Jaw clamping device

Abstract

The invention relates to a clamping device having innovative features, which can be used inside an injection molding machine to counteract the force which would tend to open the mold during the injection of a plastic material In particular, the invention relates to a mold closing unit equipped with an innovative jaw clamping device, which has the task of counteracting the opening forces generated by the filling and compaction pressures exerted by the injection unit itself, so as to overcome frequent technical drawbacks in conventional injection presses.

Description

[0001] JAW CLAMPING DEVICE

[0002] DESCRIPTION

[0003] FIELD OF APPLICATION

[0004] The present invention relates to a clamping device having innovative features, which can be used inside an injection molding machine to counteract the force which would tend to open the mold during the injection of a plastic material.

[0005] In particular, the invention relates to a mold closing unit equipped with an innovative jaw clamping device, which has the task of counteracting the opening forces generated by the filling and compaction pressures exerted by the injection unit itself, so as to overcome frequent technical drawbacks in conventional injection presses.

[0006] BACKGROUND OF THE INVENTION

[0007] Injection molding devices consist of several parts and are available in various configurations: a horizontal and a vertical configuration. Both types of machines use a power source, an injection unit, a molding unit and a closing unit to perform the steps of the molding cycle regardless of their size.

[0008] An injection unit is defined as the set of components which contribute to the plasticizing phase of the polymer. The main ones are: plasticizing screw rotated by the plasticizing motor, feeding hopper, polymer granulate mixer and dryer, melt injection cylinder. Injection molding presses are characterized by the mold closing unit, which closing the tonnages, represents the closing force required to keep the mold closed during the injection process, since the pressure which can be developed on the mold to keep it clamped during the injection of polymeric material is measured in tonnes or Kilonewtons (kN). The closing force required is proportional to the surface area of the mold figures and the pressure with which the material is injected. The closing unit has the task of keeping the two halves of the mold firmly closed. When the mold is mounted on the press, the female part of the mold (also known as the die) is fixed on the fixed side and the male part (also known as the punch) on the movable side, by means of plates.

[0009] In the case of a press with two planes, the closing unit consists of two mold-holder plates, which are connected to each other by means of movement cylinders which open and close the moving plane by sliding it centred on four columns: the two plates are called the fixed plate and movable plate. In the event of a toggle mechanism, the closing unit instead consists of three plates, the first of which is called the fixed plate integral with the base, the second of which is called the die head not constrained to the base of the press and having the task of counteracting the elongation of the columns by applying the closing tonnage to the mold, and a third plate, called the movable plate, positioned between the two fixed plates and on which a punch is mounted.

[0010] The motion of such plates is imparted with different systems. The movable plate must be carefully guided to ensure that the half molds do not close perfectly parallel. The movable plane must be guided with precision: in fact, an excessive clearance between the sliding bushings in the movable plate and the columns can lead to a lack of the necessary perpendicularity between the columns and the plane. Presses with a closing system with two planes have larger mold-holder plates and it is easier to guide the movable plate correctly during translation.

[0011] The movable plate is supported by skids to better support the weight of the mold and the plane and to not burden the columns with this load, also considering the friction between plane and columns in horizontal-type presses. The closing force of a press is generated by the stretching which is imparted on the columns.

[0012] It is therefore well known to equip injection molding machines with columns, and means are generally provided for grasping such columns to enable the plates to maintain the clamped position and withstand the high pressures applied to the half-molds. Depending on the design of the particular injection press or its closing unit, the clamping devices can be arranged in different points of the closing unit. In the closing units with one fixed and one movable mold-holder plate, it is good practice to fix the fixing device of the columns of the closing unit to the movable mold-holder plate.

[0013] Jaw-type clamping mechanisms are also used, in which the clamping jaws are rotatably fixed to an axis placed on the outside of the column and can be moved in and out of the column's annular grooves by means of a rotating or swinging movement around the aforesaid axis.

