Mold Release Question

[REK]

Hopefully this is in the right spot. I will recently be playing around with some prepreg that cure at low temperatures. The oven I've built has gone just up to165F. I will be doing tubing and I usually use conventienal methods to prep the mold. It becomes a hasle and time consuming, so I was thinking of trying something else.

I was thinking of trying the frekote 700 to prep the mold. Usually of course when this is used the aluminum will need to expand ever so slightly and then shrink down to release the cured tubing. Is 165F too low for this to work?

 

[Pat_B]

I'd suggest more of a synthetic wax product where you can be assured of the tube sliding off the mandrel. Something like Crown Mold Release. Products like Freekote were more for situations where you don't have a captive mandrel.

 

[REK]

I'd suggest more of a synthetic wax product where you can be assured of the tube sliding off the mandrel. Something like Crown Mold Release. Products like Freekote were more for situations where you don't have a captive mandrel.

Do you have a link to one specifically? I looked and there are many, so I dont know which one your referring to.

Thank you for your response.

 

[Pat_B]

Sure, here's the right one https://aervoe.com/paints_coatings/Mold-Release-and-Protector.html

 

[Barkley]

Frekote is recommended by my professional boat building buddy who works with FG and CF all the time. He doesn't use anything else.

 

[Pat_B]

It's the captive aspect of using a mandrel where a was product works much better. Most of the mold releases are intended for dies used in injection molding where pins help to push the finished part away from the die. All that's needed is a small amount of mold release to keep the plastic from sticking to the die.

In our case, a tremendous amount of friction exists between the body tube and mandrel, and the melted wax provides for the necessary gap to slide off the finished tube.

 

[REK]

Sure, here's the right one https://aervoe.com/paints_coatings/Mold-Release-and-Protector.html

Thank you I appreciate it. I had to look for one in a smaller amount so I can just do a small test to make sure it works.

 

[REK]

It's the captive aspect of using a mandrel where a was product works much better. Most of the mold releases are intended for dies used in injection molding where pins help to push the finished part away from the die. All that's needed is a small amount of mold release to keep the plastic from sticking to the die.

In our case, a tremendous amount of friction exists between the body tube and mandrel, and the melted wax provides for the necessary gap to slide off the finished tube.

I have a question,

Will this mold release make the epoxy bead or will it stay in place? I will be making small diameter tubing and getting the fabric on such a small diameter is a hassle. Will the mold release be slippery or will it grip?

 

[Pat_B]

The epoxy will bead a little bit, but it's possible to keep enough of it on the mandrel that it works out just fine. I've made hundreds of FAI airframes using the same technique as well as small stuffer tubes down to 1/8" in diameter. You only need to get enough epoxy on the mandrel so that the fiberglass attaches to it. It will then wet out nicely and you can then brush on some more epoxy over the fiberglass. In my case, I'm usually blotching it with some toilet paper in order to take off any excess epoxy. But Crown Mold Release is used by pretty much everyone on the US Spacemodeling Team for their epoxy work.

 

[REK]

The epoxy will bead a little bit, but it's possible to keep enough of it on the mandrel that it works out just fine. I've made hundreds of FAI airframes using the same technique as well as small stuffer tubes down to 1/8" in diameter. You only need to get enough epoxy on the mandrel so that the fiberglass attaches to it. It will then wet out nicely and you can then brush on some more epoxy over the fiberglass. In my case, I'm usually blotching it with some toilet paper in order to take off any excess epoxy. But Crown Mold Release is used by pretty much everyone on the US Spacemodeling Team for their epoxy work.

Dang I'd go insane making a 1/8" diameter tube. The part I struggle is aligning the fabric as straight as possible. If it goes off it tends to wrinkle. Well I'll only go far down as 3/8".

Thank you

 

[REK]

I went ahead and placed an order for a 13oz. aerosol can for $7 from another company. This will help me do a small test and see how well it works out for me. Sorry for the questions, but I always like to foresee how things go about. When using this mold release I am expecting it to melt at 155F? < yes 155F when I said, 165F, the reason is I made a little window in my oven to see the curing and going over 155F the epoxy started to bubble so 155F is my limit. After the epoxy has hardened the mold release should stay melted and allow the hardened laminate to slide off? By the way heat shrink tape is used in this process.

 

[Pat_B]

I've never measure the melting point, sorry. I use a heat gun to heat everything up and the heat gun certainly gets it very hot.

Once the wax gets melted then you need to remove your part right away. What can happen is that the wax can pulled into the matrix of the fiberglass- just a tiny amount. But that small amount is enough for the part to get stuck on the mandrel. So be sure to use enough wax to begin with, and pull your part off as soon as you can. It's especially important when using heat shrink tape because your part will be on the mandrel even tighter.

Crown mold release is a great product. The only time I even had difficulty is when I use it with carbon fiber. It sometimes takes a long time for the heat from the heat gun to transfer through the carbon fiber and get to the wax. Sometimes that's when various section of my airframe get too hot and suck up some of the wax, while other parts still are too cool to allow the wax to get slippery.

Some people will put their assembly into an oven. That certainly would give you more even heating, but I don't like putting chemicals in my oven. Many of these products have Benzen in them.

 

[REK]

I've never measure the melting point, sorry. I use a heat gun to heat everything up and the heat gun certainly gets it very hot.

Once the wax gets melted then you need to remove your part right away. What can happen is that the wax can pulled into the matrix of the fiberglass- just a tiny amount. But that small amount is enough for the part to get stuck on the mandrel. So be sure to use enough wax to begin with, and pull your part off as soon as you can. It's especially important when using heat shrink tape because your part will be on the mandrel even tighter.

Crown mold release is a great product. The only time I even had difficulty is when I use it with carbon fiber. It sometimes takes a long time for the heat from the heat gun to transfer through the carbon fiber and get to the wax. Sometimes that's when various section of my airframe get too hot and suck up some of the wax, while other parts still are too cool to allow the wax to get slippery.

Some people will put their assembly into an oven. That certainly would give you more even heating, but I don't like putting chemicals in my oven. Many of these products have Benzen in them.

Yes the mandrels will be put in an oven. I kind of figured having to remove it as fast as possible would be one of those things to consider since it can harden again. Yikes I'm already kind of not liking this, but hey you wont know for sure until you try right?

By the way I recommend making an oven with insulation sheets. The oven has been working great. Despite $150 into making one its worth it. Especially during the winter, since epoxy doesnt cure that fast in the cold.

 

[Pat_B]

That's a nice oven. I have one I built out of cement board and will have to take some pictures of it. I hooked it up to a timer and temperature control unit. I used it for curing epoxy, and frankly, never thought about using it for mandrel removal.

 

[REK]

That's a nice oven. I have one I built out of cement board and will have to take some pictures of it. I hooked it up to a timer and temperature control unit. I used it for curing epoxy, and frankly, never thought about using it for mandrel removal.

Nice sounds awesome,

If you can beat me to it, let me know if it works. I have to wait for shipping lol.