Wt of Counter wt in of Gravity Take up

(not verified)
Posted in: , on 3. Feb. 2008 - 19:15

Dear all,

I have observed that the weight of counter weight is generally 50% higher than the weight required by design or by reputed belt designing softwares.

If the design requirement is 4 MT, the total weight in GTU provided is 6 MT.

I am refering to troughing belts within steel plants.

Is it a practice? or designers wants to go safe?

Awaiting your valuable response, please.


P. Rekhawar

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 3. Feb. 2008 - 06:58

Dear Shri Rekhawar,

While designing the conveyor, one has to fulfill the following conditions :

1) The belt tension should be adequate for transmission of torque at drive pulley/s.

2) The belt tension should be adequate so that sag value does not exceed the chosen design value.

The above conditions are to be satisfied during steady running, starting and stoppage (braking if applicable). One has to find out the belt tension at the location of gravity take-up in all the above cases. Then choose the value, which is the largest, and decide the take-up force. One can add some contingency as per his design practice. Such contingency could be 5 to 10% and need not be 50% or so.

The deciding of gravity take-up force for reversible conveyor or multiple drives would require some more application of mind.

Above is the general rule. If you are comparing the counterweight force with respect to only steady state condition, you may find it large. In case of relatively small length conveyor of low installed power, the tension requirement to limit the sag will be also dominant. In that case also one may feel that the counterweight is excessive with respect to steady state etc.


Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Pune, India.

Tel.: 0091 (0)20 25871916

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 3. Feb. 2008 - 09:37

A. BELT SAG - Power & Deflection

Some design to 2% sag, as per some standards. Good design practice should hold the number to less than 1%. This is more critical for steel cord belt. The length of low tension sag zone must be considered. If long, then 1-2% sag will be a power hog. Such a condition is when belt has slight downhill slope.

B. INSTALLED POWER vs DEMAND - Design Criteria

Often designers wish to allow the operator to run the conveyor with installed power, not demand power. Since, operators will try to run with the maximum allowable tonnage regardless of design criteria. So, all structures, pulleys, take-up rating for running and acceleration/braking condition to prevent drive slip, all dynamics including control of sag (power, deflection, take-up motion,...) and belt vibration are also evaluated for installed power.


In addition, the level of drive traction should be considered for nominal and likelyhood events. Thus, drive friction may have multiple values depending on weather et al. Part of this equation may include hysteresis loss from routing of TUP wire rope and sheaves which may need compensation to meet design criteria.


If the conveyor has a relatively long horizontal run and then rises, belt will gather at the inflection point, pulling belt from the TUP. This occurs when the horizontal run coasting time will be greater than the incline stopping time. Often, the designers software gives a hint of this condition. However, the software should also have belt gathering analysis between idlers (belt sag) that shows the sensitivity during a coast-to-stop.


So, what is required for good design. This may differ according to designers experience with the product, local conditions, .... Taking information from a catalog or standard is not best practice.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450
David Beckley
(not verified)

Gravity Take-Up Mass

Posted on 6. Feb. 2008 - 12:15

There is a simple answer to this question that I woke up to many years ago and that is if you design for rubber lagged pulleys using a coefficient of friction of 0.35, as recommended in CEMA, you will experience belt slippage at the drive pulley, particularly in wet weather. For this reason people simply add more take-up mass to prevent belt slippage. I have recorded slippage in experimental work on wet rubber lagged drive pulleys where the effective coefficient of friction was as low 0.215!! If the rubber lagging is in good condition and has a diamond pattern plus transverse grooves you should be able to use a coefficient of friction of 0.25.

Dave Beckley

Conveyor Design Consultants of WA

Perth, Western Australia.

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 21. Feb. 2008 - 07:15

Good morning Rekhawar..

The answer to your question could be that one should calculate the value of the slack side tension based on mu of 0.35 as applied to Te start.

If you apply 0.35 to Te, as David says, you can get slip during starting.

Since Te start = say Te x 1.4, then there is the 40% you are looking for.


LSL Tekpro

Graham Spriggs
David Beckley
(not verified)

T2 Selection

Posted on 22. Feb. 2008 - 03:05

What Graham has proposed above is another way of skinning the cat and will no doubt give a reasonable result.

