Yes they can change during start-up and stopping. As the belt stretches and relaxes during start-up the velocities will change even as it goes around the drive pulley and as it retracts from a stretched state it can exceed the design speed.

Dynamic Analyst software by Overland Conveyor can simulate the stopping or starting of a conveyor for full dynamic analysis of any conveyor system. ■

Originally Posted by Himanshu

To all Concerned,

In order to carry out a dynamic analysis of trough belt conveyor, I disintegrated the belt into numerous finite elements. Considering the elements around the drive pulley, Can these elements have velocity greater or less than the design speed of belt? ( cuz the elements on drive pulley have constant speed due to drive motor)

Regards,

Himanshu

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The elements placed around a drive pulley can also slip depending on traction factors. Furthermore, the drive pulley speed can change with more or less (+/-) demand power. ■

Originally Posted by nordell

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The elements placed around a drive pulley can also slip depending on traction factors. Furthermore, the drive pulley speed can change with more or less (+/-) demand power.

Dear Nordel,

I think the question raised is interesting. For instance in cases of DOL starting and Fixed fill fluid coupling starting integrated with gearbox, the pulley rpm is proportional to motor speed and belt velocity at drive element is same as pulley surface speed considering there is no slip (with adequate take-up tension). Motor speed or fluid coupling output speed can only follow its torque-speed curve. If the load torque always remain positive, the motor or fluid coupling output speed can not exceed synchronous speed at any point during starting regime. However speed can go higher than rated speed, but can never exceed synchronous speed during stabilization phase. Since rated motor speed and synchronous speed difference is generally around 2%, the belt speed at drive element also can exceed by about 2% at the most disregarding local stretch etc. Well, that means we may have to force the first element to follow the motor/fluid coupling speed irrespective of the solution of differential equations. Nordel, your knowledge in this regard is immense and you may guide the question initiator. ■

Belt speed around a drive pulley is everywhere changing. The greater macro view - incomming belt is a speed "A", changes to speed "B" on exit, where "A">"B" due to belt shortening as tension is reduced from A to B. The actual condition is more complicate with belt slipping backward on entry and forward on exit. If you want a good read try Zeddes (sic) Ph.D. dissertation from Hannover University. I do not recall the actual title. He came after Hohman and did good work defining the relationship between belt motion and drive pulleys and non-drive pulleys.

There are other works that have a similar behavior - studies on metal deformation to stretch and straighten sheet metal in cold rolling where metal is passed over many bridle rollers upon which the metal is slightly pushed past yield on each roll set. After passing through a number of rollers, the shortened zones in the metals web elongate to approximate the longer zones (i.e. more motion during yielding). Although not material handling, the question of how to solve the relative motion within the bridle is similar to the solution of belt motion on pulley surface. It is quite complex. ■

I should add the above point is for a postive powered belt. If regenerative, the reverse is true. ■

Himanshu,

Did you examine a cylindrical or crowned pulley? ■

Originally Posted by nordell

Belt speed around a drive pulley is everywhere changing. The greater macro view - incomming belt is a speed "A", changes to speed "B" on exit, where "A">"B" due to belt shortening as tension is reduced from A to B. The actual condition is more complicate with belt slipping backward on entry and forward on exit. If you want a good read try Zeddes (sic) Ph.D. dissertation from Hannover University. I do not recall the actual title. He came after Hohman and did good work defining the relationship between belt motion and drive pulleys and non-drive pulleys.

There are other works that have a similar behavior - studies on metal deformation to stretch and straighten sheet metal in cold rolling where metal is passed over many bridle rollers upon which the metal is slightly pushed past yield on each roll set. After passing through a number of rollers, the shortened zones in the metals web elongate to approximate the longer zones (i.e. more motion during yielding). Although not material handling, the question of how to solve the relative motion within the bridle is similar to the solution of belt motion on pulley surface. It is quite complex.

Does the finer point made by you is taken care of while doing belt conveyor dynamic analysis as it stands today ? If it is a different research issue then it does not have much relevance to the discussion we are in. ■

Originally Posted by nordell

Belt speed around a drive pulley is everywhere changing. The greater macro view - incomming belt is a speed "A", changes to speed "B" on exit, where "A">"B" due to belt shortening as tension is reduced from A to B. The actual condition is more complicate with belt slipping backward on entry and forward on exit. If you want a good read try Zeddes (sic) Ph.D. dissertation from Hannover University. I do not recall the actual title. He came after Hohman and did good work defining the relationship between belt motion and drive pulleys and non-drive pulleys.

There are other works that have a similar behavior - studies on metal deformation to stretch and straighten sheet metal in cold rolling where metal is passed over many bridle rollers upon which the metal is slightly pushed past yield on each roll set. After passing through a number of rollers, the shortened zones in the metals web elongate to approximate the longer zones (i.e. more motion during yielding). Although not material handling, the question of how to solve the relative motion within the bridle is similar to the solution of belt motion on pulley surface. It is quite complex.

The finer point you made is good for research, but is it taken care of in today's dynamic analysis ? At least in published output we do not see that. If so, then the point is not relevant to the discussion under present thread. ■

Originally Posted by ambhad

The finer point you made is good for research, but is it taken care of in today's dynamic analysis ? At least in published output we do not see that. If so, then the point is not relevant to the discussion under present thread.

We do not do so with our standard BELTFLEX model. The frame of reference must change to do so. ■

Hi all..

In practice if you ignore this effect you will not fall into a hole.

Its really not worth worrying about..

Cheers

LSL Tekpro ■