JP2007230825A - Member for glass conveyance, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass conveyance member having a cover hard to peel off under high-temperature atmosphere and also hard to generate crack, and to provide its production method. <P>SOLUTION: The glass conveyance member 1 is provided with a base material 2 and a covering layer 3 which is formed at least on the surface of the base material 2 facing the glass to be conveyed, and at least a part of the member 1 abuts on the glass when conveyed. The covering layer 3 has a marginal region reduced in layer's thickness stepwise or gradually reduced toward the boundary portion between the end of the layer 3 and the base material 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a glass conveying member and a method for producing the same, and more particularly to a glass conveying member such as a roll used for conveying a glass plate in a high temperature atmosphere and a method for producing the same.

  Conventionally, in order to process a flat glass plate into a complicated three-dimensional shape such as an automobile window glass, a method using the phenomenon that the glass plate softens at high temperatures has been used. That is, after a glass plate cut into a predetermined size and shape is heated to a sufficient temperature in a furnace, the glass plate is formed into a desired shape at a moderate deformation rate by gravity and / or external force by using a mold or the like. This is a molding method for deforming.

  In order to realize such a forming method, it is necessary to heat and cool the glass plate with a gradual temperature curve and to reduce the displacement speed during forming. In order to obtain sufficient work efficiency while satisfying these requirements, a tunnel furnace type equipment capable of continuously forming a large number of glass plates is effective instead of a so-called batch type equipment. For this reason, in the molding of window glass for automobiles, a glass plate is carried into a tunnel furnace having a moderate temperature gradient, and the glass plate is conveyed by rotating a plurality of rolls continuously arranged in the furnace. Is mandatory.

  Further, recent window glass for automobiles is strongly required not only to have a complicated three-dimensional shape but also to have no fine defects such as scratches on the visual field surface. For this reason, a material that can be used for a long period of time without adversely affecting the product quality is required for the transport rolls used in the production.

  The poor quality of the glass plate related to the transport roll includes those caused by the adhesion of the glass plate itself to the roll surface and those caused by the adherence to the roll surface. Caused by physical or chemical effects. Furthermore, the driving force transmission portions located at both ends of the roll are often taken out of the furnace in order to avoid deterioration due to exposure to high temperatures. Therefore, it is also required that the heat escaping from the both ends of the roll to the outside of the furnace is suppressed and the thermal efficiency of the forming equipment is not lowered.

  As a transport roll that meets such a demand, a roll mainly composed of a combined fused silica powder having excellent high-temperature oxidation resistance and poor thermal conductivity is used. The roll generally has pores on the surface, and there are fine powders that are not firmly fixed inside. As a result, when the roll and glass are in strong contact, fine particles with weak adhesion fall off from the roll itself. When the desorbed silica particles generated in this way reach the higher temperature range in the molding equipment while adhering to the glass surface, the particles and glass have a high affinity, so both are firmly fixed and a new defect Result.

Needless to say, it is effective to densify the surface layer in order to prevent the detachment of these fine powders. For this reason, a method of impregnating pores of the surface layer with an inorganic substance such as SiO ₂ by a sol-gel method, or a method of forming a ceramic layer such as zirconium oxide or aluminum oxide on the surface by a thermal spraying method or the like has been proposed.

  However, in the former, it is difficult to prevent the phenomenon that the impregnated inorganic substance becomes new desorbed particles due to cracks generated when the solvent required for impregnation is removed. On the other hand, in the latter, the amount of thermal expansion of the base material and the coating is remarkably different, and furthermore, since the thermal expansion of the coating is a larger combination, this roll can be put to practical use at high temperatures without peeling off the coating. It is extremely difficult to provide. Further, a proposal has been made to fit a ceramic sleeve on the outer periphery of the silica roll (see, for example, Patent Document 1). However, it is possible to industrially produce a ceramic sleeve having a particle having a coefficient of thermal expansion smaller than that of silica. This proposal cannot be realized due to difficulties.

  Furthermore, an attempt has been proposed to form a highly wear-resistant coating mainly composed of zirconium oxide or aluminum oxide on the surface of the silica roll by a thermal spraying method or the like.

