WO2000035654A1

WO2000035654A1 - Injection molding machine with compensation of frame deformation

Info

Publication number: WO2000035654A1
Application number: PCT/EP1999/009786
Authority: WO
Inventors: Carlo Fiorentini
Original assignee: Cannon S.P.A.
Priority date: 1998-12-14
Filing date: 1999-12-10
Publication date: 2000-06-22
Also published as: ITMI982682A1; AU1976700A; IT1304164B1

Abstract

The injection molding machine is provided with a pressure actuated system (18, 19) for compensating the deformation of the frame (10) caused by the thrust of the drive unit (17) at the clamping down of the mold (13, 14); one or more hydraulically expandable membranes (20) are seated between abutting surfaces (20A, 20B) in a respective side-open seat (20) of the frame (10) of the machine, in order to generate opposite bending moments (M) capable of causing an elastic deformation of the frame (10) which opposes the deformation caused by the drive unit (17) clamping of the mold (13, 14).

Description

INJECTION MOLDING MACHINE WITH COMPENSATION OF FRAME DEFORMATION

FIELD OF THE INVENTION

The invention relates to injection molding machines of the 5. tie-rodless type for the injection-molding of plastics or molten metal material, both of the horizontal and of the vertical type, and more precisely concerns an injection press provided with a system able to compensate for the deformations of the press frame caused by the thrusts 10. generated at the clamping down of the mold.

STATE OF THE ART

Injection-molding presses comprising a C-shaped or H-shaped tie-rodless frames, more generally referred to as "'open frame" injection presses, are widely known and varyingly 15. used since they allow easy access to the working zone of the mold.

A tie-rodless press in general comprises:

a rigid frame provided with stationary platen for supporting a first member of a mold;

20. a movable platen for supporting a second member of the mold having a center line, said platen being slidably movable along guide rails which extends longitudinally to the press frame; and

drive or control means between the movable platen and

25. a shoulder member of the frame, to slide the movable platen between an open-mold condition, and a closed-mold condition in which the mold members are tightly clamped between the two platens of the machine. The control means for sliding the movable platen and for clamping the mold, usually comprises hydraulic cylinders or toggle-joint mechanisms.

Presses of this kind are illustrated and described for 5. example in US 5,979,952 or EP 0,681,520, EP 0,726,131 which represent the state of the art closest to the present invention.

As stated in EP 0,726,131, open frame injection molding machine, having no tie-bars, are in general preferable 10. because they allow a free access to the working area of the mold.

However in this type of machine the thrust generate for clamping the mold must to be absorbed by the same frame of the machine, causing deformation of the frame and ¹⁵- misalignment of the platens and the mold members, at the closure of the mold.

Several attempts have been made to avoid distortion of the press frame, but up to now none of them have been entirely successful in avoiding misalignment of the mold members of 20. the machine.

According to EP 0,681,520 and EP 0,726,131, an injection molding press or machine with open access to the mold working area have been suggested, in which to compensate the frame deformation of the press during clamping of the 25. mold, the use of heavy and bulky thrust device such as a piston-cylinder unit has been suggested on a longitudinal side of the press which is opposite to the mold.

The thrust device is actuated at the same time as the closing of the mold will occur, to generate a reaction force equal or proportional to the clamping force for closing the same mold. In this way the generation of bending moments in the press frame is prevented, allowing only an axial elongation thereof which would ensure the 5. parallel disposition between the two mold support platens be maintained.

Although this type of press is of simplified construction compared to conventional tie-rod presses, and also allows easy access to the working zone, it nevertheless has a

10. frame structure which is still complex and costly with regard to the need to use a counter thrusting system in the form of a large hydraulic cylinder which is a separate part of the press frame and which also has a considerable cost; furthermore the disposition in the press frame of the

15. counter thrusting cylinder may not be changed in respect to the longitudinal axis of the press, resulting in design limitation and in a cumbersome structure of the same press.

Therefore, in a press of the type mentioned above, an arranged of the control or counter thrusting cylinder is 20. suggested so as to act substantially in the same direction as the mold closing means; in this way the tractional stresses on the press frame are strongly increased.

Therefore, the need of counteracting devices of simplified construction to compensate for the frame deformation of an 25. open frame press, allowing a significative simplification of the same frame structure, still exists.

OBJECTS OF THE INVENTION

The general object of the present invention is to provide an injection-molding press having a tie-rodless frame, in

30. combination with a pressure actuated system for the - A - compensation of the frane deformations which, m contrast to the known solutions tending to oppose the axial thrusts at the closure of the mold, a suitable use of the elastic behaviour of the press frame and a suitable pressure . actuated thrusting device forming an essential part of the same press, s suggested in order to compensate for the frame deformation caused at the clamping of the mold.

A further object of the invention is to provide an injection-molding press of the abovementioned type, which 0. has an extremely simplified structure, thereby having a comparatively low cost.

A further object of the present invention is to provide an injection press of horizontal or vertical type, provided with a system for compensating the elastic deformations of 5. the frame, which uses hydraulically actuated thrust members having an extremely simplified and low-cost structure, forming an integral part of the press.

