MACHINE FOR PRESSURE-INJECTING SYNTHETIC RESIN MIXED WITH REINFORCING FIBRES INTO A USER MEANS

Abstract: A first screw conveyor (10) advances synthetic resin material within a conveying channel (13), and a second screw conveyor (20) advances fluid synthetic resin under pressure and mixes it with reinforcing fibres within a respective conveying channel (23); for pressure-injecting the material into the user means there is provided a chamber (30) having a thrust piston (31) axially slidable within the chamber (30) to discharge the fluid material under pressure through said exit (32). A first conduit (41) connects the final end of the channel of the first conveyor (10) to an intermediate point of the channel of the second conveyor (20), to transfer the fluid material from the first channel (13) to the second channel (23), and a second conduit (42) connects the exit end of the second conveyor (20) to the injection chamber (30); means are provided for axially driving the thrust piston (31) to compress the injection chamber (30).

Description: MACHINE FOR PRESSURE-INJECTING SYNTHETIC RESIN MIXED WITH REINFORCING FIBRES INTO A USER MEANS This invention relates to a machine for injecting synthetic resin mixed with reinforcing fibres into a user means under high pressure. The technique of mixing mineral or synthetic fibres (in particular glass fibres) with synthetic resin in order to considerably improve its mechanical properties, in particular its tensile strength, has been long known. In the known method, to inject synthetic resin (in particular thermoplastic) material into a user means, in particular into an injection mould, a mixture of synthetic resin in the fluid state and reinforcing fibres is firstly formed by co-rotating screw conveyors, in which the fibres, in the form of short regular homogeneous fibres are mixed with a mass of synthetic resin (in particular thermoplastic) in the fluid state. These fibres have to be relatively short (less than 10 mm in length) because of the intrinsic difficulties involved in handling masses formed from fibres of relatively large length (as these tend to bind together to form poorly flowable soft interwoven masses). This mixture is then cooled and reduced to small granules, and is stored, handϊed and transported in this state. Finally, the resin in granule form is fed into appropriate injection machines in which it is again brought to the liquid state by heating, and then injected into the user means (injection mould) by a thrust piston. An object of this invention is to provide a machine able simultaneously to form the resin-fibre mixture and to inject this mixture into the user means. This and further objects are attained by the invention as characterised in the claims. The invention is based on the fact of comprising: a first screw conveyor arranged to advance and to fluidize synthetic resin material within a respective conveying channel, a second screw conveyor arranged to advance fluid synthetic resin material under pressure and to mix it with reinforcing fibres within a respective conveying channel comprising a fibre feed device arranged to feed the fibres into the conveying channel, a chamber provided with a material exit to be connected to the user means for pressure-injecting the material into this latter and having a thrust piston axially si idable within the chamber to discharge the fluid material under pressure through said exit, a first conduit connecting the final end of the channel of the first conveyor, upstream of. the injection chamber, to an intermediate point of the channel of the second conveyor, upstream of its exit, to transfer the fluid material from the first channel to the second channel , a second conduit connecting the exit end of the second conveyor to the injection chamber, to transfer the material from the second conveyor to the injection chamber, means for axially driving the thrust piston to compress the injection chamber, the machine operating cyclically in such a manner as to: fluidize a synthetic resin material by means of the f i rst conveyor within its conveying channel, feed this fluid material from the first to the second conveyor via the first connection conduit, mix this fluid material with fibres within the second conveyor, feed this fluid material mixed with fibres to the injection chamber via the second connection conduit, finally, compress the injection chamber by driving the thrust piston in the downstream direction to inject the material into the user means. In a preferred embodiment, the first conveyor comprises: a conveying channel the downstream end part of which defines the injection chamber, within which the thrust piston is siidingly movable, a helical screw-compris ng shaft axially movable within the conveying channel, and means for axially moving said shaft in the downst ream direction'against the thrust piston, said compression of the injection chamber to inject the material into the user means being achieved by moving the shaft of the first conveyor in the downstream direction. The invention eliminates various changes of state of the plastic material (passage from fluid to solid state and vice versa), with consequent improvement in material qual i ty. An energy saving is also achieved because less heat is used in liquefying the material. Plant capital and operating costs are also reduced as both the plant and its operation are simplified. Machines able to form a mixture from