ADJUSTABLE BUBBLE GUIDE OR CAGE

GUIDE OU CAGE REGLABLE POUR BULLE

English Abstract

A bubble guide unit according to the present invention comprises two concentric
frames, at least one of which rotates relative to the other, through which the film
bubble passes. At least four bubble guiding rods are arranged symmetrically to each
pivotally engage one frame at one end and to freely engage the other frame near its
other end. Freely engage here means that the other end of each rod is free to pivot
to some extent as well as to move in the direction of its length beyond the pivoting
point and back. This is most easily accomplished by a pivoting ring through which
the rod passes or, less elegantly, by a fixed ring having an aperture larger than the rod
diameter.

French Abstract

Dispositif servant à guider une bulle. Le dispositif comprend deux cadres concentriques, dont au moins un tourne par rapport à l'autre, dans lesquels passe une bulle de pellicule. Au moins quatre tiges de guidage de la bulle sont disposées de façon symétrique afin d'engager un cadre par rotation à une extrémité et d'engager librement l'autre cadre près de son autre extrémité. Dans le présent contexte, l'expression engager librement signifie que l'autre extrémité de chaque tige peut tourner librement jusqu'à un certain point et se déplacer dans le sens de sa longueur au-delà du point de rotation et y revenir. La façon la plus simple d'obtenir ce résultat consiste à utiliser des anneaux rotatifs dans lesquels passent les tiges ou, ce qui est moins élégant, à utiliser des anneaux fixes dont l'ouverture est supérieure au diamètre de la tige.

Claims

WHAT IS CLAIMED IS:
1. A bubble guide unit comprising: two concentric frames, at least one of which
rotates relative to the other, through which a blown film bubble passes; and at least
four bubble guiding rods arranged symmetrically to each pivotally engage one frame
at one end and to freely engage the other frame near its other end.

Description

CA 02216177 1997-09-23
ADJUSTABLE BUBBLE GUIDE OR CiA~E
BACKGROUND OF THE INVENTION
l. Field of the Invention
The present invention relates to the ~lastics industry in general and in particular to
S al~l)alal~ls for extruding blown fi1m. More particularly, it re1ates to post extrusion
devices generally known as bubble cages or guides.
2. Re1ated Art
All hlown film is extruded either vertically~ up or down, or horizontally. In all
instances, once the polymer exits the cylindrica1 die, it is referred to as a "bubble" and
10 is drawn from the die by means of two rollers (usually known as "NIP Rnllers"~ once
the bubble has been collapsed. The distance between the die surface and the NIP
Rollers may vary between six to over hundred feet. After exiting the die, the bubble
is in~lated with air to the ~lesired di~me~er. Normally, the air intlates the ~cylindrical)
bubble through the die and once the requisite diameter has been reached inflation
l S ceases and the air is trapped between the face of the die and the NIP Roller.

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The bubble must be guided to ensure good centering and tracking with minimum side-
to-side oscillation or of~:centre movement. The guidlng has heen accomplished by
means of bubble cages; individual guiding bars; guiding bars interconnected by means
of chains, gears and the like; and a variety of other methods.
S SUMMARY OF THE~ INVENTION
The present invention provides a simple, adjustable bubble guide or cage (hereafter
guide).
A bubble guide unit according to the present invention comprises two concentric
frames, at 1east one ol which rotates relabve to the other, through which the film
10 bubble passes. At least four bubhle guiding rods are arranged symmetrically to each
pivotally engage one frame at one end and to lreely engage the other frame near its
other end. Freely engage here mean~s that the other end of each rod is free to pivot
to some extent as well as to move in the direction of its length beyond the pivoting
point and back. This is most easily accomplished by a pivoting ring through which
15 the rod passes or, less elegantly, by a fixed ring having an aperture larger than the rod
diameter.
When the two concentric frames are rotated one relative to the other, the concentric
square defined by the four N)ds will change its area, which can thus be adjusted to fit

