Engineering topics

Mckechnie, Timothy N.

Publications and source records attributed to Mckechnie, Timothy N..

14 records

NASA NTRS1995

Wire-Arc-Sprayed Aluminum Protects Steel Against Corrosion

Aluminum coatings wire-arc sprayed onto steel substrates found effective in protecting substrates against corrosion. Coatings also satisfy stringent requirements for adhesion and flexibility, both at room temperature and at temperatures as low as liquid hydrogen. Developed as alternatives to corrosion-inhibiting primers and paints required by law to be phased out because they contain and emit such toxic substances as chromium and volatile organic compounds.

Zimmerman, Frank R.↗

NASA NTRS1995

Removable Mandrels For Vacuum-Plasma-Spray Forming

Improved mandrels developed for use in vacuum-plasma-spray (VPS) forming of refractory metal and ceramic furnace cartridge tubes. Designed so after tubes formed on them by VPS, mandrels shrink away from tubes upon cooling back to room temperature and simply slip out of tube.

Krotz, Phillip D.↗

NASA NTRS1995

Wire-Arc Spraying Of Metal Onto Insulating Foam

Wire-arc spraying used to deposit protective metallic coats on thermally insulating foams. Process relatively fast and cheap, and does not damage foam or involve toxic and polluting chemicals.

Bonds, James W., Jr.↗

NASA NTRS1994

Rugged Preheaters For Vacuum Plasma Spraying

Electric preheater units built to ensure large workpieces to be coated with metals by vacuum plasma spraying heated uniformly to requisite high temperatures by time plasma torch arrives. Units similar to electrical-resistance ribbon heaters in toasters and in some small portable electric "space" heaters. Nichrome resistance-heating ribbons wrapped around ceramic insulating spools on rings and on plates. Round workpiece placed in middle of ring preheater. Plate preheaters stacked as needed near workpiece.

Woodford, William H.↗

NASA NTRS1993

Vacuum Plasma Spraying Of Copper Onto Titanium

Vacuum plasma spraying successful in depositing tenacious copper coat on flanges and other selected areas of titanium valve housing. Oxidation and concomitant brittleness eliminated.

Power, Chris↗

NASA NTRS1993

Method of fabricating a rocket engine combustion chamber

A process for making a combustion chamber for a rocket engine wherein a copper alloy in particle form is injected into a stream of heated carrier gas in plasma form which is then projected onto the inner surface of a hollow metal jacket having the configuration of a rocket engine combustion chamber is described. The particles are in the plasma stream for a sufficient length of time to heat the particles to a temperature such that the particles will flatten and adhere to previously deposited particles but will not spatter or vaporize. After a layer is formed, cooling channels are cut in the layer, then the channels are filled with a temporary filler and another layer of particles is deposited.

Holmes, Richard R.↗

NASA NTRS1993

Feeder For Oxygen-Sensitive Powders

Powder feeder for oxygen-sensitive powders facilitates transfer of powder while protecting it against oxidation. Sight gauge enables continuous monitoring of level to which feeder filled with powder, as well as for visual monitoring of quality powder. Coupling mates with specially designed containers, in which powders packaged under vacuum or inert gas. Eliminating need for unncessary handling of powders and attendant risk of contamination by oxygen. Internal funnel unloads unused powder from feeder in vacuum or inert-gas atmosphere. Pressure gauge monitors pressure of inert backfill gas.

Woodford, William H.↗

NASA NTRS1993

Alignment Fixtures For Vacuum-Plasma-Spray Gun

Fixtures for alignment of vacuum-plasma-spray guns built. Each fixture designed to fit specific gun and holds small, battery-powered laser on centerline of gun. Laser beam projects small red dot where centerline intersects surface of workpiece to be sprayed. After laser beam positioned on surface of workpiece, fixture removed from gun and spraying proceeds.

