KR20070048198A - Backflow stop for injection molding machines - Google Patents

Abstract

The invention is arranged concentrically on the longitudinal axis of the screw head 10 and the intermediate portion 14 having a distal end 12, an intermediate portion 14, a pressure ring 16 and a mounting end 20. A backflow preventing device for an injection molding machine, comprising a stop ring (18) forming an annular gap (22) together with the intermediate portion. The stop ring 18 is axially movable relative to the screw head 10 by the stroke A between the passing position and the blocking position, and includes an opening 32 for passing the plastic melt. The distal end 12 comprises a recess 40 in such a way that a slider 42 having a length L≥A greater than or equal to A is formed, which has an inner surface 34 of the stop ring 18. It abuts so that a movement to an axial direction and a circumferential direction is possible. In injection molding the plastic melt can only flow back through the opening 32. The inflowable cross section can be expanded by forming a leading edge 54 and / or by providing one or more channels 50 at the distal end 12.

Description

Backflow prevention device for injection molding machine {BACKFLOW STOP FOR INJECTION MOLDING MACHINES}

The present invention relates to a backflow preventing device for an injection molding machine according to the preamble of claim 1.

This type of backflow prevention device is installed at the discharge end of the plastic screw in the injection cylinder, acting as a "valve" to prevent the plasticized plastic material from being pressed back into the screw flight during the injection process.

A backflow prevention device according to the preamble of claim 1 is known from DE 198 36 871. In the known reverse flow prevention device, the stop ring is arranged concentrically in the middle of the screw head so as to be movable in the axial direction and the circumferential direction between the open position and the shut off position, in which the end face of the stop ring is the screw. In contact with a stop face on the back of the head end, the stop ring abuts the compression ring of the screw head in the blocking position. In other words, the stop ring is not forcibly moved together by the screw head as the screw rotates. In the following, the section in which the stop ring is displaced with respect to the screw head is called stroke A. The stop ring forms an annular gap with the intermediate portion and has holes for passing material near the end face. In the open position, the end face of the stop ring abuts the stop face of the distal back, and the plastic melt can pass through the holes and then flow through the distal end of the screw head into the screw entry chamber.

At the beginning of injection molding, the stop ring is in the open position mentioned above. The forward movement of the screw causes the plastic melt to flow in the direction of the stop ring and to move the stop ring back towards the screw. The stop ring is thereby released from the stop face of the distal end. Stroke A shrinks shorter (A '). As a result, the plastic melt can increase further and flow through the annular gap between the inner diameter of the stop ring and the outer diameter of the intermediate portion. Therefore, some pressure compensation is achieved through the backflow prevention device immediately after the start of injection molding. As a result of the injection molding process, pressure builds up in the screw entry chamber to pressurize the plastic melt through the backflow prevention device that is not yet closed, and the stroke of the stop ring continues to shrink. This stroke reduction of the stop ring is caused by the pressure loss appearing in the direction of the compression ring along the stop ring and the shear stress occurring on the stop ring as a result of the movement of the screw head. As a result of the stroke reduction, the permeable cross section between the stop ring and the compression ring becomes smaller and smaller, increasing the pressure in the region. As a result, the pressure difference formed along the stop ring can be reversed. As a result, further movement of the stop ring in the direction of the compression ring is delayed or blocked, which adversely affects the closing operation of the backflow prevention device.

In addition, the backflow prevention device known from DE 100 59 615 A1 comprises a plurality of melt lines in the form of bores in which the stop rings are not connected to one another. The stop ring is guided over the shoulder of the screw head which is smaller than the screw head outer diameter and follows at the peak. That is, the stop ring is forcibly rotated together with the base body of the backflow prevention device when the screw rotates. In this embodiment, the disadvantage is that measures must be taken to minimize the wear action of the stop ring forcibly rotating together on the inner wall of the plastic cylinder corresponding to the stop ring. This is because, in order to do so, the gap width between the components must be selected sufficiently large. This plays an important role, especially when the screw diameter is large. As a result of this action, however, a leakage flow from the screw entry chamber back through the gap after the stop ring is closed, so that the required dwell pressure for injection molding may not be provided as desired. In addition, the shear stress sensitivity of the plastic should be taken into account when dimensioning the gap width. Since there is a melt film in the gap, too narrow the gap will exert a large shear force on the plastic, which causes decomposition, discoloration or denaturation of the additive (eg oxidation of flame retardant additives). The melt component so modified enters the cavity with the clean melt, causing a deterioration of the finished molded article. In addition, too large a gap leads to the leakage flow already mentioned. As a result, in such an implementation, there is a tradeoff between low leakage flow (maximum small gap width) and, on the one hand, less wear of the backflow prevention device and cylinder and, on the other hand, a small shear stress (maximum large gap width) in the plastic. This is necessary.

The present invention therefore aims to further improve the device such that the backflow prevention device of the type mentioned in the introduction has better closing properties and less wear and material damage to the inner surface of the cylinder.

