Vacuum Bagging honeycomb core

[ian_upton]

Does honeycomb core material lend itself to vacuum bagging?

I am considering trying this when I replace a cabin bulkhead on an old Bertram 25.

The finished surface will be painted, so I thought the peelply surface from the vacuum bag would give a nice surface to start with.

I have access to partial sheets of Corecell at a considerable discount (Noah's in Toronto) and am also wondering if two pcs butted against each other would be sufficient or would this create a weak panel?

Thanks,

Ian.

[wet feet]

Be aware that there is more than one type of honeycomb.I have encountered Nomex and Aluminium in vacuum bagging situations and both do a satisfactory job.You need to be sure that the material you have access to is of the correct density to provide the strength for the job and that it has the flexibility to conform to any necessary shape.

[marshmat]

Corecell is not a honeycomb, it is a closed-cell foam. It is probably suitable for your bulkhead replacement.
I have never seen a satisfactory honeycomb core job done without vacuum bagging, on anything but a horizontal flat plate. Curved or vertical parts with honeycombs simply have to be done under vacuum bag in order to work properly, unless you want the finished product to be 75% resin and way overweight. Nomex and aluminum honeycombs both have a tendency to suck the liquid resin out of the skins; a good layup is not nearly as easy as with solid fibreglass. Honeycombs are complex materials and specifying an appropriate one for a particular job requires a good understanding of the stress distributions within the part.
A peel-ply surface has a slight texture, generally comparable to 150-220 grit sandpaper in terms of how much it deviates from perfectly smooth. It is paintable, but to get a mirror-smooth finish will require that you fair it with a microballoon filling compound.

[ian_upton]

That's for the replies.

I guess I was vague in my question. I understand that corecell and honeycomb are two different materials.

My corecell question is will you lose much in stiffness by having multiple pcs of core material within the panel or should I spend the $$ for a continous sheet?

If I am bagging a wet laminate (not infusion) do I need to prime the corecell with resin and let it kick?

My concern with honeycomb was if the voids in the honeycomb would suck up the resin and create a honeycomb cells full of resin.

Thanks,

Ian.

[Bayport_Bob]

Honeycomb cores are typically used with prepreg materials where the layup is cured in an autoclave or an oven under vacuum. There is minimal resin flow with this type of system and the hollow chambers don't fill up with resin.

[johnhazel]

Crozier Racing canoes has been vaccume bagging hand lay up carbonfiber/honeycomb for decades. These canoes are 18.5 ft long and weigh less than 30lbs. $4850 will get one for yourself but the waiting list is long. Crozier is getting tired of building.
Rimer racing canoes also builds them in a slightly faster but less stable version. Those can be had for about $4400.

The trick to bagging honeycomb core parts is to use a two step process which requires a two molds. For example if a 3/8" sandwich canoe hull is being built you need a mold for the inner layer and one for the outer. The inner mold (male) is the same shape as the outer mold (female) except that it is 3/8" smaller to make room for the core material.

Building the part:
The inner layer of cloth is laid on the male mold and wet out. Then the core material is laid onto the wet cloth and vaccume bagged down. After the epoxy cures the part is removed from the mold and trimmed/test fitted to the outer mold. Then cloth and epoxy are applied to the outer mold. The part from the previous operation is then bagged into the newly wetted cloth to crate the carbon-honeycomb-carbon sandwich.

It is amazing how flexible the part is before it gets the second skin. This is a good thing though because that flexibility allows the second side of the honecomb to make good contact as it is bagged down into the wet cloth that becomes the outer hull.

I actually have done this process in Rimer's shop and have spent several hours with Crozier in his shop too.

[tunnels]

Does honeycomb core material lend itself to vacuum bagging?

I am considering trying this when I replace a cabin bulkhead on an old Bertram 25.

The finished surface will be painted, so I thought the peelply surface from the vacuum bag would give a nice surface to start with.

I have access to partial sheets of Corecell at a considerable discount (Noah's in Toronto) and am also wondering if two pcs butted against each other would be sufficient or would this create a weak panel?

Thanks,

Ian.

