Patent Application
20170298464
The present disclosure generally relates to systems and methods for cooling heat-treated parts, such as metallic work pieces. More particularly, the present disclosure relates to systems and methods for more controlled cooling heat-treated parts of various geometries and thicknesses.
Certain metallic parts, also known as work pieces, are subjected to severe environmental stresses during use. As an example, certain components of jet aircraft turbines and turbines for power generation, particularly the rotational components, are subjected to extreme centrifugal forces and high thermal stresses during use. Such components also have complex geometries, oftentimes irregular shapes, wherein the thickness varies across the metal component.
The metal parts, usually formed of nickel and titanium superalloys, are commonly heat-treated to improve the strength and wear characteristics of the part, so that they can better withstand the rotational and thermal stresses experienced during use. The heat-treating process usually begins in a furnace, wherein the temperature is set precisely to control growth of specific strengthening microstructures. The alloy properties such as hardness, strength, toughness, ductility, elasticity, and the like of the parts can be determined by the type of microstructure, grain sizes, the heat-treatment temperature, the rate of cooling, the composition of the cooling medium, and the like.
After the alloy part is heated and held above a critical temperature for a predetermined duration, the alloy part must then be cooled. A common method of cooling the heat-treated alloy parts is by immersing the part in a fluid bath. This cooling process is commonly referred to as “quenching.” Quenching of alloy work pieces is conventionally achieved by immersing the part in a liquid coolant, such as water or oil. Immersion of the hot part in the liquid coolant rapidly cools the part at a rate that is either sufficient to maintain certain molecular characteristics of the metal that were acquired in the heat-treatment process, or to obtain certain different molecular characteristics that form during the cooling (quenching) process.
For heat-treated parts having complex shapes and alloys that are strain-rate sensitive, quenching through immersion in a liquid coolant typically does not provide uniform cooling throughout the part. Heat dissipates quickly from thin portions of the part, while thicker portions retain heat for much longer periods. The difference in cooling rates between the surface of the part and the inner portions of the part can result in the creation of varying material properties, varying grain structures, or, in extreme cases, cracks in the work piece. Air quenching as opposed to liquid immersion quenching has the advantage of producing a slower cooling of the part than achieved with a liquid bath quench. However, conventional air quenching methods have only a limited capability in cooling work pieces, because it is difficult to control the air quenching process aside from varying the length of time the heated part remains in the cooling air stream. As such, current air quenching processes are not as effective in providing uniform cooling rates to parts having complex geometries and varying thickness.
Thus, uniform cooling of work pieces having complex sizes and shapes is, at best, extremely difficult using current cooling/quenching techniques. As such, there is a need for systems and methods that enable uniform cooling and formation of the desirable metal grain structures in heat-treated parts having complex shapes and sizes, particularly for the rotational parts found in jet engines and turbine generators.
Disclosed herein are systems for the uniform cooling of a heat-treated alloy part. In one embodiment, the system for cooling a heat-treated metallic part includes a housing configured to hold the heat-treated metallic part; an upper shroud assembly comprising at least one sub-assembly coupled to the housing comprising an annular-shaped body, at least two annular channels disposed within the annular shaped body, a cover attached to the annular shaped body including at least two fluid inlets for receiving a fluid source, and a plurality of atomization nozzles annularly arranged on an outer surface of the annular shaped body comprising outlets oriented to discharge atomized fluid at the metallic part, wherein the at least two fluid inlets are in fluid communication with the atomization nozzles via the at least two annular channel; and a lower shroud assembly comprising at least one sub-assembly coupled to the housing comprising an annular-shaped body, at least two annular channels disposed within the annular shaped body, a cover attached to the annular shaped body including at least two fluid inlets, and a plurality of atomization nozzles annularly arranged on an outer surface of the annular shaped body comprising outlets oriented to cool the metallic part, wherein the at least two fluid inlets are in fluid communication with the atomization nozzles via the at least two annular channels; wherein the at least two inlets in the upper and lower shroud assemblies are in fluid communication with at least one liquid source and at least one gas source such that each one of the plurality of atomization nozzles are in fluid communication with the at least one liquid source and the at least one gas source produce an atomized fluid discharge when in use.
The disclosure may be understood more readily by reference to the following detailed description of the various features of the disclosure and the examples included therein.
Referring now to the figures wherein the like elements are numbered alike:
FIG. (“FIG.”) 1 schematically illustrates a turbine disk in accordance with an embodiment of the present disclosure;
Disclosed herein are systems and methods for the rapid and highly controlled cooling of a heat-treated metallic part. The heat-treated metallic part to be cooled can be any metallic material. In some embodiments, the heat-treated part is a high temperature aerospace alloy. Typically, these materials must have adequate performance characteristics for its intended use, such as tensile strength, creep resistance, oxidation resistance, and corrosion resistance, at high temperatures. More particularly, the systems and methods are configured to maintain highly controlled cooling across the surface of the metallic part being heat-treated by tailoring the heat transfer coefficient in specific areas of the part based on the cross-sectional thickness of the part in those locations. The systems and methods disclosed herein can be particularly advantageous in the production of jet engine and gas turbine generator components, such as turbine disks, and the like.
