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Dispensing Dynamics - Fluid Principles

Dispensing Dynamics - Fluid Principles
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Dispensing Dynamics - Fluid Principles - 1

I&J Fisnar Inc. - Dispensing Dynamics - Part 1 - Fluids Dispensing Dynamics There are five principles relevant to any dispensing application. These principles of dispensing dynamics must be understood before determining a dispensing solution. The princ iples are simple, but can provide an invaluable guide to recommending new equipment or in solving an existing equipment dispensing issue. Principles: • Air is compressible. Fluid is not compressible. This first principle explains why a fluid can be dispensed at all; if the fluid was compressible, accurate dispensing could never be achieved. The principle also explains why there is a delay in fluid flow when using an air line – the air must first be compressed before impacting the fluid. In the case of a syringe, as fluid is used and the fluid level drops, the air chamber in the syringe increases resulting in a delay and/or smaller shot size. This phenomenon brings us to the second principle of dispensing dynamics. • Dispensing fluid is related to: 1. Air pressure, 2. Time, 3. Tip size. This second principle applies to any dispensing operation including syringes and valves. Changing one of these parameters will alter the dispensing result. • A dispensed shot is equal to: ½ volume of a sphere: Volume = D³ x 0.5236 / 2. This principle will help calculate reservoir supply and fluid usage. • For repeatable shot accuracy, always use a valve. A valve has no variable air space and will therefore provide accurate and constantly repeatable shots. • The type of fluid and its viscosity will determine the valve to be used. Understanding this principle will ensure questions are raised about the fluid before recommending a suitable valve.

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Dispensing Dynamics - Fluid Principles - 2

Common Fluid Characteristics A fluid is selected for a specific application and can be a liquid or a paste. Solvents, silicones, one-part or two-part encapsulates and various pastes have unique characteristic s which are particular to each of these fluids. Viscosity One of the major characteristics of a fluid is its viscosity. Viscosity is usually stated in centipoise (cps). Fluids with high centipoise are thick and have no self- leveling capabilities, whereas fluids with low centipoise are thin and possess self- leveling properties. Since viscosity may change due to time or temperature,...

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Dispensing Dynamics - Fluid Principles - 3

Shot Size The “shot size” (amount being dispensed per shot) depend s on several factors. Changing these factors will affect the size: - Tip diameter, length and style - Dispensing time - Dispensing pressure Shots are dispensed in half sphere (V) as calculated by the diameter (D). V = Shot size (ml) D = Diameter (mm) Example: D = 2.67mm, V = 0.005 ml Dispensing solder mask shots using volumetric valve: Variables: - Selected tip size - Auger rotation speed - Auger pitch size I&J Fisnar Inc. 2-07 Banta Place, Fair Lawn, NJ, 07410 Ph: 201-796-1477 Fax: 201-794-7034

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