JP2981397B2 - Method for preventing resin burning in resin molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing resin burning in a resin molding apparatus.

[0002]

2. Description of the Related Art Conventionally, in a resin molding apparatus, for example, an injection molding machine, a resin heated and melted in a heating cylinder is injected from an injection nozzle, filled in a mold cavity, and cooled. Then, the mold is opened and the molded product is taken out.

[0003] For this purpose, a screw is disposed in a heating cylinder of the injection device so as to be able to advance and retreat and to be rotatable, and is rotated by a drive system to retreat. At this time, the resin supplied from the hopper moves forward in the heating cylinder with the rotation and retreat of the screw, and is heated and melted during that time and is stored in front of the screw head.

Next, the drive system advances the screw. As a result, the resin stored in front of the screw head is injected from the injection nozzle and filled in the mold cavity. At this time, the resin is reacted by an injection pressure applied by an injection cylinder when the resin is injected,
A part of it tends to flow backward through the groove of the screw. To prevent this, a check ring is provided in front of the screw so that the check ring contacts the seal ring when the screw is advanced. The screw and the screw head are formed separately so that the check ring does not come off from the screw, and the two are fixed by screwing the screw portion.

The screw head has a large diameter portion and a small diameter portion, and the outer diameter of the large diameter portion is made larger than the inner diameter of the check ring so that the check ring does not come off.

[0006]

However, in the conventional injection molding machine, since the screw is rotated and retracted in the measuring step, the resin is moved forward through the groove of the screw. May stay in the heating cylinder. in this case,
When the temperature of the resin rises and the resin burns, and the resin with the burnt resin is filled into the cavity of the mold as it is, black spots are formed on the molded product.

[0007] In particular, when PE (polyethylene) is used as the resin, resin burning tends to occur. Therefore, it is conceivable to lower the set temperature when the resin is heated by the heating cylinder. However, in this case, the occurrence of resin burning can be reduced, but the viscosity of the resin increases by that much, so that the cavity cannot be sufficiently filled with the resin in the injection process, and the unfilled portion of the molded product has Not only can this occur, but the unmelted portion of the resin can be filled as is.

Further, by coating the surface of the screw with a fluororesin, the melted resin is prevented from adhering to the surface of the screw or the portion where the resin stays is reduced, so that resin burning occurs. Can be prevented. However, resin burning occurs on the inner peripheral surface of the heating cylinder, and the resin that has undergone resin burning adheres to the inner peripheral surface of the heating cylinder, forming a blackened resin layer. Then, once the blackened resin layer is formed, even if the screw is rotated along the inner peripheral surface, it is not scraped off, and is firmly attached to the inner peripheral surface of the heating cylinder. Will stick. Furthermore, the blackening resin layer becomes a nucleus, and burnt resin grows.

As described above, in a resin molding apparatus in which a resin is heated and melted, and molding is performed using the melted resin, resin burning occurs in a portion where the resin stays and a blackened resin layer is formed. I will. The present invention
A resin that solves the problem of the conventional method of preventing resin burning in a resin molding apparatus and can prevent resin burning without lowering the set temperature when heating and molding the resin. An object of the present invention is to provide a method for preventing resin burning of a molding apparatus.

[0010]

For this purpose, in the method for preventing burning of a resin in a resin molding apparatus according to the present invention, the resin is heated and melted, and molding is performed using the melted resin. Then, the resin is heated to a set temperature to perform a molding cycle, and when the molding cycle is stopped, the temperature of the resin is decreased, and after the molding cycle is stopped, the resin is forcibly applied when a set time has elapsed. Move to Further, the set time is set shorter than the maximum residence time that does not cause resin burning.

In another method for preventing resin burning in a resin molding apparatus according to the present invention, a resin is heated and melted, and injection molding is performed with the melted resin. Then, the resin is heated to a set temperature to perform an injection molding cycle, and when the injection molding cycle is stopped, the temperature of the resin is reduced. Is rotated to force the resin to move. Further, the set time is set shorter than the maximum residence time that does not cause resin burning.

