Injection nozzle touch mechanism for an injection molding machine

A plurality of connecting rods are attached to an injection device located opposite a stationary platen on a base structure of an injection molding machine. The stationary platen is provided with a magnetism generating unit formed of a permanent magnet, and the connecting rods are provided with a magnetic body. As the magnetism generating unit and the magnetic body are attracted to each other by magnetism, a nozzle of an injection unit is brought into contact with a mold. By this structure, the stationary platen can be prevented from inclining during nozzle touch operation.

RELATED APPLICATIONS

The present application claims priority to Japanese Application Number 2012-270689, filed Dec. 11, 2012, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nozzle touch mechanism of an injection molding machine, configured to prevent a stationary platen from inclining during nozzle touch operation.

2. Description of the Related Art

In a mold clamping mechanism section of an injection molding machine, a stationary platen and a rear platen are connected to each other by a plurality of tie-bars, and a movable platen is disposed between these platens for movement along the tie-bars. Further, stationary and movable mold halves of a mold are attached individually to facing machined surfaces of the stationary and movable platens, whereby mold clamping and opening operations are performed.

Furthermore, an injection unit is advanced and retracted relative to the stationary platen on a machine base, and a nozzle on the distal end of an injection cylinder of the injection unit is brought into close contact with a resin injection port of the stationary platen. In this state, a resin is introduced into the mold through the injection cylinder. A nozzle touch mechanism is provided to bring the nozzle into close contact with or separate it from the resin injection port of the stationary platen. The nozzle on the distal end of the injection cylinder is configured to be pressed against the resin injection port of the stationary platen by the nozzle touch mechanism during continuous molding operation.

FIGS. 11 and 12are views showing the entire configuration of an injection molding machine comprising a nozzle touch mechanism section.FIGS. 11 and 12show states where the nozzle is untouched and touched, respectively.

The injection molding machine comprises a mold clamping section Mc and an injection section Mi on a machine base (not shown). The injection section Mi serves to melt a resin material (pellets) by heating and inject the molten resin material into a cavity of a mold40(comprising movable and stationary mold halves40aand40b). The mold clamping section Mc serves mainly to open and close the mold40.

The injection section Mi will be described first. A nozzle2is attached to the distal end of an injection cylinder1, and a screw3is inserted in the injection cylinder1. The screw3is provided with a resin pressure sensor5, such as a load cell, configured to detect the resin pressure based on a pressure on the screw3.

The screw3is rotated by a screw-rotation servomotor through a transmission mechanism6comprising pulleys, belt, etc. Further, the screw3is axially moved by an injection device advancing/retracting mechanism8. Reference numeral4denotes a hopper that supplies the resin to the injection cylinder1.

The following is a description of the mold clamping section Mc. The mold clamping section Mc comprises a rear platen31, movable platen30, tie-bars32, stationary platen33secured on a base structure9, crosshead34, and ejector mechanism35. The rear platen31and the stationary platen33are connected to each other by the tie-bars32, and the movable platen30is located so as to be guided by the tie-bars32. The movable and stationary mold halves40aand40bare attached to the movable and stationary platens30and33, respectively. If the crosshead34is advanced or moved to the right inFIGS. 11 and 12, the movable platen30is advanced to close the mold.

The following is a description of the molding operation by means of the injection molding machine. If a movable platen advancing/retracting motor (not shown) is rotated forward, a ball screw shaft38is rotated forward. Thereupon, the crosshead34threadedly engaged with the ball screw shaft38is advanced (to the right inFIG. 1), so that the movable platen30is also advanced.

If the movable mold half40aattached to the movable platen30contacts the stationary mold half40battached to the stationary platen33(or if the mold is closed), a mold clamping process is started. In the mold clamping process, a mold clamping force is generated in the mold40by further driving the movable platen advancing/retracting motor forward. Further, the cavity in the mold40is filled with the molten resin as a geared motor M1for injection device advance and retraction of the injection device advancing/retracting mechanism8, attached to the injection section Mi, is driven so that the screw3advances axially.