Simple question! what do you think will happen to the Honey comb when you put it under vacuum on a wet surface ?? remembering its got all those voids all over it ??:confused: :eek:

[lesburn1]

I have been vacuum bagging with honeycomb cores since 1986.
My process has been to lay up the outer skin in the mold, then fit the prepared honeycomb core ( in my case a Plascore polycarbonate honeycomb product) then lay in the inter skin and install the Vacuum bagging consumables. This presupposes that all the components have been cut to plan before hand and that you are using a very slow resin/hardener mixture. While this works with S-Glass, I have found that kevlar rolls up on a pvc pipe after wet out much better.

[apex1]

Simple question! what do you think will happen to the Honey comb when you put it under vacuum on a wet surface ?? remembering its got all those voids all over it ??:confused: :eek:

Not what your question suggests.................:confused: :eek:

Nothing will happen, just the core will stay in place and have contact with the wetted out surface.
Thats why it is done.

Regards
Richard

[tunnels]

Not what your question suggests.................:confused: :eek:

Nothing will happen, just the core will stay in place and have contact with the wetted out surface.
Thats why it is done.

Regards
Richard

Trouble with answering peoples questions is do we understand what they are really asking ? what you see is totally differant to what i see ! so the answers given are a little bewildering for some one that dosent know much about what they have asked about .
Lets try standing in there shoes with a blank mind looking at what they are asking about.
I have often askes "HOW MUCH VAC SHOULD BE USED TO DO THE JOB" i have never had anyone answer ! dont they know or are they to affraid that what they say might not be right ?. :confused:

[apex1]

so then Tunnels, here you can shine!

What did you mean with: "remembering its got all those voids all over it "

???

And don´t argue when your questions get no reply, YOU are the one claiming to know advanced composites! Although......

[tunnels]

so then Tunnels, here you can shine!

What did you mean with: "remembering its got all those voids all over it "

???

And don´t argue when your questions get no reply, YOU are the one claiming to know advanced composites! Although......

Honeycomb ,voids, empty spaces ,holes ,places that will fill with resin !!
I have never laid claim to advanaces composites ever ! Have been round the playground a while and been and seen a lot a stuff in differant countries. When asked i will go any where to show others how and to learn from them ! There is no black and white in this industry just varying shades of the color gray !

[apex1]

Honeycomb ,voids, empty spaces ,holes ,places that will fill with resin !!
I have never laid claim to advanaces composites ever ! !

So, core composites are not known as "advanced composites" ???

And the honeycomb spaces fill with resin when vac. bagged? How do they do that?
In my village they don´t.

Tunnels you should stay with what you know, not with what you guess!

Richard

[tunnels]

So, core composites are not known as "advanced composites" ???

And the honeycomb spaces fill with resin when vac. bagged? How do they do that?
In my village they don´t.

Tunnels you should stay with what you know, not with what you guess!

Richard

Explan in fine detail how the voids never fill with resin if you place honey comb core under vacuum on a wet layer ?? :confused:

[apex1]

Explan in fine detail how the voids never fill with resin if you place honey comb core under vacuum on a wet layer ?? :confused:

Explain how they would, you are the "expert" :p (as far as the forum understands your claims)

We are talking bagging here, not infusion!

[rxcomposite]

May I butt in?

Honeycomb is considered as an advanced composite material. So does foam core as the properties of the materials is best used to advantage.

Honeycomb is best used with prepreg but you need a glue sheet in between the honeycomb and the prepreg. Honeycomb is best when vacuum bagged.

It is not a good practice to bond immidiately the honeycombed to a wet laid up curved surface as the wet laminate will be disturbed during the vacuum process. Best bet is to let the outer laminate cure until tacky then apply a light coat of resin to the honeycomb then bag it. The resin acts as a glue.

For flat laminates or very slight curve, you can lay the honeycomb directly to the wet laminate then bag it after peel ply, perforated release film, bleeder cloth, ect.

Unless you are working with prepreg, you cannot make a double skin laminate (inner and outer) in one go. You need to make a partial laminate first of outer skin and honeycomb. The inner skin will be a little bit tricky and is a different process for flat and curved laminate.

[rxcomposite]

I use -20 to -25 inches of mercury. 27" is hard to achieve with a 2 Hp. vane pump. Aerospace and racing parts use large vacuum machine that reads up to 75" of mercury. I have never seen it but they say you cannot talk to each other when it runs. at any rate, I have never crushed a honeycomb with -26" of Hg.

