Electric heating – Metal heating – By arc
Reexamination Certificate
2001-07-24
2003-12-16
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S136000
Reexamination Certificate
active
06664508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field
This application related to gas tungsten arc welding and more particularly to a titanate flux that substantially increases weld penetration.
2. Background
The gas tungsten arc welding (GTAW) process is an arc welding process that uses an arc between a non-consumable tungsten electrode and the work piece to cause localized coalescence of the base material. The GTAW process is used to produce high quality welds in a variety of materials. Applications include welding of sheet, plate, tube, and castings for use in aerospace, power generation, shipbuilding, and other industries. GTAW can be used with filler metals or consumable inserts to produce welds in thick sections. Autogenous welds (welds without filler metals) can be made in thin sections or for root passes in thick sections.
The primary limitation of the process is low productivity due to low deposition rates and shallow penetration. The inability of GTAW to produce welds with deep penetration limits the thickness of material that can be reliably joined to less than approximately 0.10 in (2.5 mm) thick. Materials greater than 0.1 in (2.5 mm) thick typically require weld joint preparation and multiple passes to fill the weld joint. GTAW welds are also affected by heat-to-heat compositional variations in the material being welded. While variable penetration is most often encountered in stainless steel and nickel-based alloys, this phenomenon occurs in other materials as well.
A method of increasing both the amount and consistency of penetration in gas tungsten arc (GTA) weldments is to apply a thin layer of flux to the surface of the part or joint to be welded prior to welding. The use of traditional fluxes for the GTAW process is not required since shielding and arc stabilization are provided by the use of an external shielding gas. Fluxes used for GTAW to improve penetration are inherently different than those used for soldering, brazing, or other arc welding processes since they neither clean the surface of the part nor protect the weld pool from oxidation.
The use of flux for increasing penetration in mild steel materials has been described by several authors in the former Soviet Union. An article by E. D. Raimond et al. titled “Welding of High Strength Steel Using Activating Fluxes in Powder Form”
Svar. Proiz
, No. 6, pp. 18-19, suggests that the use of Soviet Flux FS-71 increased GTAW penetration in steel by 50-100 percent. No compositional details were given for the flux. A later article by O.E. Ostroviski entitled “The Effect of Activating Fluxes on the Penetration Capability of the Welding Arc and the Energy Concentration in the Anode Spot”
Svar. Proiz
, No. 3, pp. 3-4, 1977, reveals that the composition of flux FS-71 is 57.3 percent SiO
2
, 6.4 NaF, 13.6 TiO
2
, 13.6 Ti, and 9.1 Cr
2
O
3
. Another paper by L. E. Eroshenko et al, titled “An Examiantion of the Glow of Anode Vapors for the Evaluation of the Technological Characteristics of the Arc Running in Argon,
Avt. Svarka,
1979, No. 9, pp. 33-35, evaluated the enhanced penetration caused by fluorides of several alkali and alkaline-earth elements. The effects of individual fluorides were studied and the fluorides evaluated in the study were used as a basis for selecting components for titanium and steel GTAW fluxes. A similar approach to the Soviet flux design is described in U.S. Pat. No. 5,525,163 by H. R. Conaway et. al. They claim that the use of 7 to 59 percent LIF promotes penetration in 321 austenitic stainless steel. They infer that this ingredient will promote enhanced penetration in other materials such as carbon steel as well. Paskell describes a flux composed of TiO or TiO
2
(50%), Cr
2
O
3
(40%) and SiO
2
(10%) in U.S. Pat. No. 5,804,792 that is used to increase the penetration in stainless steel.
The flux reported by Ostrovski (FS-71) and flux no. 69 reported by Conaway (23.6 Al
2
C
3
, 39.4 LiF, 15.7 MgO, 5 B
2
O
3
, and 15.7 Fe
2
O
3
) were evaluated the instant effort on SA178 Gr. C mild steel pipe. Neither flux spread well or produced consistently improved penetration above what was measured without flux. Additionally, these fluxes both contain fluorides which can increase the risk of corrosion in some environments and which generated a considerable amount of fluoride based fume which is can be hazardous as well.
It is an object of the present invention to provide a flux composition for use with the GTA process that improves weld penetration in a variety of steels including stainless steel and also in nickel-based alloys.
It is an object of the present invention to reduce the cost of the GTA process by reducing the time and effort in joint preparation.
It is an object of the present invention to reduce the number of passes in a multi-pass gas tungsten arc weld.
It is an object of the present invention to reduce the distortion in a gas tungsten arc weld.
It is an object of the present invention to produce welds with mechanical properties that are not degraded through the use of the flux composition.
It is an object of the present invention to produce welds with a weld quality that is not degraded through the use of the flux composition.
The foregoing and other objects, features and advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail. It is contemplated that variations in procedures may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention.
SUMMARY
The above objects are met in the present invention by using a “titanate” penetration flux to achieve deep penetration welds in gas tungsten arc welding (GTAW). As used here, a “titanate” is a salt and/or complex oxide of titanium such as TiO
3
−2
, TiO
4
−4
, Ti
2
O
5
−2
,Ti
2
O
7
−4
, and Ti
3
O
7
2
. The titantate is selected from alkaline-earth titanates, transition metal titanates, and alkali metal titanates such as Na
2
Ti
3
O
7
or K
2
TiO
3
. Only a small amount of the titanate alone applied to the weld zone as a thin paste by mixing with a carrier fluid such as an alcohol or ketone or as part of a wire filler is sufficient to promote deep penetration GTAW of a wide variety of metals including carbon, chrome-molybdenum, and stainless steels as well as nickel-based alloys.
To control arc wander, bead consistency, and slag and surface appearance of the gas tungsten arc weldments, a wide variety of additional components may be optionally added to the titanate flux including transition metal oxides such as TiO, TiO
2
, Cr
2
O
3
, and Fe
2
O
3
, alkali oxides, alkaline-earth oxides, silicon dioxide, manganese silicides, alkali fluorides, alkaline-earth fluorides, alkali chlorides, and alkaline-earth chlorides. However, the toxicity of the plumes from halides and resulting weld corrosion may preclude halide use.
During the development of the titanate flux, it was found that a composition of TiO and/or TiO
2
, Cr
2
O
3
, and Fe
2
O
3
gave good weld penetation in GTAW but with heat-to-heat variation in carbon steel and nickel-based alloys. Such a flux has about 5-40 wt % Fe
2
O
3
, 20-70 wt % Cr
2
O
3
, and 15-70 wt % of TiO or TiO
2
or both with a more preferred composition having about 6 wt % Fe
2
O
3
, 60 wt % Cr
2
O
3
, 22 wt % TiO
2
and 12 wt % TiO.
The method of using the titanate flux is quite simple. The flux is applied to the weld zone of the metal components to be joined as a thin paste, as part of a filler wire or even as part of the shielding gas. The metal components are welded together using a gas tungsten arc welding torch.
The foregoing and other objects, features and advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail and illustrated in the accompanying examples. It is contemplated that variations in compositions and their use in the welding process may appear to a person skilled in the art without departing from the scope of or
Fountain Christopher M.
Johnson Matthew Q.
Dawsey David J.
Edison Welding Institute, Inc.
Elve M. Alexandra
Gallagher Michael J.
Gallagher & Dawsey LPA
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