Underwater pelletizer

Abstract

A cutting device for an underwater pelletizer (1), the underwater pelletizer (1) comprising a nozzle (3), the nozzle (3) comprising a cutting surface (31), in particular a conical cutting surface (31), the cutting surface (31) being rotationally symmetrical about a central axis (R) of the nozzle (3), and a nozzle (32) being formed in the cutting surface (31), the cutting device comprising a drive shaft (6) and at least one cutting head (5), the cutting head (5) comprising a plurality of cutting blades (9), the plurality of cutting blades (9) being used to cut, in the form of pellets, molten plastic material flowing out of the nozzle (32) of the nozzle (3) and formed into strands, wherein the cutting head (5) comprises a mechanism by which, by activating an actuator, the plurality of cutting blades (9) can be simultaneously adjusted relative to the cutting surface (31) in respective movement directions (B), the movement direction (B) comprising a movement component in a radial direction perpendicular to the central axis (R) and a movement component in an axial direction parallel to the central axis (R). The movement direction (B) is preferably the direction of the surface normal of the cutting surface (31) at the location of the cutting element (91) of each cutting blade (9).

Description

Technical Field

[0001] The present invention relates to an underwater pelletizer for pelletizing thermoplastic materials. Background Art

[0002] Granulating devices for shaping extruded molten plastic material to form strands in a nozzle are commonly used for the granulation of thermoplastic materials, in particular polymers such as polyethylene or polypropylene. Usually the operation is such that the hot material in a molten state is extruded through a nozzle of a nozzle arrangement formed as a perforated plate into a cooling liquid (e.g. water) in a cutting chamber. A blade arrangement is located in the cutting chamber and has a blade which sweeps through the opening of the perforated plate and cuts the material into strands so that pellets are formed. Corresponding granulating devices are known, for example, from EP 2861397 B1 and EP 3062978 B1.

[0003] This design principle has been proven many times in practice, and in particular can be generally simply scaled so that "large" granulators with high and very high yields can also be realized. However, the disadvantage here is that the perforated plate must therefore also be sized for large yield volumes and must be correspondingly formed to have a larger diameter. In fact, this means that for granulators with a yield of several tonnes (tons) per hour, the perforated plate can have a diameter of more than 1m. Such large perforated plates can usually only be manufactured in a very complex and costly manner. All other accessories of such granulators must also be enlarged accordingly, which leads to a very large construction volume and very high cost. Due to the large diameter of such perforated plates and the large weight associated with them, the replacements usually required can only take more effort, and the downtime of the granulator is accordingly long, which greatly increases the maintenance costs. There is a special problem in this regard, after the maintenance work is completed, the blade arrangement must be aligned in a complex manner with high precision, and due to the large diameter of the perforated plate and the large diameter of the blade arrangement associated with it, even very small axis alignment errors can cause damage.

[0004] From document DE 4419786 C1, a die-face pelletizer is also known, which has a cylindrical housing, into the inner space of which the plastic melt is fed, extruded through a channel radially through the housing wall, and cut into pellets by a blade rotating in a substantially water-free space, which slides through the opening of the channel along a cutting surface around the housing wall. The blade is driven by a rotor and is rotatably supported on a blade shaft, the cutting edge being pressed against the housing wall by a helical spring.

[0005] For the design proposed in this document, it is considered that as the speed of the rotor increases, increasingly powerful centrifugal forces act on the center of gravity of the blade (which does not coincide with the blade axis), so that an additional torque is generated, which depends on the rotor speed and causes the cutting edge to be additionally pressed against the housing wall. The design proposed in this document is not optimistic about the scale of large production rates with high granulation quality.

[0006] The design also does not provide for the desired ability to lift the blade from the cutting surface, which is, however, desirable for underwater pelletizing. Summary of the invention

[0007] Therefore, an object of the present invention is to overcome the above-mentioned drawbacks and to provide an improved underwater pelletizer capable of achieving high productivity with reduced equipment cost and reduced maintenance cost. Another object of the present invention is to provide an improved underwater pelletizer capable of achieving high productivity with reduced construction volume.

