Note: Descriptions are shown in the official language in which they were submitted.
METHOD AND APPARATUS FOR FORMING HOLLOW ARTICLES IN THERMO-
PLASTIC MATERIAL
The present invention relates to apparatus for forming
hollow articles such as receptacles from a thermoplas~ic web
which is prior heated to a temperature suitable for thermo-
forming.
BACKGROUND OF THE INVENTION
Such forming apparatus is described in patent FR-2 028 281
and comprises: firstly, beneath the horizontal path of a
thermoplastic weh, a mold block vertically movable between a
high position for thermoforming receptacles, in which position
said mold block is pressed against said web, and a low position
for unmolding said receptacles, the mold block being provided
with at least one forming chamber open to the top thereof and
having the same inside shape as the article or receptacle to ~e
thermoformed; and secondly, above said horizontal path, a
counter-mold block which may be fixed or free to move a little
vertically between a high position in which the bottom end of
the counter-mold block is raised a little from the horizontal
path of the thermoplastic web, and a low position in which said
bottom end is in contact with said thermoplastic web and urges
it against the top end of the mold block when in its high
position, i.e. against the top edge of each of the forming
chambers. The counter-mold block is provided with as many
cylindrical cavities as the mold block has forming chambers,
with each chamber being axially aligned with a corresponding
one of said cavities.
In that type of prior apparatus, a forming punch is
mounted to move vertically inside each cylindrical cavity with
a degree of lateral clearance relative to the inside face of
the cavity and coaxially relative ~oth to said cavity and to
the corresponding forming chamber. The forming-punch ha~ an
inactive top portion and an active bottom portion, with the
inactive portion of the punch remaining inside the cylindrical
cavity while its active portion is suitable for penetratin~
into the corresponding forming chamber down to the vicinity of
the bottom thereof, and has dimensions that are similar to but
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smaller than the dimensions of the forming chamber, with the
annular space delimited between the peripheral face of the
forming punch and the inside faces of both the forming chamb~r
and the cylindrical cavity being periodically connected to a
source of compressed gas.
In that ~ype o~ prior forming apparatus, the active
portion of the forming punch is surmounted by a cylindrical
inactive portion of a diameter identical to that of the top end
of said active portion, and of a height that is not less than
the vertical stroke of said active portion. As a result,
considerable mass needs to be accelerated and decelerated at
the beginning and at the end of each downstroke and of upstroke
of the forming punch, and this prevents the number of strokes
that the punch can perform per unit time being increasedO
Another drawback of that prior apparatus lies in the fact that
the inactive portion of the forming punch is very long, i.e.
its height is not less than the height of the active portion of
said punch, and the volume of the annular space around ~he
inactive portion of the punch constitutes a considerable dead
volume in which large quantities of compressed gas are need-
lessly consumed. In addition, the annular space surrounding
the forming punch and delimited by the punch and the inside
face of the cylindrical cavity of the counter-mold block cannot
be hermetically sealed at the end of the punch downstroke, and
as a result the compressed gas for pressing a determined zone
of the thermoplastic web against the inside face of the forming
chamber can only be injected into said annular space when the
punch stops at the end of its downstroke.
An object of the present invention is to eliminate or at0 least to mitigate the above-mentioned drawbacks.
SUMMARY OF THE INVENTION
This object is achieved in a forming apparatus of the type
specified initially by the facts tha~ the inactive portion of
each forming punch extends over an axial height that is shorter
than the maximum width of said punch, that each forming punch
is surmounted by a guide piston which slides in sealed manner
inside the corresponding cylindrical cavity of the counter-mold
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block, and that the annular space beneath the guide pis-ton is
suitable for communicating periodically with a source of
compressed gas via at least one link duct.
By virtue of this design, the masses put into motion, and
the amount of gas consumed, are both reduced and it is po~sible
to inject gas into the annular space even during the downstro~
of the forming punch.
This novel forming apparatus is also highly advantageous
when used in the context of a conventional type of sterile
packaging installation, e.g. as described in German patent
application DT-OS 2 754 816.
