Engineering News

The use of granular stainless steel as an alternative to scrap has many benefits which are being recognised far more widely overseas than in South Africa, Thos Begbie MD Eugene Rossouw tells Engineering News.

Rossouw cites the main benefits of its use as the elimination of the need for chemistry blending, laboratory analyses, raw-material yards and thus raw-material sorting.

In addition, granules generate no slag. Though granular stainless steel prices are up to 15% higher than prices charged for stainless-steel scrap, he says that granular more than earns its keep by eliminating so many of the risks commonly associated with scrap use.

Moreover, granules in all stainless-steel grades arrive precleaned and prepacked in drums, ready for immediate charging into furnaces.

In this way, users do not require special infrastructure to be built for casting and enjoy more flexibility, says Rossouw.

Thos Begbie, situated in Middelburg, has the capacity to produce 30 000 t of stainless-steel granules a year, in what is the world's first fully-computerised granulation plant, served by a 15,5 t overhead crane. Its high-volume melt facility uses stainless-steel scrap as a feedstock for the production of the granules, with molten stainless being tapped through a tundish into cold water where the metal solidifies into small granular particles that are transferred to a dewatering screen and then a kiln dryer, where moisture is removed in 2,5 minutes.

As the particles of molten metal fly through the air, they get smaller and rounder.

As fully rounded particles do not transport well on the conveyor systems, every effort is made to produce flattish granules at a preferred density of 4,5 t/m3.

Scrap metal, by contrast, packs at a density of only 1,8 t/m3.

Columbus Stainless, which adjoins Thos Begbie in Middelburg, buys granular stainless steel from Thos Begbie for use as coolant, to lower the temperature during casting and, thereby, speed up production.

The granular stainless steel is also sold to the South African foundry industry as on-grade raw material for use as a superior scrap alternative.

The Thos Begbie melt shop has two 6 t Pillar induction furnaces.

The one, a 1,5 MW unit, has a melt rate of 2 t an hour and is equipped with modern transistor capacitors and microprocessors.

The other, a 2,5 MW furnace, has a melt rate double that at 4 t an hour and has the latest integrated gate bipolar transistor (IGBT) technology, which permits rapid shutdown in the case of emergency. It is the largest IGBT furnace of its kind outside of the US.

Thos Begbie operates the only South African melt shop that uses an advanced safety system called Safeway, which continuously monitors wear of refractory lining in furnaces and indicates the area in which wear patterns are developing.

In this way, the risk of dangerous furnace burn-through is minimised and an early warning of the need for relining is provided, providing a 30% increase in refractory performance.

The melt shop operates for 24 hours a day and seven days a week, closing only four days a year.