Note: Descriptions are shown in the official language in which they were submitted.
~L2~
hum
~A~ATUS FOX O~T~INING ~IFFEkENTl~L T~NGENTI~L
vat LE SPEEDS IT DIFFERENT JOINTS OF DEFOR~LE FILM
.
The invention relates to an apparatus for obtai-n-
ing differential variable speeds at various points of a
flat film or plate, which i5 more particularly elastically or
plastically deformable.
In numerous industries, particularly in the ten:-
tile and metallurgical industries, it is common practice and
necessary to draw flat stock with the object of thinning
down or calendering these products. Sometimes it is necessa-
ry to prestress plastic, metallurgical or textile products.
Finally, in the pealing industry, plastic films are drawn
prior to placing them around palleti2ed loads and causing
them to retract naturally or not.
In general, to carry out these operations, it is
necessary to obtain different speed5 between two different
points of the film. Jo do this, it is common practice to use
two rollers turning about parallel a~:es at different rota-
tional speeds. Thus, in general, the rotational speed of
the downstream roller is higher than that of the upstream
roller. In particular, the angular speeds of the rotating
rollers are varied by mechanical, electronic, hydraulic means
and by gear boos gearings, etc. However, the devices of the
prior art do not permit variation of the differential
tial speed ratio by a value very much higher than 1, e.g., up
. . . g
'Lo 06~.
to 3. Moreover, when banderol~ng pallets In the startlng phase,
It Is not posslble to obtaln a dlfferentlal speed ratlo equal to
1 wlthout uslng coupllng devlces.
The prlmary obJect of the Inventlon Is to overcome
these drawbacks.
Accordlng to the present Inventlon there Is provlded an
apparatus for stretchlng a deformable fllm or plate, comprlslng
at least an upstream cyllndrlcal roller and a downstream cylln-
drlcal roller, sald roller havlng parallel axes of rotatlon,
means for movlng the fllm or plate over sald rollers, the radlus
Ro of the upstream roller and the radlus R1 of the downstream
roller belng varlable wlth tIme, the ratlo of the rotatlonal
speeds of the roller N1/No being constant.
The Inventlon also provldes an apparatus for stretchlng
a flat deformable fllm plate movlng along at least one stretchlng
roller rotatable about an axls (XX), the fllm or plate movlng
over the roller and restlng on a generatrlx G of the roller, the
rotatlonal speed of the roller belng constant wlth tlme, whlle
the dlstance GC1 between the supportlng generatrlx G of the ~llm
and the axls C1 of rotatlon of sald roller Is varlable wlth tlme,
sald drawlng roller comprlses a plurallty of contlguous genera-
trlces G whose dlstance to sald axls of rotatlon of sald drawlng
roller Increases contlnuously wlth tlme from the upstream genera-
trlx Go reached by the undrawn fllm to the downstream generatrlx
G from whlch Issues the drawn fllm.
Thls apparatus Is characterlzed by the fact that the
roller has a rotatlonal speed whlch Is constant wlth tlme,
whereas the dlstance from the supportlng generatrlx of the fllm
to the axls of rotatlon of the rolier is varlable wlth tlme.
3~ Accordlng to a flrst embodIment of the Inventlon, the
drawlng roller Is formed by a plurallty of contlguous generatrl-
~2~2~)61.
ces whose dlstance to the axls of rotatlon Increases contlnuously
wlth tIme from the downstream generatrlx from whlch Issues the
drawn fllm.
Accordlng to the second em'~odlment, the drawlng roller
Is a deformable cyllnder, In partlcuiar a cyllnder of revolutlon
havlng an axls of rotatlon whlch Is to i Sp laced In relatlon to the
axls of revolutlon, the dlstance between the contlguous genera-
trlces Increaslng contlnuously wlth ;-Ime from the upstream gener-
atrlx reached by the undrawn fllm
- 2a -
3 2~)61
to the downstream generatri~: frDm which issues the drawn
film.
