Hi Vikash,

By now you have learned that there are no instant answers on the internet.

If the Mountain doesn't come to Mohammed, then Mohammed will just have to go to the mountain. It seems no one is interested in quoting you for 450 kW conveyor drive VFDs. It is best to get on the phone and talk to some warmblooded people [try to avoid the cold blooded species. Their brains may have frozen as well].

Ring up your nearest Mining Company, or Quarry. Talk to the Maintenance Engineers about VFDs and Fluid Couplings. Don't be afraid to ask. You will make some good friends that way.

All the best - John.Rz

www.cospire.com / Engineering Tips ■

Dear Vikash K.,

First, to offer a comparison between the two systems in a public forum may antagonize the recipient of negative press, cause the reader to believe the writer is claiming they have an inferior product, label the writer to be biased for non-professional reasons, that the information will likely be misapplied, and therefore must be weighed against the public good. My following comments include a more general discussion than your specific details. Not having all the facts, including costs, leads to inventing assumptions, that may not be valid and therefore, limits an intelligent response.

Second, the comparison requires much pre-selection criteria. What type of fluid coupling is being compared – fixed fill, delay fill, drain-control, scoop-control, et al. What does the conveyor geometry require for prudent fluid coupling selection? Whose coupling?

Third, internals of fluid couplings are not all equal and do not have the same degree of drive efficiency (power slip loss which can vary between 2.5%-4%). Fixed fill levels cannot achieve the same degree of drive efficiency as adjustable fill couplings. The hydraulic efficiency has been perfected by some and copied by others. Construction techniques vary such as internal surface finish and baffle (internal fins) applications result in differing performance.

Fourth, the type of fluid (water, oils) and ambient temperature (sun, shade) alter the fluid in coupling’s viscous shear strength and therefore the coupling’s drive efficiency (winter, summer) and control regulation. Therefore where the coupling is to be used has a bearing on its selection and on the impact to the conveyor's design (component selections).

Fifth, the comparative fluid coupling fill level and resulting drive efficiency varies with conveyor load. In general, higher fill levels equate to higher drive efficiency. Unfortunately, the higher fill levels may not be achievable due to the need for a “soft-start” control as dictated by belt strength, conveyor geometry (vertical curve sizes, belt sag control, drive slip control, take-up type, location, regulation, et al) and so on.

Sixth, do the conveyors need a fixed speed or can they be improved with a variable speed associated with changes in production rates?

Seventh, does reliability matter? Does availability matter?

There are many more preambles which can be offered by others. Some points of interest, not in any order of importance, comparing the two concepts are:

1. Variable speed vs fixed speed – can variable speed be an advantage such as belt wear, dust mitigation, et al.

2. Drive slip energy recovery can equate to $$$$ in power savings that may exceed NPV capital cost of equipment

3. Complexity of electronics vs complexity of fluid (seals, cooling, …), possibly one electronic device used in lieu of many fluid coupling devices

4. Optimal selection of starting control and stopping control tailored to conveyor geometry that may reduce the belt strength and supporting structural requirements

5. Ability to multiplex motor control electronics resulting a big capital $$$$ savings. Ability to start many drives from one control device – 1976 at Mexico’s La Caridad copper mine I used 4 inverters to soft-start 21 motors, ranging in size from 50 hp to 600 hp on 12 conveyors and incorporated a universal spare that could replace any of the four inverters, which could have a malfunction, within less than 1 hour. The conveyors were configured with an assortment of drive systems including 1800 hp downhill to 2400 hp uphill, fabric and steel cord belts, and a mix of drive sizes.

6. Improved repair time (MTTR) by having trouble shooting annunciated in electronic form verses having to make site inspections of mechanical components.

7. Knowledge of end user’s maintenance crew and access to regional support

8. Engineers misapplication and/or misunderstanding of the needs of each system

9. Load sharing complexities – drive systems do not need to be matched to motor sizes with inverters but must be matched with fluid couplings.

10. Ability to move and spot belt repairs to a designated location.

11. Electronics (manufacturers) may not be supported after many (>15) years of service due to technical/manufacturing advancements in components.

12. Inverters (VFD) offer special load sharing methods can be implemented on complex conveyor geometries with electronics that are not possible with fluid couplings such as modern conveyors with difficult terrain and use of horizontal curves. This can strongly influence civil (cut and fill) and structural engineering. In some instances, the conveyor would not be financially feasible with a fluid coupling.

13. Understanding the advantages and disadvantages of very fact electronic regulation of the inverter must be understood by the designer and the supplier, especially when using multiple drives on one conveyor. Too often, the supplier does not understand the belt conveyor's elastic memory and subsequently does not understand how to properly tune the equipment. This leads to end user complaints about the equipment that should be directed at the designer and supplier's lack of knowledge, not the equipment's function.