Looking at the various published texts it is interesting to note that CEMA 5 page 105 advocates using the normal running Te value, which is the reason for my entry above. In CEMA 6 page 132 the wording is a little vague and confusing; however on page 174 in the worked example the normal running tensions are used to select T2. In DIN 22 101 the steady state or the normal running value of Te is used but in ISO 5048 they specify the maximum value of Te i.e. starting or stopping but use the same coefficient as DIN 22 101 for rubber lagging in clean wet conditions of 0.35.

The real problem with the selection of T2 tensions is that we are all using Euler’s rope friction equation developed in 1762!!! This formula is simply not good enough for accurate belt conveyor design; see my entry on this topic under the recent ‘ceramic lagging’ thread in this forum.

Dave Beckley.

Conveyor Design Consultants of WA

Perth Western Australia

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 22. Feb. 2008 - 07:15

Indeed, it does give a reasonable result David.

The beauty of the Te x start factor approach is that one can select the correct start factor for each application.

For example I use 1.2, 1.4, and 2 for VSD, delayed fluid coupling, and direct coupled respectively.


LSL Tekpro

Graham Spriggs
David Beckley
(not verified)

Drive Traction

Posted on 22. Feb. 2008 - 10:15


If you take a hypothetical case with a Te at motor FLT of 100 kN, a wrap angle of 180 degrees and compare the results there are some significant differences in the calculated value of T2 viz:-

Firstly, using CEMA/DIN 22 101 with a Te of 100 kN, and a coefficient of friction of 0.35, T2 = 50 kN

Secondly, using ISO 5048, which is the same as your method for 1.2 starting torque and mu 0.35, T2 = 60 kN and for 1.4 starting torque and mu 0.35, T2 = 70 kN.

Thirdly, using my method based on Te =100 kN and mu of 0.25, T2 = 84 kN

This comparison shows that the method I use is more conservative and this conservatism will allow for the belts bottom cover and the lagging becoming polished or glazed as they age, which inturn will result in the mu value decreasing.

Indecently I always design for T2 using an effective tension value that is based on the motor full load torque and not the calculated steady state value of Te.


Dave Beckley.

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 22. Feb. 2008 - 11:02

All good interesting stuff Dave..

What do we learn from it all?... well..

- Design T2 your way and there will be no drive slip.

- Design T2 my way, and there will also be no drive slip.

(I base this on the fact that I cannot ever recall any of my conveyors ever having drive slip over the last 30 years.)

- Design T2 only on running Te and mu of.35 and you are at risk.

I rest my case your honour..

Cheers Dave

LSL Tekpro

Graham Spriggs

Drive Slip Or Not

Posted on 24. Feb. 2008 - 01:39


I take issue with your out-of-hand claim that a belt-pulley contact friction must be < f=0.35 in order to work in all condition otherwise you will experience slip.

First, the problem is more complex than you or Graham claim. The factors used are old "cover your rump" numbers. Both of you are better engineers and have far greater experience than these simple assumptions demonstrate.

Please note, many conveyors have done well with the published numbers, considered by many to be standard and common practice. There is no need to cause the removal of the standard values as they apply to the many common systems simple systems for most products and light duty environments, dry and wet .

Second, there are specific conditions which do require special attention and, which in some cases, you have noted and some you have not. A little traveling music of some of the many contributions are:

1. Rubber glazing and ageing of bottom belt cover and lagging cover

2. Loss of water grooves to aid removal of moisture in contact zone

3. Slime contamination from iron, bauxite, nickel and other fine material than has little shear strength under the contact pressure

4. Reduced arc of contact due to stiff belts and shortened idler trough transition zones - Germans used to apply a 5 degree contact arc penalty when designing higher strength systems

5. Load sharing inaccuracies between adjacent drives

6. Too close proximity of non-driven pulleys that cause contact irregularities.

7. Heavy rains and belt speed which require faster than normal removal of moisture at the point of contact

8. Downhill conveyors where moisture enters at T2 which has less squeegy action

9. Ice, snow and frost conditions that obtain access to drive-pulley interface

10. Apply the work of Zedde's Doctor of Engineering Thesis on drive contact friction.

11. Geometry of the lagging, lagging grooves, bumpy surfaces, other surfaces, or not , for rubbers, ceramics; others

12. Material of lagging - some rubbers have greater grip, some ceramics have less than expected, some ceramics use different principles to create friciton

The point to this pedantic ranting is: when designing conveyors of consequence, some level of experience and know-how should be included in the procedure to “fit-for-purpose” engineering. The artificial number "coefficient of friction" is not single valued. It should be viewed as part of the cost-benefit or risk-reward HAZOP conditional analysis, with many factors, and should be associated with knowledge of the complexities.

