BACKCURVE

Description

[0001] The present invention relates to a backflow preventer for a plasticizing screw of an injection molding machine. The invention further relates to an injection molding machine with such a backflow preventer and to a method for operating such an injection molding machine.

[0002] Non-return valves, as a particularly removable component of a plasticizing screw, have a decisive influence on the quality of an injection-molded part. Among the problematic and quality-reducing issues in this context are unwanted plastic deposits that can form below the locking sleeve during operation of the injection molding machine, specifically between the locking sleeve and the intermediate section of the base body. These deposits can, for example, detach sporadically and become unintentionally visible on the surface of the injection-molded part.

[0003] Document US 6,270,703 B1 shows a backflow preventer in which an intermediate section of a base body has axially aligned rows of teeth with individual teeth. These rows of teeth are not suitable for conveying the plastic mass located between the intermediate section and the pressure ring towards the tip of the base body. The intermediate section of a base body in JP 2017 056655 shows a conveying element designed as a raised section for conveying the plastic mass, but this element is not intended for preventing or removing ring-shaped deposits. WO 2007 / 030913 A1 also shows only a similar – albeit with a dashed line – conveying element, which is not intended for preventing or removing deposits.

[0004] Further undesirable deposits can form in the area of ​​the terminal nozzle of the plasticizing cylinder, into which the end of the base body, or its tip along with the vanes, is immersed during the injection process. These deposits can also detach during operation and become visible on the injection-molded part, or lead to blockages in the fluid channel leading from the nozzle to the cavity of the injection mold, through which the liquid plastic material passes from the plasticizing cylinder into the injection mold.

[0005] The JP 2000 158499 A and JP S51 6257 A show a screw tip equipped with several elements designed to remove deposits.

[0006] Based on this, the object of the present invention is to further develop the aforementioned backflow preventer, in particular in such a way that the aforementioned deposits in the nozzle of the plasticizing cylinder and / or in the area between the locking sleeve and the intermediate section of the base body of the backflow preventer can be prevented, reduced or removed.

[0007] This problem is solved by a backflow preventer of the type mentioned above with the features of claim 1, an injection molding machine with such a backflow preventer with the features of claim 6 and a method for operating the injection molding machine with the features of claim 10.

[0008] A backflow preventer according to the invention is characterized in that the intermediate section of the base body and / or the wings thereof have one or more elongated, in particular web- or rib-like, active elements which, during operation of the injection molding machine, can counteract the formation of disruptive, ring-shaped, circumferential plastic deposits or which can remove such plastic deposits that have already formed.

[0009] According to the invention, one or more of the elongated working elements are therefore assigned to the intermediate section of the base body and / or to one or more wings thereof.

[0010] Regarding the first variant according to the invention, namely the arrangement with the intermediate section, each of the elongated active elements forms a protrusion on the outside of the intermediate section of the base body. This prevents the formation of ring-shaped, circumferential deposits of plastic between the intermediate section and the locking sleeve. The elongated active elements act circumferentially as interrupters that can prevent or reduce the formation of a closed deposit ring. Advantageously, they extend as close as possible to the inside of the locking sleeve for this purpose.

[0011] The intermediate section of the base body has three elongated working elements spaced apart from each other in the circumferential direction of the intermediate section.

[0012] As regards the basic shape of the intermediate section of the base body, the intermediate section is a cylindrical body or a conical body with a correspondingly cylindrical or conical surface, on which each of the elongated working elements is arranged, in particular attached or molded, so that each of the elongated working elements protrudes from this surface, forming the respective elevation of the outside of the intermediate section of the base body.

[0013] Each of the elongated working elements spaced apart from one another in the circumferential direction extends at least section by section, preferably over its entire length, obliquely or at an angle according to the invention to the (imagined) generatrix lines of the lateral surface of the cylindrical or conical body of the intermediate section of the base body.

[0014] In other words, each of the elongated working elements extends at an angle to the transverse plane perpendicular to the longitudinal or rotational axis of the base body, in which the intermediate section rotates. The respective angle to this transverse plane can be constant, but it can also change along the intermediate section.

[0015] The orientation of the elongated working elements, or their respective inclination, is preferably selected such that each elongated working element acts as a conveying element, which, during the operation of the injection molding machine during the plasticizing and dosing phase, in which the plasticizing screw together with the base body of the non-return valve is rotated around its longitudinal axis, conveys the plastic mass through the correspondingly rotating elongated working element(s) towards the vanes. In other words, each of the elongated working elements acts like a conveying vane of a conveyor wheel.

