Source: http://www.sumobrain.com/patents/wipo/Apparatus-compression-moulding-preforms-synthetic/WO2005058572.html
Timestamp: 2013-05-20 17:19:06
Document Index: 86010980

Matched Legal Cases: ['arts 51', 'arts 52', 'art 51', 'art 52', 'arts 51', 'arts 52', 'art 51', 'art 52', 'art 52', 'art 51']

APPARATUS FOR COMPRESSION MOULDING PREFORMS FOR SYNTHETIC RESIN CONTAINERS - Sacmi, Cooperativa Meccanici Imola Societa' Cooperativa
APPARATUS FOR COMPRESSION MOULDING PREFORMS FOR SYNTHETIC RESIN CONTAINERS
WIPO Patent Application WO/2005/058572 Kind Code:
The apparatus is for compression moulding synthetic resin preforms by pressure-inserting a mould punch (15) into a die cavity (20a) loaded with a charge (8). The preforms (9) comprise an upper neck (91) provided with projections and a hollow body (92) positioned below the neck (91). The apparatus is characterized in that each die comprises a first tubular element (51) which is axially fixed during the charge loading and moulding stage, and a second tubular element (52) which is axially movable telescopically relative to the first tubular element (51), to assume a first position in which it projects out of the first tubular element (51) to a maximum extent in order to increase the axial dimension of the die cavity (20a), and a second position in which it is retracted into the first tubular element (51) to a maximum extent in order to define the die cavity (20a) provided for the final moulding stage, and thrust means (80) to normally maintain said second tubular element (52) in its first position, the action of said thrust means (80) being overcome during the moulding stage. Inventors:
Parrinello, Fiorenzo (122/A, Via Zanardi, Medicina, I-40059, IT) Zuffa, Zeno (6 Via Raggi, Borgo Tossignano, Borgo Tossignano, I-40021, IT) Balboni, Alessandro (10 Via Budapest, Granarolo dell'Emilia, Granarolo dell'Emilia, I-40057, IT) Application Number:
PCT/EP2004/014164 Publication Date:
Sacmi, Cooperativa Meccanici Imola Societa' Cooperativa (17/A, Via Selice Provinciale, Imola, I-40026, IT) Parrinello, Fiorenzo (122/A, Via Zanardi, Medicina, I-40059, IT) Zuffa, Zeno (6 Via Raggi, Borgo Tossignano, Borgo Tossignano, I-40021, IT) Balboni, Alessandro (10 Via Budapest, Granarolo dell'Emilia, Granarolo dell'Emilia, I-40057, IT) International Classes:
B29B11/12; B29C33/44; B29C33/48; B29C43/42; B29C43/50; B29C49/02; B29C43/08; (IPC1-7): B29C43/42; B29C43/50; B29C49/02; B29C33/48 Attorney, Agent or Firm:
Corradini, Corrado (4 Via Dante Alighieri, Reggio Emilia, Reggio Emilia, I-42100, IT) Download PDF:
An apparatus for compression moulding synthetic resin preforms by pressureinserting a mould punch (15) into a die cavity (20a) loaded with a charge (8), the preforms (9) comprising an upper neck (91) provided with projections and a hollow body (92) positioned below the neck (91), the apparatus comprising a plurality of dies to be operated by pressure inserting the punch (15) into each of them to compression mould the preform (9), characterised in that each die comprises a first tubular element (51) which is axially fixed during the charge loading and moulding stage, and a second tubular element (52) which is axially movable telescopically relative to the first tubular element (51), to assume a first position in which it projects out of the first tubular element (51) to a maximum extent in order to increase the axial dimension of the die cavity (20a), and a second position in which it is retracted into the first tubular element (51) to a maximum extent in order to define the die cavity (20a) provided for the final moulding stage, and thrust means (80) to normally maintain said second tubular element (52) in its first position, the action of said thrust means (80) being overcome during the moulding stage.