[0008] In one aspect, a cutting device for an underwater pelletizer is provided, the underwater pelletizer having a nozzle, the nozzle having a cutting surface, in particular a cutting surface formed in a conical, truncated conical, cylindrical or cap-shaped shape, the cutting surface being rotationally symmetrical about a central axis of the nozzle and having a nozzle formed in the cutting surface, the cutting device having a drive shaft and at least one cutting head, the cutting head having a plurality of cutting blades, the plurality of cutting blades being used to cut the molten plastic material flowing out of the nozzle of the nozzle and formed in strands in the form of pellets, and the cutting head having a mechanism by which the plurality of cutting blades can be simultaneously adjusted relative to the cutting surface in respective moving directions by activating an actuator, the moving direction comprising a moving component in a radial direction perpendicular to the central axis and a moving component in an axial direction parallel to the central axis (R).

[0009] In another aspect, an underwater pelletizer is provided, which has a nozzle and the cutting device, wherein the nozzle has a cutting surface that is rotationally symmetric about a central axis of the nozzle and has a nozzle formed in the cutting surface.

[0010] The invention proposes a nozzle head for an underwater pelletizer, which has a rotationally symmetrical (e.g. frustoconical) cutting surface. The cutting surface can be designed so that it has a large area and a correspondingly large number of nozzles can be arranged therein, which enables a correspondingly high-yield pelletizing, while the maximum diameter of such a nozzle head is greatly reduced in terms of size compared to a conventionally constructed perforated plate.

[0011] However, the use of such a non-planar three-dimensional nozzle in an underwater pelletizer also brings new problems for the cutting device. Thus, at the beginning of the underwater pelletization, the nozzle needs to be filled with the melt, which step is carried out in an open cutting chamber. Therefore, the cutting blade that hinders this step needs to be removed and "placed" elsewhere. In the case of a conventional underwater pelletizer, this can be easily achieved: the cutting head leaves the perforated plate and the cutting blade is thus also moved axially away from the cutting surface. In contrast, in the case of a non-planar three-dimensional nozzle, such a movement of the cutting blade only in the axial direction is impossible or difficult, depending on the geometry. Therefore, according to the invention, it is proposed to configure the cutting device so that the cutting blade can move in the axial and radial directions at the same time, so that the cutting blade can be adjusted simply and safely relative to the cutting surface.

[0012] Here, it is particularly provided that the moving direction is the direction of the surface normal of the cutting face at the position of the cutting piece of each cutting blade. In other words, the cutting blade is adjusted so that each is moved perpendicular to the cutting face and can not be pushed or pulled, for example, along the cutting edge transverse to the cutting face.

[0013] The cutting head may advantageously have a blade support ring in which a plurality of cutting blade mounting portions are defined, each of the cutting blade mounting portions being defined with an incision into which the respective cutting blade is inserted, at least one guide piece being engaged in a guide groove to guide the movement of the cutting blade in and out of the incision, the at least one guide piece being formed in one of the cutting blade mounting portion and the handle portion of the cutting blade, the guide groove being formed in the other of the cutting blade mounting portion and the handle portion of the cutting blade, the guide piece and the guide groove being defined by a straight line gradually moving away from the center axis in the direction of the nozzle.

[0014] The blade support ring is further preferably arranged on the drive shaft in an axially displaceable manner and is provided with a component group, which cooperates at the respective cutting blades and acts on the axial displacement of the blade support ring. When the blade support ring is axially displaced on the drive shaft, the cutting blade is prevented from being pulled out or pushed into the respective related cutting blade mounting part. The component group is particularly capable of limiting the movement direction of the cutting blade.

