Locally pressurized type injection molding machine

Abstract: A locally pressurizing type injection molding machine includes a stationary die (12) and a movable die (13), so that a molded product can be formed by charging a resin into a cavity defined between both the dies. A pressurizing pin (33) extends through the movable die (13) and has its tip end facing at least one of a resin passage and the cavity (21). A pressurizing cylinder (41) is disposed in rear of the pressurizing pin (33) to move the pressurizing pin through the pressurizing rod (46). Therefore, the resin charged in the cavity can be pressurized by advancing the pressurizing pin (33) into a resin passage, for example, a gate, the cavity or the like and hence, it is possible not only to provide an extremely thin molded product, but also to prevent the generation of a sink mark. The area occupied by the movable platen (15) can be reduced by disposing the pressurizing rod (46) and ejector rod (59) coaxially, leading to an improved mountability.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a locally pressurizing type injection molding machine. DESCRIPTION OF THE PRIOR ART There are conventionally proposed locally pressurizing type injection molding machines in which various workings are applied to a molded product by pressurizing a local portion of a resin within a cavity, thereby eliminating the need for the boring of a thin plate, the finishing of a cut surface and the like. Fig. 1 is a view illustrating an essential portion of the prior art locally pressurizing type injection molding machine. Fig. 1(a) illustrates a molding state; Fig. 1(b) illustrates a punch vibrating state, and Fig. 1(c) illustrates a vibration punching state. Referring to Fig. 1, the prior art locally pressurizing type injection molding machine comprises a stationary die 1 mounted to a stationary platen, a movable die 2 mounted to a movable platen which is not shown, a cavity 3 defined between the stationary and movable dies 1 and 2, a sprue 4 to which a resin injected from an injection nozzle which is not shown, a gate 5 defined between the sprue 4 and the cavity 3, a stationary punch 6 disposed on the stationary die 1, and a movable punch 7 disposed on the movable die 2. The stationary and movable punches 6 and 7 are vibrated by vibrating devices (not shown) disposed within the stationary and movable dies 1 and 2, respectively, at a cooling step after the completion of a pressure maintaining step in an injection molding cycle. The stationary and movable punches 6 and 7 are previously disposed at locations where a working is applied and hence, as shown in Fig. 1(a), a heat due to a shear stress is generated in such a working portion (e.g., a boring portion or a gate 5) between the stationary and movable punches 6 and 7 by vibration of the movable punch 7, thereby softening a resin. In this state, if for example, the movable punch 7 is pushed out in one direction, as shown in Fig. 1(b), while vibrating the stationary and movable punches 6 and 7, the softened resin is cut, as shown in Fig. 1(c). In this case, a portion cut along the movable punch 7 is finished and cooled by the vibration, thereby providing a glossy worked surface of a high accuracy. In the above prior art locally pressurizing type injection molding machine, however, an actuator which is the stationary punch 6 is disposed within the stationary die, while an actuator which is the movable punch 7 is disposed within the movable die 2, resulting in an increased cost. DE-G 8 414 995 discloses an injection molding machine comprising two sets of first and second ejector pins which are respectively disposed on first and second ejector plates. Further, a first hydraulic cylinder is disposed for advancing and retracting the first ejector plate and the first ejector pin, and a second hydraulic cylinder is disposed for advancing and retracting the second ejector plate and the second ejector pins. As is shown in Fig. 1 of said document, the first ejector pin ejects a molded product and the second ejector pin ejects a sprue. In consequence, said document does not disclose a locally pressurizing type ejection molding machine, because said machine does not comprise pressurizing pins, which are advanced during the pressure maintaining step or at an initial stage of the cooling step. GB-A-1 416 870 discloses a locally pressurizing type injection molding machine comprising a stationary die, a movable die disposed for movement into and out of contact with said stationary die to define a cavity between both dies, a first ejector pin extending through said movable die with its tip end facing said cavity, a second ejector pin extending through said movable die with its tip end facing a runner channel, and a cut-off pin extending through said movable die, with its tip end facing a runner channel. The cut-off pins are forced forward by an actuating cylinder via a plate, as soon as the injection of the material to be molded is completed. The cut-off pins and ejector pins are mounted to respective plates for movement. Actuators for performing these movements of the ejecting pins and cut-off pins are not shown. