WO2004080704A1

WO2004080704A1 - A screw press having a cylindrical portion

Info

Publication number: WO2004080704A1
Application number: PCT/DK2003/000169
Authority: WO
Inventors: Roald Rosendahl; Christian Verner Christiansen
Original assignee: Atlas-Stord Denmark A/S
Priority date: 2003-03-14
Filing date: 2003-03-14
Publication date: 2004-09-23
Also published as: AU2003214028A1

Abstract

The invention relates to a screw press (1) comprising a sieve housing (2) with an inlet (3) for a substance which is pressed in the press, an outlet (4) for discharging the pressed material, and at least two oppositely rotating stems (5, 6) around which threads (7, 8) are arranged at least along the part of the stems which is positioned in the area from the inlet opening (3) to the outlet (4). The stems (5, 6) and/or a jacket (9) surrounding the stem completely or partly comprises at least a cylindrically portion (21) and disposed in the area at the outlet (4), and the diameters of the stems (5, 6) decrease evenly and linearly from the termination of the cylindrical portion (21) toward the inlet (3), and the diameter of the cylindrical portion (21) is identical with the largest diameter of the conical portion (22). This provides a screw press which gives a better compression course than the known ones, and such that more liquid is pressed away from the substance so that it is more dry when the pressed substance leaves the screw press. The efficiency of the screw press disclosed in the application is increased over known structures and may amount to 1. This also allows the press to be shortened in the cases where it is sufficient with a substance that might contain more liquid.

Description

A SCREW PRESS HAVING A CYLINDRICAL PORTION

The invention relates to a screw press comprising a sieve housing with an inlet for a substance which is pressed in the press, an outlet for discharging the pressed material, and at least two oppositely rotating stems around which threads are arranged at least along the part of the stems which is positioned in the area from the inlet opening to the outlet. The invention also relates to use of the screw press.

Screw presses comprising two oppositely rotating stems are generally known for the dehydration of materials. During the dehydration, the substance will be introduced via an inlet opening, and the rotation of the two oppositely rotating stems with threads will cause the substance to be pressed, whereby liquid will be pressed out, and at the same time the sub- stance is moved toward the outlet positioned at the other end of the screw press.

An example of such a structure is known from EP-B-358837. As stated in the opening paragraph, this also comprises a sieve housing surrounding the stems so that the liquid pressed out leaves the interior of the press via the holes/perforations provided in the sieve housing. However, the efficiency of such a structure is not satisfactory, as it is typically around 0.65. Quite simply, insufficient compression of the introduced material takes place, so that the substance leaving the press contains too much liquid, unless the press is made correspondingly longer to have a longer pressing course.

Accordingly, the object of the invention is to provide a screw press which gives a better compression course than the known ones, and such that more liquid is pressed out of the substance so that it is more dry when the pressed substance leaves the screw press. The efficiency of the screw press disclosed in the application is increased over known structures and may amount to 1. This allows the press to be shortened in the cases where it is sufficient to have a substance that might contain more liquid.

This object is achieved by a screw press of the type defined in the opening paragraph, and where also the stems and/or a jacket surrounding the stem completely or partly comprises at least a cylindrical portion and positioned in the area at the outlet, and the diameters of the stems decrease evenly and linearly from the termination of the cylindrical portion toward the inlet, and the diameter of the cylindrical portion is identical with the largest diameter of the conical portion.

The press operates in that the substance is introduced through an inlet opening. The two stems rotate oppositely each other, and the substance will therefore be pressed into the cavities which occur between the threads that engage with the opposite stem. The substance is now pressed forwards, said threads ensuring that there is a minimum backflow of the substance. The liquid pressed out is conveyed away through the cavity in the sieve housing, which is formed by a sieve plate having sieve holes of a suitable size and adapted to the product and densely arranged, preferably in the entire extent of the jacket. The liquid may optionally also leave the cavities via openings in a jacket that might optionally surround the stem itself. In any event, the liquid will be collected and be conveyed further on from there and be removed. The dehydrated substance is taken out of the outlet, where the further processing of it takes place.

When the dehydrated substance reaches the outlet, it will be very firm. Owing to the circumstance that the stem/jacket is cylindrical in the area from the outlet and at a distance therefrom corresponding to at least 5% of the total length of the stem, there will be a uniform cake thickness in this area that brings about the better drainage. As there is a smooth transition from the cylindrical portion to the conical portion, it is also ensured that there will be no accumulation of pressed substance in the transitional portion.

By providing a screw press according to the invention and as additionally stated in claim 2, a better drainage is achieved, since the drainage area is increased.

By providing a screw press according to the invention and as additionally stated in claim 3, it is ensured that the jacket is smooth in an area, and, consequently, the risk that the cake, which is relatively dry in this area, sticks to the jacket is additionally reduced, since there are no openings/holes which increase the resistance, and the cake is therefore pushed forwards via the threads and is pressed out of the outlet.

By providing a screw press according to the invention and as additionally stated in claims 4 and 5, an expedient shape of the threads is achieved.

By providing a screw press according to the invention and as additionally stated in claim 6, an expedient shape of the sieve housing is achieved, and such that the oppositely rotating threads are totally surrounded by the sieve cage.

