BE1031441B1 - Method of welding and method of manufacturing an object by welding steel parts together - Google Patents

Abstract

Method of welding, the method being of the submerged arc welding type, the method using two welding heads (1,2) to apply a weld (15) to a workpiece (14) of steel, the welding heads (1,2) being in a fixed position relative to each other, the welding heads (1,2) being moved together relative to the workpiece (14) in a direction of advance (P) to apply the weld (15), the two welding heads being a first welding head (1) and a second welding head (2), the second welding head (2) being positioned behind the first welding head (1), each of the welding heads (1,2) being a welding head with two current-carrying welding wires (3) and a non-current-carrying welding wire (4), the non-current-carrying welding wire (4) being located between the two current-carrying welding wires (3), at least one current-carrying welding wire (3) of each welding head (1,2) being a flux-cored welding wire is.

Description

; BE2023/5199

Method of welding and method of manufacturing an object by welding steel parts together.

The invention relates to a method of welding and a method of manufacturing an object by welding steel parts together.

In particular, the invention relates to a method of the type submerged arc welding, or submerged arc welding, known in English as ‘Submerged Arc Welding’. This is a welding method of the type electric arc welding, in which the arc is covered by a powder that is sprinkled on the workpiece at the location of the arc during welding. One or more welding wires are used as electrodes. These welding wires melt during welding and are therefore consumed to form the final weld.

This welding method is mainly used for the automated welding of very large workpieces such as parts of bridges, buildings and supporting structures for wind turbines, for both offshore and onshore use.

It is known to use a welding head with two current-carrying welding wires that form an electric arc and a non-current-carrying welding wire that is placed in between them. These three welding wires are in a straight line with each other. The workpiece to be welded and the welding head are moved relative to each other in a direction of progress. The current-carrying welding wires are also called 'hot' welding wires and the non-current-carrying welding wire is also called the 'cold' welding wire.

Such a welding head is known from WO2010/112068 and is marketed by ESAB under the name ‘ICE’, which stands for Integrated Cold Electrode.

In this case, an outlet of a powder feeder is usually placed in front of the welding head to be able to spread the powder used in this welding method.

In electric arc welding, the parameter HI, or Heat Input, is of great importance.

The parameter HI is defined as HI =(U.1.60)/(1000.v), where U is the welding

> BE2023/5199 is the voltage used in Volts, | is the current used during welding in Amperes and v is the travel speed, that is to say the speed in the direction of advance of the welding head or heads relative to the workpiece r, expressed in millimetres/minute. The parameter HI therefore has the units kilojoules per mm.

A maximum value of this parameter HI is specified by the steel suppliers, to ensure that the amount of heat during welding does not become so high that the steel weakens. This maximum value is usually 3.5 kJ/mm in the industry, but can also be different.

A welding process generally proceeds optimally if, with the boundary conditions of meeting the maximum value of the parameter HI and meeting the quality requirements for the weld, as much welding material as possible is applied per unit of time. This amount of welding material per unit of time is also called 'deposition'.

Welds are usually applied in multiple, typically several dozen, passes in succession. The workpiece must be cleaned of slag and residual welding powder between passes. The time required to clean the workpiece between passes is considerable, so that not all of the time can actually be used to apply a weld.

In recent years, steel types have been introduced on the market that can be welded with a parameter value of HI of 5.0 kJ/mm. In theory, this of course allows more welding wire to be melted per unit of time and therefore the deposition can be higher. However, with the known welding parameters and welding devices with an ICE welding head, this potential advantage cannot be achieved in practice.

In submerged arc welding with a named ICE welding head, a current of 1000A to 1250A, a voltage of 38V to 45V and a travel speed of 70 cm/min to 95 cm/min are generally used. The combinations of these 3 parameters used will typically result in a heat input of 3.0 kJ/mm to 3.6 kJ/mm. Typically, a deposition rate of 28 kg/h to 35 kg/h is achieved.

