DESCRIPTION

TECHNICAL FIELD

The present invention is in the field concerning the moulding of sheets made of plastics, and relates to a moulding machine for thermoplastic sheets, for example suitable for the manufacturing of the inside parts of refrigerators, freezers, other appliances, furnishings, containers, etc., comprising two or more parts or tanks arranged at a reduced distance from each other.

BACKGROUND ART

There are known moulding machines, e.g., differential pressure moulding machines, for thermoplastic sheets, comprising a pair of overlapping frames that are movable with respect to each other and together, said upper reduction and lower reduction being provided with respective protruding lower and upper edges having respective planforms that are identical or almost identical. These reductions may move away from each other, so as to allow the insertion of a sheet, and may draw near to each other, so that the borders of said edges tighten the perimetric portion of the sheet, thus blocking it in an airtight condition.

An upper face of the upper reduction may be sealed to the lower mouth of a dome or box, referred to as bell, assigned to be subjected to an underpressure in order to suck the softened sheet by applying heat, thereby forming a so-called ball. The bell and the ball are designed to house one or more shapes of a shaping mould for the sheet. Where the mould is provided with a plurality of shapes (as in the case here in point), the upper and lower reductions may be provided with respective upper and lower separators intended for matching with the respective upper and lower faces of the sheet, and for fitting between the shapes of the mould.

This mould is arranged underneath the reductions, and faces them, and comprises a base upon which the overlying shapes are fixed.

These known machines further comprise vertical actuator means designed to bring the mould base near to the lower reduction, up to a mutual matching, and to move the mould away, up to a condition where the shapes are completely underneath the edge of the lower reduction, such that the mould does not interfere with the insertion of the sheet between the reductions. As already seen, when the base of the mould matches with the lower reduction, either the shapes of the mould are inside the ball comprising the sucked softened sheet and the bell, or, in the absence of a bell, said shapes are at least in contact with the softened sheet, and deformed by the shapes themselves. The subsequent application of vacuum or underpressure between the sheet and the shapes and/or the possible application of overpressure between the bell and the sheet result in the perfect adhesion of the softened sheet to the shapes. The subsequent cooling down of the moulded sheet allows it to be removed and taken for the beginning of a subsequent cycle.

The lower separator prevents the sheet from excessively going down during its softening, and the upper separator facilitates the introduction of the softened sheet, either sucked into the ball or not sucked, into the space or gap between the shapes of the mould; in this way, the sheet acquires the shape of lobes separated by the separator. Moreover, the separators ensure the exact position and correct shape of the moulded sheet portion comprised between the two or more cavities formed by the shapes of the moulds. A drawback of these known machines is that they do not allow to go below certain ratios of the mutual distance between shapes and heights of the shapes, to the base of the mould; in fact, the lesser is the distance between shapes and heights of the shapes, the greater is the stretching which the softened sheet (either sucked into the ball or not sucked) must be subject to, but beyond a certain stretching the moulded sheet results to be too thin and fragile, or tears and breaks during the moulding.

Another drawback of said known machines is that two adjacent shapes, though they are sufficiently far from each other, have shapings and/or protrusions suitable for interfering with the insertion of the separators between the shapes by blocking it.

Prior art documents No. JP S60 92827 A and No. EP 1 561 565 Al disclose the features of the preamble of claim 1 of the present invention.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a machine suitable for moulding sheets having cavities and recesses, or vice versa, protrusions, being at a very reduced distance from each other, which is equal to or lower than the thickness of the separators, and which may be reduced as desired.

Another object is to provide a machine suitable for manufacturing sheets having protrusions and/or shapings of the portions facing the cavities and recesses or the protrusions of virtually any shape.

BRIEF DESCRIPTION OF DRAWINGS The features of the invention are highlighted hereinbelow, with specific reference to the accompanying drawings, in which:

- Figure 1 shows an axonometric partial view of the moulding machine for thermoplastic sheets subjects-matter of the present invention;

- Figure 2 shows an axonometric partial view of a variant of the machine in Figure 1 ;

- Figures from 3 onwards show front partial views of the moulding machine for thermoplastic sheets subjects-matter of the present invention, in an initial sheet moulding step where two shapes of the mould are drawing near to the softened sheet.

