JP2008030228A - Sheet welding method and sheet welding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet welding method due to a hot-iron system for certainly and strongly welding two sheets made of a sheet thermoplastic resin having wax or the like present on its surface, and a sheet welding apparatus. <P>SOLUTION: In the sheet welding method, the surfaces to be welded of two sheets 8 are superposed on upon another, a hot iron 4 is brought into a slide contact with the mutually opposed surfaces to be welded of two sheets 8 to melt the surfaces to be welded of two sheets 8 and the molten surfaces to be welded of two sheets 8 are pressed and brought into contact with each other under pressure to mutually weld the surfaces to be welded of two sheets 8. The temperature difference between the resin of the surfaces to be welded and the resin around it when the hot iron 4 is brought into contact with the surfaces to be welded is reduced by preheating the respective surfaces to be welded of two sheets 8 before the hot iron 4 is brought into slide contact with the surfaces to be melted of two sheets 8 to reduce a heat shock. Further, the sheet welding apparatus is constituted by successively arranging the hot-air nozzle 3 inserted in the gap between the superposed surfaces 8 to be melted of two sheets 8, the hot iron 4 and a pressure roller 6 for pressing the molten surfaces to be welded from above. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sheet welding method and a welding apparatus, and more specifically, a method of welding two sheets made of a thermoplastic resin by a hot metal method, the surface of which is coated with wax or the like. The present invention relates to a sheet welding method capable of reliably and firmly welding, and a sheet welding apparatus suitable for carrying out the welding method.

  A tent, an awning, a freight car top, a packaging container, and the like often use a sheet made of a thermoplastic resin, and when a large-area sheet is manufactured, a plurality of fixed sheets are welded. As a general method for welding sheets made of thermoplastic resin, a hot air method in which a welding surface to be welded is melted with hot air and pressed and adhered, and a welding surface is melted with hot water and pressed and adhered. There are two methods of hot water. However, the sheet used in the above-mentioned applications has a surface coated with a low molecular weight polyolefin such as wax or an inorganic substance such as titanium oxide for the purpose of antifouling and cannot be welded by a hot air method. There are many. Therefore, in the welding process between sheets coated with wax or the like, a hot metal method is used in which welding is performed while the welding surface is roughened by sliding contact with the hot metal.

As a welding technique using a hot iron, each inner surface (surface to be welded) of the edge portions to be welded of the two overlapped sheets is heated by contact with the iron, and each inner surface is heated and melted. A "synthetic material sheet welding apparatus" has been proposed in which the edge portions are sandwiched and pressed from both outer sides by a pair of feed rollers to weld the end edge portions together.
Japanese Utility Model Publication No. 3-19023

  By the way, when the sheets are welded together by the hot metal method as described above, the breaking strength at the boundary portion between the welded portion and the unwelded portion is small, and when the shearing force is applied, the sheet breaks at the boundary portion. There is a problem that it is easy. The present invention has been made in view of such circumstances, and an object of the present invention is a method of welding two sheets made of thermoplastic resin by a hot metal method, and in particular, there is a wax or the like on the surface. An object of the present invention is to provide a sheet welding method capable of reliably and firmly welding a sheet, and a sheet welding apparatus suitable for carrying out the welding method.

  As a result of various analyzes on the hot metal welding method, the present inventors have made the welding surface rough by moving the hot metal to contact the welding surfaces of the two sheets in the hot metal welding. While the base resin is exposed to the surface and can be integrated with welding, it is between the resin on the surface to be welded that is instantaneously heated by the contact with hot metal and the resin around the surface to be welded that is not in contact with the hot metal. It was known that a large temperature difference was produced at the boundary, and as a result, a significant decrease in strength was caused at these boundaries. As a result of further investigation, if the welding surface and its surroundings are preheated immediately before heating with hot metal, the temperature difference when the hot metal is brought into contact can be reduced, and the boundary described above The present inventors have found that it is possible to effectively prevent a decrease in breaking strength in the portion, and the present invention has been completed.

  That is, the first gist of the present invention is to superimpose the welding surfaces to be welded of two sheets made of thermoplastic resin, and to slidably contact these welding surfaces with the welding surfaces facing each other. A sheet welding method for fusing and welding pressure-bonded surfaces to each other, and preheating each of the surfaces to be welded in sliding contact with hot metal. Exist.

