WO2006080807A1

WO2006080807A1 - Injection molding machine for multicavity

Info

Publication number: WO2006080807A1
Application number: PCT/KR2006/000295
Authority: WO
Inventors: Hyuk Joong Kim
Original assignee: Hyuk Joong Kim
Priority date: 2005-01-27
Filing date: 2006-01-25
Publication date: 2006-08-03

Abstract

The present invention relates to a valve device of an injection molding machine for multicavity molds, which can control a plurality of nozzles used with a multicavity mold at one time using a single actuating source. Because the valve device of the present invention can open or close the gates of the multiple nozzles at one time using the single actuating source and can control the timing to open or close the nozzle gates, the valve device prevents the production of bad quality plastic products, and enables the manufacture of high quality molded products in large quantities. Particularly, even when resin hardens in the nozzle of the valve device and a valve pin is forcibly moved upwards or downwards in the hardening resin, the present invention prevents damage or breakage of the valve pin, thus improving stability and reliability of the valve device.

Description

INJECTION MOLDING MACHINE FOR MULTICA VITY

Technical Field

[1] The present invention relates to a valve device of an injection molding machine for multicavity molds, which simultaneously controls the opening and closing motions of a plurality of injection nozzles used with a multicavity mold using a single actuating source, and independently controls the injection amounts of the respective nozzles, thus producing high quality molded products in large quantities. Background Art

[2] Generally, an injection molding machine, which is a machine for manufacturing plastic products through injection molding, is configured such that molten resin is injected from a resin cylinder into a manifold, and the injected resin in the manifold is evenly distributed to one or more nozzles, coupled to the lower end of the manifold, through a plurality of branching resin paths formed in the manifold, prior to being injected into a cavity of a mold, which is a forming body used for manufacturing plastic products.

[3] Conventional injection molding machines are configured such that a nozzle gate is opened or closed in response to vertical motion of a valve pin, and are classified into two types, which are manifold-type injection molding machines and single-type injection molding machines, according to the number of products to be molded. A manifold-type injection molding machine has a resin feeding manifold and is typically used when it is necessary to form a plurality of products at one time, while a single- type injection molding machine is typically used when it is required to produce a single product.

[4] FlG. 1 is a sectional view illustrating a conventional valve device of an injection molding machine for multicavity molds, which can move a valve pin upwards and downwards using high pressure air as actuating pressure.

[5] As shown in FlG. 1, the conventional valve device of the injection molding machine for multicavity molds comprises a drive unit 100 and a valve device 200, with high pressure air used as an actuating source to cause vertical motion of a valve pin 210. That is, the drive unit 100 is provided with a plurality of air channels 110 and 120 to supply high pressure air from an external air source into the drive unit 100 or to discharge air from the drive unit 100 to the external air source, so that the high pressure air supplied to the drive unit 100 through the air channels 110 and 120 can move a piston 140 upwards and downwards in a cylinder 130. In the above state, the lower end of the piston 140 is coupled to a valve pin 210, thus moving the valve pin 210. Further, because the valve pin 210 is moved upwards and downwards in conjunction with the piston 140, the valve pin 210 selectively opens or closes the gate that forms the resin outlet of a nozzle 220.

[6] The nozzle 220 determines the appearance of the valve device 200, with a heater wire wound around the nozzle 220 to prevent resin from being hardened while the resin passes through the nozzle 220. The valve pin 210 is axially received in the nozzle 220 such that the valve pin 210 is vertically movable in the nozzle 220. In the nozzle 220, a resin orifice 230 is axially defined around the valve pin 210 such that the lower end of the resin orifice 230 extends to the gate of the nozzle 230 and the upper end of the resin orifice 230 is connected to a resin path 330 of a manifold 300, respectively.

[7] The above-mentioned conventional valve device of the injection molding machine for multicavity molds is operated as follows. When high actuating pressure is supplied to and discharged from the drive unit 100 through the air channels 110 and 120, the piston 140 is moved downwards or upwards and, at the same time, the valve pin 210 is operated in conjunction with the piston 140, thus executing vertical motion. As the piston 140 is moved upwards or downwards as described above, the valve pin 210 opens or closes the gate of the nozzle, so that resin from the manifold 300 may be injected into the cavity of a mold through the gate, or the supply of the resin into the mold may be stopped.

[8] Described in brief, in the operation of the conventional pneumatic valve device for controlling the nozzle gate of an injection molding machine using high pressure air, the high pressure air is supplied to a chamber of the cylinder 130 through an associated one of the air channels 110 and 120, thus moving the piston 140 downwards or upwards in the cylinder 130. In the above state, the valve pin 210 is operated in conjunction with the piston 140 and opens or closes the gate of the nozzle.

[9] However, the above-mentioned conventional valve device uses high pressure air as an actuating source to actuate the valve pin upwards or downwards, so that the valve device must have a seal structure to prevent air leakage from the valve device and requires a large-sized pressure air supply system (compressor) to supply the actuating pressure to the valve device. Thus, the valve device is problematic in that it undesirably has an enlarged volume and a complicated structure, thereby being installed in large spaces and being very difficult to repair or maintain. Furthermore, when the valve device is adapted to an injection molding machine for multicavity molds, variation in the injection amounts of nozzles of the injection molding machine is caused by variation in the dimensions of the nozzles. Thus, it is very difficult to manufacture plastic products having uniform qualities in large quantities through injection molding.

[10] In an effort to solve the above-mentioned problems, the applicant of the present invention proposed valve devices, in which a valve pin is actuated upwards and downwards using electricity, in Korean Utility Model Registration Nos. 0280604, 0280605, 0280606, 0290456, 0341515, and 0344137.

[11] Described in brief, each of the valve devices disclosed in the above-mentioned

Korean utility models comprises a valve body and a drive means. The valve body has a typical valve structure, which has a resin channel therein to receive resin through the branching resin path of the manifold and to inject the resin into a mold through the gate provided at the end of the nozzle. Further, the drive means uses a reversible motor or an actuator, which can move the valve pin upwards or downwards using electricity.

[12] The conventional valve devices disclosed in the utility models, which were filed and are held by the applicant of the present invention, have a structure using an electric reversible motor or an electric actuator as an actuating source, thus having a small- sized structure and increasing freedom when designing molds for the valve devices, and quickly and precisely controlling the movement of the valve pin.

