by Maren Weßels, Amandus Kahl, Germany


The expander technology is one of the best and most comprehensive conditioning methods for compound feed and individual components.

The annular gap expander consists of a thick-walled mixing tube with replaceable liners and cantilevered shaft which is equipped with proportioning, mixing and kneading elements.

The hydraulically adjustable cone and the pipe end form the annular gap. By means of adjusting the cone during operation, the pressure, the intensity of kneading, the product heating, and the energy consumption can be controlled and programmed continuously and instantaneously.

The maximum pressure is about 40 bar; the operating temperatures at the expander outlet are between 90 and 140°C. At the outlet, the pressure drops spontaneously, the product expands, and a part of the added water evaporates (flash evaporation). Post-drying is not required. The particle size of the expanded product can be determined by means of the downstream crushing device.


• Improved pellet quality and higher press capacity

• Use of components which are difficult to process

• Addition of large quantities of liquids

• Inactivation of harmful substances

• Elimination of salmonellae

• Improvement of the feed value

• Production of Expandat®

• Reduction of the production costs

Liquids, such as fat, molasses and vinasse, can be added to the process in larger quantities.

The effects of expanded mixtures on pelleting increase the press capacity. The pellet hardness and the fines content can be influenced by changing the operating parameters of the expander.

The treatment of the product under pressure at a high temperature and moisture content causes starch modification. Proteins, vitamins, and additives are largely saved.

On account of the precisely controllable process, value-determining ingredients are not damaged.

Pathogenic germs, such as salmonellae or moulds, are eliminated by the treatment in the annular gap expander.

The annular gap expander is available with five tube diameters and various tube lengths:

  • Diameter- 150 – 450 mm
  • Operating length- 1000 – 3000 mm
  • Drive motor - 55 – 600 kW
  • Throughput- 2 - 60 t/h

Process and product development

Interested parties and customers can test the annular gap expander with their own mixtures in our pilot plant. Our cooperation network goes far beyond machine and plant construction.

We have invested considerable research effort in the development of the expander technology and have achieved optimum research results for almost every animal species, both under animal nutrition and economic aspects.

Our network

• Research by customers and industrial research

• On-site laboratory and pilot plant

• Research institutes

• Universities

• Independent consultants

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