[0014] An example of this solution is represented by US patent application US20020086088A1, which describes a mold closing device for molding machines, which has a fixed mold-holder plate and a movable mold-holder plate, as well as columns for connecting the mold-holder plates. Pairs of gripper jaws are provided on one of the mold-holder plates, which can be moved transversely relative to the columns to selectively engage the column itself and thus clamp the mold-holder plate with the columns themselves. These jaws are characterized by the presence of translation means which transfer the movement of a hydraulic linear-motion cylinder to a rotating disc which, coupled with a fixed retaining ring causes a transverse sliding movement of said jaws. The translation means of the combined movement between the fixed retaining ring and the rotating disc are pins and / or rollers, the movement of which occurs within cams obtained in the jaws. A motion is obtained due to the dragging of the pins inside the cams, with the consequent opening / closing of the pair of jaws.

[0015] It follows that the jaw clamping device described in US20020086088A1 provides some advantages over the prior art described above, but still has the drawback of the continuous change of direction of the pins within the cams obtained inside the jaws. This solution is still not optimal in terms of molding cycle time and has the drawback that the clamping components and the relative handling wear out easily and therefore frequent maintenance is required.

[0016] In the light of the above, the need is felt to be able to arrange an engagement and clamping system in injection presses with a further reduction of the time required for the molding cycle, and at the same time less wear on the mechanical components of the clamping system.

[0017] The Applicant has found that the technical problems highlighted above can be solved by the use of a jaw clamping device which uses a roto-translational movement of the sectors constituting the jaw itself, with a consequent reduction of the friction generated and the time required for each molding cycle.

[0018] DISCLOSURE OF THE INVENTION

[0019] The present invention is expressed and characterised in the independent claims, while the dependent claims set forth other preferred and non-essential features of the present invention, or variants of the main solution idea.

[0020] It is a first object of the present invention a jaw clamping device for injection molding machines having a fixed plate and a movable plate mounted on a base and aligned, centred on tonnage columns, the clamping device being characterized in that it comprises the following components:

[0021] - a fixed disk equipped with a sequence of guide cams;

[0022] - a sectoral jaw comprising a plurality of bearings protruding from its lateral ends;

[0023] - a movable disk having a sequence of guide cams;

[0024] - a hydraulic cylinder having the function of transferring a rotary motion to the movable disk; wherein the jaw can engage or disengage from these tonnage columns as a consequence of this rotary motion transferred from the hydraulic cylinder to the movable disk.

[0025] The jaw device of the present invention can be easily used in an injection molding machine with two plates, which comprises a fixed plate constrained to the base of the machine itself and a movable plate which, through the action of handling cylinders, moves towards and away from the fixed plate. Each of these two plates has a half-mold mounted such that the contact position between the two half-molds generates a mold, within which the molten plastic material is injected to make the desired artefacts.

[0026] The handling cylinders of the movable plate are also called opening and closing cylinders of the mold and generally have a small cross-section: therefore, they are not capable of imparting the force required to counteract the force which would tend to open the mold during the injection of the plastic material. The jaw clamping device of the present invention therefore has the function, once the mold is closed, to engage on the tonnage columns, thus mechanically constraining the movable plate to the columns themselves.

[0027] Once the engagement between the jaws and the columns has occurred, consequently constraining the movable plate to the tonnage columns, the latter are pulled towards the fixed plate thanks to the action of a piston integral therewith, which is obtained inside the fixed plate. Thereby, the maximum closing force is applied to the mold, preventing it from opening under maximum safety conditions.

[0028] The jaw clamping device in accordance with the invention comprises the following basic components: a fixed disk, a sectoral jaw, a movable disk and a hydraulic cylinder having the function of transferring a short rotary motion to the movable disk.

[0029] As will become clear from the detailed description of the invention and the accompanying figures, this rotary motion brings the bearings protruding from the jaws into contact with the cams present on the movable disk. There are cams of different geometry on the fixed disk, which are opposed to those on the movable disk. These geometric constraints to which the bearings are subjected in their path within the cams of the fixed disk and the movable disk result in a roto-translation of the jaw sectors, which results in the jaw opening and closing.

[0030] In accordance with a preferred embodiment of the invention, the sectoral jaw preferably comprises three or four sectors having the shape of an arc of a circle.

[0031] A first important advantage of the jaw clamping device of the invention is related to the use of a hydraulic cylinder with a very short stroke, which further reduces the time required per each molding cycle relative to the conventional clamping systems.

[0032] A second advantage of the jaw clamping device of the invention is related to the reduction of energy required to move the jaws during their opening and closing.

[0033] The jaw clamping device is also advantageously integrally inserted in the movable plate, ensuring a greater cleanliness of the molding machine and greater protection of the jaw system from the outside environment.