CA 02216177 1997-09-23
the diameter of the guided film bubble.
Such hubble guide units may7 of course, be stacked vertically or horizontally and their
rotating frames interconnected to allow for a single adjustment mechanism.
BRlEF DESCRIPT10N OF THE DlRAWINGS
S The preferrell embodiment of the present invention wi11 now be described in
conjunction with the annexed drawing figures, in which:
Figure I is a plan view of a guide unit according to the present invention in its
maximum diameter position;
Figure 2 shows the unit of Figure I but in the ~ diameter position;
l0 Figure 3 shows the unit of Figure l but in the 3~-diameter position;
Figure 4 shows the unit of Figure l but in its minimllm diametet position;
Figure 5 shows a unit of the bubble guide construction in perspective; and
Figures 6a and 6b ~hows the unit of Figure 5 in plan view in its maximum and

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minimllm positions respectively.
DETAILED DESCRIPT:ION OF THE PREFER~ED EMB(~DIMENTS
Reterring now to Figure l the bubble guide units comprises two concentric ring-
frames a stationary outside frame 10 and an inner rotatahle frame 11. Four guidervds ~shown symbolically as lines) 12 13 14 and 15. The rod 12 is attached at one
end to a pivot 16 anchored to the outer ring 10 while it is movably attached near its
other end to a pivot 17 anchored to the inner ring l 1. The other rods 13~ 14 and 15
are similarly attached. The rods 12 13 14 and 15 must be of sufficient length so as
not retract out of the pivot 17 at the point of minimum diameter in Figure 4.
10 E~eferring now to Figures 5 6a and 6b of the drawings the preferred emhodiment is
described. It is generally critical in the blown film process to keep the film tube
aligned with the top nip and the blown film die. The blown film process is normally
an upward extrusion. However downward extrusion has been used in the past.
As may be seen the bubble guide is constructed with two counter rotating meml~ers
15 (rings in the figures) with a hole in the centre of the inner member and attached to the
rotating and stationary members are vertical connecting posts. The lower outer ring
and the lower inner ring would act like a bearing where the outer ring would remain
stationary and the inner ring being the race of the bearing that would be able to rotate.

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The outer ring holds a series of posts that can rotate around their longi111din~1 axes.
The inner ring a1so has a series of posts that will also be ahle to rotate in the same
manner. The lower rings and the upper rings are a mirror image of each other. The
posts are mounted on the rings thereby connecting the upper and lower rings. In the
S example showing which we call a square, there are tour posts on the outer ring and
four po~sts on the inner ring. The outer posts have been drilled to accept a round rod
that has been fixed with a setscrew. The four posts on the inner ring have been dril1ed
through to allow the mating rod to slide freely as required. The construction operates
as follows.
Iû With the outer ring held stationary, and the four posts with the tension rods or spokes
fixed with enough length to pass through the inner post on the same plain, and the
inner rmg is rotated, the ~spokes will move inward symmetrically. The focal distance
is compensated by allowing the spokes to retract through the inner post. Therefore,
all four posts rotating on the inner ring will collectively but independently move the
15 four parallel rods together thereby reducing the ~ meter of the opening.
There are no limitations on the number of vertical posts. However, four, six or eight
wou1d create a square, hexagon or octagon shape. The horizonta1 rods are on1y
limited in quantity by the physical restrictions.
To reduce friction, the horizonta1 rods wi11 have a covering and this cover may be in

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the form of rollers, either solid or individual that woulcl rotate on the spokes by way
of friction if enough friction were applied.
The height of the construction is unlimited and the unit shown may be stacked
repeatedly as desired.
S The diameter of the hole in the centre, its only purpose is to allow the film to pass
through the openings from the die to the top nip.
While in the drawings a bubble guide unit is shown having only four rods ~which, of
course, are arranged at staggered distances from the plane of the rings 10 and 11, in
order not to interfere with ea~h other, more rods may be employed in a unit, so as to
10 form a more than four-sided pvlygon. The additional rods would also be staggered
in di.stances from the ring-plane. There is naturally a practical limit to the number of
rods employed, depending on the ring diameter.