The invention also provides a method of forming hollow
articles such as receptacles from a thermoplastic web. In a
prior forming method, successive determined zones of the
thermoplastic web are preheated to the thermoforming
temperature, the edge of at least one preheated zone of the
thermoplastic web is clamped between the top end of a bottom
mold block containing at least one forming chamber and the
bottom end of a top counter-mold block including at least one
cylindrical cavity which is in alignment with said forming
chamber and which receives with lateral clearance a forming
punch which is disposed coaxially with said forming chamber and
which is vertically movable between a high position in which
its bottom end is fully retracted into said cylindrical cavity
and a low position in which said bottom end of the punch comes
close to the bottom of the forming chamber when the forming
chamber is in its high, thermoforming position, with a hollow
article being thermoformed from the zone of the wab which is
clamped via its edge by thrusting said zons of the web into ~he
forming chamber by means of the forming punch, and by injecting
a gas under pressure into the volume dPlimited by said clamped
zone of the web, the forming punch, and the cylindrical cavity
so as to apply said clamped zone of the web against the inside
face and the bottom of the forming chamber.
The drawbacks of this prior method ar~ the same as those
mentioned above with respect to the prior forming apparatus
described in French patent ~R-2 028 281.
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An object of the invention is to eliminate these draw-
backs. In the context of a forming method as specified above,
this object is achieved by the fact that prior to the operation
of thermoforming a hollow article or receptacle, the a~nular
space delimited by the preheated zone of the thermop].ast~c web
clamped at its edge between the mold block and the coun~er-mold
block, by the outside face of the forming punch, and by the
inside face of the cylindrical cavity, is closed hermetically,
with said hermetically-closed space being maintained throughout
the downstroke of the ~orming punch, and gas under pressure is
injected into said hermetically-closed space not later than the
end of the downstroke of the forming punch.
~ ecause of these measures, consumption of compressed gas
is reduced and the rate at which receptacles can be thermo-
formed is increased. In addition, the gas enclosed in thevolume delimited by the guide piston, the forming punch, the
zone of the thermoplastic web, and the inside face of the
cylindrical cavity forms a kind of lubricating film on the
surface of the punch which facilitates flow and stretching of
said zone by preventing thermoplastic material therein adhering
to the outside of said punch.
US patent 3 45Q 807 (G.W. Cheney) describes apparatus for
forming hollow articles such as receptacles from a thermo-
plastic sheet. The apparatus comprises a guide ~nclosure
disposed over the mold block and slidably receiving a piston in
sealed manner, which piston surmounts and is integral with the
forming punch. However, this prior forming apparatus belongs
to a category of apparatus different from the apparatus of the
invention since: (1) the prior apparatus cannot clamp the
thermoplastic web between the top edge of the formin~ chamber
provided in the mold block and the bottom edge of the guide
enclosure which may be taken as being equivalent to the
cylindrical cavity of the counter-mold block of the apparatus
of the invention; (2) its guide piston is shaped as a cutting
tool that co-operates with the cutting edge of an annular
groove provided in the top edge of the mold block; and (3) the
outside diameter of the annular space provided between the
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guide enclosure and the forming punch and delimited a-t the top
by the guide piston i5 larger than the maximum diameter of the
receptacle forming chamber.
In addition, since the prior apparatus is designed to
stretch the thermoplastic sheet prior to transforming part o
it into a receptacle, the forming punch includes a series of
channels below the guide piston and connected alternately to a
vacuum source for stretching the thermoplastic sheet, causing
it to bulge into the guide enclosure and pressing it against
the bottom and part of the periphery of the forming punch, and
to a source of compressed gas for then pressing the
thermoplastic sheet against the side wall and the bottom of the
forming chamber in the mold block.
This prior apparatu~ doPs not lend itself to thermoforming
a receptacle b~ using a forming punch and compressed gas
without prior stretching of the thermoplastic sheet either by
sucking the sheet against said punch under the action of
suction acting on the top side of the sheet, which face
subsequently constitutes the inside face of the receptacle, or
else by applying said sheet against said punch under the action
of higher pressure acting on the bottom face of said sheet,
which face subsequently constitutes the outside face of said
receptacle.
In addition, in said prior apparatus, the thermoplastic
material of the clamped sheet must be pressed against the
forming punch so as to cover its bottom face and its periphery
completely before compressed gas can be used to press said
thermoplastic material against the inside face of the forming
chamber. As a result, receptacle manufacturing throughput is
low.
Further, since the thermoplastic sheet is clamped between
two grips outside the guide enclosure and the edge of the
forming chamber, and since the formed receptacle is cut out
inside the zone in which the thermoplastic sheet is clamped,
use of the prior apparatus gives rise to very high wastage o
thermoplastic material.
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BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are described by way o~
ex~nple with reference to the accompanying drawings, in which:
Figures 1 and 2 are elevation views in vertical ~xial
section through a Eirst embodiment o~ the forming apparatu~;
Figures 3 and 4 are elevation views in vertical axial
section through a second embodiment of the apparatus, and
Figure 5 is a plan view in horizontal section through the
forming punch on line V-V of Figures 2 and 4.