[0015] The component group that cooperates at the respective cutting blades and acts on the axial displacement of the blade support ring and prevents the cutting blades may include at least one protrusion, which is formed at the handle portion of each cutting blade and cooperates in the cutout, which is formed in the end of the drive shaft or in a component fixedly connected to the drive shaft.

[0016] The aforementioned technical measures can be used alone or in combination to realize a mechanism which also allows the cutting element to be adjusted in the axial direction in a constructionally simple and at the same time operationally safe manner.

[0017] The drive shaft can advantageously be formed as a hollow shaft, through which the process water is fed into the cutting chamber of the underwater pelletizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be described in detail below with reference to the accompanying drawings:

[0019] Figure 1 Schematically illustrates an underwater pelletizer according to an embodiment of the present invention;

[0020] Figure 2 The schematic cross-sectional view more specifically shows a state in which the cutting blade of the cutting head contacts the cutting surface of the cutting head. Figure 1 The nozzle and cutting head of the underwater granulator;

[0021] Figure 3 Shows Figure 2 Details of the cutting blade and the end of the hollow shaft;

[0022] Figure 4 A cutting blade mounting portion is shown in schematic front view;

[0023] Figure 5 A cutting blade is shown in schematic front view;

[0024] Figure 6 A cutting blade housed in each cutting blade mounting portion is shown in schematic front view;

[0025] Figure 7 A schematic cross-sectional view shows a state in which a cutting blade of a cutting head is lifted from a cutting surface of the cutting head. Figure 3 nozzle and cutting head. DETAILED DESCRIPTION

[0026] Figure 1 An underwater pelletizer according to an embodiment of the present invention is schematically shown. As shown, the underwater pelletizer 1 has a cutting chamber 2, in which a nozzle 3 and a cutting head 5 are arranged. The cutting head 5 is driven by a rotary drive 12 via a hollow shaft 6 supported in a bearing 13. The rotary drive 12 is advantageously designed as a direct electric drive, and the hollow shaft 6 extends through the motor stator and is driven by it. The hollow shaft 6 is also used as a supply for process water into the cutting chamber 2. For this purpose, the hollow shaft 6 is connected to a process water supply pipe 10 via a rotary joint 11. The process water containing the pellets flows out of the cutting chamber 2 via a process return pipe 15.

[0027] Will refer to Figure 2The design and construction of the spray head 3 and the cutting head 5 are described in detail.

[0028] like Figure 2 As shown, the spray head 3 is formed as a three-dimensional rotating body with a central axis R, which also defines the longitudinal axis of the spray head, and has a plurality of nozzles 32 formed in a conical region of the spray head 3, which is referred to here as a cutting surface 31. In addition, the spray head 3 has an inner hollow space 33, into which the plastic material is supplied as a melt S, and from which the melt S leaves the spray head 3 through the nozzles 32.

[0029] The cutting head 5 is formed by a blade support ring 8 in which a plurality of cutting blades 9 are held. More specifically, each cutting blade 9 has a cutting portion 92 to which a cutting piece 91 is fastened and a handle portion 93 received and held in a cutting blade mounting portion 81.

[0030] Furthermore, the blade support ring 8 has a shaft connection portion 82, which is formed coaxially with the hollow shaft 6, and the blade support ring 8 is connected to the hollow shaft 6 via the shaft connection portion 82 in such a way that the rotational movement of the hollow shaft 6 is transmitted to the blade support ring 8. Such a connection is formed here so as to allow the blade support ring 8 to be displaced axially on the hollow shaft 6. In order to achieve the displacement of the blade support ring 8, the blade support ring 8 also has an actuation portion 83, which can be connected to the fork portion 14 (see Figure 1 ) to achieve the shift.

[0031] Therefore, in Figure 2 In the operating state of the underwater pelletizer 1 shown, the rotational movement of the hollow shaft 6 can be transmitted to the blade support ring 8, so that the cutting piece 91 of the cutting blade 9 held by the blade support ring 8 sweeps across the conical cutting surface 31 and cuts and pelletizes the strand-like molten material leaving the nozzle 31.

