WO2013054255A1

WO2013054255A1 - Method and apparatus for vacuum moulding of polyurethane material

Info

Publication number: WO2013054255A1
Application number: PCT/IB2012/055450
Authority: WO
Inventors: Piero Corradi; Claudio De Rossi
Original assignee: Cannon Ergos S.P.A.
Priority date: 2011-10-10
Filing date: 2012-10-09
Publication date: 2013-04-18
Also published as: ITMI20111848A1

Abstract

A method for moulding substantially bi-dimensional items from polyurethane foam material comprises positioning a first mould (4A) in an opening/closing and preparation station (32); advancing the first mould (4A), with the respective lower mould element (6) and upper mould element (7) coupled together in a closed configuration, along a work line (31) to a stand-by station (33); removing from rotatable support drum means (2) and at a transfer station (34) a second already moulded mould (4B). Removal comprises releasing from the rotatable support drum means (2) the entire second mould (4B) with the respective upper mould element (6) and lower mould element (7) coupled together, and lower the mould to a certain height to advance it along the work line (31), to the opening/closing and preparation station (32); transferring the second mould (4B) to the opening/closing station (32) and removing the respective moulded item; and simultaneously moving the first mould (4A) from the stand-by station (33) to the transfer station (34), and loading the entire first mould (4A) on the rotatable support drum means (2), whilst the second mould (4B) is prepared for a subsequent moulding cycle; conveying the second closed and ready mould (4B) to the stand-by station (33), generating a vacuum degree in the first mould (4A), injecting a polyurethane mixture into the mould, rotating the rotatable support drum means (2) by a step and removing a third mould (4C) therefrom which has reached the end of the respective moulding cycle. The corresponding apparatus (1) is also disclosed.

Description

METHOD AND APPARATUS FOR VACUUM MOULDING OF POLYURETHANE MATERIAL

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for vacuum moulding of polyurethane material to obtain doors and insulating panels for refrigerators, covers for chest freezers, doors and windows for buildings in general, panels or items, mostly substantially bi-dimensional, that have to be foamed internally.

For the purposes of the present invention, by the term "mould" the combination of an upper mould element and of a lower mould element is intended that cooperate to define an internal cavity that is suitable for containing the half-shells of a door for refrigerators, a panel or another similar item that internally defines a cavity into which a chemically reactive mixture is injected that is intended for forming a stiff or flexible polyurethane foam. The terms "upper" and "lower" used below refer in a non-limiting manner to a superimposed arrangement of the two mould parts for the sole purpose of distinguishing the two mould parts in the present description. In the description that follows specific reference will also be made to the production of doors for refrigerators merely by way of example of the general features of the present invention.

STATE OF THE ART

In current production of refrigerators, especially of domestic type, there is a tendency to diversify the various models by in particular modifying the aesthetic appearance, especially the geometrical shape, of the respective doors, which are often the main element of attraction, that determines the choice and purchase by consumers. A refrigerator door comprises an external half-shell, defining the visible surface of the door, and an internal half-shelf in which chambers and pockets are obtained to contain food and products to be conserved; during production, the two half-shells have to be first placed in a mould leaving between them a gap or a cavity that is filled with stiff polyurethane foam suitable for forming an insulating and stiffening layer of the door. The stiff polyurethane foam is normally obtained from a chemically reactive mixture based on a polyol and an isocyanate, which is injected and left to expand until it completely fills the wall cavity; during expansion of the foam, the door has to be suitably maintained between the lower mould element and the upper mould element in such a manner as to counteract and resist the internal thrusts generated by the expanding foam and thus avoid swelling and deformation of the door.

Today, the constantly increasing number of models of refrigerator entails an equally increasing number of geometrical shapes of the corresponding doors, with a consequent increase in containing doors dedicated to the corresponding manufacture. It is thus important to identify solutions that enable the ever increasing number of moulds to be managed in a rational and optimised manner that are often different from one another or belong to different types of refrigerator, without penalizing the productivity of the plant and avoiding or minimising undesired downtime during corresponding production. Various apparatuses have been proposed to deal with the problems set out above. For example, IT1325683 discloses a process and a plant for moulding polyurethane foam material to obtain doors of refrigerators. The plant comprises a rotating drum on which several upper mould elements are mounted, each intended to receive in a coupling manner a respective lower mould element, such as to define a certain number of stations that are angularly spaced apart from one another.

