PT ZONE: Focus on Material Handling

Single Screw/Auger – Photo – ArtThe widely used rotating single screw or auger is a familiar and straightforward approach. More (+)
Twin Screw/Auger – Photo – ArtWhere the material’s handling characteristics are too challenging for one screw, two screws operating side by side often provide the needed solution whether for floodable or hard to flow materials.The basic twin screw design employs a pair of milled, concave-profile screws set 90o out of phase with each other so they fully intermesh. More (+)

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Bulk Solids Pump – Photo – Principle ArtBSP technology does not use the usual screws/augers, belts, pockets or vibratory trays to convey the material.

Vibratory Tray / Tube – Photo – ArtBecause of ability to gently handle and move material, vibration may be a suitable strategy to control free-flowing, abrasive, friable and fibrous materials.

Cone – Photo – ArtA properly configured, tapered cone, slowly rotating about its horizontal axis, can act to induce flow toward discharge at its narrow end.

Rotary Valve/Delumper – Photo – ArtRotating material halfway around a circle gives the rotary valve an advantage similar to the twin screw and Bulk Solids Pump approaches: that of capturing material in a confined space, moving it to another point, and discharging the load.Rotary valves, also referred to as rotary airlock feeders, rely on gravity to receive and discharge material.

Pumps & Control Valves – PhotoIn the context of application in the loss-in-weight feeding of critical liquids, slurries or pastes whose specific gravity varies sufficiently to warrant gravimetric flow control, a holding tank and pump or control valve replaces the standard hopper and metering device combination required in the feeding of solid materials.Because loss-in-weight feeding involves weighing the entire material containment and handling apparatus, the type of pump or control valve employed becomes irrelevant.

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Focus on Material Handling


Focus on Material Handling

A feeder's most basic mission is to handle the material and produce a uniform and consistent discharged stream. This section details various common solutions to achieving this fundamental requirement. Advantages and limitations of each approach are also discussed.

The first leg of the gravimetric feeding triangle, material handling, refers to a feeder’s ability to condition the material (if and as required) and produce a reliably consistent and uniform volumetric discharge stream. If the feeder’s material handling system can perform this essential task, appropriate control adjustments can then be applied (based on continuous weight data) to achieve and maintain the desired gravimetric discharge rate.

Well behaved materials, such as most plastic pellets or free-flowing, non-packing powders typically pose few handling problems, tend to maintain a consistent density when handled, and thus are readily controllable.

However, more difficult materials (compacting, poor flowing, sticky, clumpy, hygroscopic, floodable, etc.), often require feeding elements and density conditioning measures specially matched to meet the handling challenge.

To accommodate the broad range of plastics resins, additives, forms and handling characteristics, a spectrum of material handling strategies is required including:

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