Interesting finding on Loctite and taper fits

SBAER · Apr 30, 2020

We did some experiments at work to determine what the torque carrying capability of joints made by interference fits created by tapers (12-16 degrees included angle) on shafts/hubs. These parts were steel and the surface finish was turned not ground. Using green Loctite retaining compound almost doubled the torque carrying capacity. I was surprised that loctite could have such a significant effect, has anyone else noticed anything like this?

GregSY · Apr 30, 2020

Well, it is Loctite, after all....

There's not enough data to tell if you really did a 'scientific' experiment or not.

Most of all, the amount of power transmitted is very significant. If you are transmitting 2 lb-ft, I can see getting to 4. Especially if your taper diameter starts at 5".

But getting 20,000HP through a 5.5" taper instead of 10,000HP? That would be another story.

And...being a turned surface is also pretty questionable...tapers are really a ground finish situation and percentage contact is critical to their effectiveness.

thermite · Apr 30, 2020

SBAER said:
.. has anyone else noticed anything like this?

Only "sort of". Usta make my screwdriver shafts (drill rod) to near-as-dammit a standard long taper I happened to have reamers for.

Everything done, handle gripped in a 4-Jaw, put MAPP gas torch to it.

Screwdriver shaft gripped in a TS drill chuck. I'd down the torch, cut power, hard RAM the shaft into the mating taper, let friction marry them up as the chuck was "braked" to a stop.

No Fine Way that shaft was coming back out of than long taper. Twist it in half down at the blade-tip area first, and HAVE done.

Tapers can be handy features. Loctite jest lets yah "get to the end" a tad lazier and faster with sorrier-finish ones.

Mind "sorry" is down in the NANO surface details, so all of 'em can benefit, no matter how well ground.

You'd probably have to section, polish, etch the joining, send out for microscopy shots to collect the proofs?

PeteM · Apr 30, 2020

Adhesively-bonded friction interfaces: Macroscopic shear strength prediction by microscale finite element simulations - ScienceDirect

Phil in Montana · Apr 30, 2020

If you really want it bite, freeze the shaft to -50 and loctite the taper and press it together ....Phil

dian · Apr 30, 2020

noticed? no, but would not have expected otherwise, as they state to use it for press fits in the instructions.

btw, you can use anaerobics only once without thorough cleaning of the surfaces. the effect of surface prep. on strenght would be a more interesting one to discuss.

steve-l · May 1, 2020

GregSY said:
Well, it is Loctite, after all....

There's not enough data to tell if you really did a 'scientific' experiment or not.

Most of all, the amount of power transmitted is very significant. If you are transmitting 2 lb-ft, I can see getting to 4. Especially if your taper diameter starts at 5".

But getting 20,000HP through a 5.5" taper instead of 10,000HP? That would be another story.

And...being a turned surface is also pretty questionable...tapers are really a ground finish situation and percentage contact is critical to their effectiveness.

I think for real security of grip all tapers need to be properly lapped, as done with prop shafts regardless of what machine process is used to create the mating tapers. That said, not all tapers are used for the purpose of grip or grip alone. For instance, tapers are very often used for precise repeatable positioning as well.. So, if the purpose of the OP's test is to compare max torque capability with and without Loctite, the joint would have to be a perfectly lapped one to start with. I think the observed increase in torque the OP witnessed could very well be that the Loctite is making up for a less than perfect mate of the tested taper.

gregormarwick · May 1, 2020

barbter said:
BTW - What is "green loctite"?
You do realise they have different numbers for different applications?

Well, he did say retaining compound...

638 is retaining compound, green colour.

MattiJ · May 1, 2020

gregormarwick said:
Well, he did say retaining compound...

638 is retaining compound, green colour.

Add 603, 6300, 620 and 648 to your list.

gregormarwick · May 1, 2020

MattiJ said:
Add 603, 6300, 620 and 648 to your list.

Fair enough!

638 is just what I have in my cupboard - used it for very large, very thin bronze sleeves that needed to be a press fit but were too fragile to actually press in. Worked great.

DanielG · May 1, 2020

There are way more than just those. The Loctite Adhesive Sourcebook has a handy chart showing which ones to use when.

Scruffy887 · May 1, 2020

OP, for every action there is an equal and opposite criticism.
But this thread is all good.

Mark Rand · May 1, 2020

or 2xx is low strength
5xx is sealing/hydraulic
6xx is high strength

and others?

SBAER · May 1, 2020

Thanks for the Sciencedirect link I will follow that up. We could have spent lots more money doing the test that's for sure. This joint is drawn together to the point that the hub is almost yielding, I would have guessed that the loctite would be squeezed right out.
The reason I brought it up was mostly for people like me that mostly do one-off repairs and need all the help they can get to make their less than perfect workmanship hold together.

DanielG · May 1, 2020

Mark Rand said:
or 2xx is low strength
5xx is sealing/hydraulic
6xx is high strength

and others?

That's not correct. The 600 series encompasses the retaining compounds, not all of which are high strength, like 641. 200 series include the threadlockers, and cover a range of strengths; 222 (purple) and 263 (red) are very different beasts.

jim rozen · May 1, 2020

barbter said:
Your surface finishes have deviations - peaks and troughs....

+1

The ast-turned parts probably had about five for ten percent surface contact between the two mating surfaces. Locktite
increased that substantially. If you *really* want them to stay together, flux, heat, and apply ez-flow silver solder....

GregSY · May 1, 2020

The people in industry who 'really' know their stuff when it comes to tapers specify an 85% or greater contact as determined by bluing/checking.

jim rozen · May 1, 2020

GregSY said:
The people in industry who 'really' know their stuff when it comes to tapers ..

Typically those folks don't use as-turned parts. If you put enough prussian blue on it, anything looks good.

DavidScott · May 1, 2020

Yes, I have held 1/4" cutting tools with great success, and the tools were used until failure with heavy cutting forces. If you do this you really need to use the correct "Loctite" for the job. The different sealants require different gaps for the glue line. I typically use 263 when gluing two pieces of metal together, but have others if the gap needs to be smaller. Glue a 1/2" square piece of metal to a bigger one and then try breaking it apart. I am pretty sure you will be surprised at how well it holds. Damn fine tool for the toolbox.

GregSY · May 1, 2020

The concept is you blue the taper, then use a taper fit gauge to see how much of the blue is undisturbed. The goal is have as little blue left as possible, not as much. Leftove blue shows an absence of contact. It's a method used by the top machinery people....for example, if you are manufacturing a 200MW steam turbine.

Interesting finding on Loctite and taper fits

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