Page 30 - MetalForming February 2020

FABRICATION
Photos courtesy of Norton | Saint-Gobain Abrasives
Finishing Steel Weld Seams
Approaches and abrasive selections differ when finishing carbon steel or stainless steel welds. Here’s how to navigate the process for each material.
application. For instance, a highly refined finish may be used for aesthetic purposes, whereas an elevator wall panel or hand rail requires a functional No.4 finish to disguise the visibility of fingerprints and scratches.
Finishers working with both mate- rials should keep them in separate areas of the shop as well as any abra- sives used to avoid cross-contamina- tion, especially when transitioning from carbon to stainless steel finishing.
Initial Weld Grinding
Weld finishing for both carbon and stainless steel involves the same initial stage: removal of excess stock from the weld itself, with the aim to grind the joint down to a level and continuous surface with the rest of the parent metal. To achieve this initial stock removal, should the surface finish be deemed nonessential, the metal worker might choose to use a simple grinding wheel with an angle grinder.
Although a grinding wheel can be used for stock removal on both mate- rials, a high level of skill and experience is necessary to achieve a passable qual- ity result on stainless steel. Often, a fin- isher may choose a flap disc when work-
Transforming a component from as-welded to final requires fore- thought and adherence to need- ed steps to ensure an ideal finish. Fol- lowing the correct finishing sequence, and using the correct techniques and abrasive products, will deliver optimal results.
Prior to welding, particularly when working with carbon steel, clean the workpiece to remove any mill scale formed from the hot rolling manufac- turing process. Mill scale can interfere with weld quality.
Finishing Carbon Versus Stainless Steel
The decision over finishing require- ments links strongly to the application of the finished piece and the base mate- rial itself. Note that not all welds require seam removal in order to achieve a functional piece. This is especially true for carbon steel—it’s almost always
painted, or the seam otherwise may not be visible. Examples include under- sea piping or when the metal serves a structural function and hides behind a panel. Note, too, that unfinished welds are inherently stronger than finished welds due to the material removal involved in grinding them down.
In finishing carbon steel, a fairly simple process, the majority of cases involve preparing the steel only where paint will be applied. A rough and well-scratched surface helps the paint adhere better to the metal than a high- ly finished surface. In fact, for powder coating applications, a coarse-grained two-step weld removal probably is sufficient.
Stainless steel, intrinsically stronger than carbon steel, generally is of much thinner gauge. This feature has impli- cations for grinding, which will be dis- cussed later. The weld finish for stain- less steel also depends on the
28 MetalForming/February 2020
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