TECHNICAL FIELD

[0001] The embodiments of the subject matter disclosed herein generally relate to submerged arc welding, and more particularly to a torch used in submerged arc welding.

BACKGROUND

[0002] Submerged arc welding (SAW) is a form of welding which is typically automated and which has a relatively high deposition rate. General components associated with SAW are now described with respect to Figures 1 and 2. A disposable wire electrode 2 passes through the torch 4, with the torch 4 including a base piece 6 and a single piece body 8 which includes a welding tip section 10. The welding tip section 10 is partially submerged in a flux 12. A portion of the disposable wire electrode 2 protrudes past the welding tip section 10 into the flux 12. An electrical arc 14 occurs between a workpiece 16 and a tip of the disposable wire electrode 2 which generates enough heat to melt the tip of the disposable wire electrode 2 and create a molten zone 18 where the welding occurs. To generate the electrical arc 14 an electrical current is introduced to the torch 4 and passed to the disposable wire electrode 2 prior to the disposable wire electrode 2 departure from the welding tip section 10. The flux 12 supports this by having a sufficient conductivity to provide a current path between the workpiece 16 and the tip section of the disposable wire electrode 2.

[0003] Figure 2 shows the SAW process in an expanded view which includes a direction of motion 24 for the workpiece 16. Additionally, a flux feed tube 20 is shown ahead of the torch 4, which deposits the flux 12. A flux removal tube 22 is used to remove excess non melted flux. The flux 12 serves the purposes of providing a conductive path between the tip of the disposable electrode wire 2 and the workpiece 16, as well as acting as a buffer between the weld and atmospheric contaminants which, if introduced into the weld, would reduce the quality of the weld. In the examples shown in Figures 1 and 2, the torch 4 is mounted in a fixed position and the workpiece is moved at a fixed speed relative to the torch 4.

[0004] As shown in Figure 1 , the torch 4 includes a body section 8 and a welding tip section 10 which are a single piece. This torch 4 needs to have adequate conductive properties to pass the desired current to the disposable electrode wire 2, have adequate electrical insulation properties to prevent a discharge 20 between the body 8 and the workpiece 16, and have the desired mechanical wear properties on its exterior surface to handle working in this welding environment. In some cases a wear coating, e.g., Teflon, may be disposed on the outer surface of torch 4, which may be copper or a copper alloy, e.g., a copper chromium zirconium alloy, to improve its mechanical wear properties. This compromise between the electrical and mechanical properties in the single piece torch 4 generally results in not being able to optimize both the desired electrical properties and the desired mechanical properties. Also with the single piece design of the body section 8 and the welding tip section 10 if a portion of the torch 4 wears faster than other portions of the torch 4, e.g., the welding tip section 10, then the entire torch 4 needs replacement which can be costly and time consuming. Additionally, an average torch lifetime in SAW is currently only 4 hours which is a relatively short amount of time. [0005] Accordingly, systems and methods for reducing cost and extending SAW torch lifetimes are desirable.

SUMMARY

[0006] According to an exemplary embodiment there is a torch for submerged arc welding (SAW). The torch includes: a conductive body having an elongated shape and an inner channel crossing the body; an insulating layer on the body and configured to reduce a current passing through the insulating layer; an outer layer provided around the insulating layer and configured to provide wear resistance; and a welding tip removably attached to the body and configured to receive an electrode that passes through the channel of the body. A material of the insulating layer is selected independent of a material of the outer housing as a function of the insulating layer is to reduce current transfer from the body to the outer housing and a function of the outer housing is to provide wear resistance.

[0007] According to another exemplary embodiment there is a method for assembling a submerged arc welding torch. The method includes: attaching a bushing to a base piece; attaching a body having an elongated shape and an inner channel crossing the body to the bushing; wrapping an insulating layer around the body; attaching an outer layer to the bushing, where the outer layer is in contact with the insulating layer; and attaching a threaded welding tip to the body. [0008] According to still another exemplary embodiment there is a method for performing submerged arc welding. The method includes: passing a current through a body having an elongated shape and an inner channel crossing the body; reducing a flow of current from the body to an outer layer by providing an insulating layer between the body and the outer layer; providing wear resistance by providing the outer layer; transferring the current from the body to a detachably attached welding tip; and transferring the current from the welding tip to an electrode to form an arc between the electrode and a metal piece to be welded, where the arc melts a tip of the electrode.