Woodford, William H.↗

NASA NTRS1992

Container Prevents Oxidation Of Metal Powder

Sealed high-vacuum container holds metal powder required free of contamination by oxygen from point of manufacture to point of use at vacuum-plasma-spraying machine. Container protects powder from air during filling, storage, and loading of spraying machine. Eliminates unnecessary handling and transfer of powder from one container to another. Stainless-steel container sits on powder feeder of vacuum-plasma-spraying machine.

Woodford, William H.↗

NASA NTRS1992

Vacuum Plasma Spraying Replaces Electrodeposition

Vacuum plasma spraying used to fabricate large parts with complicated contours and inner structures, without uninspectable welds. Reduces time, and expense of fabrication. Wall of combustion chamber built up inside of outer nickel-alloy jacket by plasma spraying. Particles of metal sprayed partially melted in plasma gun and thrown at supersonic speed toward deposition surface. Vacuum plasma-spray produces stronger bond between the grooves and covering layer completing channels and wall of combustion chamber. In tests, bond withstood pressure of 20 kpsi, three times allowable limit by old method.

Holmes, Richard R.↗

NASA NTRS1991

Salt Filler For Making Covered Channels

In simple fabrication technique, metal salts used to create such subsurface channels as those for coolant in metallic heat exchanger. Layer of metal deposited on structure by vacuum plasma spraying, sealing channels. Metal salt or salt mixture has melting temperature higher than those of waxes and aluminum and withstands high temperature of plasma spraying. After plasma spraying, salt filler dissolved quickly and easily and flushed away with water or other appropriate solvent, leaving behind covered channels.

Mckechnie, Timothy N.↗

NASA NTRS1991

Multipiece Mandrel For Spray-Forming Complex Parts

With help of multipiece mandrel, parts of complicated shapes fabricated by spray forming. Spray-forming process faster and less costly than machining. Consists of etch-resistant end cones and etchable washer between them. Etchable layer applied over mandrel and under spray-formed part helps to ensure easy removal of mandrel. Shape, size, and number of segments in mandrel readily adapted to spray forming of other complicated parts. Process eliminates need for difficult internal and external machining. Segmented mandrel reusable.

Mckechnie, Timothy N.↗

NASA NTRS1989

Vacuum plasma spray coating

Currently, protective plasma spray coatings are applied to space shuttle main engine turbine blades of high-performance nickel alloys by an air plasma spray process. Originally, a ceramic coating of yttria-stabilized zirconia (ZrO2.12Y2O3) was applied for thermal protection, but was removed because of severe spalling. In vacuum plasma spray coating, plasma coatings of nickel-chromium-aluminum-yttrium (NiCrAlY) are applied in a reduced atmosphere of argon/helium. These enhanced coatings showed no spalling after 40 MSFC burner rig thermal shock cycles between 927 C (1700 F) and -253 C (-423 F), while current coatings spalled during 5 to 25 test cycles. Subsequently, a process was developed for applying a durable thermal barrier coating of ZrO2.8Y2O3 to the turbine blades of first-stage high-pressure fuel turbopumps utilizing the enhanced NiCrAlY bond-coating process. NiCrAlY bond coating is applied first, with ZrO2.8Y2O3 added sequentially in increasing amounts until a thermal barrier coating is obtained. The enchanced thermal barrier coating has successfully passed 40 burner rig thermal shock cycles.

Holmes, Richard R.↗

NASA NTRS1988

Sectioning Coated Specimens Without Edge Rounding

New method devised for preparation of cross sections of coated specimens for scanning electron microscopy or energy-dispersive analysis without rounding edges of coatings. After cutting and polishing, specimen section remains smooth and flat so it can be examined under high magnification out to edge of coating. Sectioned blade first electroplated with hard nickel 0.003 in., then encapsulated in two layers of material: soft conductive material at bottom and 0.25 in. of hard diallyl phthalate at top. Nickel plate provides electrical path from surface of section to conductive material below.

Mckechnie, Timothy N.↗