Plate and apparatus for forming a plastic material flanged hollow article

It is disclosed a plate for a mould station to form a flanged hollow plastic container by shaping a flat billet, the plate comprising a base, a frame, an outer core to form a container of a first size and an inner core to form a container of a second size, smaller than the first size, wherein the frame is integral with the base and wherein the frame defines a frame upper surface; wherein the outer core, in a first configuration, is held elastically with its upper surface flush with the frame upper surface and, in a second molding configuration, is held with its upper surface recessed with respect to the frame upper surface; wherein the inner core, in a first configuration, is held elastically with its upper surface flush with the frame upper surface and, in a second molding configuration, is held with its upper surface recessed with respect to the frame upper surface; and wherein a retention system is provided to retain said billet substantially adhering to at least the upper surface of the inner core.

TECHNICAL FIELD

The present invention concerns in general the forming by moulding of a hollow container provided with a perimeter flange, for example a tray. In particular it concerns a plate able to cooperate with a mould to form said container. The invention also concerns a forming machine comprising at least one of said plates. The container formed can be used to contain an article, for example a food product which may be fresh, frozen, cooked, dehydrated or in any form.

BACKGROUND ART

A wide variety of products, especially food products like meat, sausages, cheese and the like, are often offered in visually attractive packages made of two webs (namely, a lower web and an upper web) using a vacuum skin packaging process, a thermoforming process or other methods.

The lower web is typically used as a support for the product and may be flat or heated and thermoformed to the desired shape, thus forming a receptacle for the product to be packaged. The lower web typically comprises a rigid or semi-rigid substrate, such as for instance of a plastic or cardboard material, and a sealing layer. The upper web is typically a flexible and formable film with a sealing layer that, in the end package, faces the sealing layer of the lower web.

Various forming machines are known in the art.

U.S. Pat. No. 6,896,506 discloses a thermoforming machine including a loading station configured to load a thermoplastic billet onto a frame. The frame has an outer ring and a billet support blade defining a channel therebetween. The billet support blade engages the billet to maintain the billet on the frame during heating of the billet. A heating apparatus is configured to heat the billet and a forming station is configured to form the billet into a container. In one embodiment, a preheating station may be utilized to perform initial heating of the billets. Such initial heating may be desired when a coining press is utilized to create an initial structure on the billet, such as adding a rim around the peripheral edge of billet.

U.S. Pat. No. 4,836,764 discloses an apparatus for the thermal pressure forming of plastic blanks into containers which includes several elements. A heater brings the plastic blanks to a melt phase by heating them to a melting temperature sufficient to relieve internal stresses therein. A conveying arrangement takes the plastic blanks through the heater. Thereafter, a press forms the plastic blanks into retortable containers.

U.S. Pat. No. 4,563,325 discloses an apparatus and method for producing articles by stretch-forming or pressure-forming of thermoplastics in the solid crystalline phase which permits forming from a billet of given thickness articles of greater wall thickness than would be formed by stretch-forming or pressure-forming the clamped billets.

U.S. Pat. No. 3,947,204 discloses an apparatus for making thermoplastic containers. The apparatus takes a measured amount of thermoplastic material which is lubricated, heated and forged into a desired shape preform with a predetermined lip configuration. The center portion of each said preform is maintained at a forming temperature while the peripheral portion thereof is clamped and rapidly brought below the softening point of the plastic resin. Blanks are forged in a forging means having a cooled lip forming means.

U.S. Pat. No. 3,546,746 discloses an apparatus for forming flanged hollow articles of work-strengthenable plastic materials. The outer edge of a blank is gripped around its periphery against a transverse seat.

U.S. Pat. No. 3,502,310 discloses a hot plate billet heater and method of heating.

U.S. Pat. No. 7,481,640 discloses a scrapless thermoforming machine including a plurality of transport trays having frames configured to hold thermoplastic billets and billet clamps.

U.S. Pat. No. 5,035,600 discloses an apparatus for converting thermoplastic blanks into shaped articles having a wheel-shaped conveyor which carries an outwardly extending link for a coupling which can engage successive blanks of a series of blanks during advancement along a first portion of its endless path.

U.S. Pat. No. 4,352,766 discloses a scrap-free, substantially solid phase, relatively low temperature process for rapidly making plastic articles from resinous powders wherein the resultant articles can comprise various polymers

NL 8501418 relates to a blow or vacuum moulding acrylic plastic roof dome.