In another aspect of the present invention, there is further provided a method for preventing resin burning, wherein the temperature of the resin is lowered by turning off a heater of an injection nozzle when an injection molding cycle is stopped. After the cycle is stopped, the heater of the heating cylinder is turned off when another set time has elapsed.

[0013] In still another method for preventing resin burning of a resin molding apparatus according to the present invention, the injection nozzle is retracted when the injection molding cycle is stopped.

[0014]

According to the present invention, in the method for preventing burning of a resin in a resin molding apparatus as described above, the resin is heated and melted, and molding is performed using the melted resin. Then, the resin is heated to a set temperature to perform a molding cycle, and when the molding cycle is stopped, the temperature of the resin is decreased, and after the molding cycle is stopped, the resin is forcibly applied when a set time has elapsed. Move to Also,
The set time is set shorter than the maximum residence time that does not cause resin burning. In this case, when the molding cycle is stopped while the resin is being heated to the set temperature and the molding cycle is being performed, the temperature of the resin is lowered, and after the molding cycle is stopped, when the set time has elapsed. The resin is forced to move.

In another method for preventing resin burning in a resin molding apparatus according to the present invention, a resin is heated and melted, and injection molding is performed with the melted resin. Then, the resin is heated to a set temperature to perform an injection molding cycle, and when the injection molding cycle is stopped, the temperature of the resin is reduced. Is rotated to force the resin to move. Further, the set time is set shorter than the maximum residence time that does not cause resin burning. In this case, when the injection molding cycle is stopped while the injection molding cycle is being performed while heating the resin to the set temperature, the temperature of the resin is reduced, and the set time elapses after the injection molding cycle is stopped. Then, the screw is rotated and the resin is forcibly moved.

In another embodiment of the present invention, there is further provided a method for preventing resin burning, wherein the temperature of the resin is reduced by turning off a heater of an injection nozzle when an injection molding cycle is stopped. After the cycle is stopped, the heater of the heating cylinder is turned off when another set time has elapsed. In this case, when the injection molding cycle is stopped while the injection molding cycle is being performed while heating the resin to the set temperature, the temperature of the resin is reduced, and after the injection molding cycle is stopped, another set time is set. Is elapsed, the heater of the heating cylinder is turned off.

According to still another method for preventing resin burning in a resin molding apparatus of the present invention, the injection nozzle is retracted when the injection molding cycle is stopped. In this case, when the screw is rotated, the resin is moved out of the heating cylinder.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a main part of an injection device according to an embodiment of the present invention, and FIG. 2 is an enlarged view of a distal end portion of a heating cylinder according to the embodiment of the present invention. As shown in the figure, a screw 12 is provided in a heating cylinder 11 of the injection device.
Are provided so as to be able to advance and retreat and rotate freely. The screw 12 is placed at the forward limit position when the injection process is completed, and is placed at the backward limit position when the metering process is completed.

The heating cylinder 11 has a cylinder head 11a near the front end (left side in the figure), and the cylinder head 11a is fixed to the main body 11c of the heating cylinder 11 by bolts 11b. An injection nozzle 14 is screwed and fixed to an end surface of the heating cylinder 11 in front (left side in the figure) of the cylinder head 11a, and a nozzle port 15 is provided in an end surface in front of the injection nozzle 14 (left side in the figure). It is formed. In addition, an injection cylinder 16 is provided behind the heating cylinder 11 (to the right in the figure), and an injection piston 17 that moves back and forth (moves in the left-right direction in the figure) in the injection cylinder 16 and the screw 12 are The couplings 19 are relatively rotatably connected.

