KR102364300B1 - Low strain welding method and apparatus - Google Patents

Abstract

The invention is intended to move along a path of travel relative to the two metallic elements 18 , 19 to be assembled,
a welding torch (3) for forming a welding bead (22) between the two metallic elements;
a cooling applicator (8), arranged behind the welding torch with respect to the travel path, for cooling the weld bead by contacting the outer surface of the weld bead, comprising a pad of mineral fiber;
A low strain welding device comprising a movable support carriage (2), designed for dispensing cooling liquid to the cooling applicator (8), and having a dispensing head (15) that wets a pad of mineral fibers with the cooling liquid.

Description

Low strain welding method and apparatus

The present invention relates to a method and apparatus for low strain welding, and more particularly, to assembling a metal sheet using a fluid-tight weld.

FR-A-2701415 discloses an electric arc welding machine for fillet welding two metal sheets of a membrane of a fluid sealed tank. However, if the thickness of the metal sheet used is reduced, the thermal deformation effect of the sheet increases, making it difficult to obtain high-quality assembly results, particularly in terms of mechanical integrity and fluidity.

One idea inherent in the present invention is to propose a method and apparatus capable of reducing the effect of thermal deformation of a sheet during welding. One idea inherent in the present invention is to propose a method and apparatus suitable for use with various walls of a fluid sealed tank, regardless of the orientation of the walls.

To this end, the present invention

- generating a weld bead for assembling two metallic elements, the weld bead being created by moving a welding torch along the path of the weld bead; and

- cooling the weld bead by passing a cooling applicator directly behind the welding torch over the outer surface of the weld bead, wherein the cooling applicator consists of a pad of mineral fiber moistened with a cooling liquid.

The use of a cooling applicator made of such mineral fibers retains the cooling liquid during capillary action, so that it is possible to apply the cooling liquid locally to a desired location, in particular to the weld bead and/or the area immediately adjacent thereto. The risk of build-up and/or uncontrolled flow of the coolant is thus greatly reduced compared to spraying the coolant directly on the element to be cooled, thereby reducing the risk of corrosion.

Also, since the position of the cooling liquid is controlled, the amount of the cooling liquid applied to the desired position can be controlled more easily and more precisely.

According to one embodiment, cooling liquid is supplied to the cooling applicator as it passes over the weld bead. Thus, continuous and relatively uniform operation of the cooling applicator can be obtained while welding is being performed.

The invention also comprises a movable support carriage intended to move along a path of travel with respect to the two metallic elements to be assembled, wherein the movable support carriage comprises:

- a welding torch for forming a welding bead between two metallic elements;

- a cooling applicator comprising a pad of mineral fiber, arranged behind the welding torch with respect to the path of travel, to cool the weld bead by contacting the outer surface of the weld bead;

- To provide a low strain welding apparatus having a dispensing head designed for dispensing a cooling liquid to a cooling applicator, the dispensing head for wetting a pad of mineral fiber with the cooling liquid.

According to some advantageous embodiments these welding methods and apparatus may have one or more of the following features.

Mineral fibers are selected for durability and heat resistance to high temperatures, preferably at least 1000°C. According to one embodiment, the mineral fiber is made of ceramic. Ceramics, particularly refractory ceramics, are heat-resistant materials and are well formed in the form of fibers.

Preferably the mineral fibers consist of ceramics containing predominantly silica together with other oxides, in particular alumina. These ceramics offer advantages in terms of chemical resistance, harmlessness, thermal stability and mechanical strength.

The cooling liquid may be selected from a variety of fluids, in particular water and liquid nitrogen. In particular, the boiling point, specific heat capacity and latent heat of evaporation at standard atmospheric pressure are the criteria for the selection of the coolant. Water is preferably selected because it has a very high latent heat, is non-toxic, and is readily available.

In order to obtain an effective and controlled contact between the coolant and the weld bead to be cooled, the interaction between the cooling applicator and the element to be assembled can be designed in a variety of ways. In one embodiment the cooling applicator slides over the outer surface of the weld bead.

In another embodiment the cooling applicator is configured to roll over the outer surface of the weld bead. To this end, the cooling applicator may have the form of a cylinder rolling over the outer surface of the weld bead, or the cooling applicator may have the form of a "tire" arranged around a cylindrical support which rolls over the outer surface of the weld bead.

Various techniques known for the welding torch can be envisioned. Preferably the welding torch is an electric arc welding torch, for example of the Tungsten Inert Gas (TIG) type.