  The second gist of the present invention is an apparatus for welding two sheets made of thermoplastic resin while moving in one direction, and is inserted between the welding surfaces to be welded of the overlapped sheets. And a hot metal slidably in contact with the welding surface, and a pressure roller that is arranged on the rear side in the apparatus moving direction with respect to the hot metal and presses the welding surface melted by the hot metal from above the sheet. The hot air nozzle is provided on the front side in the apparatus moving direction with respect to the hot metal, and is provided with a hot air nozzle that is inserted between the welded surfaces of the stacked sheets and blows hot air onto the welded surfaces. Exists in the sheet welding apparatus.

  According to the present invention, before the hot metal is brought into sliding contact with the welded surfaces of the two sheets, by preheating the welded surfaces, the resin on the welded surface when the hot metal is brought into contact with its surroundings. The temperature difference between the resin and the resin can be reduced to reduce heat shock and prevent a decrease in the breaking strength at the boundary between the welded part and the part not welded. Can be welded firmly.

  Embodiments of a sheet welding method and a welding apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a plan view and a longitudinal sectional view showing a concept of a sheet welding method and an arrangement of main members of a welding apparatus according to the present invention. FIG. 2 is a perspective view showing the outer shape of the sheet welding apparatus according to the present invention, and FIG. 3 is a plan view showing the outer shape of the sheet welding apparatus. In addition, the following description is description regarding an example of embodiment of this invention, and this invention is not limited to the following content.

  The present invention relates to a method and a welding apparatus for welding sheets made of thermoplastic resin by a hot metal method, for example, a base of a structure such as a tent, an awning, a lorry for a lorry, or a waste disposal site. Applicable when manufacturing sheets. In the present invention, the thermoplastic resin as the sheet material is not particularly limited, and examples thereof include copolymer polyolefins such as polypropylene, polyethylene, polyvinyl chloride, and ethylene vinyl oxide copolymer, and polyethylene terephthalate. In particular, the present invention is a sheet in which modifiers and additives such as low molecular weight polyolefins such as wax, fillers such as titanium oxide, ultraviolet ray inhibitors, and antistatic agents are present on the surface, that is, the surface is soil resistant. And a sheet provided with a weather-resistant coating layer, or a sheet on which a bleed material is likely to be deposited on the sheet surface in the welding process.

  First, a welding apparatus suitable for carrying out the welding method according to the present invention will be described. The welding apparatus of the present invention is an apparatus for welding, for example, side edges of two sheets (8) made of thermoplastic resin while moving in one direction, and the main part is overlapped as shown in FIG. A hot metal (4) inserted between the welded surfaces (the inner surfaces of the side edges that are the welded parts) of the combined sheet (8) and in sliding contact with the welded surfaces, and the hot metal On the other hand, a pressure roller (6) is provided on the rear side of the apparatus movement direction (welding direction) and pressurizes the surface to be welded melted by the hot metal from above the sheet. A hot air nozzle (3) that is inserted between the welded surfaces of the stacked sheets (8) and blows hot air on the welded surfaces on the front side in the apparatus moving direction with respect to the hot metal (4). Is provided.

  That is, the welding apparatus of the present invention is a self-propelled apparatus that moves in one direction at a predetermined speed by rotationally driving the pressure roller (6), along the moving direction (welding direction). From the front, a hot air nozzle (3), a hot iron (4), and a pressure roller (6) are sequentially arranged in a straight line. In FIG. 1, the arrow indicates the relative movement direction (welding direction) of the welding apparatus, and the symbol (9) indicates the welded portion that has been welded.

  More specifically, as shown in FIGS. 2 and 3, the welding apparatus of the present invention includes an apparatus main body (1) as a casing having a caster attached to the bottom surface. In such a device main body (1), in addition to a motor for driving the pressure roller (6), various circuits, that is, a power supply circuit including a constant voltage current device, a pressure roller (6), and The drive control circuit for controlling the rotation speed, the temperature control circuit for controlling the temperature of the hot metal (4) and the temperature of the hot air blown from the hot air nozzle (3), and the laser pointer (2) as a guide mechanism are turned on. A pointer lighting circuit, emergency cut-off circuit, etc. are housed. The upper surface of the apparatus main body (1) is configured as an operation panel including a display and operation buttons for displaying a temperature display, a welding speed (traveling speed), and the like.