[0016] Each of the elongated active elements defines a flow channel for the plastic on both sides in the circumferential direction, the bottom side of which is formed by a segment of the lateral surface of the cylindrical or conical body.

[0017] Each pair of circumferentially adjacent, spaced-apart elongated active elements can define a flow channel, the bottom side of the flow channel being formed by the segment of the lateral surface of the cylindrical or conical body of the intermediate section of the base body arranged between the two elongated active elements.

[0018] Along the respective flow channel, the (plasticized / liquid) plastic flows during operation of the injection molding machine towards the end of the base of the non-return valve (or the plasticizing screw, of which it is an end component during operation) towards the nozzle of the plasticizing cylinder. This occurs particularly during the plasticizing and dosing phases.

[0019] Particularly preferred is the radial distance between the inside of the locking sleeve and the outer surface of the cylindrical or conical body of the intermediate section of the base body selected by appropriate coordination of the relevant dimensions in such a way that, on the one hand, good flow of the plastic mass through the resulting flow channel between the inside and outer surface is possible and, on the other hand, the highest possible flow velocity is achieved.

[0020] For this purpose, the radial distance between the inside of the locking sleeve and the outer surface of the cylindrical or conical body of the intermediate section of the base body preferably has a value that lies in an interval between 1 mm and 6 mm, particularly preferably between 2 mm and 5 mm.

[0021] Furthermore, it is advantageous that each of the active elements terminates as close as possible to the inside of the locking sleeve. Preferably, the radial distance between the inside of the locking sleeve and the opposing elongated active element, in particular the outer surface or outer edge of the elongated active element facing the inside of the locking sleeve, is less than 0.2 mm, preferably less than 0.1 mm.

[0022] Regarding the second variant of the invention described above, namely the assignment of one or more elongated active elements to one or more wings of the base body, it is preferably provided that each wing of the base body has such an elongated active element, in particular one that is formed on or attached to the respective wing (18).

[0023] This is done in such a way that, during operation of the injection molding machine, any plastic deposits that may occur in the area of ​​the terminal nozzle of the plasticizing cylinder are removed or milled off by the elongated working elements when the wings rotate in a suitable position in the nozzle.

[0024] For this purpose, the elongated working element of each wing has or is formed by a free, radially outwardly directed, preferably linear longitudinal edge or outer edge, in particular designed as a milling edge.

[0025] In this process, the radially outward-facing free (outer) sides or free (outer) edges of the elongated active elements of the wings converge conically towards a free end of the backflow preventer or the base body.

[0026] In the context of the interaction of such a backflow preventer, in which one or more wings are equipped with one or more elongated working elements, with the injection molding machine in general, in particular with its plasticizing cylinder, the end region of the base body of the backflow preventer, which has the wings, dips in a known manner into a nozzle of the injection molding machine, in particular one end of the plasticizing cylinder, which is fluidly connected to a cavity of the injection molding machine that can be filled with plastic compound.Preferably, the base body is adapted to the contour of the particularly conical inner surface of the nozzle with the wings and the elongated working elements in such a way that the free outer surface or the free, in particular as a milling edge, particularly elongated and linear outer edge of the elongated working elements or each of the elongated working elements faces the inner surface of the nozzle and, in particular for the removal of interfering plastic deposits, runs parallel to one or the immediately opposite section of this inner surface in an immersion position.

[0027] A method according to the invention for operating an injection molding machine of the aforementioned type is characterized accordingly in that, during the injection process, the plasticizing screw comprising the backflow preventer is controlled for the removal of interfering plastic deposits arranged on the inside of the nozzle in such a way that the end region of the base body of the backflow preventer, together with the vanes, is moved into an immersion position in which the free outer side or outer edge of the elongated working element(s) facing the inside of the nozzle runs parallel to one or the immediately opposite section of this inner side and in which the radial distance of the outer side or outer edge of the elongated working element(s) is selected such that interfering plastic deposits on the inside of the nozzle are removed or can be removed by the working element(s).

[0028] Preferably, in this immersion position, the radial distance of the outer side or outer edge of the elongated working element from the immediately opposite section of the inner side of the nozzle is less than 1 mm, preferably less than 0.5 mm, so that the working element or elements move as close as possible to the inner side of the nozzle during a rotational movement of the vanes and can thereby capture / remove even thin deposits during a milling process.

