Claims:WE CLAIM

1. A method for carrying out butt welding of bulb sections of DMR 249A material using Ceramic Back Strip (CBS) by Flux Cored Arc Welding (FCAW) including a ceramic base in the centre comprising the steps of:
Preparing the free edges of bulb stiffeners to form a groove joint ;
Attaching the Ceramic Backing Strip (CBS) to the bottom surface of the groove joint while aligning the centre of groove joint and CBS ;
Performing the first run of root welding between the two base materials ;
Separating and removing the ceramic backing material from the bottom surface of the welded part after the welded metal is air cooled and carrying out gouging operation on the top of weld surface to remove surface discontinuity,
Performing the cover up runs of welding on the top of bulb part of the stiffener to match the depth of remaining weld metal deposit on bulb part and web part of stiffener; and
Performing final run of welding post minor gauging operation on the top of weldment.
, Description:METHOD FOR CARRYING OUT BUTT WELDING OF BULB SECTIONS OF
DMR 249A

FIELD OF INVENTION

The present invention relates to a method for carrying out butt welding of bulb sections of DMR 249A material using Ceramic Back Strip (CBS) by Flux Cored Arc Welding (FCAW) process.

BACKGROUND ART

Welding technology is one of key process technology of modern ships construction engineering, and in hull construction, Ship Welding quality is an important indicator of shipbuilding quality, and therefore, progress of said technology has a great significance in promoting the development tool of shipbuilding production.

In the world, high strength steel welding technology develops in a comparatively fast aspect, welding composition and technological design, and application is also in continuous expansion. In the field of manufacturing of steel structure required for special use or utilized under bad working environment, high strength steel occupies an important position, and it has been widely used in the fields such as boats and ships construction, bridge, automobile, Construction of high rise buildings etc.

OBJECT OF INVENTION

The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a ceramic backing member which is provided under the welded portion and has a bulb portion corresponding to the groove of the welded portion formed on the upper surface thereof, When the ceramic backing material is removed, a concave portion corresponding to the bulb portion is automatically formed on the bottom surface of the deposited metal, so that a gouging groove is formed in the concave portion even if the gouging operation is performed only slightly.

SUMMARY OF INVENTION

This invention is for joining of two bulb sections while using ceramic backstrip to obtain adequate weld penetration with a proper concave profile. The butt welding method includes two bulb bars with single V groove, a ceramic backing material supporting the bottom of the butt weld and a structural arrangement for attaching the ceramic support to the bottom of the welding base.; The first step is carrying out the edge preparation of bulb bars to a single V groove with root gap of 3.5 to 4 mm and an included angle of 60°. Second step would be attaching the ceramic back strip on the base side of the groove, extended from the base of bulb bar to the top with adequate structural arrangement for support. Third step is carrying out the root run weld between the base materials (Bulb bars) and subsequent runs/pass of weld while maintaining an inter pass temperature of 100-150°C. This is done till the groove for metal joining is completely filled. Fourth step is letting the job cool down naturally and removing the ceramic backing as well as supporting structural arrangement. A smooth concave surface is obtained on the back side of weld due to ceramic backing.

According to the present invention as described above, the weld groove root has an equivalent width throughout its length. During the first run of weld, the weld run completely forms up this root area of groove while a concave surface forms automatically on the bottom surface of weld metal due to the smooth surface of Ceramic Backing Strip (CBS). This deposition of pool of weld metal in a concave profile makes it possible to eliminate the back gouging of weld metal from the bottom which had been conventionally required to attain a sound welding, thus improving productivity of the welding work, eliminate the problem of affecting worker’s health and environment by avoiding gouging activity.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig 1 (a) to 1 (f) are explanatory views showing a butt joint of a bulb bar joining in accordance with the present invention.

DETAILED DESCRIPTION

The present invention relates to a butt welding method configured for welding of bulb sections of DMR 249A material using Ceramic Back Strip (CBS) by Flux Cored Arc Welding (FCAW) process.
DMR 249A steel is one of the prestigious grade of steel and developed indigenously for structural applications in hull and body of warships and submarines. Medium strength (low carbon) Low alloy steels exhibit excellent mechanical properties and are extensively used in offshore applications and construction/repair of naval ships, where corrosion resistance against marine environment is significantly required. Poor corrosion resistance of low alloy steel fails the entire ship during the service. DMR 249A steels have high strength and are easy to weld. The DMR249A shows improved mechanical properties were observed for the SMA welds and are due to higher amount of martensite. Pitting corrosion and stress corrosion cracking resistance of SMA welds were poor when compared to GTA weld.
The first step is the preparation of a groove joint. The free edge of the bulb bars, to be butt welded, is grinded to a ‘single V’ joint with a groove angle of 60° on the side opposite to the bulb face along with a root gap of 3.5 to 4 mm. The joint is such prepared that the position of welding goes from vertical on the web part of stiffener to down-hand position at the bulb part of stiffener. The joint is therein prepared and Ceramic Back Strip (CBS) is positioned at the back side of weld groove with the centre of curve of CBS perfectly aligned with the centre of butt wed joint. The whole arrangement is secured with structural members arresting both bulb bars as well as ceramic backing strip in place.
As the Single V groove joint is made ready, welding is carried out using Flux Cored Arc Welding (FCAW) process in the second step. Root run of weld is done on the web part as vertical weld run as well as on the bulb part of the stiffener as horizontal run of weld. As the root run weld is completed, the molten metal naturally solidifies, so that the weld metal is firmly bonded to the both side welding base materials. Due to presence of Ceramic Back Strip with smooth curved surface on the root side of joint, the weld profile of the root run on the ceramic side is achieved as smooth concave surface. This enables the production team to eradicate the requirement of carrying out the operation of back gouging and re-run of weld on the same surface which was done conventionally, thus improving the productivity of the welding work.

Hereinafter, a butt welding method for bulb bar using a ceramic backing member and will be described with reference to FIGS. 1 (a) to (f) .The ceramic backing material according to the present invention is attached to the bottom surface of a groove joint between two base materials arranged in a butt shape along the profile surface of bulb bar.
As the root run weld is completed, to accommodate higher depth and width of the groove, the third step is to prepare the weld joint for fill-up welding by carrying out the operation of gouging the weld profile on the top bulb surface to remove any surface weld discontinuities. The ceramic back strip can be removed at this stage as its purpose for providing a smooth concave profile to the weld is achieved.
As fourth step, horizontal runs of welding is carried out at the bulb portion of the bulb bar where the gouging operation is carried out in the fourth stage described above. This is done while maintaining the inter pass temperature within 100~150° C limit. These run of welds allow the welder to match the depth of weld metal deposits of bulb portion of the bar to that of web part of the bulb bar. Multiple runs of the weld can be carried out depending on the thickness profile of bulb section.
The gouging operation described in third stage is again carried out as a part of fifth stage, to match the depth of weld metal deposit in bulb portion of the stiffener matches the depth of weldment at web portion of the stiffener. At this stage the final run of welding is carried out in the vertical upward direction from web to bulb part of the stiffener. Following these stages ensure a complete and sound butt weld of bulb stiffeners,
As the strength of the welded portion is greatly increased by the weld metal, and the ship structure can be firmly manufactured.
Many modifications may readily be contemplated by those skilled in the art to which the invention relates. Many further modifications may readily be contemplated. The description set out above is particularly applicable to high rate clarification applications. However, in conventional clarification where the upstream or downstream processes herein described are not used, the teachings according to the invention may have considerable merit and are also applicable. The specific embodiments described, therefore, should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims.