POLYMERIC REDUCTION MATERIAL FOR GAS PRESSURE WELDING AND GAS PRESSURE WELDING METHOD

Abstract

A polymeric reduction material for gas pressure welding A1 includes a cap body 1 that is made of a thermoplastic resin, can be externally fitted to a pressure welded-side end portion of the material to be pressure welded, and is a bottomed cylindrical body, an air blocking ring 2 that is integrally provided at a bottom portion 12 of the cap body 1, is made of a thermosetting resin, and has a required diameter, a reduction sheet 3 that sandwiches the air blocking ring 2 between the bottom portion 12 of the cap body 1 and the reduction sheet 3, has a diameter equal to or larger than that of the air blocking ring 2, and is made of a thermoplastic resin. A reduction ring 5 made of a polyimide resin is wound around an outer peripheral portion of a stacked portion of the reduction sheet.

Claims

1. A polymeric reduction material for gas pressure welding comprising: an air blocking ring that can be arranged between pressure welded surfaces of materials to be pressure welded, is made of a thermosetting resin, and has a required diameter; a reduction sheet that is stacked so as to be positioned on one side of the air blocking ring or stacked so as to sandwich the air blocking ring from both front and rear sides, and has a diameter equal to or larger than that of the air blocking ring and is made of a thermoplastic resin; and a string-shaped or band-shaped reduction ring that is wound apart from the air blocking ring around an outer peripheral portion on the same plane as a stacked portion of the air blocking ring and the reduction sheet and is made of a thermosetting resin.

2. The polymeric reduction material for gas pressure welding according to claim 1, further comprising a cap body that is made of a thermoplastic resin, can be externally fitted to a pressure welded-side end portion of the material to be pressure welded, and is a bottomed cylindrical body, wherein the air blocking ring is integrally provided at a bottom portion of the cap body.

3. The polymeric reduction material for gas pressure welding according to claim 1, wherein the air blocking ring is formed in a spiral shape in which both end portions are overlapped on inner and outer sides by a predetermined length.

4. The polymeric reduction material for gas pressure welding according to claim 1, wherein the air blocking ring is made of a polyimide resin and the reduction sheet is made of a polystyrene resin.

5. The polymeric reduction material for gas pressure welding according to claim 1, wherein the reduction sheet has a total thickness of 0.17 to 2.55 mm.

6. A gas pressure welding method comprising: a step of arranging a polymeric reduction material for gas pressure welding by stacking, between pressure welded surfaces of materials to be pressure welded, an air blocking ring that is made of a thermosetting resin and has a required diameter and a reduction sheet that is positioned on one side of the air blocking ring or sandwiches the air blocking ring from both front and rear sides, and has a diameter equal to or larger than that of the air blocking ring and is made of a thermoplastic resin, and by winding a string-shaped or band-shaped reduction ring made of a thermosetting resin apart from the air blocking ring around an outer peripheral portion on the same plane of a stacked portion of the air blocking ring and the reduction sheet; and a step of heating a pressure welded part of the materials to be pressure welded by thermal power of a required gas while applying a predetermined pressure to each of the materials to be pressure welded in a direction in which pressure welded surfaces of the materials to be pressure welded are brought into close contact with each other.

7. The gas pressure welding method according to claim 6, wherein the air blocking ring is formed in a spiral shape in which both end portions are overlapped on inner and outer sides by a predetermined length.

8. The gas pressure welding method according to claim 6, wherein the air blocking ring is made of a polyimide resin and the reduction sheet is made of a polystyrene resin.

9. The gas pressure welding method according to claim 6, wherein the gas is propane gas and heating is performed with a standard flame from an initial stage of heating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 is a perspective view showing a first embodiment of a polymeric reduction material for gas pressure welding according to the present invention.

[0052] FIG. 2 is a longitudinal sectional view of the polymeric reduction material for gas pressure welding shown in FIG. 1.

[0053] FIG. 3 is an explanatory diagram showing a step of gas pressure welding using the polymeric reduction material for gas pressure welding shown in FIG. 1.

[0054] FIG. 4 is an explanatory diagram in which gas pressure welding of deformed reinforcing bars has been performed by a gas pressure welding method according to the present invention and each test piece has been notched and fractured to verify a flat fracture surface.

[0055] FIG. 5 is an explanatory diagram in which gas pressure welding of deformed reinforcing bars has been performed by a gas pressure welding method using an air blocking ring made of a polyimide resin as an antioxidant means and each test piece has been notched and fractured to verify a flat fracture surface.

[0056] FIG. 6 is a perspective view showing a second embodiment of a polymeric reduction material for gas pressure welding according to the present invention.

[0057] FIG. 7 is a longitudinal sectional view of the polymeric reduction material for gas pressure welding shown in FIG. 6.

DESCRIPTION OF THE EMBODIMENTS

[0058] Embodiments of the present invention will be described in more detail with reference to FIG. 1 to FIG. 7.

[0059] A polymeric reduction material for gas pressure welding A1 according to the present invention suppresses the formation of an oxide film on a pressure welded surface by performing a pressure welding operation while being sandwiched between pressure welded surfaces of materials to be pressure welded such as deformed reinforcing bars.

[0060] Reference is made to FIG. 1 and FIG. 2.

[0061] The polymeric reduction material for gas pressure welding A1 has a cap body 1. The cap body 1 is made of a sheet made of a polystyrene resin, which is a thermoplastic resin, and is composed of a cylindrical portion 11 and a bottom portion 12 which is a circular reduction sheet closing a proximal end portion of the cylindrical portion 11. A tip portion of the cylindrical portion 11 is provided with a flange 13 to reinforce the cylindrical portion 11 so as to be less likely to deform over the entire circumference.

[0062] Further, an air blocking ring 2 made of a polyimide resin, which is a thermosetting resin, is arranged on an outer surface of the bottom portion 12, and a circular reduction sheet 3 having a diameter slightly larger than that of the air blocking ring 2 and made of a polystyrene resin is welded with the air blocking ring 2 sandwiched between the bottom portion 12 and the reduction sheet 3.

[0063] The reduction sheet 3 is thermally deformed so as to be substantially along the outline of the air blocking ring 2 and cooperates with the bottom portion 12 to enclose the air blocking ring 2 (see the enlarged view of FIG. 2). A reduction ring 5 made of a polyimide resin is wound around an outer peripheral portion of a stacked portion of the air blocking ring 2, the bottom portion 12, and the reduction sheet 3.

[0064] It is noted that the air blocking ring 2 is circular in the present embodiment, but is not limited thereto, and for example, a ring-shaped (annular) one having a so-called irregular shape such as a polygon, an ellipse, a star, and a gear can be employed.

[0065] Furthermore, the shape of the reduction sheet 3 is also not limited to the circular shape, and various other shapes can be employed as long as a sufficient space can be secured inside the air blocking ring 2. The “diameter” in the terms “the same diameter” and “large diameter” in the present invention is used to mean not only the distance across a circle but also the distance across an ellipse, various polygons, etc., in addition to the circle.

[0066] The inner diameter of the cylindrical portion 11 of the cap body 1 is formed to have an appropriate size so as not to have looseness, difficulty in insertion, etc., in accordance with the outer diameter of the deformed reinforcing bar or the like to be the material to be pressure welded. When the cap body 1 is fitted into the material to be pressure welded, the air blocking ring 2 fits in the center of the pressure welded surface of the material to be pressure welded and the bottom portion 12 abuts against the pressure welded surface.

[0067] The thickness of the air blocking ring 2 is set to 2.25 mm in the present embodiment but can be adjusted as appropriate. The thickness of the bottom portion 12 and the reduction sheet 3 is 0.17 mm each and 0.34 mm when being stacked, in the present embodiment. When the total thickness of the reduction sheet is set in a range of 0.17 to 2.55 mm, a predetermined fracture performance can be obtained. However, it is more preferable to be set in a range of 0.34 to 1.36 mm.

[0068] The heat resistance performance of the air blocking ring 2 made of a polyimide resin is 220° C., and reaches 400° C. if it is for a short time. The air blocking ring 2 is carbonized at 800° C., does not raise a flame during the burning, has a self-extinguishing property, and does not generate toxic gas. Thus, it is also excellent in terms of safety. The heat resistance performance of the reduction sheet 3 made of a polystyrene resin is 70 to 90° C. and the melting point is 100° C. The reduction sheet 3 is decomposed at 280° C. or higher and does not generate toxic gas, so that the safety is high.

[0069] The material of the cap body 1 of the polymeric reduction material for gas pressure welding A1 is not limited to the polystyrene resin, and various resins can be appropriately employed as long as it is a thermoplastic resin such as polyethylene (PE) or polypropylene (PP). The material of the air blocking ring 2 is not limited to the polyimide resin, and various resins can be appropriately employed as long as it is a thermosetting resin such as silicon.