[13] However, each of the conventional valve devices proposed by the applicant of the present invention is problematic in that a motor or an actuator is provided for each of the nozzles in order to control the vertical movement of the valve pin for opening or closing the nozzle, thus having a complicated structure. Therefore, if the valve devices proposed by the applicant of the present invention are adapted to injection molding machines for molds capable of manufacturing a plurality of products at one time, it is difficult to change an existing actuating source with a new one or to repair the actuating source, thereby reducing workability and productivity while changing or repairing the actuating source. Particularly, a plurality of expensive actuating sources must be provided relative to respective nozzles, thus increasing the cost of producing the valve device for injection molding devices.

[14] Furthermore, the actuating sources have different performance characteristics, so that it is very difficult to synchronize the timing to open or close the nozzles. In an effort to synchronize the timing to open or close the nozzles, the voltages for the actuating sources may vary to control the operating time of valve pins for the nozzles. However, this is problematic in that it consumes excessive working time and reduces productivity.

Disclosure of Invention Technical Problem

[15] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a valve device of an injection molding machine for multicavity molds, which can simultaneously control the multiple nozzles, used with a multicavity mold, using a minimum actuating source, thus synchronizing the timing to open or close the nozzles and manufacturing plastic products in large quantities at reduced cost.

[16] Another object of the present invention is to provide a valve device of an injection molding machine for multicavity molds, which can separately and precisely control the injection amounts of respective nozzles, thus compensating for nonuniform injection amounts of the nozzles caused by errors in machining both the nozzles and the manifold in the injection molding machine, thereby manufacturing high quality plastic products in large quantities, and compensating for strain force generated when the valve pins are moved upwards or downwards while the resin in the nozzles becomes hardened, and preventing damage, deformation or breakage of the valve pin and lengthening the expected life span of the valve device, and increasing the operational reliability of the valve device. Technical Solution

[17] In order to achieve the above object, according to an embodiment of the present invention, there is provided a valve device of an injection molding machine for multicavity molds, comprising: a manifold having a branching resin path to inject resin into a multicavity mold; a plurality of nozzles provided at positions under the manifold to receive the resin from the manifold, with a resin orifice formed through each of the nozzles such that the resin orifice extends to a nozzle gate provided in an end of the nozzle, and a longitudinal valve pin received in the resin orifice to open or close the nozzle gate in response to lifting motion of the valve pin; a drive means securely placed at a predetermined position above an upper surface of the manifold, the drive means comprising a reversible motor to rotate a screw shaft projecting toward the manifold, and a lifting plate coupled to the screw shaft through a threaded engagement so as to be displaced in a vertical direction in conjunction with rotating motion of the screw shaft, with an upper end of the valve pin being coupled to the lifting plate; and a resin pressure control means for controlling an amount of resin passing through the nozzle, the resin pressure control means comprising a pressure control pin through which the valve pin passes, and the pressure control pin being configured such that an upper end of pressure control pin is moved upwards or downwards in response to a screw adjustment and a lower end of the pressure control pin is placed in a small diameter part of the branching resin path.

[18] According to another embodiment of the present invention, there is provided a valve device of an injection molding machine for multicavity molds, comprising: a manifold having a branching resin path to inject resin into a multicavity mold; a plurality of nozzles provided at positions under the manifold to receive the resin from the manifold, with a resin orifice formed through each of the nozzles such that the resin orifice extends to a nozzle gate provided in an end of the nozzle, and a longitudinal valve pin received in the resin orifice to open or close the nozzle gate in response to lifting motion of the valve pin; a drive means securely placed in a base plate provided above an upper surface of the manifold, the drive means comprising a reversible motor to rotate a screw shaft projecting toward the manifold, and a lifting plate coupled to the screw shaft through a threaded engagement so as to be displaced in a vertical direction in conjunction with rotating motion of the screw shaft, an upper end of the valve pin being coupled to the lifting plate; a cushioning means comprising a tubular bushing engaging with the lifting plate through a threaded engagement such that the bushing is selectively displaced in a vertical direction, a valve pin having an upper part placed in the bushing, the upper part of the valve pin being divided into upper and lower pins with upper and lower flanges provided at respective facing ends thereof, and upper and lower elastic members placed in the bushing so as to elastically bias the upper and lower flanges such that the upper and lower flanges are in close contact with each other; and a pin retraction amount control means held at a predetermined position on the base plate by a threaded engagement such that the pin retraction amount control means is displaced upwards or downwards in a vertical direction, with a lifting stopper provided in the pin retraction amount control means to selectively come into contact at a lower end thereof with an upper end surface of the upper pin, thus variably controlling upward movement of the valve pin. Brief Description of the Drawings

[19] FlG. 1 is a sectional view illustrating a conventional valve device of an injection molding machine for multicavity molds;

[20] FlG. 2 is a sectional view illustrating a valve device of an injection molding machine for multicavity molds according to a first embodiment of the present invention;

[21] FlG. 3 is a sectional view illustrating an opened state of a nozzle of FlG. 2;

[22] FlG. 4 is a sectional view illustrating a resin pressure control state in FlG. 2;

[23] FlG. 5 is a perspective view illustrating part of a resin pressure control means of

FIG. 2;

[24] FIG. 6 and FlG. 7 are sectional views illustrating the use of a nozzle heater block in the present invention;

[25] FIG. 8 is a sectional view illustrating a drive means according to another embodiment of the present invention;

[26] FlG. 9 is a view schematically illustrating an example of coupling a timing belt of the drive means shown in FIG. 8;

[27] FlG. 10 is a sectional view illustrating a valve device of an injection molding machine for multicavity molds according to a second embodiment of the present invention;

[28] FlG. 11 is a sectional view illustrating the opened state of the nozzle shown in FlG.

10;

[29] FlG. 12 and FlG. 13 are sectional views illustrating a state wherein a valve pin is moved upwards or downwards while resin in a nozzle becomes hardened;

[30] FlG. 14 is an exploded perspective view illustrating the important construction of a cushioning means; and

[31] FlG. 15 is a perspective view illustrating the construction of a pin retraction amount control means.

