US3766848A - Mechanical screw press - Google Patents

Abstract

A cylindrical cage is lined with spaced screen bars to define a drainage chamber, a screw extends through the chamber and has a plurality of axially spaced worms mounted on a shaft, and axially spaced stationary breaker lugs project inwardly between the flights of the worms. The screw has a recessed conical end surface which mates with a pointed conical end surface of a stationary drainage discharge cone. The discharge cone is supported for axial adjustment by a bearing and a fluid cylinder to vary the size of the annular discharge orifice defined between an orifice ring removably mounted on the cone and a bushing mounted on the frame. The recessed conical surface of the worm and the pointed conical surface on the sleeve cooperate to center the discharge end portion of the screw within the pressing chamber through a layer of compacted material between the surfaces. Each of the worms may also incorporate two diametrically opposed helical flights each extending circumferentially about 170* and which also cooperate to center the screw by balancing the lateral acting forces on the screw.

Description

French et a1.

[52] U.S. Cl 100/117, 100/149, 259/9 [51] Int. Cl B30b 9/14, B30b 9/18 [58] Field of Search 100/117, 126, 145-150;

[56] References Cited UNITED STATES PATENTS 3,093,065 6/1963 French.. 100/150 X 3,285,163 1 1/1966 Burner 100/117 X 3,555,999 1/1971 G1owacki.. 100/148 3,225,453 12/1965 Burner 100/117 X 3,400,654 9/1968 Vincent.... 100/148 3,411,435 11/1968 French et a1 100/43 3,398,677 8/1968 Theobald et a1.... 100/147 X 2,060,408 11/1936 Wood 100/148 UX 2,982,990 5/1961 Zomlefer 259/191 3,003,412

Filed:

MECHANICAL SCREW PRESS Inventors: Alfred W. French; Forest J. Starrett,

Jr., both of Piqua, Ohio Assignee: The French Oil Mill Machinery Company, Piqua, Ohio July 13, 1971 Appl. No.: 162,175

Vincent 100/117 Primary Examiner-John Petrakes Assistant Examiner-Philip R. Coe Attorney-Jacox & Meckstroth s7 ABSTRACT A cylindrical cage is lined with spaced screenbars to define a drainage chamber, a screw extends through the chamber and has a plurality of axially spaced worms mounted on a shaft, and axially spaced stationary breaker lugs project inwardly between the flights of the worms. The screw has a recessed conical end surface which mates with a pointed conical end surface of a stationary drainage discharge cone. The discharge cone is supported for axial adjustment by a bearing and a fluid cylinder to vary the size of the annular discharge orifice defined between an orifice ring removably mounted on the cone and a bushing mounted on the frame. The recessed conical surface of the worm and the pointed conical surface on the sleeve cooperate to center the discharge end portion of the screw within the pressing, chamber through a layer of compacted material between the surfaces.

. Each of the worms may also incorporate two diametri- 10 Claims, 3 Drawing Figures MECHANICAL SCREW PRESS BACKGROUND OF THE INVENTION In a mechanical screw press such as disclosed in French et al. U.S. Pat. No. 3,411,435, assigned to the assignee of the present invention, the screw includes a series of axially spaced worms mounted on a shaft, and each worm has an annular body supporting an integral helical flight. The worms and flights are spaced axially by collars mounted on the shaft, and a series of stationary breaker lugs project inwardly between the helical flights to oppose rotation of the pressed material with the worms and thereby assure generally axial flow of the material from each worm to the next successive worm.

At the discharge end of the press shown in the above patent, the screw shaft projects beyond the final discharge worm and carries a bearing sleeve which projects into a non-rotatable discharge cone. The discharge cone is provided with drainage openings and cooperates with a surrounding annular bushing mounted on the frame to define an annular discharge orifice. The cone is mounted on the end of a shaft or rod which extends from a hydraulic cylinder and is adjustable axially on the screw shaft to vary the size of the discharge orifice.

