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Do: Use advanced cleaning system controls. Clean-on-demand controls ensure the pulse jet clean-


ing system operates at peak efficiency with no overcleaning or undercleaning and prevents the wasting of expensive compressed air.


Don’t: Put off replacing filters past their useful service life to save on replacement costs.


Trying to save money by putting off filter replacement


results in much higher costs in the long run. Among other problems it creates, running filters too long leads to higher differential pressure, which causes: • Reduced suction and possibly lower production rates due to poor ventilation and production movement.


• Higher respirable dust levels at sources and pickup points (especially important in light of the new OSHA silica rule). Additionally, older bags have higher emissions overall and


are more prone to holes and tears. Even one filter with one hole can cause an entire baghouse to fail particulate matter emissions standards. So, running old bags means more chas- ing down leaks and spot changing filters, which consumes valuable man power and increases downtime.


Don’t: Store dust in the hopper.


Dust collector hoppers are for temporary storage only, which should be for just the few minutes it takes to remove dust through the discharge device (usually a rotary airlock). A dust in the hopper promotes dust re-entrainment; incoming air picks up dust in the hopper and throws it at the bottoms of filters. Storing dust in the hopper also is a severe fire/explosion hazard when handling any kind of combustible dust.


Do: Select the proper discharge device for the application.


Consider dust loading, the effect of dust on the discharge, combustible dust issues, and ease of access to storage containers.


Do: Keep discharge devices in good repair. On rotary airlocks, replace blades and grease the bearings


and chains as needed. Avoid beating on the hopper with a metal sledge hammer.


Don’t: Make modifications to the system without consulting an expert.


Someone experienced in dust collection system design and


operation should be consulted before doing the following: • Changing filter media. • Adding more pickup points. • Changing ductwork sizing and configuration. • Increasing fan capacity. • Changing temperature. • Adding sorbents without calculating the dust loading factor.


Bent or rusted cages in the baghouse system can cause early bag failure and frequent bag leaks.


DUST COLLECTION RED FLAGS


If the following situations rise up in a metalcasting facility, maintenance personnel should take a closer look at how the dust collection system is operating:


• Loss of suction. • Suddent increase in suction which might be heard as whistling. • Dented or worn ductwork. • Changes in collector differential pressure or fan amp draw.


• Plugging or failure to discharge material from the dust collector.


July 2018 MODERN CASTING | 29 Oil, water or dirt in the compressed air can make the system inefficient.


Don’t: Fly blind. Make sure your monitoring systems are accurate.


Accurate differential pressure readings are the most


important metric to monitor. Tese gauges regularly become blocked or fouled and need regular preventive maintenance to ensure proper function and accurate reading. Next in importance is emissions monitoring, such as triboelectric systems or opacity monitors. Secondary items requiring checks for accurate monitoring include fan RPMs, airflow air velocity, inlet/outlet temperature, and hopper level indi- cators. Temperature is especially important in systems where maintaining a temperature above the dew points is required to prevent condensation or to protect filters from damage.


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