Method and mold clamping press for injection molding machines

ABSTRACT

A method and a mold clamping press for injection molding machines; the press comprises a stationary platen and a movable platen operatively connected to control means which can be operated to relatively move the platens towards and away from each other. Slidable tie-rods, each connected to a respective control cylinder, axially extend between the platens passing through locking bushes rotatably supported by a platen of the press. Each locking bush and the corresponding tie-rod are provided with opposite intermeshing screw threads having an axial clearance; the bushes are made to rotate in synchronism and in a way correlated to the displacement of the movable platen, avoiding any frictional contact between the screw threads during the closing and opening of the mold. The tie-rods are then made to slide with respect to the locking bushes and the platens of the press, causing a contact between the screw threads of the bushes and the tie-rods, and a thrust of the bushes against the movable platen, of the press to generate the required tonnage for tightly clamping the mold.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

The general features of the present invention, and a number of particular embodiments, will be further described hereunder with reference to the accompanying drawings, in which:

FIG. 1 shows a side view of a press according to the invention, with the platens in the open condition;

FIG. 2 shows a view from the right-hand of the press of FIG. 1;

FIG. 3 shows a first enlarged detail of the clamping system, at one end of a tie-rod;

FIG. 4 shows a second enlarged detail of the clamping system, in correspondence with the other end of the tie-rod;

FIGS. 5, , and show, in different operative conditions, the clamping device according to the invention;

FIG. 9 schematically shows a second embodiment;

FIG. 10 shows a view from the right-hand of FIG. 9;

FIG. 11 shows a third embodiment;

FIG. 12 shows a view from the right-hand of FIG. 11;

FIG. 13 shows a fourth embodiment;

FIG. 14 shows a view from the right-hand of FIG. 13;

FIG. 15 shows a fifth embodiment;

FIG. 16 shows a view from the right-hand of FIG. 15;

FIG. 17 shows a sixth embodiment;

FIG. 18 shows a view from the right-hand of FIG. 17;

FIG. 19 shows a seventh embodiment;

FIG. 20 shows a view from the right-hand of FIG. 19;

FIG. 21 shows an eighth embodiment;

FIG. 22 shows a view from the right-hand of FIG. .

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. from to , a description is given hereunder of a preferred embodiment of an injection molding press with two platens, provided with a clamping device according to the present invention, and its operating method.

As shown in FIG. 1, a two platen press for injection molding of plastic materials, substantially comprises a first stationary platen for supporting a first half mold , and a second movable platen for supporting a second half mold , aligned according to the longitudinal axis of the press.

The movable platen is mounted on a saddle sliding along guide rails parallelly arranged to the longitudinal axis of the press.

Between the stationary platen and the movable platen extend four tie-rods , peripherally disposed at the corners of the two platens and .

More precisely, as shown in the example of FIG. 4, each tie-rod is slidably supported by the stationary platen , and is connected to any kind of actuator capable of causing the same tie-rod to shift slightly in an axial direction for a short stroke.

In particular, the actuator can be a piston cylinder unit , capable of generating a high force or tonnage necessary for the tightly clamping the two half molds and .

The fore end of each tie-rod, as shown in FIG. 3, presents a threaded portion D which extends axially through a locking bush ; the bush is supported by the movable platen to freely rotate with the possibility of shifting slightly in an axial direction for the reasons explained further on, with reference to the FIGS. from to of the accompanying drawings.

In particular, the bush is supported by the movable platen by bearings designed to enable the same bush to freely and frictionless rotate and to shift for a short axial clearance as specified further on.

In order to exert the thrust for the tightly clamping of the two half molds, by the axial shifting of the tie-rods and the respective locking bushes , each bush , at its outer end, on the side of the movable platen opposite the one facing towards the stationary platen, is provided with an annular shoulder to come against a corresponding shoulder surface of the movable platen , or associated part thereof, to exert through the tie-rods the necessary clamping force for the closure of the mold.

Guide means are also provided to maintain the bush in a central position with the screw thread constantly disengaged from the screw thread of the corresponding rod , and to allow a relative axial movement, for the purposes specified previously; said guide means can be achieved in any way whatsoever; for example, as shown in FIGS. from to , the bush can be provided on the outer surface with an annular slot in which penetrate a guide roller A idly supported at the end of an elastically flexible guide pin ; the pin with the guide roller A protrudes radially from the movable platen to guide and maintain the bush , during rotation, appropriately centred with respect to the threaded portion D of the rod . Thus the bush is able to rotate freely without frictional forces and without contact with the internal screw thread of the bush and the corresponding external screw thread of the rod , as shown in FIG. 5 of the accompanying drawings.

