The invention relates to a device for producing a ring-shaped body
from a thermoplastic material and to a method for producing a ring-shaped body from
a thermoplastic material.
Ring-shaped bodies, produced by extruding a thermoplastic material
are widely used, for instance as gaskets or other liners arranged in closures for
beverage bottles, wide-mouth bottles, jars etc. Another application are ring-shaped
closure elements, i. e. closures having a continuous hole as used for instance in
so called "sports bottles" or head pieces of tubes.
US patent 5,686,040 (White Cap, Inc.) discloses two different methods
for producing ring-shaped closure gaskets, wherein the gasket material is first
placed in the closure and subsequently reformed to obtain a desired geometry. According
to the first method, a hotmelt gasket material is dispensed into an invertedly arranged
closure by a dispensing head while the closure is rotated beneath the head. This
leads to deposit of a ring-shaped strand of material whereby the ends of the strand
overlap. During subsequent rotation of the closure the extruded ring is compressed
and partially formed by a flattening roller. According to the second method a preformed
gasket liner is inserted into the closure and heated. Finally, in both methods the
material is formed in a subsequent reformer station containing a compression punch.
The known methods for producing ring-shaped bodies require a complex
sequence of separate steps and are time-consuming. Either the ring is formed during
rotation of a closure which calls for a precise positioning and clamping of the
rotating closure in order to produce a preform having the desired shape, arranged
at the right place. Furthermore, the production of the preform using the dispensing
head and subsequently forming the gasket by first flattening and then punching the
preform needs much time. Similarly, externally preforming a gasket liner and reheating
the preform after insertion into the closure is time-consuming and requires a plurality
of devices for preforming, inserting, heating and finally punching.
Summary of the invention
It is the object of the invention to create a device pertaining to
the technical field initially mentioned, that facilitates producing of a ring-shaped
body, reduces time need and is compact and of simple construction.
The solution of the invention is specified by the features of claim
1. According to the invention the device comprises:
- a) a preforming unit comprising a ring nozzle for producing a ring-shaped preform
by extruding the melted thermoplastic material;
- b) a stripper for stripping off the preform; and
- c) a forming tool for forming the ring-shaped body by compressing the preform
against a counterpart element into a desired profile.
The ring nozzle allows for a fast production of an even, ring-shaped
preform by simultaneously forming the ring along its entire circumference. The nozzle
outlet is substantially ring-shaped and consists of a single continuous nozzle having
a circular opening or of a plurality of closely spaced nozzles arranged along a
circle or polygon. The preform produced by the ring nozzle does not show any transition
regions, where e. g. strands forming the ring overlap. Therefore, possible weak
spots and weld lines are eliminated. Because of the ring nozzle, mechanically complex
rotating parts such as a rotating dispensing head are eliminated. The stripper ensures
that the preform is fully and evenly detached from the ring nozzle such that no
material remains that could block the nozzle. Due to the forming tool the stripped-off
preform can immediately be compressed to obtain its final form, depending on the
shape of the forming tool and the counterpart element. As no reheating of the preform
is required, the construction of the device is further simplified.
Preferentially, the device further comprises a conveyor for inserting
the preform into the counterpart element. This allows for initially free forming
the ring-shaped perform, unhindered by the counterpart element. The conveyor ensures
a fast promotion of the freshly produced preform into the counterpart element, without
a substantial fall of temperature. This ensures that the inserted preform is still
in a formable state and, if desired, its temperature is still high enough to allow
for adherence of the ring-shaped body to the counterpart element. In that case a
surface layer of the counterpart element is temporarily melted as a result of the
contact by the hot preform.
Alternatively, the preform is produced directly inside the counterpart
element, the ring nozzle being inserted into the element, thereby minimizing the
complexity of the device, omitting the conveyor.
Advantageously, the stripper, the conveyor and the forming tool are
integrated into a single unit. This provides for a most compact construction of
the device and ensures that the different parts precisely match up.
Alternatively, single units may be provided for the three mentioned
parts of the device or only two of the parts may be combined into one unit.
