Glue the Ungluable

jqavins

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OK, maybe I'm covering old ground, or reopening old wounds.

I was reading wikipedia about Polyoxymethylene (POM, e.g. Delrin) which crossed my mind for some random reason, and I found this:
In order to get a high bond strength without specialized tools, treatments, or roughening, one can use Loctite 401 prism adhesive combined with Loctite 770 prism primer to get bond strengths of ~1700psi.
(Underline added.) So, if it works for Delrin, does it work for Polypropylene?

I proceeded to Henkel's (Loctite's) web site, and found the following:
  • They do have a number of products that bear the Prism™ moniker, but 401 and 770 are no among them.
  • 401 is one of many CA formulations that Loctite has.
  • The product description for 770 states:
LOCTITE® SF 770 is a primer used to make polyolefin and other low-energy surfaces suitable for bonding with LOCTITE instant adhesives. The cured performance of LOCTITE® instant adhesives is ensured on such treated surfaces. It is only recommended for difficult-to-bond substrates which include polyethylene, polypropylene, polytetrafluoroethylene (PTFE) and thermoplastic rubber materials. LOCTITE SF 770 is not recommended in assemblies where high peel strength is required.
(Underline added.) "Not recommended in assemblies where high peel strength is required" worries me a bit. There is another primer, 7239, which might be better.
LOCTITE® SF 7239 is a colorless, solvent-based, general purpose primer that improves the bonding efficiency of instant adhesives on all plastics. It is particularly effective on polyolefin, thermoplastic rubber and other low surface energy plastics that are normally difficult substrates to bond. The primer has a good ‘on-part-life’ and provides for a good aesthetic appearance of the bond line.
A search for sources to buy 7239 turned up only European results.

There are also lots of other CA variants that may or may not be better than 401 for our purposes.

I think I will contact the Loctite people and ask; this looks promising enough to be worth writing them.
 

boomtube-mk2

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I remember the old Simplex bicycle derailleurs that were made out of Delrin.
Lightweight, tough as nails and never needed lubrication as Delrin is a "Self lubricating plastic".
 

jqavins

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It would make great rail guides, but the many applications of Delrin are not the point here.

I did send a contact form the Henkel.
 

dr wogz

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I have a bunch of Delrin in various forms for a project I'm working on..

biggest issue we've run into, is that when machining Delrin, it tends to warp! (in the direction of the removed material!) OS, I have a bunch of bowed rails & guides!
 
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I have a bunch of Delrin in various forms for a project I'm working on..

biggest issue we've run into, is that when machining Delrin, it tends to warp! (in the direction of the removed material!) OS, I have a bunch of bowed rails & guides!

found this on the interweb. Hope it's helpful.

Delrin machining tips
Delrin is widely considered to be one of the most machining-friendly plastics, so it does not require any drastic precautionary measures. That being said, it responds better to certain design considerations and machining approaches than others.

  • Design for Delrin: When designing parts for Delrin machining, try to keep wall thicknesses consistent and include fillets and ribs where necessary. Large parts may be more susceptible to warping.
  • Stay cool: Delrin is sensitive to temperatures above 121°C. Air-based coolants perform better than liquid coolants and also accelerate chip removal.
  • Keep the tool clean: Although machined Delrin produces consistent and manageable chips, chip removal should be swift to avoid a gummy buildup on the tool.
  • Keep Delrin separate: To avoid contamination, it is best to use cutting tools that have not been previously used to cut aluminum or other metals.
  • Be sharp: Sharp cutting tools with a high clearance angle will deliver better results when machining Delrin, and the use of cutting lubricant may also help.
  • Not too tight: Delrin is not especially rigid so care should be taken during workholding. Light clamping forces should be used at all times.
 

dr wogz

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Thanks Norman,

2 things: this is up to the machine shop to manage, and let us know if they can't do it. This design was a bit of an experiment for the both of us. Secondly, the initial design was right, but the material choices jumped around a bit.. But once again, just because you can design it in CAD, doesn't mean it'll be a snap to fabricate! in this case, I have a 1.25" thick slab of Delrin with the middle machined out of it.. (The majority middle portion of one side is only .5" thick.. Over half the material volume was removed..)

And once again, the young know-it-all engineer didn't really know very much, and the project leader just accepted it.. (But, boy could he talk!!) The designer has since left.. I now have to deal with the parts. The project manager is still around, and is now very aware of the limits of both the [old] designer & the machinist!
 

jqavins

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Man, I know threads wander like cats, but this was really fast!

"I was just incidentally thinking about Delrin, and it led me to a possible solution for that age old problem of trying to glue to polypropylene. Wouldn't we all like to know a way to glue to polypropylene?"

"Yeah, Delrin is great!"

