Injection moulding machine for producing fibre-reinforced plastic mouldings

Abstract

An injection moulding machine for producing fibre-reinforced plastic mouldings, having a closing unit and an injection unit, wherein the injection unit has a cylinder and a screw that can be rotated and displaced in the longitudinal direction in the cylinder, the screw having a backflow stop. In the cylinder, filling openings are provided for feeding in a plastic material to be melted and fibre material. To reduce fibre breakage and ensure good mixing, according to the invention a mixing part is provided downstream and/or upstream of the backflow stop, the mixing part being connected to the screw in a rotationally fixed manner for conjoint rotation therewith and having a cylindrical main body with drop-shaped mixing elements arranged thereon.

Claims

1. An injection molding machine (1) for producing fiber-reinforced plastic moldings, comprising: a closing unit (2); an injection unit (3) having a cylinder (4) and a screw (5) that can rotate in the cylinder (4) and be displaced in a longitudinal direction of the cylinder (4), wherein a first opening (8) is provided in the cylinder (4) as a filling opening for feeding in a plastic material to be melted, a second opening (9) is provided in the cylinder (4) downstream from the first opening (8) as a filling opening for feeding in a fiber material, and the screw (5) has a backflow stop (11); and a mixing part (12) that is connected with the screw (5) in a rotationally fixed manner and co-rotates with the latter, the mixing part (12) being provided downstream from the backflow stop (11) and/or upstream from the backflow stop (11), wherein the mixing part (12) has a cylindrical base body (13) with an outer diameter (D.sub.M) that is smaller than an inner diameter (D.sub.z) of the cylinder (4), and an annular gap (18) is formed between the base body (13) and an inner cylinder wall (17) of the cylinder (4), wherein a plurality of drops (14) as drop-shaped mixing elements (14) are distributed over a periphery of the base body (13) and arranged on a surface of the base body (13) that faces the inner cylinder wall (17), wherein a top view of each drop (14) reveals a longitudinal drop axis (L.sub.T), which runs from a pointed end (16) of the drop (14) to an opposing, rounded end (15) of the drop (14), and wherein a height (H) of each drop (14) over the base body (13) is smaller than a width (B) of the annular gap (18) between the base body (13) and inner cylinder wall (17).

2. The injection molding machine according to claim 1, wherein the drops (14) are arranged on the base body (13) and aligned in such a way that the rounded end (15) of each drop (14) lies at the front when viewed in a rotational direction of the mixing part (12).

3. The injection molding machine according to claim 1, wherein the longitudinal drop axis (L.sub.T) of each drop (14) forms an angle α of 45° to 90° with a longitudinal axis (A) of the screw (5).

4. The injection molding machine according to claim 3, wherein the longitudinal drop axis (L.sub.T) of each drop (14) forms an angle α of 60° to 85° with the longitudinal axis (A) of the screw (5).

5. The injection molding machine according to claim 1, wherein the drops (14) are arranged to form several rows (R) of drops (14) each row (R) being arranged next to another when viewed over the periphery of the base body (13).

6. The injection molding machine according to claim 5, wherein the drops (14) in adjacent rows (R) are arranged offset relative to each other when viewed in a longitudinal direction of the mixing part (12).

7. The injection molding machine according to claim 5, wherein a longitudinal axis (L.sub.R) of each row (R) of drops (14) forms an angle with a longitudinal axis (A) of the screw (5).

8. The injection molding machine according to claim 1, wherein at least a proportion of the drops (14) vary in orientation relative to each other, or are arranged on the base body (13) such that their longitudinal drop axes (L.sub.T) vary relative to each other.

9. The injection molding machine according to claim 8, wherein the orientations of the drops (14) alternate relative to the longitudinal axis (A), such that the longitudinal axes (L.sub.T) of the drops (14) alternatingly lie at an angle greater than 90° and an angle less than 90° relative to the longitudinal axis (A).

10. The injection molding machine according to claim 1, wherein at least a proportion of the drops (14) are arranged on the base body (13) with an opposing alignment, such that the rounded end (15) of some drops (14) lies at the front as viewed in a rotational direction of the mixing part (12), and the pointed end (16) of other drops (14) lies at the front as viewed in the rotational direction of the mixing part (12).

11. The injection molding machine according to claim 8, wherein the work shaft has a smooth surface in the area of the backflow stop (11), or that the shaft (21) of the backflow stop (11) has a smooth surface.

