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An order placed by Wilson Bayly Holmes-Ovcon (WBHO) for four 32-32 ton portal cranes to manage materials handling at its new Copperton and Garob Wind Tower pre-cast yard in Northern Cape, South Africa, has positioned supplier Condra as the leading manufacturer within this niche of the country’s overhead cranes market.

To be delivered to Prieska before the end of September, the order brings to six the number of these giant machines that will have been delivered by Johannesburg headquartered Condra for pre-cast work in the last nine months, and to eight the total number of gantry cranes manufactured by the company over the past year.

Portal cranes for pre-cast yards are purpose-built to lift, position, stack and load reinforced concrete components.  Two have been at work for another customer in Nelson Mandela Bay since late last year, when they were commissioned at a yard supplying concrete bases and columns to coastal wind farms.

The four machines for WBHO’s Prieska yard will help produce similar components, in this case keystones each 20m in length that will be used to erect the 100m high reinforced concrete wind towers at the Copperton and Garob wind farms near Copperton.

The two farms will together generate some 140MW of electricity (573 GWh per annum) after completion in mid-2021.

Commenting on the WBHO order, Condra’s managing director Marc Kleiner said that he was happy to see the construction company renewing its trust in Condra’s products after a period of ordering from rival firms.

“We have been supplying cranes to this customer since the 1990s, and all our machines have delivered sterling service.  I believe this counted in our favour during the tender process for the Prieska order,” he said.

Kleiner added that the WBHO machine specification had been influenced by the performance of the two Class 3 M6 Condra machines commissioned in Nelson Mandela Bay last year for a second customer of the type.  WBHO was able to observe the performance of these cranes before ordering its own machines, which will be similar but designed to Class 2m M5 standard.

Two of the cranes will be delivered in August after a relatively short lead time of twelve weeks, and two in September.

Typical Condra portal crane

Each of the four identical, 28,5m-span cranes will feature two 32-ton hoists delivering lifting speeds of 3m/min over lifting heights of 9,09m, allowing pre-cast components to be simultaneously and precisely lifted at two points to minimise stress on the loads.  Cross-travel and long-travel speeds will be 20m/min and 60m/min respectively, allowing quick crane manoeuvrability along yard rails 375m in length.

The long-travel speed of 60m/min is approximately twice the standard for long-travel, and Kleiner explained that portal crane speeds for lifting, long-travel and cross-travel vary according to the key points of productivity within each application.

“The pre-sink portal cranes that we manufactured for new mines in Asia and Limpopo Province were digging machines with fast lifting speeds of one metre per second for maximised rates of earth removal,” he explained.  “By contrast, productivity at Prieska will depend on the same speed applied to the long-travel to quickly traverse the yard, with the lifting part of the operation being carried out at a more delicate 3m/min because of the need to avoid excessive stress on the loads.”

WBHO’s Prieska machines will be physically very large, each standing over 11 metres tall on 8,65-metre end-carriages, and spanning 28,5 metres between rails.  To facilitate installation, the end-carriage legs will be hinged where they join the gantry, allowing each machine to be assembled spread-eagled on the ground, with the legs descending into the vertical position as the assembled, spread-eagled machine is hoisted into position.

The hinged legs will cut conventional crane installation time by about one half.

Road transportation of the four gantry cranes to Prieska will be undertaken by Transcon Haulers, a sister company of Condra possessing the 22‑wheeler horse and low-bed trailer sets, extendable trailers and steerable dollies required by the abnormal freight presented by crane girders nearly 30 metres long.
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