This object is achieved by a backflow prevention device having the features of claim 1 and the dependent claims relate to a preferred refinement of the invention.

According to the invention the distal end comprises a slider in which the distal end has a diameter D _GL in the region between the intermediate part and the stop face of the intermediate part, the inner surface of the stop ring being axially oriented with respect to the distal end and the intermediate part in the slider. And a recess in the area in such a way as to be able to move in a circumferential direction, wherein the slider has a length L longer than the stroke A of the stop ring, the stop ring being the base body of the backflow prevention device. It is not forcibly driven in the circumferential direction by the (screw head). This action prevents the plastic melt from penetrating between the stop ring and the distal end and into the annular gap. The pressure in front of the stop ring is therefore kept constant or increased during the injection molding process. Since the pressure loss between the stop ring and the compression ring is much less than in the prior art, the pressure difference (depending on the closing characteristic of the backflow prevention device) formed along the backflow prevention device in the compression ring direction is kept constant or increases. The stop ring is released from the distal end to provide an additional face for the inlet of the stop ring, ie the head contact face of the stop ring. The backflow prevention device according to the invention has a further improved closing characteristic compared to the prior art. When the screw head is rotated, wear does not occur on the inner surface of the cylinder by the stop ring which is not forcibly driven by the screw head.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. 1 to 3 show the first variant according to different working positions, respectively, and FIGS. 4 to 6 show further variants of the backflow prevention device according to the invention.

1 is a longitudinal sectional view of the first modification in the open position.

2 is a longitudinal sectional view of the first variant in an intermediate position immediately after the start of the injection molding process.

3 is a longitudinal sectional view of the first modification in the blocking position.

4 is a longitudinal sectional view of the second modification in the open position;

5 is a longitudinal sectional view of the third modification in the blocking position.

6 is a longitudinal sectional view of a fourth modification example in the blocking position.

FIG. 7 is a plan view illustrating a state in which the backflow prevention device of FIG. 5 is viewed in an arrow direction of FIG. 5.

1 to 3 include a screw head 10 having a discharge end 12, a cylindrical intermediate 14 and a mounting end 20 for mounting to the end of the injection molding screw. In this case, the screw head 10 has a compression ring 16 between the mounting end 20 and the intermediate portion 14. A stop ring 18 is arranged concentrically with the intermediate portion 14 to form an annular gap 22 with the intermediate portion 14. The outer diameter of the stop ring 18 is such that the stop ring can move in the axial direction within the plastic cylinder (not shown) while taking the open position (FIG. 1) and the blocking position (FIG. 3) on one side. On the other hand, it is designed to allow little relative motion in the circumferential direction.

The stop ring 18 is in the axial direction with respect to the screw head, more specifically in the open position in which the stop face 30 of the distal end 12 is in contact with the head contact surface 28 of the stop ring 18 (FIG. 1). And the stop surface 24 of the compression ring 16 is moved to the blocking position (FIG. 3) in contact with the blocking support surface 26 of the stop ring 18. In the passing position the material flow passes through the gap between the faces 24 and 26, the annular gap 22 and the holes 32. In the blocking position the stop ring is in the right end position and the material cannot be compressed in the screw direction as the gap between the faces 24 and 26 is closed. Immediately after the start of injection molding, the stop ring 18 moves to an intermediate position (FIG. 2) in which the head contact surface 28 of the stop ring also falls off the stop surface 30 and the blocking support surface 26 also falls off from the compression ring 16. Take it. In order to penetrate the plastic melt into the screw entry chamber, a number of holes 32 are distributed in the circumference of the stop ring 18.

On the back surface of the distal end 12, that is, the surface facing the stop ring side, the recess 40 is provided in such a manner that a slider 42 having a diameter D _GL is formed. The slider 42 forms a support surface that extends continuously over its entire length, over which the front end 46 of the stop ring 18 can move in the axial and circumferential directions. The stop ring 18 does not follow the screw head upon rotation of the screw head. The length L of the slider 42 is longer than or equal to the stroke A of the stop ring 18 between the open position and the cut off position. Thus, during injection molding (see FIGS. 2 and 3) it is ensured that the plastic melt can only penetrate into the annular gap 22 through the openings 32. As a result, an increase in the flow rate through the annular gap (as in the case of the prior art) and consequently an increase in pressure between the stop ring 18 and the compression ring 16, which can delay the closing of the backflow prevention device do. As the pressure between the stop ring and the compression ring decreases as compared to the prior art, the pressure difference which remains along the backflow prevention device in the direction of the compression ring, which governs the closing characteristics of the backflow prevention device, remains constant or increases. As the stop ring 18 disengages from the stop face 30 of the distal end 12 at the same time as the injection molding begins, the head stop face 28 is provided as an additional transverse cross section which is thereby able to enter the compression ring 16. The force applied to the stop ring 18 in the direction of becomes greater. As a result, the closing characteristic of the non-return valve is further improved.

