Page 6 - Spring 2024
P. 6

EDM Today Magazine
                                                EDM Today Magazine
   EDM Today Magazine                      Need answers for the toughest EDM questions?

                                           You’ve come to the right place!


                                                               O-ring Basics
                                                               Per Wikipedia, “An O-ring is a mechanical gasket in

                                                               round cross-section.” O-rings are characterized by the
             QD3 DI Tank Connector Leakage
                                                               diameter of the O-ring cross section and the I.D. of
                                                               the O-ring as shown in Figure 3.  In our application, the
             I use DI tanks that utilize the QD3 style quick discon-  the shape of a torus; it is a loop of elastomer with a
                                                               O-ring effects a seal by being compressed between the
   EDM Today Magazine                           EDM Today Magazine                            EDM Today Magazine
             nect heads and have persistent leakage issues at the
                                                               bottom of the groove in the QD3 head boss and the I.D.
             connection. Any suggestions?
                                                               of the hole in the tank head as shown in Figure 4.
             - Edward
             Roger Kern’s reply:
             Before answering this question, I need to digress to
             expound briefl y on two topics:
             •  QD3 Details
             •  O-ring Basics

             QD3 Details
                                                                                                Figure 4
                                                                         Figure 3
             The QD3 head system (See Figure 1) is a two port
   EDM Today Magazine                           EDM Today Magazine                            EDM Today Magazine
             quick disconnect system that allows resin tank
                                                               O-rings are usually available in standard inch or metric
             changeover in less than one minute.
                                                               cross-section sizes and a variety of inside diameters.
                                                               O-rings are normally installed in an O-ring groove that
                                                               has a diameter somewhat larger than the O-ring I.D.,
                                                               which means the O-ring operates in a stretched state.
                                                               The amount of stretching effectively reduces the
                                                               O-ring cross section, but this is accounted for in O-ring
                                                               application design standards.
                                                               QD3 Joint Leakage Cause
                                                               Both the QD3 head and the tank head are molded
                                                               polymer components. As a result of shrinkage and
   EDM Today Magazine                           EDM Today Magazine                            EDM Today Magazine
                                                               other issues, the center distance between the bosses
                                                               on the QD3 head and the bores in the tank head can
                                                               vary somewhat. That variance can reduce the O-ring
                                                               squeeze on one side of the bores and increase it on
                                                               the other side of the bores, resulting in leakage on the
                               Figure 1
                                                               sides that have the reduced squeeze.
                                                The QD3
                                                head (See
                                                               QD3 Joint Leakage Fixes
                                                Figure 2)
                                                connects
                                                               This fi rst thing to try, and the simplest fi x, is to apply
                                                the inlet and
                                                outlet deioniz-
                                                               Toolbox Treasures feature in the Winter 2023 issue
                                                ing hoses
                                                               of EDM Today available at www.edmtodaymagazine.
                                                from the       a thickened silicone grease to the O-rings. (See the
                                                               com.) The thickened grease is often viscous enough to
                                                machine to
   EDM Today Magazine                           EDM Today Magazine                            EDM Today Magazine
                                                               stop the leak, as the pressure in this portion of the DI
                                                the resin tank
                                                               system is relatively low.
                                                by means of
                                                               If that doesn’t work, it will be necessary to change the
                                                two cylindri-
                                                               O-rings to a different size. Since O-ring cross sections
                                                cal bosses
                                                               are limited to standard sizes, the only way we can
                                                that simulta-
                                                               increase the sealing squeeze between the boss groove
                                                neously mate
                                                               bottom O.D. and the bore I.D. is to procure an O-ring
                                                with corre-
                                                               with a slightly larger I.D. This will reduce the instal-
                                                sponding
                                                               lation stretch and slightly increase the O-ring cross
                                                receiver holes
                           Figure 2
                                                in the tank
                                                               experimentation to fi nd the correct size (too small an
                                                head, and
                                                               I.D. increase may not stop the leak and too large an I.D.
             the connection is sealed with O-rings that sit in O-ring
                                                               increase may not allow the parts to fi t together), this
             grooves in the bosses. The QD3 system is my personal   section, restoring the seal. While it may take a bit of
                                                               fi x has always allowed me to successfully resolve this
             favorite for this application.
                                                                                              EDM Today Magazine
   EDM Today Magazine                           EDM Today Magazine                         EDM Today, Spring 2024 Issue
                                                               particular leak issue.
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