Injection moulding machine with separating element and relief channel

Abstract

The invention relates to an injection moulding machine with a hot runner for feeding a plasticised melt into a moulding tool, a shut-off needle aligned along a needle axis for optionally closing or opening the hot runner, a fluid piston which is connected to the shut-off needle and which is arranged in a housing and to which a fluid can be applied on both sides, wherein the hot runner and the fluid piston are separated from one another by a separating element with a needle passage, through which the shut-off needle is movably guided, wherein a relief channel is provided within the separating element and is connected to the needle passage, and wherein the relief channel is not aligned perpendicular to the needle axis, at least in portions.

Description

[0001] Injection molding machine with separating element and relief channel

[0002] The present invention relates to an injection molding machine with a hot runner for feeding a plasticized melt into a mold. A shut-off pin is provided for selectively closing or opening the hot runner. The shut-off pin is connected to a fluid piston, which is arranged in a housing with an opening and can be pressurized with a fluid on both sides. With the aid of the fluid, the fluid piston and therefore also the shut-off pin connected to the fluid piston can be moved within the housing to close or open the hot runner relative to the mold.

[0003] The fluid piston divides the housing volume into two fluid chambers, which are optionally pressurized with a fluid to move the fluid piston within the housing.

[0004] A separating element is provided between the housing and the hot runner. This element has a needle passage through which the shut-off needle is movably guided. The separating element can be either a separate element or formed integrally with the housing. The separating element can also be implemented as a housing wall. The separating element is the element that separates the space in which the fluid piston is located from the hot runner, into which the plasticized melt is fed.

[0005] In general, the needle passage is formed by a bore in the separating element, the bore diameter of which corresponds approximately to the outer diameter of the shut-off needle, so that the shut-off needle essentially closes the needle passage.

[0006] However, since the plasticized melt in the hot runner is fed under high pressure, it can happen during operation that small amounts of the plasticized melt or gas on the outside of the valve pin flow through the pin passage in the separator and enter the housing. This is fundamentally undesirable, as it impairs or even prevents the movement of the fluid piston.

[0007] Such an injection molding machine is described in DE 10 2011 056 248 A1.

[0008] To solve the problem described, an elastic seal between the separator and the valve pin is proposed. This elastic seal increases the cost, is subject to wear, and requires complex installation.

[0009] Furthermore, DE 10 2011 056 248 A1 stipulates that at least one relief bore is provided within the separating element, connecting the needle passage to the environment. The relief bores are aligned perpendicular to the needle axis. In fact, the relief bores ensure that only a small portion of the plasticized melt penetrates the housing and is instead guided out through the relief channel. The then resolidified PET, usually in the form of dust, is reliably guided out, but can affect neighboring components there. This means that the injection molding machine must be opened occasionally, and the area surrounding the separating element must be cleaned.

[0010] Based on the described prior art, it is therefore an object of the present invention to provide an improved injection molding machine which at least reduces the problems described.

[0011] According to the invention, this object is achieved by orienting the relief channel not perpendicular to the needle axis. The angled design of the relief channel extends it, allowing more PET to be absorbed in the relief channels before it escapes into the environment. The relief channel can have sections oriented perpendicular to the needle axis. However, it is essential that at least one section of the relief channel is not oriented perpendicular to the needle axis.

[0012] It has also been shown that it is advantageous if the opening of the relief channel to the needle feedthrough is located as close as possible to the fluid piston, which has a significantly lower temperature during operation than the melt in the hot runner. For reasons that have not yet been fully clarified, only a small portion of the PET residue is then present as loose dust. Instead, the dust particles conglomerate and form sausage-shaped structures, the shape of which is determined by the shape of the relief channel. Typically, the relief channel can then absorb very large quantities of the conglomerate before it is released into the environment, where it must be laboriously removed.

[0013] In a preferred embodiment, it is therefore provided that at least a portion of the relief channel is arranged further away from the fluid piston in the direction of the needle axis than the end of the relief channel connected to the needle passage. It is advantageous if the end of the relief channel connected to the needle passage is arranged as close as possible to the fluid piston.

[0014] In a further preferred embodiment, the relief channel is implemented either by means of a relief bore extending from an outer side of the separating element to the needle passage, wherein the opening of the relief bore on the outer side of the separating element is arranged further away from the fluid piston than the opening of the relief channel to the needle passage. Alternatively, the relief channel can also have several relief channel sections, wherein adjacent relief channel sections are each arranged along an axis, wherein the axes of adjacent relief channel sections enclose an angle of less than 180°. In other words, the relief channel is angled so that the PET residues experience flow resistance, which leads to greater compaction of the PET conglomerate, so that PET is guided out later and, above all, in smaller quantities.

