MATERIALS HANDLING
The longer the enclosure, the more time dust has to settle, making for a cleaner work environment
seal and clamping arrangement. With an engineered approach the height of the skirtboards is based on keeping the air speed in the enclosure below 1.0m/s. At this air speed, most nuisance dust will settle in the enclosure. When taking this approach, the quantity of air flowing through the enclosure is estimated by considering the displaced air from the initial loading, the induced air created by
Skirtboard sealing system components
the separation of the material discharge stream and any generated air from prevailing winds or process equipment such as crushers or screens. For existing enclosures simply measure
the average air speed at the exit. If the average speed is 3.0m/s then the cross- sectional area of the enclosure needs to be three times the existing area (i.e. three times the height) to reduce the exit air speed to 1.0m/s.
LENGTH OF SKIRTBOARDS As with the width of the skirtboards there are various generic rules for the extended length of the skirtboards. Te extension serves two purposes, first, it prevents spillage as the load settles into a stable profile after loading. Generic rules for containing turbulent flow range from 1.8m extension past the dump point or 1.5m plus 1.2m for every 1.0m/s of belt speed. Secondly, the extension helps settle nuisance dust without extraction, so, 1.2m per 1.0m/s for minor airflow
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and 1.8m per 1.0m/s for major airflow is one recommendation for dust control. Te ACGIH Industrial Ventilation manual provides guidance when collection is needed for respirable or hazardous dust. In general, it is good practice to make the extension generous in length and height, keeping in mind there is added friction from seals and material rubbing on the liners. Tis can be a major additional load on the drive for long lengths of skirting.
IN SUMMARY Designing an effective skirtboard system requires an iterative approach. Starting with basic capacity calculations ensures the belt is wide enough to accommodate the free belt edge, the sealing system, wear liners and expected mistracking allowance. Old design rules and fabricated solutions only work for the short term and often result in more maintenance. Installing a well-designed skirtboard sealing system for safety, ease of maintenance and less downtime is part of a cost-effective production plan with the greatest return on investment.
R. Todd Swinderman is president emeritus at Martin Engineering.
www.martin-eng.com
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