Technical Field

The invention relates to a screw press for cold pressing of oilseeds, which is used for producing vegetable oils.

Background Art

WO 2013/135303 discloses a screw press for cold pressing of oilseeds, comprising a cylindrical housing, having a screw for conveying and compressing the oilseeds, from which the oil is extracted. An inlet opening connected to a hopper for charging of oilseeds is provided in the front upper part of the housing. A zone of outlet openings for taking out the pressed out oil is provided in the housing between its rear end and the inlet opening. Within this zone, there are longitudinal spline ways on the inner wall of the housing. Between the spline ways and the end of the housing, there are rear longitudinal spline ways, the width of said rear spline ways increasing towards the housing end. The screw ends with a slightly rounded screw header coaxially placed against a press head, said press head having a central opening and a front header bevelled towards the central opening. The known press includes also a nozzle with a hole converting into a discharge opening for taking out the solid residue. Oilseeds, entering through the inlet opening, fall onto the screw, which conveys them forward, pressing them to the inner wall of the housing, and as a result, part of the oilseeds are smashed and/or chopped up, when getting in contact with the edges of the spline ways. The seed mass passes between the screw header and the press head and some of the seed oil is being pressed out. As the pressure in this zone is higher, the oil flows back through the spline ways and through the porous seed mass to the outlet zone of the housing, and the seed mass, in the form of a thick compact cylinder, enters the nozzle, where the actual pressing takes place. Due to the thickness and density of the material, a great part of the oil pressed out in the nozzle cannot flow back to the outlet zone despite the difference in the pressure, and remains in the solid residue, thus reducing the yield. Productivity is also low. For example, for standard sunflower with oil content of 42%, the yield of the known press is 28-30%, with productivity up to 50-70 kg/h.

The indexes are even lower when pressing hard seeds, for example rosehip seeds, as a big part of the seeds cannot be cut and crushed, and remain whole in the solid residue. The yield of rosehip seeds with oil content of 4.8-7% is 1- 1.3%, the productivity is 50-70 kg/h.

The low yield and productivity of the known press reduces the profitability of the pressing process and increases the cost of the pressed out oil. Besides, the high oil content of the solid residue shortens its storage life, and makes its usage difficult.

Disclosure of Invention

The primary object of the invention is to make a screw press for cold pressing of any type of oilseeds, including very hard ones, ensuring high productivity and yield; a low temperature of the pressed out oil; low oil content of the solid residue, and easy to operate.

The object is solved by making a press for cold pressing of oilseeds, having a cylindrical housing with an O-axis. The inner wall of the housing is provided with longitudinal spline ways. An inlet opening connected to a hopper for seeds is provided in the front part of the housing. A zone of outlet openings for taking out the pressed out oil is provided in the middle part of the housing. A screw with a slightly rounded screw header is provided in the housing. A press head is fixed to the housing, said press head is a solid cylinder with a central opening and a front header, located coaxially against the screw header. The front header of the press head is provided with triangular splines with a triangular cross section, which extend radially from the central opening and are located symmetrically to it, and the apexes of said triangular splines lie close to the outer wall of the press head. The press includes also a nozzle with a nozzle hole converting into a discharge opening for discharging the solid residue. The nozzle hole and the discharge opening are truncated circular cones with a small common base. The generant k _t of the nozzle hole makes a with the axis of the housing. Attached to the screw header is a screw tip which includes a cylindrical part, located into the central opening of the press head and the very beginning of the nozzle hole, and a conical part, located in the the nozzle hole and the front part of the discharge opening. The cylindrical part of the screw tip is shaped as a multiple thread screw, and the conical part - as a truncated circular cone. The generant k ₂ of the conical part of the screw tip makes b with the axis of the housing, whereby A b is smaller than A a. Between the nozzle hole and the conical part of the screw tip there is a conical gap with width b , which decreases towards the narrowest part of the nozzle hole.

Preferably, the triangular splines are 3 to 8. In one preferred embodiment triangular splines are 4.

Preferably, the outlet openings for the pressed out oil are located close to the inlet opening.

