Source: http://www.google.com/patents/US7332112?ie=ISO-8859-1
Timestamp: 2015-06-02 06:20:43
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Matched Legal Cases: ['art.\n15', 'art.\n19', 'art 18', 'art 18', 'art 18', 'art.2']

Patent US7332112 - Apparatus and method for forming densified, carbon-carbon composites - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn apparatus and method for forming a densified carbon-carbon composite. The apparatus includes: a green part molding station for forming a green part; a carbonization station for carbonizing the green part; and an impregnation station for impregnating the carbonized part with a substantially curing...http://www.google.com/patents/US7332112?utm_source=gb-gplus-sharePatent US7332112 - Apparatus and method for forming densified, carbon-carbon compositesAdvanced Patent SearchPublication numberUS7332112 B1Publication typeGrantApplication numberUS 10/852,293Publication dateFeb 19, 2008Filing dateMay 24, 2004Priority dateMay 17, 1999Fee statusPaidAlso published asUS6325608Publication number10852293, 852293, US 7332112 B1, US 7332112B1, US-B1-7332112, US7332112 B1, US7332112B1InventorsKunigal N. Shivakumar, Vishnu Sarma Avva, Mannur J. Sundaresan, Felix Abali, Anthony Cunningham, Robert L. SadlerOriginal AssigneeN.C. A&T State UniversityExport CitationBiBTeX, EndNote, RefManPatent Citations (31), Non-Patent Citations (4), Referenced by (3), Classifications (11), Legal Events (1) External Links: USPTO, USPTO Assignment, EspacenetApparatus and method for forming densified, carbon-carbon composites
US 7332112 B1Abstract
1. A method for forming a densified carbon-carbon composite, said method comprising:
(a) sealing a porous carbon part in an enclosure configured in the shape of the part;
(b) injecting a substantially curing, by-product free, high carbon yield resin into the enclosure;
(c) removing the porous carbon part from the enclosure and placing the part in a chamber without the enclosure;
(d) carbonizing said porous carbon part in said chamber without the application of compressive force;
(e) removing the part from the chamber; and
(f) re-impregnating the part in the enclosure.
2. A method for forming a densified carbon-carbon composite, said method comprising:
(a) forming a green part;
(b) impregnating said green part with a substantially curing, by-product free resin in an enclosure configured in the shape of the desired carbon-carbon composite while heating said enclosure to a temperature of only about 300� F. to only about 350� F.;
(c) carbonizing said impregnated green part without the application of compressive force to form a carbon-carbon composite;
(d) sealing said carbon-carbon composite in said enclosure configured in the shape of said green part; and
(e) re-impregnating said carbon-carbon composite with a substantially curing, by-product free resin while heating said enclosure to a temperature of only about 300� F. to only about 350� F.
3. The method according to claim 2, wherein said forming and said impregnating are performed at substantially the same location.
4. The method according to claim 2, wherein said carbonizing includes heating said green part in a non-oxidizing atmosphere in an enclosed chamber.
5. The method according to claim 4, wherein said heating involves heating said enclosed chamber to a temperature greater than about 650� C.
6. The method according to claim 4, wherein said heating involves heating said enclosed chamber to a temperature of about 950� C.
7. The method according to claim 4, wherein said carbonizing is done in a vacuum.
8. The method according to claim 4, wherein the atmosphere is a non-reactive gas.
9. The method according to claim 8, wherein the atmosphere is at a positive pressure.
10. The method according to claim 8, wherein said non-reactive gas is nitrogen.
11. The method according to claim 4, further including cleaning the atmosphere exiting the enclosed chamber.
12. The method according to claim 11, wherein said cleaning is done using an activated carbon filter.
13. The method according to claim 11, wherein the cleaning includes passing the atmosphere exiting the enclosed chamber through a water bath.
14. The method according to claim 2, further including forming a pre-form for said green part.
15. The method according to claim 2, wherein said green part forming includes configuring at least one surface for said green part into a desired shape.
16. The method according to claim 15, wherein a mold is used to configure the at least one surface of said green part into the desired shape and to thereby form a sealed enclosure.
17. The method according to claim 16, further including evacuating said sealed enclosure.
18. The method according to claim 2, further including curing said green part.
19. The method according to claim 2, further including maintaining said green part under pressure.
20. A method for impregnating a carbonized part with a substantially curing, by-product free, high carbon yield resin to form a densified carbon-carbon composite, said method comprising:
(a) impregnating a preform in an enclosure configured in the shape of said part;
(b) carbonizing said preform to produce a carbonized part without the application of compressive force;
(c) sealing said carbonized part in said enclosure;
(d) re-impregnating said carbonized part with a substantially curing by-product free, high carbon yield resin;
(e) heating said enclosure to a temperature of only about 300� F. to only about 350� F.;
(f) carbonizing said re-impregnated carbonized part without the application of compressive force;
(g) re-impregnating said part in said enclosure; and
(h) repeating steps (f) and (g) until a desired level of density is achieved.
