Stick electrode
The exposed metal tip of the strike end of an SMAW welding electrode is covered with a protective coating formed from a binder and metal particles. Because metal particles rather than graphite particles are used to provide electrical conductivity to this protective coating, flare-up of the arc when initially struck is eliminated substantially completely. In addition, the potential for weld porosity problems is also eliminated, because the metal particles of the inventive electrode do not produce CO 2 as a reaction by-product which can ultimately lead to improper welding technique.
1. A modified tip-protected stick electrode comprising an essentially rigid elongated metal rod or wire made from a weld filler metal, the metal rod or wire defining a strike end having an exposed metal tip, a proximal end opposite the strike end and lateral surfaces extending between the strike end and the proximal end, the stick electrode further comprising a protective coating covering the exposed metal tip of the strike end, wherein the protective coating comprises a binder and metal particles, wherein the amount of metal particles in the protective coating is 10-30 wt. % of the protective coating on a dry weight basis, wherein the amount of inorganic binder in the protective coating is 70-90 wt. % of the protective coating on a dry weight basis, wherein the metal particles comprise one of Al particles and Al alloy particles and one of Mg particles and Mg alloy particles, and wherein a weight ratio of the one of Al particles and Al alloy particles to the one of Mg particles and Mg alloy particles is 0.6-2.5.
2. The stick electrode of claim 1 , further comprising a flux coating covering the lateral surfaces of the metal rod or wire.
3. The stick electrode of claim 1 , wherein the metal rod or wire is essentially solid.
4. The stick electrode of claim 3 , wherein the lateral surfaces of the metal rod or wire carry a coating of copper metal.
5. The stick electrode of claim 1 , wherein the metal rod or wire defines a hollow core, the stick electrode further comprising a welding flux in the hollow core.
6. The stick electrode of claim 1 , the binder is inorganic.
7. The stick electrode of claim 6 , wherein the inorganic binder is sodium silicate.
8. The stick electrode of claim 1 , wherein the weight ratio of the one of Al particles and Al alloy particles to the one of Mg particles and Mg alloy particles is 1.0-1.5.
9. The stick electrode of claim 1 , wherein the amount of metal particles in the protective coating is 15-25 wt. % of the protective coating on a dry weight basis, and further wherein the amount in organic binder in the protective coating is 75-85 wt. % of the protective coating on a dry weight basis.
10. The stick electrode of claim 9 , wherein the amount of metal particles in the protective coating is 18-20 wt. % of the protective coating on a dry weight basis, and further wherein the amount in organic binder in the protective coating is 80-82 wt. % of the protective coating on a dry weight basis.
11. A shielded metal arc welding process, comprising:
forming a weld metal layer from the stick electrode of claim 2 ,
wherein forming the weld metal layer comprises forming a molten flux, wherein the molten flux comprises a metal oxide formed from the metal particles and a metal oxide formed from the flux coating comprising the same metal oxide as the metal oxide formed from the metal particles.
12. The stick electrode of claim 1 , wherein the protective coating is essentially free of graphite.
13. The stick electrode of claim 12 , wherein the protective coating is free of added graphite.
14. The stick electrode of claim 1 , wherein the total amount of electrically conductive particles in the protective coating is no greater than 25 wt. % based on the weight of the protective coating on a dry weight basis.
15. The stick electrode of claim 14 , wherein the protective coating is essentially free of graphite.
16. The stick electrode of claim 15 , wherein the protective coating is free of added graphite.
17. The stick electrode of claim 2 , wherein the stick electrode is configured such that, upon welding using the stick electrode in a shielded metal arc welding (SMAW) process, a molten flux is formed, the molten flux comprising a metal oxide formed from the metal particles and a metal oxide formed from the flux coating comprising the same metal oxide as the metal oxide formed from the metal particles.
18. The stick electrode of claim 1 , wherein the metal particles comprise the Al alloy particles that contain at least 80 wt % Al, and comprise the Mg alloy particles that contain at least 80 wt % Mg.