Set screws into mild steel shaft 2

[geesamand]

Hello,

I'm working with a few mechanical seal vendors on a product where our customers will be specifying a variety of seals depending on the application of our machine. This machine has a nickel-plated carbon steel shaft or 316L shaft. A couple of seal vendors are proposing cartridge designs that put cup-point set screws against the shaft on journal that has the o-ring fit of the seal rotor. (They don't want to make a special rotor that extends to the journal where the cup points belong)

I am concerned that the set screw damage to the shaft will cause damage to the o-ring even if the damage is dressed well before installing the new seal. Plus if anyone decides to dismount the seal in working condition they will need a new o-ring before re-installing.

Am I worried about nothing? Or is this a major installation and reliability issue? Your thoughts and experiences are appreciated.

David

 

[MikeHalloran]

I would call it crap. I hate setscrews.

OTOH, maybe you can arrange things so the seal vendors take the customer abuse, while you make a fortune selling replacement shafts.

OR, maybe you can arrange it so that the seal and shaft are handled and replaced as a unit, so you get all the profit from all the replacement parts.



Mike Halloran
Pembroke Pines, FL, USA

 

[geesamand]

Both novel ideas, although neither is technically feasible on this machine.

My third concern is that the customer will be disappointed about the set screw arrangement and let it reflect poorly on us.

 

[MikeHalloran]

There are now a fair number of secure shaft attachment details for pulley hubs and such that grip like crazy and don't mar the shaft.

You'd think the mechanical seal folks would at least offer some alternative that's less barbaric than setscrews.

Have you got the process control, and the stones, to mount the seal rotor solely with a Loctite retaining compound? Do consult with your Loctite rep about which cleaners and catalysts to use, but it seems eminently do-able.





Mike Halloran
Pembroke Pines, FL, USA

 

[flexibox]

This depends on the seal design. You can use grub screws that bite onto the shaft sleeve that do not touch the shaft. This will be a friction drive. You can also use shrink discs or feder rings but these options add costs to the seal.
I am sure that if you are dealing with a reputable seal company they will supply seals without grub screws directly on the shaft. Providing you are willing to pay for this feature you should have NO issues moving away from grub screws on the shaft.

Having said that I have seen hundreds of seals using grub screws directly on the shaft. If you use unbrako grub screws they tend to bite into the shaft and after you remove the seal from the shaft the oring should still be ok but if you are removing the seal you would replace all oring a anyway. Good practice is to dimple the shaft.

Trust this helps

 

[Tmoose]

Depending on the holding requirement the seal manufacturer will guarantee (until the first warrantee claim) and the service temperature maybe on of these wiil work.

http://www.palmerbolt.com/product_images/catalog19896/ssbrass.jpg

http://www.lexingtonsetscrews.com/nylon_tip_set_screws.html

Creating a drill point in the shaft at assembly, or a flat during manufacturing and using a cup point screw is much more secure, but may be tough for the maintenance crew to hit the second time