KR100322860B1 - Injection molding machine for thermoplastic resin - Google Patents

Abstract

In the injection molding apparatus for thermoplastic resin, the mold clamping hydraulic circuit is composed of a hydraulic circuit which can be selectively set in the absence of pressure or substantially no pressure upon completion of closing of the mold mounted on the clamping unit, The movable movable mold can be retracted at a low injection pressure due to the injection of molten resin by the injection unit, and the nozzle port that opens the space portion of the mold cavity is closed at the same time as the predetermined amount of resin is filled, and the high pressure mold The clamping force is generated toward the front of the mold clamping unit and the mold clamping is continued to a predetermined position.

Thus, since the mold is in no pressure or substantially free of pressure, the injection pressure can also be lowered. In addition, the amount of resin injected at one time can be increased several times without increasing the hydraulic cylinder pressure of the injection unit, and also the molded clamping force of the clamping unit can not be increased by several times its size. It can be molded without.

Description

Injection molding machine for thermoplastic resins {INJECTION MOLDING MACHINE FOR THERMOPLASTIC RESIN}

The present invention relates to an injection molding apparatus for thermoplastic resin.

In the molding of thermoplastic resins, injection molding is known as a typical method for molding three-dimensional complex articles. In the injection molding method, as is known, the thermoplastic resin material is melted, injected at a high injection pressure into the clamped mold, and then cooled to solidify in the mold, thereby achieving stable dimensional accuracy and sink marks or burrs. A molded article having a good appearance without a back is obtained.

For this purpose, a clamping force capable of withstanding high injection pressures is required, and a strong mold is also required.

Usually, an injection unit having an injection pressure of 1200 to 2500 kg / cm 2 is provided regardless of the scale of the apparatus. In this case, the screw diameter must be reduced in order to increase the injection pressure in the same apparatus. Since the injection pressure and the injection capacity are inversely related, high injection pressure is required to obtain an article with stable dimensional accuracy, and until now even a relatively large strong molding apparatus is used, only small articles are molded. Could.

The reason why such a high pressure is required in the present molding apparatus is to facilitate the operation of filling the molten resin in the mold cavity provided as the heat exchanger, and to prevent the formation of sink marks on the surface of the molded article. This is because there is a tendency to use the resin pressure in order to.

On the other hand, the molten thermoplastic resin is deprived of heat by the mold during the injection, has a property to form a skin layer on the top and back, the viscosity increases in proportion to the flow length. Accordingly, the upper and back skin layers are cured upon completion of the resin filling into the mold cavity, and the injection pressure passing layer is narrowed.

Therefore, in order to prevent the cooling → solidification → shrinkage of the resin and to correct the sink mark on the surface caused by shrinkage from the inside of the wall of the molded product, the resin is removed from the center layer by the high injection pressure. It should spread to the side. Thus, only small sized articles can be obtained even when the clamping pressure and the injection pressure of the molding apparatus are applied in tons.

As described above, since the flow length is limited compared to the thickness of the molded article, pinpoint gates are required at many positions of the large molded article even when a large-scale molding apparatus is used.

Moreover, most of the large molded articles must be light in weight, high in strength and not thermally expand upon heating. As a countermeasure against this, in the related field, glass fibers (length 1 mm to 7 mm) have been often used as reinforcing composites recently. However, in the pinpoint gate mold for molding the molten resin mixed with the glass fibers, gate wear occurs due to the flow of the glass fibers during injection, causing the gate size to be enlarged. Therefore, satisfactory gate-tearing cannot be performed when the molded article is withdrawn from the mold (during mold opening operation) and often a good molded article is not obtained by peeling or cracking at the gate portion.

For this reason, there is a disadvantage that reinforcement composites such as glass fibers that promote the wear of the mold cannot be used for molding large products which require a relatively high strength while having a small thickness and weight depending on the use of the pinpoint gate. That is, it is a reality that a resin molded article having a large area and a high strength in a state in which thickness and weight are reduced cannot be obtained by injection molding.

