FR2561573A1 - Injection-moulding machine having a material-flow unit independent of the moulds - Google Patents

Abstract

This machine comprises a press 1 having two plates 2 and 3 which can move one with respect to the other, a mould 8 composed of two parts 8a, 8b, one 8a of which comprises at least one inlet orifice 11 through which a mouldable material can be injected into the mould cavity 9, an injection unit 12 having an outlet orifice 13 for the mouldable material, and which is movable towards and away from the inlet orifice of the mould through an opening 15 of the fixed plate 2 of the press, and a flow unit 14 which is temperature-regulated and fixed to the injection unit 12 in order to direct the mouldable material between the injection unit and the mould, the opening 15 of the fixed plate 2 of the press 1 having dimensions for allowing the flow unit 14 to pass through it.

Description

 The present invention relates to an injection molding machine, of the type comprising a press having a fixed plate and a plate movable relative to the fixed plate, a mold composed of two parts which are carried respectively by the plates of the press and which delimit between they at least one mold cavity, one of the two parts of the mold comprising at least one inlet orifice through which a moldable material can be injected into the mold cavity, an injection unit having an outlet orifice for the moldable material, and which is movable towards and away from the mold entry orifice through an opening of the fixed plate of the press, and a circulation block regulated in temperature to conduct the moldable material between the injection unit and mold.

 In known injection molding machines, the circulation block is constituted either by a block with transfer chamber thermally regulated in the case of injection-transfer, or by a block with thermally regulated channels in the case of injection conventional and injection-compression. In both cases, it is a tool which is placed between the fixed plate of the press and the corresponding part of the mold and which must be adapted to each mold. In known injection molding machines, it is difficult to control and precisely adjust the temperature of the molding material in the circulation block which, in practice, is at substantially the same temperature as the mold. As a result, on each injection, a non-negligible part of the moldable material contained in the channels of the circulation block is crosslinked or vulcanized at the same time as the material contained in the cavity or cavities. This results in significant losses of moldable material on each injection.

In addition, before proceeding to the next injection, it may be necessary to remove the crosslinked or vulcanized moldable material which could have remained in the channels of the circulation block. In addition, the pressure losses generated by the paths through the channels of the circulation block hinder the flow of the moldable material, in particular in the case of moldable materials which are not very fluid, such as rubber or other elastomeric materials, which may cause incomplete filling of the mold cavity (s) and, as a result, defective molded parts. In addition, since the circulation block must be adapted to each mold, it is therefore necessary to provide as many circulation blocks as molds used with the machine, which increases the cost of tools.

 The main object of the present invention is to remedy the aforementioned drawbacks of known injection molding machines.

 To this end, the injection molding machine of the present invention is characterized in that the circulation block is fixed to the injection unit and in that the opening of the fixed plate of the press is dimensioned to allow it to pass through it. the traffic block.

 In this way, the circulation unit can be brought into contact with the mold only during the actual injection phase, and it can be released from the mold while the molded material is crosslinked or vulcanized in the mold.

It follows that
1) The temperature of the moldable material in the channels of the circulation block can be precisely controlled and regulated, thus avoiding crosslinking or vulcanization of the material in the channels of the circulation block and thereby avoiding loss of moldable material.

 2) The moldable material is injected practically directly into the cavity or cavities of the mold, the axial length of the mold inlet orifices being able to be reduced to a large extent as will be seen below, which also contributes to reducing the losses of moldable material at each injection.

3) The circulation block can comprise several injection nozzles which can be associated with the same molding cavity
or to several mold-cavities and injecting the material
moldable directly into the said cavity or cavities.

LI #) Direct injection of the moldable material into the or
mold cavities greatly reduce losses
load between the injection nozzle (s) and the cavi (s)
mold tees, which allows better filling
said cavity or cavities and, consequently, molded parts
of better quality.

5) Direct injection also eliminates the heating / cooling alternations of the moldable material
as it passes through the traffic block which
previously found between the fixed press plate and one
of the two parts of the mold, thus saving energy
gie.

6) Since it is no longer necessary that the block of
circulation is adapted to each mold, this results in a
tool economy. In addition, in the event that the machine
injection molding has several presses equipped
each of a mold, the same injection unit and the same block
traffic can be used to serve successive
presses, also contributing to a tool economy.

