CA2821997A1

CA2821997A1 - Hot runner nozzle

Info

Publication number: CA2821997A1
Application number: CA2821997A
Authority: CA
Inventors: Hans-Peter Manner
Original assignee: Otto Maenner Innovation GmbH
Current assignee: Otto Maenner Innovation GmbH
Priority date: 2010-12-23
Filing date: 2011-12-22
Publication date: 2012-06-28
Also published as: DE102010056073A1; DE102010056073B4; US20130306686A1; WO2012084252A1; EP2655037B1; EP2655037A1

Abstract

The invention relates to a hot runner nozzle (1) for injection molding tools, comprising a nozzle body having a passage channel (2) for a melt. The nozzle body comprises a feed opening (4) at a first end region (3) and an outlet opening (6) at a second end region (5). In addition to the passage channel (2) and an optional guide channel (9) for a closing needle, the nozzle body comprises at least one cavity (15a, 15b).

Description

HOT RUNNER NOZZLE
[0001] The invention relates to a hot runner nozzle for injection molding tools with a nozzle body having a passage channel for a melt, the nozzle body comprising a feed opening at a first end region and an outlet opening at a second end region.

[0002] In one hot runner nozzle of this type known from OE 10 2004 009 806 B3, it is very advantageous to have a uniform temperature level over the entire nozzle length. This avoids thermal damage to the plastic being processed because of excessive temperatures. In the colder regions of the hot runner nozzle, on the other hand, the liquid plastic may solidify rendering processing impossible.

[0003] A temperature gradient occurs on the nozzle body when the hot runner nozzle is heated using a suitable heating element. There is a higher temperature in the central region of the nozzle body than in either of the end regions of the nozzle body. The reason for this is that the hot runner nozzle attached to a mold of the injection molding tool makes contact with the relatively cool mold at its one end region. This is necessary for sealing reasons and for stability.

[0004] The contact surface between the nozzle body and the mold is located on an insulating ring that is permanently connected to the nozzle body. Although this hot runner nozzle has proven itself in practice, it still has disadvantages. For instance, despite the insulating ring, a certain amount of the heat introduced into the nozzle body by the heating element is dissipated in the mold of the injection molding tool, which reduces the temperature in this part of the nozzle body.

[0005] In the central region of the nozzle located between the end regions, no heat is dissipated in the mold. Consequently, heat accumulation is present here resulting in a higher temperature.

[0006] For this reason, the object is to create a hot runner nozzle of the type mentioned above that permits as uniform a temperature level as possible over its nozzle length when heated in the melting position.

[0007] This object is achieved by the invention in that the nozzle body has at least one cavity in addition to the passage channel and a guide channel, provided, if applicable, for a closing needle.

[0008] In an advantageous manner, during the construction of the hot runner nozzle by appropriately forming the at least one cavity, the heat flow in the nozzle body can be set so that during use of the hot runner nozzle a largely uniform temperature level results over the longitudinal direction of the nozzle body. As the partial region of the nozzle body surrounding the cavity can be designed as a single piece, leaks, such as those that may occur at joints, can be avoided from the outset in the region of the cavity.

[0009] The at least one cavity can be produced using a generative manufacturing process, in particular using selective laser sintering. In this process, the nozzle body is created in layers in that one thin layer of a powder material is applied each time over the entire area in a number of operations, for example, using a spreading knife on an appropriate base. Based on the geometry data, a laser beam is positioned to sinter the powder at each processing location corresponding to those points where the nozzle body is to be created.
The energy supplied by the laser is absorbed by the powder and results in a localized sintering or melting of particles at the processing location. Then, the structure obtained in this manner is lowered by the thickness of the layer to apply and to structure another layer in the same manner. The process steps described above are repeated until the nozzle body is finished.

[0010] In one advantageous development of the invention, the cavity is evacuated or filled with a medium that has a thermal conductivity different from the material of the wall of the nozzle body adjacent to the cavity. If the cavity is evacuated, the cavity provides a particularly high thermal insulation. The cavity may also contain a gas, such as air, however, to achieve high thermal insulation. However, it is also possible to fill the cavity with a preferably liquid or solid medium having high thermal conductivity. In this way, an effective thermal transfer to colder locations can be achieved from points where a particularly large quantity of heat accumulates during operation of the hot runner nozzle.

