Abstract
A nonreturn valve includes two half-shells, arranged in a portion of the screw with a reduced screw diameter. One or more channels for the melt to flow through from the screw into the space in front of the screw is/are provided in each of the half-shells, the channels lie substantially parallel to the longitudinal axis of the nonreturn valve or of the screw. In each of the channels are a ball and, following the ball in the direction of flow of the melt, a pin arranged substantially transversely to the direction of flow of the melt. In the direction of flow of the melt, the channels have a first channel portion, with a channel diameter less than the diameter of the ball, and a second channel portion, with a channel diameter greater than the diameter of the ball, the ball and the pin are arranged in the second channel portion.
Claims
1. A nonreturn valve (23) for a screw (20) of a plasticising unit of an injection-moulding machine, comprising two half-shells (24a, 24b), which can be arranged in a portion (21) of the screw (20) with reduced screw diameter, wherein in each of the half-shells (24a, 24b) one or more channels (25) are provided for melt to flow through from the screw (20) into the space in front of the screw, wherein the channels (25) lie substantially parallel to the longitudinal axis of the nonreturn valve (23) or respectively to the longitudinal axis of the screw (20), wherein in each of the channels (25) there are provided a ball (26) and, following the ball as seen in the direction of flow of the melt, a pin (27), wherein the pin (27) is arranged substantially transversely to the direction of flow of the melt, wherein the channels (25), as seen in the direction of flow of the melt have respectively a first channel portion (28a) with a channel diameter smaller than the ball diameter, and a second channel portion (28b) with a channel diameter greater than the ball diameter, and wherein ball (25) and pin (27) are arranged in the second channel portion (28b).
2. The nonreturn valve according to claim 1, wherein a conically configured transition (29) is provided from the first channel portion (28a) to the second channel portion (28b).
3. The nonreturn valve according to claim 1, wherein the pin (27) has a cylindrical cross-section or respectively is configured as a cylinder pin (27).
4. The nonreturn valve according to claim 1, wherein the half-shells (24a, 24b) are configured in such a way that the external diameter of the joined-together half-shells (24a, 24b), measured parallel and perpendicularly to the separation joint (31) is of equal size, in such a way that in the joined-together state a separation gap width of zero results.
5. A screw of a plasticising unit of an injection-moulding machine according to claim 1, wherein the screw (20) has a portion (21) in which no screw flight (32, 33) is present and in which the external diameter of the screw (20) corresponds to the internal diameter of the nonreturn valve (23), and wherein the two half-shells (24a, 24b) of the nonreturn valve are arranged in said portion (21) on the screw (20).
6. The screw according to claim 5, wherein the nonreturn valve (23), as seen in the flow direction of the melt, is arranged at the front end of the screw (20).
7. The screw according to claim 5, wherein the nonreturn valve (23) is arranged spaced apart from the front end of the screw (20) in such a way that, as seen in the flow direction of the melt, both in front of and also behind the nonreturn valve (23) a screw portion is present with a screw flight (32, 33).
8. The screw according to claim 5, wherein one or both half-shells (24a, 24b) are arranged by means of an anti-rotation means (30) on the screw (20).
9. The screw according to claim 8, wherein the anti-rotation means (30) is embodied in the form of one or more keys.
10. A plasticising unit of an injection-moulding machine with a screw, able to be driven rotatably and linearly, according to claim 5.
Description
[0014] The invention is to be described in further detail below with the aid of an example embodiment and with reference to FIGS. 3 to 6. There are shown:
[0015] FIG. 3a perspective illustration of a screw according to a first embodiment with a nonreturn valve according to the inventionwith sectional illustration in the region of the nonreturn valve;
[0016] FIG. 3b enlarged illustration of the part of the nonreturn valve of FIG. 3a, situated in the circle K2;
[0017] FIG. 4a perspective illustration of a nonreturn valve according to the invention;
[0018] FIG. 4b top view onto the nonreturn valve according to FIG. 4a from the direction of the arrow Z in FIG. 4a;
[0019] FIG. 5a perspective illustration of a plasticising unit with a nonreturn valve according to the inventionwith cut open cylinder and granulate hopper;
[0020] FIG. 5b enlarged illustration of the part of the plasticising unit of FIG. 5a, situated in the circle K3;
[0021] FIG. 7 second embodiment of a screw with a nonreturn valve according to the invention.