The current in welding is generally, and also in this document, specified per welding head, since each welding head has its own power source. That

3 BE2023/5199 means that in the case where two current-carrying welding wires are used per welding head, the current per current-carrying welding wire is half of the specified current, since they are fed by the same motor at the same speed.

Another important parameter is the free wire length, that is, the distance between the workpiece to be welded and the outermost part of the welding head where a welding wire still makes electrical contact with the welding head. The free wire length is also called the ‘stick-out’. The free wire length is measured in the direction in which the welding wire extends. In the case where the welding head is positioned at an angle, and therefore not all welding wires of the welding head extend over an equal distance, the free wire length of the rear welding wire is considered decisive.

In this document, the terms ahead and behind are used to indicate that a welding wire or welding head that is in front of another welding wire or welding head will be above a certain point on the workpiece before the other welding wire or welding head is over a certain point during weld application.

During automatic electric arc welding, the feed speed of the current-carrying welding wires, also called the wire speed, is automatically controlled to achieve a set target value of the current, whereby a higher wire speed results in a higher current. The wire speed of the non-current-carrying welding wire is set as a certain fixed fraction of the wire speed of the current-carrying welding wires.

As a general principle it is known from WO2010/112068 to use two mentioned ICE welding heads one after the other.

The present invention aims at improving such a method of welding, in which two said welding heads are used in succession, and relates to a method of welding, the method being of the submerged arc welding type, the method using two welding heads to apply a weld to a steel workpiece, the welding heads having a fixed position relative to each other, the welding heads being moved together relative to the workpiece in a direction of advance to apply the weld, the two welding heads being a first welding head and a second welding head, the second welding head

4 BE2023/5199 is positioned behind the first welding head viewed in a direction opposite to the direction of travel, each of the welding heads being a welding head with two current-carrying welding wires and one non-current-carrying welding wire, the non-current-carrying welding wire being located between the two current-carrying welding wires, at least one current-carrying welding wire of each welding head being a flux-cored welding wire.

A flux-cored welding wire is a welding wire that comprises a hollow steel sleeve filled with a powder, for example a metal oxide-rich mixture or a metal powder.

The combination of two mentioned welding heads with the mentioned cored wire allows to perform the process with higher current, voltage and travel speed, so that, while complying with the maximum value of the parameter HI, a higher deposition can be achieved than with traditional welding methods and desired mechanical properties are achieved. As a result, relatively less cleaning time is required between different welding passes.

This is also achieved with lower consumption of electrical energy from the electricity grid during the application of the weld.

The method according to the invention also allows easier welding at an HI value higher than 3.5 kJ/mm, for example at 5 kJ/mm.

It should be noted that a welding head is also called a welding torch.

In a preferred embodiment, the filling is made of a non-metallic basic material.

The basic material preferably has a B-value, or basicity index, calculated according to the Boniczewski formula known in the art, of 1.0 or higher, and preferably 1.5 or higher, whereby the Boniczewski formula defines the basicity index B.I. as follows:

BI = 0.5(FeO + MnO) + CaO + MgO + Na, + K,O + CaF,

SiO, +0.5(TiO, + ZrO, + ALO)

The basic material is preferably a powder.

In a preferred embodiment, both current-carrying welding wires of each welding head are identical. 5

In a preferred embodiment, the non-current-carrying welding wire of each welding head is identical to said at least one current-carrying welding wire of the same welding head.

In a preferred embodiment, the current-carrying welding wires of the first welding head are fed to the first welding head at a first speed, the non-current-carrying welding wire of the first welding head is fed to the first welding head at a second speed, the second speed being controlled to a target value that is a first fraction of the first speed, the first fraction being at least 0.70. Preferably, the first fraction is at most 1.30.

In a preferred embodiment, the current-carrying welding wires of the second welding head are fed to the second welding head at a third speed, with the non-current-carrying welding wire of the second welding head being fed to the second welding head at a fourth speed, with the fourth speed being controlled to a target value that is a second fraction of the third speed, with the second fraction being at least 0.70. Preferably, the second fraction is at most 1.30.

