Most fabricators know they can’t use the same grinding wheel on both carbon steel and stainless steel. No matter what grinding wheel a fabricator chooses, it needs to keep the potential of contamination in mind. They’re well-suited for stainless applications because they remove large chips quickly, generating less heat and distortion.Ī worker at the weld prep station grinds stainless steel pipe. This usually makes ceramic grinding wheels well worth their extra cost. This means they can remove material extremely quickly, often in just a fraction of the time other grinding wheels can. Instead of wearing down smooth, they maintain their sharp edge as they gradually break down. Wheels with zirconia grains grind faster than aluminum oxide, but in most cases a ceramic grinding wheel works best.Įxtremely tough and sharp, ceramic grains wear in a unique fashion. To that end, it helps to choose a grinding wheel with the fastest removal rate possible for the application and budget. The goal is to keep stainless steel as cool as possible throughout the process. Again, excessive heat can cause bluing and change the material properties. Grinding StrategiesĪ grinder with a low-removal-rate grinding wheel can face significant challenges working with stainless steel. A prime example is a stainless part with a good-looking gas tungsten arc weld that only needs to be blended and matched to the base material’s finish pattern. Parts that require only finishing are fabricated in such a way that they don’t require excessive amounts of material removal. Parts that undergo only grinding do so because grinding is the fastest way to remove a weld or other material, and the deep scratches left by the grinding wheel fall well within customer requirements. Quite often workpiece surfaces designed with manufacturability in mind do not require both grinding and finishing. But again, they’re not complementary processes. This sequence, moving from grinding to finishing, might still be the most effective way to meet a customer’s finishing requirements. To remove excess weld metal an operator uses a grinding wheel and leaves very deep scratches, then passes the part on to a finisher who now must spend a lot of time removing those deep scratches. And each step (finer grit) removes the deeper scratches from the previous step and replaces them with smaller scratches.īecause grinding and finishing have different goals, they often do not complement one another and, with the wrong consumable strategy, actually can work against each other. The goal is to achieve a certain final finish (scratch pattern). But in grinding, scratches are just the aftereffect quick material removal is the goal, especially when working with heat-sensitive metal like stainless steel.įinishing occurs in steps as the operator starts with a larger grit and steps down to finer-grit sanding discs, nonwoven abrasive, and perhaps a felt cloth and polishing paste to achieve a mirror finish. The confusion is understandable, considering those grinding with a large-grit wheel remove a lot of metal quickly and in so doing leave a “finish” of very deep scratches. Grinding removes material like burrs and excess weld metal, while finishing puts a finish on the metal surface. In fact, each has a fundamentally different goal. How can fabricators prevent all this? They can start by developing a knowledge of grinding and finishing, what role each plays, and how each affects a stainless steel workpiece. Add complications like contamination and passivation failure, and a once profitable stainless steel job can become a money-losing, even reputation-losing misadventure. Add an expensive, heat-sensitive material like stainless steel, and costs for rework and scrap mount even more. Mistakes in finishing can be extraordinarily expensive, considering all the value that’s already been put into the workpiece. Usually performed manually, grinding and finishing require dexterity and finesse. In this case this means the part won’t meet customer requirements. Then, alas, some significant bluing emerges on the surface-a telltale sign of excessive heat input. So the grinder spends time removing a bit more weld metal than usual. The weld looks OK, but it’s not the stack-of-dimes perfection the customer is looking for. The part consists of a plate welded vertically to a tube. Sheet metal and tubular sections flow through cutting, bending, and welding, then land at the finishing station. Imagine a fabricator lands a contract involving critical stainless steel fabrication. Images provided by Walter Surface Technologies To ensure proper passivation, a technician electrochemically cleans a longitudinal weld seam in a rolled section of stainless steel.
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