- Figures 4 and 5 show front partial views of the machine in Figure 3, in subsequent respective sheet moulding steps, in which the shapes contact the softened sheet and are in the limit conditions of maximum distance and maximum approaching from/to each other, respectively;

- Figure 6 shows a schematic, partially sectional view from a vertical plane, with the removal of some parts of the machine in the same operative step of Figure 4;

- Figures 7 and 8 show magnifications of the details VII and VIII of Figure 6; - Figure 9 shows a schematic, partially sectional view from a vertical plane, with the removal of some parts of the machine in Figure 6 in the same operative step of Figure 5;

- Figures 10 and 11 show magnifications of the details X and XI of Figure 9;

- Figure 12 shows a schematic, partially sectional view from a vertical plane, with the removal of some parts of the machine in Figure 6 in the same operative step of Figure 4;

- Figures 13 and 14 show magnifications of the details XIII and XIV of Figure 12;

- Figure 15 shows a schematic, partially sectional view from a vertical plane, with the removal of some parts of the machine in Figure 12 in the same operative step of Figure 5;

- Figures 16 and 17 show magnifications of the details XVI and XVII of Figure 15;

- Figure 18 shows a schematic, partially sectional view from a vertical plane, with the removal of some parts of an additional variant of the machine in Figure 6, in the same operative step of Figure 4;

- Figures 19 and 20 show magnifications of the details XIX and XX of Figure 18;

- Figure 21 shows a schematic, partially sectional view from a vertical plane, with the removal of some parts of the machine in Figure 18 in the same operative step of Figure 5;

- Figures 22 and 23 show magnifications of the details XXII and XXIII of Figure 21.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to Figures 1 - 11, numeral 1 indicates the moulding machine subject-matter of the present invention, for thermoplastic sheets L, for example made of one of the following materials: HIPS, ABS, TPO or PP.

These thermoplastic sheets may be brought to the softened condition by heating them up to the corresponding appropriate temperature by means of hot air insufflators, infrared or laser sources, or by means of other machine heating devices, not shown. The sheets softened at the appropriate temperature maintain their integrity and material continuity and a good thickness homogeneity, and yet may be deformed and shaped in even very complicated forms. The cooling down following the moulding tightens up the shape acquired by the sheet, and maintains it.

The machine 1 comprises a pair of frames or mounts, generally rectangular, herein generally referred to as upper 3 and lower 5 reduction means, each made of metal.

The upper 3 and lower 5 reduction means are overlapping and facing each other, and preferably lie on respective horizontal planes; such upper 3 and lower 5 reduction means are vertically movable at least with respect to each other, and are brought near to, or moved away from, each other by means of respective moving means, well- known in the art and not shown.

The upper 3 and lower 5 reduction means are provided with respective upper 7 and lower 9 protruding edges. The upper edge 7 protrudes downwards from the lower face of the upper reduction means 3, and the lower edge 9 protrudes upwards from the upper face of the lower reduction means 5, and such edges comprise vertical walls having respective planforms that are identical or almost identical, generally rectangular. In a condition of maximum mutual approaching, said free face-to-face borders of the upper 7 and lower 9 protruding edges are assigned to tighten a perimetric portion of an interposed sheet, thus blocking it or locking it therebetween, whereby they act as clamps tightening, preferably airtight tightening, the perimeter edge of the sheet.

The machine 1 further comprises a mould means 13 having a base means 15, provided with a base plate upon which there is fixed a box-like frame provided with connections for two shape means 17, 19. Alternatively, the invention provides that the shape means of the mould means may be more, e.g., three or four. These shape means may be oriented transversally or longitudinally, and may be of virtually any shape, e.g., of those in Figures 1 and 2, provided that they are suitable for not holding and for releasing the sheet moulded with the two impressions complementary to the shape means that moulded them. These impressions are joined and surrounded by an almost flat portion of the moulded sheet, hardened in contact with fixed or movable flat portions of the mould.

The shape means 17, 19 are made of metal, and are generally provided with pass- through holes for the outflow of the air trapped between them and the sheet being moulded. These holes of the shape means may be in pneumatic communication with air suction and/or blowing pumping means.

