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Many adhesive applications require fast and accurate dispensing. For high-speed, smalldrop-size, low-viscosity adhesive-dispensing applications, total cycle rates of one part per second are attainable. Thorough testing during the processdesign phase ensures reliable dispensing and the overall success of the adhesive assembly during manufacturing and throughout the life of the device.
DIAPHRAGM VALVE DISPENSE
Many adhesive-dispense applications use a pressurized fluid reservoir with a diaphragm valve. The control variables are fluid reservoir pressure vs. fluidflow restriction exerted by the dispense valve and dispense tip. The cone-shaped tip of the diaphragm is normally closed against the liquid port through the valve head, by way of the valve actuator spring.
The total opening stroke of the valve may be adjusted to pull the tip farther back out and away from the internal liquid port. A longer stroke will "pull" the adhesive up through the dispense needle tip at the front of the valve. Minimum stroke length is typically recommended, as the adhesive will need to come back "down" after the opening stroke before exiting the needle tip.
Loctite's cyanoacrylate or light-cure dispense valves are typically set at ½ turn counterclockwise.
DISPENSE-NEEDLE TIPS
Dispense-needle tips are usually chosen to match the size of the target (e.g., smaller-diameter [high-guage-number] needle tips are used to apply smaller adhesive drop sizes). The higher the needle gauge number, the more restrictive the fluid flow. The largest possible needle diameter and lowest possible reservoir pressure to achieve the desired shot/drop size should be used. In addition, long, straight needle tips are...