Working Principle of the 90-Type Peanut Oil Press

The hydraulic oil extraction process for peanuts is as follows:

Raw material → Cleaning → Shelling → Flaking → Roasting → Steaming → Cake forming → Pressing → Oil cake → Crushing → Second pressing → Rough filtration → Crude oil

The oil pump and oil cylinder of the 90-type oil press are connected by oil pipes, with pistons in both the oil cylinder and oil pump, forming a closed system. When a small pressure is applied to the piston of the high-pressure oil pump, the pressure is transmitted through the liquid (oil) to the piston of the oil cylinder of the 90-type oil press. Utilizing the diameter difference between these two pistons generates a considerable total working thrust of approximately 90 tons. This is the working principle of the 90-type oil press.

Equipment of the 90-Type Oil Press

When using a 90-type oil press, steamed and roasted material cannot be sent directly to the press for oil extraction. The loosely cooked material is first pressed into a cake form, and then oil is extracted. The 90-type oil press equipment mainly comprises cake-pressing and oil-pressing equipment.

1. Cake Pressing Equipment

Cake pressing equipment is commonly called a cake press, a cake wrapping machine, or a cake-making machine. Cake presses are mostly self-made by various factories and come in many types. The rotary manual cake press is mainly introduced here.

The rotary manual cake press uses a screw to raise and lower the cake pressing plate, pressing the cooked material into thin round cakes within the cake ring. When a backing plate and cake ring containing a specified amount of cooked material are placed in the middle of the base and secured by positioning the iron, manual force is immediately applied to rotate the flywheel via the handle, causing the screw to turn. Under the action of the screw, the cake-pressing plate moves downward along two pillars via two sliders of the rotary manual cake press until the cooked material is pressed into thin round cakes. Then, manual force is used to turn the handle to reverse the flywheel. At this time, the screw drives the cake-pressing plate upward, releasing the cake block. After the cake block is removed, the next cake pressing operation can continue.

2. Oil Pressing Equipment

The hydraulic oil press mainly consists of two parts: the hydraulic system and the oil pressing system, as shown in Figure 3-3.

Figure 3-3 90-Type Hydraulic Oil Press

1 — Base; 2 — Hydraulic cylinder; 3 — Oil pan; 4 — Pressure bearing plate; 5 — Cake ring; 6 — Fixed cylinder; 7 — Movable cylinder; 8 — Pillar; 9 — Cake blocking rod support; 10 — Cake blocking rod; 11 — Top plate; 12 — Nut; 13 — Pin; 14 — Oil inlet pipe component; 15 — Three-way safety valve component

(1) Oil Press

The oil press mainly consists of a base, a hydraulic cylinder, an oil pan, 4 pillars, a cake-bearing plate, etc. The base is fixed with anchor bolts. The hydraulic cylinder is a hollow cylinder with a closed bottom, fixed to the base and oil pan. The top plate is connected to the base through 4 steel pillars and locked with nuts. To ensure the cake blank moves in a straight line up and down, 4 cake-blocking rods are installed on the pillars, which can be opened at the front and back for loading and unloading cakes. The piston moves vertically in the hydraulic cylinder, with a pressure-bearing plate on top. During pressing, the piston rises under force, transmitting this force through the pressure bearing plate, cake blank, and top plate to the four pillars, which bear the tensile force and press the cake blank. After pressing is completed, open the return oil valve to reduce oil pressure. After the oil returns to the oil tank, the piston automatically descends. To prevent oil leakage, two sealing leather cups are installed on the hydraulic cylinder wall, with the cup mouths facing downward.

The top plate and hydraulic cylinder are made of high-strength cast iron, and the pillars and cake-blocking rods are steel components that can withstand the rated working pressure (above 35 MPa).

(2) Hydraulic System

The main parts of the hydraulic system are the hydraulic pump and oil tank. The hydraulic pump provides pressure to the piston in the hydraulic cylinder. Its structure consists of a vertical double-piston reciprocating pump and a hand-pushed screw pump, as shown in Figure 3-4.