The support carriage can be moved in a variety of different ways. According to one embodiment the welding device further comprises a chassis intended to be fixedly arranged with respect to the two metallic elements to be assembled, the support carriage being movably mounted on the chassis and guided along the path of travel by the chassis. A precise guide of the support carriage can thus be obtained.

According to an advantageous embodiment the welding device further comprises a screen, which is carried by the movable carriage and is arranged between the cooling applicator and the welding torch to protect the welding torch from splashing of the coolant. This feature significantly reduces the risk of the welding torch burning or its operation being disturbed, especially in the case of electric arc welding.

Advantageously, cooling liquid is supplied to the cooling applicator while the cooling applicator is passing over the weld bead.

According to this embodiment the welding apparatus further comprises a coolant supply pump connected to the delivery head for supplying a flow of coolant to the delivery head.

The flow of cooling liquid can be adjusted in a variety of ways. According to one embodiment the flow is set to a fixed value. The welding method can thus be carried out particularly simply.

According to an embodiment the welding apparatus further comprises a control unit configured to cooperate with the feed pump and to adjust the flow of the coolant according to one or more parameters, for example, a progress rate of the support carriage, a current by the welding torch, etc. In order to take into account the amount of heat that needs to be removed particularly effectively by this feature, the flow of the cooling liquid is automatically controlled and changed to suit the actual conditions of the welding operation.

According to one embodiment the welding device further comprises a resilient suspension member for applying pressure to the cooling applicator in the direction of the metallic element to be assembled.

This welding method can be used in a variety of applications, especially when relatively thin sheet-like metals are used. One specific application relates to the fabrication of sealing membranes for fluid-tight tanks.

In one embodiment the two metallic elements are sheet-like metal sheets to be fillet welded or butt welded, the path of the weld bead along the edge of one of said sheet-like metal plates. Such fillet welds are particularly suitable for forming tight welds for the fabrication of sealing membranes of fluid-tight tanks.

In one embodiment the sheet-like metal sheet is corrugated or has a grid pattern. The sheet, which is a lattice plate, is particularly suitable for use over a wide temperature range, and because the lattice or corrugation of the sheet-like metal plate can serve as a thermal expansion joint. According to one embodiment the sheet-like metal sheet has a first series of corrugations protruding to be spaced apart and extending in a first direction of its plane and possibly protruding and spaced apart in a second direction perpendicular to the first direction of its plane. and a second series of pleats and a flat region disposed between the pleats.

This method can be used to weld a variety of metals. According to an embodiment, the sheet-like metal plate is made of an alloy selected from unalloyed and low-alloyed steels, stainless steels, nickel-steel alloys having a low coefficient of thermal expansion and manganese-steel alloys having a low coefficient of thermal expansion. In particular, sheet-like metal plates are made of Invar®, that is, an alloy of iron and nickel having a thermal expansion coefficient of typically 1.2×10 ^-6 K ^-1 to 2×10 ^-6 K ^-1 , a thermal expansion coefficient of typically about 9×10 ^-6 K ⁻ It may be made of a nickel-iron alloy of ¹ or an iron-alloy with a high manganese content, which has a thermal expansion coefficient of typically about 7×10 ^-6 K ⁻¹ .

BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be better understood and other objects, details, features and advantages will become more apparent from the following description of various embodiments of the present invention, given by way of example only and not limitation, with reference to the accompanying drawings.

1 is a schematic side view of a welding apparatus according to a first embodiment;
2 is a perspective view of a welding apparatus according to a second embodiment used for fillet welding of two sheet-like metal plates.
3 is a view similar to that of FIG. 2, showing the welding apparatus from another angle.
Fig. 4 is a schematic side view of a welding apparatus according to a third embodiment;
Fig. 5 is a schematic side view of a welding apparatus according to a fourth embodiment;
6 is a schematic perspective cross-sectional view of a cooling applicator that may be used in a welding apparatus;
7 is a perspective view of another cooling applicator that may be used in a welding apparatus;
Fig. 8 is an exploded view of the cooling applicator of Fig. 7;
9 is a photograph taken with an optical microscope of a cross-section of a weld bead obtained without using a cooling applicator (large grain size).
10 is a photomicrograph of a cross-section of a weld bead obtained using a cooling applicator (much smaller grain size).
11 is a schematic perspective view of a corrugated metal sheet that may be assembled using a welding apparatus;
12 is a schematic configuration diagram of a control system that can be used in a welding apparatus.

