FIELD OF THE INVENTION

The present invention generally relates to Contact tips. More particularly, it relates to an improved Cu contact tip for Submerged Arc Welding (SAW) of Boiler panels.

BACKGROUND OF THE INVENTION

Submerged Arc Welding (SAW) is a fusion welding process in which the heat is produced from electric arc between work piece and a continuously fed welding wire during the passage of electric current. SAW process requires continuous consumable flux material for covering the welding wire, the arc and the weld joint. The heat generated from the arc melts base metal, electrode wire and the flux. The flux shields the molten weld metal and helps to prevent absorption of gases like Nitrogen, Oxygen & Hydrogen from air and also facilitates improved chemical and Mechanical properties of the weld metal.. The flux forms a glass like slag that is lighter in weight than the deposited weld metal and floats on the surface as a protective cover.

SAW is the widely used arc welding process and also called as Hidden Arc Welding. Generally, it is operated in the automatic mode or semiautomatic mode. A SAW contact tip consistently transfers the welding power to the wire and also directs the electrode wire to the joint. The Contact tips are made of metal, almost typically and exclusively of Copper or a Copper alloy,, because of its high electrical and thermal conductivity. Submerged arc welding is especially used in the fabrication of boilers, pressure vessels, penstocks etc..

Boilers are mainly used in power plants for generating high pressure steam, in buildings for heating water, in textile industries for sizing or bleaching and also used in other industries like sugar mills and chemical industries. The boiler panels are made by welding tubes with fins in Panel Processing Machine using Submerged Arc Welding.. In this process, Cu contact tip is used for electrical conduction and wire feeding. When the Cu contact tip inadvertently touches the steel base materials being joined, it leads to short circuiting which causes excess current flow. Hence, it leads to melting, deposition and entrapment of Cu in the weld zone or steel base metal. As a result of Cu entrapment, the affected region is prone to Assuring or cracking depending on the extent of Cu melt down on steel base materials. In case of boiler panels (tube with fin welded) which have weld defects due to Cu inclusion need to be removed and welded with new tubes and fins. It leads to additional cost due to materials replaced, labour for rework and additional time for repair. It also affects the life of the welding machine.

There are many prior art disclosing the contact tips with various features to protect the contact tips against spatter, cracking etc. For example, U.S. Patent No. 7,381,923 to Gordon et al. discloses a Ceramic cap that is fitted to the tip of the Copper body to protect against spatter and to serve as a guide for the wire emerging from the tip using SAW. U.S. Patent Appln. No. 20040079741 discloses a Ceramic contact tip extension as a thermally insulator to protect the SAW Cu contact tip. Japanese document No. 61115683 discloses a contact tip in which Ceramic cap is screwed on the tip end of the body of the contact tip in order to prevent cracking. Japanese document No. 3688682 discloses a welding tip having a Copper base tip body and a Ceramic cover which is fixed at the tip end of the tip main body to avoid sputtering. Even though there are many contact tips already available, they are not efficient to avoid Cu inclusion and hence there is a need for an improved Cu contact tip.

SUMMARY OF THE INVENTION
The object of the present invention is to provide an improved Copper contact tip to eliminate Cu inclusion, in case of Cu contact tip inadvertently touching the steel base materials being joined.

The present invention introduces a novel Ceramic cap over the Cu contact tip after making suitable modification in the Cu contact tip. As the Ceramic material is a non-conductor of electricity, in case of accidental touching of Ceramic cap on the steel base metals being welded, short circuiting does not occur. As the Ceramic cap is resistant to heat, it acts as a shroud to Cu contact tip, no Cu melting takes place and totally eliminates the possibility of Cu inclusion in the weld zone.

According to the present invention, the Ceramic cap is moulded with female thread and screwed onto the threaded portion of Copper contact tip. The Ceramic cap acts as an electrical insulator for Copper contact tip.

In a preferred embodiment of the invention, the Ceramic cap can be made with holes randomly to facilitate the dissipation of heat developed in Cu copper contact tip during welding.

The present invention of Cu contact tip with a novel Ceramic cap is utilized in Panel Processing Machine for processing boiler panels using Submerged Arc Welding (SAW) to avoid Cu inclusion which otherwise needs to be removed and welded with new tubes and fins. Thus, the cost incurred due to materials replacement, labour for rework and additional time for repair are eliminated by using this invention.
The improved Copper contact tip of the present invention also increases the life of the welding machine by eliminating the frequent short circuiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The objective of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

Fig. 1 illustrates the standard Cu tip in use & Cu inclusion in the base material.

