PLATE - TRI-BRAZE® - WELDING INSTRUCTIONS
Welding Technique:
» The amount of heat introduced into the weld can have drastic effects on the joint strength. Large heat inputs result in wide heat affected zones that are low in hardness and impact properties. Narrow heat affected zones are kept low by using small beads and multiple passes. A rough rule of thumb of passes to be used:
Min Passes = 5 x Combined Thickness
For example, welding two (2) 3/4" plates would require a minimum of eight (8) passes.
» Welding position may be flat, vertical or horizontal.
» Stringer passes should be made on alternating sides to help control distortion. Weave beads should avoided. If it is absolutely necessary to use weave beads, the deposit width should be limited to three (3) times the electrode diameter or five (5) times the diameter for wire.
» The final weld passes should be uniform in shape and contour. The beads should taper smoothly into the base plate, undercutting should not be allowed.
» Any and all visible weld imperfections should be removed before successive weld passes are made.
Post Weld:
» The completed weldment should be allowed to slow cool to ambient temperature.
» Post weld thermal treatment is generally not necessary, but is suggested when the welded component is subject to extreme load conditions. When deemed necessary, the welded component can be stress relieved by heating to 400°F and holding for one-half to one hour per inch of thickness of the plate. The cooling should be done in still air.
» Post Weld Inspection - rough, irregular shaped welds should be ground smooth to remove stress risers that could be sites for crack initiation. Ensure freedom from cracks, gouges, laps, undercut or other imperfections. Visual examination, preferably 48-72 hours after welding, should be made to ensure freedom from cracks, gouges, laps, undercuts or other imperfections.
Avoid the following weld associated pitfalls:
1. Hydrogen Cracking
» Whenever high strength steels are welded, there is always a danger of cracking due to the presence of moisture. Care should be taken to assure that electrodes and base metal surface are free from moisture. To avoid under-bead cracking, the hydrogen content of the weld should be kept to a minimum.
» Common sources of hydrogen are: (a) water and heavy rust on plate; (b) manual shielding arc electrode cuttings; (c) submerged arc welding flux that has been improperly stored; (d) contamination on surface of coiled electrode core wires.
» If hydrogen embrittlement is suspect, it is always good practice to soak the completed weld at 250°F.
2. Undercutting
» Undercutting is simply a joint that has not been properly filled. The base material is melted, mixed with the filler metal and solidified as a weld bead. It is usually characterized by high crown.
» Undercutting is probably the most common of all defects in welding. There are many causes but the most common cause is excess travel speed...quite simply, there is not enough weld metal to fill the joint.
Tri-Braze® Welding Instructions
Tri-Braze® was designed with the welder in mind. It can be easily welded using the following guidelines:
Material Preparation:
Thoroughly remove rust, scale, grease or oil from the weld areas.
Preheat: The primary affect of preheat is to control the cooling rate. It slows the cooling rate of the weld area through the critical temperature range, preventing excessive hardening and lower ductility in both the weld and heat affected zone of the base metal. If the weld is cooled too rapidly, the normal shrinkage stresses can cause the weld to crack. By cooling the weld more slowly, the shrinkage stresses relieve themselves by stretching the weld metal while the weld is still hot. This is extremely critical with highly restrained joints. Cracks can develop in any improper pass; they may then be covered by later passes so the weld cracks are not always visible on the surface.
» Preheating may be performed by furnace heating, localized gas torches, or thermal strip blankets.
» Localized preheating shall be done in a manner to assure that the weld area and 12" beyond are uniformly heated through the material thickness.
» Preheat must be maintained until all welding has been completed.
» Cyclic heating and large temperature differentials should be avoided.
» Preheat temperatures shall be measured on both surfaces of the plate when possible. Tempil® Sticks may be used for temperature determination. Minimum preheat temperatures shall be checked regularly to assure compliance with this procedure.
» The weld area should be shielded from wind and inclement weather. Shielding should also be employed until the weld area has cooled to within 50°F of ambient.
» Minimum preheat should be reached before gouging or welding is initiated.
Weld Interpass Temperature:
» Interpass temperature should be measured near the weld area; within 1" of the next weld pass in the standard location.
» Maximum interpass temperature shall be 500°F. Welding should not resume until the material has cooled below the maximum interpass temperature. Temperature measurements should be made immediately before initiating subsequent weld passes
Filler Material:
1. Shielded Metal Arc Welding:
» Welding electrodes shall meet AWS 5.5 classification. Tricon® uses and recommends Tri-Weld® 3 small electrodes for all Tri-Braze® applications .
» Electrode size for this procedure should not exceed 3/16" diameter.
» Precautions shall be taken to ensure the electrodes are free of moisture. After removal from newly opened cans, the electrodes shall be places in "hot box" holding ovens at 300 / 350°F and held until used. Electrodes exposed to moisture can be baked at 800°F for one hour then returned to the holding oven.
» Follow electrode manufacturers' recommended procedures for handling low hydrogen electrodes.
2. Flux Cored Arc Welding:
» Flux cored wires should meet AWS 5.29 specifications. Tricon® uses and recommends Tri-Weld® 3 FCG for all Tri-Braze® applications.
» Wire should not exceed 3/32" diameter.
» Recommended wire manufacturers' procedures should be followed to assure the wire is free of moisture.
» Use manufacturers' specifications for gas mixtures and parameters.
3. Submerged Arc Welding:
» Tri-Braze® can also be submerged arc welded using the proper flux and wire. Since many wires are designed to run in specific fluxes, it is advisable to check the manufacturer's recommendations.