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a locally pressurizing type injection molding machine, where the actuators are disposed outside a stationary and a movable die and the transmission of the movements of the actuators is performed with minimum space requirements, thereby providing reduced costs. This object is solved by the subject matter of present claim 1. Preferred embodiments are subject of the dependent claims 2 and 3. To achieve the above object, according to the present invention there is provided a locally pressurising type injection molding machine comprising a stationary die, a movable die disposed for movement into and out of contact with said stationary die to define a cavity between both the dies, a first ejector pin extending through said movable die, with its tip end facing said cavity, a second ejector pin extending through said movable die, with it tip end facing a sprue, an ejecting cylinder disposed in rear of said first ejector pin and that second ejector pin for simultaneously moving said first ejector pin and said second ejector pin through ejecting rods, a pressurizing pin extending through said movable die, with its tip end facing at least one of a resin passage and said cavity, and a pressurizing cylinder disposed in rear of said pressurizing pin for moving said pressurizing pin through a pressurising rod before the movement of said first ejector pin and said second ejector pin, wherein said pressurizing rod and said ejecting rods are disposed coaxially. With the above construction, the stationary and movable dies are disposed so that the movable die is moved into and out of contact with the stationary die, and the cavity is defined between both the dies. Therefore, a molded product can be formed by charging a resin into the cavity. In addition, the pressurizing pin extends through the movable die, with its tip end facing at least one of the resin passage and the cavity. The pressurizing cylinder is disposed in rear of the pressurizing pin to move the pressurizing pin through the pressurizing rod. Therefore, the resin charged in the cavity can be pressurized by advancing the pressurizing pin into the resin passage such as a gate, the cavity and the like, thereby producing an extremely thin molded product, but also preventing the generation of a sink mark. Further, the ejector pin extends through the movable die, with its tip end facing the cavity. The ejecting cylinder is disposed in rear of the ejector pin to move the ejector pin through the ejector rod. Therefore, actuators of the pressurizing pin and the ejector pin can be disposed outside the stationary and movable dies, leading to a reduced cost for the stationary and movable dies. Further, the pressurizing rod and the ejector rod are disposed coaxially, thereby reducing the area occupied by the movable platen and providing an improved mountability. Yet further, a plurality of the pressurizing rods may be disposed and synchronized by a pressurizing cross head. This ensures that an inclination of the pressurizing plate can be prevented from being generated, and the pressurizing plate and the pressurizing pin can be prevented from being damaged. Moreover, it is possible to reduce the variability in stroke of movement of each pressurizing pin to provide an uniform pressurizing force. The above and other objects, features and advantages of the invention will become apparent from a consideration of the following description of the preferred embodiments taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view of an essential portion of the prior art locally pressurizing type injection molding machine; Fig. 2 is a sectional view of a locally pressurizing type injection molding machine according to a first embodiment of the present invention; Fig. 3 is a side view of the locally