One piece shim
A one-piece or otherwise unitary annular shim member made from a carbon material is used to maintain a space between stacked annular preforms during a manufacturing process, such as densification. The one-piece structure advantageously simplifies the arrangement of the preforms in a process chamber and causes less deformation in the preforms. The carbon composition also provides beneficial thermal effects that improve the densification process. A debonding coating is provided on the annular shim member in order to facilitate separation of the annular preforms from the shim members.
The present invention relates to shim members used to space apart stacked porous substrates during a manufacturing process. A particular example of the present invention relates to carbon annular shim members used to space apart stacked annular composite material preforms especially during a densification process, such as chemical vapor infiltration (CVI).
The composite material preforms may particularly be annular preforms for making brake disks or other friction members.
An apparatus for densifying annular preforms to make brake disks and the like is disclosed in, for example, U.S. patent application Ser. No. 10/468,031 filed on Aug. 14, 2003; a representation thereof is illustrated in
The stacked substrates are separated from one another by means of spacers 30. As shown in
In the example of
The enclosure 10 is heated by means of a susceptor 14, e.g. made of graphite, which serves to define the enclosure 10 and which is inductively coupled with an induction coil 16 situated outside a casing 17 surrounding the susceptor. Other methods of heating may be used, for example resistive heating (the Joule effect).
A gas containing one or more precursors of carbon, typically hydrocarbon gases such as methane and/or propane, is admitted into the enclosure 10. In the example shown, admission takes place through the bottom 10a of the enclosure. The gas passes through a preheater zone 18 formed by one or more pierced plates disposed one above another in the bottom portion of the enclosure, beneath the plate 11 supporting the stack of substrates. The gas heated by the preheater plates (which are raised to the temperature that exists inside the enclosure) flows freely into the enclosure, passing simultaneously into the inside volume 24, into the outer volume 26, and into the gaps 22. The residual gas is extracted from the enclosure by suction through an outlet formed in the cover 10b.
Spacers 30 are individually placed block members, most usually made from alumina. However, once formed, the alumina block members are very fragile, and losses from breakage are very high. In fact, in normal usage, the conventional alumina blocks frequently last not more than 2 or 3 densification cycles. This naturally raises manufacturing costs, as the alumina blocks must be replaced.
Moreover, the proper manual placement of individual alumina block members between each preform layer is extremely time-consuming. Six such block members are shown in
Another problem related to the use of individual spacer members 30 is that they tend to cause deformations (literally, dents) in the preforms caused by the weight of preforms (and spacers) stacked thereabove. As can be appreciated from
In view of the foregoing, the present invention relates to a one-piece or otherwise unitary annular shim member for spacing apart stacked annular preforms.
A shim member according to the present invention has a generally flattened annular form with opposing first and second surfaces. At least one of the surfaces includes is shaped to at least partially define radially extending gas flow paths for communicating the interior space of the shim member with an exterior.
A shim member according to the present invention is preferably similar in radial dimensions to the annular preforms adjacent thereto. That is, the shim member preferably has a similar interior diameter and a similar exterior diameter to the annular preforms. If the shim member is not generally identical in size to the annular preforms, it is preferable to slightly undersize the shim member (i.e., have an interior diameter greater than and/or an exterior diameter less than the annular preforms), rather than have the shim member be larger (i.e., radially wider) than the annular preforms.
In one example of the present invention, the shim member is made from a carbon material (such as graphite or carbon/carbon composite) having a debonding coating formed thereon.
BRIEF DESCRIPTION OF THE DRAWINGSThe present invention will be even better understood with reference to the figures attached hereto, in which:
It is expressly emphasized that the figures herein are meant to merely illustrate examples of the present invention and are not to be construed as limiting the definition thereof in any way. It is also noted that the figures herein are not necessarily to scale, either in general or among interrelated views.
DETAILED DESCRIPTION OF THE PRESENT INVENTIONIn general, a shim member according to the present invention has certain fundamentally useful characteristics.
A one-piece or otherwise unitary construction greatly facilitates the loading of a process chamber with stacked annular preforms, in comparison to the use of several individual spacer members between every annular preform in the stack. As noted above, the conventional arrangement described above with reference to
With the use of a one-piece shim member according to the present invention, a single action of positioning the shim member replaces the several placement actions of positioning individual spacer members according to the conventional method. In comparison to the one to two days to load a process chamber in the conventional manner discussed above, the use of a one-piece shim according to the present invention could, on an equal basis, reduce loading times down to two to four hours.
