JP2007008003A - Method and apparatus for manufacturing pallet made of synthetic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and apparatus for manufacturing pallet made of a synthetic resin that can stably and certainly manufacture a synthetic-resin-made pallet having a hollow inside structure. <P>SOLUTION: There is provided the synthetic-resin-made-pallet-manufacturing method for manufacturing the synthetic resin-made-pallet having the hollow inside structure. A mold 10, which has a cavity 11 of almost the same shape as the whole or part of the synthetic resin-made pallet, is provided with a valve gate 21 that can open and close, a space changing means 34 that changes the cavity space t of a resin receiving part 17 installed in the part where the valve gate 21 is opened, and a gas injection means. After a resin raw material is supplied through the valve gate 21, the valve gate 21 is closed and a gas is injected into the mold 10. Before the gas reaches the resin receiving part 17, the cavity space t of the resin receiving part 17 is reduced by the space changing means 34. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a synthetic resin pallet used when transporting and storing various articles, and relates to a method and an apparatus for manufacturing a synthetic resin pallet having a hollow structure inside.

  In general, a plastic pallet molded by injecting synthetic resin into a mold is provided as a pallet to be used for transporting and storing cargo, and a fork part such as a forklift can be inserted from two directions. Two-way synthetic resin pallets and four-way synthetic resin pallets that can be inserted from four directions are used.

  Such a pallet made of synthetic resin has a problem that, for example, it has a square plate shape of 1 m square and is relatively large in order to load a load, and its weight increases and handling becomes inconvenient. In addition, if the resin raw material cannot be sufficiently supplied into the mold due to an increase in the size of the mold, warping or deformation occurs in the portion where the resin raw material supply is insufficient when the resin raw material is cooled and cured. There was a case. In order to reliably supply the resin raw material to prevent this, it is necessary to supply a large amount of the resin raw material, and there is a problem that the amount of the resin raw material used becomes excessively large.

  Therefore, a synthetic resin pallet is formed which is molded by a gas assist method in which a gas is injected into a synthetic resin pallet and the inside of the synthetic resin pallet has a hollow structure (see Patent Document 1). This synthetic resin pallet is lightweight because it has a hollow structure, and even a large pallet is easy to handle. In addition, since the gas is injected into the mold after supplying the resin raw material, the resin in the mold is pressed so as to spread outward, and the contact between the inner surface of the mold and the resin raw material is promoted, and the resin The cooling time of the raw material can be shortened. Therefore, the resin pressure can be increased without increasing the supply amount of the molten raw material, the resin raw material can be reliably supplied into the mold, and warpage and deformation can be prevented.

  As described above, in the gas assist method of injecting gas into the mold, if a sprue gate is used as the resin gate for supplying the resin raw material, the injected gas penetrates into the resin raw material in the gate, A hole is formed when the sprue portion is cut after injection molding. Since this hole is connected to the hollow portion of the synthetic resin pallet, rainwater or the like accumulates inside the synthetic resin pallet. Therefore, in forming a pallet by the gas assist method, when the gate portion is exposed on the pallet surface, it is necessary to use a valve gate capable of opening and closing the gate opening. The valve gate is used to supply a predetermined amount of resin raw material into the mold and close the gate, and then inject gas into the mold to prevent gas from entering the gate.

In recent years, plastics have been recycled through the enforcement of the Containers and Packaging Recycling Law, etc., and recycled resin obtained from waste plastic is placed in the core layer, and newly generated virgin resin is placed in the skin layer. Thus, a sandwich molding method has been proposed in which the amount of recycled resin used is increased.
In this sandwich molding method, two types of resin raw materials, for example, recycled resin and virgin resin are injected into a mold from one gate (see Patent Document 2 and Patent Document 3). In this method, a recycled resin as a core layer is arranged at the center of the opened gate, and a virgin resin as a skin layer is arranged so as to surround the recycled resin and injected into a mold. Since the amount of virgin resin used can be reduced and the use of recycled resin is promoted, it is widely used from the viewpoint of promoting plastic recycling.

