The present invention relates to an extrusion head, as well as to
an extrusion plant provided with such a head, in which the same extrusion head
and extrusion plant provided with such a head being the object of the invention
are also susceptible of application in the microextrusion field.
It is known that manufacture of articles of particularly reduced
sizes involves a series of technical problems that are not found in normal production
of geometrically similar articles having however much greater sizes.
Generally, when articles of micrometric sizes are to be made, shaping
of same proves to be particularly problematic, due to the fact that the reduced
material to be worked and the very small measures and tolerances to be observed
makes it very difficult to obtain products having given features; for the above
reasons, often the production methodologies and apparatus used to make products
having important sizes from a macroscopic point of view cannot be suitably "adapted"
(by a scale reduction, for example) to production of similar articles typically
having microscopic sizes.
A production field in which these operating difficulties are particularly
felt is that of microextrusion; this production process is used to obtain articles
of manufacture and/or semifinished products having the most varying uses in fields
such as medicine and precision mechanics.
A particularly interesting example concerning articles produced by
microextrusion is given by micro-pipes made of polymeric material, having features
such as external diameters in the order of a few millimetres (or less) and diameters
of the inner cavities to be estimated around some tenth of a millimetre (or less);
more generally, in the microextrusion production field articles having cross sections
of few square centimetres are manufactured which at the same time have a very high
For manufacture of these micro-pipes, generally a two-stage production
plant is utilised; in the first stage a predetermined amount of polymeric material
in a plastic state is caused to pass through an appropriate forming tool (so as
to give the workpiece the desired tubular shape), and on coming out of this stage
the workpiece thus formed is cooled so as to stabilize the obtained shape and
enable stabilization of the polymeric material.
Obviously, such a production apparatus can be used with different
polymeric materials, depending on the physico-chemical features that are wished
to be given to the finished articles: micro-pipes of soft PVC, polyurethane, thermoplastic
rubbers and others can be made.
Depending on the materials used and above all taking into consideration
the very reduced sizes typical of these products, stabilisation of the micro-article
thus formed is required to be completed without causing distortions or modifications
in the shape of the product as formed in the first stage of the production process;
at the same time the forming tool which practically is an extrusion head (or better
an extrusion micro-head) must be maintained under such operating conditions that
clogging as a result of solidification of the polymeric material inside it, is
In other words, while the extrusion micro-heads of known type must
operate at such a temperature as to enable maintenance of the polymeric material
in the fluid phase, cooling of the micro-section member obtained through the extrusion
micro-head must be carried out in such a manner that deformations of the product
due to thermal gradients and/or the concurrent action of the force of gravity are
avoided. It should be noted at this point that these problems take a particular
importance in the case of micro-extrusions, since the very reduced mass of plastic
material employed is greatly subjected to a deforming action caused by environmental
factors that obviously would be substantially of less influence in the case of
It is therefore apparent that, in accordance with the known art,
micro-heads for extrusion must be made with a material ensuring a good thermal
conductivity, so that they can be constantly and evenly maintained to the desired
operating temperature (micro-heads for extrusion made of steel are for example
For instance, during solidification of the extruded micro-product,
it is required to avoid perturbation of the atmosphere around the workpiece, because
even a light turbulence would involve convective heat exchanges and even aerodynamic
actions capable of unacceptably distorting or twisting the workpiece itself, or
even cause occlusion of the inner cavity of the hollow section members.
To conveniently cool the workpieces coming out of the extrusion micro-heads,
the known art contemplates some plant typologies: in accordance with a first typology,
the micro-workpiece from the extrusion micro-head is laid down on a moving mat
and cooled by suitably-adjusted air jets.
The known art briefly described above however has some limits; in
fact such a plant is of great accomplishment complexity due to the great sensitiveness
of the workpiece to the turbulences that can occur in the cooling air.
The above involves a great waste of technical resources to monitor
cooling; in addition, the micro-workpiece resting on the moving mat is in any case
subjected to the deforming action of its own weight, since generally this moving
mat operates in a horizontal direction. In addition, due to the fact that part
of the workpiece rests on the moving mat, cooling by air is uneven since the workpiece
portion in contact with the mat is not exposed to the cooling air (but rather this
is the place where conductive heat exchanges with the moving mat take place).
