Dry Treatment of Stainless Steel Slag

Recycling & Recovery

Dry Treatment of Stainless Steel Slag

Magnetisation of Stainless Steel allows efficient Separation
Slag is a normal and necessary “byproduct” of the steel making process and contains debris as well as a certain amount of metals. Recovering this metal content reduces the need for virgin ores and saves part of the production process.
(ed. WoMaMarcel - 09/10/2014)
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Impact Technology in all Crushing Stages

Impact crushing, which magnetizes stainless steel, has proven its value in routine operations. BHS-Sonthofen has developed a cost-efficient process for new treatment plants in which metal parts are magnetized in each stage of the process chain. The plant concept is divided into three treatment stages:

  • Coarse crushing of stones and skulls up to 400 mm in size with a BHS Rotorshredder (type RS)
  • Secondary crushing of mid-sized grain fractions with a BHS rotor centrifugal crusher (type RSMX)
  • Fine crushing of fine and sand fraction of 0 to 4 mm with a BHS rotor impact mill (type RPMV)

 

Step 1 — Coarse Crushing: Rotor Shredder

In its technical center, BHS-Sonthofen has shown that the Rotorshredder of type RS is suitable for the coarse crushing of metallic slag. The tests were performed with steel skulls from Krefeld, Duisburg and Brandenburg with an edge length of up to 600 mm and a weight of up to 50 kg.

The principle of the Rotorshredder is simple: the interior of the machine contains a rotating vertical shaft with pairs of hammers arranged one above the other, mounted on articulated joints. The slag is fed from above into the crushing chamber, and is selectively crushed as it enters the range of tools by impact, punching and shear forces. In the process, slag composites are separated and the metals are freed and magnetized. The crushed material exits the crushing chamber through a sturdy slotted gate in the housing wall, the apertures of which can be varied depending on the grain size required.

Step 2 — Secondary Crushing: Rotor Centrifugal Crusher

The screened material coming from the Rotorshredder, still containing metal and ranging in size from 4 to 22.4 mm, is further processed in the secondary crushing stage. The rotor centrifugal crusher of type RSMX, described above in detail, crushes this material, thereby separating the slag from the metal. Grain sizes of 0 to 4 mm are screened after secondary crushing and transported to the rotor impact mill. The material still containing slag after the screening and separation process is fed back into the rotor centrifugal crusher.

Step 3 — Fine Crushing: Rotor Impact Mill

Laboratory tests have shown that fine or sand fraction of 0 to 4 mm also contains usable high-quality metal. Rotor impact mills of type RPMV crush the remaining material from the screening and magnet process following treatment in the rotor centrifugal crusher.

The rotor impact mill contains a plate to which horseshoe-shaped hammers are attached. When the centrally fed material hits the rotor, it is accelerated outward by centrifugal forces. It is then caught by the horseshoe-shaped hammers, which im­pel it against the anvil ring. Repelled by the anvil ring, the material hits the hammers again and is thrown back against the anvil ring. This process repeats until the feed is small enough to pass through the gap between the impeller tip and the anvil ring, and is thereby discharged from the mill. The fraction of 0 to 4 mm can complete several cycles in the rotor impact mill. With each cycle, the metal is discharged from the machine circuit by means of neodymium separators. The slag sand produced consistently exhibits an outstanding cubical grain shape. It is, nevertheless, important to carefully consider whether this third stage makes economic sense with respect to wear-related costs.

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