[0034] A second object of the present invention is an injection molding machine consisting of an injection unit and a mold closing unit, the latter comprising:

[0035] - a fixed plate constrained to the base of this closing unit and a movable plate sliding on the base of the closing unit, both aligned and centered on tonnage columns;

[0036] - movement cylinders which position the movable plate relative to the fixed plate;

[0037] - tonnage pistons integrally inserted into the fixed plate and integral with the tonnage columns;

[0038] - one or more jaw clamping devices having the innovative features in accordance with the invention.

[0039] These and further advantages of the jaw clamping device in accordance with the invention will be more clearly shown in the following description of embodiments with reference to the accompanying figures.

[0040] DETAILED DESCRIPTION OF THE INVENTION

[0041] With reference to the attached figures 1-11, the present invention will now be described in detail taking into consideration a gripper jaw consisting of three sectors as an example. However, the inventive concept underlying the invention can also be extended to jaws having more or less sectors.

[0042] Figure 1 is a perspective view, from the side of the movable plate, of a mold closing unit comprising the jaw clamping device of the present invention.

[0043] Figure 2 is a perspective side view of a mold closing unit comprising the jaw clamping device of the present invention.

[0044] Figure 3 is an exploded view showing in succession the constituent components of the jaw clamping device of the invention.

[0045] Figure 4 is a perspective view of the clamping device of the invention with the jaw shown in the open position.

[0046] Figure 5 is a perspective view of the clamping device of the invention with the jaw shown in the closed position.

[0047] Figure 6 shows the overlapping of the geometric profiles of the cams present on the fixed disk and on the movable disk when the jaws are closed.

[0048] Figure 7 shows the overlapping of the geometric profiles of the cams present on the fixed disk and on the movable disk when the jaws are open.

[0049] Figure 8 is a perspective view of the clamping device of the present invention with the jaw closed and engaged in the tonnage column.

[0050] Figure 9 is a perspective view of the clamping device of the present invention with the jaw open and disengaged from the tonnage column.

[0051] Figure 10 is a sectional side view showing the details of a piston applying the tonnage step and is mounted integral with a tonnage column.

[0052] Figure 11 is a perspective view of the piston of figure 10, showing how this piston is obtained inside the fixed plate.

[0053] The mold closing unit 1 shown in figure 1 comprises a movable plate 2 and a fixed plate 3 constrained to the base 4 of the closing unit 1 : both the movable plate 2 and fixed plate 3 are approximately square in shape. Each of these two plates 2 and 3 has mounted a half-mold so that the contact position between the two half-molds generates a mold, within which the molten plastic material is injected to make the desired artefacts.

[0054] The movable plate 2 is provided with four circular holes at the corners, inside of which are housed four columns, which are called tonnage columns 5, as they apply the tonnage phase to the movable plate 2, as will be explained later. Also shown in figure 1 are two handling cylinders 6 of limited section, which are placed diagonally with each other on the outside of the two plates: these handling cylinders 6 have the function of moving the movable plate 2, allowing it to move closer to or farther away from the fixed plate 3 during the mold opening and closing cycle.

[0055] Once the mold is closed, jaw clamping devices 7 according to the invention are capable of engaging in the tonnage columns 5, mechanically constraining the movable plate 2 to the columns 5. Thereby, the jaw device 7 securely and reliably constrains the movable plate 2 to the tonnage columns 5. Figure 1 shows four clamping devices 7 embedded inside the movable plate 2, but only the outermost component (control flange) thereof can be seen, which will be described later.

[0056] Figure 2 is a perspective side view of the mold closing unit 1 comprising the clamping devices of the present invention. The fixed plate 3 is constrained to the base 4 of the mold closing unit 1, while the movable plate 2 can move closer to or farther away from the fixed plate 3 through the action of the handling cylinders 6.

[0057] The handling cylinders 6 are not capable of imparting the necessary force to counteract the force which would tend to open the mold during the injection of plastic material. Once the engagement between the jaw sectors and the tonnage columns 5 has occurred, the latter are pulled towards the fixed plate 3 thanks to the action of tonnage pistons 8 integral therewith: as shown in figure 2, each piston 8 is obtained inside the fixed plate 3 and its operation will be described in detail with reference to figures 10-11 below.