Operation of Polymeric Reduction Material for Gas Pressure Welding A1

[0070] Referring to FIG. 3, the use and operation of the gas pressure welding method according to the present invention and the polymeric reduction material for gas pressure welding A1 according to the present embodiment will be described. The heating gas used in the gas pressure welding method is propane gas.

[0071] Propane gas has advantages that, similar to natural gas, the thermal power is weak as compared with acetylene gas but the environmental load (CO.sub.2 emissions etc.) is small, it is easily available even in an isolated island or remoted area, and it is easy to handle due to its low risk.

[0072] In the present embodiment, the pressure welding of deformed reinforcing bars 4 will be described as an example. However, the polymeric reduction material for gas pressure welding A1, together with a polymeric reduction material for gas pressure welding A2 described later, can also be used for pressure welding (joining) of various rails, thick pipes, etc., in addition to such bar steels.

[0073] [1] Two deformed reinforcing bars 4 to be pressure welded are prepared. A pressure welded surface 40 of each deformed reinforcing bar 4 is polished and finished. The cylindrical portion 11 of the polymeric reduction material for gas pressure welding A1 is fitted into a tip portion of one deformed reinforcing bar 4 and is pushed into the deep part. As a result, the air blocking ring 2 fits in the center of the pressure welded surface 40 of the deformed reinforcing bar 4 and the bottom portion 12 abuts against the tip surface (see FIG. 3(a) and FIG. 3(b)).

[0074] [2] Next, both the deformed reinforcing bars 4 are held on the same central axis by a hydraulic pressure welding holder (not shown) and are brought into contact with each other in such a manner as to sandwich the bottom portion 12 of the cap body 1 and the reduction sheet 3 of the polymeric reduction material for gas pressure welding A1 together with the air blocking ring 2 enclosed therein between the pressure welded surface 40 of the deformed reinforcing bar 4 attached with the polymeric reduction material for gas pressure welding A1 and the pressure welded surface 40 of the other deformed reinforcing bar 4 (see FIG. 3(b)).

[0075] [3] A gas burner 6 is positioned at a specified position around the axis of a pressure welded part 400 of both the deformed reinforcing bars 4, and the deformed reinforcing bars 4 are pressed against each other at the pressure welded part with a specified pressure by the pressure welding holder. Propane gas is then used as the heating gas, and the pressure welded part is heated by a standard flame (neutral flame or oxidizing flame) from the initial stage of heating. At this time, the reduction ring 5 is also heated together.

[0076] [4] As a result, the pressure welded part 400 of the deformed reinforcing bars 4 is burned red to be a red-hot iron state, the pressure welded part 400 is gradually deformed by pressure to increase in diameter, atoms of the pressure welded surfaces 40 are diffused across the pressure welded surfaces 40 to be metal-bonded, and the pressure welded surfaces 40 are integrated without being melted (see FIG. 3(c)). By this time, the pressure of the pressure welded surfaces 40 is weakened, so that the pressure welding holder is further manually operated to adjust the pressure of the pressure welded surfaces 40 to increase.

[0077] Between the pressure welded surfaces 40, the bottom portion 12 and the reduction sheet 3 made of a polystyrene resin, which is a thermoplastic resin, become high in temperature, are melted, burned, and vaporized in a very short time to rapidly increase in volume in a slight gap (reference sign omitted) inside the air blocking ring 2 made of a thermosetting resin and not yet melted. As a result, the pressure of the air in the gap inside the air blocking ring 2 is increased.

[0078] At the time of pressure welding of the deformed reinforcing bars 4, the pressure welded part 400 can be substantially closed along outer peripheries of the pressure welded surfaces 4 of the deformed reinforcing bars 4 in a state where the reduction ring 5 is heated and not melted. As a result, in the slight gap sandwiched between the pressure welded surfaces 40 of the deformed reinforcing bars 4 inside the air blocking ring 2, the bottom portion 12 and the reduction sheet 3 are melted and burned in a very short time.

[0079] The bottom portion 12 and the reduction sheet 3 are vaporized by burning to rapidly increase in volume, whereby the air in the gap inside the air blocking ring 2 tries to be pushed out but is stopped by the reduction ring 5, and the internal pressure becomes extremely high. The pushing out of the air to the outside when the air blocking ring 2 is carbonized is instantaneously and explosively performed together with carbonation and fracture of the reduction ring 5. Oxygen in the air is combined with carbon of the polymer to become carbon dioxide gas, and the effect of suppressing oxidation around the pressure welded part 400 is further enhanced.