  At the front end of the apparatus main body (1), for example, the front left side, the laser pointer (2) is provided in a protruding state. The laser pointer (2) is a laser beam irradiation device for displaying a mark on the surface of the sheet (8). In the welding process, the welded portion to be welded (the side edge of the sheet (8) overlapped in a band shape) By placing a laser point as a mark in the center of the width direction of the part), the hot air nozzle (3), hot iron (4) and pressure roller (6) arranged behind the laser pointer (2) are covered. The welded part can be traced accurately.

  The hot air nozzle (3) is disposed on one side surface of the apparatus main body (1), for example, the left side surface. Since the hot air nozzle (3) is inserted between the two sheets (8), the base end portion is formed by a flat tube bent substantially at a right angle in a plan view and is wide in the horizontal direction. It is attached to the lower end of the rotating shaft (31). The rotating shaft (31) is vertically and freely mounted on the apparatus main body (1) by the support block (13), and is turned by a lever (33) protruding from the upper portion of the rotating shaft. Has been made. That is, when the hot air nozzle (3) performs the welding process, the operation of the lever (33) causes the blowing port to face rearward so that the overlapping portions of the sheets (8) and (8) (each weld of the welded portion) When the welding operation is finished, the lever (33) is operated so as to be positioned outside the overlapping portion.

  Said rotating shaft (31) comprises the hot air generator, and the electric heater and the ventilation fan are incorporated in the upper part of the said rotating shaft. The lever (33) also has a function as an operation switch for the electric heater and the blower fan, and the hot air nozzle (3) is inserted between the two sheets (8) by operating the lever (33). It is configured to blow hot air in some cases. And in a hot air nozzle (3), energization of said electric heater is controlled based on the detection temperature of the temperature sensor inserted in the front-end | tip part of a hot air nozzle (3), and the conditions set to the above-mentioned control circuit. Thus, the temperature of the hot air blown out is adjusted.

  In addition, as a hot air generator combined with an electric heater and a blower fan built in the rotating shaft (31), a so-called portable hot air blower mechanism having an output of about 200 to 3500 W used for heating and drying operations is used. I can do it. And the temperature of the hot air blown from a hot air nozzle (3) is normally set to 20-700 degreeC, and is adjusted according to the material and thickness of a sheet | seat (8). The hot air blowing width at the tip of the hot air nozzle (3) is about 10 to 100 mm, and the air volume of the hot air is set to 10 to 600 l / min.

  The hot tub (4) is arranged behind the hot air nozzle (3). Like the hot air nozzle (3), the hot metal (4) is inserted between two sheets (8), and thus is formed of a flat metal plate. As the metal material constituting the hot metal (4), a material having high thermal conductivity such as a copper alloy or an aluminum alloy is used. And the longitudinal cross-sectional shape along the moving direction of a hot metal (4) is designed by the streamlined type where the front-end edge was chamfered so that a to-be-welded surface might not be caught.

  The hot metal (4) is attached to the lower end of the rotating shaft (41) via the arm (42) so as to be wide in the horizontal direction in a plan view. The arm (42) extends horizontally at the lower end of the rotating shaft (41), and the hot metal (4) is perpendicular to the length direction of the arm on the side edge on the distal end side of the arm (42). And heated by an electric heater embedded in the arm (42).

  The rotating shaft (41) is vertically and freely supported by the support body (14) by the support block (14), and is turned by a lever (43) protruding from the upper portion of the rotating shaft. Has been made. That is, the hot metal (4) is inserted between the overlapping portions of the sheets (8) and (8) (welding surfaces of the welded portions) by operating the lever (43) when performing the welding process, When the welding process is finished, the lever (43) is operated so as to be removed outside the overlapping portion.

  The apparatus main body (1) is provided with a power switch, and the hot metal (4) is heated by energizing the electric heater by operating the power switch. And the hot metal (4), by controlling the energization of the electric heater based on the detection temperature of the temperature sensor inserted in the tip of the hot metal and the conditions set in the control circuit, The temperature is adjusted.

  In addition, the capacity | capacitance of the electric heater embed | buried under an arm (42) shall be about 300-1000W. In addition, the width (welding width) of the hot iron (4) is 10 to 50 mm, the length (the length of the iron along the moving direction) is 20 to 100 mm, and the thickness is 3 to 20 mm. The temperature of the hot metal (4) is usually set to 20 to 600 ° C., and is adjusted according to the material and thickness of the sheet (8).