In a preferred embodiment, the outlet openings are located transversely to the wall of the housing 1 and have the shape of a truncated cone, with the small base of the cone lying in the middle of the longitudinal spline ways, and the large base being on the outer surface of the housing. It is possible the diameter d ₂ of the small base to be within the range 0.5 ÷ 1.5 mm, and the diameter of the large base d ₂ - within the range 1.5 ÷ 2.5 mm. Preferably, d = \ mm, and d ₂ = 2 mm.

Preferably, 15° < a < 25°

It is preferable b to be larger than a by 2° to 3° It is preferable the width b of the conical gap in the narrowest part of the nozzle hole to be within the range 0.5 mm ÷ 1.0 mm.

In one preferred embodiment of a press according to the invention, the screw tip is secured to the screw by a detachable screw joint.

The advantages of the press for pressing oilseeds according to the invention are that it has high productivity and provides high yield at low temperature of the pressed out oil. What is more, the press is effective for all kind of seeds, including very hard ones, such as rosehip seeds. The solid residue has a low residual oil content, which facilitates its storage and use. The press according to the invention is easy for maintaining and working with different kind of oilseeds and no special qualification of the operators is required.

Brief Description of Drawings

Fig. 1 is a schematic longitudinal semi sectional view of a preferred embodiment of the press according to the invention;

Fig. 2 is a cross-section of the housing along A-A of fig. 1;

Fig. 3 is a front view of the press head;

Fig. 4 is a cross-section of the press head along B-B of fig. 4;

Fig. 5 is an enlarged longitudinal semi sectional view of the rear part of the press of fig. 1.

Fig. 6 is a diagram of the pressure in the different zones of the press.

Preferred Embodiment

Fig. 1 - 6 clarify a preferred embodiment of a press for pressing out of oilseeds, according to the invention. The press comprises horizontally located cylindrical housing 1 with longitudinal O-axis. Longitudinal spline ways 2 are provided in the inner wall of the housing 1. An inlet opening 3 connected to a hopper 4 for oilseeds is provided in the front upper part of the housing 1. Close to the inlet opening 3 in the housing 1 there are outlet openings 5 for discharging of the pressed out oil. In this preferred embodiment the outlet openings 5 are located transversely to the wall of the housing 1 and have the shape of truncated circular cone, where the small base of the cone is in the middle of the longitudinal spline ways 2, and the large base is on the outer surface of the housing 1. A screw 6 connected to an electric motor through a gear unit (not shown in the figure) is provided in the housing 1. The screw 6 has a slightly rounded screw header 7. A press head 8 is located coaxially against the screw header 7 of the screw 6, said press head 8 is a solid cylinder with a central opening 9 and a front header 10. Triangular splines 11 with a triangular cross section are provided in the front header 10 of the press head 8. The triangular splines 11 extend radially from the central opening 9 and are located symmetrically to it with apexes lying next to the outer wall of the press head 8. In this preferred embodiment, there are four triangular splines. The press head 8 is fixed to the housing 1 by a front flange 12. The front flange 12 holds a nozzle holder 13 in which a nozzle 14 with a nozzle hole 15 is mounted, said nozzle hole 15 converts to a discharge opening 16 to discharge the solid residue. The nozzle hole 15 and the discharge opening 16 are shaped as truncated circular cones with a small common base. The generant k _t of the nozzle hole 15 makes A a with the longitudinal O-axis of the housing 1. To the screw header 7 of the screw 6, through a detachable screw joint is fitted a screw tip 17, which comprises a cylindrical part 18 in the form of a multiple thread screw, and a conical part 19 in the form of a truncated circular cone. The cylindrical part 18 is placed in the central opening 9 of the press head 8 and the very beginning of the nozzle hole 15, and the conical part 19 is placed in the rear part of the nozzle hole 15 and the front part of outlet opening 16. A generant k ₂ of the conical part 19 of the screw tip 17 makes A b with the longitudinal O-axis of the housing 1, whereby A b is smaller than A a by 2° to 3°, thus forming a conical gap between the conical part 19 and the nozzle hole 15, the width b of the conical gap, decreasing towards the narrowest part of the nozzle hole 15. The 72-hour tests of the press, according to the preferred embodiment driven by a 15 kW electric motor and fed with raw material at a temperature of 15°C give the following results:

For standard sunflower seeds with oil content 42%:

- yield 39%;

- temperature of the pressed oil 28°C;

- productivity 400 kg/h.

