U.S. patent number 3,703,841 [Application Number 05/007,718] was granted by the patent office on 1972-11-28 for rotary shear for wrapping machines.
This patent grant is currently assigned to FMC Corporation. Invention is credited to Donald C. Crawford.
United States Patent |
3,703,841 |
Crawford |
November 28, 1972 |
ROTARY SHEAR FOR WRAPPING MACHINES
Abstract
A wrapping machine cutting head of the rotary shear type wherein
the lateral contact force between the shearing blades is effected
by a camming surface, integral with one of the shearing blades, to
laterally flex a resiliently flexible blade against a rigid blade
as the two blades move into shearing relation with each other and
with the web material intermediate two interconnected packages
wrapped and sealed in the web.
Inventors: |
Crawford; Donald C. (Green Bay,
WI) |
Assignee: |
FMC Corporation (San Jose,
CA)
|
Family
ID: |
21727769 |
Appl.
No.: |
05/007,718 |
Filed: |
February 2, 1970 |
Current U.S.
Class: |
83/341; 83/345;
83/348; 83/674 |
Current CPC
Class: |
B26D
1/626 (20130101); B65B 61/08 (20130101); B26D
1/0006 (20130101); B29C 66/1122 (20130101); B29C
66/8161 (20130101); Y10T 83/4836 (20150401); B29C
65/7461 (20130101); B29C 66/83513 (20130101); B26D
2001/006 (20130101); B26D 2001/0066 (20130101); Y10T
83/4844 (20150401); B29C 66/849 (20130101); B29C
65/18 (20130101); B29C 66/4312 (20130101); Y10T
83/4824 (20150401); Y10T 83/9399 (20150401); B29C
65/745 (20130101); B29C 65/305 (20130101); B29C
66/81422 (20130101) |
Current International
Class: |
B26D
1/00 (20060101); B26D 1/62 (20060101); B65B
61/04 (20060101); B65B 61/08 (20060101); B26d
001/28 () |
Field of
Search: |
;83/341,342,345,348,673,674 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yost; Frank T.
Claims
What is claimed is:
1. In a wrapping machine, a progressive-cut web shear mechanism
comprising:
a flat, resilient shearing blade,
a rigid rectilinear shearing blade,
rotatable shaft means rigidly mounting said resilient blade therein
substantially radially thereof in flat and normally unstressed
relation with the major portion of said blade exposed for resilient
flexure,
rotatable shaft means rigidly mounting said rigid blade therein
substantially radially thereof for cooperation with said resilient
blade,
means for cyclically driving said rotatable shaft means and thereby
said blades into and out of overlapping shearing engagement,
and,
a camming surface on one of said blades for laterally stressing and
flexing one end portion of said resilient blade as the blades
initially overlap, said stressing establishing a predetermined and
localized shearing force between said blades adjacent said camming
surface, continued shearing movement of said blades causing
progressive lateral localized flexure of said resilient blade to
maintain a uniform shearing force for severing a web of wrapping
material intermediate said blades.
2. The wrapping machine of claim 1 wherein said camming surface is
formed on said rigid blade.
3. The wrapping machine of claim 1 wherein said camming surface is
formed on said resilient blade.
4. The wrapping machine of claim 1 wherein said resilient blade
leads said rigid blade in the direction of movement of the
interposed web of wrapping material.
5. The wrapping machine of claim 1 wherein said resilient blade
trails said rigid blade in the direction of movement of the
interposed web of wrapping material.
6. The wrapping machine of claim 1 wherein there is a gear mounted
on each said shaft means and meshed with the gear of the other
shaft means to provide counterrotation of said shafts, and wherein
said blades following intersecting circular paths, so that the two
blades overlap with one blade trailing the other, and wherein said
camming surface extends beyond the pitch line of its associated
gear for interference contact with the leading blade.
Description
BACKGROUND OF THE INVENTION
One general type of continuous wrapping machine, as disclosed in
U.S. Pat. No. 2,546,721, longitudinally folds a thermoplastic film
web of wrapping material and heat seals the web to form a tube
around a series of interspaced moving articles. The tube of
articles proceeds through a cutting head unit which transversely
heat seals and severs the web between adjacent articles to form
individual packages.
