HELP - Gluing Polypropylene (Evaporative Air Conditioner Fan Blade) or replacement sources

tunzafun001 on 09/12/2019 - 15:26

Hi all,

I realise I'm up against it, but I accidentally dropped a drill on to my Breezair drum fan and broke off two blades.

A replacement plastic drum is around $300 and I would need to pull the entire unit apart to get to the fan. So keen to try and repair it first.

This is what I know:

The blades snapped off cleanly with about 3mm of surface for gluing.

The plastic is Polypropylene. I have a plastic welder, never used it. Plus I think the probability of melting the blade / changing the pitch would be too high/ risky with it being so thin.

With 3mm, I might be able to drill small holes and put some pins across the break. I would probably need to glue pins on the opposite side to balance it.

Any ideas re glues to use?

I'm thinking Loctite or Seley's 2 part plastic glue (for Polypropylene)?

Maybe make a small v-grove along the break line and fill with something? Heat glue gun, silicon

The alternate is to replace it. Any ideas where a good place is to source evaporative parts cheap? second hand parts?

cheers

Home & Garden

Comments

  • HighAndDry on 09/12/2019 - 15:30
    +1

    I'd be worried about throwing off the weight balance and cause all sorts of upstream issues with the motor/etc.

    • tunzafun001 on 09/12/2019 - 15:39

      It's belt driven (not direct) so shouldn't be too much of a problem. Also being a cast / moulded 1 piece plastic fan it is fairly inconsistent anyway.

      That being said, I'm not overly optimistic for the same reasons, but got to at least try before pulling it apart.

      • HighAndDry on 09/12/2019 - 15:41
        +1

        How much of the fan blade snapped off? Because you'd have to work out the centripetal force it'll be under….

      • Capo93 on 10/12/2019 - 23:03

        Just because it’s belt drive doesn’t lessen the chances of the blade going off balance.

        • tunzafun001 on 10/12/2019 - 23:25

          Yeah, Whatever I do one side I will do my best to equal out on the other. It was already pretty average when new, let alone with a bit of dust on it (and may present an issue in the future if dust sticks more to the repaired blade).

          When you hear some people say their units are noisy etc I bet this moulded Poly fan has a lot to do with it. Selling them for $300 must be $298 profit! But it works.

  • dcep on 09/12/2019 - 15:41
    +1

    any detrimental effect for leaving it as it is ?

    • ESEMCE on 09/12/2019 - 15:51
      +1

      THIS
      Snap/cut off 2 blades on the other side to counter-balance it all out and live with the marginal decrease in blower efficiency.

      • tunzafun001 on 09/12/2019 - 15:55

        Thought about removing opposing blades to balance.. Wonder if it would pulse weird?

        Will be the plan B.

        I'll have crack at re attaching, if they fly off.. then Plan B.

        If it's rubbish, plan C…all in with a new fan :(

  • Euphemistic on 09/12/2019 - 15:54

    In my experience glue and plastic don’t work well. Plastic welding is significantly better. I haven’t used a proper plastic welder, just a soldering iron with a flat blade. Have a practice with some spare plastic first. It’s a good time to learn.

    It’s probably better to either leave as is or remove the balancing blades.

    • tunzafun001 on 09/12/2019 - 15:56

      where do you get the plastic polypropylene rods from?

      • Euphemistic on 09/12/2019 - 21:28
        +2

        I got some rods from the big green shed to repair a kayak. I’ve also done other repairs with scrap matching plastic from whatever I can fix to match. It is sometimes even possible to steal a bit off elsewhere on the thing you are repairing. You won’t need much unless you are trying to strengthen the item.

  • geek001 on 09/12/2019 - 16:30

    I am no expert, but if I am faced with the same situation as you, I would probably go with glue+duct tape, as I think glue alone will not be strong enough. Plastic welding might work, though I have never tried it. I have seen a youtube video of someone melting in some metal wire fibres while welding to give the plastic some strength. Good luck.

    • tunzafun001 on 09/12/2019 - 20:45

      Good ideas. I have fibre glass tape which won't stretch.

