Originally Posted by jishnubhel

Dear Sir,

Recently, in one of the tenders, we have come across a new arrangement of dual drive on the return side of a 517m long conveyor (with a TPH of 2100 & 2m/s) with a lift of around 62 metres (please refer the attached sketch). The probable reasons for the arrangement are the following:-

1)Keeping the drive at zero metre elevation enables the possibility of easier maintenance and operations.

What are the precise foreseen O & M requirements?

2)The pull due to belt tension at 66.5metres will increase the slenderness ratio of the building columns and henceby the column size.

Is there any evidence for this?

My question is:-

1)Will there be any difficulty in belt training compared to conventional case of drive on the head end? Or in other words, is there any chance of the belt going off track very frequently compared to conventional drive case (ie drive connected to the head end at 66.5metres elevation)?

You main difficulty will be holding the drives down against the belt uplift. Mis-tracking is a detail affair which can occur anywhere, any time.

2)Is there any specific disadvantage in such a dual drive arrangement?

Apart from the crazy uplift forces. Structures behave better when the lines of action of the imposed forces act reasonably longitudinal to that structure. Belt tensions are generally meant to run down the stringers and columns are meant to support the structure. If you put 5 times the tension into the columns you are hardly economising on structural quantities. Is the dual drive justified in the first place?

3)Are there any specific merits for this type of dual drive arrangement over conventional arrangement?

There is no merit. Clearances around the tangent point of the curve are not shown so the potential for locating the drive nearer to the tangent point with the return belt running down to grade region are not known. That solution would have reduced the column dimensions around the GTU etc.

If we give you a free design,necessary to work out the drive weights, we open ourselves to later criticism. You need to work out the drive weights and the detailed material handling processes. If you ever have to remove a drive or high tension bend pulley the mass is likely to be very similar. Motor and gearbox will not be all that much heavier. Hoisting from high level requires a large drum storage and repair periods are greatly influenced by wind. Personnel access, equipment set down landings, monorail fixings and our old friend the GTU supports will not vary much from one design to another similar case. I can cut out 6 bend pulleys, maybe more, reduce and column weights even without analysing the drive requirements.

Thanks

Jishnu V

What is the material? 2ms^-1 seems rather slow for 2100th^-1. ■

Originally Posted by jishnubhel

Dear Sir,

Recently, in one of the tenders, we have come across a new arrangement of dual drive on the return side of a 517m long conveyor (with a TPH of 2100 & 2m/s) with a lift of around 62 metres (please refer the attached sketch). The probable reasons for the arrangement are the following:-

1) Keeping the drive at zero metre elevation enables the possibility of easier maintenance and operations.

2) The pull due to belt tension at 66.5metres will increase the slenderness ratio of the building columns and henceby the column size.

My question is:-

1) Will there be any difficulty in belt training compared to conventional case of drive on the head end? Or in other words, is there any chance of the belt going off track very frequently compared to conventional drive case (ie drive connected to the head end at 66.5metres elevation)?

2) Is there any specific disadvantage in such a dual drive arrangement?

3) Are there any specific merits for this type of dual drive arrangement over conventional arrangement?

Thanks

Jishnu V

Return side dual drives is a common practice in the industry. But there are many things that need to be taken into consideration when designing such a system. For one example the snub pulley at each drive pulley is on the high tension side of the pulley and should be on the low tension side.

To answer your questions:

2-1 - There will be no difference in the belt tracking as tracking is a function of the alignment of the system and the squareness of the splicing. Also the quality of the belting plays a factor in the tracking as well. The location of the drive has no effect on tracking.

2-2 - The main disadvantage is that you put the head pulley in high tension on both side (T1 in and T1 out) and any other pulley prior to the drive. In your diagram there is no need for the snub pulley at the head pulley. Snub pulleys are normally only installed to create a greater surface area between a drive pulley and the belt to reduce the slippage factor. Also for any dual drive arrangement the synchronization of the loads between the 2 motors is very critical as well as 100% matching components between the 2 drives.

2-3 - As you mention in #1 the main advantage is ease of maintenance. ■

Hello,

The conveyor arrangement shown by you implies that you have following aims:

- Not to have drives at head end

- Drives to be at ground level

Arrangement - 1: This is the arrangement as shown by you. This has 2 nos. of drive pulleys + 4 nos. of HT non drive pulleys + 5 nos. of LT non drive pulleys + 2 nos. of snub pulleys.

