I had always thought that head pulleys were almost always crowned? ■

Head Pulleys are not crowned for steel cord belts. ■

Ah, never been involved with steel cord belts. Learn something new all the time! ■

It is not advisable to crown any drive drum. Although this does show up more with the steel cord belts, the same theory does still apply to textile belts. As stated earlier, there are different tensions at different areas of the drum. Then, if you imagine that the centre of a crowned drum has a larger circumference than the edge, this [can] lead to a sort of rubbing effect at the edges as the tensions change. This can often be heard and the results most definitely seen (the bottom cover wears heavily at each edge section).

Hope this helps,

Stan Holcroft,

Dunlop Conveyor Belting,

Netherlands. ■

Hi Nishant

Crowning pulleys is of some value as a training help on fabric belts.

The secret is to crown only the edges of the pulleys, i.e. only 15% of the face width on each side. This is because the training forces in the middle 60% of the face cancel each other out, so its only the edges that do the training anyway.

This also means that additional belt stress due to crowning is reduced by 60%, thus allowing you to crown HT pulleys.

Also, in this way, you loose less shell thickness at the edge.

Try and avoid crowning close adjacent pulleys though, so crown the head, the drive (if not at the head) the take-up and the tail.

Cheers

LSL Tekpro ■

My understanding is that the belt naturally tracks to the 'high' point on the pulley. I've seen various references as to how this happens but can't lay my hands on them at the moment. ■

The crowning effect is that if you have a belt on a cone shaped pulley, the belt has a strong tendancy to climb up the cone towards the major diameter.

This is like when you ride a bike against a shallow curb, and the bike climbs the curb.

If you have two identical cones with one belt over both, then if the belt is in the centre, the clinbing up the cone forces cancel out.

If however, the belt wanders off the centre-line, there will be more belt on one cone and less on the other creating an imbalance in these climbing up the cone forces, and this imbalance force tries to correct the situation by putting the belt back on the centre-line again. Hence training the belt.

Since it is only the difference in these climbing up the pulley forces that does the work, then you only need cones at the ends of the pulley, as, like I said before, the middle common portion climbing up the cone forces cancel themselves out.

Cheers

LSL Tekpro ■

lagged pulleys need not be crowned ■

How so that "lagged pulleys need not be crowned" ???

LSL Tekpro ■

Sorry Ashwanik...

What you say is simply not true.

I suggest the forum ignore these comments.

LSL Tekpro ■

In that case Ash, please explain your motivation or theory behind the obviously incorrect statement that:

"There is very minimal effect of crowning if the pulley is lagged"

Crowning relies on friction to make it work. Lagging increases the friction and therefore obviously increases the effect of crowning, as we have found to be the true case in practice.

Please explain to the forum.

Thank you

LSL Tekpro ■

crowning certainly helps tracking. In case of lagging on pulleys whether crowning is recomended over rubber lagging or on steel face.

A R SINGH ■

Simply edge crown the pulley, then lag it with rubber or ceramics.

End of story.

LSL Tekpro ■

Crown pulleys are very limited in the effect of training a belt and are not recommended in more than just steel cord applications. But having said that there is some benefit.

Here is a C&P from CEMA 6th Edition

There are currently four types of pulley crowning available.

Straight Face

Straight face pulleys have no crown and are favored by the belt manufacturers. They are recommended

for all installations using reduced ply, high modulus, low stretch belts, such as those with a carcass of

steel cables or high strength tensile members.

Taper Crown

On taper crown pulleys, the face forms a "V" with the rotating axis larger in diameter in the center of

the pulley. This crown is expressed in inches of crown per foot of total face width, by which the diameter

at the center of the face exceeds the diameter at the edge. Normal crowns of this type vary from 1/16 to

1/8 inch per foot of total face width.

Trapezoidal Crown

Trapezoidal (Trap) crown pulleys have a flat surface in the middle portion of the pulley face with the

ends tapered. Trapezoidal crown pulleys may be appropriate for wider face width pulleys.

Curve Crown

Curve crown pulleys have a long, flat surface in the center of the pulley with the ends curved to a

smaller diameter. Except on short pulleys, the curved surface extends in approximately 8 inches from

the edge.

PULLEY FACE

A crowned face is effective in centering a belt on the pulley if the approach to the pulley is an

unsupported span that is unaffected by the steering action of idlers. Consequently, for troughed belts the

crown on the head pulley of a conveyor is of little value in training the belt. Some benefit may be realized

in terms of centering the belt through a tripper by having a crowned face on the tripper discharge pulley.

Crowned face on low-tension bend pulleys in the return run and on a tail pulley where there is a relatively

long unsupported span between return idler and the pulley may be slightly beneficial in centering the

belt, but the contribution to overall training is minor.

Crowned-face pulleys should never be used for any pulleys on conveyors using steel-cable belt.

Multiple-ply belts should not be used on a crowned-face pulley where the tension will exceed 76

pounds per inch per ply. However, for all belts with textile carcasses, the best recommendation is that

crowned pulleys be limited to locations where the belt will only be subjected to less than 40 percent of

its rated tension.

Only straight-face pulleys should be used for all two-pulley drives and for drive snub pulleys.