In order to overcome the problems of the prior art as described above, the present inventors have contemplated the need for a molding method that can cope with the characteristics of the thermoplastic resin naturally, and have adopted the following features to achieve this object:

(1) When the molten resin is injected into the mold in the absence of pressure, the mold is opened so that the supply resin is supplied in a thick layer without resistance.

(2) The required amount of molten resin is affected by the temperature of the cooled mold only in the minimum region.

(3) The resin supplied in the thick layer into the mold is kept circularly around the gate port formed at the center position of the mold as the center point.

(4) The gate port is blocked so that the resin does not flow back from the mold cavity.

(5) As soon as the injection proceeds in the closed state, high pressure is generated in the mold, so that the mold is opened.

(6) The entire circumferential length of the thick resin layer holding the circle functions as a film gate, and the circle expands at high speed in the mold cavity without being affected by the mold temperature in the cavity. The resin filling is then completed.

(7) Since the molten resin has the characteristics of flowing, cooling, and solidifying, as the cooling proceeds, the molten resin is solidified (cured) from the surface and the back of the mold cavity mold. Thus, the skin layer is formed on the surface and back of the resin and the thermally expanded resin shrinks toward the center layer as it cools.

(8) Since the clamping force is applied at a high pressure so as to cope with the characteristics of the resin naturally, the resin is cooled and solidified without a sink mark.

(9) Since this molding method naturally copes with the characteristics of the resin, both the injection pressure and the clamping pressure can be reduced to 1/5 to 1/7, and this molding method uses a gate disposed at a point in the center of the article. This makes it possible to produce molded articles 5 to 7 times larger in size with the capabilities of conventional injection molding apparatus.

However, 80-90% of commonly used injection molding machines have a horizontal clamping mechanism. Therefore, in the case of adopting such a horizontal clamping mechanism, the movable part is moved laterally by the injection pressure, so that the divided surface of the mold mounted on the clamping unit is less resistive and is opened more than necessary from the retainer part, and the center of the molded article The weight of the molten resin injected from the sprue gate at is caused to vary vertically along the flow direction. Since this will result in molding failure, it is necessary to ensure uniform flow in both the vertical and lateral directions while keeping the resin flow circular to the gate as the center. Therefore, there is a need for a hydraulic circuit for pressure setting that produces a back pressure to the extent that the mold is closed and at the same time without becoming pressure-free and prevents the flow difference. By the operation of 8).

However, the conventional injection molding apparatus uses a hydraulic circuit that generates a high-pressure clamping force when the mold is sealed, so that the mold is completely hermetically fixed by the above pressure. By the way, in this invention, since there are various types of means which comprise a hydraulic circuit, in this specification, it demonstrates with a directional control valve and a flow rate control valve (limiting valve). By the way, as mentioned above, the injection pressure of 1/7-1/8 is enough compared with the prior art as mentioned above. Thus, in the case of a tandem screw injection mechanism, the screw stroke possessed by the injection mechanism described above can be used, which can only be achieved by enlarging the diameter of the screw head structure. The heating cylinder head is fixed to the heating cylinder.

In a preplastic injection unit, the resin plastic injection machine can be used as it is and the diameter of the injection plunger can be used to measure the molten resin, which is several times the capacity of the molding apparatus. Can be injected. Moreover, since the nozzle is closed at the same time as the injection of molten resin into the mold is completed, the screw is rotated even during the period when the molded product is cooled, so that melting → kneading → filling is performed in the resin metering section, which greatly contributes to shortening the molding cycle. Can be.

In the case where a larger molded article is required, the injection unit invented by the inventors can be used, and the injection unit according to the present invention can be used even when the coarse powder of the recycled resin material is mixed with the new resin material in a large ratio. The extruder is capable of obtaining a capacity as well as performing stable kneading and injection at a stable melting temperature.

(a) Large capacity injection unit using extruder.

(b) Increased capacity injection units obtained by retrofitting in-line screw type injection units.