[32] <Description of the elements in the drawing>

[33] 10: manifold 20 : nozzle 25 : valve pin

[34] 30: drive means 31 : reversible motor 32 : screw shaft

[35] 33: drive pulley 34 : driven pulley 35 : timing belt

[36] 36: lifting plate 37 : sensing unit

[37] 40:resin pressure control means

[38] 50: heater block 60 : cushioning means

[39] 70: pin retraction amount control means

Mode for the Invention

[40] The present invention relates to valve devices of injection molding machines for multicavity molds and, more particularly, to a valve device of an injection molding machine for multicavity molds, which simultaneously controls the opening and closing motions of a plurality of injection nozzles used with a multicavity mold using a single actuating source, and independently controls the injection amounts of the respective nozzles, thus producing high quality molded products in large quantities.

[41] Herein below, valve devices of injection molding machines for multicavity molds according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[42] First, the valve device of the injection molding machine for multicavity molds according to the present invention may be embodied as a first embodiment and a second embodiment. FlG. 2 through FlG. 9 are views illustrating a valve device according to the first embodiment of the present invention.

[43] That is, FIGS. 2 and 3 are sectional views illustrating an opened state of a nozzle of the valve device of the injection molding machine for multicavity molds according to the first embodiment of the present invention. FlG. 4 is a sectional view illustrating a resin pressure control state of the valve device. FlG. 5 is a perspective view illustrating part of a resin pressure control means of the valve device. As shown in the drawings, the valve device of the injection molding machine for multicavity molds according to the present invention comprises a manifold 10, a plurality of nozzles 20, a drive means 30 for moving valve pins 25 upwards and downwards, and a resin pressure control means 40 for controlling resin pressure.

[44] The manifold 10 has a plate structure made of metal, with a branching resin path

10a formed in the manifold 10 so that molten resin can flow through the resin path 10a. Heaters (not shown) are embedded in the manifold 10 at positions above and below the resin path 10a and emits heat to the resin flowing through the resin path 10a, thus preventing the molten resin from being hardened. The manifold 10 has a small diameter part 10b in the resin path 10a, as shown in the drawings. The small diameter part 10b of the resin path 10a is tapered downwards such that the opening ratio of the small diameter part 10b may be increased or reduced in response to a vertical movement of a pressure control pin 41, which will be described later herein, in the resin path 10a. In the present invention, the minimum diameter of the small diameter part 10b is equal to the diameter of a resin orifice 20a of each of the nozzles 20.

[45] The drive means 30 is provided above the above-mentioned manifold 10 to move the valve pins 25 upwards or downwards, while the nozzles 20 are provided below the manifold 10 to receive resin and inject the resin into a multicavity mold.

[46] Each of the nozzles 20 has a longitudinal cylindrical structure, with a heater wire h wound around the outer circumferential surface of the nozzle 20. A resin orifice 20a is formed through the central axis of the nozzle 20 such that the resin orifice 20a communicates with the resin path 10a of the manifold 10. The resin orifice 20a of the nozzle 20 extends to the resin outlet end of the nozzle 20, which forms the gate (not shown). Although it is not illustrated in the accompanying drawings of the preferred embodiments, the gate of the nozzle is coupled to an end of the mold and injects resin into the mold so as to manufacture a molded product. Further, a heater wire h is wound around the outer circumferential surface of the nozzle 20, thereby preventing resin from being hardened while the resin flows through the resin orifice 20a of the nozzle 20.

[47] The nozzle 20 receives a longitudinal valve pin 25 in the resin orifice 20a, which is formed through the central axis of the nozzle 20. The outer diameter of the valve pin 25 is smaller than the inner diameter of the resin orifice 20a so that resin can flow through the gap defined around the valve pin 25. In the above state, the valve pin 25 opens or closes the gate in response to its vertical motion. To accomplish the above object, the upper end of the valve pin 25 passes through the manifold 10 and is coupled to a lifting plate 36 of the drive means 30.

[48] The drive means 30 comprises a plurality of reversible motors 31, which can generate reversible rotating force, and the lifting plate 36, which is coupled to the reversible motors 31 using screw shafts 32 and is moved upwards and downwards by the reversible rotating force of the motors 31.

[49] The reversible motors 31 are securely mounted to a base plate b, which is placed at a position spaced above the manifold 10 by a predetermined height. Each of the reversible motors 31 is provided with a rotating shaft, which is rotated in either direction in response to electricity applied thereto from an external power source. The rotating shaft extends towards the manifold 10 and is connected to the screw shaft 32. The screw shaft 32 is coupled at its upper end to the reversible motor 31 so as to receive the rotating force from the motor 31 and is rotatably coupled at its lower end to the upper surface of the manifold 10. The outer circumferential surface of the screw shaft 32 is externally threaded to form a thread. The screw shaft 32 having the external thread around the outer circumferential surface passes through and engages with an internally threaded hole (not shown), which is formed through the lifting plate 36 at a predetermined position, in a threaded engagement so that the screw shafts 32 move the lifting plate 36 upwards or downwards using the rotating force of the respective reversible motors 31.

[50] The lifting plate 36 is a plate-shaped member, with a plurality of valve pins 25 coupled at the upper ends thereof to the lifting plate 36. Further, at least one internally threaded hole (not shown) is formed through the lifting plate 36 at a predetermined position so as to engage with the screw shaft 32. Because the lifting plate 36 is coupled to the upper ends of the valve pins 25, the lifting plate 36 and the valve pins 25 may be moved upwards or downwards in conjunction with each other. In the present invention, the structure for coupling the lifting plate 36 to the upper ends of the valve pins 25 may be variously configured. For example, the upper ends of the valve pins 25 may be secured to the lifting plate 36 through welding or fitting. Alternatively, as shown in the drawings, the outer circumferential surface of the upper part of each of the valve pins 25 may be externally threaded, while a nut (not shown) may be locked to the lifting plate 36 through fitting so as to engage with the externally threaded upper end of the valve pin 25 through a screw engagement.

[51] To limit the moving distance of the lifting plate 36 and to define the nozzle opening position of the valve pin 25, the drive means 30 is provided with a sensing unit 37. The sensing unit 37 comprises sensors, which are placed at respective positions above and below the lifting plate 36, such that, when the lifting plate 36 approaches a sensor of the sensing unit 37, the sensing unit 37 senses the lifting plate 36, controls the operation of the reversible motors 31 and controls the vertical movement of the lifting plate 36. In the preferred embodiment shown in the drawings, the sensing unit 37 of the present invention is configured such that it senses the position of the movable lifting plate 36 and controls the operation of the reversible motors 31. However, the construction and operation of the sensing unit 37 of the present invention may be variously modified without being limited to the above- mentioned sensors if the sensing unit 37 controls the nozzle opening position of each of the valve pins 25. For example, the sensing unit 37 may comprise a potentiometer or an encoder which has been typically used for controlling motors.

