Honeycomb edge treatment

[grafp]

Can anybody give me some good ideas on how to fill in a beveled edge on on honeycomb core? I normally use a Polyurethane Foam (last-a-foam) as my core in a sandwich construction.
I have heard Kelvar pulp mixed with epoxy makes a good filler.

 

[berkshire]

Grafp,
When you say beveled edge, has the honeycomb been machined to a bevel? Or do you wish to create a bevel with a filler paste.
In the first case no filler is needed although some people pot the reduced height cores with a paste of micro balloons and resin before laying on the skins.

In the second case any short fiber filler mixed into your laminating resin with a little silica ( Cabosil or Aerosil)to make a filler paste will do.

I am presuming that you are laminating your own skins, that you are not using prefabricated sandwich.
B.E.

 

[grafp]

B.E.

Thanks for the reply. Yes, I am laminating my own skins.
My normal lay up is Fiberglass - P.U. Core - Fiberglass that is then vacuumbagged.
During the lay up my core is completely encased within the fiberglass skins. I want to switch my core material to honeycomb. The honeycomb core will be machined to a 45 degree bevel. I am worried an untreated beveled edge on the honycomb will not give me a nice smooth edge I am looking for after vacuumbagging my layup.

PG

 

[Compositepro]

Epoxy filled with micro balloons would be used for cell fill in order to save weight. That is what honeycomb is all about. Epoxy filled with kevlar pulp would be used where greater strength is required than microballoon will provide. This would be "hard points" where there are attachments to a sanwich panel.

It is also sometimes possible to simply press a low density foam into the honeycomb. You would do this before beveling.

 

[RPstress]

You can try a layer (or two) of film adhesive cured onto the top of the bevelled edge. This helps prevent core crush and keep the edge looking nice and crisp for lower cure pressures. With metallic core it means an extra op. With Nomex or similar which is being hot formed, curing the adhesive can be incorporated in the forming op. Specialised surfacing films such as Synskin (used to be Cyanamid; may now be Cytec) also claim to help. Synskin didn't (well, claimed not to) need a precure.

A co-cured face on almost any honeycomb core is going to look quite a bit worse than one on foam. A caul plate may be a low cost way to preserve flatness and prevent visible telegraphing.

This assumes it's aesthetics that matter. A bit of edge crush never did anyone any harm structurally. (To my knowledge - any disaster stories attributed to bobbly/dished in ramps?)