(c) Increased capacity injection unit obtained by expanding and modifying the diameter of the injection plunger in the prefired injection unit.

According to one preferred embodiment of the present invention, an injection molding apparatus for thermoplastic resin, comprising: an upper mold and a lower mold, which are engaged with each other to close a mold and at least one of which is a movable mold capable of moving up and down in a vertical direction; A clamping hydraulic circuit comprising a directional switching valve capable of being diseased to a neutral position upon completion of closing of the mold; A clamping cylinder comprising a forward oil supply port in communication with the drain for setting the clamping hydraulic circuit to a substantially no pressure when the directional valve is switched to the neutral position; An injection unit for injecting molten resin into a mold cavity formed by applying a resin pressure between the upper mold and the lower mold to move the movable mold; A nozzle installed between the injection unit and the mold cavity, the nozzle opening being opened in the mold cavity and having a nozzle port closed at the same time a predetermined amount of molten resin is completed into the mold cavity; According to the mold closing completion signal, the nozzle is opened to inject the molten resin into the mold cavity from the injection cylinder of the injection unit in which the molten resin accumulates, and at the same time as the closing of the nozzle by the injection unit is completed. Control means for filling said molten resin into said injection unit for a subsequent process, wherein after said predetermined amount of molten resin injection is completed, said direction switching valve is switched from a neutral position to another position. An injection molding apparatus for thermoplastic resin is provided, characterized in that the molding is performed by generating a high mold clamping force.

According to another preferred embodiment of the present invention, an injection molding apparatus according to the above embodiment, the extruder having a screw for discharging the molten resin; A band heater wound around the extruder and heating the resin; A backflow prevention unit disposed between the screw head of the screw end and an injection cylinder forming a part of the injection unit; A piston disposed inside the injection cylinder and having a larger outer diameter than the extruder, wherein the band heater is disposed on an outer periphery of the extruder, the injection cylinder having an inner diameter corresponding to the outer diameter of the piston, An injection molding apparatus for thermoplastic resin is provided, characterized in that the stroke of the piston necessary for injection of the molten resin into the mold cavity is formed.

According to another embodiment of the present invention, an injection molding apparatus according to the first embodiment described above, an extruder having a screw for discharging the molten resin; An injection cylinder accommodating the screw head therein and forming a part of the injection unit; And an on / off valve arranged to open and close the nozzle port, wherein the screw is arranged in line with the injection cylinder, and the injection cylinder has a larger diameter than the extruder, and also the injection of the molten resin. An injection molding apparatus for thermoplastic resin is provided, comprising a cylinder head into which a screw head is inserted.

The injection compression molding apparatus according to the present invention can be made by combining a clamping unit having a hydraulic circuit as described above with each of the three types of units described above. The construction and excellent effects on them will be described in detail through preferred embodiments.

1 is a side cross-sectional view of an injection compression molding apparatus showing a first embodiment of the present invention consisting of a combination of a large-capacity injection unit D using an extruder A and a longitudinal clamping mechanism.

FIG. 2 is a partial cross-sectional view of a large capacity injection unit D using the extruder A of FIG. 1.

3 is a longitudinal sectional view of the pamphlet mold for a molding fork lift mounted to the longitudinal clamping unit (C).

4 is a longitudinal sectional view of an injection unit installed in an inline mode according to the horizontal clamping mechanism of a conventional injection molding apparatus.

Fig. 5 is a longitudinal sectional view of an injection unit showing a second embodiment of the present invention.

FIG. 6 shows the invention of the invention in which the injection unit N is arranged in series with the horizontal clamping unit, and the extruder M is connected parallel or obliquely to the upper or left and right sides of the injection unit N described above. It is a longitudinal cross-sectional view of 3 embodiment.

7 is an exemplary view of a hydraulic circuit used in the clamping device according to the present invention.

