CDI designs both ways. Material carry-back elimination is usually the client's requirement to implement turnovers.

In Australia, belt turnovers have been used but are presently not a hot item in iron ore transport (BHP; Rio Tinto). In Brazil, they are extensively used in iron oreand bauxite (CVRD; MRN) with good reason. The wet, fines and sticky environment of Brazil is a good illustration that they do the job.

We have installed them on bauxite, coal and iron ore up to 1800mm wide.

The typical belt cleaner cannot do the job on sticky ores.

Your specifications are in the typical turnover range in which we have extensive experience. Our belt design software package BELTSTAT has a subroutine that solves the complexity of turnover design for steel cord belt using the standard helical twist. THe program is far more comprehensive than belt manufacturer's catalogs. Cord stress due to twist, sag and bending are incorporated together with twist length and belt safety factors.

See our website: www.conveyor-dynamics.com ■

Good day Banda..

I am one of the "pro turnover" people.

For my dual carry conveyor for example, you will appreciate that the turn-overs are mandatory, and as such, the best and most reliable design has to be used, as it is for life.

Things to remember are:

- Don't make them too short i.e. less than 22m in your case, or you will over stress the edge of the belt.

- Don't make them too long, i.e. more than 28m in your case, or you will loose too much tension on the other edge. This makes the belt floppy on one side and difficult to train.

- Do use a well thought out guide roll design. With non-horizontal, and especially vertical rolls you tend to get dirt in the bearing seals. I put protector discs over these bearings

- Don't put training idlers at the turn-over.. it's the one place that the belt is held to the centre line!

- 1200mm is my practical limit for conventional turn-overs. Any wider and you should consider rolling it over by making the centre as per a pipe conveyor.

- Turn overs protect the conveyor very nicely from top side spillage carry-back getting entrained in the tail pulley(s)

- Design the tail end turn over area such that the carry-back can easily be cleaned out, and does not bury the turn-over rolls

- History has shown that poor turn over roll life has reduced the availability of many conveyors.. most due to being buried in carry back.

- Don't be scared of a bit of high tension in the turn-over. I have put them between multiple drive pulleys quite sucessfully.

- Do calculate the running belt sag over the 25m or so turn over length, so that the central roll system is at the correct elevation

- It is a myth that an overland conveyor has to be over a certain length to warrant turn-overs, this is because it affects the 500m or so at the head end only. After that, the return rolls have normally done a pretty good job of cleaning the belt. On a lot of conveyors, the material conveyed is bad and warrants turn-overs for the 500m or so. (Belt cleaners are only as good as the people who maintain them).

- It is a myth that you always have to have turn-overs for horizontally curved conveyors. I have a 4km horizontally curved conveyor (80% of it's length curved) with no turn-overs at all. Funnily enough, the roll life is excellent despite the abrasive material conveyed. This is because the material conveyed is not very sticky.

These are just a few considerations, but I hope they help you.

LSL Tekpro ■

Regardless of the type of system you choose, it is extremely important to clean the belt properly at the head pulley. This usually requires multiple cleaners (primary and secondary). I have seen as many as five cleaners on an application such as this.

There is also another type of belt system I have seen work well in this is the fold belt. The same problems exist as with the turn over belt. ■

To further clarifiy my response on cleaning a turn over belt. The belt requires a minimum distance to turn over to protect the belt. This can sometimes be quite long depending on the belt wdith and PIW. The components from the terminal pulleys to the point where the belt is fully turned over can be overcome with carry back if the carry back is not removed at the head pulley.

Most belts respond to belt cleaning systems. It has been my expireience that depending on the total length of the conveyor, it is much more cost effective to simply clean the belt rather than going to all the expense of turning the return side run over.

As the belt length increases, the belt turn over becomes more attractive cost wise. Hope this helps. ■

Dear Banda,

Like Graham Spriggs, I tend to support the use of properly designed and maintained turnovers for long conveyor systems. Although, I prefer the type using idlers over those using tires (tyres for the Brits and Aussies), due to the improved support and lower chance of losing the turnover.

As far as belt cleaning is concerned, you should not use a turnover as a means to avoid cleaning the belt - it makes no sense to pay the energy and product lose price of carrying product back to the start point and dumping it under the tail turnover.

In my view, the prime reasons for using turnovers is to reduced maintenance costs associated with material build-up on the return idlers and spillage (carryover). As Graham has suggested, they are also useful if doing two-way conveying.

Regards, ■