The mould means 13 is below and faces the reduction means 3, 5, and the machine is provided with vertical moving means, well-known and not shown, assigned to bring said base means 15 of the mould means 13 near to the lower reduction means 5, up to a condition of mutual matching, and to move the mould away up to a condition of maximum distance from the reduction means, so as to allow the insertion of the sheet, prior to the softening thereof, and thus in a flat, rigid state, between the upper (3) and lower (5) reduction means, removed from each other. The deformation of the softened sheet may occur as a result of a direct contact with the shape means as the reduction means 3, 5, tightened on the edges of the sheet, draw near to the base means; or, a first deformation step may be achieved as a result of the differential pressure among the faces of the sheet. To this end, the machine may be provided with a bell, or with a parallelepiped-shaped box without the lower face, with the lower edge thereof being sealed to the upper face of the upper reduction means 3. In this manner, the application of an underpressure in the bell or box results in the softened sheet being progressively sucked into the bell or box, the sheet thus acquiring the increasingly more defined shape of a lobe or a dome, as shown in Figure 3 where the bell is schematically outlined by two vertical dashed lines, also shown in Figures 4 and 5. When the lobe or dome, referred to as ball, is sufficiently large in size that it contains the shape means 17, 19, the mould means and the lower reduction means are arranged so as to match with each other, the shape means 17, 19 enter the ball, and a reversal of the pressure gradient, obtained with pneumatic means of the machine, not shown, causes the softened sheet to adhere with the upper face of the mould means, and thus with the surfaces of the shape means 17, 19.

The machine 1 may comprise an optional upper separator means 31 whose ends are connected with two parallel and/or opposed sides of the upper reduction means 3, and assigned at least to give the ball a two-lobed shaped, and to insert a respective sheet portion, included between the two lobes, in the space between the two shape means 17, 19. In the case of mould means having three or more shape means, the optional upper separators may be two or more.

The machine 1 may further comprise one or more optional lower separator means 33, connected either between or with two parallel and/or opposed sides of the lower reduction means 5, with each of them 33 being faced with a respective upper separator means 31.

At least in the condition of mutual matching of the base means 15 of the mould means 13 with the lower reduction means 5, these optional upper 31 and lower 33 separator means are interposed between two adjacent shape means 17, 19, and a portion of the sheet L is interposed between said upper 31 and lower 33 separator means.

The mould means 13 of the machine 1 is provided with a set of sliding means 25 and with a set of actuator means 27 assigned to cooperate with each other to bring or move the two shape means 17, 19, or at least two adjacent shape means, near to, and away from, each other, with a well-defined, preferably rectangular and horizontal, path. Preferably, the sliding means 25 and the actuator means 27 are housed in the base means 15, and the movement of the shape means 17, 19 is limited within the perimeter area of the base means 15 itself. Moreover, when the shape means 17, 19 are at their maximum distance from each other, in any case they are inside the inner perimeter area of the reductions, in order not to interfere therewith.

Preferably, the invention provides that the sliding means 25 and a set of actuator means 27 translate both shape means 17, 19 with respective synchronous or asynchronous motions, i.e., with motions that are simultaneous and symmetrical, having the same direction but opposite senses. Alternatively, the invention provides that one of the two shape means is fixed, and that the other one is associated with sliding means 25 and actuator means 27 that translate it so as to bring it near to, and move it away from, the fixed one.

In any case, the translation occurs between the limit conditions of maximum distance D, exemplified in Figure 4, and maximum approaching C, exemplified in Figure 5. Starting from an initial operative condition, exemplified in Figure 3, in which the upper 3 and lower 5 reduction means tighten the perimeter of a softened sheet, and the mould means 13 is in a condition of maximum distance from the reduction means, and in which the actuator means 27 set the shape means 17, 19 in a condition of maximum distance D from each other, the vertical moving means bring said base means near to the lower reduction means 5 up to their mutual matching, resulting in the matching of the softened sheet with the surfaces of the shape means 17, 19, as shown in Figure 4; subsequently, and as shown in Figure 5, the shape means 17, 19 are set in a condition of minimum distance C from each other by said actuator means 27.

