Blast Nozzle and Compressed-Air Equipment Tips
- Air Compressors
- Blast Nozzles
- Air Lines The air-line ID should be as large as possible and at least four times the nozzle orifice size. This principle applies to air lines up to 100 ft. With longer hoses, especially longer than 200 ft, check the air pressure at the blast machine while blasting to determine if the air-line ID is sufficient. Air flows best through unrestricted fittings and straight air lines, so lines should be laid out in as short a length and with as few bends as possible to reduce pressure loss. (See Table 2)
- Air-Preparation Equipment
Use an air compressor that is large enough to produce the air volume and pressure required to adequately and safely pressurize the blast machine, convey abrasive to the blast nozzle, provide breathing air, and operate valves and accessories. To determine the compressor size needed for a job, add the air requirements of all the equipment that the compressor will supply and then add a 50% reserve, which will be needed to keep productivity high as the blast nozzle wears—and it will wear. To maintain peak air supply, the smallest internal diameter (ID) of the compressor air outlet should be at least four times the size of the nozzle orifice. (See Table 1)
TABLE 1: Minimum Compressor Air-Line Diameter
Replace a blast nozzle after its orifice is worn to 1⁄16” (1.5 mm) larger than its original size. A worn nozzle not only wastes air, but also may lower productivity and even cause injury if the liner fails. Carbide nozzles—tungsten, silicon, and boron—are the most popular for the majority of blasting applications because of their longevity.
TABLE 2: Approximate Pressure Loss Caused by Common Fittings
Moisture in the compressed-air supply can travel into the blast machine. If this occurs, abrasive may clump, which can cause stoppages in abrasive flow. Air-preparation equipment helps prevent these stoppages. Depending on the humidity level of the air where operators are working, varying levels of air-preparation equipment may be needed. Coalescing filters provide the minimum level of moisture removal. They collect some of the water vapors that have formed into small droplets before the droplets enter the air filter. Aftercoolers cool air to condense even more moisture and then trap the moisture before it is conveyed to the blast machine. Air dryers are the most effective option for removing moisture and also oil from air.
Courtesy of Clemco Industries Corp
