Neil,

45 degree trough angle idlers are capable of handling a higher capacity of product for a given belt width -- BUT -- the higher angle also requires longer transition lengths at all pulleys in order to prevent belt damage (longitudinal cracks at the trough junction points). This does not present a problem except at the discharge pulley, where it makes little sense to carry a greater amount of material on the carry run and then have it overflow the belt just prior to discharge. All belts, regardless of the idler troughing angle must be able to support the conveyed material while essentially flat (i.e. -- while going to the discharge pulley).

In my opinion, the real advantage of the higher angled troughing idlers is with their ability to contain material (less spillage potential) at the load point (allows some bounce room) and along the carry run (minimizes wind influence on the material and bounce effect of the idlers).

The disadvantages of the steeper idlers include the increased transition zones, increased chance for belt damage, and increased mistracking susceptibility (the wing idlers have a greater effect on tracking and the belt is affected by wind to a greater degree).

Like most conveyor components, steep trough idlers have their place and offer advantages when used judiciously. Any system should be designed with the needs of the end user in mind (even if the end user doesn't really know what those needs are) and it is incumbent on the system designer to offer the most economical system possible -- taking into account all costs, including maintenance and operational ones.

If you have specific systems to discuss, I would be willing to help as necessary (especially if I can get a trip to Australia out of it - you pay for time, my frequent flier mileage account pays for air travel).

Regards, ■

Dear Sir

High trough angles (40-45) are often used today due to better knowledge of the applications:

1. They consume more power due to the higher compound bending of the belt at the idler junction and higher pressure on the center roll - published in Bulk Solids Handling Power of Rubber Part I.

2. The high stress at the idler junction must consider the belt construction and its adequate fatigue resistance to junction failure. Thin belts tend to have inadequate resistance to troughing load support - steel cord or fabric. Thus, idler spacing also plays an important role in defining the use of high angle troughs.

3. They track better than 20-35 degree trough belts due to the increase force differential from lateral displacement - ie horizontal curve design technology.

4. Often 40-45 degree idler trough designs use a shortened center roll which yields 3 important features: a) it decreases the pressure on the center roll = lower power and junction stress,

b) balances the idler bearing loads, c) increases the cross-sectional capacity = 28% of belt width for center roll length has about 10% better capacity than the standard CEMA/DIN/ISO 37% of belt center roll length ( 3-equal roll lengths)

Lawrence Nordell

Conveyor Dynamics, Inc.

1111 wesst Holly St.

Bellingham, WA 98225

USA

ph 360/671-2200

fx 360/671-8450

email nordell@conveyor-dynamics.com

website www.conveyor-dynamics.com ■

Hello Kinder,

Earlier respondents have already provided adequate information on the subject. In general, 40 / 45 degree trough idler will be difficult to use in layout of short length conveyors (less than 15m subject to belt width) due to transition length. For longer conveyors, its use will depend upon various considerations as mentioned by earlier respondents.

One will observe from many installations that troughing angle up to 30 degree is quite common for belt width up to 1000mm. 35 degree trough idlers are quite common for belt width from 1200 mm to 1600 mm. 40 / 45 degree trough idlers are quite common for belts 1800 mm and wider. These are generally used combinations of belt width and troughing angles, as guidance and not rigid rules.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Kinder,

My opinion is that speaking about the angle of the angled idlers without considering the lenght proportion of the same in relation to the center ones will always be somewhat vague.

We also must consider the density of the material, the velocity of the system, duty cycle etc.

It takes more power and the transition lenghts are longer. It may damage the belt if not properly selected etc. All those are important facts but if you tansporting cotton, fibers, wood chips...

Can one maintain the same capacity by subtitution of loaded weight with belt speed?

In short, I believe that one needs to look at the whole system to realize if 45 deg. is more advantageous than 30 deg.



Antonio Reis

Vitrom Mfg Consultants

Your Process and Manufacturing Solutions

Phone: 209.834.1900

Fax: 209.834.1039

www.vitrom.com ■

Please keep in mind that as the belt trough angle is increased, the distance across the top edge of the belt decreases. This can be a major problem in the load zone as the cross sectional area of the chute will need to be decreased to allow sufficient edge distance for sealing

A couple of ways to overcome this is to use a smaller trough angle in the load zone, and increase the angle after the load zone, Keep in mind transition distances for the belt used must be maintained.

