please explain further as it is not very clear as to your intent with said equipment.

Ok stupid question time, what are you doing with

the Jib? Is it a jib crane with a specic length of boom? If you have a mud floor it will not hold very well with weight on it.

The other question is, is the drive separate from the head pulley? The third question is why are you not purchasing stock equipment?- a specific brand of conveying system? All the work for a system of your size has been done.

What kind of take up are you using?

Are you using DC power or AC 480-600 volt?

My question about your drive motor arrangement is this-If you do not have a rubber coupler connecting your elelctric motor to your gear box it will destroy it if the belt is overloaded as the delivered energy has to go some where if the motor circuit breaker does not trip out.

Are you using a long wall with a head gate and tail gate or room and pillar with a belt feeder breaker? You really have not told us much as far as tons per hour, belt size, splice type, whether it is a cable supported belt or on steel stands, or whether it is a hydraulic take up system of counter weight tensioner etc. ■

You need to advise on the motor frequency of synch RPM. We would still need to guess at the slack side tension and takeup dynamics. Here is a start:

1. KW = (P x V) where KW is power, P is stall traction, V is speed

2. V (m/s) (asssume motor sych RPM = 1500/60 spm) = 1500/ratio=10/60 x(0.45 x PI) = 3.53 m/s

3. P (kN) = 75 kW = P x 3.53 m/s ; P = 21.25 kN

4. Breakdown torque = 2.5 x 100% nameplate

5. Traction @ breakdown = 2.5 x 21.25 = 53.12 kN = T1-T2 = TE

6. Assume tension ratio T1/T2 = 3:1 at full traction

7. Slack traction (T2) = TE / tension ratio = 53.12/3 =17.7 kN

8. Max tension T1 = TE + T2 = 53.12 + 17.7 = 100.82 kN ■

Dear sir

In case simgle 75 kw motor is running and conveyor is also runnig at 3.5 m /sec (considering motor 1500 rpm) than 100.8 KN belt tension as calculated by Nordell is in order.

However it appears conveyor is having dual drive (it is not clear whether conveyor is having one or two 75 kw motors)

Mr Mark is interested interested in determining the the belt tension force if the Belt isjam and motor still operating.

In this case when motor is running and is not able to pull loaded conveyor due to belt stuckup or other conditions .

under the circumtrances belt speed will be zero and we cannot consider 3.5 m/sec belt speed for determining belt maximum tension

A R SINGH ■

Just a very minor observation, if the motor is 415V running at 1470 rev/min then it's likely that the supply frequency is 50 Hz not 60 Hz (unless it's running from a variable frequency unit). ■

Another minor observation:

When the belt is running and then has a belt jam, its will pull up to the peak breakdown torque, as I noted above, on its way to stall. ■

Mark J. A.,

I had occasion to address your hypothetical in a real situation.

Our customer had such a jam at his slope conveyor, at the loading area, and it resulted in the failure of his low speed backstop. The backstop was properly sized according to the manufacturers guidelines. We were asked to analize the accident and determine the back stop forces that could be developed.

Our DSI ExConTec (comprehensive convyor program) was used to determine the locked in forces. The back stops were able to engage on reversal with no back travel and we assumed that the belt did not slip on the drive pulley (as evidence indicated). The locked in forces were determined by:

1) the maximum motor torque (break down torque) and;

2) the conveyor's inertial resistance to stopping suddenly

Magnitude of the former is known, regardless of the conveyed material load, since the motor will keep driving and reach this point before the stall. Magnitude of the latter depends on the time to stop the conveyor, which also requires a corresponding magnitude of the gripping (due to Jam) force. Thus we intoduced various stopping times due to the jam and recorded the various resulting locked in forces. These were the backwards forces on the backstop.

We found it very plausible that the jammed conveyor could produce the locked in forces to fail the backstop. Indeed it did produce such forces. This incident made us rethink the criteria for sizing conveyor backstops.

I hope this actual case sheds some light on the subject.