Once the lower mould elements have each been loaded with a door to be foamed they are coupled to the respective upper mould element of the rotating drum, on which the steps of injection, polymerisation and hardening of the polyurethane foam occur. At the end of the foaming operation, with the foam now stabilised and hardened, the lower mould elements, one at a time, have to be separated from the respective upper mould elements and then removed from the rotating drum together with the respective now foamed doors. In the position below the rotating drum, a movable plane with motor- driven rollers is provided for lifting and lowering one at a time the lower mould elements that have to be coupled with or removed from the rotating drum. In order to carry out and maintain the coupling of each lower mould element with the respective upper mould element and to provide subsequent mutual separation at the end of foaming, a plurality of driving devices is further provided, each of which is dedicated to opening/closing a respective mould. Such driving devices are mounted on the rotating drum and are then rotated with the rotating drum. The aforesaid plant, especially because of the multiplicity of driving devices on the rotating drum for opening/closing the moulds, is very complex from the structural and functional point of view. Further, the structural complexity entails, from the dynamic point of view, significant inertial masses that impose functional and productive limits on the entire plant.

It would thus be desirable to simplify the plant both structurally and functionally by improving the versatility thereof, in order to also increase the productivity. OBJECTS OF THE INVENTION

One object of the present invention is to improve the apparatuses and methods for foaming substantially bi-dimensional items, in particular thermally insulating doors and panels for refrigerators or freezers.

Another object is to provide a solution that enables a foaming apparatus to be obtained that is significantly simplified from both the structural and functional point of view and in general enables the process of foaming items, in particular doors and panels for refrigerators or freezers, to be improved.

More in particular, an object of the present invention is to provide a method and un apparatus for foaming doors for refrigerators or the like that are very flexible, and that are easily adaptable to programmed or programmable production, such as to enable any change in production without having to stop the plant and such as to reduce the structural and functional complexity, thus cost, and consequently increasing also the reliability of an entire productive system.

A still further object is to provide a method and an apparatus that enable two or more operating steps to be conducted simultaneously or in immediate succession, i.e. in partially overlapping time, or which occur continuously, thus reducing the operating time and downtime of the entire plant.

A further object of the present invention is to provide, in general, an apparatus for foaming doors for refrigerators and the like that is constructionally simple, of reduced cost and size and at the same time ensures great functional flexibility and high productivity.

In a first aspect of the invention, a method is provided as defined in claim 1.

In a second aspect of the invention, an apparatus as defined in claim 9 is provided.

Owing to these aspects of the invention the previously mentioned objects can be achieved.

Further characteristics and advantages will be clear from the appended claims and from the description.

SHORT DESCRIPTION OF THE DRAWINGS The invention can be better understood and implemented with reference to the attached drawings, which illustrate an embodiment thereof by way of non-limiting example, in which:

Figure 1 is a front view of an apparatus for foaming doors for refrigerators according to the invention in a first operating position;

Figure 2 is another view of the apparatus in Figure 1 in a second operating position;

Figure 3 is another view of the apparatus in Figure 1 in a third operating position;

Figure 4 is another view of the apparatus in Figure 1 in a fourth operating position;

Figures 5 and 6 show in detail a lowering/lifting device for moulds, included in the apparatus according to the invention, respectively in a raised and in a lowered position;

Figure 7 is a side view of the apparatus according to the invention;

Figures 8 and 9 show in detail respectively a head for injecting polyurethane into a mould, in an extracted position, and an air suction nozzle in a position inserted into the aforesaid mould for generating in the latter a vacuum degree;

