APPARATUS FOR DELIVERING A CONSISTENT, CONTINUOUS FLOW OF POWDER

Abstract: The present invention concerns an apparatus for delivering a consistent, continuous flow of powder which comprises an enclosed powder reservoir (40), volumetric powder feed means (50) to move powder from the reservoir into a powder conduit (54), a conduit vibrating means (52) to vibrate the powder conduit and the powder therein, means (44) to introduce a gas under pressure through the reservoir to pressurize the reservoir and a fluid-cooled powder delivery nozzle (56) connected with the powder conduit to receive powder from the conduit for delivery from the nozzle. The apparatus is useful in process for repairing parts of gas turbine engines.

Description: This invention relates to an apparatus for delivering a consistent, continuous flow of powder, for use in a repair welding process. Modern gas turbine engines, particularly of the type designed primarily for aircraft applications, include components which are expensive to manufacture because of their complex design and materials of construction. During normal operation of such apparatus, some components can experience events such as normal wear or thermal damage. In addition, mishaps such as machining errors or other inadvertent damage can occur during initial manufacture. For example, such events or damage can occur in connection with compressor or turbine spools or disks. It has been found that, in respect to localized repair of a portion of an article rather than replacement of the portion, ordinary known means of repair such as electron beam welding and gas tungsten arc welding can adversely affect properties of the material of construction because of relatively high heat input which results in distortion and a relatively deep heat affected zone. Such an excessive heat distribution has been found to cause component cracking which is particularly critical in rotating components such as wheels, drums, and spools of gas turbine engines. US-A-4 323 756 describes a method for the production of bulk rapidly solidified articles of near-net shape, by depositing multiple thin layers of feedstock using an energy beam to fuse each layer onto a substrate. The feedstock may be in the form of metal powder or wire. One method for repairing an article having an article portion of a metallic material is described in EP-A-0 176 942 and includes the steps of concurrently applying to the article portion a metal powder, alone or in combination with another powder such as an abrasive, and a laser beam. The metal powder is of a composition substantially the same as that of the metallic material of the article portion and preferably is applied at a rate in the range of about 2-15 grams per minute. The laser is applied, in a laser beam spot, to the powder and the article portion beneath the powder within a powder density range of 10⁴ to 10⁶ watts per square centimeter to melt both the metal powder and material of the article portion to generate a molten interaction zone from the metal powder and the metallic material of the article portion. In order to further control the resultant heat affected zone, an interaction time is maintained in the range of 0.005-2 seconds between the laser beam spot and the powder along with the article portion beneath the powder, for example by relative lateral movement, to enable progressive movement, cooling and solidification of the molten interaction zone. This controls and reduces the extent of the heat affected zone in the article portion and provides a repair layer on the article portion consolidated from the applied powder and metallic material of the portion. Other forms of the method contemplate repeating such steps, if desired, to provide a plurality of superimposed, bonded-together repair layers using the preceding repair layer as the "article portion" for the concurrent application of metal powder and laser beam. In order to enable practice of the repair method the metal repair powder must be provided in a consistent continuous powder flow. Therefore it is a principal object of the present invention to provide an apparatus providing a consistent continuous powder flow. One form of the apparatus of the present invention comprises a unique combination of components including an enclosed, preferably heated powder reservoir, means to introduce inert gas under pressure into the reservoir, a mechanical volumetric powder feed means, a powder vibrator, and a fluid-cooled delivery nozzle. Together, such components deliver a consistent, continuous flow of powder. FIGURE 1 is a diagrammatic, partially sectional view of the apparatus of the present invention. The apparatus of the present invention is shown in the diagrammatic sectional view of Figure 1. The apparatus includes an enclosed powder reservoir shown generally at 40, heated by heating coils 42 for the