Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old May 12th 10, 11:49 PM posted to rec.crafts.metalworking
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Default rotational vibration


"Pete C." wrote in message
ster.com...

Karl Townsend wrote:

What happens when you change the tension on the fan drive belts? If
they
are
implicated at all, that'll change the resonant frequency. It's a bit
far
to
drive over to Blighty so we can instrument it up and workout where the
resonance is :-(

Mark Rand (Did similar work on power station foundations once)
ETFM


I've never tried that. I keep the eight belts pretty tight, 1/2"
deflection
in the three foot between pulley spacing. can't go tighter, I'd take out
bearings. What do you think running loose would do? Not much margin here,
I
smoked all the belts once, pretty spendy to rebelt this unit.

Karl


I recommend you closely inspect the spray pump as noted in my other
post. If it is a triplex pump like the one on the other unit you posted
a link for it could very well produce a "lumpy" torque load if one of
the pistons was not functioning like from a stuck inlet valve.

The other thought, is that if this lumpiness occurs once per PTO shaft
revolution i.e. 9 times a second, something may be bent, such as the
shaft the pulleys are on, causing the belt tension to cycle every
revolution.


Thanks for the thoughts. This unit has a centrifical pump, no bumps there
plus it only uses a couple horse. You have a thought on bent, I know its not
in the shafts, but possibly the fan itself is bent. The entire fan could be
removed and put on some sort of unit to check balance and vibration. Anyone
know where I might find equipment to do this?

Karl



  #22   Report Post  
Old May 13th 10, 12:19 AM posted to rec.crafts.metalworking
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Posts: 3,286
Default rotational vibration


"Sunworshipper" wrote in message
...
On Wed, 12 May 2010 10:00:08 -0500, "Karl Townsend"
wrote:

I'm repairing the same issue on my airblast sprayer for about the fifth
time. Own something long enough and the same problems keep repeating. the
sprayer has a vibration in it at 2500 tractor RPM, 540 PTO RPM. The
vibration is not like a tire out of balance but its a bucking forward to
reverse. When it gets a little lose, in a few more hours of run it will
damn
near shake the tractor off the ground. Its also a natural harmonic at
this
RPM, slow down and the vibration goes away. Unfortunately, this REALLY
reduces sprayer performance.

I'm replacing the entire PTO shaft and tightening up the clearance in the
gear box again. if everything is tight, the problem is less severe. The
is
working on the symptom, not the cause.

This is a long shot, anybody know about balancing this sort of vibration
or
changing the natural harmonic frequency?

Karl


I'll take a stab at this one. This is a insecticide sprayer, right? If
so, that kind of stuff is awfully hard on equipment. It eats at metal
and is sticky. Is the fan clean? Could it be nasties built up in the
clutch, maybe when on down time leaking in the same position.
Bad bearings, that would do it. Sucking air between the tank and pump?

Just someone tring to help that klnows what a
Malathion-Methyl-Parathion-Ketone Flop is.


Gosh, I don't know what that is.

SW


Thanks, everybody, for all the thoughts. Still waiting on Julie to get back
with parts. She's been gone eight hours now. Looks like I work the night
shift to get back in the field tomorrow. I'll plan on tearing the unit down
for a rebuild this winter. its due.

Karl


  #23   Report Post  
Old May 13th 10, 01:19 AM posted to rec.crafts.metalworking
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Posts: 6,746
Default rotational vibration


Karl Townsend wrote:

"Pete C." wrote in message
ster.com...

Karl Townsend wrote:

What happens when you change the tension on the fan drive belts? If
they
are
implicated at all, that'll change the resonant frequency. It's a bit
far
to
drive over to Blighty so we can instrument it up and workout where the
resonance is :-(

Mark Rand (Did similar work on power station foundations once)
ETFM

I've never tried that. I keep the eight belts pretty tight, 1/2"
deflection
in the three foot between pulley spacing. can't go tighter, I'd take out
bearings. What do you think running loose would do? Not much margin here,
I
smoked all the belts once, pretty spendy to rebelt this unit.

Karl


I recommend you closely inspect the spray pump as noted in my other
post. If it is a triplex pump like the one on the other unit you posted
a link for it could very well produce a "lumpy" torque load if one of
the pistons was not functioning like from a stuck inlet valve.

The other thought, is that if this lumpiness occurs once per PTO shaft
revolution i.e. 9 times a second, something may be bent, such as the
shaft the pulleys are on, causing the belt tension to cycle every
revolution.