Joseph A. Dos Santos ■

Dear Mr. Mark,

If the conveyor is subjected to overloading and finally jammed, then its speed will start reducing and come to zero. In case your drive system is directly coupled to the pulley without fluid coupling then its speed will also eventually become zero. In this situation, the speed point will shift from full speed to zero speed, on torque speed curve. The force acting on the belt will be according to shifting of this point on the graph, unless it is prevented by electrical overload protection system. In case you have fluid coupling in the drive, then also the secondary side of fluid coupling starts slowing down, in this situation the drive response and consequent force will be in accordance with the torque-speed graph of the drive system including fluid coupling.

In case of fluid coupling where the fluid is getting injected in the working chamber during starting process, the reverse situation will have a different torque-speed graph, which you have to obtain from the supplier of the fluid coupling manufacturer. In this kind of fluid coupling the usual graph considers gradually increasing quantity of fluid, but in the reverse situation the full quantity of fluid will be present when the speed starts decreasing and becomes zero.

It is to be understood that jamming (full speed to zero speed of conveyor) cannot happen instantly. Otherwise it will create infinite force and everything will break down. In conveyor the jamming will always occur within a finite time though it may be very small.

Regards,

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.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Referring to my earlier reply, i would like to add few sentences.

If the jam (i.e. gripping of belt at particular location) is extremely intense, then belt conveyor deceleration forces will surpass the drive and it could be analysed accordingly. The situation is like car hitting the wall wherein the forces generated in car due to inertial (deceleration) will be dominant rather than the force applied by drive. But such type of jam cannot occur.

Regards,

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.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Dr. Mulani,

Please see my comments (the post just before your first post). Indeed such a sudden grip can and did happen and failed the low speed backstop at our customer's slope conveyor.

The backstop prevents any back travel and can lock in the maximum drive force. How much of the maximum force locked in depends on the rate of grip (at the jam) and the belt's elastic elongation (ie the amount of back travel, or belt feed forward of the grip, that is required to relaxed the otherwise locked in tension). If the jam grip is sufficiently gradual then the max driving that is locked in will be the stalled torque value as dictated by the speed torque curve of the motor. If it is absolutley sudden then the max (break down) drive torque will be locked in. The actual answer may be in between but with a fabric belt and a sudden stop it favors the maximum value (as was the case with our customer's conveyor). This accounts for the locked in tension due to the drive effort.

Additionally there is the (conveyor and drive) inertia and its magnitude depends on how sudden the jam grip is applied. In our analysis we varied the grip rate to determine the corresponding locked in tension which was applied at the low speed backstop. The grip rate to produce the backstop failure forces turned out to be reasonable thus confirming the nature of that conveyor run-back failure.

Joe Dos Santos, PE ■

None of the above notations takes into account:

1. elastic storage modulus (steel cord or fabric belt)

2. degree of elasticity), the displacement of the stored energy body ( belt),

3. location of the windup mechanism (drive)

4. location of the motion restraint (holdback)

5. magnitude of the drives coupled mass with respect to time (eg fluid coupling vs direct drive connection)

6. conveyor geometry and mass distribution

7. type of takeup and its response characteristics to the spring action

8. holdback internal and external support spring constants

9. and so on ........

This is an elastic dynamic transient model (dynamic analysis model) such as BELTFLEX. Any rigid body model (BELTSTAT) is guess-work.

The problem must be formulated as a long elastic spring or set of individual springs and their lumped masses in series with the drive mass connected to the long spring, at one end, and the one-way motion restraint device (holdback or brake) located dimensionally along the long spring according to the model under study.

The elastic transient model does include belt line forward and reverse inertial response along the belt axis as well as drive rotational inertia all coupled as a set of lumped mass spring dampened properties. THis may include a disengaging fluid coupling motor and impeller inertia dependint on the rotating RPM.

CDI has performed many such model formulations for holdback and brake loading/failing scenarios. We have also load cell measured the dynamic response in field tests.