By providing a screw press according to the invention and as additionally stated in claims 7 and 8, a supporting, effective drainage of the substance is achieved by the uniform and very small distance between the sieve housing and the rotating and operating/pressing threads.

By providing a screw press according to the invention and as additionally stated in claim 9, a better pressing of the substance is achieved. Claims 10 and 12 define expedient relations between the threads and the face on which they are mounted.

By providing a screw press according to the invention and as additionally stated in claim 11 , a more continuous feeding of the press is brought about, as no noticeable pressing of the cake takes place in the inlet part during the passage of the substance down into the press, and therefore the cake is advanced almost without resistance to the conically extending portion, where pressing of the substance takes place, whereby it assumes another consistency.

By providing a screw press according to the invention and as additionally stated in claim 13, it is possible to increase or decrease the distance between the peripheral face of the threads and the internal face of the sieve housing, and thereby also to determine how great a pressure is to be applied to the substance.

The invention moreover relates to use of a screw press as stated in claim 14.

The invention will now be explained more fully with reference to the drawing, in which

fig. 1 shows a basic view of the entire screw press, seen from above,

fig. 2 shows a section along the line ll-ll in figure 1 ,

fig. 3 shows a detailed view of the outlet part, shown as a basic view, fig. 4 shows the compression curve for the screw press disclosed in the application in relation to the prior art.

Referring to figure 1 , the screw press 1 comprises a housing 2 having an inlet opening 3 arranged at one end of the housing and an outlet 4 at the opposite end of the housing. The housing 2 internally surrounds two stems, a first stem 5 and a second stem 6, which rotate oppositely and are preferably conical so that the diameter increases toward the outlet. The stems normally extend horizontally and are suspended from bearings 15 at each end of the housing. The stems are driven by a motor, which has an associated expedient gear structure for adjusting the speed of rotation. The mass is conveyed through the inlet opening 3 and is now pressed in the press, as it is moved forwards toward the outlet 4, where the pressed substance is discharged and subsequently treated. The liquid which is pressed out, is collected in a basket 17 surrounding the walls of the housing, there being openings by way of perforations in the housing from the interior of the housing to this surrounding cavity, and from where the liquid is conveyed away.

As mentioned, the two oppositely rotating screws themselves comprise stems 5, 6 around which threads 7, 8 are arranged. The threads may be mounted directly on the stem, or the threads may be mounted on a jacket 9, 10 surrounding the stems. The jacket 9, 10 is made of a sieve plate so that the liquid pressed out, in addition to leaving the press via the basket 17 of the housing, may also leave it via openings in the sheath/jackets 9, 10, said liquid being collected in a cavity located between the inner surface of the sheath and the outer surface of the stems 5, 6. The threads are screw- shaped, and the pitch may vary, as it may increase toward the outlet. The jacket 9, 10, which surrounds each of the stems 5, 6, is typically cylindri- cal/conical or at any rate rotation-symmetrical objects with a longitudinal axis coinciding with the axis of rotation of the respective stems. As will appear from fig. 1 , the screw press thus comprises a first stem 5 and a second stem 6, said first stem being equipped with first threads 7 and the second stem with second threads 8. The threads are screw-shaped. The first stem is surrounded by a first jacket 9, and the second stem is sur- rounded by a second jacket 10, said jackets being rotational-symmetrical, as mentioned, preferably cylindrical/conical. Thus, a first gap 11 is formed between the first jacket and the second jacket, and the volume of this first gap may be changed according to whether the pitch of the threads is changed and/or the distance between the two stems/jackets decreases to- ward the outlet. Optionally, the stems may be displaced axially, thereby causing a change. Through sieve holes are optionally provided in the jackets.

Between the inner face of the second jacket 10 and the outer face of the second stem 6 there is a second gap in which liquid may accumulate in the cases where the jacket is equipped with holes. Both jackets, i.e. the first jacket 9 and the second jacket 10, may be equipped with said holes for providing a sieve plate, or just one of the plates may be equipped with said holes. The jackets, which are preferably rotational-symmetrical, may have the same diameter or different diameters and may be arranged close to each other corresponding to a distance of up to 100 mm at the outlet end.

The screw press 1 may thus comprise a jacket 9, 10 mounted around both stems, or it may be without this constructional feature so that, instead of drainage taking place through the perforations of the jacket and down into an underlying gap, the drainage exclusively takes place via the sieve housing. In this case, the first gap 11 is thus defined by the first and second stems.

As mentioned, the stems extend conically so that the diameter increases from the inlet 3 toward the outlet 4, and the diameter of the threads de- creases from the inlet toward the outlet.

As regards the sieve housing 2 itself, it is arranged, as shown in figure 2, in such a manner that the distance between the inner face of the sieve hous- ing and the exposed peripheral face 29 of the first and second threads 7, 8 is essentially identical and the same in the entire extent of the sieve housing and of the order of down to millimetre. This existing, small free space contributes to ensuring a good pressing effect. The sieve housing is preferably made of two partially cylindrical/partially conical cups, a first cup 24 and a second cup 25, each cup being composed of additionally two elements so that each of the cups is assembled by means of assembling brackets 27 to provide this partially cylindrical/partially conical cup, and subsequently the two cylindrical cups are assembled against each other, such that the first and second cups are mirror-inverted relative to each other, and by means of an assembling strip 26 which is mounted along both the upper and the lower face.

