JP2007144460A - Apparatus for manufacturing core for casting and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for manufacturing a core for casting and manufacturing method therefor, having excellent productivity, and easily manufacturing even a hollow core. <P>SOLUTION: The manufacturing apparatus is provided with a molten salt holding furnace and a mold arranged above the furnace. The molten salt holding furnace has a closed vessel and a crucible arranged in the closed vessel. A cavity in the mold is communicated with a stoke part arranged in the crucible, and a pressurizing means for pressurize-controlling the pressure in the closed vessel and an electric resistance measuring means for measuring the electric resistant value between the mold and the molten salt existing in the crucible, are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for manufacturing a casting core using a molten salt.

When casting a casting product having a hollow part, a casting core is disposed in the cavity in advance, a molten metal is poured around it, and the core is removed mechanically or after melting and melting by solidification of the metal. Is known.
In general, in the case of sand mold casting, a core formed using a refractory material such as silica sand as a base material is used.
In the case of gravity mold casting, it is possible to use the core used in conventional sand molds, but when die casting or other pressurized mold casting is used, the core can only withstand this casting pressure. In addition to demanding strength, a smooth casting surface is often required, and conventional sand mold cores have been difficult to use.
Therefore, in general, in pressure casting such as die casting, it is the actual situation that a metal core must be used.
Therefore, it has been limited to products that have a relatively simple shape that does not have an undercut portion and that can remove the metal core.
As described above, the metal core is sufficient in strength, but is greatly restricted in terms of removing the core after casting, and there are few types of products that can be applied.
Therefore, as a substance that is excellent in strength and easy to remove the core after casting, a metal having a relatively low melting point is used as disclosed in JP-A-11-5150, and only the core is heated after casting. Although it was considered to melt out, there was no metal having an appropriate melting point, and when it was melted out, it reacted with the cast metal to form a compound, which was disadvantageous to damage the casting surface.
Accordingly, the present inventors have developed an inorganic salt-based core that is excellent in disintegration with water, and have studied a manufacturing apparatus and a manufacturing method that are excellent in the productivity of the core, and as a result, have reached the present invention.

Japanese Patent Laid-Open No. 11-5150

  In view of the above technical problem, an object of the present invention is to provide a manufacturing apparatus and a manufacturing method for an inorganic salt-based casting core that is excellent in productivity and easy to manufacture a hollow core.

  The technical gist of the present invention is an apparatus for producing a casting core, comprising a molten salt holding furnace and a mold disposed on the molten salt holding furnace. The molten salt holding furnace is disposed in a sealed container and a sealed container. The mold cavity is in communication with the stalk portion provided in the crucible, and has a pressurizing means for controlling the pressure in the sealed container, and the mold and the crucible It has the electrical resistance measurement means which measures the electrical resistance value between molten salt which has.

Here, the molten salt refers to a salt in a state where an inorganic salt is heated and melted. In a molten state, the salt is ionized and thus exhibits a very low resistance value. However, the resistance value rapidly increases as it solidifies.
Utilizing this property, the core manufacturing apparatus according to the present invention determines the solidified state by measuring the resistance value of the molten salt filled in the mold cavity.
In this case, since the mold usually has electric conductivity, a counter electrode is provided in the molten salt in the crucible, and the electric resistance between the mold and the counter electrode in the molten salt is measured to thereby determine the inside of the cavity. Determine the coagulation state.
In addition, since the electric conductivity of the molten salt varies depending on the temperature of the molten state and the electric resistance value differs, the bath temperature can be managed using this electric resistance value.

  The technical gist of the invention described in claim 2 is that, in addition to the configuration described in claim 1, the stalk portion has a double structure of main stalk and sub-stalk disposed inside thereof. When not filling the cavity, the lower end opening of the outer main stalk is set lower than the molten salt liquid level, and the lower end opening of the inner sub stalk is set higher than the molten salt liquid level. It has an electrical resistance measuring means for measuring an electrical resistance value between the molten salt and the molten salt.

  The electrode for detecting the molten salt surface height in the stalk part is made of a conductive material with sub stalk provided inside the main stalk that guides the molten salt from the crucible to the cavity so as to detect the so-called hot water cutting state. This sub-stoke itself was used as an electrode.