These comments are not.comprehensive, just a word of caution.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450
David Beckley
(not verified)

Drive Traction

Posted on 24. Feb. 2008 - 07:58

Hello Larry,

When entering a discussion on this forum I never know if I am the fish on the end of the line or the person holding the rod! I sometimes enter a thread with perhaps a too simplified statement and then get dragged in deeper and deeper, so perhaps I am the fish.

Of course I recognise that there are different circumstances relating to drive traction and that there have been improvements in rubber lagging materials, however I have seen so many gravity take-up weights in a variety of industries that have piles of steel plate and other scrap metal on top of the original weight, obviously added post commissioning to prevent belt slippage occurring. The massive change from rubber lagging to ceramic tiled lagging on old conveyors in the WA iron ore industry, because of belt slippage in wet conditions, is also an indicator of the extent of the problem. In many cases I have had the opportunity to check the calcs on these conveyors and they were generally designed for a mu of 0.35 on operating Te values. For the East Intercourse Island conveyors in 1969 I used the method advocated by Graham, using a start factor of 1.4 and mu of 0.35. Although these EII conveyors worked fine for several years slip problems did emerge when the belts and the lagging became polished and damp weather and iron ore dust combined to allow belt slip to occasionally occur. Experimental reverse engineering work on these conveyors, involving weighing take-up masses, recording motor current and introducing mist water sprays revealed the low apparent coefficient value of 0.215 quoted above.

When we worked together on the Channar overland conveyors some 20 years ago you may recall that we used a mu of 0.25 for the motor full torque Te value and 0.35 for the accelerating or braking conditions; the 0.25 value being the one that determined the take-up tension value. To the best of my knowledge the Belle Banne rubber lagging used on those 700 kW drive pulleys never slipped and the lagging lasted for 15 years or more.

You mentioned Zedde’s work on drive traction do you have an English translation of his thesis? I have tried to understand the original work but as my German is non existent I could only get the broad outline of what he was doing. I also think that the 1975 work by Oehmann and Hohmann, that was published in part in Braunkohle magazine was very informative.

To conclude I still believe that what we really need is a new drive traction formula that includes a lot more variables and hope that one day CDI might be able to develop one. Until then I am confident that some people are going to experience belt slippage if they follow the recommendations of CEMA and DIN 22 101.

Like Graham, I rest my case.


Dave Beckley

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 24. Feb. 2008 - 08:25


I would have to say - design with caution and use expertise advise

We have a yard conveyor - 500m long..2000tph with travelling stacker, chevron stacking for 2 piles

GTU at tail pulley, cermaric drive pulley with close located snubber pulley.

Belt is fabric 5ply.

When running, there is some edge buckling at the bend point up the tripper car - no spillage.

We have had a lot of wet weather in CQ of late.

We actually broke / snapped the belt in half - straight across break.

The drive is 132kW with delayed fill turbo coupling.

Loking at the belt - we could see "slip" marks on the cermamic nibs in the return side and then the normal "indent" marks. These aligned up with the linear dims back to the drive pulley and the break. The break occured on a loaded re start.

I am assuming that;

The GTU system did not keep T2 high enough for the start - the GTU is a horizontal travelling trolley - can be issue with buildup around the wheels

The loss of T2 led to drive spillage

The restoration of T2 and stoppage of slip led to a very high T1 jerk.

Belt broke (belt is unbranded - must be OS supply from Oz).

I would not think that I would see the day a belt break straight across.

Yes - Ithink that T2 and GTU selection is important and simply use of mu can be dangerous.



David Beckley
(not verified)

Take - Up

Posted on 24. Feb. 2008 - 10:50


Sorry to hear about your broken belt; it is an interesting case and I think you have tracked down the basic cause of the problem. There are a couple of comments that I would like to make in regard to this conveyor.

Firstly you mention that you have a delay fill fluid coupling and that the damage occurred after a loaded restart; do you have a time delay that prevents a restart for a minute? This time delay being necessary to allow the oil in the coupling to drain out of the working chamber and into the delay fill chamber. If you don’t have this delay you could get some very rapid restarts. The oil fill level in this coupling will also be critical to ensuring the lowest stress start. Generally I have found that delay start fluid couplings still result in rapid acceleration rates, particularly when the conveyor is empty. Have you ever measured the acceleration rates on this conveyor? You may want to consider a VVVF controlled start to replace the FC.