[0022] According to FIG. 3a, a screw 20 is configured at its front end with a portion 21 of reduced screw diameter. A screw tip 22 adjoins thereto downstream. In the portion 21, a nonreturn valve 23 according to the invention is arranged, comprising two half-shells 24a and 24b. In each of the half-shells 24a, 24b channels 25 are provided for the melt to flow through from the screw 20 into the space in front of the screw in front of the screw tip 22. The channels lie parallel to the longitudinal axis of the nonreturn valve 23 or respectively to the longitudinal axis of the screw 20. In each of the channels 25 there are provided a ball 26 and, following the ball 26 as seen in the direction of flow of the melt, a pin 27, wherein the pin is preferably arranged substantially transversely to the direction of flow of the melt. The channels 25 are configured in such a way that, as seen in the direction of flow of the melt, respectively a first channel portion 28a is present having a channel diameter which is smaller than the ball diameter, and a second channel portion 28b is present having a channel diameter which is greater than the ball diameter. The ball and pin are arranged in the second channel portion 28b. The transition 29 from the first channel portion 28a to the second channel portion 28b is preferably configured conically, from which a conical sealing seat results for the ball 26. An anti-rotation means 30 ensures that on rotation of the screw 20 no relative movement can occur between the screw and the nonreturn valve. The anti-rotation means 30 can be embodied in the form of one or more keys (not illustrated here). The anti-rotation means can, however, also take place in another suitable manner in a form-fitting manner. The half-shells 24a, 24b, the balls 25 and the pins 27 preferably consist of hardened, wear-resistant steel. The outer surface of the half-shells, in particular the external diameter of the half-shells 24a and 24b, can be additionally protected by a wear protection layer. This can be applied for example by plasma powder deposition welding. In contrast to the prior art, the screw tip 22 and the screw 20 are one component.
[0023] As can be seen in FIGS. 4a and 4b, the half-shells 24a and 24b are preferably embodiment so that in the separation joint 31 between the two half-shells a separation gap of 0 results. The external diameter of the mounted half-shells 24a and 24b, measured parallel and perpendicularly to the separation joint 31, is of equal size. Through this embodiment, a flowing back of the molten plastic between the two half-shells 24a and 24b is prevented.
[0024] FIGS. 5a and 5b show a plasticising unit with a screw according to a first embodiment of the invention. Screw cylinder 1, cylinder head 2, heating bands 4 and granulate hopper 5 can be configured in a manner known per se as in FIG. 1. Therefore, the same reference numbers can also be used here. In contrast to the prior art, the screw 20 is equipped with a nonreturn valve 23 according to the invention. The front end of the screw 20 is configured in accordance with the illustrations of FIGS. 3a and 3b, i.e. the screw 20 has a portion 21 with a reduced diameter. In this region, the two half-shells 24a and 24b can be arranged on the screw 20.
[0025] FIG. 6 shows a screw 20 according to a second embodiment of the invention. The nonreturn valve 23 does not necessarily have to sit at the front end of the screw, but rather can also be arranged further upstream. In this variant, one or more screw flights 32 are situated upstream of the nonreturn valve 23, and one or more screw flights 33 are situated downstream of the nonreturn valve 23, so that as seen in the direction of flow of the melt, after the nonreturn valve 23 a further conveying and homogenising of the plastic melt takes place. The precise number and the respective course of the screw flights 32, 33 on both sides of the nonreturn valve 23 depends on the case of application. In the embodiment according to FIG. 6, a screw flight 32 is provided upstream of the nonreturn valve 23, and a screw flight 33 is provided downstream of the nonreturn valve 23. The nonreturn valve 23 corresponds to the embodiment as has been described in further detail in connection with FIGS. 3a, 3b, 4a and 4b. In contrast to FIGS. 3a, 5a and 5b, the region 21 with reduced screw diameter and therefore the position of the nonreturn valve 23 is spaced apart further from the front end of the screw 20. The precise distance and therefore the position of the nonreturn valve 23 on the screw 20 conform to the respective case of application. Viewed in longitudinal direction of the screw 20, the nonreturn valve 23 can be arranged more or less distant from the front end of the screw 20.
LIST OF REFERENCE NUMBERS
[0026] 1 screw cylinder
[0027] 2 cylinder head
[0028] 3 screw
[0029] 4 heating bands
[0030] 5 granulate hopper
[0031] 5 nonreturn valve according to the prior art
[0032] 7 screw head
[0033] 8 pressure ring
[0034] 9 blocking ring
[0035] 10 thread
[0036] 11 wing
[0037] 20 screw
[0038] 21 portion with reduced diameter
[0039] 22 screw tip
[0040] 23 nonreturn valve according to the invention
[0041] 24a first half-shell
[0042] 24b second half-shell
[0043] 25 channel
[0044] 26 ball
[0045] 27 cylinder pin
[0046] 28a channel portion with diameter smaller than ball diameter
[0047] 28b channel portion with diameter greater than ball diameter
[0048] 29 conical ball sealing seat
[0049] 30 anti-rotation means
[0050] 31 separation joint
[0051] 32 screw flight upstream
[0052] 33 screw flight downstream
