Cast web diversion

An apparatus for cutting and diverting a freshly cast, polymeric web. The apparatus includes a pair of traversing knives that cut a tongue from the middle of a web and an air jet that diverts the continuously advancing tongue and web to waste.

BACKGROUND 
This invention relates, generally, to the production of thin films and, 
more particularly, to a semiautomatic apparatus for cutting and diverting 
a continuously advancing, freshly cast web without loss of web-forwarding 
tension. 
In existing machines, film is produced by extruding a web of molten, 
polymeric, film-forming materials onto a quench wheel and then advancing 
the web through stretching and slitting stations to one or more windups. 
During startup, the cast, unoriented web is led manually under the quench 
wheel and over rolls located adjacent the quench wheel. From those rolls, 
it is guided through a slot in the floor to a waste accumulator. After the 
desired cast profile has been achieved, a manual traversing knife is 
inserted through the web adjacent one of its sides to form a strip which 
is then cut to form a leader. When that leader has been threaded through 
the stretching stations to another waste collector, the traversing knife 
is moved across the web, thereby transferring it to the production 
thread-path. Next, the stretched, oriented film is routed through the 
slitting station to the windups. For planned stoppages at or beyond the 
stretching stations, the quenched web can be re-routed to the waste 
accumulator by first cutting a leader, guiding it to waste and then 
traversing the knife through the web. In the event of an unplanned 
stoppage, an operator uses scissors to cut a leading edge across the 
tough, thick, unoriented, amorphous, cast web and then must manipulate 
that leading edge through the slot to the waste accumulator. Forwarding 
tension is lost when the web is cut. The time required to accomplish this 
operation safely places a limit on the maximum throughput for the entire 
machine. 
SUMMARY 
The potential throughput of a machine for manufacturing film has been 
increased substantially by the provision of a semiautomatic apparatus for 
cutting and diverting a freshly cast web in its advance from a quench 
wheel to a stretching station. The apparatus includes a carriage mounted 
for movement toward and away from the path of the web and a drive for 
moving the carriage. A pair of knives are mounted on the carriage for 
pivotal movement into the web and for traversing movement in opposite 
directions through its width to cut a leader. There are actuators on the 
carriage for pivoting and traversing the knives and an air jet for 
diverting the leader to a waste collector.

DESCRIPTION 
Referring to FIG. 1, the machine into which the apparatus of this invention 
has been incorporated includes a die 10 from which a web 12 of molten 
polymer is extruded and cast onto a quench wheel 14. Web 12 is stripped 
from wheel 14 and guided over support rolls 16, 18, through a gauge 20 for 
measuring web thickness and past a manually operated, traversing knife 22 
to a roll 24. The web then advances over a roll 26 to a stretching station 
28 where it is orientation drawn in the machine direction (MD). At a 
subsequent stretching station, the web is drawn in the transverse 
direction (TD). Then, in normal production, the resulting thin film is 
advanced through a slitting station to multiple windups. 
The apparatus of the invention includes a carriage 30 slidably mounted on 
guides 32 located on opposite sides of the path of advance for web 12; the 
guide on the right hand (RH) side of the machine appears in FIG. 1. Roll 
26 is rotatably mounted on carriage 30. A pair of knives 34, 36 are 
mounted for pivotal movement into the path of web 12 and for rotation 
about their axes. Each knife is carried by a traversing block; the block 
for left hand (LH) knife 36 appears at 38 in FIG. 1. The manner in which 
the knives 34, 36 are traversed in opposite directions from a home 
position adjacent the center of the web 12 is shown in FIGS. 2 and 4. 