An apparatus as claimed in claim 1, characterised in that each die comprises, for forming the outer surface of the hollow body (92) of the preform (9), a first die component (21) and, for forming the outer lateral surface of the neck (91), a second die component (22) which remains associated with and secured to the first die component (21), said second component (22) comprising said axially fixed first tubular element (51) and said axially movable second tubular element (52).
An apparatus as claimed in claim 2, characterised in that said first tubular element (51) comprises an axial central cavity, said second tubular element (52) being telescopically coupled to the interior of the central cavity of the first tubular element (51) such that it can slide in an axial direction within this latter, its inner axial surface (52') defining the shape of the outer lateral surface of the neck (91).
An apparatus as claimed in claim 3, characterised in that said second die component (22) is divided into at least two sectors (23a, 23b) to be mutually withdrawn to extract the preform (9), each of said sectors (23a, 23b) being formed from a corresponding constituent part (51 a, 51 b) of the first tubular element (51) and from a corresponding constituent part (52a, 52b) of the second tubular element (52).
An apparatus as claimed in claim 4, characterised by comprising for each sector (23a, 23b) a pair of guide pieces (53) positioned at the two mutually contacting faces of each sector (23a, 23b), they securing the constituent part of the second tubular element (52) to the constituent part of the first tubular element (51) while leaving it free to slide in the axial direction.
An apparatus as claimed in claim 4, characterised by comprising for each sector (23a, 23b) at least one vertically extending elastic thrust means (80) interposed between the outer axial surface of the second tubular element (52) and the inner axial surface of the first tubular element (51), said thrust means (80) acting via one end on the first tubular element (51) and via its other end on the second tubular element (52).
An apparatus as claimed in claim 4, characterised in that said sectors (23a, 23b) of the second die component (22) are associated, when in their normally closed position, with the upper end of the first component (21) and are movable in a direction having a component radial to the axis (A) of the cavity (20a).
An apparatus as claimed in claim 4, characterised by comprising for each first die component (21) an upper surface (11a) at the upper end of the first component (21), said sectors (23a, 23b) of the second die component adherently resting on said upper surface (11a) in a manner slidingly movable on it.
An apparatus as claimed in claim 4, characterised in that each sector (23a, 23b) is joined to a pair of sliders (24) caused to slide along respective guides (25).
An apparatus as claimed in claim 7, characterised in that said pairs of guides (25) are pulled downwards in an axial direction to maintain the respective sectors (23a, 23b) of the second die component (22) in adhering contact with the first component (21).
An apparatus as claimed in claim 7, characterised by comprising elastic means (30) arranged to elastically urge sectors (23a, 23b) into their closed position.
An apparatus as claimed in any one of the preceding claims, characterised by comprising, for compression moulding the preforms, a plurality of shuttles which are mutually independent and able to be manipulated and operated by pressureinserting the punch (15) into each of them to compression mould the preform (9), each shuttle (10) comprising said first die component (21) for forming the outer surface of the hollow body (92) of the preform (9), said second die component (22) for forming the outer surface of the neck (91) being associated with and secured to the shuttle (10) and movable together with it, said second component comprising said first tubular element (51) which is axially fixed, and said second tubular element (52) which is axially movable.
A shuttle as claimed in claim 12, characterised in that each shuttle (10) comprises an upper surface (11 a) at the upper end of the first die component (21), said sectors (23a, 23b) of the second die component adherently resting on said upper surface (11a) in a manner slidingly movable on it.
