Oilseed Expeller Press

Overview

The Oilseed Expeller Press is a continuous screw press, also called an expeller, that recovers vegetable oil from oilseeds by mechanical squeezing. Seed enters a heated cooker, drops into the barrel, and is carried forward by a rotating worm shaft. As the shaft pushes the meal toward a restricted outlet, the volume available to the meal shrinks and pressure climbs. Oil is forced out through narrow gaps in the surrounding cage, drains into a pan below, and is pumped away, while the de-oiled solids leave the far end as a hard cake. The machine runs without a press cloth and handles seed at a steady rate for hours at a time, which is why it suits mills that process several tonnes a day.

How it works

Pressing depends on building and holding high pressure on the meal. The Screw / Worm Shaft Assembly does this with a stack of worm flights whose pitch tightens toward the discharge end. Each Pressing Worm Flight moves meal forward, and the Collar / Spacer Ring segments between worms interrupt the flow and shear the cake so oil channels keep opening. Near the outlet the Discharge Choke Cone throttles the gap through which cake can escape. Closing the cone with the Adjustment Handwheel or the powered Choke Actuator raises back pressure and lowers residual oil, but it also raises motor load and heat, so the operator trims it against the reading on the Operator HMI. The axial reaction from all this pressure is taken by the Thrust Bearing at the drive end of the shaft, and each Shaft Bearing Housing carries a radial bearing that keeps the long shaft true under load. Worm flights are locked to the splined shaft with a Shaft Drive Key at each station, so a worn worm can be pulled and replaced without scrapping the shaft.

Feed and conditioning

Even pressing needs even feed at the right temperature. The Feed & Conditioning Section section starts with the Feed Hopper, which buffers seed and screens out stones at its Hopper Trash Grate. Below it the Variable Screw Feeder meters seed into the press at a rate set by its Feeder Gearmotor. Before pressing, seed passes through the Seed Conditioning Cooker, a stack of steam-jacketed kettles where a Cooker Stirrer Shaft turns the seed against the hot floor. Heating to roughly 100 to 110 C lowers oil viscosity, ruptures oil cells, and adjusts moisture, all of which improve yield. Each Steam Jacket is drained by a Steam Trap so condensate leaves without losing live steam.

Barrel cage and oil recovery

The Barrel Cage Assembly surrounds the worm shaft and does the actual separation. It is built from many Cage Lining Bar pieces held apart by ground Cage Bar Spacer shims, so the gap between bars is wide enough to pass oil but too narrow to pass meal. The cage opens on a Cage Hinge for cleaning when the gaps blind over. Oil that drains through the bars falls into the Oil Drip Pan and runs to the Oil Collection & Filtration group. There a Foots Screen removes the fine solids carried with the oil, the Oil Transfer Pump lifts it through a Bag Filter Housing fitted with a Filter Bag Element, and the polished crude oil collects in the Crude Oil Tank.

Drive and frame

Pressing is a low-speed, high-torque duty. The Main Drive & Gearbox uses a Main Drive Motor (37 kW) coupled through a Drive Belt set to the Reduction Gearbox, which drops the speed to under 20 rpm at the worm shaft through a Shaft Coupling. A Belt Guard encloses the belts. The whole press sits on the Base Frame, a Frame Weldment machined for the bearing seats and set on Anti-Vibration Mount feet. Cake leaving the cone is crumbled by the Cake Breaker and carried off by the Cake Screw Conveyor.

Materials

The pressing parts see abrasion and high stress, so the Main Worm Shaft is alloy steel and the worms and cone are hardfaced or hardened. The cage bars are tool steel because the meal scours them constantly. Wetted oil parts such as the pan, screen, and tank surfaces are stainless to limit pickup of metal into food-grade oil. Frame and guards are mild steel.

Variants and use

Small mills run a single press with manual cone setting, while larger plants run several in parallel and add the powered Choke Actuator so the Electrical & Control Panel can hold a target motor load automatically. Pre-press machines run a looser cone to leave 14 to 18% oil in the cake for later solvent extraction, while full-press machines close the cone hard to reach 6 to 9% residual oil for direct sale. The cake itself is a protein feed for livestock, so both the oil and the solids are products. Operators choose the cone setting, cooker temperature, and feed rate for the seed in hand, since an oily seed such as sesame presses differently from a fibrous one such as copra, and the same press handles both with adjustment rather than new parts.