Double press screw

A double-screw press for separating a liquid from a two-phase solid-liquid material includes a hollow barrel and two screws disposed in the barrel. The barrel comprises a plurality of detachable barrel plates and a plurality of spacers disposed between the barrel plates and cooperating with the barrel plates in defining slits. The screws are arranged side by side with a gap defined therebetween, and are rotated by a motor to move a material, which has been charged into the barrel, efficiently from an upstream end to a downstream end of the barrel. The barrel plates and the screws have respective passages connected to cooling water sources, which supply cooling water to keep the temperature in the screws and the barrel at a desired level. The charged material is crushed and mixed in the gap between the screws, and oil is expressed from the material when it is compressed in the barrel. The expressed oil is discharged through the slits and collected in a container.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to a press for separating liquid from a 
two-phase solid-liquid material, and more particularly to a double-screw 
expeller for expressing vegetable oil from seeds. 
2. Description of the Relevant Art: 
Apparatus for expressing oil, water, and other liquids from various 
materials such as vegetable seeds, e.g., sesame seeds and sunflower seeds, 
animal meat by-products, starch, etc,, are generally classified into batch 
presses and continuous presses. The batch presses include cage presses and 
filter presses. These batch presses are mainly used to manufacture a 
Japanese alcoholic beverage known as "sake" and soy sauce since they can 
separate clear high-quality liquids from the material using cloth filter 
bags. Typical continuous presses are roller mills. In a roller mill, since 
the material from which a liquid is to be separated is pressed under a 
relatively low pressure, a large amount of liquid remains in the cake 
after expression by the roller mill. Therefore, use of the roller mills is 
primarily limited to dewatering of starch. 
Another form of continuous press is a screw press which is particularly 
suitable for expressing vegetable oil from oilseeds. One typical screw 
press comprises a barrel and a screw closely fitted in the barrel. The 
barrel may comprise a cylindrical barrel having a multiplicity of holes or 
a drainage barrel having slits extending along the screw with spacers 
therebetween. In the screw press, the seeds from which oil is to be 
expressed are fed forward by friction with the inner circumferential 
surface of the barrel. In order for the seeds to be moved by friction, 
their protective shells, known as testa, must be left uncrushed. The 
materials that can be processed by the screw press are therefore limited 
to oil seeds and materials with high fibrous content. Oil which is 
expressed by the screw press should be refined because it contains testa. 
However, the refining process is costly and laborious. Other problems of 
the screw press are that the barrel are rapidly worn by frictional contact 
with the material and the material tends to be modified in property due to 
frictional heat. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a double-screw press 
which can efficiently express a high-quality liquid from a material. 
Another object of the present invention is to provide a double-screw press 
which is highly durable and economical. 
A double-screw press according to the present invention has a hollow barrel 
having a feed inlet at an upstream end thereof, for feeding a material 
into the hollow barrel, a cake outlet at a downstream end thereof, for 
discharging a cake produced after the material is pressed, and a plurality 
of slits between the upstream and downstream ends, for passing 
therethrough a liquid which is expressed from the material. A pair of 
screws is disposed side by side in the barrel and operable in coaction 
with each other for moving the material therealong while crushing and 
mixing the same. The screws are spaced from each other by a gap depending 
on the particle size of the material. The gap is defined between the 
surfaces of the crushing means of the screws, the gap being constant 
between all surfaces along the operative length of the screws and large 
enough only to pass the material therethrough. The screws may not be held 
in full mesh with other, with the gap therebetween being large enough to 
pass the material therethrough. The material charged into the barrel is 
crushed and mixed in the gap between the screws, and oil is expressed from 
the material when it is compressed in the barrel. The expressed oil is 
discharged through the slits. The screws may be held in full mesh with 
each other depending on the material to be pressed. 
