Both sprag and roller anti-runback work in similar ways, jamming 'something' between inner and outer 'runways'.

The something in a roller unit is a number of rollers with a toothed internal runway.

The something in a sprag unit is a larger number of shaped wedging pieces.

Do a "google" and you'll turn up more detailed descriptions together with sizes and torque capacities so you can make a comparison with what you are being offered. ■

Hi Gopianth..

The sprag type often runs back a little bit before it engages, whereas the roller type engages straight away which is better.

There is also the cam type which are also good and quick to engage.

If the roll back torque exceeds 15kN-m then it is customary to install external low speed holdbacks on an extended pulley shafts.

This has the added advantage that you can remove the drive unit without the conveyor rolling back.

One school of thought insists that you must match the rating of the holdback to the rating of the drives. This rule can be applied... but not in all cases as it gets too costly, and is normally unecessary if you put the holdback in the right place.

Regards

LSL Tekpro ■

If anything I always thought it was the opposite, but checking the Renold catalogues they BOTH state instantaneous torque transmission. I suppose they should know as they make both types. ■

True Designer, the anit-rotation is not perceptable, unless you apply holdbacks on more than one drive pulley. Even here the anti-rotation is measured as a part of the spring response in the force verses displacement curve required to determine load-sharing of multiple-holdbacks on multiple-driven pulleys.

The wind-up displacement curve is typically ~ two degrees to reach the holdbacks nameplate torque rating whether sprague or cam-roller. ■

Hi all..

When we designed and put in the Majuba Colliery incline shaft conveyor for Trevor Page here in RSA, we used 3.4 Megawatt single drive on the head drive pulley.

The conveyor had a lift of 450m, so Trevor wanted two large low speed holdbacks instead of one, on the same drive head pulley.

We found that if they were sprag type one would nearly always do all the work, so we put in two roller type that engage simultaneously.

So now I tend to only use the roller type and the cam type.

Cheers

LSL Tekpro ■

Graham,

You may know, or not, that we designed the Palabora incline belt with 3 x2350 kW drives = 7050 kW. We aided in the design of 3 x 720,000 lb-ft holdbacks. The holdbacks were equipped with special customed designed load sharing system. During commissioning, 1988-1989, we fitted load cells and measured the holdbacks did load-share within 15% of the nominal.

We have now designed an improved similar system that will be installed on larger multi-drive assemblies in Brazil and similar systems in Australia. This will be a commercial product.

We warranty the holdbacks will load-share within 15% of their nameplate rating, as per equipped load-cell ouputs. It does not matter whether they have Formsprag style or Marland style cam-roller assemblies. This only includes modern holdbacks and not the old rachette design.

Most engineers are not aware of the mal-distribution of loads that occurs upon initial engagement due to the poor spring action of the basic holdback.

Have you measured such engagement forces on operating installations, beyond Trevor's Majuba incline? Are you aware we also worked on this installation for Rand Mines? ■

Ineresting Larry..

Yes... I knew you did the Phalaborwa Incline, but

No... I haven't measured the load sharing.

We were actually toying with the idea of putting in a couple of Bibby sprag holdbacks at Majuba, but decided against it when we got info on how har they can counter-rotate before they engage.

So.. we put in two big Falk jobs from bros Surtees and they worked fine.

Oh.. and no... I had no idea you had any input into Majuba. (Trevor never mentioned it, but I expect he must have got the sinusoidal curve ramp up concept in the tender document from you).

Cheers

LSL Tekpro ■

I am in awe of a machine with a drive power of 7,050 kW !!

My experience stops at a miserable 220kW on a chain conveyor. ■

Only 220kW?...

(Don't worry though Designer.. Your secret is safe with us)

Cheers

LSL Tekpro ■

Graham,

I expect you also didn't know we assisted Trevor on the Majuba 6 km overland. Re-did the banking its horizontal curve, designed by the French mob with EBL.

We then became EBL's new & improved conveyor consultant and went on to win the ZISCO 16 km overland and 14 km CRUII with EBL. Did the splice dynamic testing for SASOL's 22 km overland in Hannover with our recommendation to modify/improve/install the splice design during Christmas.

Just had to give you a little update.

I found Trevor one of South Africa's greater gentlemen, way ahead of his time. ■

Well what do you know!

Its a small world Larry. As it happens, up to September 1982, I was chief materials handling engineer for the aforesaid ELB, and worked with that "French mob", and had many portions of snail pie and pommes frite with them in Rue D'anam in Paris.

Their claim to fame then was the long curved job in Papua New Guinea.

After that I too did a 6km but S-curved overland ages ago. This was the Optimum 6km for which I did the dynamics and design for Dr Torsten Bahke of Krupp.

I also worked on the 22km Sasol overland system, and did the upgrade calcs design and dynamics to take it from 2000t/h to 2850t/h. And what do you know, ELB did the installation of that with guidance from good old Gabriel.

Nice words about Trevor..

Cheers

LSL Tekpro ■

Trevor did get the "S" start-up curve from our dynamic simulation of his system.