12. The injection molding machine according to claim 8, wherein: the backflow stop (11) is designed as an annular backflow stop and has a sleeve-shaped locking ring (23), and the locking ring (23) has a smooth surface on its interior side.

13. The injection molding machine according to claim 8, wherein the height (H) of each drop (14) is selected in such a way that an upper side of each drop (14) is spaced slightly apart from the inner cylindrical wall (17), wherein a distance between the upper side of each drop (14) and the inner cylinder wall (17) lies in a range of 0.02 to 2 mm.

14. The injection molding machine according to claim 13, wherein the height (H) of each drop (14) measures 80%-99% of the width (B) of the annular gap (18) between the base body (13) and inner cylinder wall (17).

15. The injection molding machine according to claim 13, wherein, in addition to the drop-shaped mixing elements (14), diamond-shaped mixing elements (25) are provided, wherein the drop-shaped mixing elements (14) and diamond-shaped mixing elements are alternatingly provided when viewed in a longitudinal direction of the mixing part (12).

16. The injection molding machine according to claim 4, wherein the longitudinal axis (L.sub.T) of each drop (14) forms an angle α of 70° to 73° with the longitudinal axis (A) of the screw (5).

17. The injection molding machine according to claim 13, wherein the distance between the upper side of each drop (14) and the inner cylinder wall (17) lies in a range of 0.1 to 0.5 mm.

18. The injection molding machine according to claim 1, wherein the backflow stop (11) and mixing part (12) are downstream from the second opening (9).

19. The injection molding machine according to claim 1, wherein the mixing part (12) is downstream from the backflow stop (11).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in greater detail below based on exemplary embodiments and drawing reference to FIGS. 1 to 8. Shown on:

(2) FIG. 1 is an injection molding machine according to the invention,

(3) FIG. 2A is a perspective view of a first embodiment of a mixing part according to the invention;

(4) FIG. 2B is a side view of a first embodiment of a mixing part according to the invention;

(5) FIG. 3A is a perspective view of a second embodiment of a mixing part according to the invention;

(6) FIG. 3B is a side view of a second embodiment of a mixing part according to the invention;

(7) FIG. 4A is a perspective view of a third embodiment of a mixing part according to the invention (oriented according to preferred angle);

(8) FIG. 4B is a side view of a third embodiment of a mixing part according to the invention (oriented according to preferred angle);

(9) FIG. 5A is a perspective view of a fourth embodiment of a mixing part according to the invention (varying drop orientation—first variant);

(10) FIG. 5B is a side view of a fourth embodiment of a mixing part according to the invention (varying drop orientation—first variant);

(11) FIG. 6A is a perspective view of a fifth embodiment of a mixing part according to the invention (alternating drop shape with other mixing geometries);

(12) FIG. 6B is a side view of a fifth embodiment of a mixing part according to the invention (alternating drop shape with other mixing geometries);

(13) FIG. 7A is a perspective view of a sixth embodiment of a mixing part according to the invention (varying drop orientation—second variant);

(14) FIG. 7B is a side view of a sixth embodiment of a mixing part according to the invention (varying drop orientation—second variant);

(15) FIG. 8 is a magnified view of the front end section of the screw with a correspondingly magnified view of the backflow stop and mixing part.

DESCRIPTION OF EXAMPLE EMBODIMENTS

(16) The injection molding machine 1 depicted on FIG. 1 essentially comprises a closing unit 2 only denoted schematically here along with an injection unit 3. The closing unit 1 and injection unit 3 are secured to a machine bed (not shown here) in a known manner. The spray unit 3 has a cylinder 4 with a screw 5. Several heating elements 19 are secured to the exterior side of the cylinder 4. The rear end of the screw 5 is operatively connected with a rotary drive 6 and a linear drive 7. Provided in the rear end area of the screw flights is a first opening as the filling opening 8 for feeding in a plastic material to be melted. Provided downstream from the first opening 8 in the cylinder 4 is a second opening as a filling opening 9 for feeding in a fiber material 10. The screw 5 has a backflow stop 11 at the front end. Provided downstream from the backflow stop 11 is a mixing part 12 that is connected with the screw 5 in a rotationally fixed manner and co-rotates with the latter. FIG. 8 presents a magnified view of the front end section of the screw 5 with a correspondingly magnified view of the backflow stop 11 and mixing part 12.

(17) With reference to FIGS. 2A to 7B and in conjunction with FIG. 8, various embodiments of the mixing parts according to the invention are to be described in greater detail.

