Adhesive bond strengths

[Titius BodeParticipant @titiusbode]

[Titius BodeParticipant @titiusbode]

We are having some trouble finding the best adhesive for bonding a plastic propeller to a stainless steel drive shaft. The opposite end of the shaft that holds the weight has been a success as we have a very strong joint that withstands 2500N of force before it breaks but our propeller and shaft joint is breaking at 160N. Nowhere near strong enough for what we want. Any advice?

[Russell EberhardtParticipant @russelleberhardt48058]

It depends on the type of plastic. Some are notoriously difficult to bond to.

You could try one of these

Alternatively how about knurling the end of the shaft, heating it to just under the melting of the plastic, and pushing it intu an undersize hole in the plastic part.

Russell.

[Stewart HartParticipant @stewarthart90345]

As Russell said a straight knurl will give you a good grip when I was an apprentice we made screwdrivers taht, and I'm close to completeing a resiprocating rotary engine that has its piston fixed by that method.

Stew

[Ady1Participant @ady1]

Undersizing can work well

 

I fitted an undersized aluminium cog to my backgear with no keys or anything else and it's done a great job.

I cut a shallow thread in the bore so the material could squish as it was battered into place

Took about 30 minutes to put it on with a bored out plastic drift and at times it handles some very high torque

 

Being plastic though, it's unlikely to have a lot of resistance to torque

Maybe putting a metal insert into the plastic then put the metal insert onto the shaft would be stronger

The further you can move the plastic away from the centre of the shaft the greater the resistance to torque issues you should get

Edited By Ady1 on 11/05/2012 15:15:22

[Jeff DaymanParticipant @jeffdayman43397]

Titius Bode-

What type of model is the propeller for?

What is shaft diameter and engaged length in hub, and what is prop dia and max RPM?

What is the prop made of?

You may need to incorporate a positive drive feature on the shaft to hub joint. Look at photos of small aircraft for ideas on that. Adhesives are not generally recommended for these joints in model aircraft due to extremely high forces from rapid acceleration and deceleration. The strongest adhesives have max shear strength of around 3000 psi max. Joints with large surface area can be quite strong, but joints with small areas will not be. As others have mentioned, many plastics do not bond with any adhesives well.

JD

Edited By Jeff Dayman on 11/05/2012 16:22:36

Edited By Jeff Dayman on 11/05/2012 16:23:02

[WeldsolParticipant @weldsol]

As a thought what about threaded the shaft and prop which should work, obviously using the handing off the thread so it would tighten against rotation ( that is unless you want to reverse rotation direction if this is the case then you could also cross pin it)

Paul

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

All other things being equal the axial separation strength of a bonded cylindrical joint just depends on the wetted area and the torquewise separation depends on the wetted area and the radius of interaction .

If your bonded joint is breaking as it is designed now then you need to improve the geometry of the joint .

Possibles for improving geometry :

Increase shaft dia locally .

Ferrule the propellor so that bond to plastic is at large diameter and then bond ferrule to shaft .

Note : When bonding difficult plastics like polythene it is advantageous to put deep random scrapes in the bore . With hard setting glue like Araldite or some of the Loctites the glue that enters the scrapes is strong enough to act as a mechanical key and can significantly improve joint strength .

You can develop the scrapes forming keys idea for use in a production environment and use a cut in or moulded in pattern . 

Edited By MICHAEL WILLIAMS on 12/05/2012 15:01:48

[Jeff DaymanParticipant @jeffdayman43397]

6 days later, several good replies, and no response from OP Bode. Not good.

JD

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