When a mechanical screw press such as shown in the above patent, is used for expressing moisture from an abrasive material, for example, sugar cane bagasse having abrasive foreign particles such as sand, it has been found that the bagasse and foreign particles are forced into the clearance space between the sleeve on the screw shaft and the surrounding stationary discharge drainage cone, causing the sleeve and cone to wear and substantially increasing the horsepower required to drive the screw. In addition, the replacement of the sleeve and cone result in substantial maintenance expense. Furthermore, as a result of the substantial weight of the discharge end portion of the screw and the high pressure lateral forces acting on the screw, it has been difficult to avoid significant wear on the outer surface of the helical flight on the discharge worm and also on the surrounding screen bars mounted on the discharge end portion of the cage. That is, these lateral forces are usually sufficient to cause enough deflection of the rotating screw shaft so that the helical flights SUMMARY OF THE INVENTION The present invention is directed to a mechanical screw press incorporating improved means for constructing and supporting the screw for significantly reducing the maintenance required by the press. The invention eliminates the need for the long bearing sleeve on the shaft and the resulting metal to metal contact between the sleeve and the surrounding discharge cone, and provides for retaining the screw in center relation within the pressing chamber so that the wear on the worms and the surrounding screen bars is substantially reduced. As a result, a screw press constructed in accordance with the present invention, may be oper ated continuously with less horsepower and for longer periods of time when handling abrasive materials. The invention also provides for conveniently removing and replacing at least the final discharge worm after an extended period of use.

In accordance with one embodiment of the invention, the hollow screw shaft supporting the worms, is cut off inwardly of the discharge end of the pressing chamber, and the final discharge worm is retained on the shaft by a plate secured to the shaft by a threaded fastener extending into a plug mounted within the shaft. The retaining plate has an inwardly tapering or recessed conical surface, and the final discharge worm has a frusto-conical end surface which forms a continuation of the conical surface. l

A non-rotatable discharge cone is supported within the discharge end of the pressing chamber by a ram or rod extending from a hydraulic cylinder. The discharge cone carries a replaceable orifice ring which seats on a shoulder formed on the cone and which cooperates physically contact the stationary screen bars in the to apply a hard coating on the outer surface of the flight of the discharge worm and to employ'hardened screen bars.

Even with the hardened screen bars. and worm flights, when a mechanical screw press is used to press sugar cane bagasse which commonly carries sand and other abrasive foreign material, it is occasionally necessary to stop the screw press, open the split cage and replace the final discharge worm on the screw in addition to sometimes replacing the screen bars adjacent the high pressure discharge end of the press. It is not uncommon for this replacement to require two or four men from eight to sixteen hours. This results in a substantial ser vice expense and a significant downtime for the screw press.

with a surrounding stationary frame bushing to define an annular discharge orifice. The cone also has a conical end surface which cooperates with the complementary conical surface on the discharge end of the screw to assist in holding the screw in-a concentric or centered position within the pressing chamber. When the discharge sleeve is adjusted axially by operation of the hydraulic cylinder to vary the size of the discharge orifice, the layer of compacted material confined between the conical surfaces remains substantially uniform in thickness as a result of the relative rotation of the surfaces. Thus the centering effect on the screw is maintained regardless of the spacing between the mating conical end surfaces. j

The final discharge worm, and preferably all the worms along the entire length of the pressing shaft, are constructed with a pair of diametrically opposed helical flightseach of which extends circumferentially approx imately so that there is an approximate l0 gap between adjacent ends of the opposing'flights. The two opposed flights on the worms, are effective to balance the lateral forces acting on the screw and cooperate with the mating conical end surfaces to help center the screw within the pressing chamber and thereby minimize lateral deflection of the screw and rubbing of the worm flights against the surrounding screen bars.

Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary section of the discharge end portion of a mechanical screw press having a screw shaft assembly and a stationary discharge cone constructed in accordance with the present invention;

FIG. 2 is an enlarged sectional view of a slightly modified form of the final discharge worm; and

FIG. 3 is an axial view of the discharge worm shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the discharge end portion of a screw press which includes a generally cylindrical cage which is constructed in two semi-cylindrical mating cage sections 12 each having a plurality of parallel spaced arcuate ribs (not shown) integrally connected by longitudinally extending cage members. The cage sections 12 are clamped together by a series of tie bolts (not shown) which extend within the holes 13, and the discharge end of the cage is supported by an upright end wall 14 of the main frame. An axially extending tie plate or bar 15 connects the upper end of the wall 14 to a main gear box housing (not shown) located adjacent the opposite or inlet end of the cage.