Just thought I would through in my 2 cents worth for what it is worth. ■

Dear Mr

We are factory specializing in the manufacture and export of conveyor belt, v-belt, tire and other rubber belt for more than 17 years, having higher quality and lower price.

Our company, which is the biggest and leading company for rubber belt, covers 180,000 square meters and has 1461 well qualified workers and 126 excellent technicians.

Our company has passed ISO9001:2000 quality management system certification, ISO14001:2004environmental management system certification, ISO 10012:2003 metering inspection system certification and so on

We can make conveyor belt according to our customers’ request with different standards, such as ´´DIN 22102´´(German Standard), ´´SANS 1173:2005´´ (South African Standard), ´´BS 490´´ (British Standard), ´´AS 1332-2000´´(Australian Standard), ´´RMA´´ (American Standard) and etc. ■

Dear all

We made a flat belt feeder a few years ago, where the pulley manufacturer ommitted to crown the pulleys.

As a result, the belt could not be made to track.

All the other belt feeders we have done both flat as well as ones with short wing rolls (and that is a load of them) have edge crowning on both pulleys.

These all track fine, and we are talking serious belt tensions and high class belts.

So pulley crowning works and there is no question about it.

So you must not always believe everything you read in the books, but you should take heed of what has been found to be true in practice.

That is what this excellent forum is for.

Regards

LSL Tekpro ■

Good day Ray

Please explain to the forum why you do not recommend to crown the head and drive pulleys.

Cheers

LSL Tekpro ■

As usual Graham is right.

He is right saying crowned pulleys are effective training devices, and he is right advising to crown only towards the edges, leaving the center flat.

Comments about pulley lagging is pointless. It's crowned or not.

And, yes it has to be used with care as it can be dangerous for the belt. Steelcord with elastic cords can be used with crowned pulleys.

To the guy who says it is useless: nothing affecting the drive pulleys on a conveyor is either "useless" or "harmless". Any minor modification on this point have HUGE effects.

As said Graham: these are conveyor basics... ■

Hi Ray

My 2 bobs worth are:

small width conveyors have little tracking effect from the trough idlers - esp. when empty > so crowned head pulleys have an effect

with trippers =- same applies as above..esp. with lift off curves and empty running and tripper car mis alignments on the travel rails

bucket elevators - def. crown them - both top and bottom

GTU - yes I agree - long run and with GTU, the frame is normally not well guides..get sinusoidal motion of the belt weaving. Also....can get effect from worn lagging on the preceding bend pulley with carry back materials

stacker discharge - head pulleys - non drive..esp. with chevron mode and different material rates/tranjectoris on the tripper car. watch for wear on covers - low cycle times

Cheers

James ■

We are discussing the issue of crowning of head pulleys here without a proper set of parameters and belt condition involved. Most of the time, when we install belts that are not tracking properly, it rarely is a case that require crowning on the head pulley. Double checking alignment of the tail pulley tensioning, return idlers, contamination etc would normally solve belt sway or misalignment issue.

If all else fails, I suppose the next thing to try before demolishing the conveyor structure (due to poor construction, misalignment, deformed shape etc.) I suppose we can crown the pulley as suggested by Spriggs (flat middle and tipped down on both edges). There is not really a way we can isolate all other factors insitu to realise how effective the crowning will be. IN any case tho, where we have tried crowning the pulley (both the steel drum and the hot lagging with double helical grooves), it seemd to yield positive results. I am refering to belts that are working at EP800, over 400meters in length carrying limestone normally found in cement plants.

On the side note, we have seen little and close to no effect it as on cold and hot splices, but it can be destructive on mechanical fasteners (ie superscrews). This could only mean that crowning does put some uneven stress on the belt.

To our experience, crowning does help belt tracking in most of the jobs we have handle, but then again, there are cases where the crowning of the pulley is not the issue.

It all depends on troubleshooting of the conveyor you are working on and its tracking issue. Adding those new jazzy tracking rollers or SAG idler may not always get the job done either. Personally, I believe the crowning helps simply because 99% of the time, when we had to solve these tracking problems, we would do the crowning on the head pulley and tracking issue will be solved... for at least the next 6months (since in my working environment, belts are not properly maintained and monitored). And perhaps stepping back and crunch some numbers on the conveyor to see if its properly built would help too just because we've ran into many plants who are working their conveyors way above their capacity.

Just from a layman's point of view here. ■

Originally Posted by Graham Spriggs

The crowning effect is that if you have a belt on a cone shaped pulley, the belt has a strong tendancy to climb up the cone towards the major diameter.

.......................

Cheers

LSL Tekpro

Dear Experts,

I have read that belt will always try to move towards where it can get maximum grip or tension. But pratically I find different.

Please imagine a simple conveyor only with drive & tail pulley with screw take-up.

If I am standing behind the tail pulley and move the tail pulley's left side bearing housing towards drive pulley, I find that belt drifts towards my leftside only, where tension is reduced.

( The endless length is lesser at left side than that of right side )

Belt is following the path where it can run with minimum stress or strain.

Any explanations please! ■

Yes...

The simple explanation is that your pulley on the screw take-up is cylindrical (not Conical)

Cheers

LSL Tekpro ■