In this connection, as can be seen in the various FIGS. from to , between the screw thread inside the bush and the screw thread outside the portion D of each tie-rod , there is a slight axial clearance sufficient to allow a relative axial movement between the rod and the bush , for the purposes specified further on.

Moreover, as shown in the cross-sectional views, the two screw threads present trapezoidal threads with similarly slanted sides, to transfer to the bush and from the latter to the movable platen , all the forces exerted on the tie-rods , without subjecting the same screw threads on excessive stress.

According to a further aspect of the invention, the press is provided with control means for controlling the movable platen, operated independently of the control means for the tie-rods; said control means consists of hydraulic cylinders which act to shift the movable platen towards and away from the stationary platen , respectively upon the closing and opening of the mold, and suitable means for controlling the synchronized rotation of all the locking bushes , in a way correlated to the sliding displacement of the movable platen .

In particular, in the solution shown in FIGS. 1 and 2, the means for controlling the movement of the movable platen comprise, on each side of the press, a ball bearing screw , ′ connected to the stationary platen , which engages with a screw nut , ′ rotatingly supported on one side of the movable platen .

One of the two screw nuts, for example the screw nut is in turn provided with a pulley connected, by means of a belt , to the pulley of an electric control motor .

The screw nut is in turn connected, by means of a second pulley and a belt , to a pulley coaxially arranged to the locking bush of one of the tie-rods in the lower left-hand corner of FIG. .

The bushes for locking the movable platen to the tie-rods , are in turn controlled to rotate in synchronism, for example by means of a positive drive belt which winds around corresponding pulleys coaxially arranged to the bushes , as shown in FIG. and in the enlarged detail of FIG. .

For the displacement of the movable platen it is possible to use a single screw/nut system ′, ; however, in certain cases it is preferable to make use of a double screw/nut system as shown in FIGS. 1 and 2.

The operation of the device for securing the platens to the rods and clamping the mold according to the present invention, will be now described hereunder with reference both to FIGS. 1 to of the accompanying drawings, and to the diagrams in FIGS. from to , which show the main steps of engagement and/or disengagement between the threaded portion D of each tie-rod , and the respective locking bush .

Assuming that the press is initially in the open condition shown in FIG. 1, and that the individual bushes are in turn in the retracted position with respect to the threaded portion D of the tie-rods , as schematically represented in ′ by the broken lines in FIG. .

In this condition, the screw threads of the bushes are not in contact with the screw threads of the tie-rods; consequently, the bushes can be made to rotate freely without any contact and without frictional forces between the screw threads , due to the presence of the guide pin for centring and guiding the bushes.

Due to the use of a synchronization system between the axial movement of the platen and the rotation of the bushes , the latter are able to rotate freely without any contact between the screw threads, throughout the entire forward stroke of the movable platen , as though the bushes were screwing along an ideal thread.

During the forward sliding of the movable platen , the two half molds and approach each other until their respective frontal surfaces come into contact; during this movement, the synchronizing system , , maintains the disengaged condition of the screw threads of the bushes from the screw threads of the individual rods , as shown by the continuous line in FIG. 5; this condition is ensured by the guide pins of the individual bushes .

At this point it is possible to carry out the engagement of the screw threads of the rods with the screw threads of the bushes , by means of a first short axial movement of the same rods , in the displacement direction of the movable platen , by a control imparted to the hydraulic cylinders .

This condition is shown in FIG. 6 in which it can be seen that the left sides of the screw threads have come into contact with the right sides of the screw threads .

After this first axial movement of the rods , designed to bring the screw threads and into contact each other, continuing the action of the control cylinders gives rise to a second short axial movement of the rods in order to bring the annular shoulders of each bush into contact with a corresponding shoulder surface A of the movable platen ; this condition is shown in FIG. 7 of the drawings.

By continuing the feeding of the pressurized fluid to the cylinders , it is possible to exert a drawing action on the rods , to generate a strong thrust to tightly clamp the two half molds and together.

In this condition, the guide pin is slightly elastically bent by the thrust exerted by a side of the slot on the roller A.

Upon completion of an injection step and consolidation of plastic material in the mold, it is possible to open the latter by reversing the procedure previously described.

