GB2039783A - A Rotary Blade Assembly and a Pelletizer Apparatus Provided with Such an Assembly - Google Patents

Abstract

An elongated rotary blade assembly 12 received within an outwardly open elongated channel 18 extending across the face of a rotary member 10 of a pelletizer assembly for co-operating with a fixed knife structure 16 for pelletizing material, said blade assembly 12 comprising a pair of circumferentially spaced elongated cutting blades 20, 22 seated on respective spaced portions 30,38 of the channel 18 with an elongated retaining wedge member 24 disposed between the blades 20, 22 for the frictional retention of the blades 20, 22, the wedge member 24 having a bearing surface 52 for the blade 20, a second blade bearing surface 58 engaging an upper side transverse surface of the blades 22, and a bearing surface 60 spaced inwardly from the surface 58 and engaging a surface 42 of the channel 18. <IMAGE>

Description

SPECIFICATION A Rotary Blade Assembly and a Pelletizer Apparatus Provided with such an Assembly This invention relates to an elongated rotary blade assembly and to a pelletizer provided with such a rotary blade assembly and more particularly a pelletizer having a plurality of rotating blades which co-operate with a stationary knife assembly to pelletize material fed thereto.

Pelletizers are used in various industries with one particular well known use being in the plastics industry. Plastics pelletizers are often used to cut extruded strands of plastics with glass or mineral fillings to pellet size particles for subsequent use in plastics processing. One common type of plastics pelletizer is provided with a stationary knife assembly positioned about the cutting circle of a multi-bladed rotary member and with the plastics material being cut or pelletized by the co-operation action of the rotating blades and the stationary knives.

With existing plastics pelletizers the rotary blades are releasably retained in position in two primary fashions; namely, by a bolt structure directly securing the rotary blades to the rotor or by a wedge which is co-operable with circumferentially adjacent pairs of rotary blades for the frictional retention of such blades. The releasable retention of rotary blades in peiletizers is necessary to permit their replacement, which -replacementis required on a frequent basis when an abrasive or hard material is being pelletized; for example, plastics with glass or mineral fillings, and the material also abraids the exposed portions of fasteners. Furthermore, abrasive or hard materials additionally requires that the rotary blades be manufactured of a wear resistant materiai such as a carbide.

Although directly bolted rotary blades are satisfactory in many instances such structures require one or more bores directly through the rotary blade. The inclusion of such bores in the blade constructed of hardened material, such as carbide, is costly and may result in stress risers.

Further, such bores decrease the section modulus of the blades and hence reduces the maximum bending moment that a blade can withstand at a cross-section through the bore area. In many instances, cobolt is included in the metallic compound to enhance the carbide properties to better withstand the above conditions. However, cobolt lessens the abrasive resistance of tungsten carbide and hence results in a shorter cycle between blade changes.

In other pelletizers a wedge member is positioned between adjacent pairs of rotary blades. Such structures permit the utilization of solid blades, closer spacing between adjacent blades, and simplified assembly and disassembly.

In the prior wedge systems, the wedge block is symmetrically received within a pocket in the rotor and a circumferentially spaced pair of blades would be symmetrically arranged in the pocket to bear against respective wedge surfaces. The only bearing surfaces with such prior wedge systems were transversely spaced bearing areas at adjacent surfaces of the wedge and blades and the wedge was operative to frictionally retain the blades within a respective pocket. With such prior wedge structures the blades are mounted in a radial fashion and extend in a direction substantially normal to the cutting circle.

Experience has shown that such a radial mounting arrangement can create an undesirable cutting condition as the rotating blades pass the stationary or bed knife structure. Specifically, such a mounting likens the possibility of a snapping or impact type of severing action rather th-an a shearing fashion. Inasmuch as many of the modern plastics are specifically formulated to withstand impact and snapping, power requirements as well as noise levels can be relatively high with respect to the radial rotary blade mounting. Furthermore as the blade edges become only slightly dull, these conditions become even more excessive as substantial heat is generated and the edges of the plastics being pelletized are broken rather than cut.

According to the present invention there is provided an elongated rotary blade assembly received within an outwardly open elongated channel extending across the face of a rotary member of a pelletizer assembly for co-operating with a knife structure for pelletizing material, said rotary blade assembly comprising a pair of circumferentially spaced elongated cutting blades seated on respective spaced portions of said channel with an elongated retaining wedge member disposed between the blades for the frictional retention of the blades, said wedge member including a first blade bearing surface for one of said blades, a second blade bearing surface engaging an upperside transverse surface of the other of said blades, and another bearing surface spaced inwardly from said second blade bearing surface away from a cutting circle and engaging an upperside transverse surface of said channel.