DETAILED DESCRIPTION
The apparatus 1 for forming hollow articles or receptacles
2 and as shown in the drawings serves to thermoform said
receptacles 2 *rom a thermoplastic w~b 3 followiny a horizontal
path. In general, the forming apparatus 1 forms a part of a
lS packaging installation of conventional type, e.g. as described
in French patent FR 2 02~ 765 or German patent application
DE-OS 2 754 816, and it is located immediately downstream from
a heater apparatus 4 for heating the thermoplastic web 2 as it
advances stepwise beneath the heater apparatus 4 where it is
raised to thermoforming temperature, and then through the
forming apparatus 1.
Beneath the horizontal path of the thermoplastic web 3,
the forming apparatus l comprises a mold block 5 which is
vertically movable between a thermoforming high position shown
in the drawing, and an unmolding low position (not shown) in
which the receptacle 2 which has just been thermoformed and
unmolded can be advanced by one step allowing a new length of
thermoplastic web to be inserted in the forming apparatus 1,
since the top end of the mold block 5 is then lower than the
bottom of the receptacle 2. The mold block 5 includes at least
one forming chamber 6 open to its top end and having an inside
shape which is identical to the outside shape of the receptacle
2 to be thermoformed, it being understood that the opening of
said chamber 6 is of sufficient cross-section to enable said
; 35 receptacle 2 to be unmolded. Air evacuation orifices 7 are
formed through the mold block 5 and open out into the bottom of
the forming chamber 6 to connect it to the atmosphere or to a
vacuum pump.
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Above the horizontal path of the thermcplastic web 3, the
forming apparatus 1 further includes a counter-mold block 8
which is either fixed in position or else is vertically movable
over a short distance between a low position as shown in the
drawing where it comes into contact with the thermoplastic web
3 and clamps it against the top edge of each forming chamber 6
when the mold block 5 is in its high position, and its own high
position which is raised slightly above the horizontal path of
the thermoplastic web so as to facilitate advancing the web.
The counter-mold block 8 is provided with as many cylindrical
cavities 9 as the mold block 5 has forming chambers 6, with
these cavities 9 being disposed in alignment with the forming
chambers 6. In the first embodiment shown in Figures 1 and 2,
these cylindrical cavities 9 are open at both ends. Each
cylindrical cavity 9 contains a forming punch 10 which is
coaxial with said cavity 9 and with the corresponding forming
chamber 6, and which is vertically movable, e.g. under drive
from a control rod ll forming a part of a control actuator 12
mounted on an external frame 13. The forming punch 10 has an
"inactive" top portion that does not participate directly in
the forming of the receptacle 2, and an "active" bottom portion
that does participate in forming said receptacle 2. It should
be observed that the inactive top portion of the forming punch ;~
~` lO always remains inside the cylindrical cavity 9 and outside
the forming chamber 6, whereas the active bottom portion of
said punch lO is cap~ble of penetrating vertically into the
forming chamber 6 and of pushing against the zone of thermo-
plastic web which is clamped at its edge between the mold block
5 and the counter-mold bl w k 8 around the top openin~ of said
chamber 6 (see Figures 2 and 4). The cross-section of the
inactive portion of the forming punch 10 is smaller than that
of the cylindrical cavity 9 while the active portion of said
punch 10 is similar in size but smaller than the corresponding
forming chamber 6.
As can be seen in the drawings, a degree of lateral
clearance exists between the outside of the forming punch 10
and both the cylindrical cavity 9 and the forming chamber 6.
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An annular space 14 is delimited in each cylindrical cavit~ 9
by the inside face thereof and by the outside face o~ said
punch 10. Each forming punch 10, and more precisely the
inactive top portion thereof, is surmounted by a guide piston
15 which closes the top end of the annular space 14 in airtight
manner and which is larger in croæs-section than is the punch
10 so as to fit inside the cylindrical cavity, thereby enabling
: said piston 15 to slide therein in sealed manner under the
action of the control actuator 12 and of its rod whose bottom
end is fixed to said piston 15. The annular space 14 is
periodically connected to a source of compressed gas such as
compressed air, which may be sterile if so required, by means
: of at least one link duct 16 opening out into the annular space
either close to the bottom end of the counter-mold block 8, or
else close to the top end of the forming punch 10. A control
valve (not shown) is interposed in the optionally sterile
compressed gas feed circuit between the link duct 16 and the
source of compressed gas.
