Shaft retaining adhesives

I'm trying to fix (permanently) some 10mm aluminium alloy round bars into appropriately(?) sized holes in square ali bar. I'm using Truloc 231 which is advertised as equivalent to Loctite 603. It's not working - the adhesive is failing to cure. The metal has been scrupulously cleaned, and the pieces have been machined to mate with a light push fit.

Arc advertise this stuff as a high strength retainer and suggest it's OK for a push fit, SimplyBearings are undecided as to the strength (headline is high strength, tech info says medium strength) and say it's OK for a 0.1mm gap, which is hardly a push fit. So I'm confused!

Would I be better off with Loctite 638, which according to the their website works well with passive metals such as ali?

REgards, Rob.

How were the holes formed? Could they be tri lobed from drilling, tapered, rough surfaced. All these could mean your "push fit" is just touching high spots and the remaining gaps are outside the adhesives range.

What were they cleaned with?

Rather than looking at the spec on various sellers sites it would be better to look at the makers site which does say it is high strength and suitable for press fit and sliding fits , they should have a technical dept maybe contact them.

The other thing to bear in mind is that the cure time gets longer the larger the gap that has to be filled, so your light push fit will take longer to cure than a press fit. How long had the joint been made before it failed? A 0.05mm gap may cure in 3hrs on steel but a 0.15mm gap may take 3 days . This is based on Loctite 603 data so assume Truloc would be similar

All the times you see published tend to be for steel, aluminium will take longer, typically a 3hr cure on steel may take 3 days on aluminium unless activators are used. This is based on Loctite 603 data so assume Truloc would be similar

Edited By JasonB on 13/10/2017 08:45:32

Highly polished shafts and holes might not be good candidates for adhesive joint.

Recently I have tried something like that:

Tolearances for interrupted fit were machined. Part with a hole was warmed to modest 100*C. Shaft was immersed in liquid nitrogen for 10 minutes (hospitals and higher end pubs have it, pubs are using it for making icecream - just smile to manager and come with suitable 2- 4 pint household Thermos flask - do not tighten it too much - there must be a way to escape for boiled off gas). You can store it for few days before is gone. Liquid nitrogen is cold (-196*C) - take care. Spilling it over hand usually does next to nothing as it boils off before contact with skin but touching metal cooled to -196*C guarantees nasty frostbite in no time at all. Now , with aid of thermally insulating gloves, insert/press shaft into hole and let it expand upon warming. Do your job reasonably fast, before shaft warms itself. You may pour liquid nitrogen to wide mouth thermos or thermally insulated thin walled pot for the job.

You won't disassemle it easily...

Martin

Don't you dare put the top on that thermos. It can still ice up and go bang.

Martin

Have you tried cleaning with acetone,ive heard people saying it acts as a cheap activator for aluminium .Loctite recommend using their surface activator `7649 primer N ` for aluminium when using 603 ,which is an aliphatic amine and acetone .

@ Martin Kyte,

In chemical company where i was working there were 2 opinions.

1. Don't you ever put any cap on it - may go bang if iced around.

2. Put the cap on it very lightly, in loose way. This reduces air access to liquid nitrogen.

This air access may be dangerous for entirely different reasons - oxygen from air will condense in liquid nitrogen and upon evaporation of nitrogen can concentrate itself to 80% or so. If there are there some organic impurities, what is often the case, it may then go bang for entirely different reasons.

I was puting this top very lightly, some others did and some others didn't. There was about 15 workers. Nothing have happened to anyone during 20 years. Nitrogen was handled nearly every day.

So from my perspective it seems that risks are largerly theoretical albeit from time to time accidents (like everywhere) *are* reported.

Martin

What are you cleaning the metal with ? I use acetone .

Make up a test piece using steel and see if it goes off then , maybe there is a problem with it using alloy or what you are using to clean the parts is affecting the bonding agent ?

If the steel test piece gives the same results and you are using acetone to clean everything maybe your bottle of retaining compound is crook and if you are leaving it overnight and it is still not going off then i would be looking at a new bottle .

The test piece need only to be a drilled and reamed hole in a piece of scrap that accepts a suitably turned pin from another piece of scrap and would only take a few moments to make .

