Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-04-01
2001-11-13
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C075S305000, C075S309000, C075S315000, C075S327000, C075S328000, C075S329000, C075S253000, C075S959000, C148S523000, C148S528000, C148S535000, C148S023000, C148S024000, C149S037000, C149S040000, C164S473000, C164S483000, C164S488000, C164S053000, C164SDIG001, C228S198000, C228S201000, C228S212000, C228S215000, C228S234300, C228S257000, C228S037000, C228S056100, C420S537000, C420S548000
Reexamination Certificate
active
06316125
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the art of welding. More particularly, the invention concerns an exothermic welding process for welding aluminum, a novel mixture of reactants for use in such process, and weldments resulting from the process.
BACKGROUND OF THE INVENTION
Thermite or aluminothermic reactions have been widely used to make high ampacity low impedance electrical connections. There is no better electrical connection. The connection has a current carrying capacity at least equal to that of the conductors welded. The weld makes a permanent molecular bond with the conductors. The reaction materials are contained in a crucible above a tap hole on a fusible disk. When the materials are ignited, the exothermic reaction produces molten metal and slag. The molten metal fuses the disk and runs through the tap hole to a weld chamber to weld any elements exposed to or projecting into the weld chamber. The materials are ignited at the top of the crucible, and the reaction proceeds downwardly to fuse the disk upon a slight delay after ignition. The slag separates from the molten metal rising to the top of the reaction. Any slag drawn through the tap hole forms on top of the weld in the lower end of the tap hole or a special riser chamber. Any slag adhering to the weld is removed after cooling. The crucible, tap hole and weld chamber may be formed in separable refractory molds which are clamped together around the parts being welded and to form the parts of the process noted. The mold parts are cleaned for reuse after each welding process. The reaction materials, the molds and the weld connections made by the process are sold by Erico International Corporation of Solon, Ohio, USA, under the trademark CADWELD®.
CADWELD® is a registered trademark of ERICO.
The exothermic reaction may be comprised of a reaction between aluminum (Al) and a metal oxide wherein the metal oxide is reduced providing a filler metal, i.e., the source of the filler metal is the oxide on reduction. The “Goldschmidt” reaction is the basis of the application of the process described in U.S. Pat. No. 2,229,045 to Charles A. Caldwell. The reaction is as follows:
Aluminum (Al)+Iron Oxide (Fe
2
O
3
)=heat+Aluminum Oxide (Al
2
O
3
)+Iron (filler metal) (Fe) or
Aluminum (Al)+Copper Oxide (CuO)=heat+Aluminum Oxide (Al
2
O
3
)+Copper (filler metal) (Cu)
The “Goldschmidt” reaction has been successfully utilized over the years to weld or join metals such as iron (Fe) and copper (Cu). However, the process is not particularly well adapted for use in joining together a pair of nonferrous metal pieces, such as, two pieces of aluminum (Al) to one another.
U.S. Pat. No. 3,020,610 to Rejdak discloses a method of welding aluminum (Al) and other metals, and provides a listing of various reactions which can be utilized to provide reaction products which may be utilized to provide a weldment. Unfortunately, in the method disclosed by Rejdak the weld which is formed is not suitable for some applications. For example, a weldment produced by the Rejdak method in some environments (such as continuous immersion in rainwater, for example) may be susceptible to a high level of corrosion due to the presence of certain impurities or unwanted elements in the resultant weldment which may adversely affect the life, quality and strength of the weld.
U.S. Pat. No. 2,569,956 to Schiltknecht discloses a process wherein a thermite reaction is utilized to join together a pair of nonferrous metal pieces by melting a sleeve about the metal pieces. This process is usually referred to as the “Alusuisse Process” referring to a welding system produced by Swiss Aluminum Ltd. of Zurich, Switzerland.
