Fire resistant radiating coaxial cable
A fire resistant radiating coaxial cable that employs a high-silica fiberglass yarn spacer is described. The yarn material has mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%. The yarn can be wound in a low-helix-angle helix around the center conductor such that less than half fills the annular space between it and the outer conductor. The cable is configured to maintain a relatively coaxial relation between a center conductor and an outer conductor under intense fire conditions.
1 . A fire resistant radiating coaxial cable apparatus comprising:
a center conductor;
an outer conductor having a circumference with apertures, the outer conductor surrounding the center conductor; and
a high silica fiberglass yarn between the center conductor and the outer conductor, the fiberglass yarn having a mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%, the fiberglass yarn being configured to maintain a predetermined dielectric spacing between the center conductor and the outer conductor when exposed to heat at or above 1010° C.
2 . The apparatus of claim 1 wherein the fiberglass yarn is wrapped in a helix around the center conductor.
3 . The apparatus of claim 2 wherein the helix has an average helix angle of less than 60°.
4 . The apparatus of claim 1 wherein the yarn fills less than half of a volume between the center conductor and the outer conductor.
5 . The apparatus of claim 4 wherein the yarn fills less than a third of the volume between the center conductor and the outer conductor.
6 . The apparatus of claim 1 wherein the yarn has two or more plies.
7 . The apparatus of claim 1 wherein the yarn is a braided yarn.
8 . The apparatus of claim 1 wherein the fiberglass yarn directly touches the center conductor or the outer conductor.
9 . The apparatus of claim 1 wherein the high silica fiberglass yarn has a composition weight percentage of:
(a) Na 2 O=0.0564%±0.0056%
(b) MgO=0.110%±0.011%
(c) Al 2 O 3 =3.55%±0.36%
(d) SiO 2 =96.0%±1.0%
(e) CaO=0.116%±0.012%
(f) Fe 2 O 3 =0.164%±0.016%
(g) ZrO 2 =0.0301±0.0030%.
10 . The apparatus of claim 1 wherein the outer conductor is corrugated, the apertures having been produced by milling, at a constant radius, protuberant portions of corrugations along a length of the cable, the milling breaking through the outer conductor.
11 . The apparatus of claim 1 wherein the outer conductor is a metal foil.
12 . The apparatus of claim 1 wherein the outer conductor is a loose braid, wherein the apertures are between metal strands of the loose braid.
13 . The apparatus of claim 1 further comprising:
a ceramifiable silicone rubber inner jacket or a ceramic fiber wrap inner jacket surrounding the outer conductor.
14 . The apparatus of claim 13 further comprising:
a smooth outer jacket surrounding the inner jacket.
15 . The apparatus of claim 14 , wherein the outer jacket includes an embossing or engraving aligned with the apertures.
16 . The apparatus of claim 1 wherein the apertures were laser cut.
17 . A fire resistant coaxial cable apparatus comprising:
a center conductor;
an outer conductor surrounding the center conductor; and
a high silica fiberglass yarn wrapped in a helix between the center conductor and the outer conductor, the fiberglass yarn having a mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%, the fiberglass yarn being configured to maintain a predetermined dielectric spacing between the center conductor and the outer conductor when exposed to heat at or above 1010° C.,
wherein the fiberglass yarn fills less than half of a volume between the center conductor and the outer conductor.
18 . The apparatus of claim 17 wherein the outer conductor has corrugations with apertures, the apertures having been produced by milling, at a constant radius, protuberant portions of corrugations along a length of the cable, the milling breaking through the outer conductor.
19 . A method of manufacturing a fire resistant coaxial cable, the method comprising:
wrapping a center conductor with a helix of high silica fiberglass yarn, the fiberglass yarn having a mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%; and
surrounding the fiberglass yarn and center conductor with an outer conductor, wherein the fiberglass yarn is configured to maintain a predetermined dielectric spacing between the center conductor and the outer conductor when exposed to heat at or above 1010° C.
20 . The method of claim 19 wherein the outer conductor is corrugated, the method further comprising:
milling, at a constant radius, apertures through protuberant portions of corrugations along a length of the cable, the milling breaking through the outer conductor.