Homepage » Process Engineering »

With balls and meshes

Grinding and screening solids
With balls and meshes

The eccentric vibrating mills in the ESM range not only comminute brittle solids. Over and above this, they can also be used for mechano-chemical activation of solid particles. cpp spoke to Dr. Jürg Pollmanns, Managing Director of Siebtechnik GmbH, and Jens Corell, Technical Manager of the Sampling Systems, Comminution and Laboratory Equipment Business Unit, about how these mills work and their application potential as well as about Perflux control screening machines.

The author: Lukas Lehmann Assistant Editor in Chief cpp chemical plants & processes

Siebtechnik generates about 70 % of its turnover with a wide variety of centrifuges. Alongside this, the product range includes screening machines and process equipment, grinding machines, sampling systems and laboratory equipment.
The spectrum of the grinding machines offered by Siebtechnik ranges from hammer and roller mills through jaw crushers to drum and centrifugal tube mills. In the words of Dr. Jürg Pollmanns, Managing Director of Siebtechnik GmbH, these plants are positioned in the low-to-medium performance range. “I’m talking here about throughputs from several hundred to a thousand kilogrammes per hour. Our mills are not used for mass production, in other words – they’re found in niche applications, where it is important to process products metal-free and maintain a particularly high degree of purity, or where a specific particle shape and a defined particle size and or size distribution must be attained.”
Ball mill with a single tube
The eccentric vibrating mills in the ESM range are suitable for continuous or batch wet and dry milling of brittle products of all hardness grades. The material to be ground can have a maximum feeding size of 20 mm. As a function of the material properties and the grinding time, particle sizes between 0 and 5 µm can be milled. The throughput rate is between 10 kg/h und 5 t/h, depending on the product and on the size of the mill and the grinding media.
In 1994, Siebtechnik engineers developed the single-tube eccentric vibrating mills in the ESM range in collaboration with the TU Clausthal. “In those days, only ball mills with two or three grinding tubes were available. These multi-tube systems were heavy. Relatively strong driving units were needed to move the great masses. And it was this that gave us the idea for our ESM mills”, explains Jens Corell, Technical Manager of the Sampling Systems, Comminution and Laboratory Equipment Business Unit. “The goal of this development work was a ball mill with only one grinding tube, which – with significantly less driving power – achieves a high comminution effect and throughput.”
The heart of the eccentric vibrating mills is a grinding tube mounted on four springs and powered by a lateral unbalance drive. There are generally ball-shaped grinding media in the grinding tube. Rod-shaped or cylindrical media are likewise possible. In the simplest case, they are made of forged steel. They can also be made of zirconium oxide for particularly sophisticated applications. The grinding balls can have diameters from 2 to 70 mm.
Asked about the way the mill works, Corell says: “The unbalance drive causes the tube to vibrate. This mechanical energy, or rather this impulse, is transmitted from the grinding tube wall to inside the drum from ball to ball. The balls impact against each other, thus grinding the material in the bed. They moreover migrate inside the tube. This rotary motion leads to thorough mixing and homogenisation of the product.”
The single-tube version of the ESM mills offers various welcome features. It enables short, compact grinding-tube modules to be built, of which a maximum of three are assembled to form a grinding unit. “That way, we can adapt very flexibly to the throughput rates and batch sizes customers require. What’s more, due to the short grinding tubes, we are in a position to line the tube’s inner wall with different materials without any problems. Rubber linings, wear-resistant steels and technical ceramics are just three examples. The single-tube design additionally enables cooling jackets to be employed to dissipate the heat generated by grinding, an option that is of great importance, above all for temperature-sensitive products.”
The unbalance drive arranged on the outside, axially parallel to the levelling compound, also offers several advantages for the user. On the one hand, it simplifies machine maintenance. On the other, it ensures that the normal circular vibrations in the tube are supplemented with elliptical and linear vibrations. This is how – even with grinding tube diameters greater than 650 mm – low-energy zones are reduced to a minimum. The high energy density in the tube improves the transport action, increasing the effectiveness of the grinding process and helping to cut down the process times.
Generation of reactive surfaces
Eccentric vibrating mills are not only used for crushing brittle materials. Many users also choose them for mechano-chemical activation of materials. When prompted to explain the meaning of the term “mechano-chemical activation”, Corell replies: “The grinding media impact on the solid. Through their energy, they bring about a change in the crystalline structure. This leads to lattice defects or disorders in the crystals that make the surface of the solid very reactive, so that the ground product can react with another solid”. This reaction partner can either be in the mill from the outset or added later. Mechano-chemical activation is used, for example, for manufacturing certain metallic alloys. However, chemical reactions are also possible inside the mill, such as for the production of metal sulphides. ESM eccentric vibrating mills are available in various designs for hazardous areas, e. g. with a grinding chamber, which can be rendered to-tally inert with the aid of protective gas. Besides this, Siebtechnik is capable of supplying complete systems, which, apart from the mill, contain additional components requested by the user, for instance for dosing and screening or for inerting the grinding tube.
ESM mills provide finely ground products, which in many cases are subsequently conveyed via screening machines. “The screens can handle two jobs, which have to be kept absolutely separate from each other, however”, Corell explains. “Job No. 1: The screens ensure that only solids up to a certain particle size are processed further. Siebtechnik has a variety of screening machines in different versions and sizes in its portfolio for this traditional screening task. Job No. 2: The screening machines must retain crushed grinding media or other foreign bodies contained in the material being ground that could damage the downstream plants. We offer our customers Perflux control screening machines for this policing or control tasks like this.”
Policing the bulk material stream
The machines are suitable for wet or dry screening. They reliably remove foreign materials and agglomerates from powders and suspensions. Generally installed in front of packaging or loading units, Perflux machines are meanwhile well established in the chemical and pharmaceutical industries as well as in food production.
A sturdy vibrating frame, supported on springs, forms the heart of any Perflux control screening machine. Outlet funnels, screen inserts and covers are attached to this frame. “This kind of assembly and the fact that the individual elements are fastened with screws makes the machines easy to clean and maintain”, says Corell. “One unbalance motor drives everything. It causes the vibrating frame to effect a wobbling movement, which guarantees good agitation and rapid screening of the product.”
The machines are sold for screen sizes from 150 to 800 mm with mesh widths greater than 40 µm or greater than 63 µm. The unbalanced motor rating is determined by the screen size, namely 0.16 kW for the smaller models or 0.50 kW for the larger ones.
The compact design is an essential feature of Perflux control screening machines. It enables them to be integrated simply into existing production lines. All machine components coming into contact with the product are made of stainless steel 1.4571. Higher stainless steel grades are available on request, as are types with an electro-polished surface or featuring brush devices or turnstiles. The latter disperse agglomerated solids or soft media on the screening surface and press them through the mesh with a sweeping movement. It goes without saying that Siebtechnik also offers a Perflux version for installation in hazardous areas in accordance with Atex 100a.

