Abstract
A plasticizing screw for a molding machine, includes a base element which is stretched along a longitudinal axis and a screw tip which is connected to the base element, and the screw tip is located after the base element. A return flow shut-off device includes a first anterior limit stop, a second posterior limit stop, and a shut-off ring movable in a limited manner between the two limit stops along the longitudinal axis. The first, anterior limit stop comprises a first limit stop surface facing towards the base element and the shut-off ring. The shut-off ring comprises a ring-shaped screw tip abutting surface facing towards the first, anterior limit stop. The screw tip abutting surface is formed rotationally symmetric around the longitudinal axis, and the first limit stop surface comprises a convex curvature facing towards the shut-off ring.
Claims
1. A plasticizing screw for a molding machine, in particular an injection molding machine or an injection press, comprising: a base element which is stretched along a longitudinal axis, a screw tip which is connected to the base element, wherein the screw tip is arranged—in the direction of injection—after the base element, and a return flow shut-off device, wherein the return flow-shut off device comprises a first—in the direction of injection—anterior limit stop, a second—in the direction of injection—posterior limit stop and a shut-off ring being movable in a limited manner between the two limit stops along the longitudinal axis, wherein the at least one first, anterior limit stop comprises a first limit stop surface facing towards the base element and the shut-off ring and wherein the shut-off ring comprises a ring-shaped screw tip abutting surface facing towards the first, anterior limit stop, wherein the screw tip abutting surface is formed rotationally symmetric around the longitudinal axis, wherein the first limit stop surface comprises a convex curvature facing towards the shut-off ring.
2. The plasticizing screw as set forth in claim 1, wherein the screw tip comprises several radially protruding wings, preferably the wings having constant distances to each other.
3. The plasticizing screw as set forth in claim 2, wherein each wing jointly forms a first, anterior limit stop.
4. The plasticizing screw as set forth in claim 1, wherein the convex curvature is formed in such a way that in a sectional plane which includes the longitudinal axis the first limit stop surface at least in sections forms a convex curve.
5. The plasticizing screw as set forth in claim 4, wherein the convex curve has a continuous radius, preferably between 10 mm and 700 mm.
6. The plasticizing screw as set forth in claim 4, wherein the convex curve has at least two curve sections with different radii.
7. The plasticizing screw as set forth in claim 6, wherein a first curve section—arranged on a radially inner position relative to the longitudinal axis—has a larger radius than a second curve section arranged on a radially outer position relative to the longitudinal axis.
8. The plasticizing screw as set forth in claim 1, wherein the convex curvature is formed in such a way that in a sectional plane—which is formed as a cylinder jacket around the longitudinal axis—the first limit stop surface at least in sections forms a convex curve.
9. The plasticizing screw as set forth in claim 8, wherein the radius of the convex curve is in a range between 0.5 times the nominal diameter of the plasticizing screw and 2.5 times the nominal diameter of the plasticizing screw.
10. The plasticizing screw as set forth in claim 1, wherein the screw tip abutting surface has a concave curvature, preferably in the form of a negative torus surface.
11. The plasticizing screw as set forth in claim 10, wherein the screw tip abutting surface is evenly formed.
12. The plasticizing screw as set forth in claim 11, wherein the even screw tip abutting surface forms a plane which is oriented rectangular to the longitudinal axis.
13. The plasticizing screw as set forth in claim 10, wherein the shut-off ring—additionally to the screw tip abutting surface—comprises a ring-shaped base element abutting surface facing towards the second limit stop, an outer surface in the form of a cylinder jacket and an inner surface in the form of a cylinder jacket.
14. The plasticizing screw as set forth in claim 1, wherein the base element and the screw tip are formed as separate components, wherein the screw tip is detachably connected to the base element, preferably by means of a screw connection.
15. The plasticizing screw as set forth in claim 1, wherein a helical screw flight is formed on the base element.
16. An injection aggregate for a molding machine, comprising a plasticizing cylinder and the plasticizing screw as set forth in claim 1 rotatably arranged inside the plasticizing cylinder—in particular the plasticizing screw being movable along the longitudinal axis.