-Explanation of symbols for the main parts of the drawings-

1, 58: heating cylinder 2, 61: screw 4, 58: injection cylinder

7, 8, 20: Hydraulic cylinder 17, 66: Non-return valve (part) 31, 82: Nozzle

32, 83: nozzle port 28: resin passage 35: mold cavity

46, 62: screw head 59: cylinder head A: extruder

B: Hopper C: Clamping Part D: Injection Part

G: upper mold H: lower mold

First embodiment

1 is a side cross-sectional view of an injection compression molding apparatus composed of a large-capacity injection unit (D) using a combination of an extruder (A) and a longitudinal clamping unit (C), showing a first embodiment according to the present invention, FIG. 2 is a cross sectional view of a portion of a large-capacity injection unit D using an extruder A, and FIG. 3 is a view of a brochure mold used in a forklift mounted on a longitudinal clamping unit C to perform molding. 7 is a vertical cross-sectional view, and FIG. 7 is a hydraulic circuit diagram composed of a combination of a direction change valve and a restriction valve as an example of a hydraulic circuit used in the clamping unit according to the present invention.

First, the lower mold H shown in FIG. 3 is fixed on the retainer platen 5 of the clamping unit C in FIG. 1, and the upper mold G is the movable clamping platen 6. Is fixed to the mounting. Subsequently, the small diameter hydraulic cylinder 7 moves the movable clamping platen 6 in the vertical direction by hydraulic pressure, and the hydraulic cylinder 7 is composed of the hydraulic circuit shown in FIG. The upper mold G is fitted to the lower mold H so as to move downward by the downward manipulation of the cylinder 7 to close the mold, and the clamping hydraulic circuit is free of pressure or substantially free of pressure. It is set to the low voltage circuit of the state. In FIG. 7, reference numeral 92 denotes a piston rod 92 of a clamping cylinder 93 comprising a forward clamping hydraulic circuit in communication with a drain, and 94 is a directional valve for the forward clamping hydraulic circuit. (The clamping hydraulic circuit described above in the neutral position is adjusted to a low pressure circuit with no or substantially no pressure). Reference numeral 95 denotes a restriction valve. 1 and 3, the upper end 18 of the cylinder head 16 of the injection cylinder 4 is connected to the resin passage 28 of the mold, and the nozzle 31 is connected to the upper end thereof. The port 32 is open at the upper surface of the lower mold H. The nozzle port 32 can open and close the load valve 29 by the vertical operation of the hydraulic cylinder (air pressure may be used). In addition, the injection cylinder 4, the cylinder head 16, the resin passage 28, and the nozzle 31 are each connected to the heater 57, for example, and are maintained at a predetermined set temperature. In addition, a cooling water circuit (not shown) is arranged around the nozzle port 32. Then, the screw 2 is rotated by the driving force of the motor 27 via the bearing box 26 and the heating cylinder 1 is heated to a predetermined temperature by a band heater 42 wound around its outer circumference. Therefore, the thermoplastic resin material stored in the family register B mounted on the upper side of the hopper port 19 is melted while being transferred in the direction of the injection cylinder 4 by the rotation of the screw 2, and is contained in the recycling material. Water and the like are vaporized and removed when passing through the vent port 44 position, and then the resin material is transported and kneaded while passing through the grooves 45 (see FIG. 2) formed in the screw head 46 while the injection cylinder 4 Filled into

In the piston 3 fixed to the upper end of the heating cylinder 1, the screw 2 and the screw head 46 retreat together with the piston 3 from the injection cylinder head 16 by the filling pressure of the molten resin. . Then, when backing up to the position set to display a predetermined amount of resin value, a signal for stopping the rotation of the screw 2 is activated.