The film rests on the generatrix by means of at
least one pressure member that exert5 pressure on the
roller, in particular a supporting roller, said member moving
as it rotates about its a~:is dependent upon the displacement
of the supporting generatri~:, and the film being placed
between the supporting member and the roller.
he ratio of the initial distance ~vfrom the
upstream generatrix to the a~:is of rotation to the final
distance k~from the downstream generatri~ to the axis of
rotation is adjustable.
Finally, according to a third embodiment, the film
is carried along by the rotation of two circular-oylinder
rollers having a circular base and parallel a>:es of rotation,
the upstream radius Ro and the downstream radius I being
variable with time. Furthermore the drawing ratio, more par-
ticularly the ratio of the differential tangential speed Vl
at a point of the film downstream, following drawing, to the
differential tangential speed VO at a point of the film up-
stream, prior to drawing is proportional to the ratio of the
radius l of the downstream roller to the radius ~0 of the
upstream roller.
lt will be understood that the apparatus embodying
the principles of the invention has significant advantages
over devices of the prior art. Indeed, it is easy to adjust
the drawing either by changing the position of the axis of
rotation relative to the at 5 of revolution; this modifies
0~
the distance between the generatrix on which the film rests
and the axis of rotation of the roller or by modifying the
radii of the rollers relative to one another ln addition,
several rollers, as required, can be utilized which, by
varying their radii, enables one to obtain differential
variable speeds.-
For a more complete understanding of the presentinvention, reference i5 now made to the following description
of illustrative embodiments presented hereinbelow in connec-
tion with the accompanying drawings, in which:
- Fig. 1 is a schematic view of a first embodiment of the in-
vention;
- Fig. 2 is a schematic view of a second embodiment;
- Fig. 3 i5 a perspective view of a third embodiment;
- Figs 4A and 4B show the variation of the radii of the rol-
lers for, respectively, minimum drawing and maximum drawing.
- Fig. 5 shDws a first embodiment of a roller;
- Fig. 6 shows a second embodiment of a roller;
- Fig. 7~ and 7~ show a first variation of the third embodi-
ment with minimum drawing (7~) and ma~:imum drawing ~7B);
- Figs. 7C and 7D are top plan views of on one side, a
portion of the rollers and, on the other side, the means con-
trolling the e~:pansion or the contraction of the rollers.
- Fogs. 8~ and 8~ illustrate a second variation of this last
embodiment of the invention with, respectively, minimum draw-
ing and maximum drawing.
- Fig. 9 is a side view of another variation of the roller of
the invention;
S ~L~4;~:~61.
- Fig. 10 is an enlarged view of a detail of the roller of
Fig. 9;
- Fig. 11 i5 a side view of another variation similar to that
depicted in Fig.- I;
- Fig. 12 is a schematic view of the operation of an appa-
ratus of the invention equipped with rollers such as the
roller of Fig. 11.
The apparatus of the invention enables one to ob-
tain differential tangential variable speeds at different
points of a deformable flat film or plate, more particularly
an elastically or plastically deformable film. It is well
~.nown that elastic deformation is reversible and that the
film, when no longer drawn, resumes it5 initial position,
whereas plastic deformation is partly irreversible and the
film, when no longer drawn has a final length which is
greater than its initial length.
Tangential differential speed is the speed of the
film moving along at least one roller or carried along by the
rotation of at least one roller rotating about its a~:is, the
film mDving in a direction perpendicular to the a~:is of rota-
tion of the roller and resting on a generatri~ of the
roller.
ccording to the invention the roller has a speed
of rotation N which is constant with time, while the distance
from the suppDrting generatrix of the film to the a~:is
of rotation of the roller i5 variable with time.
