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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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#1
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rotational vibration
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 |
#2
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rotational vibration
"Karl Townsend" wrote in message anews.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 I should have added, this is what the harmonic balancer on an engine is for. I have no clue about building or designing these. Also there's serious torque here, 60 horse being transmitted at 540 RPM. Karl |
#3
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rotational vibration
Karl Townsend wrote: "Karl Townsend" wrote in message anews.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 I should have added, this is what the harmonic balancer on an engine is for. I have no clue about building or designing these. Also there's serious torque here, 60 horse being transmitted at 540 RPM. Karl Since most of us don't have farms / orchards or use these items, a link to them might help us understand the issue. The "bucking forward to reverse" description makes it sound like something is momentarily freeing up and jumping forward only to have the drive slam into it a fraction of a second later, i.e. uneven loading on the drive. Adding rotating mass somewhere in the drive should change the resonant frequency. Also, you say slowing it down a bit helps, can you speed it up slightly to change the frequency without hurting performance? bumping up to 600 PTO RPM isn't likely to critically over speed anything, but might get you out of the resonant range. The harmonic dampers on an engine are basically a balanced flywheel mounted to the rotating shaft via an elastic (rubber) coupling. |
#4
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rotational vibration
"Karl Townsend" wrote in message anews.com... "Karl Townsend" wrote in message anews.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 I should have added, this is what the harmonic balancer on an engine is for. I have no clue about building or designing these. Also there's serious torque here, 60 horse being transmitted at 540 RPM. Karl One thought, if it is a square shank pto shaft it could be slide together 90 degrees out, causing all kinds of vibration. basilisk |
#5
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rotational vibration
.... Since most of us don't have farms / orchards or use these items, a link to them might help us understand the issue. Sorry, I couldn't find a good link. An airblast spray has a huge squirrel cage fan hooked by a gear box and belts to the tractor PTO. the air from the fan is nozzled down so the air leaves at over 200 mph. Takes a lot of horsepower to do this. The "bucking forward to reverse" description makes it sound like something is momentarily freeing up and jumping forward only to have the drive slam into it a fraction of a second later, i.e. uneven loading on the drive. Adding rotating mass somewhere in the drive should change the resonant frequency. Also, you say slowing it down a bit helps, can you speed it up slightly to change the frequency without hurting performance? bumping up to 600 PTO RPM isn't likely to critically over speed anything, but might get you out of the resonant range. The harmonic dampers on an engine are basically a balanced flywheel mounted to the rotating shaft via an elastic (rubber) coupling. I'll try the rotating mass idea by just boltinh a plate to a large pulley. Thanks, I wasn't thinking this simple. Still, if there was some way to have mass with the elastic coupling, it would work far better. i just have no clue how to build this. |
#6
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rotational vibration
I don't know what an air blast sprayer is, but I have used a lot of 540
rpm pto equipment and I have never had that sort of an issue with the PTO shaft itself. My guess is that the problem is deeper inside the machine and not really related to the PTO shaft at all. If you are repairing it "for about the fifth time", It sounds as though you haven't ever gotten to the real problem. Could you contact the mfr about it or a dealer? It may be a common problem. I guess you have a lot more modern tractor than any of mine. My 60 Hp Case 800 diesel only goes 1450 rpm's at 540 PTO speed. Have you really checked PTO speed? Could it be that you are over revving the sprayer? Pete Stanaitis -------------- 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 |
#7
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rotational vibration
here's a pic of a similar unit:
http://www.jacto.com/sprayers/agricu...arbus_400.html "spaco" wrote in message .. . I don't know what an air blast sprayer is, but I have used a lot of 540 rpm pto equipment and I have never had that sort of an issue with the PTO shaft itself. My guess is that the problem is deeper inside the machine and not really related to the PTO shaft at all. If you are repairing it "for about the fifth time", It sounds as though you haven't ever gotten to the real problem. Could you contact the mfr about it or a dealer? It may be a common problem. I guess you have a lot more modern tractor than any of mine. My 60 Hp Case 800 diesel only goes 1450 rpm's at 540 PTO speed. Have you really checked PTO speed? Could it be that you are over revving the sprayer? Pete Stanaitis -------------- 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 |
#8
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rotational vibration
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 A harmonic balancer is the mechanical equivalent of a second-order low pass filter for electrical signals. The differential equations are identical in form. In addition to mass (inductance) and elasticity (capacitance) you need damping (disspation). In a harmonic balancer this comes from losses in the elastic material (typically rubber), or it may come from the load. |
#9
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rotational vibration
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 So what do you repair to fix the problem? Changing over to 1000 RPM shaft would help if its a PTO shaft problem. You can check that the PTO shaft is telescoping freely. Also check that the tractor PTO shaft and machine shaft are the same height and point at each other. |
#10
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rotational vibration
Karl Townsend wrote: ... Since most of us don't have farms / orchards or use these items, a link to them might help us understand the issue. Sorry, I couldn't find a good link. An airblast spray has a huge squirrel cage fan hooked by a gear box and belts to the tractor PTO. the air from the fan is nozzled down so the air leaves at over 200 mph. Takes a lot of horsepower to do this. So this is basically a leaf blower on steroids? Unless something is loose in the drive line, this should provide a very stable drive line loading. The "bucking forward to reverse" description makes it sound like something is momentarily freeing up and jumping forward only to have the drive slam into it a fraction of a second later, i.e. uneven loading on the drive. Adding rotating mass somewhere in the drive should change the resonant frequency. Also, you say slowing it down a bit helps, can you speed it up slightly to change the frequency without hurting performance? bumping up to 600 PTO RPM isn't likely to critically over speed anything, but might get you out of the resonant range. The harmonic dampers on an engine are basically a balanced flywheel mounted to the rotating shaft via an elastic (rubber) coupling. I'll try the rotating mass idea by just boltinh a plate to a large pulley. Thanks, I wasn't thinking this simple. Still, if there was some way to have mass with the elastic coupling, it would work far better. i just have no clue how to build this. I don't know what your "bolt to large pulley" setup looks like, but if you can have oversized holes in that plate and fit rubber tubing around the bolts that go through it you'll get your elasticity. use a rubber washer on each side of the plate as well and some secure stop like nylock nuts, double nuts with a lock washer between, castle nuts and cotters, etc. so the bolt connections are secure without being over tight. |