BRIEF DESCRIPTION OF THE INVENTION

The above may be achieved by means of an injection press 0. comprising a system for compensating the frame deformations, according to Claim 1.

More particularly an injection molding machine with compensation of the frame deformation has been provided, the injection machine comprising:

5. a tie-rodless frame having a shoulder element a each end;

a stationary support platen for a first mold member, fastened to the frame of the machine; a movable support platen for a second mold member, said mold members having a center line or axis longitudinally extending to the frame of the press;

control means operatively connected between one of the

5. shoulder elements and the movable platen, said control means being constructed to slide to movable platen between a retracted open-mold position, and an advanced position to tightly clamp the mold; and

thrust means for compensating the frame deformation 10. upon clamping of the mold,

characterised in that

said thrust means comprises at least one pressure expandable membrane on at least one side of the press frame, said expandable membrane having a pressure chamber 15. connectable to a fluid pressure source, said membrane being positioned in a seating between spaced apart abutting surfaces of the frame.

Preferably one or more hydraulic membranes may be arranged in cross and/or parallel planes in respect to the axis of 20. the mold, on the side and/or at the ends of the press frame .

According to another aspect of the invention, the membrane has a flat configuration so as to exert thrusting actions over large opposite abutting surfaces on the sides of a 5. respective open-edge receiving seat, in the press frame.

The present invention therefore differs from the tie- rodless presses of the known type, in particular from the press known from EP 0,681,520, and EP 0,726,131 not only because of the different and greater constructional simplicity, but also owing to a greater freedom in design resulting from the possibility of differently positioning the thrusting membranes in the frame of the machine.

5. The above may be further clarified with reference to the accompanying drawings in which:

Fig. 1 schematically' shows a tie-rodless press provided with a system for compensation of press frame deformation, according to the invention;

10. Fig. 2 shows a cross sectional view in correspondence of a membrane;

Fig. 3 is a front view of a membrane;

Fig. 4 is a cross-sectional view of the membrane, according to line 4-4 of figure 3.

1₅. DETAILED DESCRIPTION OF THE INVENTION

The accompanying figure 1 shows a tie-rodless press comprising a rigid C-shaped frame 10 having uprights or shoulder members 11 and 12 at its ends.

The shoulder member 11 is provided with a stationary 20. support platen for a first mold member 13 intended to cooperate with a second mold member 14 fastened to an intermediate platen 15 movable along guide rails 16 of the press frame 10. The mold members 13 and 14 define a mold having a center line or main axis which extends 25. longitudinally with respect to the frame 10 of the press.

The movable platen 15 is in turn operatively connected to a control unit, shown in the form of a hydraulic cylinder 17, or toggle joint mechanism extending between the movable platen 15 and the shoulder member 12. The control cylinder 17 moves the platen 15 and the mold member 14 between a 5. retracted position, for opening the mold, and an advanced position for closing the mold, in which the movable mold member 14 comes into contact and is urged against the stationary mold member to tightly clamp the mold.

The control cylinder 17 for the movable platen 15 can be 10. selectively connected to a fluid pressure source P and to a discharge by means of a control valve 18.

The press also comprises means for compensating for the elastic deformation of the frame 10, caused by the thrust of the hydraulic control cylinder 17 or other suitable 15. operating means, such as an usual toggle joint mechanism, not shown, to clamp the mold.

According to the present: invention, in order for compensate for the deformation of the frame 10 caused by the control cylinder 17, one or more hydraulically expandable thrust

20. members have been provided, each consisting of a pressure expandable membrane 19 seated in a seat 20 having spaced apart abutting surfaces 20A, 20B which opens out at one end and on both sides of the frame 10, so as to allow elastic deformation thereof, and in which the membrane 20 extends

25. in a cross plane and/or parallelly to the main axis of the mold.

The pressure expandable membranes 19 in the case shown, are preferably in the form of flat membranes extending on a large area, arranged symmetrically with respect to the 30. frame 10, and being connected to a fluid pressure source, for example to the same source P for the cylinder 17 for closing the mold; in this way the membranes 19 are conjointly operated with each other and the control cylinder 17 for positioning and closing the movable mold member 14 against the stationary mold member 13.

5. The membrane 19 is in the form of a flat walled pressure actuable membrane having a pressure chamber 21 of rectangular or square flat shape and a small deep between the side walls 22, in respect to the width and length, substantially corresponding to the spacing between the

10. abutting surfaces 20A and 20B of the seat 20.

A possible embodiment for the expandable membrane 12 is shown in the example of Figures 2, 3 and 4; as shown the membrane 19 is in the form of a flattened tubular element, each end of which is fitted and welded into a corresponding 15. seat of a support member 23 and 24, such as a square rod as shown.

The rods 23 and 24 are provided with holes 25 to receive fastening bolts for fixing the membrane 19 into the seat 20 of the elastic structure 10 of the press, as well as are

20. provided with holes 26 and 27 opening into the chamber 21 at both ends of the membrane 19. One of the holes 26, 27, for example the hole 26 of the rod 23, can be selectively connected and disconnected to a pressure fluid source P, by a solenoid valve 28 or other pressure control device. The

25. hole 27 in the second rod is, on the other hand, closed by a plug 29, being used to vent air from the chamber 20 of the membrane, when necessary.