SUMMARY OF THE INVENTION

The Applicant has noticed that the known machines and methods have some drawbacks and are not fully satisfactory. Accordingly, the Applicant has tackled the problem of providing an improved plate, machine and method for forming a flanged hollow article, such as for instance a plastic flanged tray or the like.

In particular the Applicant has tackled the problem of providing such a forming plate and machine operable at the site of the company loading the receptacle or container with food or other items, which is able to form a receptacle or container in a precise manner starting from a billet of plastic material.

In the present description and claims a billet is intended to be a blank of thermoformable plastic film cut in a proper size and shape for forming a flanged hollow article. A billet, once a receptacle or container is formed, should not be further cut or trimmed. One preferred material for the billet is PET. As an alternative, polylactic acid (PLA), polystyrene (PS), PA Nylon and Polymethyl methacrylate (PMMA) may be used.

According to a first aspect, the present invention provides a plate for a mould station to form a flanged hollow plastic container by shaping a flat billet, the plate comprising a base, a frame, an outer core to form a container of a first size and an inner core to form a container of a second size, smaller than the first size, wherein the frame is integral with the base and wherein the frame defines a frame upper surface; wherein the outer core, in a first configuration, is held elastically with its upper surface flush with the frame upper surface and, in a second moulding configuration, is held with its upper surface recessed with respect to the frame upper surface; wherein the inner core, in a first configuration, is held elastically with its upper surface flush with the frame upper surface and, in a second moulding configuration, is held with its upper surface recessed with respect to the frame upper surface; and wherein a retention system is provided to retain said billet substantially adhering to at least the upper surface of the inner core.

Profitably, the plate can be heated by means of a heating device.

Preferably, the heating device comprises electric resistors applied to said outer core and electric resistors applied to said inner core.

Preferably, the retention system comprises a system of retention by means of a vacuum.

The plate preferably also comprises a pressurised air supply system to shape the flat billet so that it conforms to a mould cavity.

The supply system may also comprise a slot between said frame and said outer core to form the flange of said flanged container.

The supply system may also comprise a slot between said frame and said outer core to form the flange of said flanged container.

In one preferred embodiment, the plate also comprises a counter-plate or cover to retain in a sandwich arrangement a billet between said plate and said counter-plate.

Profitably, the counter-plate may be hinged to said plate so that it can be opened before the moulding phases.

In one preferred embodiment, the counter-plate is heated.

The plate may be formed of aluminium or aluminium alloy.

According to a further aspect, the present invention provides a forming machine to form flanged hollow plastic containers, said forming machine comprising a storage reservoir for the billets, a device for taking and feeding the billets, an arrangement of plates and a moulding station, wherein said arrangement of plates comprises at least two plates as set forth above.

The arrangement of plates may comprise plates arranged horizontally and which can revolve about a vertical axis.

AS an alternative, the arrangement of plates may comprise plates which can revolve about a horizontal axis.

The billet taking and feeding device may comprise two platens fixed revolving about a slanting axis and rotating alternately by approximately 180°.

DETAILED DESCRIPTION

FIG. 1show an embodiment of a flat plate according to the present invention. The plate is adapted to cooperate with a mould to form a container. The container formed can be a tray to contain and support food products or articles of various types. For the sake of convenience, the present description will refer mainly to trays but this does not constitute a limitation since the present invention is not limited to any specific type of container.

The plate1can have a substantially rectangular form and comprises a base2, a frame3, an outer core4for large trays and an inner core5for small trays.

The frame3is fixed integral with the upper face of the base2along at least part of a lower perimeter area thereof. In one embodiment (not shown), the base and the frame are in one single piece. The frame3forms a perimeter cavity to retain the outer core4. The cavity can be seen, for example, inFIG. 1.2and is defined by the substantially L-shaped section of the frame. The outer core4is shaped so as to be partially inserted in the cavity defined by the frame3.

The outer core4is held elastically with its upper surface flush with the upper surface of the frame3(FIG. 1.6.1). As shown inFIGS. 1.6.2and1.6.3, the outer core4has a thickness T3inferior to the thickness T4of the frame3. Therefore, between the lower face of the outer core4and the upper face of the base2there is an empty space (height T4-T3). As will be described below, during the moulding phase, the outer core4can be pushed towards the base2(FIG. 1.6.3) so that its upper surface is recessed with respect to the surface of the frame3. When the outer core4is pushed towards the base2, it also drags the inner core5towards the base2(FIG. 1.6.3).