The present invention utilizes an improved wedge member which carries the rotary blades in a more tangential orientation with respect to the cutting circle and also includes an auxiliary bearing surface spaced from the wedge-blade bearing surfaces to overcome the hereinabove mentioned problems, or in the least, greatly alleviate them. Specifically the tangential orientation will result in the co-operative action of the rotary blades with one bed knife structure yielding an action more closely resembling shear with respect to the plastics being pelletized.Still further if the above mentioned auxiliary bearing surface were not included the retaining force on circumferentially adjacent blades would not necessarily be uniform (i.e. due to such causes as rough mating surfaces, debris build up, tolerance inaccuracies, wear and improper blade and wedge insertion) so that one blade ri7ay have more of a tendency to move relative to the pocket than the other blade. Furthermore, since during operation each blade is subject to impact loading on a cyclical basis, such a non-uniformity of blade retaining forces can cause the "looser" blade to repeatedly move in its retaining pocket to the point that the retaining force is still further reduced. The more loosely retained blade is noisy and results in inefficient operation.Furthermore during operation even the slightest movement of any blade may result in complete destruction of the pelletizer assembly. However, the inclusion of the auxiliary bearing surface of the present invention provides a guiding surface for more uniform wedge insertion and additionally provides a bearing surface which is operative to better ensure uniformity of retaining forces on adjacent pairs of blades during operation of the pelletizer.

An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawing, in which: Figure 1 is a schematic end view of a rotor assembly portion of a pelletizer which incorporates blade assemblies constructed in accordance with the principles of the present invention: Figure 2 is a schematic side view of a portion of the rotor assembly illustrated in Figure 1; and Figure 3 is a transverse crosssectional view of a pelletizer blade assembly constructed in accordance with the principles of the present invention.

The plastics pelletizer 9 comprises a generally cylindrical rotary member 10 which carries a plurality of circumferentially spaced longitudinally extending rotary blade assemblies 12 thereon.

Rotary member 10 is rotatably driven by a central elongated shaft 14 which is suitably supported for rotation by a pelletizer housing (not shown). Shaft 14 and member 10 are coaxial with respect to a central longitudinal axis x-x and the rotary blade assemblies 12 extend in a direction essentially parallel thereto.

In operation, suitable material to be pelletized, for example, strands of plastics material from an extruder, are directed to the pelletizer 9 in the usual manner and are pelletized by the cooperation and interaction between rotary blade assemblies 12 and a stationary bed knife assembly 16. Inasmuch as this invention is to the construction of the rotary blade assemblies 12 and the operation, configuration and driving arrangement of pelletizer 9 may be of any well known type, a detailed description and showing of the pelletizer 9 is not necessary to one skilled in the art for a full understanding of the invention herein. Accordingly, Figures 1 and 2 are merely schematic representations for the purpose of illustrating the orientation of the rotary blade assemblies 12 which are shown in detail in Figure 3.

The rotary member 10 includes a plurality of circumferentially spaced outwardly open elongated blade assembly receiving channels 1 8 formed therewithin. Each channel 1 8 is open ended, extends across the longitudinal extent of the member 10 and has a generally uniform cross-section. An elongated rotary blade assembly 12 is received within each channel 1 8 and the longitudinal extent thereof is substantially co-extensive with respect to the longitudinal extent of channels 1 8 and is parallel thereto.

Rotary blade assemblies 12 each comprise: a drcumferentially spaced pair of elongated blades, the upper or trailing blade being designated 20 and the lower or leading blade being designated 22; a wedge shaped retainer member 24 for the frictional retention of blades 20 and 22 in the operating position; and a plurality of fastening means, such as bolts 26, for releasably securing the wedge members 24 to the rotary member 10.

Blades 20 and 22 are of known construction and as shown have a generally rectangular configuration with the outer or cutting edge portions thereof extending outwardly beyond the rotary member 10 and which slope generally outwardly and downwardly when supported in their operational position.

As is well known, the slope of the cutting edge portions of the blades 20 and 22 is indicative of the direction of rotation of the rotary member 10.

As shown, the rotary member 10 is rotatable in a counterclockwise direction with the trailing blade 20 being above the leading blade 22.

Accordingly, for convenience of description hereinafter, upper and lower shall respectively be referred to with respect to the upper or trailing blade 20 and the lower or leading blade 22.