JP-A-7-109139

  However, since the difference in thermal expansion between silica and ceramics is very large, it is extremely difficult to prevent the coating from peeling off. That is, when the thermal spray coating is formed, the coating ceramic is rapidly cooled from the melting temperature on the roll surface and tends to shrink, whereas the base material does not increase in temperature so that a large internal stress remains in the coating. To do.

  If the base material is made of metal having a thermal expansion larger than that of ceramics, this residual stress can be greatly reduced by a method of preheating this during thermal spraying. However, since the thermal expansion of silica is significantly smaller than that of ceramics, a method such as preheating is not effective, and this large residual stress cannot be reduced.

  In particular, both end portions of the coating formed on the base material have low adhesion to the base material, and are used in situations where a strong impact is applied to both end portions of the coating during handling, etc., and temperature rise and fall are repeated. Then, there was a possibility that partial film peeling of the coating occurred at both ends of the coating.

  Such a coating having a large residual stress has a problem that it easily peels off due to its own non-uniformity and non-uniform thermal and mechanical stress from the outside. It is practically difficult to apply this technique to a roll of an automotive window glass forming line having a large heat distribution and added heat fluctuation.

  This invention solves such a subject, and it aims at providing the member for glass conveyance which a coating | cover is hard to peel compared with the past, and a crack is hard to produce, and its manufacturing method.

  In order to achieve the above object, the present invention provides a glass transport member that transports glass while at least a part of the glass abuts on the glass, wherein the glass transport member transports at least a base material and the base material. And a coating layer formed on the surface facing the glass, the thickness of the coating layer gradually decreasing toward the boundary between the end of the coating layer and the base material Or a glass conveying member having a gradually decreasing peripheral region.

  In the case of roll conveyance, a coating layer is formed on the entire circumference of the roll as a base material, and the thickness of the coating layer gradually decreases toward the end of the roll in the axial direction, or gradually decreases, and the peripheral region of the coating layer Is formed.

  Moreover, as one aspect of the present invention, the coating layer is preferably made of one component selected from the group consisting of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, and zircon. Alternatively, the coating layer is preferably formed of at least two layers made of different components selected from the group consisting of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, and zircon. Furthermore, the base material is preferably a siliceous roll. Moreover, it is preferable that the thickness of the layer except the said peripheral area | region of the said coating layer is 0.01 mm or more and 0.3 mm or less.

  Further, the present invention is a method for manufacturing a glass conveying member, wherein a coating layer is formed by spraying a thermal spray material on a surface of a base material facing at least a glass to be conveyed to scan a thermal spray gun in a desired thermal spraying range. The coating layer is formed by narrowing the scanning range of the thermal spray gun in order from the initial thermal spray so that the thickness of the coating layer is the boundary between the end of the coating layer and the base material. There is provided a method for producing a glass conveying member, characterized in that a coating layer is formed so as to become thinner or gradually reduced toward a portion. Furthermore, as one embodiment of the present invention, it is preferable to polish the coating layer after the coating layer is formed.

  As described above, the present invention has the following effects.

  To the base material at the end of the covering layer, the thickness of the covering layer is gradually reduced or gradually reduced toward the boundary between the base material and the end of the covering layer. The decrease in the adhesive strength with time is reduced. In other words, in a furnace with a temperature distribution, strain tends to accumulate at the end of the coating layer, but it is thought that there is an effect of suppressing partial accumulation of strain by forming the thickness gradually decreasing at the end of the coating layer. Thus, the adhesion strength of the coating layer to the base material is ensured. Therefore, even if it is used in a situation where a strong impact is applied to the base material or the temperature is frequently raised and lowered, the peripheral region is hardly peeled off and can be used for a long time.

  In addition, it is possible to form a coating layer made of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, or zircon, which has conventionally had a problem with adhesion to the base material, so that the coating layer has high wear resistance. Can be formed.

  Further, the adhesion strength can be further improved by forming the coating layer from at least two layers made of different components of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, or zircon. For example, the first layer of the coating layer is mainly made of ceramics having a low coefficient of thermal expansion and low mechanical strength, and the second layer or more is mainly made of ceramics having high mechanical strength and high wear resistance. By using the material, in addition to the adhesion of the coating layer to the base material, it exhibits extremely high durability against wear and collision caused by glass sliding and the like.

