WO2008007264A2

WO2008007264A2 - Horizontal bench press for thermoplastic materials injection

Info

Publication number: WO2008007264A2
Application number: PCT/IB2007/052351
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: WO2008007264A3; ITBS20060156A1

Abstract

A horizontal press for the injection of thermoplastic materials comprises a first and a second half-mold forming a mold. The press (1) further comprises a feed screw (18) that can be rotated around its own axis of development (X) for introducing a solid thermoplastic material and feeding it to heating means (15), the heating means (15) melting the thermoplastic material; the feed screw (18) can be shifted so as to inject the melted thermoplastic material into the mold; a first mechanical transmission (24) for shifting the feed screw (18) along its own axis of development (X) and a second mechanical transmission for rotating the feed screw (18) around its own axis of development (X).

Description

HORIZONTAL BENCH PRESS FOR THERMOPLASTIC MATERIALS INJECTION

DESCRIPTION

The present invention relates to a horizontal bench press for the injection of thermoplastic materials, mixtures of metal powder or thermoplastic powder. In particular, the present invention relates to horizontal bench presses for the injection of thermoplastic materials, with low weight and small size, also referred to as "mini-presses".

It is known about horizontal bench presses for the injection of thermoplastic materials including a supporting structure onto which a stationary vertical plate is fastened. A seat for housing a first half-mold is ob- tained on such stationary plate.

Presses of known type comprise a closing assembly including a movable plate on which another seat for housing a second half-mold is obtained. Such plate can be shifted between a first position in which the first and the second half-mold are coupled with each other so as to form a mold, and a second position in which the first and the second half-mold are uncoupled. Known presses further comprise an injection cylinder into which a certain amount of thermoplastic material in powder or granules is introduced, which is melted so as to be introduced into the mold.

In detail, the injection cylinder houses a feed-pusher, which is suitably shifted so as to feed into the cylinder the thermoplastic material picked up by an appropri- ate hopper, and to inject the melted thermoplastic material into the mold.

In further detail, in the step of introduction of the thermoplastic material in powder, the feed-pusher is pushed back so as to create an injection compartment in the front portion of the injection cylinder. Such compartment is progressively filled up with the thermoplastic material conveyed by way of the rotational movement of the screw feed-pusher. In order to shift the feed-pusher, presses of known type comprises hydraulic actuators supplied by at least one pump. The pump is usually of electric type. However, horizontal presses of known type have some drawbacks. Presses of known type using shifting means of hydraulic type are generally quite noisy. In order to obviate this drawback, it can be absolutely necessary to equip the press with sound-absorbing shields, with an increase in the overall size. Moreover, in the case of hydraulically driven presses, a further drawback consists in that it is necessary to _ o _

dispose of the fluid used in hydraulic systems. Such fluid is typically toxic and polluting and must be disposed of in compliance with strict regulations. Such disposal is therefore particularly difficult and expen- sive.

Eventually, hydraulic systems prove little effective in energetic terms, since they absorb energy even when drives are deactivated. As a matter of fact, the circuit must be kept under pressure even when actuators are mo- mentarily not active.

Under these circumstance, the technical task of the present invention consists in proposing a horizontal press for the injection of thermoplastic materials without the disadvantages of prior-art presses. In particular, an aim of the present invention is to provide a horizontal bench press for the injection of thermoplastic materials that is noiseless. Still another aim of the present invention is to provide a press with low operating costs. A final aim of the present invention is to provide a press with small overall size.

These and other aims, which will be more apparent from the following description, are basically achieved by a horizontal press for the injection of thermoplastic ma- terials according to one or more of the appended claims. Further characteristics and advantages will be more apparent from the detailed description of a preferred, though not exclusive embodiment of a horizontal press for the injection of thermoplastic materials according to the present invention.