In a preferred embodiment, the free wire length of the welding wires of the two welding heads is at least 30 mm, and preferably at least 35 mm.

In a preferred embodiment, the free wire length of the welding wires of the two welding heads is a maximum of 55 mm, and preferably a maximum of 50 mm.

Thanks to a free wire length in this interval, or an interval as defined in the claims, a high deposition can be obtained even better. With a higher or lower free wire length a high deposition can indeed be obtained, but it becomes more difficult or impossible to obtain a high weld quality.

In a preferred embodiment, a flux powder of the type is used

FB according to standard EN ISO 14174:2019. This is a so-called fluoride-basic flux powder, which provides good mechanical properties of the weld.

In a preferred embodiment, the first welding head operates at a first current, the first current being greater than 1050 A, and preferably greater than 1100 A.

In a preferred embodiment, each of the current-carrying welding wires of the first welding head is passed through and in electrical contact with a first contact tip, whereby a first voltage difference is imposed between the first contact tip and the workpiece, the first voltage difference being greater than 41.0V, and preferably greater than 43.0V.

Preferably, the arithmetic product of the first current and the first voltage difference is at least 44000 VA and more preferably at least 46000

VA

In a preferred embodiment, the second welding head operates at a second current, the second current being greater than 900 A, and preferably greater than 950 A.

In a preferred embodiment, each of the current-carrying welding wires of the second welding head is passed through and in electrical contact with a second contact tip, whereby a second voltage difference is imposed between the second contact tip and the workpiece, wherein the second voltage difference is greater than 41.0V, and preferably greater than 43.0V.

Preferably, the arithmetic product of the second current and the second voltage difference is at least 41000 VA.

Preferably, a DC voltage is used for the first welding head and an AC voltage is used for the second welding head.

In a preferred embodiment, the workpiece is a carbon steel or carbon-manganese steel or austenitic stainless steel or ferritic stainless steel workpiece.

7 BE2023/5199

In a preferred embodiment, the workpiece is a workpiece of steel of one of the following types: S235, S275, S355, S420, S460, S690, and preferably of one of the following types: S355, S420, S460.

The types mentioned are understood as defined in standard EN 10027-1 and also include the types that are equivalent to it according to standard ISO/TR 20172 and/or standard ISO/TR 20173.

The invention also includes a method of manufacturing an object by welding steel parts together, the parts being welded together by a method of welding according to the invention as defined above, said object being a bridge or a supporting structure for a wind turbine or a part of a ship or a part of a nuclear power plant or a platform for the extraction of minerals at sea or for research purposes at sea.

In order to clarify the invention, a preferred embodiment of a method of welding according to the invention is described below, with reference to Figure 1, which shows a schematic side view of a workpiece and a welding device during the execution of a method according to the invention.

The schematically depicted welding device in Figure 1 comprises two well-known welding heads of the ICE type from ESAB, more specifically a first welding head 1 and a second welding head 2. The welding heads 1, 2 are located at a distance A of approximately 3 cm from each other.

The welding heads 1,2 each use, as known in the art, three welding wires, namely a front 3 welding wire and a rear welding wire 3, both of which are current-carrying, and a middle welding wire 4, which is non-current-carrying.

The first welding head 1 is positioned such that the welding wires 3,4 from the first welding head 1 run vertically. The second welding head 2 is positioned such that the welding wires 3,4 from the second welding head 2 make an angle of 15° with a vertical line. This angle of 15° is considered a positive angle since the welding wires 3,4 of the second welding head 2 protrude partly from the second welding head 2 in a direction of progress, indicated by arrow P.

8 BE2023/5199

In addition to both welding heads 1,2, there are supply nozzles 5 for welding powder, or flux powder, which are connected to a reservoir for welding powder, not shown in the figures.