Preferably the stripper, the conveyor and the forming tool are arranged
coaxially in said unit and the stripper and/or the forming tool are movable in an
axial direction relative to the conveyor. The coaxial, substantially axially symmetric
arrangement is adapted to the circular form of the body to be produced and allows
for a compact construction of the device.
Advantageously, the stripper and/or the conveyor arranged coaxially
with the forming tool are supported by the forming tool and springs are arranged
in between the stripper and the conveyor and/or in between the forming tool and
the conveyor. The springs exert defined forces in order to compress the preform.
Furthermore, once the first of the coaxially arranged parts of the device has reached
the counterpart element the remaining parts may be further advanced in the axial
direction by overcoming the spring forces between said first part and the other
parts. It is thus not necessary to individually control the motion of each of the
parts by individual drives.
Preferentially, the stripper and/or conveyor and/or forming tool comprise
a cooling system for cooling a contact region with the preform in order to prevent
bonding of the preform. Thereby it is ensured that the preform passes from the stripper
to the conveyor and from there to the forming tool. Finally, the forming tool may
be easily separated from the ring-shaped body. The cooling system may be formed
such that the cooling power is dynamically controllable, i. e. during the production
of a ring-shaped body the temperature of the stripper and/or conveyor and/or forming
tool is varied, according to the actual stage of the process. Alternatively, the
cooling power remains substantially constant during operation of the device.
Parts not having a cooling system are preferably built of or coated
by an antiadhesive material.
Preferably, the stripper is arranged such as to open and close the
ring nozzle. Thus, a separate active closure for the nozzle or a means for intermittent
injection of the thermoplastic material is saved.
Preferably, the forming tool comprises a central punch for preventing
the extruded material from entering a central region of the counterpart element.
If for example a ring-shaped gasket is formed, it is not desired that a central
region is coated by a film of the gasket material. Firstly, excess material is consumed
and secondly, in certain cases such as drug packaging, a central film must not be
formed in order to prohibit chemical reactions of the gasket material with the content
of the packaging. If a ring-shaped body with a hole is formed such as a closure
for a sports bottle or a head piece for a tube, a film would at least partially
cover the hole such that an additional tool for removing the film would be required.
These problems can be avoided by tightly pressing the central punch against a contact
surface of the counterpart element (i. e. a closure, a mold form etc.), corresponding
to the hole region, before the actual forming takes place.
Advantageously, the counterpart element is held by a spring loaded
support. This allows for adjusting tolerances if the counterpart element is replaced.
Furthermore, based on the displacement of the spring loaded support during the operation
of the device, failures during the production of the ring-shaped body may be detected,
e. g. if the preform is not correctly inserted into the counterpart element.
Alternatively, the device may comprise sensors for sensing the counterpart
element and/or failures and drivers that are able to adjust the movements of the
parts of the device accordingly.
Preferably, the ring nozzle is arranged in a substantially cylindrical
wall and the thermoplastic material is extruded in a substantially perpendicular
direction relative to the wall. The outlet of the nozzle may be arranged in the
inside wall of a cylindrical cavity, the extrusion direction pointing inwards or
in the outside wall of a cylindrical body, the extrusion direction pointing outwards
along the nozzle outlet. As such, these arrangements allow for a rotationally symmetric
creation as well as further handling and processing of the extruded ring. In the
context of the inventive device these arrangements are particularly advantageous
because the stripper, the conveyor and the forming tool may be arranged inside the
cylindrical cavity or enclosing the cylindrical body and after extrusion handle
the preform, in a rotationally symmetric way and unhampered by the ring nozzle.
Alternatively, the nozzle may be arranged e. g. as a circular opening
in a flat wall.
Advantageously, the preforming unit comprises two substantially torus
shaped chambers connected by a connector nozzle, where the thermoplastic material
is introduced in a first of said chambers and where the ring nozzle to produce the
ring-shaped preform is connected to a second of said chambers. The ring-shaped chambers
lead to an even distribution of the thermoplastic material and to an even pressure
of the material at the ring nozzle outlet. Therefore the produced preform has an
even shape, having a cross section substantially constant along its circumference.
Alternatively, other means for ensuring an even distribution may be
provided, e. g. a feeder inserting the thermoplastic material by a plurality of
access ways along the circumference of the ring nozzle combined with only a single
chamber coupled to the ring nozzle.
