Bonding UHMW

[Horst]

Is it possible? I've got a 2' x 4' x 1/8" sheet of UHMW I want to bond to 3/4" MDF.

[LHC]

I've often wondered this myself. I sort of suspect that the only thing is going to be countersunk woodscrews though

[Lew Hartswick]

I've heard of a site called something like " This to That " that may be
of help but the chem. professor I talked to some years ago said
something about the "surface energy" of polyethylene being such
that any glues won't have much success. A mechanical joint is about
the only sure or strong way to hold it.
...lew...

[LKeithR]

I've had a couple times in the past where someone wanted to "bond" UHMW to something else. Never found anything that would work; at least not reliably. A couple things we tried--seems to me that crazy glue was one of them--would "stick" the parts together but not with enough strength to do what the customer wanted...

[Harvey Melvin Richards]

Loctite 3034 is suppose to be excellent on polyethylene.

http://www.henkelna.com/us/content_data/205991_LT4809_Loctite_Structural_Adhesives_Selector_Guide.pdf

[jrude]

http://www.mcmaster.com/#uhmw-polyethylene-bonding-adhesives/=ez516e

Scroll to the bottom. It's not cheap.

[Evan]

The problems in this case are the size of the pieces and the MDF rather than the plastic. Anything that will make a good bond to MDF won't bond well to the UHMW. The surface strength of the MDF is poor so it needs something the sets slowly so it has time to soak in. Unfortunately the adhesives that will bond to UHMW are fast setting which is incompatible with that requirement as well as the size of the part.

If this is a project where nothing else will do then the UHMW can be treated with ozone to break the surface bonds and make it possible for a wide range of glues to stick. That won't be an easy service to find and is something difficult to do in the average shop since it requires special electrical equipment.

The other major problem is that UHMW has the highest coefficient of thermal expansion of the common plastics. It will expand about 20 time more than MDF with changes in temperature which will cause it to come loose and/or buckle no matter how it is fastened.

[Horst]

I'm not married to the MDF, but had not considered thermal expansion. The UHMW is going to be subjected to temps over 250 degrees. Thanks for the tips. I've got some more thinking to do!

[rmwise]

I had to make a 3' diameter lazy susan like cutting board for my wife and used 3/4" MDF and 1/4" UHMW poly on it. I used 3M Super77 contact adhesive and it's still holding up after about 7 years of use. Spray both pieces, let them sit until the solvent flashes off then stick 'em together. I did use a roller to flatten it after assembly.

[Evan]

UHMW is definitely not suitable for that temperature. It melts just above that temperature and becomes very soft at boiling water temp.

[Horst]

I'm finding an expansion rate of 7.8 · 10¯⁵ in/in°F. Does that sound about right?

[Horst]

Tivar H.O.T. (High Temp UHMW) - McMaster-Carr - +275 degrees

[Evan]

For UHMW natural I find 2x10^-4

http://www.sdplastics.com/uhmwphys.html

Don't know about the Tivar. You may want to check the deflection temp if it will be subject to heavy weights while hot.

[Horst]

If my math is right a 48" sheet would expand 1.96" with a 200* rise. Doesn't sound right.

[Evan]

I get the same and I checked 3 different places and all gave the same CLE for UHMW.

However, there is a gotcha. Once past the 116F deflection temp for UHMW the expansion is no longer linear as the material softens.