The welding device further comprises coils 6 for the welding wires 3,4 and drive motors for the welding wires 3,4. This concerns in particular for each welding head 1,2 a drive motor 7 for the current-carrying welding wires 3 and a drive motor 8 for the non-current-carrying welding wire 4. In the experiments described below, only one type of welding wire is used and all welding wires 3,4 are therefore identical.

The welding device comprises an electrical supply for each welding head 1,2. This concerns a DC supply 9 for the first welding head 1 and an AC supply 10 for the second welding head 2.

The drive motors 7,8 are controlled by control units 11. The control units 11 control the feed speed of the welding wires 3,4 on the basis of the actual current intensity supplied by the power supplies 9,10, which is used as an input value by the control units 11. If this current intensity is lower than a target value, the feed speed of the welding wires 3,4 is increased, and if the current intensity is higher than a target value, the feed speed of the welding wires 3,4 is decreased.

In the experiments below, the control units 11 are set in such a way that, for each welding head 1,2 separately, the feed speed of the non-current-carrying welding wire 4 is kept at 100% of the feed speed of the current-carrying welding wires 3, with both current-carrying welding wires 3 of a welding head 1,2 having the same feed speed.

The welding heads 1,2 are provided with contact tips, by means of which the current-carrying welding wires 3 are set to the desired voltage, more specifically first contact tips 12 in the first welding head 1 and second contact tips 13 in the second welding head 2.

The welding heads 1,2, and more specifically their contact tips 12,13, are electrically connected to the power supplies 9, 10 for this purpose. The power supplies 9,10

9 BE2023/5199 are also connected to the workpiece 14 to which a weld 15 is to be applied, so that during the application of a weld a voltage difference exists between the workpiece 14 and the contact tips 12,13, which will cause an electric arc to occur between the workpiece 14 and the ends of the current-carrying welding wires 3.

In order to apply a weld 15 to the workpiece 14, in practice the welding device is mounted on a mobile or otherwise movable carriage and moved relative to the workpiece 14 at a constant speed, the so-called travel speed, in a direction of travel indicated by arrow P.

In this process, a welding powder is continuously fed around the welding heads 1,2 via the feed nozzles 5, so that the electric arc forms under a powder cover of this welding powder. This welding powder is partly converted into a slag during the application of the weld, which must be removed from the workpiece 14 after the weld has been applied. The supplied welding wires 3,4 are melted during the application of the weld and form the final weld 15. For the sake of completeness, it should be noted that the welding powder and the slag are not shown in figure 1.

The weld is applied with a certain set free wire length, which is the distance from the contact tip 12 to the workpiece 14. The welding heads 1,2 can have a mutually different free wire length. In figure 1 the free wire length of the first welding head 1 is indicated by L1 and the free wire length of the second welding head 2 is indicated by L2. In figure 1 the welding wires 3,4 are shown shorter than the free wire length L1, L2, because in practice they are melted during the application of the weld and form the weld 15 and therefore never actually touch the workpiece 14.

During the application of a weld, a joint molten pool is formed by the welding wires 3,4 of both welding heads 1,2.

Experiment 1:

A welding process for welding, with a heat input HI of 3.5 kJ/mm on a workpiece 14 of S355 steel, as used for example for bridges or offshore supporting structures for wind turbines, was carried out by means of the welding apparatus described above, using the following products and settings:

Welding powder: UV 418 TT from supplier ‘Böhler Welding’. This is a welding powder with a classification ‘S A FB 1 55 AC H5’ according to standard EN ISO 14174.

Welding wire: Diamondspark S 55 HP from supplier ‘Böhler Welding’ This is a cored welding wire with a steel sleeve and a basic powder filling.

The combination of this welding wire and this welding powder results in a weld with the classification ‘S 466 FB T3 H5 according to standard EN ISO 14171-A/

Travel speed: 185 cm/min

Settings first welding head 1:

Voltage: DC, 45 V

Current: 1200 A

Free wire length L1: 40 mm

Settings second welding head 2:

Voltage: AC, 45 V;

Current: 1000 A;

Free wire length L2: 45 mm.