(18) As evident from FIGS. 2A and 2B as well as FIG. 8, the mixing part 12 has a cylindrical base body 13, whose outer diameter D.sub.M is smaller than the inner diameter D.sub.Z of the cylinder 4, wherein an annular gap 18 is formed between the base body 13 and inner cylinder wall 17. Several drop-shaped mixing elements (drops) are arranged on the surface of the base body 13 facing the inner cylinder wall 17, distributed over the periphery of the base body 13. The selected height H of the drop-shaped mixing elements 14 over the base body 13 is smaller than the annular gap 18 between the base body 13 and inner cylinder wall 17. The drops 14 are here arranged on the base body aligned in such a way that the respectively rounded end 15 of a drop lies at the front viewed in the rotational direction of the mixing part, and the opposing pointed end 16 at the back. A longitudinal axis L.sub.T can be set when viewing a drop 14 from above, which runs from the pointed end 16 of the drop to the essentially opposing, rounded end 15 of the drop or vice versa. The drops 14 are arranged on the base body 13 in such a way that the respective longitudinal axis L.sub.T of a drop 14 forms an angle of 45° to 90° with the longitudinal axis A of the screw. The angles preferably range from 60° to 85°, and especially preferably from 70° to 73°. FIGS. 2A and 2B show an embodiment in which the angle is somewhat smaller than 90°, while FIGS. 3A and 3B show an embodiment with an angle of 90°.

(19) As a rule, several drops 14 are arranged one after the other on the base body viewed in the longitudinal direction of the mixing part 12. This forms a row R of drops 14. Let the row R with drops 14a, 14b and 14c on FIG. 3A be mentioned as an example. Several such rows R of drops are usually arranged one next to the other viewed over the periphery of the base body, as illustrated in the exemplary embodiments depicted here.

(20) The drops in adjacent rows can be arranged offset relative to each other viewed in the longitudinal direction of the mixing part, as shown on FIGS. 3A and 3B. It is further possible that the longitudinal axis LR of the rows of drops form an angle with the longitudinal axis A of the screw, as the case on FIGS. 2A and 2B.

(21) FIGS. 4A and 4B show an embodiment with an angle in an especially preferred range, here of 71.5°. This means that the longitudinal axis L.sub.T of the drops 14 includes an angle with the longitudinal axis A of the screw of α=71.5°.

(22) FIGS. 5A and 5B show an embodiment with a varying orientation for the drops. There is a first group of drops with reference number 14A, which are aligned as in the exemplary embodiments described above. This means that the respective rounded end 15 of a drop 14A lies at the front viewed in the rotational direction of the mixing part, and the opposing pointed end 16 at the back. Viewed in the peripheral direction, several drops 14A lie one after the other on a line, and together form a circle of drops 14A. In addition, there is a second group of drops with reference number 14B, which are aligned opposite to the drops 14B. This means that the respective pointed end 16 of a drop 14B lies at the front viewed in the rotational direction of the mixing part, and the opposing rounded end 15 at the back. Viewed in the peripheral direction, several drops 14B lie one after the other on a line, and together form a circle of drops 14B. As the result of such an arrangement of drops 14A and 14B, any fiber bundles that have remained nearly endless, i.e., nearly un-shortened, are shortened by the oppositely oriented drops 14B to a length at which the remaining drops 14A can exert their homogenizing effect. If the fiber bundles were to be conveyed un-shortened through the mixing part into the plastic molding, weak points and local fluctuations of the fiber concentration would arise in the plastic molding. In the present example, circles with drops 14A and circles with drops 14B alternate. If need be, however, a sequence of circles and/or arrangement of drops 14A and 14B other than that that from FIGS. 5A and 5B can be selected.

(23) FIGS. 6A and 6B show an embodiment in which the drop-shaped mixing elements 14 are alternatingly arranged with another form of mixing elements. On FIGS. 6A and 6B, diamond-shaped mixing elements 25 are depicted as the preferred embodiment of this other form of mixing element or mixing geometry. The diamond-shaped mixing elements 25 are arranged in such a way that there is a front tip 26 and rear tip 27 viewed in the rotational direction of the mixing part. The effect is comparable to the embodiment mentioned on FIGS. 5A and 5B. This means that the embodiment according to FIGS. 6A and 6B can also be used to shorten fiber bundles via the front tips 26. The advantage to the embodiment according to FIGS. 6A and 6B is that it can be produced at a lower cost than the embodiment according to FIGS. 5A and 5B. In terms of FIGS. 6A and 6B, what was said on FIGS. 5A and 5B applies with respect to the sequence of circles with drops 14 and diamonds 25, as well as to the arrangement of drops 14 and diamonds 25 on a circle taken in and of itself. If need be, a sequence of circles and/or an arrangement of mixing elements on a circle other than that from FIGS. 6A and 6B can thus be selected.

