WO2008007265A2

WO2008007265A2 - Horizontal press for thermoplastic materials injection

Info

Publication number: WO2008007265A2
Application number: PCT/IB2007/052353
Authority: WO
Inventors: Vanni Arisi
Original assignee: Vanni Arisi
Priority date: 2006-06-28
Filing date: 2007-06-19
Publication date: 2008-01-17
Also published as: ITBS20060155A1; WO2008007265A3

Abstract

A horizontal press for the injection of thermoplastic materials comprising: an injection assembly (2) for a thermoplastic material; a mold (3) having at least one stationary half-shell (7) and at least one movable half-shell (8) shifting along a first direction (D1) between a first position in which it is coupled with the stationary half-shell (7) so as to define a cavity (9) for containing the thermoplastic materials delivered by the injection assembly (2), and a second position in which it is uncoupled from the stationary half-shell (7) so as to release a finished piece; an ejecting element (13) is coupled with the movable half-shell (8) and can be shifted therewith so as to eject the finished workpiece from the mold (2).

Description

HORIZONTAL PRESS FOR THERMOPLASTIC MATERIALS INJECTION

The present invention relates to a horizontal press for the injection of thermoplastic materials, mixtures of metal powder or thermoplastic powder. In particular, the present invention advantageously applies to relatively small presses for injection molding of thermoplastic materials, having low weight and size. Such presses are used as a rule in labs developing and prototyping objects that can be molded by in- jection of thermoplastic materials, as well as for manufacturing small-size molded objects. As is known, horizontal presses as described above are made up of an injection assembly equipped with a feed duct, inside which . is distributed, the thermoplastic material in solid (granular) form. The duct is suitably heated so as to melt the thermoplastic material contained therein, and it is provided with a feed screw that is rotated so as to feed the thermoplastic material in liquid form towards a mold. The mold is made up of two half-shells, one of which is movable towards/away from the stationary one. Thus, the coupling of the two half-shells defines a compartment containing the thermoplastic material and apt to determine the shape of the finished workpiece. When the thermoplastic material becomes solid inside the compartment, the movable half-shell shifts away from the stationary one so as to release the finished work- piece.

Moreover, an ejecting element ejects from the movable half-shell the finished workpiece, in case the latter is stuck inside said half-shell. The ejecting element is made up as a rule of a pin that can be moved from one half-shell to the other so as to interfere with the workpiece and thrust it outside the movable half- shell.

Generally, all the handling elements of the press, i.e. means for handling- the movable half-shell, the feed screw and the ejecting element, are made up of pneumatic or hydraulic circuits suitably connected to corresponding pneumatic pumps, which thanks to^' their structure make presses very light and with small overall size.

However, such presses have a big drawback due to the high noise of pneumatic means which controls the han- dling elements.

As a result, -sound-absorbing carters have to be installed, thus increasing both the manufacturing costs and the overall size and weight of the presses. In order to obviate such drawback, electromechanical systems are ^■ used for controlling the handling ele-

_ O _ ments.

Here again, however, presses have a big drawback due to the complex structure of electromechanical transmission and control means. As a matter of fact, in order to obtain a press with small overall size, particularly complex transmission systems are conceived, which results in very high manufacturing costs. The aim of the present invention is to solve the prob- lems of known technique by proposing a horizontal press for the injection of thermoplastic materials that is structurally simple and, as a result, has low manufacturing costs. This aim and others, which shall be more evident from the following description, are basically achieved by a horizontal press for the injection of thermoplastic materials, comprising the characteristics of claim 1. Further characteristics and advantages shall be more apparent from the detailed description of a preferred, though not exclusive embodiment of a horizontal press according to the present invention.

Such description shall be disclosed below with reference to the accompanying figures, given to a merely indicative and therefore non-limiting purpose, in which: - Figure 1 ^■ shows a view in lateral elevation of a press for the injection of thermoplastic materials according to the present invention;

- Figure 2 shows a longitudinally sectioned view 'of a portion of the press of Figure 1;

- Figure 3 shows a perspective view - some parts having been removed so as to show others better - of the portion shown in Figure 2;

- Figure 4 shows a partially sectioned perspective view of a structural detail of the portion shown in

Figure 3;

- Figure 5 shows a longitudinally sectioned view of a portion of the press of Figure 1 in a second embodiment ; - Figure 6 shows a perspective view - some parts having been removed or made transparent so as to show others better - of the portion shown in Figure 5; and

- Figure 7 shows a partially sectioned perspective view of the portion shown in Figure 6. With reference to the figures mentioned above, the horizontal press for the injection of thermoplastic materials is globally referred to with numeral 1. . The press 1 comprises a supporting frame 2a above which develops an injection assembly 2 for a thermo- plastic material (not shown in the accompanying fig- ures) apt to feed said material into a mold 3. In particular, the injection assembly 2 has a feed duct 4 inside which a thermoplastic material is distributed by way of a hopper 5. The thermoplastic mate- rial fed into the hopper 5 in solid form, preferably in granular form, is liquefied by heating means housed inside the duct 4.