Preferentially, the preforming unit comprises a heater for maintaining
a temperature of the thermoplastic material. The material is fed into the preforming
unit in a thermoplastic state, i. e. heated to a given temperature. The heater allows
for controlling the respective thermoplastic properties of the material in order
to obtain consistent quality preforms.
In an advantageous application of the invention the counterpart element
comprises a carrier for holding a receptacle, such that the preform is compressed
against the receptacle. Thereby, in particular a liner, preferentially a gasket,
in a closure may be produced. Closures such as screw caps made of plastic (e. g.
polyethylene, polypropylene etc.) or metal are widely used for containers such as
bottles, wide-mouth bottles or jars. In order to prohibit air entering the container
or the content flowing out, a gasket has to be arranged in between the closure and
the container. The gasket is usually attached to the closure. In many cases, e.
g. if the container contains drugs, the gasket material should not contact the content.
Therefore, it is essential to provide a gasket that does not extend over essentially
the whole inner surface of the closure but is restricted to a ring-shaped region
contacting the neck of the bottle or jar. Besides, in all cases material requirements
are reduced for a liner that is ring-shaped.
The preform is introduced into the closure in its thermoplastic state,
having a high temperature. Therefore, compression of the preform simultaneously
leads to forming the gasket and to adhering the gasket to the closure by melting
the uppermost layer of the inner surface of the closure. In the case of metal closures,
a fusible lacquer applied to the inner surface, prior to the production of the gasket
allows for the same mechanism of adhesion.
In another advantageous application of the invention the counterpart
element is a mold form for forming a closure element having a continuous hole. Such
closure elements are especially used in so-called sports bottles having a push-pull
lid. Head pieces of tubes are another example of closure elements usually having
a continuous hole. Direct molding of such a closure element avoids the need for
a separate drilling or perforating step in order to obtain the hole.
A method for producing a ring-shaped body from a thermoplastic material
comprises the steps of:
- a) producing a ring-shaped preform by extruding the melted thermoplastic material
through a ring nozzle;
- b) stripping off the preform from the ring nozzle; and
- c) forming the ring-shaped body by compressing the preform against a counterpart
element into a desired shape.
Advantageously, after stripping off, the preform is conveyed into
the counterpart element.
Preferably, a tool for stripping off and conveying the preform and
for forming the ring-shaped body is alternately moved between two end positions.
In an upper dead center the ring-nozzle is uncovered by the tool such that the preform
is produced and in a lower dead center (in which the ring-nozzle is covered by the
tool) the preform is compressed.
Other advantageous embodiments and combinations of features come out
from the detailed description below and the totality of the claims.
Brief description of the drawings
The drawings used to explain the embodiments show:
- Fig. 1
- A first device for producing a ring-shaped body according to the invention,
in the upper dead center position;
- Fig. 2
- the device in a middle position;
- Fig. 3
- the device in the lower dead center position;
- Fig. 4
- a second device for producing a ring-shaped body according to the invention.
In the figures, the same components are given the same reference symbols.
Figure 1 is a schematic representation of a first device for producing
a ring-shaped body according to the invention, in the upper dead center position.
Displayed is a cross-section in a vertical plane including the central axis of the
device, which is substantially rotationally symmetric. The device comprises a tool
section 100, a nozzle section 200 and a counterpart section 300. The tool section
100 is constituted by a combined slitting, inserting and forming tool 110 and a
guide shaft 120 guiding an upper part of the tool 110. The core of the tool 110
is made up by an inner punch 111 featuring three coaxial cylindrical sections 111a,
111b, 111c, whose diameters increase from top to bottom. Inside the inner punch
111 a cooling duct 111d is leading from the top section 111 a through middle section
111b to the bottom section 111c and back. The duct 111d allows for maintaining a
given temperature of the inner punch 111.
The outer punch 112 is attached to the guide shaft 120 and slidably
supported on the inner punch 111. The outer punch 112 is constituted by three sections
112a, 112b, 112c having increasing diameters from top to bottom such that each section
112a, 112b, 112c of the outer punch 112 rests on an outer surface of the corresponding
section 111a, 111b, 111c of the inner punch 111. In the upper dead center position
displayed in Figure 1 the sections 112a, 112b, 112c of the outer punch 112 are all
offset a certain distance up relative to the sections 111a, 111b, 111c of the inner
punch 111, such that the inner punch 111 is clearly offset of the outer punch 112.