[0015] In a preferred embodiment, the housing and the separating element are separate elements, the housing having an open housing wall or a housing opening in which the separating element is arranged and thus closes the housing, the relief channel having a channel section running through the housing.

[0016] The relief channel thus runs not only through the separating element, but also through the housing wall. Alternatively, only part of the boundary wall of a channel section can be formed by the housing wall.

[0017] In a further preferred embodiment, the relief channel comprises a first section and a second section, the first section being connected to the needle passage and having a smaller cross-section than the second section. Preferably, a third section is provided, which is connected to the second section and has a smaller cross-section than the second section. The second section thus has a larger cross-section, allowing PET residues to collect there. The third section increases the flow resistance, which contributes to the compression of the PET conglomerate.

[0018] Alternatively, the relief channel may be curved along at least part of its length.

[0019] This allows the length of the relief channel in the separating element to be increased.

[0020] In a further preferred embodiment, the relief channel connects the needle passage to the environment, preferably with a throttle element arranged within the relief channel that reduces the cross-section of the relief channel. The throttle element is particularly preferably adjustable so that the cross-section can be individually adjusted.

[0021] On the one hand, the relief channel must be designed to prevent plasticized melt from penetrating the housing and impeding the movement of the fluid piston. On the other hand, as little PET dust as possible should be discharged through the relief channel. Therefore, the throttle element can reduce the cross-section as much as possible for a given application, as long as it is ensured that no PET melt penetrates the housing. Depending on the material used and the melt pressure set in the hot runner, a different throttle element setting may be suitable.

[0022] Furthermore, the relief channel can be provided to connect the needle passage to a relief channel chamber. This ensures that no PET dust enters the environment. The relief chamber can be provided within the separating element and, for example, be formed by a relief channel section with a larger cross-section. It can be advantageous if the relief channel has no connection to the environment.

[0023] Several relief channels may be provided.

[0024] Furthermore, the separating element can have beveled surfaces on its side facing away from the fluid piston, which are designed such that the cross-section of the separating element increases from the end of the separating element facing away from the fluid piston toward the fluid piston. In other words, the separating element has a conical section at its end facing away from the fluid piston.

[0025] As already mentioned, there is a very large temperature gradient between the fluid piston and the hot runner. The chamfer reduces heat transfer from the hot runner through the separator toward the housing, which also improves the consistency of the PET residue accumulating in the relief channels, thus reducing dust emissions into the environment.

[0026] The present invention also relates to a separating element for insertion into a nozzle channel and for diverting a melt flow from a hot runner into the nozzle channel, wherein the separating element has a needle passage through which the shut-off needle is movably guided, wherein a relief channel is provided within the separating element, which is connected to the needle passage. According to the invention, the relief channel is not aligned perpendicular to the needle axis. The invention is therefore realized by using the separating element in conventional injection molding machines. The separating element can be designed as described in connection with the injection molding machine. The invention thus also relates to a separating element for use in an injection molding machine of the claimed type.

[0027] Further advantages, features, and possible applications of the present invention will become clear from the following description of preferred embodiments and the accompanying figures. They show:

[0028] Figure 1 is a schematic sectional view of a part of an injection molding machine of the prior art,

[0029] Figures 2 and 2a are sectional views of a first embodiment of a needle guide according to the invention,

[0030] Figures 3a to 3c show different views of a second embodiment of a needle guide according to the invention,

[0031] Figure 4 is a sectional view of a third embodiment of a needle guide according to the invention,

[0032] Figure 5 shows a fourth embodiment of a needle guide according to the invention and

