Steel scrap consists of discarded steel or steel products, generally segregated by composition and size or ‘grade’ suitable for melting. There are three main types of scrap which are used by the steel industry as feed stock. These are (i) internal scrap, (ii) prompt scrap, and (iii) obsolete scrap.
Internal scrap is also known as revert or home scrap. It refers to the reject metal within the steel plant which gets generated during steel making, steel casting and steel finishing activities within the steel plant. Prompt scrap is also known as process scrap and it is the waste generated during the product manufacturing by the steel plant’s customers i.e. the manufacturing industries. Obsolete scrap consists of that scrap which is recovered from discarded industrial and consumer items i.e. from ships to refrigerators and from construction beams to automobiles.
The first two categories of scrap can be returned to the steel making process with little or no pretreatment, obsolete scrap needs to be separated from contaminants, sorted and prepared for steel making. Due to the large improvements which have taken place in the steel manufacturing, steel casting, steel finishing, and product manufacturing technologies in the recent past, the amount of generation of the first two types of scraps have reduced a lot. On the other hand with resources of obsolete scrap are increasing as the world is becoming more industrialized and due to larger quantity of discarded consumer durables and worn out industrial equipment etc.
Another way of classifying steel scrap is to classify it according to the products in which the steel was used before it became scrap. The main steel scrap sources in this sense are automobiles, ships, railroads, construction buildings, machinery, white goods, packaging, electric and electronic equipment etc.
Steel scrap is considered to be free of alloys if the residual content of the following elements contained in steel do not occur at levels consistent with the purposeful creation of an alloy steel. Residual level of elements contained within the scrap shall not exceed chromium 0.20 %, nickel 0.45 %, manganese 1.65 % and molybdenum 0.10 %. The combined residuals other than manganese shall not exceed a total of 0.60 %. A scrap is considered to be off grade if it fails to meet (i) applicable size limitations, (ii) applicable requirements for the type of scrap, and (iii) applicable requirement with respect to the scrap quality.
Steel scrap in itself does not pose any risk to the environment, i.e. there are no environmental risks in transportation and storage of metal itself. However, if the steel scrap is contaminated with oil or mixed with other waste, this may be considered hazardous in relation to transportation or storage. For example, oil or any other liquid attached to scrap metal, when exposed to rain, may cause contamination to its surrounding environment.
Facts regarding recycling of steel scrap
The following are the facts associated with steel scrap and its recycling.
- Almost 40 % of the global steel production is made from steel scrap. Around 500 million tons of steel scrap is being used annually for the production of steel.
- Recycling of one ton of steel saves 1.4 tons of iron ore, 0.40 tons of coal, and 0.055 tons of limestone.
- CO2 emissions are reduced by 58 % through the use of steel scrap.
- Recycling one ton of steel scrap saves 2.3 Cu m of landfill space.
- Recycling of steel scrap uses 75 % less energy compared to creating steel from raw materials.
- Steel scrap recycling uses 90 % less virgin materials and 40 % less water. It also produces 76 % fewer water pollutants, 86 % fewer air pollutants and 97 % less mining waste.
- Steel automobile frames contain at least 25 % recycled steel scrap and a typical electrical appliance will usually be made of 75 % recycled steel scrap. Steel cans consist of at least 25 % recycled steel scrap.
General conditions applicable to steel scrap
The following are the general conditions which are applicable to steel scrap.
- All the grades of steel scrap shall not contain more than 1 % by weight of iron.
- Steel scrap is to be free from excessive rust, corrosion, dirt, oil, or grease.
- Steel scrap is to be free of hazardous materials, such as, but not limited to oil filled devices, explosives, radioactive materials, military scrap including fire arms, and ammunition casting etc.
- Steel scrap shall not include pressurized, closed or insufficiently open containers of all origin since this can cause explosion.
- Steel scrap shall not have material which are having radioactivity in excess of the ambient level of radioactivity.
- Steel scrap shall be free of non metallic materials, earth, insulation material, excessive iron oxide in any form, except nominal amounts of surface rust arising due to outside storage of the prepared scrap under normal atmospheric conditions.
- Steel scrap is to be free of all but negligible amounts of non ferrous metals and such as aluminum, zinc, tin in any form, and lead and lead containing materials. It shall be free of visible metallic copper and free of all material which is having high dissolved copper content.