Fig. 1 depicts a first embodiment of the invention.
film 1 arrives upstream in drawing apparatus 2 and issues
~2~2~
downstream therefrom. Slnce the tangentlal speed of fllm 1
upstream Is V0, the tangentlal speed of fllm 1 downstream equals
VN. Apparatus 2 enables one to obtaln tangentlal dlfferentlal
speeds VN, whlch are varlable at dlfferent polnts of fllm 1. The
latter Is flat and In Fog. 1 It Is shown perpendIcular to the
plane of the flgure. It Is a fllm whlch Is elastlcally or plas-
tlcally deformable and Is preferably made from synthetlc mate-
rlal. The length L0 between two polnts AB of the fllm upstream
15 less than the length LN between the same polnts AB of fllm 1
downstream.
Accordlng to the Inventlon, apparatus 2 permlts the
drawlng of fllm 1, I.e., the segment AB wlth a length L gradually
attalns the length H (Flg. 1).
Thls fIrst embodlment comprlses a roller 3 formed by a
pluralIty of contlguous generatrlces Go GN. Generatrlces G
are caused to rotate about an axls C by a drlve mechanlsm 4,
preferably at least two splders formed by flat clrcular sectlons
placed at each end of generatrlces GN. The center of rotatlon
C1, through whlch passes the axls of rotatlon of the splder, Is
dlsplaced In relatlon to the center o-F rotatlon C of drawlng
roller 3. The dlrectlon of rotatlon of drIve mechanIsm 4 Is the
same as that of drawlng roller 3. FlIm 1 Is carrled along by the
rotatlon of at least one roller 3 turnlng about an axis of rota-
tlon, at right angles to the plane of the Flgure, of center C.
FlIm 1 moves over drawlng roller 3 and rests on a generatrlx GN
of roller 3 at Instant tN. Thus, an Instant to fllm 1 bears on
generatrlx Go Its
42~)6~ ,
speed isVO, at instant tl= to+ it, film 1 rests on generatri~:
Gl~ its speed is Vl = VD ~avO, at in5tant to the film rests on
generatri~ Go, its speed V~= V +~ ~V~_~. Preferably the speed
increments ~V~_~ are constant) but they may also vary.
Drawing roller 3 rotates in the direction of arrow Fl and has
an angular speed of rotation N which i5 con5tant with time,
while the distance from supporting generatri~: Go to the a~:is
of rotation Df the drawing roller varies. Preferably, the
distances C~Go~ C~G~ are such that Cl Go Go and the
distance from the a~:is of rotation Cl of- drive mechanism 4 to
generatris: GD downstream is less than the distance from the
at:is of rotation to generatri~: Go downstream. This distance
O increases continuously during the interval from upstream
to downstream. The initial distance GoCI upstream equals r,
while the final upstream distance equals I.
The distance e from the center of rotation C of
drawing roller 3 to the center of rotation Cl of drive mecha-
nism 4 is adjustable; this permits adjustment of the final
tangential speed Y in relation to the initial tangential
speed VO and, thereby, the adjustment of the drawing ratio
This drawing ratio can increase up to or 3, at
any rate it is much higher than 1 and can al50 be adjusted to
be less than 1.
The drawing ratio can be made such as to equal 1
when drawing a plastic film that is utili_ed for the bande-
roling Df pallets. Thi 5 drawing ratio equalling 1 is nece~ary
at the start of the banderoling~ since the film shall
36~.
not be drawn. In this case, the distance CG~ is zero.
Thus, by displacing the center C in relation to the center O
the invention mazes it possible tD gradually adjust the draw-
ing ratio.
ccording to a secDnd embDdiment of the apparatus
Df the invention fig. 2~, the drawing roller i5 a cylinder
of revolution 'I preferably having a circular base, whose
axis of rotation ox the center C is displaced relatiYe to
the a~:is of revolution of the center C . The drawing cylinder
is deformable and is preferably made from elastomeric
material. Thus, the distance between the contiguous genera-
trices Go,GI,...~ Go increases continuously during the
rotation (direction of arrow F~) when the center of rotation
O is displaced on the upstream side in relation to the
center of revolution C3.