With reference to figure 1 and the detailed view in figure 3, the stems/jackets 9 comprise a cylindrical portion toward the outlet 4, in other words an area where the stem/jacket is not conical, but, on the contrary, has the same diameter in the entire extent, and where also threads are arranged therearound.

This cylindrical portion is positioned in extension of the outlet and has a longitudinal extent of at least 5% of the total length of the stem. In this area, the jacket will preferably not comprise perforations 22, so that there will be no drainage possibilities into the interior of the stem in this area. This contributes to ensuring that the drained substance does not get stuck, but leaves the outlet 4 with the smallest possible resistance.

With reference to figure 1 , it will be seen that also the area at the inlet opening 3 may comprise a cylindrical portion 23, which is thus also characterized in that the diameter in this area is constant, as regards the jacket/stem. The portion may be larger, smaller or essentially coinciding with the extent of the inlet opening 3 itself. Here, too, there will be no perfo- rations 22 and thus no drainage possibilities via the jacket 9 or the stems 5,

6.

Figure 4 shows the compression curve for the course of a substance through a sieve press, where the curve I indicates the invention and the curve II indicates the prior art. The compression factor K is the relation between the volume admitted into the press by rotation of the screw, and the volume leaving the press (volume flow) at a given distance from the inlet opening.

0 indicates the inlet, and <- thus indicates the distance from the inlet and toward the outlet itself. It will be noted here that the difference between the invention and the prior art is precisely that the compression factor K will asymptotically approach 1 in the use of the invention, while, in the use of generally known prior art, the compression factor will have a steep down flow arranged at II. It is precisely desirable that the compression has this course as indicated here at I, because this is indicative of the substance having been drained well at a very early point of time during the course through the sieve press and with a minimum of work. As mentioned before, the efficiency of a press according to the invention is considerably greater than that of the prior art.

Claims

PATENT CLAIMS

1. A screw press (1 ) comprising a sieve housing (2) with an inlet (3) for a substance which is pressed in the press, an outlet (4) for discharging the pressed material, and at least two oppositely rotating stems (5, 6) around which threads (7, 8) are arranged at least along the part of the stems which is positioned in the area from the inlet opening (3) to the outlet (4), characterized in that the stems (5, 6) and/or a jacket (9) surrounding the stem completely or partly comprises at least a cylindrical portion (21) and positioned in the area at the outlet (4), and that the diameters of the stems

(5, 6) decrease evenly and linearly from the termination of the cylindrical portion (21) toward the inlet (3), and that the diameter of the cylindrical portion (21) is identical with the largest diameter of the conical portion (22).

2. A screw press according to claim 1, characterized in that the jacket(s) (9) surrounding the stem/stems completely or partially comprises openings/holes (22) in the surface, said openings/holes (22) communicating with a cavity disposed below the surface of the stem/stems and for providing drainage.

3. A screw press according to claim 2, cha racte rized in that the openings/holes (22) in said stem/stems at least do not extend to the area around the cylindrical portion.

4. A screw press according to any one of the preceding claims, characterized in that the threads (7, 8) are helical/screw-shaped and extend continuously.

5. A screw press according to any one of the preceding claims, c h a r a c - t e r i z e d in that the threads (7, 8) extend conically so that the diameter of the threads is larger at the inlet part (3) than at the outlet part (4) and with an oppositely directed thread pitch between the two stems (5, 6).

6. A screw press according to any one of the preceding claims, characterized in that the sieve housing (2) comprises at least two partially cy- lindrical/partially conical cups (24, 25) having through holes/perforations.

7. A screw press according to any one of the preceding claims, characte ri zed in that the distance between the inner face (30) of the sieve housing (2) and the free termination edge (29) of the threads is essentially constant in the entire length of the sieve housing and at least in the area where the threads (7, 8) are exposed.

8. A screw press according to any one of the preceding claims, characte rized in that the distance between the inner face (30) of the sieve housing and the free termination edge (29) of the threads is at least Vz mm.

9. A screw press according to any one of the preceding claims, characterized in that the pitch of the threads (7, 8) increases toward the outlet.

10. A screw press according to any one of the preceding claims, characterized in that the threads (7, 8) are mounted on the stem (5, 6) itself.

11. A screw press according to any one of the preceding claims, char- a c t e r i z e d in that the stems (5, 6) additionally comprise a cylindrical portion (23) disposed in the inlet part (3), and that the diameter of the cylindrical portion (23) is identical with the smallest diameter of the conical portion (28).

12. A screw press according to claims 1-1 ^characterized in that the threads (7, 8) are mounted on the jacket (9) itself.

13. A screw press according to any one of the preceding claims, characterized in that the position of the stems (5, 6) in the housing may be varied and be displaced in an axial direction.

14. Use of a screw press according to claims 1-13 for the treatment of a liquid-containing substance, e.g. fish waste, sugar waste, etc.