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Grain & Feed Milling Technology is published six times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2010 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1466-3872

Digital Re-print - May | June 2010 Feature title: Horizontal twin-shaft paddle mixers

- The ultimate in mixing technology

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Before Forberg introduced its twin-shaft paddle mixing technol-ogy, a coefficient of variation

(CV) of 10 was acceptable. Today, a CV of five or less is the standard.

What led to this dramatic improvement in mixing accuracy?

The answer is that the Forberg horizontal twin-shaft paddle mixer brought about a revolution in mixing.

Imagine a chessboard as the image of a perfect mixture. How can practical mixing results get as close as possible to this ideal?

In the twin-shaft paddle mixer, the specific speed of the rotor shafts com-bined with the specific positioning and angles of the paddle blades provide excellent transport of particles (see Figure 1 and 2).

All particles in the mixture need air sur-rounding them to be able to move freely.

The filling level in the twin-shaft mixer is not more that 40 percent above the shafts.

Thus, there is surplus space in the mixer to provide air around the particles so they can move freely. The twin-shaft paddles lift the particles up in the middle of the mixer in the fluidized zone, where mixing takes place in a weightless state.

In this way, the particles are moved back and forth, up and down and across in all directions – this is the freedom of movement that is essential if particles are to be mixed as ran-domly as possible (see Figure 3).

All powder-

type products with all shapes and densities can be mixed in the Forberg® twin-shaft paddle mixer.

In some conventional mixers, the trans-port of particles is simplified and unidirec-tional, which results in poor-quality mix and long mixing time. For some materials this can even be negative as the particles can be

The ultimate in mixing technology by Kees Rodenburg, Market Support Manager, Forberg International, Norway

Horizontal twin-shaft paddle mixers

Figure 1

Figure 2

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crushed, worn down or can start forming lumps.

Because the product is fluidized, the twin-shaft paddle mixer is very gentle with the product. Extra force must be added, for example with choppers, in case any lumps in the mixture must be crushed. High speed rotating knives will create the force needed to crush soft lumps in the mixture.

Features of the twin-shaft paddle mixer

Mixing takes place in a very short time. An average mixing cycle for dry mixing can be as follows: filling 20-30 seconds, mixing 40-60 seconds and discharging 10-20 sec-onds. This gives a total cycle time of 1.5–2 minutes. A relatively small twin-shaft paddle mixer will provide a large output – thus giving savings both in investment costs and space requirements.

Liquids can be added easily to the powder mixture.

This is can be done by means of quick connec-tion nozzles (single component flat spray nozzles are most commonly used) for adding oil, fat, water, fla-vours, etc.

Spraying of liquids requires approximately one minute ensuring the best possible distribution of the

liquids in the pow-dered material. In this case, total cycle time, including spraying of liquids, will be as low as 2.5–3.5 minutes.

Liquid should be sprayed at a specific angle and at a specific distance to obtain the best possible distribution. The particles rotate around their own axes in the fluidized zone, exposing the total particle surface to the liquid during rotation. The liquid will hit the particles and be distributed in the mixture.

High melting point liquids, such as fats, can be sprayed in free flowing liquid state with special nozzle arrangements.

Homogeneous mixing is achieved in the space of a few seconds thanks to the fluidiz-ing of the material. All particles can be mixed (small, large, light, heavy, round, etc.) without segregation, since the forces of mixing are stronger than the forces of segregation dur-ing the mixing action in these mixers.

Segregation only takes place when the

product is handled after mixing, so it is recommended to minimize the distance between the mixer and the packaging point to avoid segregation.

The benefits of the mechanical fluidizing zone are gentle mixing, no segregation and very short mixing time. This gives savings in terms of minimal wear and tear and low energy consumption. Maintenance costs are also very low. The mixer's low energy con-sumption is an important consideration in reducing production costs.

Various mixer designsThe twin-shaft paddle batch mixer has

been developed over several years. Today, continuous twin-shaft paddle mix-

ers are available, notably Forberg's latest development, the rotating twin-shaft paddle batch mixer.