Another approach is to gradually make the transition form flat to full trough over the full length of the designed load zone using adjustable idlers. ■

Thats an amazing quantum of information !

I still have two specific questions and would appreciate replies / opinions -

1. In any given deep troughing application, would a steel cord belt be a preferred selection, or a textile reinforced belt ? For example, would a ST 630 belt be preferred over a EP 800/4 belt ? Why (or why not) ? Would not the presence of a weft member cause greater problems (bottom cover wear, higher idle power consumption etc.) in a multi-ply EP belt than in a weft-free steel cord belt ?

2. In a deep troughing application, how EXACTLY would one select the lengths of the wing idlers vis-a-vis the central idler in a 3-roll carrying idler arrangement (ref : Mr. Nordell's #4)? Instinctively, it seems that a belt would be most 'comfortable' on equal length idlers. Would this not be a over-riding consideration considering the extra load on the center roller could be taken care of with heavier bearings and that the replacement costs of belt are normally greater than that of idlers ?

Thanks in anticipation.

Kayem ■

Again these are only opinions and should be treated as such.

First I agree with Mr. Nordell that the effort of modeling and carrying finite analyses on a full system is the most efficient path for large projects. Of course the finite analyzes package as to meet certain criteria to be of use.

As for question #1, my opinion is that the choice of belting is most related to the required forces to move the load and not so much to the type of idler arrangement one decides to use.

In short one is exchanging thickness of belting and weight in some instances for less cross section flexibility.

In my opinion, the flexibility required to accommodate the throughing arrangement is in a different plane than the flexibility required to perform around pulleys and tensioning systems.

The types of materials that are used in the bottom cover are important in this manner:

If the material is compliant as to provide good grip at the drive system, it will resist lateral movement along the idlers and the belt will track poorly or the cover will have high wear. Certainly the alignment of the idlers and the layout structure of the conveyor have some impact on this.

If the material is less compliant as to better slide on the idlers, one can have slippage on the drive and a mess in control.



With respect to question #2, I think that the length of the belt and the alignment of the path are the main parameters determining the idler configuration.

In my opinion, as one folds the belt to form a "U" it looses its ability to accommodate changes in the following stages:

1- when it is flat or close to flat. Fortunately it slides along the idlers relatively well but it tolerates little center misalignment between drive and tail pulleys.

2- With equal length idlers, or close to that, around the 45 deg. the belt will have difficulties managing turns and the friction of the bottom cover is a significant player determining the life of the bearings on the angle idlers, much more so than if those idlers are relatively short in comparison with the center idler.

Here is where some claim that a textile-reinforced belt will stretch and perform better than a steel belt.

3- after a certain angle the belt easily manages the turns but most of the load is in the center idler.

Again as I stated above, without all the requirements it is difficult to state the benefits of some specific component arrangement. Every conveyor is a different system and must be treated as a system.

Antonio Reis ■

Not accepting or rejecting the above comments, 45 deg. trough has a distinct advantage when used with horizontal curved conveyors. The larger wing vertical projects provides better steering/ tracking control.

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

Practically all the information is available in the foregoing replies. I would like to add few basic suggestions for the benefit of those who are not so expert.

1) General belief is that deeper trough increases the conveying capacity, and hence it is the best. But is not so.

2) For usual conveyors, one should opt for deep troughing only after proper analysis of its implications. Just comparing the capacity is not adequate.

3) Deep trough means sharp bending i.e. creasing of belt at idler kink. So, naturally it will amount to some reduction in belt life (comparatively), due to earlier weakening of carcass / joints.

4) Deep trough demands careful calculations of transition lengths, radius at curvature, proper stiffness of belt in transverse direction etc.

5) My earlier reply mentions usual values of trough angle for general guidance.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

OK,

So something along the same lines but different.

Where does 5 roll troughs come into play??

With one of our stackers - cone stacking - "boiling" at the feed zone and belt wear is an issue. Due to materials - a straight down drop is required ie no forward deflection. Belt life has been increased 3 fold with 10mm covers and improved rubber grade...but could still be better..

I was thinking along the lines of increasing the belt exposure in the feed zone.