I don't know about any horiz. curved job in Papau New Guinea, I do know about the 7km curvoduc in New Caledonia. Although the French claimed the design, it was done by Olaf Klupel, then chief engineer for Beumer. Olaf published its details in an early BSH. There is an interesting story behind the NC design (by hand calc), and single handed commissioning, lose of belt during commissioning, and Olaf's subsequence law suits against him in Germany by guess who?

After we found the error in the banking angle, and problems with the dynamic response, ELB (Mr. McTurk), was in a hard place with the significant difference between the French and US calcs. So Ian split the difference and placed the banking angle between the low French and high CDI. After startup, the belt still ran into the steel until they jacked the angle to our recommendation.

After this, Mr. Bill Kerr, hired CDI to act as EBL's consultant. Then Bill retired, and another saw fit to hire our ex-employee and give us the boot.

ZISCO, CRUII, ESKOM's use of our Power Strip concept, Phil's use of our triangulated truss and trolley at Richard's Bay, 4.5 x 9 m idler spacing, and our SASOL analysis predicting a coal production shortage were our legacy. Where are you today in coal production?

I also know Torsten.

I have offered the branch without olives, to give RSA some infusion of modern design. So far no takers. Soon we will have a stronger voice.

Have you seen the publication in latest BSH by Dr. Robin Steven on Belting Curragh? How about the Newcastle announcement about their new study Grant on super low rolling resistance? ■

Originally Posted by nordell

Graham,

You may know, or not, that we designed the Palabora incline belt with 3 x2350 kW drives = 7050 kW. We aided in the design of 3 x 720,000 lb-ft holdbacks. The holdbacks were equipped with special customed designed load sharing system. During commissioning, 1988-1989, we fitted load cells and measured the holdbacks did load-share within 15% of the nominal.

We have now designed an improved similar system that will be installed on larger multi-drive assemblies in Brazil and similar systems in Australia. This will be a commercial product.

We warranty the holdbacks will load-share within 15% of their nameplate rating, as per equipped load-cell ouputs. It does not matter whether they have Formsprag style or Marland style cam-roller assemblies. This only includes modern holdbacks and not the old rachette design.

Most engineers are not aware of the mal-distribution of loads that occurs upon initial engagement due to the poor spring action of the basic holdback.

Have you measured such engagement forces on operating installations, beyond Trevor's Majuba incline? Are you aware we also worked on this installation for Rand Mines?

Dear Mr. nordell,

I am very interested in the backstops arrangement of Palabora mine. Could you show us further details?

I believed that there were two backstops on the primary pulley, there was one backstop on the secondary pulley. And I think that the two backstops on the primary pulley should display equally number, isn't it?

Bst rgds ■

Palabora Mine old incline belt was powered by 3 x 2350 kW wound rotor drives, with two primary pulley motors and holdbacks, and one secondary drive motor and holdback. Each holdback was rated at 720,000 ft-lbs nameplate.

The torque arms were about 3 meters long by memory. At the end of the arms, we designed a bevel spring washer system made up of two distinct spring constants. The deflection or torque arm displacement was on the magnitude of 75 mm for the soft spring and about 25 mm for the harder - impact shock damper. This equates to about 2 degree total travel, less the torque arm and holdback cam strain displacements.

CDI has now developed a special design which includes:

1. load sharing of large drives > 500 kW/motor - if you wish to know they load share to a reasonable degree and don't need to oversize according to mfgrs. published information. I have published information about large holdback systems on multiple drives that mal-load share better than 10:1. It is obvious this installation would have failed the holdback. Tuning the dynamics, showed 1:1 load sharing when appropriate flywheel inertia was installed. The method was successfully employed on the Morenci Mine, Arizona, in the late 1980's. This information was published in a SME paper for any who have an interest along with special shockwave detail tuning of Selby during stopping.

2. shock damping

3. mechanical read-out of force on spring system calibrated during 0-150% torque efficacy testing of each holdback shipped.

Interested parties should contact the undersigned for futher information. ■

A special note on Palabora's holdbacks. I redesigned the cam inner race to accomodate the extreme bending forces applied to the inner race member under the rollers, together with Marland during the design of Palabora. This was the world's largest incline belt and holdback at the time in 1987. Never had a problem with the holdbacks over the next 17 years ( by memory). Without the change of the inner race, there would be a chance of spalling the inner race member under the roller outer edges. ■

Originally Posted by nordell

1. load sharing of large drives > 500 kW/motor - if you wish to know they load share to a reasonable degree and don't need to oversize according to mfgrs. published information. I have published information about large holdback systems on multiple drives that mal-load share better than 10:1. It is obvious this installation would have failed the holdback. Tuning the dynamics, showed 1:1 load sharing when appropriate flywheel inertia was installed. The method was successfully employed on the Morenci Mine, Arizona, in the late 1980's. This information was published in a SME paper for any who have an interest along with special shockwave detail tuning of Selby during stopping.

2. shock damping

3. mechanical read-out of force on spring system calibrated during 0-150% torque efficacy testing of each holdback shipped.

Interested parties should contact the undersigned for futher information.

Mr. Nordell,

Thank you very much! Your reply let me know much knowledge of mul-backstops.

Morenci Copper Mine, you mentioned, have a downhill conveyor with more than 200m vertical displacement. Its braking system is quite classical.

CDI is a great company, and it promotes the development of conveyors all along.

Rgds. ■