[0033] Figures 6 and 6a show different views of a fifth embodiment of a needle guide according to the invention. Figure 1 shows a section of an injection molding machine. The structure of the injection molding machine is known per se. Only the needle valve is shown, as is known from the prior art. The needle valve has a shut-off needle 1 which is fastened to a fluid piston 2. The fluid piston 2 is arranged within a housing 3. The housing 3, with the shut-off needle 1 guided therein and the fluid piston 2, is integrated into a hot runner system here. The actual hot runner 4 can be seen, through which the plasticized plastic material is guided and which is generally heatable in order to keep the plastic flowable. The shut-off needle 1 engages through a needle feedthrough 5 in a separating element 6, which separates the fluid piston 2 from the hot runner 4.The shut-off needle 1 extends into the area of ​​a sprue nozzle 7 of the hot runner system. The hot runner 4 runs concentrically to the shut-off needle 1 up to the nozzle 7. The front end 8 of the shut-off needle 1 can close or open the nozzle 7. The fluid piston 2 is sealed against the wall 11 of the housing 3 by means of an O-ring 9. For this purpose, a sliding ring 10 is arranged surrounding the O-ring. The O-ring is guided in a groove 12 in the fluid piston 2. The fluid piston 2 divides the housing volume into an upper chamber 13 and a lower chamber 14, each of which can be pressurized with a fluid. Thus, by suitable pressure control, the fluid piston 2 can be moved up and down within the housing 3, whereby the shut-off needle 1 can be moved from the closing position in the nozzle 7 to the opening position and back.

[0034] In the embodiment shown, the housing 3 and separating element 6 are formed in one piece.

[0035] Since the plasticized melt in the hot runner 4 is generally under high pressure, it can happen during operation that a small amount of the plasticized melt presses into the needle passage 5 on the outer surface of the shut-off needle 1 and thus reaches the lower chamber 14, which prevents precise control of the shut-off needle 1.

[0036] In the embodiment shown, the housing 3 in particular must be cleaned intensively at short intervals to ensure reliable operation.

[0037] In the embodiment shown, the separating element closes the housing.

[0038] Figure 2 shows an embodiment of the needle guide according to the invention. The needle 21 is accommodated in a fluid piston 22 and penetrates a separating element 26. The housing here has an open housing wall into which the separating element 26 is inserted, thereby closing the housing.

[0039] Here, too, the fluid piston 22 divides the housing into an upper chamber 23 and a lower chamber 24, which can be supplied with a control fluid. Due to the reciprocating movement of the fluid piston 22 to move the shut-off needle 21, PET melt penetrates between the outer wall of the shut-off needle 21 and the inner wall of the needle guide of the separating element 26 upwards toward the fluid piston 22.

[0040] To prevent this, relief channels 27 are provided, which connect the needle guide within the separating element 26 to an outer side of the separating element. In the example shown, the relief channel does not run perpendicular to the needle axis, but rather forms an angle of <90° with it, approximately 75° in the example shown.

[0041] As a result, the end of the relief channel, which ends in the needle guide of the separating element 26, is moved further towards the fluid piston and thus into a colder area.

[0042] It has been shown that this measure not only increases the distance PET residues travel, allowing more PET to be absorbed within the relief ducts before it escapes to the outside, but also allows the PET dust to form a conglomerate on a larger scale. At cooler temperatures, the PET dust particles form conglomerates that are interconnected and therefore do not disperse uncontrollably.

[0043] In the example shown, the relief channel 27 has a first section 28, which provides the connection to the needle passage, a second section 29, which has a larger cross-section than the first section 28, and a throttle element 30 arranged at the end of the second section, which further reduces the cross-section at the outlet. The throttle element 30 ensures that the conglomerate of PET dust particles remains essentially within the relief channels 27 and does not escape into the environment.

[0044] The separating element shown in Figures 2 and 2a can optionally be used together with the housing and the fluid piston in conventional injection molding tools in order to realize the inventive effect.

[0045] The separating element 26 is conical at its end facing away from the fluid piston 22, as can be seen from the beveled surfaces 32. Figures 3a to 3c show various views of a second embodiment. Figure 3a shows a top view, which is intended solely to clarify the position of the sectional views shown in Figures 3b and 3c. Figure 3b shows a sectional view BB, and Figure 3c shows the sectional view CC.

[0046] In this embodiment, too, a valve pin 41 is moved by a fluid piston 42 through a separating element 46, 47 by alternately supplying an upper chamber 43 and a lower chamber 44 with a control fluid. This embodiment differs from the previous one primarily in the modified design of the relief channel.

[0047] The separating element 46, 47 is formed in two parts and consists of an inner element 46, which comprises the needle passage in which the locking needle 41 is arranged, and an outer clamping element 47, which has a bore in which the inner separating element 46 is arranged. As can be seen in Figure 3c, two relief channel sections 48 running perpendicular to the needle axis are arranged in the inner separating element 46. The inner separating element 46 has a circumferential groove 51, which is arranged at the level of the first section of the relief channel 48. PET residues emerging from the relief channel 48 thus enter the circumferential groove 51.

