Crushers control

The objective of crusher control is usually to maximize crusher throughput at some specified product size, without overloading the crusher. Usually onlv three variables can be adjusted feed rate, crusher opening, and feed size in the case of a secondary crusher. Four modes of control for a crusher are (1) Setting overload control,... 

Robustly constructed apron conveyors have proved most suitable for feeding. They fulfil all requirements applicable to a feeding system in order to obtain optimum utilization of the crusher control of the handling rate within a certain range, controllability in response to the loading condition of the crusher, feed over the full working width of the crusher, ability to start under load, feed can be stopped instantly (no after-trickle of material that could choke the slowing- down or stopped crusher). 

Control of Crushers Lower-grade raw materials, higher energy costs, larger-scale operations, and more complex, capital-intensive plants make automatic control of size-reduction equipment more important (Suominen, 21st International Symposium—Applications of Computers and Operations Research in the Mineral Industry, 1011-1018). Benefits are increased productivity, process stability and safety, improved recoveiy of mineral values, and reduced costs [Horst and Enochs, Engineering Mining J., 181(6), 69-171 (1980)]. 

Improved sensors allow computer monitoring of the system for safety and protection of the equipment from damage. Sensors include lubrication-flow monitors and alarms, bearing-temperature sensors, belt scales, rotation sensors, and proximity sensors to detect ore level under the crusher. The latter prevent jamming of the output with too high an ore level, and protect the conveyor from impact of lumps with too low an ore level. Motion detectors assure that the conveyor is moving. Control applied to crusher systems including conveyors can facilitate use of mobile crushers in quarries and mines, since these can be controlled remotely by computer with reduced labor. 

Sturtevant two-roU crushers are available in capacities from 2 to 30 hp (1.5 to 22 kW). The gap is controlled by a hand-wheel. Rolls are hard-surfaced for wear resistance. 

Han (H3) and Han and Wilenitz (H4) have also presented steady-state models of fertilizer granulators based on population balance on the granules in the process loop operating in the snowballing mode. From the viewpoint of process control some interesting interrelationships between various recycle ratios, crusher speed, crusher product size, and the granule growth rate have been established. 

Baghouse systems efficiently control particulate emissions from grinding and blending processes. Vents from feed hoppers, crushers, pulverizers, blenders, mills, and cyclones are typically routed to baghouses for product recovery. This method is preferable to using wet scrubbers. However, even scrubber effluent can be largely eliminated by recirculation. 

After inhalation exposure, the primary route of excretion is in the feces following ciliary clearance from the lungs to the gastrointestinal tract (Wrenn et al. 1981). Fecal excretion may account for as much as 97% of total excretion (Fisher et al. 1983). Higher levels of thorium-230 were excreted in the feces by active crushermen (uranium mill workers exposed to uranium ore dust in the crusher building) compared to retired workers or controls (Fisher et al. 1983). Levels of thorium-230 in the urine were comparable to those of retired workers, and the levels in both were significantly greater than controls. 

Industrial applications of these controllers have been successfully carried out in Sweden on paper machines (9.) and on an ore crusher system (3.). A good discussion of the practical aspects of the approach and an application to the control of a packed bed tubular reactor is contained in a paper by Harris et al. (12). 

Monitoring and controlling the roll speed and force and the feed screw speed and torque are adjusted through PLC for process controls. Prebreaker and flake crushers are attached sizing features. CIP capability exists. 

Pressure control, which provides settings that give maximum crusher force, and hence also throughput. 

Feeding-rate control, for smooth operation. Setting control influences mainly product size and quality, while feed control determines capacity. Flow must also be synchronized with the feed requirements of downstream processes such as ball mills, and improved crusher efficiency can reduce the load on the more costly downstream grinding. 

These tertiary crushers employ smooth or toothed heavy-duty impact and abrasion-resistant steel-rimmed rolls. The rolls are mounted inline in a horizontal manner and turn toward each other at equal speeds to create a nip into which a friable feed material is introduced (Fig. 4). Heavy-duty compression springs with automatic reset are used to dampen crushing shock and to protect the crusher from tramp iron and oversize material. An adjustable screw that adjusts spring tension changes the crusher opening. A flywheel is used to even out pulses and economize on power consumption. These crushers have a theoretical maximum reduction ratio of 4 1 and will only crush materials to about 10 mesh. Roll crushers produce a controlled product size distribution without a lot of fines. The narrow particle size distribution is achieved by controlling a combination of variables including roll speed, gap measure, differential speed, feed rate, and roll surface. 

Other plant sections, such as coal crushers and dryers, also need dedusting with the possibility to recycle the collected solids to briquetting. Modern installations will, in addition, feature subdivision of the plant into individually controlled, more or less enclosed volumes which are kept at slight negative pressure by a suction system to clean the air and satisfy environmental requirements for the workplace. 

Hammermills are capable of reducing 3 inch diameter rock to less than Vi-inch diameter in a single step. Hammermill designs typically include an outlet screen that controls die size of particles leaving the crusher. Hammermills are available in standard sizes to meet the relatively low through-put required and are shipped within reasonable delivery times from a variety of vendors. The hammermill was selected as the preferred type of rock crusher for explosives-contaminated rock debris. 

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