Slidably supported by the middle section 112b and the bottom section
112c of the outer punch 112 is a stripping sleeve 113 which has a substantially
ring shaped cross section and features a bold section 113a at its top and a blade-like
section 113b at its bottom end. In the upper dead center position the stripping
sleeve 113 rests with its bold section 113a immediately on the step between the
lower section 112c and the middle section 112b of the outer punch 112, therefore
the stripping sleeve 113 is as well offset of the outer punch 112.
A spiral spring 114 is arranged coaxially with the other elements
between the step formed by the transition between the middle section 111b and the
top section 111a of the inner punch 111 and the step formed by the transition between
the middle section 112b and the top section 112a of the outer punch 112. Another
coaxial spiral spring 115 is arranged between the bold section 113a of the stripping
sleeve 113 and the lower end of the guide shaft 120.
The nozzle section 200 comprises a ring-shaped housing 210 in which
a ring nozzle 220 and heaters 230, 231 are arranged. The ring nozzle 220 is constituted
by two substantially torus-shaped cavities 221, 222, having circular cross-sections,
arranged coaxially in a common horizontal plane. The cavities 221, 222 are connected
by a ring-shaped connector nozzle 223 having a width that is substantially smaller
than the diameter of the cavities 221, 222. The innermost part of the ring nozzle
220 is constituted by a ring-shaped outlet 224 formed as a ring-shaped opening in
the inner wall of the housing 210. At a certain angular position, the ring nozzle
220 features a feed opening where liquid thermoplastic material such as polypropylene
or polyethylene etc. is fed at a temperature of 140-280 °C, preferably about 210-230
°C and at a given constant pressure.
Due to the geometry of the ring nozzle 220, having two subsequent
chambers formed by the cavities 221, 222 and connected by the narrow connector nozzle
223 the thermoplastic material is evenly distributed in the inner cavity 222 and
therefore evenly extruded through the ring-shaped outlet 224. The heaters 230, 231
are ring-shaped coils or heating cartridges and arranged above and below on both
sides of the cavities 221, 222, parallel to their horizontal plane. This arrangement
provides for an even distribution of the heating power.
The counterpart section 300 comprises a holder 310 for tightly holding
a closure 400 as well as a support 320 for the closure 400. The support 320 is spring-loaded
in the vertical direction by means of a spring 321 and guided in a guide shaft 330.
The closure is arranged in an inverted position, i. e. its side wall 402 is pointing
up and its inner surface 401 faces the tool 110.
The device being positioned in the upper dead center, the outlet 224
of the ring nozzle 220 is not covered, such that thermoplastic material is extruded
through the outlet 224 and forms a ring-shaped preform 410 in between the wall 225
of the housing 210 of the nozzle section 200 and the inner punch 111 of the tool
section 100. As mentioned, the outer punch 112 and the sleeve 113 are retracted
relative to the inner punch 111.
Starting from the situation displayed in Figure 1, the guide shaft
120 is lowered. This leads to lowering of the outer punch 112 attached to the guide
shaft 120 and due to the springs 114, 115 simultaneously to the lowering of the
inner punch 111 as well as the stripping sleeve 113. During the lowering movement
the offset of the stripping sleeve 113 and the inner punch 111 relative to the outer
punch 112 is substantially kept. Therefore, due to the springs 114, 115, separate
drives for the three coaxial elements of the tool 110 are not required. The preform
410 is separated from the outlet 224 of the ring nozzle 220 by the blade-like section
113b of the sleeve 113, held in between the three coaxial elements of the tool 110
and moved downwards.
Figure 2 is a schematic representation of the inventive device in
a middle position reached by the steps mentioned above. The outer punch 112 is still
retracted relative to the sleeve 113 and the inner punch 111. Furthermore, the outlet
224 of the ring nozzle 220 is closed by the sleeve 113 as soon as the preform 410
is separated from the wall 225 of the housing 210 of the nozzle section 200. The
outlet 224 stays covered until the tool 110 is risen during preparation for the
next production cycle.