Film 1 rests on generatrix Go at an instant to and
a loose pulley causes the deformation of deformable sup-
porting cylinder which moves as it rotates about the
center O The film is introduced upstream on the side where
the distance r = C~Go from the center of rotation C2to the
generatrix Go is the shortest and issues downstream on the
side where the distance R = CaGN from the center of rota-
tion C2 to generatrix Go is the longest.
y adjusting the distance C~C~with the aid of
roller I, the drawing ratio, which may equal 1 when C2 merges
with C~,is adjusted.
According to a third embodiment of the invention
figs. ~-8), the film moves along two circular-cylindrical
rDllers 7, 8 having a circular base and parallel rotating
ales XX~ YY, the radius ~0 of upstream cylinder and the
radius k\ of downstream cylinder being variable with time.
Film I moves in a direction perpendicular to axles XX, YY.
ccording to the invention, tangential speed VO of
film 1 upstream is different from the tangential speed Vl of
f i 1 m I downstream.
Film 1, moving at speed V/ , can drive the set of
rollers 7 and 8. In a variation! film 1 is driven at speed Vl
by the roller 0 driven by a motor 9.
According to the invention, rollers 7~ B are ro-
tated in such a way that the ratio h of the speed of rotation
N of cylinder 8 to the speed of rotation No of cylinder 7 is
constant. They have opposed directions of rotation, cylinder
7 working in the direction of arrow F3 and cylinder 8
rotating in the opposite direction (arrow F4).
Therefore if E is the drawing ratio of the film, L
the length of a segment ~B downstream, and L is the length
of the segment RB of film 1 upstream, the following equation
is valid:
E = L
At instant t, one has Lo = Vot andLI =V~t.
L` - E,- \/'
Lo Vo
However, the tangential speed equals the radius of
the cylinder multiplied by the speed of rotatiDn of the cyl-
inder.
Therefore, Vl=
242061.
Yo = ~o~o
E = R- _ k
Yo Jo Ro ~4
according to the invention,
y varying the radii Jo and fix of upstream cylinder
7 and of downstream cylinder one varies the ratio of the
tangential speeds Y and Vl.
The distance from a generatrix GN to centers of
rotation C0 and CI thus varies with time since radii R~ and
k~ are Yariabl~.
If Ro and fil vary between the limit values r and
when Rl = r and Ro = R~ the drawing ratio E is at a mini-
mum (Fig. 4~), whereas, if Rl = and pa = r. the drawing
ratio E is at a ma::imum (Fig. 4~).
Thus, E ma and E mini = Rr YE a
If it is desired to vary the drawing ratio from
0 to lOC)~., then
- E ma::i =~ a
~n~ r
fi = ~113~ for example
r = t~b~
The average radius is 197 mm..
If it is desired to vary the drawing from 0 to
20C)%, then
E ma::i _-3
n l
r = 70 mm~ for e~:ample
fi = 173 mm
The average radius is +~7 mm~
fix
.
If a drawin9 ratio equal to 1 is desired f must
in the first case equal +1.4, and in the second case it must
equal +1.7.The ratios of the speeds of rotation are adjust-
ed by means of a gearing 10.
ccording to an embodiment of the invention illus-
trated in Fi 95. 7A, 7~ 7C and 7D~ the apparatus for the
variable predrawing or drawing comprises two drawing rollers
7 and 8 consisting uf a plurality of longitudinal curved
portions 11 forming the cylindrical surface of the roller.
The two rotating a>:les XX, YY of the rollers are parallel.