A typical structure arrangement for severing the web effects a
pressure cut by forcing a sharpened blade against one side of the
web, while the same area of the other side of the web is supported
on an anvil. Because it operates with rotary motion, this type of
cutting operation is rapid and does not unduly limit the speed of
present high speed wrapping machines. The pressure type of cutting
head, however, does have certain disadvantages which are next
described.
Adjusting the cutting members for optimum results is usually a
critical, time consuming operation in a pressure cutting structure.
Two rotary shafts are conventionally provided, one carrying the
anvil and the other carrying the knife blade, and the anvil is
usually adjusted radially of its shaft, with setscrews, into
contact with the knife when the knife and anvil are in cutting
position. It will be evident if there is less than total contact of
the cutting edge of the knife blade with the anvil, the web will
not be totally severed, and that if the contact is too firm, the
knife, anvil, bearings and gearing can be damaged.
Because the conventional cutting head has built in heat sealing
apparatus, the anvil adjustment must be carried out while the
cutting head is at operating temperature to compensate for thermal
expansion. This obviously renders the adjustment more difficult and
inconvenient than if the adjustment could be carried out when the
cutting head is cold.
Part of the conventional cutting head heat sealing apparatus
carried by the knife and anvil shafts grips or crimps the web, and
the upper shaft (usually the anvil shaft) is spring loaded to
control the web crimping pressure. Thus, if the anvil is set too
high, the web crimping members will separate as the spring loaded
upper shaft is raised by the knife, pushing the anvil upward. On
the other hand, if the radii of the crimping members plus the web
thickness are such that the spring loaded shaft raises when the
crimping members contact the web, the anvil adjustment must be
changed to compensate for this because the knife blade will not
penetrate the web. In other words, the crimping and cutting
adjustments are interrelated, such that the changing of one
adjustment usually requires changing the other adjustment.
As is evident from the preceding discussion, the conventional
cutting head has a relatively short knife life, and the pressure
cutting method is not completely efficient. An incidental
disadvantage, also, is that the described pressure cutting
operation generates considerable noise. These disadvantages in the
future are likely to become even more acute because wrapping films
and laminates are increasing in strength, and require higher
cutting pressures.
It is known that a shear type of cutting action overcomes most of
the drawbacks of devices operating with a pressure cutting action.
However, one reason why rotary shears are not universally used is
because there are critical space limitations in most wrapping
machines, due to the fact that the sealed area of the web is
desirably narrow to conserve web material, and the seal areas that
the knife passes between may be separated by only about 3/16 of an
inch for small packages. Also, most prior art rotary shears require
numerous adjustment screws for positioning one or both of the
shearing blades, and cannot be incorporated into existing sealing
heads because of space limitations. Further, adjustment screws
cannot conveniently be manipulated in a heat sealing head because
thermal expansion necessitates that any adjustment be carried out
while the sealing head is at operating temperature.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a rotary
web shear characterized by never requiring any adjustment, by a
capability of the cutting blades to maintain a predetermined
lateral force between the blades indefinitely, and by a structure
which provides maximum service life. These results are obtained by
mechanism including a unique cutting blade arrangement in which one
blade is rigid, and the other is a flat, resilient blade. A camming
surface on one of the blades flexes the latter blade as the two
blades interengage in shearing relation so that the resiliency of
the flexible blade provides the necessary lateral force of one
blade against the other.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective of a known type of wrapping machine
incorporating the rotary shear of the present invention.
FIGS. 2 and 3 are diagrammatic perspectives illustrating two
successive package forming stages of one of the several types of
packages which can be made in the FIG. 1 wrapping machine.
FIG. 4 is a section of the rotary shear mechanism of the present
invention, indicated by the arrow 4 on FIG. 1, and depicts the
initial engagement of the shearing blades as they approach an
interposed web of wrapping material.
FIG. 5 is a section similar to FIG. 4, but illustrates the shearing
blades in final shearing relation to each other and to the
interposed web of wrapping material.
FIG. 6 is an enlarged fragmentary section of the shearing blade
area shown in FIGS. 4 and 5, and illustrates the blades in an
intermediate operational position to clearly show the principle of
operation.
FIG. 7 is an enlarged fragmentary section of one of the shearing
blades shown in FIG. 6.
FIG. 8 is a diagrammatic section taken along lines 8--8 on FIG.
1.
FIG. 9 is an end elevation, at a reduced scale, of the mechanism
shown in FIG. 8.