  According to a third aspect of the present invention, there is provided a pair of heating electrodes disposed at a predetermined interval in the molten salt in the crucible.

Here, the pair of heating electrodes means that an alternating current is passed between the electrodes to form a heating means, and a stirring action can be imparted to the molten salt by applying Lorentz force to ions moving between the electrodes.
When an alternating current is passed through the molten salt, the impedance is lowered using the capacitance between the electrodes, and the current flows easily.

  The technical gist of the invention according to claim 4 is a method for producing a casting core, wherein the molten salt in the crucible disposed in the sealed container and the outside of the sealed container at a position higher than the molten salt. Measure the electrical resistance between the mold and the molten salt in the crucible by connecting the mold cavity to the stalk and pressurizing the sealed container to fill the cavity with the molten salt. And determining the solidification state of the molten salt in the cavity, and stopping or depressurizing the pressurization in the sealed container when the molten salt in the cavity reaches a predetermined solidification state. To do.

  The invention according to claim 5 makes it easy to detect a hot water cut after completion of the core manufacture, and the stalk part has a double structure of main stalk and sub-stalk disposed inside thereof, When not filling the cavity with molten salt, the lower end opening of the outer main stalk is set lower than the liquid level of the molten salt, and the lower end opening of the inner sub stalk is set higher than the liquid level of the molten salt, After the step of stopping or depressurizing the pressurization in the hermetic container, the method includes a step of determining the liquid surface height of the molten salt by measuring an electric resistance between the sub-stoke and the molten salt.

  The technical gist of the invention described in claim 6 is that the molten salt filled in the cavity is measured by measuring the resistance value between the electrode in the cavity and the electrode in the crucible by the electric resistance measuring means, and the surface of the cavity inner wall is in the cavity. It is determined that the solidified at a predetermined thickness, and then the pressurized salt is stopped or released so that the molten salt at the center of the cavity returns into the crucible so that a hollow core can be produced. The hollow core manufactured in this way is lightweight and contributes to material saving.

  In the present invention, one or two or more alkaline earths (excluding radium oxide) are added to and mixed with one or more inorganic salts in a range of 0.5 to 50% by volume after molding. When a molding material is used, the core is high in strength and excellent in disintegration with water.

Here, the inorganic salt refers to a water-soluble inorganic salt such as sodium sulfate, sodium nitrate, sodium chloride, potassium sulfate, and the alkaline earth refers to calcium oxide (quick lime) excluding radioactive alkaline earth metal radium, It means strontium oxide, barium oxide, magnesium oxide, etc., but magnesium oxide and quick lime are preferable because they have good expansibility when reacted with water and are relatively easy to drain.
Moreover, the thing which decomposes | disassembles at high temperature, such as slaked lime and magnesium carbonate, and becomes alkaline earth is included.
In addition, the molding material comprising an inorganic salt is also composed of one or more salts, one or more alkaline earths (except radium oxide) and refractories other than alkaline earths, alkaline earths. In addition, it may be added so as not to exceed 50% by volume after molding.
Here, the refractory other than alkaline earth is intended to obtain dispersed particles in salt, and examples thereof include oxide-based refractories such as alumina, silica, and mullite.
The alkaline earth may contain an alkaline earth metal hydroxide, carbonate, or a mixture thereof.
In addition, when alkaline earth metal hydroxide or carbonate is blended as an alkaline earth source, when the molding material is melted and molded, fine alkaline earth is generated by thermal decomposition, and this is the result of solidification of the inorganic salt. It acts as a crystal nucleus, making the dispersed particles finer and more uniform and contributing to the improvement of strength together with the refinement of the solidified structure of the inorganic salt.

In the casting core manufacturing apparatus according to the present invention, the measuring electrode of the electrical resistance measuring means is disposed in a timely manner in the molten salt filling path from the inside of the crucible to the cavity through the stalk portion. By measuring the resistance value, the height of the molten salt in the filling path and the solidified state of the molten salt in the cavity can be determined to control the apparatus.
As a result, the core can be manufactured stably and efficiently in a short time without unnecessary cooling of the molten salt.
In addition, since the solidified state in the cavity can be precisely controlled, a hollow core having a more excellent water disintegration can be easily produced with a desired thickness.
The molten salt in the crucible is heated by direct heating with alternating current applied, and a stirring action by Lorentz force is exerted between the molten salt and the electrode. Therefore, the temperature of the molten salt is made uniform in the crucible and stably stabilized. Can be manufactured.