Secondly, you mention that you have a tail end take-up and I assume that the drive is at the head end; with this arrangement the force required to accelerate the return belt and return idlers will have the affect of reducing the slack side tension at the drive when you need it most and belt slip could occur during acceleration. If belt slip does occur with ceramic tiled lagging it can really grab again very suddenly causing high belt stress. Even a rigid body belt tension analysis will show a drop in slack side tension during acceleration. A flexible body analysis could show a lot more information. Obviously, the take-up system at the tail end must also be able to move freely at all times.

I hope these comments will be of some value but please accept my apologies if I have stated the obvious.


Dave Beckley.

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 24. Feb. 2008 - 12:08

Hi David

Your comment wrt FC delay start time is valid....I have not checked this.

I share your views of FC use and appoications - 140% max FLT is based for one set of conditions...we have a travelling stacker..so actual load cases will vary with stacker position and direction of travel.

The tail end GTU unit is prob. the best wrt geometry for the yard conveyor but due checks have to be made to make sure it works.

I have never seen a belt break before like this - was not even at the splice.

Message is that this can happen if the system is not well designed considering all the possible scenarios.



Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 25. Feb. 2008 - 06:23

Interesting exchange of views and information. However, I am a little bit puzzled by statement by Mr. David Beckley regarding DIN standard. As far as I can see DIN standard is very specific in the need to analyse both stedy state and non - steady cases of operation and accordingly requires calculation of minimum traction forces. It is, however, true that frequently ( at least in South Africa) designs tend to ignore start up and stopping in sizing of take up parameters.

Going back in years I am aware of various design recommendations which aimed at compensating for the issues described by Mr. Nordell but "unaccounted" in the available standards. This is an interesting aspect in itself where a gap exists between knowledge gained from research and common, recommended (?) practice.


Marian Otrebski

David Beckley
(not verified)

Din 22101

Posted on 25. Feb. 2008 - 07:46


In reference to your question; I find the DIN Standard a bit confusing in this regard and maybe I have interpreted the information incorrectly. In the calculation they talk about TE max but on Page 11 of DIN 22 101 1982 it states "Recommended friction coefficients between conveyor belts fitted with rubber cover plates and pulley surfaces of differing finish for the design and layout of belt conveyor installations in the steady operating condition" The wording 'steady operating condition' being the important one as this is not peak torque conditions.

In DIN 22 101 2002 page 24 it says something similar.


Dave Beckley.

Takeup Hysteresis

Posted on 25. Feb. 2008 - 03:22

Other errors in defining the true take-up (TUP) force also lead to errors in defining the true slack side tension T2.

Non-vertical TUP systems often have trolleys on rails and wire rope and sheaves of varying complexity. These contribute drag against trolley TUP motion, which can exacerbate the degree of TUP force. Sheaves often use bushings which further add to the loses. Bending of wire rope around sheaves adds to the loses.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 26. Feb. 2008 - 07:53


"Bending of wire rope around sheaves adds to the losses"

You know, once when I extended the Namakwa Sands Dual Carry Conveyor, I needed to adjust the take-up mass a little.

It was supposed to be 11 tons. The crane scale I used to weigh it indicated 14 tons.

(I can assure you, I nearly soiled my silk underwear).. So...

I removed the counterweight, I weighed a truck, I put the counterweight on the truck and weighed it again.

Actual weight 11.2 tons.

I wonder how many people guestimate take-up masses by working out the volume and densities, and confirm with crane scales, which are about as accurate as Robert Mugabe at trying to tell the truth.

The effect of bending of wire rope around sheaves adding to the losses, is as negligible as adding the last of George Bushe's brain cells to the take-up mass.


LSL Tekpro

Graham Spriggs

Tup Hysteresis

Posted on 26. Feb. 2008 - 01:23


TUP hysteresis losses in sheaves and ropes are dependent on rope construction, tension, and size of sheave to rope diameters, so says the US and German governments.

Aside from the many projects we have worked on, it became a big concern in Hanford, Washington nuclear power plant crane lift losses. A USA government study was conducted over a number of years and at great expense, which developed the analytic loss factors. Hundreds (>200) of tests were conducted that quantified the mechanisms at work in the losses. Their main interest was in the potential rope failure in fatigue and the contributors.