1 to 5 below, including a guide rail 1 disposed on a metallic element to be welded, and a support carriage 2 slidably mounted on the guide rail 1 and guided by the guide rail 1 . A welding apparatus will be described. The support carriage (2) has a welding torch (3) facing downward so that by moving the support carriage (2) along the guide rail (1) the welding bead follows a path substantially corresponding to the path of the guide rail (1). to be formed accordingly. Therefore, before forming such a weld, the operation of placing the metallic element such that the edge to be assembled is placed under the path of the guide rail 1 or equivalently placing the guide rail 1 above the position intended for the weld bead. need to perform This may in particular be a stationary guide rail attached to the roof of a building for example or a mobile chassis which can be detachably arranged on the element to be assembled. The latter case is disclosed, for example, in FR-A-2701415.

Further, the weld bead may be formed, for example, on a wall in various directions in a prismatic tank, ie, a horizontal bottom wall, a vertical or inclined side wall, a horizontal roof wall, and the like. In this description, "upper" and "lower" mean the direction away from the element to be assembled and vice versa towards the element to be assembled, regardless of the actual orientation of the element to be assembled with respect to the earth's gravitational field.

For operation the welding torch 3 requires a supply of various feeds, for example electricity, cooling water, inert gas, combustion gas, etc., depending on the welding technique employed, which are schematically indicated by numbers 5 and 6 in FIG. 1 . is indicated. This feeding may be made using a flexible conduit from a source independent of the support carriage 2 .

The direction of travel 7 of the support carriage 2 is indicated by arrows. Behind the welding torch 3 the support carriage 2 is provided with a cooling applicator 8 made of mineral fiber, which can be formed in various ways, in this case a wheel designed to roll in the direction of travel 7 over the welding bead ( It is composed like the "tire" of 9).

The cooling applicator 8 preferably consists of a fleece of heat-resistant fibers made of ceramic. For example, the fleece available from Morgan Crucible Company plc under the trade name Cerablanket™ (128 kg/m ³ ) may be used. These are ceramics containing mainly silica with the formula SiO ₂ , alumina with the formula Al ₂ O ₃ in high proportions and other very small amounts of oxides, in particular oxides of iron, titanium, calcium, magnesium, sodium and potassium. It can withstand temperatures up to 1260° C. and has an ultimate tensile strength equivalent to 90 kPa. In addition, mineral fibers may be used.

The wheel 9 is a hub 10, for example made of metal or plastic, mounted rotatably about a horizontal axis perpendicular to the direction of travel 7 at the lower end of the support arm 11 fixed to the support carriage 2 includes

The support arm 11 may be coupled to the support carriage 2 in various ways. The upper end of the support arm 11 in FIG. 1 is rotatably attached to the upper part of the body of the welding torch 3 , in particular for overcoming the relief of the element to be welded, for example over the corrugation of a sheet-like metal plate, the support carriage 2 Allows wheel 9 to go up and down relative to welding torch 3 as it progresses. The support arm 11 in FIG. 4 likewise consists of two parts rotatably articulated, the upper part of which is attached directly to the support carriage 2 , independently of the welding torch 3 . do.

2 and 3 the support arm 11 is rotatably connected via a shaft 14 to a longitudinal flange 12 fixed to a screen 13 attached to the support carriage 2 . The screen 13 is also schematically indicated in FIGS. 1 and 4 , which is a single plate arranged between the welding torch 3 and the wheel 9 under the support carriage and extending at right angles to the direction of travel 7 .

In operation, the wheel 9 rolls along the weld bead just formed by the welding torch 3 , where a cooling liquid, such as water, is applied to immediately cool the material, especially when they are thin sheet metal. It has the effect of reducing the thermal deformation of the element. To this end, the cooling applicator 8 needs to be kept fully wetted with cooling liquid during the welding operation.

The supply of cooling liquid to the cooling applicator 8 can be performed by a device independent of the support carriage 2 . However, it is more practical to provide a nozzle attached to the feed head 15 , for example the support carriage 2 , and oriented to spray the cooling applicator 8 continuously or intermittently with cooling liquid. The feed head 15 is connected by a flexible hose 16 to a water pump, which may be independent of a source, for example the support carriage 2 .

The feed head 15 can be arranged in a variety of ways. In FIG. 1 the feed head 15 is above the wheel 9 to wet the top of the wheel 9 . In FIG. 4 the feed head 15 is behind the wheel 9 to wet the rear of the wheel 9 . Still other configurations are possible, for example in front or next to the wheel. The feed head 15 is not shown in FIGS. 2 and 3 , but may be above the wheel 9 as in FIG. 1 .

