Cutter hub holder

Abstract

A cutter hub holder for blades acting against a die plate of an underwater pelletizer including a spring-loaded blade holder that is drivingly connected with a driven shaft and biased axially toward the die plate at a variably controlled pneumatic pressure. The driving connection between the shaft and cutter hub holder includes a quick connect and disconnect drive coupling to enable the blade holder to be quickly replaced. The motor shaft has a through bore to introduce the pneumatic pressure to the cutter hub holder.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a cutter hub holder for blades acting against a die plate of an underwater pelletizer including a spring-loaded blade holder that is drivingly connected with a driven shaft and biased axially toward the die plate at a variable controlled pressure. The driving connection of the cutter hub holder between the shaft and blade holder includes a quick connect and disconnect drive coupling.

2. Description of the Prior Art

The following U.S. patents relate to developments in underwater pelletizers.

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3,196,487      4,529,370    5,110,523
3,317,957      4,614,307    5,190,768
4,123,207      4,728,276    5,435,713
4,179,255      5,059,103    5,527,176
4,500,271
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The above patents disclose (a) an arrangement that manually controls displacement of the cutter assembly to compensate for blade wear and maintain the proper blade-to-die pressure, (b) an arrangement that automatically advances the blade by a stepping motor activated by a sensor that detects blade wear by sensing the relative distance between the cutter assembly and the die, (c) a spring that exerts pressure against the knife holder assembly and (d) electronic circuits for controlling hydraulic pressure to automatically displace the drive shaft and thereby control blade-to-die pressure. However, the above patents do not disclose a structure which delivers variable pneumatic pressure to a piston and cylinder incorporated into the drive shaft to an intermediary member which, in turn, exerts a force against a spring that displaces the cutter assembly or cutter hub to maintain optimum pressure of the cutter blades toward the die face. Also, the above patents do not disclose a bayonet coupling cutter hub attachment to the drive shaft of an underwater pelletizer which permits relative axial movement therebetween.

In a cutter hub holder of this type, such as generally disclosed in U.S. Pat. No. 5,059,103 issued Oct. 22, 1991, the cutter hub is pressed against the die plate by a spring, in order to compensate for wear of the cutting blades and to ensure a permanent contact of the cutting blades with the die plate. In the known cutter hub holders the spring pressure is selected to satisfy the needs during pelletizing. This pressure force is thus always set to the highest pressure required during operation, while there are phases in operations during which a lower spring force would be sufficient. Yet, the higher the spring pressure acting on the blade holder, the greater the wear of the blades and of the die plate.

Any equipment utilizing manual adjustment methods for the cutter holder and blades requires considerably more operator attention while the equipment is running. As the blades wear, the pellet quality decreases causing the operator to constantly monitor the process and adjust the blades. The amount of adjustment that is made will vary from one operator to the next. Often the tendency is to over adjusts causing premature blade and die wear. The invention being proposed uses constants controllable pneumatic pressure to continually adjust the cutter blades. The pressure can be set as light or as heavy as required allowing the operator to move one setting with no further adjustment required. A compression spring is used in the cutter head to assure constant contact between the die and cutter.

Any equipment utilizing a compression spring alone to adjust the blades offers no flexibility for varying the pressure of the cutter blades against the die face. A spring of the desired tension must be installed in the cutter head during setup. Once the machine is running, the spring tension cannot be varied, even though a heavier or lighter spring may be required. The entire cutting process must be stopped if the spring is to be changed. With a controllable pneumatic pressure, as proposed by the instant invention, the blade to die pressure can be adjusted as light or as heavy as required with a simple air pressure regulator.

Any equipment utilizing hydraulic pressure to adjust the blades requires the use of a dedicated hydraulic power unit for controlling the blade to die pressure. The use of this method to control blade adjustment is much more involved, both mechanically and electrically. Provisions must be made on or around the equipment to house a hydraulic power unit, whereas with a pneumatic design, installing an air line is all that is required. In environments where equipment of this nature is installed, compressed air lines are commonly available. A designated control circuit is also required on the hydraulically adjusted unit for the drive motor on the hydraulic power unit. Also, when using the hydraulic method, special care must be taken to prevent hydraulic oil from leaking into the process water, even in the event of a seal failure.