pressurizing type injection molding machine shown in Fig. 2; Fig. 4 is a sectional view taken along a line B-B in Fig. 2; Fig. 5 is an enlarged view of an essential portion shown in Fig. 2; Fig. 6 is a sectional view of an essential portion of a locally pressurizing type injection molding machine according to a second embodiment of the present invention; Fig. 7 is a sectional view taken along a line C-C in Fig. 6; Fig. 8 is a front view of a movable platen in a locally pressurizing type injection molding machine according to a third embodiment of the present invention; Fig. 9 is a sectional view of the movable platen in the locally pressurizing type injection molding machine, taken along a line D-D in Fig. 8 Fig. 10 is a sectional view of the movable platen in the locally pressurizing type injection molding machine, taken along a line E-E in Fig. 8 Fig. 11 is a diagram illustrating an arrangement of ejector pins and pressurizing pins in the locally pressurizing type injection molding machine shown in Fig. 8; Fig. 12 is a sectional view of an essential portion of a locally pressurizing type injection molding machine according to a fourth embodiment of the present invention; Fig. 13 is a sectional view of an essential portion of a locally pressurizing type injection molding machine according to a fifth embodiment of the present invention; Fig. 14 is a sectional view of an essential portion of a locally pressurizing type injection molding machine according to a sixth embodiment of the present invention; Fig. 15 is a sectional view of an essential portion of a locally pressurizing type injection molding machine according to a seventh embodiment of the present invention; and Fig. 16 illustrate an application of a pressurizing rod. DESCRIPTION OF PREFERRED EMBODIMENTS The present invention will now be described by way of preferred embodiments in connection with the accompanying drawings. Referring to Figs. 2 to 5, a locally pressurizing type injection molding machine according to a first embodiment of the present invention is illustrated. This injection molding machine comprises a stationary die 12 mounted to a stationary platen which is not shown, and a movable die 13 disposed in an opposed relation to the stationary die 12 and adapted to be advanced and retreated (moved laterally as viewed in Fig. 1) into and out of contact with the stationary die 12 by a die clamping device which is not shown. The movable die 13 is fixed on a movable platen 15 with a spacer block 14 interposed therebetween. For convenience, the spacer block 14 is illustrated as being integral with the movable die 13. The movable platen 15 is adapted to be advanced and retreated along four tie bars 40 by a die opening/closing device which is not shown. At an injection step, a resin injected from an injection nozzle in an injection device which is not shown is passed from a sprue 18 through a runner 19 and via gates 20 such as a submarine gate into a cavity 21 defined between the stationary and movable dies 12 and 13. The injection step is followed by a pressure maintaining step at which the pressure in the cavity 21 is increased in order to prevent a sink mark from being produced in a molded product by cooling of the resin. This step is followed by a cooling step at which the cooling of the resin within the cavity 21 is started. In order to gate-cut the molded product during the pressure-maintaining step or at an initial stage of the cooling step, the same number of pressurizing pins 33 as the gates 20 are disposed. The pressurizing pins 33 each have a tip end face having an area corresponding to the gate 20 and is disposed at a location where the molded product is gate-cut by the pressurizing pin 33 itself. Therefore, the structure is such that the pressurizing pin 33 itself gate-cuts the molded product and hence, it is possible to simplify the structures of the stationary and movable dies 12 and 13. The pressurizing pin 33 is clamped and fixed at its trailing end by a pressurizing plate 36, so that the pressurizing pin 33 can be advanced and retreated by advancing and retreating the pressurizing plate 36. The spacer block 14 includes a restraining member disposed so that the pressurizing plate 36 may be advanced and retreated only in a predetermined extent. In Figures, a solid line indicates a retreat limit for the pressurizing plate 36, and a two-dot dashed line indicates a advance limit for the pressurizing plate 36. Two pressurizing cylinders 41 are disposed on the