[0032] At the same time, process water is supplied to the cutting chamber 2 via the hollow shaft 6. The end 61 is preferably formed as a widened cone. In addition, the spray head 3 can be formed to be coaxial at its axial front end, or, as in Figure 2 In the illustrated embodiment, when the spray head 3 has a flat surface at its axial front end, an isolated cone 4 may be provided so that the end 61 and the isolated cone 4 cooperate to guide the process water entering from the hollow shaft 6 directly to the cutting surface 31 and the cutting blade 9 .

[0033] Figure 2 It is further shown that the end portion 61 is also configured to form a cutout 62, as shown in FIG. Figure 3 Specifically, the protrusion 95 formed at the handle portion 93 of each cutting blade 9 can be fitted into the cutout 62 .

[0034] Figure 3The cutting blade 9 is shown in a schematic side view. Figure 2 As described above, the cutting blade 9 has a handle portion 93 and a cutting portion 92 to which a cutting member 91 is fastened. Guide grooves 94 are formed on both sides of the handle portion 93. In addition, two protrusions 95 extending in the direction of the end portion 61 are formed at the handle portion 93, and a notch 96 is formed between the two protrusions 95, and the notch 96 is defined in the lateral direction by the flat contact surface 62a.

[0035] Figure 3 Also shown is the end 61 of the hollow shaft 6 , in which a cutout 62 is formed, which is delimited and limited in the transverse direction by two wings 63 .

[0036] like Figure 3 As shown by the arrow in , it is arranged here that one of the fins 63 cooperates with the cutout 96 and at the same time one of the projections 95 cooperates with the cutout 62. Under the interaction of the projection 95 and the fin 63, a linear guide is formed in such a manner that the projection 95 and the fin 63 can move relative to each other in a first direction defined by the extension direction of the flat contact surfaces 96a and 62a formed at the projection 95 and the fin 63, respectively, and movement in a direction perpendicular to the contact surfaces 96a and 62a, respectively, is prevented.

[0037] Will refer to Figures 4 to 6 The mounting of the cutter blade 9 in the cutter blade mounting portion 81 will be described. Figure 4 The cutting blade mounting portion 81 is shown in a schematic front view. The cutting blade mounting portion 81 has a cutout 811, which is open toward the bottom and forms a guide piece 812. The size of the opening 811 is formed so that the handle portion 93 of the cutting blade 9 can be pushed into the opening 811 from the front, and the guide piece 812 cooperates with the guide groove 94 formed on the side of the handle portion 93 of the cutting blade 9 (see Figure 5 ). Figure 6 A plurality of cutting blade mounting portions 81 are schematically shown, each of which has a cutting blade 9 inserted therein. Figure 6 The cutting blade mounting portion 81 is shown in the form of a straight line arrangement, but in fact the cutting blade mounting portion 81 is located on an arc to form a blade support ring 8.

[0038] The axial displaceability of the blade support ring 8 described above, combined with the linear guidance using the projections and fins 63 also described above, and combined with the action of the guide tabs 812 engaging in the guide grooves 94, forms a mechanism, as will be seen in reference to Figure 7 Specifically, by this mechanism, the cutting blade 9 can be adjusted radially away from the cutting plane 31 and toward the cutting plane 31 relative to the central axis R, or in a direction including a radial component.