SUMMARY OF THE INVENTION

As used herein, the cutter hub holder of the present invention includes the components which interconnect the blade holder or cutter hub on which the cutter blades are mounted and the drive shaft of the electric drive motor which rotates the cutter hub with the cutter blades mounted thereon.

According to the present invention the cutter hub carrying the blades is pressed against the die plate at variable pressure by the cutter hub holder so that the optimum pressure for the current operational state is always used. This means that during normal operation pelletizing can be made at a lower pressure while it is possible to respond with a short-term higher blade pressure in response to changes occurring during operation.

Such higher pressure of the cutter hub against the die plate during operation may, for example, be required if a polymer layer forms on the cutting surface of the blades as a result of smearing. Such a layer will reduce the cutting performance and the quality of the cut pellets so that the plant must be shut down to remove the polymer layer which results in substantial disruptions and interruptions in operation. The cutter hub according to the present invention permits the removal of a polymer layer forming on the cutting surface by a short-term increase in the pressure of the blades against the die plate so that the cutting surface is cleaned. Subsequently, production can be continued at a gentle, lower blade pressure.

For another example, it is necessary to start pelletizing a material of very low viscosity at a high pressure of the blades against the cutting surface. After stabilization of the extrusion and pelletizing process, the pressure of the blades against the cutting surface may, however, be reduced and pelletizing can be made at a lower pressure which will minimize the wear of the blades and the die plate.

With the cutter hub holder according to the invention, the pressure of the holder and thus the pressure of the blades against the die plate may be adapted to the current operational requirements, so that the wear of the blades and of the cutting surface and/or of the die plate can be limited to the inevitable amount.

A preferred embodiment of this invention provides that the holder can be pressurized pneumatically in the direction of the die plate. The pneumatic pressure can be controlled in a simple way so that the control equipment permits a simple and fast adjustment of the pressure currently needed.

A further inventive development provides that the drive shafts such as that of an electric motor, is provided with an axial bore, with the end of the bore pointing to the cutter hub holder being extended to a cylinder bore and with the other end being connected to a source of compressed air by a rotary transmission leadthrough, and that the cylinder bore contains a piston, the piston rod of which is connected with the holder or is acting indirectly on the holders.

The cutter hub holder is conveniently constructed as a tubular head piece connected with the shaft or with an intermediary connected with the shaft in such a way that it can be shifted axially but cannot be rotated, with the head piece having a through bore stepped with at least two annular shoulders or a pocket hole stepped with at least one annular shoulder and with a pressure spring being inserted between the outer annular shoulder of the through hole or the bottom of the pocket hole and the piston rod. The pressure exerted by this pressure spring may be varied by changing the position of the piston rod and may thus be adapted to the currently needed pressure of the blades against the die plate.

In order to permit a fast replacement of the blades and cutter hub without prolonged interruption of the operation, a further inventive development provides that the head piece of the cutter hub holder is drivingly and separably connected to the shaft or an intermediary connected with the shaft by a bayonet coupling. The bayonet coupling may conveniently be constructed in conjunction with the pressure spring so that the pressure spring will keep the bayonet coupling in its locked position.

The bayonet coupling consists of two parallel grooves in the shaft, one of which is open at an end of the shaft. The other groove terminates inwardly of the end of the shaft and the grooves are connected with each other at their inner ends by a radial circumferential groove. The head piece includes a key protruding into its bore which engages and can be shifted in the grooves of the shaft. The head piece can be pressed axially on the shaft until the key reaches the inner end of the open ended groove and then rotated so that the key enters the other groove which serves to lock the head piece to the shaft but still permits axial movement of the head piece in relation to the shafts. Conveniently, the pressure of the spring is selected so that it roughly corresponds to or is even higher than the highest pressure of the blades against the die plate. In order to remove the head piece it is only necessary to press the same axially inwardly against the spring and to turn it against the direction of rotation of the drive so that the key can be pulled out of the open ended groove of the bayonet coupling. The key and groove arrangement is preferably duplicated at diametrically opposite areas of the shaft and head piece.