synthetic resin material and relatively long fibres (exceeding 20 mm in length) can also be used. The invention is described in detail hereinafter with the aid of the accompanying figures, which illustrate a non-exclusive embodiment thereof by way of non-limiting example. Figure 1 is a perspective view of the machine of the invention. Figure 2 is a partly sectional view of the machine of Figure 1 taken from above, in a first operating position. Figure 2A shows the same view as Figure 2 but in a second operating position. Figure 2B shows the same view as Figure 2 but in a third operating position. Figure 4 is a front view, in the direction of the arrow IV of Figure 2. The machine of the invention comprises a first screw conveyor (indicated overall by 10 i n the figures) having its auger consisting of a shaft 11 with a surrounding helical screw 12 and arranged to rotate within a cylindrical conveying channel 13, the surface of which substantially adheres to the profile of the helical screw, and which extends axially within a cylindrical casing 14 defining the shell of the channel 13. In the upstream region of the conveyor 10 there are provided means (of known type) for rotating the shaft 11, and a hopper 16 for feeding solid synthetic resin material (in small pieces) to the channel 13. On the outer surface of the shell 14 there are provided heating means, in particular heating panels 140, for heating the channel 13 to a temperature such as to maintain the thermoplastic resin processed in its interior in a fluid state. By the action of the screw 12 and the heating means 140, the conveyor advances and mixes the synthetic resin material within the conveying channel 13, fluidizing it by the means 140. The final downstream part 13 ! of the channel 13 proceeds without interruption beyond the downstream end of the conveyor 10 to define a cylindrical cavity which terminates with a final surface 30' comprising a material exit 32 connected to the user means, and within which there is positioned an axially slidable thrust piston 31 sealing against the part 13'. Within said final part 13' the piston 31 defines between itself and the final surface 30' a closed chamber 30 for injecting the fluid material under pressure through the exit 32 and into the user means. The chamber 30 is cylindrical and has the same cross-section as the entire channel 13. The volume of the chamber 30 varies as the axial position of the piston 31 varies, this latter compressing the chamber 30 when driven downstream, to discharge the material under pre'ssure through said exit 32. The exit 32 is positioned at the final end of the chamber 30, and is connected to the material user means 33, in particular to an injection mould (of which only a portion is shown in the figures). In detail, the final surface 30' is conical, with its axis coinciding with the axis of the chamber, the exit 32 being positioned at its vertex. The piston 31 has a first portion 31a of cylindrical surface which sealedly slides against the surface of the chamber 30, a conical front end portion 31c which mates with the final surface 30' of the chamber 30, and an intermediate portion 31b of cylindrical surface positioned downstream of the first portion 31a and having a diameter less than the chamber 30, to create an annular interspace with the surface of this latter. The conveyor 10 also comprises means (of known type, not shown in the figures) positioned in the upstream region to axially move the shaft 11 in the downstream direction against the thrust piston 31, to compress the injection chamber 30 and inject the material into the user means 33 via the exit 32. To the downstream end of the shaft there is fixed a shut-off means 35 (see Figure 2A) arranged to close the cross-section of the conveying channel 13 and the injection chamber 30, and comprising in its interior a valve means 36 to prevent passage of the fluid material in an upstream direction but to allow it to pass downstream. Specifically, the valve means 36 comprises a duct 37 enabling fluid to pass through the shut-off means 35 from one side of it to the other. Within the duct 37 there is provided a valve seat 38 with its concavity facing downstream and on which there acts a ball valving element 39 subjected to the thrust of the flow passing through the duct 37. When the flow is directed from upstream to downstream, the valving element 39 is urged against the seat 38 to close the passage. In contrast, when the flow is directed downstream the valving element withdraws from the seat 38 to open the passage. " An intermediate chamber 19 is defined within the final part 13', between the shut-off means 35 and the piston 31. The machine of the invention also comprises a second screw conveyor 20, arranged to mix fluid synthetic resin material with reinforcing fibres within a respective conveying channel 23 and to cause it to advance under pressure. This conveyor is preferably constructed in accordance with the teachings of Italian patent application RE99A000111 filed on 10.11.99 and entitled "Machine for forming mixtures of synthetic resin and reinforcing fibres". In detail, the screw conveyor 20 comprises two counter-rotating augers, each of which consists of a shaft 21 with a surrounding helical screw 22. The shaft axes are parallel and lie in the same horizontal plane. The profiles of the helical screws 22 intersect along the central part but (obviously) do not touch the adjacent shaft 21. One