V Belt Pulley Bore Diameter 5

[edison123]

I received a 250 HP motor with some "noise" problem. On examination, I found that the noise was coming from the 8 groove, V belt pulley of the motor.

The motor shaft dia is 109.92 mm and the pulley bore is 110.20 mm i.e. 0.28 mm loose fit. The key was also loose both in the shaft and the pulley.

The motor runs smoothly without the coupling.

I would appreciate if any one can point out the kind of fit of V belt pulleys (loose fit, mallet fit or interference fit) require.

Any pointers to web references would be nice.

(I did google v belt pulleys but got 43,800 hits and the few sites I saw did not have this fit information).

Thanks

 

[JJPellin]

For this large a shaft and such a high horsepower, this should be an interference fit. For ease of assembly, this is usually accomplished with a tapered bushing. We commonly use QD bushings or Taperlock (spelling?) bushings. In both cases, the bushing is split and sized to slip over the shaft. When the bushing is bolted to the pulley, the taper on the OD of the bushing pulls into the taper in the ID of the pulley which compresses the bushing against the shaft and creates the interference. If you are stuck with the use of a straight bore pulley, it can be very difficult to achieve an interference fit and still have assembly and disassembly practical. I would suggest that you purchase a new pulley manufactured with a tapered bushing.

 

[edison123]

Thx JJPellin.

It is either a pulley with a taper hub & sleeve or reshaft the motor. It is a no-brainer.

My client has been running this motor with this issue (production pressure) for over six months. The end result was the damaged motor bearings due to all the knocking.

 

[Cheddarcaveman]

I would deffinately go for a taperLock type bushing for ease of assembly/dis-assembly. The better known ones are Fenner - please see the link below.

http://www.fptgroup.com/products/taperlockbushes.asp

 

[bingopin]

Taper lock bushings are widely used for an application like this and work very well. Having said that, be aware that the bushing will crack or split very easily in the key slot.
Have seen several split over the years.

 

[MikeHalloran]

Until you can get a proper pulley with a taper-lock bushing, Loctite makes a compound with sugar- like goobers in it that would take up the clearance. Sorry, I forget the actual name, but your local Loctite rep will know.





Mike Halloran
Pembroke Pines, FL, USA

 

[edison123]

Thank you all for your helpful tips. I have already advised the client to go for the taper lock coupling.

Mike

Will loctite work for such a clearance (0.28 mm) ?

 

[MikeHalloran]

I think Loctite calls it "gap filling sealant" or something like that. It's _intended_ for problems like yours.

Another alternative is a wrap of .005" shim stock, and regular Loctite.

Again, temporarily, until you get the correct part.




Mike Halloran
Pembroke Pines, FL, USA

 

[jdubu]

Another thing to consider is that with an 8 groove pully you should be useing a matched set of belts. Other wise the slight differance in belt lenght cause both vibration and lower belt life. I also agree fully with the other guys the pully needs a qd or eq bushing and a tight fitting key

 

[Artisi]

The fenner coupling is a wise choice based on experience of hundreds of unit in heavy duty applications including direct coupled diesel engine driven pump sets.

 

[edison123]

Thank you all for your posts.

I have two questions.

1. The existing pulley is cast iron. Should I go for cast steel in case of taper lock ?

2. The existing pulley has 4 holes of 2 inches dia centrally in the thin stem area above the central hub. What is the purpose of these holes ?

(One theory is weight reduction, but given the total weight of the pulley, these holes on the thin stem do not save much in weight.)

 

[MikeHalloran]

1. Use whatever material is offered in the size that you need.

2. My guess is that the holes are intended to provide relief of shrinkage stresses and prevent cracking as the casting cools. In a much older casting, you'd see curved spokes instead.





Mike Halloran
Pembroke Pines, FL, USA

 

[diskullman]

Belt matching is almost obsolete, as all belt manufacturer's have tightened up their tolerences. You can still order matched belts, at a much higher price, they just give you belts that are consecutive from the mandrel. For excessive belt whip or turnover, you can get a banded belt, which has an external cover. For excessive vibration, I would recommend the Fenner Power-Twist link belt, as it transmits the proper horsepower, and it's link design absorbs a lot of vibration that normal belts will transmit.

Russell Giuliano

 

[edison123]

One final question

I have a 1300 dollar quote for cast steel and a 1000 dollar quote for cast iron pulley.

Is spending additional 300 dollars for cast steel pulley worth it (in terms of better strength, less brittle, durability etc.) ?

Also, are the v-belts different for cast steel and cast iron pulleys ?

 

[MikeHalloran]

The cast steel part is less likely to fracture when the maintenance crew drops it. Stuff happens.

I'm not aware of a preference on the part of the belts.



Mike Halloran
Pembroke Pines, FL, USA

 

[SteveWag]

You should caution your installimg guys to follow the instructions concerning NOT lubricating the taper surfaces. I've seen a number of cracked or broken pulleys when millwrights put Never-Seeze or some such stuff on the taper. There will be jacking holes provided for removal, don't worry about rusting or freezing.

Steve

 

[edison123]

A feedback.

Motor fitted with cast iron, taperlock pulley. Working fine for the past 3 days.

I thank you all for your valuable tips.

*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[quark]

You may have problems with cast iron if the alignment is not proper or if you have excessive tension on the belts. I saw the pulleys dusting off (I don't know a better word, let us say powdered at the fit) and ultimately being thrown out of the shaft. Secondly, you should be careful while removing the tapered bush. Many people use screw drivers to widen the gap and this ultimately results in a crack at 180[sup]0[/sup] position.

Otherwise, it is a good suggestion and decision as well.

 

[Tmoose]

As others have said, A hub retained by simple keyed shaft is really not a very useful power transmission system. A hard working design carefully evaluated for shear strength of the key and bending strength of the shaft does not stand a chance against the micro-motions allowed by a slip fit pulley, even with a few well tightened setscrews lending a hand. A strong radial or axial grip forms the only foundation worth considering.

What type of bearing is at the drive end of the motor? Some bigger motors headed for belt drive service have roller bearings at the drive end to handle the radial belt loads. I'd be sure the replacement motor (or the rebuild, assuming the worn shaft can be replaced economically) is meant for belt driven application. I think if the motor bearing that failed was a ball bearing, its failure is more likely from mis-application than the impact of a loose pulley whacking around on the shaft.

The design of the belt drive should be evaluated. What was the outside or pitch diameter of the drive pulley? The largest diameter pulleys should be used to reduce the belt tension (installation AND operation) Larger diameter pulleys cost more, but may require fewer belts, and regardless have lower tension requirement. Some motor specs include a minimum pulley diameter, and I believe that is an attempt to prevent subjecting the motor to unnecessarily cruel belt loads.