  This sandwich molding method has a two-layer structure of a core layer and a skin layer at the stage of supply from the valve gate. In a method of supplying resin from a plurality of gates in injection molding of a general synthetic resin pallet, a two-layer structure cannot be formed at a portion where the flow of resin raw material collides, or the resin of the core layer is easily exposed on the surface. Or, since it is necessary to replace the two layers of resin remaining in the runner of the resin for connecting a plurality of gates with a skin material, it becomes a factor of reducing the ratio of the core layer. For this reason, the number of the resin raw material supply paths into the mold is as small as possible, that is, the number of valve gates is as small as possible.

  When such a sandwich molding method is applied to a synthetic resin pallet, it is necessary to increase the diameter of the valve gate in order to sufficiently supply the resin raw material to the mold of the synthetic resin pallet. In some cases, it is necessary to further increase the diameter of the valve gate. In addition, in order to sufficiently supply the resin material into the mold, it is necessary to increase the cavity distance between the molds and make the synthetic resin pallet thick, but with a thick synthetic resin pallet, Further, the weight increases and handling becomes more difficult. In addition, the thick synthetic resin pallet has a problem in that it takes time to cool the resin raw material in the mold, causing deformation and warping.

Therefore, it has been studied to apply the above-described gas assist method to the sandwich molding method.
Japanese Patent Laid-Open No. 10-218179 Japanese Patent Laid-Open No. 06-190860 Japanese Patent Laid-Open No. 06-126769

However, the gas assist method using the valve gate has the following problems.
In the vicinity of the valve gate, there is a high-temperature resin raw material just supplied into the mold. Further, the valve gate has a high temperature because it has a molten high-temperature resin material inside. Therefore, the resin raw material near the valve gate is held at a high temperature.

  In this state, when the valve gate is closed and gas is injected, the gas preferentially enters the portion where the resin in the vicinity of the valve gate is held at a high temperature, and the portion that easily deforms at a high temperature, that is, the valve gate. In some cases, the resin material in contact with the film is stretched to form a film. Thus, there existed a problem that the part which became a film form did not have intensity | strength, and was damaged at the time of the shaping | molding process and use of a synthetic resin pallet.

In particular, in the above-described sandwich molding with a single-point gate, it is necessary to increase the diameter of the valve gate, and the portion where the resin held at a high temperature exists increases, so it is difficult to apply the gas assist method.
Further, when a plurality of valve gates are provided in order to reduce the diameter of the valve gate, it is necessary to reduce the component ratio of the core layer as described above. Then, for example, when a recycled resin is used for the core layer, the amount of the recycled resin used is reduced, so that there is a problem that it is not possible to promote plastic recycling.

  The present invention has been made in view of such circumstances, and provides a manufacturing method and a manufacturing apparatus for a synthetic resin pallet that can stably and reliably manufacture a synthetic resin pallet having a hollow structure inside. For the purpose.

  A method for producing a synthetic resin pallet according to the present invention is a method for producing a synthetic resin pallet having a hollow structure inside, and a gold provided with a cavity having substantially the same shape as the whole or part of the synthetic resin pallet. The mold includes an openable / closable valve gate opened in the mold, a resin receiving portion provided in a portion where the valve gate is opened, and an interval changing means for changing a cavity interval of the resin receiving portion, Gas injection means, and after supplying a resin raw material into the mold through the valve gate, the valve gate is closed and gas is injected into the mold, and the gas is injected into the mold. Before reaching the receiving portion, the interval changing means reduces the cavity interval of the resin receiving portion.

  The synthetic resin pallet manufacturing apparatus according to the present invention is a synthetic resin pallet manufacturing apparatus having a hollow structure, and includes a cavity having substantially the same shape as the whole or a part of the synthetic resin pallet. A mold, an openable / closable valve gate opened in the mold, a resin receiving portion provided in a portion where the valve gate is opened, and an interval changing means for changing a cavity interval of the resin receiving portion. And a gas injection means.

  According to the method for manufacturing a synthetic resin pallet according to the present invention, after supplying the resin raw material, the valve gate is opened by closing the valve gate to reduce the cavity interval and injecting gas into the mold. As a result, the gap between the cavities is reduced and the resin pressure at the resin receiving portion is increased, and gas can be prevented from entering the portion. Therefore, a film-like portion is not formed in the vicinity of the valve gate, and a lightweight and high-quality synthetic resin pallet can be manufactured stably and reliably.