  The pressure roller (6) is arranged behind the hot metal (4). The pressure roller (6) is provided in order to pressurize the welded portions of the two sheets (8) whose welded surfaces have been melted by the hot metal (4) from above the sheets and bring the welded surfaces into close contact with each other. . The pressure roller (6) is made of a heat resistant resin or metal. A part of the load of the pressure roller and the load of the apparatus main body (1) is applied to the welded portion of the sheet (8) by the pressure roller (6). The weight of the pressure roller (6) is as follows: Usually, the load applied to the welded portion is set to be about 0.5 to 5 kg / cm.

  The pressure roller (6) is configured to rotate in one direction by a motor housed in the apparatus main body (1). And according to the material and thickness of sheet | seat (8), the rotational speed is comprised so that adjustment is possible by the above-mentioned drive control circuit. The pressure roller (6) is driven in conjunction with the above-mentioned hot metal (4). That is, the pressure roller (6) is driven to rotate when the hot metal (4) is inserted between the two sheets (8) by the operation of the lever (43) of the rotating shaft (41). It is configured to stop when the hot iron (4) is removed during the period 8).

  The width of the pressure roller (6) is usually designed to be slightly larger than the welding width, specifically about 10 to 80 mm, and the diameter of the pressure roller (6) is designed to be about 50 to 150 mm. ing. And the rotational speed of the pressure roller (6) is set to the range of 2-50 rpm.

  In the welding apparatus of the present invention, the welded portion of the two sheets (8) is usually smoothly placed in front of the apparatus moving direction (welding direction) with respect to the pressure roller (6). A guide roller (5) for guiding to 6) is attached. A grip (7) for carrying or positioning the entire welding apparatus is provided at a position corresponding to the upper side of the pressure roller (6) on the rear side surface side of the apparatus main body (1).

  Further, although not shown, in the welding apparatus of the present invention, the hot air nozzle (3) and the hot iron (4) are used to reliably destroy the coating layer on the surface to be welded of the two sheets (8). Between them, there may be arranged a file plate inserted between the welded surfaces of the stacked sheets (8) and roughening the welded surfaces.

  As will be described later, the welding apparatus of the present invention preheats the surfaces to be welded of two sheets (8) with a hot air nozzle (3), and then contacts the hot metal (4) with a pressure roller (6). Due to the pressure contact, the temperature difference between the resin on the welding surface and the surrounding resin can be reduced. As a result, it is possible to prevent a decrease in breaking strength at the boundary portion between the welded portion and the unwelded portion, and the two sheets (8) can be more firmly welded.

  Next, the welding method of the present invention using the welding device will be described together with the function of the welding device. The welding method of the present invention is applied to the welding of the sheet (8) as described above. In the welding method of the present invention, for example, a side edge which is a welding surface to be welded of the two sheets (8). The inner surfaces of the parts are overlapped, the hot metal (4) is brought into sliding contact, the welded surfaces are melted, and the welded surfaces are welded together by pressure contact. Moreover, in the present invention, when the hot metal (4) is slidably contacted, the resin on the surface to be welded heated by the hot metal (4) and the periphery of the surface to be welded that the hot metal (4) does not contact. In order to make the temperature difference with the resin as small as possible, each surface to be welded is preheated. Moreover, in said preheating, a hot air is sprayed on each to-be-welded surface.

  Specifically, as shown in FIG. 1, in order to weld, for example, side edges of the two sheets (8), first, the side edges are overlapped with each other, and then the above-described welding device is arranged. . When arrange | positioning a welding apparatus, a welding apparatus is mounted on a sheet | seat (8) in the state along a side edge part which is a welding part, and a pressure roller (6) is applied from the sheet | seat upper direction. Next, the hot air nozzle (3) and the hot iron (4) are inserted from the lateral direction between the side edges of the stacked sheets (8), that is, between the upper and lower surfaces to be welded. As shown in FIGS. 2 and 3, the hot air nozzle (3) rotates the lever (33) approximately 90 to the rear side of the apparatus so that the outlet port is directed to the rear side of the apparatus and is positioned between the upper and lower welding surfaces. Can be inserted. Further, the hot metal (4) can be inserted between the upper and lower surfaces to be welded by turning the lever (43) approximately 90 times forward.