Figure 10 is a diagram in which, according to time, various operating steps are shown that are performable by the apparatus and the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the attached Figures, an apparatus 1 is shown for vacuum moulding of polyurethane material to obtain, in a non-limiting manner, doors for refrigerators or covers for chest freezers. Although the description that follows refers to foaming doors for refrigerators, the apparatus 1 can also be used for foaming doors and windows for houses and buildings, panels, and, in general, any mainly be-dimensional item, i.e. items that are substantially flat or have two dimensions that are much greater than a third dimensions. The apparatus 1 comprises a rotatable supporting drum 2 configured for simultaneously supporting a plurality of moulds 4 and for advancing step by step the aforesaid moulds 4 along a circular operating pathway 5. Each entire mould 4, thus the respective lower mould element 6 coupled in a closed configuration with the respective upper mould element 7, is clasped to the supporting drum 2 to be subjected to a moulding cycle, and at the end of the moulding cycle, it is released and removed from the supporting drum 2. In addition to the structural and functional simplification of the drum 2, achieved owing to the fact that on the drum 2 mould parts do not remain permanently, as will be seen in greater detail below, greater versatility of use of the entire apparatus 1 is obtained. In particular, the extreme flexibility of use enables one or more moulds to be replaced with great freedom, for foaming, also simultaneously, models of items that are each time different, depending on production requirements.

The apparatus comprises advancing means 30 for advancing the moulds 4 on a work line 31 along which several stations are provided, disclosed further on, in particular an opening/closing and preparation station 32 for the moulds 4, a stand-by station 33 for the moulds 4 before they are loaded onto the supporting drum 2, and a transfer station 34 for transferring the moulds 4 onto or from the supporting drum 2. In the stand-by station 33 heating means can be provided for heating the moulds 4 to prepare the moulds 4 for the subsequent step of injecting the polyurethane mixture.

The advancing means, in particular comprises a conveyor belt 30, but can, alternatively, be of the roller type or be of another suitable type.

The conveyor belt 30, at the opening/closing and preparation station 32, comprises a belt portion 35 with a variable lying plane, i.e. a tiltable or balancing plane, can will be disclosed in greater detail below.

In the embodiment disclosed here, the supporting drum 2, in a non-limiting manner, is rotatable around a horizontal rotation axis 3.

In particular, but in a non-limiting manner, the supporting drum 2 is provided with four seats, each of which is suitable for receiving a respective mould. In other words, in the non-limiting embodiment disclosed here, the supporting drum 2 can simultaneously support up to four moulds 4.

Each mould 4 comprises a lower mould element 6 and an upper mould element 7 which are mutually couplable and uncouplable and cooperating to define an internal cavity that is suitable for containing half-shells 8 of a door for refrigerators, into which a dosed quantity of chemically reactive mixture has to be injected that is intended for forming a stiff or flexible polyurethane foam. It has to be remembered that a refrigerator often has two doors, one for the conservation compartment and the other for the freezing compartment; to simplify the productive cycles, the two doors can be treated simultaneously in a single "set", and consequently the containing moulds are joined together, being fixed, for example, to a single supporting pallet. Thus, with appropriate ploys, the apparatus 1 can be set up to operate on the aforesaid "sets" and pallets.

The supporting drum 2 is provided, for each of the four seats, with coupling means 9 that is drivable to support the moulds 4 is a removable manner.

In particular, the coupling means 9, as more clearly visible in Figures 5 and 6, include protruding elements 10 that are movable in a direction that is transverse to the horizontal rotation axis 3 to engage with, and disengage from, suitable clasping seats 1 1 obtained in the moulds 4. The moulds 4 can in this manner be clasped to or released from the respective drum 2 seats.

Owing to the coupling means 9 that enable the whole of the moulds 4 to be removed, in addition to greater versatility and flexibility of use of the apparatus, also a reduction of the weight and inertia of the drum 2 is obtained, thus a functional structural simplification and an increase of structural reliability is obtained. As shown in Figures 7 and 8, the apparatus 1 comprises an injecting head 12, operatively connected to the supporting drum 2, and suitable for injecting a dosed quantity of polyurethane material into a respective mould 4 when the latter is in a set position 22 on the drum 2. The injecting head 12 is part of a supplying or injecting device 13, shown schematically in Figure 7, which removes and mixes together suitable doses of isocyanate and polyol to obtain the polyurethane mixture for foaming items.

