Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-
~o~
FIELD OF INVENTION
The present invention relates to processes and
apparatus for blow molding thermoplastic preforms and more
particularly to the extraction from the mold of blow-mold products.
BACKGROUND OF THE INVENTION
It is known to industrially manufacturehollow bodies of
a thermoplastic material by extruding a tubular preform of this
material through an annular die, enclosing this preform in the
interior of a mold and blowing air under pressure into the inter-
ior of this preform to inflate it and cause the plastic material
to contact the walls of the mold, which are cooled so that at
the contact of which the plastic material solidifies.
The moldthat is utilizedgenerally comprises two half-molds
between which the preform is extruded. The "plug" which passes
from the mold at its lower portion and which is constituted by
the excess of plastic material, serves generally for the removal
from the mold of the hollow body, thus obtained, by means of
automatic pincers. These advance the hollow body to finishing
stations where, among other operations, the plug is removed.
This mode of manufacture has a number of disadvantages
particularly when, for reasons imposed by their ultimate utiliza-
tion (filling, automatic handling etc.), the hollow body products
must have a base with a very pronounced concavity.
These disadvantages which will be described in greater
detail later, with reference to the annexed drawings, can be
summarized as follows.
If the pincers seize the plug while the mold is still
closed, the displacement of the mold-halves perpendicularly to
the plane of the mold joint at the time of opening of the mold
has the effect of enforcing an ascending movement of the hollow
body by an amount equal to the concavity of the bottom. Since
the body is held by the pincers through the intermediary of the
-1- ~
7~
plug, there results either a deformation of the bottom or a
premature tearing and separation of the plug.
If to avoid this disadvantage, the pincers only seize
the plug at the end of the course of opening of the half-molds,
the hollow body is no longer supported in the plane corresponding
to the plane of the mold joint and there is the risk that the
body will be caught and displaced by one or the other of the half-
molds. In addition, the pincers must seize the plug which is not
properly guided and already cooled, this substantially affecting
the regularity of the subsequent steps of the process.
SU~IARY OF THE INVENTION
An object of the invention is to remedy these disadvantages
by providing an apparatus for blow molding in which the pincers
which support the plug at the bottom of the hollow body accompanies
the same in its successive displacements at the opening of the
mold parallel to the plane of the mold joint by imposing a move-
ment on the pincers capable of disengaging it without any stresses
from the half-molds.
Accordingly, a first aspect of the invention provides
a process for blow-molding hollow bodies in a mold having half-
molds which are closed along a mold joint during blow-molding and
are laterally displaced with respect to one another to open the
mold for removal of the formed hollow body, the half-molds
.. ..
imposing a translation movement on the hollow body during
opening of the mold in a direction in the plane of the mold joint
from which the half molds laterally separate, a plug being formed
at the bottom of the hollow body during molding which plug is
seized by pincers prior to the opening of the mold such that
the hollow body is supported by the pincers during mold opening,
an improvement comprising displacing the pincers, during mold
opening, in said direction over a distance at least equal to that
imposed on the hollow body by the half-molds during opening of
-2-
.'
.
~'7~
the mold.
A second aspect of the invention provides an apparatus
for blow-molding hollow plastic articles comprising two half-
molds closable along a mold joint during blow molding and laterally
displaceable to open the mold for removal of a formed hollow
article, a plug being formed at the bottom of the article during
molding and extending from the bottom of the mold, pincer means
supported below said mold for engaging said plug to support the
hollow article during opening of the mold, said mold bearing
against said article and imposing a displacement thereon in a
direction in the plane of the mold joint during opening of the
mold, and means for displacing said pincer means, during opening
of the mold, by an amount at least equal to that of the movement
simultaneously imposed on the hollow article by said mold.
Preferably, the means for displacing said pincer means
comprises a guide ramp and a feeler, one of which is coupled to
the pincer means and the other to one of the-half-molds, said
feeler bearing against said guide ramp to produce displacement
of the pincer means upon lateral movement of said one half-mold.
The control means can be mechanical, hydraulic or
electrical and there can be introduced as desired a demultiplication
or correction between the movement of the feeler and that of the
pincers. It is advantageously adjustable in the course of
utilization of the apparatus. The feeler can be solid with the
pincers.
In one embodiment for carrying out the invention, a
mechanical means is employed which comprises a rigid member fixed
to the pincers and carrying a roller constituting the feeler.
The ramp is inclined in the direction of the plane of the mold
joint, the difference inlevel between the extremities of the
ramp being at least equal to the concavity at the bottom of the
hollow body, and means are provided for moving the pincers in
~ -3-
74V~
the direction of the mold, parallel to the plane of the mold
joint, during the opening of the ~olcl.
BRIEF DESCRIPTION OF THE DRAWINGS
The schematic drawings attached hereto will make clear
the novel characteristics of the invention and the technical
progress produced thereby with respect to the known apparatus. The
~.
-3a-
~r )
Ci`7~ .D!
.
~74(~
drawings only show in detail the portions of the half-molds
which directly concern the invention, the other members being
known to those skilled in the art and having been omitted or
simply schematically illustrated.