[0011] In one advantageous embodiment of the invention, the medium is a metal having a higher thermal conductivity than the material of the wall of the nozzle body adjacent to the cavity. The metal may contain, in particular, copper and/or aluminum. These metals have high thermal conductivity but are available at a relatively affordable cost and are workable.
The metal or the medium is filled into the cavity when fabricating the hot runner nozzle preferably by way of a fill opening provided in the wall of the cavity. If needed, the cavity may have a vent opening in addition to the fill opening. The fill opening and, if applicable, the vent opening are plugged after filling the cavity. In the case of a solid medium, the fill and/or vent opening is preferably plugged by means of the medium itself.

[0012] In a refinement of the invention, the cavity runs in the form of a ring around the passage channel. In this way, a very uniform temperature level of the nozzle body is provided around the circumference.

[0013] It is advantageous if the nozzle body has at least one contact surface that can be connected to a mating surface of an injection molding tool, if the nozzle body has at least one first cavity adjacent to the contact surface and at least one second cavity that is spaced farther from the at least one contact surface than the first cavity, [0014] - if the first cavity is filled with a first medium and the second cavity with a second medium that has a higher thermal conductivity than the first medium, and/or [0015] - if the first cavity is evacuated and the second cavity filled with a thermally conductive medium.

[0016] This measure provides a particularly uniform temperature level all along the nozzle body.

[0017] In one preferred development of the invention, the nozzle body has a nozzle tube surrounding the passage channel wherein the nozzle tube is connected with at least one nozzle body part having the contact surface, this part consisting of a material having a lower thermal conductivity than the material of the nozzle tube and wherein the at least one first cavity is located in the at least one nozzle body part and the at least one second cavity is located in the nozzle tube. Different powder materials may also be used to fabricate the different partial regions of the nozzle body in a generative process. In this way, the thermal flow during operation of the hot runner nozzle from the nozzle body into the mold of the injection molding tool is reduced particularly effectively such that an even more uniform temperature level results along the longitudinal direction of the nozzle body.
The nozzle tube preferably consists of metal and the nozzle body part of ceramic.

[0018] Various steels, nonferrous metals, sinter metals, ceramics, etc. are suitable as powder materials for the generative fabrication of the nozzle body. These different materials can be melted together in a high-strength manner using the laser beam. In part, even very wear-resistant materials can be used, for example, to build a guide for the closing needle in the nozzle.

[0019] In one advantageous embodiment of the invention, the nozzle body has a preferably one-piece nozzle tube surrounding the passage channel wherein the nozzle tube has at least two cavities that are spaced apart in the longitudinal direction of the passage channel and wherein a section of the nozzle tube that does not have any cavities is located in the longitudinal direction between said cavities. This provides both high mechanical stability for the nozzle tube and a uniform temperature level on the nozzle tube.

[0020] If necessary, the nozzle body may have at least two cavities that are connected to one another by way of at least one connecting channel that has a smaller cross-section than the cavities. In this way, a plurality of cavities can be filled at the same time with the first medium and/or the second medium in a simple manner during fabrication of the nozzle body.

[0021] In one preferred development of the invention, the at least one cavity or one section extends in the shape of a spiral or coil around the longitudinal central axis of the hot runner nozzle. As a result of this measure, the thermal conductivity can be influenced if necessary over the entire length of the nozzle tube.

[0022] It is advantageous if the nozzle body has a base body onto which one partial region is applied in layers by means of a generative method, this region having the at least one cavity. The base body may, in this respect, consist of a high-strength material having the I
required resistance to pressure, temperature and wear. The base body can be fabricated using a conventional manufacturing method. However, it is also conceivable to manufacture the base body from a used hot runner nozzle in which, for example, the needle guide of the closing needle is worn. In this case, the worn partial region of the needle guide can be removed, for example, by grinding off the hot runner nozzle and then, using the generative manufacturing method, reapplied on the remaining part of the hot runner nozzle.

[0023] One exemplary embodiment of the invention is explained below in more detail based on the drawing. The single figure shows a longitudinal section through a hot runner nozzle.

[0024] Identified with 1, a complete hot runner nozzle for an injection molding tool has a nozzle body that has one passage channel 2 for a melt. The passage channel 2 has one feed opening 4 at a first end region 3 facing the injection molding tool when in the position of use and an outlet opening 6 for the melt at a second end region 5 at some distance from this.

