Substitute for EPON 828? 3

[KirbyWan]

Howdy all,

I am trying to find a material substitution for EPON 828. This is to repair a DC-10 antenna panel which is a laminate honeycomb core panel made from 250°F cure prepreg fiberglass. The DC-10 SRM 51-43-01 provides a wet layup repair using EPON 828 or Hetcon 92. I want to use the same process only with EA9390 adhesive and cure cycle similar to B757 SRM 51-70-17.

The problem I am having is finding data on these old adhesives. The Epon 828 data sheet is very short on strength properties. It can be cured with dozens of different curing agents and it lists the strenght of up to 10000 psi without mentioning which curing agent was used. I can't find any information on Hetcon 92.

Does anyone have recomendations for how to substitute materials? I can't really do a test since I don't have Epon 828 data to compare against. There is plenty of data on EA9390 from Henkel and in BMS 8-301, but what do I compare it to.

Thanks to the community for pointing me in the right direction.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

taking a pointer from your tag-line ...

what's the critical criteria ? strength or stiffness ?

is the old panel completely U/S, or could it be used as a test coupon ?

can you set up somethinglike a 3- or 4- point bend test and compare old and new ??

can you do calcs on the new ... put in some antenna load, a bit of P/A, ... ??

 

[KirbyWan]

The old panel is in excellent condition. We are using the fiberglass wet layup repair to blank the holes. That said I don't want to do more damage to the panel then I need to. Besides finding information on the original material of the panel is not a problem. 250°F cure prepreg fiberglass has lots of info on it. It's the repair method I'm trying to do a material sub on.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

you'd put the old panel into a 250 cure cycle ?

if you're "just" blanking the old antenna install, what about a Al blanking plate ? similar to the antenna footprint, 0.05" thick ...

 

[KirbyWan]

The point of using the EA9390 is that it can cure at 200°F. If we cure the panel at 250°F there is a good chance of blowing the panel out during the cure cycle. This is normally avoided at 200°F. If it wasn't for that we would just go back to the original material as defined in the production drawings and use that as a substantiation.

Do you have a reference for the Al blanking plate? Note this antenna panel is a panel roughly 4' by 4'

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

wooo ... 4' x 4' ... here i was thinking of a VHF antenna.

is the panel loaded, particularly by cabin pressure ? (i suspect not, but have learnt to ask)

is the 4' x 4' the size of the panel or the size that needs to be repaired ?

how well do you get on with your local cert people and the customer ? this affects how much substantiation you need to do

on one level, if it is "just" a fairing panel, and the material susbtitution sounds reasonable to you (and to the others involved) then maybe a bit of "hand waving" is enough; i'd've thought the detail design of how you finish the reapir (and join to the existing panel) is porbably more important than the details of the materials used.

on another level, if the panel sees significant load then you need a good story as to why this repair is good-to-go. one "simple" possibility is to do a stiffness test on the finished part.

Al balnking plate is standard industry practice for covering a removed antenna. if the hole is 4' x 4' then you'll need more than just a plate, stiffeners as well. if the plate is loaded, more analysis ...

 

[KirbyWan]

When I mean blanking out the holes I mean that there are fastener holes all around the part that are used to attach it to the airplate. If you want to fit it to a different DC-10 the holes will not line up the same. Well some may but not all and most not well. So we want to remake the panel edge so that it's like new with no fastener holes so they can be drilled on istallation. We do not have access to the aircraft, just the panel so we can't fit it up and see which need to be repaired.

this panel is a fairing panel, so one face of it is an airflow surface, but it is outside the pressure vessel. There are no significant pressure loads. Think of it like any external fairing panel. The antenna part did kind of throw me, because it doesn't looke like an antenna. It looks more like an access panel to an antenna. But Antenna, Assy-ADF Sense AFT is how it is reference in the part drawing. This antenna P/N is AAN 7017

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

sorry kirby, i'm getting confused. it sounds like you're repairing a panel (that's not interchangeable) to install on another plane. so you want to repair the panel to blank the attmt holes, so you can re-drill them on installation. and we're not removing the antenna ??

cutting off the edge band and gluing on a new one doesn't sound like a good idea.

filling holes, then drilling a new pattern also doesn't sound like a good idea.

remaking the panel with a new composite, and confirming the stiffness against an existing panel works.

making an Al s/m replacement panel works (though more work than it's work than it's worth ??

maybe cuting of the composite edge band and fabricate an Al replacement, riveted onto the composite panel ??