In addition, the structure of the one-piece shim member according to the present invention better supports the weight of the one or more annular preforms stacked thereon over a greater area, in comparison to the conventional use of individual spacer members, as illustrated in
As just mentioned, the one-piece shim member preferably has about the same radial width as the annular preform, or is slightly narrower (for example, by about 5 mm with respect to the outside and/or inner diameters thereof). If the one-piece shim member were wider than the annular preform, the exposed portions would tend to have a residue build up (such as pyrolytic carbon) thereon from the decomposition of the densification gas. This would either reduce the useful life of the shim member or entail additional refurbishment procedures to remove such buildup. In addition, if the shim member extended radially outward beyond the outside edge of the annular preforms, it could cause a problem in positioning several annular preform stacks in a process chamber for simultaneous processing (as is frequently done). This would negatively affect production efficiency to the extent that fewer stacks could be processed together because of spacing issues within the process chamber.
In general, the one-piece shim member according to the present invention includes radially extending channels or other features on one or both surfaces thereof that, in net effect, at least partly define gas flow paths communicating the radially interior side of the one-piece shim member with the radially exterior side thereof. The mention of “partly” defined gas flow paths is made here because in some cases, the gas flow paths are also partly defined by the opposing surface of one of the annular preforms in cooperation with the structure of the one-piece shim member. The cross-sectional area of the gas flow paths using the one-piece shim is preferably comparable, in net effect, to the cross-sectional area presented in the prior art arrangement. However, this consideration may vary in accordance with individual situations.
It will be appreciated that the collective cross-sectional area of the gas flow paths presented can be affected, for example, by either adjusting the size of each channel or the like, or by providing more of the channels or the like. A deciding factor in this regard is maintaining a desirable level of support for the overlying annular preform(s).
Generally, the one-piece shim member according to the present invention should be made from a material that can withstand temperatures of up to about 1100° C., and preferably (for safety purposes) up to about 1200° C. to 1400° C. The chosen material is preferably minimally reactive with the preform at the operational temperatures mentioned.
Examples of materials appropriate for the one-piece shim member as contemplated include, without limitation, carbon materials such as graphite, carbon/carbon, and woven carbon fiber yarns; molded ceramics; and metallic materials such as stainless steel, Inconel alloy, titanium, molybdenum, tantalum, and tungsten.
A carbon/carbon material can be made into an annular shim according to the present invention in a known manner from a 2-D or 3-D preform (that may be needled) or laminated from multi-layers of woven carbon fiber fabric, and then densified using a CVI or resin impregnation process.
Carbon/carbon based starting materials can be molded and/or Machined into shape in a known manner, and graphite used as a starting material can be machined in a known manner into a desired geometry from a blank.
In
Annular shim member 300 has a plurality of spaced apart generally regularly shaped raised portions (some of which are indicated at 304a) alternating with relatively lowered portions therebetween (some of which are indicated at 304b) on one side thereof. Likewise, the other side of annular shim 300 has corresponding spaced apart generally regularly shaped raised portions (some of which are indicated by broken lines at 302a) alternating with relatively lowered portions therebetween (some of which are indicated at 302b).
In this example, edge portions of the raised portions 302a, 304a overlap an edge of a corresponding raised portion on the other side of annular shim member 300. See, for example,
Lowered portions 302b, 304b define radially extending channels or gas flow paths through which the densification gas can flow from an interior of the stacked annular preforms to the exterior. As mentioned above, the collective cross-sectional area that these channels present for densification gas flow may, in general, vary according to a specific processing situation. However, in general, the cross-sectional area should usually be comparable to that presented when using the conventional spacer members 30 mentioned above.
In
Annular shim member 400 has a structure similar to that of annular shim member 300, in that both sides thereof have relatively raised portions 402a, 404a alternating with relatively lowered portions 402b, 404b. Here, again, the relatively lowered portions 402b, 404b define radially extending channels or gas flow passages through which the densification gas can pass from an interior of the stacked annular preforms to an exterior thereof.