:facepalm:
 

rocket_troy

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No doubt all this has probably been mentioned plenty of times before, nevertheless:
PP and PE are notoriously difficult to bond to for regular adhesives. CA is probably the best bet for *untreated* surfaces of PE and PP but still not great. You really need to oxidize the surface of PE or PP in order to achieve a good bond either via blue flame exposure or plasma treatment.
Another alternative is to melt just the surface with a butane flame and quickly hit that with *hot* hot melt glue ie. to create a partial weld between the PE/PP and the glue. Of course, that method is risky to distort the material.

TP
 

rocket_troy

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I was unaware that something bonded to Teflon.
I've never tried bonding to PTFE, but it doesn't surprise me at all that it's bondable. Decades of processing PU based composite propellant taught me a long time ago that PTFE and other flavours of Teflon aren't always as slippery as they're famous for - in fact, they often make matters worse in the case of Teflon coating.

TP
 
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dhbarr

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I've never tried bonding to PTFE, but it doesn't surprise me at all that it's bondable. Decades of processing PU based composite propellant taught me a long time ago that PTFE and other flavours of Teflon aren't as slippery as they're famous for - in fact, they often make matters worse in the case of Teflon coating.

I would guess that Titebond PlasticBond or PlasticWeld might be more than half as good for less than half the cost.
 

rocket_troy

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I would guess that Titebond PlasticBond or PlasticWeld might be more than half as good for less than half the cost.
Not sure if you're referring to PTFE bonding or PE/PP; irrespective, you'll find that (pretty much in every case) the fine print with most of these "plastic adhesives" will state they're not suitable for bonding to PE or PP.

TP
 

dhbarr

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Not sure if you're referring to PTFE bonding or PE/PP; irrespective, you'll find that (pretty much in every case) the fine print with most of these "plastic adhesives" will state they're not suitable for bonding to PE or PP.

And the expensive one from the same company will state that it -is- suitable and contain largely similar components. 🙃
 

Grog6

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I made a gaming mousepad a few years ago, and I was able to buy some teflon sheet 1/16"x 2' by2', that was treated to be bondable; I stuck it to my desk with double sided tape.
Unfortunately, it was too featureless to work with my mouse very well.
I roughed it up, hit it with methylene blue, and hit it with 80 grit, and there was enough of a pattern to work. :)
 

BABAR

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This is often literally outside the box, and it won't work for external fins, but if you have something that conforms to a body tube or other surface, it's da bomb.

Dental Floss and thin CA.

I kid you not. I use it in many of my balsa Heli's and Air Brakers for the forward hub, either wrapped around or sewn through the corners AND wrapped around, do 2 or three wraps of floss, tie a tight knot, and wick thin CA into it. Your balsa will break before the bond does. Also makes awesomely strong tape hinges for helicopters and elevons and those kind of things when used with duct tape. I'm well into my second decade using this technique.

It does leave a bump on the surface of the hub or tube, usually I am covering that with tape or something anyway.

I don't do much with through the wall fins, but if you were willing to cut the fin slots all the way to the end of the tube, you could use this technique to hold the fins to the motor mount (drill some holes, use a needle and pass it through one fin hole near the base, then the next, and so forth, round at least 2 times. You'd have to attach the fins to the mount and then slide the mount into the body tube, hence the slots need to go all the way to the end. Not optimal, but plenty strong.

for tape hinges, see posts 3-5
(2) Build Thread for Whopper Flopper Chopper | The Rocketry Forum
 

jqavins

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[Y]ou'll find that (pretty much in every case) the fine print with most of these "plastic adhesives" will state they're not suitable for bonding to PE or PP.
Or PTFE. And I'll wager the only reason they don't mention POM is that it's obscure and very rarely used from the typical consumer point of view.
 

jqavins

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Nothing is unglueable. You just need the right glue.
I wonder what bonds well to ice. I mean, if it's kept cold and solid, with a smooth flat face, I'm sure there is something that would work. But what? It has to be something which can be applied and will cure (or dry) while cold. Hmmm. Construction adhesive for building igloos.
 

jqavins

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Here's the response from Henkel.
Joseph,

Thank you for your recent inquiry via the Henkel website.

You are correct - SF 770 is an adhesion promoter used on difficult-to-bond plastics and elastomers in conjunction with a CA. CA's are gap-constrained (up to .010" max), and wouldn't necessarily be the best bonding agents for some of your substrates. If you wanted to evaluate this type of system before purchasing industrial sizes, you can try Loctite Plastics Bonding System, a retail product. Here is the datasheet.

https://dm.henkel-dam.com/is/conten...-Bonding-System-Carded-4-ml-2-g-2016-08-26pdf

Another industrial product that bonds well to polyethylene is Loctite AA 3035, which is a 2-part acrylic, optimized for polyolefin bonding. This would be purchased through a Loctite Industrial distributor (Grainger, Fastenal, Motion Industries, R S Hughes, etc.)