17. A molding machine comprising a closing unit and the injection aggregate as set forth in claim 16.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] Further details and advantages of the present invention are described more fully hereinafter by means of the specific description with reference to the embodiments by way of example illustrated in the drawings, in which:
[0044] FIG. 1 is a schematic side view of a molding machine together with an injection aggregate,
[0045] FIG. 2 is a partial longitudinal section through the return flow shut-off device during metering,
[0046] FIG. 3 is a partial longitudinal section through the return flow shut-off device with an exaggerated tumbling or wobbling motion,
[0047] FIG. 4 is a front view of the screw tip,
[0048] FIG. 5 is the cross section A-A according to FIG. 4,
[0049] FIG. 5a is an alternative detail to FIG. 4,
[0050] FIG. 6 is the cross section B-B according to FIG. 4,
[0051] FIG. 7a+7b are perspective views of the screw tip without shut-off ring from different points of view,
[0052] FIG. 8 is a simplified and perspective view of the convex curvature of the first limit stop surface,
[0053] FIG. 9+10 are simplified and perspective views of the convex curvature of the first limit stop surface with further details and
[0054] FIG. 11 is a longitudinal section similar to FIG. 3 with three layers with different hardness.
DETAILED DESCRIPTION OF THE INVENTION
[0055] In FIG. 1, a molding machine 2 is illustrated schematically. This molding machine 2 comprises a closing unit 13 and an injection aggregate 11.
[0056] The closing unit 13 comprises a stationary mold mounting plate 16, a movable mold mounting plate 17, a mold tool mounted to the mold mounting plates 16 and 17, a front plate 19 and a drive device 20 for the movable mold mounting plate 17. In the closed state of the mold tool 18 a cavity C is formed in the mold tool 18.
[0057] The injection aggregate 11 comprises a plasticizing cylinder 12 and plasticizing screw 1 which is movably supporter in the plasticizing cylinder 12. The plasticizing screw 1 is—about the longitudinal axis L—rotatably supported in the plasticizing cylinder 12. In addition, the plasticizing screw 1 is linearly movable in the direction of injection E along the longitudinal axis L. The plasticizing screw 1 is driven by a, preferably electromotive, drive device 14. The injection aggregate 11 also comprises a feed hopper 15 by way of which raw plastic material, preferably in the form of granules, can be fed into the plasticizing cylinder 12. The raw plastic material is melted in the region of the screw flights 10 by rotating the plasticizing screw 1 and by heating the plasticizing cylinder 12. For the injection of the raw plastic material melted to a melt, the plasticizing screw 1 is moved in the direction of injection E, whereby the melt is injected through the screw pre-chamber 22 via the injection channel into the cavity C.
[0058] The plasticizing screw 1 comprises the base element 3 and the screw tip 4. These two components can be formed in one piece. Preferably, these two components are formed as separate parts which are detachably connected to each other. In the region of the base element 3, for example, a helical screw flight 10 is formed. The screw tip 4 comprises a return flow shut-off device 5. This return flow shut-off device 5 comprises a first, in the direction of injection E anterior limit stop 6, a second, in the direction of injection posterior limit stop 7 and a shut-off ring 8 which is movable in a limited manner between the two limit stops 6 and 7 along the longitudinal axis L. The first, anterior limit stop 6 comprises a first limit stop surface A6 for the shut-off ring 8, the limit stop surface A6 is facing towards the base element 3 and the shut-off ring 8. The shut-off ring 8 comprises a ring-shaped screw tip abutting surface A8 facing towards the first, anterior limit stop 6, wherein the screw tip abutting surface A8 is formed rotationally symmetric around the longitudinal axis L. The shut-off ring 8—additionally to the screw tip abutting surface A8—comprises a ring-shaped base element abutting surface A3 facing towards the second limit stop 7 (together with the second abutting surface A7), an outer surface Za in the form of a cylinder jacket and an inner surface Zi in the form of a cylinder jacket.
