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Craters produced by single electrical discharges in kerosene under conditions similar to Electro-Discharge Machining were formed on the following metals: Al, Cr, Cu, Fe, Mg, Mo, Nb, Ni, Ta, Ti, V, W, and Zn. Anode and cathode crater volumes were measured by a profilometer imaging technique and except for Nb, Mo and Ta, the cathode craters were always found to be larger. An empirical equation was developed to relate the volume of the electro-erosion craters formed to the physical properties of the electrodes. Crater morphology and surface texture were studied using both Scanning and Transmission Electron Microscopy. An Electron Microprobe was used to determine the distribution of cross deposited metal in the case of dissimilar electrodes. Crater volumes and morphologies resulting from single electrical discharges in liquid and dry nitrogen were shown to be radically different from those produced in kerosene. [ABSTRACT FROM AUTHOR]

A refractory protective coat has been developed that greatly reduces scale formation and is capable of lowering sandblasted casting roughness 30 to 50%. When applied as a thin film to the refractory model, it remains as a tacky base which will fix wax and plastic. [ABSTRACT FROM AUTHOR]

Roughness criteria are usually given for the surfaces of structures to prevent premature structural failure, added drag, and added flow noise. Structural roughness criteria usually deal only with long-wavelength roughness, or waviness, which is specified in terms of clearance under a batten of a particular length. Drag-roughness criteria usually deal only with the short-wavelength roughness as measured by a profilometer. Flow-noise roughness criteria, however, must include both the long- and short-wavelength components of the roughness and, in the case of water, separate criteria are needed for boundary-layer turbulence and cavitation-induced noise. A more unified description of roughness and roughness criteria is given in terms of its wavelength spectrum. Hydraulically smooth surfaces are believed to have no roughness related component of drag or turbulence induced flow noise. In water, the surface is considered to be hydraulically smooth if the roughness height in inches is less than about 0.01 divided by the free-stream velocity in knots. The expected increase in turbulence induced flow noise in water as a function of roughness and flow speed are then determined from available data on local skin friction. [ABSTRACT FROM AUTHOR]