KR102261932B1 - Injection Machine for casting polyurethane - Google Patents

Abstract

The present invention relates to: an injection apparatus for injecting mold urethane into a mold having a higher temperature than mold urethane; and to a method for manufacturing a product with the injection apparatus which includes a quantitative injection part for injecting a fixed amount of the mold urethane into the injection apparatus and a batch tank for supplying the mold urethane to the quantitative injection part, wherein the mold includes a movable mold and a driving mold. The method comprises the following steps: mold closing a fixed mold and the driving mold at a predetermined primary pressure, and injecting mold urethane; mold closing the fixed mold and the driving mold at a pressure higher than the primary pressure after the filling is completed.

Description

Injection machine for casting polyurethane

The present invention relates to an injection device for mold urethane, and more particularly, by improving the inside of the mold, the injection machine and the batch tank, the injection device can be used stably and continuously, and problems such as unmolding and air bubbles do not occur in plastic products it is to do

Injection molding is a method commonly used for molding plastic products using a thermoplastic resin that has changed to liquid after pressurization and heating.

Pellet, the raw material for injection molding, is supplied to the screw nozzle of the injection machine through a hopper. Under high temperature and high pressure, as the screw rotates, the pellets are liquefied at a temperature between 180 and 250 degrees. The liquefied raw material is injected into the mold at about 30 to 60 degrees from the nozzle of the injection machine to make a plastic product.

In injection molding, when raw materials are injected into the mold, plastic products are made by cooling, so high pressure and high speed are essential when injecting liquefied raw materials. In order to satisfy these characteristics, the plastic injection machine requires high-speed injection, technology for maintaining mold cooling, and the like, and technologies for this are being developed.

In molding plastic products, there is also a casting molding method in addition to injection molding. Typically, a thermosetting resin, Casting Polyurethane (liquid urethane) is poured into the mold and then cured or solidified.

Although the casting molding method has lower work productivity compared to injection molding, making it difficult to mass-produce, and the physical properties of the product vary depending on the ability of the operator during each operation, it is used with sufficient meaning in itself. However, since cast urethane is specialized for casting molding, it was not easy to imagine that plastic products could be made by injection.

A prior art for producing plastic products by injection of molded urethane is disclosed in Patent Publication No. 1388650. This can be said to be the first invention to suggest that molded urethane can be injected.

The prior art is an injection machine for injecting mold urethane into a mold, a quantitative injection unit for injecting a fixed amount of mold urethane into the injection machine, a batch tank for supplying mold urethane to the quantitative injection unit, and a mold from the batch tank to the quantitative injection unit It includes a valve for opening and closing the inflow of urethane, and a valve for opening and closing the discharge of the mold urethane from the quantitative injection unit toward the injection machine.

In the prior art, the mold urethane is manufactured, nitrogen is filled in the batch tank, the mold urethane is discharged to the quantitative injection unit with the nitrogen pressure, and the mold urethane is injected into the mold in the injection machine through a valve that opens and closes the supply and discharge of the mold urethane. to inject.

(Prior art 001) Korean Patent Publication No. 10-1388650

There are two methods for molding a plastic product, injection and casting, which are in no way interchangeable, but the prior art has considerable significance in that it is the first to suggest that a plastic product can be molded by injection of a molded urethane.

As such, the technology of using molded urethane for injection has emerged, but there is no problem such as bubbles or unmolding inside the injection molded product, and a technology that allows the injection device using molded urethane to operate normally for a long time should be developed. it is not the case.

The present invention is to provide an injection device for a mold urethane capable of continuous operation in order to solve the above points, and to avoid bubbles and non-molding problems in the injection-molded product.

In order to achieve the above object, the present invention is an injection machine for injecting mold urethane into a mold, a quantitative injection part for injecting a fixed amount of mold urethane into the injection machine, and a batch tank for supplying molded urethane to the quantitative injection part However, it provides an injection device for mold urethane in which the temperature of the mold into which the mold urethane is injected is higher than that of the mold urethane.

In addition, the mold is made of a fixed mold and a movable mold, and the fixed or movable mold has a passage connecting the injection part and the vacuum pump, and the passage is opened and closed by the operation of a pin located in the fixed or movable mold. It is preferable to do so. And it is preferable that the pressure at which the movable mold and the movable mold are mold-closed can be adjusted in two stages.

In addition, it is more preferable that a cooling groove is formed in a nozzle portion for injecting the mold urethane into the mold in the injection machine, and a heating groove is formed in the nozzle shaft portion into which the mold urethane is introduced.