[0059] FIG. 2 shows the screw tip 4 in a side view; the shut-off ring 8 and the plasticizing cylinder 12 are illustrated sectioned. It is visible that the outer surface Za of the shut-off ring 8 in the form of a cylinder jacket is distanced from the inner wall of the plasticizing cylinder 12 by the distance s. The shut-off ring 8 abuts with its, preferably even, screw tip abutting surface A8 the first limit stop surface A6 of the first, anterior limit stop 6. In the shown embodiment the screw tip 4 comprises several radially protruding wings 9 which are arranged at constant distances to each other. Each of these wings 9 forms a first, anterior limit stop 6. These wings 9 comprise—in addition to the first, anterior limit stop 6—a surface 23 (which jointly forms the conically formed tip of the screw tip 4) being remote from the first, anterior limit stop 6 and the opposing lateral surfaces 24 and 25, which limit and jointly form the longitudinal channels passing between the wings 9. Preferably, this surface 23 is inclined to the longitudinal axis L by an angle between 20° and 45°. In this FIG. 2 (and also in further Figures) the distance between the shut-off ring 8 and the first, anterior limit stop 6 and the second, posterior limit stop 7 is relatively small because of the schematic illustration. In real, these distances—and thus the scope of movement for the shut-off ring 8—are substantially larger.
[0060] In FIG. 2, the injection aggregate 11 is carrying out the metering. This metering takes place in that the plasticizing screw 1 is moved backwards relative to the plasticizing cylinder 12 (see the large arrow), thus, contrary to the direction of injection E. As a consequence, the melt located in the region of the screw flights 10 of the base element 3 are pressed forward in the direction of injection E (see the multitude of small arrows). By way of the melt pressure, the shut-off ring 8 is moved forward in the direction of injection E relative to the plasticizing cylinder 12 until the screw tip abutting surface A8 abuts the first limit stop surface A6 of the first, anterior limit stop 6. As a consequence, the melt can first flow through the gap between the shut-off ring 8 and the second limit stop surface A7. Then, the melt flows between the shut-off ring 8 and the smaller neck region 26 of the screw tip 7 and reaches—via the longitudinal channels limited by the wings 9—the screw pre-chamber 22. This metering is carried out until the plasticizing screw 1 has reached its rearmost position and the screw pre-chamber 22 is completely filled with melt.
[0061] For the injection the plasticizing screw 1 is then moved relative to the plasticizing cylinder 12 in the direction of injection E. The shut-off ring 8 (initially) cannot be jointly moved with the plasticizing screw 1 because of the melt located in the screw pre-chamber 22, so that the shut-off ring 8 reaches a position in which the base element abutting surface A3 abuts the second limit stop surface A7 of the second, posterior limit stop 7 of the return flow shut-off device 5. A return flow of the melt into the region of the base element 3 is prevented by way of this abutting. The entire melt located in the screw pre-chamber 22, thus, can be injected (for example after opening a shut-off needle which locks the injection channel 21) into the cavity C by a movement of the plasticizing screw 1 in the direction of injection E.
[0062] In FIG. 3 it is illustrated how relative movements between the components can occur especially during metering and a simultaneous rotary movement of the plasticizing screw 1 (see large arrow) because of the relative fast movements and because of the prevailing pressure in the plasticizing cylinder 12. Especially, tumbling motions occur. On the one hand, the plasticizing screw can carry out a tumbling motion about the longitudinal axis L.sub.Z of the plasticizing cylinder 12. This means, the longitudinal axis L of the plasticizing screw 1 deviates from the longitudinal axis L.sub.Z of the plasticizing cylinder 12 or tumbles around this axis. This tumbling motion is illustrated by the (exaggerated) angle β. On the other hand, also the shut-off ring 8 of the return flow shut-off device 5 can carry out a tumbling motion about the longitudinal axis L.sub.Z of the plasticizing cylinder 12 and/or about the longitudinal axis L of the plasticizing screw 1. This tumbling motion is illustrated by the (exaggerated) angle α. By way of these tumbling motion(s) high surface loads occur especially in the case of previously known return flow shut-off devices 5 because of deviations and deflections between the shut-off ring 8 and the first, anterior limit stop 6, which can lead to a premature malfunction of the return flow shut-off device 5.
[0063] In order to counteract this disadvantage, it is visible in FIG. 3 to some extent that the first limit stop surface A6 of the first, anterior limit stop 6 comprises a convex curvature facing towards the shut-off ring 8. As a consequence, a constant surface load as possible and a higher lifetime is reached. Specifically, the convex curvature is formed in such a way that in the section plane—which forms the sheet plane in FIG. 3 and includes the longitudinal axis L—the first limit stop surface A6 at least section-wise forms a convex curve K.