The function of members 12 for guiding portions 11
of rotating axles XX and YY into radial translation is to
move them away or bring them closer together. The function
of~rive mechanisms,/13 for rotating the portions 11 is to pivot
them about a::es XX and YY and, finally the function of con-
trol units 14 is to activate guide members 12.
referably~ drive mechani5ms l for rotating said
portions 11 consist of hubs l which enable the latter to
rotate about a::les XX or YY, which are fluted axles. These
fluted axles pivot on bearings l
embers l for guiding said portions 11 in such a
way as to slide in radial translation con5ist of ramps 17
which rest in grooves 18 provided in hubs l Each cylinder
11 has at least two hubs 15. Hubs 15 of a cylinder 7 slide
simultaneously along fluted axles XX or YY.
fiamps are cap e of sliding radially in grooves 18.
Thus, the radius of cylinders 7 and 8 can vary by sliding
ramps 17 radially in grooves 18 and, 5imultaneously, by
-- 12 61.
sliding hubs 15 in an a~:ial direction.
Each cylindrical roller 7~ 9 has at least one
flange 19 to ensure the end guidance of pDrtions 11. Stops 2
can slide radially in relation to flange 19.
The apparatus also includes control units 14 to
activate guide means 12 $or causing portions 11 to slide
in radial and a::ial translation. Control units 14 consist
of a double fork 21 pivoting about an a~:is 22 perpendicular
to rotating ales XX, YY of rollers 7, B. Double for 21 acts
by means of a supporting rim 2~ placed at one end of rotating
ales XX, YY of the rollers, on a thrust ball bearing 23.
Thus, when double fork 21 leans on the side of up-
stream roller 7 (Fig. 7A), it acts on stop 23, causing hubs
15 of upstream cylinder 7 to slide a~:ially. Hubs 15 are dis-
placed to the end of ale XX which does not have the stop ?3.
Hubs 15, as they move compress return spring 24. Portions 11
and rasps 17 lie flat on sliding hubs 15 owing to circumfe-
rential springs 75 located on each level of ramps 17.
Hubs 15, as they move along ale XX, push portions
11 radially outwardly, thus ensuring the increase of the
radius of roller 7, which assumes the value R.
y contrast, fork ?1 is connected at its other end
on the side of downstream roller By hubs 15 are in a position
opposite to hubs 15 of downstream cylinder 7. Return spring
?4 urges the sliding hubs and the control units to the posi-
tion corresponding to the minimum value of the radius of
downstream roller 9, which assumes the value r.
Gearings 26 permit the adjustment of the rota-
3~
tional speed of uprstream roller 7 in relation to the rota-
tional speed of the downstream roller.
In Fig. 7A, there is a radius fi upstream and a
radius r downstream, the drawing ratio being at a minimum.
y contrast by rocking in the opposite direction
of forl. 21 (Fig. 7~), a radius r is obtained upstream and a
radius fi downstream, the drawing ratio being at a mas:imum.
The pivoting of fork 21 is controlled by a control
unit 27. us shown, this unit can be a hydraulic, pneumatic or
electric actuating cylinder or a manual nut-and-bolt system.
Thus, there corresponds to each po5ition of control unit 27
for controlling the font 21 a value of the radii of rollers
7 and i.e., a value of the drawing coeffici~nt~ Positions
of control unit 77 can be controlled by electrical means on
the basi 5 of predetermined or programmed set values.
In another embodiment (Figs. 8A and 8~) of the
apparatus of the invention gearing 26 is placed on the side
of control units 14. Pamps 17 are integral with a shaft 18
concentric with rotating as:le XX which has a stop 29 on which
rests spring 24. For 21, as it swivels compresses spring 24
which brings about the displacement of hubs 15 as:ially in the
direction of arrow F4, to in the direction of movement of
fork 21. fiamps ?7 slide in grooves l which causes the
downstream cyhlinder to es:pand. By contrast, upstream
cylinder 8 is not compressed.
Preferably, portions 11 have on the outer surface
an adhesion-promoting lining.