Fig. 2 (A), (B) and (C) illustrate the standard Cu contact tip, modified Cu contact tip and a newly developed Ceramic cap, and the Ceramic cap fastened to the threaded Cu contact tip, respectively.

Fig. 3 illustrates the use of newly developed Ceramic cap with modified Cu contact tip for SAW welding of Boiler panel.

Fig. 4 illustrates the preferred optional features for Ceramic cap of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an improved Copper contact tip to eliminate Cu inclusion, in case of Cu contact tip inadvertently touching the steel base materials being joined. The present invention is to insert a Ceramic cap over the Copper contact tip after making appropriate modification on the contact tip. The Ceramic cap of the present invention is suitable for Submerged Arc Welding (SAW) process.

Fig. 1 illustrates the use of conventional Cu contact tip in welding process and Cu inclusion in the steel base material during accidental touching of the conventional Cu contact tip with the base metal being welded.

Fig. 2 (A) illustrates a standard Cu contact tip. It is used in the SAW process. When this Cu contact tip accidentally touches the steel base metals being joined, it leads to short circuiting, melting, deposition and entrapment of Cu in the weld zone or base metal which ultimately results in the cracking of the base metals. In order to overcome the problems in conventional tips, the present invention discloses a modified Cu contact tip and a novel Ceramic cap as shown in Fig. 2 (B). The length of the modified portion in Cu contact tip is 13 mm. The novel Ceramic cap of the invention has a length of 12.50 mm, top diameter of 12 mm and bottom diameter of 8 mm. The wire passes through the Copper contact tip which is protected by Ceramic cap. The Ceramic cap is fixed to the Copper contact tip via matching threads provided both in the Ceramic cap and Cu copper contact tip. That is, the tip is modified or threaded in such a way that it accommodates the novel cap and also the cap is moulded to contain female thread. Fig. 2 (C) depicts the cap made of Ceramic which is fastened to the Cu contact tip through the threaded part.
Referring to Fig. 3, the use of modified Cu contact tip with the novel Ceramic cap in the Panel Processing Machine for fabricating boiler panels using Submerged Arc Welding is depicted. The Ceramic cap of the present invention acts as a shroud to Cu contact tip and hence no melting of Copper takes place. This completely eliminates the inclusion of Copper in the welding zone or steel base metal when the eventual touching of the newly developed contact tip with the steel base metal being welded takes place.

Fig. 4 shows the preferred optional features of the Ceramic cap of the invention. The Ceramic cap can be made with holes at random as given in the figure 4 to facilitate the dissipation of heat developed in Cu contact tip during welding.

The improved Copper contact tip of the present invention also increases the life of the welding machine by means of eliminating the frequent short circuiting.

While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention as claimed.

WE CLAIM:

1. An improved Cu contact tip is provided for use in Submerged Arc Welding (SAW) process comprising a novel Ceramic cap over the end of the said contact tip to avoid Cu inclusion in the base metal.

2. The Cu contact tip according to claim 1, wherein the said cap is made of an electrically non-conducting and heat resistant Ceramic material.

3. The Cu contact tip according to claim 1, wherein the said Ceramic cap is moulded to contain female thread and it is screwed to the said copper contact tip after modifying the tip by threading.

4. The Cu contact tip according to claim 1, wherein the said Ceramic cap acts as a shroud or electrical insulator to the said Copper contact tip; wherein this contact assembly eliminates the melting of the said Copper contact tip during welding process.

5. The Cu contact tip according to claim 1, wherein the said Ceramic cap prevents the short circuiting even in the case of accidental touch of Copper contact tip on the base metal; results in enhancing the life of the welding machine

6. The Cu contact tip according to claim 1, wherein the said Ceramic cap comprises holes at random to facilitate the dissipation of heat developed in Cu copper contact tip during welding.

7. The use of an improved Copper contact tip comprises a Ceramic cap for boiler panel fabrication in panel processing machine using Submerged Arc Welding.

8. The use of the Cu contact tip according to claim 8, eliminates the cost incurred due to materials replacement, labour for rework and additional time for repair while at the same time producing boiler panels free of weld defects and Cu inclusion.