In order to solve these drawbacks at least partly, a different plant
typology was adopted in which the workpiece is caused to come out of the extrusion
micro-head and is plunged into a water-containing tank.
In this way, cooling of the workpiece is more regular and quicker
and in addition it is possible to counteract the deforming action due to the weight
of the workpiece itself (since the hydrostatic water pressure occurs in an almost
even manner over the whole outer surface of the workpiece); in addition, still
for the purpose of avoiding undesired effects due to weight, the product can be
extruded along a vertical direction and it can be plunged into the cooling tank
This known technique too, however, has some problems that in this
case are represented by the necessity to physically separate the extrusion micro-head
from the cooling tank. It should be noted that this tank must be kept to a temperature
capable of maintaining the polymeric material in the fluid phase (at least until
this material leaves the head itself); therefore if the head should be put in
contact with the cooling water, a temperature gradient would be set therein that
would lead to an immediate clogging of the plant (because the polymeric material
would solidify within the extrusion head, owing to the sudden temperature drop
to which the head would be submitted due to water cooling).
The above described phenomena involve important operating and planning
constraints in the manufacture of plants for micro-extrusion; substantially, some
spacing between the extrusion micro-head and the cooling tank is to be taken into
consideration. Unfortunately this involves temporary exposure of the workpiece
to an open environment which can be hardly controlled (in other words, the workpiece
must travel along a length exposed to the external environment starting from its
coming out of the head until reaching the cooling tank); this introduces into
the manufacturing process the already mentioned risks of generating distortions
resulting from atmospheric turbulence, weight-related effects (in the case of
workpieces extruded along a horizontal direction, for example), accidental water
flows overflowing in the length exposed to air, close to the extrusion head and
all other events that may act on the workpiece in an uncontrolled manner along
the "free length" to be travelled over by the workpiece before it enters the cooling
In short, the production technologies of known type involve a greater
complexity of the manufacturing plants (in order to eliminate the great number
of causes giving rise to the workpiece distortion still during the solidification
step and also prevent binding) that ultimately negatively affect the production
flexibility and economic advantage in operation, servicing and use of the plant
Under this situation, the technical task underlying the present invention
is to devise an extrusion head capable of substantially obviating the above mentioned
Mainly, it is an object of the present invention to devise an extrusion
head that can be adapted to production processes of micro-extrusion by only carrying
out appropriate scale reductions.
Within the scope of this technical task it is an important aim of
the invention to devise an extrusion head capable of making articles of manufacture
of any shape, while offering the desired accuracy features and preventing clogging
In addition, the present invention aims at devising an extrusion
head that can be positioned with great freedom relative to the cooling tanks, so
as to minimize bulkiness and general complexity of the production plant itself.
Another important aim of the invention is to devise an extrusion
head of simple accomplishment and involving particularly reduced production costs.
The technical task mentioned and the aims specified are substantially
achieved by an extrusion head having the features set out in one or more of the
A preferred by not exclusive embodiment of an extrusion head in accordance
with the invention is now described by way of non-limiting example with the aid
of the accompanying drawings, in which:
- Fig. 1 is a sectional side view of a plant comprising an extrusion head in
accordance with the invention;
- Fig. 2 shows a head section taken along line II-II in Fig. 1;
- Fig. 3 shows a section taken along line III-III in Fig. 1; and
- Fig. 4 is an alternative embodiment of the head shown in Fig. 1.
With reference to the drawings, the extrusion head in accordance
with the invention is generally identified by reference numeral 1.
It substantially comprises a main body 2 and an auxiliary body 4.
In turn, the main body 2 made of thermally conductive material, has an extruder
duct 3 inside it (which passes through said body 2 along a specific operating
direction that in turn can be oriented in a horizontal or vertical way or inclined
to the ground, depending or requirements). Obviously, the extruder duct 3 extends
starting from an inlet orifice 3a and goes on until an outlet orifice 3b from which
the formed workpiece emerges. As can be seen in the accompanying drawings, the
extruder duct 3 is practically defined by a flow surface 3c disposed internally
of the main body 2.
Conveniently, the cross section of the extruder duct 3 can be of
any form, depending on the shape to be given to the product; in addition, the passage
area of the extruder duct can be substantially constant or varying (decreasing,
for example) along its operating extension direction starting from the inlet orifice
3a and reaching the outlet orifice 3b.