14. Fluid coupling does offer an advantage in trouble shooting simple conveyors. Many clients prefer simplicity and do not have necessary electronic component field support. Given today's high $$$$/hour for production, simplicity counts.

15. You may not be able to use the same motor from the fluid drive due to incompatibility with the inverter of choice, necessary torque verses speed curve differ between inverter and fluid coupling, and the need to ground the motors bearing assembly when using an inverter.

16. Fluid couplings offer a mechanical overland protection one can argue is more fail-safe. However, there are many problems one can also list associated with "what-if-failure" scenarios resulting from fluid coupling seal and bearing failures, wrong fluid fill levels being applied, problems with the coupling being too strong for the conveyor, imbalance of coupling halves, et al. I have seen fluid couplings pull down a building structure due to their misuse.

17. VFD's, in general, need a special protective environment to maintain the health of the electronics against temperature extremes, moisture and dust. More so than the fluid coupling.

This list is not complete, it is a start. ■

Excellent stuff,

Is that what we need engineers for?

Regards - John.Rz ■

Thanks John,

I offer some corrections to the above and add the following:

Corrections:

pt 13: " very fast" not "very fact"

Pt 16: "overload" not "overland"

Additions:

17. Inverters can be used to minimize belt flap vibration by shifting (up or down) the operating speed away from a critical modal frequency thereby saving idler life, minimizing idler frame strength, reducing vibration energy and power loss, and reducing environmentally cursed flap noise.

18. Since inverters can be literally removed from a “fixed belt speed” operating circuit paradigm, the inherent reliability is vastly improved. By installing a second MCC for each motor, the inverter power module can be: a) shared/used for a second, third, … conveyor drive, b) can be parked or idled and be out of the operating/normal running circuit, and c) can substantially lower spares inventory and cost. It can then be tuned/altered/repaired off-line as required. All of these benefits/features were used on La Caridad. When using very large conveyors, this offers great capital cost benefits, great power savings (2-4%), all the prior noted features, and superior reliability and availability by eliminating a starting or stopping control device (fluid coupling) that otherwise has to be installed on every motor while in its running operation. For La Caridad the savings over a fluid coupling system or wound rotor drives exceeded $1.5 million (USD) in 1976 dollars.

19. See prior VVVF Drive forum and other Google postings (note: some is sales literature and should be considered as such):

https://forum.bulk-online.com/showth...threadid=13106

http://domino.automation.rockwell.co...0?OpenDocument

http://www.voithturbo.com/applicatio...4ecr298e.pdf

http://www.nwalliance.org/research/reports/E00-054.pdf

20. Dr. Robin Steven (Goodyear/Veyance Technology) has now written two papers on the 20 km Curragh overland and its many innovations applied to its design. Some include: a) improved rubber rolling resistance and its benefits, b) adjustable speed drives (VFD) that deliver tonnage rate on demand and the savings derived, c) variable geometry curved transfer chute, d) belt wear, e) wide pitched idlers and the use of variable idler roll diameter, ….

The first paper was presented at the Newcastle University Material Handling conference in Australia, 2007. The second will be forthcoming in the Bulk Solids Handling magazine in the coming issue.

21. I will publish the benefits of the adjustable speed control and other features of the Curragh design in a coming BSH issue as well. In part, this article will counter the argument that adjustable speed control do not produce strong economic benefits. This claim was made, in a technical paper, by a Voith coupling user/engineer/technician/fan. I tried searching on-line for the article without success. I have it at work and will so post it Monday. ■

Forty years before now when I selected couplings for connectong motor to gear box of a higher rating for equipment like conveyor, which requires starting from fully loaded belt, I used Fluid couplings.

After twenty years, I was still seleting fluid coupling as VFD was available but users did not have experence in using it. Cost was another consideration.

Today, both systems are reliable. It is your choice. ■

More stable: 1.Highest casting technology,Dynamic balance is the most stable

2.Flexible drive:Enhancing accelerate the dynamic balance of the whole unit

3.Low pressure casting processarts seldom imbalance , high-speed rotating is very small

More faster:Improve the start performance of motor, reduce the starting current, reduce the start impact

More convenient:Users do not need to purchase oil

More safer:1.No leak within three years, Adopte the imported FKM oil seal replace domestic NBR seal (100 ),resistance to high temperature (200 ),double the service time.

2.Static seal(ie flanges)adopt high quality O seal and special seal glue(specialty for automobile gearbox)to double seal.(compared to normal only sealing gasket or O seal).