A plurality of axially extending-elongated screen bars 16 are mounted on the ribs of each cage section 12 and are circumferentially spaced to define longitudinally extending drainage slots or openings 17 therebetween. The screen bars 16 are secured within each cage section by reatining bars 18 to define a cylindrical pressing chamber 20 having an inlet end (not shown) and a discharge end 22 which abuts the frame member 14.

An elongated screw 25 extends through the pressing chamber 20 and includes a hollow shaft 26 which is connected through a gear box to a suitable drive motor 28. A series of pressure worms, including a discharge worm 29 and a final discharge worm 30, are successively mounted on the shaft 26 within the pressing chamber 20 and are secured to the shaft by a key 31. The worm 29 includes a generally cylindrical body 32 and a pair of diametrically opposed integral helical flights 33 each of which extend circumferentially around thebody 32 approximately 170 as will be explained later in connection with FIGS. 2 and 3.

A series of annular collars 36 are mounted on the shaft 26 interspaced between the pressure worms and form gaps or spaces between the worms. A series of breaker bars are secured to the retaining bars 18 and include lug portions 38 which project inwardly into the pressing chamber 20 in the areas of the annular collars '36 and between the worms to minimize rotation of the material being pressed with the screw 25. A final breaker bar or lug 39 projects inwardly adjacent the discharge end of the final discharge worm 30, and an annular wear bushing 41 surrounds the flight 33 of the worm 29 to assist in minimizing the wear on the final discharge worm and the surrounding screen bars.

The final discharge worm 30 (FIGS. 2 and 3) inv cludes an annular body 42 which tapers outwardly toward the discharge end of the screw 25. A pair of diametrically opposed helical flights 44 are formed as an integral part of the body 42, and each flight extends circumfercntially around the tapered body approximately 170 as mentioned above in connection with the worm 29. A frusto-conical end surface 45 is formed on the final discharge worm 30 and extends outwardly from a counterbore 47. A retaining plate or member 50 seats within the counterbore 47 and includes a cylindrical portion which projects into the end portion of the hollow screw shaft 26. The retaining member 50 is secured to the shaft by a screw 52 which is threaded into a plug 54 welded to the inner surface of the screw shaft 26. The retaining plate 50 has a recessed conical end surface 55 which forms a continuation of the frustoconical surface 45 on the worm 30 so that the entire end surface of the screw 25 is generally conical.

A large diameter counterbore 59 is formed within the frame member 15 and receives a hardened stationary discharge ring 60 having a frusto-conical inner surface 61 which continues inwardly onto a smaller adjacent stationary discharge bushing or ring 62. The discharge rings 60 and 62 are retained by an annular plate 64 which is secured to the end frame wall 14 by a series of screws 66.

A frame extension member or bracket is rigidly secured to the retaining plate 64 and projects outwardly to support a double acting fluid or hydraulic cylinder 72. The cylinder 72 has a piston rod 74 which is axially aligned with the screw 25 and is slidably sup ported by a bearing 75 mounted on the frame extension member 70 and by a bearing 76 mounted on the outer end of a guide tube 77 rigidly secured to frame extension 70. The rod 74 includes an integral spline 78 which engages a tubular spline 79 confined within the tube 77 to prevent the rod 74 from rotating.

A support plate 82 is mounted on the projecting end of the rod 74 and supports a non-rotatable hollow discharge cone 85 having a frusto-conical portion 86. A cylindrical surface 87 is formed on the cone portion 86 and receives a onepiece orifice ring 88 which seats against a radial shoulder 89. The outer surface of the ring 88 cooperates with the inner surface of the surrounding frame bushing 62 to define an annular discharge orifice 90. An annular array of openings or holes 92 are formed within the cone portion 86 and provide an inward escape of expressed fluid which drains from the cone 85 through an outlet 93 formed within the lower portion of the support plate 82. The sleeve 85 includes a pointed tip portion 94 which has a conical end surface 95 mating with the conical end surface 55 on the screw 25.

