Device for granulating plastic

Abstract

Device for granulating plastic, comprising a granulating head closed off by a perforated plate (2) and a knife head which interacts with the perforated plate (2) and can be replaced by a grinding device (6), in a granulating housing (1) through which water flows, wherein the grinding device (6) has a base body (7) which can be fastened to the knife head shaft (5) and grinding wheels (8) which are rotatably mounted in the base body (7) and parallel to the knife head shaft (5), characterized in that the grinding wheels (8) are mounted in the base body (7) by means of shafts (9) which, on the side facing away from the grinding wheels (8), carry gears (10) which mesh with a common gear ring (11) which is coaxial with the knife head shaft (5), and in that the base body (7) rotates relative to the gear ring (11).

Description

[0001] The invention relates to a device for granulating plastic with a granulating head closed by a perforated plate and a knife head cooperating with the perforated plate and replaceable by a grinding device in a water-flowing granulating housing, wherein the grinding device has a base body fastenable to the knife head shaft and grinding wheels rotatably mounted in the base body and parallel to the knife head shaft.

[0002] In conventional granulation devices for plastics, the plastic strands emerging through the perforated plate of the granulation head are cut by the knives of the knife head, and the cut granules are cooled and discharged using water that flows through the granulation housing. The cutting quality depends, among other things, on the flatness of the surface of the perforated plate facing the knives. This surface is subject to wear, so that wear-related maintenance of the perforated plate requires grinding the surface of the perforated plate that interacts with the knives of the knife head. For this purpose, it is known (US 2010 / 0 081 363 A1) to replace the knife head with a grinding device whose grinding wheel is mounted on the knife shaft by means of a ball joint so that it can be pivoted to a limited extent on all sides. This ensures that the grinding wheel rests evenly on the perforated plate over the circumference.However, grinding wheels coaxial with the cutter head shaft pose the risk of creating annular grooves in the perforated plate surface. To counteract this risk, it is known (DE 44 22 200 A1) to mount the grinding wheel eccentrically on the cutter head shaft and drive it at a different speed than the cutter head shaft.

[0003] Furthermore, a grinding device with multiple grinding wheels has already been proposed (WO 2009 / 052882 A1). These wheels are mounted at a radial distance from the cutter head's rotation axis and are freely rotatable in a base body attached to the cutter head shaft. Due to this eccentric mounting with respect to the cutter head shaft, they rotate around their own axes in addition to rotating with the cutter head shaft, thus eliminating the risk of scoring. However, the advantage of not having to provide a complex drive for the grinding wheels comes at the cost of uneven rotation of the grinding wheels, which depends on the friction between the grinding wheels and the perforated plate.

[0004] In order to align the cutting edges of the knife head of a granulating device by grinding them into a geometrically uniform orbit, it is also known (DE 43 16 478 C1) to mount the knife head in a grinding device separate from the granulating device, vertically oriented in a non-rotatable but axially displaceable manner above a coaxial, drivable grinding wheel, so that the knives of the knife head are pressed against the grinding wheel during the grinding process solely by the weight of the knife head. However, such a grinding device is unsuitable for grinding a perforated plate within the granulating device.

[0005] The invention is therefore based on the object of creating a grinding device for the perforated plate of a granulating device which allows advantageous machining of the perforated plate of the granulating head using comparatively simple structural means.

[0006] Starting from a device of the type described at the outset, the invention achieves the stated object in that the grinding wheels are mounted in the base body by means of shafts which, on the side facing away from the grinding wheels, carry gears meshing with a common gear ring coaxial with the cutter head shaft, and in that the base body rotates relative to the gear ring.

[0007] By providing a common gear ring that meshes with the drive gears for the grinding wheels, a positive drive for the grinding wheels can be ensured in a structurally simple manner, because for this purpose, only a relative rotation of the gear ring relative to the base body in which the grinding wheels are rotatably mounted is required. This requirement is already met by a gear ring that is non-rotatably connected to the granulation housing, since the base body in the granulation housing is driven by the cutter head shaft. To meet special requirements, however, the gear ring can also be driven, which allows the grinding wheels to be driven independently of the speed of the cutter head shaft.For this purpose, the gear ring, which is rotatably mounted relative to the granulating housing, can be equipped with a vane ring actuated by the water flow in the granulating housing. This eliminates the need for complex design requirements and additional drive energy to drive the gear ring. Depending on the direction of rotation of the gear ring relative to the direction of rotation of the cutter head shaft, the speed of the grinding wheels can be increased or decreased compared to a drive via a non-rotatably mounted gear ring.