You have to cut the edges of the honeycomb to 45 degree. Use a very sharp utility knife. If you want a perfect edge, you may fill up the eges with microbaloon putty then sand it before the inner skin is bonded.

Use ridgid honeycomb for flat panels, "Hex" hexagonal honeycomb for curved surfaces, "OX" over expanded honeycomb for compound surfaces.

[hoytedow]

I use -20 to -25 inches of mercury. 27" is hard to achieve with a 2 Hp. vane pump. Aerospace and racing parts use large vacuum machine that reads up to 75" of mercury. I have never seen it but they say you cannot talk to each other when it runs. at any rate, I have never crushed a honeycomb with -26" of Hg.

You have to cut the edges of the honeycomb to 45 degree. Use a very sharp utility knife. If you want a perfect edge, you may fill up the eges with microbaloon putty then sand it before the inner skin is bonded.

Use ridgid honeycomb for flat panels, "Hex" hexagonal honeycomb for curved surfaces, "OX" over expanded honeycomb for compound surfaces.Thanks. I am learning a lot from this thread.

[tunnels]

May I butt in?

Honeycomb is considered as an advanced composite material. So does foam core as the properties of the materials is best used to advantage.

Honeycomb is best used with prepreg but you need a glue sheet in between the honeycomb and the prepreg. Honeycomb is best when vacuum bagged.

It is not a good practice to bond immidiately the honeycombed to a wet laid up curved surface as the wet laminate will be disturbed during the vacuum process. Best bet is to let the outer laminate cure until tacky then apply a light coat of resin to the honeycomb then bag it. The resin acts as a glue.

For flat laminates or very slight curve, you can lay the honeycomb directly to the wet laminate then bag it after peel ply, perforated release film, bleeder cloth, ect.

Unless you are working with prepreg, you cannot make a double skin laminate (inner and outer) in one go. You need to make a partial laminate first of outer skin and honeycomb. The inner skin will be a little bit tricky and is a different process for flat and curved laminate.

At last someone has given me the answers and information i have been asking about .
Not everyone has used Honeycomb , i have laid lots a foam , lots a balsa but never used Honeycomb .
Getting an informative answer is like getting blood from a stone !
Thank you so much !!:D

[rxcomposite]

Thanks for the nice words tunnels and hoytedow. I do not consider myself an expert. Just 17 years in the composite industry.

I am glad I am no longer bounded by "confidentiality" so I can share my knowledge. Some are trade secrets which prevented me from sharing in the early days. You will not find that in the books.

[apex1]

I use -20 to -25 inches of mercury. 27" is hard to achieve with a 2 Hp. vane pump. Aerospace and racing parts use large vacuum machine that reads up to 75" of mercury. I have never seen it but they say you cannot talk to each other when it runs. at any rate, I have never crushed a honeycomb with -26" of Hg.

We should add: less is more in common prepreg or resin film layups!

8psi or (when I remember right 20Hg) are a lot of vac. pressure on a average core layup (too much for most applications in boat building).
On a wet film layup you would print through from 4 or 6 psi upwards. (depending on material of course)

A honeycomb "sucks" resin into the root when in contact with a wet layup, but the cells are not filled with resin. First, there isn´t enough resin to fill the cells, second there is no way (almost) to suck the resin out of the wet fibre.
At say, 25 psi and above you would deal with that problem amongst others, sure.
But there still is not enough resin to fill the cells to some extend. The layup though would be for the landfill.

And to come back to the original question:

Does honeycomb core material lend itself to vacuum bagging?

No, it is a MUST.


Regards
Richard

[tunnels]

:D We should add: less is more in common prepreg or resin film layups!

8psi or (when I remember right 20Hg) are a lot of vac. pressure on a average core layup (too much for most applications in boat building).
On a wet film layup you would print through from 4 or 6 psi upwards. (depending on material of course)

A honeycomb "sucks" resin into the root when in contact with a wet layup, but the cells are not filled with resin. First, there isn´t enough resin to fill the cells, second there is no way (almost) to suck the resin out of the wet fibre.
At say, 25 psi and above you would deal with that problem amongst others, sure.
But there still is not enough resin to fill the cells to some extend. The layup though would be for the landfill.

