Dear Sirs

Regarding exposure to Ultraviolet we have supply many with different effects.

We have pipe conveyor belts which have lasted up to 10 years.

There are many different types of rubber covers to cope with a particular application. i.e. for pet coke may be oil resistant, and some of these are better or worse for dealing with ultraviolet or ozone.

In anycase in all our applications the belts are either worn or damaged throughout their design for other reasons.

Paul Holt

Dosco Overseas Eng Ltd

UK ■

Dear Mr. Singh,

THe longitudinal cracking is both a combination of ageing and tensile stress of the outer cover being pulled into the pipe configuration with repeated stress cycling over the idlers.

There are many conventional belts with ozone surface cracks from less bending stress. Some have run for more than 30 years. The cracks become an issue if they collect contaminants that can not be easily cleaned or cause corrosion of steel cords.

The issue of belt life can be divided into two catagories:

1. failure of covers that cause production loss

2. failure of internal structural integrity that puts the belt strength at risk

Sometimes these conditions seem as one. We investigated the Phosbucraa 96 km overland , in Morocco, some years back. All 625 splices were failing from heat and sun exposure. The conveyor was installed in 1972 and we were evaluting it in about 2000. The rubber was reverting to its uncured state becoming soft without strucural integrity, The operators could not rebuild failed splices due to the rubbers age.

THis was a point of dispute between CDI and mfgrs. We recommended the splices could be rebuilt so there was no need to replace the belt. The belt could still transport phosphate. However the spoice failures (625) caused a lose of transport availability down to 50%. Ship demurage became costly.

The full belt replacement was on the order of $50 million dollars.

Repair of 625 splices would have cost about $2 million. What a lose!

Modern belts will last longer with less risk. ■

Dear Mr. Singh

We have tested the rubber hardness and it tends to age harden. In most of our applications in Europe we put a solid top sheet on the conveyor for both safety and adverse weather protect. If exposed continuously to the climate a good ozone resistant rubber should be used on the outside surface and what is most appropriate on the inside for the carried material.

However other factors are usually more prevalent in determining the actual life of the belt as apposed to the computorised design life which is usually based on wear factors.

Paul Holt

Dosco Overseas Eng Ltd

UK ■