Expandable coating cocoon leak detection system

Development of system and materials for detecting leaks in cocoon protective coatings are discussed. Method of applying materials for leak determination is presented. Pressurization of system following application of materials will cause formation of bubble if leak exists

Trends in Black-White Test-Score Differentials

Until the 1970s, there were few signs of change in the historic difference of one standard deviation between average ability or achievement test scores of blacks and whites in the United States. From about 1970 to the mid- to late 1980s, there was a substantial convergence of the average achievement test scores of black and white youth; however, from the mid- to late 1980s to 1992, test scores began to diverge again. Although we place the greatest weight on data from the National Assessment of Educational Progress (NAEP), the convergence also appeared in other test series. Herrnstein and Murray's highly visible work, The Bell Curve, stands almost alone in minimizing the importance of the convergent trend. We also find a longer-term trend of convergence between the verbal abilities of blacks and whites in data from the General Social Survey (GSS), which covers adult cohorts born since 1909.

Image Transformations and Printing of Plaster Layers in Spiral Growth Manufacturing

Spiral growth manufacturing (SGM) is a high speed rapid manufacturing technique in which objects are built up, layer by layer, by simultaneously depositing, levelling and selectively consolidating thin powder layers onto a rotating build platform. The size and position of the jetted droplets are mapped by the position and greyscale level of pixels within an 8 bit greyscale bitmap image. This paper reports on the development of software in which mathematical algorithms apply geometric transformations to images in preparation for printing onto a rotating substrate. In support of this work, dimensional accuracy measurements of printed images and methods to correct radial print density variations are reported. The accuracy of printed images were found to be within ±0.2mm of their predicted size. The experimental work is briefly extended to the direct printing of plaster layers, formed by mixing two reactive ink solutions.Mechanical Engineerin

Further Developments in Process Mapping and Modelling in Direct Metal Selective Laser Melting

This paper advances previous reported work on the mapping and modelling of single tracks and layers produced in powder beds of tool steel and stainless steel powders by a CO2 laser. For single tracks it reports on predicted and simulated track masses. It validates the simulations, including the use of absorption close to 1.0 when cylindrical tracks are formed. It also reports on melt pool temperature calculations and estimated melt pool dimensions which are used, in conjunction with bed physical properties, to explain why the single tracks form as either continuous with a crescent shape cross-section, continuous with an elliptical section, discontinuously irregularly broken, discontinuously balled or only partially melted as scan speeds and laser powers change. It then extends its scope, experimentally, to consider effects of scan spacing on single layer formation.Mechanical Engineerin

Spiral Growth Manufacturing (SGM) – A Continuous Additive Manufacturing Technology for Processing Metal Powder by Selective Laser Melting

Spiral growth manufacturing is a new innovative powder based rapid manufacturing technique. The innovation exists in the methodology in which powder layers are deposited. Unlike other pre-placed powder systems, the deposited layers move relative to the location at which they are processed. This is made possible by a rotating build drum into which powder is deposited, in spiralled layers, from a stationary hopper. With this configuration powder can be continuously deposited and levelled and simultaneously processed, eliminating delays in the build cycle. Stainless steel and cobalt-chrome powder is selectively melted using a 100W flash lamp pumped Nd:YAG laser. This paper reports on factors affecting build rate and on build strategies for creating a number of axis-symmetric thin and thick walled cylinders. Experimental results suggest that build rate for thin walled structures bonded to a substrate will ultimately be governed by tangential movements of the powder particles when frictional forces are not sufficient to accelerate the particles along a curved path, provided that enough laser power is available for melting. Even melt pool balling, which is evident when melting one layer at high speeds, diminishes in multiple layer builds due to re-melting and infilling.Mechanical Engineerin