[0029] As regards the nozzle, its inner surface can preferably be continuously conical without steps or rounding, in particular from an outer opening plane of the nozzle to an inner end section.

[0030] Further features of the invention will become apparent from the attached claims, the following description of preferred embodiments of the invention, which are to be understood as exemplary only and not as limiting, and from the attached drawing. This drawing shows: Fig. 1 shows a sectional view of a backflow preventer according to the invention together with a flange having a nozzle of a plasticizing cylinder of an injection molding machine which is not otherwise shown.

[0031] In the Fig. 1A schematic representation of a non-return valve 10 is shown, as it can be used as a potentially detachable component of a (otherwise not shown) plasticizing screw in a plasticizing cylinder 11 of an injection molding machine, forming the screw tip 30. The non-return valve 10 is generally rotationally fixed but detachably connected to the rest of the plasticizing screw, for example by screws. A permanent connection is also conceivable, of course.

[0032] The plasticizing cylinder 11 is in Fig. 1 only a terminal flange 12 is shown, in which a nozzle 13 of the plasticizing cylinder 11 is arranged, which in turn is fluidly connected in a known manner via a fluid channel 14 to the cavity of an injection molding tool of the injection molding machine.

[0033] The basic structure of an injection molding machine is well known from the prior art, so further components of it are not shown for the sake of simplicity.

[0034] The backflow preventer 10 has a (in this case solid) base body 15, usually made of steel, which has a front free end 17 (terminal tip of the screw or the backflow preventer 10) in an end area 16.

[0035] In the end region 16 of the base body 15, namely adjacent to the free end 17, several wings 18 are arranged distributed around the circumference, between which flow channels 19 for the (not shown) plasticized or liquid plastic mass are formed in the circumferential direction.

[0036] The base body 15 of the backflow preventer 10 further comprises an intermediate section 20 with a cylindrical body 21, which directly adjoins the vanes 18 and is integrally connected to them. At least theoretically, it is also conceivable that the body 21 has a slightly conical shape.

[0037] A locking ring or a locking sleeve 22 is arranged coaxially to this intermediate section 20 at a radial distance to the cylindrical body 21.

[0038] The locking sleeve 22 is axially movable in a known manner. When the locking sleeve 22 moves axially towards the end region 16 of the base body 15 or towards the wings 18, it abuts the end region 16, in this case the bottom sides of the wings 18, in a known manner. When moving in the opposite direction, it abuts a pressure ring 23, which is also known per se and is rotationally fixed to the base body 15, namely, in this case, on a cylindrical pin 24 adjacent to and integrally connected with the intermediate section 20.

[0039] In a manner also known per se, during the plasticizing or metering phase of the injection molding machine, the liquefied plastic mass displaces the locking sleeve 22 towards the end region 16 or the free end 17 of the base body 15, thereby creating a gap between the locking sleeve 22 and the pressure ring 23 through which the liquid plastic can flow. During the subsequent injection phase, the molten plastic in the screw chamber of the plasticizing cylinder 11 then presses the locking sleeve 22 back against the pressure ring 23, thus closing this gap.

[0040] During operation of the injection molding machine, unwanted, particularly ring-shaped, plastic deposits form between the intermediate section 20 of the base body 15 and the locking sleeve 22 in known non-return valves. These deposits can negatively affect the quality of the injection-molded parts produced by the machine. For example, these deposits can detach from time to time and become unintentionally visible on the surface of the respective injection-molded part.

[0041] To prevent this, the intermediate section 20 has a cylindrical body 21 with a correspondingly cylindrical surface 21a and elongated, in this case web-like, working elements 25 arranged on it. The elongated working elements 25 can be directly integrally formed, i.e., integrally connected with the cylindrical body 21, but of course they can also be attached to the cylindrical body 21, for example by welding to it.

[0042] As can be seen, several of these elongated active elements 25 are present in the circumferential direction of the cylindrical body 21 or the intermediate section 20, each spaced apart from the others (in relation to the circumferential direction).

[0043] Between two circumferentially adjacent elongated active elements 25, corresponding flow channels or flow channels 26 for the liquid plastic are formed, each of which is bounded on the bottom side by a segment 27 of the outer surface 21a arranged between the elongated active elements 25.

[0044] The elongated active elements 25 act circumferentially as interrupters, preventing the formation of a closed deposit ring. Advantageously, they extend as close as possible to the inner surface 28 of the locking sleeve 22. In the present example, the distance between the outer surfaces 29 of the respective elongated active elements 25 facing the inner surface 28 of the locking sleeve is less than 0.2 mm.