It is an object of the present invention to provide a cutter hub holder for an underwater pelletizer which permits reduction of wear of the blades and of the die plate while maintaining full control of all operational states by biasing the holder toward the die plate at a controlled variable pressure, preferably using a pneumatic pressure.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of the cutter hub holder and associated drive assembly.

FIG. 2 is a longitudinal sectional view of the head piece.

FIG. 3 is an and view of the head piece.

FIG. 4 is a perspective view of the intermediary portion of the shaft with the grooves forming a portion of the bayonet coupling.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although only one preferred embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practical or carried out in various ways. Also, in describing the preferred embodiment, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

The cutter hub holder according to the present invention is described with reference to the cutter hub holder of an underwater pelletizer generally constructed in the same way as disclosed in U.S. Pat. No. 5,059,103. The cutter hub holder according to the present invention is generally designated by the reference numeral 30 and differs from that disclosed in the aforesaid patent by the features which will be more fully described in the following.

The motor shaft 1 of the electric drive motor 2 is provided with a generally central bore 3. At its power take-off end, the central bore 3 is extended to a cylinder bore 4 via an annular shoulder 4A. This cylinder bore 4 contains a pneumatic piston 5 which is connected with a piston rod 6.

The power take-off end of the shaft 1 carries a tubular intermediary 7, the rear end of which is extended to a sleeve 8 which laps over the shaft 1 and is connected with it. The intermediary 7 is provided with a front cylindrical part 9 which has a smaller diameter than the sleeve 8. This cylindrical part 9 is provided with a smaller diameter through bore 9A which is substantially aligned with bore 3 and the cylinder bore 4 and receives a sliding member 10 fixed to the piston rod 6.

As shown in FIG. 4, the cylindrical part 9 of the intermediary 7 is provided with external grooves forming part of a bayonet coupling and includes an open end groove 12 and parallel groove 13 which is closed at its outer end. The inner end of the grooves 12 and 13 are connected with each other by a radial peripherally groove 14. Groove 12 is offset in relation to groove 13 against the direction of rotation of the shaft as indicated by the arrow 15 in FIG. 4. The grooves 12, 13 are machined into the surface of the cylindrical part 9 generally parallel to the axis of the part 9.

The cylindrical part 9 of the intermediary 7 holds the head piece 16. The head piece 16 consists of a rotationally symmetrical part with a blind bore 16A having an annular shoulder 17 at its inner end as shown in FIG. 2. The head piece 16 telescopically receives the cylindrical part 9. A pressure spring 18 is inserted in bore 16A between slide piece 10 and a generally central recess 17A which forms shoulder 17.

The bore 16A of the head piece 16 is provided with diametrically opposite keys 20 which protrude radially into the bore 16A and are held in place as by welding or the like. The front end of the head piece 16 is provided with an external thread 21 on which the cutter holder 22 is threaded as shown in FIG. 1.

To place the head piece 16 onto the cylindrical part 9, the keys 20 are inserted into the opposite bayonet grooves 12 and are pushed inwardly to the bottom of these grooves, thus compressing the pressure spring 18 so that the keys 20 can be locked in grooves 13 by arcuate shifting through the radial grooves 14. Further, the keys 20 are preferably shorter longitudinally than the grooves 13 which enables axial movement of the head piece 16, as shown by arrow 30 in FIG. 4. This axial movement of head piece 16 against the resistance of spring 18 moves the cutter hub or blade holder 22 and cutter blades 23 toward die face 24 as shown in FIG. 1.

The other end 25 of the motor shaft 1 is provided with a stationary rotary transmission leadthrough 26 at which the compressed air line is connected through a pressure regulating valve to sense and control the pneumatic pressure entering the bore 3 in motor shaft 1. The flange 27 fixed at the motor housing serves, as is basically known from U.S. Pat. No. 5,059,103, for the attachment of the water box with water flow and return lines and the die plate 28 across which the blades 23 of the cutter hub 22 wipe.

