Hexacor compared with other composites?

[kengrome]

I've been discussing Hexacor core material with the manufacturers, but I do not know how to compare it with other composite core materials, nor do I know if it will work as a hull material. I welcome input from anyone who can evaluate the technical info they provide, or just compare it with other products on the market. Their web site is http://www.hexacor.com/ and here's an excerpt that provides the basics:

The Hexacor Polypropylene Honeycomb is the next-generation polypropylene honeycomb that is the strongest on the market today. With its all-round superior properties and competitive pricing, it is fast becoming a popular composite core material for increasing strength and stiffness at reduced weight.

Hexacor is the polypropylene honeycomb of choice for the following reasons:

• Strongest in the market
• Thinnest in the market
• Most technologically advanced:
  • Honeycomb panels are manufactured as a single sheet and not by joining smaller sheets together
  • Honeycomb panel surfaces are completely flat and without trapped air, which facilitates lay-up
  • Low resin wastage
  • Skin facings are strongly fused onto the honeycomb core, hence no known delamination issues
  • Available in different grades of strength

Unique Cell Matrix

Hexacor polypropylene honeycomb are made up of cell structures that are round rather than hexagonal, more closely resembling honeycomb structures that exist in nature. The round cell structures give the resulting cell matrix 3 orientations vs. the 2 orientations in hexagonal matrices. As a result, Hexacor polypropylene honeycomb properties are more uniform in all directions across the entire sheet of honeycomb.

Superior Quality

Hexacor polypropylene honeycomb cells are fused together rather than glued. Without the presence of glue as the "weakest link" in the honeycomb matrix, Hexacor polypropylene honeycomb sheets are more resilient.

Every cell in a Hexacor polypropylene honeycomb is very stable. Hexacor's manufacturing technology allows it to produce honeycomb cells that are extremely consistent regardless of any honeycomb sheet size.

[Alik]

You should look at shear strength of hexacor.

We are using hexacor for sides, cabins, bulkheads, acommodation bulkheads and also for bottoms of displacement boats. For hull, we prefer to give some extra thickness to skins to ensure the properties. We also have experinece of vacum bagging hexacor honeycomb - very positive.

[masalai]

I am not sure which it is but something similar can be "shaped" with the heat from a hair-dryer to soften it - this may be a disadvantage in areas where heat is an issue - engine rooms, on deck in the sun etc

Just a wild guess and some lateral thinking in relation to lay-up & forming ready to lay-up. I would be happy to be howled down by the knowledgable if I am wrong... All a learning experience ... Thanks.

[juiceclark]

Sorry to pop-in with a rookie question: but how much lighter can it be than the highest grade plywood after all the little holes are full of resin?

Tony in Sw FL

[masalai]

Not so Juicy. Air... The little sample I have is as light as a feather. in grams/square meter - I forget... My sample has fine woven glass on each side. At ambient (26 deg Celsius or less) is quite strong - good capacity to carry people when placed between 2 saw horses... (sorry three times I tried to correct that and typed "sore whores", now I can correct it Again no numbers - I think my sample is called "nidaplast"

[allan white]

Alik,

How to you stop the resin from filling the cores while vac infusing?

A

[kengrome]

Alik, how to you stop the resin from filling the cores while vac infusing?

It appears that you can get it with a PP skin over the holes, which means the resin cannot get inside. Look on this page:

http://www.hexacor.com/products/codes.htm

... and you'll find this description of one of their products:

PP-8H-2 would be polypropylene honeycomb, 8mm cell diameter, high strength grade, with polyester veil and polypropylene film barrier

[kengrome]

You should look at shear strength of hexacor.

Thanks Alik. Unfortunately my problem is that I don't know how much shear strength is required ...

I can compare this stuff to plywood for example, but if I see that Hexacor's shear strength is half that of plywood, does that make it "strong enough" for the same boat hull I could otherwise build in plywood?

This is the kind of question I run into when I compare materials I've never used before with materials I have used extensively.

[Alik]

2allan white: I have never saild we infuse this core. We vacum bag it. The fabric on both sides of honeycomb prevents resin form filling the cells.

2kengrome:
When one calculates sandwich structures the shear strength is critcal. With plywood it is different story.

[kengrome]

When one calculates sandwich structures the shear strength is critcal. With plywood it is different story.

This makes it even more difficult for me then, doesn't it? Is there a rule of thumb I can use that would answer a question like this:

"What is the minimum sheer strength that I should accept when using Hexacor as the core hull material for a moderate speed planing power boat?"

[Alik]

Do not use hexacor on the bottom of planning powerboat. Other areas have to be claculated considering particular structure, panel size, boat size, etc. Please refer to ISO12215-5 as guideline. There is no easy universal answer... we do it for every boat.

[rambat]

Its not good to put open cell core of any kind in a hull bottom, The core face laminate is too thin when calculated as needed to prevent water migrating into those cells. If you make the outer laminate thick enough to prevent migration it won't require a core. We used it once in a 50' offshore race boat, temperature differentials and a dry as possible lamination allowed those cores to suck up water like combs full of honey. With less expensive, lighter and stronger foam cores I don't know why they are still promoted in any cored lamination, but be warned about using them in bottoms. Corecell can be heated and formed as well as a hexcell core

[Alik]

2rambat:
This is correct, but for displacement boats we use honeycomb panels to shape the sharp-chine bottom, then we use extra layers on outside skin to prevent water penetration. Rest of boat is a real sandwich.

The primary concern here is that Hexacor is cheap, but foams are damned expensive.

[kengrome]

Its not good to put open cell core of any kind in a hull bottom, The core face laminate is too thin when calculated as needed to prevent water migrating into those cells. If you make the outer laminate thick enough to prevent migration it won't require a core.

What kind of resin did you use?

We used it once in a 50' offshore race boat, temperature differentials and a dry as possible lamination allowed those cores to suck up water like combs full of honey.

A "dry as possible lamination" seems to suggest that not enough resin was used to properly seal the bottom, which would lead to water infiltration -- especially in a polyester build. I suspect that epoxy might be substantially more waterproof, am I wrong about this?

With less expensive, lighter and stronger foam cores I don't know why they are still promoted in any cored lamination, but be warned about using them in bottoms.

I don't know enough about these synthetics to know the answer to this one either, but my gut feeling is that the Hexacor won't fail like some foams might by separating within the core itself.

[Trimariner]

With less expensive, lighter and stronger foam cores I don't know why they are still promoted in any cored lamination, but be warned about using them in bottoms.

IT appears from your statements that you have very little or no knowledge of PP honeycombs! Hexacor PP High strength has a shear of .8 I have subjected the bare core to submersion for months and have experienced no water intrusion into the core,and as to foams being cheaper I suggest you check your facts regarding this also!
On a site named www.austrol.com.au there is an interesting impact video of PP honeycomb, listed under polycore in the menu column! The melt point for polypropylene is 160 c and the skin on the outside is Polyester allowing any resin to be used for laminating, it can be thermoformed by preheating, it has to reach 80 to 85 deg c to soften if a boat was to suffer a sun that was that hot I would certainly not like to be in it!
There are a number of PP honeycombs on the market Hexacor, Polycore,Nidaplast, Plascore, Tubus are a few that are popular Polycore and Hexacor have the Highest shear and compressive strengths so go check the out.