  In the case of roll conveyance, by using a siliceous roll as a base material and forming a coating layer thereon as in the present invention, the adhesive strength between the base material and the coating layer is improved by utilizing the characteristics of the silica roll. Therefore, it can be suitably used as a roll of a heating furnace for manufacturing window glass for automobiles. That is, since a coating layer that is in close contact with the surface of the roll made of siliceous is formed, fine particles and the like are not dropped from the base material, and because the mechanical strength of the coating layer is high, fine powder is also dropped from the coating layer. Since there is nothing, when it uses as a roll for glass conveyance, the quality fall of glass can be prevented. Moreover, since the coating layer is only formed on the surface of the roll made of siliceous material and has almost the same thermal characteristics as the conventional transport roll, it can be installed without changing the specifications of the conventional heating furnace.

  Furthermore, when the thickness of the layer excluding the peripheral portion of the coating layer is 0.01 mm or more, it is easy to form the coating layer by a simple method such as thermal spraying, and when the coating layer is 0.3 mm or less Even when force is applied, the coating layer is difficult to peel off.

  In addition, the range of the reciprocating scan of the spray gun is narrowed sequentially from the initial spraying, and the coating layer is laminated, so that the thickness of the coating layer reaches the boundary between the end of the coating layer and the base material. Thus, the glass transport member of the present invention is suitably obtained by forming the coating layer so as to be gradually reduced or gradually reduced.

  Further, by polishing the coating layer after forming the coating layer, friction between the coating layer and the glass can be suppressed when the glass comes into contact with the coating layer, and the falling off of the coating layer can be avoided.

  Hereinafter, a preferred embodiment of the member for conveying a glass according to the present invention will be described in detail.

  FIG. 1 is a cross-sectional view, as viewed from the front, showing an embodiment of a glass transport roll that is suitably used among the glass transport members according to the present invention. A roll 1 shown in FIG. 1 includes a base material 2 and a ceramic coating layer 3 that covers the surface of the base material 2 (at least a portion facing the glass product). The cross section of the base material 2 in a side view is circular, and metal end caps 4 are fixed to both ends of the roll 1.

  The base material 2 is made of a material made of siliceous. Silica is superior to other materials such as metals in terms of cost, thermal characteristics, and high temperature durability of the base material. Further, instead of silica, cermet such as cemented carbide, oxide ceramics such as alumina and zirconia, non-oxide ceramics such as silicon nitride and SiC, or carbon may be used as the base material.

  The covering layer 3 is selected from the group consisting of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, or zircon on the surface of the base material (at least the portion that comes into contact with the glass), and is composed of at least two layers of an intermediate layer and an outer layer. The

  For example, as shown in FIG. 1, the first layer 5 covering the surface of the roll base material 2 is mainly composed of cordierite which is a composite oxide of aluminum, silicon and magnesium and / or zircon which is an oxide of zirconia and silicon. Are preferred. Cordierite and zircon have a very low coefficient of thermal expansion and good consistency with a silica roll base material.

  The ceramic second layer 6 covering the surface of the first layer 5 is preferably composed mainly of at least one component selected from the group consisting of zirconium oxide, yttrium oxide and aluminum oxide. These ceramics have relatively high mechanical strength and hardness, inevitably high wear resistance as a coating, and the mechanical strength of cordierite and / or zircon constituting the first layer 5 is , Significantly lower than the zirconium oxide and / or aluminum oxide constituting the second layer. For this reason, when the high internal stress in the second layer 6 generated when the coating is formed exceeds a certain level, a minute crack or the like is induced in the first layer 5 by the stress. The internal stress generated in the layer 6 is reduced. As a result, the coating layer 3 does not peel and can be used stably for a long period of time, and it is possible to reduce the disadvantages of glass caused by dust generation from the roll.

  As shown in FIG. 1, the coating layer 3 is formed with a peripheral region in which the thickness of the coating layer gradually decreases at an angle a toward the boundary between the roll base material 2 and the end of the coating layer 3. Yes. Although only the right end of the covering layer 3 is shown in FIG. 1, the thickness of the covering layer is also gradually reduced at the left end.

