Rotary screw valve dispensers
Also known as an Archimedes or auger screw dispenser, this technology is extremely popular because of its high versatility and satisfactory volumetric accuracy for all but the most precise applications (Fig. 6).These valves can be found dispensing virtually any material depending on the internal tolerance configuration of the individual valve. It works best however, with medium - to high-viscosity materials.
The rotary screw valve offers high flexibility in dispensing dots; however, volume and repeatability are influenced by the syringe level, air pressure, material viscosity, temperature, and the motor or clutch timing of the mechanism. However, the accuracy of any specific valve model is dependent on the precision of its construction.
This technology is best used for dispensing beads and lines of material, but the rotary screw valve can dispense dots with satisfactory results for a wide range of applications. It is a general workhorse in electronics assembly and PCB production, excelling in applications such as glob topping, underfill for flip chip applications and gasketing. The rotary screw valve does a far more accurate job than any of the previous valves, and works well with both adhesives and solder paste.