And to come back to the original question:



No, it is a MUST.


Regards
Richard

Thank you !
At last there is some good and useful info starting to surface .The process for vac bagging is basisly easy to do ,just i know it all came to work with us and stuffed a couple of big panels we were making .
I ill explain a little later the whats and whys when i find the pictures i am looking for on my dvd disc.
Keep the info flow going this is all good stay !! There are little traps for people to watch out for and i totally agree there are secrets that you wont find in books . Some of the panels we were making were 16 mtrs long x 4 mtrs wide x 50mm cores with 56 layers of glass each side some even had Carbon as well . Sometimes took 30 guys to get the panels off the table for the crane to be able to pick them up . :eek:

[rxcomposite]

I cant remember the conversion right now but the tech rep says we are applying about 50 lbs/inch2 to the laminate, that is prepreg laminate.

The root of the honeycomb gets about 0.002 to .003 of resin in our coupon test section.

Most likely you will get print through on the laminate. Even WR will show a print through.

I won't reccommend Honeycomb on the hull of the boat. Not even on the deck. It is great for interior panels.

[rxcomposite]

Tunnels,

If you are making 16 meter long panels, watch out for curving of the laminate when it is pulled out of the mold. I have described the heat absorption of the tool somewhere in this forum before. That is the tool sucking the heat out of the resin while it is exotherming.

[rxcomposite]

Going to sleep

[apex1]

I won't reccommend Honeycomb on the hull of the boat. Not even on the deck. It is great for interior panels.

I dare to disagree, (in some details)

It is rubbish!

Replace it with a light wood and be fine. Several times the shear strength and no rot. (opposed to common belief)

In high tech applications and aircraft, were every single gram counts, these composites have a high value.

In boats for average (including circumnavigations) use, it is wasted money, complicates the whole stuff and never pays back. (the opposite)

For a homebuilder it is nothing but mad, even to think about it.

Regards
Richard

[rxcomposite]

For Racing boats that is out of the water most of the time, honeycomb will do but for commercial applications it is not advisable.

Honeycomb has air cells. Fiberglass is known to have osmosis after 5-10 years. The air void tends to fill with water after some time.

Some core manufacturers offer foam filled honeycomb. This might be a solution, but personally, I have not tried this so I cannot offer even an opinion.

[rxcomposite]

Tunnels,

With 56 layers on a side of a cored laminate, that would be 0.65 x 56 layers=36 mm. of laminate of pure WR600. What are you building? Bridges?

But you say 30 men needs to lift it so I beleive it is not a typo error. Drop me a line in the private message forum. You might be overdoing it a lot and wasting your material.

Rx

[Herman]

On to the original question of the topic starter:

Get yourself the quarter sheets of Core-Cell. They are great for your application. You can easily butt-join them in the works, but make sure there is some resin or glue between them. If you wish, you can pre-coat (hotcoat) the sheets, this will make bonding more bullet proof. Although a slurry-type of bonding paste should do the job without hot coating. (you can always run a test)

About honeycomb: do not bother, unless weight is a more then critical factor.

[marshmat]

Re. bagging pressure (vacuum):
29.9 inches of mercury, 760 torr (mm Hg), 1 atmosphere. That's the most you'll get: pull a perfect vacuum in the bag, and your bagging pressure will be that of the surrounding atmosphere.
Reports of bagging at 75 inches Hg are for parts that are cured in pressure autoclaves. Take your normal vacuum bagged mould and part, and seal it inside a giant pressure vessel that goes up to five atmospheres and 120 degrees Celsius during the cure. The only place I've ever seen/used such a machine is at a helicopter factory where we were curing a solar car's body/chassis assembly.

Re. resin in the cells of the honeycomb: If the mould is airtight, the resin is not subject to any pressure differential, and is not forced in any particular direction. The pressure of the bag is transferred only through the solid components: the honeycomb and the fibres. The vacuum does not suck resin into the cells. Do note that this applies only to standard vacuum bagging: infusion systems are carefully designed to ensure that the resin IS subject to a pressure differential, by keeping one end of the resin system at higher (ambient) pressure, and attempting to infuse with honeycomb in the layup will probably result in resin-filled cells.
The cells will, however, tend to fill with resin purely due to gravity, as it drips down from the layers above. Unless you know about this and plan around it, you might end up wetting out the top layers over and over again until the piece is heavy and solid.
Of course, I'd have a pretty hard time recommending most honeycomb materials for wet layups; they're really designed for the heat-cured prepregs used by the aerospace industry.

