Blanket : top, bottom or both ?

[ben_mtl]

Hi there !

I'm looking at heating my press but as blankets are a pretty expensive component I'm wondering how it would work buying only one blanket for now and wait for some more money for the other.
Regarding the electronic it's fine, anyway each blanket would need a separate control, my concern is only about how it would affect the cure of my skis.
Will the temperature be "homogenous" (not sure of this word) enough throughout the ski to significantely reduce my curing time or will I still have to wait several hours for the "non-heated" side to cure ?
How will this affect the camber of the ski ? Better heating from top or bottom ?

My main point now is reducing curing time (improving resin properties would be great also !) as the bladder I have is slightly deflating when the pressure's on and I don't want to have the compressor running every 10 minutes to keep the pressure (sleeping in the room just above the garage)

I know one option would be to get a better bladder but anyways I want to heat the press and it was a real pain in the a$$ to get my firehose.

Thanks for your help !

Ben

[KevyWevy]

we've been using a heating blanket just on the bottom without any negative effects. but we also turn of the heat and let the ski cool under pressure for the night.

we press around 50psi at 200*F, so by the time the ski has been press for long enough, the bladder is also warm

just fix your leaks with some liquid nails if you can.

[ben_mtl]

I believe the firehose is porous and is the main source of leaks... it's pretty old stuff so I only press @40-45PSI, I'll double check my end clamps and fittings though.

How long do you keep the heating on ?

[KevyWevy]

oh, weird. just glob some of that liquid nails stuff inside the hose where the clamps are at the end. this has worked well for is... if its not your fittings and its the hose, i'd say just get a new one. if you check out the ski builders store, its only $9 per foot. if you're only doing one ski at a time, its only going to cost ~$60

my roommate made a PID controller for the blanket, pretty much like what everybody else has done on here.

[Dr. Delam]

The ideal situation is to have top and bottom heat. This gives you the most control over what your camber is going to do.

You can definitely have success with one blanket though and dramatically decrease your cure time. If I am using just one heat source I find that an hour is sufficient for full cure throughout the ski. I try to let it cool enough to handle before pulling it out.

I have found that using a no camber mold, I get about one cm of camber using bottom heat only, and one cm reverse camber using top heat only.

Another alternative to two heat blankets is a cat track. You can stick it in the oven at the same temp as the heat blanket to get results consistent with your mold.

Another point to remember is the type of epoxy you are using. Some are designed to cure best at elevated temps so make sure you've got the right stuff.

Good luck.

[Raccoon]

Hello Ben,

Could you please let me know how are your laminates with only one blanket? we have recently build a kiteboard pneumatic press and we have purchase only 1 blanket. Our plan is to heat the bottom of our press because we are using 3D core. thanks
Julien
PS: I'm from Lac St Jean, Quebec

[MontuckyMadman]

I heat bottom only. I take it slow as to not mess up the camber. 2.5 hours to temp. Might be excessive but I get good results. 55 psi.
I use a thermocouple on the bottom AL cassette. If I set the pid to 120F the blanket ramps to about 140F before the cassette temp catches up.
You don't ant to push the base material over like 190F or it warps and gets funkey.
Sorry don't know C.

[Docta]

THis is an area of great interest to me now as well. I am working on heating my press, and have some blankets on the way. My plan was to pregheat the entire press with a cheap blanket capable of gettin the whole thing to about 110, then use the 180 degree blanket to heat the cat track up and heat that way. With a one or two hour press do you still think I could get camber changes?

[powderho]

I only have heat on the bottom of my press. And while it works fine now, it has been a learning experience. My mold is flat under foot, and my first few pairs came out with all sorts of camber. Around 15mm. And the tips and tails flattened out....which sucks. It was full operator error on my part. My initial thought was that I needed the potentially coldest spot in the layup to reach 175. So that's where I placed the TC. I ramped up the temperature a few times over a few hours to reach final temp. Still, I bet the bottom of the laminate was over 250 degrees at one point and the epoxy had already been cured for an hour before the top was finally cured. I now use multiple TC's throughout the laminate to monitor the temps. I control the PID off the hottest TC now to make sure nothing is overheating. My skis are coming out with around 3-5mm of camber now. I think the biggest contribution to this is that I'm preheating the cattrack up to around 125 degrees on my last pair. My cattrack is about 115 lbs of 3/4" steel tubing that sucks up the heat, and it stays hot for a long time. I have been inflating my press to 10-20 psi, cranking the heat, and waiting until right before the skis are going in to deflate the press. My goal is to get the epoxy curing closer to the same time. I don't really care about press time. It still takes a long time for the temp on top of my 18ga al top cassette sheet to reach 175 even when it starts at 125. I always let the skis cool down under pressure overnight. It took me a few pairs to realize that too much heat, and pressure for that matter, is no good.

[ben_mtl]

Racoon -> I finally went with 2 blankets as I got a deal with a group buy.
I experienced some camber variations though as the 2 blankets don't heat at the same speed and I suspect my cat-track to rub some heat from the top blanket. I need to buy a new set of TCs to be placed directly on the cassette and stop using the ones in the blankets.