FIG. 1 is an explanatory view showing a longitudinal section of a casting core (core) manufacturing apparatus 10 (hereinafter simply referred to as an apparatus) according to the present invention.
The apparatus 10 has a mold 20 for casting the molten salt 1 and forming a core, and a molten salt holding furnace 30 for supplying the molten salt 1 to the cavity 24 of the mold 20 is disposed below the mold 20. The mold 20 and an electrical resistance measuring means 70 for measuring and determining the state of the molten salt 1 in the molten salt holding furnace 30 are provided.
The mold 20 has a cavity 24 formed between the upper mold 21 and the lower mold 22, and the lower mold 22 has a gate 23 that opens the cavity 24 downward together with the lid 40 a of the sealed container 40. Yes.
The molten salt holding furnace 30 includes a crucible 50 and a stalk portion 60 in a sealed container 40.
The crucible 50 is provided with the crucible heating means 51 and the crucible heating means 52, and the molten salt 1 in which the inorganic salt-based molding material is melted is stored in the crucible 50.
In the molten salt holding furnace 30, the upper end of the stalk part 60 is connected to the cavity formed by the lower mold 22 and the lid 40a of the hermetic container 40 to communicate with the cavity, and the lower part of the stalk part 23 is inserted into the crucible 50. Thus, the lower opening is immersed in the molten salt 1 in the crucible 50.
The upper end of the stalk portion 60 only needs to be connected to the gate and communicated with the cavity. In this way, in addition to communicating with the cavity through the opening of the lid 40a of the hermetic container, the lower mold directly penetrates the lid 40a. You may connect to the gate part.
The sealed container 40 of the molten salt holding furnace 30 includes a pressurizing means 43 for injecting a pressurized gas from outside the container into the internal space 41 inside the container.
The apparatus 10 injects pressurized gas into the internal space 41 of the sealed container 40 by the pressurizing means 43 and pressurizes the molten metal surface 1 a facing the internal space 41 of the molten salt 1 in the crucible 50, thereby A differential pressure is generated between the space in the space 24 and the molten salt 1 is filled into the cavity 24 from the stalk portion 60 through the gate 23 by this differential pressure and molded.

The stalk portion 60 has a double cylinder shape of a main stalk 61 and a sub stalk 65. The outer main stalk 61 hangs down from the gate 23 until the lower end opening is immersed in the molten salt 1, and the inner sub stalk 65 is a gate. The lower end opening of the sub stalk is at a position higher than the molten metal surface when the molten salt is not pressurized and filled in the cavity.
The sub stalk 65 is formed of a conductive material, and the main stalk 61 and the sub stalk 65 are double cylinders. Therefore, a space 66 is provided between the main stalk 61 and the sub stalk 65 in a portion immediately below the gate 23. Is formed.
The main stalk 61 has a spacer 63 provided with a communication hole for communicating with the gate 23, and the spacer 63 is provided with a gas introduction hole 64 a that opens toward the space part 66 in the stalk part 60. is there.
The apparatus 10 includes a molten salt discharge gas introduction means 64 for introducing a gas into the space 66 through the gas introduction hole 64a.

The electrical resistance measuring means 70 is provided with a measuring electrode for measuring a resistance value between the molten salt 1 in the crucible 50 in the filling path of the molten salt 1 from the stalk portion 60 through the gate 23 into the cavity 24. A plurality are arranged.
These measuring electrodes are used to determine the level of molten metal in the filling path of the molten salt 1 and the solidified state in the cavity. In the crucible 50, the crucible 50 is immersed in the molten salt 1 stored in the crucible 50. 71, a sub stalk 65 is provided as a stalk part electrode in the stalk part 60, and a lower mold 22 is provided as an in-cavity electrode in the cavity 24.
The crucible inner electrode 71 may be provided in the stalk part as long as it can be immersed in the unsolidified molten salt 1.