Arrangement - 2: Your aforesaid aim can be also achieved by reviewing layout which will have 2 nos. of drive pulleys + 3 nos. of HT non drive pulleys + 5 nos. of LT non drive pulleys + 2 nos. of snub pulleys. In this case drives and horizontal gravity take-up will be at one place (ground level) and constitute a single composite arrangement. It has one pulley less and attending HGT is easier compared to VGT.

Arrangement - 3: This arrangement will have standard dual drive at head end and VGT at some intermediate location. The head end dual drive will comprise of 2 drive pulleys and 1 LT non drive pulley. In addition it will have 4 nos. of LT non drive pulleys and 1 snub pulley.

Merit / demerit:

A) Arrangement - 1 and 2: These have 3 nos. or 4 nos. HT non drive pulleys more compared to arrangement - 3. The HT non drive pulleys weight and price will be comparable to drive pulleys. Your shown arrangement -1 will be applying large lift up force on foundation due to belt tensions. So arrangement - 1 drive foundation are likely to be expensive (its exact structural arrangement is not clear).

The head end tower do not have weight of drives but the horizontal thrust acting at top will be huge corresponding to 2 x T1. Tall structure of such height with horizontal large thrust at top is likely to make the structure expensive.

B) Arrangement - 3: The head end structure will be subjected to less horizontal thrust corresponding to (T1 + T2) instead of 2 x T1. The tower can easily take vertical load of drives. The tower structure is likely to be economical in spite of some vertical load of the drives . It might appear that the drives are likely to increase cross section of tower but it seems it may not be so. In case of arrangement -1 and 2, to withstand the large horizontal thrust it would be necessary to have certain cross section of tower and this may turn out to be nearly same as for arrangement - 3.

It is better to ask quotation for all 3 arrangements. See their economy and suitability, and opt for one which suits you. This will also provide supporting papers for the decision so made rather than relying on opinions about the subject, which could be conflicting.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis 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: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Dear Mr.Jishnu,

Will one single drive pulley with dual drive arrangements on both side of the pulley can't be considered? I think it can reduce numbers of pulleys.

Regards, ■

Hello,

Referring to Shri S. Ganesh query, the information is as below:

For a specific conveyor, suppose during conveyor design 500 kW drive power is allocated to particular drive pulley. Now, whether there is 1 x 500 kW single drive at one end of this drive pulley or 2 x 250 kW drives (i.e. one 250 kW drive at each end of this drive pulley); then there is no change / advantage in belt tensions and conveyor design.

Sometimes, the design engineers opt for dual drive type of arrangement as below to achieve standardisation. Suppose conveyor total power is 300 kW and designer wants to have 200 kW power for primary drive pulley and 100 kW drive for secondary drive pulley. So one can do this as below:

- 200 kW motor for primary drive and 100 kW motor for secondary drive. This will have a 2 sizes of motors.

- 100 kW two motors coupled to primary drive pulley (one at each end) and 100 kW drive for secondary drive pulley. This means only one type of motor for conveyor.

Ishwar G. Mulani

Author of Book: ‘Engineering Science And Application Design For Belt Conveyors’. Conveyor design basis 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: conveyor.ishwar.mulani@gmail.com

Website: www.conveyor.ishwarmulani.com ■

Dear Shri.Mulani sir,

If two separate drive pulleys installed in a single conveyor, I have seen problems due to non synchronisation between the drive motors, whether they are operated by variable frequency drive or by DOL method.

As a maintenance engineer, I would opt for dual drive pulley, which will have two drives, i.e., one drive on each side of the pulley.

Please offer your opinion.

Thanks and many regards,

S.Ganesh. ■

I asked about the dual drive necessity in an earlier reply. Ishwar's advice is valued.

Simplistically, as usual, belt tension approaching a drive is limited by the coefficient of friction, wrap angle and the departing tension. If there is insufficient difference available between the approaching and departing tensions there is insufficient force to shift the material burden and its associated losses. Extra drive pulleys, usually one, are then necessary to provide the full tractive effort. Such an unfortunate situation regularly occurs and synchronisation problems are commonplace, even on these forums.

Conveyor belts still have their limits. ■

Originally Posted by Gary Blenkhorn

Return side dual drives is a common practice in the industry. But there are many things that need to be taken into consideration when designing such a system. For one example the snub pulley at each drive pulley is on the high tension side of the pulley and should be on the low tension side.