We will now describe, by way of purely indicative example
and in no way limitative, an embodiment of this
invention with reference to the accompanying drawings in which
Figure 1 shows, in vertical section, the main elements
of the injection molding machine of this
invention, the elements being shown in the rest position
in the lower part of figure 1 and in position of
work in the upper part of figure 1.

Figure 2 shows, also in section and larger
scale, a detail of the machine shown in Figure 1.

Figure 3 shows, in side elevation, the block of
circulation of the machine of figure 1.

Figure Lt is a front view of the circulation block of
Figure 3.

Figure 5 is a front view of the associated mold holder
to the fixed plate of the press of the injection molding machine
tion shown in Figure 1.

FIG. 6 is a view, half in vertical section, half in
side elevation of the mold holder shown in Figure 5.

Figure 7 shows a key for fixing a
molding shell on the mold holder of Figures 5 and 6.

Figure 8 is a partial sectional view showing how
the key of figure 7 can be removed from the mold holder
Figures 5 and 6 to detach therefrom the associated molding shell.

Figure 9 is a partial sectional view showing how
the molding shell is retained in the associated mold holder by the key of FIG. 7.

 FIG. 10 is a partial view in section on line 10-10 of FIG. 5.

Figure 11 is a sectional view along line 11-11 of
Figure 5.

 Figure 12 is a sectional view along line 12-12 of Figure 5.

 Figure 13 is a side elevational view of an injection molding machine according to the present invention, comprising several presses and two injection units.

 FIG. 14 is a top view of the molding machine shown in FIG. 13.

As shown in Figure 1, the injection molding machine of the present invention includes a press
1 having a fixed plate 2 and a movable plate 3 which can be approached and moved away from the fixed plate 2 by means of two hydraulic cylinders 4 (Figures 13 and 14). Side view, the fixed plate 2 has an L shape and is fixed by its horizontal part to the frame 5 of the machine. Front view, the movable plate 3 has an approximately rectangular shape and it is slidably mounted, by means of sockets 6, on two parallel and horizontal rods 7 which are fixed by one of their ends to the fixed plate 2. The two sockets 6 are located in two diagonally opposite angles of the movable plate 3 and the cylinders of the jacks 4 are fixed in the other two diagonally opposite angles of the movable plate 3, their piston rods passing freely through the latter, being parallel to the rods 7 and being fixed by their ends to the fixed plate 2.

 Between the plates 2 and 3 of the press 1 is a mold 8 composed of two parts or molding shells 8a and Bb, which are carried respectively by the plates 2 and 3 in a manner which will be described in detail below and which delimit between them at least one molding cavity 9. The molding shell 8a comprises at least one inlet orifice 11, for example four inlet orifices as will be seen below, through which a moldable material can be injected into cavity 9.

 An injection unit 12 (more fully visible in FIGS. 13 and 14), having an outlet orifice 13 for the moldable material, can be approached and moved away from the inlet orifices 11 of the mold 8 in a manner which will be described in detail later. As shown in Figure 1, the injection unit 12 is fixed a circulation block 14 (see also Figures 3 and 4), which can pass freely through an opening 15 of the fixed plate 2 when the unit d injection 12 is brought into the working position as shown in the upper part of FIG. 1, and which is completely out of the opening 15 when the injection unit 12 is in the rest position shown in the lower part of Figure 1.

 As shown in Figures 1, 3 and Lt, the circulation block 14 comprises a first iota part, which has a central channel 16 axially aligned with the outlet orifice 13 of the injection unit 12 and which is fixed detachable from the latter by a clamping ring 17 made of a thermally insulating material and by screws 18. A washer 19, made of an insulating material, provides thermal insulation between the part 14a and the injection unit 12 and plays the role of a seal for the moldable material circulating in the channels 13 and 16. The circulation block 14 also comprises at least one part 14W forming a nozzle holder and of elongated shape, which extends in the direction of the mold 8 and which comprises a channel 21, the internal end of which communicates with channel 16 of the iota part.

