You might be able to get in contact with Adi Fritella (sic). Adi used to be the marketing man for Melco in South Africa.

websitewww.melcoconveyors.com

Now that Adi has left, you might try Mel Cohen, the owner.

I would be supprised if Melco did not make them.

Having siad that, I find it to be a gadget with a greater liability than a proper holdback. Fitting hundreds or thousand of the little devils to idlers seems over the top. Might hammer your availability.

Note, you cannot relax them like you can a proper holdback. ■

Lyle..

When a local idler chap came to sell the concept to me, the main marketting thrust was to save the day on an inclined conveyor if the belt broke.

This was accompanied by a video of them cutting the belt to demonstrate that the downhill belt only moved back about 2m after the chop.

The uphill belt did not move so I can only assume it was clamped... Hhmmm...

I remain unconvinced on this one, as I have never come across anyone who has good solid practical experience of them.. which indicates to me that they are probably not that popular.

Cheers

LSL Tekpro ■

Dear Graham,

Do you mean what you said? He cut the belt on a decline conveyor with anti-roll back idlers? Doesn't this defeat the purpose of the downhill? How will it ever move downhill?

I am sure this is an oversight. Just like you cannot use a holdback on a downhill and why we use brakes.

I see it only on an incline.

Puzzled. ■

Lyle..

Seems we are singing from the same hymn sheet.

I wonder though if we will get a harmony from someone who also has had experience. I hope so.

Larry...

You probably were wearing the wrong reading glasses or had them all steamed up or something when you saw my post....so...

It was an incline conveyor they cut on the carry side.

Once cut, half the belt wants to go downhill, and the other half wants to go uphill. Therefore the one-way idlers could possibly the stop the downhill belt from going downhill (moved 2m)

There is nothing to stop the uphill belt taking off up the hill but it did not budge, therefore I assume they clamped it.

On the TV, I saw David Copperfield walk though the great wall of China! so, though convincing at the time, I do not believe everything I see on the box... anti-roll back idler demonstration included.

Cheers

LSL Tekpro ■

Out of curiosity why are you trying to stop the belt from rolling back? Is it because you have an incline that needs to be stopped under load or is it for belt repairs? ■

The cheapest solution is make sure your gear box has a anti-reverse locking pin or stop. Your belt can go only one way. ■

Lyle

We built a monster incline conveyor with a single head pulley 3.4MW drive on it.

We put a low speed holdback which could do the duty on the pulley shaft on the opposite side from the drive.

We however had a nervous client who said what happens if the holdback fails? (the lift of this conveyor was 0.5km!)

So we put another holdback between the 3.4MW drive and the pulley.

This worked fine.

On another major high lift installation in Namibia, I had 2 primary drives and one secondary.

I put a single low speed holdback on the spare secondary drive pulley shaft extension that could do the duty. I also put in a high speed integral holdback on the secodary drive for back-up.

This also worked fine.

So.. the bottom line is, use integral holdback for light duty, Low speed holdback for heavy duty, and have a back-up for extremely heavy duty.

Personally, I would not go the one-way idler route due to cost and always wanting to keep it simple.

The other thing is that if you are supersticious and take heed of ridiculous urban ledgends, you would cough up loads of money, and always install low speed holdbacks rated at full installed power.

This is not the case, and you actually have to calculate the holdback requirements for each case based on wrap angles, run back torques, conveyor configuration and so on. (If I remember correctly, this was covered on a previous thread.)

Good luck..

LSL Tekpro ■

Lyle..

I find your maths very interesting as you are correct that for mu=0.3, and with only the middle roll fitted you cannot hold the belt from running back for any decent incline angle.

This puts an end to the concept for me.. thank you Lyle for pointing it out.

Regarding the holdback being rated for full installed power for aborted start and jammed tail, you simply have to put the holdback on the pulley with the most suitable wrap to just be able to hold the belt in the worst load condition.

For example, an overland conveyor feeding into a silo could just run back with only the inclined head section loaded.

It therefore needs a holdback for this load case. So select any pulley on the clean side of the belt with just enough wrap to hold the belt, and install a holdback suited to the run-back duty. In this way you cannot overstress the holdback whatever happens.

This is only one example, but I have also been successful in putting holdbacks in various LT and secondary type positions for the various conveyor configurations and holdback duties.

Saves you a fortune in holdbacks.

Cheers

LSL Tekpro ■

A major point is missed. If the belt breaks, what belt tension exists to support the belt between idlers? None, other than the acceleration from the pull of gravity and belt beam stiffness. In most cases, the sag will become dominant in short order.

Thus, the belt will cave-in between the idlers without the necessary axial tension and axial stiffness, which is lost with the break.

