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Comminution technology as a quality factor in the manufacture of carbon black

Comminution technology as a quality factor in the manufacture of carbon black

State-of-the-art solutions for maximum end-product fineness values: Comminution technology as a quality factor in the manufacture of carbon black

Carbon black can be found in car tires, plastics, and many other chemo-technical products. The required qualities of this substance are just as diverse as its applications. The comminution method is very important in determining the required specifications for the production process.

Regardless of the production process, this applies to the maximum end-product fineness values. The current solutions, have reached the limits of mechanical feasibility. These days, high-performance car tires are, resistant to abrasion, UV rays, and high temperatures. This is due to an important industrial base material called carbon black which improves the mechanical properties of plastics and determines the characteristic properties of many other chemical products. The prerequisites for this constitute precisely defined quality grades, and in some cases, maximum end purity values.

In order to produce standardized high-performance carbon black material, an elaborate manufacturing process is necessary. We can make a distinction between two fundamental processes: incomplete combustion and pyrolysis. Precise control of the quality and target fineness of the end product must be possible for both processes. The comminution technique used plays a central role in accomplishing this. However, in view of the fact that incomplete combustion and pyrolysis are completely different processes, separate process-technological solutions are called for in each case.

Grinding and classifying techniques in the case of incomplete combustion

Carbon black consists of incompletely burnt hydrocarbons. Therefore, the incomplete combustion of heavy or light crude oil has become the classic manufacturing process for carbon black. Usually, efforts are made to achieve an extremely pure carbon black so that it can be used as filler for high-quality rubber products. In order to achieve this, the particles would need to be separated after the combustion process. However, at this point the particles would still contain numerous agglomerates commonly called “grit”.

These so-called grits must be milled or removed. Therefore, the particles will either be run through an in-line grinding process in a downstream mill, or separated by an air classifier.

High-speed hammer mills  are conventionally used for this, but this established technology has a decisive disadvantage: it only allows a comparatively coarse fineness up to a grit level of some 60-70 ppm (parts per million). To achieve the kind of high quality demanded these days, classifier mills have become the mill of choice for processing carbon black.

In light of this, Hosokawa developed the new Mikro® E-ACM  especially for carbon black applications. The machine, available in various machine sizes from 10 HP to 300 HP, permits a grit level of only 5-2 ppm at a grinding fineness of 45 μm (325 mesh), thus increasingthe value and quality of the finished product.

Grinding and classifying technology in one machine

This new application-specific development forms part of the Mikro ACM product line. Just as all models in the product line, it is characterized by the combination of grinding and classifying technology in a single machine. The pneumatically fed product enters the grinding zone in the bottom section of the machine. Comminution is a result of the product particles being accelerated by the rotating grinding elements and impacting against the stationary liner. The E-ACM has a special rotor design, which extends the grinding zone and improves the grinding efficiency.

The Process

Air is drawn through the mill by the downstream fan. This air cools, conveys and classifies, while intercepting the feed product and then routing it to the classifying zone in the upper part of the machine, where a separately driven dynamic classifying wheel is located. The centrifugal force of the rotating wheel and the opposing centripetal force of the air, along with the varying particle mass, results in a mechanical separation into a coarse and a fine fraction. The coarse material is rejected by the classifying wheel and is redirected back into the grinding zone for final comminution. The fines pass through the classifying wheel and exit the classifier mill. The cut point is set as a function of the classifying wheel speed and can also be easily adjusted before or even during operation.

One of the major advantages of this combined grinding-classifying process is that no material is lost. In contrast, a conventional classifier classifies only around 15 - 20 per cent of the material, which can then at very best be ground to poorer qualities. Other advantages of the E-ACM are its low energy consumption and ease of handling, especially when compared to other grinding processes.

 
Learn more about carbon black grit reduction in our educational webinar

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