Figure 3-4 Hydraulic Pump Structure Diagram

1 — Oil tank; 2 — Pump base; 3 — Connector; 4 — Screw; 5 — Pressure column sleeve; 6 — Sealing ring plate; 7 — Connection sleeve; 8 — Sealing ring II; 9 — Small piston; 10 — Large piston; 11 — Pump body; 12 — Steel ball; 13 — Pressure oil pipe; 14 — Oil inlet valve

There are two pistons in the pump, a large one and a small one, with the small piston sleeved inside the large piston. During light pumping (low pressure), the large piston is used for pressurization. At this time, with the help of the connector, pressure transformation sleeve, and connection sleeve, the whole forms with the small piston, moving up and down together. During heavy pumping (high pressure), the small piston is used for pressurization. At this time, after rotating the handle on the pressure column sleeve 180°, the large piston disengages, and the small piston can move up and down alone. On the clamp plate above the pump base, there are insertion rods and sleeves to drive the pistons up and down. At the beginning of pressing, use light pumping (0-4MPa). At this time, the pressure per unit area in the hydraulic system is low, requiring a large, rapid oil supply. Using the large piston for pressurization, due to its large area, each cycle can press in more oil, meeting the need for rapid pressure rise. When switching to small piston pressurization, the oil pressure in the hydraulic system is higher, so the oil supply does not need to be too large, allowing a smaller piston to be used for pressurization. Because the small piston has a small area, each working cycle presses in less oil, reducing the effort required. Configuring light and heavy pumps in the hydraulic pump structure can reduce labor intensity, improve work efficiency, and meet pressing requirements.

Between the large piston and the pump body, and between the small piston and the inner wall of the large piston, sealing rings are installed and tightened with nuts to prevent oil leakage. The hydraulic pump is equipped with an oil inlet valve and an oil drain valve to prevent impurities from entering the hydraulic cylinder. A safety valve is installed in the hydraulic oil pipe system. Using an adjustment screw, the pressure can be set to 40 MPa. When the oil pressure exceeds this value, the safety valve opens due to the oil pressure, and the oil overflows from the overflow hole on the valve body, flowing back to the oil tank, reducing the oil pressure and ensuring safe operation. Oil pressure can be observed on the pressure gauge. According to the reading, the oil pressure level can be known, facilitating operation.

III. Operation of the 90-Type Oil Press

1. Operation

1. Before the first startup, check all parts of the oil press, including whether the oil tank has sufficient oil, whether connecting parts are loose, whether the hydraulic system leaks oil, whether the piston moves up and down flexibly, and whether the pressure gauge and safety valve are normal and sensitive.

2. During operation, first remove the pins on the movable shoulder, pull open the movable shoulder, turn away the cake blocking rods, and load the pressed cake blanks. The cake’s layers should be neat and stable, not slanted, and filled up to the top plate. Then turn the cake blocking rods, close the movable shoulder, and insert the pins.

3. Rotate the handwheel to close the return oil valve. Press the hand lever to pump oil into the hydraulic cylinder, causing the piston to rise and press the cake blanks. First use light pumping (0-4MPa), then use heavy pumping (up to 35MPa) for pressing. The maximum rising distance of the piston should not exceed 500mm. An oil groove is opened on the piston below 500mm to control the piston’s stroke.

4. After pressing is completed, slowly open the return oil valve to let the oil return to the oil tank. After the piston reaches its lowest position, close the valve properly.

Machine Maintenance

① Daily, before starting and during pressing, pay attention to the cleanliness of the piston surface. It should not be contaminated with dirt or oil stains.

② The oil in the oil tank should be kept clean. When adding oil to the tank, it should be filtered. After a period of use, the oil in the tank should be re-filtered or replaced with new oil.

③ When pressurizing with the hydraulic pump, do not do it too quickly or fiercely to prevent damage to mechanical parts. The hydraulic shock generated thereby can also easily damage hydraulic components. When reducing pressure, open the return oil valve to allow oil in the hydraulic cylinder to return to the oil tank. The valve should also be opened slowly to avoid a sudden pressure drop.

④ It is strictly prohibited to arbitrarily lengthen the swing handle of the hydraulic pump, causing overload operation of various components.

⑤ It is strictly prohibited to adjust the safety valve to a pressure gauge reading above 40MPa to avoid expansion and cracking of pipes and the hydraulic cylinder.

⑥ Pay attention to the operation of the machine during operation. For vulnerable parts such as leather cups, sealing devices, steel balls, pistons, etc., inspect, repair, and replace them in time. Tighten loose nuts and regularly inspect and clean the machine.

⑦ After the oil pressing season, the oil press should be completely overhauled, wiped clean, lubricated with grease on parts prone to rust, and wrapped with oil paper or kraft paper to prevent rust.

IV. Main Technical Data

Table 3-1 Main Technical Data of Hydraulic Oil Press