would drastically reduce the time.

i am thinking about using a heat tape, like the ones here to http://www.heatingtapes.com/Price_5_10-01.pdf ‘candy cane stripe’ my mold. any feedback would be appreciated before i pull the trigger.



#2

The supplier/chemist I buy resin from he states his cure time drops by half for every 10 degrees above 70 degrees Fahrenheit. I’ve tested it and it more or less works. Of course it only works maybe up to 90 degrees and isn’t exactly accurate but the larger point being that the resin cure time is shortened with the addition of heat.

Chemically it makes sense too but it really depends on your resin and hardener formulation. I suggest testing your theory by mixing up cups of epoxy, putting them in a controlled heater and checking the results. With that you know whether it works and also how fast it works, saving you the time of unmolding and destroying an undercured part

#3

One of my customers uses a 5 hour open time epoxy at 180 degrees C, for a cure time of a couple of minutes.

Heat always works when speeding up resin.

As for heat tape: This might work. Most customers I have, that are using heated alu moulds, use heating elements made from MICA. (www.ref.nl). I am sure there is a similar company in your area.

I just ordered a carbon-filled coating, which should be able to be used in acting as a heating source. With this coating about anything can be heated. (if it can be painted, it can be heated). Have not received it yet, though. Have a 8 ft mould that I want to heat up.

#4

thanks for the input. i am using a rhino epoxy with the slow hardener, which is what a former employer used and tested extensively.

its good advice to practice with the cure times at different temps, and tables like that i think are available from the supplier.

please tell me more about this paintable heating element you are talking about, can you send me a link to the product?

i will let you know how my latest efforts turned out, i have had a three layer all fiberglass shaft curing now. i cranked up the heat in my apartment, and left over night. when i open it it will have been curing for over day, so i will be upset if it hasn’t fully cured.

#5

updates… just opened the mold. i went with fiberglass this sleeve as i am trying to get the process down. think i’m there, or close anyway. now need to figure out the heating of the mold, and i’ll be rocking and rolling.




drew

#6

Remember that a 24 h cure for a slow epoxy, even at high room temperature, might not be enough for a decent product. Best is to postcure, or cure with heat. But you are already walking that road.

Paintable heat film: www.future-carbon.de

A quote from the Email I got:

thank you for your inquiry regarding samples and information of our product Carbo e-Therm.

I am sorry to inform you that, due to the rapidly increasing amount of requests, we are not able to send free product samples.
We can offer you our Carbo e-Therm LT Demo-Kit:

A suitcase containing everything you need to make first experiences with Carbo e-Therm by your own application.
The suitcase contains a power supply, cables and clips, contact negatives, a film for coating and 250ml of Carbo e-Therm.
You can order the Demo-Kit at a price of 100€ plus shipping costs.

The selling prices for our Carbo e-Therm are scaled as follows:

0,5ltr. = 175,50€

1-5ltr. = 295,10€/ltr.

6-50ltr. = 191,82€/ltr.

51-200ltr. = 138,70€/ltr.

Please note that all the prices above are without shipping costs.

I ordered the suitcase, and a liter of goo.

#7

Oh, also take a look at MICA elements, they might be the most suitable solution for you.

#8

Bloody beautiful!!!
1: FIRST AND FOREMOST!!! CHECK THE RESIN DATASHEET! Do not add a heater without a temp controller if you should NOT go above the recommended cure temp. 100c cure, and 150c post cure does not mean you can let it heat unchecked to 200c for a “faster cure” You can exotherm your epoxy and do baaaad things to your apartment.
2: Heater tape should work. The aluminum should spread the temp to make it even, unless you wrap it with no gaps…then no worries about uneven heating. There are many kinds of wrap on/glue on heaters. Even a silicone sheet heater on each side might work. There are many controllers available, some temp controlled, some just wattage controlled. Get snazzy, and throw in a PID control :wink: You also might want to insulate the mold somehow, so all the heat doesn’t just escape into the air.
3: what are those cutouts next to the hole cutout? areas for resin to seep? Also, what bladder are you using?

#9

riff - thanks! i am looking into all of the cure temps, and anything i do - i will have to make sure i have temperature control. last thing i want is to make the 6pm news, or worse…

the cutouts are for seepage. they were probably not necessary, but i did not know since it was my first tool and bladders were completely new to me. While it results in a little flash, it does control where the resin can go, it necks down between the main cavity and the resevoirs, it about .5mm, if i recall. if i had it to over, i may just leave those out, but since its for a hobby sport of mine (that i hardly even get to play here on the west coast!) i don’t have any plans to recut any aluminum right now.

the bladders that i use are latex from piercan http://www.piercanusa.com/ funny that when i was first searching for bladders a few months back, i was living in san diego, and working in oceanside. piercan is located in san marcos, about 4 miles from my office. talk about convenience - right in my back yard!

drew

#10

i use heat blankets for curing small parts.i wrap the mold with the heat blanket.then wrap that with a shipping blanket to hold the heat in.i also use a thermometer with a temp probe on the mold surface.i can get 140 f most of the time.with what you have i think 2 heat blankets would work well.i use plasco resin with the medium hardener.you can post cure it to as high as 250 f.the post cure really helps with the strength of the parts.

