Fluid sprinkling – spraying – and diffusing – Combining of separately supplied fluids – Serially arranged mixing zones
Reexamination Certificate
2000-05-23
2001-09-04
Scherbel, David A. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Combining of separately supplied fluids
Serially arranged mixing zones
C239S434500, C239S079000, C417S197000, C118S308000
Reexamination Certificate
active
06283386
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to kinetic spray coating wherein metal and other powders entrained in an air flow are accelerated at relatively low temperatures below their melting points and coated onto a substrate by impact.
BACKGROUND OF THE INVENTION
The art of kinetic spray coating, or cold gas dynamic spray coating, is discussed at length in an article by T. H. Van Steenkiste et al., entitled “Kinetic Spray Coatings”, published in Surface and Coatings Technology, Vol. 111, pages 62-71, on Jan. 10, 1999. Extensive background and reference to prior patents and publications is given as well as the current state of the art in this field as summarized by the thirteen listed authors of the referenced article.
The work reported on was conducted with an apparatus developed for the National Center for Manufacturing Services (NCMS) which improved upon the prior work and apparatus reported in U.S. Pat. No. 5,302,414 Alkhimov et al., issued Apr. 12, 1994. These sources have reported the kinetic spray coating of metals and other materials by gas accelerated impact on certain substrates with varying degrees of success using a high pressure kinetic spray system with a kinetic spray nozzle based upon concepts taught by Alkhimov et al. and other sources.
The method involves feeding metallic or other material types in the form of small particles or powder into a high pressure gas flow stream, preferably air, which is then passed through a de Laval type nozzle for acceleration of the gas stream to supersonic flow velocities greater than 1000 m/s and coated on the substrate by impingement on its surface. While useful coatings have been made by the methods and apparatus described in the referenced article and in the prior art, the successful application of these methods has been limited to the use of very small particles in a range of from about 1 to 50 microns in size. The production and handling of such small particles requires special equipment for maintaining the smaller powder sizes in enclosed areas and out of the surrounding atmosphere in which workers or other individuals may be located.
Accordingly, the ability to utilize a kinetic spray coating process for coating metal and other particles larger than 50 microns would provide significant benefits.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus by which particles of metals, alloys, polymers and mechanical mixtures of the foregoing and with ceramics and semiconductors, having particle sizes in excess of 50 microns, may be applied to substrates using a kinetic spray coating method.
The present invention utilizes a modification of the kinetic spray nozzle of the NCMS system described in the Van Steenkiste et al. article. This system provides a high pressure air flow that is heated up to as much as 650° C. in order to accelerate the gas in the de Laval nozzle to a high velocity in the range of 1000 m/s or more. The velocity is as required to accelerate entrained particles sufficiently for impact coating of the particles against the substrate. The temperatures used with the various materials are below that necessary to cause their melting or thermal softening so that a change in their metallurgical characteristics is not involved.
In the NCMS apparatus, particles are delivered to the main gas stream in a mixing chamber by means of an unheated high pressure air flow fed through a powder feeder injection tube, preferably aligned on the axis of the de Laval nozzle. In a prior apparatus, the diameter of the injection tube in the similar spray nozzle of Alkhimov et al. had a ratio of the main air passage cross-sectional area to powder feeder injection tube cross-sectional area of 5-15/1. The kinetic spray nozzle of the NCMS apparatus, with its higher air pressure system, had a ratio of main air passage diameter to powder feeder injection tube diameter of 4/1 and a comparable ratio of main air passage cross-sectional area to powder feeder injection tube cross-sectional area of 17/1. In both of these cases, the apparatuses were found to be incapable of applying coatings of particles having a particle size in excess of 50 microns.
The present invention has succeeded in increasing the size of particles which can be successfully applied by a kinetic spray process to particles in excess of 100 microns. This has been accomplished by decreasing the diameter of the powder feeder injection tube from 2.45 mm, as used in the spray nozzle of the NCMS apparatus reported in the Van Steenkiste et al. article, to a diameter of 0.89 mm. It has also been found that the deposit efficiency of the larger particles above 50 microns is substantially greater than that of the smaller particles below 50 microns.
While the reasons for the improved operation are not entirely clear, it is theorized that reduced air flow through the powder injection tube results in less reduction of the temperature of the main gas flow through the de Laval nozzle with the result that the larger sized particles are accelerated to a higher velocity adequate for their coating by impact against a substrate, whereas the prior apparatus were incapable of accelerating larger particles to the required velocity. It should be noted that the air flow and particle velocities upon discharge from the nozzle vary roughly as the square root of the gas temperature. Also, the fine particles have been found to be more sensitive to stray gas flow patterns which can deflect the particles, particularly near the substrate, lowering the deposition efficiency. Finally, the fine particles have a high surface to volume ratio which can lead to more oxide in the powder and, therefore, in the coating.
In a further development, a still smaller powder feeder injection tube of 0.508 mm diameter was tested and found also capable of coating large particles between 45 and 106 microns. But, it was also found to be difficult to maintain a uniform feed of large particles through a tube of such small diameter.
As a result of this invention, it is now recognized that the kinetic spray coating of metals and other substances using air entrained particles greater than 50 microns and up to in excess of 100 microns may now be accomplished by proper selection of the characteristics and flow capabilities of the kinetic spray nozzle and accompanying system. It is expected that with further development and testing of the apparatus and method, the size of particles that may be utilized in coating powders may be further increased.
These and other features and advantages of the invention will be more fully understood from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings.
REFERENCES:
patent: 2861900 (1958-11-01), Smith et al.
patent: 3100724 (1963-08-01), Rocheville
patent: 4416421 (1983-11-01), Browning
patent: 5302414 (1994-04-01), Alkhimov et al.
patent: 5356672 (1994-10-01), Schmitt, III et al.
patent: 5459811 (1995-10-01), Glovan et al.
patent: 5795626 (1998-08-01), Gabel et al.
patent: 5876267 (1999-03-01), Kanda
Surface & Coatings Technology 111 (1999) 62-71, entitled “Kinetic Spray Coatings” by T. H. Van Steenkiste et al.
Gorkiewicz Daniel W.
Moleski Jerome J.
Smith John R.
Teets Richard E.
Van Steenkiste Thomas H.
Fildes & Outland, P.C.
National Center for Manufacturing Sciences
Nguyen Dinh Q.
Scherbel David A.
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