Upgrading aluminum draws the world’s attention

An early December article on the website of the Switzerland-based World Economic Forum (WEF) points to “aluminum’s infinite recyclability” as “the answer to the aluminum industry’s emissions issue.”

The four co-authors of the WEF article write, “Over 90 percent of current aluminum emissions are associated with primary production. But secondary, or recycled, aluminum uses just 5 percent of the energy required for primary production.”

Boosting aluminum’s already high global 73 percent recycling rate is one task required to further reduce emissions for the light metal. The WEF co-authors also state, “The challenge with [aluminum] automotive scrap lies in sorting the aluminum alloys to retain the quality and value of the original components.”

Increased dismantling before shredding offers one alternative, say the authors, but in most nations that generate large numbers of end-of-life vehicles (ELVs), the labor market is tight, so hiring people to take vehicles apart by hand may run into a barrier of its own.

Scrap processors and their technology vendors continue to seek out automated sorting improvements. In one recent example, Germany-based Steinert GmbH supplied equipment to Sweden-based Stena Recycling at one of its facilities in Roskilde, Denmark.

“Advancements in technological sorting represent one of the greatest differences” in today’s market, says Jesper Fournaise of Stena. “Now, here in our own country, we’re able to use X-ray technology to meet very high quality standards in order to put the metal back into commercial use.”

Another Germany-based technology provider, Erdwich Zerkleinerungs-Systeme GmbH, engaged in a project in Austria that sought to better separate aluminum from magnesium during and after the shredding process.

After consulting with Erdwich, the Austrian firm decided to install an Erdwich RM1350 ripper. An advantage of this twin-shaft ripper developed by Erdwich, compared to the shredder used previously, is that the blades “do not simply shred the input material, but literally tear it apart due to their special shape. This allows the plant to grip the aluminum scrap far better, and there are fewer blockages or damage to the machine,” states Erdwich.

To further purify the aluminum, Erdwich soon started planning and implementing what it calls a complete plant concept into which the existing twin-shaft shredder was integrated. The shredding plant was supplemented by a hammer mill also developed by Erdwich, but it entailed a few challenges.

“For one thing, the space available for the plant was limited to a very narrow, half-open hall, which required planning with centimeter precision and foresight,” says Harald Erdwich, managing director of Erdwich GmbH. “On the other hand, the input material consists in part of undefinable components such as nonmetallic impurities or even solid iron parts, which made sorting difficult. Therefore, it was necessary to implement several processes and the corresponding equipment to separate different materials and alloys.”

While ultra-fine materials such as sand or dirt particles are sorted out by a vibrating screen, a magnetic drum separator ensures that ferrous portions are removed from the shredded aluminum scrap using magnetic technology.

A zigzag air separator also separates foil and wood particles from the metallic components, and an eddy current separator is responsible for filtering out plastic parts. For impure alloys, a fourfold sorting device also is provided, which works, among other methods, by means of X-ray detection. “This makes it possible to achieve a particularly fine separation of the material and thus a high degree of grade purity,” states the equipment company.

Erdwich says the input fractions are not always composed in the same way, so the company what for it was a new concept: three different modes that can be set for the efficient processing of the material.

“In mode A, the aluminum scrap is fed directly into the RM1350 pre-shredder by means of a gripper or stacker and then re-shredded by means of our HA800 hammer mill,” says Harald Erdwich. “The mixed fractions are separated using various sorting techniques and then discharged into containers provided by the customer.”

Mode B enables the faster processing of pure aluminum scrap. After shredding in the twin-shaft shredder, separation of ferrous and stainless material is carried out by means of a double magnetic stage.

In Mode C, double feeding is used in order to be able to process input materials made up of different compositions simultaneously. This makes it possible to process both pure aluminum scrap, as in mode B, and aluminum/copper cast material in parallel. The latter is fed via the mobile conveyor belt into the vibrating feeder, crushed by a hammer mill and then separated by means of X-ray sorting and transported into containers.

The different modes can be selected on the operator panel by before the system is started. Depending on the composition of the material and the mode, a throughput of up to 2,500 kilograms per hour (5,500 pounds per hour) can be achieved.

“The shredding process for aluminum scrap, in particular, must be constantly monitored,” says Harald Erdwich. “As soon as aluminum is shredded to less than 4 millimeters (0.15 inches), or if the input material contains aluminum alloys with magnesium components, it can ignite and trigger an explosion.”

He continues, “To avoid accidents, the cutting mechanism geometry of the ripper is designed in such a way that the material is shredded as gently as possible under temperature-reduced conditions. Sensors also ensure that no excessive dust concentration can occur inside the hammer mill if, for example, there is a filter defect or other failure of the extraction/filter system.”