Sustained, and rising demand for iron and steel scrap has made prices climb worldwide, particularly for the premium grades of scrap so valuable to primary steelmakers and iron and steel foundries. There are less-desirable grades of scrap that are more available, and though these “neglected” grades — such as castiron turnings — are no replacement for the better-quality iron units, they can be processed more cost-effectively now thanks to a new briquetting system.
Daniel Zeiler of Metso Lindemann (www.metsominerals.com) states that the “by-product” value of cast-iron chips might increase by 140% if they are briquetted for use as a feed material. When scrap was cheap, machining centers might have sold their chips to scrap dealers at a low price, just to get rid of them. Now, this bulky waste material can be briquetted and sold, or reused.
Metso produces a range of machinery and equipment for heavy manufacturing, including quarrying, aggregate production, mining and minerals processing, recycling. Metso Lindemann builds heavy machinery for metal handling, and to date has sold more than 60 of its hydraulic briquetting presses for reprocessing metal chips, in 25 countries.
One user is Fritz Winter Eisengiesserei GmbH and Co. KG, a large, gray and ductile iron foundry in Germany. Winter bought Metso’s top model, the MUB 630, in 2005 and has been operating it day and night, according to the machine builder. The throughput is 40,000 metric tons/year of cast iron chips — a byproduct of Winter’s in-house machining and finishing of cast-iron brake discs, crankcases, and cylinder liners. The reclaimed iron — reconstituted as large briquettes — are returned to the production process when they are smelted in Winter’s 300,000-tons/year cupola furnace.
Cast iron turnings are hard, short, and brittle, and therefore hard to form into stable briquettes without any binding agent, like cement used in self-reducing C-bricks.
Lindemann briquetting machines are double-side actuated, meaning two press rams work in opposition to each other, in order to compensate for the frictional forces between the briquette and press bushing. The cylindrical cast-iron briquettes have a diameter of 155 mm. The length of the briquettes can be freely adjusted between 50 and 200 mm. According to Metso, one important feature is the high briquette density, around 5.5 kg / dm3, which comes close to solid cast iron, with a density of 7.2 kg / dm3. Furthermore, the briquettes have a low tendency to crumble in storage, or during transport and charging.
A cupola loaded with chip briquettes tolerates a certain portion of fines, but it may “choke” if the briquettes disintegrate too early in the smelting process. Unlike loose chips, stable briquettes protect the metal against oxidizing. Loose chips oxidize more readily in storage, and also when charged into induction furnaces. The iron oxide is lost material for the melt yield and is discharged with the slag. In a cupola furnace iron oxide is reduced, but at the expense of melting energy. The reduction has to be compensated by a higher portion of coke.
The steady rise of metal prices and scrap demand worldwide encourages scrap collectors and processors to broaden their sources, and an obvious result of this is that collectors’ scrap qualities are diminished. Accurate scrap processing techniques like shredding, cleaning, and metal sorting therefore increase in importance, to keep the desired level of metallic quality for melt shops.
Metso Lindemann, and another Metso company, Texas Shredder, supplied nearly two-thirds of all the 700 large-sized shredders now installed aroud the world. Metso Lindemann offers a line of scrap recycling machinery and plants, which cut, crush, clean, and sort scrap with an eye on melting quality.
“The calculation of pay back for the purchase of a machine has dramatically changed,” stated Zeiler. “The contribution of briquetting to higher metal yield has become more valuable. The calculations have to be reckoned again, and should be updated.
Excerpted from FM&T May 2007 issue, pg. 16.