Wearing body for receiving a twin screw for extruding meltable material

Abstract

A wearing body or bushing having an axial twin borehole for receiving a twin screw for extruding meltable material, in particular plastic. In order to avoid cracking and to save material, the wearing body has a radial cross section with an outer contour, which is convexly curved over the entire circumference and is in the form of an oval, and with first and second axes of symmetry, which run perpendicularly to one another and define a point of intersection which lies on the extrusion axis. The width of the oval on the first axis of symmetry is greater than the height of the oval on the second axis of symmetry.

Claims

1. A wearing body in the form of a straight cylinder having an axial twin borehole configured to receive a twin screw for extruding meltable material, said cylinder comprising a radial cross-section having an outer contour which is convexly curved over an entire circumference and configured in the form of an oval, and first and second axes of symmetry which extend in perpendicular relationship to one another and define a point of intersection which lies on an extrusion axis, said oval defined by a width on the first axis of symmetry and a height on the second axis of symmetry, said width on the first axis of symmetry being greater than the height on the second axis of symmetry, said oval including two first circular arcs each in symmetric relationship to the first axis of symmetry, and two second circular arcs each in symmetric relationship to the second axis of symmetry, said first circular arcs being defined by a radius which lies on the second axis of symmetry, and said second circular arcs being defined by a radius which lies on the first axis of symmetry, said two first circular arcs and said two second circular arcs forming a closed oval, so that at contact points of the first and second circular arcs their radii lie respectively on one another, wherein the radii of the first and second circular arcs, lying on one another, define an angle to the second axis of symmetry, said angle lying between 15 and 25.

2. The wearing body of claim 1, wherein the twin borehole defines two channels, said second axis of symmetry extending between the two channels of the twin borehole.

3. The wearing body of claim 1, wherein a ratio of the width of the oval to the height of the oval lies between 1.3 and 1.6.

4. The wearing body of claim 1, wherein the radius of the first circular arcs is greater than the radius of the second circular arcs.

5. The wearing body of claim 1, wherein a ratio of the radius of the first circular arcs to the radius of the second circular arcs lies between 2.3 and 3.5.

6. The wearing body of claim 1, wherein the twin borehole defines two channels defined by a radius, wherein a ratio of the radius of the second circular arcs to the radius of the channels of the twin borehole lies between 1.25 and 1.55.

7. The wearing body of claim 1, wherein the twin borehole defines two channels, said second circular arcs defining centre points which lie on centre points of the channels of the twin borehole.

8. The wearing body of claim 1, wherein the oval is an ellipse.

9. The wearing body of claim 1, wherein the cylinder has a radial projection at an axial end.

10. An extrusion cylinder for a twin-screw extruder, said extrusion cylinder comprising: a wearing body in the form of a straight cylinder having an axial twin borehole configured to receive a twin screw for extruding meltable material, said cylinder comprising a radial cross-section having an outer contour which is convexly curved over an entire circumference and configured in the form of an oval, and first and second axes of symmetry which extend in perpendicular relationship to one another and define a point of intersection which lies on an extrusion axis, said oval defined by a width on the first axis of symmetry and a height on the second axis of symmetry, said width on the first axis of symmetry being greater than the height on the second axis of symmetry, said oval including two first circular arcs each in symmetric relationship to the first axis of symmetry, and two second circular arcs each in symmetric relationship to the second axis of symmetry, said first circular arcs being defined by a radius which lies on the second axis of symmetry, and said second circular arcs being defined by a radius which lies on the first axis of symmetry, said two first circular arcs and said two second circular arcs forming a closed oval, so that at contact points of the first and second circular arcs their radii lie respectively on one another, wherein the radii of the first and second circular arcs, lying on one another, define an angle to the second axis of symmetry, said angle lying between 15 and 25.

11. An extruder, comprising a twin screw, an extrusion cylinder which includes a wearing body in the form of a straight cylinder having an axial twin borehole which receives the twin screw for extruding meltable material, said cylinder comprising a radial cross-section having an outer contour which is convexly curved over an entire circumference and configured in the form of an oval, and first and second axes of symmetry which extend in perpendicular relationship to one another and define a point of intersection which lies on an extrusion axis, said oval defined by a width on the first axis of symmetry and a height on the second axis of symmetry, said width on the first axis of symmetry being greater than the height on the second axis of symmetry, said oval including two first circular arcs each in symmetric relationship to the first axis of symmetry, and two second circular arcs each in symmetric relationship to the second axis of symmetry, said first circular arcs being defined by a radius which lies on the second axis of symmetry, and said second circular arcs being defined by a radius which lies on the first axis of symmetry, said two first circular arcs and said two second circular arcs forming a closed oval, so that at contact points of the first and second circular arcs their radii lie respectively on one another, wherein the radii of the first and second circular arcs, lying on one another, define an angle to the second axis of symmetry, said angle lying between 15 and 25.

Description

(1) The invention is explained in further detail below with the aid of example embodiments and with reference to the drawings.

(2) FIG. 1a shows an oval wearing body in a radial cross-sectional view taken along section line 1a-1a in FIG. 1b.

(3) FIG. 1b shows the oval wearing body according to FIG. 1a in the section view taken along section line 1b-1b in FIG. 1a along an axis of symmetry.

(4) FIG. 1c shows the oval wearing body according to FIG. 1a in the section view taken along section line 1c-1c in FIG. 1a along another axis of symmetry.

(5) FIG. 2a shows an elliptical wearing body in a radial cross-sectional view taken along section line 2a-2a in FIG. 2b.

(6) FIG. 2b shows the elliptical wearing body according to FIG. 2a in the section view taken along section line 2b-2b in FIG. 2a along an axis of symmetry.