The quick connect and disconnect capability of the cutter hub 22, head piece 16 and intermediary 7 is provided by the bayonet grooves 12, 14 and 13 coacting with the keys 20. When the components are in an assembled relation, and it is desired to quickly disconnect the cutter hub 22 after the flange 27 has been separated from the water box and the motor housing and related structure have been moved away from the die face, it is only necessary to exert an axial force on the cutter hub 22 to compress the spring 18 sufficiently to align the keys 20 with the grooves 14 and rotate the cutter hub 22 in a counterclockwise direction as indicated by the arrow 15 in FIG. 4. As soon as the keys 20 become aligned with the grooves 12, the cutter hub 22 along with the head piece 16 and intermediary 7 can be moved axially of the cylindrical part 9 until the keys 20 exit from the grooves 12. This quick disconnect capability permits fast replacement of the cutter hub and blades without prolonged interruption of the operation of the underwater pelletizer.

To assemble the cutter hub 22, head piece 16 and intermediary 7 onto the cylindrical part 9, it is only necessary to align the keys 20 with the open end of the grooves 12 and move the assembly inwardly axially by compressing spring 18 until the keys align with the grooves 14. The cutter hub 22, head piece 16 and intermediary 7 are then rotated partially in a clockwise direction until the keys 20 move through the grooves 14 into alignment with the grooves 13 at which time the inward force is released from the cutter hub 22 and the spring 18 will maintain the keys 20 in the grooves 13. However, the keys 20 still are capable of longitudinal movement axially in the grooves 13 with cutter hub 22 and cutter blades 23 biased toward die face 24 as determined by the force of the spring 18 and the pneumatic pressure exerted against piston 5. With this construction, the quick connect and disconnect capability of the cutter hub holder 30 enables quick removal and replacement of the cutter hub 22. Further, the displacement of the piston by a controlled pneumatic pressure will alter the force biasing the cutters 23 toward the die face 24 through the resilient characteristics of the spring 18 which can be compressed or released to provide the optimum spring bias of the blades 23 toward the die face 24 by the pneumatic pressure controlling movement of the piston 5, piston rod 6 and sliding member 10.

As above described, the cutter hub holder 30 of this invention includes those components which interconnect the cutter hub or blade holder 22 with the motor shaft 1. These components include head piece 16, spring 18, sliding member 10, intermediary 7, piston rod 6, piston 5, cylindrical bore 4 with shoulder 4A and the bayonet coupling between the cylindrical part 9 of the intermediary 7 and the head piece 16.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

1. A cutter hub holder for blades acting in conjunction with a die plate of an underwater pelletizer comprising a bade holder drivingly connected to a driven shaft and biased axially toward the die plate at a variable controlled pressure by a spring and pressurized pneumatically in the direction of the die plate, said shaft being provided with an axial bore, the end of the shaft bore adjacent the holder including a cylinder bore, and the other end of the shaft bore being connected to a source of compressed air by a rotary transmission leadthrough, said cylinder bore slidably receiving a piston and piston rod acting on the holder through said spring.

2. A cutter hub holder according to claim 1 wherein the drive shaft is the shaft of an electric motor.

3. A cutter hub holder according to claim 1 wherein said holder is constructed as a tubular head piece drivingly connected with an intermediary connected with the shaft and axially movable in relation to the shaft, said intermediary including a bore extending therethrough receiving said piston rod, said spring being engaged between said piston rod and said head piece and axially movably mounting the head piece on said intermediary.

4. A cutter hub holder according to claim 3 wherein said head piece is removably and axially movably mounted on said intermediary and a bayonet coupling removably mounting the head piece on the intermediary.

5. A cutter hub holder according to claim 4 in which the bayonet coupling comprises a pair of parallel grooves in said intermediary, one of which is open at an outer end and the other groove being closed at an outer end, said pair of grooves being connected with each other at their inner ends by a radial peripheral groove, said head piece having at least one key protruding radially into a bore therein in engagement with said grooves and enabling the head piece to shift axially when said key is engaged with the other of said pair of grooves.

6. A cutter hub holder according to claim 5 in which said intermediary includes two diametrically opposed pairs of grooves and said bore in the head piece includes two keys.