I have seen grain conveyors (South Aust. GC) use 50deg. troughs in the feed zone , then revert to 45 deg., which I presume was for acceleration of the grain at the transfer.

I can not make the belt wider due to the 2 structural beams for the stacker beam....hence, stuck with 100mm wide belt and belt speed of 2.6m/sec up 15deg incline!!

Prok make a 5 roll equal roll trough for 1000mm belt.

A higher trough also leands itself to getting the material away from the skirt plate/seals.

Transition distance will eb an issue as the drive/tail pulley is close to the feed point.

Suggestions pls....

Thanks

James Morrish ■

Dear Mr. James Morrish,

One will rarely find 5-roll fixed frame idlers. 5-roll idlers are mostly in garland (suspension) type. These idlers being in garland type, they are not suitable for use on inclined conveyors due to their plane not being perpendicular to belt velocity. You are referring to incline boom conveyor and so I have mentioned above point.

5-roll garland idlers have distinct advantage at loading point. They have ability to absorb very high impact energy, and hence are used at loading points in conveyor which is handling material at the rate of 25000 mtph and so on. Needless to say that, this advantage is also applicable for lower capacity.

5-roll garland idlers are rarely used all along the conveying route. The advantage is that it can form deep trough with minimum strain on belt. This will be beneficial for exceptionally strong and thick carcass.

The marginal advantage in capacity is as below :

Material surcharge angle : 10 degree

1000 mm belt, 3 equal roll, 40 degree trough, cross section 99903 sq. mm

1000 mm belt, 5 roll, 25 and 55 degree, cross section 108283 sq. mm (8.3% increase)

Material surcharge angle : 20 degree

1000 mm belt, 3 equal roll, 40 degree trough, cross section 117139 sq. mm

1000 mm belt, 5 roll, 25 and 55 degree, cross section 124598 sq. mm (6.4% increase)

Material surcharge angle : 10 degree

1800 mm belt, 3 equal roll, 40 degree trough, cross section 346514 sq. mm

1800 mm belt, 5 roll, 25 and 55 degree, cross section 372740 sq. mm (7.6% increase)

Material surcharge angle : 20 degree

1800 mm belt, 3 equal roll, 40 degree trough, cross section 404510 sq. mm

1800 mm belt, 5 roll, 25 and 55 degree, cross section 427757 sq. mm (5.7% increase)

As can be seen, there is limited gain in capacity. The belt carcass of exceptional thickness is a special case and to be analysed accordingly. The 5-roll garland idlers are very costly compared to 3 roll idlers and hence they are not very commonly used, as a substitute to 3-roll idlers.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

The response may be old but hopefully still active to the general reader. We are probably going over the top on this subject. Some prior commentary may confuse the lay observer. I wish to comment on a few points some of which are elluded to by others:

Given: Coal @ 900 kg/cm; free edge = 125 mm; surcharge angle = 20 degrees; V =5 m/s

1. 5 equal roll (5ER) trough @ 1000mm wide belt has very limited use due to:

a) given center length of 5 ER @ 240 mm (24% center len. of belt width) the belt will have less capacity than a 3 roll with a 260mm (26%) center roll troughed at 35,40 or 45 degrees ie.:



5 ER @25 & 55 deg. ;roll = 240 mm = 1347 t/h, 1% loss in cap.

3 ER @35 deg. w/ roll = 371 mm = 1365 t/h, basis

3 UER @45 deg. w/ roll = 260 mm = 1568 t/h, 16% gain

b) as center roll length gets shorter so does its ability to trough and train. You will need reasonably supple belt to make 24% center roll length percentage of belt width. Even 26% and 37% have their limits wrt belt stiffness.

2. 5 ER @ 25x55 trough and 3 UER 45 degree trough have same capacity for 1800mm belt:

C = 6682 vs. C= 6705 t/h, respectively for 5ER and 3 UER.

Where is 5 roll advantage? Both exceed 3ER@35 degrees. where capacity = 6070 t/h. They are 10% higher than 3ER.

3. 5 roll set is used at loading point to help contain spillage of fine particles as they escape when belt is dialated below skirt during impact.

4. 5 roll set is used on large systems when belt is >=2000 mm due to loading on bearings, shells, end disks, and spacing for economics of investing in larger equipment and in necessary belt junction fatigue stress reduction at idler inflection points -- to the point Mr. Mulani made.