  Further, the synthetic resin pallet manufacturing apparatus according to the present invention includes a valve gate that can be opened and closed, an interval changing means for changing the cavity interval of the resin receiving portion, and a gas injection means. After the supply into the mold, the valve gate is closed and gas is injected, and before the gas reaches the resin receiving portion, the interval between the cavities of the resin receiving portion can be reduced by the interval changing means.

  A method for manufacturing a synthetic resin pallet according to an embodiment of the present invention includes supplying a resin material constituting a core layer and a resin material constituting a skin layer into the mold from the valve gate, A synthetic resin pallet having a skin layer is manufactured. In this manufacturing method, even if the gate valve has a large diameter, gas can be prevented from entering the resin receiving portion. Therefore, a synthetic resin pallet having a core layer and a skin layer is formed by supplying resin from a single point gate. Can do. Here, when the recycled resin is used as the resin material constituting the core layer, the amount of the recycled resin used can be ensured, and the plastic recycling can be promoted.

  In addition, in the manufacturing method in which the gas is injected into the mold after the cavity interval of the resin receiving portion is reduced, the gas is injected after the cavity interval is reduced, so that the gas can be surely intruded into the resin receiving portion. Can be prevented. In addition, in order to confirm that the space | interval of a cavity became small before gas injection | pouring, it is preferable to provide a position sensor etc. in the manufacturing apparatus of synthetic resin pallets.

  In the manufacturing method of supplying the resin raw material into the mold in a state where the cavity interval of the resin receiving portion is larger than the cavity interval of the peripheral portion of the resin receiving portion, the resin receiving portion is enlarged and the resin raw material is Therefore, the resin raw material can be reliably supplied into the mold even with a single gate.

Further, by making the interval changing means a movable pin that can be moved forward and backward disposed on the side facing the valve gate, the cavity interval of the resin receiving portion can be changed by controlling the forward and backward movement of the movable pin, and more reliably. High quality synthetic resin pallets can be manufactured.
Further, by setting the diameter of the valve gate within the range of 10 mm to 20 mm, the supply of the resin raw material into the mold can be promoted, and the portion where the resin raw material is held at a high temperature by the valve gate is provided. The gas can be reduced, and the gas can be prevented from entering more reliably.
In order to exert such an effect more reliably, it is more preferable that the diameter of the valve gate is within a range of 12 mm to 20 mm.

Hereinafter, a method for manufacturing a synthetic resin pallet according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIGS. 1 to 4 show a part of a manufacturing apparatus used in the method for manufacturing a synthetic resin pallet according to this embodiment.
The synthetic resin pallet to be molded in this embodiment is formed into a square box having a side of 1.1 m as a whole, for example, and an upper surface plate-like portion that forms the upper surface (loading surface) of the synthetic resin pallet; The upper surface type member having a lower surface plate-shaped portion that forms the lower surface and a girder portion that connects the upper surface plate-shaped portion and the lower surface plate-shaped portion, and the upper surface plate-shaped portion and the girder portion are integrally molded. And heat-welding the lower surface mold member formed by integrally molding the lower surface plate-like portion and the spar portion in a state where the spar portion of the upper surface mold member and the spar portion of the lower surface mold member are in contact with each other. It is to be molded.

  As shown in FIGS. 1 and 2, the synthetic resin pallet manufacturing apparatus 1 includes a mold 10 having a cavity 11 having substantially the same shape as a part of the synthetic resin pallet, and one cavity 11 of the mold 10. A valve gate 21 opened in the section, a movable pin 30 that faces the valve gate 21 and that can be moved back and forth toward the valve gate 21, and a gas valve 40 that injects gas into the cavity 11 of the mold 10. I have.

  The mold 10 is formed with a cavity 11 having substantially the same shape as an upper surface mold member having an upper surface plate-like portion of a synthetic resin pallet and a girder portion extending from the upper surface plate-like portion. As shown in FIG. 3, a cavity 11 is formed on the portion forming the upper surface (loading surface) of the upper surface plate-like portion of the mold 10 so as to be substantially planar in order to stably load the load. Is formed. A single point of the opening of the resin valve 20 for supplying the resin raw material, that is, the valve gate 21 is provided at the center of the upper surface, which is a so-called single-point gate mold 10.

