Showing papers on "Spray forming published in 1992"

Fluid flow, heat transfer, and solidification of molten metal droplets impinging on substrates: Comparison of numerical and experimental results

Abstract: A mathematical representation has been developed, and computed results are presented describing the spreading and solidification of droplets impacting onto a solid substrate. This impingement is of major practical interest in plasma spraying and spray forming operations. Experiments in which molten metal drops were made to impinge onto a substrate were used to test the model. High-speed videography was used to record the spreading process, which typically took a few milliseconds for the experimental conditions employed. A comparison was made of the theoretical predictions with the experimental measurements; these were found to be in very good agreement, suggesting that the theoretical treatment of the model is sound. These calculations permit the prediction of the time and extent of the spreading process, the solidification rate, and the effect of process parameters, such as droplet size, droplet velocity, superheat, and material properties, provided that a value of the thermal contact coefficient is known. The most important finding of the modeling work is that for large droplets (∼5-mm diameter) with low impinging velocities (∼2 m/s), spreading and solidification appear to take place at comparable rates; in contrast, for small (∼100−µm diameter) particles impacting at a high velocity (∼100 m/s), the time scale for spreading appears to be shorter than the time scale for solidification (within the range of parameters of this study.)

Direct processing of electroslag refined metal

Abstract: A method for the electroslag refining of metal is provided The method involves providing a refining vessel to contain an electroslag refining layer floating on a layer of molten refined metal An ingot of unrefined metal is lowered into the vessel into contact with the molten electroslag layer A refining current is passed through the slag layer to the ingot to cause surface melting at the interface between the ingot and the electroslag layer As the ingot is surface melted at its point of contact with the slag, droplets of the unrefined metal are formed and these droplets pass down through the slag and are collected in a body of molten refined metal beneath the slag The refined metal is held within a cold hearth At the bottom of the cold hearth, a cold finger orifice is provided to permit the withdrawal of refined metal from the cold hearth apparatus The refined metal passes from the cold finger orifice as a stream and is processed into a sound metal structure having desired grain structure A preferred method for forming such a structure is by spray forming

Thermal spray shape deposition

Abstract: This paper describes a new spray-forming process based on thermal spray shape deposition. Shape deposition processes build three-dimensional shapes by incremental material buildup of thin, planar crosssectional layers. These processes do not require preformed mandrels and can directly build three-dimensional structures of arbitrary geometric complexity. The basis for the thermal spray approach is to spray each layer using a disposable mask that has the shape of the current cross section. Masks can be produced from paper rolls, for example, with a CO2 laser. In addition to applications for rapid prototyping, this approach makes possible the fabrication of composite structures and integrated electronic/mechanical assemblies that are not feasible with conventional manufacturing technologies.

Metal spray forming using multiple nozzles

Abstract: Metal is spray cast onto a moving substrate using at least two sprays, the first of which has a solid fraction greater than 20% at the time the spray contacts the substrate, but less than the solid fraction of the second spray.

Spray forming: Science and technology

Abstract: Spray forming involves sequential gas atomization of a melt into a spray of fine droplets and their deposition on a substrate to build up a high-density preform. The rapid solidification inherent in spray deposition generates refined, equiaxed and low segregation microstructures. A number of promising features of this near-net shape manufacturing process are highlighted and compared, wherever possible, with the conventional casting and PM techniques. Some commercial nozzles used to create spray and mechanisms associated with spray generation are described. The consolidation of the droplets and the development of the microstructure in the deposit are primarily governed by the nature of the spray and the thermal state of droplets on the deposition surface. Several microstructural characteristics of the deposit are presented and their origin in spray deposition is discussed.

Thermal spray coatings : properties, processes, and applications : proceedings of the Fourth National Thermal Spray Conference, 4-10 May 1991, Pittsburgh, Pennsylvania, USA

Abstract: The proceedings of the Fourth National Thermal Spray Conference, held in Pittsburgh, Pa., May 1991, comprise major sections including processing science, spray forming and composites, coating characterization and evaluation, wear and erosion, surface treatment, ceramics and intermetallics, feedstock

Method and apparatus for producing strip products by a spray forming technique.

Abstract: Apparatus for producing strip comprises atomising means for producing a spray of metallic particles or droplets at elevated temperatures, a hollow receptor roll positioned below the atomising means on which the metallic particles or droplets are received and heating means positioned within the interior of the receptor roll. The apparatus is operable to vary in a controlled manner the temperature of the external surface of the receptor roll on which the metallic particles or droplets are deposited.

