Material holding, feeding, and metering

Date: 2015-10-07; view: 552.

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The movement of material from the place where it is to place where it is needed can be time consuming, expensive, and troublesome. The material can be damaged or lost in transit. It is important, therefore, that it be done smoothly, directly, with the proper equipment and so that it is under control at all times. The several factors that must be known when a material handling system is designed include:

1. form of material at point of origin, e.g., liquid, granular, sheets, etc.

2. characteristics of the material, e.g., fragile, radioactive, oily, etc.

3. original position of the material, e.g., under the earth, in cartons, etc.

4. flow demands, e.g., amount needed, continuous or intermittent, timing, etc.

5. final poison, where material is needed, e.g., distance, elevation differences, etc.

6. in-transit conditions, e.g., transocean, jungle, city traffic, inplant, etc., and any hazards, perits, special events or situations that could occur during transit

7. handling equipment available, e.g., devices, prices, reliability, maintenance needs, etc.

8. form and position needed at destination

9. integration with other equipment and systems

10. degree of control required

Other factors to be considered include:

1. labor skills available

2. degree of mechanization desired

3. capital available

4. return on investment

5. expected life of installation

Since material handling adds expence, but not value, it should be reduced as much as possible with respect to time, distance, frequency, and overall cost. A straight steady flow of material is usually most efficient. The use of mechanical equipment rather than humans is usually, but not always, desirable – depending upon the duration of the job, frequency of trips, load factors, and characteristics of the material. When equipment is used, maximizing its utilization, using the correct equipment, proper maintenance, and safety are important considerations.

The proper material handling equipment can be selected by analyzing the material, the route it must take from point of origin to destination, and knowing what equipment is available.

Material handling may be divided into classifications or actions related to the stage of the process. For some materials the first stage is its existence in its natural state in nature, e.g., in the earth or ocean. In other cases the first stage would be its receipt at the factory's receiving dock. Subsequent material handling actions might be:

1. holding, feeding, metering

2. transferring, positioning

3. lifting, hoisting, elevating

4. dragging, pulling, pushing

5. loading, carrying, excavating

6. conveyor moving and handling

7. automatic guided vehicle transporting

8. robot manipulating

9. identifying, sorting, controlling

10. storing, warehousing

11. order picking, packing

12. loading, shipping

Material may be in solid, liquid, or gaseous form. Solid material may be in end-product shapes or in intermediate forms of slabs, sheets, bars, wire, etc., which may be rigid, soft, or amorphous. Further, each item may be unique or all may be the same, allowing for indiscriminate selection and handling. Items may be segregated according to some characteristics or all may be commingled in a mixed container. They might have to be handled as discrete items, or portions of a bulk supply may be handled. If bulk, as coal or powder, their size, size distribution, flowability, angle of repose, abrasiveness, contaminants, weight, etc., must be known. In short, before any material can be held, fed, sorted, and transported, all important characteristics of its form must be known.

Devices used to hold material should be selected on the basis of the form of the material, what is to be done to it while being held (e.g., haeted, mixed, macerated, dyed, etc.), and how it is to be fed out of the device. Some such devices are tanks, bins, hoppers, reels, spools, bobbins, trays, racks, magazines, tubes, and totes. Such devices may be stationary – either with or without moving parts – or moving, e.g., vibrating, rotating, oscillating, or jogging.

The material holding system is the first stage of a material handling system. Efforts should be made to assure that the holding devices never become empty, lest the entire system's flow stops. They can be refilled manually or automatically and have signals to call for refills at carefully calculated trigger points.

Material can be fed from its holding devices to processing areas in several modes: randomly or by selection of individual items, pretested or untested, linked together or separated, oriented or in any orientation, continuous flow or interruptible flow, specified feed rate or any rate of flow, live (powered) or unpowered action, with specific spaces between items or not.

The feeding and metering devices selected depend on the above factors and the properties of the material. Some, but not all, possible devices include: pumps, dispensers, applicators; feedscrews, reciprocating rams, pistons; oscillating blades, sweeps, arms; belts, chains, rotaries, turnables; vibratory bowl feeders, shakers; escapements, mechanisms, pick-and-place devices.

There is frequently a need to transfer material from one machine to another, to reposition it within a machine, or to move it a short distance. This can be accomplished through the use of ceiling-, wall-, column-, or floor-mounted hoists, mechanical-advantage linkages, powered manipulators, robots, airflow units, or special devices. Also turrets, dials, indexers, carousels, or conveyors can be used; their motion and action can be: in-line (straight line) – plain (without pallets or platens), pallet or platen equipped; rotary (dial, turret, or table) – horizontal, vertical; shuttle table; trunnion; indexing or continuous motion; synchronous or nonsynchronous movement; single- or multistation.