September, 2013
www.us-tech.com
Page 59
Progressive Cavity Pumps Provide Precise, Even Dispensing
By David Upton, Sales Manager, FRC-Fluid Research Corp., Tustin, CA
to the electronics industry. Material manufactur- ers sell formulations of these adhesives and sealants based on the benefits they provide, and rely on their customers to accurately identify and apply formulations for potting/encapsulation or adhesion for a specific function. Customers select a material and a material manufacturer because of the benefits and capabilities that a specific formu- lation provides for their end-product. From a liq- uid dispensing point of view, the challenge is in supporting the expec- tations of customers and materials manufacturers — which is where the proper meter/mix/dispensing tech- nology becomes critical. Ideally, dis- pensing system solutions should deliver and blend the chemistries according to customer specifications, and should provide a means of deliv- ery so the material is applied accord- ing to end-user expectations. Most dispensing systems are
P
engineered to accurately meter mul- tiple-component adhesives and sealants, regardless of viscosity, and typically provide programmable con- trol of material component ratios, dispense volumes, and flow rates. Dispensing equipment has tradition- ally been configured with piston or metering rod displacement pumps or gear pumps. Both pump styles have been used in the past because of their precision delivery capabilities. However, both designs suffer from high wear rates when used for pump- ing moderately to highly filled or abrasive materials. In contrast, progressive-cavity
(PC) pumps can provide an ideal means for dispensing a variety of materials, even those with abrasive components. PC pumps have an internal helix-shaped rotating ele- ment called the “rotor” and a double- helix-shaped stationary external ele- ment called the “stator”. The inter- ference fit between rotor and stator creates a series of sealed cavities that are continually filled with material at the pump assembly inlet and gen- tly move the material, relatively undisturbed, to the pump outlet. As a result, solid materials that are small- er than the cavity size can be dis- pensed effectively without damage to the dispensed materials or to the pump. This makes the PC pump the correct choice for handling materials containing abrasive fillers without incurring undue wear. The amount of wear in a dispens-
ing tool is usually equal to the size, makeup, and percentage of filler pres- ent in the dispensed material over the lifespan of the dispensing tool. But in a PC pump, materials with fillers as fragile as glass microballoons or as destructive as sand can be successful- ly processed with minimal wear. The component ratios in a dispensed mate- rial may shift slightly as wear does occur, but this wear can be compensat- ed for by a simple recalibration of the PC pump. This recalibration capabili- ty helps to extend the useful operating lifetime of a PC pump. However, if a seal on a piston or metering rod fails in a dispensing system based on that technology, the system is likely to break down and leak materials into
roper dispensing is essential for the precise application of two-part epoxy-, silicone-, and urethane-based adhesives and sealants vital
the production area. PC pumps are capable of consistently accu-
rate dispensing of fluid media, independent of media viscosity. PC pumps exhibit exceptional resistance to abrasive/filled content and chemical- ly aggressive fluids, and are well suited for trans- ferring a wide range of materials for electronics manufacturing, including:
PC pumps can dispense a variety of materi- als, even those with abrasive components. (Photo courtesy of D-Wave Systems)
l Abrasive-filled polymers. l icrosphere-filled polymers. l Thixotropic materials.
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