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Thread: HDPE yard cart repair and welding

  1. #1
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    Default HDPE yard cart repair and welding

    I need some ideas on how to best repair this garden cart for a family member who really likes it. It mostly gets used for light duty work. Some folks moved heavy rocks with it many years ago, possibly starting this. I moved heavy wet sand with it last Fall.... I want to do it in a way that has a good chance of lasting, and hopefully not make it look too Franken-cart. The original weight limit was 200 lbs.

    It has three cracks, located in a critical area of 3/16" thick HDPE (I think) - on either side of a support rib and the top bucket edge transition. If it was just one crack, in a less critical area, I'd probably stitch it with zip ties or stainless safety wire. This looks like pure HDPE, with no fiber reinforcement, etc.

    I am considering an approximately 1/16" x 4" or 5" aluminum plate (which I would *machine* from billet!), all the way across, secured with aluminum pop rivets (1/8" or 3/16"?). I also have some 3/16" clear polycarbonate.

    I understand the stress and strain need to be distributed by the repair, and not concentrated in any one area - that would just create new cracks. An aluminum plate that is too thick or rigidly attached would probably just crack the plastic in other areas.

    I know the crack ends need to be drilled. I have wondered whether a hot poker would be better than a drill. Some of the crack-end drilling will be tricky, as the cracks seem to end near the critical top edge. If the crack is already into the top edge, that's going to make a good repair more tricky.

    This video from India demonstrates the use of heated pieces of steel to weld a plastic bucket. Surprisingly, no effort seems to have been made to check the ends of the crack. I'm not sure what they're using for filler. Any ideas on common sources? I think the edges of the 3/16" parent material might need some beveling - and quite a lot of fill.

    https://www.youtube.com/watch?v=Gk_3ekupiyQ

    I don't want to spend a bunch of time doing the plastic welding only to have it not add anything to the final strength or longevity. I sure don't need to seal it for water, etc. I'm not sure the welding adds much in this case, except a bunch of time and fumes.

    The cracks are about 3" to 4" inches long. One gotcha to welding is I'd want to do that on the smooth inside face, where I also want to locate the plate. So excess filler would be a concern.

    Most likely, I can just rivet the plate on it and it will be Just Fine for many years - so long as it is not used heavily. Thanks for your ideas.


    Location of cracks inside of bucket, near handle.



    Interior crack detail. Crack #3 cannot be seen but it parallels crack #2, on either side of vertical support rib.



    Backside crack overview and detail.


  2. #2
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    Crack #3.



  3. #3
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    I'd just plastic weld it. Done right it will "add strength". I have a pro plastic welder, but now just use my temperature controlled heat gun, simple tools (like temperature controlled soldering iron, small steel pipe with lip for feeding rod etc. Slightly groove out the cracks first, tack together with soldering iron and stop the crack ends with the iron tip. Lay in the rod.

    The key is "temperature control".


    If you are going to put in aluminum, I'd make it a lot thicker than 1/16th, bend the ends up and place between the ribs. Secure with bolts.
    Last edited by lakeside53; 05-16-2018 at 12:17 PM.

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    The white color suggest to me that it may be PVC. It's not hard to tell PVC from HDPE when looking at it personally but the very solid looking color and the way it cracked sure does suggest PVC to me.

    That's not to say it can't be heat welded. But it would alter the method I'm thinking.

    I've done some dirt bike motorcycle parts heat welding using a 40 watt soldering iron that was temp controlled by running it with a lamp dimmer box I made up for such things. It's an extension cord into a standard double gang electrical box intended for holding two switches. But instead there's a lamp dimmer and a regular duplex outlet. In instead of the usual soldering tip the iron I have accepts 5/16nc threaded tips so I bent a bolt and then ground and filed it to a sort of ironing shoe shape with no sharp corners. Some scraps of the same plastic was used as a filler and for building up the weld on the back side. Using this tool is a rather slow process but it worked nicely.

    I believe that most plastic welders use a hot air source. The key is a small outlet. Lakeside, what size outlet is on the heatgun you use? Also my "iron" method involved blending the sides and filler with a bit of stirring. Do you still do that with the hot air source?

    I'm thinking that for a one off I'd use whichever I had the most handy or had to buy the least stuff or spend the least money. My iron method certainly worked and with a bit of "troweling" the weld with the smooth face of the little shoe shape I made up it even looked fairly decent. Best of all I was able to do the job with stuff I had on hand.

  5. #5
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    It appears the cracks are in the area where the 'handle' meets the bucket?

    I suggest adding aluminium reinforcement to the take the weight and reduce stress on the cracked areas.

  6. #6
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    Any other advice on this, and the methods and merits of welding 3/16" plastic?

    Part of the point of this is to get some experience plastic welding.. though this may be a big and difficult high-load project to start on.

    Anyone tried to neck down a heat gun to a small stream of hot air? I've seen some videos of commercial attachments. The air stream is followed by a hot 'shoe' that presses the melted plastic and a filler strip together.

    I still need to find a source for filler rod - quite a bit of it.

    I'm not sure how to tell for certain whether it is HDPE or PVC. Rubbermade sells carts described as HDPE, and this looks similar to them. Though this one is older. Other carts from them are a fiber-reinforced plastic (we also have one of those).