That is to say, the pressure in the cylinders is released, thereby nullifying the drawing action on the rods ; consequently, due to the opposite thrust now exerted on the rods by the cylinders , the bushes will be made to move back until the shoulders are disengaged from the surfaces A of the movable platen , maintaining the contact condition between the screw threads and by the biasing action exerted by the pin on the bush , which returns to its initial position; this condition is shown in FIG. 8 of the accompanying drawings.

Lastly, by means of the hydraulic cylinders , the rods are once again made to slightly move back to allow the screw thread of each rods to disengage from the screw thread of the corresponding locking bush , thereby restoring the condition shown in FIG. .

In this condition, the movable platen can now be made to move backward again, by reversing the motor of the screw nut/ball screw system and , making the bushes once again rotate in synchronism to maintain their screw threads disengaged from those of the rods throughout the entire opening stroke of the press.

In the case shown in the FIGS. from to , the pin performs the dual function of a guiding and centring the threaded bush , and of a biasing means to return and maintain the bush in a disengaged condition of the screw threads; these guiding and centring functions of the threaded bush may be obtained by different means either of the passive type, or of the active type in substitution of the flexible pins .

For example, the pins may be replaced by two packs of Belleville washers acting on the two ends of each threaded bush , or by positively controlling the movement of the bush in one or both directions, by means of an appropriate hydraulic, pneumatic, electromagnetic or other type of actuator or control system.

From the foregoing, it is clear that the most highly innovative feature of the press and its operative method primarily consists in the use of tie-rods which are movable with respect to both the mold platens, and in the use of locking bushes rotatingly and axially movably supported by one of the platens of the press, and in which the bushes present an internal screw thread which is maintained constantly disengaged and not in contact with a corresponding screw thread at one extremity of the tie-rods, while the same bushes are made to rotate in synchronism during the sliding displacement of the movable platen of the press, and in a way correlated to the forward and backward movement of the same platen.

In this way the screw threads of the bushes and of the rods can be quickly engaged and disengaged with one another for securing and respectively releasing the movable platen with respect to the tie-rods of the press, thereby enabling the almost immediate clamping and opening of the molds.

In the case of FIG. 1, the locking bushes and the synchronizing system have been disposed on the movable platen of the press, while the hydraulic cylinders for drawing of the tie-rods have been disposed on the stationary platen ; however, their disposition may also be reversed as compared to that shown, without prejudice to the general features of the present invention.

In the example shown in FIGS. 1 and 2 use has also been made of a first control means for controlling the movable platen, consisting of a screw/nut system , operated by an electric motor , and a second control means consisting of the hydraulic cylinders to axially move the rods and secure them to the platens and to exert the necessary force ensuring the clamping and tight closing of the two half molds and .

Moreover, in the example shown in FIGS. 1 and 2, the system for synchronizing the rotation of the locking bushes and the sliding movement of the movable platen , makes use of the screw nut system , directly as a means of transducing the sliding movement of the movable platen and of correlation with the rotation of the bushes .

It is understood however that within the scope of the present invention other solutions are possible, in particular with regard to the use and type of the control means and of the system for synchronizing the rotation of the locking bushes, and for coordination with the sliding of the movable platen.

Several of the numerous possible solutions are shown in the examples of the remaining figures in which the same reference numbers of the previous figures have been used to indicate similar or equivalent parts.

A second solution is shown in FIGS. 9 and 10 in which the screw/nut system , of the previous example has been replaced by at least one hydraulic cylinder , two in the case shown, fastened to the stationary platen , while its rod is connected to the movable platen .

In this case, the synchronization between the rotation of the various bushes for locking the platen to the rods , and the sliding movement of the movable platen are always obtained by means of a mechanical movement transducer comprising a fixed ball-type screw and a nut screw rotatingly supported on one side of the movable platen , centrally disposed beneath the press; a pulley rotates with the nut screw to control the driving belt which winds around the pulley to synchronize the rotation of the various bushes locking the platen to the rods of the press.

For the remainder, the press of FIGS. 9 and 10 operates in a wholly identical manner to the press of the preceding example.

FIGS. 11 and 12 show a third embodiment, substantially similar to that of FIGS. 9 and 10, the only difference being that now the hydraulic cylinder which controls the sliding of the movable platen , has been replaced by a rack type control device comprising a rack on one side of the press, fastened to the stationary platen , and a gear wheel connected to an electric motor supported by the movable platen . Consequently, in FIGS. 11 and 12 the same reference numbers as in FIGS. 9 and 10 have been used to indicate similar or equivalent parts.