In accordance with the present invention, the main body can be made
of steel, to ensure the necessary mechanical-strength properties and the substantial
resistance to chemical attacks (in the case of use of polymeric materials that
are particularly active from a chemical point of view). Alternatively, it is at
all events possible to use another material to make the main body, provided at
least the essential requirement of thermal conductivity is met (for instance, the
main body can be made of thermally conductive ceramic material).
As a matter of fact, the extruder duct 3 (which is formed within
the main body) must be maintained, under operating conditions, to a temperature
(referred to as extrusion temperature) enabling maintenance in the liquid phase
of the polymeric material with which the extruded workpiece is wished to be made,
so as to avoid binding of the plant. For this reason, the extruder duct must be
maintained to a temperature at least as high as the melting temperature of the
polymeric material being used and, for doing so, the necessary amount of thermal
energy is required to be sent to the extruder duct 3 by conduction through the
massive part of the main body 2.
Advantageously, the auxiliary body 4 is connected to the main body
2 and can be interposed, under operating conditions, between the main body 2 itself
and the external environment, so as to prevent heat passage at least between the
extruder duct 3 and the surrounding atmosphere.
To achieve the above illustrated function, the auxiliary body 4 is
made of a thermally insulating material; in particular, the material chosen to
make the auxiliary body 4 is of such a nature that it has a melting temperature
and/or a temperature of physico/chemical degradation higher than the extrusion
temperature of any article of manufacture to be made by extrusion through head
1 in accordance with the present invention (in particular, the auxiliary body 4
must not be submitted to deformations due to pressure and/or heat to which it is
exposed). In other words, the material of which the auxiliary body 4 is made must
be able to keep its physical integrity (i.e. it must remain in a solid aggregation
state if exposed to temperatures causing melting of the polymeric material with
which the micro-extruded workpieces are being made), as well as its chemical integrity
(i.e. it must not be subjected to processes such as carbonisation, vulcanization
or others capable of irreversibly modifying its physico-chemical properties).
By way of example, it is possible to say that if a polymeric material
which is fluidized and extruded to a temperature of 180°C is selected for operation,
the material of which the auxiliary body 4 is to be made must have a melting temperature
higher than 180°C (so that it does not melt thereby losing its shape and not ensuring
thermal insulation of the main body 2). In addition, the same material must not
be subjected to chemical degradation or carbonisation at 180°C.
In accordance with the present invention, the auxiliary body 4 can
be made of a wide variety of materials; for instance, the so-called PEEK material
or PTFE material (also known under the commercial name of TEFLON) can be used.
In addition or as an alternative to these two materials, also used can be, by way
of example and depending on the present requirements, quartz, artificial diamond,
electro-conductive ceramic material, thermo-insulating ceramic material or a predetermined
thermosetting polymeric material. In making the auxiliary body 4, an appropriate
combination of these substances can also be used, depending on current technical
and/or economical requirements.
It should be also noted that the present invention, on the basis
of the just described range of materials, is able to ensure a correct operation
of the extrusion micro-head 1 with a very wide range of polymeric materials for
extrusion. Obviously, the present invention is able to correctly operate in all
cases in which the materials already mentioned with reference to the known art
are used (polyurethanes, thermoplastic rubbers, soft and hot melt PVCs).
From a construction point of view, from the accompanying drawings
it is possible to see that the main body first of all comprises a base element
5 of substantially prismatic conformation and a forming element or former 6 connected
to the base element 5.
The base element 5 has an inner cavity defining a first section 3d
of the extruder duct 3; conveniently, the first section 3d comprises the inlet
orifice 3a and a first portion of the flow surface 3c.
On the other hand, the forming element 6 has a corresponding inner
cavity, which in turn defines a second section 3e of the extruder duct. In particular,
the second section 3e comprises the outlet orifice 3b and a second portion of
the flow surface 3c (obviously, the first section 3d and second section 3e are
brought into fluid communication so that, by mutual cooperation, they form the
whole extruder duct 3).
For structural integrity of head 1, there is also the presence of
fastening means 7 which is operatively active between the base element 5 and forming
element 6 to keep them in a predetermined relative geometrical arrangement.