    Quote Originally Posted by lakeside53 View Post
    I'd just plastic weld it. Done right it will "add strength". I have a pro plastic welder, but now just use my temperature controlled heat gun, simple tools (like temperature controlled soldering iron, small steel pipe with lip for feeding rod etc. Slightly groove out the cracks first, tack together with soldering iron and stop the crack ends with the iron tip. Lay in the rod.

    If you are going to put in aluminum, I'd make it a lot thicker than 1/16th, bend the ends up and place between the ribs. Secure with bolts.
    Do you hand feed the rod, loose? Do you just rub the iron around and then feed into the melted section? Or is there a 'hot flat shoe' pressing it together?

    If I go thicker on the aluminum, I am concerned there won't be enough flex to distribute the load and it may cause cracking at the joints. But yes, maybe 1/8" or 3/32".

    Quote Originally Posted by BCRider View Post
    But instead there's a lamp dimmer and a regular duplex outlet. In instead of the usual soldering tip the iron I have accepts 5/16nc threaded tips so I bent a bolt and then ground and filed it to a sort of ironing shoe shape with no sharp corners. Some scraps of the same plastic was used as a filler and for building up the weld on the back side. Using this tool is a rather slow process but it worked nicely.

    I believe that most plastic welders use a hot air source. The key is a small outlet. Lakeside, what size outlet is on the heatgun you use? Also my "iron" method involved blending the sides and filler with a bit of stirring. Do you still do that with the hot air source?

    I'm thinking that for a one off I'd use whichever I had the most handy or had to buy the least stuff or spend the least money. My iron method certainly worked and with a bit of "troweling" the weld with the smooth face of the little shoe shape I made up it even looked fairly decent. Best of all I was able to do the job with stuff I had on hand.
    Those are good questions. That's a good idea to form a new tip for an iron. Experimenting with longer bolts might eliminate the need for a dimmer. This is pretty heavy plastic, so I can see where that is going to help me and hurt me. I also wonder whether I should have a piece of backing material while I am welding. Something that won't draw out too much heat, but will contain the backside of the puddle while I am feeding in.

    Quote Originally Posted by The Artful Bodger View Post
    It appears the cracks are in the area where the 'handle' meets the bucket?

    I suggest adding aluminium reinforcement to the take the weight and reduce stress on the cracked areas.
    On this cart there are two support beams from the horizontal handle to the cart - just at the sides. Newer carts seem to have a third beam at the center, and they also have a bunch more beef across the top lip of that area. I think when the cart is heavily loaded and unbalanced, you have to lift quite a lot with the handle. That seems causes the cart to distort, like the side walls are being squeezed in. That, plus UV degradation, are my guesses for the failure.

  7. #7
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    I would make a patch and use GOOP sealant and pop rivites. Goop sticks real good and tough I use it a lot.

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    Quote Originally Posted by true temper View Post
    I would make a patch and use GOOP sealant and pop rivites. Goop sticks real good and tough I use it a lot.
    Oh, that is an interesting idea. GOOP is really wild stuff. It somehow sticks like crazy, even to the bottom of old shoes.. and it is incredibly tough. So on those flat surfaces it might help to stabilize the plate to the flat hdpe. I suppose it would eventually cure under the plate, despite lack of air?

    Given that this cart is outside year round, water will get into any cracks and freeze-expand. So there is that.

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    ....I also wonder whether I should have a piece of backing material while I am welding. Something that won't draw out too much heat, but will contain the backside of the puddle while I am feeding in.
    No need. The heat does not move through the plastic to that extent. And it never turns to anything with a low enough viscosity to run like water or paint anyway. When melted to welding condition it's a bit like pushing thick grease around with a teaspoon.

    On identifying what sort of plastic it is that's a tough one. First off is that I've only ever seen ABS and PVC fail with the sort of tight narrow cracks like you have in the cart. HDPE tends to stretch more and when it does crack it tends to be in longer straight lines.... at least until the UV from the sun has been on it for a lot of years and it becomes brittle.

    To aid with identifying the sort of plastic it is HDPE will tend to feel almost waxy and things like the blue and grey Rubbermaid storage totes and many plastic cutting boards are made from HDPE. On the other hand ABS and PVC have a more proper slick like surface. Go around to a building supply and check the white Sched 40 plastic and the white or light green drain lines used for direct buried use. Those are PVC. Then look at the black pipe and fittings used for internal drain plumbing and those are ABS.

    You say that the cart is very old. If it sits out all the time and the sun has done its damage to it then these might be the first of many new cracks. The UV attacks the plastic and makes it brittle. A really good example of this is in the video link below. Good fresh stock is tough and shatter resistant. Old stock made brittle by exposure to UV light? Not so much.

    https://www.youtube.com/watch?v=rOOAwAw-WIU

    You might also look around on the bottom and outside of the molded tub. There will almost certainly be identifying marks. And one of those codes should refer to the type of plastic that the tub is made from. And the Interwebz will aid you with the codes that identify the type of plastic. Heck, there may even be a recycling triangle on it somewhere that will lock down the sort of plastic and leave no doubt at all.

  10. #10
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    ID the plastic by taking some scrapings from say one of those gusset plates and conducting a burn test according to:

    http://www.recycledplastic.com/index...3Fp=10331.html

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