FIGS. 13 and 14 show a fourth possible solution which differs from the preceding ones in that the means for controlling the sliding of the movable platen , in this case consists of a linear electric motor, centrally disposed beneath the platens of the press, comprising a stationary member and a movable member connected to the movable platen , as schematically shown.

Control of the synchronized rotation of the various locking bushes on the rods , is also achieved by means of a belt drive , , and is derived from the linear movement of the movable platen by means of a screw/nut system , , in which the rotation of the screw nut is transmitted to the locking bush of at least one of the drawing rods, by means of a belt drive , as shown, or in any other suitable way.

Consequently, also in FIGS. 13 and 14 a part of the same reference numbers as the previous figures have been used to indicate similar or equivalent parts.

FIGS. 15 and 16 show a fifth solution which differs from the preceding solutions in that use is made of an electronic interlocking system for synchronizing the rotation of the locking bushes , with one another and in a way correlated to the sliding movement of the movable platen .

The control of the movable platen is again achieved by means of a screw/nut system , and ′, ′ operated by a motor in a way similar to the solution of FIG. 1; in this case, the control to the second nut screw ′ is transmitted by means of a first mechanical belt drive , , while the synchronization between the movement of the platen and the rotation of the bushes , is achieved by means of an electric or electronic transducer comprising, for example, a linear movement or positional transducer operatively connected to the movable platen of the press; the output signal of the transducer is transmitted to a port of an electronic control unit which governs the running of an electric motor which, by means of a second belt drive , or in any other way, drives the synchronized rotation of the various locking bushes on the rods of the press.

In these figures, the reference numbers of the previous figures have once again been used to indicate similar or equivalent parts.

FIGS. 17 and 18 show a sixth solution which, like the previous solution, uses an electronic system for the synchronization and coordination between the movement of the movable platen and the rotation of the clamping bushes on the rods .

This solution differs from that of FIGS. 15 and 16 in that control of the sliding of the platen is again achieved by means of two hydraulic cylinders ; consequently the same reference numbers as the previous figures have again been used to indicate similar or equivalent parts.

FIGS. 19 and 20 show a seventh solution which also makes use of an electronic synchronizing system and which, on the contrary, uses a rack-type control , and an electric motor for the displacement of the movable platen .

Lastly, FIGS. 21 and 22 show an eighth solution which also uses an electric or electronic synchronizing system, similar to that of the previous solutions, in which the movable platen is now driven by a linear control motor , similar to that of the solution of FIG. .

It is understood, however, that what has been described and shown in the various figures, has been given purely by way of example, and that other modifications or variations may be made, without departing from the scope of the claims.

CLAIMS

1. Method for clamping molds in an injection molding press of the type comprising: a first platen for supporting a first half mold; a second platen for supporting a second half mold, at least one of said platens being slidably movable with respect to the other one, parallel to a longitudinal axis of the press; a plurality of peripheral tie-rods parallely extending to said longitudinal axis between the two mold supporting platens of the press; first control means being provided for moving one platen towards and away from the other one, upon the closure and opening of the mold; and second control means for the tie-rods, and threaded bush members parallely arranged to the longitudinal axis of the press, said bush members having a threaded portion operatively connectable to a threaded portion of said tie-rods, to provide a high clamping force to tightly close the mold, the method comprising the steps of: supporting the tie-rods axially sliding with respect to both the platens of the press; providing a locking bush, for each tie-rod, rotatably and movably supported in the axial direction, by one of the platens of the press; each locking bush and the corresponding tie-rod including opposite interengaging screw threaded portions having an axial clearance between them; moving one of the platens in respect to the other one for closing and respectively for opening the mold by actuation of said first control means maintaining the screw threaded portions of the locking bushes and the tie-rods frictionless disengaged by synchronously rotating the locking bushes; interengaging the screw threaded portion of the tie-rods with the screw threaded portion of the locking bushes by causing an axial sliding movement of the bushes by said second control means, to urge a shoulder member of the bushes against a corresponding shoulder surface of the platen of the press; and subsequently providing a clamping force to tightly close the mold, by generating a high axial force on the tie-rods and the locking bushes.

2. Method according to claim 1, wherein the step of synchronizing the rotation of the locking bushes, is provided by deriving their rotational movement from said first control means.

3. Method according to claim 2, wherein the step of synchronizing the rotational movement of the locking bushes, is performed by a mechanical drive directly connected to said first control means.

