6061 vs 2024

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by GESchwarz, Dec 31, 2008.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Jan 3, 2009 #21

    MalcolmW

    MalcolmW

    MalcolmW

    Well-Known Member

    Joined:
    Jan 22, 2007
    Messages:
    118
    Likes Received:
    6
    GESchwarz;

    you mentioned getting an alodine kit. Consider getting:

    [FONT=&quot]Iridite 14-2 chromate conversion concentrate is available from McDermid, Inc., #8659 This is the same thing as alodine (and a lot cheaper than getting it from Aircraft Spruce, etc.) I think McMaster-Carr carries it.[/FONT]
    [FONT=&quot] [/FONT]
    [FONT=&quot]Distilled water produces best results. However, rainwater caught from the roof is very low in mineral ions and is an acceptable substitute (discard the first five minutes of runoff – that is the roof rinse water & is dirty).[/FONT]
    [FONT=&quot]
    [/FONT]
    [FONT=&quot]If you feel up to doing industrial quality surface preparation, this is the absolute best etching method:
    [/FONT]
    [FONT=&quot]Chromic acid cleaning solution:[/FONT]

        • [FONT=&quot]10 parts/wt. Sodium Dichromate. [/FONT]
        • [FONT=&quot]30 parts/wt. 96% Sulfuric Acid. [/FONT]
        • [FONT=&quot]100 parts/wt. distilled water.[/FONT]
    [FONT=&quot](Dissolve the dichromate in the water, then add sulfuric acid slowly, stirring carefully.)[/FONT]



    This is nasty stuff, and will etch skin and clothing with equal ease. Be very careful around it if you choose to use it.

    Fly safe,

    MalcolmW
    [FONT=&quot] [/FONT]
    PS: When working with chromic acid or Iridite solutions, wear nitrile rubber gloves (Harbor Freight – low cost). Also a long apron and shop face shield – safety first and last.
     
  2. Jan 3, 2009 #22

    Midniteoyl

    Midniteoyl

    Midniteoyl

    Well-Known Member

    Joined:
    Sep 4, 2003
    Messages:
    2,406
    Likes Received:
    500
    Location:
    Indiana
    I always say it's for a 'three-wheeled off-road vehicle' :)

    Good info, Malcolm, Thanks
     
  3. Jan 3, 2009 #23

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,152
    Likes Received:
    2,381
    Location:
    Port Townsend WA
    Malcolm,
    I was wondering if you use the "water break test" or other means to help determine that you have a good oil free surface?

    The water break test is simple: if water lays flat on the surface like a sheet of glass, that is good. If water beads up on the surface, that indicates possible poor adhesion.
    BB
     
  4. Jan 3, 2009 #24

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,179
    Likes Received:
    108
    Location:
    Ventura County, California, USofA.
    Thanks for the tips. I had forgotten about the water break test. I worked with acid at Rocketdyne for many years, so I know what a whiff of this stuff is like. Back in the good old days we just washed this stuff down the drain. How do I neutralize this stuff? Will a box of baking soda (Stand Back!) and it's safe to go down the gutter, or do I have to contain every drop and take it to some hazmat depot?

    Orion, we ought to try the water break test after cleaning an oily surface with acetone, and MEK to see how they do as far as leaving residue.

    How much better will my adhesion be with the chromic acid vs the alodine method? I guess there is really only one way to find out.
     
  5. Jan 3, 2009 #25

    orion

    orion

    orion

    Well-Known Member

    Joined:
    Mar 3, 2003
    Messages:
    5,800
    Likes Received:
    135
    Location:
    Western Washington
  6. Jan 3, 2009 #26

    MalcolmW

    MalcolmW

    MalcolmW

    Well-Known Member

    Joined:
    Jan 22, 2007
    Messages:
    118
    Likes Received:
    6
    Hello,

    Thank you, Midniteoyl for the wonderful phrase, 'three-wheel off-road vehicle.' Priceless!

    To BBerson - we used the equivalent of the 'water-break' test - we wanted to see the water 'sheet-off' the cleaned aluminum... same, I suspect.