Thanks for the thoughts. This unit has a centrifical pump, no bumps there
plus it only uses a couple horse. You have a thought on bent, I know its not
in the shafts, but possibly the fan itself is bent. The entire fan could be
removed and put on some sort of unit to check balance and vibration. Anyone
know where I might find equipment to do this?

Karl


If the "bump" is indeed at the rotational frequency of the PTO, I'd be
looking at the drive sections that rotate at that RPM. Presumably the
fan is overdriven from the 540 RPM PTO to a higher RPM so an issue there
wouldn't manifest once per PTO rev.

If the drive pulleys from the PTO shaft aren't concentric, there would
be a cyclic variation in belt tension on each revolution, and since the
belt will tend to move in and out in the groove with tension, it would
also translate into a cyclic change in the drive ratio. It could be
subtle, but with that much HP and mass involved, it could become
significant at that resonant frequency.

Since you report that the problem keeps coming back, it may be that an
issue like pulley concentricity has always been there, but becomes more
apparent over time as everything loosens up and the vibration can have
more effect. Perhaps get out the dial indicator and mag base and check
the run out on the drive pulleys?
  #24   Report Post  
Old May 13th 10, 03:41 AM posted to rec.crafts.metalworking
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Posts: 3,286
Default rotational vibration


"Pete C." wrote in message
er.com...

Karl Townsend wrote:

"Pete C." wrote in message
ster.com...

Karl Townsend wrote:

What happens when you change the tension on the fan drive belts? If
they
are
implicated at all, that'll change the resonant frequency. It's a bit
far
to
drive over to Blighty so we can instrument it up and workout where
the
resonance is :-(

Mark Rand (Did similar work on power station foundations once)
ETFM

I've never tried that. I keep the eight belts pretty tight, 1/2"
deflection
in the three foot between pulley spacing. can't go tighter, I'd take
out
bearings. What do you think running loose would do? Not much margin
here,
I
smoked all the belts once, pretty spendy to rebelt this unit.

Karl

I recommend you closely inspect the spray pump as noted in my other
post. If it is a triplex pump like the one on the other unit you posted
a link for it could very well produce a "lumpy" torque load if one of
the pistons was not functioning like from a stuck inlet valve.

The other thought, is that if this lumpiness occurs once per PTO shaft
revolution i.e. 9 times a second, something may be bent, such as the
shaft the pulleys are on, causing the belt tension to cycle every
revolution.


Thanks for the thoughts. This unit has a centrifical pump, no bumps there
plus it only uses a couple horse. You have a thought on bent, I know its
not
in the shafts, but possibly the fan itself is bent. The entire fan could
be
removed and put on some sort of unit to check balance and vibration.
Anyone
know where I might find equipment to do this?

Karl


If the "bump" is indeed at the rotational frequency of the PTO, I'd be
looking at the drive sections that rotate at that RPM. Presumably the
fan is overdriven from the 540 RPM PTO to a higher RPM so an issue there
wouldn't manifest once per PTO rev.

If the drive pulleys from the PTO shaft aren't concentric, there would
be a cyclic variation in belt tension on each revolution, and since the
belt will tend to move in and out in the groove with tension, it would
also translate into a cyclic change in the drive ratio. It could be
subtle, but with that much HP and mass involved, it could become
significant at that resonant frequency.

Since you report that the problem keeps coming back, it may be that an
issue like pulley concentricity has always been there, but becomes more
apparent over time as everything loosens up and the vibration can have
more effect. Perhaps get out the dial indicator and mag base and check
the run out on the drive pulleys?


Thanks Pete, more good suggestions.

Julie hit a home run on the PTO rebuild. The fleet farm store was stocked
out. So, she found a specialty drive line shop and had everything rebuilt
with top-of-the-line parts. She's not only a great go-fer, she's a good
looker too. (That means she can find stuff)

I'm puttin' the machine back in the field tomorrow but a complete rebuild on
this unit is job 1 at end of season.

Karl


  #25   Report Post  
Old May 13th 10, 04:30 AM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Feb 2010
Posts: 1,624
Default rotational vibration

On Wed, 12 May 2010 10:00:08 -0500, "Karl Townsend"
wrote the following:

I'm repairing the same issue on my airblast sprayer for about the fifth
time. Own something long enough and the same problems keep repeating. the
sprayer has a vibration in it at 2500 tractor RPM, 540 PTO RPM. The
vibration is not like a tire out of balance but its a bucking forward to
reverse. When it gets a little lose, in a few more hours of run it will damn
near shake the tractor off the ground. Its also a natural harmonic at this
RPM, slow down and the vibration goes away. Unfortunately, this REALLY
reduces sprayer performance.

