Assembly EndUser: The Use of Valves in Automatic Liquid Dispensing Systems
Many sectors of the electronics industry use accurate liquid and paste dispensing systems to solve the problems of gluing, filling, and encapsulating. While a small percentage of these applications might use hand-held dispensing equipment, the majority require automatic dispensing robots for large-volume applications and/or applications requiring high precision. For such applications, the material is usually dispensed using valves. The material is supplied to the valves by either cartridges or pressure reservoirs. In configuring the proper dispensing system, it is not only important to select the correct robotic system, but also the suitable valve for the material being dispensed. Many factors and parameters must be considered when setting up a dispensing system, including material viscosity, the required flow rate of the dispensing material, the precision of dispensing, and the speed of the process.
Dispensing valves from I&J Fisnar Inc. can satisfy all special requirements and can be used for a great variety of applications and materials.
The best known processes for high-precision dispensing of extremely low material quantity using very dense paste-loaded materials are the application of dispensing solder paste before the SMD pieces are positioned on a PCB or the high-precision application of heat-conductive paste on a very small area. I&J Fisnar's PDV-1000 dispensing auger-type valve is excellent for executing such jobs easily and accurately. The valve is equipped with a stainless-steel Archimedes auger driven by a servo motor. The valve is available in three types, with either 8-, 16- or 32-pitch augers. The control and activation of the valve servo motor is provided by way of the PDC-2000 control system. This control system also provides rotation in a range of selectable speeds. In an automatic work environment, the PDC-2000 allows the setting of the dispensing time in the time range from 0.01 to 65.5 seconds. Furthermore, at the end of the dispensing cycle, a reverse time and rotating rate can be programmed, ensuring that the material will not drop from the dispensing tip; instead, it is sucked back into the valve. The minimum quantity dispensed is 0.00003 cm3 (0.03 mm3), the minimal point dimension is 0.5 mm, and the precision of the dispensed amount is +/- 1%. The control system can be started with a pedal or from an external control device with a + 24 V DC signal, and can work automatically (with timing) or manually (continually).
Another typical application is the high-quantity and high-pressure dispensing of materials with high viscosity, such as silicones, glues, RTV, and various greases. The model 790HPNM high-pressure valve, or the 790HPSSNM in stainless steel, is suited for such jobs. The viscosity of the dispensing material may also be 3,000,000 cps, and the highest material pressure is 2500 psi (ca. 175 bar). The integrated valve spindle is designed to create a small back suction upon closing, which inhibits dropping of the material at the end of the cycle. The valve can operate using three-way valves, where the closing is achieved via a spring, and respectively with automatic equipment using four-way valves such as Model VC-1195A (110v) and Model VCE-1195A (220v), which are capable of operating two valves at the same time. These controllers can be started using a pedal or with an external process control device with dry contact.
The LV-0126NM valve is another type of high-pressure valve suited for dispensing high-viscosity materials (viscosity max. 1,000,000 cps) with a lower material flow rate than the 790HPNM valve can provide. With the LV-0126NM valve, the material flow rate can be regulated by changing the needle valve opening using a thumb screw on top of the valve. The maximum applicable material pressure is 3.500 psi (247 bar), but only 30 PSI (2.2 bar) pressure is needed to open the valve. This valve can be operated using a three-way dispensing controller such as Model DSP501A, or with the recommended Model VC-1195A with a four-way valve for faster action.
The stainless-steel MV-0180SSNM-A from the MV-0180 valve family is recommended for low-quantity dispensing of materials with low-to-medium viscosity (max. 200,000 cps), such as solvents, electrolytes, alcohols, dyes, and UV- and other adhesives. It is a needle valve, which provides controls to adjust the material flow rate. For dispensing anaerobic materials, the valve body is made of plastic (MV-0180-PNM). Control of the valve is possible using a dispensing controller such as I&J Fisnar Model DSP501A or Model JB1113. Pressure of 85-95 PSI (5.9-6.6 bar) is required to open the valve. The internal spring securely closes the valve at the end of the dispensing cycle.
The DV 509 diaphragm valve family was developed for the widest range of materials with middle and low viscosity. It is available in these types: the model DV509-UHMWH-H for acids and reagents; the DV509-UV-H for UV adhesives; the universal DV-509, used for cyanoacrylate adhesives, anaerobic materials, electrolytes, dyes, inks, and other solvents.
The 710PTNM valve with pinch tube mechanism is a special valve for use with all low-viscosity materials. It is perfect for dispensing cyanoacrylates, lacquers, dyes, electrolytes, acids, reagents, anaerobics and other solvents. The pinch tube assembly, the only wetted part, can be easily replaced, allowing fast change.
Finally, the SV1217 spray valve family is excellent for selective spraying of various low-viscosity materials. For fast spray applications, the SV1217 and its stainless-steel version, the SV1217SS, are available. This valve has a spread angle of 28° with a circular spray pattern. It is ideal for applying alcohols, dyes, conformal coating and other materials.
To ensure precise control of the spray valve, SVC100 spray valve control equipment with microprocessor has been developed. This control system allows users to open the valve with pre-programmed air pressure. It also monitors the timing cycle, provides the pressure necessary to atomize material and delivers a delayed burst of air to clean the valve at the end of the process when the valve closes. This timing ensures complete cleaning of the valve at the end of the spraying process, preventing material from drying in the valve. The SVC100 can be operated using a pedal or using a signal from an external control device.
For more information, visit http://www.ijfisnar.com.
The author is an I&J Fisnar Inc. distributor in Hungary. The article was initially published in the April 2005 issue of ELEKTROnet, and the translation is reprinted with the author's permission.