The barrel has a plurality of barrel plates having respective openings 
through which the screws extend, and a plurality of spacers disposed 
between the barrel plates and cooperating with the barrel plates in 
defining the slits. Since the particle size of the material becomes 
progressively smaller as it is compressed, it is preferable for the slits 
to have a larger width near the upstream end of the barrel and a smaller 
width near the downstream end thereof. Therefore, the thickness of the 
spacers is progressively smaller from the upstream end to the downstream 
end. To prevent the material from flowing backward along the screws, the 
edges of the barrel plates which define the openings in the barrel plates 
and the outer peripheral surfaces of the screws are disposed closely to 
each other. 
The double-screw press further includes a means for supplying a cooling 
medium such as cooling water to prevent some charged materials from being 
modified in property by heat. The cooling medium supplying means comprises 
passages defined in the screws and connected to a cooling water source. 
The cooling water source supplies cooling water into the passages in the 
screws to keep the temperature in the screws and barrel at a desired 
level. Each of the barrel plates also has a passage defined therein around 
the opening therein. The passages in the barrel plates are connected to 
another cooling water source, which supplies cooling water into the barrel 
plates to keep the temperature in the barrel at a desired level. When it 
is necessary to increase the temperature in the screws and the barrel, a 
heated medium such as heated water, steam, or the like may be supplied to 
the passages in the screws and the barrel plates. 
The principles of the present invention will be described with particular 
reference to expression of vegetable oil from seeds. However, the present 
invention is also applicable generally to separation of a liquid from a 
solid, such as dewatering of industrial wastes having high water contents. 
The above and further objects, details and advantages of the present 
invention will become apparent from the following detailed description of 
a preferred embodiment thereof, when read in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIGS. 1 and 2, a double-screw press 10 according to the present 
invention comprises a horizontal barrel 12 and a pair of screws 14 
extending horizontally in the barrel 12 and rotatable about their own axes 
by a suitable actuator 15 such as a motor. As shown in FIG. 3, the barrel 
12 comprises a plurality of barrel plates 16 which have openings 17 
through which the screws 14 extend, inverted U-shaped upper spacers 18 
disposed between upper portions of adjacent ones of the barrel plates 16, 
slender rod-shaped lower spacers 20 disposed between lower portions of the 
adjacent ones of the barrel plates 16, and end plates 22 at the opposite 
ends of the barrel 12. The barrel plates 16 and the two end plates 22 have 
through insertion holes 23, 24, respectively see FIG. 2. Tie bars (not 
shown) are inserted through the insertion holes 23, 24, and nuts (not 
shown) are tightened on opposite ends of the tie bars. Therefore, barrel 
plates 16, upper and lower spacers 18, 20, and the end plates 22 are 
firmly fastened together, completing the barrel 12. 
The barrel 12 has a feed inlet 26 for feeding a material into the barrel 
12, in the form of a hopper which is vertically mounted on an upper 
surface of the upstream end of the barrel 12. The barrel 12 also has a 
cake outlet 28 in one side of the downstream end thereof, for discharging 
a cake from the barrel 12 after expression of oil from the material. 
Vertical slits 30 are defined between the barrel plates 16. The slits 30 
are progressively narrower from the upstream end to the downstream end so 
that the widths of the slits 30 match the particle sizes of a material 
which is continuously pressed and moved forward in the barrel 12. 
Therefore, the spacers 18, 20 are thickest at the upstream end of the 
barrel 12, and thinnest at the downstream of the barrel 12. 
As shown in FIG. 4, each of the barrel plates 16 has a passage 32 defined 
therein and extending closely around the opening 17. The passage 32 is 
connected to a cooling water source 33 which supplies cooling water into 
the barrel 12 to keep the temperature therein at a desired level. If 
necessary, a heated medium source for supplying a heated medium such as 
steam, heated water, heated oil, or the like may be connected to the 
passages 32, depending on the material to be pressed. 
The screws 14 extend horizontally parallel to each other in the opening 17 
in the barrel plate 16. In order to prevent the material, which is being 
pressed, from moving backward along the screws 14, the gap between the 
screws 14 and the edges of the barrel plates 16 which define the openings 
17 should be as small as possible. If the screws 14 operate in full mesh 
with each other, they can feed the material at a maximum rate, but mix and 
grind the material at a minimum rate. If the screws 14 operate in partial 
mesh with each other, i.e., with a gap S (FIG. 5) left therebetween, they 
feed the material at a lower rate, but can mix and grind the material at 
an increased rate. The gap S is adjusted depending on the nature and 
particle size of the material to be processed. For example, the gap S is 
smaller when relatively small seeds such as sesame seeds or rapeseeds are 
pressed, and larger when larger-particle materials such as palm kernels 
are pressed. If a material which has already been crushed is supplied, 
then the screws 14 are held in full mesh with each other during operation. 