  By forming the peripheral region so as to gradually reduce the thickness of the coating layer 3, it is possible to prevent the adhesion strength at the end of the coating layer 3 from decreasing with time. Although the cause is not necessarily clear, it is thought that gradually decreasing the thickness of the end portion of the coating layer has the effect of reducing the partial accumulation of strain, and therefore suppresses the decrease in adhesion strength. That is, there is a difference in the coefficient of thermal expansion between the base material and the coating layer, and when the roll is actually installed in a heating furnace, there is a temperature distribution in which both ends of the roll are slightly lowered during heating. Although the distortion tends to accumulate at the end of the film, the structure of the present invention reduces the partial accumulation of distortion and secures the adhesion strength.

  Therefore, the angle a is preferably 45 ° or less, and more preferably 30 ° or less in order to reduce the partial accumulation of strain.

  In addition, as shown in FIG. 2, even when a peripheral region where the thickness of the coating layer becomes thinner stepwise at an angle b toward the boundary portion between the roll base material 2 and the end of the coating layer 3 is formed. Good. In FIG. 2, only the right end of the covering layer 3 is shown, but the left end is similarly formed so that the thickness of the covering layer decreases stepwise. Similarly, the angle b is preferably an angle of 45 ° or less, and preferably an angle of 30 ° or less in order to reduce the partial accumulation of strain. Moreover, although the coating layer shown in FIGS. 1 and 2 is formed of two layers of the intermediate layer 5 and the outer layer 6, the coating layer may be a single layer. In FIG. 2, the same parts as those in FIG.

  Therefore, when the roll for transporting glass provided by the present invention is applied to a transport roll of equipment for molding automobile glass or the like, the coating layer does not peel off even in practical use and can be used stably for a long period of time. It is possible to reduce the disadvantages of glass due to dust generation.

  The thickness excluding the peripheral region of the coating layer 3 is preferably 0.01 mm or more and 0.3 mm or less, and more preferably 0.05 mm or more and 0.2 mm or less. When the thickness of the coating layer 3 is less than 0.01 mm, it is difficult to form a uniform coating layer by a simple method such as thermal spraying. On the other hand, if the thickness of the coating layer 3 exceeds 0.3 mm, large scale cracks are likely to occur in the coating layer when an external force is applied.

  It is preferable that the coating layer 3 of the glass conveying component of the present invention is formed by a thermal spraying method. The coating layer 3 can be formed on the siliceous base material 2 whose surface has been roughened by sandblasting or the like, by plasma spraying or high-speed flame spraying. As a method for roughening the base material 2, any method such as water blasting and mechanical polishing can be used.

  The surface roughness of the siliceous base material 2 roughened to increase the adhesion strength with the coating layer 3 is preferably Ra (centerline average roughness) of 0.1 μm or more, more preferably Ra. The thickness is 4 μm or more, and more preferably Ra is 6 μm or more.

  When a coating layer is formed on a siliceous base material by a thermal spraying method, adhesion to the base material is improved. The cause of this is not necessarily clear, but the compatibility of the raw material particles flying to the surface of the base material 2 by thermal spraying and the wettability of the surface of the base material 2 may be better than a combination of conventionally known materials. Conceivable.

  The spraying operation is performed by supporting the both ends of the roll and rotating the roll at a constant speed while reciprocating the spray gun in the axial direction of the roll or keeping it at a constant distance in the desired spraying range or scanning several times in one direction. However, it is performed by spraying the raw material particles. At this time, thermal spraying is performed by shortening the scanning distance in the axial direction of the roll of the thermal spray gun for each scan or every arbitrary multiple scans. That is, the scanning distance of the spray gun is shortened so that the coating layer is not formed on the upper layer at both ends of the coating layer formed by scanning a certain distance of the spray gun.

  By this method, it is possible to form a peripheral region in which the thickness of the coating layer gradually decreases or gradually decreases toward the boundary portion between the end portion of the coating layer and the base material. However, it is not limited to this method.

  The thermal spray raw material is preferably a raw material manufactured by a sintering method. Although it is possible to use the raw material manufactured by the melt pulverization method, it tends to be difficult to control the density and the like of the coating layer. If the coating layer becomes too dense, it becomes weak against thermal shock or the like, and if it becomes too coarse, sufficient mechanical strength of the coating layer cannot be obtained.

