[TheForge] Another pulley question (brazing cracks)

[Ralph Sproul]

	Mike, I find cast machine parts weld fairly well if they are clean. It is
the oily parts that really give you the hard time as the oil has impregnated
the material or sap can do the same thing in a sawmill.

	The part your kind of leaving out on this note is information being 2
cracked spokes out of 3? 0r, 2 out of 4?

	 Brazing is a lower temp than cast rod welding - so there isn't as much
stress implied during the repair.  Of course your still doing a high temp
repair and preheating the entire thing to braze would be your best bet for
slow cooling not to damage the repaired area.
	I usually V out the damaged crack area - mostly to remove any chance of a
crack running into a loose "chard" that looks intact - but really isn't.
Grinding usually makes this obvious. I also drill the end of cracks - but in
this case I'm assuming the spokes are pretty much broke off/thru......if
not - drill the end of the cracks.
	Your saying the sheave is cracked on two spokes - so your center should be
intact, and the outer perimeter true to it correct? I'm assuming here that
you've got at least 4 spokes and 2 cracked....... You can take this Sheave
and put it on a shaft (and run it in V blocks against a fixed point to see
if it's out)- to make sure the cracks aren't an idication that the center is
no longer in the center of the pulley - which no matter how you repair one
that's out - it's gonna vibrate like all get out.
	Now once you know the pulley is starting into the repair as centered and
true - you can proceed figureing you stand a good chance of coming out good
on this one cuz you haven't started with a piece of junk and wonder why it
wobbles.

	The 900 rpm is much better than a 3600 rpm sheave duty for a
repair.......but still a consideration to be careful about. I'd use the v
blocks and shaft again after your done - and you'll tell if you've got a
true hub after the repair - then you'll be able to mount it and see how she
runs for vibration.

	Using your bricks to make an oven to preheat the entire thing is a good
idea - then braze it up, and let her cool slowly with the heat of the bricks
making it cool even slower.  Cast iron is kind of a pest to repair - but if
you go thru the motions and do a decent job - it should work and hold up
just fine.  Just heating a spoke with a cold rim around it - could leed to
stress......that's why I'd heat the whole thing.

That's the way I'd approach it I guess......  What the heck, it's junk till
you try - you can't loose much exept'n for some gas and rod.  Of course when
you first fire it up (to 900 rpm) stand to the side in case it gets exciting
quick.   :-)    If it lasts 10 minutes - it'll probably last your life time.

Ralph

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net]On Behalf Of Mike Spencer
Sent: Thursday, November 24, 2005 11:34 PM
To: theforge at mailman.qth.net
Subject: [TheForge] Another pulley question (brazing cracks)



Ralph and others with cast iron brazing experience:

What do you think of brazing two spokes cracked near the hub in a
2-sheave cast iron pulley?

It's ca. 16" diameter, takes two B belts.  I would use it 900 RPM on a
2" shaft, 15-20 HP and a fair amount of starting torque but no impact
loads while running.

I have refractory brick and ceramic blanket so I could build a box and
pre-heat it pretty good with propane, then braze it.  Any other
precautions?  Bad idea altogether?  Grind a deep V?  Cool slowly? Very
slowly?

I've brazed up some cast stuff before but never a spoked wheel and
never for a dynamic load.  Suggestions or tips welcome.


Background if yr interested:

I have a 20 HP Wisconsin air-cooled, 2400 RPM industrial engine.  Have
in mind connecting it to a small jackshaft with a flexible coupling
(or maybe U-joints). A 6" pulley on the jackshaft would drive the 16"
pulley on a heavier shaft which in turn would drive the 24" gear on my
A&O 300# hammer.


- Mike

--
Michael Spencer                  Nova Scotia, Canada       .~.
                                                           /V\
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^

--


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