The injection piston 17 is moved forward (moves to the left in the drawing) in the injection process, and retracts (moves to the right in the drawing) in the measuring process and suckback.
Let me do. Band heaters H1 to H4 for heating and melting the resin in the heating cylinder 11 are provided on the outer periphery of the heating cylinder 11 in contact with the heating cylinder 11. Band heater H for preventing the resin in 14 from solidifying
5 and H6 are disposed in contact with the injection nozzle 14.

Further, a cover 25 is fixed above the heating cylinder 11 at a predetermined interval, and surrounds the band heaters H1 to H4. 27 is a fixed platen. In the measuring step, the screw 12 is rotated by a drive system (not shown) and moves backward (moves rightward in the figure). At this time, the resin supplied from a hopper (not shown) falls through the hopper opening 18 connecting the hopper and the heating cylinder 11 and enters the heating cylinder 11, and the groove is formed with the rotation and retreat of the screw 12. It moves forward (to the left in the drawing) along 20, while being heated and melted in the heating cylinder 11 and stored in front of the screw head 22 (to the left in the drawing). At this time, the pressure of the resin generated due to the melting becomes a reaction force against the screw 12, and the screw 12 is retreated by the reaction force. The screw head 22 is fixed in front of the screw 12 (to the left in the figure) via a seal ring 32.

Next, in the injection step, the injection cylinder 16 advances the screw 12 (moves to the left in the drawing). As a result, the resin stored in front of the screw head 22 is injected from the injection nozzle 14, and is injected into the cavity between the mold (not shown) attached to the fixed platen 27 and the mold attached to the movable platen (not shown). Will be filled.

When the resin is injected, an injection pressure is applied by an injection cylinder 16. Then, due to the reaction force against the injection pressure, a part of the resin tends to flow backward (to the right in the drawing) through the groove 20 of the screw 12. In order to prevent this, a check ring 31 is provided on the screw head 22, and a seal ring 32 is fixed to the front end face of the screw 12.
Accordingly, when the screw 12 is advanced, the check ring 31 comes into contact with the seal ring 32, and the respective end surfaces thereof are in close contact with each other to seal the space therebetween.

The screw 12 and the screw head 22 are formed separately, and the two are fixed by screwing a screw portion 35. The screw head 22 has a conical portion 22a, a large-diameter portion 22b, and a small-diameter portion 22c from the front to the rear. The outer diameter of the large-diameter portion 22b is larger than the inner diameter of the check ring 31. This prevents the check ring 31 from coming off.

Further, the check ring 31 has an annular resin flow path 37 between the check ring 31 and the small diameter portion 22c of the screw head 22.
In the measuring step in which the screw 12 is retracted, the resin flow path 37 is opened, and the resin is sent to the front of the screw head 22 via the resin flow path 37. On the other hand, in the injection step in which the screw 12 advances, the check ring 31 contacts the seal ring 32,
The resin flow path 37 is shut off. Therefore, it is possible to prevent the resin from flowing backward.

When the check ring 31 is arranged in a non-corotating manner, the check ring 31 does not rotate even if the screw 12 rotates in the measuring step. On the other hand, when the check ring 31 is arranged in a co-rotating manner, when the screw 12 rotates in the measuring step, the check ring 31 also rotates. Therefore, a locking portion (not shown) for preventing relative rotation between the screw head 22 and the check ring 31 is formed.

The screw 12 has a supply section Pa in which a deep groove 20 is formed in the rear, a compression section Pb in which a groove 20 gradually becomes shallower from the rear to the front in the center, and a shallow groove 20 in the front. And a weighing unit Pc. Next, the flow of the resin in the heating cylinder 11 will be described with reference to FIG.

