About Triple/S >Glossary of Terms
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GLOSSARY OF TERMS
The following conveying and screening terms are written as a form of reference for material handling in the processing industries.
Conveying
Engineering
Screening
CONVEYING
Accumulation Conveyor
This storage conveyor is simply a horizontal discharge bin with no mechanisms or moving parts in the food zone. This feature offers quick and thorough clean-out for enhanced sanitation and a greatly reduced risk of cross contamination between product runs.
Bed Section
Conveying equipment which has a belt which can be made from a variety of materials such as cotton or PVC that carries or conveys material to a distribution point. It is held together by pulleys at either end for continuous flow.
Bed
The pan or bed where the material being conveyed is held, slides or moves across while in movement down the conveying line.
Bed Length
How long the pan length is.
Bed Width
How wide the pan is.
Belt
The belt can be made of several materials such as cotton or PVC. It is placed around atleast two pulleys to create a continuous motion to carry materials.
Belt Speed
Is measured in Feet Per Minute (FPM). A section of belt that moves past a fixed point within a given point in time.
Diverter
A diverter moves materials to a different point or section of the conveying process. Can be used to sort, accumulate or merge material.
Drive
The mechanism that gives the conveyor power.
Gate
A gate opens and material is moved to a different point or section of the conveying process. Can be used to sort, accumulate or merge material.
HZ
A unit of electrical frequency. Usually a unit of frequency is equal to one cycle per second.
Overall Length
In terms of a belt conveyor it is the dimension from the outside of each pulley containing the belt.
Overhead Drive
A drive that is installed over a conveyor.
Slat Conveyor
A conveyor that is available in a range of widths and materials. The conveyor slats are attached to chains which glide on special sanitary UHMW polyethylene chain rails that provide excellent tracking.
Variable Speed
A drive that can change speeds.
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ENGINEERING
Angle of Repose (o)
Angle of Repose is something many people are familiar with. It is defined as the angle which forms between a horizontal plane and the slope of a pile (at rest), which has been formed by dropping from some elevation. In general, it is related to many of the flow properties of a material and is thus an indirect indication of flowability potential. Angle of Repose gives a reproducible numerical value for a given material, so it has been adopted as a standard measurement for general flowability behavior.
Determining the Angle of Repose is a simple means by which to indirectly quantify physical properties such as size, shape, porosity, and cohesion, all of which directly affect the ability of a material to flow. Bulk solids with an Angle of Repose between approximately 25 degrees and 35 degrees are generally considered free flowing.
Actually, there are two separate types of Angle of Repose: filling and emptying which occur when a material is poured into bins, trucks, railcars or other storage structures, and when it is removed, or drained, from them. Filling and emptying Angles of Repose are not always equal.
Angle of Fall (o)
When a material lies in a pile at rest, it has a specific Angle of Repose. If the supporting surface experiences vibrations, impacts or other movement, the material on the sloped sides of the pile will dislodge and flow down the slope. The new Angle of Repose that forms is referred to as the Angle of Fall. This parameter provides an indication of particle size, shape, uniformity and cohesion—and thus the flowability of the material.
Angle of Difference (o)
The Angle of Difference is calculated by subtracting the Angle of Fall from the Angle of Repose. This parameter is related to the internal cohesion of the granular particles. The larger the Angle of Difference, the more flowable the material.
Angle of Spatula (o)
The Angle of Spatula provides an indication of the internal friction between particles. It is determined by inserting a flat blade into a pile of granular material and lifting vertically (Figure 4). The new Angle of Repose, which the material forms relative to the blade surface, is known as the Angle of Spatula. This simulates movement of the supporting surface and material-handling behavior that will be encountered in real settings. Generally, bulk solids with an Angle of Spatula less than approximately 40 degrees are considered free flowing.
Bulk Density (lb/ft3 or kg/m3)
In addition to the Angle of Repose, most people are familiar with Bulk Density because it is used to determine effective capacities for storage bins and containers. It is also fundamental to the structural design of these vessels. This parameter is defined as the mass of a granular material that will occupy a specific volume, such as a bin or railcar. Bulk density includes not only particle mass but also the air entrained in the void spaces between the particles.
Actually, there are two unique types of bulk density that are important: Packed Bulk Density and Aerated Bulk Density. Aerated Bulk Density, also known as Loose Bulk Density, is the easiest to measure and is determined by pouring a quantity of granular material into a container of known volume. This is representative of the bulk solid that has not been subjected to compression or packing. Packed Bulk Density, on the other hand, is the bulk density of the material after it has been compressed, and thus the entrained air has been displaced. This is representative of the material’s actual bulk density in storage and transport, and is a more realistic quantity to use.
Compressibility (%)
Some granular materials have a propensity to become tightly packed; others do not. After determining Aerated and Packed Bulk Densities, the Compressibility of a material can be calculated as: C stands for Compressibility (%), BDP is the Packed Bulk Density, and BDA is the Aerated Bulk Density. This parameter provides an indication of particle size, shape, uniformity and cohesion, and thus the overall flowability of the material. Bulk solids with a Compressibility less than approximately 18 percent are considered free flowing.
Uniformity (unitless)
The relative homogeneity of the size and shape of the particles within a bulk solid (i.e., uniformity) has a direct effect on a material’s ability to flow. This can be quantified by determining the screen size that will allow 60 percent of a sample to pass through (which is generally a relatively large mesh size) and the screen size that will allow 10 percent to pass through (which is generally a relatively small mesh size). Uniformity is then calculated by dividing the 60 percent mesh size by the 10 percent mesh size. Thus, the smaller the uniformity value, the more homogeneous the particle sizes and shapes. A material that is more uniform will have a tendency to have better flowability than a material with a wide range of particle sizes.
Dispersibility (%)
Dispersibility is a measure of the propensity for a granular material to form dust and thus lose mass to the surrounding air. It is especially important during vertical flow (e.g., pile formation after spout or conveyor discharge). The more dispersible a material, the higher the potential for mass loss due to dust generation.
It is important to realize that all of these parameters are very much influenced by many other factors, including methods of filling and emptying; height of material fall, spout, gate or orifice opening size; vibration or movement to which the storage vessel is subjected; temperature; humidity; moisture content, and chemical composition, such as protein, fat, starch and carbohydrate levels. With all of these confounding variables, it is no wonder that the flowability issue is so complex.
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SCREENING
BLINDED
When the openings of a screen are closed, either by plastering with damp sticky material or by wedging of on-size particles in the opening.
BULK DENSITY
The weight per cubic foot of the material being measured in a loose fill in a volumetric measuring box with the top struck level with the edges of the box.
SCREEN EFFICIENCY
The percentage of the true undersize in the feed that actually passes through the screen openings.
SCALPING
Separation of part of the total feed as coarse oversize by retention on openings (round, square or slotted) more than half again as large in diameter or width as the largest particle in undersize.
SCREENING
Removing part of the total feed as a fine fraction passing through the screen openings.
SIZING
Separating a particulate material into three or more fractions.
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