auger rotates right-handed and the other left- handed and are counter-rotating, so as to convey the material in the same direction. The direction of rotation is such that the helical screws rotate upwards along the central part (within whicn the profiles intersect). The augers are inserted into a corresponding pair of channels 23' and 23", which together define the said conveying channel 23, and which intersect and substantially adhere to the profile of the helical screws 22, except along the central part where the two channels intersect. The two channels 23' and 23" are provided within an uninterrupted cylindrical shell 24, which defines the channel wal 1. In the upstream region of the conveyor 20 there are provided means 25 (of known type) for rotating both the shafts 21. The initial (upstream) part, indicated by A, of the conveyor 20 is used to firstly feed and then drive the fed reinforcing fibres and comprises, for feeding the fibrous material to the channel 23, an entry port having its axis perpendicular to the horizontal plane defined by the axes of the two screw shafts 21. Above this entry port there is a reinforcing fibre feed device 26 which feeds the fibres into said initial part of the screw conveyor 20 via the entry port. Specifically, the feed device 26 comprises a hopper 27 to receive and contain a mass of the fibrous material, and two rotary means 28 of parallel horizontal axis, each of which comprises a shaft 281 driven by a respective motor 283 and carrying at last one and preferably two elastic blades 282. The material mass formed from reinforcing fibres (possibly together with inert fillers in powder or small piece form) is fed loose into the hopper 27, through which it tends to fall by gravity, to pass through the entry port and i nto the space between the helical walls of the screws 22 about the shafts 21. The action of the rotary means is here particularly effective in that, during their rotation, the blades 282 interfere with the lower portion of the hopper 27 and undergo flexure. When they subsequently rise to a higher level where they are immersed in the mass of fibrous material lying in the hopper 27, they el stically assume their normal profile to suddenly (in the manner of a loaded spring) strike the mass of reinforcing fibres accumulated in that region above the entry port, to displace it and mix it with an effectiveness which has been found experimentally to greatly facilitate the descent of the reinforcing fibres through the entry port. By virtue of the described characteristics, the reinforcing fibres then fall into the initial part A of the conveyor 20, to be distributed and fill the free spaces between the helical walls of the screws 22. Here , the rotation of the screws 22 firstly drags the reinforcing fibres into rotation on the outer walls of the channels 23' and 23" and then in their lower region, where they finally encounter a closed part of the channel 23 with the result that the rotation of the screws 22 then causes the material to advance axially along the channel 23. The machine of the invention comprises a first conduit 41 connecting the intermediate chamber 19, upstream of the injection chamber 30, to an intermediate point of the channel 23 of the second conveyor 20, to transfer the fluid material from the first channel 13 to the second channel 23. Said connection conduit 4ι opens into the downstream end of the initial reinforcing fibre feed and thrusting part A of the conveying channel 23. Said conduit 41 consists in particular of a pipe which connects a through hole 44 provided in the shell 14 in a point immediately upstream of the final part 13' and communicating with the intermediate chamber 19, to a hole 45 provided in the shell 24. Downstream of the part A, the conveying channel 23 continues, to define a further part B within which the plastic material and the reinforcing fibres are mixed and conveyed. This part B preferably comprises a portion (not shown in the figures) in which the screws 22 are shaped to produce effective homogeneous mixing of the fibre-resin mixture, followed by a portion (also not shown in the figures) in which the screws 22 are shaped to produce an effective axial thrust. A second conduit 42 is also provided connecting the exit end of the second conveyor 20 to the injection chamber 30, to transfer the material from the second conveyor 20 to the injection chamber 30. Said connection conduit 42 consists in particular of a pipe which connects the exit 47 of the second conveying channel 23 to a hole 48 provided in the chamber 30, in correspondence with the intermediate portion 31b of the piston 31, when this latter lies in its final axial position adhering to the final surface 30' of the chamber 30. A valve 51 controlled by an external actuator (not shown) is positioned in the conduit 42, to open and close the connection to the chamber 30. Heating panels 430 and 460 are positioned on the outer surface of the conduits 41 and 42 respectively. Identical heating panels 240 are positioned on the outer surface of the cylindrical shell 24 of the second conveyor 20. These panels are arranged to heat the members on which they are fitted to a temperature such as to maintain in a fluid state the thermoplastic resin being processed in thei r interior. The machine operates cyclically, in the following manner. The piston 31 is movable between an initial axial position (shown in Figure 2) in which its upstream end