[0058] Figure 3 is an exploded view showing the sequence of constituent components of the jaw clamping device 7 of the present invention.

[0059] Starting from the left of fig. 3, the presence can be noted of a fixed disk 9 comprising six guide cams 10, i.e., two cams for each sector of the jaw 11. The fixed disk 9 is constrained inside the movable plate 2 shown in figures 1-2, and is not subject to any rotation.

[0060] In the clamping device 7, the fixed disk 9 engages with the jaw 11 comprising three sectors 12 in an arc of a circular, each sector extending by an angle of 120 degrees. At the two side ends of the jaw 11 there are roller bearings 13, capable of rotating along an axis parallel to the longitudinal axis of the jaw 11. As shown in figure 3, the roller bearings 13a protruding from the left side of the jaw 11 are housed in the guide cams 10 of the fixed disk 9, while the roller bearings 13b protruding from the right side of the jaw 11 are housed in the guide cams 15 of the movable disk 14.

[0061] In the preferred embodiment of the invention shown in figure 3, each sector 12 of the jaw 11 provides a total of four roller bearings 13a, 13b which are housed in the cams of the fixed disk 9 and movable disk 14.

[0062] In the movable disk 14 there are six guide cams 15, which are opposed to the guide cams 10 present in the fixed disk 9.

[0063] The clamping device 7 of the present invention further comprises a hydraulic cylinder 16 having the function of moving the movable disk 14, causing it to make a short rotary motion through the pin of the movable disk 17. The hydraulic cylinder 16 is supported by a control flange 18, which is integral with the movable plate 2 and also has the task of centering and guiding the movable disk 14. There is also a centering band 19 between the movable disk 14 and the control flange 18: it is a component having the function of providing adequate centering in the positioning and support for the rotation of the movable disk 14 with a reduced friction coefficient.

[0064] Figures 4-5 show the constituent components of figure 3 assembled to form the jaw clamping device 7 in accordance with the invention.

[0065] In particular, fig. 4 is a perspective view of the clamping device 7 with the jaw 11 shown in the open position. The hydraulic cylinder 16 is shown in a retracted position within a slot 20 present in the control flange 18, a position which corresponds to a mutual distancing of the three sectors 12 of the jaw 11 : this means that the jaw device 7 does not exert its engaging and constraining action on the movement of the tonnage columns 5 illustrated in figures 1-2.

[0066] Therefore, there are slits 21 present between the sectors 12 of the jaw 11 and thus the teeth 22 present on the inner circular crown of the jaw 11 do not engage the grooves 23 of the tonnage column 5 (not shown in fig. 4), thus allowing the movement of the movable plate 2 to the desired position through the use of the handling cylinders 6. Figure 5 is a perspective view of the clamping device 7 with the jaw 11 shown in the closed position. The hydraulic cylinder 16 is shown in an extended position inside the slot 20 of the control flange 18, a position which corresponds to the mutual approach of the three sectors 12 of the jaw 11 : this means that the teeth 22 on the inner circular crown of the jaw 11 engage the grooves 23 of the tonnage column 5.

[0067] The slits between the sectors 12 of the jaw 11 have disappeared due to the close contact between the sectors 12, while the teeth 22 on the inner circular crown of the jaw 11 can engage the grooves 23 of tonnage column 5 (not shown in fig. 5).

[0068] Figure 6 shows the overlapping of the geometric profiles of the guide cams present on the fixed disk 9 and the movable disk 14 when the jaws are closed, while figure 7 shows the overlapping of the geometric profiles of the guide cams when the jaws are open.

[0069] As explained above, the rotation of the movable disk 14 puts the roller bearings 13b of the jaw 11 in contact with the guide cams 15 present on the movable disk 14. The guide cams 10 present in the fixed disk 9 are of a different geometry with respect to the cams 15 of the movable disk 14, as can easily be deduced from figures 6-7.

[0070] The geometric constraints existing between the guide cams 10, the guide cams 15 and the roller bearings 13a, 13b result in a roto-translation of the three sectors 12 of the jaw 11, which results in the opening, or alternatively, the closing of the clamping device 7 of the present invention.

[0071] This roto-translational movement allows a high displacement of the sectors 12 of the jaw 11, which can engage or disengage completely from the tonnage column 5 in a very short time, as a consequence of the very limited stroke of the hydraulic cylinder 16 inside the slot 20.

