Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/120734
Equipment Management A calm pool area at the back of the screw washer allows for maximum fine sand retention. Polyurethane wearing shoes often provide the best wear life on natural sand. • To ensure that the sand product discharging from a fine material screw washer is as dry as possible, the proper amount of wash back, or flushing water, needs to be injected in the dry deck dewatering area. The addition of water in two places in the dry deck area ensures the least amount of moisture in the sand discharging from a fine material screw washer. The addition of a dewatering screen following a screw washer can reduce the moisture content of sand by up to half. Maintenance While the fine material screw washer may be among the simplest machines to maintain in an aggregate plant, appropriate safety precautions must always be taken, including a lock out-tag out of the motor starters. Proper lubrication of the bearings that support each end of the screw shaft should provide long bearing life since the speed of a shaft is very slow in comparison to other types of process equipment. The lubrication needs of seals on submerged rear bearings, if a part of the manufacture's design, are less than the needs of the bearing itself, but assure proper protection of the rear bearing. A non-lubricated seal almost always leads to more frequent rear bearing failures and subsequent downtime with a loss of production. If the discharge end of the screw shaft is supported by a standard pillow block bearing, it is often recommended that a lube line be run down the support to near ground level so that maintenance personnel can regularly supply grease if a service platform is not at the level of this bearing. Typically, the screw shaft is turned by a motor/V-belt drive and shaft-mounted reducer. Changing of the reducer gear oil in accordance with the manufacturer's recommendation usually provides long life for this component. If the reducer on the machine has been in service for several years, periodic evaluation for contaminants in Screw shaft speed, which in many instances is set by the manufacturer for the original application, may need to be adjusted if the screw is turning too fast for finer sand. the gear oil is warranted to avoid an untimely failure in the middle of a critical production period. Periodic inspection of V-belts for both wear and tensioning is also recommended to reduce downtime and unexpected failure. The need to replace wear shoes can easily be made by visual inspection. Replacement shoes are typically available in the manufacturer's standard iron, urethane, or rubber types. The best abrasion-resistant material for wear shoes may be dependent upon the chemical composition of the sand being dewatered and its physical structure. The most abrasive sand may be manufactured (granite-like) sand that can abrade or gouge synthetic wear shoes, which means these shoes do not often provide suitable life when compared to their costs. Doing your own check-up or getting the assistance of the manufacturer's local distributor/representative can often provide more product-sized sand retention and less downtime, providing the highest possible availability for the operation of a fine material screw washer. AM Dave Schellburg is McLanahan Corp.'s application specialist - Processing Engineering and Rick Madara is its sales manager - Aggregate Processing. They may be contacted at dschellberg@mclanahan.com and rmadara@ mclanahan.com. Aggregates Manager April 2013 31