Immediately before the shift from the condition of maximum distance D to that of minimum distance C, or in the latter condition C, depending on the circumstances and as required, the pneumatic means of the machine create a pressure differential that causes the softened sheet to adhere with the mould, and especially with the shape means 17, 19 and with the flat or almost flat portion of the mould, between and around said shape means 17, 19. This embodiment of the machine 1 , which provides the mobility of the two or more shape means, allows, amongst others, to mould sheets with very deep impressions and/or with a very narrow gap therebetween, whereby otherwise their making would be impossible due to an excessive thinning of the softened sheet or to a breaking thereof.

Each of the shape means 17, 19 may be provided with a respective sliding means 25, as exemplarily shown in Figure 6, or with a pair of lateral sliding means 25; alternatively, a single sliding means 25 or a single pair of face-to-face sliding means 25 may allow independent sliding of all shape means 17, 19.

Each of the sliding means 25 comprises at least one static element and at least one dynamic element, preferably fixed to the base means 15 of the mould means 13 and to the respective shape means 17, 19, respectively, and vice versa. These static and dynamic elements of the sliding means 25, for example, consist of at least one among a recirculating ball linear guide with at least one carriage, a prismatic or cylindrical guide with sliding blocks or with rolling means, a track or a channel for the sliding of at least one carriage provided with rolling means, or similar solutions for the same function.

Preferably, the machine 1 comprises one sliding means 25 for each shape means 17, 19, where each sliding means 25 comprises one or two recirculating ball linear guides fixed to the base means 15 and at least one carriage for each linear guide fixed to the respective shape means 17, 19.

Preferably, tha machine 1 comprises two actuator means 27 acting each between the base means 15 of the mould means 13 and the respective shape means 17, 19, such that each actuator means 27 moves the respective, corresponding shape means 17, 19 independently from the other. This preferred embodiment, as exemplarily shown in Figure 6, guarantees maximum operative flexibility and meets any and all moulding needs. Alternatively, the machine may comprise a single actuator means 27 acting between a respective single shape means 17, 19 and the base means 15 of the mould means 13, whereas the remaining shape means 17, 19 is rigidly fixed to the base means 15; or the single actuator means 27 may be of a type acting on both shape means 17, 19 by moving them together or almost at the same time. Each of the actuator means 27 comprises at least one static member and at least one dynamic member consisting of at least one among rack and motorized pinion; double acting hydraulic or pneumatic cylinder with single or double shaft, linear electric actuator with single or double arm; threaded motorized bar engaged with one or two female screws where the at least one static member of one actuator means 27 is fixed to the base means 15 of the mould means 13, and at least one dynamic member of the latter actuator means 27 is fixed to the respective shape means 17, 19.

Either of the optional upper 31 and lower 33 separator means, or both, which may be implemented additionally or alternatively to the sliding means 25 and the actuator means 27, and thus also on machines provided with shape means 17, 19 - where the synergistic effects produced, however, are minor and different -, may be provided with heating means, not shown, e.g., of the electrical resistance type or in which a heated fluid is circulated to heat and soften the adjacent portion of the sheet L, the latter otherwise being difficult to heat due to its position and to the fact that it may be shielded by upper 31 and lower 33 separator means. Furthermore, the invention provides that the upper separator means 31 may be of a movable kind, not shown. For example, the movable upper separator means may be of the type of a barrier that vertically rotates around a rotating horizontal constraint pin of one end thereof, and fixed to the opper reduction means 3, or of a rotating articulated type, or of an axially translating type, or of a telescopic type, or the like. This solution, for example, allows to cool down more rapidly the sheet portion adjacent to the separator means, and, above all, to remove the upper separator 31 even when in a condition of maximum approaching C, at the end of the moulding, the space between the shape means 17, 19 does not allow a vertical translation of the upper separator means.

The machine 1 may comprise a set of optional flange means 37, 39, being each interposed or interposable between a flank or side of one of the shape means 17, 19, perpendicular to the sliding means 25, and a facing internal side of the lower reduction means 5 or a facing lower separator 33.

The optional flange means 37, 39 are assigned - at least during the moulding - to fill the gaps between the upper reduction means and the shape means 17, 19 as well as between the latter, and to form a flat or almost flat surface designed for matching with the portions of sheet L, first softened and then moulded around the impressions. Each of said flange means may be fixed 37 and assigned to the sliding of a lower portion of the respective shape means 17, 19, or movable 39.