The means for heating the crucible 50 includes a crucible heating means 51 in which a pair of electrodes 51 a are disposed so as to be immersed in the molten salt 1 in the crucible 50, and a crucible outside heating means 52 attached to the outside of the crucible 50. Yes.
The crucible heating means 51 energizes the molten salt 1 and heats it by Joule heat, and energizes an alternating current such as a commercial power source between the electrodes 51a.
The electrode 51a has a long shape such as a rod shape and is arranged so that its longitudinal direction is substantially perpendicular to the energization direction between the electrodes.
As a result, the direction of the magnetic field formed by the electrode 51a and the direction of movement of ions in the molten salt 1 are substantially perpendicular, and the molten salt 1 is agitated by applying a force by Lorentz force to the ions.
By this stirring action, the temperature of the molten salt 1 in the crucible 50 can be made uniform.
The crucible heating means 52 is used for preheating when the inorganic salt-based molding material is not melted and cannot be heated by energization of the crucible heating means 51 before continuous operation of the apparatus 10. The molding material is heated and melted to obtain molten salt 1 until 51 can be used, and may be stopped during continuous operation.

Next, a core manufacturing method using the core manufacturing apparatus of the present invention will be described.
First, the pressurizing means 43 is operated from the non-pressurized state of the molten salt 1 shown in FIG. 1 to inject a pressurized gas into the sealed container 40 to pressurize the molten salt 1 in the crucible 50.
The gas injected into the hermetic container 40 may be inert to the molten salt, and nitrogen, argon, air, and the like are conceivable.
As for the molten metal surface of the molten salt 1, the molten metal surface 1 a facing the internal space 41 of the sealed container 40 is pressurized, but the inside of the stalk portion 60 is not pressurized, and the stalk portion 60 communicates with the cavity 24. Has a gap between the upper mold 21 and the lower mold 22 that leads to the outside of the sealed container 40, so that a differential pressure is generated between the air pressure in the stalk portion 60 and the internal space 41 of the sealed container 40. Due to this differential pressure, the molten salt 1 passes from the stalk portion 60 through the gate 23 and is filled into the cavity 24 as shown in FIG.
At this time, the exhaust means 42 is closed to seal the sealed container 40.
The height of the molten metal surface 1b in the stalk portion 60 that changes when the molten salt 1 is filled is the electric resistance measuring means 70, the crucible inner electrode 71, the stalk portion electrode (sub stalk) 65 or the cavity inner electrode (lower It is possible to determine whether or not these electrodes have been reached by measuring the resistance value between the mold 22).
Therefore, the pressurization state of the pressurizing unit 43 may be controlled in response to the determination of the electric resistance measuring unit 70.

The molten salt 1 filled in the cavity 24 is cooled by the mold 20 and solidifies.
Since the resistance value of the molten salt 1 increases as it solidifies, this solidified state is measured by measuring the resistance value between the electrode in the cavity (lower mold) 22 and the crucible electrode 71 by the electric resistance measuring means 70. It can be determined regardless of the molding time within 24.
For example, when NaCl is used as the inorganic salt, the resistance value of the molten salt 1 is approximately 40,000 times the difference in resistance value between the solid state and the molten state. Since the conductivity changes depending on the bath temperature, the bath temperature state can be managed by the electric resistance measuring means.
Therefore, since it can move to the next process at the timing when the solidification state becomes optimal, the core can be manufactured stably and efficiently without wasting production time.
Since the solidification state in the cavity 24 can be set finely in this way, in addition to the state in which the molten salt 1 in the cavity 24 is all solidified, only the vicinity of the inner wall of the cavity 24 is solidified to a predetermined thickness, The setting of forming the hollow core can be facilitated by not solidifying the part.
FIG. 4A shows a state in which the molten salt 1 is completely solidified in the cavity 24 to form the core 2, and FIG. 4B shows a horizontal cross section in the gate 23 in the state of FIG. Show.

When the molten salt 1 is pressurized and filled, the molten salt 1 tends to be filled into the space portion 66 of the stalk portion 60, but the space portion 66 is sealed by closing the discharge gas introducing means 64. There is a gas, and this gas leaves the space 66 a in the space 66 even when the molten salt 1 is pressurized and filled.
The introduction hole 64a of the discharge gas introduction means 64 is provided so as to face the space 66a portion that is left when the molten salt is pressurized and filled, thereby preventing the molten salt 1 from entering the hole.
An annular molten metal surface 1c of the molten salt 1 that faces the space 66a is formed in the space 66 when the molten salt 1 is pressurized and filled.