I have that report and have used the Hanford laboratory equipment to measure loss factors in ropes with respect to belt splices. Belt splices are also influenced by their cord diameter to pulley diameter. Why are pulleys sized to the steel cord diameter? Bridgestone also made a fatigue study on their special rope designs.

Germany also conducted research into rope losses over sheaves. Their work was also published together with the theory behind the losses. Their work was made a part of the Hanford study. A company in Los Angeles, Tension Member Technology, purchased the equipment from Hanford. They do a successful business into ropes and sheaves failure mechanisms in steel and non-steel ropes. The owner was the principle party at Hanford.

There is a mine in Chalice Idaho where we were called in to assess the TUP pulley shaft failure. If part, the TUP pulley loads where larger than the designer had predicted which contributed to the shaft fatigue break. There were two gravity TUP towers, on each side to split load. Special load cells were placed at the counterweight and at the trolley. We measured 44% losses in the sheave and ropes Did the same thing on a conveyor at the Syncrude Oil Sands. The same method was applied to 9km downhill at El Abra in Chile and so on.

Disbelieve at your own expense. I will kndly decline to visit your many successful installation for fear of catching a cold.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 26. Feb. 2008 - 01:37

In the Chalice sudy, the losses where measured with conveyor in operation to determine the hysteresis losses during variations in the TUP movement and TUP tension function.

We determined the influence on drive traction (T2) and on all pulley forces with their structural loads that where impacted by the large hysteresis losses.

TNT have better than a dozen different machines to measure rope and sheave fatigue interaction up to 200 mm rope diameter.

There is a lab in Scotland that also performs tests on larger ropes and their hysteresis and fatigue properties in the dynamic state.

Read any major rope house design catalog, such as Haggie Rand in RSA, which apply these rope/sheave losses and fatigue to the deep mine hoists.

Haggie Rand Ltd: P.O. Box 52: Germinston, South Africa: 1400. Phone: 27-11-825 1076: FAX: 27-11-873 9389.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 26. Feb. 2008 - 02:26

Hi Larry..

"We measured 44% losses in the sheave and ropes"

One of the pre-requesites for the take-up rope system is that the sheaves must actually rotate, and be blessed with a suitable dose of Shell Alvania 3 all purpose grease for good measure.

(Failing that, next time you are in South Africa, I could help you get your sheave loss meter fixed.)

It is hot summer here at present, I'm sure you wouldn't catch cold should you visit, and I would be delighted to show you some of our installations.

I'm sure you would be very impressed.


LSL Tekpro

Graham Spriggs
David Beckley
(not verified)

Rope And Sheave Friction

Posted on 27. Feb. 2008 - 06:24

I agree with Larry that an allowance should be made for take-up hysteresis. In Australia the crane design standards nominate a friction allowance of 2% per sheave for rolling element bearings and 4% for plain bushed sheaves. I believe these values include an allowance for bending the wire rope. I specify a flexible wire rope such as 6x36 or 6x41SW and use a minimum sheave diameter of 24 x the rope diameter. I think the 4% allowance for plain sheave may be too low, particularly after several years of no maintenance. I have never used plain bushed sheaves and agree with Graham that they should be avoided. I have also been advised by bearing suppliers not to use deep groove ball bearings on the basis that the weight will sit there vibrating and this can damage the race of the sheave bearings. For this reason I specify full complement roller bearings for the rope sheaves.

If you have a complicated wire rope system the friction can add up to a reasonable amount.


Dave Beckley

Re: Wt Of Counter Wt In Of Gravity Take Up

Posted on 27. Feb. 2008 - 07:49

Wishing one and all well.

Rather than carry the torch any further I suggest a little bed time storybook from your favorite wire rope supplier. You guys need to become informed of what the rope suppliers publish on rope bending on sheaves drag losses separate from sheave drag. From memory its about 4% per sheave, not including the bearing drag. This assumes a rope to sheave ration acceptable to the rope manufacturer.

I like the idea of visiting the esteemed systems of South Africa that have eluded my radar. Since I see Graham wandering Australia in search of an idea or two, turnabout is fair play.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: www.conveyor-dynamics.com nordell@conveyor-dynamics.com phone: USA 360-671-2200 fax: USA 360-671-8450