The inactive top portion of the forming punch 10 extends
over an axial height that is smaller than the maximum width of
said punch 10 and is preferably fairly small while remaining
large enough for the guide piston 15 to be kept far enough away
from the path of the thermoplastic web 3 when the forming punch
10 is in its low position. Advantageously, the axial height of
the:inactive top portion of the forming punch 10 lies in the
range one-tenth to five-tenths of the maximum width of said
punch 10.
The link duct~s) 16 may be provided in the guide piston 15
close to the periphery thereof so as to have axes parallel to
the piston 15 and the punch 10, and to open out directly into
the top end of the annular space 14. Under some circumstances,
it may be advantageous to form the link duct(s) 16 in the side
wall of the counter-mold block 8 so that these ducts open out
: either radially or else obliquely into the annular space 14
close to the bottom end of said block 8, with the axes of the
openings of these ducts 16 being preferably situated in a plane
perpendicular to tha axis of the punch 10 and of the piston 15.
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The control rod ll lies on the same axis as the orming
punch 10 and its bottom end is fixed to the side o~ the guid~
piston 15 furthest ~rom the said punch 10. A port:Lon o thi~
bottom end which is 31~gh-tly lon~er than the height o~ the
cylindrical cavity 9, or the height of the assembly constituted
by the punch lO and the piston 15, has an axial channel 17
whose top end situated outside the cylindrical cavity 9 is
alternately connected to the atmosphere and to a source o~
compressed air via a valve (not shswn). In this case, the link
duct 16 formed through the g~ide piston 15 is in alignment with
the coaxial channel 17 and penetrates a short distance into the
inactive portion of the forming punch 10 and is connected
firstly to the bottom end of the coa~ial channel 17 and
secondly to the central ends of a plurality of radial channels
18 formed horizontally through the inactive portion of the
forming punch 10 and opening out into the vicinity of the
bottom face of the piston 15 in the peripheral face of the
forming punch lOo
It should be observed that inso~ar as the jets of
compressed gas are injected into the annular space 14 either in
a plane perpendicular to the axis of the forming punch 10 and
of the piston 15, or else along directions that are steeply
sloping relative to said plane, these jets break firstly inside
the annular space 14 either against the inside face of the
cylindrical cavity 9 or else against the outside of the punch
10 before being deflected towards the clamped ~one of the
thermoplastic web 3a and the inside of the forming chambar 6.
This ensures that the jets of compressed air are ne~er directed
directly against the thermoplastic web which they might
puncture.
The forming apparatus 1 may also advantageously ~e used in
a sterile packaging installation for goods that are sterile or
sterilized, in paxticular in an installation of the type
: described in German patent application DT-OS 2 754 816. To this
end, the bottom end of the counter-mold block 8 is mounted in
~ sealed manner to the sterile tunnel 19 of a packaging installation,
; with the tunnel 19 having vertical side walls that co-operate
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with the sides of the thermoplastic web 3 so as to avoid
excessive leakage of sterile gas that fills the volume delimi~ed
by said tunnel 19 and which is at a small positlve relati~e
pressure. The bottom end of the counter-mold block 8 p~netrate3
in airtight manner into the sterile tunnel 19. The cylindrical
cavity 9 of the counter-mold block 8 is closed at its top end
by a cover 20 provided with a central opening 21 through which
the bottom length lla of the control rod 11 is guided. Inside
the cylindrical cavity 9, i.e. over the portion of the bottom
length lla that penetrates into the said cavity 9, said bottom
length lla is surrounded in sealed manner by a protective
bellows 22 which extends from the cover 20 either down to the
guide piston 15 or else down to a point on the bottom point lla
which is close to said piston 15. The bottom end of the
protective bellows 22 is fixed in airtight manner either to the
piston 15 or else to the bottom end lla of the control rod 11
close to said piston 15. The top end of the protective bellows
22 is fixed in airtight manner to the cover 20 around its
central opening 21, or else it is mounted as a sealing gasket
between the top end of the counter-mold block 8 and the bottom
face of the cover 20. The structure of the bellows 22 is of
conventional type, and inside each of its bellows folds 22a it
may contain a stiffening washer 22b surrounding the bottom
length lla in such a manner as to be free to slide therealong.