movable platen 15 on a diagonal line connecting two tie bars 40, as shown in Figs. 2 and 3, so that the pressurizing pins 33 can be advanced and retreated by operation of the pressurizing cylinders 41. To this end, a piston rod 42 of the pressurizing cylinder 41 is fixed to a pressurizing cross-head 43 by a bolt 44, and four sleeve-like pressurizing rods 46 are fixed to the pressurizing cross-head 43 to project forwardly (rightwardly as viewed in Fig. 2). On the other hand, the pressurizing plate 36 has a sleeve-like protrusion 47 projectingly formed on a portion corresponding to an end face of the pressurizing rod 46 to extend rearwardly (leftwardly as viewed in Fig. 2). It should be noted that the number of the pressurizing rods 46 disposed need not be necessarily four, but if required, the number of the pressurizing rods 46 can be increased or decreased. Thus, when the pressurizing cylinder 41 is operated to advance the piston rod 42, the pressurizing rod 46 is advanced through the cross head 43. Then, a tip end of the pressurizing rod 46 abuts against the sleeve-like protrusion 47. Therefore, if the pressurizing cylinder 41 is further operated to advance the piston rod 42, the pressurizing pin 33 is advanced through the pressurizing plate 36. The pressurizing rods 46 are clamped and fixed to the pressurizing cross head 43, and hence, the four pressurizing rods 46 can be synchronously advanced by operation of the pressurizing cylinders 41. In this manner, it is possible to prevent an inclination of the pressurizing plate 36 from occurring, so that the pressurizing plate 36 and the pressurizing pin 33 are prevented from being damaged. Moreover, it is possible to reduce the variability in stroke of movement of each pressurizing pin 33 to provide a uniform pressurizing force. A single ejector pin 51 is disposed so that its tip end faces the sprue 18, and a plurality of ejector pins 52 are disposed so that their tip ends face predetermined points of the cavity 21. Trailing ends of the ejector pins 51 and 52 are clamped and fixed to the ejector plate 53. The spacer block 14 includes a restraining member disposed so that the ejector plate 53 may be advanced and retreated in a predetermined extent. In Figures, a solid line indicates a retreat limit for the ejector plate 53, and a two-dot dashed line indicates an advance limit for the ejector plate 53, as in the pressurizing plate 36. An ejecting cylinder 55 is disposed at a central portion of the movable platen 15, so that the ejector pins 51, 52 may be advanced and retreated by operation of the ejecting cylinder 55. For this purpose, an ejecting cross head 57 is fixed to a piston rod 56 in the ejecting cylinder 55, and as shown in Fig. 4, a single ejecting rod 58 is fixed to a central portion of the ejecting cross head 57, while four ejecting rods 59 are fixed to the ejecting cross head 57 at locations corresponding to the pressurizing rods 46, the ejecting rods 58 and 59 projecting forwardly. The ejecting rods 59 are disposed to extend through the pressurizing rods 46. On the other hand, protrusions 60 and 61 are projectingly formed on the ejector plate 53 at locations corresponding to the ejecting rods 58 and 59 to extend rearwardly. Thus, if the ejecting cylinder 55 is operated to advance the piston rod 56, the ejecting rods 58 and 59 are advanced through the ejecting cross head 57. Then, tip ends of the ejecting rods 58 and 59 abut against the protrusions 60 and 61. Thereafter, if the ejecting cylinder 55 is further operated to advance the piston rod 56, the ejecting pins 51 and 52 are advanced through the ejecting plate 53. It should be noted that a flange portion 55a is projectingly formed radially outwardly on the ejecting cylinder 55, and the pressurizing cylinder 41 is fixed to the flange portion 55a. The pressurizing cylinder 41 and the ejecting cylinder 55 are actuated by a hydraulic pressure, and a hydraulic pressure source 71 is connected with the pressurizing cylinder 41 through a solenoid directional control valve 73 and connected with the ejecting cylinder 55 through a solenoid directional control valve 74. Any of the solenoid directional control valve 73 and the solenoid directional control valve 74 can assume a position A, a position B and a neutral portion, so that they causes the piston rods 42 and 56 to be advanced respectively when in their positions A and to be retreated respectively when in their positions B. If the ejecting rods 58 and 59 are retreated by a