Spray forming method

Abstract: PURPOSE:To precisely measure the height of the pre-formings and to calculate the piling yield at the same time by calculating the piling height of the pre- formings based on the measured value of the piled weight on the base plate with the load cell arranged at the downside of the base plate. CONSTITUTION:At first, the density of the molten metal 2 is measured before executing with spray forming. The weight of the pre-formed body 9 is measured with the load cell 12 following to the beginning of the stream down of the molten metal 2. The data from the load cell 12 is inputted in the computer, the height of the pre-formed body is calculated with the density of the molten metal 2, the weight of the pre-formed body, and the area of the base plate. If the data of the weight of molten metal obtained from the load cell 11 is checked, the piling yield can also be calculated.

The cutting performance of high-speed steel end mill produced by spray forming process

Abstract: A spray forming technique, which can produce semi-finished products with high density and rapid solidification structure in a single operation, has been developed recently. This method is called the Osprey process. This process can control size and distribution of carbides and takes lower production cost than powder metallurgy (P/M) process owing to a single operation. In this paper the cutting performance of high-speed steel (HSS) end mill produced by Osprey process was investigated by comparison with conventional ingot metallurgy (I/M) and P/M ones. This Osprey HSS end mill exhibited superior wear resistance to I/M and P/M ones in milling tool steel (SKD 11), but some chippings and fracture appeared at the end cutting edge in milling stainless steel (SUS 304) in small feed rate.

Toughness enhancement of al-li-cu-mg-zr alloys produced using the spray forming process

Abstract: An Al-Li alloy consists essentially of the formula Al bal Li a Cu b Mg c Zr d wherein "a" ranges from about 1.9 to 3.4 wt %, "b" ranges from about 0.5 to 2.0 wt %, "c" ranges from 0.2 to 2.0 wt % and "d" ranges from about 0.3 to 1.2 wt %, the balance being aluminum. The alloy is solidified at a cooling rate of about 10 3 °-10 4 ° C./sec by spray forming, and is characterized by a substantial absence of prior particle boundaries.

Recent INEL spray-forming developments

Abstract: Spray forming is a near-net-shape fabrication technology in which a spray of finely atomized liquid droplets is deposited onto a suitably shaped substrate or mold to produce a coherent solid. The technology offers unique opportunities for simplifying materials processing, oftentimes while substantially improving product quality. Spray forming can be performed with a wide range of metals and nonmetals, and offersproperty improvements resulting from rapid solidification (eg. refined microstructures, extended solid solubilities and reduced segregation). Economic benefits result from process simplification and the elimination of unit operations. Researchers at the Idaho National Engineering Laboratory (INEL) are developing spray-forming technology for producing near-net-shape solids and coatings of a variety of metals, polymers, and composite materials using de Laval nozzles. Results from several spray-forming programs are presented to illustrate the range of capabilities of the approach as well as the technical and economic benefits. These programs involved the production of low-carbon steel strip and SiC particulate reinforced aluminum strip; recent advances in spray forming tooling using low-melting-point metals are also described.

Nozzle, vessel and spray forming.

Abstract: An improved nozzle which allows molten metals to be sprayed at low metal flow rates. This is useful for the Plasma Arc Melting process which used a hearth to prevent ceramic inclusions in the end product. The new nozzle design avoids metal freeze-off at the nozzle tip because a bore insert is positioned into a standard nozzle. The bore insert is a conduction heater, e.g., it is fabricated from boron nitride or the like. In use, molten metal is in contact with the insert so it maintains the insert at about the temperature of the molten metal; this then maintains the nozzle tip at a higher temperature than that of a standard nozzle. Freeze-off in the nozzle is non-occurring as long a molten metal is in the crucible.

Improvements to the continuous spray forming of metal strip

Abstract: Continuous lengths of metallic strip are produced by a method in which a free falling stream of molten metallic material is atomised by a plurality of gaseous jets pre-heated to a temperature within the range 400 DEG C to 1200 DEG C to form a spray 6 of molten metal particles which collect on the surface of an internally heated hollow receptor roll 10 and are peeled from the receptor roll in the form of a continuous strip The receptor roll may be coated with a dried layer of colloidal silica after shot blasting