FIGS. 10 and 11 are schematic perspectives illustrating the
operation of the apparatus shown in FIGS. 4 and 5.
FIGS. 12 and 13 are isometric views of the two cooperative shearing
blades used with the rotary shear mechanism illustrated in FIGS. 4
and 5.
FIG. 14 is an isometric view of a blade holder for mounting the
FIG. 13 shearing blade.
FIGS. 15 and 16 are isometric views comparable to FIGS. 12 and 13,
and illustrate a further embodiment of shearing blades usable with
the rotary shear mechanism of FIGS. 4 and 5.
FIGS. 17 and 18 are sections comparable to FIGS. 4 and 5, and
illustrate a further embodiment of the rotary shear of the present
invention.
FIG. 19 is an isometric of a blade holder used in the FIG. 17 and
18 rotary shear.
FIGS. 20 and 21 are isometric views of two cooperative shearing
blades used with the rotary shear mechanism shown in FIGS. 17 and
18.
FIG. 22 is an isometric illustrating packages having a novel type
of shearing cut which facilitates opening.
FIG. 23 is a schematic fragmentary isometric illustrating a
modification of the shearing blades to produce the package shown in
FIG. 22.
FIGS. 24 and 25 are, respectively, a section and a fragmentary
elevation of the flexible shearing blade used in the FIG. 23
apparatus.
FIG. 26 is an exploded isometric of the FIG. 23 apparatus, but
omitting the flexible shearing blade.
FIG. 27 is a fragmentary section, similar to FIG. 4, showing a
circumferentially adjustable blade structure.
FIG. 28 is a fragmentary isometric of a portion of the FIG. 27
apparatus.
FIG. 29 is an enlarged fragmentary plan of the central portion of
the apparatus shown in FIG. 28.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The wrapping machine 30, FIG. 1, is typical of the basic form of a
known type of machine with which the present invention may be used.
U.S. Pat. No. 2,546,721 discloses a similar form of the same
machine. According to the specific requirements of the user, the
wrapping machine 30 can use different web materials including
plastic films, paper, foil and cellophane, and can produce
different types of seals including glue or heat seals. The general
sequence of operation is that articles A are carried by the pushers
of the upper flight of a chain conveyor 31 along a linear path in
the direction of the arrow 32.
A supply roll B feeds a web C of wrapping material under a forming
plow D and the web and articles are continuously moved through the
machine. The forming plow folds the web edges downwardly into a
tube surrounding the lane of articles. In the present example, the
longitudinal seam of the tube is heat sealed downstream of the
plow, thus producing a series of interspaced articles A (FIG. 2) in
a continuously moving tubular web 33.
Lateral conveying belts E (FIG. 1) are provided to grip and move
the entubed articles downstream through a cutting head unit F
(shown also in FIG. 3) which transversely heat seals and severs the
tube 33 between adjacent articles to form individually sealed
packages P. The packages may be discharged from the machine for
further handling on a lateral discharge conveyor G, or by similar
means, according to the requirements of a particular installation.
The cutting head unit F incorporates the rotary shearing mechanism
of the present invention, and is next described, first in
conjunction with FIGS. 4 and 5.
Cutting head F includes two driven shafts that vertically straddle
the package tube 33, an upper cutting head shaft 34 and a lower
cutting head shaft 36. Shaft 36 is driven in timed relation to the
package tube 33, and the two shafts are interconnected by
intermeshed gears 37 (indicated by pitch lines 37 in FIG. 4) to
counter-rotate. The upper and lower shafts respectively carry a
heated crimping jaw 38 and a heated crimping jaw 40. The crimping
jaws contain electrically energized cartridge heaters 42 and grip,
flatten and heat seal that portion of the web intermediate the
articles. The cutting head shafts are driven in a manner that
provides a matching of the cutting head velocity with the web
velocity during the crimping, sealing and cutting operations.