The worst case is where the drive is located just before the tail station, the belt jams at the tail, and the holdback is located at the head pulley. This maximizes the stored energy that can be imposed on the holdback. Of course this is not the possed problem of the thread starter.

The second factor is the kinetic energy that must be held due to the reverse action of the belt when the holdback engages.

The third important factor is the holdback's elastic foundation and how it cushions the shock wave.

THe belt extension is obviously maximized when the motor applies is breakdown torque to the belt line.

THe solution requires a complex mathermatical formulation not easily constructed in a spread sheet. It requires solving a forth order non-linear differential equation set with 2-dimensional spacial orientation and all the attending points above. ■

Larry,

What makes you say that "non of the above notations takes into account: etc, etc"?

The analysis that I describe was performed with the DSI ExConTec (complete conveyor simulation and analysis program) and takes into account all of these issues and any others that are relavent.

Though not applicable in our case (ours is a connected drive) your example of a disengaging fluid coupling drive is trivial. If the conveyor slows gradually to a fluid coupling disengaging speed it will not produce the inertial forces that will bind-up in the the belt and fail the hold-back on recoil.

Larry, I don't mean to trivialize your complex analysis. Indeed dynamic elastic response (shock waves) will create, locally, higher than average tensions as well as correspondingly lower than average tensions. The stored energy will be the same regardles of the complexity. The stored energy between the jam and the restraint (hold-back) is the locked driving tension (near the break-down motor torque if the jammed stop is sufficiently fast) and the inertial energy stored in that same portion of the stretched belt. Any stretch that is outside of the the locked portion of the belt will relax independently settling at a tension distribution which is dictated by the take-up tension and no driving torque (when the drive is de-energized).

Bound tension between the jam and restraint (hold-back) will be of a magnitude that will fail the hold-back if the stop due to jamming is sufficiently sudden. Such was the case at our customer's slope conveyor. That occurence and the jamming force/stopping time, that failed the hold-back, was easily simulated and determined with the DSI ExConTec Complete Conveyor Simulation and Analysis Program.

Joe Dos Santos, PE ■

Dear Joe,

I take your response to be strongly worded. You must be very passionate about your work. Good! However, please do not anticipate others to be mind readers. If you do not state the facts, then there is room to doubt the background. As such, I felt the comments missed, by your earlier dialog, needed a modern interpretation.

You now state the "DSI ExConTec " is the tool that makes the analysis spot on. I am not aware of the power of this analysis. Is it published? If so, where? If it is published and shows field verification we should give it the respect it is due. I did visit your website and lifted a quote on:

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Special features of the DSI "Expanded Conveyor Technology"

5. In the analysis, belt tension becomes negative (compressive) when it drops below 0. This, though not realistic (as belt becomes slack), allows continued analysis indicating the tension increase required to correct the slack belt problem.

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Here, in this point 5, you allow the belt tension to go negative. As you note, in real life such is not the case. I contend you cannot obtain a proper belt dynamic response with negative belt tension treatment. You do not capture the true time dependent shockwave elastic mechanics and therefore you will be inaccurate.

Your kind comment about not wanting to trivialize does if fact do so. This does not bother me, but may degrade your offering.

I do not agree that the "stored energy will be the same regardless of complexity ( of analysis? ). I am not sure I get your point on this complexity issue. Maybe its like the trivail issue? We could put it to the test.

I am mistified in your perception of the fluid coupling disengaging as trivial. This word is twice used in your comments to convey a meaning that I do not understand. Maybe, I should not try and so will let it drop. Anyway, regardfing the fluid coupling, when the belt is pulled taught, and forward motion reverses, the mass of the drive may dictate the peak holdback force. When a fluid coupling is used, the hodlback force intensity may be higher from the decoupling action.

CDI has measured many holdback installation including where the holdback(s) has failed. We feel confident our procedures, using elastic transient analysis, does accurately predict and correspond to the field measurements.

Much more could be said on the technical analysis of holdbacks. I believe it is going outside the scope of this forum. ■

Larry,

I hope we don't get too far off of Mark J. A's intent (when he started this thread). I do enjoy the intellectual exchange.