Figs. and show other forms of construction of
14 21~61.
the rollers. On the left side of each figure, there is pro-
vided a half-roller 3b with a smaller radius and on the right
side a half-roller 31 with a larger radius.
ln Fig half-roller 30, file half-roller 31, con-
sists of portions 3? that are integral with radial compress-
ible elements ~3. Freferably, they are made from elastomeric
material. These radial elements 33 are located between radial
fled partitions 34 an radial movable partitions 35 that
are integral with a shaft 3~ capable of sliding a~:ially. When
shaft 36 is moved a~:ially, movable partitions 35 move closer
to fled partitions 34, the elastomeric element i5 compressèd
a:ially and deformed radially as it urges portion - radially
outwardly. The radius of the roller increases. When movable
partitions 35 move away from fled partitions 34, the elasto-
meric element returns to its initial form. Preferably the
elastomeric elements are placed at each end of portions ll.
In Fig. 6, portions 11 are displaced by means of a hydraulic
device. This displacement of piston shaft 37 brings about the
displacement of support 38 of portion ll, with the hydraulic
liquid transmitting the pressure between shaft-piston 37 and
support 38.
The hydraulic liquid is iocated within the chamber
formed by hollow shaft 39, with shaft 37 sliding a~:ially and
support ~8 sliding radially.
In certain applications) the devices described
hereinabove, particularly in Figs. 1, 5~ 6, 7~-7D,8A and 88
have the disadvantage that the portions strike against the
tensely stetched film, thereby producing a noise due to the
~42~
repeated blDws of the portions or metal bars on the taut
film.
Furthermore, the drawn film undergoes a transverse
shrinkage, that is to say, the final width of the drawn film
i5 smaller than its initial length. This is a drawbacl: for
the good quality of the bandernling obtained in the pacling
industry.
oreover~ the portions forming the cyl i nders of re-
volution, which consist of metal bars, can cause the
taut film to be torn because of the metal edges that can be
more or less cutting.
In addition, the portions or metal drawing bars are
returned by return springs whose purpose is to give a
smaller radius to the drawiny cylinder if the latter was
previously provided with a larger radius Now, these return
springs are placed within the drawing cylinders made up of
the various portions, and the practical construction of these
devices is complex:.
Therefore the invention is also directed toward
remedying these drawbacl~s by providing the rollers with e>:-
ternal elastic means for returning the portions to the a>:is
of revolutiun.
Freferably, these eternal return devices consist
of at 1east one elastic band placed around and within the
portions.
For e>:ample~ the elastic bands are circular rings
that are spaced a distance from one another. Preferably,
rings are made integral with the portion5, e.g., by adhesive
16 2C)~.
..
bonding.
The fact that external elastic return means are
placed on the portions permits elimination of the return
springs which cause the decrease of the cylinder radius.
moreover, the elastic bands considerably reduce the noise
created by the portions or metal bars striling against the
taut film. In addition the elastic devices also constitute
means for protecting the film, because they cover the cutting
edges of the portions or petal bars thus preventing the
drawn film from contacting these portions or metal bars.
oller 40 depicted in Fig. 9 may either be a roller
of the type shown at 3 of Fig. 1 or of the type illustrated
at 7 and 8 of Figs. 7Q-7D~ 8A-B~, or 30, l depicted in Figs.
5 and I.
This roller 40 consists of a plurality of longitu-
dinal portions 41l,41~ 41~, which form the cylindrical sur-
face of roller 40.
- according to the invention, roller 4C is provided
With eternal means 42 for returning the portions 41 to the
X-X a~:is.
Therefore! when portions 411, 41~, 41~ are moved
with the aid of the separating means described hereinabove in
order to increase the radius Ro or radiu5 rl, the eternal
elastic devices 42 return the portions 41l, 412~ 41~ to the
XX axis of the cylinder of revolution 40.
These eternal elastic means 42 consist of an elas-
tic band placed around and outside of portions 411~ 41~, 41~.