In order to improve the closing characteristic, a part of the stop face 28 may already be used as the retractable cross section in the open position. Several embodiments in this regard are shown in FIGS. 4 to 6. It is up to the person skilled in the art to create additional shapes with flowable cross sections.

According to FIG. 4, for example, the outer diameter D _AE of the distal end 12 may be smaller than the outer diameter D _AS of the front end 46 of the stop ring 18, resulting in a leading edge 54. ) Is formed.

According to FIGS. 5 and 6, the distal end 12 may comprise at least one channel 50, for example disposed axially or at any angular position, wherein the distal end 12 in the channel bottom region. The diameter D _K ) may be equal (FIG. 5), larger (not shown) or smaller than the diameter D _GL of the slider 42 (FIG. 6). If the diameter D _K in the channel bottom region is smaller than the diameter D _GL of the slider 42, the length L _K of the channel 50 is within the region of the length L of the slider 42. Adjusted to end, resulting in a shoulder 52. Within the shoulder, the stop ring 18 is always in close contact with the slider 42, and plastic melt cannot reach from the annular gap 22 into the channel 50 or vice versa, and subsequently opens the openings 32. Only flow through

7 shows the embodiment according to FIG. 5 as seen from the direction of the arrow 5 in FIG. 5. Four channels 50 are distributed over the circumference of the distal end 12, and four openings 32 are provided over the circumference of the stop ring 18.

Finally, it should be noted that, unlike the ones shown in the figures, the mounting end in the screw head may be formed integrally with the compression ring and the intermediate part. In this case, the distal end is fixed to the intermediate part, for example by screwing.

* Drawing code list *

10: screw head

12: distal end

14: middle part

16: compression ring

18: stop ring

20: mounting end

22: annular gap

24: stop face of compression ring

26: blocking support surface

28: head contact surface

30: stop face of distal end

32: openings for plastic melt

34: Inside face of stop ring

36: recess in the front end of the stop ring

38: Edge of stop ring

40: recess in distal end

42: slider

44: outer surface of the distal end

46: front end of the stop ring

50: channel

52: shoulder

D _GL : outer diameter of the slider 42

D _K : Diameter at the bottom of the channel 50

D _AS : outer diameter at front end 46 of stop ring 18

D _ES : outer diameter of the distal end 12

D _SP : outer diameter in the middle region and the rear region of the stop ring 18

D _M : Outer diameter of middle part 14

Claims (8)

A screw head 10 having a distal end 12, an intermediate portion 14, a pressure ring 16 and a mounting end 20 and concentrically arranged in the longitudinal axis of the intermediate portion 14, Backflow prevention device for injection molding machines comprising a stop ring (18) capable of moving not only in the circumferential direction but also by stroke A with respect to the screw head (10) between blocking positions, in the open position the stop ring is a head contact surface. (28) abuts the stop face 30 of the distal end 12, in the blocking position the stop ring abuts the stop face 24 of the compression ring 16 via the stop support face 26, For the injection molding machine, the stop ring 18 and the intermediate portion 14 form an annular gap 22, and in the stop ring 18 are provided openings 32 for passing the plastic melt. In the backflow prevention device, The distal end 12 has a recess 40 between the stop face 30 of the distal end and the intermediate part 14 in such a way that a slider 42 having a diameter D _GL is formed, the slider having the stop Characterized in that the inner surface 34 of the ring 18 abuts in axial and circumferential direction and the slider 42 has a length L longer than the stroke A of the stop ring, Backflow prevention device for injection molding machine. The method of claim 1, A leading edge 54 is formed as the outer diameter DAS at the front end 46 of the stop ring 18 is larger than the outer diameter DAE of the distal end 12. , Backflow prevention device for injection molding machine. The method according to claim 1 or 2, Characterized in that at least one channel 50 is provided in the distal end 12 which is arranged axially or at any angular position and extends into the area of the slider 42. Backflow prevention device for injection molding machine. The method of claim 3, wherein The diameter D _K of the distal end 12 in the bottom region of the channel 50 is smaller than the diameter D _GL of the slider 42, and the channel 50 is the length of the slider 42. Ending in region (L), characterized in that the slider 42 in the region has a shoulder 52 on which the stop ring 18 is supported, Backflow prevention device for injection molding machine. The method according to claim 3 or 4, Characterized in that the diameter D _K of the distal end 12 in the bottom region of the channel 50 is equal to or greater than the diameter D _GL of the slider 42, Backflow prevention device for injection molding machine. The method according to any one of claims 1 to 5, Characterized in that the front end 46 of the stop ring 18 is tapered conical, Backflow prevention device for injection molding machine. The method according to any one of claims 1 to 6, The outer diameter D _AS at the front end 46 of the stop ring 18 is smaller than the outer diameter D _SP at the middle and rear regions of the stop ring 18, and the stop ring 18 is Characterized in that it is formed conical in the transition region to the front end 46, Backflow prevention device for injection molding machine. The method according to claim 6 or 7, The openings 32 are characterized in that they are arranged in the conical region of the stop ring 18, Backflow prevention device for injection molding machine.

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