#11

i may try the blanket, but after talking to the process engineer at my old company, she suggested going with the fast hardener to get the speed i require. after reading on the site http://rhinoliningsepoxy.com/products/systems/1401-21_~_4101-21/212/283 i see i can mix the two hardeners to get the exact gel window i desire.

#12

hee…Rhino Linings makes an epoxy!!

#13

yeah, i forget the history, but rhino acquired another epoxy manufacturer here in san diego.

not sure of the groups feelings on it, but my previous employer tested a number of epoxies, vinyl esters, even had the materials lab at calpoly do development work for us, and the rhino 1401-21 / 4101-21 system is what we came away with as being the best for our application.

as an aside, i found dealing with them to be great. i can order right from the company, (price was less than ordering through compositesOne) by a pretty significant margin, which makes me wonder why my old company didn’t order directly from the manufacturer… they were good at burning money, however!

#14

Which Cal Poly are you referring to?

#15

ya I believe that they acquired Jeffco…

#16

updates…




#17

nice work!

#18

Damn, Herman… you write/read/comprehend english very well!!

About this carbon-filled coating… I don’t queit understand how it works or the purpose of it… as any object can be heated without a coating. What does the coating do?

#19

drewp, I’m very interested in how you made this bladder molded tube? Can you show us the bladder? Is the mold machined from aluminum? It looks to be a very nice mold. Also how did you wrap the bladder with cf?
What type of heat source did you end up using if any?

Yes epoxy is very temperature sensative… just 5 to 10degrees F can slow or speed up the cure. It can work to your advantage as far as adjusting the cure time. Also read up on your resin system to see what it says about elevated temp curing and the ramp schedule. I think some epoxies may overheat and boil if exposed to elevated temps before their gel state and very possibly changing the physical properties to be different than stated on the data sheet. It doesn’t look like your part had air trapped in the surface so i doubt this happend to your tube part.

Reason i am interested in exactly how you made the tube is i would like to bladder mold some tubes myself… but 3" andx 4" diameter.

#20

fastrr -
here are a couple of pics of my bladders. I purchase them from piercan usa i experimented with different diameters. its important that the bladder is as close to the finished diameter of the part. too small you risk puncturing the bladder, too large and the bladder will not full expand, and can pinch the inner layer of the material. the lengths i use are the 52", as i want to be able to trim my part to 40ish inches.


the tool is two halves, with a threaded and tapered bung that is inserter into the mold. as you can see the bladder in fitted around the bung, and pressure forces the taper of the bung to pinch against the mold the higher the pressure.

the latest broom used the following layup:

  1. Heavy carbon biaxal 1.25" diameter from soller composites
  2. 9oz uni carbon strips rolled around the first layer
  3. 9oz uni carbon strips rolled around the second layer, making sure the seams are not in the same orientation to protect against weakening
  4. Heavy carbon biaxal 1.25" diameter

as a note, i had tried using uni sleeve, but the elastic binders made it harder to work with, and about three times the price per foot of the uni tape that i ended up using.


i use a dowel in the bladder to give it some shaper during layup. i use white plastic sink fittings with a taper to load the socks on then pull the part over the workpiece. it helps because otherwise the biax sleeve wants to bind on the lower layers. i resin up the bladder, apply the sleeve then re epoxy the workpiece after each layer.

the parts are loaded into the mold (that had been lightly heating in a blanket) and the dowel used for support is removed. after bolting and clamping, i initially inflate the bladder to 60% of the final pressure to make sure things are not sticking, then relieve the pressure to allow it to settle (like you would for inflating a bicycle tube) then i work the pressure up to the final pressure, and pray i don’t hear any leaks. i had damaged a bladder along the process before, which means all the work and materials for naught!

its nice having the heat source to initiate the cure. since i make these in my apartment, you can imagine how loud my air compressor is, so i charge it in the closet using a comforter to muffle the noise. over the course of 5 hours or so, i do lose a few psi, so its important to have the epoxy kick before the tank pressure drops below the pressure used for the mold.

hope this helps! let me know if you have other questions or want to see more pics. it will be a few weeks before i make my next one, since they are out of stock of the bladders i use (i do not reuse them, though its possible you could in some cases) and they have to make a run to fulfill the 25 i ordered.

drew