[0045] The elongated active elements 25 run - as can be clearly seen - obliquely or at an angle to the axial or longitudinal axis of the backflow preventer 10. In other words, the elongated active elements 25 run - in this case over their entire longitudinal extent - obliquely or at an angle to (the imaginary) generatrix of the lateral surface 21a.

[0046] The orientation of the elongated working elements 25, or their respective inclination, is selected such that each elongated working element 25 acts as a conveying element. During the operation of the injection molding machine, in the plasticizing and dosing phase, in which the plasticizing screw, together with the base body 15 of the non-return valve, is rotated about its longitudinal axis, the plastic mass is conveyed by the co-rotating elongated working elements 25 towards the free end 17 of the non-return valve 10. This increases the flow rate of the liquid plastic mass in the area of ​​the intermediate section 20 compared to non-return valves without such elongated working elements 25.

[0047] By appropriately adjusting the relevant dimensions, the radial distance between the inner surface 28 of the locking sleeve 22 and the outer surface 21a of the cylindrical body 21 of the intermediate section 20 of the base body 15 is chosen so that, on the one hand, good flow of the liquid plastic mass through the respective flow channel 26 between the inner surface 28 and the outer surface 21a is possible and, on the other hand, the highest possible flow velocity is achieved.

[0048] For this purpose, the radial distance between the inner surface 28 of the locking sleeve 22 and the lateral surface 21a of the cylindrical body 21 of the intermediate section 20 of the base body 15 has a value in the present case that lies in an interval between 2 mm and 4 mm.

[0049] Plastic deposits can also form on the conically tapered inner surface 33 of the nozzle 13. To remove these deposits during operation of the screw or when the base body 15 of the non-return valve 10 is rotating, the vanes 18 are also equipped with elongated working elements 30. In this case, one working element 30 is arranged on each vane 18, specifically on one of the outer surfaces 31 of each vane 18 facing the inner surface 33 of the nozzle 13 (either molded or attached there).

[0050] In the following case, each elongated functional element 30 has an elongated outer edge 32, which serves as a milling edge. In the Fig. 1In the immersion position of the base body 15 shown, these elongated outer edges 32 each run parallel to a section of the inner surface 33 directly opposite it, at a small distance. This parallel alignment of the outer edges 32 to the inner surface 33 is maintained throughout the entire rotation in the immersion position shown, so that the outer edges rotate with the smallest possible, constant distance to the inner surface 33. In this way, the elongated working elements 30 are moved as close as possible to the inner surface 33 of the nozzle 13 during the rotational movement of the vanes 18 and can then capture and remove even thin deposits during a milling process.

[0051] In the present embodiment, in this immersion position, the radial distance of the outer edges 32 to the immediately opposite section of the inner surface 33 of the nozzle 13 is less than 1 mm. Reference symbol list

[0052] 10 Backflow preventer 11 Plasticizing cylinder 12 Flange 13 Nozzle 14 Fluid channel 15 Base body 16 End section 17 Free end 18 Vane 19 Flow channels vane 20 Intermediate section 21 Cylindrical body 21a Shell surface 22 Locking sleeve 23 Pressure ring 24 Pin 25 Actuating elements intermediate section 26 Flow channels intermediate section 27 Segment 28 Inside of locking sleeve 29 Outside of acting elements 30 Actuating elements vane 31 Outside surface vane 32 Outer edge 33 Inside of nozzle