Each of the screws 14 comprise a plurality of segments 34 which are axially 
detachably coupled together so that they may easily be replaced or other 
segments may easily be added. If several segments 34 are added and 
corresponding barrel plates 16 and spacers 18, 20 are also added, the 
barrel 12 can be axially elongated. As shown in FIG. 6, each of the screws 
14 has a hollow space 36 in which a pipe 38 axially extends. The pipe 38 
has an inlet 40 at one end thereof which is exposed out of the screw 14. 
The inlet 40 is connected to a cooling water source 45. A smaller-diameter 
inner pipe 42 horizontally extends from the inlet 40 to a position near 
the opposite end of the pipe 38. The inner peripheral surface of the pipe 
38 and the outer peripheral surface of the inner pipe 42 jointly define a 
passage 44 therebetween which communicates with an outlet 46 near the 
inlet 40. When cooling water is supplied from the cooling water source 45 
to the inlet 40 of each screw 14, the cooling water flows through the 
inner pipe 42 and then the passage 44 and out of the outlet 46. The 
cooling water which flows in the screws 14 serves to keep the temperature 
in the screws 14 and the barrel 12 at a desired level. 
Operation of the double-screw press 10 thus constructed will be described 
below. 
A suitable quantity of sunflower seeds, for example, is charged into the 
barrel 12 through the feed inlet 26. The screws 14 which are spaced the 
gap S from each other are rotated in opposite directions as indicated by 
the arrows in FIG. 5. The charged sunflower seeds are crushed and mixed in 
the gap S between the screws 14. Since the sunflower seeds which tend to 
rotate with one of the screws 14 are prevented from so rotating by the 
other screw 14 (i.e., by its helical rib), the sunflower seeds effectively 
move forward from the upstream end to the downstream end of the barrel 12 
while sliding on the surfaces of the screws 14. The screws 14 may be 
rotated in the same direction depending on the material to be pressed. Oil 
is expressed from the sunflower seeds which are crushed and mixed when the 
seeds are compressed by the progressively smaller volume of the internal 
space of the barrel 12 and also by subsequently charged sunflower seeds. 
The expressed oil flows out of the barrel 12 through the slits 30 and is 
collected in a container (not shown). The cake is discharged from the cake 
outlet 28. The cake may be used as a high-protein material though it 
contains unwanted components such as chlorogenic acid, for example. 
A sunflower seed contains 50% by weight of oil. When oil was expressed from 
threshed sunflower seeds using a single-screw press, the expressing 
efficiency (i.e., the ratio of expressed oil to the oil content of the 
sunflower seeds) was only 20%. The low expressing efficiency was caused 
since the sunflower seeds stayed in the barrel and turned into a paste, 
with the result that separation of the liquid phase from the solid phase 
was not sufficient. When oil was expressed from sunflower seeds which had 
not been threshed, the expressing efficiency was 75%. when oil was 
expressed from sunflower seeds using the double-screw press of the present 
invention, the expressing efficiency was 90% or higher, and 93% at 
maximum. The electric power consumed per kilogram of expressed oil was 0.2 
kilowatt for the double-screw press and 1.25 kilowatts for the 
single-screw press. This power consumption difference was due to different 
frictional effects which the double- and single-screw presses had on the 
sunflower seeds. 
Although there has been described what is at present considered to be the 
preferred embodiment of the present invention, it will be understood that 
the invention may be embodied in other specific forms without departing 
from the essential characteristics thereof. The present embodiment is 
therefore to be considered in all aspects as illustrative, and not 
restrictive. The scope of the invention is indicated by the appended 
claims rather than by the foregoing description.