The DSI ExConTec is based on my accumulated research and experience. As you know my work in sandwich belt high angle conveying prompted my expansion of the conveyor equations to address:

1) High angles (CEMA and other standards for conventional conveyors don't recognize angle on the rationale that the cosine of the conventional conveying angle is sufficiently close to 1)

2) Belt travel resistance which is due to deforming the belt by cause other than the load. Most notable is the resistance along a convex curve regardless of material load but this also applies to horizontal curves. Our derived load equivalents solve for these resistances.

3) Belt travel resistance due to deformation of the material unconfined (in a conventional conveyor) or confined (in a sandwich belt conveyor).

These principles once formulated highlight the short comings of the conventional conveyor equations before their full expansion or generalization.

The DSI ExConTec, as a complete simulation and analysis computer program, was written in 1997 & 1998. It was prompted by a DSI study contract to upgrade an overland conveyor system in Alabama. This provided a proving ground though the equations were previously proven at other installations long before their use in the DSI ExConTec. We analyzed fully the pre-upgrade system and field monitored the conveyors to support or refine our analysis. Indeed as you know from our description we are proud of our "Discretionary Factors" that allow us to refine the analysis model to reflect the actual behavior of a particular conveyor, when it is known, or merely to reflect a customer's philosophy when appropriate.

Slack belt was a problem at one of the flights and a previous CDI Analysis had failed to reveal the cause of the slack belt (CDI failed to reveal it because of incorrect input data). Our DSI ExConTec similation revealed it and we were able to correct it.

As you know their can't be negative tensions as the belt will buckle in response. We can use a negative tension alarm that will stop the analysis (since the analysis becomes invalid) or we can formulate equatuaions (knowingly incorrect equations) that will allow compression, allowing the analysis to continue. We chose the latter as this allows an invalid solution that reveals approximately the tension increase to produce a valid solution.

I presented the basis for the DSI ExConTec, publicly at SME 2000 in Denver. My presentation included a real project simulation. Larry, you were in attendance and I recall being surprised that you had no questions or comments. It was published in the proceedings and shortly after in Bulk Solid Handling, of Clausthal Germany.

The DSI ExConTec has been used many times since including at the haldback failure that I have mentioned.

Most recently we used it to simulate the uncontrolled run-back at a major (5000 HP) slope belt.

Responding to your two points: 1) Stored energy and dynamics, 2) Fluid coupling disengagement:

1) I may be over simplifying, failing to account for some added impact but my contention regarding stored energy (between jam and restraint) remains. The highs of a shock wave have exactly corresponings lows, and over the distance between jam (at the loading area) and restraint (at the head end), the highs cancel the lows. The net energy stored that then releases at the hold-back failure is the bound up drive torque and the inertia.

2) If by disengaging you mean that the inertia is decreased and the deceleration is increased, that is correct. With a fabric belt (high elongation, compared to steel), the motor having reached breakdown torque, not much of the maximum tension will be given up (not until failure of the hold-back) if the jam stop is sufficiently fast. ■

Mr. De Santos:

1. I missed your claims, at the SME 2000 conference, to have developed an elastic transient (dynamic analysis) model and the submission of validations. I will do the appropriate reading.

2. We have over 30 publications validating theory to practice and noting advancements dating from 1977. You can find many CDI expository studies of theory verses field measurement and verifications, with given conveyor specs., and the notation of the specifications and accuracies for others to follow. Often other researchers, academics and engineers cite our work. We do collaborate with others in the field as a courtesy as they develop competing software tools.



3. You claim to have corrected a CDI fault or flaw or oversight. This may be so. We do not profess to be flawless. However, I know of no installation, in the last 20 years, since the completion of BELTFLEX (1980), where such a claim has been layed against CDI. Since you have now made a public accusation, that we are culpable in failing to adequately analyze a belt conveyor of significance, tell us the story with some backup. Is the client Drummond Coal? Tell us the nature of the error or incorrect input data. Is my memory correct that you were working for Continental Conveyor at the time we worked on the Drummond Coal 8000 hp incline? Did you know of the missing facts at that time? Is Edmond O'Donovan aware of your claim, since I believe he did the analysis when he worked at CDI?