The lower cutting head shaft 36 is fixed, and the upper cutting
head shaft 34 (FIGS. 6 and 7) is biased downward at each end by
springs 43, to provide a predetermined web gripping pressure
between the crimping jaws 38 and 40. For this purpose, and as is
known from the above identified patent, the wrapping machine 30
includes a pair of bearing blocks 45 (FIG. 8) for the upper shaft
34, a pair of bearing blocks 47 for the lower shaft 36, and a
vertical slide mechanism 49 for each end of the two shafts. Each
slide mechanism is mounted in a cutout portion of a frame member
51, under a fixed yoke 53, and a bolt 54 is threaded through the
yoke into the slide mechanism for elevational positioning of the
slide. The spacing between upper and lower shafts is maintained
equal to the pitch diameter of the counterrotating gears 37 by
spacer blocks. The upper bearing blocks are urged downward by the
springs 43 to provide the above mentioned web gripping
pressure.
In one type of conventional prior art cutting head installation,
the upper and lower cutting head shafts 34 and 36 respectively
carry a knife blade and an anvil member so adjusted that the
cutting edge of the anvil knife will penetrate the web to the
surface of the anvil without causing the upper shaft 34 to be
displaced upward and remove the gripping pressure on the web. This
is obviously a tedious adjustment to achieve initially, and an
adjustment which cannot long be maintained because this pressure
type of cutting action produces relatively rapid wear of the
cutting edge.
The present invention eliminates the inefficient pressure type of
web cutting blades and provides a more efficient shearing cut by
means including a rigid blade 44 and a flat resiliently flexible
blade 46. A particular feature of the invention is structure which
allows mounting the blades within the crimping jaws in generally
radial relation to their axes of rotation so that the shear can be
incorporated into existing wrapping machines. Another feature is
structure which causes the latter blade to laterally flex as it
contacts the rigid blade so that its inherent resiliency effects a
predetermined contact force with the rigid blade along the line of
shearing contact between the two blades.
A further feature of the present invention is that no adjustment
screws or other means for positioning either shearing blade is
required. The importance of this feature is that the cutting action
of the blades is not adversely affected by thermal expansion due to
heat transfer from the adjacent heaters of the sealing head. Thus
the shearing blades are installed when the sealing head is cold,
and there is no need of adjustment when the sealing head is at
operating temperature.
The rigid blade 44, shown also in FIG. 12, has an enlarged base
portion 58 that is mounted in a recess of the lower cutting head
shaft 36 and is locked therein by set screws 60, only one of which
is shown in FIGS. 4 and 5. The screws seat against the bottom
surfaces of a milled slot 62. The outer portion of the blade 44
extends through a slotted portion 64 of the lower crimping jaw 40,
which is removably bolted to the shaft 36 by bolts 66 (FIG. 8) to
permit installation of the blade and repair or replacement of the
crimping jaw. A groove 68 (FIG. 12) is formed near the outer end
surface 70 of the blade 44 in order to provide a shearing edge 72
where the groove and end surface merge. When the rigid blade 44 is
mounted in the cutting head, the shearing edge 72 is at the same
radial distance from the rotational axis of the lower shaft 36 as
the arcuate outer gripping surface of the gripping jaw 40.
At one end, the end surface 70 merges with a projecting cam portion
74, the active camming surface 76 of which is inclined rearward
relative to the direction --indicated by the arrow 77--of rotary
movement of the blade. The shearing edge 72 defines the lower
margin of the camming surface 76, and the camming surface provides
the initial engagement of the rigid blade 44 with the flexible
blade 46.
Of rectangular shape, thin and flat, the flexible blade 46 (FIGS. 4
and 13) is carried by a blade holder 78 which is locked by set
screws 80 (only one of which is shown) in a recess of the upper
cutting head shaft 34. The blade extends outward through a slotted
portion 82 of the upper crimping jaw 38. It will be noted that the
flexible blade 46 is rearwardly offset from a radial plane 84 of
the upper cutting head shaft 34, as is the crimping jaw 38. This
provides operating clearance for flexure of the blade 46, and
additionally allows early engagement with the rigid blade 44 for a
purpose later described. It will be noted, also, that nearly all of
the blade 46 is cantilevered from the blade holder 78 to allow
substantial lateral flexure of the blade. Upper and lower crimping
surfaces 85 and 86 of the crimping jaws 38 and 40, however, are in
indexed relation so that there is coextensive interengagement of
the crimping surfaces. By offsetting the blade 46 from the plane
84, it is possible to interengage the blade 46 and anvil 44 in
proper cutting relation sooner than would otherwise be the case.