In addition, the batch tank is provided with a vacuum connection port connected to a vacuum hose to form a vacuum therein, and a nitrogen connection port connected to a nitrogen supply hose to inject nitrogen therein, to perform a vacuum or nitrogen It is desirable to be able to supply

In the case of using the injection device for mold urethane according to the present invention, normal continuous operation is possible by injection of mold urethane, and there are advantages in that there are no bubbles or unmolded plastic products. However, the effect of the present invention is not limited to the verbal description, but includes everything that can be inferred by a person skilled in the art through the present invention.

1 is a view showing an injection device for a mold urethane as an embodiment of the present invention;
2 is a view showing an injection machine as an embodiment of the present invention;
3 is a view showing a mold as an embodiment of the present invention;
4A to 4C are a method of removing air bubbles in a mold as an embodiment of the present invention.
5 is a view showing the front of the batch tank as an embodiment of the present invention;
6 is a view showing a plane of the batch tank as an embodiment of the present invention;

Specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. Examples are provided to easily explain the present invention to those skilled in the art, and the present invention is not limited to the embodiments. The terms used in the present application are used only to describe embodiments, and terms such as “include” or “have” do not mean that a component exists, but does not exclude the possibility of other components. The drawings are made to facilitate understanding of the present invention and are not necessarily drawn to scale.

1 shows an injection device for a mold urethane of the present invention, which is the same as in the prior art. The injection machine 10 for injecting the mold urethane into the mold 20, the quantitative injection unit 110 for injecting a fixed amount of the mold urethane into the injection machine 10, and the quantitative injection unit 110 To supply the mold urethane a valve 145 for opening and closing the inflow of the mold urethane from the batch tank 120 to the quantitative injection part 110, the mold urethane from the quantitative injection part 110 to the injection machine 10 It includes a valve 155 for opening and closing the discharge of.

General plastic injection is made in a high-speed and high-pressure manner in which the pellet is melted at high temperature and high pressure, and then the material at a temperature of 180 to 250 degrees is injected into a mold between 30 to 50 degrees and cooled. Since the melted raw material has a fairly high viscosity, it is not affected by gravity and is injected at high pressure by the screw pressure.

On the other hand, the cast urethane in the present invention is basically used for casting and is quite different from the material in the general plastic injection method. The viscosity is quite low as about 5,000 to 20,000 cps (centipoise), and curing begins to occur when the temperature is usually about 90 degrees or more. In addition, due to the low viscosity, it is inevitably affected by gravity. Most of the injection machines have a material supply nozzle located in the center, so when the mold urethane is injected, there is a point that bubbles are generated or not molded therein.

The present invention has solved this point by controlling the temperature and vacuum in the mold in the injection device for the mold urethane of FIG. 1 . In this regard, the injection machine drawing of FIG. 2 and the mold drawing of FIG. 3 will be described using the method of removing air bubbles in the mold of FIGS. 4A to 4C .

In the present invention, unlike conventional injection, the temperature of the injected mold urethane is lower than the temperature in the mold.

Specifically, the temperature of the mold 20 is maintained at 90 degrees or more, preferably 130 to 170 degrees, and the mold urethane is injected here at about 40 to 50 degrees, and after a time of about 1 to 10 minutes, the mold urethane is formed It was made to harden while equipped. If the temperature inside the mold 20 is higher than 170 degrees, rapid hardening may occur and bubbles or cracks may occur on the surface of the plastic product, and if it is lower than 130 degrees, it takes a long time to produce the product, so 130 to 170 degrees is preferable.

In addition, in order to maintain the temperature inside the mold 20 at 130 to 170 degrees, a heating means such as a hot wire or a heater rod and a temperature sensor (not shown) are installed in the mold 20 to maintain the temperature through the control unit, and also with the Separately, the mold urethane should be maintained at 40 to 50 degrees. The temperature maintenance of the mold urethane will be described again below.

In molding the product by injecting the mold urethane, the most important part is to remove the bubbles of the mold urethane. Three methods can be used to remove the foam of the mold urethane.

First, as a method of using the vacuum in the mold, this will be described. After sealing the inside of the mold with a silicone O-ring 24 and vacuuming the inside of the mold using a vacuum pump 25, injection is performed from the nozzle part of the injection machine. Here, the vacuum is 99% or more, which is different from the 80% vacuum used in conventional injection, and proceeds differently from the existing injection mold method.

The mold 20 is made of a stationary mold 22 or a movable mold 23, and a passage 29 is formed in any one of the stationary mold 22 or the movable mold 23, and the passage 29 The part through which the mold urethane is injected and the vacuum pump 25 are connected. A pin 28 is located in the passage 29 , and the pin 28 moves up and down by the operation of the shut-off valve 27 to close the passage 29 in the fixed mold 22 or the movable mold 23 . open or close.