lies in correspondence with the hole 44, and a final axial position (shown in Figure 2A) in which it lies against the final surface 30'. The shaft 11 of the first conveyor 10 is axially movable between an initial axial position (shown in Figures 2 and 2B) in which it is completely retracted within the conveying channel 13, and a final axial position (shown in Figure 2A) in which it is in or nearly in contact with the piston 31 lying in its final position. At the beginning of the cycle (Figure 2) the shaft 11 and the piston 31 are both in their initial axial position. In this axial position, the piston 31 is in or nearly in contact with the shut- off means 35 (the volume of the intermediate chamber is a minimum), with those of their ends in or nearly in mutual contact lying in correspondence with the hole 44. The internal space within the connection conduits 41 and 42, the chamber 19, the chamber 30, and that part of the channel 23 downstream of the hole 45 is filled with synthetic resin, and the piston 31 is immersed in the resin. Firstly, the shaft 11 is moved axially in the downstream direction, without rotating, until in its final axial position, in order to thrust the piston 31 in a downstream direction and into the injection chamber 30, until it reaches its final axial position against the final surface 30' (Figure 2A). During this stage the * valve 51 closes the connection between the chamber 30 and the second conveyor 20, this being maintained inactive. As a result of said movement, the injection chamber 30 is compressed and the material contained in it is discharged through the exit 32 and injected into the user means 33. The shut-off " means 35 does not need to be in contact with the piston 31. On the contrary, the intermediate chamber 19 can have a small volume, filled with fluid material (which is practically incompressible), in that the valve 36 closes the passage through the shut-off means 35, and hence the piston is thrust by the material filling the chamber 19. In the next stage (second stage) the shaft 11 of the first conveyor 10 is rotated until the shaft 1 1 has moved rearwards into its initial axial position (shown in Figure 2), its rotation then being halted. The piston however remains at rest against the final surface 30' . During this stage the rotation of the helical screw 12 causes the material to advance along the screw. This material passes through the shut-off means 35 (the valve 36 is open) and enters the intermediate chamber 19, with the result that as the piston 31 is in its end-of-travel position against the surface 30 "' and the chamber 19 is filled with material, the rotation of the helical screw 12 causes axial retraction of the screw, which continues until it returns to its initial axial position. During this stage the rotation of the screw 12 also serves to mix the plastic material within the channel 13 to make it fluid and uniform. During the next stage (third stage), while maintaining the shaft Ii at rest and the exit 32 closed, the valve 51 is opened and the second conveyor 20 operated to feed into the injection chamber 30 the fluid material mixed with reinforcing fibres present in the second part B of the conveying channel 23 and in the second conduit 42. The material enters the chamber 30 at a point (hole 48) downstream of the portion 31a of the piston 31, hence putting the chamber 30 under pressure and causing the piston 31 to withdraw to i ts initial axial position. This movement causes compression of the intermediate chamber 19, with consequent simultaneous transfer of the material present in it to the second conveyor 20 via the first connection conduit 41 (as shown in Figure 2B) . During this stage there is hence a circulation of the fluid material (indicated by arrows F in Figure 2B) from the intermediate chamber 19 to the second. conveyor 20 via the first connection conduit 41, and from the second conveyor 20 to the injection chamber 30. The material fed to the second conveyor 20 is mixed homogeneously thereby within its second part B, and fed to the injection chamber 30. On termination of this stage the piston 31 is returned to its initial axial position (shown in Figure 2) in or nearly in contact with the shut-off means 35. In the next stage the cycle recommences as heretofore described. By virtue of the described operation, the synthetic resin material is firstly fludized within the relative conveying channel 13 by the action of the first conveyor 10 and of the heating means 140. This fluid material is then fed to the second conveyor 20 through the first connection conduit 41. The fluid material is then mixed with reinforcing fibres in the second conveyor 20. This fluid material mixed with reinforcing fibres is then fed to the injection chamber 30 through the second connection conduit 42, and finally the injection chamber 30 is compressed by movement of the thrust piston 31 in the downstream direction, to inject the material to the user means via the exit 32. The maximum volume of the injection chamber 30 is determined by the initial axial position of the rotatable shaft 11. Consequently by controlling this position with appropriate sensor and control means, the required quantity of reinforced plastic material for injection through the exit 32 can be determined. Numerous modi cations of a practical and applicational nature can be made to the invention, but without leaving the scope of the inventive idea as claimed below.

