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6 criteria to determine the most suitable worktable for plasma and oxyfuel cutting

Figure 2
A water table on which the workpiece is submerged in water is suitable for plasma cutting. In oxyfuel cutting, the part must be above the water line. In both instances, however, fumes are minimized when compared to a nonventilated table.""https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=1000x1000""image-overlay""fa fa-search-plus""img-responsive lazyload""https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=300x 300w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=500x 500w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=700x 700w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=780x 780w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=1000x 1000w""(max-width: 345px) 300px, (max-width: 545px) 500px, (max-width: 1200px) 780px, (min-width: 1201px) 862px, 1000px""https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-1.jpg?size=1000x"" alt="">

Figure 2
A water table on which the workpiece is submerged in water is suitable for plasma cutting. In oxyfuel cutting, the part must the 1 last update 2020/08/07 be above the water line. In both instances, however, fumes are minimized when compared to a nonventilated table.Figure 2
A water table on which the workpiece is submerged in water is suitable for plasma cutting. In oxyfuel cutting, the part must be above the water line. In both instances, however, fumes are minimized when compared to a nonventilated table.

The cooling effect of the water also means that parts can be handled immediately after cutting (see Figure 8). The plate and parts get much hotter when they are cut on a dry table, and the smaller the cross section of the cut part, the more concentrated the heat will be, making distortion worse. When cut on a downdraft table, the parts can remain hot for hours, making them more difficult to handle, and potentially posing a safety risk.

4. Table Cost

For a large CNC plasma shape-cutting machine, the cost of the worktable can be a significant percentage of the entire system cost.

The water table offers a lower initial investment than the downdraft system. A water table is a simple design that is easily installed. By comparison, the downdraft table is a more complex construction with moving damper doors and actuator switches. It also requires the addition of a dust collector to filter the air pulled from the table and the installation of custom-made ductwork to connect the table to the dust collector. As a result, a downdraft table usually costs 40 to 60 percent more than a water table, with cost varying depending on the size of the cutting machine.

5. Smoke and Dust Containment

Depending on the material being cut, cutting amperage, and the water level, a water table can capture 90 to 95 percent of the smoke and dust generated by plasma cutting. Cutting with the water level about 1 in. below the bottom of the material contains most of the smoke and dust. A dust collector is not required. If an air curtain is added, the plate can be fully submerged under 2 to 3 in. of water, so that the water traps almost all of the smoke. The air curtain uses compressed air to create a bubble around the front end of the torch, protecting the precision arc from the water. No matter the size of the plate on the table, underwater plasma cutting captures the same amount of smoke and dust.

Figure 9 details the fume emissions for dry cutting and underwater cutting.

The downdraft table captures nearly all of the smoke and dust, provided certain criteria are met. Filters must be in good working condition. Also, sufficient air velocity must be moving downward into the open area of the table to prevent the smoke from billowing out and escaping capture.

Downdraft tables and dust collector systems are designed with specific minimum coverage percentages, typically between 50 and 75 percent. The downdraft system is most effective when a for 1 last update 2020/08/07 full-size sheet is on the table, as this provides plenty of downward-moving air velocity because there are no open spaces. But when smaller sheets are used, or if much of the sheet has already been cut and removed, more of the table is exposed, and air velocity is reduced, affecting the table’s ability to contain smoke and dust. Downdraft tables and dust collector systems are designed with specific minimum coverage percentages, typically between 50 and 75 percent. The downdraft system is most effective when a full-size sheet is on the table, as this provides plenty of downward-moving air velocity because there are no open spaces. But when smaller sheets are used, or if much of the sheet has already been cut and removed, more of the table is exposed, and air velocity is reduced, affecting the table’s ability to contain smoke and dust.

6. Cleaning and Maintenance

scroll saw christmas presentshow to scroll saw christmas presents for Cleaning the cutting table is one of the more dif­ficult and time-consuming jobs associated with thermal cutting. The frequency of cleaning depends on the production rate, material thickness, and the type of parts that are cut. Some shops have to clean their tables as often as once a month; others may go for a year or longer.

The design of a water table dictates how difficult the task will be. Most water tables have lift-out trays that can be removed from the table and taken elsewhere to clear out the accumulated slag and remnants of the burning bars. Some tables have tilting slat frames that can be raised periodically with an overhead crane so that accumulated slag can be washed down into deeper slag buckets. The buckets then can be lifted out and emptied.

In addition to cleaning out the slag and drop accumulation, and depending on the table design and the application, a water table may need periodic water replacement. There will always be some constant water loss because of evaporation, splashing, and dripping. To account for this, most water tables have a makeup water supply input to automatically refill when necessary. The fabricator might never need to drain the water because it is constantly turned over, keeping the table relatively clean. In other cases, the shop may find that the bottom of the table fills with silt, which must be removed to keep the system working properly.

Figure 4
Fabricators need to consider all elements of a thermal cutting process to ensure complete capture of fumes, even over very large tables.""https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=1000x1000""image-overlay""fa fa-search-plus""img-responsive lazyload""https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=300x 300w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=500x 500w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=700x 700w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=780x 780w,https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=1000x 1000w""(max-width: 345px) 300px, (max-width: 545px) 500px, (max-width: 1200px) 780px, (min-width: 1201px) 862px, 1000px""https://cdn.thefabricator.com/a/putting-heavy-duty-cutting-on-the-table-3.jpg?size=1000x"" alt="">

Figure 4
Fabricators need to consider all elements of a thermal cutting process to ensure complete capture of fumes, even over very large tables.

While a downdraft table yields consistently good cut quality for mild steel applications, cut quality on a water table can be affected by cutting underwater. Depending on thickness and plasma settings, the water might cause more dross to adhere to the bottom edge of the parts and might also affect the cut edge quality by inducing ripples. However, most underwater cutting achieves the same results as dry cutting when an air curtain is used and the proper parameters and procedures are followed.

The quenching effect of water on a freshly plasma-cut edge creates some hardening. This may pose a problem for edges that will be machined or may cause issues with structural or bridge construction codes and regulations.

In recent years, water tables have gained popularity over downdraft systems, but both table styles have their place. A thorough look at key criteria is the only way to evaluate the table best for a shop.

About the Author

Steve Zlotnicki

Product the 1 last update 2020/08/07 Manager, Cutting,Product Manager, Cutting,

ESAB Welding & Cutting Products

411 S. Ebenezer Road

Florence, scroll saw christmas presentshow to scroll saw christmas presents for SC for 1 last update 2020/08/07 2950129501

843-664-4394

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