I'm replacing the entire PTO shaft and tightening up the clearance in the
gear box again. if everything is tight, the problem is less severe. The is
working on the symptom, not the cause.

This is a long shot, anybody know about balancing this sort of vibration or
changing the natural harmonic frequency?


C'mon, Karl. You know better than to ante up with such scant tidbits
of info. What sprayer, what tractor, what pump, how straight is the
PTO shaft in use, does it happen with the pump disconnected, is there
any play in the PTO yoke-to-shaft interface, are the yokes greased up
good and slick, etc.?

--
You will find that the mere resolve not to be useless,
and the honest desire to help other people, will, in
the quickest and delicatest ways, improve yourself.
-- John Ruskin


  #26   Report Post  
Old May 13th 10, 04:45 AM posted to rec.crafts.metalworking
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Posts: 1,624
Default rotational vibration

On Wed, 12 May 2010 16:26:55 -0500, "Karl Townsend"
wrote the following:


"Don Foreman" wrote in message
.. .
On Wed, 12 May 2010 13:46:32 -0500, "David Courtney"
wrote:

"Karl Townsend" wrote in message
. octanews.com...
I'm repairing the same issue on my airblast sprayer for about the fifth
time. Own something long enough and the same problems keep repeating.
the
sprayer has a vibration in it at 2500 tractor RPM, 540 PTO RPM. The
vibration is not like a tire out of balance but its a bucking forward to
reverse. When it gets a little lose, in a few more hours of run it will
damn near shake the tractor off the ground. Its also a natural harmonic
at this RPM, slow down and the vibration goes away. Unfortunately, this
REALLY reduces sprayer performance.

I'm replacing the entire PTO shaft and tightening up the clearance in
the
gear box again. if everything is tight, the problem is less severe. The
is working on the symptom, not the cause.

This is a long shot, anybody know about balancing this sort of vibration
or changing the natural harmonic frequency?

Karl


Elastomeric coupling? (page 2): "The flexible element absorbs the
unavoidable torsional vibrations..."
http://pdf.directindustry.com/pdf/ko...-46550-_2.html


Put a flywheel on the load side of this and you have a harmonic
balancer.

Karl, what is the frequency of the vibration? Is it about 9 Hz
(synchronous with PTO speed) or is it considerably lower? If it's
lower, and if there is some sort of governor that maintains PTO speed
at 540 RPM in presence of varying load, then the vibration might be
that governor hunting.


How's you know that??? Yes its right at 9 bangs per second.


Aha! 540/9 = 60. It's merely a 60 cycle hum, Karl. Throw a capacitor
at it. gd&r


BTW, pretty good info in the catalog David found.


I thought your Arbus exploded diagrams were fantastic, too.

--
You will find that the mere resolve not to be useless,
and the honest desire to help other people, will, in
the quickest and delicatest ways, improve yourself.
-- John Ruskin
  #27   Report Post  
Old May 13th 10, 05:24 AM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: May 2010
Posts: 2
Default rotational vibration

Is the shaft 'in phase' and not twisted? I have put as high as 140 hp
through a 540 pto shaft running a 66 inch blower spinning a fan weighing
close to 200 pounds. I never had any vibration problems at any speed up to
600 rpm. Rent, buy, or borrow an adjustable strobe light and check
different areas as it runs. If the fan is easily dissembled rest shaft of
each end of the fan on parallel, level angle irons with the ^ up to check
for balance.

"Karl Townsend" wrote in message
anews.com...

"Sunworshipper" wrote in message
...
On Wed, 12 May 2010 10:00:08 -0500, "Karl Townsend"
wrote:

I'm repairing the same issue on my airblast sprayer for about the fifth
time. Own something long enough and the same problems keep repeating. the
sprayer has a vibration in it at 2500 tractor RPM, 540 PTO RPM. The
vibration is not like a tire out of balance but its a bucking forward to
reverse. When it gets a little lose, in a few more hours of run it will
damn
near shake the tractor off the ground. Its also a natural harmonic at
this
RPM, slow down and the vibration goes away. Unfortunately, this REALLY
reduces sprayer performance.