 

[KirbyWan]

RB,

It's a pretty standard repair. Just step back the plies 1/2" each so that the plies are to the part edge except right where a fastener is. Then lay up plies in each step. Add an extra ply and a sanding ply vacuum bag and cure and it's good as new. Proving it is the tough part.

And BTW, there are SRM repairs for just filling the holes with RT cure adhesive and chopped fiber, but the number of holes you can repair is limited.

Also I don't know what the antenna is. I just have a panel. I don't know if the panel _is_ the antenna or if the antenna bolts to the panel. There is one odd circular fitting on the interior of the panel, but it doesn't go through the panel. I am at a loss too about what the antenna is.

-Kirby

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[KirbyWan]

Oh, and a star for your help.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

sounds to like you know what you're talking about, do your local cert people buy into it ? could the customer's cert people have (or create) a problem with it ? sounds like you need an RDA to cover the work, since you're outside the SRM ... maybe Boeing might help (ha, ha)

would it be unreasonable to manufacture a test specimen ? maybe compare before and after ? (afte being the panel with a bunch of holes repaired in a presumably conservative manner ... adjacent holes off-set towards each other a conservative amount ??)

 

[KirbyWan]

You lost me on RDA. Do you mean DER approval? I would consider this a minor repair on secondary structure using an SRM repair with the only adjustment being a material substitution, so no regulator approval needed, just customer concurrance.

I eventually found some property data that shows the EA9390 has strength (at least with one test method) as strong or stronger then the original fiberglass prepreg. I was just hoping to have more information, particularly on EPON 828

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rb1957]

RDA = Repair Design Approval ... if you were going beyond the SRM. depending on your relationship with the cert. people and the customer, maybe the customer's buy-off is enough, maybe you need an approval ... i know it's "only" secondary structure, but too many times secondary structure has caused problems with primary structure.

 

[KirbyWan]

O.K. I looked it up. That looks like the european version of FAA DER approval, only more general. I think the FAA give US repair stations a bit more latitude with repair approvals then the EASA.

For each individual repair design, this EASA approval is based on:

...

3) minor repair data determined to be acceptable data (under 14CFR part 43) as determined by a U.S. maintenance organisation under FAA’s authorized system.

I think I'm reading that if it's acceptable under FAA system it's good enough for EASA. And the FAA system is DER approval is only needed on major repairs. I would not consider this a major repair. QED.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[Compositepro]

EPON 828 is a basic liquid epoxy resin but it would only make-up about half of a resin formulation. There are several other ingredients that go into a formulation which can give a wide range of properties. You would need to use a qualified formulation.

 

[KirbyWan]

Compositepro,

Here's a page from the DC-10 SRM. It shows the Epon 828 with two possible hardeners. Epolite 2323 and Hardener 956. This is as qualified a formulation as the SRM gives and it still dosen't bring me closer to the quality of information I would like to have to substantiate this repair.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[Compositepro]

Well that SM does, indeed, give you a formulation. Epon 828 is still available. It used to be made by Shell but is now made by Hexion. Hardener 956 sounds like an old Ciba-Geigy product which would probably now be owned by Huntsman. Epolite 2323 is 4,4'mehylene dianiline (MDA) which pretty tighly reulated as a cancer causing chemical these days. It used to be a very common curing agent. These products still seem to be readily available.

 

[KirbyWan]

CompositePro,

I guess the products are still available, but we have a few resin systems that we use regularly that we prefer to use. Perhaps I should just tell purchasing to bite the bullet and buy the SRM qualified materials. But we work with EA9390 alot and like the system. It's strong, durable and we are familiar with it. What I'm really lacking is good data on Epon 828 with a specific curing agent.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[berkshire]

Kirby,
Contact Miller Stephenson chemical co in Danbury Ct

http://www.miller-stephenson.com/

They sell Epon resins and used to have data sheets showing the heat deflection curves and tensile strengths for different hardeners.
B.E.

 

[KirbyWan]

Thanks berkshire. A good idea, but no dice. While they sell the Epon resins, they don't carry either of those curing agents. As a matter of fact they said that MDA (the epolite 2323) is toxic enough that if they were going to repackage it they are required to have a doctor on hand. Yikes!

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.