Note: Descriptions are shown in the official language in which they were submitted.
3~
Pelletizers are used in various industries with one
particular well known use being in the plastics industry.
Plastic 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 bed knife
assemb'y positioned about the cutting circle of a multi-bladed
rotary member and with the plastic material being cut or pel-
letized by the well known cooperative action of the rotating
blades and the bed knives.
With existing plastic pelletizers the rotary blades are
releasably retained in position in two primary fashions; namel~,
by a bolt structure directly securing the rotary blades to the
rotor or by a wedge which is cooperable with circumferentially
adjacent pairs of rotary blades for the frictional retention
of such blades. The releasable retention of rotary blades in
pelletizers is necessary to permit their replacement, which
replacement is required on a frequent basis when an abrasive or
hard material is being pelletized; for example, plastics with glass
or mineral fillings, requires frequent blade changing and also
abraids the exposed portions of fasteners. Furthermore, abrasive
or hard materials additionally requires that the rotary blades be
manufactured of a wear resistant material 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
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bores decrease the section modulus of the b]ades 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 a solid blade, 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 than a shearing fashion. Inasmuch as many of the
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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.
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 aux-
iliary 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 cooperative 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 may 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 moYe in its
retaining pocket to the point that the retaining force is still
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further reduced. The more loosely retained blade is noisy and
results in inefficient operation. Fur~hermore during operation
even the slightest movement of any blade may result in complete
destruction of the pelletizer assembly. ~owever, the inclusion
of the auxiliary bearing surface of the present invention pro-
vide~ a guiding surface for more uniform wedge insertion and
additionally provides a bearing surface which is operative to
better insure uniformity of retaining forces on adjacent pairs of
blades during operation of the pelletizer.
In summary, therefore, the present invention may be seen
as providing a rotary blade assembly of the type received within
respective ones of a plurality of circumferentially spaced out-
wardly open elongated channels extending across and inwardly of
the face of a rotary member of a pelletizer assembly to form a
cutting circle comprising: a pair of circumferentially spaced
elongated cutting blade means seated on respective circumferen-
tially spaced portions of a respective one of the channels with
the ends of such blades located inwardly of such one channel
being spaced from the bottom of such one channel to provide an
inner side surface portion of such one channel, and elongated
retaining means disposed between opposed surfaces of the blade
means, having transversely spaced longitudinally extending
bearing surfaces in engagement with the opposed surfaces of the
blade means, and having integral bearing means engaging the
side surface portion of such one channel.
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These and other a~vantage~ of this inventiorl will
become more readily appa--ent: upon a reading of the Eol]owinq
description and drawings in which:
Fig. 1 is a schematic end view of a rotor assembly
portion of a pelletizer which incorporates the blade assemblies
constructed in accordance with the principles of the present
invention;
Fig. 2 is a schematic side view of a portion of the
rotor assembly illustrated in FigO l; and
Fig. 3 is a transverse cross-sectional view of a
pelletizer blade assembly constructed in accordance with the
principles of the present invention.
One known form of a 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 rotary blade assemblies 12 extend in
a direction essentially parallel thereto.
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In operationr sui.-table mater:i.a]. to be pel.].ctized, for
e~ample, plast.ic s-trallds r~om an cxtr~l(ler, are cli~ected -~o
pel.letizer 9 in the usual marlTIe:l^ and are pel].et.ized by the known
Goopexation .lnd interactiorl betwee}l rotary hlade assemblies 12
and a stationary bed kn.ife assembly 16. Inasmuch as thi.s
invention is to the construction of the rotary blacle assemblies
12 and the operation, configuration and driving arrangement of
pelleti~er 9 may be of any well known type, a detailed descrip-
tion and showing of the pelletizer 9 is not necessary to one
skilled in the art for a full understanding of the invention herein.
Accordingly, Figs. 1 and 2 are merely schematic representations
for the purpose of orientation of the rotary blade assemblies
12 which are shown in detail in Fig. 3.
