Re: Idler Forward Tilt/Five Roll Idlers
HEllo Adi,
Although you make a point of belt width and wear with offset and tilted rolls, you do not discuss a quantitative position.
I can point to many offset roll systems that have no problems with wear, which have been operating for 8 years or more and transport high tonnage (> 7000 t/h) and at high speed (~6m/s).
The case of forward tilt is a case of wear pressure. No pressure no wear. Like with the above, we have been involved with many installations that have no forward tilt and have no problems. However, belts wider than 1400 mm, having medium to high speed ( > 5m/s), higher density ore (> 1500 kg/cm) and medium to high tonnage (>4000 t/h) do exhibit wear in varying degrees with forward tilt.
THe industry should begin to study the threshold criteria for pressure that produces unacceptable wear. To date, no one is working on such a criteria, only babble on forward tilt acceptabililty.
South Africa has a few mines that are, at present, in this league. ■
Idler Forward Tilt
Hi Adi,
You have opened up a very broad topic which will create a wide variety of experiences as some conveyor systems don't seem to have any belt or idler wear problems, others will have horror stories. There will be variation even on very similar designs. For this reason I believe it is important to state that a basic principle of conveyor system design is that all rotating components should be aligned square to the direction of belt travel and that their vertical alignment should be such that the face pressure across them is even. This is complicated by the troughability of the conveyor belt, the wear profile (loading), the transitions and the elastic modulus of the belt (how much it will distort laterally to configure to changes in trough angle/tension).
Separate to this is my concern on the design of offset idlers. It is very difficult to get the belt to evenly contact all idlers in an offset configuration under all load conditions. If this translates to lack of sufficient idler to belt face pressure such that the idler slips relative to the belt speed we have the mechanism for belt and/or idler shell wear. This is made more likely the higher the belt modulus and the wider the offset.
Complicating this for many maintenance personnel is structure alignment and carryback. We also use idlers to track or train conveyor belts, in doing this we must recognise we create either a high pressure point of a point of speed differential that can induce idler shell wear or belt cover wear. Given all this, at many sites idler maintenance (mainly labour) can represent up to 40% of all conveyor system maintenance costs. It is why, you may recall that we developed the idler management software so that there was a simple method of data acquisition, storage and analysis so that the actual root cause of issues can be identified.
Trust this adds to the debate
All the best
Col Benjamin
colin.benjamin@gcsm.com.au ■
Re: Idler Forward Tilt/Five Roll Idlers
Hi Adi..
The time old question about off-set idlers- should the central roll lead or lag?
The answer is fortunately simple, and lies in the belt friendly configuration, where the rolls are located either side of a pipe.
For a 3 roll set for example the cental roll is up-steam.
This means that the two wing rolls are downstream.
The rotation of the wing rolls is therefore in the direction that any spilt material will be thrown out.
The rotation of the central roll is therefore in the direction that any spilt material would be trapped, but it is highly unlikely that any spillage can get under the middle of the carry belt.
Therefore the cental roll must lead for 3-rolls, and lag for 5-rolls.
(As for acellerated wear for off-sets, forward tilt etc.. I really don't know what everyone is getting at. In practice I have never come across this even at 3100t/h at 4.2m/sec on a reasonably tight horizontal curve)
Cheers Adi
LSL Tekpro ■
Re: Idler Forward Tilt/Five Roll Idlers
One thing I have seen repeatedly in situations such as this is idler alignment. This is also true in untilted idler configuation. While idlers are often aligned perpendicular to structure, they are often not centered on the frame left to right. Most idler brands have enough room in the bolt slot that they can be moved right to left as much as 3/4". This also contributes to belt tracking problems. Next time you walk a conveyor, sight down the idlers and you will see what I am talking about.
This applies more pressure on some rolls more than others which in turn MAY cause belt wear, roll wear, and increased beraing failure. ■
Idler forward tilt/five roll idlers
Dear All,
The thread on belt installation has stimulated an alternative thread regarding the provision of forward tilt (tilt in the direction of belt travel) of wing rolls and its effect on belt life. I would submit the following comments:
1.With regard to the supposed accelerated wear on belting I quote from two South African experiences. In both instances the contractor required that the idlers in the curve be supplied with a minimum 2 degree forward tilt. The installations are the Syferfontein (1200mm belt running 2000tph coal at 4m/s) and Wonderwater (900mm wide belt) conveyors for Sasol Coal. In both instances the V return idlers were also supplied with forward tilt. Both installations are well known to contributors to this forum. To my knowledge both installations are still equipped with the original belting (15 years in the case of Syferfontein) and there have been no reports of excessive cover wear.
2.Idler bases are generally fabricated elements and achieving repeatable accuracy on a continuous basis is often difficult. It is also accepted that ‘backward’ tilt would result in inaccurate and erratic belt tracking. Therefore idler manufacturers tolerance the alignment of the wing rolls such that any variation would result in forward tilt and would indicate the direction of travel on the idler base.
3.I have experienced the rapid wear of idler shells of V return rolls (and presumably this would be related to accelerated wear of the covers) on underground conveyors. Typical (South African) u/g support structure incorporates built in supports for the V return rolls. Typically these supports allow a forward tilting of the axes by 25mm that generally yield a forward tilting of the order of 2 degrees (except where double slots on the ends are provided which would double the tilt). The structure is symmetrical, and typically, in order to achieve tracking as quickly as possible, operators adjust both V return rolls in the forward tilt position. The result: - excessive idler shell wear and also pinching of the belt into the gap between rolls.
4.Regarding accelerated wear due to the use of five roll idler systems – thread started by Colin Benjamin. Five roll idler systems are very common in South Africa particularly in underground coal applications. My understanding from Colin’s thread is that the accelerated wear is a result of idler alignment in that not all rollers are in contact with the belt and thus a high pressure point is created at the rolls that are in contact with the belt. Is this a correct summary?
Anglo American specifications require the use of five roll idlers for all belt widths wider than 1200mm (concession have been given for overland conveyors to utilize three roll systems) in order to standardize on the use of 127mm diameter rolls with 25mm diameter shafts. It would be interesting to have their reply and also that of South African belting manufacturers to this question.
5. Also resulting from Col’s thread. Any research being undertaken on the effect of ‘off-set’ idlers? What are the effects on belting and idler loads when compared to ‘in-line’ systems? Should the center roll lead or lag?
Adi Frittella
AFRIPP PROJECTS CC ■