Not quite so structural foams?

Discussion in 'Composites' started by RSD, Oct 14, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Oct 14, 2019 #1

    RSD

    RSD

    RSD

    Well-Known Member

    Joined:
    May 20, 2019
    Messages:
    209
    Likes Received:
    42
    To get started and learn/practice carbon fibre layups etc I'm going to make a new centre console for my boat. It probably doesn't need the "structural" foams that are used in homebuilt aircraft, and because I'm only going to need a couple of sheets and road transport for sheets is very expensive here in Australia I'm looking for a cheap readily available foam - something that I can get from somewhere other than a specialty composites supplier. Any suggestions?

    I've seen mentioned on here "pink foam" that you get from Lowe's or Home Depot - what type of foam is that? We don't have those stores here unfortunately :-(
     
  2. Oct 14, 2019 #2

    RSD

    RSD

    RSD

    Well-Known Member

    Joined:
    May 20, 2019
    Messages:
    209
    Likes Received:
    42
    and I might be tempted to put some Graphene into it to see what it is like...
     
    SoaringEagleRick likes this.
  3. Oct 14, 2019 #3

    Voidhawk9

    Voidhawk9

    Voidhawk9

    Well-Known Member HBA Supporter

    Joined:
    Mar 26, 2012
    Messages:
    250
    Likes Received:
    138
    Location:
    Timaru, NZ
  4. Oct 14, 2019 #4

    RSD

    RSD

    RSD

    Well-Known Member

    Joined:
    May 20, 2019
    Messages:
    209
    Likes Received:
    42
  5. Oct 14, 2019 #5

    RSD

    RSD

    RSD

    Well-Known Member

    Joined:
    May 20, 2019
    Messages:
    209
    Likes Received:
    42
  6. Oct 14, 2019 #6

    Voidhawk9

    Voidhawk9

    Voidhawk9

    Well-Known Member HBA Supporter

    Joined:
    Mar 26, 2012
    Messages:
    250
    Likes Received:
    138
    Location:
    Timaru, NZ
    Extruded polystyrene is used as the core for the wings in Rutan canards, as one example. Using epoxy - I am not sure of compatibility with all resins.

    Should work, though a smooth surface as it describes isn't ideal for bonding, you may need to sand or remove the face.
     
    wsimpso1 likes this.
  7. Oct 14, 2019 #7

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,071
    Likes Received:
    1,812
    Location:
    US
    The "pink" foam is by Owens Corning (brand name "Foamular") and the blue foam is by Dow (brand name "Styrofoam"). The generic label for both is "Extruded Polystyrene," or "XPS." It is sometimes confused with "Expanded Polystyrene" or EPS. EPS is the weak stuff that looks like a lot of tiny balls squeezed together to make a sheet (or a cheap cooler for beer). XPS is quite a bit tougher. Don't use EPS, use only XPS.
    One thing that causes confusion, at least in the US, is that the general public uses the term "styrofoam" to refer to the beady white foam used to make cheap coolers, coffee cups, etc. These are really made of EPS foam.
    If you tell the folks at the home supply place that you want XPS, that might work.
     
    Topaz and wsimpso1 like this.
  8. Oct 14, 2019 #8

    AdrianS

    AdrianS

    AdrianS

    Well-Known Member

    Joined:
    Jul 5, 2014
    Messages:
    384
    Likes Received:
    234
    Location:
    Australia
    I've used that stuff. It's way denser than I'd use as a core - I was gluing disks of it into polypipe (with blue solvent glue) for a hydroponics project.