In a mold opening process, if the movable platen advancing/retracting motor is driven in the reverse direction, the ball screw shaft38is rotated in the reverse direction. As this is done, the crosshead34is retracted, a toggle mechanism is operated to bend, and the movable platen30is retracted toward the rear platen31. When the mold opening process is completed, an ejector pin (not shown) is pushed out of the movable mold half40a, whereby a molded article is ejected from the movable mold half40a.

If the nozzle touch mechanism in the state ofFIG. 11is shifted to the state ofFIG. 12so that a nozzle touch occurs, a moment equivalent to the product of a nozzle touch force and the distance from the lower surface of the stationary platen to the nozzle center is generated, possibly causing the stationary platen to tilt or overturn.

Japanese Patent Application Laid-Open No. 9-277306 discloses a nozzle touch mechanism configured so that a pair of rotation/linear motion conversion mechanisms are arranged axially symmetrically with respect to the center of an injection unit. In this configuration, the points of action of the respective screw shafts of the rotation/linear motion conversion mechanisms on the stationary platen are made axially symmetrical with respect to the point of action of a nozzle of an injection cylinder, so that the stationary platen can be prevented from being inclined or overturned by a nozzle touch.

In the nozzle touch mechanism described above, the stationary platen can be prevented from inclining or overturning as the point of action of a nozzle of an injection cylinder is made axially symmetrical with respect to the points of action of the respective screw shafts of the rotation/linear motion conversion mechanisms on the stationary platen, but connecting rods may hinder the maintenance of a swivel of the injection unit or the nozzle tip. Since a nozzle touch mechanism section is located near a front plate of an injection molding machine, moreover, the maintenance of a screw joint is not easy.

Furthermore, Japanese Patent Application Laid-Open No. 2001-315157 discloses a nozzle touch mechanism of an injection molding machine, which uses an electromagnet to bring a nozzle into contact with a sprue bushing of a mold by pressure bonding with a predetermined force.

Since this nozzle touch mechanism uses the electromagnet, electric current must always be kept flowing while the force is being generated. If electric power consumption increases or power failure occurs when generation of the force is required, the pressing force of the nozzle becomes so small that a resin inevitably flows out.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a nozzle touch mechanism of an injection molding machine, capable of economically performing reliable nozzle touch operation while preventing a stationary platen from inclining or overturning.

The present invention relates to a nozzle touch mechanism of an injection molding machine, configured to press a nozzle on a distal end of a cylinder against a mold attached to a stationary platen with a predetermined nozzle touch force. The stationary platen is secured to a base structure of the injection molding machine such that a front plate of an injection device is located opposite the stationary platen and the cylinder is secured to the front plate.

A first aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device and a plurality of connecting members arranged at the sides of the cylinder and provided to the injection device. Further, one of the stationary platen and the connecting members is provided with a magnetism generating unit comprising a permanent magnet, and the other with a magnetic body. The magnetism generating unit is configured to generate magnetism to attract the magnetic body, thereby bringing the nozzle into contact with the mold.

A second aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device, a plurality of magnetic connecting members arranged at the sides of the cylinder and supported at one ends thereof by a proximal portion of the cylinder, and a magnetism generating unit comprising a permanent magnet provided on that part of the stationary platen which faces the other ends of the magnetic connecting members. The magnetism generating unit is configured to generate magnetism to attract the magnetic connecting members, thereby bringing the nozzle into contact with the mold.

A third aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device, a plurality of connecting members arranged at the sides of the cylinder and supported at one ends thereof by a proximal portion of the cylinder, a magnetic detachably-attaching plate detachably attached to the other ends of the connecting members, and a magnetism generating unit comprising a permanent magnet provided on that part of the stationary platen which faces the other ends of the connecting members. The magnetism generating unit is configured to generate magnetism to attract the magnetic detachably-attaching plate, thereby bringing the nozzle into contact with the mold.