Referring to FIGS. 2 and 3, the worms 29 and 30 are each constructed similar to a worm which includes an annular body 102 having a set of axially extending threaded holes 103 and an outer frusto-conical surface tapering outwardly toward the discharge end of the pressing chamber 20. The worm 100 further includes a pair of diametrically opposed helical flights 104 which are formed as an integral part of the body 102. Preferably, each of the helical flights 104 extends circumferentially about so that opposing ends of the flights 104 define diametrically opposed axially extending passages or gaps 106 of above 10. The two diametrically opposed flights 104 cooperate to balance the lateral acting forces on the screw 25 and thus cooperate with the centering effect of the conical surfaces 55 and 95 t0 assurethat the discharge end portion of the screw 25 does not sag but remains centered within the pressing chamber 20. The double flights 104 may also be used on the preceding worms of the screw 25 to provide additional balancing of the laterally active forces.

When the mechanical screw press is operating for continuously expressing fluid from a material such as sugar cane bagasse, the compressed pulp or bulk material is discharged through the annular orifice 90. The discharge cone 85 is positioned axially by actuating the fluid cylinder 72 to adjust the area of the orifice 90 according to the back pressure desired in the pressing chamber 20. Preferably, when the cone 85 and the rod 74 are completely extended to obtain the minimum area of the discharge orifice 90, there is a gap of approximately one-fourth inch between the recessed conical end surfaces 45 and 55 on a screw 25 and the pointed conical end surface 95 on the cone 85.

As a result of the high pressure exerted on the material within the discharge end portion of the pressing chamber 20, the material flows into the gap or space between the surfaces 55 and 95 and the relative rotation between the screw 25 and the cone 85 produces a uniform layer of compacted material within the gap or space. It has been found that this layer of material cooperates with the conical surfaces 55 and 95 to effect centering of the discharge end portion of the screw 25 within the pressing chamber 20.

It has also been found that even when the cone S5 is retracted to increase the area of the discharge orifice 90, the layer of compacted material between the relative rotating conical surfaces 55 and 95 is still effective to produce centering of the final discharge worm 30 within the chamber 20. For example, when the space between the conical surfaces 55 and 95 is upwards to 2% inches, the compacted layer of material between the surfaces is still effective to hold the axis of the screw 25 in alignment with the axis of the sleeve 85 and cylinder rod 74.

In summary, it is apparent that a mechanical screw press constructed in accordance with the present invention, provides desirable features and advantages. For example, the invention eliminates the long bearing sleeve on the screw shaft as shown in the above patent and thereby eliminates the resulting wear problem and the additional power required to drive the screw. Furthermore, the generally conical end surface 55 on the screw 25 cooperates with the pointed generally conical end surface 95 on the stationary discharge cone 85 to produce self-centering forces on the discharge end portion of the screw. These self-centering forces remain effective even though the non-rotating discharge cone 85 is adjusted axially and the, space between the surfaces 55 and 95 changes. As a result, when the screw press is operating to express moisture from a material containing abrasive foreign particles such as sugar cane bagasse containing sand, the wear on the outer surface of the flight 44 and on thesurrounding screen bars 16, is significantly reduced.

Furthermore, when the worms are constructed as shown in FIG. 2 and 3, the diametrically opposed helical flights of less 180, cooperate with the conical surfaces 55 and 95 to help in centering the screw within the pressing chamber 20. By balancing the lateral acting forces on the screw. It is also apparent that the double flighted worms may be conveniently removed and replaced by new worms. To accomplish this, the hydraulic cylinder 72 is actuated to retract the nonrotating discharge cone 85, after which the cone is removed from the support plate 82. .The worm retaining plate 50 is then removed from the end of the screw shaft 26, and the final discharge worm 3th is pulled from the shaft 26 simply by extending pull bolts through axially extending holes within the support plate 82 and threading the pull bolts into the holes 103 within the discharge worm. When the rod 74 and support plate 82 are retracted, the final discharge worm 100 is pulled from the screw shaft 26. Before the worm is pulled, however, one of the gaps 106 is aligned with the final breaker lug 39 by rotating the screw.