By applying these parameters and this welding wire and welding powder, an average deposition, determined over twelve welding passes, of 70.6 kg/h was achieved, with an energy consumption of 1.8 kWh/kg.

It should be noted that energy consumption is measured as the energy consumption that the welding equipment has taken from the electricity grid, which is higher than the energy supplied to the welding wires by means of the electrical power supplies due to losses in the welding equipment.

The mechanical properties of the weld have been tested by means of the tests for fully penetrated joints as stated in table 2 of standard EN ISO 15614-1. All results of these tests comply with the requirements stated in the same standard.

Experiment 2:

Experiment 2 is identical to experiment 1, except that an S355 steel was used for which a heat input HI of 5 kJ/mm is permissible, and a travel speed of 120 cm/min

An average deposition rate of 77.3 kg/h was achieved over twenty-one welding passes, with an energy consumption of 1.6 kWh/kg.

The mechanical properties of the weld have been tested by means of the tests for fully penetrated joints as stated in Table 2 of EN ISO 15614-1.

All results of these tests meet the requirements set out in the same standard.

Experiment 3:

In experiment 3, a traditional welding machine with one ICE welding head was used, with the same welding wires and welding powder and a workpiece of the same material as in experiment 1.

The travel speed was 70 cm/min. The settings of the single welding head were:

Voltage: DC 45 V;

Current: 1200 A;

Free wire length: 40 mm.

An average deposition rate of 35.0 kg/h was achieved over twelve welding passes, with an energy consumption of 2.0 kWh/kg.

The mechanical properties of the weld have been tested by means of the tests for fully penetrated joints as stated in Table 2 of EN ISO 15614-1.

All results of these tests meet the requirements set out in the same standard.

Claims (22)