APPARATUS FOR COMPRESSION MOULDING PREFORMS FOR SYNTHETIC RESIN CONTAINERS TECHNICAL FIELD The present invention relates to the compression moulding of preforms (semi-finished pieces), typically intended for the subsequent production (typically by blow moulding) of synthetic resin containers, the preform being moulded by pressure-inserting a punch (mould male part) into a hollow die (female mould part) loaded with a charge of solid, pasty or liquid material, in particular a thermoplastic resin, the preform comprising an upper neck provided with projections and a hollow body lying below the neck. More precisely, the invention relates to an apparatus having a plurality of dies for compression moulding preforms, each die being able to be manipulated and operated by pressure-inserting the punch into it to compression mould the preform. The hollow body of the preform has an externally smooth axial shape, in particular free from undercuts, and can hence be extracted with axial movement from a relative first die component, which can therefore be constructed with a monolithic body, in particular a body free from parts which have to be radially withdrawn from each other for this extraction. In contrast, the preform neck possesses projections forming undercuts which prevent its extraction from the die by simple movement in the axial direction. This means that the die must be composed not only of said first component, but also of a second die component provided to form the neck, this second component being constructed in a number of separable sectors which have to be manipulated, with consequent mechanical complications which make it advantageous to position the entire neck-forming mould part (i. e. the punch and the neck die component) on that apparatus part which inserts the punches into the dies. PRIOR ART Technical problems arise if the material charge is not completely contained within the cavity of that die part forming the hollow preform body, whether inserted into the cavity in the form of a more or less elongate cylinder or in substantially fluid (more or less liquid) form. In the first case, the cylinder necessarily has a diameter substantially less than the minimum diameter of the die, to enable it to be rapidly inserted into its interior; consequently, in particular for containers having a capacity less than about 0.3 litres, the (axial) length of the charge is greater than the cavity of the first die component, hence the charge when inserted into said cavity projects externally upwards. This results in problems and/or complications in amalgamating and combining the die components during the stage following the insertion of the charge into the first die component (and prior to inserting the punch into the die cavity), caused by the fact that the charge can project out of the cavity not only upwards but also radially (especially if pasty and hence unable to fold about itself radially out of the cavity), it hence not being possible to lower the second die component onto the first in an axial direction, because it would strike the top of the charge. Similar obstacles and complications occur in the other case, in which the charge is substantially liquid and the capacity of the cavity of that die part forming the hollow body is insufficient to contain it. DISCLOSURE OF THE INVENTION An object of the present invention is generally to increase the volume of the die cavity to enable it to receive the charge in order to solve said technical problems. Anther technical problem arises from the fact that, in producing the charge to be inserted into the die (typically by separation from a continuous shapeless mass delivered by an extruder means), (small) size differences are inevitably obtained compared with the predetermined reference size, while the volume of the (closed) mould chamber, which must be completely filled with polymer material to form the preform, is instead constant; there is hence the problem of compensating the inaccuracy in the mass of the charge compared with the reference value. Another object of the present invention is therefore to compensate the error in the charge mass in moulding the preform. These and further objects are attained by the present invention, as characterised in the claims. The invention is based on the fact that each die of the apparatus comprises a first tubular element which is axially fixed during the charge loading and moulding stage, and a second tubular element which is axially movable telescopically relative to the first tubular element, to assume a first position in which it projects out of the first tubular element to a maximum extent in order to increase the axial dimension of the die cavity, and a second position in which it is retracted into the first tubular element to a maximum extent in order to define the die cavity provided for the moulding stage, and thrust means to normally maintain said second tubular element in its first position, the action of said thrust means being overcome during moulding. According to a preferred embodiment, each die comprises, for forming the outer surface of the hollow body of the preform, a first die component and, for forming the outer lateral surface of the neck, a second die component which remains associated with and secured to the first die component, said second component comprising said first tubular element and said second tubular element. Said second die component is divided into at least two sectors which can be withdrawn from each other to extract the preform, each of said sectors being formed by a corresponding constituent part of the first tubular element and by a corresponding constituent part of the second tubular element. Preferably, the apparatus of the invention comprises, for compression moulding the preforms, a plurality of shuttles which are mutually independent and able to be manipulated and operated by pressure- inserting the punch into each of them to compression mould the preform; each of said shuttles comprises said first die component and said second die component which is permanently associated with and secured to the shuttle and movable together with it, said second component being divided into at least two sectors able to be withdrawn from each other to extract the preform, said second component comprising said first tubular element which is axially fixed, and said second tubular element which is axially movable. BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in detail hereinafter with the aid of the accompanying figures, which illustrate one embodiment thereof by way of non-limiting example. Figure 1 is a perspective view of the shuttle shown in partial section. Figure 2 is a section on the plane ll-ll of Figure 4. Figure 3 is a section on the plane III-III of Figure 4. Figure 4 is a plan view of Figure 1 from above. Figure 5 is a section on the plane V-V of Figure 3. Figure 5A shows the same section as Figure 5, but with the sectors 23a, 23b withdrawn from each other. Figure 6 is a schematic plan view of a turntable apparatus for moulding preforms by means of a plurality of shuttles according to the invention. Figures 7A-7D show a succession of stages during the formation of the preform by a plurality of shuttles according to the invention. Figures 8A and 8B show further stages in which the punch and then the preform are extracted from the die Figure 9 shows an example of a preform obtained by the illustrated shuttle. Figure 10 is an enlarged detail of Figure 7D. BEST MODE FOR CARRYING OUT THE INVENTION An example of a preform to be obtained according to the invention is shown in Figure 9. This preform, indicated by 9, is used to produce (typically by blow moulding) PET thermoplastic resin bottles and comprises a neck 91, having the final shape required for the bottle, and a hollow body 92 intended, during the production of the bottle, to form the container part of this latter. Generally, the neck 91 is provided with projections defining, for example, a radially outward projecting thread able to receive a usual screw cap. The preform is obtained by a compression moulding process in which a punch 15 (male mould element) is pressure-inserted into a hollow die (female mould part) loaded with a charge 8 of material (solid, pasty or liquid), in particular a thermoplastic resin. The die cavity 20a forms the outer surface of the preform, whereas the outer surface of the punch 15 forms the inner surface thereof. The figures and the ensuing description refer to the preferred embodiment, in which the apparatus operates by means of a plurality of shuttles 10 (i. e. mutually independent movable members) for compression moulding the preform, each shuttle comprising a main body 11 containing a first die component 21, the shuttles being not mutually constrained and being manipulated and operated within the apparatus, which pressure- inserts the mould punch into each of them to compression mould the preform. However, the invention also provides a second embodiment in which said main bodies 11, and with them the first die components 21, are constrained to move rigidly together (for example by being fixed to one and the same rotary frame of a turntable) instead of being carried by mutually independent shuttles. Essentially, the shuttle 10 of the invention comprises a main body 11 carrying and enclosing a first die component 21, the inner surface of which shapes the outer surface of the hollow body 92 of the preform 9. The main body 11 can either be separated from the first die component 11, in which case it acts only as a support therefore (as shown in the figures), or can be in one piece therewith. According to the invention, each die comprises a first tubular element which is axially fixed (at least while loading the punch and during the moulding stage) and a second tubular element 52 which is axially movable telescopically relative to the first tubular element 51. Each shuttle 10 comprises, for forming the outer surface of the neck, a second die component 22 which is permanently associated with and secured to the shuttle 10 and moves together therewith, and is formed from the first tubular element 51 and from said axially movable second tubular element 52. The first tubular element 51 is generally of an axially symmetrical tubular shape and comprises an axial central cavity. The second tubular element 52 has the shape of a tubular wall, its inner lateral surface 52'defining the shape of the outer lateral surface of the neck 91. The second tubular element 52 is telescopically coupled to the first tubular element 51 within its central cavity, such that it can slide in an axial direction within it; it also possesses a convex shoulder 521 which abuts against a corresponding undercut recess 511 provided in the first tubular element 51 when it is withdrawn to its maximum extent from this latter (see the left part of Figure 3). The second tubular element 52 can assume a first position in which it projects out of the first tubular element 51 to a maximum extent in order to increase the axial dimension of the die cavity 20a (as shown in the left part of Figure 3), and a second position in which it is retracted into the first tubular element to a maximum extent (as shown in the right part of Figure 3) in order to define the die cavity 20a provided for the final moulding stage (as further described hereinafter). This aspect is very important not only if the charge is substantially solid, but also if it is substantially liquid and has a volume greater than the volume of the cavity of the first component 21, as the charge must be able to be inserted into a cavity (the cavity 20a) having a capacity such as to contain it completely. The second die component is divided into at least two complementary sectors 23a, 23b (in the illustrated embodiments these sectors are two in number), able to be withdrawn from each other, in particular in a direction having a component radial to the axis A of the cavity 20a, to enable the preform to be extracted; when in their closed position, the sectors 23a, 23b intimately adhere to each other along two respective mating faces 23' (these faces being in particular flat and perpendicular to the direction in which the two sectors 23a, 23b approach and withdraw from each other), and also mate with the upper end of the first component 21 to give rise to the die cavity 20a which shapes the entire outer surface of the preform. Each of said sectors 23a, 23b is formed from a corresponding constituent part (51 a or 51 b respectively) of the first tubular element 51 and from a corresponding constituent part (52a or 52b respectively) of the second tubular element 52. The two (or more) constituent parts 51 a and 51 b hence form the first tubular element 51 and, correspondingly, the two (or more) constituent parts 52a and 52b form the second tubular element 52. In the embodiment illustrated in the figures, each constituent part 51a and 51 b is defined by the entire first tubular element 51 divided into two equal symmetrical parts by a plane passing through the axis A, and likewise each constituent part 52a and 52b is defined by the entire second tubular element 52 divided into two equal symmetrical parts by the same plane passing through the axis A. Each die also comprises thrust means 80 which normally maintain the second tubular element 51 in its first position, and of which the action is overcome during the moulding stage. Figure 6 shows a plurality of identical shuttles not constrained to each other, which are manipulated and handled by a turntable apparatus 40 for compression moulding the preforms. The apparatus 40 is shown in Figure 6 in an extremely schematic manner as its conformation is not critical; it can also be of a different type, for example it can be rectilinear. What is important is that the apparatus, after a charge 8 has been inserted in the cavity 20a of the die positioned in each shuttle 10, operates by pressure-inserting a punch 15 into each cavity 20a to compression mould the preform. In the embodiment shown in Figure 6, the shuttles 10 are initially inserted into the apparatus 40 by a usual rotary inserter 45 which inserts them into a feed turntable 41 pertaining to the apparatus 40, which rotates the shuttles 10 through a path slightly less than 360°. (In the second embodiment, the bodies 11 are rigidly secured to the turntable 41 and consequently rotate constantly therewith, without abandoning it). During the initial part of the path of the turntable 41, a respective charge (solid, pasty, or liquid) is inserted into the cavity 20a of the shuttles 10 by a suitable dispensing device 43 (of known type). The apparatus 40 then inserts a respective punch 15 into each shuttle 10 while this advances together with the turntable 41. The punches 15 are not shown in Figure 6, but only in Figures 7 and 8; the means for manipulating the punches 15 are not shown as these are of indeterminate type. During the final part of the path, the shuttles 10 leave the turntable 41 via a rotary extractor 46. Figures from 