Can Loctite 638 really be this good?

Hi MichaelG, sorry, I wasn't implying in my last post that you meant 338 and I understood you had made a typo when I read your post to Robin. What I was saying, is that I mistakenly thought you had meant 338 instead of asking you if you meant 638. So my apologies go to you for reading your paragraph incorrectly in the first place and not explaining that in my last post.

Hoping I have cleared the misunderstanding.

Regards Nick.

No problem at all, Nick ...

We’re all falling over ourselves being polite and apologetic on this thread

MichaelG.

Yes, it can. It has pretty good gap filling and cures in the presence of metallic ions so surface area is a good thing. I have seen it do some things I would not have believed possible and would not think twice about trying it first.

Thanks Brian, but no apology necessary - as MichaelG said we all make mistakes. The internet is a wonderful thing in allowing nearly instantaneous communication with people you've never met, but it brings problems - stuff you'd sort out in an instant in casual conversation over a pint can result in misunderstanding when rendered in casual reading/ writing.

I'll certainly report back - it's an interesting experiment, whichever way it goes.

Hopper - you may well be right! But the bloke who brought it round, with touching faith in my abilities, wants it repaired. It's a bit more complicated than just replacing the tube:

I'd have to remake the sticking up bit or redesign, which I could do, but at a price.

Ken - I'd be surprised if Henkel would warrant anything for this application. But thanks for the suggestion - good to know that they are amenable to technical questions from small scale users.

Robin

Got a bottle of the 638 and use it once in a while. Great stuff... when used correctly. However, I don't think it the best solution here. The actual 'effective' contact surface would only be that 2mm rim where it contacts the plate. And considering the thin wall and the doubtful condition of the metal... well, I'm just not comfortable with that idea.

My choice would be for a classic brazed join. Assuming the extruder pipe as well as the flange are properly prepared then the braze metal would not only bond underneath the flange at the point of contact, but would also flow out to a slight distance from the join, giving a wider, stronger bond. In addition to that, if the metal is properly cleaned and prepared, the braze material will also serve to flow into and fill slight surface pitting which will reinforce the metal that much more.

A properly fluxed gas braze would be my preference, but an electric TIG brazing would also serve.

The actual 'effective' contact surface would only be that 2mm rim where it contacts the plate.

Not true - you really need to read the thread. This ‘suggestion’ has already been raised and killed off almost instantly. Your solution is, unfortunately, not applicable to the thread.

@'not done it yet', I stand corrected.

However...

Even when bored out and fitted around the cylinder, the brazed connection still has the ability to wet out slightly on the surface of both parts. In theory, offering a somewhat stronger bond.

My comment was about your disregard of the previous writings. Nothing to do with whether brazing was bettr. On that I agree with you, but the OP was trying to justify loctite.

Personally, If I were using loctite I would let the tube into recess and glue that. Even if it meant turning off a couple of mm, or so, from the tube.

My idea of a flange is not a plain annular ring stuck in place, as proposed by the OP.

If the anaerobic is to be used in shear, which is better than inntension, would it be feasible to; ?

Sandblast the outside of the tube for a short distance.

Turn up a close fitting ring.

Make up an oversize endplate so that it can be secured ton the ring by drilling and tapping. ( Use as many setscrews as needed, and of a suitable size, to withstand any pressure )

Loctite the ring to the cleaned tub

Howard

I am biased in that I am a big fan of Loctite 638, I have put some parts together with it in the past where I thought the joint was a bit risky to rely on a Loctite connection, but the 638 has always come up trumps.

I,m sure a brazed joint would be more belt and braces but I wouldnt be at all surprised if a 638 joint would work also, the surface pitting in the tube should certainly provide a good key and if the mating face of the flange is well abraded I think it stands a good chance of success, my thoughts anyway.

The one thing I have found with 638 is that it in ideal conditions it can grab very quickly so alignment of the parts needs to be in quick time otherwise it will be a case for the blowlamp to free the misaligned parts.

Ron

A further couple of questions: As I’m not conversant with the action of this extruder, is the ring likely to be pushed further on or off the tube? What is stopping an increased surface area of the tube being utilised?

removed

Edited By duncan webster on 02/04/2021 18:28:43

Hi ndiy. To clarify, here's a sketch,

which maybe I should have posted in the first place! So the 'ring' is being pushed off the tube.

There is no reason in principle why an increased surface area shouldn't be used, but the bloke I'm doing it for is cost conscious and 6mm black plate is cheap.

Anyhow, I have glued the flange (as I shall persist in calling it) in place and it seems rock solid. We won't know until it's tested in use, at which time I shalll report back.

Interestingly (perhaps) soft solder (tin/silver/copper) has roughly the same shear strength as 638 for this type of joint, under lab conditions at least. I discounted that possibility for this job because I was worried that if it failed residues might compromise future silver soldering.

Robin.

Edited By Robin Graham on 04/04/2021 00:37:34

Edited By Robin Graham on 04/04/2021 00:52:19

Doesn’t look like it is being pushed off the plate to me - if the 6mm plate, to which it is bolted and is resisting the piston down-force, is supported from below? Doesn’t look to be a hand-held device wit 5kN force.🙂. It already looks effectively, as I suggested above?

Edited By not done it yet on 04/04/2021 10:16:01

If the end of the tube is a good fit against the steel plate, the chances of the contents of the tube being forced between tube and plate seem to be small, especially if the contents of the tube are highly viscous. Consequently, other than friction between the material and the inner wall of the tube, there would seem to be relatively small forces subjecting the Loctite to shear (which is it s optimum strength anyway )

If accurately made, as drawn, I would feel inclined to try it.

If the forces are large enough, the 6 mm supporting plate is likely to deflect, with the risk of failure possibly following.

There is the possibility that the portion of the perspex that is unsupported may fail before the Anaerobic joint., ,by bending over the edge of the hole in the 6 mm steel plate.

Howard

If you are anywhere near Kings Lynn and it's worth the journey I will gladly weld or braze the job for you. PM me. Noel.

The tube has the rack for the lever to the piston connected to the side that creates the upwards force load on the flange.

Perhaps if the rack was connected to the underside of the flange that supports the perspex die instead of the side of the cylinder the load on the flange to the cylinder join is greatly reduced and the glued and or swaged join will suffice.

Eric.

When Brian Woods feels he has made a mistake, there is hope for us all !!

Regards Brian, never knew you to be wrong yet !

I cannot see sticky stuff working on that either.