To answer your questions:

2-1 - There will be no difference in the belt tracking as tracking is a function of the alignment of the system and the squareness of the splicing. Also the quality of the belting plays a factor in the tracking as well. The location of the drive has no effect on tracking.

2-2 - The main disadvantage is that you put the head pulley in high tension on both side (T1 in and T1 out) and any other pulley prior to the drive. In your diagram there is no need for the snub pulley at the head pulley. Snub pulleys are normally only installed to create a greater surface area between a drive pulley and the belt to reduce the slippage factor. Also for any dual drive arrangement the synchronization of the loads between the 2 motors is very critical as well as 100% matching components between the 2 drives.

2-3 - As you mention in #1 the main advantage is ease of maintenance.

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I disagree with Gary:

2-1 Tracking - The selected dual drive arrangement will be harder to track and maintain alignment. Having multiple dirty side contacts is bad enough. Having two at high tension is worse. Having one above the other is more problematic with the upper pulley feeding the lower with sludge and dilating the lower diameter which will cause belt splice stress, drive instability and difficulty in load sharing. Having 5 pulleys in near distance allows telegraphing of poor alignments to exacerbate tracking.

2-2 Agree with elimination of head snub.

2-3 The mid-station drive is good for lazy maintenance crews and bad for belt operation:

1. First, likely problem with 11 pulleys vs. 2. The 11 have 3 high tension dirty side contacts before the drive adding to undesirable drive fluctuations and is detrimental to belt splice endurance.

2. Second, belt tracking noted in 2-1 is a serious disadvantage to operation

3. The 11 will lower system availability with high pulley count all other noted problems

4. The 11 will cause much higher fluctuation of TUP system - higher stored energy on return strand between head and drives

5. The 11 will likely cause higher pulley repair of lagging on dirty side contacts

6. The 11 will likely cause higher pulley replacement rate due to higher fluctuating fatigue stress unless designed for this condition

7. The 11 will have a large wind sail with the high drive & TUP drop-rise-drop-rise configuration. Making pulley manufactures very happy. Bad on budget and maintenance.

You save a few shekels on belt to spend on 11 pulleys, their support system verses one head drive and one tail take-up. My vote is better operation and reliability with 2 pulley system.

As Mr. Gately states, why 2 m/s? You will need a 1800 mm belt @ 2 m/s vs 1200 mm belt @ 4.5 m/s. Then you get advantages of:

1. Lower belt width and strength 1800 mm vs 1200 mm and ST rating from ST-1500 N/mm to St-800 N/mm

2. Larger carry idler spacing to 3-4-5m vs 2m and same for return

3. Few pulleys at much lighter load

4. Lighter TUP mass and all auxiliaries

In summary, a better cost effective and reliable system than your proposed. No dirty side contacts, saving 9 pulleys, simple drives (could be 2 x 300 or 1 x 600 KW on one head pulley), much lower idler cost and maintenance, and so on. ■

I had thought that the upper left inset as shown referred to the alternative head end drive.

Going on for ever on this one I noticed that the head end needed a bit of explanation anyway.

Why is the belt lifted over a brow at the carrying side and then left to almost scrub a cross member after the snub drum? If the carrying belt was run directly to the head drum the wrap would increase and the column heights would be marginally reduced throughout and there would be less need to carry worn out rollers up to the brow.

Both strands are elaborately misguided. Even if most of the water has run back downhill there should be better cleaning room at the head end, snub or no snub.

Once a concept goes astray it stays astray.....(I had trouble spell checking that.) ■

Originally Posted by johngateley

I had thought that the upper left inset as shown referred to the alternative head end drive.

Going on for ever on this one I noticed that the head end needed a bit of explanation anyway.

Why is the belt lifted over a brow at the carrying side and then left to almost scrub a cross member after the snub drum? If the carrying belt was run directly to the head drum the wrap would increase and the column heights would be marginally reduced throughout and there would be less need to carry worn out rollers up to the brow.

Both strands are elaborately misguided. Even if most of the water has run back downhill there should be better cleaning room at the head end, snub or no snub.

Once a concept goes astray it stays astray.....(I had trouble spell checking that.)

===========================================================

John,

You certainly give greater observation than I.

The head pulley has no target symbol and I guess has no drive.

Right on the convex head end. Bad Juju - no gain but lots of pain - idler failures, splice failures and for what - slight change in discharge trajectory at 2 m/s?

The design has many flaws when compared to modern practices. They know not what they practice.

Our solilique may not be heard, is often misunderstood, and is without merit to the masses. ■