Continuous twin-shaft paddle mixer - The continuous twin-shaft paddle mixer has many of the same advantages as the twin-shaft batch mixer. It is very gentle with the products, has low energy consumption, high capacity, little space requirement and flexible filling. Throughput is very significant as the average retention time is approximately one minute (see Figure 4).

For obtaining good mixing quality in a continuous mixer, an accurate feeding of the ingredients is demanded. Continuous mixers are suitable for mixing a limited number of components, which have similar properties. One or two different liquids can be sprayed onto the product mixtures.

Rotating twin-shaft paddle mixer - The rotating twin-shaft paddle mixer has com-bined the mixing technology of the standard Forberg® batch mixer with a new solution for the filling and discharge (see Figure 5). Within seconds, the whole machine is tilted from its filling position to its discharging posi-

Horizontal twin-shaft paddle mixers

Figure 3

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Forberg International AS Hegdalveien 77 NO-3261 Larvik Norway Tel +47 33 13 34 34 Fax +47 3313 34 35 sales@forberg.no

www.forberg.no

• The smartest solution where mixing is essential

• The sanitary design meets all your expectations to feed safety

GFMT10.03.indd 21 28/05/2010 10:16

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shaft paddle mixer is a versatile machine, in which many processes beyond mixing can be performed. Forberg focuses on further development of industrial processes, in close cooperation with customers and research institutions. In the field of poultry feed for layers conditioning of mash feed has been a new development.

Steam heat treatment of mash feed - For many reasons, today’s most common poultry feed is pelletized, crumbled feed. There are several possible reasons for using this kind of feed. For instance, broilers do need as high as possible energy input in short possible time. Pelletized feed is cooked and sanitized. This gives efficient and secure nourishment for the birds. Finally, food regulations and the industry are based on established technol-ogy.

Mash feed is now getting more widely used, mainly for layers.

For layers, mash feed has several advan-tages. They are gained by using more time to eat. Structure feed is more natural feed and gives better development of the gut. Though the use of mash feed is mainly restricted to layers, mash feed is more natural feed than pelleted feed. The system technology offers the possibility to heat treat big amounts of mash feed without taking the detour through a pellets press and milling the pellets down later on. The process is more economical.

Cooling of pellets is less efficient due to poor heat transfer rate (surface).

The steam heat treatment system is designed as a batch system. It makes it possible do dose exactly and to achieve the correct recipe, hence controlling the nutritional value of the mash feed. In addi-

Advantages of the rotating twin-shaft mixer:• Completely closed mixing chamber• Only one valve for charg-

ing and discharging• Reduced cleaning surfaces

with integrated hopper• CIP (cleaning in place) is easy to

realise. Washing water can eas-ily be discharged through the washing-docking station

• High production capac-ity due to short cycle times

• Mixing under vacuum (as an option) enables the design of new production processes. Oxygen sensitive products can be mixed under an inert atmosphere

• Less product damage due to miss-ing edges of discharge doors

• Smaller tolerance (minimised gap) between mixing paddles and mixer housing can be achieved

• In comparison with stationary batch mixers, the new and innova-tive F-RM machines combine high mixing quality and short mixing time with the discharge behaviour and convenience of a cone bin

The well-known rotating vacuum coater, F-RVC, has the same design as the F-RM but is reinforced and equipped with vacuum equipment. This machine gives the optimum result for deep core vacuum coating as used widely in high fat applications and medication lines (see Figure 7).

Research and DevelopmentMixing and processing - Mixing processes

will always be one of the core processes in feed and food manufacturing. The twin-

tion. This results in a whole list of practical, operational benefits.

The rotating mixer (called the F-RM) has one inlet valve in the top where the product is introduced into the mixer. The valve closes and the mixing cycle is started.

