Within this cycle, the handling of aluminum chips is particularly important for four industries: rolling mills, pressing plants, machining operations and smelting plants. In general, loose chips have a large volume and low weight, i.e. they have a low bulk density, typically 140 to 250 kg/m³. This makes both storage and transportation more expensive - both internally and externally. The chips are therefore pressed. The technology used is important here. Ruf machines can compact up to 2,200 to 2,400 kg/m³, in some cases even more. For comparison: the average density of solid aluminum is 2,700 kg/m³.

Briquetting in the...

Rolling mill: Chips are produced here when the cast surface is milled. In addition, so-called edge trimming chips are produced during processing into sheets, coils or foils. Both need to be briquetted. If the company is affiliated with a smelting plant, the pressed aluminum is fed directly to it (highest added value). Otherwise, it is stored and sold on the scrap market.

Due to the high density compared to loose chips, the use of briquettes reduces storage and transportation costs. Briquettes also generate higher sales revenues because they are more suitable for melting down.

The benefits: reduced storage and transport costs, lower operating costs thanks to in-house recycling, optimized sales revenue.

Press shop: Chips are primarily produced by "turning" and sawing cast round billets and finished extruded profiles. As only a few of these companies have a smelting plant attached, storage and transportation costs are particularly significant. Higher sales revenues are also achieved, above all because extrusion plants have pure chips with a clearly defined composition. These can be used as alloying additions when melting down, which is popular with smelting plants as they do not have to purchase as many expensive alloying and aggregate materials.

The advantages: reduced storage and transport costs, optimized sales revenue, optimized remelting.

Machining company: Machining companies can be found in the automotive industry, aviation and mechanical engineering, among others. For them, handling chips as a "waste product" from machining is part of their daily business. Here, too, the advantages of briquetting in terms of storage and transport costs are just as evident as the optimization of sales revenue, as briquetting reduces the volume by a factor of six to twenty, depending on the shape of the chips. In addition, there is another important factor in this area of application: the recovery of cooling lubricants, emulsions or oil.
Ruf systems are equipped with an integrated collection device for liquids for this purpose. This keeps the storage area clean - in the interests of orderly production processes and practised environmental protection. If machines also work automatically and only the supply and removal of chips or briquettes has to be carried out by operating personnel, personnel costs are also reduced and occupational safety is increased.

The advantages: reduced storage and transport costs, recovery of the emulsion, optimized sales revenue, occupational safety and environmental protection.

Briquettes in the smelting plant

Remelters and refiners are smelting plants that differ, among other things, in the products they produce. Remelters mostly produce wrought alloys in the form of wire, billets and rolling ingots. Refiners produce casting alloys, usually in the form of ingots. Both utilize chips, among other things. The difference between melting down loose or briquetted aluminum is significant in each case. This is because the light metal "burns" very quickly when exposed to flame instead of melting. As the ratio of surface area to thickness is particularly high in the case of chips, a lot of material is lost through this burn-off. In addition, the large free aluminum
surface of the chips has a high tendency to form oxide. This is also lost in the melting furnace in the form of dross.

Another problem factor when melting aluminum: If the liquid metal suddenly comes into contact with other liquids such as cooling lubricants, an almost explosive reaction takes place. The issue of residual moisture is correspondingly important. The moisture content of loose chips is often 20 percent or more. If briquetting is not used, the moisture must be removed from the chips using centrifuges and other drying systems. Briquetting, on the other hand, is more economical, especially if high-quality systems are used. This is because a correspondingly high pressing force reduces the moisture content to three to five percent. If the briquettes are then stored dry, this value is reduced to less than two percent. This means that the briquettes can be melted down safely and efficiently.

The benefits for remelters and refiners: reduced storage costs, increased safety, improved product quality, efficiency and metal yield, reduced plant investment, optimized sales revenue.

Briquettes have an additional advantage for refiners: due to the burn-off and oxidation, loose chips cannot be charged in some melting units at all or only at very high cost. The melting process of loose chips in the rotary drum furnace requires salt. The problem here is that the remaining salt slag has to be disposed of or treated at great expense. Hearth-type melting furnaces can be equipped with so-called vortex devices, which are operated in combination with electromagnetic or mechanical pumps. In this way, the chips are stirred into the melt. This works well for the most part, but is expensive. In addition to the purchase costs, the equipment requires space, regular maintenance and additional personnel and operating costs - especially due to high wear and tear. Briquetting means that no or only small quantities of salt are required. The ancillary costs are reduced.

More yield in the melting process

Regardless of the stove technology, the melting process works best with highly compressed briquettes. The decisive factor here is the density of the briquettes, which should be between 2,200 and 2,400 kg/m³. The density of liquid aluminum depends on the alloy and averages around 2,350 kg/m³. As a result, the briquettes hardly float, which reduces burn-off and oxide formation to a minimum. For this reason, refiners usually report a yield that is at least two percent higher. Some even confirm a five to seven percent higher metal yield.

Christian Hamers, freelance technical consultant at Ruf, Andreas Jessberger, sales manager at Ruf Maschinenbau / ag
AMB, Hall 8, Stand C58