We recently worked with our Weld.com Advisor, Dale Spilker, on a Stick Welding 6010 Downhill video regarding 3G Open Root Butt Joints. In the video (embedded below), the downhill method for the root was performed using ⅛” Bohler Q 6010 electrodes, AWS Spec A5.1, with a manufacturers amperage rating between 80 and 110 amps. He also used a 3/32” Bohler Fox EV50 7018 electrode, AWS Spec A5.1, with a manufactures amperage rating between 80 and 110. This was used for the uphill fill and reinforcement. This particular joint configuration or something similar can be found in Pipe welding, shipbuilding and the repair industry. As well as any applications where the backside of the joint isn't easily accessible by a welder.
For this particular weld, he used a common joint configuration using 2 plates each of which were 7" long by 4" wide, by 3/8" thick, A-36 Mild steel. These plates were prepped with a 30 Degree bevel, a 3/32” land and a 3/32” root opening. This created an overall groove angle of 60 degrees. For this joint, he also used run off tabs to control penetration at the beginning and end of the joint. For some applications run off tabs can be utilized, it's a personal recommendation, but this joint could also be run without the run off tabs.
For this weldment a Lincoln Precision TIG 375 is used, for the duration of this weld the machine will be using a Direct Current Electrode Positive Polarity.
For the root weld on this joint he used a drag angle of about 10-15 degrees with some deviation as needed. The machine was set at 93 amps. Throughout the weld, he applied slight pressure to the rod to aid in breaking down the edges of the bevel. This allows us to see a slightly deeper root penetration as well as a more consistent profile on the backside of the joint.
Stops and starts for the root pass will be feathered out (ground) which will allow for proper penetration on the restart, different welders use different techniques for this. Personally, he uses a 4 ½ inch grinder with a slimmer grinding wheel or cutting wheel.
Once he completed the root, he removed all the slag with a wire wheel and then proceeded to inspect the backside of the root. During inspection, you should be looking for proper joint penetration as well as a consistent bead profile. In simple terms it should look like a bead was run on the rear side of the joint. Undercut at the toes of the weld on this side are something that should be avoided or if occurs it should be thoroughly inspected.
Before the fill passes are started and after he completed visual inspection of the joint, he then grinds the root paying close attention to the area of the joint where the weld toe meets it. In most cases, he will end up grinding this portion down to shiny metal. Caution should be taken not to grind too deep. Keep in mind the bead you are grinding on is very thin.
The reason why he prefers to grind the root in this manner is to avoid slag entrapments between the root and his next pass. Doing this can also help repair an area of the root that may not have initially had the best appearance or penetration.
FILL AND REINFORCEMENT
Once all the steps mentioned above are complete, he starts the process of filling the joint. This next layer is commonly called the hot pass throughout the welding industry. For this pass he uses a 5-10 degree push angle with his machine set at 91 amps. He used weave beads to fill this joint. Throughout the hot pass you will see him pause on the edge of the joint generally keeping a mental count of how long the pause is just to create consistency throughout the joint. All while keeping an eye on the molten weld pool to ensure it has penetrated the root and each member of the joint. Once the fill passes are complete if time allows, Dale prefers to allow the joint to cool for roughly 10 minutes.
Throughout the reinforcement, he will have his machine set at either 93 or 94 amps. Before starting the welding process, he likes to mentally plan for his reinforcement layer. Some things that he considers are rod size, groove opening dimensions as well as bead width requirements. For this joint, he prefers to stay under 3/8ths of an inch which should set up nicely to do a 2 bead reinforcement layer. Throughout the reinforcement layer, he uses the weave bead technique pausing constantly to allow the cross section of the weld to fill in.
Upon completion, always do a visual inspection of the weld, checking for obvious defects such as undercut, underfill, porosity and incomplete fusion.