[0064] FIG. 4 shows a front view of the plasticizing screw 1 according to FIGS. 2 and 3. Specifically, this plasticizing screw 1 comprises a screw tip 4 and three wings 9 with the surfaces 23. The conical section 27 of the neck region 26 is visible in the region of the longitudinal channels between the lateral surfaces 24 and 25. In addition, the second limit stop surface A7 is visible. Further, the shut-off ring 8 and its screw tip abutting surface A8 are illustrated. The outermost circular line illustrates the inner wall 12i of the plasticizing cylinder 12.
[0065] The section line A-A is marked in FIG. 4. The section plane (including the longitudinal axis L) resulting from this section line A-A is illustrated schematically and simplified in FIG. 5. Especially, it is visible that the first limit stop surface A6 forms a convex curve K. This convex curve K forms a pitch circle with the radius r.
[0066] The center of this pitch circle is located distanced (or spaced) from the longitudinal axis L. In a preferred embodiment the radius r is between 10 mm and 700 mm.
[0067] Different than illustrated in FIG. 5, the convex curve K can also comprise several sections with different radii. Correspondingly, it is schematically illustrated in FIG. 5a that the convex curve K has two curve sections K1 and K2 with different radii. Accordingly, a first (relative to the longitudinal axis L) radially inner curve section K1 has a larger radius than a second (relative to the longitudinal axis L) radially outer curve section K2.
[0068] In FIG. 4, also the section line B-B is marked. This section line B-B corresponds to a section plane in the form of a cylinder jacket which is formed around the longitudinal axis L. When this section plane in the form of a cylinder jacket is outspread and “pressed flat”, this results in the schematically and simplified illustrated section plane B-B according to FIG. 6. As this section plane B-B mainly leads through the wings 9 and the shut-off ring 8, the corresponding components can be seen in FIG. 6. Specifically, the sections through the three wings 9 are illustrated, wherein each of these wings 9 comprises the two lateral surfaces 24 and 25, the conical surface 23 and the first limit stop surface A6. The shut-off ring 8 especially comprises the screw tip abutting surface A8 and the base element abutting surface A3. As illustrated in FIG. 6, the first limit stop surface A6 also in this section plane B-B has the form of a convex curve K. This convex curve K has the form of a pitch circle with the radius r. In a preferred embodiment this radius r is between 10 mm and 700 mm. Different than illustrated, the convex curve K can also have several sections with different radii. For example, it can be provided that a first curve section which is centrally arranged between the lateral surfaces 24 and 25 of the wing 9 jointly forming the first limit stop surface A6 has a smaller radius r than two second curve sections which are located nearer to the lateral surface 24 and 25. This means, the first limit stop surface A6 is flatter or less curved in a region which is near to the lateral surfaces than in the central region. Of course, this can also be formed conversely.
[0069] FIGS. 7a and 7b show perspective views of the screw tip 4 from different angles. The (fin-shaped) wings 9 directly merge in the tip of the screw tip 4 and form a displacement body 29. The shut-off ring 8 is not illustrated in FIG. 7. This shut-off ring 8 would be arranged around the small neck region 26 of the screw tip 4. The base element 3 is missing in these FIGS. 7a and 7b too. However, also the connection region 30 is illustrated in the FIGS. 7a and 7b. For example, this connection region 30 can comprise an external thread which corresponds with an internal thread formed in the base element 3. It is also illustrated in FIGS. 7a and 7b that the first limit stop surface A6 has a convex curvature.
[0070] FIG. 8 schematically illustrates the ball-like surface form of the limit stop surface A6. The spatial axis Z is oriented parallel to the longitudinal axis L. The two additional spatial axes X and Y are oriented rectangular to each other and are each rectangular to the spatial axis Z. The convex curvature of the first limit stop surface A6 is formed in a way which results in the angle δ relative to the spatial axis Y and in the angle ε relative to the spatial axis X.
[0071] FIG. 9 illustrates the ball-like surface form of the limit stop surface A6 just like FIG. 8. This ball-like surface or partial sphere surface allows an all-round uplift because the pressure occurring during closing can act onto the entire sphere surface. This pressure occurring during closing of the return flow shut-off device 5 (indicated in FIG. 9 by seven arrows) acts on all sides onto the limit stop surface A6. The shut-off ring 8 is raised from the wings 9 by this process, whereby the return flow shut-off device 5 closes very fast. The arrow with the reference sign F represents the resulting force F.