Optimistic for 2011

Facts & figures

In 2010, Siebtechnik achieved a turnover of 37 million euros – just under 18 % less than in its record year 2008 when the Mülheim company, which can look back on a long business tradition, reported 45 million in sales. “This is an after-effect of the global eco-nomic crisis”, explains Dr. Jürg Pollmanns, Managing Director of Siebtechnik GmbH. “It hit centrifuges, which are the mainstay of our sales, with something of a time lag. While all other Business Units were forced to struggle in 2009, centrifuges were still going strong due to a comfortable backlog of orders from 2008. This backlog underpinned a turnover of 43 million euros for the Group as a whole in 2009, the year when the recession was worst. It was actually the second-best sales figure in Siebtechnik’s almost 90-year history.”
Pollmanns is very optimistic for the current financial year 2011. “We are profiting from the spirit of optimism prevailing in the market, which we owe to very good orders on hand. What’s more, we shall be launching a new, continuous fine screen machine and a new range of centrifuges in the coming months. We are naturally hoping for a positive impact from both of them on the way sales develop.”
Siebtechnik makes its money from exporting machines. The Asian market is still extremely important for this plant manufacturer, which is why the company is investing a substantial amount this year in its Chinese subsidiary. The management has ambitious plans to expand production, sales, marketing and distribution in the Far East.
All Whitepaper

All whitepapers of our industry pages

Current Whitepaper

New filtration technology for highly corrosive media


Industrie.de Infoservice
Vielen Dank für Ihre Bestellung!
Sie erhalten in Kürze eine Bestätigung per E-Mail.
Von Ihnen ausgesucht:
Weitere Informationen gewünscht?
Einfach neue Dokumente auswählen
und zuletzt Adresse eingeben.
Wie funktioniert der Industrie.de Infoservice?
Zur Hilfeseite »
Ihre Adresse:














Die Konradin Verlag Robert Kohlhammer GmbH erhebt, verarbeitet und nutzt die Daten, die der Nutzer bei der Registrierung zum Industrie.de Infoservice freiwillig zur Verfügung stellt, zum Zwecke der Erfüllung dieses Nutzungsverhältnisses. Der Nutzer erhält damit Zugang zu den Dokumenten des Industrie.de Infoservice.
AGB
datenschutz-online@konradin.de