[52] The resin pressure control means 40 controls the amount of resin that passes through the nozzles 20. The resin pressure control means 40 comprises a pressure control pin 41, which is placed at a lower end thereof in the resin path 10a of the manifold 10 and is moved upwards or downwards to control the opening ratio of the resin path 10a, thus controlling the pressure of resin passing through the resin path 10a. The resin pressure control means 40 further includes a support body 42, which movably supports an upper end of the pressure control pin 41 such that the pin 41 may be moved upwards or downwards. A control bar 43 is provided in the resin pressure control means 40 so as to be manipulated by a worker and to transmit the manipulating motion of the worker to the pressure control pin 41.

[53] The pressure control pin 41 is a tubular hollow member, which is configured such that a valve pin 25 passes through the axial center of the pin 41. The upper end of the pressure control pin 41 passes through the manifold 10 so as to project outside the upper end of the manifold 10, while the lower end of the pin 41 is placed in the small diameter part 10b of the resin path 10a. In other words, the upper part of the pressure control pin 41 is externally threaded around the outer circumferential surface thereof and engages with an internally threaded part of the support body 42 through a threaded engagement, so that the pressure control pin 41 can be moved upwards or downwards relative to the support body 41 in a screw-type adjustment manner. The lower end of the pressure control pin 41 is tapered downwards to form a tapered end and is placed in the small diameter part 10b of the resin path 10a. In the preferred embodiment, the small diameter part 10b of the resin path 10a of the manifold 10 is tapered downwards such that, when the pressure control pin 41 is moved downwards, the opening ratio of the small diameter part 10b is reduced. The tapered small diameter part 10b is configured such that the minimum diameter of the small diameter part 10b is equal to the diameter of the resin orifice 20a of the nozzle 20.

[54] The support body 42 is secured to the manifold 10 through welding or fitting such that the support body 42 is immobile relative to the manifold 10 and has an internally threaded central hole, so that the externally threaded part of the pressure control pin 41 engages with the internally threaded central hole of the support body 42 through a threaded engagement.

[55] The control bar 43 is provided with gear teeth, which engage with the external surface of the upper end of the pressure control pin 41 through a worm gear engagement. A tool insert groove is formed on an end surface of the control bar 43 so that a worker can rotate the control bar 43 using a tool, such as a screwdriver. To prevent the control bar 43 from being undesirably moved upwards, downwards, leftwards or rightwards, the control bar 43 is preferably supported by at least one bearing 43b and a support structure 43c, as shown in FlG. 5. Furthermore, the pressure control pin 41 is preferably configured such that the upper end of the pin 41, which engages with the control bar 43 through a worm gear engagement, has a diameter larger than that of the lower end of the pin 41. Due to the large diameter of the upper end, the pressure control pin 41 can be finely manipulated while it is moved upwards or downwards.

[56] The above-mentioned resin pressure control means 40 is operated as follows. When the control bar 43 is manipulated to rotate in either direction, the pressure control pin 41 is moved upwards or downwards in conjunction with the rotating motion of the control bar 43. For example, when the control bar 43 in the state shown in FlG. 2 is rotated in one direction, the pressure control pin 41 may be moved downwards in conjunction with the rotating motion of the control bar 43 so that the opening ratio of the small diameter part 10b can be reduced as shown in FlG. 4, thus reducing the amount of resin passing through the nozzles 20. In the preferred embodiment of the present invention, the lower end of the pressure control pin 41 is placed in the resin path 10a of the manifold 10, which linearly communicates with the resin orifice 20a of the nozzle 20. However, the location of the lower end of the pressure control pin 41 according to the present invention may be variously modified without being limited to the above-mentioned location if the lower end of the pressure control pin 41 can control the opening ratio of the resin path of the manifold. For example, the lower end of the pressure control pin 41 may extend downwards to reach a position adjacent to the gate of the nozzle 20. In the above state, the resin orifice 20a of the nozzle 20, in which the lower end of the pressure control pin 41 is placed, is configured to have a small diameter part corresponding to the tapered end of the pressure control pin 41.

[57] FlG. 6 and FlG. 7 are sectional views illustrating the use of a nozzle heater block in the valve device of the injection molding machine for multicavity molds according to the present invention. The construction of FIGS. 6 and 7 is similar to that of FIGS. 2 through FlG. 5. However, the valve device according to this embodiment is characterized in that it is provided with a heater block 50, in which a heater wire 50h is embedded so as to heat the nozzle 20. In the present invention, the heater block 50 may have a single sheet structure comprising one metal sheet as shown in FlG. 6 or a laminated sheet structure comprising a plurality of laminated metal sheets having a predetermined thickness as shown in FlG. 7.

[58] The above-mentioned heater block 50 is provided with an installation hole, in which the nozzle 20 is installed, with the heater wire 5Oh embedded in the heater block 50 at a position around the installation hole. Thus, when the valve device of the present invention is adapted to an injection molding machine having multiple nozzles 20 specifically used with a multicavity mold, it is not necessary to wind a heater wire around each of the nozzles 20, thus improving work efficiency while fabricating the injection molding machine having the multiple nozzles 20.

[59] FlG. 8 and FlG. 9 illustrate another embodiment of the drive means constituting the valve device of the injection molding machine for multicavity molds according to the present invention. In the present embodiment, the general construction of the valve device of the injection molding machine for multicavity molds remains the same as that described for the embodiment of FlG. 2 through FlG. 5, and those elements common to the two embodiments will thus carry the same reference numerals in the following description. As shown in FIGS. 8 and 9, the drive means 30 of this embodiment is characterized in that, although it uses a single reversible motor 31, the drive means 30 can operate a plurality of screw shafts 32 at one time and stably moves the lifting plate 36 while maintaining the balance of the lifting plate 36.