I'm replacing the entire PTO shaft and tightening up the clearance in the
gear box again. if everything is tight, the problem is less severe. The
is
working on the symptom, not the cause.

This is a long shot, anybody know about balancing this sort of vibration
or
changing the natural harmonic frequency?

Karl


I'll take a stab at this one. This is a insecticide sprayer, right? If
so, that kind of stuff is awfully hard on equipment. It eats at metal
and is sticky. Is the fan clean? Could it be nasties built up in the
clutch, maybe when on down time leaking in the same position.
Bad bearings, that would do it. Sucking air between the tank and pump?

Just someone tring to help that klnows what a
Malathion-Methyl-Parathion-Ketone Flop is.


Gosh, I don't know what that is.

SW


Thanks, everybody, for all the thoughts. Still waiting on Julie to get
back with parts. She's been gone eight hours now. Looks like I work the
night shift to get back in the field tomorrow. I'll plan on tearing the
unit down for a rebuild this winter. its due.

Karl




  #28   Report Post  
Old May 13th 10, 12:18 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Jun 2007
Posts: 3,286
Default rotational vibration

....
C'mon, Karl. You know better than to ante up with such scant tidbits
of info. What sprayer, what tractor, what pump, how straight is the
PTO shaft in use, does it happen with the pump disconnected, is there
any play in the PTO yoke-to-shaft interface, are the yokes greased up
good and slick, etc.?

....

All Right, Larry, you're agitating.

I have to say RCM really came through for me this time. Whole bunch of good
ideas. Even with all the political OT crap, this is a pretty good group.
BTW, this problem is all Obama's fault - everything else is.

Karl



  #29   Report Post  
Old May 13th 10, 02:45 PM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: May 2010
Posts: 7
Default rotational vibration

On May 12, 11:00´┐Żam, "Karl Townsend"
wrote:
I'm repairing the same issue on my airblast sprayer for about the fifth
time. Own something long enough and the same problems keep repeating. the
sprayer has a vibration in it at 2500 tractor RPM, 540 PTO RPM. The
vibration is not like a tire out of balance but its a bucking forward to
reverse.


Universal joints are widely used to transfer rotational motion
through shafts which are not perfectly aligned. A feature of these
devices is that the output shaft does not rotate in precise synch with
the input shaft. There is a cyclic "lead" and "lag" introduced by the
mechanism. A nice explanation of this phenomenon is presented in the
wikipedia posting on universal joints. Use google with search words
"universal joint" and pick up on the Wikipedia link.
In practice, universal joints are used in pairs, aligned so that
the cyclic lead and lag introduced by the first joint is cancelled out
by by the second joint. This correcting action is dependent on having
the two joints mounted in phase with each other, and this is why many
setups use a rectangular telescoping shaft to connect the two joints.
That way, it is impossible to get them connected out of phase. If
mounted incorrectly, a pair of U-joints can aggravate the lead-lag
problem rather than correct it.
The symptom described in the case of Karl's sprayer is the sort
of pulsing torque which would be introduced by either a single U-joint
or a pair of U-joints which got mounted out of phase. My belated
input to this discussion is a suggestion that Karl to grab a cool
refreshment and take a reflective look at his setup. Are the U-joints
in phase? (Refer to the wiki photo to see the right way.) Are the
PTO shaft and sprayer shaft set up to be parallel, and not too far out
of alignment? With power off, rotate the shaft by hand to feel for
increased resistance at some point in a complete rotation.

Pat



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Old May 13th 10, 05:49 PM posted to rec.crafts.metalworking
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Posts: 124
Default rotational vibration

"Karl Townsend" wrote in message
anews.com...

Elastomeric coupling? (page 2): "The flexible element absorbs the
unavoidable torsional vibrations..."
http://pdf.directindustry.com/pdf/ko...-46550-_2.html


I bet this would work real well if I could redesign the drive line to use
a coupling. maybe this winter.

Thanks for the link.

Karl


It looks like the DynaFlex LCR series is made for PTO applications...
maybe there is one that will "bolt right on" without too much effort?
http://www.lord.com/portals/0/vibrat..._couplings.pdf
Catalog page 103... which is page 17 of the pdf; shows the LCR series.
There is a note that they can be either "through bolted"... or the metal
inserts can be tapped or counter-bored to accept fasteners; so there is a
variety of mounting choices.




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