3.Special safety device to prevent overload, protection of motor, the working machine damage due to overload

4.Material upgrading, more reliable, more durable

Most durable:1.Adopte imported bearing(SKFFAG) replace the domestic bearing

and it will easily maintain for its body-integral design. Fewer equipment and flexible control. ■

Originally Posted by Vinayak

Forty years before now when I selected couplings for connectong motor to gear box of a higher rating for equipment like conveyor, which requires starting from fully loaded belt, I used Fluid couplings.

After twenty years, I was still seleting fluid coupling as VFD was available but users did not have experence in using it. Cost was another consideration.

Today, both systems are reliable. It is your choice.

Dear Vikash,

The Opinion given by Mr.Nordell, contain every Tit-bits needed to know.

While going for a new system,it is worth considering the VFD.

If the existing system is Fluid coupling system,Why do you want to change to VFD.Your system may not require a multiple speed.

As suggested by Nordell,you need an MCC near the motors due to voltage drop.

The motors have to be derated for running in lower speed for cooling purpose.

If you still like to go for VFD,You can approach any one reputed VFD manufacturer. One suggestion is to go for VFD and Motor of the same make for better matching.

That does not mean different manufacturers product does not match.

Rgds,

Narayanan Nalinakshan, ■

Hello,

User of the equipment is the right party to opine about his experience regarding which one he has found better, as per ‘his perception’. I do not have opinion about it, but some apparent and external differences between the two are as below:

1) Price and life expectancy

2) When the conveyor has to stop / trip by any reason, then in case of scoop type fluid coupling, motor can continue to run and only conveyor will stop by automatic emptying of oil from working circuit. This becomes an important issue in case of HT motor, which cannot be started immediately without cooling period (number of starts per hour). Thus scoop type fluid coupling permits stoppage and starting of ‘conveyor proper’ many times successively. In case of VVVFD drive, conveyor stoppage means stoppage of motor also. So one has to see how many starts / stops are permitted if these are different for motor with VVVFD drive compared to usual starts / stops mentioned in motor specifications (including interim cooling period).

3) Scoop type fluid coupling will have mostly mechanical maintenance. As against this, VVVD drive will have maintenance of electricals and electronics of specialised nature. The user has to see which way he will be comfortable.

4) The VVVFD drive requires space for installing panel and other electricals, near drive or at some place, which can be a matter of concern, sometime. The issue to be seen for LT drive and HT drive (both may have a different need). Requirement for ventilation / air conditioning as applicable. Also the suitability for prevailing environment condition.

5) VVVFD drive is useful for soft (gradual) start including constant acceleration start-up (irrespective of load condition), like scoop type fluid coupling.

VVVFD drive’s other provision of operating conveyor at reduced speed, has limited application. It is possible when: 1) Conveyor is practically stand-alone type, and its feed rate control can be directly linked to the concerned conveyor. 2) Conveyor is discharging into some stockpile or bunker (and not to the down-line system).

Most of the material handling plants have complex system comprising of feeders, crushers, screens, stackers, reclaimers, interconnecting chute work and so on, which are tuned during commissioning to operate for handling rate upto design capacity at set speed, without botheration for adjusting individual equipment operational speed. Any tempering with the operational speed of conveyor/s within such system can become hazardous.

As an example, ship unloader is set to unload material at certain peak capacity, and down-line equipment / conveyors are also set to deal with this peak capacity all the time. Now, there is situation that ship unloader unloading has become less, and seeing the less cross section on belt, the conveyor operator reduces the speed. Then the situation arises that the ship unloading rate is normal and starts feeding accordingly. If there is a communication between ship unloader operator and concerned specific operator of conveyor, then everything will be fine, otherwise it will result into material blockage in chutes and damage to equipments. Such thing can happen due to lapse (forgetting to communicate due to work pressure to manage his own machine).

Air traffic control type communication perfectness and reliability is impossible among operating / concerned engineers in material handling plant. Some may be in meeting or attending more crucial issues of material handling management, rather than to involve in conveyor / equipment speed management. My point is only to emphasise that keeping provision to vary / choose conveyor speed, is unnecessary and hazardous for the entire plant of such complex nature. Also, it puts unnecessary burden on plant operational management for vigilance and introduces element of apprehension and risk all the time. As against this, the fixed speed conveying system is fool-proof with simple activity of on-off.

Well, user / buyer / other is free to have his own opinion, and opt for the system accordingly.

Regards,

Ishwar G. Mulani

Author of Book: Engineering Science And Application Design For Belt Conveyors (new print November, 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: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■