New twists on extrusion

by Suzi Fraser
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By Suzi Fraser Dominy

In all areas of feed production — livestock, pet and aquatic — manufacturers are looking to extrusion equipment suppliers for innovations to help them achieve greater versatility, higher throughput, less downtime, and lower operating costs.

CONICAL CO-ROTATING TWIN SCREWS

One of the more recent and interesting innovations that helps address these requests from feed producers is the Conical Co-Rotating Twin Screw extruder (C2TX) from Wenger Manu-facuring that pro-vides twin screw versatility with single screw simplicity. The conical design of the C2TX barrel, coupled with the new Back Pressure Valve, provides a unique barrel profile that is capable of producing the complete range of products without requiring screw configuration changes during product changeover.

The Back Pressure Valve (BPV) was developed to monitor and control residence time within the preconditioner and to assist in controlling the amount of mechanical energy applied to the extruded product. It is installed just prior to the final die. The BPV allows on-line control of final product characteristics such as product density, cell structure, and level of starch gelatinization. Changes of extruder configurations to achieve these parameters are no longer necessary, thus eliminating costly downtime.

The new DDC Retention Time Control system allows the extruder operation, and minimizes recipe waste during the extruder startup and shutdown modes. Time and temperature may also be automatically recorded to document production of safe, clean foods.

VERSATILE MIXING HEAD

Final products that include a mixture of shapes and colors can now be processed in one production run, rather than having to be mixed after processing. With new die hardware developed jointly by Wenger and Extru-Tech Inc., product of varying shapes and colors can be extruded simultaneously from the same formulation, eliminating the additional bins, mixing and handling equipment traditionally required.

REPLACEABLE BARREL LINERS

Barrel wear is an inherent part of extrusion technology but it is costly. Typically, the cost due to worn barrel components for a steam extruder can be around US$0.50-0.60 per tonne of processed material, and can be as high as US$1.50. For a feedmill processing 2 tph, this cost can be as high as US$10,000 per annum.

To reduce wear cost, Millbank Technology (N.Z.) Ltd. has developed a split barrel concept utilizing replaceable hardened barrel liners, whereby for only a modest increased capital outlay over conventional modular barrels, extruder wear and maintenance costs can be reduced dramatically, while performance is increased and downtime minimized.

The liners are made from Nihard steel and will last at least 5 times longer than normal iron barrels, resulting in less maintenance down time. Once worn, the liners can be quickly and easily replaced without needing completely new barrels. Typically the cost of replacing worn barrel components can be cut by more than half of conventional barrels.

Split barrels also make clearing blockages easier and quicker. Coupled with quick release clamps, a machine can be completely stripped down and cleared of blockages in only minutes rather than hours.

While the split barrels were originally developed for the Miltenz 6000-model extruder, split barrels will shortly be available for nearly the complete range of Miltenz extruders. In addition split barrels with hardened liners will be able to be easily retrofitted to existing Miltenz extruders – you don’t even need to replace existing clamps or intake housing.

TEMPERATURE REGULATION

Clextral Inc. has introduced another co-rotating twin-screw extruder to its modular Evolum range. The Evolum LT 145 has been specifically designed for the pet food and fish feed industries, offering the appropriate torque for each application, high output, rapid start-up and shut down, and quick cleaning and maintenance. The new optimized temperature regulation of the barrel offers better control of the density (with direct effect on floating or sinking properties in case of fish feed) over a wider range of product sizes/formulations. The Operator Interface Terminal may be mounted at the side of the frame.

The modular Evolum LT 145 is available in several versions, including various ranges of motor size, screw speed and barrel L/D ratio to achieve output rates from 5 to 10 tph.

EXPANDER FEATURES

Amandus Kahl is well known for the development of the annular-gap expander and it has brought certain design features from the expander to its OEE model extruders, making it strikingly different from most traditional designs.

Just like the cone of the Kahl annular gap expander, die and knives of OEE extruders are fastened to a hydraulically actuated piston. The die can therefore be advanced and retracted during operation of the machine. This possibility facilitates the start of the machine and offers higher operational safety, as the die can be advanced in case of overload, so that the machine will not be overstressed.

The extruder also can be equipped with two different outlet heads. The swivelling heads are mounted to the case and can be exchanged quickly. For this reason, the machine can be operated either as an expander or as an extruder.

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