It can be seen in
In contrast, because annular shim member 400 is relatively thinner than annular shim member 300, there is no equivalent planar thickness of the constituent material therein. Thus, it is only possible to trace an undulating path (corresponding to the alternating raised and lowered portions) along an outside edge of annular shim member 400. (See, for example,
In
Most generally, annular shim member 500 differs from annular shim members 300 and 400 in that, relatively, the raised portions 502a, 504a on the opposite sides of annular shim member 500 are aligned, as are the lowered portions 502b, 504b. See, especially,
In one example, one can consider the manufacture of annular shim member 500 from the perspective of forming corresponding channels 502b, 504b on opposite faces of a carbon (e.g., graphite) blank having an initial thickness at least on the order of the thickness of the annular shim member 500 at locations where the raised portions 502a, 504a correspond.
As mentioned above, the aforementioned geometries can be obtained by any known and appropriate process, especially, but not only, machining or molding or both.
When using carbon materials to manufacture shim members according to the present invention for use with composite carbon annular preforms, there is sometimes a problem of the shim member adhering to the preforms after a densification process. In order to address this issue, the provision of a debonding coating on the surface of the shim member is contemplated in order to help avoid such adhesion.
One example of a useful debonding coating includes a first layer formed on the shim member made from MoSi2, and a second layer formed on the first layer made from Al2O3. These layers can be formed using a known process of plasma spraying, for example. The MoSi2 layer acts as a bridging layer to improve the adhesion of the Al2O3 layer to the structure.
It should be noted that the provision of a carbon-based shim member, especially a graphite shim member, has additional benefits during manufacture. In general, the provision of graphite shim members to the annular preform stack adds to the thermal mass of the stack so as to facilitate heating, and in turn, densification. This is beneficial because it is relatively difficult to raise the temperature of the preforms alone. (In a conventional process, the top and bottom of a stack of preforms have the highest level of densification because of their larger exposure to heating compared to intermediate preforms in the stack.) Also, because of the good thermal conductivity of the carbon shim members, a more uniform temperature distribution can be provided across the radial width of the adjacent annular preforms.
While the present invention has been described with respect to what are believed to be the most practical embodiments thereof, it is particularly noted that this is by way of example only, and appropriate modifications and variations thereof are possible within the spirit and scope of the claims appended hereto.
Claims
1. An annular unitary shim member having first and second opposing surfaces,
- wherein the member is made from a carbon material having a debonding coating formed thereon, the member including a plurality of radially extending channels formed on at least one of the first and second surfaces.
2. The member according to claim 1, wherein a plurality of radially extending channels is formed on both of the first and second surfaces.
3. The member according to claim 2, wherein the plurality of channels formed on the first surface is substantially aligned with the plurality of channels formed on the second surface.
4. The member according to claim 2, wherein the plurality of channels formed on the first surface is offset in a circumferential direction from the plurality of channels formed on the second surface.
5. The member according to claim 1, wherein the carbon material is one of a carbon/carbon material and a solid graphite material.
6. The member according to claim 5, wherein the carbon/carbon fiber material is a woven carbon fiber yarn fabric.
7. The member according to claim 1, wherein the debonding coating comprises a first layer of MoSi2 formed on the carbon material, and a second layer of Al2O3 formed on the first layer of MoSi2.
8.-14. (canceled)
15. A method for manufacturing a unitary annular shim from a carbon material, the method comprising:
- forming an annular member from a carbon material, the annular member having first and second opposing faces and a radially extending channel formed on at least one of the first and second opposing faces; and
- forming a debonding coating on the annular member.
16. The method according to claim 15, wherein forming the debonding coating comprises forming a first layer of MoSi2 on the carbon material, and forming a second layer of Al2O3 on the first layer of MoSi2.
17. The method according to claim 16, wherein forming the debonding coating comprises using plasma spraying to form the first layer of MoSi2 on the carbon material and the second layer of Al2O3 on the first layer of MoSi2.
18. The method according to claim 15, wherein forming an annular member comprises machining a graphite blank.
19. The method according to claim 15, wherein the carbon material is one of a carbon/carbon fiber material and a woven carbon fiber yarn fabric.
20.-22. (canceled)
23. The member according to claim 5, wherein the carbon/carbon material comprises one of a needled carbon preform and a woven carbon fabric laminate.
24. The method according to claim 15, wherein the carbon material is one of a needled carbon preform and a woven carbon fabric laminate.
Type: Application
Filed: Mar 2, 2004
Publication Date: Aug 24, 2006
Inventor: Kenny Chang (Union, KY)
Application Number: 10/548,122
International Classification: C23C 4/00 (20060101); B05D 1/08 (20060101); B32B 3/02 (20060101);