In the event of a stoppage, whether planned or unplanned, actuators for 
knives 34, 36 and a roll 40 are energized by signals from the logic unit 
in a programmed controller. Typically, an unplanned stoppage is initiated 
automatically by the detection of a break in the web at MD stretching 
station 28. Roll 40 is swung into a nipping engagement with roll 26 and 
knives 34, 36 cut a tongue from web 12. That tongue is diverted to a chute 
42 by a jet device 43 and guided between a pair of rolls 44, 45 by air 
streams in the chute. The air streams are introduced through slot jets 46, 
47. Excess air is exhausted through a vaned opening 48 and a Coanda 
surface is provided between slot jet 46 and opening 48. After the tongue 
reaches rolls 44, 45, actuators move the rolls 44, 45 into nipping 
engagement and the tongue is delivered to a waste shredder. By this time, 
knives 34, 36 have travelled through the edges of the web and are returned 
to their home positions. The full width of web 12 is advanced to waste by 
nip rolls 44, 45; the trailing end of the cut length is exhausted into the 
aisle between carriage 30 and MD stretching station 28. Web-forwarding 
tension is retained on both lengths, throughout the cut-and-divert cycle, 
by rolls 26, 40, 44, 45. 
Home positions for the RH and LH knives are shown at 34h, 36h in FIG. 2. 
When first inserted through web 12, the leading LH knife has its cutting 
edge disposed in parallelism with the machine direction. Before its 
insertion, the cutting edge of the trailing RH knife is located slightly 
to the left of the LH cutting edge and is disposed at an intersecting 
angle with respect to the MD slit to be cut by the LH knife. During a 
cutting cycle, the knives are sequenced, as follows: 
the knives are pivoted into operative positions 36o, 34o, 
both knives are rotated to traversing positions 34t, 36t, and 
the knives are traversed in opposite directions through the edges of web 
12, withdrawn and traversed back to their home positions. 
Structural arrangements and relationships in a useful embodiment of the 
apparatus are shown in FIGS. 3 and 4. Guides 32 are attached to upright 
frame members 49 located at the sides of the machine and receive bushings 
50 that are carried by side plates 52 of carriage 30. Each side plate 52 
also carries an internally threaded follower 54 that receives an upright 
drive screw 56. Screws 56 are driven through a gear box on a horizontal 
frame member atop frame members 49 and operate to raise and lower the 
carriage between the positions shown in FIG. 1. The carriage can be locked 
in the raised position, during startup, by pinning an ear 58 to a similar 
ear on the horizontal frame member. 
Roll 26 is supported by bearings in a flange block 60 and is driven through 
a coupling 62 by a speed reducer and motor mounted on the LH side plate 
52. 
Air jet assembly 43 includes a pair of plates 64, 65 that are bracketed to 
the mount for a motor 66. Plate 64 has an elongated plenum 68 that is 
connected to a valved source of air under pressure and discharges to a 
slot jet defined by a groove milled into the adjacent face of plate 65. 
The jet is directed at the path of advance of web 12. Motor 66 is coupled 
to a sprocket wheel 69 through a chain. Wheel 69 is coupled to a LH screw 
70 and a RH screw 72. The inner ends of screws 70, 72 are supported by 
bearings located in a box 74 and the outer ends by bearings 75 mounted on 
side plates 52 of carriage 30. Box 74 is bracketed at the mid-points of 
guide shafts 76, 77 for LH and RH traversing blocks 38, 78. Blocks 38, 78 
carry bushings 79 that receive shafts 76, 77 and, between the bushings, 
internally threaded sleeves 80, 82 that receive the screws 70, 72. In this 
manner, blocks 38, 78 are traversed to-and-fro the home positions of 
knives 36, 34. 
LH knife 36 is fastened to the bottom end of a holder 84 that is round in a 
mid-length 85 (FIG. 4). Length 85 is rotatable in a bore that extends 
through a bar 86. At the upper end of holder 84, there is a follower 88 
that travels in an elongated cam 90 as block 38 is traversed. Cam 90 is 
attached to a part on the frame. Along its side, bar 86 is attached 
rigidly to another bar 92 which is pivoted at 94 between the spaced ears 
of a mounting bracket 96 carried by block 38. At its upper end, bar 92 is 
pivotally attached to the rod of an actuator 98. The other end of actuator 
98 is pivoted to a bracket attached to the top of block 38. When actuator 
98 is extended to move knife 36 out of the path of advance for web 12, a 
catch at the inner edge of bar 92 is latched by a detent 100 that is 
pivoted to the rod of an actuator 102. 