4. Method according to claim 2, wherein third independent control means are provided for causing the rotation of the locking bushes, and an electronic interlocking system between the movable platen and said third control means for synchronizing the rotational movement of the bushes and the sliding of the movable platen of the press.

5. A locking device for locking a tie-rod to a mold supporting platen of a press, comprising: a displaceable tie-rod extending through the platen of the press, said tie-rod having an outer threaded portion thereon; a locking bush rotatably supported by the platen, said locking bush having an inner threaded portion engageable and disengageable with the outer threaded portion of the tie-rod; the threaded portions of the tie-rod and the locking bush being constructed and arranged to provide an axial clearance allowing a relative axial displacement between them; an annular shoulder on the locking bush to be urged against a shoulder surface of the platen; guide means rotatably engaging the locking bush to maintain the threaded portion of the same bush, disengaged from the threaded portion of the tie-rod, upon rotation of the bush and during displacement of the platen; and control means to provide an axial displacement between the threaded portions of tie-rod and the bush, and to urge said annular shoulder against said shoulder surface at the clamping of the mold.

6. Press for the injection molding of plastic materials, comprising: a stationary platen for supporting a first half mold; a movable platen for supporting a second half mold, said platen being slidingly movable along a longitudinal axis of the press; a plurality of peripheral tie-rods parallelly extending between the platens of the press, each of said tie-rods having a threaded portion at one end; first control means being provided to displace the movable platen towards and away from the stationary one; and second control means for the tie-rods and threaded bushes having threaded portions operatively engageable with threaded portions of the tie-rods to generate a clamping the force for tightly close the mold; the tie-rods being movably supported in the axial direction by the platens of the press, through locking bushes rotatively supported by one of the platens of the press; the threaded portions of each locking bush and the respective tie-rod having an axial clearance between them, to allow a relative axial movement of the tie-rod in respect to the locking bush; each locking bush comprising an annular shoulder to engage a shoulder surface of a platen, by a short axial movement of the same bush; and means for providing a synchronized rotation of the locking bushes correlated to the sliding displacement of the movable platen of the press, and to maintain the threaded portion of the bush disengaged from the threaded portion of the corresponding tie-rod; said second control means provided for selectively causing a first sliding movement of the tie-rods with respect to the locking bushes, along said axial clearance to bring the screw threaded portions into contact with each other, respectively a second sliding movement of the tie-rods and the locking bushes to bring the annular shoulders of the bushes into engagement with the shoulder surfaces of a platen, and to tightly clamp the two half molds.

7. Press according to claim 6, wherein the tie-rods and the second control means are supported by the stationary platen, while the locking bushes and the means for synchronizing the rotation of said locking bushes are supported by the movable platen of the press.

8. Press according to claim 6, wherein rotational guide means for the locking bushes constructed and arranged to maintain the screw threaded portion of each bush disengaged from the screw threaded portion of the corresponding tie-rod, during displacement of the movable platen of the press.

9. Press according to claim 8, wherein said guide means comprise an elastically yieldable pin fastened to the movable platen of the press, said pin having a guide roller running into an annular slot on the outside surface of the locking bush.

10. Press according to claim 8, wherein the first control means for controlling the movable platen comprise at least one actuator, and in that said means for synchronizing the rotation of the locking bushes are operatively connected to said actuator, or to said movable platen, by a movement transducer device.

11. Press according to claim 10, wherein the first control means for controlling the movable platen comprise at least one linear actuator, and in that the movement transducer device in turn comprises an operative mechanical connection between the linear actuator and the means for synchronizing the rotation of the locking bushes.

12. Press according to claim 10, wherein the first control means for controlling the movable platen comprise a linear actuator and in that the movement transducer device comprises a position sensing means for sensing the position of the movable platen, and an electronic transducer operatively connected to an electric motor for actuation of the means for synchronizing the rotation of the locking bushes.

13. Press according to claim 11 or 12, wherein the linear actuator comprises a screw and nut drive system, which extends between the two platens of the press.

14. Press according to claim 11 or 12, wherein the linear control actuator comprises at least one hydraulic cylinder which extends between the stationary platen and the movable platen of the press.

15. Press according to claim 11 or 12, wherein the linear actuator comprises at least one rack system which extends between the stationary platen and the movable platen of the press.

16. Press according to claim 11 or 12, wherein the linear actuator comprises at least one linear induction motor which is operatively connected to the movable platen of the press.

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