    It's a great hobby material - you can cut it with a handsaw or jigsaw, heat bend it with a hot air gun, glue it with pipe glue - it's the perfect companion for polypipe.
     
    wsimpso1 likes this.
  9. Oct 14, 2019 #9

    SoaringEagleRick

    SoaringEagleRick

    SoaringEagleRick

    Member

    Joined:
    Dec 15, 2013
    Messages:
    8
    Likes Received:
    8
    Location:
    Hoogeveen, Netherlands
    Epoxy works fine with XPS, polyester does not due to the styrene that is released.
     
    wsimpso1 likes this.
  10. Oct 14, 2019 #10

    RSD

    RSD

    RSD

    Well-Known Member

    Joined:
    May 20, 2019
    Messages:
    209
    Likes Received:
    42
    Many thanks for all the replies. Went to Bunnings (our version of Home Depot) tonight and while looking in aisles for the other products I stumbled across some XPS tucked away on the top shelf that I don't think the staff even knew was there - its not on their website either. Price is reasonable, comes in 1200 x 600 sheets (4' x 2') in thicknesses of 30 and 50mm (1.25" and 2").

    How well does a router work with XPS?
     
  11. Oct 14, 2019 #11

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,873
    Likes Received:
    1,856
    Location:
    North Carolina
    Use a very sharp bit. I'd be tempted to try touching up a new one with my finest diamond stone. You may need to turn the speed down. If you melt it over the blade, pick the globs off then soak the blade in acetone to remove the rest.
     
    wsimpso1 likes this.
  12. Oct 14, 2019 #12

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    5,917
    Likes Received:
    3,146
    Location:
    Saline Michigan
    Pink foam is a very fine grained Owens-Cornings polystyrene foam. It hot wire cuts and laminates just as nicely as Dow's light blue polystyrene foam insulation sheet. I use them interchangeably for tooling but use neither for airframe laminates.

    I stick to the old advice of using Dow blue flotation billet for airframe parts. It hotwires nicely, is lower density than the foam insulation boards and has bigger cell sizes, but makes tough airplane parts. The process for making it was known at one time to not contain any silicones, while there was concern about other styrene foams having silicones in their processes. As thermal insulation, silicones are no big deal, but in bonding of composites to it, even tiny amounts of silicone in the foam can contribute to debonding.

    Do not get me wrong - Dow and Owens foam polystyrene insulation boards may be just fine, but at one time the direction from Rutan Aircraft Factory was to use flotation billet from Dow and be happy.

    Now if you are going to make a structure where the foam matters not to it, you could use anything for the form and be happy. You could even make the foam shape into a mold by putting a stretchelon film over the foam.

    Good luck dealing with the supply variance issues there.

    Billski
     
    TejasNW and stanislavz like this.
  13. Oct 14, 2019 #13

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    5,917
    Likes Received:
    3,146
    Location:
    Saline Michigan
    This is expanded bead foam - white coffee cup foam. In my shop this is tooling only. It is noticeably softer and less cohesive (it crumbles easily) than extruded foams. I did manufacture the male molds for my fuselage using it as I could get the sizes I wanted and it hotwires and sands nicely. I would NOT leave this stuff in a laminated part of anything I wanted to hold together for long. It can come from many sources and has unknown silicone presence in its manufacture.

    Billski
     
  14. Oct 14, 2019 #14

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    5,917
    Likes Received:
    3,146
    Location:
    Saline Michigan
    Polyester and Vinylester resins will melt any polystyrene foam. Gasoline, any solvent that works as a lacquer thinner or contains styrene monomer will dissolve polystyrene. Styrene foams should not be used in tanks. Gas and diesel have components that will diffuse through fiberglass is small but sufficient quantitities to reduce foam to small puddles of solid polystyrene in the low spots. I have seen this in an accident teardown...

    Epoxy only on all polystyrene foams. Want to make a tank for anything beyond water, like gasoline, diesel, Jet A, or oil? Use fuel safe foams like PU or PVC. In the Rutan Long Ez and Defiant, fuel tanks were the strakes of the main wing and made of epoxy and PVC foams.

    The outer wings, canard, tip sails, etc were all separate structures from the fuel tanks and hotwire cut from blue flotation billet, and work just fine.