Each channel 1 8 comprises: circumferentially spcaced upper and lower longitudinally extending blade seating portions 30 and 36, respectively; and a longitudinally extending wedge receiving portion 42 circumferentially intermediate portions 30 and 36. Upper blades seating portion 30 has a downwardly facing surface 32 which engages an adjacent upwardly facing portion of trailing blade 20 and an outwardly facing radially innermost surface 34 which engages the radially innermost end of blade 20. Similarly, lower blade seating portion 36 has an upwardly facing surface 38 which engages an adjacent downwardly facing portion of the leading blade 22 and an outwardly facing radially innermost surface 40 which engages the radially innermost end of blade 22.

When operationally seated, blades 20 and 22 have the circumferentially spaced facing surfaces thereof, which spaced surfaces are engaged by the wedge member 24 for the blade retention, spaced slightly from surfaces 34 and 40, respectively in a manner that wedge member 24 can extend inwardly therefrom into wedge receiving portion 42.

The wedge receiving portion 42 of channel 18 is in open communication with blade seating portion 30 and 36 and comprises: a radially innermost surface 48; an upper surface 44 which extends between the lower end of surface 34 and the uppermost surface 48, the extent of surface 44 being shown as generally parallel to the extent of surface 32; and a lower surface 46 which extends between the upper end of surface 38 and lowermost end of surface 48, the extent of surface 46 being shown as generally parallel to the extent of surface 38. Surfaces 44 and 46 taper slightly inwardly from the radially outermost ends thereof and are shown as being generally parallel to the respective surfaces of wedge member 24.

Wedge member 24 is an elongated formed member having: an upper blade bearing surface 52 which continuously engages a radially intermediate portion of the downwardly facing surfaces of the trailing blade 20; an upper wedge relief surface 54 which is spaced downwardly from surface 52, and extends inwardly therefrom, a lower blade bearing surface 58 which has a radially outer portion thereof in continuous engagement with a rear or radially inward portion of the upwardly facing surface of the leading blade 22 and extends inwardly therefrom such that the portion of surface 58 which is not in engagement with blade 22 is spaced upwardly from surface 46 of wedge receiving portion 42; and an inner or rear bearing surface 60 which is spaced downwardly from surface 58, is parallel thereto and which continuously engages a transversely intermediate portion of surface 46 of wedge receiving portion 42. It is to be noted that the description hereinabove of wedge member 24 insofar as the relationship thereof with respect to various surfaces of channel 18 and blades 20 and 22 is directed to a fully positioned and assembled rotary blade assembly 12 within a respective channel 18.

With a blade assembly 12 such as described hereinabove, the blades 20 and 22 and retaining wedge member 24 are easily positioned within the channel 1 8. The fact that surface 60 is displaced inwardly from the portion of surface 58 which engages leading blade 22 permits a relatively loose but guided (by surface 60) initial positioning of wedge member 24.

The positioning of each blade assembly 12 may be accomplished by the longitudinal sliding of blades 20 and 22 and wedge member 24 into the open ended channel 18; or, if preferred, by rotating rotary member 10 to index the particular blade assembly 1 2 for which blades 20 and 22 are to be replaced or initially positioned to a registry where channel 1 8 faces upwardly. In the latter instance the blades 20 and 22 and wedge member 24 may merely be radially inserted or dropped into channel 1 8. In either event, the rear bearing surface 60 significantly aids in the proper positioning of blade assembly 12. Specifically, by maintaining engagement between surface 60 and surface 46 during positioning of wedge member 24, a positive guiding of the member 24 throughout insertion thereof is accomplished.

Thus the tendency for tilting the wedge during insertion is substantially reduced. Furthermore, in the event of minor tolerance variances between mating surfaces of member 24 with adjacent mating surfaces of blades 20 and 22, the rear bearing surface 60 will tend to smooth out insertion during the passage of member 24 over these areas of tolerance variance. In both of the above instances, wedge member 24 would have more of a tendency to be finally positioned in a slightly tilted orientation if the member 24 was only guided into final position by the surfaces 52 and 58.

When the primary elements assembly 12 are positioned, inwardly projecting through bore 62 and blind and threaded bore 64, respectively within members 24 and 10, are coaxial aligned.

Bolts 26 extend through bores 62 and into respective bores 64. When the bolts 26 are tightened, wedge member 24 is drawn inwardly and releasably retained in final operating position for the frictional retention of the blades 20 and 22. During this tightening up phase, surface 60, in conjunction with the direct wedge-blade bearing areas, aids in guiding the wedge member 24 into proper orientation for the even frictional retention of blades 20 and 22. To aid in the removal of bolts 26, flexible protective snap-in caps 66, which may be formed of plastics or the like, are provided. As shown, the caps 66 are positioned in a manner to cover bore 63 and thus prevent a build-up of material therein or the abraiding of the head of bolt 26.