[0009] According to still another exemplary embodiment there is replaceable welding tip for attaching to a welding torch used in submerged arc welding. The replaceable welding tip includes: a substantially cone shaped section being configured to guide an electrode and transfer current to the electrode; a threaded section connected to the substantially cone shaped section, where the replaceable welding tip includes a copper tungsten material, and a composition of the tungsten is in a range of 15 to 30 percent of the copper tungsten material; and an aluminum oxide coating on at least a portion of an outer surface of the welding tip. The welding tip is in a range between 10 and 40 mm in length and a portion of the welding tip is submerged in a flux when performing the submerged arc welding.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings illustrate exemplary embodiments, wherein: [0011] Figure 1 illustrates a traditional submerged arc welding (SAW) process;

[0012] Figure 2 depicts a traditional SAW process and the direction of travel for parts to be welded;

[0013] Figure 3 shows a SAW torch according to exemplary embodiments;

[0014] Figures 4-5 illustrate a welding tip according to exemplary embodiments;

[0015] Figure 6 shows a flowchart for a method for assembling a torch according to exemplary embodiments; and

[0016] Figure 7 shows a flowchart for a method for performing SAW according to exemplary embodiments;

DETAILED DESCRIPTION

[0017] The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

[0018] Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0019] As described in the Background section, and shown in Figure 1, a conventional submerged arc welding (SAW) torch has a body and a tip which are a single piece.

According to exemplary embodiments, a torch body can include various separate pieces which are assembled to attain the desired mechanical and electrical properties and a replaceable welding tip can be used. An exemplary torch 300 for use in SAW is now described with respect to Figure 3.

[0020] The torch 300 includes a base piece 302, a bushing 304, e.g., a

polytetrafluoroethylene bushing, an electrically conductive layer or body 306 attached to the bushing 304, an insulating layer 308 formed over the body 306, an outer layer 310 formed over the insulating layer 308, a washer 312 found at a distal end of the body 306, and a replaceable welding tip 3 14 that is detachably attached to the washer 312 and the body 306. As shown in Figure 3, the bushing 306 may extend under the insulating layer 308. The body 306 of the torch has an elongated shape which is generally cylindrical. A channel 316 is formed through the body 306 and it is open to atmosphere at the ends of the torch 300. The electrically conductive body 306 is a conductor, e.g., a copper beryllium alloy, with an elongated shape and the channel 316 is configured to guide electrode 318, e.g., a disposable wire electrode. The insulating layer 308 is an electrical insulator, e.g., glass fiber tape, which can include a glue for adhering to the body 306, and which generally dissipates upon heating. The outer layer 310, e.g., a stainless steel, acts as a housing for the torch body and maintains good mechanical wear resistance properties in the SAW environment. The washer 312 can be a plastic component, e.g., a Duratec (RS component). The replaceable welding tip 314 is attached to and detached from the electrically conductive layer 306 as desired, e.g., screwed on/off via mating threaded sections. The replaceable welding tip 314 may be chosen from a material, e.g., copper tungsten with the tungsten having a composition approximately in the range of 15 to 30 percent, which exhibits acceptable electrical and mechanical properties, such as wear resistance, conductivity and heat resistance.

[0021] The different compositions used for the conductive body 306 and the welding tip 314 allow for the conductive body 306 to have a higher conductivity than the welding tip 314. However, according to an embodiment, to compensate for the reduced conductivity of the welding tip 314, its length is reduced to be between 10 and 40 mm. This exemplary torch 300 allows for a longer lifetime, e.g., 36 hours as compared to a traditional 4 hour average lifetime as two functions of the torch are fulfilled by different materials. More specifically, the resistance to wear is achieved by the outer layer 310 and the electrical insulation is achieved by the insulating layer 308. By separating the layers responsible for these two functions, the appropriate material for these two layers may be selected without trading off properties, as is happening in the conventional torches. In other words, while for a traditional torch a same material is selected for both wear resistance and electrical insulation, two different materials are selected in the exemplary embodiment for these two different functions. Thus, the trade made between the wear resistance and electrical insulation in the traditional torch is avoided in the exemplary torch.