This is an important feature, as it allows ample time for the web
severing to be completed by the time the blades are in opposite
alignment as shown in FIG. 5. Stated differently, the disclosed
structure will accomplish the complete web severing operation
within less than 15 degrees of rotation of the shafts 34 and 36. It
should be mentioned here that the crimping jaws 38 and 40 are
conventional in prior art structures, the only change being that
the mounting holes for the bolts 90 (FIG. 8) which secure the upper
jaw are repositioned (or their clearance apertures are slotted) so
as to permit the angular offset of the upper crimping jaw as shown
in FIG. 4.
As best shown in FIGS. 8 and 14, the base of the flexible blade 46
is seated against a tapered ledge portion 92 of the blade holder
78, thereby angling one of its shearing edges 94 (FIG. 13) of the
blade downward toward the cam portion 74 of the rigid blade 44, and
positioning the flexible blade ahead of the rigid blade when they
are in shearing relation. The angular relation of the shearing
surfaces of the flexible and rigid blades is such that the blades
first contact on the inclined camming surface 76 (FIG. 12). The
camming surface thus flexes the adjacent portion of the flexible
blade, and as the two blades move toward opposite alignment the
shearing edge 94 of the flexible blade 46 moves scissors-fashion
across the cutting edge 72 of the rigid blade 44. It is now evident
that the groove 68 of the rigid blade 44 provides clearance for the
lower portion of the flexible blade 46 as the shearing action
progresses across the interengaged blades, and that the force
provided by flexure of the resilient blade remains substantially
constant after it is begun.
An important consideration is that the offset relation of the
flexible blade 46 (FIG. 4) relative to the radial plane 84 allows
the shearing action to begin early in the shearing cycle so that
the shearing action is completed by the time the blades are
positioned as shown in FIG. 5, at which point they being to
separate in the obvious manner. This allows ample time, even though
the total shearing is effected in less than 15 degrees of rotation
of the shafts 34 and 36, for severing the web before the blades
separate to open position as the cutting head shafts 34 and 36
rotate past their FIG. 5 positions. FIGS. 10 and 11 clearly show
the interrelation of the shearing blades and their cooperative
action in effecting a progressive shearing cut across the
interposed web indicated in phantom outline.
In rotating from the FIG. 5 to FIG. 4 position to index again
between the incoming article illustrated, and the next following
article, the flexible blade 46 is released from engagement with the
rigid blade 44, and the inherent resiliency of the blade causes it
to spring back to its normal planar condition. It is obviously
necessary to design the flexible blade 46 so that it is not flexed
beyond its elastic limit, in order to assure that the shearing
pressures does not change with repeated use. Reorienting the blade
will position a new shearing edge 94 in web cutting position, thus
extending the useful life of the blade.
The geometrical considerations which assure satisfactory results
are obviously related to the dimensional arrangements of a
particular machine, but are here set forth in general terms. The
inclination of the shearing edge 94 (FIG. 8) of the flexible blade
46 relative to the rigid blade 44 parallels prior art practice to
obtain a progressive point contact, as in Nystrand U.S. Pat. No.
3,247,746. This inclination is governed by the ledge 92 (FIG. 14),
and in the present case the included angle a between the shearing
edge and the rigid blade 44 (the angle between ledge 92 and the
base of the blade holder 78) may approximate 1.degree.. Since the
flexible blade is inclined, various points along its length are at
different distances from the rotational axis of the shaft 34.
Therefore, and as is conventional in a progressive shear, the
shearing edge 72 (FIG. 12) of the rigid blade 44 is at an angle b
from a radial plane of the lower cutting head shaft 36 so as to
assist in maintaining contact with the flexible blade. In the
present instance, where the shafts 34 and 36 are each about 2 5/16
inches from the median plane of the tubular web 33, the angle b is
approximately 10 minutes.
The preload camming surface 76 (FIG. 6) of the rigid blade is at an
angle c relative to the general plane of the blade, the optimum
value of which will vary with shears having different dimensional
arrangements, but which in the present case is effective at about 5
degrees. The shearing edge 72 (FIG. 7) is inclined relative to the
end surface 70 at an angle d which may advantageously be about
75.degree.. The stated angular relations are all intended merely as
workable examples, and not as precise limits.
FIGS. 15 and 16 illustrate a second embodiment of the rigid and
flexible blades 44 and 46, wherein the rigid blade 44a is
essentially the same as the rigid blade 44 except that the cam
portion 74 is omitted, and the counterpart of the cam surface is a
beveled cam surface 74a on the corner of a flexible blade 46a.