Claims

1. Non-return valve for a preplastifying spindle of an injection molding machine, comprising a base body (15) with wings (18) arranged in an end section (16), a pressure ring (23) connected to the base body (15) and a locking sleeve (22) that can be moved axially relative to the base body (15), having preferably a cylindrical inner surface, which surrounds an intermediate section (20) of the base body (15) arranged between the wings (18) and the pressure ring (23) at a radial distance, wherein the intermediate section (20) of the base body (15) and / or the wings (18) of the base body (15) have elongated working elements (25, 30), wherein the working elements (30) of the wings (18) can counteract the formation of disruptive plastic deposits during operation of the injection molding machine, and wherein the intermediate section (20) of the base body (15) is a cylindrical or conical body with a correspondingly cylindrical or conical outer surface, on which three elongated working elements (25) are arranged, wherein the elongated working elements (25) are spaced apart from one another in the circumferential direction of the intermediate section (20), characterized in that each of the elongated working elements (25) of the intermediate section (20) of the base body (15) delimits a flow channel for the plastic in the circumferential direction on each of its two sides, the bottom side of which is formed by a segment of the lateral area of the body of the intermediate section (20), and forms a raised portion on the outer side of the intermediate section (20) in such a way that the formation of annular closed, circumferential deposits of plastic between the intermediate section (20) and the locking sleeve (22) is prevented, wherein each of the elongated working elements (25) of the intermediate section (20) runs at least in sections obliquely to imaginary generatrices of the lateral surface of the cylindrical or conical body of the intermediate section (20), wherein each of the elongated working elements (25) of the intermediate section (20) is not arranged circumferentially on the lateral surface of the intermediate section (20), and / or each wing (18) of the base body (15) has an elongated working element (30) which has a free, radially outwardly facing elongated outer edge or is formed by such an edge, wherein these outer edges of the wings (18) conically taper towards each other in the direction of a free end of the base body (15).

2. Non-return valve according to claim 1, characterized in that each of the elongated working elements (25) of the intermediate section (20) is attached to or formed on the body of the intermediate section (20).

3. Non-return valve according to one or more of the preceding claims, characterized in that each of the elongated working elements (25) of the intermediate section (20) runs obliquely to the imaginary generatrices of the lateral surface of the cylindrical or conical body of the intermediate section (20) over the entire length thereof.

4. Non-return valve according to one or more of the preceding claims, characterized in that the radial distance between the inner side of the locking sleeve (22) and the respective opposite elongated working element (25), in particular an outer side or outer edge of the elongated working element (25) facing the inner side of the locking sleeve (22), is less than 2 mm, preferably less than 1 mm.

5. Non-return valve according to one or more of the preceding claims, characterized in that the radial distance between the inner side of the locking sleeve (22) and the outer surface of the cylindrical or conical body of the intermediate section (20) of the base body (15) has a value that lies within an interval between 1 mm and 6 mm, particularly preferably between 2 mm and 5 mm.

6. Non-return valve according to one or more of the preceding claims, characterized in that one or more or each wing (18) of the base body (15) has (if applicable, each) an elongated working element (30), the working element (30) being especially formed on or attached to the respective wing (18).

7. Injection molding machine with a non-return valve according to one or more of the preceding claims 1-6.

8. Injection molding machine according to claim 7, characterized in that the injection molding machine has a nozzle (13) arranged in particular in a flange (13) and connected in a fluid-conducting manner to a cavity of the injection molding machine that can be filled with plastic material, into which, during the injection process, the end section (16) of the base body (15) of the non-return valve immerses together with the wings (18), wherein the base body (15) with the wings (18) and the elongated working element(s) (30) is adapted to the contour of the particularly conically tapering inner side of the nozzle (13) in such a way that the free outer side or the free, in particular elongated and linear outer edge of the or each of the elongated working elements (30), in particular designed as a milled edge, faces the inner side of the nozzle (13) and, in particular for removing disruptive plastic deposits, runs parallel to one or the respective directly opposite section of this inner side in an immersed position.

9. Injection molding machine according to claim 8, characterized in that, in this immersion position, the radial distance between the outer side or outer edge of the or each of the elongated working elements (30) and the respective directly opposite section of the inner side of the nozzle (13) is less than 0.2 mm, preferably less than 0.1 mm.

10. Injection molding machine according to claim 8 or 9, characterized in that the inner side of the nozzle (13) is continuously conical without any steps or roundings, in particular from an outer opening plane of the nozzle (13) to an inner end section.

11. Method for operating an injection molding machine according to claims 7 to 10, wherein during the injection process, the preplastifying spindle comprising the non-return valve is controlled to remove disruptive plastic deposits located on the inner side of the nozzle (13) in such a way that the end section (16) of the base body (15) of the non-return valve is moved together with the wings (18) into an immersion position in which the free outer side or outer edge of the or each of the elongated working elements (30) facing the inner side of the nozzle (13), runs parallel to one or the respective directly opposite section of this inner side, and in which the radial distance of the outer side or outer edge of the or each of the elongated working elements (30) is selected such that disruptive plastic deposits on the inner side of the nozzle (13) are or can be removed by the working element (30), in particular selected such that the distance from the respective directly opposite section of the inner side of the nozzle (13) is less than 0.2 mm, preferably less than 0.1 mm.