Belt Cover Wear = Chute Design !!
Kayem,
The opinion I offer has been stated many times in this forum. Approximately 96-99% of belt wear, for most ore transport conveyors, is a product of granular shear work on the belt cover. This assumes impact damage is nil.
Cover rubber compounds play a roll in extending belt like when the designer has ignored the chute design and installed a rockbox or direct vertical impact of ore onto the belt. As I have published, based on theory and field measurements, abrasion damage is proportional to the shear action of the individual particles that make contact with the belt during loading. Our DEM (discrete element method) modeling of many chutes is shown to be very accurate in classifying the shear work and impact forces that make up belt cover damage.
We have extended belt life 10 (TEN) times their prior life by providing appropriate chute geometry with the same rubber compound.
The button abrasion test you refer to has many limitations and cannot mimic real world applications. It can be used as a relative comparison between rubbers for the specific test procedure. It is a poor predictor of belt life.
How can this simple test mimic granular dynamic action? Professor Hagar (Univ of Hanover) published rotating drum studies, in TransTech, where a drum of specific size was lined with the rubber cover sample, filled with the product, and then rotated for a specific number of revolutions , speed, slurry, etc. to determine if there were differences. The differences were significant.
1. The rubber button specimen is not the belt and can not be used to predict the life of a belt unless prior callibration factors are known and even then it is a crude estimator.
2. The rubber button fills the abrasive medium voids during the test thereby influencing the abrasion index. This does not mimic real world conditions.
3. Heat is generated within the specimen, during the test, reducing the abrasive resistance. Again, Not Real World (NRW).
4. The test grinding material does not have the product characteristics (NRW).
5. Your assumption that ore shear flow action stops in about 5 meters has a likelyhood of 1/1000. It depends on the ore's forward velocity and pressure of flow stream. Most ore is accelerated to belt speed in 0.5 to 2 meters from point of impact depending on ore: granular shape, granular size, tonnage, material density, belt speed, slope loading angle, moisture conditions, and chute design. Some prill, marble like or round shaped materials may take many times your estimate.
Go look at our website and read the literature again.
www.conveyor-dynamics.com
L. Nordell
Conveyor Dynamics, Inc. ■
Re: Abrasion Loss Of Cover Rubber
ADDED COMMENTS
The skirtboard design can also play a role in belt wear. The restriction of the skirts to flow and entrapment of materials can due major damage. Flow resistance, by the skirt siding and alignment of wear plates, play significant roles in belt cover wear damage.
LKN
Conveyor Dynamic, Inc. ■
Re: Abrasion Loss Of Cover Rubber
Dear Mr. Kayem,
The reputed belt manufacturer will already have the formula for calculating belt cover wear life. The creation of such formula requires extensive field testing for various kinds of materials under various kinds of feeding and impact situation. This issue has been covered in my book with numerical examples. It is based on the method / theory of reputed German belt manufacturer.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyor
Email : parimul@pn2.vsnl.net.in ■
Re: Abrasion Loss Of Cover Rubber
Mr. Mulani:
I strongly disagree with your comment "rely on belt manufacturer" for selecting cover stock compound and thickness to deliver a required life.
We write such specifications. Belt mfgs. will and do issue guarantees today, with the aid of granular flow simulation, that defines the damage mechanics. They do not like to issue guarantees for a hyothetical (new design) conveyor, from field measurement databases, unless the designs are quite similar to the database. They know this leaves them vunerable to replacement if the guess is incorrect. They admit they have limited knowledge.
Palabora had a ten (10) year belt life guaranty. The belt wore out in less than 3 years. The German belt manufacturer did not stand behind his warranty even though he approved the chute drawings. After his belt failed to deliver the 10 years of wearable service, he said the chute was at fault. He walked away from the warranty and waited for the suit.
The client placed an order for a second belt, from the same mfg., with the mfg. relying on the life prediction being set by our DEM simulation. A redesign of the chute, based on the simulation, predicted a +20 year life improvement. The belt mfg. based his new warranty on this life prediction.
The change in chute design was finished in 1994. It is now 9 years from the change. The belt still in operation and has most of its top cover life left. This is in spite of others applying another curved loading point further up the slope which is causing some damage.
Reference our website for Palabora publication details. Palabora is the first analytic treatment of ore flow in chutes. I discount slug flow (proposed by Prof. Roberts) as being too constitutively simplistic and too inaccurate to yield understanding of 3-D flow mechanics.
I am willing to dicuss this further in India, during the Bulk India Symposium in Dec., or BELTCON 12 in South Africa where I am delivering papers on chute design influence on belt life and influence/benefits on other design attributes.
Lawrence Nordell
Conveyor Dynamics, Inc.
web: www.conveyor-dynamics.com ■
Re: Abrasion Loss Of Cover Rubber
Dear Mr. Nordell,
Referring to my earlier message, I add following information.
New / different methods are always welcome, encouraged and appreciated. However, my point is that in case of life calculation for belt, it would need exhaustive data from field, spread over long time and geographical space, for practical verification. This would be feasible / practical for long time establishment / institute.
However if one can manage this, it is highly appreciated.
The issue has also contracual implication i.e. some other party cannot stand guarranty for the make of some body else's item, that is how the belt manufacurer comes in to picture. Therefore, unless the paricular supplier of belt agrees to the said method it will not carry contractual responsibility.