U.S. Pat. No. 5,062,903 to Brosnan et al. discloses a process whereby a reducing agent is used to produce heat to melt a filler metal, which then flows out to provide a weldment. Other product components are left behind in the slag with reaction gases released. The process is generally summarized as follows:
Reducing agent+filler metal+metallic compound=heat+weld metal+slag+gases
The Brosnan et al. invention has been used to weld aluminum metal by using aluminum powder as both the reducing agent and filler metal, and calcium sulfate (CaSO
4
) as the metallic compound. The basic reaction is:
Al+CaSo
4
=heat+Al
2
O
3
+CaS+Al
The weld metal produced by this reaction was essentially pure (99%) aluminum (Al). However, the reactions were not necessarily uniform and stable and weldments sometimes had lower strengths than that of the aluminum pieces to be welded. The solidified weld metal also had excess porosity in some instances. The process lacked uniform repeatability and stability.
U.S. Pat. No. 5,171,378 to Kovarik et al. discloses an invention which improves on the Brosnan et al. process through the addition of silicon (Si) which strengthens the weld metal considerably. The porosity is also reduced through the addition of sodium chloride (NaCl).
U.S. Pat. No. 5,490,888 to Assel et al. discloses an invention which further improves upon both the Kovarik et al. and Brosnan et al. processes through the addition of two or more metallic compounds which are exothermically reduced by a reducing agent, such as calcium sulfate (CaSO
4
). Assel et al. discloses that the reaction mixture preferably contains at least one metallic compound which is a Group I metal sulfate compound such as Li
2
SO
4
, Na
2
Sl
4
, or K
2
SO
4
.
Among the major drawbacks of the Brosnan et al., Kovarik et al. and Assel et al. processes in welding aluminum is that the welds produced by these processes do not possess a suitably high tensile strength, and in the reaction the slag produced by the processes does not necessarily readily uniformly and repeatedly separate from the weld metal thereby sometimes causing contamination of the weld metal and non-uniform results.
SUMMARY OF THE INVENTION
The present invention provides a new and improved method and exothermic reaction mixture for use in the process for producing molten weld metal. The molten weld metal is used for joining one preferably nonferrous metallic piece with at least one other metallic piece. The method and exothermic reaction mixture have advantages over the prior art, which include a more uniform and improved purity of the metal yield (i.e., improved slag separation), and improved strength and higher quality corrosion resistant weld. An important advantage is consistent repeatability. These advantages are accomplished by a process wherein powdered filler metals of conductive metal are fused in the heat generated by an exothermic reaction mixture to form a molten weld metal, which is primarily an aluminum alloy, thereby welding together the at least two nonferrous metal pieces.
The method is particularly well suited for use in joining one piece of a nonferrous metal such as aluminum (Al) with at least one other piece of a nonferrous metal, which is preferably also aluminum. The reaction mixture for joining the at least two pieces of aluminum may comprise from about 22% to about 27% by weight of a metal sulfate; from about 54% to about 62% by weight aluminum (Al) powder; from about 5.0% to about 6.0% by weight copper (Cu) powder; about 5.3% to about 6.2% by weight of a Group I metal hexafluoroaluminate flux; about 4.7% to about 5.3% by weight of a supplemental oxidizing agent; and about 1.0% to about 1.2% by weight silicon (Si). The supplemental oxidizing agent may be selected from the group consisting of potassium permanganate and sodium chlorate.
Further, the present invention includes a weldment joining at least two pieces of aluminum to one another comprising greater than or equal to about 85 percent by weight aluminum, about 10 percent copper, and the balance of the alloy being primarily manganese (Mn) and silicon (Si).
REFERENCES:
patent: 2229045 (1941-01-01), Cadwell
patent: 2280178 (1942-04-01), Stroup
patent: 2569956 (1951-10-01), Schiltknecht
patent: 2831760 (1958-04-01), Rejdak
patent: 3020610 (1962-02-
Gaman Nicolae
Nieuwelaar Harrie van den
Erico International Corporation
Koehler Robert R.
Renner , Otto, Boisselle & Sklar, LLP
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