R & D journey for the towable cable arch
A tier one miner asked TEAM to design an enlarged service arch to suit the CAT 797 trucks to enable dual sided loading from their 4100 X PC shovels. The design of the traditional service arch was too low and did not have adequate width to pass the CAT 797 or other ultra trucks safely.
In open-cut mining operations, electric shovels and draglines are often used for mineral extraction and overburden removal. Power is provided from heavy-duty electric cables. As the equipment moves around the mine, so do the roadways for the heavy haulage vehicles that transport the mined coal or ore from the pit. This creates an issue where the cables and roadways intersect. There is a need for the cable to be safely routed across the roadway to ensure they are not damaged or power cut to the mining machines.
Cable Arches are structures used to lift electric cables and other services high enough of the ground so that vehicles can travel underneath without damaging those cables or services. When used with electric shovels they also allow for a second access point to the shovel enabling double-sided loading of trucks which increases productivity. However as the shovel moves along the working face the arch must be frequently relocated.
The challenge was to make a Cable Arch large enough for a fully laden ultra truck to pass through (14m wide x 11 m high internal measurements). It needed to be strong enough and stable enough to be relocated by being dragged across terrain of various different types of surface. The arch must be relatively easy to use as well as have inbuilt safeguards to protect the arch from damage and the users from harm. It also must be highly visible day
and night and constructed to withstand the rigors of the harsh mining environment.
The solution was the clever use of folding stabilizer arms which prevent the skids of the arch from trying to close together whilst towing. The arms are stored along the inside of the skids and swing into place when required. The arms are reversible being able to be swung to either end of the skids and hence allowing the arch to be towed in either direction.
The result is a towable cable arch that is stronger, lighter, and with a lower centre of gravity than previous designed. It can now be moved safely around the mine site with readily available equipment. This saves time and improves the efficiency of the truck / shovel fleet.
Our scope was to design and supply a Cable Arch meeting specific internal dimensions that would allow a fully laden mining dump truck to pass underneath and be relocated by towing. This would be a considerable improvement over other forms of cable crossings.
Specific objectives included:
internal dimensions of 14.5m wide by 11m high
able to relocate with minimal preparation or dismantlement
315 mm water poly pipes
the structure should withstand the extensive towing forces that will be present during relocation of the structure
be easy to construct and simple to operate.
TEAM has previously supplied cable arches that could be transported by being picked up and carried on the headboard of dump trucks. Although the brief this time was for an arch which could be towed we initially started by looking to modify our existing design (an open web truss design).
The decision was taken early on to move away from this design and instead use a trapezoidal box section style made from 10mm, 350 grade steel plate. We hypothesized that this construction would allow the structure to be lighter and flex more smoothly whilst still remaining robust.
TEAM developed and tested several designs on this theme in order to achieve the required specifications.
Numerous computer-based models were created and the structure analyzed to ensure that:
its strength could withstand the application
predict the design’s structural and vibrational behavior and
calculate the centre of gravity and predict the design’s behavior under tow.
Resonant frequency analysis modelling on the braces was performed as well as field testing of a prototype.
Tests were completed to ensure that the cable arch could be towed from either side using just one pair of swinging arms and that these arms could withstand the huge forces applied to them whilst under tow in preventing the main structure from distortion and vibration.
It was also important that the design incorporate components with dimensions that ensured that initial transportation to site could be completed without specialized equipment or additional costs. These components also had to maintain the structural requirements of the product..
In the end
The result of our innovative cable arch design is that in essence - we have designed a better mousetrap. Cable arches aren’t new and neither is double-sided loading but our Arch makes the process work more smoothly and efficiently and the net result is greater productivity and profits for the operator.
The difference between having a towable cable arch as opposed to using cable towers is that there is considerable time saved by being able to just hook up and tow the arch to its new location, as opposed to unhooking and lowering the cable and then dragging the towers individually and then lifting the cable back in place.
The estimate by our client suggested an extra 350 hours availability of the electric shovel per annum, which results in greater productivity and hence more dollars on the bottom line, which is what all mining companies are aspiring to in this downturn in the mining sector.
Learn more about how one of our Towable Cable Arches can help you.