Basic Concept of Oil Press

1. Compression Curve of the Pressing Chamber

in the pressing chamber of Xinxiang Hongyang Brand screw oil press, due to the increasing width of pressing screw threads, the decreasing screw pitch and the thickening spiral diameter, etc, after raw material enters to feeding section, the material is propelled and compressed as the pressing screw rotates. The degree of compression changes as the material moves through the pressing chamber. Depicting the variation in the compression degree of raw material as it was propelled through the pressing chamber into a drawing, which is called compression curve of pressing chamber. The compression curve of pressing chamber runs as Figure 5-1

Figure 5-1 Compression Curve of the Pressing Chamber

From Figure 5-1, it can be seen that the compression process of the material in the pressing chamber is divided into three sections, analyzed as follows:

1. Feeding Section: In the feeding section, the material starts to be compressed, expelling air and moisture, undergoing plastic deformation, and beginning to release oil. Therefore, a small amount of oil droplets and bubbles can be seen at the front end of the pressing cage.

2. Pressing Section: The space in the pressing chamber in the pressing section decreases rapidly and regularly. The material is subjected to intense pressure, causing the particles to combine and form a continuous porous mass that expels a large amount of oil. During this process, the material also experiences various types of friction while being compressed.Specifically, pressing screw interrupt, pressing chamber’s knife bar, pressing rod edge’s shearing action cause raw material displacement, breakage and mixing, which continually open oil pathway, allowing for rapid and thorough oil extraction

3. Cake Forming Section: In the cake forming section, the material has formed into tile-shaped cakes that advance almost as a single unit, resulting in significant axial compression resistance. At this stage, the compressibility of the tile-shaped cakes is minimal, but it is necessary to maintain high pressure to ensure thorough oil drainage. This process should be extended for an appropriate amount of time, and the axial resistance should be reduced (the geometric dimensions of the screw change very little at this point). If the pressure is reduced too early, the hot cake will expand and loosen, reabsorbing oil, which is detrimental to pressing. The discharged cakes generally expand slightly due to elasticity or expansion.

2. Compression Ratio and Total Compression Ratio

1. Free Volume of the Screw: The free volume of the screw refers to the space volume enclosed by the screw in each lead (pitch) within the pressing chamber.

2. Compression Ratio: The compression ratio is the ratio of the free volumes of the screw in two adjacent leads. If the free volumes of the screw in two adjacent leads are Vn and Vn+1, respectively, then the compression ratio is:

3. Total Compression Ratio: The total compression ratio is the ratio of the free volume of the first lead where the material enters to the free volume of the lead at the cake discharge end. If the free volume of the first lead is V_in and the free volume of the lead at the cake discharge end is V_out, the total compression ratio ε is: