Method and machine for moulding bonded plastics material

Abstract: In moulding bonded plastics material, in particular expanded polystyrene in combination with rigid sheet polystyrene, the rigid material (2) is firstly preformed, while simultaneously separating the preformed portion from the starting material, and the preformed piece is transferred to the moulding stage while contained in the preforming half-mould (33). While the expanded material is being moulded by sintering and the pulse action of steam, the previously moulded piece (P) is discharged. The preforming half-mould (33) is moved alternately between the preforming position and the moulding position, to cooperate with relative counter-moulds (36, 41). The scrap is recovered without being involved in the moulding stage.

Description: This invention relates to a method and machine for moulding bonded plastics material, in particular expanded plastics material in combination with rigid plastics material, such as expanded polystyrene with rigid sheet polystyrene. For moulding these materials, which requires the application of steam to sinter the expanded plastics material, with its simultaneous adhesion to the rigid material, it is already known from Italian patent No. 1,185,507 to use a mould consisting of two half-moulds which together define a moulding cavity for housing the two materials, one of which, namely the more rigid sheet material, is firstly preformed in contact with only the lower half-mould, the other material then being moulding onto the first by sintering in the closed mould. In this method, the rigid sheet plastics material is retained at its end edges and then firstly hot-deformed by moving the relative half-mould beyond the plane of the sheet material, after which the material is made to adhere exactly to the half-mould by creating a vacuum between the half-mould and the material. The upper half-mould is then lowered and the expanded plastics material is moulded within the resultant cavity, steam being applied in pulses alternating with the application of vacuum, to enable the expanded material to sinter onto the more rigid material. This known method and apparatus have the advantage of requiring only a single mould consisting of two half-moulds movable relative to each other, with resultant constructional advantages. However, a vacuum application stage for preforming is still required, as otherwise it would not be possible to make the more rigid material adhere perfectly to the shape of the preforming half-mould, there being no corresponding counter-mould in that the one provided has a shape which corresponds instead to the part to be moulded in expanded material. Vacuum application alone is not always able to produce the required shape, especially in the case of the more complex mould shapes, as in such cases it is difficult to cause the material to adhere to the mould at every point. To overcome this difficulty, preforming has to be effected in a mould separate from the main mould, however this complicates the apparatus because of the larger number of components and the consequent more complicated handling of these and of the material. A further drawback of the known method and apparatus is that those portions of the material which are peripherally clamped undergo inevitable alteration during moulding and have mostly to be discarded as they cannot be recycled, this representing a substantial material wastage and posing disposal problems. GB-A-1447110 discloses an apparatus in which all the steps of manufacture of a foamed article having a plastic skin bonded thereto are performed automatically in a mould cavity formed between a pair of closed complementary moulds clamped in a simple stationary moulding machine, which cavity is not opened until the article is finished. DE-A-3637660 relates to a machine consisting of at least two moulding cavities and half-mould being displaceable between them, the two stages of preforming and forming of the expanded plastics material being performed in the two different stations (i.e. moulding cavities). The object of the present invention is to overcome the drawbacks and limitations of the known method and apparatus by providing a method and machine for moulding bonded plastics material which does not require a preforming stage effected exclusively by vacuum, and in addition does not require doubling of the mould arrangement, ie the provision of one mould for preforming the rigid material and one for moulding the expanded plastics material onto the rigid material, hence resulting in a constructionally and operationally simplified arrangement. A further object is to provide a method and machine which enable the scrap material to be recovered without it undergoing alteration during the preforming and/or moulding operations. The term "rigid" is to be understood herein in a relative sense, as a material having generally higher intrinsic rigidity characteristics than the plastics material to which it is bonded; this term therefore also covers a material in thin sheet form. These objects are attained according to the present invention by a method for moulding bonded plastics material, in particular expanded plastics material in combination with rigid plastics material, according to claim 1. To implement the method according to the invention a machine for moulding bonded plastics material is proposed according to claim 7. A method and machine of the invention have the advantage of providing perfect preforming in that a counter-mould is used in this stage, and in addition the structure is simplified compared with a machine comprising separate preforming and moulding counter-moulds, as the present invention uses a single half-mould for both preforming and moulding, and only this half-mould has to be moved. As this half-mould moves with only the preformed material portion, and hence separated from the feed material, the scrap can be advantageously carried to recovery without it undergoing any contamination by lubricants, detaching agents, expanded material beads or other substances, so that the scrap can be recycled. In addition the scrap cutting operation after the moulding has been unloaded from the machine is eliminated. Special means for clamping the edges of the rigid material are not essential as the half-moulds themselves can advantageously clamp the material during preforming, and in addition special means for transferring the preformed material between the moulds are not required, as the actual half-mould itself effects the transfer. Further details and advantages of the invention will be more apparent from the detailed description of a preferred but not exclusive embodiment thereof given hereinafter and illustrated on the accompanying drawings, in which: Figure 1 is a side elevation of a machine according to the invention; Figure 2 is a schematic plan view of the same machine with certain parts removed for simplicity; Figure 3 is a front view of a part of the machine of the preceding figures, limited to only the preforming mould; Figure 4 is an enlarged side elevation of a part of the machine, showing the zone comprising the preforming and moulding moulds; Figure 5 is a view to a larger scale than the preceding figures showing a part of the preforming mould at the moment of preforming; Figure 6 is an indicative scheme of the centralized control section for controlling the operations involved in moulding a piece of bonded plastics material; Figures 7 to 12 schematically illustrate the successive operating stages in obtaining a piece of bonded plastics material by the method and machine of the invention. With reference firstly to Figures 1 to 3, a machine for moulding bonded plastics material, such as an expanded plastics material, in particular expanded polystyrene, in combination with a rigid plastics material, in particular rigid sheet polystyrene, comprises substantially a preforming station 1 for the rigid plastics material 2, a moulding station 3 for moulding the expanded plastics material onto the preformed material, a station 4 for feeding the rigid material 2 to the preforming station 1, and means 5 for feeding the expanded plastics material to the moulding station 3. The machine also comprises a discharge station 6 and, if the rigid plastics material 2 requires it, a preheating station 7 positioned upstream of the preforming station 1. The moulding station 3 also comprises means 8 for pulse-feeding steam for sintering the expanded plastics material, in accordance with a known method, for example as described and illustrated in the cited Italian patent 1,185,507 and feed means 9 for a cooling fluid. The feed station 4 comprises means for feeding the rigid plastics material 2, consisting essentially of a roller 10 for unwinding the material 2 and a roller 11 for winding the scrap 12, the roller 11 being rotated intermittently by a motor 13 controlled by a control centre indicated schematically by 14 (see Figure 6). The material 2 is guided by guide means 15 at least at the preforming station 1, and advances in the direction of the arrow F1. The preheating station 7 is preferably formed from a preheater 16, in particular of infrared type, supported and guided transversely (arrows F2 in Figure 2) to the direction of movement of the continuous material 2 by a guide member 17 between an operating position overlying the material 2 (position indicated by full lines in Figure 2) and a rest position offset to the side thereof (position indicated by dashed lines in Figure 2). The number of heater elements 18 and/or their power and/or the residence time of the preheater 16 above the material 2 are obviously chosen according to the material and the preforming requirements. The preheater 16 is driven for example by a motor 19 and a belt 20 which is connected at one point to the preheater and deviated about a fixed shaft supported in position within the structure 17. The motor 19 is also controlled by the control centre 14. The preforming station 1 and moulding station 3 comprise substantially a plurality of spaced-apart vertical columns 21 fixed to a plate-type base 22 and along which there slide relative sleeves 23 with which there is rigid a horizontal platform 24, which can therefore be raised and lowered vertically, for example by means of toggle mechanisms indicated overall by 25, driven in pairs by respective motors 26 which are also controlled by the control centre 14. A table 27 of length substantially equal to the longitudinal horizontal dimension of the two stations 1 and 3 is slidable horizontally on the support 24 in the direction of the arrow F3, ie substantially perpendicular to the direction of advancement F1 of the rigid material 2 in the illustrated embodiment. The table 27 is driven by a motor 28 via a belt 29 connected to a point on the table 27 and deviated about a fixed shaft 30, the table 27 being guided on longitudinal guides 31 fixed to the support 24 and slidingly engaged by respective slide blocks 32 of the table 27 within the two rows of columns 21. The table 27 carries on its left side (Figure 1) a preforming half-mould 33 and on its right side a resting platform 34, possibly spring-loaded (springs 35), for the moulded pieces P. The preforming half-mould 33 cooperates in the preforming station 1 with a counter-mould 36, which in the illustrated embodiment is vertically movable via sleeves 37 slidable on the columns 21, but could also be fixed. The configuration of the facing impressions of the half-mould 33 and counter-mould 36 is such that when in the preforming position, ie with the mould closed, they define a preforming cavity corresponding to the shape to be given to the preformed portion of material 2. The counter-mould 36 is movable for example hydraulically by means of a cylinder-piston unit 38, of which the cylinder is fixed to a cross-member 39 of the preforming station 1, and the piston is rigid with the counter-mould 36. Its operation is controlled by the control centre 14. The half-mould 33 can be provided with temperature control systems and with systems for applying a vacuum to the impression, via suitable passages. According to one characteristic of the invention, separation or cutting means, best visible in Figure 5, are associated with the counter-mould 36 and consist of blades 40 arranged in such a manner as to separate from the rigid material 2 the portion to be preformed, by cutting it away peripherally during the preforming stage, as described hereinafter. The moulding station 3 is formed from a fixed half-mould 41 of known type for moulding expanded material by steam pulses, for example as described in the cited Italian patent 1,185,507. The drawing therefore illustrates only some generally typical components of this mould, such as the feeders 42 for the material 43, connected to a material container 44, the steam feed pipes 8 and the cooling pipes 9 which terminate in sprayers 45. Condensate discharge means and means for creating a vacuum in the moulding cavity are also provided. The reference numeral 46 indicates the impression which cooperates with the impression in the preforming half-mould 33 to define the moulding cavity for the two bonded materials (rigid + expanded). Said mould also comprises expulsion devices, of known type and therefore not shown in detail, for discharging the moulded pieces P. To the side of the moulding station 3 there is a discharge station 6 comprising substantially a pusher element 47 operated for example pneumatically by a cylinder-piston unit 48 controlled by the control centre 14 in a direction perpendicular to the direction of movement of the table 27, and a conveyor belt 49 or other conveyor device. The conveyor belt 49 has its upper branch at the level of the resting platform 34 (when the table 27 is in its raised position), on which the pusher 47 also operates, so that the belt 49 receives the moulded pieces P from said platform 34 and conveys them to a collection device, not shown, in a direction parallel to the feed direction of the material 2. The belt 49 winds about a roller 50 and is driven intermittently by motor means 51 together with the pusher element 47. As shown schematically in Figure 6, all the drive members for moving the various previously described movable elements of the machine are controlled by a control centre 14 in a predetermined sequence, as will now be described with reference to Figures 7 to 12. The first stage in the moulding of the bonded material is the preforming of the rigid plastics material 2. For this purpose the material 2 in strip form is fed through one step and, if necessary, preheated below the preheater 16 positioned in its operating position for a predetermined time, after which the preheater is withdrawn into its rest position. Figure 7 schematically illustrates the situation slightly before preforming. With its next step the material 2 reaches its preforming position in the relative mould 1. The motors 26 and the hydraulic device 38 are operated simultaneously by the control centre 14 to bring the two half-moulds 33 and 36 into contact with each other substantially in the plane of the material 2 (Figure 8). This is deformed into the shape of the impressions of the two half-moulds, the preformed portion being