This application relates to methods of making components.
A gas turbine engine typically includes a compressor section in fluid communication with one or more bleed valves. During engine start-up, a bleed valve changes between opened and closed positions depending on pressure within the compressor. The bleed valve is driven to the opened and closed positions with help from a piston at low and high operating pressures, allowing air entering the compressor to be compressed and delivered to engine components.
The piston is typically made of a heavy metal based alloy and therefore often experiences vibration and wear life complications.
A method for making a component includes the steps of providing a preform formed of carbon fibers. A first densification is performed forming a carbon composite. A first hardening of the carbon composite is performed. The method machines the carbon composite to form a shape. The method then performs a second densification and a second hardening. The method then final machines the carbon composite to form a final shape of the component.
A preform 10 is illustrated in
The carbon fibers may include polyacrylonitrile (PAN), rayon carbon fiber, and pitch-based carbon fiber, which includes isotropic pitch carbon fiber and mesophase pitch carbon fiber. In one example, the carbon fiber is PAN forming a 3D preform. In another example, PAN can form a 2.5D preform. 2.5D can be referred to as a 3D structure that is restricted to the second dimension. That is, the second dimension capable of showing only a limited portion of the 3D structure. For example, a 2.5D preform has a lesser thickness in the iz-direction increases, the preform progresses towards a 3D structured preform. Both the 2.5D and 3D preforms may have a structure capable of infiltration.
The preform 10 is typically a shape and size that can be efficiently machined to a desired final shape. As shown in
As shown in
CVI is a process of introducing a matrix material carried by a gas into the system. With time the matrix material will infiltrate and subsequently “build-up” on the preform, thus reducing open porosity and sealing the surface.
An example of pitch infiltration is a process of introducing solid pitch powder around the preform and heating the pitch to a temperature slightly above its melting temperature in the system having a controlled nitrogen or argon atmosphere. Heating helps to manage pitch viscosity which can be used to guide the melted pitch to fill open porosity of the preform. Pressure and/or vacuum can also be used to guide or facilitate infiltration of the pitch and manage fiber orientation in the preform. The process further includes reducing the temperature below 100° C. to solidify the pitch. Next, the pitch may be stabilized by again heating the pitch below or close to its melting point. Stabilization converts the pitch from thermoplastic to thermoset, which allows the preform to undergo carbonization without subsequently melting. Accordingly, the preform is carbonized at a range of 1300-3000° C. to help release byproducts of the pitch. Note, yield of the pitch during carbonization is over 80%, generally. This means at least 80% of the pitch remains in the preform, after carbonization. Such a yield can leave subsequent open porosity. A single pitch infiltration can significantly reduce open porosity, but multiple pitch infiltrations can reduce open porosity to less than 5% in some cases.
In this example, CVI can be performed using rough laminar (RL) pyrocarbon as the matrix material and/or pitch infiltration can be performed using mesophase pitch. Both RL pyrocarbon and mesophase pitch are graphitizable forms of carbon which can be useful in managing carbon structure. Mesophase pitch is a carbonaceous liquid crystal state in which molecular groups are regularly oriented so as to show optical anisotropy. This feature manages its crystal orientation to the direction desired and manages its crystal size at liquid state and further manages its graphitization degree after carbonization and/or graphitization.
The preform 10 is densified to a density range of 1.60-1.75 g/cm3 in one example. The preform 10 may now be considered a carbon composite 20. At this stage, composite surface porosity has been considerably reduced.
As shown schematically in
Referring to
In
As shown in
A carbon composite 30 is shown schematically in
In this example, the carbon composite 30 includes an upper portion 31, an intermediate portion 32, and a lower portion 33. Each of the portions 31-33 have a cylindrical shape with an inner diameter D. Notably, the upper portion 31 has an outer diameter substantially larger in comparison to that of the intermediate portion 32 and lower portion 33. Furthermore, the lower portion 33 has an outer diameter intermediate in size compared to that of the intermediate portion 32 and upper portion 31.
Along the lateral edge of the upper portion 31, a plurality of protrusions 34 are defined by grooves. A lip 37, defined by pocked 35, is shown extending radially from the radial face of the upper portion.
Similarly, along the lateral edge of the lower portion 33, a plurality of protrusions 36 are defined by grooves; and a lip 39, defined by pocket 38, extends radially from the radial face of the lower portion.
The densification and hardening steps described above can be used to obtain a carbon matrix of the carbon composite 30 with an improved storage modulus and, thus, improved vibration resistance. The first densification provides a baseline material for continued densification. The baseline material allows two different densification processes to be used. CVI allows quick surface infiltration, capable of sealing open porosity of the surface of the preform. The sealing the surface of the composite via CVI densification enables the composite to sustain pressures experienced under standard operating conditions. Pitch infiltration allows full infiltration from the inside of the composite to the surface of the composite, thus filling all open porosity. In light of this invention, a specific densification process can be chosen to meet the needs of a particular application. For some applications, all open porosity may need to be filled instead of just filling surface open porosity, especially for applications that require substantial vibration resistance.
Compared to current pistons, the method described above can obtain a composite having at least 75% reduced weight by replacing typical metal components with a carbon composite. The method can achieve a vibration resistance increase of 300%-400% because by nature of the carbon composite, the crystal structure can be changed via high temperature carbonization and/or graphitization to manage composite damping (storage modulus). Both rough laminar pyrocarbon CVI and mesophase pitch infiltration enable composite structures changeable to or close to graphite with high temperature carbonization or graphitization. Notably, as degree of graphitization increases, the storage modulus of the composite increases. A 100% increase in wear life can also be achieved by managing the carbon composite crystal structure and high temperature carbonization. As the structure changes to or close to graphite, the composite can exhibit lubricant characteristics. Furthermore, composite redesign flexibility can be increased in comparison to typical metal components. For example, in metal pistons, a carbon/graphite ring is required on the edge for sealing purposes. A carbon/graphite composite piston eliminates the need for such a ring because the composite piston is an inherently good sealing material.
The foregoing description shall be interpreted as illustrative and not in any limiting sense. A person of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.
This application claims priority to U.S. Provisional Application No. 63/000,729 filed Mar. 27, 2020.
Number | Date | Country | |
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63000729 | Mar 2020 | US |