A new U.S. patent, recently issued to Wenger Manufacturing, Inc., Sabetha, Kansas, U.S., promises the ultimate in control of final product characteristics in extrusion processes. Assigned patent number 6,773,739, the patent officially reads, “Extruder system for processing food products has an adjustable back pressure valve and a superatmospheric post-extrusion product treatment assembly.”
“What that really means,” says Bob Hauck, Director of Extrusion Technology at Wenger, “is that we have developed an innovative processing tool that couples a back pressure valve (BPV) with an external density chamber (EDC). This new External Density Management System, or EDMS, allows our customers to increase capacity over vented configurations by as much as 25 to 50 percent. This is also an important advancement for the aquatics industry, as it will allow processors to make both floating and sinking aquatic feeds with a wide range of properties, without the need for extruder configuration changes.”
As Hauck explains, one method of controlling final product characteristics is to adjust the extruder die restriction. However, as part of the patent, Wenger has developed a back pressure valve that can be used to adjust die restriction while the extrusion system is in operation. The variable-opening BVP is mounted on the end of the extruder just prior to the final die. As a result, the operator can adjust specific mechanical energy (SME) and extrusion pressure on-line for control of critical product properties, including bulk density, shape definition, size and uniformity of cell structure, shape definition and water and fat absorption.
“Naturally, we’ve included a by-pass feature in the back pressure valve to divert product from the EDC and die/knife assembly for service and start-up/shutdown procedures,” Hauck adds. “This also allows the processor to divert off-spec product prior to final processing.”
The BPV is only one half of the new equation, however. The new patent also recognizes the use of Wenger’s new external density chamber, which allows the desired pressures to be externally maintained in the knife enclosure by a special airlock through which the product discharges. Compressed air is then used to generate the required pressure in the chamber. As pressure increases, the water vapor point increases, which reduces product “flash-off expansion” and, thus, increases density. The ability to control pressure external to the extruder and die also allows the operator to better control fat absorption properties.
According to Hauck, the innovative EDMS will soon be available on a wide variety of Wenger extrusion processing systems, including both single and twin screw extruders. It also provides potential in a wide variety of applications, including the production of pet foods, livestock feeds, human foods and aquatic products.
Wenger Manufacturing, Inc., headquartered in Sabetha, Kansas, USA, is a global designer, manufacturer and distributor of extrusion processing equipment and related replacement parts. Wenger systems are distributed in over 90 countries, through international sales offices in the U.S., Europe and Asia.
For more information contact Doug Baldwin: dbaldwin@wenger.com