The number of nozzle holders 14b is equal to the number of inlet holes 11 of the mold 8. In the case where the mold 8 has four inlet holes 11, four nozzle holders 14b are provided, as is more particularly visible. in the figure
4. An injection nozzle 22 is mounted at the outer end
of channel 21 of each nozzle holder 14b, each nozzle being aligned
axially with one of the inlet orifices 11 of the mold 8. Preferably, each injection nozzle 22 is mounted axially floating in the external end of the channel 21 of the nozzle holder
14b corresponding as is more particularly visible in FIG. 2 Due to this floating assembly and due to the differential pressure exerted on each injection nozzle 22 during the injection of the moldable material, each injection nozzle 22 s' will apply perfectly against the edge of the corresponding inlet orifice 11 of the mold 8, even if the edges of all the orifices 11 are not exactly in the same plane or even if the front faces of all the nozzle holders 14b do not do not lie exactly in the same plane due to manufacturing or mounting tolerances, as shown in FIG. 2. Furthermore, the outlet orifice of each injection nozzle 22 preferably has a diameter smaller than that of the corresponding inlet 11 of the mold 8, so that the moldable material can nevertheless be injected correctly into the orifice 11 even if it is not perfectly aligned with the injection nozzle 22 like this. is shown in the p upper part of figure 2.

Between the nozzle holders 14b and the part 14a, the circulation block 14 comprises a part 14c in which at least one channel 23 is formed (FIG. 1), for example four channels in the case where there are four nozzle holders 14b , which connect the channels 16 and 21. Preferably, the part 14c is detachably fixed to the part 14a by screws 24 (FIG. 4) and each nozzle holder 14b is detachably fixed to the part 14c. For this purpose, the rear part of each nozzle holder
14b is threaded and screwed into a corresponding tapped hole in part 14c. In this way, the part 14c and the number of the nozzle holders 14b can be easily changed as a function of the number of inlet orifices 11 of the mold 8.

Heating means are associated respectively with the part 14a and with each nozzle holder 14b of the circulation block 14, to keep the moldable material circulating through the ca
nals 16, 21 and 23 at a predetermined temperature and clearly
lower than that prevailing in the mold 8 for the crosslinking or vulcanization of the moldable material. It depends on the moldable material used and is chosen in such a way that the latter remains in a plastic and fluid state inside the channels 16, 21 and 23. As is more particularly visible in FIG. 1, the heating means ace
associated with each nozzle holder 14b may for example be constituted by an electric heating resistor 25 helically wound and concentrically surrounding the nozzle holder 11b.

Likewise, the heating means associated with part 14a may for example be constituted by four electric heating resistors 26, in the form of sticks which are inserted respectively into cylindrical holes 27 in part 14a. At one of their ends, the resistors 26 are mechanically connected to a terminal box 28 and electrically to a cable
supply 29.

Of course, instead of electrical resistors
heating described above, one could -use # a circulation of hot fluid, for example hot oil, in the cylindrical holes 27 and in a liner surrounding each nozzle holder 14b.

 As shown in Figures 3 and Lt, the part 14a of the circulation block 14 has two pins 31, having a frustoconical end, which can engage in corresponding holes (not shown) formed in the rear face of the fixed plate 2 for index the circulation block 14 relative to the fixed plate when the injection unit 12 is brought into its working position shown in the upper part of FIG. 1.

As shown in Figure 1, each of the two plates 2 and 3 of the press 1 door, on the side facing the other plate, a mold holder 32 or 33, respectively, which is temperature controlled and thermally insulated from the tray 2 or 3 corresponding with a lining 34 or 35, respectively in insulating material. As shown in the
Figures 5 and 6, the mold holder 32 carries, on its turned side
towards the fixed plate 2, two pins 36 which are engaged in corresponding holes of the plate 2, these holes possibly being the same as those which receive the pins 31 of the circulation block 1lut. As is more particularly visible in FIG. 5, the mold holder 32 comprises, in its central part, an opening 37 in the shape of a cross, which communicates with the opening 15 of the fixed plate 2 and which has sufficient dimensions to allow the free passage through it of the four nozzle holders 14b of the circulation block 14 without lateral contact with them. The mold holder 32 further comprises, in its face facing the mold holder 33, a cavity 38, of circular section , able to receive the rear part which is partly cylindrical and partly frustoconical of the molding shell 8a.

The latter is detachably fixed in the cavity 38 by two keys 39 (one of them is shown in Figures 5 and 6, the other in Figure 7), which are slidably engaged in grooves 41 with T-shaped section of the mold holder 32 and in a circular groove 42 formed in the periphery of the rear part of the molding shell 8a (see also Figures 9 and 11). Each of the two keys 39 has, at one end, a head 39a having two holes 43 and 4lut. A hook 45 can be engaged in the hole 43 as shown in FIG. 8 to extract the key 39 from the corresponding groove 41 to release the molding shell 8a and thus allow, if desired, its replacement by another shell molding to obtain another model of molded part. The other hole 44 is intended to cooperate with a ball locking device 46 making it possible to lock, by elastic snap-fastening, the key 39 in the corresponding groove 41 as shown in Figure 10. After removal of the two keys 39, the molding shell 8a can be extracted from the cavity 38 of the mold holder 32. This extraction is facilitated by a pusher 47 having a beveled end Lt7a, which acts on the rear part frustoconical of the molding shell 8a as shown in FIG. 11.