  Further, in the part forming the back side of the upper surface mold member of the mold 10, as shown in FIG. 4, a pair of edge beams 12 extending along two opposing sides of the square formed by the upper surface plate-shaped portion, A central girder portion 13 extending in parallel with the edge girder portion 12 and positioned between the edge girder portions 12 is formed. In other words, the synthetic resin pallet manufacturing apparatus 1 forms an upper surface mold member of a so-called two-way pallet.

  A plurality of grid-like ribs 14 are formed on the back side of the upper plate-like part and inside the edge girder part 12 and the central girder part 13, and the cavity 11 is provided so that the rectangular chamber part 15 is formed by these ribs 14. It has been. A movable pin 30 is arranged at the center of the portion forming the back side of the upper surface mold member of the mold 10, that is, at the portion facing the valve gate 21, as shown in FIG. A gas valve 40 for injecting gas into the cavity 11 of the mold 10 is opened near the movable pin 30. Further, a gas channel 16 is formed which extends from the gas valve 40 into the cavity 11 and serves as a gas passage path.

As shown in FIGS. 1 and 2, the resin valve 20 has a cylindrical body, one end of which is a valve gate 21 opened in the cavity 11 of the mold 10, and the other end is supplied with a resin raw material (not shown). A raw material supply path 22 extending from the means is provided.
Inside the resin valve 20, a valve pin 23 is disposed so as to be able to advance and retract in the axial direction of the cylindrical body formed by the resin valve 20, and the valve gate 21 can be opened and closed by the operation of the valve pin 23. Has been. Here, in this embodiment, the diameter of the valve gate 21 is set in a range of, for example, 10 mm to 20 mm, and the outer diameter of the valve pin 23 is set in a range of, for example, 13 mm to 27 mm.

Further, the movable pin 30 provided so as to face the valve gate 21 is formed in a substantially cylindrical shape, and its outer diameter is made one step larger than the diameter of the valve gate 21 as shown in FIGS. In this embodiment, for example, it is set to 40 mm. One end side of the movable pin 30 is disposed so as to protrude into the cavity 11 of the mold 10, and the other end surface of the movable pin 30 is an inclined surface inclined with respect to the axis of the movable pin 30.
On the other end side of the movable pin 30, a moving means 31 for moving the movable pin 30 so as to advance and retreat is provided. The moving means 31 is an inclined block 32 that is linked with the other end surface (inclined surface) of the movable pin 30. And a cylinder 33 that moves the inclined block 32 so as to be movable back and forth in a direction perpendicular to the moving direction of the movable pin 30.

As shown in FIG. 1, by moving the inclined block 32 in the X direction, the inclined surface of the inclined block 32 and the other end surface of the movable pin 30 are interlocked, and the movable pin 30 moves along the inclined surface of the inclined block 32. Retreat away from the valve gate 21.
On the other hand, as shown in FIG. 2, by moving the inclined block 32 in the Y direction, the other end surface (inclined surface) of the movable pin 30 is pressed by the inclined block 32 so that the movable pin 30 approaches the valve gate 21. Advance.
As described above, the movable pin 30 can be moved forward and backward by the moving means 31.

  A cavity portion between the movable pin 30 and the valve gate 21 is a resin receiving portion 17. By moving the movable pin 30 so as to move backward from the valve gate 21, the cavity interval t of the resin receiving portion 17 is increased, and by moving the movable pin 30 closer to the valve gate 21, the cavity of the resin receiving portion 17. The interval t can be reduced. That is, the movable pin 30 and the moving means 31 constitute an interval changing means 34 for changing the cavity interval t of the resin receiving portion 17.

  In this embodiment, for example, nitrogen gas, which is a kind of inert gas, is injected into the cavity 11 of the mold 10 from the gas valve 40 provided in the vicinity of the movable pin 30.

Next, a synthetic resin pallet manufacturing method using the synthetic resin pallet manufacturing apparatus 1 having this configuration will be described. FIG. 5 shows the relationship between the opening / closing operation of the valve gate 21, the advance / retreat operation of the movable pin 30, and the gas injection timing.
First, as shown in FIG. 1, the inclined block 32 is moved in the X direction, the movable pin 30 is retracted so as to be separated from the valve gate 21, and the cavity interval t of the resin receiving portion 17 is increased. Here, in this embodiment, the cavity interval s of the portion forming the upper plate-like portion is 3 mm, and the cavity interval t of the resin receiving portion 17 is 5 mm.