A fourth aspect of the nozzle touch mechanism of an injection molding machine comprises an injection device advancing/retracting unit configured to advance and retract the injection device, a plurality of connecting members arranged at the sides of the cylinder and supported at one ends thereof by a proximal portion of the cylinder, a magnetism generating unit comprising a permanent magnet provided on the other ends of the connecting members, and a magnetic body provided on that part of the stationary platen which faces the other ends of the connecting members. The magnetism generating unit is configured to generate magnetism to attract the magnetic body, thereby bringing the nozzle into contact with the mold.

Each of the connecting members may comprise a connecting rod and a connecting rod adjusting member, and the length of the connecting member may be adjusted by the connecting rod adjusting member.

Each of the connecting members may be slidably supported by a base secured to the proximal portion of the cylinder, and be secured to a pressing plate by a spring.

The magnetism generating unit may comprise a variable-polarity magnet, a polarity switching coil arranged around the variable-polarity magnet and configured to change the polarity of the variable-polarity magnet, and a fixed-polarity magnet, and the permanent magnet may comprise the variable-polarity magnet and the fixed-polarity magnet.

According to the present invention, there can be provided a nozzle touch mechanism of an injection molding machine, capable of economically performing reliable nozzle touch operation while preventing a stationary platen from inclining or overturning.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of some embodiments of a nozzle touch mechanism of an injection molding machine. An outline of the configuration of the injection molding machine is similar to that of the prior art example shown inFIGS. 11 and 12.

Embodiment 1 of the nozzle touch mechanism of the injection molding machine according to the present invention will be described with reference toFIGS. 1 and 2.

The connecting rods21and the detachably-attaching plates22are symmetrically disposed in pairs on the left and right sides of the injection cylinder1. As in the conventional case, a nozzle touch mechanism section is advanced and retracted by utilizing torque fluctuation of a geared motor or servomotor or using a proximity switch. As the nozzle touch mechanism section is advanced, the injection cylinder1, along with the connecting rods21and the detachably-attaching plates22, moves (or advances) toward the stationary platen33. As the magnetism generating unit10and the detachably-attaching plates22are magnetically connected, a nozzle touch on the tip of a nozzle is made and a nozzle touch state is maintained. The configuration of the magnetism generating unit10will be described later.

In the nozzle touch state, the detachably-attaching plate22is pressurized by the spring55(FIG. 2), besides being magnetically connected to the magnetism generating unit10. Thus, the nozzle tip can be reliably brought into close contact with a mold even if the length of the nozzle or cylinder is changed due to temperature expansion or the reaction force of a resin pressure.

The spring55used in the nozzle touch mechanism ofFIG. 2and its surroundings will be described with reference to the enlarged view ofFIG. 10.

InFIG. 10, reference numeral21denotes a connecting rod;54, base;55, spring;56, guides;57and59, bushes;58, nut;60, bolts; and61, pressing plate. One end of the connecting rod21is secured to the pressing plate61and slidably supported by the base54(forming a part of the injection cylinder1), which is secured to the water jacket53or the front plate51. The spring55is wound around that part of the connecting rod21which is located between the base54and the pressing plate61.

Further, one end of the guide56on the side of the pressing plate61is larger in diameter than the other part, so that the pressing plate61is kept from moving toward the front plate51.

FIGS. 5 and 6are diagrams illustrating the magnetism generating unit of the nozzle touch mechanism ofFIG. 1in magnetized and demagnetized states, respectively.

The alnico magnets12are disposed between the electromagnetic coils11. As shown in the enlarged diagram ofFIG. 7corresponding to a portion surrounded by broken line H inFIG. 5, the electromagnetic coils11are configured so that coil wires15are wound around shafts that extend from the alnico magnets12toward the neodymium magnets13. In each two adjacent electromagnetic coils11in a pair, their respective coil wires15are oppositely wound.

The polarity of each alnico magnet12changes each time the electromagnetic coils11are energized. If the electromagnetic coils11in the demagnetized state are energized, the magnetized state shown inFIG. 5is established. In this state, the alnico and neodymium magnets12and13are made homopolar so that lines of magnetic force16are formed as indicated by broken lines inFIG. 5. Thereupon, the magnetic cores14become strong magnets to be connected to the detachably-attaching plates22.