. According to a first embodiment of the invention
17 6~
shown in Fig. 9, the elastic band is made up of several
tircular rings 4~l~ 43l~ 4-~N of axles XX spaced a distance
from one another. These circular rings withJ e.g.~ a height
h, have a radius r which is substantially equal to the ra-
dius r of the drawing roller i.e., radius r of bands 43~ is
slightly smaller than the smallest radius the roller can
have. Thus, band 43l' 4~ 43~ keep portions 41l, 41 , 41~
substantially contiguous when these bands 43l, 43~, 43~ are
not drawn.
When portions 41l, 41~ are subjected tn an axial
displacement toward arrow F directed outwardly so as to
separate portions 41l, 41l~ 41~from the axis of revolution XX
of roller 40~ the elastic bands 43l' 43~, 43~ are e~:posed to
a radial force which causes the bands to have a radius that
is larger than their initial radius, substantially equal to
the radius desired for the drawing roller. The bands are
then subjected to a force that draws them.
When the means for separating portions 43l - 41~
are inactive, the bands are no longer subjected to force F3
and, since they are elastic, they have a tendency to return
to their initial shape and to tare back their initial radius
r and thereby subjecting portions 41t, 412, and 41~ to
a force which is opposite to force Fs in order to return them
to their original position.
Preferably, circular rings 43l~ 432~ 43~ are spaced
a distance e from one another.
Preferably, the distance e between two successive
rings 43l~43l is a few millimeter5, e~9.r more particularly
~24;~
18
about to 3 mm.
Fig. 10 shows an enlarged view of two rings 43l~4~1
and film 1 which rests on these two rings. us can be seen,
film 1 rests on rings 43l and 432 , whereas it does not rest
on the portions thenlselves when they are located between
rings 43l- 431~ that is when it lies in the space formed
between rings 43l and 431-
Fig. 11 depicts a secDnd embodiment of the inven-
tion. The band forming the elastic means 42 i5 composed of
parts 44 and 45. The first part 44 i 5 a band which is heli-
cally wound in one direction while the second part is
another band which i5 wound in the opposite helical direc-
tion.
The first part 44 i wound in the direction oppo-
site to the direction of rotation of roller 40, while the
second upper part is wound in the direction of rotation of
roller 4C~.
Li~ewise~ the spires of bands 44 and 4S are not
contiguous and they are spaced apart by a distance e.
Preferably this distance _ measures a few millimeters and,
more preferably7 appro.imately 2 to 3 mm.
Therefore, the helical spires are not opposed and
are symmetrically distributed relative to the longitudinal
ai:is Z-Z of the film which is drawn. Thus, the direction of
winding of the helixes of bands 44 and 4S is such that the
film is exposed to a component of reaction of the helical
spires on the film, said component being directed to the
external edge 1~0 and 110 of drawn film 1 (Fig. 18). Conse-
19 21~)6~
quently~ film 1 is subjected to tran5verse drawing in thedirection of the components uf reaction of the helical turns
on the film tdirection and sense of arrows r) and the film is
then not subiected to transverse shrinl~age as it is being
drawn, Dr at least it is subjected to less transverse shrink-
age than when it is drawn by rollers that do not have an
elastic helical band. The plane of a spire encloses an acute
anyle with the direction of displacement vn of the drawn
film. Freferably~ is less than 46.
Furthermore, according to the invention, an advan-
tage of the elastic means is that the portions 41~, 41~ 5
which are often metal bars, do not strive the film, since the
elastic means are situated between the film and these metal
bars This reduces the noise produced by the apparatus.
In addition, since the film does not rest directly
on portions 411, 41~, it i5 less lively to be torn by the
cutting edges of these portions 411, 41N.-
Finally, it is preferable that the circular rings41l~ 432~ 43~ or the helically wound bandc 41, 4~ be integral
with portions 411, 41~, e.g., that they be adhesion-bonded.
The rings and the helical bands preferably consist
of a vulcanized sheet of rubber.