predetermined amount by retreating the piston rod 56, the tip ends thereof is moved away from the ejecting plate 53, so that the ejector plate 53 cannot be further retreated. Likewise, if the pressurizing rod 46 is retreated by a predetermined amount by retreating the piston rod 42, the tip end thereof is moved away from the pressurizing plate 36, so that the pressurizing plate 36 cannot be further retreated. Thereupon, a return pin 65 and a return spring 66 are disposed between the ejector plate 53 and the stationary die 12. Thus, with the retreating movement of the ejector rods 58 and 59, the ejector plate 53 is guided to the return pin 65 and forcedly retreated by the action of the return spring 66. A return pin 67 and a return spring 68 are also disposed between the pressurizing plate 36 and the stationary die 12. Thus, with the retreating movement of the pressurizing rod 46, the pressurizing plate 36 is guided to the return pin 67 and forcedly retreated by the action of the return spring 68. In the locally pressurizing type injection molding machine having the above-described construction, the movable platen 15 is advanced to effect the closing and clamping of the dies, and the resin is injected from the injection nozzle which is not shown. The resin is charged through the sprue 18, the runner 19 and the gates 20 into the cavity 21. If a solenoid a of the solenoid directional control valve 73 is energized either in the middle of the pressure maintaining step for maintaining the pressure on the resin or at initial stage of the cooling step for the cooling the resin within the cavity 21, the piston rod 42 in the pressurizing cylinder 41 is advanced. During this time, the pressurizing cross head 43 and pressurizing rods 46 fixed to the piston rod 42 are also advanced, so that the pressurizing rods 46 pushes the pressurizing plate 36. Then, the pressurizing pin 33 mounted to the pressurizing plate 36 pushes the resin in the gates 20 to gate-cut the resin. If the cooling step is completed and the opening of the dies is conducted, a solenoid a of the solenoid directional control valve 74 is energized, thereby permitting the piston rod 56 in the ejecting cylinder 55 to be advanced. During this time, the ejecting cross head 57 and ejector rods 58 and 59 fixed to the piston rod 56 are also advanced, so that the ejector rods 58 and 59 push the ejector plate 53. Then, the ejector pins 51 and 52 mounted to the ejector plate 53 push the sprue 18 and a molded product which is not shown, thereby ejecting the molded product, the sprue 18 and the runner 19. Alternatively, the runner 19 and the molded product can be separated by conducting the ejection of the sprue 18 and the runner 19 and the ejection of the molded product conducted at discrete timings, respectively, leading to simplified structures of the stationary and movable dies 12 and 13. As described above, the pressurizing rod 46 is sleeve-shaped, so that the ejector rod 59 extends within and through the pressurizing rod 46. Therefore, the pressurizing rods 46 and the ejector rod 59 are disposed coaxially, so that a space for the pressurizing rod 46 can be easily insured. In general, in a straight-hydraulic die clamping system designed to conduct the opening and closing of dies by a hydraulic cylinder, a support post (which is not shown) is disposed for transmitting a clamping force to a back of a die-mounting surface of the movable platen 15 and hence, it is extremely difficult to newly dispose a pressurizing device in addition to a usual ejecting device. According to the present invention, each of the ejector rods 59 of the ejecting device and each of the pressurizing rods 46 of the pressurizing device are disposed coaxially. Therefore, it is possible to easily dispose the pressurizing device. Moreover, because the resin after being charged can be pressurized by the pressurizing device, it is possible not only to provide an extremely thin molded product, but also to prevent the generation of any sink mark. A second embodiment of the present invention will be described below in connection with Figs. 6 and 7. Referring to Fig. 6, a locally pressurizing type injection molding machine of the second embodiment comprises a movable platen 15, a tie bar 40, an ejecting cylinder 71, and a guide post 72 for supporting the ejecting cylinder 71. A cross head 74 is fixed to a piston rod 73 in the ejecting cylinder 71, and ejector pins 75 and 76 are fixed to the cross head 74 to project forwardly (rightwardly as viewed in Fig. 6). On the other hand, a plate 77 is fixed to a die plate (which is not shown) of the movable platen 15 by a bolt 78. The plate 77 has a hole 79 centrally defined therein, through which the ejector pin 75 is passed. Pressurizing cylinders 81 are disposed at four places around the hole 79. Each of the pressurizing cylinder 81 includes a sleeve-like piston 82 having an increased diameter at its central portion and has a front end face adapted to abut against a pressurizing pin which is not shown. The ejector pin 76 is adapted to pass through the piston 82. The pressurizing cylinder 81 has an oil chamber connected to a solenoid directional control valve 83, so that the piston 82 and the pressurizing pin can be retreated by switchover of the solenoid directional control valve 83. It is noted herein that reference numeral 84 is an oil passage through which an oil is supplied to the oil chamber in the pressurizing cylinder 81. A third embodiment of the present invention will be described in connection with Figs. 9 to 11. Referring to Figs. 9 and 11, a locally pressurizing type injection molding machine of the third embodiment comprises a movable platen 15, a tie bar 40, an ejecting cylinder 85, a pressurizing cylinder 86, a guide post 87 for supporting the ejecting cylinder 85, and a guide post 88 for supporting the pressurizing cylinder 86. As shown in Fig. 10, a cross head 10 is fixed to a piston rod in the ejecting cylinder 85, and an ejector rod 90 is fixed to the cross head 89 to project forwardly (rightwardly as viewed in Fig. 10). In addition, as shown in Fig. 9, a cross head 91 is fixed to a piston rod in the pressurizing cylinder 86, and a pressurizing rod 92 is fixed to the cross head 91 to project forwardly. In this case, the ejector rod 90 and pressurizing rod 92 are not coaxially and disposed at discrete positions, respectively. In this embodiment, the pressurizing pin 33 (see Fig. 2) is disposed to face the gate, so that the resin is gate-cut by the pressurizing pin 33, but alternatively, when the resin is only pressurized, the pressurizing pin 33 can be disposed to face another resin passage such as the runner 19, the cavity 21 and the like. A fourth embodiment of the present invention will be described below in connection with Fig. 12. A locally pressurizing type injection molding machine of the fourth embodiment comprises a movable platen 15, an ejector rod 59, and a plurality of pressurizing cylinders 101 disposed on the movable platen 15. A sleeve-like pressurizing piston 102 is slidably received in the pressurizing cylinder 101 and has a sleeve-like pressurizing rod 103 integrally formed thereon to extend forwardly (rightwardly as viewed in Fig. 12) therefrom. In this case, a pressurizing cross head 43 (see Fig. 2) as in the first embodiment is not required. In addition, the pressurizing cylinders 101 can be controlled dependently from one another and operated at different timings of motion or in different pressurization programs. Referring now to Fig. 13, an essential portion of a locally pressurizing type injection molding machine according to a fifth embodiment of the present invention is illustrated in a sectional view. As shown in Fig. 13, the injection molding machine of the fifth embodiment comprises a movable platen 15, an ejector rod 59, and a plurality of pressurizing cylinders 111 disposed on the movable platen 15. A pressurizing piston 112 is slidably received in each of the pressurizing cylinders 111 and has a pressurizing rod 113 integrally formed thereon to extend forwardly (rightwardly as viewed in Fig. 13) therefrom. In this case, a pressurizing cross head 43 (see Fig. 2) as in the first embodiment is not required. In addition, the pressurizing cylinders 111 can be controlled dependently from one another and operated at different timings of motion or in different pressurization programs. Fig. 14 illustrates an essential portion of a locally pressurizing type injection molding machine according to a sixth embodiment of the present invention in a sectional view. As shown in Fig. 13, the injection molding machine of the sixth embodiment comprises a movable platen 15, an ejecting cylinder 55, a piston rod 56, an ejecting cross head 57, and ejector rods 58 and 59. A plurality of pressurizing cylinders 121 are disposed on the movable platen 15. A pressurizing piston 122 is slidably received in each of the pressurizing cylinders 121 and has a piston rod 123 integrally formed thereon