[0039] Figure 7 Such a situation is shown, the actuating portion 83 is activated in a manner to axially displace the blade support ring 8 on the hollow shaft 6, so that the blade support ring 8 moves away from the spray head 3. Since the protrusion 95 of the cutting blade fitted in the opening 62 abuts against the fin 63 (is introduced between the protrusion 95 and enters the opening 96 formed therein), it is possible to prevent the cutting blade 9 from moving with the blade support ring 8 so that the cutting blade 9 is pulled out of the cutout 811 in the cutting blade mounting portion 81. At the same time, the guide piece 812 in the cutting blade mounting portion 81 is not arranged parallel to the central axis R, but is angled therewith, so that the guide piece 812 defines a slope that increases in the direction of the spray head 3, which is a straight line extending through the guide groove 812, gradually moving away from the direction of the spray head 3. Now, if the blade support ring 8 moves away from the nozzle 3, the effect of the slope of the guide groove 812 is that the cutting blade 9 held by the wing 62 moves outward in a direction away from the central axis R, so that the cutting element 91 is lifted from the cutting surface 31 as shown by the arrow B, which shows the moving direction of the cutting element 91 or the moving direction of the cutting blade 9 as a whole. Here, the moving direction B is defined by the interaction of the protrusion 95 and the wing 62 that form a linear guide, and more specifically, by the extension direction Q of the contact surfaces 96a and 62a away from the central axis R. For example, if the extension direction Q is perpendicular to the central axis R at 90°, the moving direction of the cutting element 91 or the moving direction of the cutting blade 9 is also perpendicular to the central axis R. However, preferably, the cutting blade 9 or its cutting element 91 is lifted in a direction that satisfies both radial departure from the central axis R and axial departure from the nozzle 3. Here, it is particularly preferred that Figure 7 In the illustrated situation, the cutting blade 9 or its cutting element 91 are lifted from the cutting surface 31 along the direction of the surface normal forming the cutting surface 31, that is, each cutting element 91 moves from the cutting surface 31 along the direction perpendicular to the cutting surface 31 at the position of the cutting element 91. However, it should be noted that, as shown by the straight line P extending through the cutting surface 31 and the straight line P' parallel to the straight line P and extending through the cutting element 91, the cutting element 91 also moves away from the cutting surface 31 respectively with respect to different movement directions B, so that the cutting element 91 remains parallel to the cutting surface 31.

[0040] although Figure 7Such an example is shown, because the blade support ring 8 is moved axially away from the nozzle 3 on the hollow shaft 6, the cutting blade 9 is lifted from the cutting surface 31 and adjusted away from the cutting surface 31, but it is easy to understand that the adjustment of the cutting blade 9 in the direction toward the cutting surface can also be achieved, because the blade support ring 8 is moved axially toward the nozzle 3 on the hollow shaft 6, so that the cutting blade 9 is pushed into the cutting blade mounting portion 81, and due to the effect of the protrusion 95 and the wing 62 that form a linear guide, the cutting blade 9 is moved in the moving direction of the cutting piece 91 toward the cutting surface 31 (with the same direction as the cutting piece 91). Figure 7 Move the cutting blade in the opposite direction of movement B).