    GESchwarz - here's some info on disposing alodine and chromic acid waste:

    [FONT=&quot]Dichromate (including Alodine, etc.) Disposal[/FONT]

    [FONT=&quot]Dichromates (alodine contains dichromates) are potentially hazardous substances. Care should be taken in handling them and the disposal of solutions containing dichromates. Ingestion and inhalation of dichromate dust is toxic and should be avoided. Putting bare skin in dichromate solutions can contribute to the development of an allergic sensitivity and should be avoided. The following is a method to dispose of used dichromate solutions: [/FONT]
    [FONT=&quot]Chemically, the following procedure should work. Add a strong alkaline (baking soda, lye [sodium hydroxide], etc) to the dichromate solution until it becomes alkaline. Determine this by using litmus paper, which should be available from many sources, including Edmund Scientific, if you are in the [/FONT][FONT=&quot]US[/FONT][FONT=&quot]. This will cause the dichromate to convert to chromium hydroxide (very insoluble). [/FONT]
    [FONT=&quot]Either filter or let stand for a week to let the precipitate settle out. The supernatent liquid (the liquid above the sludge) can be washed down the drain with 50 times its volume of water. The precipitate (Chromium Hydroxide) can be washed with hot water to remove the sodium sulfate, dried, packaged and labeled, and then taken to a toxic waste disposal site or company.[/FONT]
    [FONT=&quot]If you choose to filter the solution to remove the sludge, a double layer of coffee filters should work, though lab grade filter paper would be best. (*Don't* use your coffee maker for this step!). At that point, you should be able to dispose of the liquid which should be chromium free and give the filtered sludge to a place that handles hazardous waste. The trivalent chromium is less toxic (according to my sources) but I still wouldn't just toss it down the drain.[/FONT]
    [FONT=&quot]For an alternative means of disposal of the chromium hydroxide sludge: Mix the wet sludge (precipitate) with dry concrete mix (right, the bagged stuff from Home Depot, Lowes, etc.) to form a stiff mix. Use for setting posts, making blocks, etc. This will tie up the chromium in a very insoluble form and harmless to the environment.[/FONT]
    [FONT=&quot]That's about it. I offer this in the spirit of information sharing and NOT as expert advice. If anyone can and wants to add to or correct any of this, I would welcome it.[/FONT]

    Lastly, I don't know whether chromic acid etch is superior to a good alodine surface prep. Both use dichromates, but the chromic acid is also the same thing that chemical laboratories use to clean reagent and analytical grade glassware - it takes off every bit of organic material (with a vengeance). Be very careful if you choose to use it.

    I hope that this helps and the best of luck with your project. It sounds like you want to do things properly and you should end up with a durable structure doing so.

    All the best, and fly safe.

    MalcolmW
     
  7. Jan 3, 2009 #27

    MalcolmW

    MalcolmW

    MalcolmW

    Well-Known Member

    Joined:
    Jan 22, 2007
    Messages:
    118
    Likes Received:
    6
    To BBerson;

    I believe the material used to prepare aluminum surfaces for painting is based upon phosphoric acid, and there are several commercial packages for this purpose. This type of surface prep is actually quite good, and may be sufficient for adhesive bonding, particularly so for acrylic adhesives. After all, today's high performance paints are polymers (urethanes in particular) which have the same substrate cleanliness requirements.

    And yes, if the cleaner is water-based, the final rinse should pass the 'water-break' test as an assurance of cleanliness.

    All the best, and fly safe.

    MalcolmW
     
  8. Jan 3, 2009 #28

    MalcolmW

    MalcolmW

    MalcolmW

    Well-Known Member

    Joined:
    Jan 22, 2007
    Messages:
    118
    Likes Received:
    6
    Okay, this'll be my last post for a while, however, I just stumbled over this reference to adhesive use in truck body construction:

    [FONT=&quot]Here’s an example of replacing rivets and other fasteners in a demanding truck body application:[/FONT]
    [FONT=&quot] [/FONT]
    [FONT=&quot]Replacing rivets: Vehicle body manufacturer switches to adhesives

    This article also has other links.

    MalcolmW
    [/FONT]
     
  9. Jan 3, 2009 #29

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,179
    Likes Received:
    108
    Location:
    Ventura County, California, USofA.
    Many thanks again to all of you for your generous support. You should be proud of yourselves. Your example is in the highest tradition of the Experimental Aircraft Association.

    Your posts not only benifit me, but all those who will ever search for your knowledge. I will have you know that a Google search I did last night pulled up a Homebuiltairplanes.com thread; so everything that is going on here is accessible directly from the WWW. That thread was MalcolmW's input on adhesives from about a year ago. That info is more valuable and relevant to me now than it was a year ago.
     

Share This Page



arrow_white