Next, in FIG. 2, the shaft 25 is inserted into the fixing plate 23 of the injection cylinder 4 fixed to the upper surface of the bed 10 of the injection unit and the shaft fixing plate 48 fixed to the upper surface of the bed 10. It is inserted and fixed with nuts 49 and 24. Both ends of the hydraulic cylinder 20 are fixed by the extruder fixing plate 47 and the heating cylinder retainer plate 22, between which a shaft 25 is inserted, and the hydraulic piston 21 in the hydraulic cylinder 20 described above. ) Is fixed to the shaft 25 and inserted. The hydraulic cylinder 20 is made to be slidable with respect to the shaft 25 and the hydraulic piston 21. In the heating cylinder retainer plate 22 and the extruder fixing plate 47, the front injection circuit E and the rear injection circuit F communicate with each other by the hydraulic circuit communication ports on the right and left sides of the two hydraulic cylinders 20, respectively. In FIG. 1, when the upper mold G (movable mold) fixed to the movable clamping platen 6 of the clamping unit C is lowered and engaged with the lower mold H to receive a mold sealing completion signal, The nozzle rod valve 29, which has been shut off until then, immediately descends to immediately open the nozzle port 32, and at the same time, injection of the high pressure oil from the circuit E starts forward. Since the injection cylinder 4 communicates with the injection cylinder head 18 and the resin passage 28 and also communicates with the nozzle port 32, the molten resin filled in the injection cylinder 4 is transferred into the mold cavity 35. It is injected, and the upper mold G starts to rise under the influence of the injection pressure.

When the injection is started, a resistance force is generated in the molten resin in the injection cylinder 4 to generate a repulsive force for reversing the backflow prevention ring 17 as the backflow prevention portion fitted in the outer periphery of the screw head 46, thereby producing a molten resin. The non-return ring 17 is brought into contact with the valve seat 50 so as not to flow back into the screw 2, so that the injection amount is constant every cycle. Subsequently, the upper mold G rises by the pressure of the injected resin, and at the same time as the injection is completed, the load valve 29 rises to block the nozzle port 32, and the high pressure oil of the clamping unit C The clamping is started by supplying the large diameter hydraulic cylinder 8, and the upper retainer plate 52 of the mold comes into contact with the stopper 51 (see FIG. 3) disposed in the lower mold H, and the molded product is previously The molding is completed by cooling to the determined predetermined thickness.

On the other hand, at the same time as the nozzle port 32 is blocked, the screw 2 starts to rotate and thus the molten resin is filled, thus greatly contributing to the shortening of the next cycle time. The mold is opened by the cylinder 7, the extrusion rod 53 disposed in the clamping unit C is raised to push the extrusion plate 33 of the mold, and the molded article is placed on the extrusion pin 34 (see FIG. 3). It is pushed up from the lower mold H and taken out. In this manner, even when the molded article has a size of 1500 mm x 1500 mm, the molded article is highly sophisticated without sink marks or orientation distortions, leaving only a fine surface injection port at one position in the central region.

Second embodiment

4 is a longitudinal sectional view of an injection unit installed in line with a horizontal clamping unit of a conventional injection molding apparatus, and includes a heating cylinder 58, a cylinder head 59, a nozzle 60, and a screw top 61 ), A screw head 62, a hopper 63, a hopper port 64, a heating band heater 65 and a backflow prevention ring (valve) 66 are shown in cross section. The resin material stored in the hopper 53 is transferred from the hopper port 64 as the screw 61A in the heated heating cylinder 58 rotates, and the resin material is melted and kneaded as it approaches the screw head 62, Passes through the outer diameter portion of the seat valve 69 inserted in the screw head 62, and then passes through the inner diameter portion of the backflow prevention ring (valve) 66, and then the molten resin is disposed at the upper end of the screw head 62. The inside of the cylinder head 59 is filled through the recessed groove 68. In this case, the backflow prevention ring (valve) 66 is advanced in front of the seat surface 67 of the seat valve 69 by the transfer pressure of the molten resin to form a molten resin passage. L denotes a stroke, and molten resin is filled to the entire stroke of the injection unit. Since the nozzle 60 is in close contact by pressure with the sprue port disposed on the mold cavity side installed in the horizontal clamping unit (not shown), the resin is not leaked by the injection pressure. In response to the forward operation of the screw 61A by the injection start signal, the backflow prevention ring 66 is brought into contact with the seat face 67 of the valve seat 69 by the melt resin pressure in the heating cylinder 58. Resin is injected into the mold at a constant injection amount every cycle.