7A to 7D show a succession of operative stages relative to the insertion of the punch 15 with consequent compression moulding of the preform; said stages can be implemented by downwardly moving the punch (as shown in the figures), or alternatively by upwardly moving the shuttles 10. Initially, the sectors 23a, 23b which form the component 22 are in their closed position and the second tubular element 52 is raised upwards to a maximum extent relative to the first tubular element 51. By virtue of this arrangement (Figure 7A), the axial dimension of the cavity 20a and hence the volume defined by the die cavity 20a attain their maximum value, which is greater than the volume of the cavity 20a when this is in the final moulding stage (as further described below) ; the charge 8 is loaded into the cavity 20a in this first position, and even if it should project upwards from the cavity of the first component 21 (in the case of a charge of substantially solid material, as shown in Figure 5A) it would still be contained completely within the cavity also defined by the second component 22, and more so because the second tubular element is in a raised position: hence in the case of a liquid charge, its volume will certainly be totally contained within the die cavity 20a. During the next stages (Figures 7B and 7C) the punch 15 penetrates into the die cavity 20a and the charge 8 is compressed and deformed, and compelled to assume the shape of the volume defined within the cavity. During the final stage (Figure 7D), a body 16 rigid with the punch 15 presses on the upper end of the second tubular element 52 until it has reached said second position, retracted to a maximum extent into the first tubular element, so that the charge assumes the final shape required for the preform 9. The charge mass error can be compensated during this final compression stage. For this purpose, when the punch 15 attains its maximum extent of axial penetration into the die cavity, the lower end 523 of the second tubular element 52 does not make contact with the upper surface 11a of the body 11 (see Figure 10), but instead it remains at a distance (of a few tenths of a millimetre) therefrom. The punch 15 can hence vary its maximum extent of penetration into the die cavity, to consequently also vary the corresponding volume of the chamber remaining enclosed between the die and the punch (moulding chamber) and in particular vary the axial distance between the surface of the upper end 21'of the first die component 21 and the portion 522 of the inner axial surface 52'of the second tubular element 52 which faces towards the said upper end 21'. Between this surface portion 522 and the upper end 21'a circular collar 94 forms on the preform, usually used to manipulate/transport the final bottle obtained from the preform, during the filling and closure of the bottle. The charge mass error is hence compensated as the penetration of the punch 15 into the die cavity stops when the charge completely fills the moulding chamber and attains a predetermined pressure ; when this happens the punch attains a distance between said surface portion 522 and the upper end 21' (or a distance between the lower end 523 of the tubular element 52 and the upper surface 11 a of the body 11) which is greater or less than a predetermined design distance, depending on whether the mass of the charge 8 inserted into the die is correspondingly greater or less than the predetermined value. As a result, the collar 94 of the obtained preform will have a greater or lesser thickness depending on the charge error; in practice this thickness variation is of the order of a few tenths of a millimetre and in any event is of no practical consequence. In a subsequent stage of the moulding procedure (which can be relatively soon or late after the stage of Figure 7D), the punch 15 is extracted from the preform 9 while its neck 91 remains clamped between the sectors 23a, 23b of the second component 22, these being maintained in their closed configuration (see Figure 8a); during this stage, as there is no thrust of the body 16 on the second tubular element 52, this rises into said first position by the action of the thrust means 80 and lifts the preform 9 with it from the die cavity; this simplifies the subsequent withdrawal of the preform from the die. This withdrawal takes place in a subsequent stage, in which the sectors 23a, 23b are withdrawn from each other and from the preform 9, leaving this free to be extracted from the cavity 20a in an axial direction (see Figure 8B). Alternatively, after withdrawing the upper body 14 by an extent such as to release the two sectors 23a, 23b, these can be firstly withdrawn from each other to release the preform 9, which can then be extracted from the cavity 20a together with the punch 15, after which the preform can be detached from the punch 15. In the embodiment shown in the figures, the sectors 23a, 23b of the second die component 22 are located, when in their normally closed position, on