Fume duct joint with clamping collar

A clamping collar for clamping two generally cylindrical fiberglass reinforced plastic duct section end portions superimposed on a generally cylindrical fiberglass reinforced plastic slip collar having a centrally disposed, circumferential rib, the clamping collar comprising:

• first and second clamp portions, each clamp portion having a generally cylindrically arcuate metal outer skin with a predetermined thickness and a predetermined radius of curvature, each outer skin bounded-by opposed ends, each end extending radially in a flange having a plurality of generally collinear holes, each clamp portion further having a generally cylindrically arcuate metal inner skin with a predetermined thickness and a predetermined radius of curvature such that the outer and inner skins can be congruently juxtaposed, each inner skin rotationally offset from and attached to the juxtaposed outer skin so that an end portion of the inner skin extends beyond a radial flange to form a seal guide which slides under the opposed flange of the other clamp portion when the clamp portions are disposed circumferentially about the two duct section end portions, each inner skin having an inner surface, each inner skin inner surface having a multiplicity of punched protrusions, each protrusion having a bifurcated apex whose bifurcations are brought into penetrating contact with one of said duct section end portions as the two clamp portions are tightened about the end portions;
• and
• a plurality of bolts and nuts, each bolt passing through a pair of corresponding holes in each pair of opposed flanges and secured by an adjustably tightenable nut.

A clamping collar for clamping two generally cylindrical fiberglass reinforced plastic duct section end portions superimposed on a generally cylindrical fiberglass reinforced plastic slip collar having a centrally disposed, circumferential rib, the clamping collar comprising:

• a clamp portion having a generally cylindrically arcuate metal outer skin with a predetermined thickness and a predetermined radius of curvature, the outer skin bounded by opposed ends, each end extending radially in a flange having a plurality of generally collinear holes, the clamp portion further having a generally cylindrically arcuate metal inner skin with a predetermined thickness and a predetermined radius of curvature such that the outer and inner skins can be congruently juxtaposed, the inner skin rotationally offset from and attached to the juxtaposed outer skin so that an end portion of the inner skin extends beyond a radial flange to form a seal guide which slides under the opposed flange when the clamp portion is disposed circumferentially about the two duct section end portions, the inner skin having an inner surface having a multiplicity of punched protrusions, each protrusion having a bifurcated apex whose bifurcations are brought into penetrating contact with one of said duct section end portions as the clamp portion is tightened about the end portions;
• and
• a plurality of bolts and nuts, each bolt passing through a pair of corresponding holes in each pair of opposed flanges and secured by an adjustably tightenable nut.

A method for assembling a fume exhaust duct joint comprising a generally cylindrical fiberglass reinforced plastic slip collar having an outer surface with a centrally disposed, circumferential rib extending therefrom, and first (upstream) and second (downstream) generally cylindrical fiberglass reinforced plastic duct sections, each duct section terminating in an end portion proximal to said slip collar, each end portion having an inner surface and an outer surface, the method comprising the steps of:

• coating the entire inner surface of each said end portion with a relatively thin layer of adhesive sealant;
• coating the entire outer surface of said slip collar with a relatively thick layer of said sealant;
• inserting said slip collar into said end portion of said upstream duct section until the end portion abuts said circumferential rib;
• beveling smooth any sealant extruded into the interior of the slip collar;
• inserting said slip collar into said end portion of said downstream duct section until the end portion abuts said circumferential rib;
• spreading sealant extruded onto said end portion outer surfaces laterally and circumferentially around said surfaces;
• surrounding said end portions with a bifurcated clamping collar comprising first and second clamp portions;
• and
• tightening said clamp portions about said end portions.