Welding/bonding thick HDPE

[theoldwizard1]

I have watched a few videos on the above topic and all of them show tools that work for thin (<1/2") sheets of HDPE.

I am contemplating a project that would require the use of thick (2x4) "bar stock" HDPE that would require a sharp corner. Has anyone done this and how was it accomplished ?

HDPE can be easily bent, especially when warmed up. Is it feasible to bend the corner as tight a possible (after warming), then notch out the outside and weld in a square section to make a sharp corner ?

Are there any good adhesives for bonding HDPE ?

 

[6PTsocket]

I have watched a few videos on the above topic and all of them show tools that work for thin (<1/2") sheets of HDPE.

I am contemplating a project that would require the use of thick (2x4) "bar stock" HDPE that would require a sharp corner. Has anyone done this and how was it accomplished ?

HDPE can be easily bent, especially when warmed up. Is it feasible to bend the corner as tight a possible (after warming), then notch out the outside and weld in a square section to make a sharp corner ?

Are there any good adhesives for bonding HDPE ?

Polyethelene as in high density polyethelene (HDPE) is one of a group referred to as low energy plastics that includes polypropalene and teflon. They do not work with most adhesives. Loctite makes a primer that is actually hexane that conditions the surface to accept their cyanoacrylates (crazy glue). Their industrial grade 401 is far better than any condumer grade crazy glue. I have seen adhesives made specifically for these plastics but they are not cheap. Just google: adhesive for HDPE and you should get a hit. I have welded the smaller size stuff myself. All of these plastics are thermoplastics, they melt and can be welded with hot air or soldering iron style welders and the appropriate welding rod but big pieces could be a problem.

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[MoonRise]

What exactly are you trying to accomplish?

HDPE does not bond easily. (didn't we just go through this maybe last week or so?)

Just how tight of a bend radius are you trying to get and can you live with?

And why can't you just take the 'big' chuck of HDPE and use it pretty much as is? Maybe with a bit of machining on corners/edges as needed?

 

[theoldwizard1]

What exactly are you trying to accomplish?

Boat frame with a hard chine.

 

[theoldwizard1]

From research what I found out is it can be done, but it takes finesse !

Forget joining with pretty much any adhesive. None are recommended. Welding will not go very deep and is primarily for tacking sheets/blocks together. You can bend HDPE with judicious use of heat. The following steps are about the best you can do to make a 90° corner.

• Start with a piece that is longer than the 2 sides you want to join
• Make a 90° notch with a router that is almost full depth
• Carefully apply heat at this notch so that both side of the notch are "soft"
• Fold at the notch so that the 2 soft edges are in contact and clamp until they cool
• Weld bead will help some
• gusseting with screws is the best you can do

 

[ducksface]

Inset (like a door hinge) stainless steel corner(butterfly) Cover with thin hdpe if you don't want the stainless seen.

Or two slots, insert the stainless corner(like a biscuit), bolts through(or hdpe plugs through if you need total protection)
Or inside and outside Inset stainless gusset, bolts through.

Have you seen the Teflon Chine guards available at West Marine?

 

[txlch]

Would solvent welding work?

 

[GSRinmyCRX]

i have installed a number of watermains that were HDPE. there is a slick machine that contractors use to melt and weld lengths of pipe together. there are a lot of videos out there. watching a few of them might give you an idea of a method of how to do it.

a heat plate is used to heat up the HDPE maybe you could find a piece of metal and stick it in the oven to use as a make shift heat plate.

also making sure it is held together during the cooling is very critical. if its joined properly you wont be able to tell where one piece ends and other begins.

Levi

 

[theoldwizard1]

i have installed a number of watermains that were HDPE. there is a slick machine that contractors use to melt and weld lengths of pipe together. there are a lot of videos out there. watching a few of them might give you an idea of a method of how to do it.

a heat plate is used to heat up the HDPE maybe you could find a piece of metal and stick it in the oven to use as a make shift heat plate.

also making sure it is held together during the cooling is very critical. if its joined properly you wont be able to tell where one piece ends and other begins.

Levi

I have seen them and the work well ... for pipe ! A couple of key things.

• The pipe wall thickness is probably <1"
• The heating mechanism has some kind of indicator that the plastic is hot enough to join and it will not overheat it to the point of sagging
• There is typically some kind of tool that holds the 2 pieces in alignment until they are cool.

