thermal cutting tables

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Thermal cutting produces particulate that has to be filtered. Material removed during cutting generates slag smoke and fine thermally created particles. Slag typically drops to the bottom of the table floor while smoke and fine particles rise above the work piece unless adequate downward airflow— generated by the dust collection system—overcomes the thermal rise. Particles can range from sub- micron to dozens of microns in size and controlling them requires a properly selected and installed filtration system. System designs depend on the cutting environment and process parameters. A large plasma table has different airflow requirements than a small laser table. Plasma cutting produces different particle-size ranges than laser cutting. Even related functions such as automated material loading systems affect system designs because of increased cutting time. These factors are into design requirements just as much as material type and thickness cutting kerf widths and part nesting. In essence a well-designed dust collection system should transform the entire cutting work envelope into an effective fume-capture system. Design for Safety Getting dust collection right is essential for both environmental and operational reasons. In recent years OSHA has significantly lowered the permissible exposure limits of many dusts including manganese as well as hexavalent chromium from cutting chromium-rich metals like stainless steel. The EPA continues to focus on not only the reduction of particulates 2.5 microns and smaller but also other metal compounds including cadmium chromium lead manganese and nickel all produced in a variety of metal fabrication and finishing operations. Air used in controlling thermal cutting fume and contaminants can contain hot sparks. If sparks are not eliminated they can be conveyed to potential fuel throughout the dust collection system. Controlling ignition sources is therefore critical to avoid the damage and disruption fires create. Also if filtered air is returned to the production area secondary filters can confirm the operational performance of primary filters ensuring the returned air is clean and safe. Shops also must consider risks from capturing particulate of different materials when they may be incompatible. This could include particulate from dissimilar metals as an example where the metals and metal oxides may represent the potential for a thermite reaction. Combustion risks affect filter system layouts and design decisions. The National Fire Protection Association NFPA publishes several standards that can be applied to help mitigate the many risks associated with combustible metal dusts. The Hood Effective dust collection starts with hoods that efficiently capture and control particulates. System performance is limited to what the hood can accomplish. Buying the most expensive dust collector and installing high-efficiency filters will not increase overall efficiency beyond 50 percent if the hood captures only half the dust and fume.

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When thermal cutting the cutting table is the capture hood. The hood must pull consistent air volumes continuously to capture contaminants. If it doesn’t dust and fume escape. Surface Loading Versus Depth Loading Fiber area not filter area is a key to effective filtration. Designing a filter should therefore include lots of small fibers to increase the available fiber surface area by orders of magnitude. Basic traditional filter media enhanced with a layer of nanofibers will provide the best filtration performance in capturing fine particles from thermal cutting. This layer of nanofibers increases the filter media’s efficiency dramatically when working with thermally generated particles. Nanofibers also prevent fine particles from embedding deep within the filter fibers forcing particles to accumulate at the media’s surface see Figure 1. This creates an extremely effective surface-loading filter.

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