Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a method and apparatus
'~ for sealing a tube of thermoplastics material by welding.
It relates in particular, bu-t not exclusively, to the
welding of a cylindrical tube which is in one piece and
consists of flexible plastics material, such as for example the
filling neck of a container used for the vacuum packing of
large quantities of loose powdered products accordiny to
known methods.
A neck of -this type, which generally has a thickness of
the order of lmm. and consists of a material which melts upon
the application of hea~ such as polyethylene, is generally
sealed in an air-tight manner by the action of heat, this
neck being compressed in the form of two walls placed
'' side-by-side between two solid jaws heated to an adequate
temperature to ensure melting and welding of the material in
the area to be sealed.
'' Such a method, which comprises heating the contact area
of the two walls placed side-by-side, iOe. in reality the
only area for which there is any purpose in causing melting,
with a view to its welding, through these walls, comprises
several drawbacks.
One of these drawbacks resides in the very difficult
~-, control of the flow of the molten material as the jaws
penetrate the latter, a drawback which is further increased
by frequent irreyularities in thickness of the neck over its
periphery and by the difference in thickness frequentl,v found
' from one neck to another.
,~ Moreover, it is difficult to determine an exact optimum
, welding time in view of these differences in thickness from
one neck to another or the periphery of the same neck.
An object of the invention is to overcome these
drawbacks by providing a method and apparatus for welding by
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riction, which have the advantage of causing heating and
melting solely of the areas of the two walls placed side-by-
side which are in contact.
~ method of welding by friction is already known, but
the latter applies to two separate rigid parts which are
retained rigidly and which, provided that a clearance exists
which enables them to move one with respect to the other,
whilst remaining in contact under pressure, can be welded
by friction.
According to the invention -there is provided a method
for sealing a tube of flexible thermoplastics material by
welding, comprising flattening the tube in the area to be
welded, so as to give its wall the configuration of two walls
placed side-by-side and connected by two flat folds arranged
parallel to the general direction of the tube in said area,
pressing the two walls one against the other under pressure
in said area, imparting alternating relative movement to the
two walls in said area, whilst continuing to press them
together, so as to bring about friction heating of their
~, 20 opposed faces in said area and their localised melting, then
interrupting said movement and bringing about welding of the
molten areas by cooling of the latter.
This method differs from the known method for ~elding by
friction in that the two walls to be welded are in fact
different parts of one and the same tubular wall before welding.
The frictional movement, leading to this welding, acting on
the flexibility of this single wall in the area of the folds of
the latter connecting the two basic walls defined by the
flattening of the tube.
The invention will now be further described, by way of
example, with reference to the accompanying drawing in which:
Figure 1 is a perspective view of the upper part of a
container provided for the vacuum packing of large quantities
of loose powdered ma-terials, this container comprising a
neck capable of being hermetically sealed by the method
. according to the invention;
Figure 2 shows a vi.ew of the neck, in the course of -the
carrying out of the sealing me-thod according to the invention,
in a direction at right-angles to the general direction of
this neck, and
Figure 3 is a sectional view through the plane III-III
of figure 2.
Figure 1 illustrates the upper part of a contair.er 1 made
in one piece from thermoplastics material such as polyethylene
for example, the wall of this container having a thickness,
for example of the order of lmm. such that it is flexible,
but nevertheless strong.
The container 1 has a general substantially parallelepipedal
shape and at the centre of one of its sides comprises a filling
- neck 2, the shape of which is that of a cylinder of revolution
about an axis 3 for example and which projects from the-container.
~- 20 Like the remainder of the wall of the container, the wall of
; this neck 2 which consists of a material which melts under the
application of heat and generally in one piece with a
substantially identical thickness is intended to be sealed in
an air-tight manner by carrying out the invention, for e~ample
in an area 4 located transversely with respect to its general
direction, defined by the axis 3.
To this end, as shown in figures 2 and 3, one begins by
flattening the neck 2.by means of two jaws 5 and 6 comprising
opposing faces 7 and 8 respectively, located parallel to each
other on either side of the neck 2 and having a dimension greater
then the lenyth of the outer semi~circumference oE the neck, in
a transverse direction with respect to the axis 3, the dimension
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of these faces parallel to the axis 3 in turn beiny less -than
this dimension. In prac-tice, parallel to the axis 3, the jaw 6
has a dimension less than the corresponding dimension of the
jaw 5, however the two jaws being located along the same mean
plane 9 arranged transversely with respect to the axis 3 in the
region of the area ~ to be welded.
The faces 7 and 8 may haye a flat general shape as in the
example illustrated, or may have complementary curved shapes,
however their shape having to be suitable for allowing their
movement along the plane 9, parallel to themselves, whilst
preserving a constant mu-tual distance apart at any point.
referably, the faces 7 and 8 are ridged to provide
-~ better adherence to the wall of the neck 2, which they are
intended to drive by friction, as will become apparent hereafter.