The injecting head 12, shown in an extracted position in Figure 8, is supported by a first slide 14 that can be moved by a suitable first driving cylinder 15. The first driving cylinder 15 enables the injecting head 12 to be moved near the mould 4 when the step of injecting the polyurethane mixture at the first position 22 has to be carried out. In particular, the injecting head 12 engages with a suitable opening 16 of the mould 4 in such a manner as to be in communication with the cavity defined internally by the half-shells 8. A suitable washer is provided that enables a seal contact to be obtained between the injecting head 12 and the opening 16 of the respective mould 4.

With reference to Figures 7 and 9, the apparatus 1 comprises an air suction nozzle 17 connected to a pneumatic circuit 18 and operationally connected to the supporting drum 2. The air suction nozzle 17 acts to suck air from the respective mould 4 to generate a vacuum degree inside the mould 4, for example a vacuum degree comprised between 600 and 900 absolute millibars, such as to facilitate and optimise foaming operations. The air suction nozzle 17 is drivable in a manner that is operationally correlated with the injecting head 12; air suction enables the gases to be removed that are generated inside the mould 4 and enables the polyurethane mixture to be distributed better, comprehensively improving the foaming process.

In a manner that is structurally and functionally similar to what has been disclosed for the injecting head 12, the air suction nozzle 17, shown in a position coupled with the respective mould in Figure 9, is supported by a second slide 19 that can be moved by a suitable second driving cylinder 20. The second driving cylinder 20 enables the air suction nozzle 17 to be brought near the mould 4 to permit the air-sucking step. In particular, the air suction nozzle 17 engages with a suitable further through opening 21 obtained in a side wall of the mould 4, nevertheless remaining separated by the half-shells 8. As the reciprocally assembled half-shells 8 are not sealed together but have narrow openings, sucking the air through the further opening 21 of the mould 4 also affects the zone interposed between the half- shells 8, generating the vacuum degree required therebetween.

In particular, the air suction nozzle 17 rests on the external surface of the mould 4 and engages sealingly with the further opening 21 by means of a suitable seal. The transfer station 34, placed near a region underneath the supporting drum 2, comprises lifting and lowering means 40 (between shown in Figures 5 and 6), that is suitable for lifting and lowering a respective mould 4 relatively to the supporting drum 2. The lifting and lowering means 40 comprises a lifting table 41 shaped for restingly receiving a respective mould 4. The lifting table 41 is fixed below to a vertically movable rack element 42. The rack element 42 engages with a toothed wheel 43 rotated by an electric motor 44. The rack element 42 is positioned in such a manner as not to interfere with the conveyor belt 30 and in such a manner as to enable the items conveyed by the conveyor belt 30 to pass underneath the lifting table 41 when the lifting table 41 is in the raised position 41. , Alternatively, the lifting table 41 can be supported and driven by a hydraulic or pneumatic cylinder or by other suitable driving means.

The opening/closing and preparation station 32 comprises an uncoupling/coupling device 36 that lifts an upper mould element 7 to uncouple the latter from the respective lower mould element 6 to enable a moulded item to be removed and to enable a further item to be prepared for moulding, in particular introducing further shells of a refrigerator door. The lower mould elements 6 and upper mould elements 7, once they have been prepared are mutually coupled by the uncoupling/coupling device 36 that lowers the upper mould element 7, bringing the upper mould element 7 near the lower mould element 6.

Owing to the uncoupling/coupling device 36 it is possible for an operator 60 to access easily both the lower mould element 6 and the upper mould element 7 to perform various cleaning, maintenance, preparation operations etc ... Further, the operator 60 is facilitated in the operation of replacing the upper mould element 7 and/or the lower mould element 6 with other different mould elements, depending on the geometrical shapes of the external half- shells of the doors that are required.

The uncoupling/coupling device 36 for lifting and lowering 40 comprises a clasping bracket 37 shaped for clasping a respective upper mould element 7. The clasping bracket 37 is suspended on the upper part by a further rack element 38 which is vertically movable. The further rack element 38 engages a further toothed wheel 39 rotated by a further electric motor 45. Alternatively, the clasping bracket 37 can be supported and rotated by a hydraulic or pneumatic cylinder, or other suitable driving means. In the opening/closing and preparation station 32, the belt portion 35, as mentioned previously, defines a support portion 46 for the moulds 4 that is movable in such a manner as to be able to vary a lying plane thereof. In particular, the belt portion 35 is tiltable in a rotatable manner around an axis 50, so as to reach the tilted position 48 visible in Figure 1. The belt portion 35 is tiltable by a motor-driven adjusting device that is not shown.