Regards,
Ishwar G Mulani.
Author of Book : Engineering Science and Application Design for Belt Conveyor.
Email : parimul@pn2.vsnl.net.in ■
Re: Abrasion Loss Of Cover Rubber
Mr. Mulani,
I believe you don't get the point.
Until the last 7 years, belt manufacturers carried the burden of guarantying life of belt. They understand their approach is inadequate. They acknowledge the physics produces the damage. They acknowledge there now is a way to quantify the physics, ergo to provide a meaningful connection to the life calculations beyond the quasi emperical haze of history and maybe and overdesign for lack o ffundemental knowledge.
Some manufacturers will only guaranty belt life based on the DEM approack we offer. Some owner operators insist on DEM predicting life of service based on the shearwork and impact work quantifiers.
You don't need exhaustive data from the field. You need to quantify the physics. The rest has already been been.
This is the future. You comments are not.
Lawrence Nordell
Conveyor Dynamics, Inc. ■
Belt Manufacturers Experience
Dear Mr. Mulani,
from their wide field of supplies belt manufacters have a reliable basis for wear estimations and are with their predictions very often more precise than those who have only a theory.
In the case of the Palabora Tunnel Belt actually the reason for the premature wear was a faulty chute together with a unfavourable truck dispatch etc. With our help a consultant developed a curved chute, which he before probably even did not know. This consultant also forgot to mention that he himself was involved in this project during the design of the conveyor.
Some consultants take a limited responsibility only and normally do not give the same warranties as a supplier.
I think you can rely at least on German belt manufacturers.
Please contact me directly, if you need more information.
Best regards, Rainer Alles ■
Re: Abrasion Loss Of Cover Rubber
Dr. Alles:
Its nice to see you are still in circulation Rainer. I see by the tone of your dialog, you still have doubts. Its OK. I still have doubts too.
Since you have made direct reference to the Palabora chute design and its consultant, I must correct your statement of understanding.
1. I was the design consultant to Palabora for the overall conveyor system as you know.
2. I did not get involved in the chute design in 1987-88 during its initial design development. We did not know the chute's vital importance. One rockbox looks like another. Why should the client pay the high priced consultant to investigate the chute design when the belt manufacturer says its OK?
3. ContiTech did evaluate the proposed belt life, reviewed and approved the chute design to provide a 10 year belt life warranty.
4. The belt was destroyed in less than 3 years due to a poor chute design as you suggest.
5. I do not recall any design involvement by ContiTech. Contitech did approve our curved chute design and issued a warranty of 10 years for the new belt based on your review of the CDI curved chute.
6. No designer or operator had designed and installed a curved chute, in primary crushed hard rock, up to the Palabora installation.
7. Palabora contracted Conveyor Dynamics, Inc. (CDI) to propose a fix to their short life dilema. We studied the problem for 1 month before making a proposal to design the curved chute. It took another 5 months to complete the design with wear predictions for belt and liners. A number of publications have been made on this installation. Others have copied its methods.
8. We now accurately predict belt life for our chute designs based on the software developed during and after Palabora. This software has been in development for 9 years. Its accuracy is now well proven on many installations and minerals.
9. Belts do from time-to-time fail to meet their warranty claims. It is always somebody elses fault. German, Japanese, North American, yada yada have such experiences.
The world holds many mysteries. Let's not make Gods of some and fools of others until we all agree the mysteries are solved.
Lawrence Nordell
President
Conveyor Dynamics, Inc.
www.conveyor-dynamics.com ■
Re: Abrasion Loss Of Cover Rubber
For this test, DIN abrasion tester would help. It is one of the most common testing machine for rubber. ■
Abrasion Loss of Cover Rubber
Hi,
To THEORETICALLY ascertain the life of the top cover rubber of any conveyor belt, I am trying to evolve a formula based on the DIN 53516 test for wear resistance. The way I look at it is as follows -
1. The test sample is of a specific dimension and hence the surface area exposed to abrasion during the test is defined.
2. The length of traverse during the test as well as the longitudinal traverse speed is defined
3. The maximum volume loss is specified
4. The grid size of the emery paper is defined and therefore the number of points of contact between the emery paper and the test sample can be computed.
In an actual application, the parallels are - to my mind - as under :
1. Wear usually occurs in the central (approx) 35% of the belt surface. since the length of the belt is known and since the belt is usually considered due for removal by the time the cover rubber thickness has worn down to - say - 1 mm, the total volume loss can be calculated.
2. For an optimally loaded belt, about 85% of the belt width carries the material conveyed. Therefore, depending on the grid size, the number of lumps resting on the carrying run at any point of time can be computed. Each lump may be assumed to have one point of contact with the belt.
3. If we assume that material movement, relative to the belt, stops within - say 5 m - of the loading point, we can define this as the abrasion zone and consider all abrasion occurs at this zone. Therefore, depending upon the center distance and the belt speed, it is possible to compute how long it will take for the volume loss (see 1 above) will take.
Yes ! There are plenty of 'gaps' in the above reasoning but I believe it's not too far off the mark.
May I request considered opinion from those who believe that theories & formulae do have some value in this mad world ?
Thanks
Kayem ■