After the mixing cycle has finished, the entire machine is rotated upside down and the product is discharged through the same opening as for filling. The machine is then rotated back 180° and is ready for a new charge. A feature for the F-RM is the automatic washing and drying of the mixer (see Figure 6).

The F-RM is designed for the feed, food, chemical and pharmaceutical industries where airtight processes are a must and cleaning is critical. It is also possible to mix under vacuum, or under an inert atmosphere to avoid oxidation of highly sensitive products. Application of steam or liquid nitrogen for sterilisa-tion or coating is another interesting option.

Figu

re 4

Figu

re 5

Figu

re 6

Figure 7

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tive components. There is no high-pressure treatment like in a pellets press.

Vitamins and other thermo-sensitive materials like enzymes can be added after heat treatment. There is no need for encap-sulated vitamins. There is no need for over-dosing. The thermo-sensitive components can be dosed in the exactly needed amount after heat treatment of the product.

feed because of gelatinization and micro agglomeration. The danger of de-mixing is hereby reduced, and can be reduced further by spraying of oil.

For feed with optimum nutritional value mixing is a basic process. The steam heat treatment system also serves as a complete mixing plant. The feed is always perfectly mixed.

Additional pre- and post-steam heat treatment mixing installations are not necessary. A modern mixer with mix-ing quality CV <5 makes over-dosing of ‘minor ingredients’ unnecessary. There is no danger for quality degradation of ingredients.

The steam heat treatment system is a very flexible production method where addi-tion of vitamins and other thermo-sensitive products can take place. More oil or fat can be added to the mash feed compared to pelleted feed. Spraying of acid in order to prevent further bacterial growth is also possible.

The ‘gentle’ steam heat treatment of the feed ensures preservation of thermo-sensi-

tion, it gives full control of the process and guarantee that the product will be uniformly treated.The main achievements of the process are:

• Destruction of salmonellae. The product is a pathogen free feed by reduction of other bac-teria spores in the mash

• Production of feed with course structure. The use of a roller mill gives good results with mash feed

• Feed with nutritional value that ide-ally meets requirements of the layers

• Preservation of thermo-sensitive com-ponents during production process

• In production of feed with coarse structure, the use of a roller mill gives good results with mash feed. Generation of fines is also minimal.

• Steam heat treatment of mash feed leaves the natural struc-ture of the feed unchanged.

No fibers are destroyed during the treatment due to the gentle mixing in the twin shaft mixer. The end product has improved flow properties compared to traditional mash

Figure 8 Figure 9

Related Companies:Andritz Feed & Biofuel BVSpaarpot 112, 5667 KZ, GeldropThe Netherlands

Tel: +31 40 2627777Fax: +31 40 2627753Email: andritz-fb@andritz.comWebsite: www.andritz.com

Wynveen International BVPO Box 38, HETEREN, 6666 ZGThe Netherlands

Tel: +31 26 4790699Fax: +31 26 4790698Email: info@wynveen.comWebsite: www.wynveen.com

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GFMT10.03.indd 2 28/05/2010 10:15

The solution behind the solution.

Bühler AG, Customer Service, CH-9240 Uzwil, Switzerland, T +41 71 955 30 40, F +41 71 955 33 03, service.gp@buhlergroup.com, www.buhlergroup.com

Your mill is our priority. No one knows our systems as well as we do. We built

them, and we will do everything we can to ensure that they continue to improve

your company’s productivity. With fully customized service plans we are able to

provide everything from reliable troubleshooting and original replacement parts

to technology upgrades, preventative maintenance, and consulting services.

Are you satisfied? Then we are too.

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LINKS• Seethefullissue• VisittheGFMTwebsite

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June 2010

• Flour mill design

In this issue:

• Grain storage - The Canadian way

• Simultaneous determination of

mycotoxins

• Hygienic Compact

Containment System

• The use of peripheral machines

in flour mills of today

• Horizontal twin-shaft paddle mixers

The ultimate in mixing technology

GFMT10.03.indd 1 28/05/2010 10:15

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