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www.us-tech.com
August, 2017
Progressive Cavity Pumps Enable Precision and Repeatability Continued from page 50
shifting series of tightly sealed cavities, which move a precise, consistent volume of material steadily toward the pump outlet. From there, fluid is driven to the dispense tip
outlet with a flow rate that depends on the rotor rotation in the feed direction. This process is pre- cisely controlled by the desired specifications dialed into a proprietary controller paired with the system. With this technology, the flow rate is
adjustable at any time by changing the motor speed on the controller, as opposed to having to stop operation to adjust the pump itself, further enhancing speed and flexibility. The fluid is dis- pensed from the tip by a voltage signal applied to the motor, and shearing is achieved by reverse z- motion and tip retraction.
Numerous Benefits
Since the system is in constant motion and provides nonstop flow, it is protected from many of the fluctuations in fluid pressure that adversely affects deposition accuracy in many operations. Progressive cavity technology all but eliminates the frequent occurrence of small surges of pressure that suddenly increase the output of the material dispensed, and then drop back, decreasing the size of the bead a few moments later. With other pumps, this is not only seen as the level of materi- al decreases in the tube, but also with any instabil- ity in the pressure source. Instability may be caused by an air compressor that might drop in pressure if another load is placed on it simultane- ously, or surge when it is removed. Many operations using other types of pumps
are also impacted by temperature changes, which impact viscosity. A small increase in temperature can decrease viscosity and increase flow speed, and detrimentally increase the size of the deposition. On the other hand, a small decrease in tempera- ture can cause the fluid to thicken slightly and reduce the size of the deposition. Progressive cavity technology protects
against these unfortunate scenarios with its tight seal between the rotor and stator helping to ensure that the material in the cavities is well-protected from ambient temperatures. This also helps keep the system resistant to
material leaks, which can also degrade perform- ance and create waste. Progressive cavity pumps can typically self-heal leaks at pressure up to 2 bar (30 psi) or higher.
tool for numerous applications during assembly, such as dispensing both sealing compounds and oils. Using one tool type for several applications can cut down on parts inventory, streamline train- ing issues, and provide other cost- and productivi- ty-enhancing benefits. Configurations exist that can even dispense two-component epoxies with precise mixing ratios, while retaining the same dispensing accuracy.
Chemical Compatibility Progressive cavity dispensing pumps are
available from several companies, with some that manufacture their own brands and others that purchase and relabel the equipment. Usually sold as a set, the controller brand is proprietary to the system and must be paired with the pump. While design and performance can be similar,
the material composition of the stator can differ widely among suppliers. Most operators should investigate this before purchase if they plan to dis- pense any type of caustic or aggressive solvent, such as acetone, MEK or xylene. Rubber blends used for the stator are propri-
etary and can differ in the level of chemical resist- ance they provide and the range of dispensed materials they can be paired with. Some manufac- turers provide stators that are made from stan- dard rubber; these pumps can only be used with benign, non-corrosive materials. Most all manufacturers will ask for the
TSR2000 series automated dispensing robot. This technology is also more gentle and pro-
tective of the fluid itself. Many types of pumps flat- ten soft solids and lead to reduced material per- formance or clogging of the needle. The continuous moving rotor and soft stator causes less percussive impact on the material than, for example, a piston or centrifugal pump. Even very soft, solid powders, flux, and fillers can be mixed into the liquid with- out damage or losing performance. With the wide range of viscosities it can han- dle, the pumps allow many users to adapt a single
MSDS for the materials that operators will be dis- pensing to help ensure compatibility with the sta- tor and other elements of their systems. Some will also accept samples of the material to test in a lab setting to ensure compatibility, as well as to pro- vide users with estimated performance data, dis- pensing photos and settings information before purchase.
Another possible factor to consider is the rel-
ative availability of accessories and equipment that might be teamed with the pumps in operation, such as robots and automation, pressure tanks and
Continued on page 59 Continued on page 54
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