The production of metallic parts, such as turbine components, generally begins with the shaping of a billet, e.g., an alloy billet in the case of turbine components. The alloy billet is forged into the desired shape under heat and pressure. In order for the shaped part to have the desired microstructure and mechanical properties, the shaped part is then heated and held at a predetermined temperature for a predetermined duration. The part is then cooled in a separate step, commonly referred to as quenching. For most applications, uniform cooling of the heat-treated part is desired because it will promote the development of a uniform grain structure within the alloy composition and minimize distortion of the piece. The cooling method described herein rapidly produces the desired microstructure of the material and desired mechanical properties while avoiding physical defects in the part, such as cracking or distortion that may occur in other systems and processes. Advantageously, the cooling process, also referred to herein as a quenching process, provides a substantially uniform and rapid reduction in temperature.
While the cooling systems and methods disclosed herein can be useful for the rapid and controlled cooling of any heat-treated part, the systems and methods are particularly useful for heat-treated metallic parts intended to be used as components in jet turbine engines and generators. The turbine components, such as turbine disks and casings, are typically circular in shape with radial cross-sections having complex geometries and/or varying thickness across the diameter of the part. In one embodiment, the turbine components are axisymmetric. As such, for ease in discussion, further description of the cooling systems and methods will be with respect to the controlled cooling of a turbine disk having a complex geometry. However, it is to be understood that the systems and methods described herein are not limited to turbine disks, but are applicable to any heat-treated part where controlled cooling is highly desirable.
Referring to
In other embodiments of a turbine disk, the disk could include channels or grooves (not shown) cut inwardly into the part, further altering the thickness profile of the disk. These dissimilar portions will exhibit different cooling rates due to the differences in thickness. If the same amount of cooling were applied to the entire disk, the thicker portions would retain heat longer than their thinner counterparts. In other words, the thicker portions, such as defined by the second portion 14 and ridge 18 will retain heat for a longer period and thus take longer to cool than the thinner portions, such as the inner annular portion 12 and the outer portion 16. These thinner portions are capable of dissipating heat more quickly than the thicker second portion 14 and ridge 18. The cooling systems and methods disclosed herein are able to cool such turbine disks at a substantially more uniform rate than that previously known, despite the disk's complex shape and varying thickness profile. Moreover, relative to other systems and processes, the cooling systems provides a significant reduction in the cooling rate.
Turning now to
As noted above, the guide and actuation rods 106 are coupled to one or more of the horizontal and/or vertical beams 108110 of the housing 104 to vertically position the upper and/or lower shroud assemblies 150, 200 within the housing 104 such that a selected one or both can be selectively positioned about the part to be treated as may be desired for different applications, e.g., the upper shroud assembly can be raised or lowered as desired. In some embodiments, a selected one of the upper shroud assembly 150 or the lower shroud assembly 200 is fixedly coupled to the housing 104 and is not configured to move vertically.
As shown more clearly in
For ease in understanding as it relates to construction of the upper shroud assembly 150, specific reference will now be made in
As shown more clearly in
The plurality of atomization nozzles 162 are generally configured to be concentrically disposed about selected portions of the part to be cooled, wherein each atomization nozzle 162 includes an outlet oriented towards the part to be fluidly cooled. With regard to manifold sub-assembly 154, the atomization nozzles 162 are configured to discharge cooling fluid towards a surface of the part to be cooled in an angled direction along a z-axis. In contrast, annular manifold sub-assembly 153 has the atomization nozzles 172 therein (see
Referring back to
The various atomization nozzles in the upper and lower shroud assemblies 150, 200 are configured to atomize and project a fine spray of droplets onto the heat-treated part to be cooled in a pattern that provides uniform cooling of the heat treated part regardless of thickness variation. The droplet spray pattern can be configured to be substantially repeatable. The number and spacing between adjacent nozzles is not intended to be limited and may be optimized for the intended application. For example, the atomization nozzles may be axisymetrically disposed radially about the annular array at equal distances or in some embodiments, the spacing between adjacent atomization nozzles may or may not be equal.
