Change in one type of technology often dictates change in another. The changes to steel cutting technology in the past three decades have been very significant and, with the development of high-speed fibre lasers, are now influencing the quality of steel that the industry uses.
Swiss steel cutting technology company Bystronic has taken the lead in the development of fibre lasers, with the introduction of the Bystronic 10kW ByStar fibre laser. Represented exclusively in South Africa by First Cut, the foremost local experts in the provision of consumables and capital equipment, this new generation of Bystronic fibre lasers continues to set new records for speed, accuracy and unmatched productivity.
“However, the radical technological advances such as those incorporated in the ByStar have also driven changes in steel technology. A very relevant example is that of stretcher-levelled steel,” explains First Cut’s Managing Director, Andrew Poole.
The introduction of stretcher-levelled steel to South Africa is comparatively recent. The leader in this field is the steel company Allied Steelrode, which has installed South Africa’s first purpose-built steel-stretching plant in a 15000m2 facility in Midvaal, Gauteng.
The equipment used to make stretcher-levelled steel requires a major capital investment. The forces needed to stretch steel sheet are immense; and machines that can apply this level of force, are both very large and highly sophisticated.
“However, it is a great service to provide to industry, as the demand for quality stretcher-levelled steel is very considerable,” says the Group CEO of Allied Steelrode, Arun Chadha, adding that, to complete their value-add and market differentiation strategy, the stretcher-levelled product is branded ‘ASSM’ or ‘Allied Steelrode Stretcher Material’.
The heavy gauge stretcher leveller produces flat sheet and plates that stay flat after secondary operations like laser, plasma or water jet cutting; as well as shearing, turret punching, bending, forming, welding and finished assembly. It has the capability to stretch steel from 1.20 mm to 13 mm thick, 2000 mm wide and up to 15 metres in length.
Chadha explains that when steel is produced at a mill, there is uneven cooling, thus causing internal stresses in material. The traditional cut to length lines exert immense pressure through standard roller levelling to produce steel sheet/plate. This steel may appear flat but it has latent stresses in its structure.
Non-stretched material has what is known as ‘memory’: which tends to make standard leveller-rolled flat sheets return to their original coiled form. “As soon as energy/heat is applied to non-stretcher levelled steel sheet, it tends to buckle,” Chadha adds.
However, if steel is stretched under tremendous pressure past its yield or ‘stretch’ point, the trapped internal stresses are relieved, and the steel will not distort when cut or when heat is applied to it.
The stretcher leveller achieves this by stretching the entire cross section of the strip, from top to bottom and edge to edge.
Today, most sheet steel components are cut on lasers, many of which are supplied in South Africa by First Cut. The use of stretcher-levelled steel is essential when using a laser to cut components. The reason for this is that the laser head travels at great speeds only a few millimetres above the steel during cutting.
“Should the steel buckle, there is a real danger that the laser head will collide with the upturned steel, damaging this very expensive component in the process,” explains Bystronic Sales Director at First Cut, Gareth Jackson.
He explains that the second advantage to be gained from using stretcher-levelled steel is that when commencing with a cutting operation, the laser head needs a starting point.
“Before stretcher-levelled steel was available, the head would have to start cutting ten millimetres from the edge of the sheet. Now, the head can cut as close as two millimetres from the edge of the sheet,” he says.
For any volume operation, this represents a significant reduction in the scrap rate and a better yield from every sheet.
“This is crucially important for customers, as cost-savings from producing less scrap can be as much as 15 percent,” Jackson points out.
Importantly, with manufacturing the world over moving towards Industry 4.0 standards and automation, the use of stretcher-levelled steel allows for trouble-free continuous production with a minimum of technical supervision.
“The stretcher leveller we have installed at Allied Steelrode is a one of a kind in South Africa and represents the very latest in this type of technology. A major advantage thereof is that it can – without marking the steel in any way – process 15 metre-long steel sheets even high tensile material for example 8mm at 800MPa.
This is very useful for those customers involved in manufacturing crane components, truck bodies or long girders, for example,” explains Chadha.
The stretcher plant, which needed to be especially manufactured to Allied Steelrode’s specifications, was ordered in 2013 and installed in the new purpose-built factory in the first quarter of 2015.
“Since then, the demand for memory-free flat steel has been so high, that a second stretcher leveller has been ordered to provide the required additional capacity. We are very proud of this, as it bears testimony to our ‘first mover’ or ‘early adopter’ status and the investment we made in this critical technology,” he comments.
“From our point of view – and as the local representative of Bystronic capital equipment – we wholeheartedly endorse the use of stretcher-levelled steel as the material of choice for the fabrication and manufacturing sectors,” continues Jackson.
“In summary, the use of stretcher-levelled steel with our Bystronic fibre lasers is beneficial in two ways. It maximises potential operational time while optimising productivity and – ultimately and extremely importantly – customer satisfaction,” he concludes.