For what I am think of, gusseting, deep rabbets, and screws and/or through bolts are the only reasonable solutions.

 

[theoldwizard1]

Would solvent welding work?

No. HDPE is pretty much impervious to most solvents.

 

[Hammer1963]

There are stainless connectors/staples available for what you are trying to accomplish. They require a specific tool that heats the staple which allows it to be buried into the material. Welding with a specific filler rod can be utilized to help with strength and appearance. Once again, special tooling is required. I have also used stainless dowel pins and stainless screws for plastic in certain high stress situations. They are all out there if you are able to locate them

 

[jask]

6PT has it right there are chemical and mechanical bond issues that make this sort of project extremely prone to failure, welding requires identical filler rod and extremely good control of heat and oxidization products that will cause a bond to fail under thermal or impact cycling. The stock dimensions you are talking about are available from industrial suppliers who are also able to custom profile if you need production quantities and can often access near net profiles from other suppliers. HDPE has radius minimums and any improperly radiused notches will eventually be your failure point.
call a few of the industrial suppliers in your area and they may point you at some technical resources.

 

[smon]

Pick up a plastic welder from harbor freight for $60. Don't use the rods it comes with though. Order some different sized rods and some HDPE sheets (cutting board) for gusseting on amazon.

It's pretty forgiving stuff to weld. To me, it's easier than welding Poly.

I have seen a bunch of adhesive "fixes" on HDPE bins and not a single one has held up.

You can also get a tip to "stitch" seams for extra strength using HDPE ribbon.

Does the inside corner need to a sharp 90* corner? Or can it be slightly rounded inside?

You could bring two pieces together at slightly more than 45* angles and then fill the gap with the welder.

 

[theoldwizard1]

Pick up a plastic welder from harbor freight for $60.

Hot air welders are not going to work for 2" stock. They are fine for thin sheet stock.

 

[smon]

I was able to work with 1" thick stuff fairly well with the hot air welder by slowly bridging the gap. Took forever, but worked and was plenty strong.

Not sure what your application is though.

What about baking a piece of iron at 350* and using it like a hotplate? Get both sides just to the melting point then clamp it together. Might require some cleanup on the inside. You could then use a router on the outside and stitch it together for extra strength.

 

[theoldwizard1]

For what I am think of, gusseting, deep rabbets, and screws and/or through bolts are the only reasonable solutions.

End of discussion.

 

[morrillm06]

what about getting 3/8 rods of the same Material, pinning it in two locations with in but leave them a 1/4 inch short. You could then plug weld the pins in and also weld around the joint its self? Just a thought

 

[JonnyMac]

Didnt lilscorpion use this stuff for making all sorts of awesome projects? I reckon he should have some good insight into its use...

 

[jonahhaley14]

I have watched a few videos on the above topic and all of them show tools that work for thin (<1/2") sheets of HDPE.

I am contemplating a project that would require the use of thick (2x4) "bar stock" HDPE that would require a sharp corner. Has anyone done this and how was it accomplished ?

HDPE can be easily bent, especially when warmed up. Is it feasible to bend the corner as tight a possible (after warming), then notch out the outside and weld in a square section to make a sharp corner ?

Are there any good adhesives for bonding HDPE ?

There is a specific machine used in salt water pipe line disposal wells where they fee the 2 ends of 6-18 in poly pipe in it secures both sides wit 2 roller per pipe and holds it 1 in and 1/2 away from a movable heating plate. In drops down and heats up to HIGH temps then quickly moves and the machine basically smashes the pipe together and hold it for the alloted preprogrammed time to fuse the 2 joints together. So it can be do e what you are asking now the pro lem your going to face isn't getting them to heat up and be weldable it's going to be able to pressure them together enough to properly fuse and seal together. Good luck

 

[speed bump]

Build a jig that you can force the ends together, get two plate heaters that are as big as you can get. Look heat times in a fusion table. Heat the ends until hot, pull the heaters, you have 15-20 seconds to slam together and start tightening your jig. Leave set for 15 minutes.

If haul truck drivers can operate a fusion machine on heavy wall pipe mostly successfully the average person should be able to as well.

 

[dogdog]

ultrasonic welder ?