4. The conveyor capacity slope correction using the cosine angle on the belt's crossection was published as a part of the early DIN 22101 in the late 1980's. Maybe, I did not get your meaning or the point of this so I am willing to be taught that I missed the point.

5. Idler roll pressure influence on vertical and horizontal curves as they affect rolling resistance: We have practiced this condition since the mid 1980's as we developed our horizontal curve engineering (20 km Channar Overland in Australia prefeasibility in mid 1980's). For most conveyors, the significance is not dramatic. Our publications reflect this understanding. This predates your 1997 development by 10 years. I believe we discussed this very point when we published the results of the ZISCO 16 km overland commsissioning in Zimbabwe in 1995-1996.

6. Negative belt tensions do not exist as you note. Negative tensions imply buckling. You say your analysis cannot track the belt tension when you find negative tension.

There will be "no negative belt tensions" or belt buckling as long as:

a) belt motion remains in one direction when large belt sag occurs that becomes supported by the ground or stationary structural device.

b belt motion can reverse direction many times but cannot hit the ground or supports when doing so.

7. BELTFLEX can track the above "negative" belt tensions, and show they are positive, where other less accurate dynamic analysis routines predict negative tensions. We published this point in 1984, defined by a five point rheology based model, with the specific notation on 2-dimensional wave equation theory that corrects the error of "negative tension" phenomena.

8. What caused you to present this contention in a public forum claiming CDI ihas made a significant professional error? You do not afford a private discussion to see if the facts bear out your claims that CDI made an eror. I do acknowledge that we may have not got right what ever you have studied. We keep all of our records dating back to 1980. I am disappointment with your lack of professional courtesy in this manner.

I am confident we do good work as our measurements and 500km of successful installation tell us.

I appologize to the forum members for this discussion which should have been handled in another way. Still, there are some relevant points of interest that may prove to be an aid. ■

Larry,

1. I don't dispute your good work. I have followed it over the years and it has led the way in high tech conveyor analysis

2. You do have the tendency to dismiss the work of others as you did when you made assumptions on what we did or didn't consider in the analysis that we described

3. All work that I have described is since the founding of Dos Santos International in 1987. Again you have assumed wrong on the customer or customers

4. We did not correct any CDI analysis. We performed our study and analysis and got repeated correlation with the field

5. In a previous CDI study, a first analysis using BELTSTAT, failed to predict a slack belt condition because of incorrect take-up tension input. Had the correct data been used BELTSTAT would have predicted the slack belt occurrance. BELTFLEX was subsequently used, with the same input data, to predict the slack belt condition.

6. I am familiar with the angle correction that you mention but that is a load derating factor to account for the true surcharge angle. The generalization (the expanded conveyor technology, presented at SME 2000) affects all of the power tension equations.

7. The curve resistances (also presented at SME 2000) go beyond the roll pressures and include belt and material flex, unconfined and confined.

If you wish to continue the discussion outside of the forum please see my contact information ■

please help about telescopic conveyors how works.

working systems, chain or gearbox or hydromotor systems?

drawing,phtos,or link....

thanx. ■

Mr. Alibasar,

Your question may be too general.

1. A shuttle coneyor may be a conveyor on a wheeled carriage or structure that travels to different positions along its conveying length. Typically a single feed point loads the shuttle conveyor at various points along a skirted length and discharges the material to different points depending on the range of shuttle travel. Often shuttle conveyors have reversing belts increasing the discharge range.

2. It is also possible to create a shuttle head on a single conveyor by arranging the head and bend pulley on a common travelling structure. This is popular at telescoping stackers and shiploaders and at conveyor shuttle heads for optional discharge onto multiple cross conveyors, etc.

We can, on a consulting contract basis, provide a dedicated design for your requirements.

Joe Dos Santos ■