With a blade assembly 12 as described, the wedge member 24 provides three bearing areas; namely an upper bearing area directly communicating with the upper blade 20 for wedging the blade 20 into the seated position, a lower bearing area directly communicating with the lower blade 22 for wedging the blade 22 into the seated position and an inner bearing area at surface 60 for ease of assembly and for facilitating the maintenance of the engagement of the upper and lower seating areas during operation of the pelletizer 9. The upper bearing area of the wedge member 24 extends inwardly of the outer periphery of the rotary member 10 a distance to provide a sufficient area to obtain the desired wedging action on the upper blade 20.

The upper wedge relief surface 54 is provided to permit the inner end of the wedge member 24 to be freely inserted into the channel 1 8. Surface 60 which forms the lower inward bearing surface engages the lower surface 46 of the channel 1 8.

With such three bearing areas the rotary blade assembly 12 becomes locked with respect to the rotary member 10 for the surface 60 engages member 10 at surface 46 and the blades 20 and 22 are biased into engagement, by means of the wedging action, with the rotary member 1 0. The blades 20 and 22 are individually and sequentially subjected to cyclical impact loading; however, each impact load which may tend to shift the wedge member 24 within the channel 1 8 is opposed by two spaced bearing engagements to maintain the wedge member 24 in the proper position. Thus, when the lower or leading blade 22 impacts, the load will be resisted by the rotary member 10 at surface 30; however, any tendency of the wedge member 24 to tilt or pivot, and thus cause one of the blades 20 or 22 to loosen, is resisted at surface 60. Similarly, when the upper or trailing blade 20 impacts surface 60 will provide this same bearing to ensure the wedged retention of blades 20 and 22.

The embodiment described herein is the presently preferred embodiment; however, it is understood that various modifications may be made by those knowledgeable in the art without departing from the scope of the invention as defined by the appended claims. For example: the invention herein is equally applicable to pelletizers other than the application to a plastics pelletizer as is described herein; more or less rotary blade assemblies may be provided on the rotary member 10 and the proportional spacing therefore may be varied; the configuration of the inward bearing surface 60 may be varied, such as a plurality of adjacent transversely extending notches on a tapered V configuration with the apex being at the innermost end thereof; and the like.

Claims (12)

Claims

1. An elongated rotary blade assembly received within an outwardly open elongated channel extending across the face of a rotary member of a pelletizer assembly for co-operating with a knife structure for pelletizing material, said rotary blade assembly comprising a pair of circumferentially spaced elongated cutting blades seated on respective spaced portions of said channel with an elongated retaining wedge member disposed between the blades for the frictional retention of the blades, said wedge member including a first blade bearing surface for one of said blades, a second blade bearing surface engaging an upperside transverse surface of the other of said blades, and another bearing surface spaced inwardly from said second blade bearing surface away from a cutting circle and engaging an upperside transverse surface of said channel.

2. A rotary blade assembly as claimed in claim 1, in which said another bearing surface is parallel to said upperside transverse surface of said other of said blades and is spaced downwardly therefrom.

3. A rotary blade assembly as claimed in claim 1 or claim 2, including a wedge relief surface extending inwardly away from such a cutting circle from said first blade bearing surface, said wedge relief surface being spaced downwardly from said first blade bearing surface.

4. A rotary blade assembly as claimed in any preceding claim, in which the inner end of said wedge member is operationally spaced outwardly toward said cutting circle from the inner end of said channel.

5. A rotary blade assembly as claimed in any preceding claim, including fastening means releasably securing said wedge member within said channel.

6. A rotary blade assembly as claimed in claim 5, in which said fastening means extends along an axis circumferentially intermediate said blade bearing surfaces and generally parallel to one of said blade bearing surfaces.

7. A rotary blade assembly as claimed in claim 6, in which said axis is parallel to said first blade bearing surface.

8. A rotary blade assembly as claimed in any of claims 5 to 7, in which said fastening means is inwardly countersunk within said wedge member.

9. A rotary blade assembly as claimed in claim 8, including removable cap means positioned intermediate said blades to substantially cover said wedge member in the vicinity of said fastening means.

10 A rotary blade assembly as claimed in claim 9, in which said cap means is frictionally retained in position.

11. A rotary blade assembly as claimed in any preceding claim, in which the rotor is provided with a plurality of circumferentially spaced blade assemblies.

12. An elongated rotary blade assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

1 3. A pelletizer apparatus provided with an elongated rotary blade assembly as claimed in any preceding claim.