[60] The drive means 30 comprises a drive pulley 33, which is integrated with the rotating shaft of the reversible motor 31 generating a rotating force such that the drive pulley 33 can be rotated along with the rotating shaft of the motor 31. A plurality of driven pulleys 34 is rotatably arranged in the same plane as is the drive pulley 33. The drive pulley 33 is coupled to the plurality of driven pulleys 34 using a timing belt 35 so that the driven pulleys 34 can be rotated in conjunction with the drive pulley 33. In the above state, each of the driven pulleys 34 is coupled to a screw shaft 32 at an end thereof, which is the lower end of the driven pulley 34 in the drawings, so that the screw shafts 32 are rotated along with the respective driven pulleys 34. The screw shafts 32 pass through and engage with internally threaded holes (not shown) of the lifting plate 36 through a threaded engagement.

[61] In the present invention, the screw shafts 32 may be appropriately arranged according to the number of nozzles 20 and the shape of the lifting plate 36 such that the screw shafts 32 can maintain stable balance of the lifting plate 36 during vertical movement of the lifting plate 36.

[62] When the reversible motor 31 of the above-mentioned drive means 30 is rotated in one direction, the drive pulley 33 is rotated in the same direction in conjunction with the motor 31. Thus, the driven pulleys 34, which are coupled to the drive pulley 33 using the timing belt 35, and the screw shafts 32, which are coupled to the respective driven pulleys 34, are rotated in the same direction, thereby moving the lifting plate 36 upwards or downwards along with the valve pins 25, so that the nozzles 20 are opened or closed. [63] The operation of the above-mentioned valve device of the injection molding machine for multicavity molds according to the present invention will be described herein below.

[64] First, the nozzles 20 are opened and closed as follows. When electricity is applied to the reversible motor 31 in the state in which the nozzles 20 are closed, as shown in FIG. 2, the screw shafts 32 coupled to the reversible motor 31 are rotated in one direction. Thus, the lifting plate 36, which engages with the screw shafts 32 through a threaded engagement, is moved upwards. As the lifting plate 36 is moved upwards, the valve pins 25, which are secured to the lifting plate 36, are moved upwards, thus opening the gates of the nozzles as shown in FIG. 3. In the above state, when the lifting plate 36 has moved upwards to reach a predetermined height, the sensing unit 37 senses the lifting plate 37 placed at the height and controls the operation of the reversible motor 31, thus maintaining the opened state of the nozzle gates. Furthermore, if the reversible motor 31 is rotated in a reverse direction in the state in which the nozzle gates are opened, as described above, the screw shafts 32 are rotated in the reverse direction in conjunction with the rotating motion of the motor 31, thus moving the lifting plate 36 downwards and closing the nozzle gates, as shown in FIG. 2.

[65] The nozzle opening and closing operation of the drive means 30 will be described with reference to FIG. 8 and FIG. 9. When the reversible motor 31 is turned on, the driven pulleys 34, which are coupled to the drive pulley 33 of the reversible motor 31 through the timing belt 35, are rotated in either direction. In the above state, the driven pulleys 34 are coupled to the respective screw shafts 32, so that the lifting plate 36 is moved upwards or downwards along with the valve pins 25 due to the rotating motion of the screw shafts 32, thus opening or closing the nozzle gates.

[66] Second, the injection amount of the nozzles 20 can be controlled by increasing or reducing the opening ratio of the branching resin path of the manifold as follows. When the control bar 43 of the resin pressure control means 40 in the state of FIG. 2 is rotated in one direction using a tool, such as a screwdriver, the pressure control pin 41, which engages with the control bar 43 through a worm gear engagement, is rotated in the same direction as the rotating motion of the control bar 43, and is moved downwards. Thus, due to the downward movement of the pressure control pin 41, the opening ratio of the small diameter part 10b of the resin path 10a is reduced, as shown in FIG. 4, thus reducing the amount of resin passing through the resin path 10a. On the contrary, if the control bar 43 is rotated in a reverse direction, the pressure control pin 41 is moved upwards and increases the opening ratio of the small diameter part 10b, thus increasing the amount of resin passing through the resin path 10a. The above- mentioned resin pressure control means 40 is installed relative to each nozzle 20 and precisely controls the amount of resin passing through the nozzle 20, so that the valve device of the present invention easily controls the resin injection amounts of the plurality of nozzles 20.

[67] The above-mentioned valve device of the injection molding machine for multicavity molds according to the first embodiment of the present invention is configured such that it controls the multiple nozzles of the injection molding machine, which is used with a multicavity mold, by opening or closing the nozzle gates simultaneously using a single actuating source. Thus, the valve device eliminates a difference in the time of opening or closing the nozzle gates, thereby preventing the production of molded products having bad quality caused by the variation in the opening or closing time. Therefore, the injection molding machine having the multiple nozzles controlled by the valve device of the present invention can manufacture high quality plastic products in large quantities. Furthermore, the valve device of the present invention does not require work for separately opening or closing the multiple nozzles, thus improving workability during a molding process. The valve device also has a simple construction so that it secures desired operational reliability of the injection molding machine and remarkably reduces the cost for producing the injection molding machine. Particularly, the injection amounts of the respective nozzles can be separately and precisely controlled using a resin pressure control means of the valve device, so that the present invention compensates for nonuniform injection amounts of the nozzles caused by errors in machining both the nozzles and the manifold in the injection molding machine, thereby manufacturing high quality plastic products in large quantities. Therefore, the present invention improves the operational reliability of the injection molding machine and increases freedom when machining the nozzles and manifold, thereby improving productivity.

[68] FIG. 10 through FIG. 15 are views illustrating a valve device of an injection molding machine for multicavity molds according to a second embodiment of the present invention. FIG. 10 and FIG. 11 are sectional views illustrating the closed state and opened state of a nozzle gate, respectively. FIG. 12 and FIG. 13 are sectional views illustrating a state in which a valve pin is moved upwards or downwards while resin in a nozzle hardens. FIG. 14 is an exploded perspective view illustrating the important construction of a cushioning means. FIG. 15 is a perspective view illustrating the construction of a pin retraction amount control means.

[69] As shown in the drawings, the valve device of the injection molding machine for multicavity molds according to the second embodiment of the present invention comprises a manifold 10, a plurality of nozzles 20, and a drive means 30 for moving a valve pin 25 upwards and downwards. Furthermore, the valve device has a cushioning means 60 for absorbing external pressure higher than a predetermined pressure when the external pressure is applied to the valve pin 25, thus cushioning the valve pin 25. The valve device further comprises a pin retraction amount control means 70, which determines the extent of retraction the valve pin 25, thereby controlling the opening ratio of the nozzle gate. In the second embodiment of the present invention, the construction of the manifold 10 and the nozzles 20 remains the same as that described for the above-mentioned first embodiment, therefore further explanation is thus deemed unnecessary.