The outer core4, analogously to the frame3, forms a cavity to retain the inner core5. The inner core5fits partially into the cavity defined by the outer core4. The inner core5is held elastically with its upper surface flush with the upper surface of the outer core4(FIG. 1.6.1). The inner core5(where it fits into the cavity of the inner core) has a thickness T1inferior to that of the outer core4. Therefore, between the lower face of the inner core5and the upper face of the base2there is an empty space. As will be described below, the inner core5can be pushed towards the base2, countering the elastic force which maintains the upper surface of the inner core flush with the upper surface of the outer core and the frame. Pushing the inner core towards the base, the upper surface of the inner core5is recessed with respect to the upper surface of the outer core4. This configuration is shown inFIG. 1.6.2.

The elastic retention of the outer core4and the inner core5with respect to the base2is obtained by means of springs (as in the embodiment shown) or could be obtained by means of pneumatic or hydraulic cylinders.

Preferably, the plate1also comprises an air supply circuit to supply compressed air during the moulding phases. The same circuit permits the creation of a vacuum to retain a billet substantially adhering to the outer surface11of the plate1.

The circuit comprises at least one connection8to connect the circuit to a compressed air supply or, alternatively, to a vacuum pump (not shown). Preferably, at least one primary connection8aand at least one secondary connection8bare provided.

The at least one primary connection8ais conveniently connected to an inner chamber10of the inner core5. The inner chamber10communicates with the outside via small holes13. Preferably the holes13are in an orderly symmetrical configuration (FIG. 1.5a). Via the holes13, air of the circuit can flow out or a vacuum can be created to retain a billet substantially in contact with the outer surface11of the plate1.

The at least one primary connection8bis conveniently connected to an outer chamber9. According to the position of the outer core with respect to the base, the outer chamber9is defined between the base and the lower surface of the outer core (FIG. 1.6.1) or between the frame and the outer core (FIG. 1.6.3).

Furthermore, between the frame3and the outer core4there is a slot14which, as will become clear below, permits the formation of a flange during formation of the tray. Analogously, also between the outer core and the inner core there is a slot15with analogous function.

FIG. 1.5bshows the ducts that convey air to the slots14and15.

The plate1is conveniently made of metal, for example aluminium, aluminium alloy or steel. It can be heated by heating elements, for example flat heating elements19glued to the lower face of the inner core and the outer core. InFIG. 1.6the flat heating elements are shown thicker in order to facilitate identification.

FIGS. 2.1, 2.2 and 2.3show three moulding phases of a large tray, i.e. moulded with the outer core4of the heated plate1.

The mould20comprises a mould cavity21with a flat upper edge22and a flange-forming surface23which develops externally to the mould cavity around the flat upper edge22. It should be noted that the form of the mould cavity is not relevant for the present invention and will therefore not be described in detail. Also the form of the flange-forming surface23can be different from that illustrated in the various figures and in particular in the enlargement ofFIG. 2.3. Typically, the flange-forming surface23comprises, starting from the edge22, an inclined (or vertical) surface and a substantially horizontal surface.

InFIG. 2.1the mould20is shown open, i.e. separate from the relative plate1. Both the mould20and the plate1are shown partially in section. In the same figure, the plate1is shown with a thin billet31fixed to it. The billet31is held adhering to the face11of the plate1by means of an air suction (vacuum) system. Since the plate1is heated, the billet31, which is made of a thermoformable plastic material, softens due to the contact with the plate. A suitable material is polyethylene terephthalate (PET) or similar. As an alternative, polylactic acid (PLA), polystyrene (PS), PA Nylon and Polymethyl methacrylate (PMMA) may be used.

As will be specified also below, to further improve heating of the billet31, it can be closed in a sandwich arrangement between the plate1and a counter-plate, also heated. Obviously, the counter-plate must be removed before the plate1(with the billet attached to it) is rested on the mould20.

