DEAR MR IRFAN,

DO YOU HAVE PHOTOGRAPH OF ABOVE BELT CONVEYOR WITH

ROLLER DETAIL ETC.

THANKS ■

Dear irfan,

The failure, you describe, is at the location where the belt is bending longitudinally between a side roller and the horizontal middle roller.

This bending induces longitudinal shear forces at the bending location.

The resulting shear stresses, together with other shear stresses, are over stressing the belt construction, leading to damaging the belt by fatiguing.

As the damage seems to occur only at one side, it could be that there are also symmetry problems present.

(May be one side is pulling more than the other side, altough that should be noticed by alignment problems)

Success ■

Dear Mr. Irfan,

The issue you have mentioned is belt cracking at idler kinks. You can check on following points :

1) Please check that belt carcass is suitable for troughing angle versus belt width. This can be checked by referring to published data of belt manufacturers. I can also comment if you mention carcass thickness and belt thickness.

2) If you are using in-line trough idlers, then gap between two rollers should be less / equal to 10 mm for belt width upto 1800 mm. In case of offset idler the central roller and side roller should overlap in plan.

3) Roller edges should not be sharp, but rounded.

4) The pulley top (precisely belt tangent point to pulley) and central rollers top should be on straight line. The pulley top can be marginally up, if the same has been considered to reduce transition distance, but pulley top should never be lower than ‘central roller top’ level.

5) Installation should restrict the idler up-down misalignment within allowable limit. If any central roller top is up than general level, than there would be severe pinching of belt at that place, which can cause damage to belt.

6) Use the transition idler angle and placement as per calculated values, and not by thumb rule. Use transition idlers to increase troughing angle by increment of 10 degrees to 15 degrees.

7) The skirt plate / rubber should be away from idler kink.

8) The belt tension too, by take-up in conjunction with transition distance.

9) Too old belt or stored at improper place, or plant environment is chemically active causing deterioration of rubber elasticity, or belt quality to be checked.

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

This sort of longitudinal cracking along the idler junctions is caused as others have said by flexing and is indicative of the belt lacking the carcass strength for the load being carried or by the load impacting on the idler junctions. If the former you have to go to a heavier belt maybe an extra ply. If the latter you have to spread the way the load is dropping onto the belt at the transfer. If the cause is the latter it is usually only one longitudinal crack, if the former you have 2 i.e.along each idler junction.

Col Benjamin

Gulf Conveyor Systems ■

Hi Irfan,

This is a very light weight belt so it may well be that it is too light for the application but to give you an answer we need to know;

> Tonnage

> Belt Width

> Whether the cracking is along both or only one idler junction

> If mainly one then we need to see how the belt is loaded

When you look at these questions and your own answers I am certain you can reach your own conclusions. Ask the belt supplier to give his opinion re load support.

Regards

Colin Benjamin

Gulf Conveyors ■

Dear Mr. Irfan,

I have noted the certain information about the belt. Please also mention the belt width, belt speed, name of material, bulk density and lump size. Your belt width looks to be regular type, but it is to be seen in context of belt width. I presume the belt carcass is EP.

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Hi Irfan,

For this belt width the belt specification is very light even though the loading is modest. I would suspect your problem is lack of load support and you need a belt with a heavier carcass

Col Benjamin

Gulf Conveyor Systems P/L ■

This crack is without doubt due to the transition distance being to short.

The edge sections are stretched more as they leave the tail end of the conveyor (the central part has a shorter length). Due to this, the belt actually tries to push down the rollers back into the shorter area. This places pressure on the area at the bend and causes de-lamination at this point. This happens all the more with cheap belting, particularly if using cotton fabric plies. Cheaper belt tends to have adhesion rates around 4.5 or 5 (the actual figure required by DIN and ISO standards) Our own brand will give you around 25, so this wouldn't happen.

Also, as stated by others, you are working on the limit of load support for this type and width which could affect it too. If you give me your e-mail address, I can send you more detailed information about this (if you don't understand what the transition distance is) if you forward me your e-mail details. Pakistan is actually on of the areas I cover can better try and sort out your problems.

Regards,

Stan ■

I have to agree wth Stan. Most longitudinal cracks in this location are caused by insufficient transition distance particularly at the drive/head pulley. If the head pulley isn't properly raised above the beltline, the belt will be pulled heavily down into the 'crotch' of the idlers resulting in longitudinal cracking at that point. ■

Your problem is the belt you are using is not sufficient in load support. The material is too heavy and the belt is too light, which pushes the belt down in the gape between the idlers. While too short of a transition will cause cracking, it will not be longitudinal. It will be in chevron or V patern starting at the edge and slanting towards the middle of the belt in the direction of travel. Mfg. should have load support data to help you select the proper carcass in relation to the material you are handling.

Regards,

Ron Marler

Legg Co Inc.

USA ■