While this construction is essentially a reversal of the formerly
described blade arrangement, it simplifies the construction and
provides four camming surfaces, one for each shearing edge 94a,
each surface being positioned for use when the blade is reoriented
for using a different shearing edge.
FIGS. 17 and 18 are comparable to FIGS. 4 and 5, and illustrate a
second embodiment of the invention which is characterized by a
somewhat unobvious inverted construction. Thus, a rigid blade 44b
is carried by the upper cutting head shaft 34b, but without the
angular offset of the flexible blade 46 (FIG. 4). Thus, the upper
crimping jaw 38b is not angularly offset. The lower crimping jaw
40b is angularly offset and a flexible blade 46b is mounted in the
crimping jaw. FIGS. 19, 20 and 21 illustrate, respectively, a
channel shaped holder 96 for the rigid blade 44b, the rigid blade
44b, and the flexible blade 46b. It should be noted that the holder
96 has walls of uniform thickness along its length, and thus mounts
the base edge 98 of the blade 44b parallel to the rotational axis
of the upper shaft 34b. In order to obtain the non-parallel
relation which is indicated by the angle a in FIG. 8, the breadth
of the blade 44b (FIG. 20) varies uniformly along its length from a
narrow breadth 100 to a wider breadth 102. Further, the rigid blade
44b is provided with a shearing edge 72b that defines one edge of a
tapered narrow side 70b, in the same manner which is indicated by
the angle b (FIG. 12) for the rigid blade 44.
As in the blade embodiment shown in FIGS. 15 and 16, the rigid
blade 44b is absent any camming surface to flex a shearing preload
into the flexible blade 46b, but instead, camming surfaces 74b are
formed at each corner of the flexible blade, and on each side of
the blade. Each camming surface functions in a manner similar to
the camming surface 74, even though the flexible blade 46b (FIGS.
17 and 18) will be seen to trail the rigid blade 44b.
Thus, in the embodiment shown in FIGS. 17 and 18, the shearing
operation begins at the same 15.degree. before the blades are
oppositely aligned, when one leading camming surface 74b engages
the shearing edge 72b (FIG. 20) at or near the lowest corner 104
thereof. As in the FIG. 4 embodiment the flexible blade 46b is
laterally sprung or flexed to provide and maintain positive
engagement between the shearing edge 72b and the engaged one of the
shearing edges 94b of the flexible blade, and the point contact
between the two shearing edges progresses along the length of the
blades as the blades approach opposite alignment.
An advantage of the last described structure is that it is less
prone to accidental damage if an article is not properly registered
in the web of wrapping material such that the blades strike the
article. In this case, the flexible blade 46b will spring away from
the rigid blade 44b, whereas in the FIG. 4 and 5 embodiment the
flexible blade 46 will deflect toward the rigid blade 44.
Therefore, there is less possibility of structural damage due to
improper article-web registration when the FIG. 17 and 18
arrangement is used.
FIG. 22 illustrates a modified type of shearing cut which
facilitates tearing open one end of the finished package P. With
this objective, the web severance is carried out by shearing blades
which form a triangular tab 106 of the end of one package, and a
matching notch 108 on the end of the adjacent package. The notch
108 localizes tearing force when the two adjoining web portions 110
and 112 are forced in opposite directions. FIG. 23 shows one
arrangement for effecting the improved shearing cut, and FIG. 26
illustrates some of the basic parts of the arrangement in exploded
perspective. A rigid blade 44c is provided with a central recess
113 to receive a blade holder 116 which is secured therein by
screws 118 that extend through the blade and into threaded
apertures in the blade holder. An angular notch 120 in the blade
holder fits over a triangular punch blade 122 that extends up into
the path of a flexible blade 46c and slightly higher than the upper
edge 70c of the rigid blade. To accommodate the punch 122, the
flexible blade is provided with two recesses 126, a selected one of
which is aligned with and closely receives the punch. With this
construction, the upper edges of the punch form an offset extension
of the shearing edge, and function in the obvious manner to form
the tab and notch arrangement illustrated in FIG. 22.