[70] The drive means 30 is provided on a base plate b, which is placed at a position spaced above the manifold 10 by a predetermined height. The drive means 30 comprises a reversible motor 31, which can generate reversible rotating force. A lifting plate 36 is coupled to the reversible motor 31 using a screw shaft 32, and is moved upwards and downwards by the reversible rotating force of the motor 31. Described in detail, the base plate b, on which the reversible motor 31 is securely mounted, is placed at a position spaced above the manifold 10 by a predetermined height. The reversible motor 31 is provided with a rotating shaft (not shown), which is rotated in either direction in response to electricity applied thereto from an external power source. The rotating shaft of the motor 31 extends towards the manifold 10 and is connected to the screw shaft 32.

[71] The screw shaft 32 is coupled at its upper end to the reversible motor 31 so as to receive the rotating force from the motor 31 and is rotatably coupled at its lower end to the upper surface of the manifold 10. The outer circumferential surface of the screw shaft 32 is externally threaded to form a thread. The screw shaft 32 having the external thread around the outer circumferential surface engages with an internally threaded hole (not shown), which is formed through a predetermined position of the lifting plate 36, through a threaded engagement, so that the screw shaft 32 moves the lifting plate 36 upwards or downwards using the rotating force of the reversible motor 31. The lifting plate 36 is a plate-shaped member, with a plurality of valve pins 25 coupled at the upper ends thereof to the lifting plate 36. Further, at least one internally threaded hole (not shown) is formed through the lifting plate 36 at a predetermined position to engage with the screw shaft 32.

[72] The drive means 30 may be configured such that it limits the moving distance of the lifting plate 36 according to the operation of detecting rpm of the reversible motor or the sensing operation for sensing the position of the lifting plate 36 using sensors placed above or below the lifting plate 36. The method of limiting the moving distance of the lifting plate 36 may be variously executed using conventional techniques.

[73] The general operation of the valve device of the injection molding machine for multicavity molds according to the second embodiment of the present invention remains the same as that of the valve device according to the first embodiment. However, in the second embodiment, the valve device of the injection molding machine for multicavity molds absorbs and reduces vertical force, which is applied to the valve pin 25, using the cushioning means 60 and controls the extent of retraction the valve pin 25 using the pin retraction amount control means 70, thereby controlling the opening ratio of the nozzle gate.

[74] The cushioning means 60 comprises a bushing 61 and a valve pin 25. The valve pin 25 is divided into two parts, which are an upper pin 25a and a lower pin 25b. The upper pin 25a and the lower pin 25b are supported by upper and lower elastic members 64 and 65 such that the two pins 25a and 25b are in close contact with each other.

[75] The bushing 61 is a hollow tubular member, which is externally threaded around the outer circumferential surface thereof so that the bushing 61 engages with an internally threaded hole (not shown) of the lifting plate 36 through a threaded engagement. The head of the bushing 61 protrudes upwards outside the upper surface of the lifting plate 36. The head of the bushing 61, which protrudes outside the upper surface of the lifting plate 36, is configured as a polygonal shape, so that the bushing 61 is preferably rotated using a spanner or a wrench. Furthermore, when the bushing 61 is rotated in either direction, the bushing 61 is moved upwards or downwards due to the threaded engagement of the bushing 61 with the lifting plate 36. When the bushing 61 is rotated to be moved upwards, the vertical inner space of the bushing 61 is enlarged. However, when the bushing 61 is rotated to be moved downwards, the vertical inner space of the bushing 61 is reduced.

[76] As described above, the bushing 61 is displaced in a vertical direction relative to the lifting plate 36 in response to rotating motion of the bushing 61 in either direction. One end of the valve pin 25 and the upper and lower elastic members 64 and 65 are placed in the bushing 61.

[77] The valve pin 25 is configured such that the upper part of the pin 25, which is placed in the bushing 61 of the lifting plate 36, is divided into two parts: the upper pin 25a and the lower pin 25b. The facing ends of the upper pin 25a and the lower pin 25b are respectively provided with upper and lower flanges 62 and 63 having enlarged diameters. In the above state, the outer diameters of the upper and lower flanges 62 and 63 are preferably smaller than the inner diameter of the bushing 61. As shown in the drawings, the upper end of the upper pin 25a protrudes outside the upper surface of the lifting plate 36, and comes into contact with the lower end of a lifting stopper 71 of the pin retraction amount control means 70, which will be described in detail later herein, so that the upward movement of the upper pin 25a is limited.

[78] The upper and lower elastic members 64 and 65 are placed in the bushing 61 so as to elastically bias the upper pin 25a downwards and the lower pin 25b upwards, respectively, and preferably comprise conventional coil springs. The upper and lower elastic members 64 and 65 are configured such that they are elastically deformed by an external force smaller than the resin pressure acting in the nozzle 20. As shown in the drawings, the upper elastic member 64 is fitted over the upper pin 25a at a position above the upper flange 62 in the bushing 61, while the lower elastic member 65 is fitted over the lower pin 25b at a position below the lower flange 63 in the bushing 61. Due to the above-mentioned construction, the upper and lower elastic members 64 and 65 elastically bias the movable upper and lower pins 25a and 25b downwards and upwards, respectively, such that the upper and lower pins 25a and 25b come into close contact with each other in the bushing 61.

[79] When resin hardens in the nozzle 20 and the valve pin 25 is forcibly actuated so that it executes its vertical motion in the hardened resin, the upper and lower elastic members 64 and 65 of the cushioning means 60 are selectively elastically deformed, thus cushioning the valve pin 25 by absorbing the external force applied to the valve pin 25.

[80] The pin retraction amount control means 70 limits the extent of retraction of the valve pin 25, thus controlling the amount of resin passing through the nozzle gate. The pin retraction amount control means 70 comprises a lifting stopper 71, a casing 72, a rotor 73 and a control knob 74, and is held in the base plate b because the casing 72 is installed in an installation hole (not shown) of the base plate b through fitting.