Inside the duct 4 develops a feed screw 6, partially shown in Figure 2, set in rotation by a corresponding electric motor (not shown and described in detail) for feeding the thermoplastic material in liquid form towards said mold 3.

Also the mold 3 is arranged above the supporting frame 2a beside the injection assembly 2, and has at least one stationary half-shell 7 and at least one movable half-shell 8.

As is better shown in Figure 1 and 2, the half-shells 7, 8 include corresponding plates 7a, 8a, which can be coupled with one another so as to define a cavity 9 for containing the thermoplastic material.

In particular, the plates 7a, 8a have corresponding inner surfaces 10 facing one another, on which are obtained hollows defining in cooperation with one another the cavity 9. The plate 7a of the stationary half-shell 7 further comprises an opening 11 (Figures 2 and 3) for the passage of the thermoplastic material, so as to put in fluid communication the duct 4 of the injection assembly 2 with the cavity 9. The movable half-shell 8 is associated to handling means 12, better described in the following, apt to move said half-shell 8 along a first direction ^λλDl" between a first position in which it is coupled with the stationary half-shell 7 so as to define said cav- ity 9 for containing the thermoplastic material delivered by the injection assembly 2, and a second position in which it is uncoupled from the stationary half-shell 7 so as to release a finished workpiece. The movable half-shell 8 is further associated to an ejecting element 13 apt to eject the finished work- piece from the mold 2 when the movable half-shell 8 is in its second position.

In particular, the ejecting element 13 is coupled with the movable half-shell 8 so as to slide therewith dur- ing its movement between said first and second position.

The ejecting element 13 comprises a first electric motor 14 connected to the plate 8a of the movable half- shell, on a rear region of said half-shell 8 facing away from said inner surface 10. The first electric motor 14 includes a rotating shaft 15 with a horizontal development transversal to the first direction "Dl" and extending at least partially inside a compartment 16 obtained inside the movable half-shell 8. Between the first electric motor 14 and the rotation shaft 15 there can be a reduction gear for the number of rotations of the shaft 15, so as to adjust the torque of the latter. As shown by way of example in Figure 3, 4, 6 and 7, the first electric motor 14 can have its own drive shaft having a horizontal development parallel to the first direction ^λλDl". In this case, an orthogonal reduction gear, e.g. a pair of conical pinions, is placed between the rotation shaft 15 and the drive shaft. The ejecting element 13 further includes a thrust device 17 associated to the first electric motor 14 so as to eject the finished workpiece housed inside the cavity 9. As is better shown in Figure 4 and 7, the thrust de- vice 17 is made up of at least one pin 18 housed inside a duct 19 obtained in the movable half-shell 8, so as to put in communication the compartment 16 with said cavity 9. The pin 18 can be moved along a second direction ^λλD2" parallel to its longitudinal development and to the first direction ^λλDl", between a first position in which at least one first end 18a of said pin 18 is arranged between the two half-shells 7, 8, and a second position in which it is retracted inside the duct 19. Advantageously, when the pin 18 is in the first position, the first end 18a thereof thrusts outside the finished workpiece coupled with the inner surface 10 of the movable half-shell 8. The thrust device 17 further includes a transmission element 20 associated to the rotation shaft 15 and to a second end 18b of the pin 18 facing away from the ^• first one 18a, so as to move said pin 18 between the first and second position thereof. In a first embodiment shown in Figures 1 to 4, the transmission element 20 is made up of an eccentric portion 21 engaged to the shaft 15 of the first motor 14 so as to rotate around the longitudinal development of said shaft 15. Still more particularly, the eccentric portion 21 com- prises a cam 22 having an outer cylindrical surface 23 associated to the pin 18.

It should be noted that the second end 18b of the pin 18 has a contact surface 24 associated to the outer cylindrical surface 23 and sliding thereon during the rotation of the cam 22 so as to move the pin with a to-and-fro motion along the second direction ^ΛλD2". Thus, the cam 22 turns the rotational movement imparted by the first motor 14 into a rectilinear motion of the pin 18. Preferably, the contact surface 24 is kept in constant contact with the outer cylindrical surface 23 by way of a spring-back element 25.

As is better shown in Figures 3 and 4, the spring-back element 25 is made up of a helical spring 25a develop- ing around the pin 18, which spring is compressed in the first position of the pin 18 so as to thrust said contact surface 24 against the cam 22.