(7) FIG. 2c shows the elliptical wearing body according to FIG. 2a in the section view taken along section line 2c-2c in FIG. 2a along another axis of symmetry.

(8) In the following embodiments, symmetrical elements and reference numbers are to be read together, even if not specified explicitly everywhere.

(9) FIG. 1a shows the radial cross-section of an oval wearing body according to the first example embodiment. The wearing body is configured axially as a straight cylinder Z and has an axial twin borehole ZB with two axial channels or respectively bores K, K. The twin borehole ZB is axially symmetrical to a first axis of symmetry SA1 and to a second axis of symmetry SA2. The first axis of symmetry SA1 and the second axis of symmetry SA2 stand perpendicularly to one another and their point of intersection E lies on the extrusion axis EA. The second axis of symmetry SA2 runs between the channels K, K. The channels K, K have respectively a radius r3, which extends from their respective centre point MK, MK to their circumference.

(10) The radial cross-section of the cylinder Z has an outer contour AK, convexly curved over the entire circumference of the cylinder Z, with two first circular arcs KB1, KB1 and two second circular arcs KB2, KB2. The first circular arcs KB1, KB1 are axially symmetrical to the first axis of symmetry SA1. The second circular arcs KB2, KB2 are axially symmetrical to the second axis of symmetry SA2.

(11) The first circular arcs KB1, KB1 have a radius R1, which extends from their respective centre point M1, M1 up to their circumference on the outer contour AK. The centre points M1, M1 of the first circular arcs KB1, KB1 lie on the second axis of symmetry SA2.

(12) The second circular arcs KB2, KB2 have a radius r2, which extends from their respective centre point M2, M2 up to their circumference on the outer contour AK. The centre points M2, M2 of the second circular arcs KB2, KB2 lie on the first axis of symmetry SA1.

(13) The radius r1 of the first circular arcs KB1, KB1 is greater than the radius r2 of the second circular arcs. The radius r1 of the first circular arcs KB1, KB1 intersects the first axis of symmetry SA1.

(14) The first circular arcs KB1, KB1 and the second circular arcs KB2, KB2 directly adjoin one another alternately and form a closed oval. At the contact points KP of the respective circular arcs, their radii r1, r2 lie on one another, i.e. the centre points M1, M1 of the first circular arcs KB1, KB1, the centre points M2, M2 of the second circular arcs KB2, KB2 and the respective contact points KP form an axis. This axis and the second axis of symmetry SA2 span the angle g.

(15) In this example embodiment, the centre points M2, M2 of the second circular arcs KB2, KB2 lie respectively on the centre points MK, MK of the channels K, K. In alternative example embodiments, the centre points of the channels and the centre points of the second circular arcs are not congruent.

(16) The cylinder Z has a radial width a along the first axis of symmetry SA1 and a radial height b along the second axis of symmetry SA2. The radial width a is greater than the radial height b.

(17) The cylinder Z has at an axial end a radially outwardly directed projection V. In this example embodiment, the projection V extends over the entire circumference of the cylinder Z. In alternative example embodiments, no projection is provided, or a projection is only provided in sections and/or a variable height of the projection is provided.

(18) FIG. 1b shows the wearing body according to the first example embodiment in the sectional view taken along section line 1b-1b of FIG. 1a, and FIG. 1c shows the wearing body according to the first example embodiment in the section view taken along section line 1c-1c of FIG. 1a. FIGS. 1b and 1c show that the cylinder Z has an axial length e, whilst the projection V has a shorter axial length f. The projection V has, in addition, a radial height h.

(19) FIGS. 2a, 2b and 2c show a wearing body according to a second example embodiment of the invention. Identical elements are given therein the same reference numbers as in the first example embodiment (FIGS. 1a, 1b and 1c). The explanations with regard to the first example embodiment also apply to the second example embodiment, in so far as they do not contradict the following explanations.

(20) In this example embodiment, the cylinder Z has an elliptical cross-section. Consequently, the first and second circular arcs KB1, KB1, KB2, KB2 are respectively arranged in a punctiform manner in the apexes of the ellipse and are connected with one another by an elliptical path. The main axis of the ellipse lies on the first axis of symmetry SA1. The secondary axis of the ellipse lies on the second axis of symmetry SA2. The first circular arcs KB1, KB1 lie on a circle, the diameter of which corresponds to the radial height b of the cylinder Z. The second circular arcs KB2, KB2 likewise lie on a circle, the diameter of which corresponds to the radial width a of the cylinder Z. In this example embodiment, the radius r2 of the second circular arcs KB2, KB2 is greater than the radius r1 of the first circular arcs KB1, KB1.

(21) The example embodiments are respectively supplemented by a housing body, complementary to the wearing body, an extrusion cylinder with a corresponding wearing body and/or housing body and a twin-screw extruder with a corresponding extrusion cylinder (not illustrated).

LIST OF REFERENCE SIGNS

(22) Z cylinder e length of the cylinder ZB twin borehole K, K channels of the twin borehole AK outer contour SA1 first axis of symmetry SA2 second axis of symmetry E point of intersection of the axes of symmetry EA extrusion axis a radial width of the oval/cylinder b radial height of the oval/cylinder KB1, KB1 first circular arcs KB2, KB2 second circular arcs r1 radius of the first circular arcs r2 radius of the second circular arcs r3 radius of the channels of the twin borehole KP contact point of the respective circular arcs MK, MK centre point of the channels of the twin borehole M1, M1 centre point of the first circular arcs M2, M2 centre point of the second circular arcs g angle of the axis through the respective centre points of the first and second circular arcs to the second axis of symmetry SA2 V radial projection f length of the projection h height of the projection