5 shows a second embodiment according to the present invention, where the screw head 62B has the same structure as the screw head 62 in FIG. 4 but its outer diameter is twice that of the screw head 62. The screw 61A is the same as the screw 61A of FIG. 4, and the thread assembly 70 of the screw head 62B has the same thread size. The upper end of the heating cylinder 58 is made of a large diameter 71, and can perform the same length of stroke as in FIG. 4, and has a heating cylinder having an inner diameter twice as large as that of the heating cylinder 58 of FIG. A large diameter screw head 62B having a thread assembly 70 in 58B is inserted and assembled.

The large cylinder head 59B described above is fixed to the upper end of the heating (injection) cylinder 58B having a large diameter, and a band heater 65B is attached to its outer circumference. A load valve 72 capable of opening and closing is disposed at the nozzle 60B.

Therefore, the injection unit K including the injection cylinder 58B having an inner diameter twice as large as that of the conventional injection cylinder 58 is a unit having a volume four times as compared with the conventional one. The chain arrow shown inside the injection unit K indicates the flow of the molten resin flowing from the screw 61A. FIG. 5 shows the screw head 62B in the position where the resin starts to be filled into the injection cylinder head 59B by the rotation of the screw 61A, the operation of which is the same as that described in FIG.

The horizontal clamping unit having the hydraulic circuit and the injection unit shown in FIG. 5 is assembled in series to constitute an injection molding apparatus, wherein the nozzle port 73 is a sprue disposed at a mold center installed in the horizontal clamping unit. In pressure contact with the gate port. In the order as described in FIG. 4, the injection of the predetermined amount of molten resin is completed, and at the same time, the resin passage of the nozzle 60B is closed by the rotatable rod valve 72 and is operated in a strong mold clamping direction. Compression molding is performed by pressure (clamping pressure of the injection molding apparatus installed in the injection unit shown in FIG. 4). Accordingly, the passage of the nozzle 60B is closed by the load valve 72, and the screw 61A starts to rotate to melt the resin, stir and fill the resin. Since this operation continues even during the cooler in the conventional apparatus, an article having a volume of several times can be molded in a high cycle as a feature of such a molding apparatus. By the way, in the conventional molding apparatus, it is necessary to inject molten resin at a high pressure into the clamped mold in order to form an injection pressure such that a sink mark is not generated during flow → filling → cooling → solidification in the mold. For this reason, the screw 61A cannot be rotated until this period ends. Moreover, the opening and closing valve may be mounted in the nozzle, but is different from the purpose of using such a nozzle port opening and closing valve in a conventional apparatus. That is, in the case of molding the nylon resin, the nylon resin at the nozzle port forms a long stretched yarn form as it is attached to the sprue as soon as the mold is opened, and the molded article is immediately taken out after cooling due to the nature of the nylon resin. Needs to be. Then, the molded article is stuck and not drooped, and in the case of automatic molding, the stuck article is pressed and crushed by clamping in the next cycle, and often damages the mold. In view of the foregoing, for the purpose of improving the separation of the twisted yarn type described above, the load valve 72 is opened by the injection pressure, and the nozzle and the injection unit, which were in contact with the mold as the cooler passes, retreat and melt. The rod valve 72 is blocked by the spring force so that the molten resin does not leak through the nozzle port 73 while the resin is filled by the rotation of the screw 61A. Then, when the mold clamping is completed, the entire injection unit K is advanced to start the injection for molding as the nozzle 60B is in pressure contact with the mold sprue pot.