RH knife 34 is mounted and actuated in the same manner as knife 36 except 
that its mounting bracket 104 is disposed at angles slightly divergent 
from parallelism with planes in and perpendicular to the normal path of 
travel for web 12, i.e., the mount for knife 34 is tilted about two axes. 
As a consequence, the cutting edge of knife 34 is slightly to the left of 
knife 36 when both are in the home positions 34h, 36h (FIG. 2). Another 
factor bearing on the position of the cutting edge of knife 34 when in the 
home position is its relative length (FIGS. 5B and 6B). 
During startup, the carriage is raised to the elevated position shown at 
30' in FIG. 1. When a full web has been established to and through the 
stretching stations, the carriage is lowered to its operating position. 
Then, the molecularly oriented, thin film is routed through the slitting 
station to the windups. In the event of a stoppage, whether planned or 
unplanned, web 12 is automatically cut and diverted to waste in a set 
sequence of activities, as follows: 
nip roll 40 engages transfer roll 26, 
LH knife 36 is inserted through web 12 in a snap action, 
RH knife 34 is pivoted through the mitered edge cut by lead knife 36, 
the knives are rotated to their traversing positions 36t, 34t, 
the knives traverse toward the edges of web 12, 
air jet 43 diverts the tongue cut by knives 34, 36 to chute 42, 
rolls 44, 45 close on the tongue, 
the knives traverse through the web, retract and return to their home 
positions, 
carriage 30 is raised and locked manually in its elevated position, and 
nip roll 40 retracts. 
As indicated above, knife 36 is inserted into the taut, tensioned web 12 in 
a snap action. That action is initiated by pressurizing actuator 98 in 
advance of actuator 102. When the latter is pressurized, detent 100 
releases bar 92 and the sharp point of knife 36 is pivoted through the 
web. Only one side of the sickle blade on knife 36 is bevelled. The other 
side is flat. Thus, with knife 36 mounted as shown in FIGS. 2-4, it cuts a 
slit with a mitered or square right edge. That mitered edge presents an 
ideal target for the tilted, sickle blade on knife 34 as it is inserted 
into the web. Like knife 36, the sickle blade of knife 34 is also flat on 
its right side and bevelled on its left side (FIGS. 2, 5B, 6B) 
Controls for initiating the motions and sequences outlined above are in the 
form of limit switches, break detectors and similar devices already known 
to those skilled in the art. Two examples of plates adapted to engage 
limit switches are shown at 106, 108 on bar 92 (FIG. 3). Another limit 
switch and its actuator are shown at 110, 112 in FIG. 3; it is the signal 
from switch 110 that stops the drive for screws 70, 72 when traversing 
knives 34, 36 reach their home positions. Similar devices located 
throughout the machine are connected to the programmed controller which, 
in turn, provides control signals for such elements as actuators 98, 102. 
Parts, elements and relationships for imparting rotational motions to LH 
knife 36 are shown in FIGS. 7-10. Length 85 of holder 84 has a blade 114 
press-fitted in a slot therethrough and extending therefrom into a wedge 
shaped opening 116 in the upper end of bar 86. A passage 118 extends from 
opening 116 through bar 86 and into a retainer plate 120 for a spring 122 
that engages blade 114 and biases the LH knife toward its position 36h 
(FIG. 2). At the outset of traversing motion, the cam follower 88 engages 
cam 90 (FIG. 3) and, against the bias of spring 122, rotates the LH knife 
to its position 36t. Follower 88 is carried by an internally threaded boss 
124 on a lever 126 that is pinned to an upper, reduced end 128 of knife 
holder 84. When the LH knife has moved through the edge of web 12, 
follower 88 leaves cam 90 and spring 122 returns it to its position 36h. 
Functionally similar parts and elements impart rotational motions to RH 
knife 34. 
In a usage of a machine equipped with the apparatus disclosed herein, 
divert efficiency over an extended period was 100% and this permitted an 
increase of about 6.5% in its throughput.