Such description will be disclosed below with reference to the accompanying drawings, provided to a merely and therefore non-limiting purpose, in which:

- Figure 1 is a sectional side view of the horizontal press for the injection of thermoplastic materials according to the present invention;

- Figure 2 is a sectional side view of a detail of Figure 1;

- Figure 3 is a perspective view of a detail of Figure 1, some parts being removed so as to show others better;

- Figure 4 is a perspective view of a detail of Figure 3.

With reference to the figures above, the numeral 1 globally refers to a horizontal press for the injection of thermoplastic materials according to the present invention.

The press 1 comprises a supporting structure 2 developing mainly horizontally, onto which is fastened a stationary vertical plate 3. The latter has a first seat 4 for housing a first half-mold (not shown in the fig- ures ) .

The press 1 further includes a closing assembly 5. The latter comprises a movable plate 6 having a second seat 7 for housing a second half-mold (not shown) . Such plate 6 can be shifted between a first position in which the first and the second half-mold are coupled with each other so as to form a mold, and a second position in which the first and the second half-mold are uncoupled. The movable plate 6 slides along suitable guiding bars 8 parallel to each other.

The press 1 comprises a housing and supporting box- shaped body 9, which is slidingly associated to the supporting structure 2. In detail, the box-shaped body 9 comprises at least one sleeve 10 inserted into a hori- zontal guide 11 secured to the supporting structure 2. The press 1 includes an injection cylinder 12 for melting and injecting the thermoplastic material into the mold. The injection cylinder 12 faces the fist seat 4 of the stationary plate 3. In further detail, the injection cylinder 12 comprises an end body 13 fastened on a first end 12a thereof and at least partially inserted into a hole 14 obtained in the stationary plate 3. The melted thermoplastic material thus gets out of the injection cylinder 12 through the end body 13 and is injected into the mold (Figures 2 and 3) . The injection cylinder 12 is fastened to the box-shaped body 9 with a second end 12b thereof, opposite the first one .

The injection cylinder 12 further comprises heating means 15 for melting the thermoplastic material. Such heating means 15 include at least one heating element 16 with an electric resistance, wound up on an outer surface 12c of the cylinder 12. Preferably, the heating means 15 comprise a plurality of heating elements 16 ar- ranged along the outer surface 12c of the cylinder 12. A plurality of temperature sensors 17 is further arranged along the injection cylinder 12. Preferably, the temperature sensors 17 are thermocouples. The injection cylinder 12 further comprises a feed screw 18 housed therein. The feed screw 18 can be rotated along its own main axis of development ^XλX" for introducing a certain amount of solid thermoplastic material. Moreover, the feed screw 18 can be shifted so as to inject the thermoplastic material, which has been melted by the heating elements 15, into the mold.

The feed screw 18 further includes a head body 19 connected to a first end 18a of the feed screw 18 near the first end 12a of the injection cylinder 12. The head body 19 is basically ogive-shaped so as to help the in- jection of the melted thermoplastic material into the mold.

In further detail, the feed screw 18 can be rotated and shifted backward with respect to the stationary plate 3 so as to introduce the thermoplastic material in powder, and forward with respect to the stationary plate 3 so as to inject the melted thermoplastic material into the mold.

During operation, in a filling step the feed screw 18 is rotated and shifted backward. Thus, near the first end 12a of the injection cylinder 12, the feed screw 18 shifting backward clears a portion of space, thus defining an injection compartment 20. The thermoplastic material in powder is simultaneously picked up by gravity from a hopper 21 connected to the cylinder 12 by means of an access opening 22 obtained on said cylinder 12, and thanks to the rotational motion of the feed screw 18 is conveyed into said injection compartment 20. During the transfer from the hopper 21 to the injection compartment 20 the thermoplastic material melts. Then the feed screw 18 is shifted forward without rotating, so as to inject the melted thermoplastic material into the mold, thus emptying the injection compartment 20. The feed screw 18 further comprises a non-return valve 23 for preventing the melted thermoplastic material from leaking out along the feed screw 18 during the injection step.