The downward movement of the inner punch 111, the outer punch 112
and the sleeve 113 continues until the most prominent element, the inner punch 111,
reaches the inner surface 401 of the closure 400. It thereby prohibits entering
of any material in a middle circular section of the inner surface 401. The guide
shaft 120 together with the outer punch 112 is further lowered against the increasing
spring force exerted by the spring 114 arranged between the now resting inner punch
111 and the outer punch 112. Simultaneously, the sleeve 113 is lowered due to the
spring 115 until the blade-like section 113b reaches the inner surface 401 and defines
the outer limit of the cavity built in between the inner punch 111, the outer punch
112, the sleeve 113 and the closure 400.
Figure 3 is a schematic representation of the inventive device in
the lower dead center position. This position is reached by finally lowering exclusively
the outer punch 112 until an offset remains relative to the inner punch of about
0.8 mm, corresponding to the thickness of the ring-shaped body to be produced. Thereby,
the preform 410 is completely lowered and compressed against the inner surface 401
of the closure 400 until a gasket of the desired profile is formed, defined by the
limiting surfaces of the elements of the tool 110. Due to the rapid transportation
of the freshly produced preform 410 into the closure 400, at this stage the temperature
of the preform 410 is still at about 80-90% of the melt temperature. Therefore,
in a contact region of the inner surface 401 of the closure 400 and the hot preform
410 an upper layer of the material of the inner surface 401 is melted and the gasket
adheres to the closure 400.
As soon as the desired shape is reached and adhesion has taken place
the inner punch 111 is cooled by guiding a cooling liquid through the cooling channel
111d of the inner punch 111. This leads to solidification of the ring-shaped body
such that the tool 110 may be retracted from the closure 400.
Next, during retraction of the tool 110 the closure 400 is removed
from the holder 310 and a new closure is inserted into the holder 310 by a star
wheel or other transportation means known as such. As soon as the tool 110 has moved
above the outlet 224 of the ring nozzle 220 extrusion of a new preform can start.
Figure 4 is a schematic representation of a second device for producing
a ring-shaped body according to the invention. In contrast to the device displayed
in Figures 1-3, the ring nozzle 550 is included in the tool section 500. The tool
section 500 comprises a combined extruding, slitting, inserting and forming tool
510 and a guide shaft 520 guiding the upper part of the tool 510. The core of the
tool 510 is again made up by an inner punch 511 featuring three coaxial cylindrical
sections 511a, 511b, 511 c, whose diameters increase from top to bottom. Slidably
supported by the inner punch 511 is an outer punch 512 which is a combined stripping
sleeve and forming tool constituted by three sections 512a, 512b, 512c having increasing
diameters from top to bottom such that each section 512a, 512b, 512c of the outer
punch 512 rests on an outer surface of the corresponding section 511a, 511b, 511
c of the inner punch 511. In the position displayed in Figure 4 the sections 512a,
512b, 512c of the outer punch 512 are all offset a certain distance up relative
to the sections 511a, 511b, 511c of the inner punch 511, such that the outer punch
512 is retracted relative to the inner punch 511. The bottom section 512c of the
outer punch 512 features a blade-like end portion adjacent to the inner punch 511
and a punch portion corresponding to a desired profile of the gasket to be formed.
Slidably supported by the middle section 512b and the bottom section
512c of the outer punch 512 is a sealing tool 516 which has a substantially ring
shaped cross section and features a bold section 516a at its top end and a contact
section 516b at its bottom end. Coaxial spiral springs 514, 515 are arranged between
the inner punch 511 and the outer punch 512 and between the sealing tool 516 and
the lower end of the guide shaft 520.
The ring nozzle 550 and a heater 560 are integrated in the tool 510.