The opening/closing and preparation station 32 further comprises holding means 47 to retain on the support portion 46 the respective lower mould element 6, and to prevent the latter from being able to slip when it is in the tilted position 48. The holding means can comprise a retaining wall 47 that projects upwards from an end zone of the support portion 46. The functioning of the apparatus 1 is now disclosed with reference to the diagram in Figure 10 in which for the sake of simplicity of exposition the sequence of operating steps of only two of the four moulds 4 is disclosed, in particular of a first mould 4A and of a second mould 4B. Steps A to G refer to the first mould 4A, whereas steps H to Q refer to the second mould 4B and will be explained below in turn. In the diagram, the corresponding duration of each step is indicated in a non-limiting manner.

A first mould 4A, positioned in the opening/closing and preparation station 32, (as shown in Figure 1 ) is opened to remove an already foamed door contained inside the first mould 4A and to be prepared and loaded with a subsequent door to be foamed and then to be reclosed.

The first mould 4A is then moved to the stand-by station 33 to wait for a seat of the supporting drum 2 to become vacant. In the stand-by station 33, the first mould 4A can also undergo heating prior to the step of injecting a polyurethane mixture. In the meantime, the lifting/lowering means 40 rises (step H) to remove a second mould 4B that has completed the operating pathway 5 and which has reached the end of the moulding cycle. A release step I thus occurs and subsequently a lowering step L of the second mould 4B, which is positioned on the conveyor belt 30. The conveyor belt 30 is then driven to transfer the second mould 4B to the opening/closing and preparation station 32 (step M) and, simultaneously, the first mould 4A is conveyed from the stand-by station 33 to the transfer station 34 (step A). Whilst the second mould 4B is opened (step N), by driving the coupling/uncoupling device 36 and consequent tilting of the tilting support portion 46, the first mould 4A is lifted (step B) and clasped (step C) to the supporting drum 2. The second mould 4B, after being opened, is subjected to a step O in which the already moulded door is removed and another door to be moulded is introduced. Whilst step "0" of the second mould 4B is taking place, the first mould 4A is subjected to an air-suction step D to generate a vacuum degree therein and is subjected to a step E of injecting and filing with polyurethane mixture. The injecting head 12 and the air suction nozzle 17 respectively suck the air and inject the polyurethane mixture. In particular, the injecting head 2 is moved near the first mould 4A, facing the opening 16, or casting gate, and coming into sealing contact therewith. Simultaneously, the air suction nozzle 17 is rested on the mould 4A and driven to suck air for a period of time that may comprise about 2 or more seconds, depending on operative circumstances (door dimensions, etc .). Subsequently, the injecting head 12 injects the polyurethane mixture for about 2-3 seconds or more, (also here in function of the specific operative circumstances such as door dimensions, etc..) and the vacuum degree is then maintained by keeping together the first mould 4, the injecting head 12 and the air suction nozzle17 for a further period of time that may vary from 15 to 20 seconds. Subsequently, it is possible to disengage the injecting head 12 and air suction nozzle 17 from the mould 4A inasmuch as, at this point, the polyurethane mixture has already reached a certain degree of reticulation that prevents the polyurethane mixture from exiting from the half- shells 8. The supporting drum 2 is thus ready to be rotated by a pitch.

The second mould 4B, once loaded with a new door to be foamed, is closed (step P) and is subsequently transferred to the stand-by station 33 (step Q) before being subjected to a new moulding cycle.

In the meantime, the polyurethane mixture introduced inside the first mould 4A continues the polymerisation/hardening process. As mentioned above, after the polyurethane mixture has been introduced the supporting drum 2 is rotated by a pitch (step F), and stops (step G), to position a third mould 4, which has substantially reached the end of the moulding cycle, in the release and removal position. The first mould 4A is thus advanced by steps along the operating pathway 5 along which it proceeds and the process of polymerisation/hardening of the polyurethane mixture is completed.