to extend rearwardly (leftwardly as viewed in Fig. 14) therefrom. A pressurizing cross head 125 is disposed at a trailing or rear end of the piston rod 123, so that it can be advanced and retreated by operation of the pressurizing cylinders 121. On the other hand, a pressurizing plate 127 is advanceably and retreatably disposed forwardly (rightwardly as viewed in Fig. 14) of the movable platen 15, and a rear or trailing end of a pressurizing pin 128 is fixed to the pressurizing plate 127. The pressurizing plate 127 and the pressurizing cross head 125 are interconnected by a pressurizing rod 130. In this case, the pressurizing rod 130 is mounted further outside a peripheral edge of the movable platen 15 rather than extending through the movable platen 15. A seventh embodiment of the present invention will be described. Fig. 15 illustrates an essential portion of a locally pressurizing type injection molding machine according to the seventh embodiment of the present invention in a sectional view. As shown in Fig. 15, the injection molding machine of the seventh embodiment comprises a movable platen 15, an ejecting cylinder 55, a piston rod 56, an ejecting cross head 57, and an ejector rod 59. A plurality of pressurizing cylinders 131 are disposed on a peripheral edge of the movable platen 15. a pressurizing piston (which is not shown) is slidably received in each of the pressurizing cylinders 131 has a pressurizing rod 133 integrally formed thereon to extend forwardly (rightwardly as viewed in Fig. 15) therefrom. A pressurizing plate 127 is fixed to a front end of the pressurizing rod 133, and a pressurizing pin 128 is fixed at its rear end to the pressurizing plate 127. In this case, the pressurizing rod 133 does not pass through the pressurizing rod 133. It should be noted that the pressurizing rod 46, 92, 103, 113, 130 and 133 in each of the embodiments can be used for traction or rotation of a core or the like. Fig. 16 illustrates an application of a pressurizing rod. Referring to Fig. 16, there are shown a movable platen 150, a pressurizing rod 151, a pressurizing plate, an angular pin 153, a slide core 154, and a molded product 156. In this case, the angular pin 153 can be advanced and retreated by the pressurizing rod 151, thereby moving the slide core. Therefore, a special mechanism for moving the slide core 154 is not required, leading to a simplified structure. Although the embodiments of the present invention have been described, it will be understood that the present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the scope of the invention defined in claims.

Claims: A locally pressurising type injection molding machine comprising: (a) a stationary die (12), (b) a movable die (13) disposed for movement into and out of contact with said stationary die (12) to define a cavity (21) between both the dies, (c) a first ejector pin (52) extending through said movable die (13), with its tip end facing said cavity (21), and (d) a second ejector pin (51) extending through said movable die (13), with it tip end facing a sprue (18), (e) an ejecting cylinder (55) disposed in rear of said first ejector pin (52) and that second ejector pin (51) for simultaneously moving said first ejector pin (52) and said second ejector pin (51) through ejecting rods (58, 59), (f) a pressurizing pin (33) extending through said movable die (13), with its tip end facing at least one of a resin passage and said cavity (21), (g) a pressurizing cylinder (41) disposed in rear of said pressurizing pin (33) for moving said pressurizing pin (33) through a pressurizing rod (46) before the movement of said first ejector pin (52) and said second ejector pin (51), wherein (h) said pressurizing rod (46) and said ejecting rods (58, 59) are disposed coaxially. A locally pressurizing typ injection molding machine according to claim 1, in which a plurality of said pressurizing rods (46) are disposed and synchronized by a pressurizing cross head (43). A locally pressurizing type injection molding machine according to claim 1, in which: said each ejector pin (51, 52) is fixed to an ejector plate (53), and said pressurizing pin (33) is fixed to a pressurizing plate (36) and extends in the forward direction through said ejector plate (53) .

Inventors: SAWAYA ATSUSHI, SAWAYA, ATSUSHI, SAWAYA, ATSUSHI, SUMITOMOJUKIKAI SANNO APT. 1-406
Applicants: SUMITOMO HEAVY INDUSTRIES, SUMITOMO HEAVY INDUSTRIES, LTD
Application year: 1993
Main classification: B29C45
IPC codes: B29C45