The rotary member 10 includes a plurality of circum-
ferentially spaced outwardly open elongated blade assembly
receiving slots or channels 18 formed therewithin. Each slot or
channel 18 is open ended, extends across the longitudinal extent
of member 10 and has a generally uniform cross-section. An
elongated rotary blade assembly 12 is received within each
channel 18 and the longitudinal extent thereof is substantially
co-extensive with respect to the longitudinal extent of channels
18. Rotary blade assemblies 12 each comprise: a circumferentially
spaced pair of elongated blades, the upper or trailing
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blade being designated 20 and the lower or leading blade beinq
designated 22; a wedge shaped retainer member 24 ~or the fric-
tional retention of blades 20 and 22 in operating position;
and a plurality of fastening means, such as bolts ~6, for
releasably securing wedge members 24 to rotary member 10.
Blades 20 and 22 are of known construction and as shown have a
generally rectangular configuration with the outer or cutting
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- ~L~ ~dge 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
J~
trailing blade 20 being above the loadin~ blade 22. Accordingly,
for convenience of description hereinafter, upper and lower
shall respectively be referenced with respect to the upper
or trailing blade 20 and the lower or leading blade 22,
Each channel 18 comprises: circumferentially spaced
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 blade~ 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
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acing surface 38 whlch ~ngages an adjacen-t downwardly fac:inc~
portion of leading b:lade 22 and an ou-twa~dly fac.ing radial.ly
innermost surEace 40 which engages the radially innermost end
of blade 22. When opera-tionally seated, blades 20 and 22 have
the circumferentiall.y spaced facing surfaces thereof, which
spaced surfaces are engaged by wedge member 24 for the blade
retention, spaced slightly from surfaces 34 and 40, respective-
ly in a manner that wedge member 24 can extend inwardly there-
from into wedge rec~iving portion 42.
The wedge receiving portio~ 42 of channel 18 is in open
communication with blade seatinq portions 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 innermost 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 the lowermost end of sur-
face 48, the extent of surface 46 being shown as generally parallel
to the extent of surface 380 Surfaces 44 and 46 taper slightly
radially inwardly from the radially outermost ends thereof and
are shown as being generally parallel to the respective surfaces
of wedge member 24.
Weage 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 trailing blade 20; an upper wedge relief sur~ace 54 which is
spaced downwardly from surface 52, and extends inwardly there-
from; a lower blade bearing surface 58 which has a radially
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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 con-
tinuously 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 18. 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 accom-
plished 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 12 for which blades 20 and 22 are to be replaced or
initially positioned to a registry where channel 18 faces
upwardly. In the latter instance the blades 20 and 22 and
wedge member 24 may merely be radially inserted or dropped into
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11f~;~S~9
channel 18. In either event, ~he rear bearin~ surface 60 sig-
nificantly 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 accom-
plished. 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 of assembly 12 are positioned,
inwardly projecting through bore 62 and blind and threaded bore
63, respectively within members 24 and 10, are coaxial aligned.
Bolts 26 extend through bores 62 and into respective bores 64.
When 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
wedse-blade bearing areas, aids in guiding the wedge member 24
into proper orientation for the even frictional retention of
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blades 20 and 22. To aid in the removal of bolts 26, flexible
protective snap in caps 66, such as of plastic or the like,
are provided. As shown caps 66 are positioned in a manner to
cover bore 63 and thus prevent the 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 upper blade 20 for wedging blade 20
into seated position, a lower bearing area directly communicating
with lower blade 22 for wedging blade 22 into 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 in-
wardly 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 18. Surface 60 which forms the
lower inward bearing surface engages the lower surface 46 of the
channel 18. 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 memher 10. The blades 20 and
22 are individually and sequentially subjected to cyclical impact
loading; however, each impact load which may tend to shift the
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wedge member 2~ within the channel 18 is opposed by two spaced
bearing engagements to maintain the wedge member 2~ 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
insure the wedged retention of blades 20 and 22.
The invention 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 claims set forth hereinafter. 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 lO 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.