Edited By XD 351 on 13/10/2017 12:08:52

The problem is the surface of aluminium. Anaerobic adhesives react with the metal in the absence of oxygen .

Aluminium is called a passive metal due to the oxide layer as opposed to steel which has an active surface ,it is the oxide layer that causes the problem.

The loctite 7659 primer makes the surface active.

Brass copper works best with anaerobic adhesives which is probably why loctite 7659 primer N has some copper compound in the ingredients.

I dont think the adhesive is bothered which metal it reacts with to dry as long as some metal is there .

Ive heard of putting copper sulphate solution on the joint and letting it dry ,then applying the adhesive. Loctite probably use some organic copper salt that is soluble in acetone ,which is why the stuff is a green/blue colour.

I don't know if you're looking for anything other than Loctite but I've used this other british make called bondloc, this is the specific one; **LINK**

It seems to hold together very well and the strength is a lot better than other locking adhesives I've used.

Michael W

If you do go down the activator route them probably best to use the one from Truloc, probably no different to Loctite's one but best to be safe.

Hi Robin,

If I could just reply to your original post.

Loctite 638 is in my limited experience a really strong bond

I have just made a crankshaft, 1/4" diameter, using loctite 638 to to bond it to the crank webs which are made from 5/16" mild steel plate. Same for the crank pin also 1/4" diameter.

Rock solid, I have pinned them as well with 16g panel pins but it was hardly necessary.

Hope this helps Geoff

638 actually performs worse on aluminium than 603, only making 60% strength after a week!

Hi Jason/Robin

I thought I would share this with you. The first photo is a scrap piece of aluminium with 4 x 1/4" holes drilled through it. The end hole has a 1/4" round bar loctited in with 638.

I left this overnight and to test the strength I clamped the bar very tightly in the bench vice using soft jaws. I then tried to break the seal by rotating the alloy bar. The whole assembly rotated without breaking the joint. I tightened the vice more as hard as I could and the joint still remained firm. I was amazed how strong it was.

The second photo is the crankshaft for the Jepson engine, again 638 on the shaft and crank pine, and incredibly strong joints.

best geoff

Geoff, is the round bar in the test piece aluminium or steel? if steel then that would have kicked off the reaction as only one of the two metals being joined needs to be active.

Comparing Loctite 638 and 603 is made unnecessarily difficult by the slightly different formats and contents of the TDS data sheets. How hard would it be for Loctite to use a common format and provide sensible explanations of how to decide which to use when. Methinks ulterior motives for the "superficially same but actually different" style used.

Anyway 638 TDS gives Compressive Shear Strength between same material pins and collars of 4,200 psi for steel and 2,700 psi for aluminium. Pretty much in line with the graph although that actually implies about 2,500 psi by my maths.

603 TDS doesn't give all that information but it does give 3,260 psi for steel pins and collars. Graphs on the one I downloaded imply that bond for aluminium gets up to around 75% of that for steel viz :- 2445 psi.

So its pretty much a wash after a week.

Have to assume that Compressive Shear Strength is actually a meaningful parameter for behaviour out in the real world. I think I can see how its a reliable and reasonably easily measurable test parameter but what it adds up to in the real world I know not. Can do the maths but it still doesn't mean much. Torque on a specified size bar in a specified hole would be so much easier for ordinary folk. We've all sheared bolts in the past so have some sort of feel.

One really annoying thing about Loctite (and other suppliers of similar nostrums) is that its not made clear how quickly headline performance drops off if you don't do things exactly right. Reading between the lines of several less than satisfactory conversations with Loctite tech reps I'd hazard a guess that most casual users are working around the 1,500 psi region even with the uber strong stuff. Still quite a lot as a 1" shaft in a 1" deep hole is "pi" square inches. Implies something over 4,500 lb to push it out even at 1,500 psi if you have full coverage. But it isn't that simple on a real component.

Clive.

Edited By Clive Foster on 13/10/2017 18:04:27

Edited By Clive Foster on 13/10/2017 18:22:55

Martin K & Martin D

The big near spherical lab dewars we used at RARDE to cool IR detectors were specially made for liquid nitrogen and had loose fitting caps with a similarly loose fitting fibre like plug extending down right through the neck. Neck was maybe 2" diameter by 3" ish long and the dewar case a couple of foot or so diameter. Never had icing or other problems. Normally we'd get filled dewars on a Monday. If plans changed and we didn't use any, or not much liquid nitrogen there would still be some left next Monday.