[0080] Heat is transferred from the pressure welded part 400 to an internal direction, but a temperature difference occurs between the center portion and the surface portion. For example, when only a thermoplastic resin having a low melting point is used as the reduction sheet, the burning of the reduction sheet disappears at a place near the surface portion by the time when the temperature of the center portion of the deformed reinforcing bar 4 rises, and the reduction sheet does not serve as oxidation suppression.

[0081] Accordingly, a polymer resin, such as polyimide, having a high heat resistance and a high antioxidant effect is preferred in a portion near the outer peripheral portion of the surface of the deformed reinforcing bar 4. However, when only a high heat-resistant resin is used, an incompletely burned soot-like residue remains in the center portion of the pressure welded surface 40 without being discharged to the outside, and this causes a reduction in strength (in particular, fatigue strength) of the pressure welded part 400.

[0082] Further, while the air blocking ring 2 is not melted yet, the intrusion of the air into the gap inside the air blocking ring 2 is blocked. Combined therewith, the formation of an oxide film on the pressure welded surface 40 can be suppressed.

[0083] As just described, according to the polymeric reduction material for gas pressure welding A1 of the present invention, in the case of using natural gas, propane gas, hydrogen gas, or the like, which is inferior in thermal power to acetylene gas, in performing gas pressure welding of the materials to be pressure welded such as the deformed reinforcing bars 4, the formation of residue such as an oxide film and a metal residue on the pressure welded surface 40 is suppressed even if heating is performed with a standard flame from the initial stage of heating so as to obtain sufficient thermal power, and pressure welding with sufficient strength can be performed.

Pressure Welding Fracture Test 1

[0084] Next, a pressure welding fracture test 1 will be described with reference to FIG. 4. In the pressure welding fracture test 1, gas pressure welding of the deformed reinforcing bars 4 was performed by the gas pressure welding method using the polymeric reduction material for gas pressure welding A1 according to the present invention shown in FIG. 1 and FIG. 2, and the deformed reinforcing bars 4 were notched and fractured to prepare test pieces T1 to T5, and a flat fracture surface 7 generated on a fracture surface of each test piece was verified.

[0085] In each of the pressure welding fracture tests below, the size and position of the flat fracture surface generated on the fracture surface are the requirements for verification. The flat fracture surface is a fracture surface on which there are many specific oxides, has an appearance like a smoothed fracture surface, and is one of internal defects of a solid metal material.

[0086] Because the cause of occurrence of the flat fracture surface is complicated, it is not easy to identify the cause. However, the oxide residue on the flat fracture surface or the pressure welded surface may occur, for example, even if there is a slight defect that cannot be called an error in individual pressure welding operations.

[0087] As just described, when a flat fracture surface is generated for some reason, a large oxide or a dense group of oxides is formed on the pressure welded surface of the material to be pressure welded, a region in which metal bonding is not formed on the pressure welded surface increases, and the fatigue strength as the pressure welded material is reduced. In particular, when a large number of flat fracture surfaces are generated in the central portion of the material, it is said that this is especially conspicuous.

[0088] In the pressure welding fracture test 1 shown in FIG. 4, the flat fracture surface 7 was generated on the fracture surface of each of the test pieces T1, T2, T3 except the test pieces T4, T5. In the following description, the expressions of the front, the rear, the top, and the bottom are based on the directions shown in FIG. 4. That is, they are the front (X1), the rear (X2), the top (Y1), and the bottom (Y2), and the same applies to FIG. 5 showing a pressure welding fracture test 2 described later.

[0089] First, the flat fracture surface 7 generated on the test piece T1 in which a cut portion C has a half-moon shape was observed at a rear edge portion from a lower portion to partially an upper portion of the fracture surface excluding the cut portion C and was not observed in the vicinity of the central portion of the material. The flat fracture surface 7 generated on the test piece 2 in which the cut portion C similarly has a half-moon shape was observed at the rear edge portion from substantially the entire circumference of the upper portion of the fracture surface to partially an upper portion of the lower portion and was not observed in the vicinity of the central portion of the material.

[0090] Furthermore, the flat fracture surface 7 generated on the test piece T3 in which the cut portion C has substantially a half-moon shape and a part thereof entered the lower portion of the fracture surface was observed in the vicinity of the rear edge portion of a boundary portion between the upper and lower portions of the fracture surface and was not observed in the vicinity of the central portion of the material. As just described, in these test pieces T1, T2, T3, there was no flat fracture surface 7 that covered the vicinity of the central portion of the material, and the flat fracture surfaces 7 were all positioned near the outer peripheral edge portion of the fracture surface.