the upper end of the main body 11 of the shuttle, they being associated with the upper end of the first component 21 as a continuation of it, and being movable in a direction radial to the axis A of the cavity 20a. The main body 11 of the shuttle 10 also comprises a horizontal upper surface 11a positioned at a level slightly lower than the upper end of the first die component 21, on which the sectors 23a, 23b of the second die component 22 adherently rest in a manner slidable on it. The two constituent parts 51 a and 51 b of the first tubular element 51 adherently rest on the upper surface 11 a, while the two constituent parts 52a and 52b of the second tubular element 52 lie adhering to the outside of the upper end of the first die component 21, relative to which they can slide in the direction of the axis A. For each sector 23a, 23b there are provided a pair of parallelepiped guide pieces 53 at the two mutually contacting faces 23', they being rigidly fixed to the constituent part 51 a, 51 b of the first tubular element 51 and being connected to the constituent part 52a, 52b of the second tubular element 52 so that it participates in the radial movement of the sectors 23a, 23b while remaining free to slide in the axial direction; for this purpose each constituent part 52a, 52b comprises a pair of vertical grooves 524 along which the guide pieces 53 slide (see Figures 2,5 and 5A in particular). For each sector 23a, 23b there are also provided one or more vertically extending elastic thrust means (three are provided in the embodiment illustrated in the figures), each of which consists of a linear gas actuator inserted into a cylindrical vertical recess 81 interposed between the outer axial surface of the second tubular element 52 and the inner axial surface of the first tubular element 51. The thrust means 80 act via their upper end 82 on the second tubular element 52 and via their lower end 83 on the first tubular element 51. Each sector 23a, 23b (in particular each constituent part 51 a, 51 b of the first axial element 51) is joined to pair of sliders 24 which are fixed to two opposing sides of the sector and are in the form of parallelepiped blocks caused to slide along respective horizontal parallel guides 25 consisting of rods passing through the blocks, to determine the direction in which the two sectors 23a, 23b approach and withdraw from each other. To maintain the respective sectors 23a, 23b in adhering contact with the upper surface 11 a of the main body 11, the pairs of guides 25 are constantly pulled downwards in an axial direction by a pair of vertical tie bars 27. In detail, the tie bars 27 are slidingly inserted into vertical channels 28 provided in the main body 11 and have their upper ends 28 joined to respective blocks 29, to each of which the ends of two guides 25 are abuttingly joined; the tie bars 27 are instead pulled constantly downwards by precompressed springs 26. Two pairs of elastic means 30 are applied to the body 11 on two opposing sides of each shuttle 10 in the angular position occupied by the tie bars 27, to elastically urge the sectors 23a, 23b into their closed position. Each elastic means 30 comprises a lever 31 which has a hinge pin 31 a of horizontal axis fixed to the main body 11, has one end connected by a connection rod 32 to a slider 24, and has its other end connected by a tie bar 33 to a pre-stretched spring 34. A pair of said means 30 is applied to each slider 24 to urge the sectors 23a, 23b towards the axis A. The purpose of the means 30 is to maintain the two sectors 23a, 23b urged against each other while inserting the charge 8 into the die cavity 20a. During compression of the charge 8 within the cavity 20a, the sectors 23a, 23b are locked in their closed position by means of known type, for example comprising an upper body 14 associated with the punch 15 and movable vertically relative thereto, it possessing a frusto-conical cavity 14' which mates with the likewise frusto-conical outer lateral surface 23"of the sectors 23a, 23b, or by other means able to prevent the sectors from moving apart by the pressure produced in the cavity 20a. During this compression stage, the punch 15 closes the die cavity earlier than traditional machines, as the upper end of the element 51 is initially located at a higher level ; possible discharge of plastic material is hence prevented. During the preform extraction stage (shown in Figure 8b), the two sectors 23a, 23b are gripped by known means (indeterminate and not shown in the figures) which withdraw them from each other by overcoming the thrust of the springs 34. Numerous modifications of a practical and applicational nature can be made to the present invention, but without leaving the scope of the inventive idea as claimed below. Previous Patent: MOULDS FOR THE PRODUCTION OF PLASTIC ABRASIVES AND SUPPORT THEREOFNext Patent: METHOD FOR PRODUCING INJECTION MOLDED PARTS, INJECTION MOLDING DEVICE FOR IMPLEMENTING SAID METHOD A... Privacy Policy | Terms of Use | ©