Today more than ever, there is an increased demand for higher plant production capacities and efficiencies to offset the increasing costs for labor and materials.
Plants involved in processing large volumes of bulk materials are particularly interested in more efficient material handling systems to (1) reduce labor and maintenance costs, (2) improve blending of non-uniform raw material feed to processing facilities, (3) improve blending of finished bulk materials from storage.
Dragscraper systems are being used effectively for handling a variety of bulk materials in both indoor and outdoor storage. Materials being handled include ores, chemicals, coke, clay, and stone, to name a few. Handling capacities these machines can provide vary from a few tons to over 1500 tons per hour.
The basic components of a Dragscraper machine consist of a bottomless Crescent scraper, a two or three-drum Dragscraper hoist assembly including gas, diesel, or electric power unit, operating cables, guide blocks, and either fixed or mobile head and tail structures. They are presently available in sizes through 15 cubic yards, for operating spans up to 1000 feet.
In reclaiming from a rectangular shaped ground storage, the Crescent scraper can load out material to a belt conveyor, installed at grade along one side of the storage area or, if-the head tower includes a mobile scraper ramp, the material can be loaded directly into hopper cars parked on RR tracks parallel to the storage pile.
A Dragscraper storage machine is equipped with rail mounted self-propelled head and tail towers. This machine stockpiles petroleum coke in a long rectangular shaped storage area. The coke is delivered to the storage area in side dump rail cars. The scraper machine builds a high pile and also reclaims the coke up a ramp on the head tower, for discharge directly into hopper bottom rail cars. The rail cars are parked on two sets of tracks, spanned by the mobile head tower. A single operator at a control console in the head tower handles the entire stockpiling and reclaiming operation. This machine has been in continuous service for more than fifteen years.
The machine includes two self-propelled towers traveling on rail tracks paralleling two sides of the storage area. A track cable is suspended between the two towers and a carriage rides the track cable. A fall block is suspended from the carriage by a hoisting line. The Crescent scraper is attached to the fall block and controlled by two haulage lines and the hoist line. In stockpiling, the loaded scraper can be raised gradually so the load is spread in a thin layer on the storage pile.
An indoor Dragscraper machine can reclaim ammonium sulphate which is a corrosive non-caving type material. The Dragscraper system includes an elevated tail trolley, as well as a low sidewall trolley. The machine is particularly suitable for handling corrosive materials since only the Crescent scraper and cables contact the material.
The flexibility of the automatic control equipment makes it possible to adjust the Dragscraper system to changes in handling characteristics of the material as they occur. The accuracy of control settings governing travel of the Crescent scraper is one-tenth of 1%, which makes this material handling system very effective in confined indoor storage areas.
The most expensive component of a Dragscraper machine is the Dragscraper hoist with power unit. This assembly can be located outside the storage area enclosed on a stationary concrete or steel foundation. The service life of the hoist is comparable to the service life of motor generator sets; 20 year service without major repairs is not unusual.