[0072] In accordance with a preferred embodiment of the invention, the cams of the movable disk are all linear, while those of the fixed disk are half linear and half curved according to a very large radius. This prevents the bearings from jamming and allows a smoother and more linear movement of the system.

[0073] Figures 8-9 show perspective views of the clamping device 7 in accordance with the invention, respectively engaged or disengaged from the tonnage column 5. In particular, figure 8 shows the hydraulic cylinder 16 in an extended position inside the slot 20 of the control flange 18, so that the three sectors 12 of the jaw 11 are closely approached to each other: the jaw 11 exerts its constraining action on each movement of the tonnage column 5. The teeth 22 protruding from the inner annular surface of the jaw 11 are perfectly engaged within the grooves 23 along the tonnage column 5, whereby the latter is completely constrained to the clamping device 7.

[0074] Figure 9 shows the hydraulic cylinder 16 in a retracted position inside the slot 20 of the control flange 18, so that the three sectors 12 of the jaw 11 are spaced from each other and the jaw 11 does not exert its clamping action on the motion of the tonnage column 5. The teeth 22 protruding from the inner annular surface of the jaw 11 are not engaged in the grooves 23 present along the tonnage column 5, whereby the latter is free to move and at the same time the movable plate 2 can be brought into the desired position through the use of the handling cylinders 6. The clamping device 7 is therefore disengaged from the tonnage column 5.

[0075] The opening and closing of the four clamping devices 7 shown in figure 1 has been described above with independent movement, providing a hydraulic cylinder 16 for actuation on each individual clamping device 7.

[0076] Alternatively, the movement of the four clamping devices 7 can also be achieved in pairs, as depicted in figures 1 and 2, by mechanically joining the movable disks 14 of the lower jaw and the upper jaw by means of synchronizing rods 24, which are integral with the movable disk 14 through the pins of the movable disk 17: thereby, only two hydraulic cylinders 16, positioned for example in the two lower clamping devices 7, can be used to simultaneously move the four clamping devices 7. It is also possible to use a single hydraulic cylinder 16 with three synchronizing rods 24 always integral with the pins of the movable disk 17, which in turn are integral with the movable disk 14, to simultaneously move the four clamping devices 7.

[0077] As mentioned above, the handling cylinders 6 are not capable of imparting the necessary force to counteract the force which would tend to open the mold during the injection of plastic material. This counteract force is ensured by this sequence of operations:

[0078] A) once the mold is closed, the jaw clamping devices 7 engage on each tonnage column 5, thus mechanically constraining the movable plate 2 to the tonnage columns 5;

[0079] B) Once the engagement between the sectors 12 of the jaw 11 and the tonnage columns 5 has occurred, the latter are pulled towards the fixed plate 2 thanks to the action of a tonnage piston 8 integral therewith.

[0080] By means of the sequence of operations A) and B) above, the maximum closing force is applied to the mold, preventing an opening thereof during the molding step in maximum safety conditions.

[0081] Figures 10-11 show the structural configuration of the piston 8 having the function of applying the tonnage to the handling column 5.

[0082] As illustrated in figures 10-11, the tonnage piston 8 is mounted integral with the tonnage column 5. Furthermore, unlike the conventionally employed mold closing units, the tonnage piston 8 in the configuration of the present invention is embedded directly within the fixed plate 3 and is not obtained in a separate special chamber. As a further advantage, this allows to obtain a more compact mold closing unit 1 relative to the prior art.

[0083] As shown in Fig. 10-11, the tonnage piston 8 can move within two cylindrical chambers. The larger chamber, called tonnage chamber 25, is used for the tonnage of the column 5 filling this chamber with a suitable fluid, usually hydraulic oil, and pressurizing it. Thereby, the tonnage columns 5 move for a very short stretch, bringing their grooves 23 in contact with the jaw 11 in the closed position: thereby the tonnage force is applied to the movable plate 2.

[0084] The smaller secondary chamber 26 is used for the displacement of the tonnage column 5 to re-position it correctly relative to the clamping device 7 and thereby enable the jaws 11 to disengage from the columns 5.