This fastening means 7 can be made in different manners (for instance,
shown in Fig. 1 is an embodiment in which this means consists of a flange, which
however can be replaced by a series of fastening nuts or any other interconnecting
device of known type), provided it has sizes capable of withstanding the thermal
and mechanical stresses to which head 1 is submitted during the production processes.
Advantageously, the auxiliary body 4 has a geometric conformation
adapted to separate the extruder duct 3 from the surrounding atmosphere at least
from a thermal point of view; in this way possible temperature drops are avoided;
in fact said temperature drops would involve binding of head 1 following a sudden
solidification of the polymeric material with which the micro-workpiece is being
The conformation of the auxiliary body 4 is determined depending
on this operating feature; in other words, the auxiliary body 4 can have any shape,
provided it can be interposed between the extruder duct 3 and the surrounding
atmosphere. In accordance with the present invention, in addition, the auxiliary
body 4 acts as a thermal-cutting element, inhibiting heat exchanges of a conductive
nature that may take place between the external environment and the thermo-conductive
mass of the main body 2.
It should be also appreciated that the present invention is dedicated
to optimization of the geometry of the components forming the extrusion head 1;
in particular, the conformation of the auxiliary body 4, as well as positioning
of same relative to the main body 2, can be selected in the most appropriate manner,
so as to prevent arising of heat exchanges in the most critical regions of the
main body 2.
Taking into consideration the above statements, in accordance with
a particularly advantageous embodiment of the present invention, the auxiliary
body 4 can be substantially shaped as a laminar body (of a disc-shaped conformation,
for example) and can be positioned close to the outlet orifice 3b of the extruder
Conveniently, the auxiliary body 4 has a through cavity substantially positioned
at the outlet orifice 3b (so as to enable extrusion of the micro-workpiece).
By virtue of this particular architecture, sudden temperature drops
are avoided close to the outlet orifice 3b of the extruder duct 3 which in most
cases of practical interest appears to be the most critical point (and consequently
the one most exposed to clogging phenomena), because it is directly exposed to
the external environment.
It should be noted, in fact, that the flow surface 3c of the extruder
duct 3 is separated from the external environment by an important amount of thermally
conductive material (because the base element 5 is a rather massive body) and
therefore practically cannot be subjected to high thermal changes (obviously, provided
head 1 is constantly maintained to a given temperature under operating conditions).
Likewise, the inlet orifice 3a is connected, still under operating conditions,
to a system supplying polymeric material in the fluid phase, and therefore it
is separated from the external environment (and in addition it is exposed to a
Turning back to the outlet orifice 3b, it should be noted that the
forming element 6 housing it is, in terms of thichness, thinner than the base element;
in addition, as also specified in the following, the operating requirement of
cooling the micro-workpiece in order to stabilize its shape, involves exposure
of the outlet orifice 3b (or even of the end portion of the extruder duct 3) to
rather low temperatures. This can lead to a heat loss localized at the portion
of the forming element 6 close to the outlet orifice 3b, and give rise to the
already mentioned binding phenomena.
In accordance with the present invention, the particular positioning
of the auxiliary body 4 prevents the region of the forming element 6 around the
outlet orifice 3b from cooling, while at the same time enables exit of the extruded
micro-article that, on the contrary, will be free to lose heat in an optimal manner.
Advantageously, the shape of the auxiliary body 4 can vary, depending
on the operating modalities; for instance, the auxiliary body 4 may partly or fully
circumscribe the forming element 6.
Still in the context of the present invention, the auxiliary body
4 can be also made following the particular construction architecture shown in
Fig. 4: in this case, as can be seen, the auxiliary body 4 comprises a plurality
of laminar elements 4a, suitably shaped and mutually interconnected so as to define
thermally insulating gaps 4b (for instance, filled with insulating substances
or even under vacuum). In this manner conductive heat exchanges are practically
limited by the reduced contact surfaces between the laminar elements 4a (that
can be also made of thermally conductive material, steel or aluminium for example,
in addition to the previously listed materials), whereas convective heat exchanges
are practically inhibited due to the presence of the thermally insulating gaps
Conveniently, should the auxiliary body 4 be made as a laminar body,
it would have a thickness (in the extension direction of the extruder duct 3) proportional,
according to a given factor, at least to the thermal conductivity of the thermo-insulating
material of which the auxiliary body 4 itself is made and to the temperature difference
between the external environment and the extrusion temperature to which the extruder
duct 3 is maintained, under operating conditions. In accordance with the present
invention, by suitably selecting said proportionality factor, different thicknesses
can be calculated that will be chosen to make different auxiliary bodies 4 to
be used in an interchangeable manner depending on current requirements.