  In this state, the valve pin 23 of the resin valve 20 is moved to open the valve gate 21, and the resin material is supplied into the cavity 11 of the mold 10. Here, in this embodiment, polypropylene (PP) is used as a resin material constituting the synthetic resin pallet, and two types of resin materials are supplied from the valve gate 21.

  In the central portion of the valve gate 21, a recycled resin obtained by recycling the waste plastic is disposed, and a newly generated virgin resin is disposed so as to surround the recycled resin, so that the inside of the cavity 11 of the mold 10. It is supplied to. Here, in this embodiment, the temperature of the virgin resin constituting the skin layer is 250 ° C., and the temperature of the recycled resin constituting the core layer is 230 ° C., and the molds of these virgin resin and recycled resin are used. For example, the injection pressure is 8.8 MPa.

After supplying a predetermined amount of resin raw material, the valve gate 21 is closed by the valve pin 23, and as shown in FIG. 2, the inclined block 32 is moved in the Y direction so that the movable pin 30 approaches the valve gate 21. The cavity interval t of the resin receiving portion 17 is reduced. Here, in this embodiment, the cavity interval t of the resin receiving portion 17 is 2 mm, which is smaller than the cavity interval s of the portion forming the upper surface plate-like portion.
As shown in FIG. 5, the valve gate 21 and the movable pin 30 have a slight time lag until the operation is completed due to the injection pressure, but the closing of the valve gate 21 (T _V1 ) and the advancement of the movable pin 30 are completely completed. After (T _P1 ), nitrogen gas is injected from the gas valve 40 into the cavity 11 of the mold 10 (T _G1 ).

In this way, a synthetic resin pallet having a sandwich structure in which the virgin resin is arranged in the skin layer and the recycled resin is arranged in the core layer and the inside is formed into a hollow structure is formed.
According to this manufacturing method, since the recycled resin and the virgin resin are supplied from a single valve gate 21 opened in the mold 10, there is no portion where the flow of the resin raw material collides, and the recycled resin constituting the core layer. And virgin resin constituting the skin layer are prevented from being mixed.

  Further, gas is supplied after the resin raw material is supplied, and the resin raw material in the mold 10 is pressed against the mold 10 to accelerate the cooling of the resin raw material, and the resin is supplied without excessively increasing the resin supply amount. The pressure can be increased, and the occurrence of warpage or deformation during molding of a synthetic resin pallet is prevented. Further, the rib has a hollow structure, and even a relatively large and thick synthetic resin pallet is lightweight and easy to handle.

  Here, in the synthetic resin pallet manufacturing method according to the present embodiment, a predetermined amount of resin raw material is supplied into the mold 10 to close the valve gate 21 and advance the movable pin 30 to advance the cavity of the resin receiving portion 17. Since the gas is injected into the mold 10 after the interval t is reduced to 2 mm, it is possible to prevent the gas from entering the resin receiving portion 17 due to an increase in the resin pressure of the resin receiving portion 17. Therefore, it is possible to prevent the gas from entering the resin that is easily deformed at a high temperature in the vicinity of the valve gate 21 and to prevent a part of the synthetic resin pallet from becoming a film.

  Further, since the resin raw material is supplied into the cavity 11 of the mold 10 in a state where the cavity interval t of the resin receiving portion 17 is set to 5 mm larger than 3 mm which is the cavity interval s of the peripheral portion of the resin receiving portion 17, The supply of the resin material is promoted, and the resin material can be reliably supplied into the cavity 11 of the mold 10. Therefore, the diameter of the valve gate 21 can be reduced, the portion where the resin raw material is held at a high temperature can be reduced, and gas can be reliably prevented from entering the resin receiving portion 17.

Here, it is preferable to set the aperture of the valve gate 21 within the range of 10 mm to 20 mm as in the present embodiment, since gas can be reliably prevented from entering while promoting the supply of the resin raw material. In order to further secure this effect, it is more preferable that the diameter of the valve gate 21 be in the range of 12 mm to 20 mm.
In the present embodiment, the outer diameter of the valve pin 23 is in the range of 13 mm to 27 mm. However, when the aperture of the valve gate 21 is in the range of 12 mm to 20 mm, the outer diameter of the valve pin 23 is combined with this. Is preferably in the range of 16 mm to 27 mm.

