THE overland conveyor system at El Abra mine first went into operation in June 1996. It is part of an exceptional project, the centerpiece of which is the CV-103 system, which incorporates a PHOENOCORD St 6800 steel cord conveyor belt 20,000 metres in length and 1600mm in width.
After 19 years of continuous service and 900 million tonnes of conveyed copper ore, the belt was finally replaced. Its exceptional service life was made possible not least by the PHOENOTEC protection system and the special wear and abrasion resistant carrying and running side covers of the belt.
Freeport-McMoran’s and Codelco’s El Abra mine is in northern Chile at an elevation of 4000 metres. Its porphyry copper deposits with sulphide and oxide mineralization deliver 8500 t/h of aggressive copper ore. After primary crushing, pieces have edges measuring as much as 300mm. They are taken to the ore stockpile 9600 metres away by conveyor, traveling at about 6 m/s and covering an altitude difference of -510 metres. Because the belt conveys the ore downhill, its four 1800kW rotor motor drives generate about 6000kW of electricity an hour, which is later used to process the ore. The brake discs measure 2500mm in diameter and are capable of halting the entire belt within 80 seconds in an emergency. The trough angle of the upper run is 40 degrees.
A longer service life
Produced in Germany, the PHOENOCORD St 6800 was designed for a service life of at least 17 years. Realizing this ambitious goal involved a number of special measures:
- A special notch and abrasion resistant rubber compound was developed for the belt covers, which also offers a high elongation at break and high tensile strength.
- The covers of the belt’s carrying and running sides were equipped with PHOENOTEC synthetic single-cord transverse reinforcement – an additional wear protection system that doubles the belt’s resistance to impact damage and ripping.
The 1600mm-wide belt has 82 steel cords integrated into it. These measure 12.4mm in diameter and give it a minimum breaking strength of 6800 N/mm. The cover is 14mm thick on the carrying side and 10mm on the running side, bringing overall belt thickness to 36.4mm.
Eleven years after going into operation and having conveyed 500 million tonnes of ore, the belt was found in 2007 to have lost no more than 2.7mm of thickness to abrasion wear and just 1.4mm on average.
Given the belt’s extremely rough, heavy, sharp-edged cargo and extreme climatic conditions in which it operates, a service life of 19 years is exceptional.
The belts were installed 19 years ago and operate in extremely challenging conditions:
- At 3900 metres altitude, in air pressure of 600 hPa (compared with 1000 hPa at sea level).
- In sandstorms with wind speeds of up to 150km/h.
- In an earthquake zone 2.
- In daily temperature variations of 20 degrees C.
To meet the tough demands of this project – ie producing splices with a service life which matches that of the belt and fatigue strength of 50% according to DIN 22110 standard – a robust, air-conditioned hall was set up. The splices, which measure almost 6 metres in length, were produced in a four-step layout. Work was carried out in strict accordance with regulations and supported by state-of-the-art machinery and fresh splicing materials. The result was a belt that ran perfectly from the word go.
Test of endurance
In late 1996 there was a major incident at the site in which two front-loaders pressed in on the system’s tunnel causing it to collapse. This abruptly brought the belt to a standstill and the huge forces caused it to tear just behind the point of impact. The tear, however, was in the belt rather than one of the splices, as might have been expected.
To ascertain that the incident had not caused further damage, a section of belt, including a splice, was cut from the most severely affected area and sent to Germany for testing. Examinations revealed that in every parameter measured, it was still as good as new.
The Institute for Transport and Automation Technology at the University of Hannover tested the splice to DIN 22110 standard. This meant the fatigue strength of the trial belt, manufactured in factory conditions in 1995, had successfully been reproduced by the splicing team in Chile. This outstanding result proved not only that the incident had had no impact on the belt, but also that the belt had been spliced with the same care and success in Chile as the first test version.
Incidentally, the replacement for the damaged section of belt was produced in record time in Germany and ready to go within just one week.
The new belt will be constantly monitored by Minera El Abra to detect any external or internal changes using the revolutionary PHOENOGUARD PX monitoring system. This allows virtually every cubic millimeter of the entire conveyor belt to be monitored constantly, delivering real-time information about its overall condition and the state of all components. The advantage is invaluable as damage can be detected and eliminated as soon as possible.
PHOENOGUARD PX constantly digitalizes the entire belt while it is in operation, recording all data and comparing it with target values. As well as showing damage on the computer screen, it provides a large, clear picture of any areas of concern – all at the press of a button.
PHOENOGUARD PX allows downtimes and production stops to be kept to a minimum. Other issues the system can detect include foreign objects, protruding cords, belt miss-tracking, abnormal cover wear, insufficient belt cleaning and the condition of transverse cords and sensor loops. The state of splices, which are always the weak point in a belt, can also be examined visually at any time by checking the position of cord ends.
Top-quality components and state-of-the-art technologies have a key role to play in the lifeline of a copper mine and make a lasting contribution to efficiency, which is especially important in times of low raw materials prices.
The recently installed PHOENOCORD St 6800 belt is expected to last considerably longer than 20 years and require far fewer maintenance stops. Innovative PHOENIX technology is helping El Abra mine work even more efficiently.