The press 1 further includes a first mechanical transmission 24 for shifting the feed screw 18 along its own axis of development ^ΛλX", and a second mechanical transmission 25 for rotating the feed screw 18 around its own axis of development ^λΛX".

The press 1 further comprises a first electric motor 26 associated to the first mechanical transmission 24, and a second electric motor 27 associated to the second mechanical transmission 25. The first motor 26 is independent from the second motor 27. Both motors 26, 27 are supported by the box-shaped body 9. The first mechanical transmission 24 comprises a movable slider 28 connected to the feed screw 18 so as to shift the latter along its own axis of development ^XλX". The slider 18 is associated to a worm 29. In further detail, the slider 28 comprises a female screw 30 placed between said slider 28 and the worm 29. During opera- tion, the worm 29, when rotated, shifts the slider 28, which is associated to the feed screw 18 and thus shifts the latter along its own axis of development ^VX". The worm 29 is fastened to the box-shaped body 9 and shifted by the first electric motor 26. In further de- tail, the first electric motor 26 is connected to the worm 29 by means of a suitable gearing 31. The press 1 further comprises a shaft 32 fastened coaxi- ally to the feed screw 18 and connected to the movable slider 28 for shifting and rotating said feed screw 18. In detail, the slider 28 is slidingly secured to the shaft 32 and can be rotated with respect to the latter. The movable slider 28, actuated by the worm 29, thus shifts the shaft 32, and therefore the feed screw 18, during the forward and backward movement. However, the slider 28 enables the rotation of the shaft 32 and of the feed screw 18.

The slider 28 has a first through hole 33 arranged near a first end 28a thereof, through which the shaft 32 gets through the slider 28. The slider 28 further has a sec- ond through hole 34 arranged near a second end 28b of the slider 28, opposite the first one, in which the female screw 30 is housed. Preferably, the slider 28 is T- shaped. The first mechanical transmission 24 comprises at least one pair of opposite conical roller bearings 35, which are placed in the first hole 33 between the slider 28 and the shaft 32. The conical roller bearings 35 enable the slider 28 to transfer to the shaft 32 a force parallel to the axis of development ^ΛλX" of the feed screw 18 and allow the latter to rotate with respect to the slider 28 .

The slider 28 slides along two parallel rods 26 acting as a guide for preventing unwanted rotations of said slider 28, which might lead to an offset of the shaft 32 and of the feed screw 18 with respect to the injection cylinder 13.

The second mechanical transmission 25 is actuated by the second motor 27 for rotating the feed screw 18 and the shaft 32. The shaft 32 is associated to the second motor 27 and is slidingly movable with respect to the latter. The second mechanical transmission 25 further comprises a toothed wheel 37 associated to the second motor 27. In detail, the toothed wheel 37 is coupled to the second motor 27 by means of a secondary toothed wheel 37 connected to the second motor 27 (Figure 4). The toothed wheel 37 further comprises a bushing 38 stiffly connected to its center. The bushing 38 has a plurality of projections 39 placed at the same distance and pointing towards the center of the bushing 38.

Said shaft 32 further has a plurality of grooves 40 parallel to the axis of development ^ΛλX" of the feed screw 18. The shaft 32 and the toothed wheel 37 are coupled to each other so that the projections 39 of the bushing 38 engage into the grooves 40 of the shaft 32. Thus, when the toothed wheel 37 is rotated by the second motor 27, the bushing 38 rotates the shaft 32 and the feed screw 18. However, the shaft 32 can slide inside the bushing 38. Stated otherwise, the shaft 32 is turnably secured to the toothed wheel 37 and slidingly movable with respect to the latter.

The press further comprises control means of per se known type, which are therefore not disclosed in detail, operatively connected to the first and second mechanical transmission so as to coordinate the operation thereof, and preferably operatively active so as to control the operation of the first and second electric motor. The present invention achieves the aims set forth. As a matter of fact, the use of the electric motors 26, 27 for shifting the feed screw 18 enables to reduce acoustic emissions and emissions of pollutants generated during operation. This allows to avoid the installation of sound-absorbing panels, and thus the overall size is quite small.