  In the above welding apparatus, when the hot air nozzle (3) is inserted between the upper and lower surfaces to be welded by operating the lever (33), the hot air generator (electric heater and blower fan) built in the rotating shaft (31) Operates to blow hot air between the upper and lower surfaces to be welded. On the other hand, when the hot metal (4) heated to the set temperature and controlled in temperature is inserted between the upper and lower surfaces to be welded by operating the lever (43), the motor of the apparatus main body (1) is operated, and the pressure roller (6) rotates. Thereby, a welding apparatus welds to-be-welded surfaces, moving to one direction at a constant speed along the side edge part of the piled sheet | seat (8).

  That is, in the present invention, the hot air nozzle (3) heats each welding surface and the resin around it with hot air, and the hot metal (4) slides on the surface of each heated welding surface while sliding. The surface is roughened and further heated and melted. At that time, the hot metal (4) slides on the surface to be welded, thereby destroying the inorganic substance existing on the surface to be welded, the low molecular weight polyolefin coating layer, etc., and exposing the resin of the base material to the surface. . The pressure roller (6) applies a load to the welded portion from above the sheet to bring the melted welded surfaces into close contact with each other. As a result, a belt-like welded portion is formed, and the two sheets (8) are joined.

  When the surface to be welded and its surroundings are heated by the hot air nozzle (3), the temperature of the hot air is usually 20 to 700 ° C, preferably 200 to 700 ° C, and the amount of hot air is usually 10 to 600 l / min. Preferably, it is 200 to 600 l / min. On the other hand, when the surface to be welded is heated and melted by the hot metal (4), the temperature of the hot metal (4) is usually 20 to 600 ° C, preferably 100 to 500 ° C.

  As described above, in the present invention, before the hot metal (4) is brought into sliding contact with the welding surfaces of the two sheets (8), the welding surfaces are preheated with the hot air nozzle (3), The heat shock can be reduced by reducing the temperature difference between the resin on the surface to be welded when the hot metal (4) is brought into contact with the resin around it. As a result, it is possible to prevent a decrease in breaking strength after welding at the boundary portion between the welded portion and the non-welded portion, and the two sheets (8) can be securely and more firmly welded.

  Furthermore, in the present invention, when a file plate is arranged between the hot air nozzle (3) and the hot metal (4), each welding surface softened by the hot air can be more reliably roughened. When contacting 4), the inorganic substance and the low molecular weight polyolefin can be dispersed in the matrix resin, and the matrix resin can be exposed on the surface. Therefore, the side edge portions can be welded and integrated more firmly. In the above embodiment, the method of moving and welding the welding device to the stationary sheet has been described, but in the present invention, the welding device may be moved relative to the sheet, For example, it is also possible to fix the welding apparatus and move and weld the sheets to be welded.

Example 1:
In accordance with the welding method of the present invention, two polypropylene hood cloth sheets were welded, then a fracture test was performed to peel off the welded portion, the shear strength of the welded portion was measured, and the fracture mode of the welded portion was observed. The hood cloth sheet used as a sample has a width of 30 cm, a length of 60 cm, a thickness of 0.61 mm, a weight of 500 g / m ² , a longitudinal tensile strength of 43 N / cm, and a lateral tensile strength of 43 N / cm. The surface was coated with a saturated hydrocarbon wax with an average thickness of 3 μm. As a welding apparatus, an apparatus having a basic structure shown in FIGS. 2 and 3 was used. A file plate was placed between the hot air nozzle and the hot metal. The hot-spring was made of brass whose side surface shape was formed into an airfoil, and had a width of 22 mm, a length of 42 mm, and a maximum thickness of 6 mm. At the time of welding, the above-mentioned two samples were welded by overlapping 22 mm in the length direction. Conditions at the time of welding are as shown in Table 1. In the destructive test, the above-mentioned welded sample is loaded into a precision universal testing machine (manufactured by Shimadzu Corporation, trade name: Autograph AGS-500D), the distance between chucks is set to 150 mm, and the tensile speed is set to 200 mm / min. Went. As a result, as shown in Table 1, the shear strength was 1300 N / 30 mm, and an original fabric fracture was observed at the fracture portion.

Example 2:
A hood cloth sheet similar to that of Example 1 was welded under the same conditions as in Example 1 except that the surface of the sample hood cloth sheet was not coated with wax, and a destructive test was performed. As a result, as shown in Table 1, the shear strength was 1300 N / 30 mm as in Example 1, and the original fabric fracture was observed in the fractured portion as in Example 1.