12 BE2023/5199 Conclusions 1.- Method of welding, the method being of the submerged arc welding type, the method using two welding heads (1,2) to apply a weld (15) to a steel workpiece (14), the welding heads (1,2) being in a fixed position relative to each other, the welding heads (1,2) being moved together relative to the workpiece (14) in a direction of advance (P) to apply the weld (15), the two welding heads being a first welding head (1) and a second welding head (2), the second welding head (2) being positioned behind the first welding head (1), each of the welding heads (1,2) being a welding head with two current-carrying welding wires (3) and a non-current-carrying welding wire (4), the non-current-carrying welding wire (4) being located between the two current-carrying welding wires (3), at least one current-carrying welding wire (3) of each welding head (1,2) being a filled welding wire. 2. Method according to claim 1, wherein a welding powder is used to form a powder cover on the workpiece (14), the welding powder being a welding powder of the type FB as defined according to standard EN ISO 14174:2019. 3. Method according to any of the preceding claims, wherein the welding heads (1,2) have a mutual distance of less than 15 cm and preferably less than 7 cm. 4. Method according to any of the preceding claims, wherein the filled welding wire has a basic filling. 5. Method according to any of the preceding claims, wherein the first welding head makes a first angle with a vertical line, wherein the second welding head makes a second angle with a vertical line, wherein the first angle is between 25° negative and 10° positive, wherein the second angle is between 10° negative and 25° positive, wherein a positive angle means that the welding wires of the welding head in question partially protrude from the welding head in question in the direction of advance, wherein a negative angle means that the welding wires of the welding head in question partially protrude from the welding head in question against the direction of advance. 13 BE2023/5199 6. Method according to any of the preceding claims, wherein the free wire length (L1) of the welding wires (3,4) of the first welding head (1) is at least 32 mm and at most 48 mm, and preferably at least 35 mm and at most 45 mm. 7. Method according to any of the preceding claims, wherein the free wire length (L2) of the welding wires (3,4) of the second welding head (2) is at least 32 mm and at most 52 mm, and preferably at least 40 mm and at most 50 mm. 8. Method according to any of the preceding claims, wherein the first welding head (1) operates with a first current, wherein the second welding head (2) operates with a second current, wherein the first current is higher than the second current. 9. Method according to any of the preceding claims, wherein each of the current-carrying welding wires (3) of the first welding head (1) is guided through a first contact tip (12) and is in electrical contact therewith, wherein a first voltage difference is imposed between the first contact tip (12) and the workpiece (14), wherein each of the current-carrying current-carrying welding wires (3) of the second welding head (2) is guided through a second contact tip (13) and is in electrical contact therewith, wherein a first voltage difference is imposed between the first contact tips (12) and the workpiece (14), wherein a second voltage difference is imposed between the second contact tips (13) and the workpiece (14), wherein the first voltage difference and the second voltage difference are both at least 42 V, and preferably both at least 43 V. 10. Method according to any of the preceding claims, wherein the first welding head (1) operates with a first current, the first current being higher than 1050 A, and preferably higher than 1100 A. 11. Method according to claims 9 and 10, wherein the arithmetic product of the first current and the first voltage difference is at least 44000 VA and preferably at least 46000 VA. 12. Method according to any of the preceding claims, wherein the second welding head (2) operates with a second current intensity, wherein the second current intensity is higher than 900 A, and preferably higher than 950 A. 14 BE2023/5199 13. Method according to claims 9 and 12, wherein the arithmetic product of the second current and the second voltage difference is at least 41000 VA. 14. Method according to any one of the preceding claims, wherein the current-carrying welding wires (3) of the first welding head (1) are fed to the first welding head (1) at a first speed, wherein the non-current-carrying welding wire (4) of the first welding head (1) is fed to the first welding head (1) at a second speed, wherein the second speed is controlled to a target value that is a first fraction of the first speed, wherein the first fraction is at least 0.70 and at most 1.30, wherein the current-carrying welding wires (3) of the second welding head (2) are fed to the second welding head (2) at a third speed, wherein the non-current-carrying welding wire (4) of the second welding head (2) is fed to the second welding head (2) at a fourth speed, wherein the fourth speed is controlled to a target value that is a second fraction of the third speed, wherein the second fraction is at least 0.70 and at most 1.30. 15. Method according to any of the preceding claims, wherein the welding heads (1,2) are moved relative to the workpiece (14) in the direction of advance (P) at a speed of at least 100 cm/min, and preferably at least 110 cm/min. 16.- Method according to any of the preceding claims, wherein both current-carrying welding wires (3) of each welding head (1,2) are said flux-cored welding wires. 17.- Method according to any of the preceding claims, wherein both current-carrying welding wires (3) and the non-current-carrying welding wire (4) of each welding head (1,2) are identical. 18. Method according to one of the preceding claims, wherein all welding wires (3,4) of both welding heads (1,2) form a joint weld pool. 19. Method according to any of the preceding claims, wherein the free wire length (L1) of the welding wires (3,4) of the first welding head (1) is greater than the free wire length (L2) of the welding wires (3,4) of the second welding head (2). 20.- Method according to any of the preceding claims, wherein the workpiece is a workpiece (14) of carbon steel or carbon-manganese steel or austenitic stainless steel 15 BE2023/5199 steel or ferritic stainless steel. 21. Method according to any one of the preceding claims, wherein the workpiece is a workpiece (14) made of steel of one of the following types as defined in standard EN 10027-1: S235, S275, S355, S420, S460, S690, or of one of the types which are equivalent thereto according to standard ISO/TR 20172 and/or standard ISO/TR 20173. 22.- Method for manufacturing an object by welding steel parts together, the parts being welded together by a method according to any one of the preceding claims, said object being a bridge or a supporting structure for a wind turbine or a part of a ship or a part of a nuclear power plant or a platform for the extraction of minerals at sea or for research purposes at sea.