When the neck 2 has been flattened by the jaws 5 and 6,
in the area 4, its wall has the configuration of two walls
joined by a face corresponding to the inner face 10 of the
neck, respectively 2a and 2b, in -this case flat like the
faces 7 and 8, these two walls 2a and 2b being connected by
~ 20 two flat folds 2c and 2d respecti~ely, arranged parallel to
i the general direction 3 of the neck.
Opposing forces represented by the arrows F, directed at
right-angles to the faces 7 and 8 are applied to the two jaws 5
and 6, which forces apply the basic walls 2a and 2b one against
the other with a predetermined pressure.
One of the jaws, for example the jaw 5, is stationary
and the other jaw, in this case the jaw 6 is retained by a
resilient mounting and is integral with an arm 11 which
~ connects it to a vibrator device 12, constituted for example
- 30 by two vibrators 13 of known type which are retained by a
resilient mounting and rotate in opposite directions, in
order to impart to the jaw 6 an alternating movement in a
-5-
direction 14 parallel to its face 8 and to the face 7 of
the jaw 5, along the plane 9.
During this movementl since the Eorces F are maintained
so that the walls 2a and 2b remain joined under pressure by
the inner face 10 of the neck, an alternating relative
movement in the direction of arrow 14 is imparted to these
: two walls 2a and 2b owing to the fact that they are connected ..
by friction respectively to the jaw S and to the jaw 6, rub
one against the other in the region of the face 10 and become
heated. The folds 2c and 2d move on themselves alternately
in one direction and the other, the areas of the wall of
the neck 2 located in the immediate vlcinity of these folds
2c and 2d alternately forming part of the walls 2a and 2b.
This movement also results in friction of the material against
itself, in the region of the face 10 of the neck, in the
immediate vicinity of the folds 2c and 2d and heating of the
.
material also occurs in this area.
If the frequency and amplitude of the relative movement
of the two jaws 5 and 6 designated by the double arrow 14
and if the pressure by which the two walls 2a and 2b press
against each other in the re~ion of their face 10 under the
action of the imposing forces F imparted to the jaws 5 and
6 are chosen appropriately, the heating which thus occurs over
the entire face 10 in the area 4 results in localised melting
of the material in this region, after a period of alternating
relative movement of the two jaws which can be easlly determined
by a man skilled in the art. The opposing forces F accentuate
the mutual frictional effect of the walls 2a and 2b in the
region of the face 10, which accelerates the heating and after
melting of the material causes a mixing of this material
belonging initially respectively to the wall 2a and to the
wall 2b.
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If the rela-tive movement of the two walls 2a and 2b
is then in-terrupted whilst maintai.niny the application of the
opposing forces F to the jaws 5 and 6 and if cooling of the
material is then brought about or allowed, the intimately
mixed material of -the walls 2a and 2b solidifies and one
obtains an air-tlght weld of these two walls of the fold 2c
to the fold 2d, i.e. air-tight transverse sealing of the
neck 2 in the area 4.
~`~ It should be noted that cooling and solidification of
the molten material may be consecutive with stoppage of the
-. relative movement imparted by the jaws 5 and 6, without it
being necessary to bring about cooling. In fact, the mass of
; molten material is very small with respect to the mass of
cold solid material surrounding it, which, after stoppage of
the alternating relative movement of the jaws, spontaneously
causes virtually instantaneous cooling and solidification of
~: the molten material. This provides the possibility of
-~ opening the two jaws in order to release the sealed neck
immediately after the stoppage of the vibrator device 12.
.~ 20 Naturally, the invention may have numerous variations
not diverging from its scope, in particular as regards the
. amplitude and frequency of the relative movement of the two
jaws 5 and 6, as regards the intensity of the forces F and as
~ regards the dimensions of the jaws 5 and 6. These values vary
.~ in particular as a function of the dimensions of the neck 2
or more generally of the tube to be sealed transversely and
in particular of the thickness of the wall of this neck or
this tube.
As a non-limiting example, good results have been
obtained as regards welding a tube such as 2. neck 2 of
polyethylene having a thickness of the orde~ of lmm, by
applying to the jaws 5 and 6, to which opposing forces of
-7-
2.8 tonnes were applied, a relative movement as designated
by the arrow 14, of the ampli-tude of the order of 3 to 4mm
at a frequency of the order of 50Hz.
It was -thus possible to obtain a perfectly air-tight
weld, making it possible to maintain the vacuum inside the
container l.
Naturally, the width of the weld obtained, i.e. its
dimension on the welded wall at right-angles to the mean
plane 9 of the jaws 5 and 6, depends on the dimension at
right-angles to this plane 9, of the thinner jaw, i.e. of
the jaw 6.
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