Comparative Example 1:
After welding a polypropylene hood cloth sheet similar to that in Example 1 by a conventional hot metal welding method, the fracture test is performed in the same manner as in Example 1 to measure the shear strength of the welded portion, and the welded portion is destroyed. The morphology was observed. The welding apparatus used was a commercially available automatic welding machine “Uniplan-Wedge type” (trade name) manufactured by Leister Proscess Technologies. Such a welding apparatus is an apparatus having substantially the same structure as that in the first embodiment except that the hot air nozzle is not provided. The conditions during welding were as shown in Table 1. As shown in Table 1, the result of the fracture test after welding was a shear strength of 700 N / 30 mm, and an original fabric fracture was observed at the fractured portion.

Comparative Example 2:
A hood cloth sheet similar to that of Example 1 was welded under the same conditions as in Comparative Example 1 except that the surface of the sample hood cloth sheet was not coated with wax, and a destructive test was performed. As a result, as shown in Table 1, the shear strength was 700 N / 30 mm as in Comparative Example 1, and the original fabric fracture was observed in the fractured portion as in Comparative Example 1.

Reference example 1:
After welding a polypropylene hood cloth sheet similar to that of Example 1 using a conventional hot air welding method, the fracture test is performed in the same manner as in Example 1 to measure the shear strength of the welded portion, and the fracture mode of the welded portion is determined. Was observed. The welding apparatus used was a commercially available automatic welding machine “Uniplan” (trade name) manufactured by Leister Proscess Technologies. Such a welding apparatus is an apparatus provided with a hot air nozzle and a pressure roller. The conditions during welding were as shown in Table 1. As shown in Table 1, the results of the fracture test after welding were as follows.

  According to the above results, it can be understood from the comparison of the fracture forms of the welded portion that the base material of the resin sheet can be welded to each other by the hot metal method in the sheet coated with wax. However, from the comparison of shear strength, when welding is performed only with hot iron, the shear strength is low, which is considered to be due to heat shock. On the other hand, according to the welding method of the present invention, the heat shock when the hot metal is brought into contact can be reduced by heating the welded part and its surroundings with hot air before the hot metal is brought into contact. Strength can be remarkably increased.

It is the top view and longitudinal cross-sectional view which show the concept of the welding method of the sheet | seat which concerns on this invention, and arrangement | positioning of the main members of a welding apparatus. It is a perspective view which shows the external shape of the welding apparatus of the sheet | seat which concerns on this invention. It is a top view which shows the external shape of the welding apparatus of the sheet | seat which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1: Device main body 13: Support block 14: Support block 2: Guide device 3: Hot air nozzle 31: Rotating shaft 33: Lever 4: Hot water 41: Rotating shaft 42: Arm 43: Lever 5: Guide roller 6: Pressure roller 7: Grip 8: Seat 9: Welded part

Claims (6)

  The welding surfaces to be welded of the two sheets made of thermoplastic resin are overlapped, the hot metal is slid in contact with the welding surfaces facing each other, the welding surfaces are melted, and the welding surfaces are welded by pressure contact. A method for welding sheets, wherein the surfaces are welded to each other, and each of the welding surfaces is preheated when the hot metal is brought into sliding contact with each other.   The welding method according to claim 1, wherein each welding surface is preheated by blowing hot air.   The welding method according to claim 1 or 2, wherein the sheet is a sheet on which an inorganic substance or a low molecular weight polyolefin is present.   An apparatus for welding two sheets made of thermoplastic resin while moving in one direction, and being inserted between the welded surfaces to be welded of the overlapped sheets and slidably in contact with the welded surfaces; A pressure roller that is arranged on the rear side of the apparatus moving direction with respect to the hot metal and presses the welding surface melted by the hot metal from above the sheet, and the apparatus moving direction with respect to the hot metal The sheet welding apparatus is provided with a hot air nozzle that is inserted between the welded surfaces of the stacked sheets and that blows hot air on the welded surfaces on the front side of the sheet.   The welding apparatus according to claim 4, wherein a filing plate is disposed between the hot air nozzle and the hot metal between the welded surfaces of the stacked sheets and roughens the welded surfaces.   The welding apparatus according to claim 4 or 5, wherein the sheet is a sheet on which an inorganic substance or a low molecular weight polyolefin is present.