7. A cutter hub holder for blades acting in conjunction with a die plate of an underwater pelletizer which comprises a blade holder drivingly connected to a driven shaft and biased axially toward the die plate at a variably controlled pneumatic pressure, said blade holder also biased toward the die plate by a coil spring, said coil spring being pressurized pneumatically in relation to the die plate for controlled variation in the pressure exerted on the blade holder toward the die plate, said driven shaft being provided with an axial bore having one end connected to a source of compressed air controlled by a pressure regulator, said bore at an opposite end including a piston and piston rod slidable in the bore and engaging said spring for exerting a variably controlled force on the blade holder.

8. The cutter hub holder as defined in claim 7 wherein said cutter hub holder includes a tubular head piece supporting said blade holder, said head piece being axially movable in relation to the driven shaft and rotatably driven by said driven shaft, said spring being positioned in a bore in said head piece with one end of the spring exerting a force on the head piece and the other end of the spring being compressed and expanded by movement of said piston and piston rod.

9. The cutter hub holder as defined in claim 7 wherein said driven shaft and said blade holder are provided with a quick connect/disconnect coupling to enable the blade holder to be quickly and easily replaced.

10. The cutter hub holder as defined in claim 9 wherein said quick connect/disconnect coupling includes a bayonet coupling between the blade holder and driven shaft.

11. A quick connect and disconnect coupling between a blade holder drivingly connected to a driven shaft and biased axially toward a die plate of an underwater pelletizer which comprises a tubular member connected with the blade holder and telescopically engaged with the driven shaft, said quick connect and disconnect coupling comprising a bayonet coupling of the tubular member with the driven shaft to enable quick replacement of the blade holder.

12. The quick connect and disconnect coupling as defined in claim 11 wherein said bayonet coupling enables axial movement of the tubular member in relation to the driven shaft when the bayonet coupling drivingly connects the tubular member and driven shaft to enable biased movement of the blade holder toward the die plate.

13. The quick connect and disconnect coupling as defined in claim 12 wherein said tubular member includes an intermediary drivingly and axially movable in relation to the blade holder, said driven shaft including a, bore communicated with a variably controlled source of pneumatic pressure, said intermediary including a bore extending between the bore in the driven shaft and a bore in said tubular member, a spring positioned in the bore in the tubular member, and a piston and piston rod associated with said bores and said spring to be moved axially in response to variably controlled pneumatic pressure introduced into the bore in the driven shaft for varying the pressure exerted on the blade holder by said spring.

14. The quick connect and disconnect coupling as defined in claim 13 wherein said driven shaft includes parallel slots having inner ends connected by a peripheral slot, one of said slots having an open outer end communicating with the end of the driven shaft, the other of said slots having a closed outer end spaced inwardly from the end of the driven shaft, said intermediary includes a key engaged in said slots with the key and intermediary being movable longitudinally of the driven shaft when the intermediary key is in the closed end slot, said intermediary being assembled and disassembled in relation to the driven shaft by inward axial movement of the key in the closed end slot by overcoming the resistance of said spring, rotational movement of the key in the slot connecting the inner ends of the parallel slots into alignment with the open end slot and outward axial movement of the key in the open end slot until the key exits from the open end slot.

15. In an underwater pelletizer having an adjustable cutter hub holder axially movably and drivingly connected between a cutter hub having cutter blades mounted thereon and a driven shaft, said driven shaft including a through bore connected with a variable controlled source of pressure to bias the cutter hub and cutter blades toward a die plate of said underwater pelletizer.

16. In an underwater pelletizer as defined in claim 15 wherein said variable controlled source of pressure includes a spring in said through bore and a regulated source of pneumatic pressure communicated with said through bore and varying the biasing force exerted by said spring to bias the cutter hub and cutter blades toward a die plate of said underwater pelletizer.

17. In an underwater pelletizer as defined in claim 16 wherein said through bore includes a piston movable axially in said bore in response to pneumatic pressure variation in the bore, said piston transferring force to said spring to vary the biasing force on said cutter hub by varying the force exerted on said spring by said piston.

18. A cutter hub holder for blades acting in conjunction with a die plate of an underwater pelletizer comprising a blade holder drivingly connected to a driven shaft, a spring extending axially of said driven shaft and biasing said blade holder axially toward the die plate, a variably controlled source of pneumatic pressure exerting an axial force on said spring and exerting a variable controlled axial biasing force through said spring toward said blade holder.