[0091] The test piece T4 was tested with the cut portion C in a half-moon shape, and the test piece T5 was tested with the cut portion C occupying about three quarters in the circumferential direction of the material by making a cut from two directions, but no flat fracture surface 7 was observed on the fracture surface.

Discussion

[0092] For test pieces T1 to T5, considering the point that the flat fracture surface 7 was not observed on the fracture surface (test pieces T4, T5) or was not observed in the central portion of the fracture surface (in the vicinity of the central portion of a cross section of the pressure welded part) (test pieces T1, T2, T3), it can be assumed that the strength of the pressure welded part as the pressure welded material can be sufficiently secured.

[0093] For the confirmation, although not listed as test data, other five test pieces were prepared in addition to T1 to T5 in the same condition (the pressure welding method according to the present invention) as the pressure welding fracture test 1 and were each subjected to a tensile fracture test. As a result, all of the five pieces underwent a fracture of the base material, and a sufficient strength of the pressure welded part was observed although the test was a simulated one which did not verify the flat fracture surface.

Pressure Welding Fracture Test 2

[0094] In this pressure welding fracture test, in order to confirm that the combination of the air blocking ring 2, the reduction sheet 3, and the reduction ring 5 of the polymeric reduction material for gas pressure welding A1 according to the present invention has an advantage in that the flat fracture surface generated on the pressure welded surface is less likely to occur in the central portion of the fracture surface, the pressure welding fracture test 1 and a pressure welding fracture test 2 shown in FIG. 5 were compared.

[0095] In the pressure welding fracture test 2, only an air blocking ring (not shown) having the same structure as the above air blocking ring 2 was sandwiched between pressure welded surfaces 40 of deformed reinforcing bars 4, and the deformed reinforcing bars 4 were subjected to gas pressure welding, notched and fractured to prepare test pieces T6 to T10, and a flat fracture surface 7 on a fracture surface of each test piece was verified.

[0096] In the pressure welding fracture test 2 shown in FIG. 5, the flat fracture surface 7 was generated on all fracture surfaces of the test pieces T6 to T10 in which cut portions C have a half-moon shape. First, the flat fracture surface 7 generated on the test piece T6 was observed at a place from a lower edge portion to the vicinity of the central portion of the fracture surface excluding the cut portion C. The flat fracture surface 7 generated on the test piece T7 was observed at a place from the central portion to an upper edge portion of the fracture surface.

[0097] The flat fracture surface 7 generated on the test piece T8 was observed at a place from the central portion to the lower edge portion of the lower portion of the fracture surface. The flat fracture surface 7 generated on the test piece T9 was observed along a diametrical direction of an upper portion and the lower portion of the fracture surface. Further, the flat fracture surface 7 generated on the test piece T10 was observed from the central portion to a peripheral edge portion of the upper portion of the fracture surface.

Discussion

[0098] The flat fracture surfaces 7 of the test pieces T6 to T10 are all such that a part thereof was positioned in or near the central portion of the fracture surface. Therefore, as described above, considering the point that the fatigue strength is said to be reduced when a large number of flat fracture surfaces are generated in the vicinity of the central portion of the fracture surface of the material, it is difficult to assume that the strength of the pressure welded part as the pressure welded material is sufficiently secured.

[0099] For confirmation, although not listed as test data, five other test pieces were prepared in addition to T6 to T10 in the same condition as the pressure welding fracture test 2 and were each subjected to a tensile fracture test. As a result, only one piece underwent a fracture of the base material, and the others underwent a fracture of the pressure welded surface. That is, although the test was a simulated one which did not verify a flat fracture surface, it can be assumed that the strength of the pressure welded part is not sufficient in the pressure welding performed with only the air blocking ring sandwiched.

[0100] As just described, in each test piece obtained by the gas pressure welding method using the polymeric reduction material for gas pressure welding A1 according to the present invention, the effect of suppressing the generation of the flat fracture surface in the central portion of the fracture surface has been seen as compared with the test pieces obtained by using only the air blocking ring as the antioxidant means. In this regard, it has been clarified that there is an advantage in combining the air blocking ring 2, the reduction sheet 3, and the reduction ring 5, but not the air blocking ring alone made of a polyimide resin.

[0101] Reference is made to FIG. 6 and FIG. 7.