The supporting drum 2 is arranged in such a manner as to position a third mould 4C, which has reached, or almost reached, the end of the moulding cycle, in the transfer station 34 near the lifting/lowering means 40. The third mould 4C can be released, lowered and surrendered to the conveyor belt 30 according to the same operative modes already disclosed for the second mould 4B with reference to the steps H, I and L, and so on. The dwell time of a moulded door inside the respective mould after injection of the mixture is about 180 seconds.

As can be seen from what has been disclosed, the apparatus 1 and the corresponding method enable the objects declared above to be achieved. In particular, great versatility of use of the apparatus 1 is achieved that enables, in an extremely flexible manner, any type of mould to be changed at any moment to adapt to variable geometrical shapes of the half-shells of a door, without this resulting in undesired lengthy machine stops. Owing to the apparatus 1 , it is possible to intervene freely in the course of a production cycle to change type and/or model or door or doors being produced without having to stop the productive process. This is possible owing to the complete removability of the entire moulds from the supporting drum 2, which can be replaced or repaired or subjected to any other type of operation without necessarily stopping the operation of the drum. Further, the supporting drum 2 is structurally simplified inasmuch as no complex tightening and opening devices are required for each pair of half-moulds, each mould being opened and closed outside the drum 2 by a single coupling/uncoupling device 36. Owing to the configuration of the supporting drum 2, as it is structurally less complex, it is more reliable, less bulky and lighter. Thus the supporting drum 2, having reduced inertia mass, is also drivable more quickly. It is possible to configure and dimension the apparatus 1 in a desired manner in function of the dimensions/type of items to be obtained and variations and/or additions to what has been disclosed and illustrated in the attached drawings are possible.

Claims

1. Method for moulding substantially bi-dimensional items from polyurethane foam material, according to which a plurality of moulds (4, 4A, 4B, 4C), each comprising a lower mould element (6) and an upper mould element (7) which can be coupled/uncoupled to each other, are moved along an operating pathway (5) on rotatable support drum means (2) and along an underlying work line (31 ) where preparation operations, opening/closing operations of the moulds (4, 4A, 4B, 4C) and removal operations of moulded items are carried out, characterised in that it comprises the steps of:

a) positioning a first mould (4A) in an opening/closing and preparation station (32);

b) advancing said first mould (4A), after it has been prepared, with the respective lower mould element (6) and upper mould element (7) coupled together in a closed configuration, along said work line (31 ) to a stand-by station (33);

c) removing from said rotatable support drum means (2), and at a transfer station (34), an entire second mould (4B), comprising a respective upper mould element (6) and lower mould element (7), that has reached the end of a moulding cycle along said operating pathway (5), wherein said removing comprises releasing said second mould (4B) from said rotatable support drum means (2) and lowering said second mould (4B) to a certain height, such that the respective upper mould element (6) and lower mould element (7) coupled together can be advanced along said work line (31 ), to said opening/closing and preparation station (32);

d) transferring said second mould (4B) from said transfer station (34) to said opening/closing station (32) and removing the respective moulded item; and simultaneously

d1 ) moving said first mould (4A) from said stand-by station (33) to said transfer station (34), and

e) loading the upper mould element (6) and the lower mould element (7) coupled together of said first mould (4A) on said rotatable support drum means (2), whilst said second mould (4B), once it has been opened and the respective moulded item has been removed, is prepared for a subsequent moulding cycle; and subsequently

f) conveying said second mould (4B), which is closed and ready for moulding, to said stand-by station (33),

g) performing the air sucking operation to generate a vacuum degree in said first mould (4A) and the operation of injecting a dosed amount of polyurethane material into said first mould (4A); and

h) rotating by a step said rotatable support drum means (2) and, at said transfer station (34), removing from said rotatable support drum means (2) an entire third mould (4C) which has reached the end of the respective moulding cycle and is ready to be moved to said opening/closing and preparation station (32) in order to allow for the removal of the respective moulded item and to allow the start of a subsequent moulding cycle.

2. Method according to claim 1 , wherein there is provided cyclically repeating said steps a) to h).

3. Method according to claim 1 or 2, wherein during said step a) there is provided opening said first mould (4A) by uncoupling said upper mould element (7) from said lower mould element (6), loading said first mould (4A) with half-shells (8) of said first object to be moulded and coupling said upper mould element (7) back to said lower mould element (6).