It is also apparent that the minimum size of the orifice 90 may be conveniently changed simply by retracting the cone 85 and replacing the orifice ring 88 with another ring having a greater or lesser outer diameter. Previously, it was necessary to interchange either the entire cones or the frame bushings 62 to change the minimum size of the orifice. This was an expensive and time consuming operation.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A mechanical screw press for expressing fluid from a material, comprising means defining an elongated pressing chamber having an inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotationof said screw, a retaining member connected to said shaft for retaining the final said worm on said shaft, said retaining member forming a gener ally conical end surface on the discharge end portion of said screw within said chamber, a cone member positioned within said outlet and projecting into said chamber, a generally frustoconical surface on said cone member and having drainage means therein, means for supporting said cone member concentrically within said outlet and said pressing chamber, said cone member cooperating with said outlet to define an annular discharge orifice, means forming a generally conical end surface on said cone member adjacent said end surface of said screw, and said end surface of said cone member cooperating with said end surface of said screw and the material compressed therebetween to effect substantial centering of said discharge end portion A of said screw within said chamber. a

2. Amechanical screw press for expressing fluid from .a material, comprising means defining an elongated pressing chamber having inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one out- 1 wardly projecting helical flight, means for rotating said screw, means for compressing material within said 1 chamber as the material moves toward said outlet in response to rotation of said screw, said screw having a ta- 7 member axially within said discharge end portion of said chamber.

i 3. A mechanical screw press for expressing fluid from a material, comprising means defining an elongated pressing chamber with an inlet and an outlet, an elongated rotatable screw extending through said chamber and including a shaft, a series of worms mounted on said shaft, each of said'worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, a cone member positioned within said outlet in axial alignment with said screw, means for moving said cone member axially, a rigid orifice ring mounted on said cone member and cooperating with said outlet to define an annular discharge orifice, means forming an annular seat on said cone member for positioning said orifice ring, and said orifice ring being removable from said seat to provide for replacing said orifice ring.

4. A mechanical screw press for expressingfluid from a material, comprising means defining an elongated pressingchamber having an inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means forrotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, a retaining member connected to said shaft for retaining the final said worm on said shaft, said retaining member forming a generally conical end surface on the discharge end portion of said screw within said chamber, a cone member positioned within said outlet and projecting into said chamber, means for supporting said cone member concentrically within said outlet and said pressing chamber, an orifice ring mounted on said cone member and coopervating with said outlet means to define an annular discharge orifice, said orifice ring being removable from said cone member to provide for conveniently replacing said orifice ring, means forming a generally conical end surface on said cone member adjacent said end surface of said screw, and said end surface of said cone member cooperating with said end surface of said screw and the material compressed therebetween to effect substantial centering of said discharge end portion of said screw within said chamber.

5. A mechanical screw press for expressing fluid from a material, comprising means. defining an elongaged pressing chamber having an inlet and an outlet, an

elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, at least the final discharge worm includes a pair of diametrically opposed said flights each extending circumferentially no greater than 180, a retaining member connected to said shaft for retaining the final said worm on said shaft, said retaining member forming a generally conical end surface on the discharge end portion of said screw within said chamber, a cone member positioned within said outlet and projecting into said chamber, means for supporting said cone member concentrically within said outlet and said pressing chamber, said cone member cooperating with said outlet to define an annular discharge orifice, means forming a generally conical end surface on said cone member adjacent said end surface of said screw, and said end surface of said cone member cooperating with said end surface of said screw and the material compressed therebetween to effect substantial centering of said discharge end portion of said screw within said chamber.

6. A screw press as defined in claim 2 wherein said cone member includes a hollow portion having a frustoconical outer surface, means defining drainage openings within said frustoconical surface, a tip member rigidly secured to said hollow member, and said tip member having a pointed said generally conical end surface.

7. A screw press as defined in claim 1 wherein at least the final discharge worm including a pair of diametrically opposed said flights, and each of the latter said flights extends circumferentially approximately 8.'A press as defined in claim 2 including a retaining member mounted on the discharge end of said shaft and having means for securing the final discharge worm to said shaft, and said retaining member having a generally conical said end surface.

9. A press as defined in claim 1 comprising a hollow said shaft, a plug member mounted within the discharge end portion of said hollow shaft, and a threaded fastener securing said retaining member to said plug member.