The demagnetized state shown inFIG. 6is established as the electromagnetic coils11in the magnetized state are energized. If the demagnetized state is established, the lines of magnetic force16cease to appear on the surfaces of the magnetic cores14, as indicated by broken lines inFIG. 6. Thus, the detachably-attaching plates22are separated from the magnetism generating unit10.

Embodiment 2 of the nozzle touch mechanism according to the present invention will be described with reference toFIG. 3.

The nozzle touch mechanism shown inFIG. 3differs from the nozzle touch mechanism of Embodiment 1 (FIG. 2) in that a connecting rod adjusting member23is provided between a connecting rod21and a detachably-attaching plate22. While an injection cylinder1and a nozzle2vary in length, the connecting rod adjusting member23serves to adjust the length of the connecting rod21so that the tip of the nozzle2can appropriately contact a stationary platen33of a mold.

FIGS. 8 and 9are enlarged views showing the connecting rod adjusting member23in the nozzle touch mechanism ofFIG. 3and its surroundings.

In the example ofFIG. 8, the connecting rod21, detachably-attaching plate22, and connecting rod adjusting member23are penetrated individually by holes, and a thread groove is formed on the inner surface of the hole in the connecting rod21. A screw24having its proximal end portion secured to the detachably-attaching plate22penetrates the hole in the connecting rod21, and an external thread formed on the tip end of the screw24is threadedly engaged with the thread groove of the hole in the rod21. Thus, the length of a combination of the connecting rod21, detachably-attaching plate22and connecting rod adjusting member23can be adjusted by rotating the detachably-attaching plate22relative to the connecting rod21and the connecting rod adjusting member23.

In the example ofFIG. 9, the distal end of the connecting rod adjusting member23is shaped so that it can be fitted into the connecting rod21in such a manner that an external thread formed thereon engages with an internal thread formed inside the connecting rod21. Further, the screw24having one end portion secured to the detachably-attaching plate22penetrates holes that penetrate the detachably-attaching plate22and the connecting rod adjusting member23. Also in the example ofFIG. 9, the combination of the connecting rod21, detachably-attaching plate22, and connecting rod adjusting member23can be adjusted, although the range of the length adjustment is somewhat smaller than in the example ofFIG. 8.

Embodiment 3 of the nozzle touch mechanism according to the present invention will be described with reference toFIG. 4.

The nozzle touch mechanism shown inFIG. 4differs from the nozzle touch mechanism of Embodiment 1 (FIG. 2) in that the detachably-attaching plates22of Embodiment 1 are omitted and connecting rods21are magnetic members. Thus, according to this embodiment, the nozzle touch mechanism is not provided with the detachably-attaching plates22, so that the parts count can be reduced.

In the embodiments of the nozzle touch mechanism according to the present invention, the magnetism generating unit10is provided on the side of the stationary platen33, the magnetic detachably-attaching plates22are provided on the side of the connecting rods21, or the connecting rods21are provided as magnetic members. Alternatively, however, a magnetic member, e.g., a magnetic body, and the magnetism generating unit10may be provided, for example, on the sides of the stationary platen33and the connecting rods21, respectively, only if the magnetism generating unit10and the detachably-attaching plates22(or the connecting rods21, in the case where the detachably-attaching plates22is not used) are magnetically connected.

Although the neodymium and alnico magnets are used for the permanent magnet in the embodiments of the nozzle touch mechanism according to the present invention, moreover, they may be replaced with magnets of other types. In the present embodiment, furthermore, the magnetized and demagnetized states are switched in such a manner that the polarity of the alnico magnets is inverted by energizing the electromagnetic coils disposed around the alnico magnets. However, the polarity may also be changed by other means.

In the embodiments of the nozzle touch mechanism according to the present invention, moreover, the length adjustment of the connecting rod21in each connecting rod adjusting member23is performed by means of the screw24that penetrate the detachably-attaching plate22, adjusting member23, and connecting rod21or the screw that penetrates the detachably-attaching plate22and the adjusting member23. However, other means may be used for the length adjustment.