The variable annular volume 23 surrounded by the bellows 22 and
essentially delimited by the bottom face of the cover 20, by
the inside face of the bellows 22, and by that portion of the
bottom length lla which penetrates into the cylindrical cavity
9, and also, where appropriate, by a portion of the top face of
the guide pis~on 15, is permanently connected to the atmosphere
via the central guide opening 21 in the cover 20 and/or via a
breathing hole 24 formed through said cover 20 inside the top
rim of the bellows 22. The annular chamber 25 provided inside
the cylindrical cavity 9 and delimited by the inside face
thereof, by the outside face of the protective bellows 22, by
thP top face of the guide piston 15, and, where appropriate, by
the free portions of the bottom length lla housed inside the
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cavity 9, and by the bottom face of the cover 20 where not
covered by the bellows 22, is fed with gas while the apparatus
is in operation and is permanently filled with a s-terile gas a-t
a small positive pressure relative to atmospheric pr0~ure,
said feed taking place via an inlet orifice 26 formed through
the side wall of the counter-mold block 8 close to the cover 20
and connected to a suitable feed circuit which enables the
pressure in said annular chamber 25 to be maintained
substantially constant in spite of variations in the volume of
said chamber 25. It should be observed, that for sterile
; packaging of goods, the link duct(s) 15, including the radial
channels 18 opening out into the annular space 14 and the
coaxial channel 17, are periodically connected outside the
cylindrical cavity 9 to a source of sterile gas under pressure
via a control valve (not shown). -
In order to facilitate resterilizing and cleaning of theannular chamber 25 and of all the parts delimiting it, this
chamber is sui-table for connection to a sterilization circuit
(hot water, superheated steam at high pressure) firstly via the
inlet orifice 26 and secondly via an outlet orifice 27 provided
in the side wall of the counter-mold block 8 at a location
which is diametrically opposite to the location of the inlet
orifice 26 and which is situated slightly above the guide
piston 15 when in its high position with the forming punch 10
fully received inside the cylindrical cavity 9 and where the
annular folds 22a of the bellows 22 are close together and in
mutual contact (Figure 3). It is advantageous for the forming
punch 10 to be coated with a layer of flexible plastic material
based on silicone. This makes it possible for the punch 10 to
come quickly to a constant temperature at a value close or
equal to the temperature of the thermoplastic web 3 during
thermoforming, and for it to maintain said temperature.
The method of thermoforming a thermoplastic receptacle 2
using the above-described forming apparatus can be understood
from the description. A zone of thermoplastic web 3a preheated
to the thermoforming temperature is clamped at its edge between
the top end of the mold block 5 surrounding the opening ~o the
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forming chamber 6 and the bottom end of the counter-mold block
8 surrounding the cylindrical cavity 9 which then contains ths
forming punch 10 fully retracted therein. Because o~ the
structure of the apparatus, in particular Because of the guide
piston 15 provided in the cylindrical cavity 9 above the punch
10, the annular space 14 is closed hermetically as soon as the
preheated zone of web 3a is clamped and prior to the operation
of thermoforming a receptacle 2 from said zone of web 3a. The
volume of t~s annular space 14 changes during the therm~-
forming operation with the forming punch 10 being lowered andwith compressed gas being injected. Since this annular space
14 is hermetically closed throughout the entire downstroke of
the forming punch lO during which it leaves the cylindrical
cavity 9 in part to penetrate into the forming chamber 6 down
to the vicinity of the bottom thereof, gas under pressure may
be injected therein as soon as said space 14 is closed and gas
is injected therein not later than at the end of the downstroke
of the forming piston 10. Consequently, if so required for
some of the materials constituting the thermoplastic web 3, it
~ is possible to inject gas under pressure into the hermetically
closed annular space 14 during the downstroke of the forming
piston 10. The compressed gas may be injected into the annular
space 14 close to the top end of the punch 10 and beneath the
bottom face of the piston 15, or else close to the bottom end
of the counter mold block 8 inside the cylindrical cavity 9
thereof. It is advantageous to inject the compressed gas into
the annular space 14 in the form o multiple gas jets and to
orient them in such a manner as to ensure that they do not
strike the clamped zone of web 3a directly. To this end, the
gas under pressure is injected in the form of radial jets
extending substantially in a plane perpendic~lar to the axis of
the cylindrical cavity 9 and inside said cavity. Under such
circumstances, the gas jets are directed either substantially
perpendicular to the wall of the cylindrical cavity 9 and
towards said wall, or else perpendicular to the axis of said
cavity 9 and towards said axis. The gas jets thus b~yin by
striking either the wall o~ the cavity 9 or else the outside of
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the forming punch lO prior to being deflected towards the
forming chamber 6 and towards the clamped zone of web 3a.
The person skilled in the art will be able to modi~ the
present invention without going beyond the scope o the
protection defined by the accompanying claims.
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