Transferred to ordinary plastic bodied thermos flasks for on bench supply with plastic funnels to get the stuff into the detectors. Laid half a filing card over the top to keep it in. Boss man considered the special lab grade stainless steel dewars unsafe. far as I recall we never broke a thermos with liquid nitrogen although a couple did get dropped and died from impact. Replaced by Joule-Thompson type coolers run by high pressure nitrogen or air to produce liquid nitrogen direct in the detector body. Theoretically easier on the supply side but a right faff at times. Especially when the tiny orifice iced up.

Clive

Edited By Clive Foster on 13/10/2017 18:23:31

Edited By Clive Foster on 13/10/2017 18:24:28

Not specifically relevant to this thread but loosely related by liquid nitrogen. Back in the early 70's I was working as a contractor in an engineering hangar at Luton airport, we were engaged in servicing a Boeing 707 which belonged to some obscure African airline. I was working on one wing and alongside me was an apprentice who had been given the job of replacing a bush holding one of the flap tracks, and he was struggling there was no way he could get the bush to even enter the hole where it was meant to be. I watched him struggle and get more and more frustrated, eventually I took pity and took him to one side and said to him was there anywhere, either in the hangar or nearby, where he could get a small quantity of liquid nitrogen, he looked at me as though I was from another planet then it dawned on him what I was proposing he should do to achieve his task. He went off in seartch of the required liquid nitrogen and very shortly returned clutching a metal receptacle, with heavily gloved hands, which contained an amount of the required liquid, merrily bubbling away. He proceeded to immerse the bush in the liquid for a few minutes then took it out and with his gloved hands offered it up to the hole in the flap track, it literally fell into place and when it warmed up it was well and truly secured. A little while later his mentor came by to see how he was getting on with his task and was gobsmacked to see the task completed. He quizzed the apprentice as to how he had succeeded so easily and the apprentice told him about using the liquid nitrogen, his mentor said to him how had he known about how to use it and he replied that a friendly contractor had explained what to do. Engineering is always a learning process, we never stop learning.

Dave

If you want to compare Loctite you need 356776_9294_LT5021_Retaining_Brochure_F

It will tell you all you want to know for joint design and product selection, and if you want to use an equivalent you will have the right loctite to start from.

It includes examples, design advice, performance guides, product selectors and a big table comparing all types across the same wide range of factors.

Neil

Thanks for replies. I think the problem is just that these things take a lot longer to cure on ali than less passive metals as JasonB said. I've used Truloc 231 on steel and brass before, and the joints sieze in under a minute. A couple of the ali joints now seem to have set, but not all - so other factors are at work. Perhaps small differences in the gap have a big effect - I didn't machine everything to the nth degree.

In reply to Jason's question about hole making procedure I just whacked them out in the lathe with a slot drill in the tailstock chuck, so probably not entirely round. Everything cleaned with acetone.

I was by a Halfords today and got something called Granville Bearing Fit and Studlock which seems to have done the job, albeit tardily - apparently it is OK for a 0.5mm gap, so maybe that reinforces Jason's points.

I was looking for a quick fix by using adhesive - in the time this has taken I could have drilled and tapped for grubscrews many times over, but I guess that's how one learns.

Rob.

Geoff, is the round bar in the test piece aluminium or steel? if steel then that would have kicked off the reaction as only one of the two metals being joined needs to be active.

Hi Jason, it's mild steel, so a good point dissimilar materials.

As I had some 1/4" diameter aluminium bar last evening I bonded a short length in the other end of the test piece. I then repeated the test this morning, holding the bar tightly in the vice and rotating the test piece. This time after some effort I managed to crack the joint. So from that you could say that 638 is much more effective used on M.S. as your graph link indicated.

Neil's recent link in an earlier post was of interest, the flow chart on page 16 indicates that 638 was ideal for my jepson engine crankshaft.

I only pinned this crankshaft and crank pin as I had already pre drilled the 1/16" holes in the web. It's now what my Dad would have called " a right belt and braces job". All good fun GEOFF