Figures 1, 2 and 3 are three sections perpendicular to
the plane of the mold joint illustrating, respectively, the
conventional phases of extrusion, blowing and extraction of a
hollow body;
Figures 4 and 5 are partial sections analogous to those
above, illustrating two types of incidents encountered with
the known apparatus in the course of the opening phase of the
mold;
Figure 6 is a sectional view perpendicular to the
plane of the joint of the mold of an embodiment of apparatus
according to the invention;
Figure 7 and 8 are analogous sections showing the oper-
ation of the apparatus according to the invention, respectively,
during the phases of opening of the mold and extraction of the
hollow body.
DETAILED DESCRIPTION
As is seen in Figures 1-3, the conventional process
for blow molding of hollow bodies comprises firstly the extrustion
through an annular die lof a preform 2 of a thermoplastic material.
This preform is then enclosed (Figure 1) in a mold constituted
by two half-molds capable of being laterally displaced with
respect to the plane of the mold joint.
If air under pressure is then inflated into the preform,
for example, via an axial conduit 11 in the head of the die 1,
the material constituting this preform comes into contact with
the internal walls of the half-molds 3 and 4. The walls are
cooled by means, not shown, such that the thermoplastic material
issolidified on contact to produce a vessel 5 (Figure 2),
~(~7'~5
the excess of plastic material forming a plug 6 which passes to
the exterior of the mold and which will be ultimately removed.
As shown in Figure 3, the plug 6 can be seized by
pincers 7 which permit extracting the vessel 5 from the mold after
opening thereof and for transport of this vessel to following
work stations.
As it has already been indicated, this conventional
process of manufacture presents serious disadvantages, notably
when the bottom of the vessel that is desired to be obtained has
a pronounced concavity. In fact, when the half-molds 3 and 4
are laterally displaced from one another at the time of opening -
of the mold, their displacement perpendicular to the plane of
the joint of the mold produces a displacement of the vessel 5
parallel to this plane of the joint by an amount equal to the
concavity of the bottom. If the pincers 7 have seized the plug
during this phase, there is the risk of either deforming the
bottom of the body or provoking a separation of the plug from the
; vessel (Figure 4). If one waits for the half-molds to arrive at
the end of travel to seize the plug by the pincers 7, the vessel
5 is no longer supported during the opening of the mold so that
it can be carried by one or the other of the half-molds risking
rocking in the direction of the plane of the joint (Figure 5).
In order to remedy these serious disadvantages, the
apparatus according to the invention, shown in Figure 6, comprises
pincers 17 which seize the plug 16 at the bottom of the vessel
before the opening of the mold but which accompany the vessel in
its ascending movement along the plane of the joint during the
opening phase. In this figure, there is again seen the two half-
molds 13 and 14 between which has been formed a vessel of
thermoplastic material whose excess forms the plug 16 which extends
from the mold. According to the invention, the pincers 17 which
seize the plug before opening of the mold are mounted on a column
-- 5 --
. , -: . : . . :
- - : : : : . - . - -..,
., . .. .:, .. : . . . . : . ~
10 ;~4(~R ~
18 capable of being displaced parallel to the plane of the mold
joint and to wnich is rigidly fixed an arm 10, the extremity of
which forms a carrier for a roller 9 which is rota,able around
an axle.
A guide ramp 11 directed perpendicularly to the plane
of the joint of the mold has a difference in level between its
extremities greater than the concavity of the vessel to be formed
said ramp 11 being fixed to the bottom of the half-mold 13. The
roller 9 is adapted to be in contact with the ramp 11 during the
opening phase of the mold so as to be urged by this ramp in the
same manner as the bottom of the vessel 15 by the corresponding
face of the half-mold 13.
This is going to be described in detail with reference
to Figures 6 and 7.
During the blowing phase of the preform, the column 18
is displaced in the direction of the mold. At the end of the
travel, the roller 9 bears against the extremity of the ramp 11
at the maximum distance from the plane of the~joint while simul-
taneously the pincers grip the plug 16.
When the mold is opened after cooling of the vessel 15
(Figure 7) the column 18 continues to be urged in the direction
of the bottom of the mold such that the roller 9 is applied
against the ramp 11 and rolls thereon when the half-molds 13 and
14 are laterally displaced from one another. The pincers 17 are
displaced in the direction of the mold parallel to the plane of
the mold joint and they displace the plug 16 and the vessel 15,
the latter being thus disengaged from the half-molds without
application of any stresses on its base, the axis of the vessel
remaining parallel to the plane of the ]oint of the mold. If
desired, instead of connecting the roller 9 directly to the pin-
cers 17 by the arm 10, a corrective factor of demultiplication
can be introduced by an appropriate coupling arrangement.
~ - 6 -
: .- : . : .
1(~'74Vti ~ :
At the end of opening of the mold (Figure 8) the col-
umn is displaced in the opposite direction and the pincers 17
remove the vessel 15 from the mold. The displacement of the
column 18
- 6a - :
.,'' : . ... .. - : .-.. , . - . . ,
.. . . . . . . .
- . . . .
. . . . . .. , . , . -
~0~4V~; ri
is effected in any conventional manner, as for example, by a
hydraulic cylinder.
It can be seen that the extraction of the vessel is
effected, consequently, without any secondary stresses applied
to the vessel which otherwise would cause a reduction in the
cycle of fabrication. The absence of accidental stoppage due
to contact of the vessels in the mold leads to a more regular
operation of the apparatus according to the invention.
-- 7 --