IMHO, honeycombs are better left out of most boat applications, although they do have some merit in win-at-any-cost racers where the engineering costs are easily borne and the long-term downsides are less noticeable.

[Herman]

I sold the ABN-Amro Volvo70 boats their honeycomb. I guess they were OK with it...

With infusion, you will surely fill the cells. Will make for a nice resin-rich laminate...

One of my customers runs an autoclave, built (and sometimes used) for 12 bars, 400 degrees C. It is a relatively small autoclave (120x3 meter or so) and consumes 107 kW of heating power when heating up. I must admit it is research facility, which does help...

[rxcomposite]

[QUOTE=marshmat;378607]Re. bagging pressure (vacuum):
29.9 inches of mercury, 760 torr (mm Hg), 1 atmosphere. That's the most you'll get: pull a perfect vacuum in the bag, and your bagging pressure will be that of the surrounding atmosphere.
Reports of bagging at 75 inches Hg are for parts that are cured in pressure autoclaves. Take your normal vacuum bagged mould and part, and seal it inside a giant pressure vessel that goes up to five atmospheres and 120 degrees Celsius during the cure. The only place I've ever seen/used such a machine is at a helicopter factory where we were curing a solar car's body/chassis assembly.

QUOTE]

Marshmat, you are absolutely correct! I have doubts myself until my friend gave me the defective vacuum gauge they were using and true enough, it reads in cm/Hg and the number 75 (cm.) is equivalent to 29.5 inches. A near perfect vacuum. It takes them 4 hours of sustained vacuum to check if the part would leak before they infuse.

[tunnels]

Tunnels,

With 56 layers on a side of a cored laminate, that would be 0.65 x 56 layers=36 mm. of laminate of pure WR600. What are you building? Bridges?

But you say 30 men needs to lift it so I beleive it is not a typo error. Drop me a line in the private message forum. You might be overdoing it a lot and wasting your material.

Rx

Its 5 to 6 layers of glass plus carbon each side , not 56 layers !!
The panels were used in the construction of Collision bulheads for up front and also watertight panels in the forward end and aft end of the engine room ,these panels were very big and ended up being fitted in two pieces . BY nesting panels together on the big table that had the same glass layups and specifications we were able to produce a lots of panels quickly and efficently with very little waste .
We had to use human lifting power to move the big panels off the table as we had a tent built and suspended from the ceiling to completely cover and seal the table and 2 meters wide walking space around all sides for comfortable working space.
So when one 16 mtr x 4 meter panel was release off the table then it had to be man handles out from under the tent and laid on timber laid on the floor to then be cut to the sizes of the bulkhead patterns that had been made !. :D

[rxcomposite]

Tunnels,

Ok. :) I thought you had a contract for bridge panels.

Good idea. I do that also. Make the panel as large as I can then cut the parts needed. Saves materials and time.

Cheers,
Rx

[johnhazel]

Explan in fine detail how the voids never fill with resin if you place honey comb core under vacuum on a wet layer ?? :confused:

In real life they dont. I have done this myself and know well (helped build) composites honeycomb sandwich in 3 separate shops. It's because the vaccume is everywhere inside the bag. The bag pushes against the part giving it a tight squeeze and there is not enouh resin in the cloth to move into the cells of the honeycomb. My experiencce is with fiber to resin ratio of about 1:1.

[tunnels]

In real life they dont. I have done this myself and know well (helped build) composites honeycomb sandwich in 3 separate shops. It's because the vaccume is everywhere inside the bag. The bag pushes against the part giving it a tight squeeze and there is not enouh resin in the cloth to move into the cells of the honeycomb. My experiencce is with fiber to resin ratio of about 1:1.

Personally i have never used Honeycomb for anything !I understand it has its place !. The amount of resin used in the glass would be a crusial factor also the thickness of the core its self .Like all things there tricks to what we do .

Keep the information coming this is all good stuff!!:P