APPARATUS FOR POROUS MATERIAL DENSIFICATION
The present invention relates to an inductive heating apparatus, particularly using a liquid deposition precursor, for densifying porous articles. The inductive heating apparatus using induction coils that are made from machined or milled flat metal plates, such as copper plate, instead of bending a member (especially a hollow member) into a coil shape. The induction coils according to the present invention can be more precisely and more consistently fabricated than conventional bending techniques.
1 . A method of manufacturing an inductive heating coil comprising machining or milling a metal plate having oppositely facing first and second sides to define a spiral metal inductive heating coil having oppositely facing first and second sides.
2 . The method of claim 1 , wherein the metal plate is a copper plate.
3 . The method of claim 1 , wherein machining or milling comprises computer-controlled machining or milling, respectively.
4 . The method of claim 1 , further comprising fixing a metal water cooling tube to one side of the spiral metal heating coil structure so as to follow the spiral metal heating coil structure.
5 . The method of claim 4 , wherein fixing the metal water cooling tube comprises brazing the metal water cooling tube to the spiral metal heating coil structure.
6 . The method according to claim 4 , wherein the metal water cooling tube is rectangular in cross-section.
7 . An inductive heating assembly comprising:
a support frame;
at least one pair of spiral induction heating coils mounted on the support frame and being aligned with one another in a generally parallel orientation, the pair of induction heating coils being spaced apart from each other by a coil separation distance; and
an electrical power supply electrically connected to the pair of induction heating coils;
wherein each spiral induction heating coil is fabricated from a machined or milled flat metal plate, the machining or milling defining a spiral form of the spiral induction heating coil.
8 . The assembly according to claim 7 , wherein each spiral induction heating coil of the at least one pair of spiral induction heating coils is provided with a water cooling tube extending in a spiral orientation along the spiral form of the spiral induction heating coil.
9 . The assembly according to claim 8 , wherein each water cooling tube is brazed to a respective spiral induction heating coil.
10 . The assembly according to claim 7 , wherein each induction heating coil has a gap of at most about 0.75 inches between adjacent turns of induction heating coil.
11 . The assembly according to claim 7 , wherein each induction heating coil has an outside diameter of about 25 inches.
12 . The assembly according to claim 7 , wherein each induction heating coil has an inside diameter of about 3 inches.
13 . The assembly according to claim 7 , wherein the support frame is made from a G-10 glass material.
14 . The assembly according to claim 7 , wherein each heating induction coil is provided with one or more boltheads arranged to provide means for mounting the heating induction coil on the support frame.
15 . The assembly according to claim 14 , wherein the means for mounting the heating induction coil is adjustable for adjusting a space between the at least one pair of induction heating coils.
16 . The assembly according to claim 7 , wherein the support frame is provided with one or more supports for supporting a workpiece being heated by the at least one pair of heating induction coils between the respective heating induction coils at a periphery of the workpiece.
17 . A method of densifying a porous article in an inductive heating apparatus, comprising:
mounting one or more porous articles in one or more corresponding inductive heating assemblies, each inductive heating assembly comprising:
a support frame;
at least one pair of spiral induction heating coils mounted on the support frame and being aligned with one another in a generally parallel orientation, the pair of induction heating coils being spaced apart from each other by a coil separation distance; and
an electrical power supply electrically connected to the pair of induction heating coils;
wherein each spiral induction heating coil is fabricated from a machined or milled flat metal plate, the machining or milling defining a spiral form of the spiral induction heating coil;
immersing the inductive heating assembly having the porous article mounted therein in a reaction chamber in a liquid densification precursor, such that the liquid precursor infiltrates a porosity of the porous article;
providing electrical power to the at least one pair of spiral induction heating coils to cause the porous article to be inductively heated to temperature to cause the liquid precursor to pyrolyze and leave a pyrolytic deposition product within the porosity of the porous article, thereby reducing the porosity of the porous article.
18 . The method according to claim 17 , wherein the porous article has an initial bulk density before densification between about 0.2 to about 0.5 g/cc.
19 . The method according to claim 17 , wherein the porous article has a final bulk density after densification between about 1.50 and about 1.90 g/cc±0.04 g/cc.
20 . The method according to claim 17 , further comprising rotating the porous article about an axis perpendicular to the at least one pair of spiral induction heating coils.
21 . The method according to claim 17 , wherein the liquid precursor is chosen from the group consisting of: cyclopentane, cyclohexene, 1-hexene, gasoline, toluene, methylcyclohexane, n-hexane, kerosene, hydrodesulfurized kerosene, and benzene, and combinations thereof.
22 . The method according to claim 17 , wherein the porous article is inductively heated to a temperature of between about 900° C. and about 1500° C.
23 . The method according to according to claim 17 , wherein the porous article is substantially round, and has a diameter no larger than a diameter of the pair of induction heating coils.
24 . The method according to claim 17 , wherein a plurality of heating assemblies is provided.
25 . The method according to claim 17 , wherein the electrical power supplies of the plurality of heating assemblies are connected to a common electrical bus.
26 . The method according to claim 17 , further comprising a heat treatment step after the porous article is densified as desired, the heat treatment step comprising:
draining the precursor liquid completely from the reactor chamber,
heating the densified porous article to a temperature between about 1600° C. and about 2400° C. while applying a pressure between about 760 Torr and about 780 Torr, and
gradually ramping down the applied heating temperature to zero at the end of heat treatment.
27 . The method according to claim 17 , comprising:
setting an initial frequency and power supply to the induction coils, the initial frequency and power supply being effective to accumulate sufficient heat at a geometric center region of the porous article to cause pyrolysis of liquid precursor vapor preferentially in the pores located in the geometric center region of the preform,
providing electrical power to the induction coil at the initial frequency sufficient to densify the geometric center region of the preform before substantially densifying other interior regions and an exterior surface of the porous article,
after densifying the geometric center region of the porous article, providing electrical power the induction coils at one or more frequency settings, the power level and frequency setting being effective to heat the interior of the porous article to cause pyrolysis of the liquid precursor vapor and preferentially deposit a pyrolytic product in the pores located adjacent to the geometric center region,
adjusting the power level supplied to the induction coils at one or more frequency settings, the quantity of power and frequency setting being effective to progressively densify the interior regions of the preform in a radial direction outwards from the geometric center region of the preform, and
gradually ramping down the power to zero at the end of the densification process.