Extruder die head

Abstract

An extruder die head, preferably a blown film head, comprises an internal cylindrical mandrel and a jacket, which envelops concentrically said mandrel. Between said mandrel and jacket an annular channel is formed that empties into a die slit. At least one melt-supplying line empties into the annular channel in the area opposite the die slit. To avoid slits between the central mandrel and the jacket, enveloping said mandrel, where the polymer melt can accumulate and deposit, the mandrel is made as one piece with a flange-like foot and is provided in its area, adjacent to the foot, with at least one borehole, which feeds in the melt. On the mandrel adjacent to the foot is shrunk a ring, which seals the slit between both. On the ring is mounted a cylindrical jacket and is connected sealingly to said jacket, which envelops the mandrel, forming an annular channel.

Description

[0001] The invention relates to an extruder die head, preferably a blown film head, comprising an internal cylindrical mandrel and a jacket, which envelops concentrically said mandrel. Between said mandrel and jacket an annular channel is formed that empties into a die slit. The invention also comprises at least one line, which empties into the annular channel in the area opposite the die slit and which feeds a melt.

[0002] Blown film heads of this type exist. Usually the mandrel exhibits one or several helical groove(s), whose depth decreases in the direction of the die slit, starting from the feed channel(s) so that the polymer melt overflows more and more the webs, which define the channels, and assumes a uniform flow in the axial direction. The prior art extruder die heads exhibit the special problem that the mandrel on the other side of the beginning of the annular channel is fitted sealingly into a cylindrical borehole of the jacket. If, however, the extruder die head becomes warm due to the polymer melt, flowing through said extruder die head, the jacket expands more, on account of its larger diameter, than the central mandrel so that between the two of them a slit can form, into which penetrates the polymer melt that is fed in under pressure. Since the melt can accumulate in the area of this slit and because of its long residence time in the hot die head, where it can decompose and become brittle, particles of the deposited melt can be dragged along by the melt. Said particles become obvious in the extruded film tube or the inflated film bubble as the defective spots.

[0003] Therefore, the object of the invention is to provide an extruder die head of the class described in the introductory part, wherein slits, in which the polymer melt can accumulate, deposit and become brittle, are avoided between the central mandrel and the jacket, enveloping said mandrel.

[0004] The invention solves this problem in that the mandrel is made as one piece with a flange-like foot and is provided in its area, adjacent to the foot, with at least one borehole, which feeds in the melt, and that on the mandrel adjacent to the foot is shrunk a ring, which seals the slit between both, and that on the ring is mounted a cylindrical jacket and is connected sealingly to said jacket, which envelops the mandrel, forming an annular channel.

[0005] In the case of the extruder die head of the invention, the mandrel is reliably sealed with respect to the flange-like foot, which can be connected to the mandrel as one material piece, by means of the ring that is shrunk on. The ring is shrunk on the mandrel with such a pretension that even if the mandrel and the ring become warm, no slit, into which the melt can penetrate and become brittle in said slit, can form between the two. The cylindrical jacket is mounted on the ring and connected sealingly to it.

[0006] A preferred embodiment provides that the mandrel exhibits in its area adjacent to the foot one or several helical groove(s), which exhibit(s) a depth that decreases in the direction of the die slit and which is (are) closed in the direction of the foot. The boreholes, which feed in the melt, empty in the initial regions of the grooves in the vicinity of the foot. In this respect the shrunk-on ring encloses sealingly the groove-free end of the mandrel and its initial region that is provided with the grooves. In this embodiment the shrunk-on ring seals without a gap the groove edges in the foot region of the mandrel so that from the grooves the melt, fed into the initial region of the grooves, can enter into the annular space between the mandrel and the jacket. In this space the melt can assume increasingly and uniformly an axial flow.

[0007] Preferably the foot and the ring are provided with radial annular surfaces, which lie in a common plane and which can lie sealingly on each other and can be mounted together so as to seal.

[0008] Preferably the ring and the jacket are also provided with annular surfaces, which lie in a common radial plane and which lie sealingly side by side and are mounted together.

[0009] To fasten the jacket to the ring, the jacket can be mounted by intercalating the ring through an expansion screw connection with the annular surface of the foot.