[81] The casing 72 is provided with a through hole (not shown) along a central axis thereof, and at least part of the through hole of the casing 72 preferably has an angular shape, such as a rectangular shape, so as to prevent the lifting stopper 71 from undesirably rotating. In the casing 72, the rotor 73 is installed such that it is prevented from moving upwards or downwards, but is rotatable. In the above state, the outer circumferential surface of the rotor 73 is machined as a worm wheel, with a threaded hole formed through the central axis of the rotor 73, so that the lifting stopper 71 engages with the threaded hole of the rotor 73. The rotor 73 is rotated in either direction in conjunction with the control knob 74.

[82] The control knob 74 is a longitudinal member having a predetermined length. One end of the knob 74 is externally threaded to engage with the outer circumferential surface of the rotor 73 through a worm gear engagement, while the other end of the knob 74 extends outside the valve device and may be knurled to allow a worker to easily and reliably rotate the knob 74 by holding the knurled surface with the fingers. Alternatively, the outside end surface of the knob 74 may be provided with a tool insert groove, so that a worker can rotate the knob 74 using a tool, such as a screwdriver. To prevent undesired upward, downward, leftward or rightward movement of the control knob 74, the control knob 74 may be supported by a bearing (not shown), which is a conventional support to rotatably support a rotating shaft. [83] The lifting stopper 71 is a longitudinal member, which is fitted into an internally threaded hole of the rotor 73 such that the lifting stopper 71 can move upwards or downwards in conjunction with rotating motion of the rotor 73, but cannot rotate. Described in detail, the lifting stopper 71 is externally threaded around the outer circumferential surface of an upper end thereof so that the stopper 71 engages with the rotor 73 through a threaded engagement. Furthermore, the circumferential surface of the lower end of the lifting stopper 71 has an angular shape and is fitted into the through hole of the casing 72, so that the stopper 71 is prevented from being rotated. Due to the structure of the lifting stopper 71, in which the stopper 71 comes into contact at its lower surface with the upper surface of the upper pin 25a of the valve pin 25, the stopper 71 can limit the upward movement of the valve pin 25.

[84] To adjust the maximum upward movement of the valve pin 25, the pin retraction amount control means 70 will be manipulated as follows. When a worker rotates the control knob 74 in either direction, the rotor 73 is rotated in conjunction with the rotating motion of the control knob 74, thus moving the lifting stopper 71 upwards or downwards. Therefore, the position of the lifting stopper 71 which limits the maximum upward movement of the valve pin 25 can be adjusted.

[85] Herein below, the operation of the above-mentioned valve device of the injection molding machine for multicavity molds according to the second embodiment of the present invention will be described.

[86] First, to open or close the nozzle 20, the valve device is operated as follows.

[87] When the reversible motor 31 is turned on in the state in which the nozzle 20 is closed as shown in FIG. 10, the screw shaft 32 coupled to the reversible motor 31 is rotated in one direction, so that the lifting plate 36, which engages with the screw shaft 32 by a threaded engagement, is moved upwards.

[88] Due to the upward movement of the lifting plate 36, the valve pin 25 coupled to the lifting plate 36 is moved upwards along with the lifting plate 36 until the valve pin 25 opens the nozzle gate, as shown in FIG. 11. Furthermore, when the reversible motor 31 in the state in which the nozzle gate is opened is rotated in a reverse direction, the screw shaft 32 is rotated in the same direction in conjunction with the rotating motion of the motor 31, thereby moving the lifting plate 36 downwards and closing the nozzle gate, as shown in FIG. 10.

[89] Second, if the valve pin 25 is forcibly moved upwards or downwards in the state in which the resin in the resin orifice 20a of the nozzle 20 is hardened, the cushioning means 60 is operated to cushion the valve pin 25 as follows.

[90] If the resin in the resin orifice 20a of the nozzle 20 is hardened in the state in which the nozzle gate is closed, as shown in FIG. 12, the lower pin 25b of the valve pin 25 cannot move upwards, due to the hardened resin in the resin orifice 20a. When the lifting plate 36 in the above state is moved upwards, the bushing 61, engaging with the lifting plate 36 through a threaded engagement, is moved upwards along with the lifting plate 36. In the above case, the upper pin 25a placed in the bushing 61 is brought into close contact with the lower pin 25b by an elastic biasing force of the upper elastic member 64.

[91] Because the lower pin 25b in the bushing 61 cannot be moved upwards, the lower elastic member 65 is compressed by the distance that the lifting plate 36 moves upwards, and compensates for the movement of the plate 36. In the above state, the upper elastic member 64 expands in an opposite direction.

[92] Furthermore, when resin in the resin orifice 20a of the nozzle 20 is hardened in the state in which the gate of the nozzle 20 is opened, as shown in FIG. 13, the hardened resin prevents the lower pin 25b of the valve pin 25 from being moved downwards. If the lifting plate 36 in the above state is moved downwards, the bushing 61 engaging with the lifting plate 36 through a threaded engagement is moved downwards along with the lifting plate 36, and the upper pin 25a of the valve pin 25 comes into close contact with the lower pin 25b. Thus, the upper elastic member 64 is compressed by the distance that the lifting plate 36 moves downwards, and compensates for the movement of the lifting plate 36. In the above state, the lower elastic member 65 expands in an opposite direction.

[93] Thus, in the state in which the resin in the resin orifice 20a of the nozzle 20 is hardened and restricts vertical motion of the lower pin 25b in the orifice 20a, either of the upper and lower elastic members 64 and 65 may elastically expand or may be elastically compressed to compensate for vertical force applied to the lower pin 25b. In the above state, the worker stops the operation of the injection molding machine and removes the hardened resin from the resin orifice 20a of the nozzle 20 prior to restarting the injection molding machine. Therefore, the present invention can prevent damage or breakage of the valve pin 25 even if resin hardens in the nozzle.

[94] Third, the process of adjusting the injection amount of the nozzle 20 by controlling the extent of retraction of the valve pin 25 is executed as follows. As shown in FIG. 15, when the control knob 74 of the pin retraction amount control means 70 is rotated in one direction, the rotor 73, engaging with the control knob 74 through a worm gear engagement, is rotated in the same direction, thus moving the lifting stopper 71 downwards.

