UHMW bonding

[Scott Taylor]

Does anyone know of a good way to bond two pieces of UHMW together vs. screws?

[Brad Schmid]

There are acrylic and rubber based adhesives specifically made for bonding UHMW plastic to itself or to other materials. In the past, I have found info on both the Crown Plastics and Reltek sites:

http://www.crownplastics.com/p-s-adh...htm?snti=3-3-0
http://www.reltekllc.com/adhesives-for-uhmw.htm

I'm sure there are others. I have yet to try and buy some, so I have no idea how easy it is to get, or what minimum quantities and cost are. My impression is that most of this stuff seems tailored towards industrial applications.

Hope that helps.

By the way, welcome to SMC Scott!

[Cliff Rohrabacher]

Yes I made Butt Joint machinery to do that many years ago.

You have to
1.) Take a skim cut to remove any impurities from the edged to be joined.

2.) heat the material to it's melt point & not a scosh more..

3.) quickly sweeze and hold the parts together squishing the congealing molten material out like so much excess glue.

4.) trim the squeeze out - or not - at your preference.


Heat the material with a Heated Steel plate. sandwitched between the stock in a little jig you made to position the parts.

In your fixture make allowance for a lot of squeeze out (a 1/4" or more depending on material thickness) by making a channel under the joint area in your fixtire

[Dave Anderson NH]

UHMW, Polyethylene, Polypropylene, and Delrin are considered low surface energy plastics. They are difficult to bond with normal run of the mill acrylic or rubber based pressure sensitive adhesives. My best advice is to use one of the 3M 300LSE series acrylics which are specially formulated for low surface energy materials. The 3M part numbers vary based on thickness of the adhesive 9471LE is .002" thick, 9453LE is .0035" thk, and 9472LE is .005" thick. As a general rule of thumb, you pick the thinnest adhesive which will completely wet out both surfaces. In other words, the rougher and less planar the two mating surfaces, the thicker you have to go. The thinnest workable bond line is the strongest since there is less tendency of the adhesive to shear.

Addy Protocol: I work design with and specify pressure sensitive adhesives in my work and have used all of these products. I also did a week training course at 3M several years ago.

[Bill White]

Dave,
By golly that was the most knowledgeable answer to this oft-asked question I have ever heard. Would I expect to be able to order these items at an auto body supply?
TIA
Bill

[Dave Anderson NH]

Not likely to find them at an auto body supply Bill. Body shops wouldn't have a use for this particular adhesive. You almost certainly will have to go to a 3M distributor. These are not cheap adhesives and they come only in rolls 60 lin yds long. As an example, a roll of 9453LE 1" x 60 yds is about $14 when I order 6-10 rolls. If you go to www.3m.com/bonding you can get data sheets, MSDS sheets, and find a reasonably local distributor.

[Scott Taylor]

Thanks for the welcome. I am glad to have found this site. It seems pretty well packed with true exerience.

Also Thanks for the replies re: the UHMW. Dave, what do you mean by "wet out?"

What I would like to do is use a small sheet as a base for a Tenion Jig combined with some 3/4" pieces for the miter slot. The rest would be constructed of wood. I am leary of the strength of the material and it's ability to hold screws. (Especially in such a small thickness.) I want to keep the tolerance between the base and the slot as tight as possible with no possibility of movement.

[Dave Anderson NH]

Hi Scott, "Wet out" means that the adhesive has complete surface contact with both surfaces. It further means that there are no voids, and there are no spots where the 2 UHMW surfaces actually touch each other. If you choose to go the route of using a pressure sensitive adhesive (psa) the unit should sit 24 hours after the adhesive bond has been made in order for the bond to develop full strength.

[Scott Taylor]

Thanks Dave. I'll look into that 3M stuff and see if I can find a local dist. What kind of bond does this provide? How would you equate it?

[Cliff Rohrabacher]

Thanks Dave. I'll look into that 3M stuff and see if I can find a local dist. What kind of bond does this provide? How would you equate it?

It's strictly mechanical. The polymer exudes oils that interfere with most any bonding process so the glue must have a high penetrating ability.

[David Epperson]

Wouldn't one of those plastic welding setups from HF work on this?

[Charles Grosjean]

Does anyone know of a good way to bond two pieces of UHMW together vs. screws?

Look into 3M DP-8005, available from McMaster Car or your local 3M distributor, McMaster probably being much less trouble. You will probably have to buy the applicator gun too, but then you can use 3M epoxies which are great.

[Dave Anderson NH]

Scott- The bond strength is high and approaches a structural bond. In one customer application 2 pieces of polypropylene are bonded with a 1" wide lap joint in for use as an air dam in a high temp gradient amplifier which powers MRI machines. After 7 years there is no degradation and there have been no failures. I don't know the wattage of these amps, but they get hot enough to require 8 6" muffin fans for cooling airflow.

David- I'm not familiar with the HF machine, but plastic welders will work fine on UHMW as they will on PVC, or any member of the polyolefin family (UHMW, HDPE, LDPE, PP). The hardest part is finding someone who will sell you a small quantiy of the welding rod and not require you to buy 10-20 pounds of it.

[Rob Luter]

Scott -

If I understand your application, the base and miter slot key will be made of UHMWPE? As long as you use material that's 3/4" to 1" thick I suspect that conventional joinery will work just fine. The stuff machines up very well with sharp tools. We use a lot of it at work for tooling and fixturing components. Machine a shallow (1/16" to 1/8" ) keyslot into the underside of the base to accept the miter slot key. It will be rock solid and depend on the screws only for clamping force at that point.

UHMWPE will hold screws just as well, if not better than, wood of the same thickness. The best screws to use are not unlike the sheetrock/multipurpose screws so common at the borg. Sharp points, steep thread angles, small minor diameters. These do a great job of cutting into the material rather than pushing it out of the way. Use care when driving a bugle head design into the surface of UHMWPE though, as if you're not careful the head will be pulled into the plastic deeper than you want and you'll get a proud area around the screw head. A shallow spot face to hold a small washer under the head will prevent this. This can be used to your advantage as well. If you run a thin saw kerf about 1/2 in to the center of each end of the miter slot key you can use a strategically placed bugle head screw to spread the ends of the key apart by overdriving it. Depending on the fit between the key and the slot in your saw bed, a 1/4 to 1/2 turn on the screw can open the key enough to completely eliminate any slop.

Dave makes a good suggestion regarding the 3M 300LSE adhesives. I have a few years of experience with those as well, using them to attach polycarbonate graphic overlays on the front plates of panels that have been painted with a low energy polyester powdercoat. The stuff hangs on great, but it's not like a wood to wood glue joint. You will be able to take it apart without damaging the UHMWPE. If you have any graphic arts companies around where you are check with them. They often have this sort of stuff for laminating onto nameplates and overlays. There is generally a bit of scrap that they chuck into the hopper after the run. Free is good

Best of luck on your jig.

- Rob

[David Epperson]

David- I'm not familiar with the HF machine, but plastic welders will work fine on UHMW as they will on PVC, or any member of the polyolefin family (UHMW, HDPE, LDPE, PP). The hardest part is finding someone who will sell you a small quantiy of the welding rod and not require you to buy 10-20 pounds of it.

The unit from Harbor Freight is a low presure heated air unit (5psi) with a small air directing nozzle. As for rods, I sort of figured to do the same as we used to do with TIG welding stainless, and that was to simply shear thin strips from a thinner sheet of the same material.