I am assuming that you are talking about non drive pulleys. Is the pulley moving on the shaft axially or the pulley and shaft are moving together? What type of bearing housings are being used? In large pillow block bearing housings you need to have one bearing "floating" and one bearing "fixed" removing any axial clearance between the bearing and the housing. In other words one bearing has the fixing rings in the housing and one does not. If both bearing are "floating" (no fixing rings in either bearing housing) you can experience what you are describing. If it is just the pulley moving then the locking hubs do not have the correct torque to hold the pulley from moving on the shaft.

Ensure that the pulley and bearing blocks are 100% perpendicular to the conveyor frame. ■

Following on from Gary:

Fortunately you seem to have a near perfect belt that is looking after other hardware.

Are the fixing rings fitted? If so, which way is the shift?

Is the belt central to the pulley when on a central pulley? Either the belt follows pulley shift or the pulley follows belt shift.

Crowned pulleys? No shell is perfectly cylindrical (tool wear) even with NC vertical borers.

If the shaft isn't squealing and the belt is running OK you'd better leave it alone until the next shut down when you can check for fixing rings and tightened bushes. ■

I believe something has come loose inside the bearing. I have seen it before where a maintenance person forgot to lock the lock nut with the tabs from the lock washer allowing the lock nut to become loose over time. As per louispanjang if it is not giving you any grief at this time I would wait until an opportune time to give the bearings a thorough inspection and retighten as per the bearing manufacturers spec. Also ensure that the correct fixing ring(s) were used there should be no room for axial movement between the fixed bearing and the housing once the fixing ring(s) are installed.

All pulley shaft assemblies need a fixed and a floating bearing no matter what the ambient temperature is. You can experience heat increases from rolling friction as well. Underground operations typically do not have ambient temperature fluctuations but all assemblies are required to have a fixed and floating bearing. ■

...which explained that when a shaft is subject to bending there is rotation at the supports in the plane of bending. This is agreed in many mechanical engineering texts. Take it from there.

"Since in many of the conveyors, the pulleys are running in ambient temperature , does the concept of "Fixed" and "Floating" ends , applicable ?"!???????????

How far do you think a pulley is supposed to expand? ■

"...may be reduced" ??????? "checking the clearances is a very very laborious job..." You've just said it all. Aren't you glad I'm not an Owner's Engineer in India. If there is of ever was such a person.

Manufacturers handbooks used to advise that when a bearing was heard knocking it should be replaced.

Screwing a locknut tighter will not expand the inner race to reduce internal clearance, unless the inner race is made from soft material: and even then.

Please read the handbooks before trying to confuse the forum members who are almost daily asked questions about hopefully hypothetical problems on your apparently disastrous plant.

Very recently we have read of couplings blasted into oblivion; splices failing regularly and drums walking on shafts. It is appropriate to ask who in the name of creation sanctioned such a plant in the first place? ■

Once upon a time I worked for a pulley manufacturer that required I do field investigations. In addition to the other comments, I can say pulley manufacturing can be the culprit. Here are some additional causes I have seen:

1. Older taper lock type devices, taper bore would go out of tolerance and bore the taper with a spherical seat that results in a rocking action, ultimately stretchs the locking bolts, thus loosening the clamping actions = walking on the shaft.

2. Shaft deflection at the locking device is too large, improper shaft size = stretched or broken locking bolts and walking.

3. Pulley can walk on the shaft from improper connection of the shaft to the locking device due to the manner of the shaft design and the containment with the taper sleeve nut on the taper inner lock device on Ringfeder type devices. Shaft moves and pulley stays in place. ■

Originally Posted by sganesh

The taper bore provides a simple method of mounting that allows controlled stretching of inner ring to obtain the maximum gripping power. As the inner ring stretches, the grip increases. Bearings are manufactured to allow this stretching of inner ring.

The grip and clearance are controlled by checking internal clearance by tightening the nut sufficiently by a specific amount.

Regards,

Sganesh:

What are you trying to say in English with this lecture? The discussion is about the pulley moving off its centerline along the pulley shaft axis. How does your note apply?

If you are commenting about the inner ring of a typical taper-lock assembly, the inner ring does not expand, it just slides on the shaft when tension is applied to the bolts. ■

It would be helpful to know more details of the locking device and its application.

Some Ringfeder type devices (narrow vs. wide) do not have a self-locking taper and are subject to bolt stretching when the shaft deflection is not compatible. Results in bolt stretch, locking ring failure and pulley walking. Wider locking devices usually are self locking. ■

Reading the entire discussion it is not clear to me if the pulleys ares walking on the shafts or the shaft is walking in the fixed bearing. Please clarify.

Joe Dos Santos ■