[0085] The correct re-positioning of the column 5 is detected by position transducer 27 - a position transducer is present for each single column 5. The maximum stroke which can be achieved by the tonnage piston 8, in combination with the pitch of the grooves 23 present on the columns 5 and in combination with the movement performed by the handling cylinders 6, allow the tonnage force to be correctly applied to any size of mold thickness.

[0086] In summary, the jaw clamping device in accordance with the present invention allows achieving the following important advantages relative to similar jaw devices used in the prior art:

[0087] A) The hydraulic cylinder 16 which moves the movable disk 14 has a very short stroke: this results in a reduced opening and closing time of the jaws 11 and lower energy consumption; B) The use of bearings 13 protruding from the jaws 11 significantly reduces friction, which is of the rolling rather than sliding type, as is the case with the pins used in the clamping devices of the prior art;

[0088] C) The jaw 11 is integrally inserted in the movable plate 2, thereby ensuring a greater cleanliness of the molding machine and a greater protection of the jaw device 7 from the outside environment.

[0089] The present invention is not limited to the particular embodiments previously described in relation to figures 1-11, but numerous modifications can be made to it in detail, within the reach of the person skilled in the art, without thereby departing from the scope of the invention itself, as defined in the appended claims.

Claims

CLAIMS1. A jaw clamping device (7) for injection molding machines having a movable plate (2) and a fixed plate (3) mounted on a base (4) and aligned, centered on tonnage columns (5), the clamping device (7) being characterized in that it comprises the following components:- a fixed disk (9) equipped with a sequence of guide cams (10);- a sectoral jaw (11) comprising a plurality of bearings (13a, 13b) protruding from its lateral ends;- a movable disk (14) having a sequence of guide cams (15);- a hydraulic cylinder (16) having the function of transferring a rotary motion to said movable disk (14); wherein said sectoral jaw (11) can engage or disengage from said tonnage columns (5) as a result of said rotary motion transferred from said hydraulic cylinder (16) to said movable disk (14).

2. The jaw clamping device (7) according to claim 1, characterized by the fact that said movable plate (2) moves away from or approaches said fixed plate (3) by the action of handling cylinders (6).

3. The jaw clamping device (7) according to anyone of the previous claims, characterized by the fact that said rotary motion connects said bearings (13b) with the guide cams (15) on said movable disk (14).

4. The jaw clamping device (7) according to anyone of the previous claims, characterized by the fact that the guide cams (10) on said fixed disk (9) are of a different geometry and opposed to the guide cams (15) on said movable disk (14).

5. The jaw clamping device (7) according to anyone of the previous claims, characterized in that the roller bearings (13a) protruding from one end of said jaw (11) are housed in the guide cams (10) of said fixed disk (9), while the roller bearings (13b) protruding from the other end of said jaw (11) are housed in the guide cams (15) of said movable disk (14).

6. The jaw clamping device (7) according to anyone of the previous claims, furthercomprising a control flange (18) joined with said movable plate (2) and having the function of centering and guiding said movable disk (14) and supporting said hydraulic cylinder (16).

7. The jaw clamping device (7) according to anyone of the previous claims, characterized by being integrally inserted inside said movable plate (2).

8. The jaw clamping device (7) according to anyone of the previous claims, characterized in that said jaw (11) comprises three or four sectors (12) having the shape of an arc of a circle.

9. The jaw clamping device (7) according to anyone of the previous claims, characterized by the fact that the geometric constraints existing between said guide cams (10), said guide cams (15) and said bearings (13a, 13b) result in a roto-translation of the sectors (12) of the jaw (11).

10. The jaw clamping device (7) according to anyone of the previous claims, characterized in that successively to the engagement of said jaw (11) on said tonnage column (5), a tonnage piston (8) exerts a pulling action on said tonnage column (5) towards said fixed plate (3).

11. An injection molding machine consisting of an injection unit and a mold closing unit (1) comprising:- a fixed plate (3) constrained to the base (4) of said mold closing unit (1) and a movable plate (2) sliding on said base (4), both aligned and centered on tonnage columns (5);- handling cylinders (6) moving said movable plate (2) relative to said fixed plate (3);- tonnage pistons (8) integrally inserted into said fixed plate (3) and joined with said tonnage columns (5); said mold closing unit (1) being characterized by the fact of comprising one or more jaw clamping devices (7) according to anyone of claims 1-10.

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