In the depicted embodiments, the atomization nozzles disposed in the upper and lower shroud assemblies 150, 200 are generally configured to be spaced apart from the surfaces defining the complex geometric part to be cooled at a distance from about 1 to about 24 inches, which may be oriented to spray an atomized fluid onto the heat treated part at an angle that is not normal to the surface. In other embodiments, some or all of the atomization nozzles may spray at an angle that is normal to the surface of the heat-treated part to be cooled. Each array of atomization nozzles within the upper and lower shroud assembly 150 or 200 can be in a circular pattern that can be axisymmetric around the heat-treated part and oriented to spray inwardly towards the heat-treated part to be cooled. The atomization nozzles are in fluid communication with one or more fluid sources (not shown), which are not intended to be limited. Generally, the fluid sources include at least one gas and at least one liquid. A regulator (not shown) can be employed to control fluid flow for each array. Using air and water as exemplary fluid sources, a system using the atomization nozzles can be configured to selectively spray a fine mist of water in the form of fine droplets upon the surfaces of the part to be treated, wherein the water is gravity fed, lifted via a Venturi effect as is generally well known in the art, or fed via pressurized accumulators or a similar system to achieve required pressures. Air pressures are controlled from greater than 0 to 300 pounds per square inch (psi) and water pressure is controlled from greater than 0 to 300 psi. The fluid can be externally mixed as a mixture or within conduits (i.e., upstream of the nozzle) or internally mixed within the atomization nozzle. In this manner, each part surface that requires a different cooling rate can be sprayed with a set of atomization nozzles whose fluid pressures, e.g., water and air pressure, are tailored to achieve that surface's cooling rate such that the cooling rates are substantially uniform for the different thicknesses. The fluid pressures may be adjusted via the regulator during cooling to adjust a surface's cooling rate as may be desired to provide the intended metallurgical properties. The fluid sources may be contained within vessels (not shown) fluidly connected to the fluid inlets, e.g., 166,168 using a conduit (not shown) or via a manifold (not shown).
Using fluid sources that include at least one gas and at least one liquid is beneficial relative to gas-only or liquid-only cooling. Gas only provides convective cooling that limits the minimal spacing between nozzles to permit egress of the gas after contact with the part surface. With regard to liquid-only quenching systems, liquids are non-compressible and thus functions hydraulically, which limits it practicality. By use of gas-liquid atomization, more effective cooling has been realized in terms of uniformity and efficiency. In one embodiment, an air and water mixture is atomized within the atomization nozzles and sprayed onto the part to be cooled. In one embodiment, the water (or liquid) is fed to the atomization nozzles via a pump, compressed gas, or the like. To minimize pulsing flow such as may occur with the use of pumps that hydraulically deliver the liquid to the atomization nozzles, the liquid can be pressurized using a gas, i.e., gas over liquid delivery, to provide a more constant fluid flow to the atomization nozzles.
A part holder (not shown) such as a cantilevered beam, support surface, or the like can be employed in the housing 104 to support the part during cooling. The cantilevered beam or like support can be fixedly attached to the housing or may be separate therefrom. The part holder is generally configured to permit maximum impact of an atomized air-water mixture onto the heat-treated part to be cooled, the mechanics of which be discussed in greater detail below.
Optionally, a selected one or both of the plates 170, 270 (see
Optionally, the atomization nozzles can be configured to vertically oscillate during the cooling process. In this optional embodiment, the plurality of atomization nozzles can be selected to vertically oscillate or alternatively, the shrouds 150 or 200 upon which the atomization nozzles are disposed, can configured to move in a horizontal direction during the cooling process. Thus, oscillation relative to a stationary heat treated part to be cooled can be effected in the horizontal direction, the vertical direction, or both the horizontal and vertical directions as may be desired for some applications.
In operation of the exemplary cooling system 100, a heated-treated part 10 at an elevated temperature is removed from a furnace and inserted into the cooling system. One or both shroud assemblies 150, 200 are first vertically positioned to accommodate insertion of the heat-treated part and repositioned such that the upper and lower shroud assemblies 150 and 200 and arrays of atomization nozzles thereon are concentrically disposed about the heat-treated part. The heated part may be seated on a cantilevered beam (not shown) or the like. A fluid mixture of gas and liquid, e.g., air and water, is then fed to the atomization nozzles, wherein the pressures of the air and water are effective to atomize the water so as to provide fine droplets to about the surface of the heat-treated part, thereby, in the case of an air/water mixture, generating mist. The liquid component of the atomization fluid can be the primary coolant for the cooling system. The spray is continued until a desired temperature is reached, e.g., ambient temperature. In some embodiments, the temperatures of the air and/or water can vary prior to discharge from the atomization nozzles.
The period of time required to cool the forging (i.e., heat-treated part) will generally depend upon the cross-sectional area of the forging. The cooling rate may be constant throughout the cooling process or ramped by adjusting the fluid pressures to the nozzles and/or by selection of the atomization nozzles.
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