4A , after the stationary mold 22 and the movable mold 23 are mold-closed, the nozzle part of the injection machine 10 contacts the injection part 21 of the stationary mold 22 . And the vacuum pump 25 operates to form a vacuum inside the mold, and when the vacuum degree reaches a predetermined value, for example, -99 kpa, the shut-off valve installed in the stationary mold 22 or the movable mold 23 (27) works, the pin (28) blocks the part where the mold urethane is injected and the passage (29) where the vacuum pump is connected.

Even if the passage 29 is blocked, the vacuum pump 25 continues to operate in order to prevent the vacuum state from being broken. And the injection machine 10 is filled with the liquid urethane at a fairly high speed through the nozzle unit, and the vacuum pump 25 stops the operation at the time when the mold is filled to some extent, for example, when the mold is filled to about 95%, and the purge is performed.

Even in this state, as the shut-off valve 27 is driven, the pin 28 continues to close the passage 29, and when product molding is completed, the shut-off valve 27 is turned off and the pin 28 closes the passage 29. will be open After that, the nozzle part of the injection machine is separated from the mold 20, and the movable mold 23 is moved to obtain a molded plastic product.

In general plastic injection, since raw materials have high viscosity, high injection pressure and high mold pressure are required. In addition, when the raw material is injected into the mold, the viscosity rises rapidly due to the lower mold temperature than the raw material, so the mold must be very rigid and the machine must not be deformed due to the high viscosity material. In the conventional method, a gas evacuation hole was installed in the mold, and a vent was performed in the area where the gas was concentrated. Since the viscosity was high, the gas easily escaped from the inside of the mold when high pressure was applied. However, vacuum was also used in the conventional method, which is for maintaining the cleanliness of the mold and decontamination of the mold, and the vacuum degree is about -80 to -85 kpa.

However, unlike the conventional mold urethane of the present invention, since the viscosity is quite low, injection can be performed with a lower injection pressure and a lower mold closing pressure than before. However, since the viscosity is quite low, even when a certain amount of material is injected and molded, the molded urethane leaks between the sealing surfaces of the mold, and this leakage became a factor causing the product to be unformed or a large amount of air bubbles were generated.

Therefore, there is a need for a method that allows a fixed amount of raw material to enter the mold while smoothly removing the gas in the mold during urethane injection. For this purpose, a vacuum in the mold is used. Even when low-viscosity urethane is sprayed at low pressure by making the inside of the mold at an almost perfect level of vacuum, the desired shape can be created without air resistance.

As such, unlike the conventional injection method, the reason for vacuuming in the present invention is to approach it from the bubble removal side of the product, and the vacuum is also quite different. In this vacuum system and degree of vacuum, a passage 29 to which a vacuum pump 25 is connected is formed in any one of the fixed mold 22 or the movable mold 23, and the passage 29 is driven by the pin 28. This is achieved by opening and closing

Meanwhile, for bubble removal, an injection process in which the mold 20 is closed using a two-step pressure as shown in FIG. 4B may be used.

First, when closing the fixed mold 22 and the movable mold 23, the mold urethane does not flow down, and the mold is closed with a low pressure primary pressure.

After that, the mold urethane is filled in the mold 20, and the injection speed is lowered when the mold is about 90% filled. And in a lowered speed state, injection is performed as much as 101 to 102%, ie, 1 to 2%, compared to the amount of urethane required for the final product. Reducing the speed after 90% injection is to prevent the mold urethane from overflowing or flowing between the fixed mold 22 and the movable mold 23, which are molded at low pressure, to some extent.

And after a certain time has elapsed, the mold closing pressure of the mold 20 is raised to a higher pressure than the primary pressure, whereby the mold urethane is pressurized. And, for example, in the case of 102% filling, it is to remove the internal air bubbles together with the 2% material after pressing. After curing is completed, the mold 20 is opened and closed to take out the product and remove the scrap formed on the edge of the product.

In this method, the process after opening and closing the mold 20 and taking out the product is the same as the vacuum method mentioned above, until the fixed mold 22 and the movable mold 23 are molded at a low pressure, which is the primary pressure. The method is to control the mold pressure in two stages as a means for removing air bubbles.

In addition, other means may be used for defoaming. 4c, the temperature of the stationary mold 22 and the movable mold 23 is maintained at 70 degrees to 90 degrees higher than the temperature of 40 degrees to 50 degrees of the urethane mold, and the injection operation is performed.