purpose of controlling the moisture content at a low level in the powder. Also included is a gas inlet port 44 through which a preferably dry inert gas such as argon, represented by arrow 46, is introduced to maintain powder 48 in reservoir 40 under pressure and to assist in powder transport. Associated with the powder reservoir is a mechanical, volumetric powder feed mechanism such as powder feed wheel 50 of a type commercially available. For example, the type used in one form of the apparatus of the present invention was a modified Metco powder feed "L" type wheel. Downstream of wheel 50 is a vibrator such as air actuated vibrator 52 associated with conduit 54 to inhibit powder particles moving in conduit 54 from adhering one to the other or to walls of the conduit 54. Conduit 54 terminates in a water-cooled powder delivery nozzle 56 which directs the powder, assisted by the pressurized inert gas, in a consistent flow, such as toward an article or workpiece surface. It has been found that reflection from the laser beam can result in clogging of powder passing through nozzle 56. Therefore, such a nozzle, preferably having at least a tip portion made of a material, such as copper or aluminum, which is highly reflective to the wave length of the laser used, is fluid cooled, such as by water, to avoid such problem and to assist in a consistent flow of powder. Such consistent flow of powder results from the combination of use of powder maintained in a low moisture condition, under a positive inert gas pressure, being fed by a mechanical, volumetric powder feed mechanism along with a powder vibrator, and a cooled nozzle through which the powder passes toward the article surface. The apparatus of the present invention has been used for practicing the repair method of EP-A-0 176 942. Associated with the apparatus of the present invention is a laser 58 emitting a beam 60 having a beam axis 62. Beam 60 has a focal plane 64 beneath article portion or workpiece surface 66 to provide at the surface a beam spot 68 of a size in the range of 0.127 mm-5.08 mm (0.005-0.2 inches), and preferably in the range of 1.27-3.81 mm (0.05-0.15 inches). The laser beam is applied in the powder density range of 10⁴ to 10⁶ watts per square centimeter while controlling the interaction time between the beam spot and the powder and article portion beneath the powder in the range of 0.005-2 seconds. Such control is obtained by relative lateral motion shown by arrow 70, for example from a table moving the article in the direction shown at a rate to provide the desired interaction time. The powder is fed from nozzle 56 at an angle in the range of about 35-60 degrees from the article surface and preferably in the range of about 40-55 degrees. Greater than about 60 degrees makes it difficult from the nozzle and powder to avoid premature interaction with the laser beam, and less than about 35 degrees makes it difficult to deliver the powder concurrently with the laser beam at the spot desired on the aricle surface. As the powder and laser beam are applied concurrently to the article surface, a molten interaction zone is generated in the area of the beam spot. As relative lateral movement is provided between the laser beam spot and the article carrying its superimposed powder, progressive movement, cooling and solidification of the molten interaction zone occurs. This provides consolidated repair layer 72 as shown in Figure 1. After application and consolidation, excess of the repair layer material added can be shaped to a desired configuration, such as by machining, grinding, dressing of abrasive particles, etc. In this way, there is provided a repaired article having a minimized heat affected zone and desired mechanical properties.

Claims: 1. Apparatus for delivering a consistent, continuous flow of powder, for use in repair welding the apparatus including an enclosed powder reservoir (40), volumetric powder feed means (50) to move powder from the reservoir (40) into a powder conduit (54), and a conduit vibrating means (52) to vibrate the powder conduit and the powder therein; characterized in that it further comprises: means (44) to introduce a gas under pressure through the reservoir to pressurize the reservoir (40); and a fluid-cooled powder delivery nozzle (56) connected with the powder conduit (54) to receive powder from the conduit for delivery from the nozzle. 2. The apparatus of claim 1 in which the reservoir (40) is heated to maintain low moisture in powder within the reservoir. 3. The apparatus of claim 1 in which the powder delivery nozzle (56) includes at least a tip portion made of copper or aluminum.

Inventors: COOPER, ERNEST BROWN, JR., MEHTA, PAUL PANKAJ, OTTEN, ROBERT RICHARD
Applicants: GENERAL ELECTRIC COMPANY
Application year: 1985
Main classification: B05B7
IPC codes: B23P6, B05B7, C23C26, B23K26, F01D5, C23C24