#11
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rotational vibration
Karl Townsend wrote: here's a pic of a similar unit: http://www.jacto.com/sprayers/agricu...arbus_400.html Ah. Looking at that, it brings up the question of the spray pump. If there is a problem with the triplex pump with one cylinder not working for some reason, you would get a lighter load each time that piston was supposed to be on it's pressure stroke, possibly allowing the flywheel effect of the blower to drive the pump ahead of the PTO drive momentarily with the PTO catching up a fraction of a second later causing the drive line to experience the forward - reverse bucking you noted. |
#12
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rotational vibration
"Karl Townsend" wrote in message
anews.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 |
#13
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rotational vibration
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 |
#14
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rotational vibration
On Wed, 12 May 2010 10:00:08 -0500, "Karl Townsend"
wrote: 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 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 |
#15
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rotational vibration
On Wed, 12 May 2010 13:46:32 -0500, "David Courtney"
wrote: "Karl Townsend" wrote in message tanews.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. |
#16
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rotational vibration
"Don Foreman" wrote in message ... On Wed, 12 May 2010 13:46:32 -0500, "David Courtney" wrote: "Karl Townsend" wrote in message ctanews.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. BTW, pretty good info in the catalog David found. Karl |
#17
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rotational vibration
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 |
#18
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rotational vibration
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. |
#19
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rotational vibration
"Karl Townsend" wrote in message anews.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 Karl: I'm not clear on how your system would lose mechanical balance. And I don't know all the variables here but it sure sounds close to my balancing my helicopter rotor which was turning at 500rpm. With an electronic balancer that senses where the rotating item is when the accelerometer, or in our case the velocimeter, reading is maxed, it is relatively easy to determine where weight needs to be added to achieve balance. This is however a simple explanation of a single plane balancing operation. Items with some lateral extent like the cranshaft and flywheel system of a car have two planes to worry about. If a single plane balancer could work for you, most helicopter operations have the equipment. My guess is that you are quite a trip from my zip code 93527. If you were close, I do have a balancer and some experience with it on helicopters. |
#20
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rotational vibration
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. SW |
#21
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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
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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
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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
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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
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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
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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
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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
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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
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rotational vibration
On May 12, 11:00�am, "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 |
#30
Posted to rec.crafts.metalworking
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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. |
#31
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rotational vibration
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. BINGO!!!! This is just what I need. And I've got room to install this. You get a FREE BAG OF APPLES. But, just ask Bob Swinney, its hard to collect the prize. Thanks a bunch, Karl |
#32
Posted to rec.crafts.metalworking
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rotational vibration
"Karl Townsend" wrote in message
anews.com... 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. BINGO!!!! This is just what I need. And I've got room to install this. You get a FREE BAG OF APPLES. But, just ask Bob Swinney, its hard to collect the prize. Thanks a bunch, Karl You're welcome... don't worry about the prize, it's the thought that counts. LOL David |
#33
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rotational vibration
On Wed, 12 May 2010 16:32:59 -0500, "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 Going looser will drop the resonant frequency of that part of the system. Doesn't help if the field ends up smelling of burned rubber instead of insecticide though. Lots of ideas from lots of folk. We have faith in you :-) regards Mark Rand RTFM |
#34
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rotational vibration
"David Courtney" wrote in message ... "Karl Townsend" wrote in message anews.com... 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. BINGO!!!! This is just what I need. And I've got room to install this. You get a FREE BAG OF APPLES. But, just ask Bob Swinney, its hard to collect the prize. Thanks a bunch, Karl You're welcome... don't worry about the prize, it's the thought that counts. LOL David Demand Strawberries! |
#35
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rotational vibration
Karl Townsend wrote:
here's a pic of a similar unit: http://www.jacto.com/sprayers/agricu...arbus_400.html "spaco" wrote in message .. . I don't know what an air blast sprayer is, but I have used a lot of 540 rpm pto equipment and I have never had that sort of an issue with the PTO shaft itself. My guess is that the problem is deeper inside the machine and not really related to the PTO shaft at all. If you are repairing it "for about the fifth time", It sounds as though you haven't ever gotten to the real problem. Could you contact the mfr about it or a dealer? It may be a common problem. I guess you have a lot more modern tractor than any of mine. My 60 Hp Case 800 diesel only goes 1450 rpm's at 540 PTO speed. Have you really checked PTO speed? Could it be that you are over revving the sprayer? Pete Stanaitis -------------- 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 If your PTO shafts are not the same height as in this picture it WILL give you vibration! When the rear U joint is not the same height, the speed change from the front U joint is not cancelled by the rear U joint. This is why all good designed machinery has a way to adjust the PTO shaft or drawbar up or down to align the PTO shaft. |
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