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heating a vacuum press

Posted: Thu Dec 05, 2019 11:50 am
by Wheatlpa
So i am going down the road of building a vacuum press. I think i have all of the details working out regarding the pump, the table, the mould (although hoping the Wvmtnbiker is able to provide photos of his with out the metal on top) and the frame for the silicone. My next question is on heat. I have a bunch of epoxy (Entropy CPM/CPS) left over from building my second pair of skis using my friends hydraulic press. From what I understand this epoxy is meant to be cured at ~80 degrees C.

So, what can you guys suggest to heat up my press to ~80C or should i just buy different epoxy that cures at a lower temperature? If i should use different epoxy what would you recommend.

Thanks in advance, after a couple of years of thinking about it and trying other peoples set ups i am excited to build my own!

Pat

Re: heating a vacuum press

Posted: Thu Dec 05, 2019 7:51 pm
by Wvmtnbiker
I’ll get Picts for you - I’m on the road so I’ll get some posted beginning of next week. Look on alibabba for heat blankets. I used Ali rubber and gave them the dimensions and wattage, wire for 110 blanket. I’ve found the emails but can’t find a link but I’ll keep looking - cost was 115 and 45 shipping. They’ll make anything you want size wattage etc. They’re have been some recent posts about heat blankets with supplier links. Search PID heat controller - lots of info and not difficult to build yourself. You can heat top or bottom or both. If you’re only heating from one side plan on camber being different from the camber of your mold. Definitely have to add heat with entropy - data sheets say 180 F for 20 min I think. I think most people who vacuum press heat for several hours with different ramp up times based on their individual blankets. I usually heat for at least an hour after the blankets hit 180 and longer if I’m only heating from one side.

Re: heating a vacuum press

Posted: Thu Dec 05, 2019 8:11 pm
by Wvmtnbiker

Re: heating a vacuum press

Posted: Fri Dec 06, 2019 6:27 am
by Wheatlpa
Again, great information! I have built PID controllers for my brewing set up so no worries there. I do have a question about your statement on heating top and bottom though. When using my friends pneumatic press heating top and bottom was easy but how do you manage that with a vacuum table? If you are heating on the bottom i assume you would need to have the heat blanket between the mould and the skis. The only way i see that happening is sandwiching the heating pad between 2 layers of the aluminum sheeting underneath the skis with the top blanket outside the vacuum just laying on top. I also assume that the hole through the vacuum table for the wires will need plenty of silicone to seal up any potential leaks.

Does that sound about right?

I will look through the posts on the PID controllers for more information on the wattage (i have no idea what this represents so you might get a PM from me :D ) and i assume that the size will be wide enough to cover two skis on the mould and long enough to stick out either end or at least sized to the longest ski i think i might make.

Re: heating a vacuum press

Posted: Fri Dec 06, 2019 7:49 am
by Wvmtnbiker
That all sounds right - I use a very thin piece of metal, then the lower heat blanket and then the thicker metal above if heating from the bottom. lately I've just been heating from the top - I lose a little camber but that's the plan. The heat blanket is 195cm x 34cm which is the width of the molds/metal with the leads coming out at the end - its easier for me in the vacuum press to deal with the wire at the end. It has 1 cm wire spacing and is 1200W according to the email - ill check this to be sure though. I did specify to the manufacturer that I didn't want a draw higher than 13 amps - was thinking old garage with 15amp outlets. It seems to work well - I think other people on the forum have higher wattage blankets and many do 220 vs 110.

Re: heating a vacuum press

Posted: Fri Dec 06, 2019 8:27 am
by Wheatlpa
i will read up on heating from the top only as i would like to cut down on the complexity of my first (only??) build. I hear you about the lower wattage, i have an unheated garage so depending on the epoxy (that is my next question to you) i might move this operation into my basement which does not have a 220v outlet anywhere convenient.

So last 2 questions on this topic.
1. When you are heating just on top. Are you laying the heating blanket outside of the vacuum sheet on top of the silicone? i assume yes but always helps to check.

2. I assume with the 1200w you are getting lower temps, what epoxy are you using for your skis?

again, you have been really helpful with all of these questions and i appreciate it.

Re: heating a vacuum press

Posted: Fri Dec 06, 2019 8:49 am
by Wvmtnbiker
I might be wrong about the wattage - it might be 1800w. Ill check when I get home. I have no problem getting it hot enough. I use Entropy and using only top heat Ill press for about 1:45 -2:00 hours. I have made the mistake of pulling too early. Heat blanket just goes on top - I have to put some wood blocks/small sand bags/free weights to keep the blanket flush with the top but it works - definitely ghetto.