[0041] Reference numerals list

[0042] 1Underwater pelletizer

[0043] 2 Cutting Room

[0044] 3 Nozzles

[0045] 4 isolated cones

[0046] 5 Cutting head

[0047] 6Hollow shaft

[0048] 8 blade support ring

[0049] 9 cutting blades

[0050] 10 Process water supply pipe

[0051] 11 Rotary joint

[0052] 12 Rotating drive element

[0053] 13 Bearings

[0054] 14 Fork

[0055] 15 Process return pipe

[0056] 31 Cutting surface

[0057] 32 Nozzle

[0058] 33 Internal hollow space

[0059] 61 end

[0060] 62 Incision

[0061] 62a Contact surface

[0062] 63 Wing

[0063] 81 Cutting blade mounting part

[0064] 82 Shaft connection

[0065] 83 Actuator

[0066] 91 Cutting pieces

[0067] 92 Cutting Department

[0068] 93 handle part

[0069] 94 Guide groove

[0070] 95 protrusion

[0071] 96 Opening

[0072] 96a Contact surface

[0073] 811 Incision

[0074] R Center axis

[0075] P Line extending through the cutting surface

[0076] P' extends through the straight line of the cut piece

[0077] Q The extension direction of the contact surfaces 62a and 96a

[0078] S Melt

[0079] W Process water

Claims

1. A cutting device for an underwater pelletizer (1), the underwater pelletizer (1) comprising a nozzle (3), the nozzle (3) comprising a cutting surface (31), the cutting surface (31) being rotationally symmetrical about a central axis (R) of the nozzle (3), and a nozzle (32) being formed in the cutting surface (31), in, The cutting device comprises a drive shaft (6) and at least one cutting head (5), wherein the cutting head (5) comprises a plurality of cutting blades (9), wherein the plurality of cutting blades (9) are used to cut the molten plastic material flowing out of the nozzle (32) of the nozzle (3) and formed into strands in the form of pellets, and is characterized in that: The cutting head (5) has a blade support ring (8), a plurality of cutting blade mounting portions (81) are defined in the blade support ring (8), each of the cutting blade mounting portions (81) is defined with a cutout (811) into which the respective cutting blade (9) is inserted, at least one guide piece (812) is engaged in a guide groove (94) to guide the movement of the cutting blade (9) to be pushed into and pulled out of the cutout (811), the at least one guide piece (812) is formed in one of the cutting blade mounting portion (81) and the handle portion (93) of the cutting blade (9), the guide groove (94) is formed in the other of the cutting blade mounting portion (81) and the handle portion (93) of the cutting blade (9), and the guide piece (812) and the guide groove (94) are defined by a straight line that gradually moves away from the center axis (R) in the direction of the nozzle (3).

2. The cutting device according to claim 1, characterized in that The blade support ring (8) is axially displaceably arranged on the drive shaft (6), and the blade support ring (8) has an actuating portion (83) as an actuating member, the actuating portion (83) forming a fitting point for displacing the blade support ring (8), and A component group is provided, which cooperates at the respective cutting blades (9) and has the function of blocking the cutting blades (9) when the blade support ring (8) is axially displaced, so that when the blade support ring (8) is axially displaced on the drive shaft (6), the cutting blades (9) are pulled out or pushed into the respective related cutting blade mounting parts (81).

3. The cutting device according to claim 2, characterized in that: By activating the actuator, the plurality of cutting blades (9) can be simultaneously adjusted relative to the cutting surface (31) in respective movement directions (B), wherein the movement directions (B) include a movement component in a radial direction perpendicular to the central axis (R) and a movement component in an axial direction parallel to the central axis (R), and The set of components cooperating at the respective cutting blades (9) and having the effect of blocking the cutting blades when the blade support ring (8) is displaced axially defines the movement direction (B).

4. The cutting device according to claim 3, characterized in that: The component group that cooperates at each of the cutting blades (9) and has the function of preventing the cutting blades when the blade support ring (8) is axially displaced includes at least one protrusion (95), which is formed at the handle portion (93) of each of the cutting blades (9) and cooperates in the cutout (62), which is formed in the end (61) of the drive shaft (6) or in a component fixedly connected to the drive shaft (6).

5. The cutting device according to claim 3, characterized in that: The moving direction (B) is the direction of the surface normal of the cutting surface (31) at the position of the cutting piece (91) of each cutting blade (9).

6. An underwater pelletizer (1), comprising a nozzle (3) and a cutting device according to any one of the preceding claims, wherein the nozzle (3) has a cutting surface (31), the cutting surface (31) is rotationally symmetrical about the central axis (R) of the nozzle (3), and a nozzle (32) is formed in the cutting surface (31).

7. The underwater pelletizer (1) according to claim 6, characterized in that The rotationally symmetrical cutting surface (31) is conical, truncated conical, cylindrical or cap-shaped.

8. The underwater pelletizer (1) according to claim 6 or 7, characterized in that The drive shaft (6) is formed as a hollow shaft, and process water is supplied to the cutting chamber (2) of the underwater pelletizer (1) through the hollow shaft (6).

Images