10. A screw press as defined in claim 3 wherein said seat comprises a shouldered outer surface on said cone member, and said orifice ring is seated on said outer

Claims (10)

1. A mechanical screw press for expressing fluid from a material, comprising means defining an elongated preSsing chamber having an inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, a retaining member connected to said shaft for retaining the final said worm on said shaft, said retaining member forming a generally conical end surface on the discharge end portion of said screw within said chamber, a cone member positioned within said outlet and projecting into said chamber, a generally frustoconical surface on said cone member and having drainage means therein, means for supporting said cone member concentrically within said outlet and said pressing chamber, said cone member cooperating with said outlet to define an annular discharge orifice, means forming a generally conical end surface on said cone member adjacent said end surface of said screw, and said end surface of said cone member cooperating with said end surface of said screw and the material compressed therebetween to effect substantial centering of said discharge end portion of said screw within said chamber.

2. A mechanical screw press for expressing fluid from a material, comprising means defining an elongated pressing chamber having inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, said screw having a tapered end surface terminating within said chamber inwardly of said outlet, a hollow cone member projecting into the discharge end portion of said chamber and having a tapered end surface opposing said end surface of said screw, means for supporting said cone member concentrically within said outlet and said pressing chamber, means on said cone member cooperating with said outlet to define an annular discharge orifice, means defining drainage openings within said cone member between said end surface of said screw and said discharge orifice, and means for moving said cone member axially within said discharge end portion of said chamber.

3. A mechanical screw press for expressing fluid from a material, comprising means defining an elongated pressing chamber with an inlet and an outlet, an elongated rotatable screw extending through said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, a cone member positioned within said outlet in axial alignment with said screw, means for moving said cone member axially, a rigid orifice ring mounted on said cone member and cooperating with said outlet to define an annular discharge orifice, means forming an annular seat on said cone member for positioning said orifice ring, and said orifice ring being removable from said seat to provide for replacing said orifice ring.

4. A mechanical screw press for expressing fluid from a material, comprising means defining an elongated pressing chamber having an inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, a retaining member connected to said shaft for retaining the final said worm on said shaft, said retAining member forming a generally conical end surface on the discharge end portion of said screw within said chamber, a cone member positioned within said outlet and projecting into said chamber, means for supporting said cone member concentrically within said outlet and said pressing chamber, an orifice ring mounted on said cone member and cooperating with said outlet means to define an annular discharge orifice, said orifice ring being removable from said cone member to provide for conveniently replacing said orifice ring, means forming a generally conical end surface on said cone member adjacent said end surface of said screw, and said end surface of said cone member cooperating with said end surface of said screw and the material compressed therebetween to effect substantial centering of said discharge end portion of said screw within said chamber.

5. A mechanical screw press for expressing fluid from a material, comprising means defining an elongaged pressing chamber having an inlet and an outlet, an elongated rotatable screw extending within said chamber and including a shaft, a series of worms mounted on said shaft, each of said worms having at least one outwardly projecting helical flight, means for rotating said screw, means for compressing material within said chamber as the material moves toward said outlet in response to rotation of said screw, at least the final discharge worm includes a pair of diametrically opposed said flights each extending circumferentially no greater than 180*, a retaining member connected to said shaft for retaining the final said worm on said shaft, said retaining member forming a generally conical end surface on the discharge end portion of said screw within said chamber, a cone member positioned within said outlet and projecting into said chamber, means for supporting said cone member concentrically within said outlet and said pressing chamber, said cone member cooperating with said outlet to define an annular discharge orifice, means forming a generally conical end surface on said cone member adjacent said end surface of said screw, and said end surface of said cone member cooperating with said end surface of said screw and the material compressed therebetween to effect substantial centering of said discharge end portion of said screw within said chamber.

6. A screw press as defined in claim 2 wherein said cone member includes a hollow portion having a frustoconical outer surface, means defining drainage openings within said frustoconical surface, a tip member rigidly secured to said hollow member, and said tip member having a pointed said generally conical end surface.

7. A screw press as defined in claim 1 wherein at least the final discharge worm including a pair of diametrically opposed said flights, and each of the latter said flights extends circumferentially approximately 170*.

8. A press as defined in claim 2 including a retaining member mounted on the discharge end of said shaft and having means for securing the final discharge worm to said shaft, and said retaining member having a generally conical said end surface.

9. A press as defined in claim 1 comprising a hollow said shaft, a plug member mounted within the discharge end portion of said hollow shaft, and a threaded fastener securing said retaining member to said plug member.

10. A screw press as defined in claim 3 wherein said seat comprises a shouldered outer surface on said cone member, and said orifice ring is seated on said outer surface.

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