[0025] The hot runner nozzle 1 is broadened at its first end region 3 forming a head similar to that of a screw. At its end facing away from the outlet opening 6, the first end region 3 has a roughly disk-shaped nozzle carrier 7 on whose rear surface facing away from the outlet opening 6 are located the feed opening 4 and a first needle guide 8 surrounding a guide channel 9 for a closing needle, not shown in more detail in the drawing, that engages in the passage channel 2. The first needle guide 8 is made of a material that is more resistant to wear than the material of a partial region of the nozzle carrier 7 bordering the first needle guide 8.

[0026] The feed opening 4 is offset perpendicular to the longitudinal direction of the hot runner nozzle 1 with respect to the needle guide 8 and the passage channel 2 has a channel section in the nozzle carrier 7 that runs perpendicular to the longitudinal direction of the hot runner nozzle 1, said section connecting with the feed opening 4 with another channel section running along the longitudinal axis of the hot runner nozzle 1 to the outlet opening 6.

[0027] At the end facing away from the outlet opening 6, the first end region has a nozzle seat 10 that is also roughly disk shaped and connected over a flat area with the nozzle carrier 7, the hot runner nozzle 1 making contact with the injection molding tool at this seat.
The nozzle seat 10 is bonded with the nozzle carrier and is made of a material having a lower thermal conductivity than the material of the nozzle carrier 7. The nozzle carrier 7 may, for example, be made of metal and the nozzle seat 10 made of ceramic.

[0028] At its front side facing away from the nozzle carrier 7, the nozzle seat 10 is bonded with a nozzle tube 11 that is arranged roughly concentrically with the passage channel 2 and runs in the longitudinal direction of the hot runner nozzle 1. The nozzle tube 11 preferably consists of metal, in particular of steel. To thermally decouple the nozzle tube 11 from the injection molding tool, an air gap is provided between the outer shell of the nozzle tube 11 and the injection molding tool.

[0029] The nozzle tube 11 has a nozzle section 12 on the end spaced away from the nozzle seat 10, this section being connected to the other nozzle tube 11 as a single piece.
The nozzle section 12 has, at its free end, the outlet opening 6 and the section tapers conically toward the outlet opening 6. At the outlet opening 6, the nozzle section 12 has a second needle guide 14 located in a straight line extension of the first needle guide 8 and made of a material that is resistant to wear.

[0030] Adjacent to the nozzle section 12, the hot runner nozzle 1 has a ring-shaped shoulder at its second end region, this shoulder forming a recess holding an insulating ring 13. The hot runner nozzle 1 makes contact with a support point of the injection molding tool on the insulating ring 13.

[0031] In addition to the passage channel 2 and the guide channel 9 for the closing needle, the nozzle body has a plurality of first cavities 15A and a plurality of second cavities 15B. The first cavities 15A are filled with air and the second cavities 15B
with a metal having a higher thermal conductivity than the material of the nozzle-body walls bordering the cavities 15A, 15B involved. The metal may be copper, in particular. The walls bordering each of the individual cavities 15A, 15B are connected to one another as a single piece. In this way, joints where melts may leak from the nozzle body are avoided on the cavities 15A, 15B.

[0032] The cavities 15A, 15B are each of a ring shape and surround the passage channel 2 without interruption. In the nozzle seat 10 and the insulating ring 13, a first cavity 15A is provided that serves to reduce the thermal loss from the nozzle body into the injection molding tool and/or the interior cavity of the injection molding tool.

[0033] Furthermore, a plurality of second cavities 15B is provided in the nozzle tube 11.
Second cavities 15B that are adjacent to one another are spaced apart by nozzle tube sections, which have no cavities 15A, 15B, in the longitudinal direction of the nozzle tube 11 marked by the double arrow.

[0034] In the region of the nozzle tube 11, the second cavities 15B are located roughly in the center between the inner and outer shells of the nozzle tube 11. With the exception of any fill openings provided on the cavities 15B, the second cavities 15B of the nozzle tube 11 are spaced apart from the outer shell and the inner shell of the nozzle tube 11.