In a second embodiment shown in Figures 5 to 7, the transmission element 20 is made up of a toothed ele- ment, e.g. a toothed wheel 20', engaged to the rotation shaft 15 so as to rotate around the longitudinal development of said shaft 15.

In this second embodiment, the pin 18 is provided on its second end 18b with a plurality of engagement por- tions 18' , made up of a rack for instance, cooperating with the transmission element or toothed wheel 20' so as to move the pin with an alternating motion along the second direction ^λλD2". In this case, the connection between the toothed wheel 20' and the rack 18' turns the rotational movement im- parted by the first motor 14 into a rectilinear motion of the pin 18.

In this case, the motor thrusts the pin 18 alternatively to and fro, and th'ere is no need for spring- back elements as in the first embodiment.

As is better shown in Figures 2 and 3, the handling means 12 include a worm 26 having a longitudinal development parallel to the first direction "Dl"^", and provided with a first end 26a engaged to the movable plate 8, and with a second end 26b facing away from the first one.

The second end 26b of the worm 26 can be inserted at least partially into a protection compartment 27 being part of said frame 2a (Figure 2) . Between the compartment 27 and the stationary half- shell 7 further develops at least one sliding guide 28 parallel to the worm 26 and developing in a corresponding hole 28a obtained in the movable half-shell 8. Preferably, the handling means 12 comprise four guides 28 getting through corresponding holes 28a obtained on the movable half-shell 8 so as to make said movable half-shell 8 slide on the guides 28 between the first and second position thereof. The handling means 12 further comprise a female screw 29 housed inside the compartment 27 and operatively associated to the second end 26b of the worm 26. The female screw 29 is set in rotation by a second electric motor 20 suitably connected to said female screw 29 by way of transmission means 31.

In particular, the transmission means 31 comprise a first toothed wheel 32 fitted onto a shaft 33 of the second electric motor 30 extending transversally to the longitudinal development of the worm 26. The first toothed wheel 32 is engaged with a second toothed wheel 34, operatively associated to the female screw 29 and coaxial to the longitudinal development of said worm 26. As a matter of fact, it should be noted that the transmission means 31 include a tubular sleeve 35 developing coaxially around the worm 26 and housed inside the compartment 27. The sleeve 35 has an outer surface 35a connected to the second toothed wheel 34 and an inner surface 35b connected to the female screw 29.

The first and the second toothed wheel 32, 34 are basically conical in shape, so as to impart the rotation from the shaft 33 to the female screw 29, which moves the worm 26. Thus, depending on the direction of rotation imparted by the second motor 30 , the worm 26 slides along the first direction ^λλDl" so as to move the movable half- shell 8 between the first and second position thereof. Advantageously, the press 1 includes electronic con- trol means (not shown and described in detail since they are of known type) so as to synchronize the movements of the movable half-shell 8 to the ones of the ejecting element 13. Thus, when the movable half-shell 8 is coupled with the stationary shell 7, the thermoplastic material in liquid form is fed into the mold 3. When the material cools down and gets back to its solid state, the movable half-shell 8 is moved to its second position in which it gets uncoupled from the stationary one 7. Now, in the first embodiment, the ejecting element 13 is activated so as to rotate the aforesaid cam 22, which imparts a rectilinear motion to the pin 18. In the second embodiment, the ejecting element 13 is activated so as to rotate the aforesaid toothed wheel 20', which imparts the rectilinear motion to the pin 18 by way of the rack 18'. Therefore, the pin 18 thrusts the solidified thermoplastic material (finished workpiece) outside so as the eject the latter from the movable half-shell 8. Then the movable half-shell 8 goes back to its first position, so as to repeat another cycle for manufacturing a finished workpiece.

The invention has important advantages and achieves the aim set forth. First of all, it should be pointed out that the press 1 is simple from a structural point of view. As a^' matter of fact, thanks to the arrangement of the ejecting element 13, a small electric motor 14 can be used for rotating in one direction only the cam 22 or in both directions the toothed wheel 20' .

Moreover, it should be taken into account that, by placing the first electric motor 14 directly on the movable half-shell 8, a small and structurally simple thrust device 17 can be used. As a consequence, the press 1 has a small size and low manufacturing costs.

Claims

1. A horizontal' press for the injection of thermoplastic materials comprising:

- an injection assembly (2) for a thermoplastic mate- rial;

- a mold (3) having at least one stationary half-shell (7) and at least one movable half-shell (8) movable along a first direction (Dl) between a first position in which' it is coupled with the stationary half-shell (7) so as to define a cavity (9) for containing the thermoplastic materials delivered by said injection assembly (2), and a second position in which it is uncoupled from said stationary half-shell (7) so as to release a finished piece obtained with said thermo- plastic material;

- handling means (12) for said movable half-shell (8); and

- an ejecting element (13) engaged to said movable half-shell (8) so as to eject said finished workpiece from the mold (2) .

