This mechanical extraction process covers both high pressure single pressing and low pressure pre-pressing prior to a solvent extraction process.

Solvent extraction is not really economically viable below 250 tons per day so full or single pressing is used by smaller oil mills and produces a cake containing around 5-6% residual oil. High pressure machines have capacities from 10 to 120 tons per day.

Similarly, if we undertake large extraction projects requiring a combined pre-press/solvent plant engineering package, we use specialist pre-press suppliers. Pre-pressing generally produces a cake containing 15-18% residual oil before it is fed to the Crown extractor which produces a residual of less than 1%. These plants are usually in the 500-2000 tons per day range and capable of handling several seeds with individual pre-press machine capacity up to 500 tons per day.

The Operation:

Generally a screw press consists of a continuous, helical thread or 'wormshaft' which revolves concentrically within a stationary, perforated cylinder or 'cage'. As suitably prepared material is conveyed along the length of the barrel, an increase in pressure causes the oil to be "expelled" and drained through small spacing in the bars lining the cage.

The compressed de-oiled material or cake is discharged from one end of the barrel and the oil and some solids ('foots' or 'fines') collected in the base of the press for further clarification.

A cooker is normally mounted above the press and its feed is regulated by a central system monitoring the loading on the main press motor.

Crown Iron can design, supply and build any size and type of extraction plant be it a high pressure screw press mill, pre-press/solvent extraction facility or a direct extraction plant.