Operation of the thrust generating membrane 19 according to compensate for the deformation of frame 10, according to

₃₀. present invention is essentially as follows: when the control valve 28 is operated to disconnect the chamber 20 of the membranes 19 from the pressure source P, no pressure inside the chambers 21 will exist, and no thrust will be exerted by the membranes 19 against the abutting surfaces 20A, 20B of the seats 20; therefore, the elastic structure 5. 10 will not be subject to any deformation or bending moment. In these conditions, the thrusts caused by the membranes 19 on the surfaces 20A, 20B will be zero.

Differently, when the chamber 21 of the membranes 19 is connected to the source P of a fluid under pressure, such

10. as an oil pressure source to feed the chamber 21 of the membranes with a pressure which may be of the order of tens or hundreds of atmospheres, or higher depending on the thrusting forces to be produced a very small quantity of oil under high pressure will be fed into the chamber 21

15. depending by the small volume of the same chamber, which will tend to expand or to spread out the side walls 22 of the membrane 19, pushing them with high forces against the opposing surfaces 20A and 20B inside the seat 20.

Since the membrane 9 may extend over a large flat surface, 20. having a considerable thrusting area, compared to the small deep of the seat 20 the two abutting surfaces 20A and 20B of the seat 20, will be subjected to high thrusting forces tending to open the seat, which forces are proportional to the hydraulic pressure inside the chamber 21 of the 25. membranes 19, to cause a deformation of the frame 10 opposing to and which compensate for the deformation of the same frame caused by the cylinder 17 at the clamping down of the mold; however, since the expansion of the membrane 19 is extremely small or negligible, in keeping with the 30. maximum deformation permissible for the frame structure 10, the oil quantity under pressure to be supplied into each membrane 19 will also be minimal or entirely negligible compared to conventional hydraulic actuating systems. The thrust of the membranes 19, owing to the elastic deformation which the structure 10 undergoes, may be therefore used to compensate for the deformation in the frame 10 of the press, preventing misalignment of the two 5. members 13 and 14 of the mold.

As previously mentioned, the innovative principle which forms the basis of the molding press according to the present invention, and which is distinguishing from the conventional injection presses previously known, consists 10. in the generation, inside the same rigid structure of the frame 10, of opposing bending moments M in one or several points, at the same time as the deformations caused by the mold closing cylinder 17 will occur.

In other words, unlike the previous solutions which tended

15. to keep the frame 10 of the press prevently subjected to axial stressing forces, by pressure cylinders not forming an integral part of the press frame, which are acting in the same direction as the mold closing device, according to the present invention the capacity of the press frame 10 to

20. be elastically deformed is used so as to generate, by means of one or more hydraulically expandable membranes, a counter deformation inside the entire press frame, so as to react to and compensate the deformation induced by the thrust generated by the hydraulic cylinder 17 or by another

25. control unit on the movable platen at the clamping of the mold.

In the case shown, expandable membranes obtained from a tubular element which has been suitably flattened or welded to end bars for fixing to the press structure 10 have been 30. used; however, it is obvious that, it is possible to form the membranes in another manner different from that shown, such as by using opposite plates having peripheral sealing means, or by metal sheets, or differently positioning the same membranes in respect to positions shown in figure 1, without departing from the present invention.

Claims

1. An injection molding machine with compensation of the frame deformation, the injection machine comprising:

a tie-rodless frame (10) having a shoulder elements 5. (11, 12) a each end;

a stationary support platen for a first mold member (13), fastened to the frame (10) of the machine;

a movable support platen (15) for a second mold member (14), said mold members (13, 14) defining a mold having a 10. center line longitudinally extending to the frame (10);

control means (17) operatively connected between one

(12) of the shoulder elements (11, 12) and the movable platen (15), said control means (17) being constructed to slide to movable platen (15) and the mold member (14)

15. between a retracted open-mold position, and an advanced position to tightly clamp the mold (13, 14) ; and

thrust means (19, 20) for compensating the frame deformation upon the clamping of the mold (13, 14), characterised in that

20. said thrust means (19, 20) comprises at least one pressure expandable membrane (19) on at least one side of the frame (10), said expandable membrane (19) having a pressure chamber (21) connectable to a fluid pressure source (P) , said membrane (19) being positioned in a seat

25. (20) between spaced apart abutting surfaces (20A, 20B) of the frame (10) .

2. An injection molding machine according to Claim 1, characterized in that said membrane (19) is in the form of an elastically expandable membrane having a flat shape.

3. An injection molding machine according to Claim 1, characterized by comprising one or more membranes (19)

5. symmetrically arranged in receiving seats (20) provided in the press frame (10) .

4. An injection molding membrane according to Claim 3, characterized in that the membrane or membranes (19) is/are arranged in cross plane in respect to the center

10. line of the mold (13, 14) .

5. An injection molding machine according to Claim 3, characterized in that the membrane or membranes (19) is/are arranged in plane parallel to the center line of the mold (13, 14) .