Diaphragm Design Manual - Simrit

While the primary function of the bead is to seal the diaphragm to the housing, some feel that itoffers a degree of confidence in preventing diaphragm pull out. This is true to some extent, butpullouts are generally the result of over clamping, crushing and / or fabric-to-rubber adhesionfailure.For optimum sealing the beads should be placed on the pressure side of the diaphragm thusenabling the system pressure to assist in sealing the bead.Advantages of Tear Drop Beads:1. Provides for a more even draw of the fabric onto thediaphragm. W hile smoothing out possible wrinkles, italso aids in keeping the fabric in place within the part.2. Provides for a positive location of the part in the trimdie, which controls the concentricity.3. Provides for backpressure in the mold to allowpositive flow of the rubber and flushes out trappedgasses in the bead.Table 14 – Advantage of Tear Drop BeadsBead ProfileWhile the most common bead shapes are circular or shaped like a “D”, Simritrecommends a bead design known as the Tear Drop (see Figure 19 and Table 15).This design allows for the flash point to be above or below the flange plane, unlike thecircular, which flashes in the middle or the “D” bead which flashes at the bottom.This flash point difference is critical in improving the quality of the bead fill and reducingbead flash. Improved fill means less trapped air in the bead making a morehomogeneous compression feature. Less flash means fewer assembly issues due toexcessive flash extension.Cylinder Diameter (CD) .25" / .99" 1.00" / 2.50" 2.51" / 4.00" 4.01" / 8.00" 8.01" & UpBead Width .094" .125" .187" .250" .250"Bead Height .095" .135" .200" .270" .270"Table 15 – Suggested Bead DimensionsWH© Copyright FNGP 200940