Each of the movable flange means 39 is operated between a lower position and an upper position, in which an upper flat face thereof lies on the geometric plane defined by tthe borders in mutual contact with the upper 7 and lower 9 protruding edges, and is interposed between one of the shape means 17, 19 and the lower reduction means 5 or between one of the shape means 17, 19 and a lower separator means 33. In the lower position, the flat face of each movable flange means 39 is ^' below said geometric plane.

The driving of the movable flange means 39 is achieved by respective dropping and lifting means or by transmission means of the actuator meansi 27.

The machine in Figures 6 - 11 is provided with two shape means 17, 19, each being provided with a respective sliding means 25 having a recirculating ball linear guide and carriages, and with a respective actuator means 27 comprising a pinion driven by an electric motor or gearmotor whose body is fixed to the base means 15. Said pinion is engaged with a rack parallel to the guide of the sliding means 25 and fixed to the corresponding shape means 17, 19. Apart from the pinion, each motor drives, by means of a rim, a pair of ring-shaped belts or chains, each of them being engaged with a respective secondary rim coaxially fixed to a secondary pinion.

This machine is provided with two movable flange means 39 for each shape means 17, 19. The lateral profile of these movable flange means 39 is in the form of a rectangular trapezium, the minor basis of which defines the matching face for the sheet L, whereas the inclined side is bound to an inclined guide of the lower portion of the respective shape means 17, 19 such that the face of the minor basis can move between two limit positions, one lying on said geometric plane defined by the borders of the upper 7 and lower 9 protruding edges, and the other below said plane, in which the respective movable flange means 39 does not interfere with the movements of the respective shape means 17, 19. Said inclined rack is engaged with the respective secondary pinion. In this way, not only does the driving by the motor of the actuator means 27 translate the corresponding shape means 17, 19 but also coordinately positions the corresponding movable flange means 39 such that they do not interfere with the motion of the shape means 17, 19 and form the matching plane for the portion of the sheet moulded around the impressions.

The variant of the machine shown in Figures 12 - 17 is provided with two shape means 17, 19 provided each with a respective sliding means 25 having a recirculating ball guide and carriages, and a respective actuator means 27 comprising a cylinder fixed to the base means 15 of the mould means 13, having a double acting piston and with two opposed shafts, each acting on a respective lower, lateral portion of the respective shape means 17, 19 by means of a respective connecting rod and crankshaft; the central connection pin between connecting rod and crankshaft is connected rigidly, or by means of a resilient, flexible coupling, or by means of a loop, to a corresponding movable flange means 39 bound to slide along a respective inclined guide of said lower, lateral portion of the respective shape means 17, 19. The driving, e.g., hydraulic, pneumatic or electric driving, of the shafts of an actuator 27 translates the corresponding shape means 17, 19 and coordinately positions the corresponding movable flange means 39.

An additional variant of the machine shown in Figures 12 - 17 is provided with two shape means 17, 19 and with fixed flange means 37 consisting of foils or plates fixed to the lower separator means, and upon which there are shoulders, obtained from the lower portions of the shape means 17, 19, sliding downwards. Each of the shape means 17, 19 is provided with a respective sliding means 25 comprising a recirculating ball guide and carriages and/or a plurality of guide pins fixed to a shape means 17, 19 or slidable in respective calibrated seats obtained in, or fixed to, a base means 15 of the mould means 13; said guide pins may be provided with compressed helical springs partially engaged with the seats and designed for the elastic recovery of the plays. Each of the shape means 17, 19 is further provided with a respective actuator means 27 comprising a motor or gearmotor, e.g., an electric motor or gearmotor, whose body is fixed to the lower portion of the respective shape means 17, 19; said motor drives, in an axially rotatable manner, a screw or a threaded bar axially bound to the motor and to the corresponding shape means 17, 19, and parallel with the sliding means 25 and/or with the guide pins. Both ends of the screw are engaged with respective female screws fixed to the base means 15 of the mould means 13. The driving of the motor causes the screw to rotate and causes an axial translation of the screw itself with respect to the female screws, and the consequent translation of the corresponding shape means 17, 19.