Claims: CLAIMS 1. A machine for injecting synthetic resin mixed with reinforcing fibres into a user means, characterised by comprising: a first screw conveyor (10) arranged to advance and to fluidize synthetic resin material within a respective conveying channel (13), a second screw conveyor (20) arranged to advance f l ui d synthetic resin material under pressure and to mix it with reinforcing fibres within a respective conveying channel (23), a chamber (30) provided with a material exit (32) to be connected to the user means for pressure-injecting the material into this latter, and having a thrust piston (31) axially slidable within the chamber (30) to discharge the fluid material under pressure through said exit (32), a first conduit (41) connecting the final end of the channel of the first conveyor (10) to an intermediate point of the channel of the second conveyor (20), to transfer the fluid material from the first channel (13) to the second channel (23), a second conduit (42) connecting the exit end of the second conveyor (20) to the injection chamber (30), to transfer the material from the second conveyor (20) to the injection chamber (30), means for- axially driving the thrust piston (31) to compress the injection chamber (30), the machine operating cyclically in such a manner as to: fluidize a synthetic resin material within the f i rst conveyor (10), feed this fluid material from the first to the second conveyo r (20) via the first connection conduit (41), mix this fluid material with reinforcing fibres within the second conveyor (20) , feed this fluid material mixed with reinforcing fibres to the injection chamber (30) via the second connection conduit, finally, compress the injection chamber (30) by driving the thrust piston (30) in the downstream direction to inject the material into the user means. 2. A machine as claimed in claim 1, characterised in that the first conveyor (10) comprises: a conveying channel (13) having a downstream end part (13') within which the thrust piston (31), which delimits the injection chamber (30), is siidingly movable, a helical screw auger (11, 12) axially movable within the conveying channel (13), and means for axially moving the shaft (11) of the auger in the downstream direction against the thrust piston (31), said compression of the injection chamber (30) to inject the material into the user means being achieved by axially moving the shaft (11) of the first conveyor (10) in the downstream direction. 3. A machine as claimed in claim 2, characterised in that the first conveyor (10) comprises a shut-off means (35) fixed onto the downstream end of the shaft (11), to close the cross-section of the final part (13') of the first conveying channel (13), and having a valve means (36) preventing passage of the fluid material when directed upstream but allowing said material to pass when directed downstream. 4. A machine as claimed in claim 2, characterised by comprising the following cyclic operation: the shaft (11) of the first conveyor (10) is firstly moved axially in the downstream direction from its initial position in which it l es completely within the f rst conveying channel (13), to its final forward axial position, in order to urge the piston (31) downstream, so compressing the injection chamber (30) and injecting the material into the user means, the shaft (11) of the first conveyor is then rotated until the shaft (11) has been returned rearwards into its initial axial position, after which this rotation is halted, the second conveyor (20) is then operated to feed fluid material mixed with reinforcing fibres into the injection chamber (30) via the second connection conduit (42), with resultant withdrawal of the piston (31) into its initial axial position and simultaneous transfer to the second conveyor (20), of the material lying within the intermediate chamber (19) defined between the shut-off means (35) and the piston (31). 5. A machine as claimed in claim 1, characterised in that the second screw conveyor (20) comprises two helical screw augers counter-rotating within a corresponding pair of channels which define said conveying channel (23), their cross-sections mutually intersecting and substantially adhering to the profile of the helical screws (22), said conveying channel (23) having an initial part (A) for the feed and subsequent thrusting of the reinforcing fibres; and a reinforcing fibre feed device (26) provided with rotary means (28) for dragging/mixing the reinforcing fibres and for feeding them into said initial part (A) of the screw conveyor (20). 6. A machine as claimed in claim 5, characterised in that said first connection conduit (41) opens into the downstream end of the initial reinforcing fibre feed and thrusting part (A) of the conveying channel (23), which extends to define a further mixing and conveying part (B) for the plastic material and fibres.

Inventors: CATTANEO LUCA, CATTANEO, LUCA
Applicants: CATTANEO LUCA, CATTANEO, LUCA
Application year: 2001
Main classification: B29C45
IPC codes: B29C45