simultaneously cut away from the material strip 2 along a perimetral line by the blades 40. In the illustrated example two pieces are preformed simultaneously, so that two portions 52 are cut away from the strip (Figure 2), while the scrap 12 remains in a continuous piece and with the subsequent advancement steps of the material 2 is wound onto the roller 11, and can be advantageously recycled after suitable treatment. During the preforming, for which it may be convenient to use vacuum even though this is not essential, the previously moulded piece P is retained in the fixed half-mould 41, present in the moulding mould 3. When the rigid material 2 has been preformed, the control centre 14 gives the command for separating the half-moulds 33 and 36, and simultaneously operates the members for expelling the piece from the half-mould 41. With the consequent lowering of the table 27 the preformed portion is retained on the half-mould 33, while the previously moulded piece P is released from the half-mould 41 and remains on the support platform 34 (Figure 9). When the table 27 attains its lowered position the control centre 14 transmits a command to the motor 28 to move the table 27 towards the right in Figures 7 to 12, to position the half-mould 33 with the preformed piece below the fixed half-mould 41 and position the support table 34 within the discharge zone (Figure 10). The command for raising the table 27 is now given and the half-moulds 33 and 41 come into contact to define the cavity for moulding the expanded plastics material by the already known method, the material being injected by the feeders 42 into the moulding cavity, and the steam being pulse-fed into the half-mould 41 to sinter the material and bond it to the preformed rigid material, while the pusher 47 is operated to push the prepared piece P, moulded during the previous stage, onto the discharge belt 49 (Figure 11). When the moulding stage is concluded, the table 27 is lowered and the mould 3 opened, the moulding piece P however being retained in the upper half-mould 41, for example by vacuum. This temporary retention of the piece P in the upper mould 41 can advantageously serve to complete the sintering or cooling operations while the half-mould 33 is moved into the position for preforming the next piece. The strip material 2 has in the meantime been advanced through one step. It will be apparent that the machine is now in position for a further preforming and moulding operation, and the aforedescribed cycle can be repeated. For these operations a single half-mould is used, to be moved into cooperation with two half-moulds (one for preforming and one for moulding), the moulding being performed on the rigid material portion after it has been already separated from the feed strip, so that the residual material is in no way subjected to transformation or action which can deteriorate it and make it no longer suitable for reuse or recycling. The particular arrangement of the moulds in relation to the feed and discharge makes the machine particularly rational and of small overall size. It should be noted that the same results can be obtained by making the half-mould 36 fixed, hence further simplifying the machine. As the preformed material is fed to the moulding stage on the same preforming half-mould, additional means for transferring the material between the preforming and moulding stages are not required, and in addition the movement of the fed material is sufficient to recover the scrap. Moreover, the method and machine according to the invention enable bonded material to be moulded in which the rigid material is of very small thickness. The machine achieves high productivity, even though the preforming and moulding stages take place not simultaneously but in succession. It should however be noted that the preforming time is much shorter than the moulding time, it hence being this latter which substantially determines the duration of a moulding cycle. As it is in any event necessary to transfer the material from the preforming to the moulding operations, the additional time due to the preforming represents a negligible factor compared with the other advantages of a constructional character which the machine of the invention offers. As is apparent from the drawings, the machine is suitable for the simultaneous moulding of several pieces and/or can be easily adapted in this sense. Modifications can be made in addition to those already described. For example, the table 27 could be raised hydraulically. The pusher 47 could be operated slightly before or after the moulding stage (by arranging the pusher 47 and the belt 49 at the height which the table 27 occupies when in its lowered position). The feed of the rigid material 2 and/or the discharge of the finished pieces P could be in line with the moulds 1 and 3. The movement of the table 27 could also be achieved by a rack and pinion system. It would also be possible to reverse the position of the half-moulds 33, 36 and 41 in the sense that the horizontally traversable half-mould could be arranged above the other two.

