How do you hold a honeycomb core in a female mold while pulling a vacuum???
04-25-2003, 09:03 PM
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How do you hold a honeycomb core in a female mold while pulling a vacuum???
I’ve got a female (concave) mold and I want to lay-up a face sheet of graphite, then a 1/4” honeycomb core, followed by another graphite face sheet. I’ll wet layup the first face sheet into the mold, then add the honeycomb, then the other face sheet.
Question: Does anyone have any tips on how to hold the core material in the mold while I add the top sheet and the pull a vacuum on it? Last time I tried it I just let the vacuum pull it down, but it pulled the first face sheet (against the mold) down too and put a bunch of wrinkles in it.
Help?
Thanks
Russ
Question: Does anyone have any tips on how to hold the core material in the mold while I add the top sheet and the pull a vacuum on it? Last time I tried it I just let the vacuum pull it down, but it pulled the first face sheet (against the mold) down too and put a bunch of wrinkles in it.
Help?
Thanks
Russ
04-26-2003, 09:20 AM
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How do you hold a honeycomb core in a female mold while pulling a vacuum???
Hi Russ,
I have done a bit of work with composites, especially carbon.
The best way to do this may be in three steps.
first lay in your carbon against the mould, then a sheet of `peel ply`(nylon shower curtin works fine/as just about any nylon material) then your bleeder material and vacuum bag it first.
once that has cured, while its still in the mould, pull out the peel ply and you will be left with a very good surface to bond too, lay in your honeycomb (after coating the edge with slightly thickened epoxy), and vacuum it in place. (use a reduced vacuum and try small plastic bags filled with sand to keep it inplace while you ste up the vacuum bagetc
if you can, you might be able to lay on your final layer(s) as well. (but it sounds like it is here that you are having trouble)
In practice it is generally easyier to lay honey comb onto convexes and fill the surface with light weight fillers.
of course sometimes you don`T have this luxury.
Regards,
Japan man
I have done a bit of work with composites, especially carbon.
The best way to do this may be in three steps.
first lay in your carbon against the mould, then a sheet of `peel ply`(nylon shower curtin works fine/as just about any nylon material) then your bleeder material and vacuum bag it first.
once that has cured, while its still in the mould, pull out the peel ply and you will be left with a very good surface to bond too, lay in your honeycomb (after coating the edge with slightly thickened epoxy), and vacuum it in place. (use a reduced vacuum and try small plastic bags filled with sand to keep it inplace while you ste up the vacuum bagetc
if you can, you might be able to lay on your final layer(s) as well. (but it sounds like it is here that you are having trouble)
In practice it is generally easyier to lay honey comb onto convexes and fill the surface with light weight fillers.
of course sometimes you don`T have this luxury.
Regards,
Japan man
05-01-2003, 02:34 AM
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How do you hold a honeycomb core in a female mold while pulling a vacuum???
Russ,
If you can afford do the layup in prepreg form. It makes life much easier. What you would do is lay all your cfrp layers in first, add a layer of film adhesive, then cut your honeycomb into triangular pieces to fit the curvature correctly, if you want you can put a small amount of foaming adhesive around the honeycomb to bond those pieces together, another layer of film adhesive, and lay on your top layers of cfrp. Now the tricky part bring up your vaccume slowly and try to keep things where you want then pull your final vac. Cure w/ heat 6 hrs and you have an airworthy part. These products are pricey but they do a very good job. This is how radomes are built/repaired.
Thaddeus
If you can afford do the layup in prepreg form. It makes life much easier. What you would do is lay all your cfrp layers in first, add a layer of film adhesive, then cut your honeycomb into triangular pieces to fit the curvature correctly, if you want you can put a small amount of foaming adhesive around the honeycomb to bond those pieces together, another layer of film adhesive, and lay on your top layers of cfrp. Now the tricky part bring up your vaccume slowly and try to keep things where you want then pull your final vac. Cure w/ heat 6 hrs and you have an airworthy part. These products are pricey but they do a very good job. This is how radomes are built/repaired.
Thaddeus
05-09-2003, 01:04 AM
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How do you hold a honeycomb core in a female mold while pulling a vacuum???
Hello,
After laying up the first sheet add microballons to one side of the honeycomb, if you prepare them sticky, it will mostly solve your time for about two minutes more than enough to wet the second sheet.
When ready for vacum make sure the bag is goofy enough and have a lot f breather especially on the center to avoid wrinkles and air bubbles...make sure the center is on touch with the mould.
Best Regards, Roderick Woolvett
www.manque-aircraft.com
After laying up the first sheet add microballons to one side of the honeycomb, if you prepare them sticky, it will mostly solve your time for about two minutes more than enough to wet the second sheet.
When ready for vacum make sure the bag is goofy enough and have a lot f breather especially on the center to avoid wrinkles and air bubbles...make sure the center is on touch with the mould.
Best Regards, Roderick Woolvett
www.manque-aircraft.com
05-14-2003, 03:46 PM
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How do you hold a honeycomb core in a female mold while pulling a vacuum???
I agree with guy about using pre pregs but it is another world if you have not used them before. To even consider it your mould will need to handle a min of 65 degrees C. Regular polyester resin moulds will handle around 80-90 degrees.
SP systems have a thickend type of resin/glue especially for bonding in cores like honeycomb. It is called pre gel and could be used in one shot with the first skin or after the first skin has cured. Other wise maybe you can put something temporary at the edges (hot melt glue) of the core just to hold it from springing out while the vacuum is pulled.
SP systems have a thickend type of resin/glue especially for bonding in cores like honeycomb. It is called pre gel and could be used in one shot with the first skin or after the first skin has cured. Other wise maybe you can put something temporary at the edges (hot melt glue) of the core just to hold it from springing out while the vacuum is pulled.