FIG. 3 is an enlarged view of the heating cylinder in the embodiment of the present invention. As shown in the drawing, a spiral (helical) flight 51 is formed on the screw 12, and a valley 52 is formed between each adjacent flight 51. And
The valley 52 is formed continuously along the flight 51 and becomes the groove 20 as a whole. By the way, the cycle time of an injection molding machine usually lasts several seconds to about 2 minutes. When the injection molding is performed smoothly, the screw 12 rotates or moves forward (moves to the left in the drawing) during the cycle time. The resin adhering to the inner peripheral surface of the heating cylinder 11 is heated by the reaction force of the resin stored in front of the screw head 22 so that the heating cylinder 11
Flows in the direction of the arrow A through the gap between the inner peripheral surface of the flight 51 and the outer peripheral surface of the flight 51.

Here, since the root of the screw 12 is water-cooled to prevent overheating, the temperature of the resin in the supply section Pa is about 100 ° C. lower than the temperature of the resin in the measuring section Pc. Therefore, the resin flowing in the direction of the arrow A is sufficiently cooled, and the blackened resin layer is not formed by the resin burning, and the resin burn does not grow due to the blackened resin layer as a core.

Next, the conditions under which resin burning occurs will be described with reference to FIG. FIG. 4 is a relationship diagram between the maximum residence time of the resin and the temperature. In the drawing, the horizontal axis represents the maximum residence time of the resin, and the vertical axis represents the temperature of the resin. In addition, polyethylene was used as the resin. As described above, when the resin stays in the heating cylinder 11, resin burning occurs. Therefore, in order to prevent the occurrence of resin burning, it is preferable to move the resin before the predetermined time elapses. The maximum residence time during which resin burning does not occur varies depending on the temperature of the resin.

In the figure, L1 is a limit line for the occurrence of resin burn. When the residence time of the resin is changed, if the temperature of the resin becomes higher than the temperature of the limit line for occurrence of resin burn L1, resin burn occurs. L2 is a line showing the transition of the temperature of the resin when the heating of the heating cylinder 11 is continued,
L3 is a line showing the transition of the temperature of the resin when the heating of the heating cylinder 11 is stopped.

As shown in the drawing, when the heating of the heating cylinder 11 is continued, the temperature of the resin represented by the line L2 is reduced to the limit of the resin burning until the limit point C at which the residence time of the resin is 2 minutes. It does not rise above the temperature of line L1. Therefore, by causing the resin to move until the residence time of the resin becomes 2 minutes, it is possible to prevent the occurrence of resin burning.

When the heating of the heating cylinder 11 is stopped by turning off the band heaters H1 to H4, the temperature of the resin represented by the line L3 until the limit point D at which the residence time of the resin becomes 4 minutes. Does not become higher than the temperature of the resin burning occurrence limit line L1. Therefore, by causing the resin to move until the residence time of the resin becomes 4 minutes, it is possible to prevent the occurrence of resin burning.

Incidentally, the temperature of the resin reaches the limit points C and D when the injection molding cycle is stopped. For example, injection molding may be artificially terminated because a required number of molded articles can be molded. However, when such an injection molding cycle is stopped, the temperature of the resin reaches the limit points C and D. To reach. Therefore, in order to prevent the occurrence of resin burn, a signal by switching a switch when a required number of molded articles are molded, or a count end signal to a preset counter (not shown) in which the required quantity is set in advance is sent. When these signals (hereinafter referred to as “injection molding end signal”) are generated, the injection nozzle 14 is retracted and separated from the fixed platen, and the set temperature of the injection nozzle 14 is set to the set temperature of the heating cylinder 11. Any lower set temperature (30 ° C. in this embodiment)
To change it. Further, the band heaters H5 and H6 of the injection nozzle 14 can be turned off.

Then, after retreating the injection nozzle 14,
Each time the first set time elapses, the screw 12 is rotated for the second set time to force the resin in the heating cylinder 11 to move. In this case, the the injection molding end signal is generated, the control unit (not shown) initiates time counting by the first timer T _1. Then, every time the time measurement by the first timer T ₁ is completed, the time measurement by the second timer T ₂ is started, and the screw 12 is rotated at the set rotation speed until the time measurement by the second timer T ₂ is completed. I try to make it. Note that the first set time is set shorter than the maximum residence time.

