When welding galvanized and other coated materials a layer of oxides and brass builds up on the face of the electrode. During the first twenty five to fifty welds while this layer builds up and develops equilibrium, the welding results can be inconsistent. This period is called conditioning.
All spot welding electrodes mushroom during use and when this happens the resultant weld eventually is unacceptable. Before this happens most operations either dress or change the electrode to get the face back to original operating conditions.
When a job is set up properly and the electrodes and water cooling are maintained it is still possible to have weld variation during a production day. It is very common that the line voltage at most production plants can vary during the day because of the demand on the Utility Company. The problem could be your feed to your plant or the Utility Company's main grid. It also could be overloaded power buses within the facility.
Back up electrodes are used for projection welding electrodes. They are normally used on the lower side and are flat faced. There is no need for a defined weld face since the projection concentrates the weld current and heat into a desired spot for nugget creation.
Some resistance welding applications call out forces above the limits of tapered electrodes. The RWMA Manual Fig 18.3 shows force vs taper. It shows that above 2400 Lbs force tapers are not viable. Above this force specially designed High Pressure/High Force Electrodes must be used. These electrodes can be straight shanks, threaded or flanged electrodes. They are available from several manufacturers. Contact your electrode supplier for assistance.
Reference: RWMA Resistance Welding Manual 4th Edition
Do you have a question that is not covered in our knowledgebase? Do you have questions regarding the above article? Click here to ask the professor.