In the embodiment shown in FIG. 5 the cooling applicator 8 slides behind the welding torch 3 in the direction of travel 7 over the welding bead. To this end, a cooling applicator 8 made of mineral fibers is configured as a thick cuboid or cylindrical pad, and is accommodated in a housing 35 having a tubular shape of a square cross section or a circular cross section. The feed head 15 is mounted on the housing 35 and oriented downwards to deliver coolant to the top surface 34 of the cooling applicator 8 . The cooling liquid diffuses over the thickness of the porous cooling applicator 8 to reach the surface 36 of the welded element. The housing 35 confines the splash and flow of the coolant, protecting the welding torch 3 from the splash by acting as if it were a screen.

The welding torch 3 and the housing 35 can be mounted independently of each other on the support carriage 2 . In the example of FIG. 5 they are suspended from the support carriage 2 on resilient suspensions 37 , 38 which apply downward pressure, so that they can follow an embossed profile. It may be fixed or rotatably mounted to the carriage 2 depending on the application.

6 is a perspective cross-sectional view of a housing 35 of an alternative form embodiment, as the effect of a suspension spring 40 mounted between a grate element 39 and a support bar 41 coupled inside the housing 35, The housing grate element 39 applies pressure to the top surface 34 of the cooling applicator 8 . The grate element 39 allows the flexible cooling applicator 8 to conform to the shape of the element to be welded without obstructing the passage of the cooling liquid, particularly when over corrugations.

In one embodiment the coolant supply is adjusted automatically by the control unit 26 schematically indicated in FIG. 12 . The control unit 26 is provided by various sensors 27 to provide various operating parameters of the welding station, such as the progress v of the support carriage 2, the flow rate D of the coolant, the current by the welding torch 3 ( I) use an input signal representing, etc. Using the control program, the control unit 16 generates a control signal for operating the circulation pump 28 .

Objects that may be pursued by such a control program are, for example,

- evaporating all or almost all of the coolant in the presence of a power source to avoid build-up of the liquid which may cause corrosion or create a hazard;

- lowering the temperature of the weld bead below a certain threshold.

The control unit 26 may be used together to control various actuators of the welding station, such as a drive motor 29 for driving the support carriage 2 , a current source 30 for a welding torch, and the like.

7 and 8 show a wheel 109 including another embodiment of a cooling applicator 108 . Here, the cooling applicator 108 consists of three porous disks made of mineral fibers that form the hub and “tire” of the wheel 109 . These three disks are fastened between two rigid end plates 20 and engage two stub shafts 21 projecting toward each other from the center of the two end plates 20 . In this embodiment the volume of liquid that can be absorbed by capillary action is greater. The rest of the operation is the same.

The cooling applicator is not necessarily a wheel. In one embodiment not shown, it is a pad of mineral fiber that slides over a weld bead.

As can best be seen in Figure 2, in one embodiment a welding apparatus is used to fillet weld two flat sheet-like metal plates, ie to weld them on top of each other. More specifically, the welding torch 3 is guided along the edge 17 of the top sheet 18 superimposed on the bottom sheet 19 to form a welding bead 22 along the edge 17 .

9 and 10 show cross-sections of weld beads on two Invar® sheets 0.7 mm thick when the cooling applicator is not used (FIG. 9) and when used (FIG. 10). The reference scale E in FIGS. 9 and 10 is 200 μm.

A photograph through an optical microscope makes it possible to evaluate the particle size of the material in the region of the weld bead 22 . The molten zone, shown at the large grain size in FIG. 9 , extends over the entire thickness of the assembly, up to the underside of the bottom sheet 19 . On the other hand, in FIG. 10 , the grain size of the weld bead 22 rapidly decreases with depth, and the lower half 23 of the lower sheet 19 maintains a certain portion of the original grain size, which is less because the melting zone is more confined. means deep. This is a result of the heat pump action performed by the coolant.

This fillet weld can be used to form a tight assembly in a sealed tank membrane, particularly between two corrugated seat plates. An example of such a membrane is shown in FIG. 11 .

Two corrugated seat plates 18 , 19 are shown. The sheet-like metal plates 18 and 19 protrude from the lower surface in the drawing and extend in the y direction of the plane, and are a series of first corrugations 31 spaced apart at regular intervals, and similarly, protrude from the lower surface in the drawing and perpendicular to the y direction. and a series of second pleats 32 extending in the x-direction and spaced apart at regular intervals. A flat region 33 is arranged between the pleats 31 , 32 .

The fillet weld can be formed in the same way along the edge 17 by moving the support carriage 2 together with the welding torch 3 in the x direction.