Third embodiment

6 is a cross-sectional view in which the injection unit N is arranged in series with a horizontal clamping unit (not shown), and the extruder M is parallel to the injection unit N described above, or left and right sides of the injection unit N. Is placed inclined to. A check valve or rod valve 74 for opening and closing the molten resin passage is disposed at the connecting portion. The resin material stored in the leopard 80 is transferred in the heating cylinder 76 by the rotation of the screw 75 inserted in the heating cylinder 76 heated to the temperature set by the band heater 77. The melt kneaded resin while being conveyed to the upper end of the screw 75 is conveyed into the injection cylinder head 86 of the injection unit N as the load valve 74 is opened. The injection plunger 84 is reversed at the pressure of the resin. When the above-mentioned injection plunger 84 retreats to a predetermined position, the rotation of the screw 75 is stopped by the relevant signal. At the same time, the connecting passage is closed by the load valve 74 and the injection plunger 84 supplies the high pressure oil through the oil pressure circuit port 91 of the hydraulic cylinder 89 connected to the rear end of the plunger 84. As a result, the injection by the hydraulic ram 90 inserted into the hydraulic cylinder 89 is started. Molten resin is filled in the mold cavity through sprues in the mold engaged by the high pressure mold clamping force, and injection pressure is filled into the mold cavity by passing molten resin through the sprue in the mold. It is applied as is until completion. In this respect, the molding method in this embodiment is the same as that described for the second embodiment. In Fig. 6, the open / close rotary rod valve 82 is a nozzle of the injection part N of the prefiring injection unit. In addition to 81, the inner diameters of the injection cylinder 85 and the injection cylinder head 86 are made larger, so that the injection plunger 84 inserted therein prevents the molten resin from leaking to the outside. Has an outer diameter size and structure (specific structure not shown). The illustrated figure shows a state in which a predetermined amount of molten resin is completely filled. The screw 75 is stopped by the metering completion signal, and the passage is also closed by the rotary load valve 74 of the connection, whereby the nozzle port of the closed rotary load valve 82 of the closed nozzle 81 ( 83, the high pressure oil is supplied to the oil supply port (oil pressure circuit port) 91 of the hydraulic cylinder 89, the injection plunger 84 connected with the hydraulic ram 90 is advanced, Resin is filled from the nozzle port 83 into the mold cavity through the sprue of the mold. As mentioned above, in a mold installed and closed in a clamping unit having a hydraulic circuit, the movable clamping platen retreats under the influence of the injection pressure and the separating surface of the mold is slightly opened due to the small resistance. On the other hand, the nozzle port 83 is cut off by the rod valve 82 as soon as filling is completed and the high pressure oil is supplied to the clamping oil pressure circuit in all directions according to the signal to generate the clamping force, and molding is performed. Cooling results in a molding. On the other hand, at the same time as the nozzle port 83 is blocked by the load valve 82, the load valve 74 of the connecting part is operated to open the passage to rotate the screw 75 and transfer the resin to the resin in the hopper 80. The resin is transferred into the injection cylinder 85 while performing melt → kneading. Then, the injection amount can be increased four times by expanding the inner diameter of the injection cylinder 85, for example, twice. When a large amount of resin is required, the screw 75 is used over the entire period of the cooling time in the mold in the conventional apparatus + the opening operation time of the mold + the recovery time of the product + the mold closing time by the screw 75. Since the molten resin can be filled in the injection cylinder 85 by rotating a), the above injection unit has a very big advantage that can contribute to a high cycle (high cycle) process. The clamping unit provided with the hydraulic circuit can be quickly filled even at low injection pressure (1/5 to 1/8 of the conventional injection pressure). In addition, even if the resin shrinks during cooling and solidification, the compression pressure is continuously applied in the direction of shrinking. Thus, even when the molded product is large, a product having a highly precise and beautiful surface without sink marks or directional distortions is obtained.

By the way, in the conventional injection molding apparatus, the pressure of the injection hydraulic cylinder is 18-20 tons in the molding apparatus whose clamping force is 100 tons.

The following description is based on the comparison with the conventional injection molding apparatus.

