Hydraulic oil press is the oil press that transmits pressure by oil and processes oilseeds under static pressure. There are manual and electric type according to the power source of the oil pump. It can be divided into vertical and horizontal type by the way of putting pressure on flakes. Vertical hydraulic oil press (figure 1) is fixed with a cylinder on the base. A cylindrical piston is installed in the cylinder and the piston top connects with the cake bearing plate as a whole. The material is prepressed into cake coated with the cake ring. Generally, 20 ~ 40 cakes are piled up between the cake bearing plate and the roof. The cakes are separated by thin plate with holes. The driven piston pushes up and produces pressure to press the cake and extract oil. After extraction, the oil pump stops inflating and the piston falls. The slag cake would be discharged and new cakes are fed repeatedly for intermittent oil extraction. About 2 ~ 5 hours are needed for each pressing.
When in use of electric pump, circular oil system can be formed to control several hydraulic oil presses at the same time. The structure and working principle of horizontal hydraulic oil press are basically the same with the vertical type. Its installation is convenient with smooth flow of oil and there is no residual oil in the cake ring. But it covers a large area and need to be equipped with the heavy hammer, the pulley or screw mechanism. The pressure of hydraulic oil press is large with higher single oil extraction rate. There are few movement parts, thus it is easy for maintenance and repair. However, the labor intensity of cake feeding and discharging is large.
Screw oil press is the oil press that pushes the material forward continuously within the pressing chamber and extract oil under dynamic extrusion. In addition to the feed hopper, the pressing chamber is the main operation section. It is composed of a worm shaft and a cylinder press cage. There are single-stage pressing and two-stage pressing. The single stage pressing has only one horizontal pressing chamber, while the two-stage pressing has another straight pressing chamber for first stage pressing. The worm shaft is composed of several worms and spacing rings on the shaft. Each worm has certain pitch and screw. The screw pitch of each worm on a shaft is gradually shortened from the feed inlet to the discharging mouth and the screw depth becomes shallow gradually. Thus, the volume of pressing chamber decreases gradually from the inlet to the outlet. The material fed into the pressing chamber is pushed towards the outlet along the snail rank of worm and the pressure increases gradually to extract oil in succession. There are spacers between the cage bars of cylindrical pressing cage in order to form the oil gap. The oil extracted would flow out through the gap.
The press cage of large screw oil press is equipped with the scraper and the scraper edge is deep into the pressing chamber and directed at each spacing ring in order to prevent the material from slipping inside the pressing chamber and prevent material return. It can also adjust the cake thickness and control the pressure of pressing chamber accordingly to reduce the rate of residual oil. In addition, the machine is also equipped with cake clamping part to make the surface of slag cake bright and clean and the frying pan for continuous operation of cooking and pressing of oil mill plants.
The screw oil press used for pre-press has larger pressure for prepressing of oil mill plants. Cakes after prepressing would be put in the oil press for pressing or extraction. Thus, the change of inlet and the outlet of pressing chamber volume is bigger with larger production capacity.
Screw oil press can be used for continuous operation and the labor intensity is lower. The slag cake is thin and small, convenient for comprehensive utilization. But the main working parts in the pressing chamber are easy to wear that they should be changed constantly, which increases the operation cost.
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