Exaggerated sag will bring the belt to a stand-still quite quickly. There is insufficient force to further pull the belt downhill once the belt has drooped and spilled its contents between each set of carry side rollers.

Belt axial travel will be just sufficient to feed the sag as the belt finds earth. Furthermore, belt travel will only occur until the resistance from belt sag is balanced with the remaing gravity pull.

Idler frame strength may not be sufficient and result in multiple frame failures.

Backward motion and loss of belt restraint is far more significant when the restaining belt friction and wrap are compromised over the restraining holdback pulley(s). This usually occurs with hydroplaing, takeup bottoming, insuffcient takeup force, imbalanced holdback restraint, et al.

A belt can travel downhill during threading where there is insufficient gravity force to induce high sag before the acceleration action takes it downhill.

Belt will pile up at the bottom of the hill, if the sag starts at the bottom and is fed by the takeup motion, without a belt break. ■

Before I am tarred and feathered, I must qualify the prior posting.

CDI has simulated broken belt action in our dynamic model BELTFLEX. The process allows the forcing function to drop belt tension to zero and observe the resulting 2-D axial and vertical action.

BELTFLEX simulates belt sag during all dynamic states for the full belt loop and takeup action.

If the belt has a high incline/decline slope, stiff bending modulus, relatively short idler spacing and high tension at the break point, belt sag will translate and accumulate more toward the tail station. This will result in most of the belt ending up at the tail rather than sag between the idlers along its axis.

Therefore, there are a range of behaviors that can result from a belt break depending on the noted conditions. The movement of belt away from the break can vary dramatically. ■

Dear Lyle,

Yes, I digressed to reach a different point of interest.

On that subject, it is not jamming. The belt takes the catenary shape between rolls roughly like a suspension bridge according to the tension between idlers. Once the level of sag exceeds about 10%, the belt is further pulled into the spacing by its own weight.

I have been involved on idler poping from their sockets. Quintette had a 13 km overland that had the idlers popped from their sockets by the stopping shock wave and excessive sag.

Assume the belt is moving forward and belt tension drops to where there is significant sag. The sag geometry pushes on the roll face, gathers under the roll while continuing to move forward. The net affect is to pull the roll out of its support.

It did so on the Quintette Mine in BC, Canada, for about 150 rolls. The belt then settled on the ISO supports. When the belt was started, with no one inspecting the loss of idlers, the belt was slit by the sharp metal support protrusions. A $9 million failure.

We have photos on many such failures. It is relatively common.

Catenary popping is new to me, but, I can dig it. ■

A point of potential interest..

From my observation of the great decline manriding belt failure at a Platinum mine in Rustenburg, once the belt snaps, there is a tremendous amount of potential and srtain energy that is instantaneously converted to kinetic energy ending up in the belt zooting off down the decline, as well as up it to a lesser extent.

In this particular case, the belt plus 15 men wiped out a significant section of the conveyor, severely injuring the men and all but killing two of them.

So.. getting back to the original topic, using one way idlers in this instance would be about as much use as trying to overthrow Robert Mugabe with a half empty water pistol.

LSL Tekpro ■

Dear Lyle,

This solution is not used in Brazil , at least I never saw it .

I am not sure if the contact between belt and rollers will be enough to bear all possible return forces wich can appear in some situations, like the forces wich will appear in a turned off conveyor, in the moment in wich it were in a quasi movement state.

Alexandre Calijorne

Caltra Projetos & Consultoria

email & phone contacts:

caltrapc@yahoo.com.br

phone: +5531-9112-9694 ■

Hi Graham, Larry,

Yes Melco did (and I believe still do) produce the one way roller. This was in order to maintain existing markets when great salemanship convinced (other idler manufacturers) that the one way roll was the only method to prevent runback in the case of a belt snap. So out of the window goes good design and maintanance to prevent belt snapping. I always had my doubts particularly after having seen the man-riding belt snap that Graham refers to. The belt did not sag at the tail - it shot back and sagged between idlers (deep cavity due to man riding on top and bottom), until the free end snared itself around the trough idler bases, pulled a few of them out and eventaually stopped, with a man trapped inside of the loop.

Why did the belt snap - it was hanging on by three cords of 62.

Result - install one way idlers, increase belt class.

My view - the belt, if it snaps,will slide over the face of the idlers.

Of interest is that tehre was a move in South Africa to replace holdbacks with one-way idlers on teh basis that this was a safer and (in the case of slow speed holdbacks) a more economical solution.

Oh by the way Graham, a higher belt class was installed, with heavier covers, which justified installation of additional drive pack AND ADDITIONAL PULLEYS. The take up remains in its original head position. One good thing is that adequate maintenace has been recognised as an indespansable tool.

Regards,

Adi Frittella ■

Does this type of idler have a ratchet or sprag clutch type of mechanism. ■