Advantageously, the extrusion head 1 in accordance with the present
invention further comprises a given number of interconnecting elements 4c which
are operatively interposed between the auxiliary body 4 and at least the forming
element 6 (see Fig. 1) to mutually connect them. Obviously, these interconnecting
elements 4c that can be of any known type, are at all events selected and positioned
in a manner adapted to constitute a possible passage channel for heat exchanges
between the external environment and the forming element 6. Possibly, these interconnecting
elements 4c can be thermally insulated, obviously depending on current requirements.
The extrusion head 1 further comprises thermal-conditioning means
which is active at least on the base element 5 (and preferably on the forming element
6 as well) so that, under operating conditions, the temperature at least in the
extruder duct 3 is maintained at least as high as the extrusion temperature of
the workpiece. This thermal-conditioning means, not shown in the accompanying
drawings, is well known and consists of heating elements (electric resistors, for
example) and/or forced-ventilation systems (conveying air at given temperatures
to head 1).
Also part of the present invention is a plant for carrying out extrusion
operations which, by virtue of the peculiar features of the invention itself, can
also easily adapt itself to production processes of micro-extrusion.
This plant comprises at least one extrusion head 1 (having one or
more of the hitherto described features) and at least one cooling tank 8 which,
in turn, holds a predetermined amount of coolant to enable cooling of the article
of manufacture extruded through the head 1 itself. Typically, the coolant can be
water, which is advantageous from an economical and practical point of view; at
all events, if particular requirements make it necessary, the physical nature of
the coolant can be varied so that the ratio of the specific weight of the extruded
article to the specific weight of the liquid itself be included within a predetermined
value range; also qualitatively and quantitatively varied can be the modalities
for carrying out heat exchanges between the coolant and the extruded article, for
example by adjusting the coolant to a temperature adapted to avoid thermal shocks
(obviously depending on requirements).
Due to an appropriate selection of the coolant (carried out based
on the above described criterion) the extrusion conditions can be optimized so
as to minimize the deforming effects of the hydrostatic thrust on the length of
the extruded (or micro-extruded) product coming out of head 1.
Advantageously, due to the structural features described above, the
outlet orifice 3b of the extruder duct 3 in the plant in accordance with the present
invention is substantially disposed so that it faces the inside of said cooling
tank 8; according to this construction architecture (shown in Fig. 1), the auxiliary
body 4 is operatively interposed between the coolant and the main body 2 and in
this way inhibits heat exchanges between the main body 2 itself and the coolant.
In other words, in the plant in accordance with the present invention, the extrusion
head 1 can be connected almost directly with the cooling tank 8 without causing
sudden temperature drops at the region of the extruder duct 3 which is the closest
to the coolant mass (that in the absence of the auxiliary body 4 would withdraw
an important amount of heat from the forming element 6, thereby greatly lowering
the temperature of said element).
From a physical point of view, a direct exposure of the workpiece
to the coolant, just out of the extrusion head 1, involves an important advantage:
in fact, due to a sudden contact with the liquid, the outer part of the workpiece
solidifies almost instantaneously and is subjected to thermal shrinkage. On the
contrary, the inner part losing heat in a more progressive manner, tends to exert
a uniform pressure on the solidified outer part of the workpiece; combination of
these two uniform pressures helps in maintaining the cross-section of the workpiece,
to the benefit of accuracy and finishing of the workpiece itself.
In more detail, the cooling tank 8 has an interfacing wall 9 designed
to receive head 1, under operating conditions; said cooling tank 8 further comprises
an exit wall 10 (opposite to the interfacing wall 9) carrying a discharge orifice
11, preferably coaxial with the outlet orifice 3b of the extruder duct 3, to enable
exit of the extruded article, after its passage through the cooling tank 8 and
after stably taking its established shape.