4. Method according to claim 3, wherein said opening, in said opening/closing^' and preparation station (32), comprises lifting said upper mould element (7) in relation to said lower mould element (6) and tilting said lower mould element (6) to facilitate the operations of preparing said first mould (4A).

5. Method according to any one of claims from 1 or 4, wherein on said work line (31 ), and at said stand-by station (33), a heating step for the respective mould is provided.

6. Method according to any one of the preceding claims wherein said step e) comprises lifting and clasping said first mould (4A) to said rotatable support drum means (2).

7. Method according to any one of the preceding claims, wherein there is provided generating a vacuum degree ranging between 600 and 900 millibars.

8. Method according to any one of the preceding claims, wherein said substantially bi-dimensional items comprise refrigerator doors, covers for chest freezers, panels, door and/or window leaves or the like.

9. Apparatus for moulding substantially bi-dimensional items from a polyurethane material, characterized in that it comprises in combination: — rotatable support drum means (2) provided with clasping means (9) for removably supporting and advancing along an operating pathway (5) a plurality of moulds (4, 4A, 4B, 4C) for said items, said moulds (4, 4A, 4B, 4C) comprising lower mould elements (6) and upper mould elements (7) which are mutually couplable and uncouplable,

— injecting means (12, 13) and air suction means (17, 18) operatively connected to said rotatable support drum means (2) in order to inject a dosed amount of polyurethane material and generate a vacuum degree within a respective mould (4, 4A, 4B, 4C),

— an opening/closing and preparation station (32) suitable to allow the mutual uncoupling and coupling of an upper mould element (7) from and to a respective lower mould element (6) in order to allow the removal of a moulded item and the preparation of a further item to be moulded, respectively,

— a stand-by station (33) suitable to accommodate an entire mould (4, 4A, 4B, 4C)), comprising a respective lower mould element (6) and a respective upper mould element (7), coming from said opening/closing and preparation station (32) and ready for a moulding cycle;

— a transfer station (34) comprising lifting and lowering means (40) for lifting and lowering a lower mould element (6) and a respective upper mould element (7), coupled together, of a respective mould (4, 4A, 4B, 4C) relatively to said rotatable support drum means (2),

— advancing means (30, 35) for advancing said moulds (4, 4A, 4B, 4C), with the respective lower mould elements (6) and upper mould elements (7) coupled together, along a work line (31) between said opening/closing and preparation station (32), said stand-by station (33) and said transfer station (34).

10. Apparatus according to claim 9, wherein said rotatable support drum means (2) can be actuated to rotate by steps about a horizontal rotation axis (3), and wherein said coupling means (9) comprises protruding elements (10) which are transversely movable relative to said horizontal rotation axis (3) for engaging with, and disengaging from said moulds (4, 4A, 4B, 4C).

11. Apparatus according to claim 9 or 10, wherein said air suction means (17, 18) is configured to generate a vacuum degree ranging between 600 and 900 millibars in a respective mould (4, 4A, 4B, 4C).

12. Apparatus according to any one of claims 9 to 11 , wherein said lifting and lowering means (40) comprises a lifting table (41) which is supported and moved by a hydraulic or pneumatic cylinder, or by a rack element (42) geared to a toothed wheel (43) coupled to an electric motor (44).

13. Apparatus according to any one of claims 9 to 12, wherein said advancing means (30, 35), at said opening/closing and preparation station (32), comprises a tilting support portion (46) and holding means (47) to hold a respective mould (4, 4A, 4B, 4C) in a tilted position (48), an adjusting device being further provided to change the tilting degree of said tilting support portion (46) in order to facilitate carrying out the preparation operations of the respective mould by an operator (60).

14. Apparatus according to any one of claims 9 to 13, wherein said opening/closing and preparation station (32) comprises an uncoupling/coupling device (36) suitable to lift/lower an upper mould element (7) in order to couple/uncouple the latter to/from lower mould element (6) such that a moulded item can be removed and a further item to be moulded can be prepared.

15. Apparatus according to any one of claims 9 to 14, wherein said advancing means (30, 35) comprises conveyor belt means or roller conveyor means.