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Genrec Engineering’s repair of a damaged dragline excavator boom for one of South Africa’s leading coal mines was achieved in just 10 weeks – a record for the local industry. The company was responsible for a full-scale investigation into the damaged boom structure at the site in August 2017, as well as the repair.

Producing coal for domestic thermal energy production and for export to global markets, the dragline excavator is an essential component of the mine’s open-pit mining. It is used in combination with drilling and blasting and dozers to expose the seam before wheel loaders and dump trucks are deployed in extensive load and haul operations.

According to Genrec Engineering’s Managing Director of CMTI Consulting, Dr Danie Burger, there is no other steel fabricator and engineering company in South Africa with the necessary infrastructure, as well as capacities and technical competence to take on such a complex project. Had the boom been sent to the original equipment manufacturer’s premises in Australia for repairs, it would have taken up to four times longer to return the dragline excavator back to service with obvious negative ramifications on the mine’s production, he adds.

The boom comprises a 37-ton (34-t) mid-section, which is 30 m long and 13 m wide, and the 43-ton (39-t), 32 m long and 13 m wide front portion. Both have a transportation height of 3.5 m.

It was completely remodelled by Genrec Engineering’s design team with assistance from CMTI Shared Services, in a process that took about a week-and-a-half to complete.

The original drawings of the Bucyrus dragline excavator were more than 30 years old, so the Genrec Engineering team had to get updated versions from Caterpillar. These were used to generate models to develop the manufacturing drawings and upgrades to the boom, in addition to the manufacturing sequence, work procedures and transport sections.

Genrec Engineering also had to locate and source up to 34 tons (31 t) of chord material from various Australian mines to supplement insufficient supplies of the required specification. The chords were buttered up and machined to specification and all lacing laser cut to fit assembly. It took about three weeks of round-the-clock operations to complete the complex laser cutting by approved specialists located in Vanderbijlpark, with Genrec Engineering team members located permanently on site to advise, as well as monitor progress and quality.

They were delivered to the plant in the correct assembly sequence and welding was then undertaken in a 2,200 m² bay converted for specialised manufacturing projects. Starting with pre-heating, the roots were undertaken with tungsten-inert gas welding and CO2 used as a filler. Non-destructive testing was done using magnetic-particle, phased array ultrasonic, radiographic and ultrasonic testing. Personnel from NJM Heat Treatment & NDE Services, as well as NDT specialists, were stationed permanently on site to ensure that sound productivity rates were maintained and quality standards were adhered to.

One of the complexities of the welding operations was the varying diameters and positioning of the larger chords and smaller lacing, says Mark Prince, Divisional Director of Genrec Engineering. A total of 2.3 tons (2.1 t) of weld material and eight weld feeders were sourced from Australia to supplement available resources for this project, and 129 welders were tested by Genrec Engineering, with 52 metal inert gas, or gas metal arc, and tungsten inert gas welders employed to work on this project, together with 18 boiler makers and assistants. Five specialist boom welders, as well as an expert boom weld engineer and project co-ordinator from Australia, were also brought in.

As part of the project, Genrec Engineering was also tasked with upgrading the dragline excavator’s boom-point box. A special furnace was designed and developed around this box and soaked at 600°C for six hours and then cooled down to 37°C for five days. The furnace was heated with gas at a rate of 37°C/h to 600°C.

A canopy was designed to allow sand blasting to continue in the workshop while welding progressed, to maintain high productivity rates. The components were transported to the mine site by Mammoet using a 13-wheel Nicolas trailer and resting on 11-ton (10-t) cradles specially designed and manufactured by Genrec.

It took three days to transport the two loads to site as part of the last phase of the project. “This is the largest abnormal load to have ever travelled on the Gauteng road network, and Genrec Engineering was also involved in the extensive road survey, in addition to obtaining all necessary road permits from the Gauteng Department: Roads & Transport,” says Prince.

The mid-section of the dragline excavator boom was dispatched to site at the end of November and the front end in early-December. It was successfully assembled by Caterpillar’s southern African dealer, Barloworld Equipment, on site in December over a period of four weeks.

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