When the plate1is rested on the mould20, the billet31is brought into contact with the edge22of the mould and is retained in position (FIG. 2.2). Obviously, the contact with the mould occurs only at the edge22and the billet31is “pinched” between plate1and edge22. In other words, the billet31protrudes from the edge22of the mould. The protruding part of the billet is not supported by the edge22of the mould. Analogously, the billet31is not mechanically supported in the zone inside the edge22of the mould, i.e. in the mould cavity21.

A further movement of the plate1and the mould20nearer to each other causes crushing (i.e. recessing) of the outer core4with respect to the outer surface of the frame3. In this way the area along the outer perimeter of the billet31forms a perimeter flange42visible also in the moulded tray40. Conveniently, formation of the perimeter flange42can be aided by a jet of air emitted from the slot14between the outer core4and the frame3. Said jet of air promotes adhesion of the area along the outer perimeter of the billet to the above-mentioned flange-forming surface23.

Preferably, after formation of the flange, the cavity41of the container40is formed. The cavity can also be formed before forming the flange or during formation of the flange. To form the flange, the vacuum that retained the billet31on the heated plate is released. Via jets of pressurised air, emitted via the same holes13through which the plate was retained by the vacuum, the billet31is pushed to adhere to the mould cavity63(FIG. 2.3).

Subsequently, the plate1is moved away from the mould20and the tray formed40is removed from the mould20.

FIG. 3is analogous toFIG. 2.3but shows the final phase of moulding of a small tray, i.e. moulded with the inner core5of the plate1.

The moulding process is analogous to the one described in detail for the large tray and will not be described again. The difference lies in the fact that when the plate1is pressed towards the mould20, the inner core5is crushed (i.e. recessed) with respect to the outer surface of the outer core4. In this way the area along the outer perimeter of the billet31forms a perimeter flange42visible also in the moulded tray40. Conveniently, formation of the perimeter flange42can be aided by a jet of air emitted from the slot15between the outer core4and the inner core5. Said jet of air promotes adhesion of the area along the outer perimeter of the billet to the above-mentioned flange-forming surface23.

Subsequently, the plate1is moved away from the mould20and the tray formed is removed from the mould.

As mentioned above, a billet positioned on a plate1according to the invention can be retained adhering to the flat outer surface11of the plate by means of a suction system. The plate1, if necessary with the billet adhering to its flat surface11, can be translated, rotated or roto-translated. In other words, the billet remains adhering and “secured” to the plate even when the plate moves (or tilts). Therefore, a billet can be loaded on a plate and the plate with the billet loaded can then be moved towards the mould.

In any case, to guarantee that the billet does not substantially move with respect to the plate, a counter-plate may be provided to close in a sandwich arrangement a billet between the plate1and the corresponding flat counter-plate. Conveniently, also the counter-plate could be heated so as to heat the billet on both its two faces. This allows better, more uniform and more reliable softening of the billet.

In an advantageous embodiment, the counter-plate can be hinged along one side of the plate1.

The plate and mould system as described above forms a mould station which can be incorporated in a forming machine for flanged trays (or, more generally, containers). Two possible embodiments of a forming machine are described below.

FIG. 4is an axonometric view of a first embodiment of the machine50according to the present invention. In particular the machine50is in one configuration of its work cycle.

The machine50according to the first embodiment preferably comprises a frame55, a storage reservoir60for the billets31, a device70for taking and feeding the billets31, an arrangement100of heated plates1and a mould station200. Preferably, a conveyor belt80is also provided for conveying the formed trays40towards a packaging area or a storage zone of the trays40. The storage or packaging area is not shown in the drawings as it is not relevant for the purposes of the invention.

The frame55is illustrated schematically but it is clear that it can take any form, also different from the one illustrated.

The billet storage reservoir60is configured so as to keep a certain number of billets31in an orderly manner so that they can be easily withdrawn by the billet taking and feeding device70. The billets31can be stacked to form a substantially vertical pile but they are preferably stacked to form a substantially horizontal pile. This makes the machine more compact.

Preferably, the billet taking and feeding device70comprises a first taking platen71and a second taking platen72mounted so that they can rotate about a slanting pin with angle of 45°. Each platen has an upper face71A,72A and a lower face. The lower face is provided with means73suitable for retaining a billet31taken from the billet storage reservoir60and releasing it on one of the plates1of the arrangement of heated plates100. By way of example, the means73suitable for retaining the billet31and releasing it can comprise a suction cup73with suction system. Preferably a plurality of suction cups is provided in a symmetrical configuration. The upper face71A and72A of the platens is preferably connected to pneumatic cylinders74with dual stem so that the suction cup can be moved close to (or away from) the plate1on which a billet will be loaded. The pneumatic cylinders74also allow the platen to be moved close to a billet of the storage reservoir or move it away after the billet has been taken. Preferably, the structure on which the platens are fixed rotates approximately 180° with an alternating movement.