5. We had to use a 5 roll set on a project when the country's mfgrs. could not readily build the 3 ER necessary equipment.

6 There are a number of added issues which take too much to comment on here. Surely, the design community would embrace the 5 roll system if it had merit.

Lawrence Nordell

www.conveyor-dynamics.com ■

and ....

45 degree trough will better contain material, reducing spillage of larger rock, than a 35 degree trough.

May be its been said before. The thread is getting long.

LKN ■

Not quite a direct response to the question posed, but here's some info on 5 roll idlers.

The 5 roll fixed form trough idlers are used extensively in the South African and Australian mining environments for belt conveyors 1200mm and wider.

Generally became common due to use of solid woven PVC belts in underground coal mines where improved troughability due to the reduction in individual change in belt slope (eg 22,5 deg i.s.o. 45 deg) was significant.

The individual rolls are also lighter and would have smaller shaft/bearing combinations than a 3 roll system. This obviously simplifies maintenance tasks underground and in general the rolls would be more readily available from a selection of idler suppliers.

Within the South African market they have also been used extensively in surface applications and were specified in the Anglo American Corporation idler specification for use in conveyor belts 1200mm and wider.

The reduced shaft/bearing requirements are a result of shorter face length rolls and a reduction in the load carried by the centre roller (typically 70% for 3 roll and 45% for 5 roll). ■

I am currently working at an installation which has about 10,000 sets of 45 degree troughing idlers installed on 43 different belts (1800 x ST1250). (suspended type with short centre roll). There is, of course, a somewhat marginal increase in theoretical capacity using 45 degree, but as with most plants, there are many other influences in the plant which have a far more profound effect on total tph or MTPA than this marginal increase in burden CSA. We now have problems with belt longitudinal cracking at the trough lines as the belts get to 10+ years life (see my new thread on this subject). They have all soft loading chutes (although retrofitted - not original) so the 45 degrees at the loading point is not a particular advantage. They do not have a problem with spillage at the head end transition either, because with the belt speeds (3.1 and 5 m/sec) and the product (coal) the product does not have a chance to 'flow' outwards much in the transition. With 45 degree idlers, concave curves and trippers (we have 9 of them) become bigger problem. Also, the belt gets a permanent 'set' along the trough lines which makes return belt cleaning & ploughing difficult and makes contact 'points' on the return idlers. My advice is to not use them - look at other ways of getting the extra few percent (e.g. speed) ■

The technology of idlers and belts is pretty mature. The parameters are well tabulated by the belt and idler manufacturers and there are reliable rules of design conforming to these parameters. In this light both low and high troughing angles have advantages to be exploited at each unique application.

No one has pointed out a subtle but real advantage of a high troughing angle. That is, the material slide back tendency is reduced with increased troughing angle. This was actually demonstrated, many years ago (1940's), by A. Vierling. I don't suggest that this be used as a basis for determining the incline angle but it can be used to salvage a bad situatuion.

In a particular project the writer had to replace the truss structure (the original structure was damaged beyond repair) at a high capacity iron ore conveyor. This conveyor, inclined at 16.5 degrees, suffered frequent slide-backs of the material. We thus took this opportunity to make improvements to eliminate the side-backs. Towards this end we made some improvements at the transfer onto this conveyor and we replaced all of the existing 35 degrees troughing idlers with 45 degrees troughing idlers. The improved capacity of the 45 degree troughing allowed us to slow the belt speed without overloading. This project was a resounding success and material back-slides were completely elliminated.

Joe Dos Santos ■

Good morning everyone..

Just one point in favour of 35 degree idlers.

If you have a conveyor with a tight horizontal radius, there is a tendancy for the edge of the belt to lift off the outer wing roll around the outside of the curve.

The belt on the inner wing roll is forced against this roll.

Conversly, the belt on the outer wing roll wants to lift off.

The higher the belt tension, and the more vertical the wing roll, the more the belt will tend to lift. If empty, and it does lift, then the belt will pass the point of no return, fold over, and the outer portion will end up on top of the inner portion on the inner roll.

To overcome this possibility, I have occasionally been forced to use 35 degree idlers instead of 45 degree ones to counteract this effect.

Thanks

LSL Tekpro ■