Re: heating a vacuum press

Posted: Fri Dec 06, 2019 9:03 am
by Wheatlpa
So the epoxy that I have (Entropy super sap CPM/CPS) should be fine in a vacuum press as long as I get the heat up to 180. If so great news as I have several skis worth of resin/hardened left.

With heat on top do you get a bounce back on the camber? So if I make my mould with a 5mm camber I can expect the camber to be a little less. I assume that also impacts the rocker tip if you want to have an early rise...

Re: heating a vacuum press

Posted: Fri Dec 06, 2019 9:48 am
by Wvmtnbiker
In my case it’s been less than 2mm. I usually do the layup, start to press and make sure everything is lined up correctly. Then as the press is reaching full pressure I use a laminate roller on the top of each ski at the tips and tails to make sure the top sheet is smooth. Then I’ll add heat about 20 min later for about two hours if only heating from the top. Then I turn the heat off and pull the skis out at around 140F. Lots of different variables here but this method works well for my setup. I got to this method by lots of trial and error and several pairs of $200 wall ornaments. In my case the wall ornaments were the result of not testing everything before layup. It goes without saying but test your pressure before you start your layup, also make sure your heat blanket is at the right temp by monitoring it with more than one thermometer - a cheap k type thermo couple was giving an incorrect temp reading and I under heated one pair and toasted another. Lesson learned hopefully.

Re: heating a vacuum press

Posted: Sat Dec 07, 2019 8:38 am
by Wvmtnbiker

Re: heating a vacuum press

Posted: Sat Dec 07, 2019 11:48 am
by MadRussian
do you ever read this forum? Everything you asked has been discussed many, many times.
Not always given straightforward solution because everybody do stuff little different and you have to read between the line and find your own solution for your own possibly unique problem.

Because if you read it you would find:
CPM cure just fine at the room temperature not in 30min but in 24 hours It will cure to dry and full cure in seven days

highly unlikely you can heat vacuum press to 180°for 30 min heat cure

you can easily use heat blanket even at 100° to improve cure quality of room temperature epoxy still 24 hours

if cure with heat only from above there is a possibility(at least in air press) ski/board will looks like banana or reverse camber

good luck on your journey.
Maybe you should start your own Journal so people and you in the future can follow your progress

Re: heating a vacuum press

Posted: Mon Dec 09, 2019 8:50 am
by Wheatlpa
MR, thank you for taking the time to reply. It is good to know the CPM/CPS that i have will work at lower temperatures. At least i do not have to buy more...at least until i have finished the batch that i have.

I have started a journal to document my build, i hope you will point out anything i am doing wrong.

Wvmtnbike: thanks again for the photos, i did not think that the mould you are using was spaced out like that. I would have thought that the vacuum would have pulled the metal sheet a little down through the gaps...but obviously your sheets are a little stiffer than the aluminum that i have access to. I will have to test this out when i get it set up.

I have found that DraftSight will be discontinuing their free software starting end of December, so i am currently looking at nanoSoft as a drawing tool. i have also found a person in town who has a CNC machine so they can cut the templates out for the tip and tail of the mould. Unfortunately it is too small for the camber. I will be doing that one by hand.

Re: heating a vacuum press

Posted: Thu Dec 12, 2019 5:48 am
by Wheatlpa
last question from me on this topic...maybe.

I am in the process of ordering 2 heating mats from Alibaba (thanks for the link Wvmtnbiker!) and I was wondering how I control the temperature of these mats. I am planning on building a controller with 2 PIDs (one for each mat) and 2 SSRs to control the power. In my brewing set up i have a thermocouple attached to a temperature probe in the liquid. In the vacuum i would assume i would need a flat sensor that can withstand the pressure of the press and it has to be flat enough to fit between the mat and the aluminum sheet under the ski during the press and another between the silicone sheet and the upper heating mat.

I have looked on the auber website for something suitable and have found a couple of things that seem like they might work (https://www.auberins.com/index.php?main ... cts_id=273) but not sure (i have an email question into them now on this topic) So i thought i would ask the forum as well.

Re: heating a vacuum press

Posted: Tue Dec 31, 2019 8:27 am
by Wheatlpa
Well the two heat blankets have arrived from China, in the end maybe not as cheap as i had hoped but not much i can do about that now.

Along with the power wiring i also seem to have another two leads that i think are the temperature sensors for the mats. Anyone have any tips on connecting them to my PIDs? You can check out the photo of the heat blanket in my build album here: https://photos.app.goo.gl/KX1ctzDuPpw3Qiu49