    Billski
     
  15. Oct 14, 2019 #15

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    5,917
    Likes Received:
    3,146
    Location:
    Saline Michigan
    Hmm. Ran the calc, and that is 12 pcf, or about double the density we usually use in Divinycel PVC foam. It might take a bit more effort to cut and machine it. I do not know if silicones are present, so you may have some debond risk with it. That is one of the nice things about Divinycel - it is made for use in aerospace structures and is specifically clean of anything that might interfere with bonding.

    Billski
     
  16. Oct 14, 2019 #16

    DanH

    DanH

    DanH

    Member

    Joined:
    May 20, 2019
    Messages:
    6
    Likes Received:
    4
    Just fine. Requires nothing special.

    [​IMG]
     
    wsimpso1 likes this.
  17. Oct 14, 2019 #17

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member HBA Supporter

    Joined:
    Aug 22, 2016
    Messages:
    247
    Likes Received:
    62
    Location:
    Lt
    Hi ! I want photo of this process if possible.
     
  18. Oct 14, 2019 #18

    Victor Bravo

    Victor Bravo

    Victor Bravo

    Well-Known Member

    Joined:
    Jul 30, 2014
    Messages:
    6,109
    Likes Received:
    4,885
    Location:
    KWHP, Los Angeles CA, USA
    The movie special effects people use something called "green death foam", which is a typical Hollywood FX nickname.

    In the real world, the stuff is also called "floral foam" and it is sold (here in USA) as small blocks of foam for florists to stick flower stems into, to make a small display. They put candy skewers and other things into it, to make an attractive presentation. Most Craft and Hobby stores here sell it, Walmart and many others here.

    Find a local flower shop or floral display maker and see if they have it, it is medium green in color, very light, and very rigid. Very fine "grained". Probably not as good for a "real" aircraft structure because it will fracture more easily than the common aircraft foams. Also, podiatrists (foot doctors) use this material to make a mold of your feet, they have you step onto a block of this, and it leaves a perfect impression of your foot, arch, etc.

    The "green death" name comes from the fact that when you sand it, it creates a very fine and highly irritating dust, so the Hollywood guys making monsters and movie props and such get covered with that dust and have to be sent through a car wash afterward :)

    So absolutely wear a dust mask, eye protection, etc. But epoxy resins should not melt or soften it, and it will surely work for a non-critical part. They come in smaller blocks, which means you may have to glue a few of them together to make the size you need. But you won't have to buy a huge expensive block either.
     
  19. Oct 14, 2019 #19

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    5,917
    Likes Received:
    3,146
    Location:
    Saline Michigan
    This is thread drift, so I will be brief. Sorry the film photos I have do not show much. Read this for a summary of the process, then feel free to .

    https://www.homebuiltairplanes.com/forums/threads/foam-less-molds.3792/page-2#post-27332

    https://www.homebuiltairplanes.com/forums/threads/female-plug-mold.2436/#post-14728

    https://www.homebuiltairplanes.com/...ess-percentage-for-composite.5464/#post-42551, go down to post 20.

    That is probably enough...

    Billski
     
  20. Oct 14, 2019 #20

    SVSUSteve

    SVSUSteve

    SVSUSteve

    Well-Known Member

    Joined:
    Aug 21, 2007
    Messages:
    3,889
    Likes Received:
    938
    Location:
    Evansville, Indiana
    I imagine someone else already pointed it out but one of the major things you have to be aware of is that polystyrene dissolves if you expose it to a lot of common solvents including gasoline (avgas or mogas). This has caused at least one crash I am aware of where a fuel leak caused the wing to fail in flight.

    However, it does have an advantage that if you need to make a compound curve but just need the "skin" (for example, something non-structural like decorative trim). You make the core out of cheap styrofoam and once the epoxy has cured, you take a bottle of nail polish remover (acetone) and pour it on the exposed bit of the core. You can then pour and scoop out the resulting goop.

    EDIT: Yup, Billski pointed it out. Mea culpa for not reading further down first.
     

Share This Page



arrow_white