2. The press according to the preceding claim, wherein said ejecting element (13) includes: a first electric motor (14) connected to said movable half- shell (8) so as to be shifted with said movable half- shell (8) between the first and the second position; and a thrust device (17) associated to said electric motor (14) so as to move along a second direction (D2) parallel to said first direction (Dl) , between a first position in which it interferes with the finished workpiece so as to eject it, and a second position in which it is retracted inside the movable half-shell (8) .

3. The press according to the preceding claim, wherein said first electric motor (14) comprises a ro- tation shaft (15) and wherein said thrust device (17) includes: at least one pin (18) housed inside a duct (19) obtained in said movable half-shell (8), which can be shifted along said second direction (D2) between a first position in which at least one first end (18a) of the pin (18) is arranged between the two half-shells (7, 8), and a second position in which the pin (18) is retracted inside said duct (19) , and a transmission element (20) associated to said rotation shaft (15) and to a second end (18b) of the pin (18) facing away from the first one (18a) .

4. The press according to the preceding claim, wherein said rotation shaft (15) has a longitudinal development transversal to said first direction (Dl) .

5. The press according to claim 3 or 4 , wherein said transmission element (20) includes a toothed wheel (20') .

6. The press according to claim 5, wherein said pin (18) is provided with a plurality of engagement portions (18') cooperating with said toothed wheel (20') so as to shift said pin (18) along said second direction (D2) .

7. The press according to any one of the claims 2 to 4, wherein said thrust device (17) comprises a cam (22) operatively associated to said first motor (14).

8. The press ^'according to any one of the claims 2 to 7, wherein said thrust device (17) includes a spring- back element (25) for bringing back the device (17) from the second to the first position.

9. The press according to any one of the claims 3 to 8, wherein said transmission element (20) includes an eccentric portion (21) engaged to said rotation shaft (15) for rotating around the longitudinal development of said shaft (15) .

10. The press according to the preceding claim, wherein said eccentric portion (21) includes a cam

(22) having an outer cylindrical surface (23); said second end (18b) of the pin (18) having a contact surface (24) associated to the outer cylindrical surface

(23) and sliding thereon during the rotation of the eccentric portion (21) so as to move the pin (18) with a to-and-from motion along the second direction (D2) .

11. The press according to the preceding claim, wherein said transmission element (20) further includes a spring-back element (25) for keeping the con- tact surface (24) of the pin (18) abutting against the outer cylindrical surface (23) .

12. The press according to the preceding claim, wherein said spring-back element (25) includes a helical spring (25a) developing around said pin (18).

13. The press according to any one of the preceding claims, wherein said handling means (12) comprise: a worm (26) having a longitudinal development parallel to said first direction (Dl) and having a first end (26a) connected to the movable half-shell (8) and a second end (26b) facing away from the first one; a female screw (29) operatively associated around said second end (26b) of the worm (26) ; a second electric motor (30); and transmission means (31) placed between said second electric motor (30) and said female screw (29) .

14. The press according to the preceding claim, wherein said handling means (12) further include at least one sliding guide (28) parallel to said worm (26) and developing inside a corresponding through hole (28a) obtained in the movable half-shell (8); said movable half-shell (8) sliding along said sliding guide (28) ,

15. The press according to claim 11 and/or 12, wherein said second electric motor (30) includes a ro- tating shaft (33) transversal to the longitudinal development of the worm (26) ; said transmission means (31) comprising a first toothed wheel (32) fitted onto said rotating shaft (33) , and a second toothed wheel (34) meshed with said first toothed wheel (32) and en- gaged to said female screw (29) .

16. The press according to the preceding claim, wherein said first and second toothed wheel (32, 34) are basically of conical shape.

17. The press according to claim 13 and/or 14, wherein said second toothed wheel (34) is coaxial to the longitudinal development of said worm (26) .

18. The press according to any one of the claims 13 to 15, further comprising a tubular sleeve (35) developing coaxially around said worm (26) and having an outer surface (35a) connected to the second toothed wheel (34) and an inner surface (35b) connected to said female screw (29) .

19. The press according to one or more of the preceding claims, wherein said half-shells (7, 8) include corresponding plates (7a, 8a) having inner surfaces

— 1± QO _— (10) facing one another and defining said cavity (9); said plate (7a) of the stationary half-shell (7) having an opening (11) for the passage of the thermoplastic material so as to put in fluid communication a feed duct (4) of the injection assembly (2) with said cavity (9) .