In the first embodiment the arrangement100of heated plates comprises four plates1arranged horizontally in the shape of a star or cross, i.e. at 90° with respect to one another. The plates1are substantially identical to one another and will be generically marked by the reference number1already used above in this description. The letter (A, B, C and D) after the number1is added for convenience of description of operation of the machine50.

Preferably each plate1A-1D also comprises a counter-plate (possibly heated)1′A,1′B,1′C and1′D hinged at one of its sides in the manner of a cover, typically the inner short side. Thanks to the cover, a billet31can be positioned on the heated flat plate1and closed in a sandwich arrangement between the cover76and the upper face of the plate.

FIG. 4shows the four heated plates1A,1B,1C and1D. The heated plate1A is being loaded with a billet and therefore has its cover1′A open (FIG. 5). The heated plate1B is heating a billet (loaded in the previous cycle) which is closed in a sandwich arrangement between the plate and the cover1′B. The heated plate1C is heating a billet (loaded two cycles previously) closed in a sandwich arrangement between the plate and the cover1′C. The heated plate1D, on the other hand, is cooperating with one of the two moulds20A,20B of the mould station200to form a tray40. Obviously, the cover1′D is open, i.e. raised.

The arrangement of heated plates can be rotated about a vertical axis V1by means of a motor101. The rotation can be clockwise or anti-clockwise. In the embodiment ofFIG. 4the rotation is clockwise (as indicated by the arrow around the axis V1). At each cycle, each heated plate1is rotated 90° so that it sets to the same position after four cycles. Each heated plate1remains at a standstill in position for a preset time in order to permit the moulding of a tray40and, simultaneously, loading of a billet31on the adjacent heated plate in the direction of rotation.

The mould station200comprises a mould20configured to cooperate with a plate1to form a tray40from a billet31positioned on the plate1. Preferably the mould station200comprises a first and a second mould20A,20B fixed to an L-shaped arm24with their cavity21facing downwards. The L-shaped arm24can rotate alternately around a vertical axis V2between a first position and a second position. In the first position, the first mould20A is releasing a formed tray (for example onto a conveyor belt, downstream of the mould station as inFIG. 4) and the second mould20B is forming a new tray40. In the second position, the operations of the two moulds20A and20B are inverted and the second mould20B is releasing a formed tray onto the conveyor belt upstream of the mould station.

Therefore, preferably, downstream of the mould station a conveyor belt80is provided on which the formed trays40are placed.

Four phases of the machine will now be described (from the machine start-up phase) according to the first embodiment and the phase in which the machine is in a steady state.

Phase 1 (Initial)First platen71takes a billet;Second platen72releases a billet onto first plate1A;First plate1A is loaded with a billet from second platen72, cover1′A open;Second plate1B not loaded with billet, cover1′B closed;Third plate1C not loaded with billet, cover1′C closed;Fourth plate1D not loaded with billet is in the mould station, cover1′D open.

Phase 2First platen71releases a billet onto the plate1D;Second platen72takes a billet;First plate1A loaded with a billet, cover1′A closed;Second plate1B not loaded with billet, cover1′B closed;Third plate1C not loaded with billet is in mould station, cover1′C open;Fourth plate1D is loaded with billet from platen71, cover1′D open.

Phase 3First platen71takes a billet;Second platen72releases a billet on the plate1C;First plate1A loaded with a billet, cover1′A closed;Second plate1B not loaded with billet is in the mould station, cover1′B open;Third plate1C is loaded with billet from platen72, cover1′C open;Fourth plate1D loaded with billet, cover1′D closed.

Phase 4First platen71releases a billet on the plate1B;Second platen72takes a billet;First plate1A loaded with a billet is in the mould station, cover1′A open; a tray40is formed;Second plate1B is loaded with billet from platen71, cover1′B open;Third plate1C loaded with billet, cover1′C closed;Fourth plate1D loaded with billet, cover1′D closed.