  As described above, according to the method for manufacturing a synthetic resin pallet according to the present embodiment, it is a sandwich structure having a core layer made of recycled resin and a skin layer made of virgin resin, and the inside is a hollow structure. The synthetic resin pallet can be manufactured stably and reliably with high quality, and the amount of recycled resin can be secured to promote plastic recycling.

In this embodiment, the gas valve 40 is disposed near the movable pin 30. However, the present invention is not limited to this, and the gas valve 40 may be provided at a position away from the movable pin 30. In this case, as shown in FIG. 6, gas injection may be performed at a timing (T _G2 ) slightly earlier than the closing (T _V2 ) of the valve gate 21 and the end of advancement of the movable pin 30 (T _P2 ). In short, before the injected gas reaches the resin receiving portion 17, the advance of the movable pin 30 is completed and the cavity interval t of the resin receiving portion 17 may be reduced.

  Further, the method of manufacturing the synthetic resin pallet in which the upper surface mold member and the lower surface mold member are respectively molded and the upper surface mold member and the lower surface mold member are thermally welded has been described, but the present invention is not limited to this. You may apply to the manufacturing method of the synthetic resin pallets which shape | mold a face plate-shaped part, a lower surface plate-shaped part, and the girder part which connects these integrally.

It is the elements on larger scale which show the state which enlarged the cavity space | interval of the resin receiving part in the synthetic resin pallet manufacturing apparatus which is an Example of this invention. It is the elements on larger scale which show the state which made the cavity space | interval of the resin receiving part small in the synthetic resin pallet manufacturing apparatus which is an Example of this invention. It is a figure which shows the part which shape | molds the upper surface of an upper surface type member. It is a figure which shows the part which shape | molds the back surface of an upper surface type | mold member. It is a figure which shows valve gate opening and closing, operation | movement of a movable pin, and gas injection timing. It is a figure which shows the other Example of the manufacturing method of the synthetic resin pallets which concerns on this invention.

Explanation of symbols

10 Mold 11 Cavity 17 Resin receiving portion 21 Valve gate 30 Movable pin 34 Interval changing means 40 Gas valve

Claims (7)

A method for producing a synthetic resin pallet having a hollow structure inside,
A mold having a cavity having substantially the same shape as the whole or a part of the synthetic resin pallet is provided with an openable / closable valve gate opened in the mold and a portion where the valve gate is opened. A resin receiving portion, an interval changing means for changing the cavity interval of the resin receiving portion, and a gas injection means are provided,
After supplying the resin raw material into the mold through the valve gate,
The valve gate is closed and gas is injected into the mold, and the cavity interval of the resin receiving portion is reduced by the interval changing means before the gas reaches the resin receiving portion. A method for producing a synthetic resin pallet.   The synthetic resin pallet having the core layer and the skin layer is manufactured by supplying the resin raw material constituting the core layer and the resin raw material constituting the skin layer into the mold from the valve gate. A method for producing the described synthetic resin pallet.   The method for manufacturing a synthetic resin pallet according to claim 1 or 2, wherein gas is injected into the mold after the cavity interval of the resin receiving portion is reduced.   The composition according to any one of claims 1 to 3, wherein the resin raw material is supplied into the mold in a state where the cavity interval of the resin receiving portion is larger than the cavity interval of the peripheral portion of the resin receiving portion. Manufacturing method of resin pallets.   The method for manufacturing a synthetic resin pallet according to any one of claims 1 to 4, wherein the interval changing means is a movable pin that is movable back and forth disposed on a side facing the valve gate.   The method for producing a synthetic resin pallet according to any one of claims 1 to 5, wherein the aperture of the valve gate to the mold is within a range of 10 mm to 20 mm. An apparatus for manufacturing a synthetic resin pallet having an internal hollow structure,
A mold provided with a cavity having substantially the same shape as the whole or a part of the synthetic resin pallet, an openable / closable valve gate opened in the mold, and a resin provided in a portion where the valve gate is opened A synthetic resin pallet manufacturing apparatus, comprising: a receiving portion; an interval changing means for changing a cavity interval of the resin receiving portion; and a gas injection means.

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