[0048] In the sectional view rotated by 90°, which is shown in Figure 3b, a second relief channel section 49 is shown which is not arranged perpendicular to the needle axis and which is also connected to a throttle element 50.

[0049] PET residues that enter the circumferential groove 51 are then guided away from the needle via the second relief channel 49.

[0050] Here too, the side of the separating element 47 facing away from the fluid piston 42 has bevelled surfaces 52. In other words, the separating element is conical at its end facing away from the fluid piston.

[0051] Figure 4 shows a third embodiment of a separating element according to the invention. Here, too, a shut-off needle 61 is guided by means of a fluid piston 62 within a separating element 66, wherein the upper chamber 63 and the lower chamber 64 are alternately supplied with a control fluid. The separating element 66, here again designed as a single piece, closes the housing 72. The corresponding contact surfaces between the housing 72 and the separating element 66 are stepped and sealed by O-rings. In this embodiment, the relief channel has two sections 68 and 69, with the second section 69 having a larger cross-section. The second section 69 and the first section 68 are realized using a stepped bore. However, the end of the second section 69 is closed by a plug 70.A further relief channel section 71 is arranged at an angle thereto and connects the second section 69 with the outside of the separating element 66.

[0052] Here too, the side of the separating element 66 facing away from the fluid piston 62 has beveled surfaces 73. In other words, the separating element 66 is conical at its end facing away from the fluid piston 62.

[0053] Figure 5 shows a fourth embodiment. The closure needle 81 is guided within a separating element 86 and moved back and forth by a fluid piston 82 when the upper chamber 83 and the lower chamber 84 are alternately supplied with a control fluid.

[0054] Here, too, several relief channels are provided, wherein the relief channel has a first section 88 and a second section 89, which have been created by means of a stepped bore. However, the stepped bore is closed using the plug 90. In addition, a further relief channel section 91 is provided, arranged at an angle to the first and second sections of the relief channel, which connects the second section 89 to the outside of the separating element 86. In contrast to the embodiment of Figure 4, however, here the channel is led to a section of the outside of the separating element 86 that would normally be covered by the housing 92. In order to still have a connection to the environment, the housing 92 has recesses 93 designed as notches on its side facing the separating element 86, through which recesses air and, if applicable, PET residues can be transported to the outside.

[0055] Here too, the side of the separating element 86 facing away from the fluid piston 82 has beveled surfaces 94. In other words, the separating element is conical at its end facing away from the fluid piston.

[0056] Finally, Figures 6 and 6a show a fifth embodiment of the invention. The closure needle 101 is also held by a fluid piston 102 and guided by a separating element 106. Movement is achieved by alternating actuation of a control fluid into the upper chamber 103 and the lower chamber 104. The sectional view shows that the relief channel 108 is curved. The outer end of the separating element 106 is formed by a section 109 with a larger cross-section, which ends with a throttle element 110. The connection of the relief channel 108 to the needle guide cannot be seen in Figure 6, as this connection lies in a different sectional plane. The separating element or the curved relief channel can be produced, for example, by 3D printing or casting.

[0057] What all the described embodiments have in common is that the opening of the relief channel for the needle guide is located in an area surrounded by the lower chamber, which can be supplied with a control fluid. If a section is taken perpendicular to the needle axis in the area where the opening of the relief channel for the needle guide is located, the lower chamber can also be seen in this sectional view.