Claims: A method for moulding bonded plastics material, in particular expanded plastics material in combination with rigid plastics material, in which the rigid material (2) is firstly preformed in a first mould (1) defined by a counter-mould (36) and a movable half-mould (33), the rigid plastics material (2) is continuously fed and continuously recovered in the form of material (12) from which the potions (52) to be preformed have been cut away, said recovered material (12) constituting scrap material conveyed to recovery, the method being characterized in that the expanded plastics material is moulded onto the moulded rigid material by steam applied in pulses in a second mould (3) defined by said movable half-mould (33) and a fixed half-mould (41), said portion (52) of the material to be preformed is completely separated from the rigid starting material (2) during the preforming, the preformed material being transferred to the moulding stage within the preforming half-mould (33), and in that the rigid plastics material (2) and the scrap material (12) are advanced in a direction (F1) perpendicular with respect to the direction (F3) of transfer of the preforming half-mould (33) between the preforming stage and the moulding stage. A method as claimed in claim 1, characterised in that the moulded piece is retained in the moulding position while the preforming half-mould (33) returns to the preforming station (1). A method as claimed in one of the preceding claims, characterised in that the moulded piece is released from the moulding station (3) after the next piece has been preformed. A method as claimed in one of the preceding claims, characterised in that the moulded piece is transferred to a discharge station while the next preformed piece is transferred to the moulding station (3). A method as claimed in one of the preceding claims, characterised in that the rigid plastics material (2) is preheated prior to the preforming stage. A method as claimed in claim 5, characterised in that the rigid plastics material (2) is preheated by infrared rays. A machine for implementing the method claimed in one of the preceding claims, comprising a mould (1) for preforming a rigid plastics material (2) and a mould (3) for moulding an expanded plastics material onto the rigid plastics material, means for feeding the rigid plastics material to the preforming mould (1) and means (5) for feeding the expanded plastics material to the moulding mould (3), plus means (8) for applying steam in the form of pulses to said moulding mould, furthermore comprising means (40) for separating the portion of material to be preformed associated with said preforming mould (1) and operating conjointly with the preforming mould (1), further comprising recovery means for recovering scrap material coming out of said preforming mould, said means (40) extending along the entire edge of the portion to be separated, the machine being characterized in that the two moulds (1, 3) have a single movable half-mould (33) associated successively in time with relative preforming and moulding countermoulds (36, 41), whereby said counter-mould (36) and said half-mould (33) are vertically slidable, said feed means and recovery means are independent from said movable half-mould (33) and in that said half-mould (33) is horizontally movable in a direction (F3) perpendicular to the direction (F1) of advancement of the rigid plastics material (2). A machine as claimed in claim 7, characterised in that said feed means for the rigid plastics material (2) comprise a roller (10) for upwinding the material (2) and said recovery means comprise a roller (11) for winding the scrap material (12), plus a guide (15) for guiding the material between said rollers (10, 11), A machine as claimed in claim 7, characterised in that the moulding countermould (41) is fixed and is associated with said means for feeding the expanded plastics material and the steam. A machine as claimed in one of claims 7 or 9, characterised in that said movable preforming half-mould (33) is carried by a table (27) slidable horizontally on a vertically movable support (24). A machine as claimed in claims 10, characterised in that said horizontally movable table (27) also comprises a resting platform (34) for the moulded pieces (P), said moulding mould (3) comprising expulsion means (6, 47) operable conjointly with the preforming stage of said preforming mould (1). A machine as claimed in claim 10, characterised in that said support (24) is operable by toggle mechanisms (25). A machine as claimed in one of the preceding claims, characterised in that means (7) for preheating the rigid plastics material (2) before entering the preforming mould (1) are provided. A machine as claimed in claim 13, characterised in that said means (7) for preheating the rigid plastics material (2) comprise a preheater device (16) positioned upstream of the preforming mould (1). A machine as claimed in claim 13, characterised in that said preheater device (16) is movable between an operating position overlying the feed material and a rest position laterally offset from it. A machine as claimed in claim 13 or 14, characterised in that said preheater device is of infrared type.

Inventors: VISMARA MARIO, VISMARA, MARIO
Applicants: DEVI SPA, DEVI S.P.A.
Application year: 1992
Main classification: B29C44
IPC codes: B29K105, B29C33, B29C44, B29C67