In short, the present invention operates to fill the mold cavity with resin and to remove the sink mark with a clamping force of 100 tons, the injection unit being reduced injection pressure by a quarter by doubling the diameter of the injection section of the molding apparatus. 4 times the injection amount can be obtained. In the present invention, the injection unit is for melting and kneading the resin while supplying the resin into the mold cavity to supply the resin into the mold, and the sink mark is prevented by the mold clamping force. In fact, the molding apparatus of the present invention is suitable for molding large products which require several times the amount of resin than usual. For this purpose, a tie bar spacing for mounting a mold for forming a large product and a stroke spacing for opening and closing a mold to take out a molded article are, of course, necessary and have a clamping force of 100 tons. A mold clamping unit is required. However, the hydraulic equipment element used in the hydraulic circuit and the rotating member for generating the driving force (electric motor, hydraulic motor, etc.) can be controlled and performed at the same flow rate and pressure as in the conventional apparatus.

In addition, most molded articles can be obtained by using molds designed for use in conventional injection molding, but these molds may cause flashing due to the retreat of the moving part during injection. One mold can be partially modified to be used in the molding of the present invention.

In addition, it is possible to easily obtain a mold capable of molding an article which can be molded at the same time based on the concept of molding by a clamping pressure or an article that cannot be molded without using a split mold. In addition, in the conventional molding method, it was difficult to mold an article having a hinge portion (a portion made of an extremely thin linear recess that can be bent like a hinge). However, in the molding method according to the present invention, the molten resin is introduced into and filled with the cavity, and at the same time, the compression molding method is performed, so that a molded article having a long hinge portion or a plurality of hinge portions can be easily molded. Thus, the large box-shaped article can be assembled simply by bending the hinge portion. The mold can be a simple structure, such as a plan view of the plan, this molding method provides a great advantage in the industry that can significantly reduce the transportation cost, packaging cost and storage cost.

Claims (3)

In the injection molding apparatus for thermoplastic resin, An upper mold and a lower mold engaged with each other to close the mold and at least one of the movable molds capable of vertically moving up and down; A clamping hydraulic circuit comprising a direction switching valve switchable to a neutral position upon completion of closing of the mold; A clamping cylinder including a forward oil supply port in communication with the drain for setting the clamping hydraulic circuit to a substantially no pressure when the directional valve is switched to the neutral position; An injection unit for injecting molten resin into a mold cavity formed by applying a resin pressure between the upper mold and the lower mold to move the movable mold; A nozzle installed between the injection unit and the mold cavity, the nozzle opening being opened in the mold cavity and having a nozzle port closed at the same time a predetermined amount of molten resin is completed into the mold cavity; According to the mold closing completion signal, the nozzle is opened to inject the molten resin into the mold cavity from the injection cylinder of the injection unit in which the molten resin accumulates, and at the same time as the closing of the nozzle by the injection unit is completed. Control means for filling said molten resin into said injection unit for subsequent processing, Characterized in that the molding is performed by generating a high mold clamping force after completion of the predetermined amount of molten resin injection by switching the direction switching valve from a neutral position to another position. Injection molding apparatus for thermoplastic resin. The extruder according to claim 1, further comprising: an extruder having a screw for discharging the molten resin; A band heater wound around the extruder and heating the resin; A backflow prevention unit disposed between the screw head of the screw end and an injection cylinder forming a part of the injection unit; A piston disposed inside said injection cylinder and having a larger outer diameter than said extruder, The band heater is disposed on the outer periphery of the extruder, The injection cylinder has an inner diameter corresponding to the outer diameter of the piston, and the stroke of the piston necessary for injection of the molten resin into the mold cavity is formed to be possible. Injection molding apparatus for thermoplastic resin. The extruder according to claim 1, further comprising: an extruder having a screw for discharging the molten resin; An injection cylinder accommodating the screw head therein and forming a part of the injection unit; And an on / off valve arranged to open and close the nozzle port, The screw is arranged in line with the injection cylinder, The injection cylinder has a larger diameter than the extruder described above, and further includes a cylinder head into which the screw head is inserted during the injection of the molten resin. Injection molding apparatus for thermoplastic resin.

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