Central Dust Collection Complicates Multi-Cabinet Systems
Large plants often rely on one central system to pipe compressed air to all air tools and blast equipment, because doing so can be more efficient than operating compressors at several locations within the plant. This example often leads plant engineers to believe that a central dust collector can provide the same efficiencies. The difference: a compressor keeps a large reserve tank pressurized, cycling on only when air demand in the plant takes the reserve below a predetermined pressure; but a dust collector has no vacuum reserve. It must run continuously, whether it’s supporting all the blast cabinets in the plant or just one.
For applications where all the cabinets do not routinely run at once, using dedicated dust collectors for each cabinet reduces energy and media consumption and increases overall efficiency.
When It Causes Problems
The explanation: If the collector is sized to exhaust dust and air from 10 cabinets and only one is running, it will pull too much air through that one cabinet. This can carry good media into the collector and spoil the working mix. In shot peening applications, the inability to maintain the proper working mix can cause wide fluctuations in peening intensity and coverage.
Insufficient inlet openings will leave dust and media to build up in the cabinet sump. An open door in one or more of the other cabinets reduces the amount of air drawn through the operating cabinet(s), thereby reducing the amount of media conveyed from the sump to the reclaimer. And, every time doors open or close on any other cabinet, airflow through the other cabinets will fluctuate, affecting media cleaning.
Having several blast cabinets tied to one dust collector creates other problems as well. (1) Keeping the vacuum properly balanced may require a complex system of baffles, dampers, air make-ups, ductwork, and auxiliary blowers. Keeping everything properly tuned can turn into a full-time job. (2) When the central dust collector needs repair or maintenance, all blasting stops.
When It Does Work
For some applications, a central dust collection system does make sense. If the plant already has a busy blast room with a dust collector, connecting one or two small cabinets to hand the occasional small parts run can increase a plant’s capacity at the cost of the cabinets only. Because the blast room dust collector will draw much more air than the cabinet reclaimers can handle, it’s necessary to install a high-quality damper in the duct work to control the flow of air. If a plant operates several automated or manual cabinets more or less continuously, a central collector can save on the initial purchase, save space, and conserve energy.
A final word of caution – never connect blast equipment to a dust collector serving welding or grinding equipment. Some types of dust from blasting may ignite if exposed to sparks or hot slag particles.