[0102] A polymeric reduction material for gas pressure welding A2 according to the present invention has a cap body 1. The cap body 1 is made of a sheet made of a polystyrene resin. The cap body 1 is composed of a cylindrical portion 11 and a circular bottom portion 12 closing a proximal end portion of the cylindrical portion 11. A tip portion of the cylindrical portion 11 is provided with a reinforcing flange 13 over the entire circumference.

[0103] The cap body 1 is such that the bottom portion 12 and a reduction sheet 3 are welded with an air blocking ring 2a sandwiched therebetween to be thermally deformed and the air blocking ring 2a is enclosed (see the enlarged view of FIG. 7). The air blocking ring 2a is made of a polyimide resin and has a spiral shape in which both end portions are overlapped on inner and outer sides by a predetermined length. A reduction ring 5 made of a polyimide resin is wound around an outer peripheral portion of a stacked portion of the air blocking ring 2a, the bottom portion 12 serving as the reduction sheet, and the reduction sheet 3.

[0104] The inner diameter of the cylindrical portion 11 of the cap body 1 is formed to have an appropriate size so as not to have looseness, difficulty in insertion, etc., in accordance with the outer diameter of the deformed reinforcing bar or the like to be the material to be pressure welded. When the cap body 1 is fitted into the material to be pressure welded, the air blocking ring 2a fits in the center of a pressure welded surface 40 of the material to be pressure welded and the bottom portion 12 abuts against the pressure welded surface 40.

[0105] The thickness of the air blocking ring 2a and the thickness of the bottom portion 12 and the reduction sheet 3 are the same as those of the air blocking ring 2, the bottom portion 12, and the reduction sheet 3 of the above polymeric reduction material for gas pressure welding A1. The heat resistance performance and characteristics of the air blocking ring 2a and the heat resistance performance and characteristics of the bottom portion 12 and the reduction sheet 3 are also the same as those of the air blocking ring 2, and the bottom portion 12 and the reduction sheet 3.

[0106] The material of the cap body 1 of the polymeric reduction material for gas pressure welding A2 is not limited to the polystyrene resin, and various resins can be appropriately employed as long as it is a thermoplastic resin such as polyethylene (PE) or polypropylene (PP). The material of the air blocking ring 2a is not limited to the polyimide resin, and various resins can be appropriately employed as long as it is a thermosetting resin such as silicon.

[0107] The polymeric reduction material for gas pressure welding A2 has almost the same structure as the polymeric reduction material for gas pressure welding A1 with the only difference between the air blocking ring 2a and the air blocking ring 2. Therefore, regarding the use and operation of the polymeric reduction material for gas pressure welding A2, the description of the operation of the polymeric reduction material for gas pressure welding A1 is incorporated for the portion in common with the polymeric reduction material for gas pressure welding A1, and only differences will be described.

[0108] The polymeric reduction material for gas pressure welding A2 has the air blocking ring 2a having a spiral shape in which both end portions are overlapped on the inner and outer sides by a predetermined length, so that the heated and pressed air blocking ring 2a is crushed and expanded, and in particular, “the portions where both end portions are overlapped on inner and outer sides by a predetermined length” are crimped to each other and a ventilation portion is closed at an early stage. Furthermore, at least the crimped portion has a wide width and a high density.

[0109] Therefore, it can be assumed that, in a situation where the air blocking ring 2a is sandwiched between the pressure welded surfaces 40 of the deformed reinforcing bars 4 at a specified pressure, the strength increases as compared with the air blocking ring 2 of the polymeric reduction material for gas pressure welding A1 and the timing at which the air blocking ring 2a is heated and carbonized to be fractured is slightly delayed. Accordingly, the pressure of the air blown out to the outside is further increased, and the effect of suppressing the oxidation around the pressure welded part 400 is further enhanced.

[0110] The terms and expressions used in the description and the claims are only for the purpose of description and are not limiting, and there is no intention to exclude terms and expressions equivalent to the features and a part thereof described in the description and the claims. It is obvious that various modifications can be made within the scope of the technical idea of the present invention.

TABLE-US-00001 DESCRIPTION OF REFERENCE NUMERALS A1 Polymeric reduction material for gas pressure welding 1 Cap body 11 Cylindrical portion 12 Bottom portion 13 Flange 2 Air blocking ring 3 Reduction sheet 4 Deformed reinforcing bar 40 Pressure welded surface 400 Pressure welded part 5 Reduction ring 6 Gas burner A2 Polymeric reduction material for gas pressure welding 2a Air blocking ring T1 to T5 Test piece T6 to T10 Test piece 7 Flat fracture surface C Cut portion