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I found sand blasting aluminum prior to powder coating is a big no-no.

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  • #31
    Re: I found sand blasting aluminum prior to powder coating is a big no-no.

    Originally posted by bp
    I have to reply by saying the "dirt" you speak of may not be dirt at all and could it possibly be 'Die Pick-up' from the extrusion process? If you are using a 6063 prime alloy extrusion you should not have a problem, but if you are using a hard alloy like 6061 or a low tempered aluminum such as a T-5 you may be seeing pick-up wich is misinterpeted for dirt.
    Wipe your raw part lightly with your finger tip or toilet paper. If you feel small bumps or if it catches the paper it is most likely die pickup. At this point a light sanding and tach clothing will give a perfect finish.
    Perhaps what you say is true, but I doubt it that is the case here.. The glass bead only shows up when the part has been blasted (I only use 6061).

    There is no doubt in my mind what the problem was, I did sufficient testing to prove it. I have proved (to myself at least) that bead blasting aluminum will imbed the media in the pores and I've done so in 2 different fields, injection molding and powder coating. I have since stopped blasting and the problem has gone away, completely. I now get perfect pieces every time.

    I understand using a different technique, pressures, or media may change the out come, but I have since moved on to different finishing techniques. I only posted this thinking your average individual may find the information useful.

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    • #32
      Re: I found sand blasting aluminum prior to powder coating is a big no-no.

      Soda blasting requires high-pressure as the media is a fine powder, So to get it MOVING you need SPEED..

      I bet if you did it with a 3/16ths nozzle in a standard gun with a cabinet the results would be the same but on a smaller scale..

      The old "The smaller a garden hose ID the faster the water sprays" trick instead of the larger ID with low water pressure..

      IF you have never changed the ID of the tip on your blasting gun before then try it!, Either you will like the smaller nozzle and more control.. or just plain HATE how much slower a process it is cleaning a part bare..

      Rob
      Attached Files
      DIY Groups Powder-Coating - Metal-Casting - Metal-Chipping - Metal-Polishing - Fiberglas - CNC Tables - GOT LINKS?

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      • #33
        Re: I found sand blasting aluminum prior to powder coating is a big no-no.

        1 Nozzle does not fit all jobs.
        1 have 4 or 5 that I use. Dependinf on what I'm blasting..
        Softer metal will pit real nice with HIGH pressure and course media...
        The right tool for the job....

        Jim S...
        Jim Shuster
        www.backyardpowdercoating.com Sold.....
        www.chrissys68mustang.com Hobbie
        www.photogserver.net Web Hosting.

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        • #34
          Re: I found sand blasting aluminum prior to powder coating is a big no-no.

          I have to agree with Jim
          right tool for the right job I never said soda blasting was for everyone just a simple suggestion
          to give it a try the soda blaster I own is only 29" high 8" wide weight about 17 lbs
          I use many different nozzles according to the different jobs and with this model only have
          to produce 125 psi . There are larger models available in fact they range from 250.00 like mine to 3995.00
          Jim Eaton

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          • #35
            Re: I found sand blasting aluminum prior to powder coating is a big no-no.

            If you have already sand blasted an aluminum part with glass beads (oops ), what is the easiest way to remove the glass beads before you powder coat it?

            -Scott

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            • #36
              I found preheating or boiling the part in water will get most of it, but it seems that a few grains always show up in the paint (pc) no matter what.

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              • #37
                Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                Originally posted by sab0276
                If you have already sand blasted an aluminum part with glass beads (oops ), what is the easiest way to remove the glass beads before you powder coat it?

                -Scott
                I still have not had a problem like this occur to me. I started with alum oxide and it was great. I ran out at an inopportune time and all I could get was glass bead. I used it for a while and actually used it longer than I should. Because it was all broken down and no longer working like it should. Oh, and it was now messy as all hell.
                Then I loaded back up on the alum oxide. Using a vacuum while blasting all the glass bead dust is gone. Leaving only alum oxide. Which I will stick with from now on.