  • jackinyourbox on 09/12/2019 - 16:47

    Polypropylene is almost impossible to glue. It’s slippery as fck.

    You have to plastic weld. If you can not obtain same plastic rods, buy a cup and cut to strips and use that to stitch to the broken blades. You could also reinforce with carbon fibre mesh/ fibreglass and then epoxy over that in a similar fashion to repairing car bumpers

    • tunzafun001 on 09/12/2019 - 20:50

      Been researching, Loctite and selleys do a polypropylene 2 part glue. Looks like an initial solvent layer unstabalises the bonding structure of PP, then I think the second is just super glue.

      Plastic cups.. good idea. I thought they were all PET plastic. Will look up PP numbers.

    • tunzafun001 on 10/12/2019 - 13:26

      Any advice on the most common ways of getting some PP for welding strips (do you mean the red microwave safe plastic cups)?

      Just had a browse in the shops…Plastic disposable knives are PP…Basically welding rods.

  • crentist on 09/12/2019 - 18:49

    With 3mm, I might be able to drill small holes and put some pins across the break. I would probably need to glue pins on the opposite side to balance it.

    Glue on PP basically won't work well, since the surface tends to be too chemically and physically stable. Too easy to lift right off. Maybe one of the 2-parts glues will mess it up the internal structure enough to get a bond onto anything, otherwise a plastic welder may stand a chance of melting the edges into each other.

    From the drill+pin idea though, how about some holes on each side, place a few staples into some (maybe not all) of them and bend, essentially (loosely) stapling the whole thing together. And then go over the whole area with a hard-forming resin to create an enveloping solid layer that doesn't just go over each side, but also through the holes.

    If that works at all, you'd have a solid resin join that doesn't need to bond with the PP at all, because it's essentially threaded through holes with a little metal reinforcement.

    • tunzafun001 on 09/12/2019 - 20:43

      Hmm, some good ideas here… I think the resin will be too heavy. But, I might try fishing line instead of staples to keep weight down (line offset with drilled holes)..now to work out which knot to use.

      • endotherm on 09/12/2019 - 22:23

        Try using cable ties instead. The weight should be insignificant closer to the hub, and shouldn't affect balance. Most techniques for auto repair of plastic bumpers should translate to this repair. https://www.youtube.com/watch?v=M6hlVoX0B_k

        • tunzafun001 on 09/12/2019 - 23:44

          Cheers, but I was thinking more this..

          https://youtu.be/C8gZjw1Bkeo

          • However the polyethylene zip tie wouldn't fix to polypropylene.
          • endotherm on 10/12/2019 - 03:54

            @tunzafun001: I was suggesting cable ties for mechanical strength. You can use cable ties for "filler rod" if you are welding to the appropriate plastic, but I wasn't suggesting it here. I thought cable ties would give a stronger grip across the crack and more leverage/compression than trying to lace fishing line through, anchored at a single point with an unknown knot.

            • tunzafun001 on 10/12/2019 - 10:25

              @endotherm: All good, appreciate it. The issue will be the outer ring end has an extremely small attachment site (about the width of a single zip tie). That end I think maybe a melted / glued metal pin inside and maybe some heatshrink tube over the top to stiffen/ secure it all up.

  • tunzafun001 on 09/12/2019 - 23:49

    Ok, glued with 2 part plastic glue, some melted metal links, plastic melted and tacked along the crack (possibly some melted cup strips or rods as well), stitched together with line and taped either side..might hold.

    Great ideas all-round. Thanks all!

    • peteru on 10/12/2019 - 14:49

      Don't forget gaffer tape for that sleek finish. If you are not using gaffer tape, you are not trying to fix it. ;-)

  • tunzafun001 on 12/12/2019 - 21:58

    Update - They are reattached!

    Using Selleys polypropelene/ ethylene plastic glue (2 part glue), then melted along the join with a soldering iron,then melted a bit of disposable plastic knife on the small edges.

    Put a pin in one blade, but don't think it was required.

    Gave them a good yank and they were solid. Ran the fan flat out, then flat out blocked duct (to load it up). All holding.

    Thanks all for the advice.

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