[0072] In FIG. 10, in turn, the limit stop surface A6 is illustrated as a partial sphere surface. The limit stop surface A6 can be made of at least two different materials each having a different wear resistance. For example, the hardness is a substantial parameter for the wear (or abrasion). Specifically, the layers R1, R2 and R3 (illustrated as concentric rings)—consisting of different powders—are welded onto the surface. This leads to different abrasion properties. The lifetime is determined by the hardest layer R3. This layer R3 has the highest resistance against wear. The layers R2 (middle concentric ring) and R3 (outermost concentric ring) which are located further outward have a smaller and decreasing abrasion resistance. These layers R2 and R3, thus, already wear in the case of a smaller resistance. By way of this structure a constant abrasion of the limit stop surface A6 is reached so that a sphere-like surface remains also after a longer operating time. By this maintenance of the convex form (sphere surface) the pressure (described in FIG. 9) is still acting all-round, whereby the closing properties of the return flow shut-off device 5 remains over the whole lifetime on a high level.
[0073] Referring to FIG. 10, the center of the concentric layers R1, R2 and R3 forms the point of the (partial) sphere surface of the limit stop surface A6 which is nearest to the shut-off ring 8. In this case, the center point which has the largest distance to the edge coincides with the point which is nearest to the shut-off ring 8. In addition, in this embodiment the sphere center point has the same distance to the longitudinal axis L (extending in the direction z) as the point which is nearest to the shut-off ring 8.
[0074] FIG. 11 is a cross section of the return flow shut-off device 5 together with the shut-off ring 8, wherein the shut-off ring 8 is illustrated in a (slightly exaggerated) inclined position. The limit stop surface A6 of the wing 9 comprises the layers R1, R2 and R3, each having a different hardness. In this case, the layer R1 can consist of the base material (for example steel). The hardness of the layer R2 is larger than the hardness of the layer R1. The hardness of the layer R3, in turn, is larger than the hardness of the layer R2. The closer the layer is located to the longitudinal axis L, the larger is the hardness of the layer. The layers R1, R2 and R3 are each arranged (partially) circular around the longitudinal axis L.
LIST OF REFERENCE SIGNS
[0075] 1 plasticizing screw [0076] 2 molding machine [0077] 3 base element [0078] 4 screw tip [0079] 5 return flow shut-off device [0080] 6 first, anterior limit stop [0081] 7 second, posterior limit stop [0082] 8 shut-off ring [0083] 9 wings [0084] 10 screw flight [0085] 11 injection aggregate [0086] 12 plasticizing cylinder [0087] 12i inner wall of the plasticizing cylinder [0088] 13 closing unit [0089] 14 drive device for the plasticizing screw [0090] 15 feed hopper [0091] 16 stationary mold mounting plate [0092] 17 movable mold mounting plate [0093] 18 mold tool [0094] 19 front plate [0095] 20 drive device for the movable mold mounting plate [0096] 21 injection channel [0097] 22 screw pre-chamber [0098] 23 surface of the wings [0099] 24 lateral surface of the wings [0100] 25 lateral surface of the wings [0101] 26 neck region [0102] 27 conical section [0103] 29 conical displacement body [0104] 30 connection region [0105] A3 base element abutting surface [0106] A6 first limit stop surface [0107] A7 second abutting surface [0108] A8 screw tip abutting surface [0109] L longitudinal axis [0110] E direction of injection [0111] K convex curve [0112] K1 first curve section [0113] K2 second curve section [0114] Za outer surface in the form of a cylinder jacket [0115] Zi inner surface in the form of a cylinder jacket [0116] C cavity [0117] s distance of the shut-off ring to the plasticizing cylinder [0118] L.sub.Z longitudinal axis of the plasticizing cylinder [0119] β angle of the tumbling motion of the longitudinal axis L about the longitudinal axis L.sub.Z [0120] α angle of the tumbling motion of the shut-off ring [0121] r radius of the convex curve K of the first limit stop surface A6 [0122] δ angle to the spatial axis y [0123] ε angel to the spatial axis x [0124] X spatial axis [0125] Y spatial axis [0126] Z spatial axis [0127] F resulting force [0128] R1 layer [0129] R2 layer (with medium hardness) [0130] R3 (hardest) layer