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                • #38
                  Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                  Originally posted by mtumbleson
                  I found preheating or boiling the part in water will get most of it, but it seems that a few grains always show up in the paint (pc) no matter what.
                  Do you pre-heat then boil or boil then pre-heat?

                  -Scott

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                  • #39
                    I would boil it first....

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                    • #40
                      Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                      I havent had this problem, either with alox or glassbead. I use 60 psi and hold the gun at a 45. Could it be a difference in the media itself? Different grits or brands? Could it be differences in different Al alloys?

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                      • #41
                        Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                        I know I’m a newb on the forum but Ive been doing coatings (ceramic, thermals and powders) since 2000. I use Alum oxide and glass. Ive never had a problem with glass but have always been told to use alum ox. for anything getting coated. mainly because the glass burnishes the surface and seals it so to say.

                        That’s where the problem may be. Its trapping glass in the pores as said many times above. And when you pre heat it it’s pushed out.

                        Example of my process for a Alum intake with paint on it.

                        1. Soak in a 20gallon tub of Napa brand carb cleaner to pull paint or old powder coating off.
                        2. Rinse really good and dry.
                        3. Media blast it.
                        4. Bow off really good
                        5. Preheat to outgass,etc
                        6. Let cool down so its warm to the touch (not to hot the powder melts) but with enough heat you can start to see the powder flow.
                        7. Bake

                        So far so good.

                        Every now and then I have to strip a part and redo it but that’s part of the business I guess. If I’m not happy with the part then I won’t give it back to a customer.
                        Last edited by FSTFBDY; 03-11-2006, 07:35 PM.

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                        • #42
                          Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                          This thread made for some really interesting reading...
                          I have been Powder Coating for several years (hobbyist) and have used both glass bead and aluminum oxide on all types of metals and alloys.

                          I am trying to remeber the last pieces of aluminum that I completed and how the surface turned out. I do not recall any rasied spots (beads) showing up in the cured powder, but most of what I was coating were cast engine parts and brackets. Not exactly smooth to begin with.

                          I have had excellent results from the Aluminum Oxide and have used it on steel, aluminum, copper, brass and pot metal. As long as you do a thorough cleaning afterward, problems in the finish should not arise.

                          Thanks for the great posts, even though I am a few months behind in a reply!

                          Curtis
                          Curtis Ashcroft
                          M and C's Plating & Powder Services

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                          • #43
                            Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                            Originally posted by mtumbleson
                            No all I ever used was glass bead. I will concider it though...

                            This is the problem. Alum Ox or Silica does not have the same difficulties as Glass Bead. The problem with the glass is that it breakes up into small particles and imbedds itself in the alum. When blasting, the action creates heat in the Alum, this, as you know and stated, opens opres, and suckes in the smaller glass bead particles. Then, bakinkg, the pores re-open and it comes out. Al Ox and Silica are larger particles and don't get sucked into the pores as easilly. I have blasted with Silica on Alum quite effectivly. Both Cast and machined Al
                            Dan Pesonen
                            Bandit Powder Coat <<From Powder to Perfection>>
                            Forest Grove, BC Canada

                            Personal motto:
                            "If it ain't broke, modify somethin till it is"

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                            • #44
                              Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                              Since I posted this, I found that using lower pressures and holding the tip at a 45-60 degree angle to the (aluminum) object yielded great results. In the beginning I was using a small tip, super high pressures, and blasting at a 90 degree angle.

                              I still avoid blasting aluminum unless there is no other option...

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                              • #45
                                Re: I found sand blasting aluminum prior to powder coating is a big no-no.

                                YUp, steeper angle and lower pressure would equal less penetrating force for the bead.
                                Dan Pesonen
                                Bandit Powder Coat <<From Powder to Perfection>>
                                Forest Grove, BC Canada

                                Personal motto:
                                "If it ain't broke, modify somethin till it is"

                                Comment

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