[0058] List of reference symbols

[0059] 1 locking needle

[0060] 2 fluid pistons

[0061] 3 housings

[0062] 4 hot runner

[0063] 5 Needle guide

[0064] 6 Separator

[0065] 7 Sprue nozzle

[0066] 8 front end of the locking needle

[0067] 9 O-ring

[0068] 10 sliding ring

[0069] 11 Wall of the housing

[0070] 12 grooves

[0071] 13 upper chamber

[0072] 14 lower chamber

[0073] 21 needle

[0074] 22 fluid pistons

[0075] 23 upper chamber

[0076] 24 lower chamber

[0077] 26 Separator

[0078] 27 relief channel

[0079] 28 first section

[0080] 29 second section

[0081] 30 throttle element

[0082] 41 locking needle

[0083] 42 fluid pistons

[0084] 43 upper chamber

[0085] 44 lower chamber

[0086] 46 Separator

[0087] 47 Separator

[0088] 48 relief channel

[0089] 49 Relief canal section

[0090] 50 throttle element

[0091] 51 groove 52 bevelled surfaces

[0092] 61 locking needle

[0093] 62 fluid pistons

[0094] 63 upper chamber

[0095] 64 lower chamber

[0096] 66 Separator

[0097] 68 first section

[0098] 69 second section

[0099] 70 plugs

[0100] 71 relief canal section

[0101] 81 locking needle

[0102] 82 fluid pistons

[0103] 83 upper chamber

[0104] 84 lower chamber

[0105] 86 Separator

[0106] 88 first section

[0107] 89 second section

[0108] 90 plugs

[0109] 91 relief canal section

[0110] 92 housings

[0111] 93 recesses

[0112] 101 locking needle

[0113] 102 fluid pistons

[0114] 103 upper chamber

[0115] 104 lower chamber

[0116] 106 Separator

[0117] 108 relief channel

[0118] Section 109

[0119] 110 throttle element

Claims

Patent claims 1. Injection molding machine with a hot runner for feeding a plasticized melt into a mold, a shut-off needle aligned along a needle axis for selectively closing or opening the hot runner, a fluid piston connected to the shut-off needle, which is arranged in a housing and can be acted upon by a fluid on both sides, wherein the hot runner and the fluid piston are separated from one another by a separating element with a needle passage through which the shut-off needle is movably guided, wherein a relief channel is provided within the separating element and is connected to the needle passage, characterized in that the relief channel is at least partially not aligned perpendicular to the needle axis.

2. Injection molding machine according to claim 1, characterized in that at least a part of the relief channel is arranged further away from the fluid piston in the direction of the needle axis than the end of the relief channel connected to the needle passage.

3. Injection molding machine according to claim 2, characterized in that the relief channel is realized either by means of a relief bore which extends from an outer side of the separating element to the needle passage, wherein the opening of the relief bore on the outer side of the separating element is arranged further away from the fluid piston than the opening of the relief channel to the needle passage, or has a plurality of relief channel sections, wherein adjacent relief channel sections are each arranged along an axis, wherein the axes of adjacent relief channel sections enclose an angle of less than 180°.

4. Injection molding machine according to one of the preceding claims, characterized in that the housing has an open housing wall or a housing opening in which the separating element is arranged, wherein the relief channel has a channel section running through the housing or a channel section whose boundary wall is formed at least in part by the housing.

5. Injection molding machine according to one of the preceding claims, characterized in that the relief channel has a first section and a second section wherein the first section is connected to the needle passage and has a smaller cross-section than the second section, wherein preferably a third section is provided which is connected to the second section and has a smaller cross-section than the second section.

6. Injection molding machine according to one of the preceding claims, characterized in that the relief channel is curved at least along part of its length.

7. Injection molding machine according to one of the preceding claims, characterized in that the relief channel connects the needle passage with the environment, wherein preferably a throttle element is provided which is arranged within the relief channel and reduces the cross section of the relief channel, wherein particularly preferably the throttle element is adjustable.

8. Injection molding machine according to one of claims 1-6, characterized in that the relief channel connects the needle passage with a relief chamber, wherein the relief chamber is preferably formed by a relief channel section with a larger cross-section.

9. Injection molding machine according to one of the preceding claims, characterized in that several relief channels are provided.

10. Injection molding machine according to one of the preceding claims, characterized in that the separating element has beveled surfaces on its side facing away from the fluid piston, which are designed such that the cross section of the separating element increases from the end of the separating element facing away from the fluid piston in the direction of the fluid piston.

11. Injection molding machine according to one of the preceding claims, characterized in that the fluid piston divides the interior of the housing into an upper chamber and a lower chamber, the lower chamber being delimited by the separating element, the opening of the relief channel for the needle guide being arranged such that there is a sectional view perpendicular to the needle axis, in which both the opening of the relief channel for the needle guide and the lower chamber are arranged.

12. Separating element for insertion into a nozzle channel and for diverting a melt flow from a hot runner into the nozzle channel, wherein the Separating element has a needle passage through which the closure needle is movably guided, wherein a relief channel is provided within the separating element, which is connected to the needle passage, characterized in that the relief channel is at least partially not aligned perpendicular to the needle axis.

13. Separating element for use in an injection molding machine according to one of claims 1 to 11.

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