While maintaining at the above temperature, the vacuum pump 25 connected to the mold 20 is used to remove air bubbles for the urethane in the mold. While maintaining a vacuum pressure of about -85 kpa, defoaming is performed for a certain period of time, for example, 10 seconds to 5 minutes to remove air bubbles, and a purge operation is performed.

After that, the temperature of the mold 20 is raised to 130 to 170 degrees, and the mold urethane is cured, and then demolded to produce a product. And the temperature of the mold 20 is then cooled to maintain 70 to 90 degrees again for product production. After putting the liquid molded urethane having the property of maintaining the liquid phase at a certain temperature into a mold at a certain temperature, it is degassed to remove bubbles and unmolding using vacuum pressure in the mold, and the temperature is raised to cure.

However, in this case, the mold must be made of a material with good heat transfer, and the mold repeats cooling and heating.

The injection machine 10 of the present invention will be described.

The temperature inside the mold 20 is between 130 and 170 degrees, and the nozzle part of the injection machine 10 comes into contact with the mold 20 for about 1 to 10 minutes when the mold urethane is injected. Since the mold 20 must maintain its temperature, the temperature of the nozzle part of the injection machine 10 in contact with it rises. However, the nozzle part of the injection machine 10 should be maintained at about 40 degrees so that the liquid urethane is not cured therein and the original properties are maintained.

To this end, in the present invention, a cooling groove 13 is installed in the nozzle cover 12 of the nozzle unit, and cooling is performed using cooling water or the like. In addition, this cooling groove 13 is installed as a whole so that only a part of the nozzle is not cooled locally, and may be installed in a kind of spiral shape, and the amount and temperature of the cooling water can be controlled so that the temperature of the mold urethane is maintained at about 40 degrees. .

On the other hand, unlike the nozzle part, the body part where the mold urethane is injected into the injection machine is in contact with the atmosphere, so the temperature is 40 degrees or less. Therefore, in order to maintain the temperature of the mold urethane inside it at about 40 degrees, the body part must be heated.

Heat-heating oil, a heating wire, etc. can be used for heating, and the heating groove 18 is formed in the body-part cover 17, and the body part can be heated as a whole using the heat-heat oil. The heating groove 18 may be formed in a kind of spiral shape surrounding the entire body portion, and the thermal oil of the thermal oil tank 160 to be described later may be used as the thermal oil.

Next, the batch tank 120 and the thermal oil tank 160 of the present invention will be described.

The batch tank 120 has a heat oil space 121 on the outside to maintain the temperature of the mold urethane at 40 to 50 degrees. To prevent the liquid molded urethane from being hardened by local heat or its physical properties from being deteriorated, a hot water heating method is used from the outside of the tank, and the temperature variation is reduced by circulating the heat oil from the bottom to the top.

Meanwhile, the batch tank 120 removes air bubbles through a vacuum process and serves as a pressure cylinder for supplying the liquid urethane to the quantitative supply unit 110 . It is connected through a vacuum pump and a vacuum hose connection port 127 to remove air bubbles through additional mixing. A vacuum gauge 124 is installed to check the degree of vacuum, and a purge valve capable of evacuating the vacuum after completion of the vacuum operation is also installed.

The inside of the batch tank 120 is equipped with two upper and lower rows of stirring blades 122 for additional mixing of materials and removal of air bubbles during the vacuum process, and rotates at an appropriate speed using a stirring motor 125 and a reducer 126 . can do. It is possible to remove the mixing of the materials and the air bubbles therein through a vacuum operation of about 1 to 2 hours.

After the vacuum operation, the batch tank 120 is filled with nitrogen through the nitrogen connection port 128 . Since the mold urethane reacts with moisture contained in the air, it is always maintained and pressurized with nitrogen at about 2 to 7 bar, except for the vacuum process, in order to prevent contact with moisture. It is also possible to supply the molded urethane to the quantitative injection unit 110 using this nitrogen pressure.

A thermal oil tank 160 is installed to supply thermal oil to the batch tank 120 , the thermal oil therein is heated by the thermal oil heating rod 164 , and this thermal oil is heated by the batch tank 120 . In addition, it can be used for heating the body of the injection machine described above.

On the other hand, liquid urethane should be stored and used for as long as possible after it is formed by mixing the materials. If it can only be used for a certain period of time, it is because the entire equipment is quite limited in the storage of liquid urethane. Moreover, when stored for a certain period of time or longer, there is a problem in that the entire injection equipment must be disassembled and cleaned.

The most important part is the liquid urethane temperature in the batch tank and the humidity inside the tank. When liquid urethane comes in contact with humidity, it hardens, so pressurize with nitrogen so that there is no moisture in the batch tank. The temperature of the liquid urethane should be such that partial curing does not occur, and it is preferable to maintain the lowest temperature at which partial curing does not occur, and the lowest temperature is preferably 40 to 50 degrees.