The apparatus 10 detects that the molten salt 1 in the cavity 24 has solidified to form the core 2 by the electric resistance measuring means, and then operates the discharge gas introducing means to turn the pouring gate from the inlet 64a of the stalk part 60. The exhaust gas is introduced toward the space 66 immediately below the space 23.
Then, it separates as shown in FIG. 3 by the weight of the molten salt.
Whether the molten metal surface 1b of the molten salt 1 separated and descending toward the crucible 50 in the stalk part 60 is above the sub stalk 65 or below the sub stalk 65 is determined by an electric resistance measuring means. This can be determined by measuring the resistance value between the stalk part electrode (substoke) 65 and the crucible inner electrode 71.
The pressurizing means 43 that has been pressurized and filled with the molten salt 1 is stopped, the exhaust gas introducing means 64 is operated almost simultaneously, and the exhaust port 42a of the exhaust means 42 is opened to the outside of the sealed container 40 and released. The internal space 41 is depressurized.
Thereby, the molten metal surface 1b of the molten salt 1 in the stalk part 60 falls smoothly and rapidly, and the unsolidified molten salt is recovered in the crucible 50.
Thus, since the molten metal surface 1b can be dropped rapidly, the manufacturing time of the core 2 can be shortened while preventing the molten salt 1 in the stalk portion 60 from being cooled and solidified.
After the core 2 formed in the cavity 24 is separated from the molten salt as shown in FIG. 4C, the upper mold 21 is opened by a mold opening / closing means (not shown), and the core 2 is taken out by a robot or the like. The mold 21 is closed to the state shown in FIG.

Next, the case where a hollow core is manufactured will be described.
In the production of the hollow core, after the molten salt 1 is filled into the cavity 24 as shown in FIG. 2, the molten salt 1 in the cavity 24 is transferred to the cavity 24 by the electrical resistance measuring means 70 as shown in FIG. It is determined that the hollow core 3 has been formed by solidifying a predetermined thickness from the vicinity of the inner wall, and the discharge gas introduction means 64 is operated to introduce the discharge gas toward the molten salt 1 directly below the gate 23.
In this state, when the discharge gas is introduced from the injection port 64a of the discharge gas introduction means toward the molten salt 1 immediately below the gate 23, the introduced gas tries to separate the molten salt 1 into the cavity 24 side and the crucible side. However, since the molten salt 1 inside the hollow core 3 is unsolidified, the gas enters the hollow core 3, drops the unsolidified molten salt 1 in the hollow core 3 toward the crucible 50, and the cavity 24 Only the hollow core 3 remains separated in the interior as shown in FIG.
The introduction time of the discharge gas may be controlled by determining the state of the molten salt with an electric resistance measuring means.

Of the cores formed in this way, a core obtained by using one or more inorganic salts as a molding material and an alkaline earth and, if necessary, a refractory other than the alkaline earth, Has high strength and can sufficiently withstand pressure casting of aluminum alloy, magnesium alloy and brass alloy.
Moreover, removal of the core after casting can be facilitated by simply immersing the product in water.
When a hollow core is used, the core after casting can be removed more rapidly.
If this water-soluble core is used, a product that could not be manufactured due to the difficulty of removing the core in the past can be manufactured not only by ordinary gravity casting but also by die casting.
Further, even when an alkaline earth metal hydroxide or carbonate is used as the alkaline earth source, the inorganic salt decomposes at the time of temperature dissolution, so that shrinkage of the molded body can be avoided in advance.
This core is further characterized in that the inorganic salt has a function of preventing excessive contact between “water-disintegrating components (MgO, CaO, etc.)” and water. The “component” swells and causes fine cracks (cracks) in the inorganic salt, and further functions to promote water disintegration and promote disintegration.
This means that water penetrates excessively into the core, and the “water-disintegrating component” swells over a wide area and acts on the product by applying a compressive stress to fix it. It has a synergistic effect to avoid getting to.
As described above, the core to be manufactured is easy to remove the core after casting, and the obtained casting surface is extremely smooth, which brings about a great technical and economical effect.

