Assembly in Action: Polymers Improve Valve's Reliability
The redesigned valve is used in humidifiers, pneumatic automation systems, beverage dispensers and other equipment. The valve's main components are a solenoid assembly, valve body and plunger. When the solenoid coil is energized, a spring load elastomer-tipped plunger is drawn away from an integral seat in the valve body, allowing fluid to flow through the unit.
The new valve solenoid assembly is encapsulated with Rynite PET thermoplastic polyester resin from DuPont (Wilmington, DE). Its coil bobbin is injection molded from Rynite PET or, for food or beverage equipment, Delrin acetal resin. The valve body is injection molded from Delrin.
Prior to this design, encapsulation was done with thermoset epoxy and a metal valve body. Existing valve lines use thermoset epoxy encapsulation, and the bodies are made of machined brass, stainless steel or aluminum.
In switching to Rynite for encapsulation, the company achieved shorter time cycles, eliminated volatile organic compounds emissions from epoxy and eliminated secondary finishing. The strength and moldability of Rynite also allowed integrating a support bracket into the encapsulation.
Another key feature involves using the inner diameter of the bobbin to guide the valve's plunger. This eliminates a precision-welded metal assembly incorporating a nut, a guide sleeve for the plunger and an end stop.
A cylindrical metal end stop, which eliminated plunger travel, is now insert-molded in the encapsulation. Tolerances for end stop positioning are much closer with the new design, ±0.002 inch instead of ±0.005 inch, which helps assure consistent valve operation.
For the injection-molded body, Delrin provides strength, stiffness and dimensional stability required to replace machined metal. The body also has a smooth attractive surface.
For more information about acetal resins and thermoplastic polyester resins, call DuPont at 800-441-0575, visit www.dupont.com/enggpolymers or Reply 5.