[0008] To ensure that the blade ring is exposed to the water flow through the granulating housing in a fluidically favorable manner, a water flow guide can be assigned to the blade ring. The design of the blade ring, the water flow guidance through the granulating housing, and the guide device thus provide a drive for the grinding wheels that meets the respective requirements, ensuring particularly favorable grinding conditions for surface grinding of the perforated plate.

[0009] The drawing shows an example of the subject matter of the invention. Fig. 1 shows a device according to the invention for granulating plastic in a section in the area of ​​the grinding device in a schematic longitudinal section, Fig. 2 this device in a section along the line II-II of Fig. 1 and Fig. 3 one of the Fig. 2 corresponding representation of a modified embodiment of the grinding device.

[0010] According to the embodiment according to the Fig. 1 and Fig. 2, the device for granulating plastic comprises a part of a granulating housing 1 through which water flows, which accommodates a granulating head in a housing part not shown for reasons of clarity, of which only the perforated plate 2 is shown. The plastic strands emerging from the granulating head through the holes 3 of the perforated plate 2 are cut into granules by means of a knife head, which are cooled and discharged by the water flowing through the granulating housing 1 in the direction of arrow 4. A knife head shaft 5 serves to drive the knife head, on which a grinding device 6 can be mounted instead of the knife head required for granulating the plastic in order to grind the surface of the perforated plate 2 facing the knife head flat if necessary.

[0011] This grinding device 6 has a disk-like base body 7 that is non-rotatably connected to the cutter head shaft 5, in which grinding wheels 8 are rotatably mounted at a radial distance from the cutter head shaft 5 and evenly distributed around the circumference. The shafts 9 of the grinding wheels 8, which are mounted in the base body 7, are each provided with a gear 10 on the side opposite the grinding wheel 8, whereby these gears 10 mesh with a common ring gear 11 that is non-rotatably connected to the granulating housing 1 via a support ring 12. When the cutter head shaft 5 is driven, the gears 10 roll on the non-rotatably held ring gear 11 and drive the grinding wheels 8 at a consistent peripheral speed according to the given transmission ratios.

[0012] Again Fig.3, it is also possible to decouple the rotational speed of the grinding wheels 8 from the speed of the cutter head shaft 5. For this purpose, the gear ring 11 is freely rotatably mounted on the base body 7 and provided with a blade ring 13, which is acted upon by the water flowing through the granulating housing 1, discharging the cut granules and which drives the gear ring 11 in rotation relative to the base body 7. Consequently, the rotational movements of the base body 7 and the gear ring 11 overlap, with the effect that a drive for the grinding wheels 8 can be set that is independent of the speed of the cutter head shaft 5.

[0013] The flow conditions of the blade ring 13 with the water pumped through the granulating housing 1 can be improved by a guide device 14. However, this guide device 14 must not rotate with the base body 7 and must therefore be assigned to the granulating housing 1.

Claims

[1] Device for granulating plastics material, comprising a granulating head closed by a perforated plate (2) and a knife head cooperating with the perforated plate (2) and replaceable by a grinding device (6) in a granulating housing (1) through which water flows, wherein the grinding device (6) comprises a base body (7) attachable to the knife head shaft (5) and grinding discs (8) rotatably mounted in the base body (7) and parallel to the knife head shaft (5), characterized by that the grinding wheels (8) are mounted in the base body (7) by means of shafts (9) which, on the side facing away from the grinding wheels (8), carry gears (10) meshing with a common gear ring (11) coaxial with the cutter head shaft (5), and that the base body (7) rotates relative to the gear ring (11). [2] Device according to claim 1, characterized by that the gear ring (11) is supported in a rotationally fixed manner relative to the granulating housing (1). [3] Device according to claim 1, characterized by that the gear ring (11) which is rotatably mounted relative to the granulating housing (1) carries a blade ring (13) which is acted upon by the water flow in the granulating housing (1). [4] Device according to claim 3, characterized by that a guide device (14) for the water flow is assigned to the blade ring (13).

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