- Steel scrap shall free of alloyed steels as well as stainless steels
- Steel scrap shall be free of all but negligible amount of combustible non metallic materials such as rubber, fabric, wood, and lubricants etc.
- Steel scrap shall be free of large pieces of materials which are non conductor of electricity.
- Steel scrap shall be free of waste arising out of steel melting, surface conditioning, grinding, sawing, welding, and torch cutting operations etc.
- Bulk densities of different types of scraps vary in the range of 0.4 tons/Cu m to 1.0 tons per Cum.
Specifications and standards
Currently, specifications and standard classifications for steel scrap exist at all levels, international, European, national, as well as between individual parties. It is clear that for the reason of marketing and trading, standards and specifications are needed not only to set the price but also used as reference for classification and controlling of the quality. In many cases based on the production need, steel scrap is processed according to the bilateral specifications agreed upon between the scrap processor and smelters.
Traded steel scrap is basically classified according to several properties as given below.
- Chemical composition of metals
- Level of impurity elements
- Physical size and shape
- Homogeneity or variation within the specification
Institute of Scrap Recycling Industry (ISRI) of USA has developed specifications for steel scrap which are known as ISRI specifications. This American standard provides the norms for classification of steel scrap and is used internationally. EFR and EUROFER have developed the European steel scrap specifications. These specifications cover the requirements from the safety perspective, the excluded elements for all grades from a cleanliness point of view, and the tolerance for residual and other metallic elements. These also provide a detailed description of the specifications by category, which corresponds to the type of scrap. National industry associations of some countries such as UK, Spain, Belgium, France and Germany etc. have developed their own specifications for steel scrap. There are also bilateral contract/specifications made as agreements or contracts in trade between two parties. Such a specification is usually based on a standard classification with additional requirements suitable for the desired production process or product.
Basically for the purpose of electric steel making, heavy melting scrap (HMS) is used. It is industrial or commercial scrap steel greater than 6 mm thick, such as plates, beams, columns, and channels etc. and may also include scrap machinery or implements or certain metal stampings. HMS is usually broken into two categories namely HMS 1 and HMS 2. The difference between the two is that HMS 1 does not contain galvanized and blackened steel while HMS 2 does contain galvanized and blackened steel.
Steel scrap processing
Processing of steel scrap involves size reduction, cleaning, sorting, shredding, pressing, shearing and crushing. Steel scrap processing also results into increasing of the density of the scrap mass.
- Pressing – Pressing means using a baler to press thin sheet steel scrap into bales. The pressed sheet steel scrap might be waste from a punching press or cutter. In the press, the thin, light steel sheet is compressed into cubes. Pressing is also used e.g. to reduce the volume of junk cars (logging). The purpose of pressing is in fact to reduce the volume of the light scrap sheet metal and to increase the volume weight to a weight suitable for the electric steel making. Moreover, pressing can also reduce transport costs and facilitate storage. Pressing can also include briquetting, i.e. pressing lathe chips into briquettes.
- Crushing – Crushing is done with various metal crushers. Crushing is used in the processing of thin or dirty sheet steel scrap and junk cars. The purpose of crushing is to break down the steel scrap metal into smaller pieces so that the different metals can be separated and the impurities removed. For example, crushing cars produces clean, palm-sized, rust-free clumps that can be picked off later with a magnet. In this phase, also the plastics, wood, rubber, sand and other impurities are crushed so small that they can be removed.
- Shearing – Shearing means the cutting and pressing of thicker scrap steel. Shearing takes place in big, guillotine-like scrap shears. Steel beams and miscellaneous scrap are cut into – 60 cm or – 80 cm pieces. Shearing increases the bulk density of the scrap, making it easier to handle and portion out.
- Shredding – Shredders incorporate rotating magnetic drums to extract iron and steel from the mixture of metals and other materials.
- Sorting – Sorting is the process of separating the different metals and other materials. This is done using magnets, eddy current separators, screening, blowing/suction (air classifier), flotation (gravitational separation), optical separation and manual separation.
Schematics of typical scrap processing cycle is at Fig 1.
Fig 1 Schematics of typical scrap cycle