[0010] If the extruder die head is a blown film head, boreholes or channels can be provided in the known manner between the channels, feeding in the melt, in order to feed in and exhaust in the known manner the blowing air.

[0011] One embodiment of the invention is explained in detail below with reference to the drawing. The single figure is a schematic of an extruder die head with a cut ring, which is shrunk on the mandrel, and a cut jacket.

[0012] The blown film head 1 comprises an internal mandrel 2, which is made as one piece with a flange-shaped foot 3. Starting from its region in the vicinity of the foot, the mandrel 2 is provided with multiple rows of helical grooves 4, whose depth decreases in the direction of the die slit 5. The initial regions of the grooves 4 are closed in the direction of the flange-like foot 3. Into the initial regions of the grooves 3 empty the boreholes 6, through which the melt is fed in over the non-illustrated boreholes and channels. On the mandrel 2 is shrunk sealingly a ring 7, whose cross section is rectangular and whose bottom annular surface rests flush on the radial annular surface 8 of the foot 3. Said annular surface forms with the jacket of the mandrel 2 a right angle step. The shrunk on ring 7 envelops the initial region of the helical grooves 3 of the mandrel, and in particular in such a manner that it rests with considerable pretension sealingly on the shaded part of the mandrel, thus on the webs and edges, defining the grooves. The region of the mandrel 2, enveloped by the ring 7, is defined by the dashed line 9 in the direction of the die slit 5. Thus, at the upper edge of the ring 7, marked by the dashed line 9, the melt enters into the ring slit 10. On the ring 7 is mounted a cylindrical annular jacket 11. The annular channel or annular slit 10 is formed between said jacket and the mandrel 2, enveloped by said jacket. This annular slit 10 empties in the illustrated manner into the die slit 5.

[0013] The cylindrical jacket 11 is provided on its bottom end with a radial annular sealing surface, which rests flush and sealingly on the upper annular surface 12 of the ring 7 that is shrunk on. The cylindrical jacket 1 is provided with axial boreholes (not illustrated), which align with the boreholes of the ring 7. Into these boreholes are inserted tightening screws (not illustrated), which are screwed into the threaded boreholes (not illustrated) in the bottom flange-like foot 3.

Claims

1. Extruder die head (1), preferably a blown film head, comprising an internal cylindrical mandrel (2) and a jacket (11), which envelops concentrically said mandrel, between said mandrel and jacket an annular channel (10) being formed that empties into a die slit (5), and comprising at least one line (6), which empties into the annular channel (10) in the area opposite the die slit and which feeds in a melt, characterized in that the mandrel (2) is made as one piece with a flange-like foot (3) and is provided in its area, adjacent to the foot, with at least one borehole (6), which feeds in the melt, and that on the mandrel (2) adjacent to the foot (3) is shrunk a ring (7), which seals the slit between both, and that on the ring (7) is mounted a cylindrical jacket and is connected sealingly to said jacket, which envelops the mandrel (2), forming an annular channel (10).

2. Extruder die head, as claimed in claim 1, characterized in that the mandrel (2) exhibits in its area adjacent to the foot (3) one or several helical groove(s) (4) which exhibit(s) a depth that decreases in the direction of the die slit (5) and which is (are) closed in the direction of the foot (3) and in their initial regions in the vicinity of the foot empty the boreholes (6), which feed in the melt, and that the shrunk-on ring (7) encloses sealingly the groove-free end of the mandrel and its initial region that is provided with the grooves (4).

3. Extruder die head, as claimed in claim 1 or 2, characterized in that the foot (3) and the ring (7) are provided with radial annular surfaces, which lie in a common plane.

4. Extruder die head, as claimed in any one of the claims 1 to 3, characterized in that the ring (7) and the jacket (11) are provided with annular surfaces, which lie in a common radial plane.

5. Extruder die head, as claimed in any one of the claims 1 to 4, characterized in that the jacket (11) is fixed in position with the ring (7).

6. Extruder die head, as claimed in any one of the claims 1 to 5, characterized in that the jacket (11) is mounted by intercalating the ring (7) through expansion screw connection with the annular surface (8) of the foot (3).