As can be viewed from Fig. 1, the interfacing wall 9 comprises a
housing seat 9a designed to receive, under operating conditions, at least part
of the interconnecting elements 4c (in particular, if the interconnecting elements
4a are stud bolts as shown in Fig. 1, their heads are received in the housing seat
9a in such a manner that they do not come into contact with the coolant); internally
of the housing seat 9a there is a fastener 9b which is also connected to the auxiliary
body 4 (by the same stud bolts 4c as shown in Fig. 1, for example).
Fastener 9b serves as a fitting element for correct coupling of head
1 with the cooling tank 8, but it may also be unnecessary, provided the auxiliary
body 4 is suitably sized.
Conveniently, fastener 9b can have any shape (preferably, the shape
of this fastener will partly match with that of the housing seat 9a), and at all
events it has a passage port 9c axially centred relative to the outlet orifice
3b, which enables the coolant to directly graze the auxiliary body 4, around the
outlet orifice 3b. In this way, the extruded article comes directly into contact
with the coolant without passing through a section of the duct that can expose
it to dangerous thermal gradients.
Consistently with the above description, if fastener 9b is not present,
the housing seat 9a can be suitably shaped so that the portion of the auxiliary
body 4 close to the outlet orifice 3b is directly exposed to the coolant; in other
words, the passage port 9c can be directly formed in the housing seat 9a (see Fig.
The present invention may advantageously involve a different structure
of the plant as hitherto described; in fact, the interfacing wall 9 can be integrally
passed through by the forming element 6 that in this way would be partly contained
within the cooling tank 8 (and immersed in the coolant); in this case, in order
to avoid cooling of the extruder duct, the auxiliary body 4 may fully surround
at least that portion of the forming element 6 that is immersed in the cooling
tank 8, or it may be even inserted into the forming element 6 so as to circumscribe
the extruder duct 3 and at the same time surround the outlet orifice 3b.
Advantageously, the plant in accordance with the present invention
can be indifferently used both for extrusions (or micro-extrusions) carried out
along a horizontal progress line and for extrusions (or micro-extrusions) "by
drop" in which the extruded (or micro-extruded) piece is ejected from head 1 which
is vertically oriented above the cooling tank 8. Within the context of the present
invention, the extrusion head may also be oriented in any intermediate position
between the horizontal and vertical positions, depending or requirements.
For completion of the production plant in accordance with the present
invention, appropriate delivery means 12 for the polymeric material to be extruded
can obviously be installed (see Fig. 1 again); of course, this delivery means
12 is operatively active upstream of the inlet orifice 3a of the extruder duct
3 for admission thereto of a predetermined amount of polymeric material to be
extruded, and may consist of any apparatus of known type (shown in Fig. 1, by way
of example, is an Archimedes' screw held in a duct connected with the inlet orifice
The invention achieves important advantages.
It should be appreciated, first of all, that due to the peculiar
construction architecture, both types of heads, i.e. for extruding pieces of macroscopic
sizes and for micro-extrusions, can be indifferently made; in other words, the
structural features of the present invention are applicable through mere adaptation
of the geometrical measures of the different components, in the field of micro-extrusion
and extrusion of bigger objets, without creating problems in terms of accuracy
and finishing of the article of manufacture.
Secondly, it should be pointed out that the particular construction
of the head for micro-extrusions as herein described and claimed allow a perfect
maintenance of the ideal thermal conditions inside it, independently of the fact
that part of the head is directly in contact with a mass of coolant at a greatly
lower temperature; this enables compactness of the production plant to be maximized
and above all eliminates the presence of the "free length" that the workpiece just
extruded and still hot (and therefore externally deformable) must cover before
being submitted to cooling in water.
It will be also appreciated that the materials selected for construction
of the extrusion head in accordance with the present invention are of low costs
and easily available on the market, which is advantageous in terms of working
capacity and cost reduction.
In addition, the present invention allows use of a wide range of
polymeric materials due to the physico-chemical features of its components (enabling
the operating temperatures and pressures to be selected within a very wide range
for working of the different polymeric materials as required).
Another advantage of the present invention is given by the fact that
a wide variety of sections of the extrusion head can be accomplished without resorting
to complicated working operations and without being obliged to use particularly
expensive materials; this results once more in a great operating flexibility and
an advantageously increased running of the production plant.