[0035] The thermal conductivity of the nozzle tube 11 is increased by the second cavities 15B so that, while operating the hot runner nozzle 1, a largely uniform temperature level is reached along the nozzle tube 11. Temperature differences that may occur along the length of the nozzle tube 11 cause a thermal flow in nozzle tube 11 that reduces the temperature difference.

[0036] A second cavity 15B that surrounds the passage channel 2 in the shape of a ring is provided, also in the nozzle carrier 7. This second cavity 15B is located between the straight extension of the outer shell of the nozzle tube 11 and the outer circumference of the nozzle carrier 7 and runs concentrically with the second cavities 15B of the nozzle tube 11. With the exception of any fill opening provided on the second cavity 15B of the nozzle carrier 7, the second cavity 15B is spaced apart from the outer circumference of the nozzle carrier 7.

[0037] All second cavities 15B may be connected to one another to influence thermal conductivity over the entire nozzle length.

[0038] It would also be feasible to implement the second cavities 15B in the region of the nozzle tube 11 and the nozzle section 12 as a single piece, for example, as a spiral-shaped or coil-shaped cavity winding around the central axis of the hot runner nozzle 1.

Claims

1. Hot runner nozzle (1) for injection molding tools comprising a nozzle body having a passage channel (2) for a melt, this channel having at one first end region (3) a feed opening (4) and at a second end region (5) an outlet opening (6) characterized in that the nozzle body has at least one cavity (15A, 15B), in addition to the passage channel (2) and a possibly also present guide channel (9) for a closing needle.

2. Hot runner nozzle (1) according to Claim 1 characterized in that the cavity (15A, 15B) is evacuated or filled with a medium having a different thermal conductivity than the material of the wall of the nozzle body bordering the cavity (15A, 15B).

3. Hot runner nozzle (1) according to Claim 1 or 2 characterized in that the media is a metal having a higher thermal conductivity than the material of the wall of the nozzle body bordering the cavity (15A, 15B).

4. Hot runner nozzle (1) according to one of the Claims 1 to 3 characterized in that the cavity (15A, 15B) surrounds the passage channel (2) in the form of a ring.

5. Hot runner nozzle (1) according to one of the Claims 1 to 4 characterized in that the nozzle body has at least one contact surface (10A, 13A) that can be connected to a fitting mating surface of an injection molding tool; in that the nozzle body has at least one first cavity (15A) adjacent to the contact surface (10A, 13A) and at least one second cavity (15B) that is spaced farther away from the at least one contact surface (10A, 13A) than the first cavity;
- in that the first cavity (15A) is filled with a first medium and the second cavity (15B) with a second medium having a higher thermal conductivity than the first medium;
and/or - in that the first cavity (15A) is evacuated and the second cavity (15B) filled with a thermally conductive medium.

6. Hot runner nozzle (1) according to Claim 5 characterized in that the nozzle body has a nozzle tube (11) surrounding the passage channel (2); in that the nozzle tube (11) is connected with at least one nozzle body part having the contact surface (10A, 13A), this part consisting of a material having a lower thermal conductivity than the material of the nozzle

7 tube (11); and in that the at least one first cavity (15A) is located in the at least one nozzle body part (11) and the at least one second cavity (15B) is located in the nozzle tube (11).
7. Hot runner nozzle (1) according to one of the Claims 1 to 6 characterized in that the nozzle body has a preferably one-piece nozzle tube (11) surrounding the passage channel (2); in that the nozzle tube (11) has at least two cavities (15B) apart from one another in the longitudinal direction of the passage channel (2); and in that a nozzle tube section not having any cavities is located in the longitudinal direction (16) between the said cavities (15B).

8. Hot runner nozzle (1) according to one of the Claims 1 to 7 characterized in that the nozzle body has at least two cavities that are connected by way of at least one connecting channel having a smaller cross-section than the cavities ( 15A, 15B).

9. Hot runner nozzle (1) according to one of the Claims 1 to 8 characterized in that at least one cavity (15A, 15B) or one section of such a spiral-shaped or coil- shaped cavity extends around the longitudinal center axis of the hot runner nozzle (1), in particular in the nozzle tube (11).

10. Hot runner nozzle (1) according to one of the Claims 1 to 9 characterized in that the nozzle body has a base body on which a partial region is applied in layers by means of a generative method, this region having the at least one cavity (15A, 15B).