[95] Therefore, due to the downward movement of the lifting stopper 71, the maximum upward movement of the upper pin 25a, which is in close contact with the lower surface of the lifting stopper 71, is reduced in comparison with the location shown in FIG. 10. Because the maximum upward movement of the valve pin 25 is reduced, the lower end of the lower pin 25b cannot completely open the tapered nozzle gate, thus reducing the amount of resin passing through the nozzle gate. The above-mentioned pin retraction amount control means 70 is installed relative to each of the multiple nozzles 20 and precisely controls the amount of resin passing through the associated nozzle 20, so that the present invention can easily and efficiently control the resin injection amounts of the multiple nozzles 20 at one time.

[96] As described above, the valve device of the injection molding machine for multicavity molds according to the second embodiment of the present invention includes a cushioning means in which the upper part of the valve pin is divided into two pins and the two pins are combined together using elastic members such that the cushioning means stably and reliably compensates for vertical force which is applied to the valve pin and may deform the valve pin. Thus, the second embodiment solves problems, which may occur due to increased maintenance cost of the valve device caused by deformation, damage or breakage of the valve pin, and reduced productivity due to stoppage of injection molding machines caused by the malfunction of the valve pin. Furthermore, the second embodiment can control the opening ratio of the nozzle gate by adjusting the extent of retraction of the exposed valve pin, thus providing a valve device having a simple structure and requiring no complex seal structure, thereby improving reliability of the valve device and improving workability while repairing the valve device. Industrial Applicability

[97] As apparent from the above description for the construction and operation of the present invention, the injection molding machine having the resin pressure control means according to the present invention can precisely control the amount of resin injected from nozzles through simple manipulation by a user. Thus, the valve device can compensate for nonuniform resin injection amounts of the nozzles caused by errors in machining both the resin orifices of the nozzles and the branching resin path of the manifold in the injection molding machine having the multiple nozzles, thereby being advantageous in that it increases the quality of the molded products.

[98] Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claim.

Claims

[1] A valve device of an injection molding machine for multicavity molds, comprising: a manifold having a branching resin path to inject resin into a multicavity mold; a plurality of nozzles provided at positions under the manifold to receive the resin from the manifold, with a resin orifice formed through each of the nozzles such that the resin orifice extends to a nozzle gate provided in an end of the nozzle, and a longitudinal valve pin received in the resin orifice to open or close the nozzle gate in response to lifting motion of the valve pin; a drive means securely placed at a predetermined position above an upper surface of the manifold, the drive means comprising a reversible motor to rotate a screw shaft projecting toward the manifold, and a lifting plate coupled to the screw shaft through a threaded engagement so as to be displaced in a vertical direction in conjunction with rotating motion of the screw shaft, with an upper end of the valve pin being coupled to the lifting plate; and a resin pressure control means for controlling an amount of resin passing through the nozzle, the resin pressure control means comprising a pressure control pin t hrough which the valve pin passes, and the pressure control pin being configured such that an upper end of pressure control pin is moved upwards or downwards in response to a screw adjustment and a lower end of the pressure control pin is placed in a small diameter part of the branching resin path.

[2] The valve device of the injection molding machine for multicavity molds according to claim 1, wherein the drive means further comprises: a sensing unit provided at positions above and below the lifting plate such that the sensing unit senses the lifting plate when the lifting plate approaches the sensing unit, thereby controlling the operation of the reversible motor and limiting a nozzle gate opening and closing position.

[3] The valve device of the injection molding machine for multicavity molds according to claim 1 or 2, wherein the drive means further comprises: a drive pulley integrated with a rotating shaft of the reversible motor, a driven pulley integrated with the screw shaft so as to levelly move the lifting plate upwards or downwards, and a timing belt to couple the driven pulley to the drive pulley, thus causing the driven pulley to be rotated along with the drive pulley.

[4] The valve device of the injection molding machine for multicavity molds according to claim 1 or 2, wherein the resin pressure control means comprises: a support body securely mounted to the upper surface of the manifold, with the upper end of the pressure control pin passing through the support body through a threaded engagement such that part of the upper end of the pressure control pin protrudes outside an upper surface of the support body, and a control bar engaging with an outer circumferential surface of the upper end of the pressure control pin protruding outside the upper surface of the support body through a worm gear engagement, so that the control bar is manipulated by a worker to cause the pressure control pin to be operated in conjunction with the control bar, wherein the nozzle is inserted into an installation hole of a heater block having a sheet structure comprising at least one metal sheet, with a heater embedded in the heater block to heat the nozzle and prevent the resin in the nozzle from being hardened.

[5] A valve device of an injection molding machine for multicavity molds, comprising: a manifold having a branching resin path to inject resin into a multicavity mold; a plurality of nozzles provided at positions under the manifold to receive the resin from the manifold, with a resin orifice formed through each of the nozzles such that the resin orifice extends to a nozzle gate provided in an end of the nozzle, and a longitudinal valve pin received in the resin orifice to open or close the nozzle gate in response to lifting motion of the valve pin; a drive means securely placed in a base plate provided above an upper surface of the manifold, the drive means comprising a reversible motor to rotate a screw shaft projecting toward the manifold, and a lifting plate coupled to the screw shaft through a threaded engagement so as to be displaced in a vertical direction in conjunction with rotating motion of the screw shaft, an upper end of the valve pin being coupled to the lifting plate; a cushioning means comprising a tubular bushing engaging with the lifting plate through a threaded engagement such that the bushing is selectively displaced in a vertical direction, a valve pin having an upper part placed in the bushing, the upper part of the valve pin being divided into upper and lower pins with upper and lower flanges provided at respective facing ends thereof, and upper and lower elastic members placed in the bushing so as to elastically bias the upper and lower flanges such that the upper and lower flanges are in close contact with each other; and a pin retraction amount control means held at a predetermined position on the base plate by a threaded engagement such that the pin retraction amount control means is displaced upwards or downwards in a vertical direction, with a lifting stopper provided in the pin retraction amount control means to selectively come into contact at a lower end thereof with an upper end surface of the upper pin, thus variably controlling upward movement of the valve pin. [6] The valve device of the injection molding machine for multicavity molds according to claim 5, wherein the pin retraction amount control means comprises: a tubular casing securely held in the base plate; a rotor placed in the casing so as to be rotated in a normal direction or a reverse direction, the lifting stopper engaging with a center of the rotor through a threaded engagement such that the lifting stopper is moved upwards or downwards; and a control knob engaging at a first end thereof with an outer circumferential surface of the rotor through a worm gear engagement and projecting outside the valve device at a second end thereof, thus transmitting a rotational manipulation force to the rotor.