IDH #1677288 - 50 ml dual cartridge

IDH #720228 - manual applicator gun

IDH #1573149 - mix nozzles (10 pk)

We have recently had supply chain issues with this product, so it's unclear which distributors may have some on hand, or how long it might take to be back in stock. TDS is attached.

If you need further assistance, please contact Technical Information at (800) 562-8483, option #1.

Regards,

Catherine Scoville

Henkel Corporation | General Manufacturing & Maintenance | ACM Technical Information Services

Customer Support Center | Canada Toll Free 800.263.5043 | USA Toll Free 800.LOCTITE (562.8483)

Digital Resources │LOCTITE®TDS/SDSDistributorsEquipment

I guess I might just buy some 770 and give it a try, though I'd still like to ask which CA they recommend to go with it for PP. (I asked that question, but this response did not answer it.)
 

kramer714

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I have a bunch of Delrin in various forms for a project I'm working on..

biggest issue we've run into, is that when machining Delrin, it tends to warp! (in the direction of the removed material!) OS, I have a bunch of bowed rails & guides!
A lot of thermoplastics are extruded or pressed with a preferential direction and/or with thermal stresses in the skins. Fun to see someone trying to machine the 'bow' out of it, the more you machine the worse it gets.

Frequently you need to anneal these materials before machining and/or take a skim cut off of both sides of a panel while keeping it restrained (we use vacuum chucks at the day job). Typically a bar will get shorter and thicker during annealing. You will have the same issues with moisture causing bowing / twisting. Typically the annealing step will remove the moisture too.

If I remember right acetal anneals at something like 150C, the temp is above the Tg but below the softening point. IF you are concerned about creep you can use sand (DRY!!) to support the part. Check the data sheet for the acetal alloy you are using to find the proper temperatures.

Mike (actual structures / materials engineer) K
 

Funkworks

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I wonder what bonds well to ice.

An idiot's tongue 😝.

Seriously, the existence of frost suggests ice even bonds to something as smooth as glass. Something to consider is that the glues we're familiar with are "exothermic" I think. They release heat, so they could melt the ice instead of bonding to it in solid form. An interesting subject to look into.
 

kramer714

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A lot of thermoplastics are extruded or pressed with a preferential direction and/or with thermal stresses in the skins. Fun to see someone trying to machine the 'bow' out of it, the more you machine the worse it gets.

Frequently you need to anneal these materials before machining and/or take a skim cut off of both sides of a panel while keeping it restrained (we use vacuum chucks at the day job). Typically a bar will get shorter and thicker during annealing. You will have the same issues with moisture causing bowing / twisting. Typically the annealing step will remove the moisture too.

If I remember right acetal anneals at something like 150C, the temp is above the Tg but below the softening point. IF you are concerned about creep you can use sand (DRY!!) to support the part. Check the data sheet for the acetal alloy you are using to find the proper temperatures.

Mike (actual structures / materials engineer) K

Replying to my own post.... kinda sad.

For adhesives to low energy plastics like acetal homo-polymer (Delrin), CA are not great, almost no peel strength.

You should look at an acyrlic or urethane adhesive Take a look at 3M DP8010. If the part is flat, the VHB tapes (the real stuff not the crappy amazon or home depot double side tape) actually work well. I have used these for bonding teflon wear strips to aluminum airplane structures (day job). Urethanes are OK but the acrylic will work better from my experience.

Some 2 part acrylics work with a primer that is actually a catalyst for the adhesive.
 

jqavins

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Seriously, the existence of frost suggests ice even bonds to something as smooth as glass. Something to consider is that the glues we're familiar with are "exothermic" I think. They release heat, so they could melt the ice instead of bonding to it in solid form. An interesting subject to look into.

Oh, sure, ice itself bonds to many things. It can even be used as "solder", and a bit of soap as flux helps. Take two panes of glass, microscope slides, or the like. Put a drop or two of water between them with a little bit of soap to aid wetting, then put the whole thing in the freezer. The panes will be soldered together.

But what I was musing over was what other material will bond to ice that's maintained solid. Two blocks of it, or one piece of ice and one of something else, and something applied in between as glue. (Not warm water, which would weld ice blocks.)
 

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I wonder what bonds well to ice. I mean, if it's kept cold and solid, with a smooth flat face, I'm sure there is something that would work. But what? It has to be something which can be applied and will cure (or dry) while cold. Hmmm. Construction adhesive for building igloos.

Hmm, if cold enough, your tongue will glue to ice.
 

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An idiot's tongue 😝.

Seriously, the existence of frost suggests ice even bonds to something as smooth as glass. Something to consider is that the glues we're familiar with are "exothermic" I think. They release heat, so they could melt the ice instead of bonding to it in solid form. An interesting subject to look into.

Beat me to it.
 

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