An explanatory view of a core manufacture device concerning the present invention is shown. Explanatory drawing of the state which pressurized the molten salt and was filled in the cavity is shown. Explanatory drawing of the state which introduce | transduced the molten salt discharge gas directly under the gate is shown. The explanatory view of the state which shape | molds a core is shown, (a) shows the state in which the core was formed in the cavity at the time of the pressure filling to the cavity of molten salt, (b) is the gate part when the core was formed (C) shows the state which isolate | separated the core from molten salt. The explanatory view of the state which shape | molds a hollow core is shown, (a) shows the state in which the hollow core was formed in the cavity at the time of the pressure filling to the cavity of molten salt, (b) when the hollow core was formed The horizontal direction cross section of a gate part is shown, (c) shows the state which isolate | separated the hollow core from molten salt.

Explanation of symbols

1 Molten salt 1a Molten salt surface 1b facing the space Molten salt surface 1c facing the space in the stalk part Molten salt surface 2 facing the space in the cylindrical space part 2 Core (core)
3 hollow core 10 core manufacturing apparatus 11 insulation and airtight means 20 mold 21 upper mold 22 lower mold (electrode in cavity)
23 Pouring port 24 Cavity 30 Molten salt holding furnace 40 Sealed container 40a Sealed container lid 41 Internal space 42 Exhaust means 42a Exhaust port 43 Pressurizing means 43a Pressurizing port 50 Crucible 51 Heating means in crucible 51a Heating means electrode in crucible 52 Heating outside crucible Means 60 Stoke part 61 Main stalk 63 Spacer 64 Discharge gas introduction means 64a Inlet 64c Molten salt discharge gas 65 Sub-stoke (Stoke part electrode)
66 Space 66a Space 70 left during pressure filling of molten salt Electrical resistance measuring means 71 Electrode in crucible

Claims (7)

A molten salt holding furnace, and a mold disposed thereon,
The molten salt holding furnace has a sealed container and a crucible disposed in the sealed container,
The mold cavity communicates with a stalk portion provided in the crucible, and has a pressurizing means for pressurizing and controlling the pressure in the sealed container,
An apparatus for producing a casting core, comprising an electrical resistance measuring means for measuring an electrical resistance value between a mold and a molten salt contained in a crucible.   The stalk portion has a double structure of main stalk and sub-stalk disposed inside thereof. When the molten salt is not filled in the cavity, the lower end opening of the outer main stalk is made of molten salt. The lower end opening of the inner sub stalk is set lower than the liquid level and higher than the liquid level of the molten salt, and has an electric resistance measuring means for measuring the electric resistance value between the sub stalk and the molten salt. The casting core manufacturing apparatus according to claim 1, wherein:   3. The casting core manufacturing apparatus according to claim 1, further comprising a pair of heating electrodes disposed in the molten salt in the crucible at a predetermined interval. The molten salt in the crucible disposed in the sealed container and the cavity of the mold disposed outside the sealed container and at a position higher than the molten salt are communicated at the stalk portion, and the inside of the sealed container is pressurized to form the cavity Filling the inside with molten salt;
Determining the solidification state of the molten salt in the cavity by measuring the electrical resistance between the mold and the molten salt in the crucible;
And a step of stopping or depressurizing the pressure in the sealed container when the molten salt in the cavity reaches a predetermined solidified state.   The stalk portion has a double structure of main stalk and sub-stalk disposed inside thereof. When the molten salt is not filled in the cavity, the lower end opening of the outer main stalk is made of molten salt. The lower end opening of the inner sub stalk is set lower than the liquid level and higher than the liquid level of the molten salt, and the electric power between the sub stalk and the molten salt after the process of stopping or releasing the pressure in the sealed container is set. 5. The method for producing a casting core according to claim 4, further comprising a step of measuring the resistance and determining the liquid surface height of the molten salt. The molten salt in the crucible disposed in the sealed container and the cavity of the mold disposed outside the sealed container and at a position higher than the molten salt are communicated at the stalk portion, and the inside of the sealed container is pressurized to form the cavity Filling the inside with molten salt;
Determining the solidification state of the molten salt in the cavity by measuring the electrical resistance between the mold and the molten salt in the crucible;
And a step of stopping or depressurizing the pressurization in the closed container when the cavity surface portion of the molten salt in the cavity reaches a solidified state.   An inorganic salt-based hollow core product manufactured using the manufacturing method according to claim 6.

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