  Since the coating layer 3 is formed by collision, adhesion, and lamination of the droplets in which the raw material is melted, the surface of the coating has considerable irregularities. The possibility that a part of the coating will fall off when sliding is not low. Therefore, it is preferable to polish the formed coating layer. As for the roughness of the surface of the coating layer 3, it is preferable that Ra is 10 micrometers or less, More preferably, it is 5 micrometers or less, More preferably, it is 3.5 micrometers or less. The method of adjusting the surface roughness can be selected from mechanical polishing of the coating layer after spraying with a diamond tool or fine powdering of the spraying raw material, but is not limited thereto.

  Further, after forming the coating layer, it is effective to perform heat treatment in order to release the internal stress accumulated in the coating layer by thermal spraying or finishing. The heat treatment is generally performed in the air, but it can also be performed in a non-reducing atmosphere such as in nitrogen or argon. The heat treatment temperature is preferably 400 ° C. or higher and 1200 ° C. or lower, and more preferably 500 ° C. or higher and 1000 ° C. or lower. When the heat treatment temperature is 400 ° C. or higher, the internal stress is suitably released, and when it is lower than 1200 ° C., the coating layer is stably adhered.

  The size of the roll can be changed depending on the furnace to be installed, but generally the diameter is 45 to 90 mm, and the length is 1500 to 3500 mm. As shown in FIG. 1, the coating layer 3 does not need to be provided on the entire surface of the base material 2, and is coated in a range where glass may pass on the roll when the roll is installed in the furnace. It only has to be. The range to be coated is appropriately determined depending on the type of furnace and the size of the glass to be conveyed. If the coating layer 4 is provided in a wide range, it can respond to various glass sizes to be conveyed. For example, if the size of the roll 1 is in the above range, the size of the window glass for an automobile can be covered by setting the area where 10 to 200 mm from the end of the conveying surface of the roll 1 is not provided with the coating layer 4.

  Examples of the present invention will be further described below, but the present invention is not limited thereto. An example is a case where the peripheral area | region where the thickness of the layer of the edge part of a coating layer becomes thin in steps is formed in the surface of the silica roll which this invention provides. A comparative example is a case where a coating layer is formed on a silica roll with a constant layer thickness as usual. The results of comparing these characteristics are shown below.

(Example)
A silica roll made of the same cylindrical porous silica sintered body having a diameter of 55 mm and a length of 1500 mm was prepared, and the surface of the silica roll was roughened with # 80 abrasive paper. After the silica roll is washed and dried, the roll is fixed to a sample stage that rotates at a constant speed, and the spray gun is scanned twice at a distance of 1400 mm in the axial direction, so that the surface of the silica roll has a thickness of about 100 μm. Cordierite was sprayed to form the first layer of the coating layer.

  Next, the spray gun was reduced in width by 1380 mm, 1360 mm, and 1340 mm every three reciprocations in the axial direction, and a second layer of zirconium oxide (8YZ) coating layer added with 8% yttrium oxide was formed. At this time, as shown in FIG. 2, the second layer of the coating layer was formed so that the scanning range was shortened to L1, L2, and L3 with respect to the center C of the scanning range. In FIG. 2, only the left side of the roll is shown, but the same applies to the right side. Thermal spraying was performed by a plasma spraying method. Cordierite prepared a raw material powder by a melt production method, and zirconium oxide used a hollow spherical raw material powder. After the thermal spraying, the coating layer was polished, and the thickness of the coating layer of the first layer and the second layer was 150 μm, and the Ra of the polished surface was a coating layer having a thickness of 0.5 μm.

  The created roll was installed in a roller hearth furnace for forming window glass for automobiles, and actually used as a transport roll for several days. After use for several days, the roll was taken out from the furnace, and several cubic test pieces of about 10 mm were cut out from the center of the end of the coating layer from the center of about 150 mm so as to include the coating layer.

(Comparative example)
A silica roll made of the same cylindrical porous silica sintered body having a diameter of 55 mm and a length of 1500 mm was prepared, and the surface of the silica roll was roughened with # 80 abrasive paper. After the silica roll is washed and dried, the roll is fixed to a sample stage that rotates at a constant speed, and the spray gun is sprayed twice at a distance of 1400 mm in the axial direction to spray about 100 μm thick cordierite. The first layer of the coating layer was formed.