[0022] Using the exemplary torch 300 shown in Figure 3, the path of current flow is now described. Current is applied to the base piece 302 and passes to the electiically conductive body 306. From the electrically conductive body 306, the current mainly passes to the welding tip 314 and not to the electrode 318 as an air gap is present between the conductive body 306 and the electrode 318. From the welding tip 314 the current then passes to the electrode 318 while the electrode 318 is inside of the welding tip. The diameter of the channel 316 is large enough, as related to the diameter of the electrode 318, such that the majority of the current passes from the electrically conductive body 306 to the welding tip 314, i.e., the insulating ability of the air and the distance between the electrode and the inner surface of the electrically conductive body 306 makes it less desirable for most of current to pass to the electrode 318. Additionally, the insulating layer 308 generally prevents (or reduces) current from going from the electrically conductive body 306 to the outer layer 310, thus preventing the formation of arc 20 shown in Figure 1.

[0023] According to exemplary embodiments, welding torch 300 can have a replaceable welding tip 314 as shown in Figures 3-5. The welding tip 314 can have a threaded section 502 for attaching and detaching the welding tip 314 from the conductive body 306 of the torch 300. The welding tip 314 can be configured to guide and receive the electrode 318. External mechanical wear can be a factor for this welding tip 314 in the lower region 504 of the welding tip 314. This mechanical wear can occur from, for example, the welding tip 314 coming into contact with the chamfered edges of the metal workpieces to be welded.

Additionally, according to an exemplary embodiment, an aluminum oxide layer 506 can be flame sprayed onto the welding tip 314 to improve its wear resistance. The aluminum oxide layer 506 can be on the outer surfaces of the welding tip 314 as well as on the inside surfaces of the welding tip 314, e.g., the inner surfaces which contact the electrode 318. The threaded section 502 can be masked to prevent the aluminum oxide layer 506 to be deposited on the threaded section 502.

[0024] Utilizing the above-described exemplary systems according to exemplary embodiments, a method for assembling a SAW torch is shown in the flowchart of Figure 6. The method for assembling a submerged arc welding torch includes: at step 602 attaching a bushing to a base piece; at step 604 attaching a body having an elongated shape and an inner channel crossing the body to the bushing; at step 606 wrapping an insulating layer around the body; at step 608 attaching an outer layer to the bushing, wherein the outer layer is in contact with the insulating layer; and at step 610 attaching a threaded welding tip to the body.

[0025] According to an exemplary, the above described exemplary welding torch 300 can be used in a SAW process for welding large steel containers, e.g., 2000 ton containers, used in vessel fabrication. Weld deposition rate can be approximately 10 kg/hour. The torch 300 is in a fixed station with the workpiece(s) moving at a fixed speed. A power source (not shown) can apply a current of approximately 600 amperes to the torch 300 in the novel configuration. Torch life, on average, can be approximately 36 hours, with the first point of excess wear often being the welding tip 314. Welding tips 314 which may be substantially cone shaped are replaced by unscrewing them from a threaded portion of the conductive body 306. According to alternative exemplary embodiments, the exemplary welding torch 300 can be used in other SAW applications with different weld deposition rates, different currents and different types of workpieces to be welded.

[0026] Utilizing the above-described exemplary systems according to exemplary embodiments, a method for performing SAW is shown in the flowchart of Figure 7. The method for performing submerged arc welding (SAW) includes: at step 702 passing a current through a body having an elongated shape and an inner channel crossing the body; at step 704 reducing a flow of the current from the body to an outer layer by providing an insulating layer between the body and the outer layer; at step 706 providing wear resistance by providing the outer layer; at step 708 transferring the current from the body to a detachably attached welding tip; and at step 710 transferring the current from the welding tip to an electrode to form an arc between the electrode and a metal piece to be welded, where the arc melts a tip of the electrode.

[0027] The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article "a" is intended to include one or more items.

[0028] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.