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Cool when the aluminum is hot

There is a perfect degree and type of cooling that is needed to mould the perfect metal, say aluminium industry experts, as they share their views on the importance of process cooling systems

| | Jun 3, 2015 | 7:32 pm
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There is a perfect degree and type of cooling that is needed to mould the perfect metal, say aluminium industry experts, as they share their views on the importance of process cooling systems

 
By Rajiv Pillai | Features Writer
 
Aluminium is the third most plentiful element in the earth’s crust, comprising eight per cent of the planet’s soil and rocks. In nature, aluminium is found only in chemical compounds with other elements, such as sulphur, silicon and oxygen. Pure metallic aluminium can be economically produced only from aluminium oxide ore, necessitating a number of processes, with anodising being one of them.
Anodising requires process cooling – by the truck-loads. And reliable cooling, at that.
 

Cooling critical!

A cooling system failure during the manufacturing process can result in loss of lives, says S K Sarkar, the General Manager at India-headquartered Unimark International. “Suppose cooling is done in a haphazard way, and the water goes into the hot metal liquid, there can be explosions,” Sarkar says. “People can die. And it has happened in a few cases.”

A lesser morbid result would be a defective product, says Sarkar, and Dr Marcello Rossi, the Technical Director at Italy-based Italtecno, agrees. “It’s not possible to have a great product during anodising if you do not have a cooling system,” Dr Rossi says. “All plants need cooling.”

To counter the possibility of cooling failure, industry experts resort to installing sufficient safety measures, such as monitoring devices and alarms. Sarkar is of the view that in the event of any defect in the cooling system, the entire manufacturing process must be shut down to avoid fatalities.

 

The right kind of cooling

The anodising of aluminium is performed by making the part that is to be anodised – the “anode” or positive end of an electrical circuit – within an acid electrolyte. With electricity applied through the acid from the cathode, an oxide layer develops in and on the outer layer of the metal. This outer layer can be formed so that it has a porous quality and the aluminium oxide layer can be dyed in many colours. With process cooling systems, the right kind of surface layer will be formed.

Describing this further, Sarkar says, “Surface cooling is very important, and we do surface cooling so that the skin of the metal becomes hardened; however, inside it’s still liquid. This means that the surface is hard but if you go inside the core, it is still boiling at 1,000 degrees C.”

From a safety point of view, sufficient skin on the metal should be formed by cooling, so that the liquid metal will not spill. However, Sarkar warns, the cooling cannot be overdone, as the property of the metal will be lost.

 

The right kind of systems

Since the anodising process generates a lot of heat, cooling is a must, particularly for hard coating processes. Anodising chillers will do most of the work by removing process heat using either an air- or water-cooled chiller. “It’s very important for this part of the world [Middle East] to have this kind of chiller and cooling system, in order to be sure about the quality of the final product,” Rossi says. “Just one or two degrees more than the requisite degree, and there could be problems in terms of quality.”

Air-cooled units are generally installed outside, and eliminate the need for a tower. Water-cooled units are the most efficient method, though, particularly in warmer climates. They are installed inside a building, with a cooling tower outside. Sarkar says there are a number of cooling approaches available, depending on the availability of water or the imperativeness that needs to be shown to conserve water. For instance, in large parts of Europe, water is available in plenty, relatively speaking. Rossi talk of how some European plants have a lot of water at their disposal. “In Italy, for example, they use ground water for cooling solutions,” Rossi says. Sarkar, speaking from a scenario of limited water resources, says: “Instead of water cooling, there is partial water cooling and partial air cooling. You can reduce the consumption of water. Water becomes hot, so we have to again recycle to make it cool. We can’t afford to drain the water every time.”

Another method is to not use water at all. Sarkar talks about “vigorous air cooling” being sufficient to get the job done. However, an inherent disadvantage in the air-cooled system is that the blowing air represents a hazard during the initial stage of cooling, when the metal is still in a liquid state, thereby giving rise to the possibility of it spilling over. Given sufficient time, the metal will cool down automatically on its own. After this, Sarkar says, it is safe to adopt vigorous air cooling.


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