For rosehip seeds with 6% oil content:

- yield 3%;

- temperature of the pressed oil 30°C;

- productivity 100 kg/h.

Industrial Applicability

The press can be conditionally divided into several zones in view of the processes going on in the zones, as shown in fig. 6.

Zone A covers the section from the inlet opening 3 to the end of the outlet openings 5. Oilseeds are put into the hopper 4 and through the inlet opening 3 enter the housing 1 and fall onto the screw 6. The quantity of oilseeds in the hopper 4 provides some 800-900 mm seed column on the inlet opening 3. In its rotation the screw 6 drags the seed mass forward and conveys it to the rear end of the housing 1 , repeatedly loosening it at low pressure, thus making the seed mass porous. When moving forward the oilseeds are pressed against the edges of the screw 6 and the longitudinal spline ways 2 provided in the inner wall of the housing 1, whereby some of the oilseeds are smashed and/or chopped up, and the pressed out oil passes through the porous seed mass and exits through the outlet openings 5 with a temperature close to that of the raw material. Zone B covers the section between the zone for taking out the pressed oil, where the outlet openings 5 are located, and the end of the screw 6. The pressure in this zone is higher than the pressure in zone A and steadily raising towards the end of the screw 6 to reach values of about 50 bar. Smashing, chopping and crushing of the oilseeds continues in this zone. The seed mass is porous as it is subjected to repeated loosening by the screw 6 and is of a low temperature, as the pressure in this zone is low - up to about 50 bar. The pressed out oil in this zone flows back through the porous seed mass because the pressure there is lower, and leaves the housing 1 through the outlet openings 5. Passing through the porous seed mass, the pressed out oil is filtered and cooled to a temperature close to that of the incoming raw material.

Zone C covers the section between the screw header 7 of the screw 6 and the front header 10 of the press head 8. The seed mass pushed out by the screw 6 enters the space between the screw header 7 of the screw 6 and the front header 10 of the press head 8, where it is subjected to repeatedly and consecutively pressing into a thin layer of about 1-2 mm, and loosening by the radially located triangular splines 11 in the front header 10 of the press head 8. The pressure in this zone rises sharply to about 300 bar. When pressed onto the edges of the triangular splines 11 the remaining whole oilseeds are cut and/or fragmented. The oil pressed out in this zone returns in a backward flow to zone A, where filtered and cooled the oil exits the press through the outlet openings 5.

Zone D covers the section from the front header 10 of the press head 8 to the middle of the central opening 9 where the cylindrical part 18 of the screw tip 17 is located. As it passes through this zone the material is repeatedly loosened by the cylindrical part 18 which is in the form of a multiple thread screw, thus retaining its porosity. The pressure in this zone rises to reach about 400 bar at the end of the zone, and the temperature of the material also rises. The remaining whole seeds are pressed against the edges of the multiple thread screw and are cut and/or crushed. The pressed out oil returns backwards to the outlet openings 5 and exits filtered and cooled.

Zone E covers the section from the middle of the central opening 9 to the end of the nozzle hole 15. The material enters the gap between the nozzle hole 15 and the conical part 19 of the screw tip 17, which narrows towards the end of the nozzle hole 15. In this zone the pressing continues in a thin layer of 0.3 to 0.5 mm at high pressure, reaching about 700 bar at the end of the nozzle hole 15, where the gap is smallest. Due to the small thickness of the layer and the large difference in the pressure the pressed out oil flows backwards to zone D and from there through the porous seed mass reaches the outlet openings 5 through which it exits filtered and cooled to a temperature of 20 °C - 40 °C depending on the temperature of the raw material.

Zone F covers the section of the discharge opening 16. The solid residue enters the discharge opening 16 in the form of a thin-walled hose, which sputters as it exits the discharge opening 16, since the oil content is very low.

The press can run in a continuous mode of operation for up to 11 months, after which the screw tip needs to be replaced as because of the great friction it wears out faster than other parts of the press.

The press can press all types of oilseeds by changing the speed of the motor depending on the hardness of the seeds.

Maintenance of the press is easy and does not require special training of personnel.