In this case, the resin in the heating cylinder 11 moves little by little as the screw 12 rotates. As a result, the temperature of the resin represented by the lines L2 and L3 does not become higher than the temperature of the resin burn limit line L1. Therefore, occurrence of resin burn can be prevented. In this case, the resin in the groove 20 moves forward of the screw 12, and the resin in the gap between the inner peripheral surface of the heating cylinder 11 and the outer peripheral surface of the flight 51 moves in the direction of arrow A.

Further, since the resin can be maintained at a high temperature during the injection molding cycle, there is no need to lower the set temperature when heating the resin. Moreover, since only the injection molding sequence needs to be changed, there is no need to change the structure of the injection device. Further, when the injection molding end signal is generated, the injection nozzle 14 is retracted, so that not only can the resin be moved by rotating the screw 12, but also the heating cylinder can be moved. 11 can be discharged. Therefore, the movement of the resin becomes effective.

Next, the injection molding may be interrupted due to a trouble such as a drop failure at the time of taking out the molded product. In such a case, the injection molding cycle is stopped.
The temperature of the resin reaches the limit points C and D. Therefore, in order to prevent the occurrence of resin burn, the screw 12
When the screw rotation stop signal is generated, the injection nozzle 14 is retracted to separate from the fixed platen when the screw rotation stop signal is generated.

Thereafter, every time the third set time elapses, the screw 12 is rotated for the fourth set time to force the resin in the heating cylinder 11 to move. in this case,
Wherein the screw rotation stop signal is generated, the control unit starts the time measurement by the third timer T _3. Then, the screw 12 until the time measurement by the fourth timer T ₄ (not shown) each time to terminate the time measurement by the third timer T ₃ starts, and ends the time measurement by the fourth timer T ₄
Is rotated at the set number of revolutions. Note that the third set time is set shorter than the maximum residence time. In addition, the third set time and the first set time can be made equal, and the fourth set time and the second set time can be made equal. And the third timer T
₃ and the fourth timer T ₄ is reset by the injection molding resumed.

In this case, the resin in the heating cylinder 11 is discharged from the nozzle port 15 little by little as the screw 12 rotates. As a result, the temperature of the resin represented by the lines L2 and L3 does not become higher than the temperature of the resin burn limit line L1. Therefore, occurrence of resin burn can be prevented. Further, when the interruption of the injection molding is continued for a long time, after the screw rotation stop signal is generated, the set temperature of the heating cylinder 11 is changed to be lower at the time when the fifth set time has elapsed, Stop the injection molding machine.

In this embodiment, a method for preventing resin burning in an injection molding machine has been described. However, the present invention is also applicable to a resin molding apparatus such as a sealing molding machine, a MIM, a blow molding machine, an extrusion molding machine, and a ceramic molding machine. can do. It should be noted that the present invention is not limited to the above-described embodiments, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, in the method for preventing burning of a resin in a resin molding apparatus, the resin is heated and melted, and molding is performed with the melted resin. ing. Then, the resin is heated to a set temperature to perform a molding cycle, and when the molding cycle is stopped, the temperature of the resin is decreased, and after the molding cycle is stopped, the resin is forcibly applied when a set time has elapsed. Move to Further, the set time is set shorter than the maximum residence time that does not cause resin burning. In this case, when the molding cycle is stopped while the resin is being heated to the set temperature and the molding cycle is being performed, the temperature of the resin is lowered, and after the molding cycle is stopped, when the set time has elapsed. The resin is forced to move.

Therefore, since the resin is moved before the maximum residence time elapses, it is possible to prevent the resin from burning. Further, since the resin can be maintained at a high temperature during the molding cycle, there is no need to lower the set temperature when the resin is heated to perform the molding.

