What Is the Extrusion Technology in Soybean Oil Production?

The extrusion machine utilizes screw extrusion methods, much like a screw being tightened, to create high pressure within the machine. There are two types of extrusion processes: wet extrusion and dry extrusion. Wet extrusion involves adding water or steam to the material, while dry extrusion involves no added water or steam. 

Wet extrusion is applied to soybean processing, which involves adding water or steam to soybean flakes. Adding moisture helps in softening the soybeans, as soybeans contain antinutritional factors such as urease (a type of biomass). The extrusion process effectively reduces urease activity, making soybeans easier for animals to absorb and enhancing nutritional value compared to non-extruded soybeans.

In oil extraction factories, the primary benefits of extrusion are: Extruded materials become porous, resembling a honeycomb structure, allowing hexane to penetrate more effectively during the extraction process, thereby improving oil yield.Extruded materials are denser compared to flake materials, enabling higher output with the same extraction equipment.

Soybean Oil Production Process and Extrusion Steps:

Soybean Flake Extrusion Process: 

During the extrusion process, soybean flakes are forced into the extruder and exposed to high-pressure steam, undergoing intense mixing, heating, extrusion, adhesion, and gelatinization within the limited space of the machine chamber. This transforms their structural organization and results in extruded material.

Key components include the extruder cylinder, screw shaft, shear pins, steam injection pins, hydraulic nozzle head, hydraulic system, bearing lubrication system, and drive mechanism.

Principles of Soybean Flake Extrusion: 

Inside the extruder chamber, a spiral shaft with intermittent screw blades is installed. Shear pins extend into the cylindrical wall, protruding into the spaces between the screw blades. When the machine operates, the rotating screw blades and shear pins mix and stir the materials thoroughly within the cylinder. The screw pitch gradually decreases from the feed inlet to the discharge outlet, causing the material volume to compress, ensuring better cohesion. Steam injection pipes on the cylinder wall spray 4-6 bar direct steam into the materials to increase moisture, elevate temperature, and soften the material.

Soybean flakes are fed evenly and forcibly into the extrusion chamber via a screw conveyor. The flakes are simultaneously pushed forward by the screw shaft while undergoing compression, friction heating, cutting, mixing, and steam injection, resulting in structural changes. The material emerges from the extrusion machine in continuous strands through template slot holes at the end of the extruder.

When materials are transported to the discharge end of the tapered nozzle head inside the extrusion chamber, temperatures rise to 105-115°C and moisture content to 11%-13% due to extrusion, friction, and direct steam. The internal pressure of the material increases to 13-40 times normal atmospheric pressure. Upon exiting through the slot holes, the pressure instantly drops to atmospheric levels, causing moisture to evaporate rapidly, creating numerous micropores within the material. These pores make the extruded material highly porous, with countless microchannels and surface cracks.

Under the conditions of high-temperature cooking, mixing, extrusion, and pressure, proteins within the material soften and gelatinize, transforming into a cohesive gel-like substance. The elastic nature of gelatinized proteins enables the formation of porous extruded particles.Extrusion enhances soybean processing by compressing, heating, mixing, and steaming flakes to alter structure. It creates porous materials with improved properties, optimizing oil extraction efficiency and increasing yield.