【SMM Scrap Aluminum】Common ISRI Classifications of Aluminum Scrap and Their Applications

In the international trade of scrap aluminum, the Institute of Scrap Recycling Industries (ISRI) classification standards serve as the universal benchmark, enabling buyers and sellers to transact with precision based on material composition and properties. Among the many categories defined by ISRI, three stand out for their prevalence and industrial significance: Zorba, Twitch, and Tense. Understanding their distinct characteristics and market uses is key to optimizing recycling processes and advancing a circular aluminum economy.

Zorba, officially known as Shredded Non-ferrous Scrap, Mainly Aluminum, is a shredded blend of primarily aluminum with auxiliary non-ferrous metals such as copper, lead, magnesium, stainless steel, nickel, tin, and zinc in elemental or alloy form. Free of radioactive substances, slags, and excessive ash, Zorba is produced through a combination of gravity separation, air classification, flotation, sieving, and magnetic separation to remove free iron and oversized ferrous contaminants. To streamline trade, each Zorba batch carries a numerical grade—“Zorba 89,” for instance, denotes 89 percent non-ferrous metal content. ISRI’s reporting system classifies Zorba not only under aluminum scrap but also within the broader hardware scrap category, reflecting its dual role in the metal recycling chain.

Twitch, or Floated Fragmentizer Aluminum Scrap from Automobile Shredders, consists of lightweight aluminum fragments separated by floatation from end-of-life vehicles, small appliances, and beverage cans. ISRI’s stringent quality criteria mandate that Twitch be fully dry, with free zinc, magnesium, and iron each capped at 1 percent; total non-metallic impurities limited to 2 percent (with rubber and plastic under 1 percent); and absolute exclusion of peroxides, airbag canisters, or any sealed pressurized items. As downstream industries demand ever-higher aluminum purity, Twitch has emerged as a premium scrap grade. Typically sorted out of Zorba, it can be further refined—North Texas Shredding, for example, reduces zinc and magnesium levels to achieve up to a 95 percent recycling yield. This ultra-refined Twitch meets the exacting purity requirements of automotive and other high-performance sectors while boosting the overall efficiency of aluminum reclamation and minimizing waste.

Tense, referred to as Mixed Aluminum Castings, encompasses assorted clean aluminum cast parts—ranging from automotive to aerospace castings—excluding ingots and free of iron, brass, soil, or non-metallic debris, with oil and grease content kept below 2 percent. Enriched with silicon or magnesium alloys to enhance hardness and strength, Tense is ideally suited for applications demanding high mechanical strength and elevated temperature tolerance. Common end uses include automotive body components, large machinery parts, and substantial architectural elements not in contact with water.

Zorba (Picture taken from Scrap News - Recycle in Me ISRI)

Twitch (Picture taken from Scrap News - Recycle in Me ISRI)

Tense (Picture taken from Scrap News - Recycle in Me ISRI)