 In order to facilitate the filling of the mold cavity 9 with the moldable material, the cavity 9 can be placed under vacuum.

For this purpose, the molding shell 8a has a channel 48
(Figure 12) which communicates with a channel 49 (Figures 5 and 12) of the mold holder 32 can be connected to a vacuum pump (not shown).

 The molding shell 8a comprises, in its face facing the mold holder 32, four cavities 51 (only two of them are visible in FIGS. 1 and 2), which communicate with the opening 37 in the form of a cross of the holder mold 32 and which have sufficient dimensions to receive, without lateral contact, the front end of the four nozzle holders 14b, respectively. The four inlet holes 11 of the molding shell 8a are respectively formed in the bottom of the cavities 51. This makes it possible to significantly reduce the axial length of the inlet holes 11 and, consequently, to reduce the length of the cores molding, so the material losses.

As is more particularly visible in FIG. 2, a washer 52, made of thermally insulating material, is placed around the inlet orifice 11 in the bottom of each cavity 51. The washer 52 has three functions: it serves as axial support for the injection nozzle 22 and for the corresponding nozzle holder 14b, it serves as a seal and it serves to isolate the nozzle holder 14b tightly relative to the molding shell 8a.

 Heating means are associated with the mold holder 32 to heat the mold to a predetermined temperature (the temperature necessary for the crosslinking or vulcanization of the moldable material injected into the cavity 9). As shown in FIGS. 1 and 5, the heating means can for example consist of two sets of four electric heating resistors 53, in the form of a stick, which are inserted respectively in cylindrical holes 54 of the mold holder 32. The four resistors 53 of each set are mechanically fixed to a terminal box 55 and are electrically connected to a power cable 56, itself connected to a current source (not shown) like cable 29. two terminal boxes 55 also carries a thermometric probe 57, for example a thermocouple, which is inserted into a corresponding hole 58 in the mold holder 32 to measure its temperature.

 The mold holder 33 and the molding shell 8b have roughly the same structure as the mold holder 32 and the molding shell 8a, respectively, so that it is not considered useful to describe them in detail. It will simply be noted that the mold holder 33 and the molding shell 8b do not have channels similar to channels 48 and 49 and that the molding shell 8b does not have inlet ports similar to the ports 11 and no cavities similar to the cavities 51 of shell 8a. On the other hand, the molding shell 8b comprises, in the bottom of the molding cavity 9, a cavity 59 with a central hole 61 in which there is an ejector 62 for ejecting the molded parts. At its rear part, the ejector 62 is connected to the piston rod 63 of a hydraulic cylinder 64 (FIGS. 13 and 14). The cylinder of the hydraulic cylinder 64 is fixed to the movable plate 3, while its piston rod passes through openings formed in the movable plate 3 and in the mold holder 33 and aligned with the central opening 61 of the molding shell 8b.

 Preferably, as shown in FIGS. 13 and 14, the injection molding machine comprises several presses 1 each equipped with a mold. -Each press 1 and the associated mold 8 have a structure similar to that described above. As is more particularly visible in FIG. 14, the presses 1 can advantageously be arranged in two parallel rows, each press of a row being placed opposite a press of the other row. In this case, the injection molding machine comprises two injection units 12 located between the two rows of presses 1.

 for example, each injection unit 12 can comprise, in a known manner, a worm plasticizing device 65, supplied with moldable material, for example an unvulcanized rubber tape, from a coil 66, and a jar of transfer 67, which is supplied with plasticized moldable material from the plasticization device 65 and to which the circulation block 14 is fixed, for injecting a predetermined quantity of moldable material into a selected mold. The two injection units 12 are carried by a carriage 68 which can be moved between the two rows of presses 1 on two rails 69 parallel to the rows of presses by means of an actuating device that a cable actuator 71. Thus, the two injection units 12 can be brought into correspondence with a selected pair of mutually opposite presses 1. Each injection unit 12 is slidably mounted on two parallel guide rods 71 of the carriage 68, which extend horizontally and perpendicular to the rails 69. A hydraulic cylinder 73 whose cylinder is fixed to one of the two injection units 12 and whose piston rod is fixed to the other injection unit 12, allows, when actuated , to move the two injection units in opposite directions to bring each injection unit 12 into working relationship with the mold of a selected press 1 or to bring each injection unit 12 into a rest position at the 'deviation from the p resse in the mold from which the last injection took place, to allow the displacement of the carriage 68 and the two injection units 12 along the rails 69 to another pair of presses 1.