  Subsequently, the thermal spray gun was similarly reciprocated at a distance of 1400 mm in the axial direction to form a second layer of a zirconium oxide (8YZ) coating layer to which 8% of yttrium oxide was added. At this time, the centers of the scanning ranges were all the same. Thermal spraying was performed by a plasma spraying method. Cordierite prepared a raw material powder by a melt production method, and zirconium oxide used a hollow spherical raw material powder. After the thermal spraying, the coating layer was polished, and the thickness of the coating layer of the first layer and the second layer was 150 μm, and the Ra of the polished surface was a coating layer having a thickness of 0.5 μm.

  The created roll was installed in a roller hearth furnace for forming window glass for automobiles, and actually used as a transport roll for several days. After use for several days, the roll was taken out from the furnace, and several cubic test pieces of about 10 mm were cut out from the center of the end of the coating layer from the center of about 150 mm so as to include the coating layer.

-Adhesion strength and heat resistance recycling test-
As shown in FIG. 3, the adhesion strength was measured using the test pieces cut out in Examples and Comparative Examples. After the cut specimen was bonded to two aluminum alloy jigs 13 via a two-component epoxy adhesive layer 12, a tensile test was performed by pulling the jigs 13 in the tensile direction 14, respectively. The tensile test was performed at a measurement temperature of room temperature (about 20 ° C.) and a tensile speed of 0.1 mm per minute.

As a result of the measurement, the adhesion strength of the silica roll of the example was 2.6 N / mm ² . In comparison, the adhesion strength of the silica roll of the comparative example was 0.1 N / mm ² or less, which is below the measurement limit. From the above tests, it was confirmed that the coating layers (Examples) provided by the present invention showed good results in the tests.

  As described above, the present invention can be applied to a roll used in a roller conveyor for conveying a glass plate in a heating furnace. In addition to rolls, it is obvious that the present invention can be applied to an apparatus or jig for handling various glass products in a heated atmosphere (a jig for holding, supporting, holding or placing a glass member). It can also be applied to uses other than glass production.

It is sectional drawing in the front view which shows one Embodiment of the roll which concerns on this invention. It is sectional drawing in the front view which shows other embodiment of the roll which concerns on this invention. It is a side view which shows the outline of the test method for measuring the adhesive strength of a coating layer.

Explanation of symbols

1: Roll 2: Base material 3: Coating layer 10: Thermal spray coating 11: Silica base material 12: Epoxy adhesive 13: Aluminum jig 14: Tensile direction

Claims (7)

  A glass conveying member that conveys glass while at least part of the glass abuts against the glass, the glass conveying member comprising a base material and at least a coating layer formed on a surface of the base material facing the glass to be conveyed And the covering layer has a peripheral region in which the thickness of the layer is gradually reduced or gradually decreased toward the boundary portion between the end of the covering layer and the base material. A glass transporting member.   The glass coating member according to claim 1, wherein the coating layer is made of one component selected from the group consisting of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, and zircon.   2. The glass conveying member according to claim 1, wherein the coating layer is formed of at least two layers made of different components selected from the group consisting of zirconium oxide, aluminum oxide, yttrium oxide, cordierite, and zircon.   The said base material is a siliceous roll, The member for glass conveyance in any one of Claim 1 to 3.   The glass conveying member according to any one of claims 1 to 4, wherein a thickness of the coating layer excluding the peripheral region is 0.01 mm or more and 0.3 mm or less.   A method for manufacturing a glass conveying member that forms a coating layer by spraying a thermal spraying raw material on a surface of a base material facing at least a glass to be conveyed in a desired thermal spraying range, and scanning the thermal spraying gun By gradually reducing the range of the initial spraying to form the coating layer, the thickness of the coating layer is stepped toward the boundary between the end of the coating layer and the base material. A method for producing a glass conveying member, wherein the coating layer is formed so as to be thinned or gradually reduced. The manufacturing method of the member for glass conveyance of Claim 6 which grind | polishes this coating layer after forming the said coating layer.

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