For ensuring even distribution of the material to be extruded, the ring nozzle is
constituted by two substantially torus-shaped cavities 551, 552 in the inner punch
511 having circular cross-sections and arranged in a common horizontal plane. The
cavities 551, 552 are again connected by a ring-shaped connector nozzle 553 being
substantially narrower than the cavities 551, 552. The outermost part of the ring
nozzle 550 is constituted by a ring-shaped outlet 554 formed as a horizontal ring-shaped
opening in the outer surface of the inner punch 511. The ring nozzle 550 is fed
by thermoplastic material through a duct 556 arranged along the vertical axis of
the inner punch 511 connected to a flexible hose 557 at the upper end of the inner
punch 511. The heater 560 is ring-shaped and arranged above the cavities 551, 552,
parallel to their horizontal plane.
The counterpart section 600 is built similarly to the counterpart
section 300 displayed in Figures 1-3, comprising a holder 610 and a support 620
for holding and supporting the closure 400, a guide shaft 630 for guiding the support
620 and a spring 621 for pushing the support 620 together with the closure 400 in
an upward direction. In contrast to the counterpart section 300 of the first device
the counterpart section 600 allows for removing the closure 400 from the holder
610 without having to retract the tool 510, e. g. by retracting the spring-loaded
support 620 until the closure 400 may be removed sideways.
In the position shown in Figure 4, the outlet 554 of the ring nozzle
550 is open such that thermoplastic material is extruded through the outlet 554.
Thereby, a ring-shaped preform 410 is produced directly inside the closure 400,
in the space between the inner punch 511 and the side wall 402 of the closure 400.
During the production of the ring-shaped body, the inner punch 511 is tightly pressed
against the inner surface 401 of the closure 400 such that no material is able to
enter the middle circular section of the inner surface 401.
Next, the guide shaft 520 is lowered such that the inner punch 512
attached to the guide shaft 520 is moved downwards until the preform 410 is separated
from the outlet 554 of the ring nozzle 550 by the blade-like end portion of the
bottom section 512b of the outer punch 512. After that, the outer punch 512 and
the sealing tool 516 are further simultaneously lowered until the contact section
516b of the sealing tool 516 reaches the closure 400 and prohibits liner material
from entering an outer section of the inner surface 401 of the closure 400. Further
lowering of the guide shaft 520 leads to compression of the preform by the punch
portion of the outer punch 512.
In order to ensure solidification of the gasket and to prohibit bonding
of the gasket to the elements of the tool 510 the punch section 512b of the outer
punch 512 may be cooled by a cooling system (not displayed).
Next, the support 320 is retracted such that the closure 400 is removed
from the tool 510 and a new closure may be inserted. At the same time the sleeve
513 as well as the outer punch 512 are retracted such that the opening 524 of the
ring nozzle 520 is uncovered and extrusion of a new preform can start.
The geometry of the ring nozzle may be adapted to the extrudable material
processed, the geometry of the device and the type and profile of the ring-shaped
body to be produced. The ring nozzle may contain only a single chamber arranged
prior to the nozzle itself or more than three chambers. A plurality of chambers
may be arranged on different horizontal levels and the cross-section of the chambers
may be other than circular. The cross-section of the connector nozzle(s) may be
optimized in order to ensure a most even distribution of the thermoplastic material.
Finally, also the geometry of the ring nozzle itself is variable in a wide range:
alternatively, the ring nozzle may be composed of a large number of single nozzles
having circular outlets, arranged side-by-side along a circle or it may be composed
by several nozzles having rectangular closures, arranged along a polygon.
The profile of the formed liners is not restricted to the one described
and displayed above. A large variety of different profiles is achievable by the
invention, such as for gaskets for carbonated soft drinks (CSD) or hot-fill bottles.
The extrudable thermoplastic material may be chosen from a wide selection
of materials including e.g. Nitrogen foamed polymers.
The inventive device may be used to produce closure elements having
a continuous hole. In this case the counterpart element comprises a mold form which,
together with the forming tool, defines the cross-section of the closure element
formed from the extruded thermoplastic material.
Finally, a plurality of devices according to the invention may be
defined in a single apparatus, either for parallel processing of a plurality of
workpieces or for sequentially processing single workpieces by different operations
(e. g. producing a closure element having a hole in a first device and subsequently
inserting a gasket into the closure element in a second device).
In summary, it is to be noted that the invention creates a device
that facilitates producing of a ring-shaped body, reduces time need and is compact
and of simple construction.