(24) FIGS. 7A and 7B show an embodiment in which the selected orientation of the drop shape is alternatingly greater or less than 90° relative to the longitudinal screw axis A. This means that the respective longitudinal axis L.sub.T alternatingly lies at an angle greater or less than 90° relative to the longitudinal screw axis A. A pulsating flow can be achieved with such an arrangement. As a result, the pulsating fiber-loaded melt runs through various pressure levels, and the fiber cluster that might have remained behind due to the resultantly generated extensional flow can be gently dissolved.

(25) As initially evident from FIG. 8, the backflow stop 11 is designed as an annular backflow stop. The latter comprises the following components (viewed from back to front): pressure ring 20, shaft 21, head 22 and locking ring 23. Provided for attachment in the worm shaft is a thread 24, which can be screwed into a matching thread of the worm shaft or screw 5. As opposed to the prior art mentioned at the outset (DE4236662C2, DE102009056653A1), both the worm shaft in the area of the back flow stop 11, i.e., the shaft 21 of the backflow stop, and the interior side of the locking ring 23 have a respective smooth surface. The mixing part 12 is connected with the screw 5 in a rotationally fixed manner downstream from the backflow stop. In the present exemplary embodiment, the mixing part is fastened by means of a pin 28 in a matching recess in the head 22 of the backflow stop 11.

(26) Further evident from FIG. 8 is how the mixing part 12 is designed relative to the inner cylinder wall 17. The mixing part 12 has a cylindrical base body 13 (see FIG. 2B), whose outer diameter D.sub.M is smaller than the inner diameter D.sub.Z of the cylinder 4, wherein an annular gap 18 is formed between the base body and inner cylinder wall 17. As evident from FIGS. 2A to 7B, several drop-shaped mixing elements or drops 14 are arranged on the surface of the base body 13 facing the inner cylinder wall 17, distributed over the periphery of the base body 13. The selected height H of the drop-shaped mixing elements 14 over the base body 13 is smaller than the annular gap 18 between the base body 13 and inner cylinder wall 17.

(27) The height H of the drops 14 on the upper side of the base body 13 should preferably be selected in such a way that the upper side of the drops is spaced only slightly apart from the inner cylinder wall 17. This distance can lie within a range of 0.02 to 2 mm, preferably within a range of 0.1 to 0.5 mm. However, the height of the drops 14 over the base body 13 can also be set as a function of the size of the annular gap 18 between the base body and inner cylinder wall. The height of the drops 14 over the base body 13 should preferably measure 96% of the width B of the annular gap 18. Expressed differently, this means that the drops 14 extend proceeding from the base body 13 in the radial direction away from the base body, and in so doing correspondingly protrude into the annular gap 18 by a specific percentage.

(28) The mixing part is arranged downstream from the backflow stop in the present exemplary embodiment. However, the mixing part can also be arranged upstream from the backflow stop. An inventive mixing part can possibly also be arranged on either side of the backflow stop. The same or different mixing parts can here be used.

(29) Additional details about the injection molding machine itself are known to the expert, and thus need not be described in any more detail at this juncture.

REFERENCE LIST

(30) TABLE-US-00001  1 Injection molding machine  2 Closing unit  3 Injection unit  4 Cylinder  5 Screw  6 Rotary drive  7 Linear drive  8 First filling opening-plastic material  9 Second filling opening-fiber material 10 Fibers 11 Backflow stop 12 Mixing part 13 Base body 14 Drop 14A Drop aligned in the rotational direction of the mixing part 14B Drop aligned opposite the rotational direction of the mixing part 15 Front, round end of a drop 16 Rear, pointed end of a drop 17 Inner cylinder wall 18 Annular gap 19 Heating element 20 Pressure ring 21 Shaft 22 Head 23 Locking ring 24 Thread 25 Diamond-shaped mixing element 26 Front tip 27 Rear tip 28 Pin A Longitudinal axis of screw D.sub.M Outer diameter of the base body D.sub.Z Inner diameter of the cylinder H Height of a drop over the base body L.sub.T Longitudinal axis of drop L.sub.R Longitudinal axis of row R Row of drops in the longitudinal direction of the mixing part