 Each row of presses 1 can be associated with a single longitudinal conveyor 74 or several transverse conveyors 75 (one per press 1) for the evacuation of the molded parts to a finishing station QU a sorting station or a storage place. Preferably, the single conveyor 74 will be used if all the parts molded in the row of presses 1 are identical, while separate conveyors 75 will preferably be used if the parts molded in the row of presses 1 are different.

 Of course, all the molds located in the presses 1 of the same row must have the same number of inlet ports 11 and the circulation block 14 of the injection unit 12 associated with said row of presses must include the same number of nozzle holders 14b as the number of inlet orifices il of each mold in said row. On the other hand, the molds of the same row of presses 1 can correspond to different models of molded parts and the molds of a row of presses do not necessarily have the same number of inlet orifices as the molds of the another row of presses.

 From the above, it is clear that the present invention provides an injection molding machine which makes it possible to inject a moldable material directly into one or more mold cavities with minimal losses of moldable material, this advantageous result being mainly due to the fact that the circulation block 14 is physically and thermally separated from the mold 8 and fixed to the injection unit 12. In addition, it will be noted that the entire circulation block # on 14 does not need 'be changed according to the mold used. It is enough to change the part 14c and the number of the nozzle holders 14b of the circulation block according to the number of inlet orifices 11 of the mold used. In addition, it is possible to obtain a large variety of molded parts simply by changing the two molding shells 8a and 8b, which can be produced in the form of pre-machined pancakes so that they can be detachably fixed respectively to the two mold holders 32 and 33 described above, which include the heating means of the mold and which can remain permanently fixed to the plates 2 and 3 of the press 1. to obtain a molded part of selected shape, it suffices to machine one or more molding cavities having the shape in a pair of pre-machined wafers in stock. Furthermore, it will be noted that, in the case where the injection molding machine comprises several presses, a single circulation block 14 is used in cooperation with the different presses, whereas, in the molding machines pa r injection previously known, each press was equipped with its own block with transfer chamber or regulated channels. All these devices allow a substantial saving on tooling.

 It will also be noted that the injection molding machine of the present invention lends itself particularly well to programmed automation of its operation allowing different dosages, temperatures and injection times and an automatic selection of the molds to be successively supplied by the or the injection units 12 as a function of the different vulcanization times of the various parts being manufactured in the molds, hence an optimization of the production.

 It goes without saying that the embodiment of the present invention which has been described above has been given by way of purely indicative and in no way limitative example, and that numerous modifications can easily be made by those skilled in the art. art without departing from the scope of the present invention. Thus in particular that, instead of being heated by electrical resistors 53, the mold holders 32 and 33 can be heated by a hot fluid, for example hot oil, circulating in channels formed in the two holder or circulating in a liner surrounding the two holder. In addition, in the case where several presses are provided, instead of being arranged in two parallel rows, the presses can be arranged circularly. In this case, the one or two injection units 12 can be carried by an auxiliary chassis which can rotate around an axis located at the center of the circular arrangement of the presses, or the presses can be carried by an auxiliary chassis rotating around of a frame supporting the one or both injection units 12.

Claims (13)

