Conductive silicone and fluorosilicone gasket sheet, waterjet-cut to your drawing

Fillers, from the cited datasheets

The filler sets resistivity, shielding, density and how the gasket behaves against the flange metal; the binder sets temperature and fluid behavior [S15][S11]. The rows below compile per-grade figures from three manufacturer tables and one fabricator page, so treat them as the shape of each family and let the compound datasheet govern the part [S15][S11][S14][S31]. Resistivity is the maximum as supplied, by the method the sheet names; shielding is the minimum at 10 GHz plane wave in the MIL-DTL-83528 fixture; temperature is the maximum continuous figure the sheet gives.

Parker's two-value temperatures mean the first is the MIL-DTL-83528 conformance value, which requires life testing at 1.25 times the maximum, and the second a practical limit for 1000 hours compressed 7 to 10 percent between flanges [S15]. Fluorosilicone grades survive the specification's fluid immersion test and silicone grades do not, which is why fuel and oil exposure moves a drawing from Type A or B to Type C or D [S10][S14]. The sources describe nickel-graphite as lower in cost, with fair corrosion resistance against aluminum; silver-aluminum very good, silver-copper poor, nickel-aluminum excellent; the full galvanic picture is on the galvanic compatibility guide and the filler comparison on the conductive elastomers page [S15].

Thickness, sheet size and tolerance

Sheet dimensions are the manufacturers' published stock sizes; the waterjet cuts any of them to the drawing.

Flat gasket design rules

A flat conductive gasket should not be deflected more than about 10 percent in the handbook, whose die-cut table reads 5 percent minimum, 10 percent nominal and 15 percent maximum, and 5 to 10 percent in the Laird table [S9][S11]. Laird's flat-sheet data give 40 to 115 psi at 5 percent deflection and 280 to 345 psi at 20 percent for 0.045 to 0.125 in sheets, so the bolt pattern has to deliver that pressure evenly, within 2.0 in on stiff flanges and 0.75 in on sheet metal where high shielding is needed [S11][S9]. Width is never less than thickness, holes sit no closer to an edge than the sheet thickness, webs are no narrower than the thickness, and bolt holes either fit the threads closely from machined dies or carry a seal under each bolt head [S9]. Flat gaskets show free-state variation, so the handbook recommends inspection fixtures rather than free-state measurement [S9]. The groove, fastener and finish rules are on the design guide.

Conductive sheet can be bought with an adhesive laminated by the sheet maker: one fabricator names a conductive acrylic and a conductive silicone transfer adhesive for conductive sheet [S31]. The handbook warns that non-conductive adhesive applied to the conductive part of a gasket seriously degrades shielding, so an adhesive-backed flat gasket carries a conductive adhesive or keeps the adhesive off the contact face, and the drawing says which [S9].

How we cut it

Gaskets are cut in our own shop in Orange, California, on the waterjet, from sheet bought from a QPL-83528 listed maker when the drawing calls out MIL-DTL-83528, so the material qualification stays the manufacturer's and the cut adds a dimensional inspection against your drawing. Send a DXF, DWG or PDF with hole-to-hole datums; a rule-die drawing cuts cleanly on the waterjet, and machined-die tolerances apply where the drawing calls them [S9]. The certificate of conformance for a cut gasket chains to the material manufacturer's lot certification, with the type letter, sheet thickness and lot named. The custom gaskets page covers the file formats and the process for every sheet material, and the gaskets hub lists the non-conductive sheets, including plain silicone sheet for a cover that needs no shielding.

Three other routes to a conductive part

A part that is not a flat gasket takes one of three routes, all supplied to order from the material manufacturers rather than cut here. Molded shapes cover O-rings and D-rings, flat washers, waveguide and connector-flange gaskets, jam-nut seals and over-molded parts, with any solid cross-section down to 0.040 in and outer dimensions to 34 in [S15][S9]. Extruded profiles run from a 0.028 in solid O to a 2.00 in flat ribbon in solid and hollow O, D, P, rectangle and channel sections, supplied on reels or cut to length [S9]. Spliced rings joined from extrusion, with a cold-bonded or vulcanized joint, serve rings over 2 in inside diameter where the groove corner radius is at least 2.5 times the strip width [S9]. Form-in-place beads are a fourth route run by the gasket manufacturer or the housing maker on the housing itself, never stocked as a part [S9].

What to send

Eight items let a conductive sheet gasket be quoted in one pass.

1. The drawing: DXF, DWG or PDF with hole-to-hole datums, or a photo with a ruler if no drawing exists [S9].
2. The sheet thickness from the stock list above, or the free height the joint needs at about 10 percent deflection [S11][S9].
3. The filler and binder, or the MIL-DTL-83528 type letter from the drawing; the MIL-DTL-83528 guide explains the letters [S14].
4. The hardness, if the drawing names one, from the 45 to 85 Shore A range [S15][S11].
5. The flange metal and its finish, with the filler your drawing names; the galvanic compatibility guide shows the pairings [S9][S15].
6. The environment: temperature extremes, fuels or oils, salt fog or weather [S15][S14].
7. Adhesive backing yes or no, and conductive or not [S31][S9].
8. The quantity and the paperwork the order needs: certificate of conformance, lot conformance values, a first article report.

Send those through the request a quote form and a Conquest representative replies with a quote in the compound you specify.

Where conductive sheet is used, and the usual alternatives

A flat cover or flange that must shield as well as seal. The print or the sheet datasheet governs; these are the sheets usually specified instead:

• Silicone sheet (non-conductive): the cover needs heat and weather resistance but no shielding.
• Conductive O-rings: the joint has an O-ring groove and needs 10 to 25 percent deflection rather than the 10 percent a flat gasket gives.
• Custom gaskets: the drawing is for any other sheet material on the waterjet.