Controlled-rate dispensing

In contrast to the emphasis placed upon the enhancement of storage capacity with bin discharge screws, feeders designed for controlled-rate dispensing have the prime objective of securing reliable, predictable, and controllable solids flow. Two conditions have to be satisfied first, to ensure the flow channel is smooth and continuous in all conditions of operation second, that the volume of the feed screws fills in a consistent manner with loose solids in as uniform a state of density as possible. In general, a mass flow channel best serves both objectives, due to its performance reliability and because the total flow channel passes all the... 

One of the conditions for the dispensation was that the hoists will be designed to use a closed-loop braking system, which provides a more controlled rate of retardation than other types of braking systems used in hoisting applications, irrespective of the position of the conveyance in the shaft. This ensures, in most cases, smaller loads on the ropes under braking. 

Z Acceleration — Certain printing mechanisms involve striking the surface with the quill pin to dispense a droplet onto a substrate. Control of the acceleration rate can be useful in ejecting the droplet without crashing the pin into the substrate (sometimes called overdriving Figure 4.30). Not all arrayers have this feature. 

At present the only reliable method of dispensing powder shotcrete admixtures directly into the wet mix at a uniform rate at the nozzle is by the use of a log feeder. In this method the powder is compressed to a log which, when placed in the feeder, is gradually ground off and carried away in the air stream to the nozzle. The accelerator mixes with the other shotcrete ingredients at the nozzle and in transit to the sprayed surface. The amount of admixture added is controlled by the rate of advance of the log in the feeder. The method of dispensing liquid admixtures in a wet mix is essentially the same as that used in the dry-mix operation, except that admixture is injected into the air stream instead of the water line. 

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