Phase 5 (Steady State)Second platen72releases a billet on plate1A;First platen71takes a billet;First plate1A is loaded with a billet from platen72, cover1′A open;Second plate1B loaded with billet, cover1′B closed;Third plate1C loaded with billet, cover1′C closed;Fourth plate1D loaded with billet is in the mould station, cover1′D open; a tray40is formed;Tray40formed in the previous phase deposited on conveyor belt80.

Therefore when the machine1is in a steady state, at each cycle a tray8is formed and placed on the conveyor belt.

Starting from the axonometric drawing ofFIG. 8, a second embodiment of the machine50according to the present invention is now briefly described. The machine50according to the second embodiment has several analogies with the machine according to the first embodiment. The same reference numbers will be used to indicate the same parts or functionally equivalent parts. The main difference with respect to the machine50of the first embodiment is that the heated plates1rotate about a horizontal axis H1instead of a vertical axis V1.

Preferably, the billet take and feed device70comprises a first taking platen71and a second taking platen72mounted in order that they can rotate about a slanting pin with angle of 45° so that, at each cycle, one is arranged substantially horizontally and the other substantially vertically. Rotation of the plates, fixed to a supporting structure, is preferably obtained by means of an electric, pneumatic or hydraulic motor.

In the second embodiment the arrangement100of plates1comprises four flat plates1A,1B,1C and1D arranged to form the lateral surfaces of a parallelepiped with square section. Preferably each plate1also comprises a cover1′A,1′B,1′C and1′D hinged at one of its short sides. A billet31can be arranged on the flat plate1and closed in a sandwich arrangement between the cover1′ and the upper face of the plate.

The arrangement100of plates1can be rotated about the horizontal axis H1by means of a motor. The rotation can be clockwise or anti-clockwise. Each heated plate1is rotated 90° so that it sets to the same position after four cycles. Each plate1remains at a standstill in position for a preset time to permit the moulding of a tray40and, simultaneously, loading of a billet on the adjacent plate.

The mould station200comprises a first mould21A and a second mould21B fixed aligned with a bracket24and with their concavity facing upwards. The bracket24can rotate about a vertical axis V3between a first position and a second position. In the first position, the first mould does not cooperate with a plate1and the tray formed, still housed in the mould, is taken by a revolving tray taking device and placed on a conveyor belt80. In the first position the second mould21B is forming a new tray. In the second position the operations of the two moulds21A and21B are inverted. The bracket24rotates preferably in an alternating manner by approximately 180°.

The above description of the four phases of the machine according to the first embodiment and of the phase in which the machine is in a steady state is the same also for the second embodiment and will not be repeated.

The machine according to the second embodiment is more compact than the machine according to the first embodiment. Conveniently, therefore, two or more machines can be positioned side by side supervised by one single operator and with only one conveyor belt (FIG. 10).

According to the present invention, and contrary to the known solutions, a billet suitable for forming a tray is supported on a plate1having a substantially flat surface11. The plate according to the invention holds the billet still by means of a suction system. The billet31is therefore retained and kept flat substantially throughout its surface and not only along one of its edges. The plate according to the invention comprises a heating system so that, while the billet is retained, it is also heated in a uniform manner and softened. This facilitates the forming process, making it more accurate and predictable, with the result that accurately shaped trays are obtained.

The plate, with the billet retained on its surface, can be moved by a translatory or rotatory movement (or a combination thereof) to reach a mould station and to cooperate with a mould.

Advantageously, a billet can be closed in a sandwich arrangement between a plate and a counter-plate (preferably also heated).

A further advantageous characteristic of the plate according to the present invention is that it can be set up to form containers of two or more different dimensions.

Thanks to the moulding system and the machines according to the present invention, it is possible to form the trays directly in the place where they are filled. Therefore, flat billets are transported and not bulky trays already formed. Transport and storage costs are drastically reduced. Furthermore, in the place where the trays are formed, there is no waste since billets are formed already in the correct size and shape. The waste deriving from cutting of the billets remains in the place where the billets are obtained starting from a roll of plastic film, therefore this waste does not have to be transported but can be recycled forming further plastic film which in turn is cut into billets.

Thanks to the heated plate in two dimensions, the same machine can be used to mould trays of a first size and trays of a second larger size. The only modification consists in replacement of the mould cavity each time.