Moreover, presses as described above have low operating costs. As a matter of fact, the press 1 absorbs energy only when the feed screw 18 has to be shifted, since no hydraulic circuits are present that have to be kept un- der constant pressure. Furthermore, the absence of hydraulic circuits means that no operating fluids are present that have to be disposed of, thus increasing press operating costs. An advantage of presses as described above consists in that the mechanical transmissions are designed so as to separate the shifting and the rotational movements of the feed screw 18 from each other. Thus, the elements of the mechanical transmissions 24, 25 are simpler and lighter.

Claims

1. A horizontal press for the injection of thermoplastic materials, comprising a first and a second half-mold so as to form a mold; characterized in that it further comprises:

- a feed screw (18) that can be rotated around its own axis of development (X) for introducing a solid thermoplastic material and feeding it to heating means (15), the heating means (15) melting the thermoplastic materi- als; the feed screw (18) being shiftable so as to inject the melted thermoplastic material into the mold;

- a first mechanical transmission (24) for shifting the feed screw (18) along its own axis of development (X), and a second mechanical transmission (25) for rotating the feed screw (18) around its own axis of development

(X) •

2. The press according to claim 1, comprising a first electric motor (26) associated to the first mechanical transmission (24) .

3. The press according to claim 1 or 2, in which the first mechanical transmission (24) and the second mechanical transmission (25) can be actuated independently one from the other.

4. The press according to any one of the preceding claims, in which the first transmission (24) comprises a movable slider (28) connected to the feed screw (18) for shifting the feed screw (18) along its own axis of development (X) .

5. The press according to claim 4, in which the slider (28) is engaged onto a worm (29); a female screw (39) being placed between the slider (28) and the worm (29) .

6. The press according to claim 5, in which the worm (29) is operatively connected to the first electric motor (26) .

7. The press according, to one of the claims 4 to 6, further comprising a shaft (32) fastened coaxially to the feed screw (18) for shifting and rotating the feed screw (18 ) .

8. The press according to claim I₁ in which the slider (28) is slidingly secured to the shaft (32) so as to shift the feed screw (18) ; the shaft (32) being turnable with respect to the slider (28) .

9. The press according to claim 8, in which at least one pair of opposite conical roller bearings (35) is ar- ranged between the slider (28) and the shaft (32) .

10. The press according to any one of the preceding claims, comprising a second electric motor (27) associated to the second mechanical transmission (25) .

11. The press according to claim 10, in which the shaft (32) is slidingly movable with respect to the second mo- tor (27) .

12. The press according to claim 10 or 11, in which the second mechanical transmission (25) further comprises a toothed wheel (37) associated to the second motor (27) .

13. The press according to claim 12, in which the shaft (32) is turnably associated to the toothed wheel (37) and slidingly movable with respect to the toothed wheel

(37) .

14. The press according to claim 12 or 13, in which the toothed wheel (37) comprises in its center a bushing

(38) associated to the shaft (32) .

15. The press according to claim 14, in which the bushing (38) has a plurality of radial projections (39) engaging into a corresponding plurality of parallel grooves (40) of the shaft (32) , or conversely.

16. The press according to claim 10, in which the first electric motor (26) has a longitudinal development parallel to the longitudinal development of the second electric motor (27).

17. The press according to claim 10, in which the first (26) and the second (27) motor have a longitudinal development parallel to the axis of development (X) of the feed screw (18) .

18. The press according to claim 5, in which the worm (29) has a longitudinal development parallel to the axis of development (X) of the feed screw (18) .

19. The press according to claim 7, in which the shaft (21) has a longitudinal development parallel to the one of the worm (29) .

20. The press according to any one of the preceding claims, characterized in that it comprises press control means operatively connected to said first and second mechanical transmission so as to coordinate the operation thereof.

21. The press according to claim 20, characterized in that said control means are operatively active so as to control the operation of said first and second electric motor.