You've forgotten to ask about horizontal curvature & both strands loaded. But you have managed to try for nearly everyting else.

It would be unwise to profer advice on such a wide topic without some actual details being available. I suggest you read relevant texts & publications on this complex matter & then provide more information. ■

Hello,

As said by the earlier participant, it is not practical to narrate exact design procedure in forum. However, I am mentioning some basic points to be taken care during designing by the readers at large, and this is not addressed to the experts.

The conveyor is considered decline conveyor if looking from tail end to head end it has got negative inclination with respect to horizontal i.e. head end level minus tail end level is of negative value. The material is conveyed from tail end to head end.

The conveyor designer knows that steady running belt conveyor motional resistance R is comprising of following two components as below:

Conveyor resistance R = (Frictional resistances) + (Material lift resistance Mm.g.H) in newton force. In this Mm is material mass kg/m and H is the lift in m, g is gravity acceleration constant 9.81 m/s2. The material acceleration resistance happens to be comparatively of small value and not mentioned here.

The frictional resistances are always positive because friction simply opposes the motion whereas the material lift resistance will be negative when H is of negative value. In a sufficiently sharp declined conveyor, the material lift resistance of negative value will exceed the frictional resistance. In this situation, conveyor will tend to run on its own and overshoot the design speed unless prevented by the restraining torque or braking torque by drive. Such conveyor and situation is called regenerative conveyor.

Rule - 1:

Now, conveyor often runs empty when there is no feeding. In this situation, magnitude of Mm will be zero and therefore helping force Mm.g.H will be also zero. So the same conveyor has frictional resistance of positive nature only and it will be demanding power to operate. So first rule is that there is no pure (singularly) regenerative conveyor. The regenerative conveyor has to always operate in positive power mode and also in regenerative power mode. Therefore designer has to design such conveyor proper operation considering both situations:

-Maximum positive power demand mode at drive when it is empty (or also material on leveled belt and up-inclined zones only but not on declined zones).

-Maximum negative power situation when it is fully loaded (or also material on declined zones only but not on leveled belt and not on up-inclined zones).

Rule - 2:

The conveying usual (basic) friction coefficient value is 0.02. However, this can have variation from 0.012 to more than 0.02 as per statutory practice. In case of decline and regenerative conveyor it is mandatory to design it considering usual friction coefficient 0.02 or more for maximum positive power condition i.e. empty condition, etc. and f = 0.012 for maximum negative power (regenerative situation), at design capacity. This is rule number 2.

Rule - 3:

The conveyor will have usual arrangement of drives. There are no separate drive to operate for positive power mode and separate drive to operate for negative power mode. Same drive automatically takes care of positive power mode or negative power mode without manual intervention. The designer chooses location of drives considering economy and feasibility. This is rule number 3.

Rule - 4:

Restraining torque during continuous operation is applied by drive electrical - mechanical features and not by traditional mechanical brakes. Mechanical brakes will wear out quickly and are not suitable for continuous operation (restraining torque purpose).

Rule - 5:

Mechanical brake in drive gets applied only in case of system (conveyor) stoppage command. Often there are 2 brakes wherein one is supposed to stop the conveyor, however if it fails to achieve this within prefixed time then another brake also acts. This is for safety reason (also for avoiding extra strain in conveyor due to harsh braking by two brakes simultaneous operation).

Rule - 6:

During positive power mode, the belt which is approaching to drive pulley will have more tension compared to the belt going away from pulley which will have less tension. This difference is tractive pull applied by the drive pulley.

At the drive pulley during negative power mode, the belt which is approaching to drive pulley will have less tension compared to the belt going away from pulley which will have more tension. This difference is restraining pull applied by the drive pulley.

Rule - 7:

Belt tension notations with respect to locations are always kept fixed and final at conveyor ends whether it is positive power mode or negative power mode. So belt which is approaching to head pulley has always tension T1 and belt which is leaving the head pulley will always have tension T2. At tail end, belt which is approaching to tail pulley has tension T3 and belt which is going away from tail pulley will have tension T4. Their numerical values will be according to drive location. Changing these notations will create confusion in interpretation.

For general information I have attached motor torque speed curve for induction motor, UK publication : Herbert Vickers Induction Motor. This type of motors have inbuilt restraining torque that comes into action moment it crosses synchronous speed. As an example, when motor is running at 1480 rpm (synchronous speed 1500 rpm) it applies positive torque but when it becomes say 1520 rpm, it automatically applies restraining torque of practically same magnitude. So such motor tends to run around 1500 rpm whether resisting torque is positive or negative. Thus induction motor or its variants like slip ring motor, frequency variation, etc. can have consideration for probable suitability. Widely used other example is hoisting motor of EOT crane where motor operate for positive power when lifting load and negative power when lowering the load. This is for general information. The reader to consult electrical experts about the type of motor and electrical system to be used.

Conveyor design mechanical and operational aspects are fixed by conveyor designer in association with electrical engineer.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis is ISO (thereby book is helpful to design conveyors as per national standards of most of the countries across world). New print Nov., 2012.

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

Email:

href="mailto:conveyor.ishwar.mulani@gmail.com">conveyor.ishwar.mulani@gmail.com

Visit website:

href="http://www.conveyor.ishwarmulani.com" target="blank">www.conveyor.ishwarmulani.com

Attachments

induction motor torque speed graph.jpg (JPEG)

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Let me check it, very good share, thank you. ■