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Piezo Jet Valve Dispensing: Precise Dots at 1,500 Times Per Second
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in the desired pattern far faster than a mechanical pneumatic-based solu- tion, which must open and close and reset, a process that expends about 20 extra milliseconds each time. In this way, speeds up to 2,000
percent faster than contact-based solutions — two times faster than pneumatic jet solutions — can be achieved. For speed-sensitive, high- volume, high-throughput applica- tions, the increase in yield can be extraordinary and highly profitable. Another significant advantage
of piezo jet technology is its ability to deliver up to 1,500 Hz speed, even to those operations involved with the production of substrates with irregu- lar heights or those where hard-to- access “nooks and crannies” must be reached. Since the fluid is shot rather
than dropped, nozzles can be more readily angled to reach the exact point where material is required. Further, since the nozzle does not need to drop down on the item, products with irreg- ular protrusions, such as a mother- board with tall components, will not be damaged, as they might be when using a contact-based valve that must come down close to the substrate, eliminating a common source of dam- age, waste and downtime.
How it Works In a piezo jet valve cycle, the
fluid starts inside the valve, held between the tappet (piston) and the nozzle. The electronic piezo crystal oscillates up and down at a high rate of speed, generating kinetic energy that forces the fluid to shoot out under carefully controlled pressure to form a perfect bead of material at the target location. A complete, five-step piezo jet-
ting cycle consists of: rising time, the total time for the tappet to move to open position; open time, the total time the valve stays opened; falling time, the total time for the tappet to move to closed position; needle lift, the stroke length, which is based on the viscosity of the material; and the delay time, the time the valve stays closed, waiting for the next cycle. All of these steps can occur,
repeated over and over again, up to 1,500 times per second continuously, with that number an objective basis for comparison with other dispensing methods being considered. Under real- world conditions, the number of drops dispensed per second will be impacted by factors that include desired shot size, the viscosity of the material and the speed of the horizontal movement of the substrates being assembled.
Piezo Considerations When considering upgrading to
the power of a piezo jet valve dis- pensing system, a vital point to be aware of is that the phrase “jet valve” can refer to both the older pneumatic jet valve, as well as the newer piezo crystal-driven jet valve technology. While both technologies are signifi- cantly faster than familiar contact dispensing options, such as the auger valve or progressive cavity pump, the newer piezo version of the jet valve can deliver some two times the speed of the incumbent pneumatic version. Nevertheless, since “jet valve”
referred only to “pneumatic jet valve” for so many years, many still use the terms interchangeably, and many potential users and even valve man- ufacturers are relatively unfamiliar with the piezo jet valve or have not yet had the experience of seeing it in action. Currently, several manufactur-
ers provide piezo jet valve dispensing solutions, and, as one would expect, a number of aspects of their design as related to both the valve itself and the related controller can differ sig- nificantly. For example, a key issue to con-
sider is the relative ease of identify- ing the right “recipe,” the combina- tion of parameters to ensure correct placement and the correct amount of material. Piezo valves gain much of their small dot consistency through not only making use of tiny aperture nozzles, but also by providing the flexibility to fine-tune both material pressure and jetting pressure.
February, 2020
Once the correct parameters are
determined, the valve is extremely accurate and consistent in maintain- ing them, but getting to that point often takes trial and error. Key in reducing the challenge are the capa- bilities of the controller provided, as well as any assistance that might be available from the manufacturer. As to the latter, some manufacturers might just look at an MSDS and ren- der an opinion. Others will offer some level of hands-on testing of material in a lab to ensure efficacy. Further, they might be willing to use the knowledge gained to help the user more quickly fine-tune the parameters for operation. It pays to inquire before the sale.
Is a Piezo Jet Value Right for You?
There are also some limitations
to consider. For example, potential users should take into account the type of materials they wish to dis- pense. Piezo jet valves can be used with materials demonstrating a very wide range of viscosities — up to two million centipoise or more and including materials as thick as sili- cone and urethane rubber. However, due to the need to
evenly shoot the material, those that have solid particles blended into them, such as solder paste with its ultra-fine metal particles, typically are not the best candidates for jet valve dispensing technology. Finally, obtaining the superior
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