It should be apparent that the package illustrated in FIG. 22
represents only one of many design variations which could provide
the easy open feature. For example, the V notch could be at both
ends of the package. Also slits could be utilized instead of
notches. Any of these package design variations could be produced
by a variety of means. The slitting or punching operations might be
done on the wrapping machine, either upstream of or at the sealing
and cutoff station. The wrapping film might also be supplied in
pre-punched or pre-slit form.
In the practice of the herein disclosed invention, it has been
found preferable to provide a precise adjustment of the rigid blade
44, 44a or 44b, circumferentially of its mounting shaft. The reason
for this is that practical manufacturing tolerances are sometimes
not sufficient to assure uniform shearing action among different
machines, or among the blades of a rotary shear having more than
one rigid and flexible blade assembly. It has been found, however,
that there is a simple and effective remedy which enables the
production of the rotary shear with only the usual manufacturing
tolerances. FIGS. 27-29 diagrammatically illustrate this aspect of
the invention in conjunction with a lower cutting head shaft 36d,
gripping jaws 38d and 40d, a rigid blade 44d, and a flexible blade
46d. All of these elements are comparable to the FIG. 4 apparatus,
except that the cutting head shaft carries two blades 44d.
An integral pad 128 of the shaft 36d is provided with a radial
recess 130 of uniform width and depth. A roll pin 132 (only one
being shown in FIG. 28) is mounted at each end of the recess to
restrain the rigid blade 44d from endwise movement in the slot. The
back surface 134 of the rigid blade 44d is planar and parallel to
the adjacent wall of the slot 130, and is engaged by a pressure
plate 136 that locks the blade in adjusted position under the
pressure of a plurality of locking screws 138.
Adjustment of the blade 44d is carried out by rotatively
positioning an eccentric member 137 when the locking screws 138 are
loose. For this purpose, the eccentric 137 is threaded through an
aperture in the pad 128, and is provided with an off center pin 140
that lies within a vertically elongate slot 142 formed in a
positioning wedge 144. The wedge tapers from end to end and is
unrestricted by the roll pins 132. That portion of the blade which
contacts the wedge 144 has a complementary but opposite wedge
shape, as shown at 146 (FIG. 29) and the remote side surfaces of
the pressure plate 136 and the wedge 144 are parallel. It will be
evident, therefore, that when the locking screws 138 are loose,
rotating the eccentric 137 will move the concealed blade-engaging
face of the wedge 144 toward or away from the blade, whereby the
circumferential position of the blade relative to the shaft 36d can
be altered. In this manner the gearing which provides driving power
to the shaft 36d can provide a degree of coarse adjustment, and a
final, precise adjustment can be carried out with the wedge and
eccentric apparatus described.
From the preceding description and the accompanying drawings, it is
believed to be apparent the the rotary shear mechanism of the
present invention provides a marked improvement over present
wrapping machine web severing devices. Thus, the web shearing
mechanism has been completely isolated from the crimping jaws as
far as setup and operation is concerned. Since the structures for
the heat sealing and severing operations are independent of one
another, each can be easily set up for optimum effectiveness, and
the normal wear of either structure does not affect the other.
Further, the disclosed geometry of the rotary shear mechanism
wherein the shearing blades are substantially radial with respect
to their mounting shafts, and wherein the cam surface on one or the
other blades preloads the shearing pressure in the flexible blade,
allows the shearing to occur within a very narrow segment of a
complete revolution of the cutting head shafts. This is
advantageous because it produces a severing operation as fast, or
faster, than a conventional pressure cutting operation. The rotary
shear of the present invention is thus easily incorporated in a
conventional wrapping machine, even though the machine may operate
with a very small space between articles.
A basic aspect of the present invention is considered to the
structural features of arranging one of the shear blades so that
its shearing edge is at a radius of rotation substantially equal to
the pitch radius (phantom line 37) of the gears 37, and arranging
the other blade so that its shearing edge is inclined end to end,
whereby the radius of rotation of the shearing edge varies. The
shortest radius to this edge is greater than the pitch radius of
the gears to assure overlapping of the two shearing blades. The
camming surface which flexes the flexible blade projects beyond the
gear pitch line in order to fully preload or flex the latter blade
by the time the shearing edges begin to shear the web.
Although the best mode contemplated for carrying out the present
invention has been herein shown and described, it will be apparent
that modification and variation may be made without departing from
what is regarded to be the subject matter of the invention.
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