Numerical example

The desired flow rate of cooling water is determined before and after welding, for a welding energy equivalent to 89 kJ/m corresponding to the operating parameters: current (I) = 43 A, voltage (U) = 11.7 V and progress rate (v) = 34 cm/min. It was determined experimentally by weighing the wetted applicator. A water flow rate of 8.6 ml/m, that is, 0.097 ml/kJ, was measured to evaporate the cooling water entirely without any observable build-up.

According to the theoretical calculation, it is found to consume 8.9 ml/m of water under the same conditions. These calculations are based on the assumption that after the temperature is increased from 20°C to 100°C, evaporation of water occurs, causing the metal to cool from about 800°C to 500°C. Convergence between these results indicates that the cooling water is effectively completely consumed by the heat pump, rather than being diffused into areas where it is not required. The minimum flow rate corresponds to about 8 ml/m, i.e., about 0.090 ml/kJ, for a welding energy of 89 kJ/m. If it is desired to further lower the temperature of the metal after passing through the cooling applicator, the flow rate can be increased to about 20 mL/m, or about 0.225 mL/kJ, without water accumulation. These results are given as indicators and give a value corresponding to the amount of water required to cool the fillet weld between two 0.7 mm thick metal sheets.

"Include", "consisting of" and combinations thereof do not exclude the presence of elements or steps other than those recited in a claim.

Any reference signs placed between parentheses in a claim shall not be construed as placing a limitation on the claim.

Claims (16)

generating a weld bead (22) for assembling two metallic elements (18,19), the weld bead being produced by moving a welding torch (3) along the path of the weld bead;
and cooling the weld bead by passing a cooling applicator (8) directly behind the welding torch over the outer surface of the weld bead, wherein the cooling applicator consists of a pad of mineral fiber soaked in cooling liquid. According to claim 1,
The method wherein the mineral fiber is made of ceramic. 3. The method of claim 2,
The method consisting of a ceramic containing the mineral fiber while containing the most silica, together with other oxides. 4. The method according to any one of claims 1 to 3,
When the cooling applicator (8) passes over the weld bead, cooling liquid is supplied to the cooling applicator (8). 4. The method according to any one of claims 1 to 3,
wherein the cooling liquid is selected from water and liquid nitrogen. 4. The method according to any one of claims 1 to 3,
The cooling applicator (8) slides over the outer surface of the weld bead. 4. The method according to any one of claims 1 to 3,
The cooling applicator (8) is configured to roll over the outer surface of the weld bead. 8. The method of claim 7,
The cooling applicator (8) rolls over the outer surface of the weld bead in the form of a "tire" arranged around a cylindrical support. 4. The method according to any one of claims 1 to 3,
The welding torch (3) is an electric arc welding torch. 4. The method according to any one of claims 1 to 3,
The two metallic elements (18, 19) are sheet-like metal plates to be fillet welded or butt welded, the path of the weld bead following an edge (17) of one of the sheet-like metal plates. 11. The method of claim 10,
wherein the sheet-like metal plate (18, 19) is made of an alloy selected from unalloyed and low-alloyed steels, stainless steels, nickel-steel alloys having a low coefficient of thermal expansion and manganese-steel alloys having a low coefficient of thermal expansion. a movable support carriage (2) intended to move along a path of travel relative to the two metallic elements (18, 19) to be assembled, said support carriage (2) comprising:
a welding torch (3) for forming a welding bead (22) between the two metallic elements;
a cooling applicator (8), arranged behind the welding torch with respect to the travel path, for cooling the weld bead by contacting the outer surface of the weld bead, comprising a pad of mineral fiber;
and a dispensing head (15) designed for dispensing cooling liquid to the cooling applicator (8) and for wetting the pad of mineral fibers with the cooling liquid. 13. The method of claim 12,
further comprising a chassis (1) intended to be fixedly arranged relative to said two metallic elements to be assembled,
The movable support carriage (2) is movably mounted on the chassis, and is guided along the travel path by the chassis (1). 14. The method of claim 12 or 13,
a screen (13, 35) carried by the movable support carriage (2) and arranged between the cooling applicator (8) and the welding torch (3) to protect the welding torch from splashing of coolant Device. 14. The method of claim 12 or 13,
a coolant supply pump 28 connected to the delivery head 15 for supplying a flow of the coolant to the delivery head; and
a control unit (26) cooperating with the feed pump, configured to adjust the flow of the coolant according to one or more parameters selected from the group consisting of a progress rate of the movable support carriage (2) and a current by the welding torch (3); more inclusive devices. 14. The method of claim 12 or 13,
The device further comprising an elastic suspension member (38, 37) for applying pressure to the cooling applicator (8) in the direction of the metallic element (18, 19, 36) to be assembled.

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