As such, in the case of the lowest temperature, a different method is required to inject it because the viscosity is relatively high. When the molded urethane is filled in the quantitative injection unit 110 by using the pressure of nitrogen, the case where the molded urethane is not filled due to its viscosity occurs, the piston rod 116 in the cylinder 112 of the quantitative injection unit 110 The mold urethane is supplied by supplying the mold urethane to the space 115 in the quantitative injection unit 110 using the pressure of nitrogen in the batch tank 120 while moving backward using hydraulic pressure. In other words, the mold urethane supply is pulled in the front and pushed in the back.

In addition, it is preferable to appropriately adjust the size of the pipe to suit the high viscosity, and the inflow from the batch tank 120 as well as the quantitative injection unit 110 and the batch tank 120 to the quantitative injection unit 110 . The pipe 140, the discharge pipe 150 from the quantitative injection unit 110 to the injection machine 10 is also provided with an insulating material so that the internal mold urethane can be maintained at 40 to 50 degrees.

To prevent partial hardening due to temperature difference in all parts and each part, and to facilitate the flow of mold urethane, the inside of the metering unit and each connecting pipe in contact with the liquid urethane, the inlet pipe 140 and the outlet pipe The inside of 150 is preferably coated so that the liquid urethane flows smoothly without stagnation.

On the other hand, the injection machine 10 of the present invention is preferably a plunger (cylinder) type in order to inject liquid urethane, and the quantitative injection unit 110 is 1.5 to 2 times larger than the capacity of the nozzle unit of the injection machine 10. While pressurizing in the injection unit 110, the plunger of the injection machine 10 is prevented from not being buffered.

In addition, the present invention provides a valve between the injection machine 10 , the metering injection unit 110 , the batch tank 120 , the batch tank 120 and the metering injection unit 110 , and between the metering injection unit 110 and the injection machine 10 . In addition, it may include an injection machine 10 , a batch tank 120 , and a valve between the injection machine 10 and the batch tank 120 . The liquid urethane is pressurized by the nitrogen pressure in the batch tank 120 and enters the injection machine 10 , and the injected amount is controlled by the inner diameter and the forward length (stroke) of the plunger in the injection machine 10 .

In this case, it is preferable to make the nitrogen pressure for pressurizing the liquid urethane in the batch tank 120 constant, and a pressure sensor can be used to measure and control the nitrogen pressure through the inside of the batch tank 120 to be constant. And the valve between the batch tank 120 and the injection machine 10 is opened, and after buffering the material in the injection machine 10 by pressurizing the material in the batch tank 120, the valve is closed, followed by injection into the mold.

As described above, the present invention relates to an injection device using molded urethane, and all matters shown in the above description and accompanying drawings are exemplary and should not be construed in a limiting sense.

10: injection machine 11: injection machine nozzle unit 12: nozzle unit cover
13: cooling groove 16: injection machine body 17: body cover
18: groove for heating 20: mold 21: injection hole
22: fixed mold 23: movable mold 24: O-ring
25: vacuum pump 26: vacuum sensor 27: shut-off valve
28: pin 29: euro 110: metering unit
112: cylinder 114: inlet 115: fixed amount injection space
116: cylinder 120: batch tank 121: heat oil space
122: agitation blade 123: nitrogen gauge 124: vacuum gauge
125: stirring motor 126: reducer 127: vacuum hose connection port
128: nitrogen connection port 130: urethane inlet 131: pressure safety valve
132: inner window 133: flexible hose 140: inlet pipe
145: inlet on-off valve 150: discharge pipe 155: discharge on-off valve
160: heat oil tank 161: tank body 162: heat oil pump gear
163: heat oil gas discharge unit 164: heat oil heating rod
165: heat oil inlet 170: control panel

Claims (2)

delete an injection machine 10 for injecting the mold urethane into the mold 20 having a higher temperature than the mold urethane; a quantitative injection unit 110 for injecting a predetermined amount of mold urethane into the injection machine 10; and a batch tank 120 for supplying mold urethane to the quantitative injection unit 110, wherein the mold 20 manufactures a product with an injection device including a movable mold 22 and a movable mold 23 As a way to
Mold-closing the fixed mold 22 and the movable mold 23 at a predetermined primary pressure and injecting the mold urethane; lowering the injection rate when charging 90% and charging 101% to 102%; After the filling is completed, the step of mold closing the fixed mold 22 and the movable mold 23 at a pressure higher than the primary pressure; Manufacturing method comprising the

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