In another method for preventing burning of a resin in a resin molding apparatus according to the present invention, a resin is heated and melted, and injection molding is performed with the melted resin. Then, the resin is heated to a set temperature to perform an injection molding cycle, and when the injection molding cycle is stopped, the temperature of the resin is reduced. Is rotated to force the resin to move. Further, the set time is set shorter than the maximum residence time that does not cause resin burning. In this case, when the injection molding cycle is stopped while the resin is heated to the set temperature and the injection molding cycle is being performed, the temperature of the resin is decreased, and the set time elapses after the injection molding cycle is stopped. Then, the screw is rotated and the resin is forcibly moved.

Therefore, since the resin is moved before the maximum residence time elapses, it is possible to prevent the resin from burning. Further, since the resin can be maintained at a high temperature during the injection molding cycle, there is no need to lower the set temperature when performing the injection molding by heating the resin. Moreover, since only the injection molding sequence needs to be changed, there is no need to change the structure of the injection device.

In another embodiment of the present invention, there is further provided a method for preventing resin burning, wherein the temperature of the resin is lowered by turning off the heater of the injection nozzle when the injection molding cycle is stopped. After the cycle is stopped, the heater of the heating cylinder is turned off when another set time has elapsed. In this case, when the injection molding cycle is stopped while the injection molding cycle is being performed while heating the resin to the set temperature, the temperature of the resin is reduced, and after the injection molding cycle is stopped, another set time is set. Is elapsed, the heater of the heating cylinder is turned off. Therefore, when the injection molding cycle is temporarily interrupted, it is only necessary to turn off the heater of the injection nozzle.

In the method for preventing resin burning of another resin molding apparatus according to the present invention, the injection nozzle is further retracted when the injection molding cycle is stopped. In this case, when the screw is rotated, the resin is moved out of the heating cylinder. Therefore, the resin can be effectively moved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an injection device according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a tip portion of a heating cylinder according to the embodiment of the present invention.

FIG. 3 is an enlarged view of a heating cylinder according to the embodiment of the present invention.

FIG. 4 is a relationship diagram between the maximum residence time of the resin and the temperature.

[Explanation of symbols]

 11 heating cylinder 12 screw 14 injection nozzle H1 to H6 band heater

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Okamura 1 at 731 Naganumaharamachi, Inage-ku, Chiba-shi, Chiba Chiba Works, Sumitomo Heavy Industries, Ltd. (72) Inventor Hiroyoshi Shizuki Inage-ku, Chiba-shi 731, Naganumahara-cho 1 Chiba Works, Sumitomo Heavy Industries, Ltd. (56) References JP-A-1-44720 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 45 / 00-45/84 B29C 47/00-47/96

Claims (4)

(57) [Claims] 1. A method for preventing resin burning in a resin molding apparatus for heating and melting a resin and molding the molten resin, wherein: (a) heating the resin to a set temperature to perform a molding cycle; ) when said molding cycle is stopped, lowering the temperature of the resin, (c) after said molding cycle is stopped, moves the resin forcibly when the time set has elapsed, (d) the setting time is resin burning prevention method of a resin molding apparatus, characterized in that that will be shorter than the maximum residence time does not cause resin burning. 2. A resin burning prevention method for a resin molding apparatus for heating and melting a resin and performing injection molding with the melted resin, comprising: (a) heating the resin to a set temperature and performing an injection molding cycle;
There, when the (b) the injection molding cycle is stopped, lowering the temperature of the resin, (c) after the injection molding cycle is stopped, forcing the resin by rotating a screw when the set time has elapsed is moved to, (d) the set time, resin burning prevention method of a resin molding apparatus, characterized in that that will be shorter than the maximum residence time does not cause resin burning. Wherein (a) lowering the temperature of the resin by turning off the heater of the injection nozzle when the injection molding cycle is stopped, the (b) after the injection molding cycle is stopped, the other set time 3. The method according to claim 2, wherein the heater of the heating cylinder is turned off when the time has elapsed. 4. The method according to claim 3, wherein the injection nozzle is retracted when the injection molding cycle is stopped.