Sheathed metallic needles for producing z-channels in fibrous preforms
A needle array suitable for perforating a fibrous preform includes a backplate, a plurality of needles removably attached to and extending away from the backplate, and a collar disposed around each of the plurality of needles. Each of the plurality of needles includes a metallic body, and a polymer sheath covering the metallic body.
1 . A needle array suitable for perforating a fibrous preform, the needle array comprising:
a backplate;
a plurality of needles removably attached to and extending away from the backplate; and
a plurality of collars, each of the plurality of collars disposed around a respective needle of the plurality of needles and having frustoconical geometry tapering from widest proximate the backplate to narrowest distal from the backplate;
wherein each of the plurality of needles and each of the plurality of collars comprises:
a metallic body; and
a polymer sheath covering the metallic body, the polymer sheath comprising one of polyvinyl alcohol and polyvinyl butyral.
2 . The needle array of claim 1 , wherein the collar abuts the backplate.
3 . The needle array of claim 1 , wherein each of the plurality of needles has a diameter ranging from 100 microns to 1,000 microns.
4 . The needle array of claim 3 , wherein a thickness of the polymer sheath ranges from 0.05 microns to 127 microns.
5 . The needle array of claim 1 , wherein the collar is offset from the backplate.
6 . The needle array of claim 1 , wherein the plurality of needles have a cylindrical geometry between a base and a tip.
7 . An assembly comprising:
a tooling fixture configured to mount a fibrous preform therein during a chemical vapor infiltration process, the tooling fixture comprising a plurality of infiltration holes configured to receive infiltrating reactant vapors; and
a needle array comprising:
a backplate;
a plurality of needles removably attached to and extending away from the backplate, each of the plurality of needles comprising:
a metallic body; and
a polymer sheath covering the metallic body, the polymer sheath comprises one of polyvinyl alcohol and polyvinyl butyral;
wherein each of the plurality of needles is aligned with a respective infiltration hole of the plurality of infiltration holes; and
a plurality of collars, each of the plurality of collars disposed around a respective needle of the plurality of needles in a position offset from the backplate.
8 . The assembly of claim 7 , wherein the tooling fixture is formed from graphite.
9 . The assembly of claim 7 , wherein each of the plurality of needles has a diameter ranging from 100 microns to 1,000 microns.
10 . The assembly of claim 9 , wherein a thickness of the polymer sheath ranges from 0.05 microns to 127 microns.
11 . The assembly of claim 7 , wherein each of the plurality of collars is formed from a polymer-coated metallic material.
12 . A method of preparing a fibrous preform for use in a ceramic matrix composite, the method comprising:
inserting a plurality of needles belonging to a needle array through the fibrous
preform, each of the plurality of needles comprising:
a metallic body; and
a polymer sheath covering the metallic body;
removing the plurality of needles to form a plurality of z-channels in the fibrous preform; and
subsequently, heating the fibrous preform to decompose polymer contaminants within the plurality of z-channels;
wherein a respective collar is disposed around each of the plurality of needles, each collar comprising:
a metallic body; and
a polymer sheath covering the metallic body; and
wherein the fibrous preform is mounted in a tooling fixture comprising a plurality of infiltration holes configured to receive infiltrating reactant vapors during a chemical vapor infiltration process and wherein each of the plurality of needles is aligned with a respective infiltration hole of the plurality of infiltration holes.
13 . The method of claim 12 , wherein the polymer sheath of each of the plurality of needles and each collar is formed from one of polyvinyl alcohol and polyvinyl butyral.
14 . The method of claim 13 , wherein the contaminants are formed from the same material as the polymer sheath.
15 . The method of claim 12 , wherein the step of heating the fibrous preform occurs during chemical vapor infiltration.
16 . The method of claim 12 , wherein the plurality of needles are removably attached to and extend away from a backplate and wherein each collar is offset from the backplate.