21. The method according to claim 20, further including evacuating said sealed enclosure.
22. The method according to claim 21, further including surrounding said sealed enclosure with an outer chamber to facilitate evacuating of said sealed enclosure.
23. The method according to claim 21, wherein said evacuating and said impregnating are affected substantially along the same path.
24. The method according to claim 21, wherein said evacuating and said impregnating are affected substantially along different paths.
25. The method according to claim 20, further including curing said resin impregnated carbonized body.
26. The method according to claim 20, further including pressuring during said impregnating.
27. The method according to claim 20, further including heating said resin prior to said impregnating.
28. The method according to claim 20, further including pumping said resin to said sealed enclosure.
29. The method according to claim 28, wherein said pumping is at a pressure just sufficient to fill said sealed enclosure with said resin.
30. The method according to claim 29, further including a second, packing pumping to a pressure for impregnating said carbonized part with said resin.
31. The method according to claim 30, wherein said packing pressure is substantially greater than said fill pressure.
32. The method according to claim 31, wherein said packing pressure is up to about 850 psi.
33. The method according to claim 32, wherein said fill pressure is as low as about 14 psi.
34. The method according to claim 20, wherein said resin has a viscosity of less than about 100 cps at 175� F.
35. The method according to claim 34, wherein said resin has a viscosity of less than about 50 cps at 175� F.
36. The method according to claim 20, wherein said substantially curing by-product free, high carbon yield resin is a cyanate ester.
37. The method according to claim 20, wherein said substantially curing by-product free, high carbon yield resin has a carbon yield value of greater than about 25 wt. %.
38. The method according to claim 20, wherein said substantially curing by-product free, high carbon yield resin has a carbon yield value of greater than about 60 wt. %.
39. A method for densifying a carbon-carbon composite comprising the steps of:
(a) sealing a porous carbon part in an enclosure configured in the shape of said porous carbon part;
(b) impregnating said porous carbon part with a substantially curing, by-product free, high carbon yield resin while heating said enclosure to a temperature of only about 300� F. to only about 350� F. to produce an impregnated part;
(c) removing said impregnated part from said enclosure and placing said impregnated part in a chamber without said enclosure;
(d) carbonizing said impregnated part in said chamber without the application of compressive force to form a carbon-carbon composite;
(e) removing said carbon-carbon composite from said chamber and placing said composite in said enclosure;
(f) re-impregnating said carbon-carbon composite with a substantially curing by-product free, high carbon yield resin while heating said enclosure to a temperature of only about 300� F. to only about 350� F.;
(g) removing said re-impregnated carbon-carbon composite from said enclosure and placing said composite in said chamber without said enclosure;
(h) carbonizing said re-impregnated carbon-carbon composite without the application of compressive force; and
(i) repeating steps (e), (f), (g) and (h) until a desired level of density is achieved.
40. The method of claim 39, further comprising the steps of creating a preform, impregnating said preform in said enclosure and carbonizing the preform without the application of compressive force to create said porous carbon part.
This application is a continuation of U.S. application Ser. No. 09/962,789, filed Sep. 25, 2001, now abandoned, which is a divisional of U.S. application Ser. No. 09/313,232, filed May 17, 1999, now U.S. Pat. No. 6,325,608.
TABLE 1 SOLVENT CVD IMPREGNATION PRESENT INVENTION Carbon Fabric Carbon Fabric Carbon Fabric Polymeric Polymeric Matrix Polymeric Matrix Matrix Green Part Green Part Carbonization Carbonization Step Carbonization Step Step Go to Vat Go to Impregnation Station CVD Impreg- Vacuum/Pressure of Vacuum/Pressure nation solvated resin No Gaseous By-products during Resin Curing High Carbon Yield Resin Dry to Remove Solvent Cure Cure Further Carbonization Step Further Carbonization Step Impregnation/Cure The known processes include, among others, chemical vapor deposition (CVD) and a solvent-based system that uses a solvent to liquefy the polymeric resin for impregnation into the carbon fiber structure. Both these processes and the present invention use a carbon fabric and a polymer resin as basic components. These components are combined to from a “green part” which will have a carbon and a non-carbon component. The green part then goes through a first carbonization step after which other steps are conducted depending on the method employed. The impregnation and carbonization steps are repeated until a desired level of density is achieved.
With the CVD process, it is difficult to densify the central regions of thick items. This is because the initial densification steps tend to block the outer regions of the part. As these outer regions become blocked, it becomes every more difficult to force the gas to the center of the part.