 1. Injection molding machine comprising a press (1) having a fixed plate (2) and a plate (3) movable relative to the fixed plate, a mold (8) composed of two parts (8a, 8b) which are carried respectively by the press plates and which delimit between them at least one molding cavity (9), one (8a) of the two parts of the mold comprising at least one inlet orifice (11) through which a moldable material can be injected into the mold cavity, - an injection unit (12) having an outlet orifice (13) for the moldable material, and which is movable towards and away from the inlet orifice of the mold to through an opening (15) in the fixed plate (2) of the press, and a circulation block (1lut) regulated in temperature to conduct the moldable material between the injection unit and the mold, characterized in that the block circulation (14) is fixed to the injection unit (12) and in that the opening (15) of the fixed plate (2) of the press (1) is dimensioned for the straighten pass the circulation block (1lut) through it.  2. Injection molding machine according to claim 1, characterized in that the circulation block (14) comprises a first part (iota) which is detachably fixed to the injection unit (12) and which comprises a channel (16) axially aligned with the outlet orifice (13) of the injection unit, at least a second part (14b) forming a nozzle holder and of elongated shape, which extends in the direction of the mold (8) and which comprises a channel (21) whose internal end communicates with the channel (16) of the first part (La), and an injection nozzle (22) mounted at the external end of the channel (21) of the second part (14b).  3. Injection molding machine according to claim 2, characterized in that the injection nozzle (22) is mounted axially floating in the channel (21) of the second part (14b) of the circulation block (14).  4. Injection molding machine according to claim 2 or 3, characterized in that the circulation block (14) comprises a third part (14c) which is located between the first and second parts (14a and 14b), and in which at least one channel (23) is formed which connects the channels (16 and 21) of the first and second parts.  5. Injection molding machine according to claim 4, characterized in that the first, second and third parts (11a, 14b and 14c) of the circulation block (14) are detachably fixed to each other.  6. Injection molding machine according to any one of claims 2 to 5, characterized in that heating means (25 and 26) are associated respectively with the first and second parts (14a and 14b) of the circulation block 524) .  7. Injection molding machine according to any one of claims 1 to 5, characterized in that thermal insulation means (19) are provided between the injection unit (12) and the circu-lation block (1lut).  8. Injection molding machine according to any one of claims 2 to 5, characterized in that each of the two plates (2 and 3) of the press (1) door, on the side facing the other plate, a door -mold (32 or 33) regulated in temperature and thermally isolated from the corresponding plate, the mold holder (32) associated with the fixed plate (2) of the press (1) comprising at least one opening (37) which communicates with the opening (15) of the fixed plate (2) and which has sufficient dimensions to allow the free passage through it of the second part (14b) forming a nozzle holder of the circulation block (14) without lateral contact with this second part.  9. Injection molding machine according to claim 8, characterized in that each of the two mold holders ((32 and 33) comprises, in its face facing the other mold holder, a cavity (38) capable of receiving a shell. molding (8a) defining the molding cavity (9) with the molding shell  (8b) carried by the other mold holder, and fixing means  (39) for detachably fixing the molding shell (8a or 8b) in the corresponding cavity of the mold holder (32 or 33), and in that the molding shell (8a) carried by the mold holder (32) associated with the fixed plate (2) of the press (1) has at least one inlet orifice (11) for the moldable material, which is aligned with the injection nozzle (22) of the circulation block (14 ) -.  10. Injection molding machine according to claim 9, characterized in that the molding shell (8a) provided with at least one inlet orifice (11) comprises, in the face facing the corresponding mold carrier (32) , at least one cavity (51) communicating with the opening (37) of said mold holder (32) and having dimensions sufficient to receive, without lateral contact, the end of the second part (14b) forming a nozzle holder for the block of circulation (1lut), the inlet orifice (11) of said molding shell (8a) being located in the bottom of said cavity (51) so as to have an axial dimension as small as possible.  11. Injection molding machine according to claim 10, characterized in that a washer (52) of thermally insulating material is placed around the inlet orifice (11) in the bottom of the cavity (51) of the molding shell (8a) to serve as an axial support for the injection nozzle (22) of the circulation block (1lut) when the injection unit (12) is approached from the mold (8).  12. Injection molding machine according to any one of claims 9 to 11, characterized in that the inlet orifice (11) of the molding shell (8a) has a larger diameter than the outlet orifice of the injection nozzle (22).  13. Injection molding machine. according to any one of claims 1 to 12, comprising several presses (1) each equipped with a mold (8), mounting means (68, 69) allowing relative movement between the injection unit (12) and the presses (1), so that the injection unit can be associated momentarily and successively with each of the  presses, and an actuating device (73) capable of bringing  the injection unit in injection relation with the mold (8)  of the press (1) with which it is momentarily associated, characterized in that the presses (1) are arranged two to  two facing each other, and in that it includes a second uni  injection tee (12) having a circulation block (14) with at  minus an injection nozzle oriented in an opposite direction  to that of the circulation block (14) of the first in  jection (12), and in that the actuating device (73)  is mounted between the two injection units (12) for the  move in opposite directions.