In a preferred embodiment, the green part is constructed from a preform comprised of multiple layers of a woven carbon fabric that are tacked together. In one approach, the layers are tacked together with a low melt, powdered epoxy material such as Shell Chemical's Epon 1031. The layers with the powdered epoxy therebetween are compacted in a vacuum bag and then heated until the melting temperature of the epoxy is reached. The relatively stiff, bonded layers are referred to as a preform. It will be appreciated by one of ordinary skill that for composites having a flat shape, the epoxy bonding step may be omitted. However, for more complicated shapes, creating a preform is desirable. The preform is them impregnated with a resin to create a carbon-carbon green part that will be transformed into a carbon-carbon composite.
Referring now to the drawings in general and FIG. 1 in particular, it will be understood that the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. As best seen in FIG. 1, an apparatus for forming a densified carbon-carbon composite, generally designated 10, is shown constructed according to the present invention. The apparatus 10 includes three major sub-assemblies: a green part molding station 12 (FIG. 1); a impregnation station 214 (FIG. 2); and a carbonization station 16 (FIG. 4).
The green part molding station 12 is a resin transfer molding (RTM) station and includes a mold 18 having at least one surface configured to the shape of the part to be made. As shown in FIGS. 3A-3C, preferably the mold 18 is enclosed and includes an upper part 18 a and a lower part 18 b. A seal 19 (See FIG. 2) is provided in the lower part 18 b to provide an airtight seal between the mold components during use. The mold 18 further includes a resin injection port 26 and a second evacuation port 30 for providing entrance and exit points, respectively, for the matrix. A resin reservoir 23 holds a supply of resin and communicates with the mold 18 via entrance conduit 17 and pump 25. A resin reservoir heating means is also provided to lower the viscosity of the resin sufficiently so that it may be pumped. A vacuum source 24 is connected to the mold 18 at the evacuation port 30. A preferred vacuum source is a vacuum pump. Alternatively, the vacuum source 24 may be connected to the mold at the injection port 26 via a “T” fitting to reduce the number of openings provided in the mold. In yet another embodiment, the vacuum source 24 may be connected to an external chamber for evacuating the mold 18. The green part molding station 12 further includes a platen press 22 which is provided with a heating means 20 for curing the resin.
The present invention further includes an impregnation station 214 (FIG. 2) that, in a preferred embodiment, is substantially identical to the green part molding station. That is, essentially the same station may be used to form the molded green part and to impregnate the carbon-carbon composite. The impregnation station includes a mold 218 having at least one surface configured to the shape of the part to be made. This mold 218 is substantially identical to the mold 18 described above. The impregnation station 214 includes a resin reservoir 223, inlet conduit 217, platen 222, platen heater 220, exit conduit 215, pump 223, resin heater 225, and vacuum source 224 as described above with respect to the green part molding station 12.
Both the green part molding station 12 and the impregnation station 214 further include appropriate valving, gauges and temperature sensors as needed to control the process of the present invention. These items have been omitted from the illustrations for the purpose of clarity but are properly within the scope of the claimed invention.
The impregnation/densification steps of the present invention include placing the preform or carbon-carbon composite item 213 in the impregnation mold 218 and heating the mold to a temperature of between about 300-350� F. while being held closed by the platen 22. In order to maintain the proper viscosity and flowability of the matrix, the inlet conduit 217 and the outlet conduit 215 which connects the vacuum source 224 are heated. In a preferred embodiment, the inlet conduit 217 is maintained at a temperature of about 175� F. and the outlet conduit 215 is maintained at a temperature of about 200� F. Other temperatures may be used depending on the makeup of the resin being used. Next, a vacuum is pulled in the mold. The amount of this vacuum should be sufficient to ensure that proper impregnation is achieved. A vacuum of less than about 25 torr is desirable with a vacuum of less than about 10 torr being preferred. More preferably, a vacuum of less than about 2 torr is achieved. After a proper vacuum is achieved, the matrix is pumped into the mold. Desirably, the matrix is pumped at a pressure sufficient to fill the mold, about 150 psi, although a fill pressure as low as about 14 psi can be used. The pressure may then be raised to a packing pressure that is substantially higher than the pressure used to fill the mold. A packing pressure of about 300 psi is desirable in the practice of the present invention, although a packing pressure up to about 850 psi can be used. It will be appreciated that the impregnation of both the green part and the carbon-carbon composite is carried out solely by the hydraulic pressure created when the resin is introduced into the mold. The resin temperature, initial filling pressure and the packing pressure should be selected to achieve the desired densification. The parameters discussed herein are exemplary only and may be varied depending on many factors apparent to one of ordinary skill.
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