Technical Review & Discussion
The Use of The Weibull Statistical Method To Assess The Reliability of a Development Engineered Casting Component R. MacKay, Nemak of Canada Corporation, Windsor, Ontario, Canada D. Szablewski, Transportation Technology Center, Inc., Pueblo, CO, USA
Reviewer: The authors’ state that “the vacuum level is tar- get at -27 + 2”. A vacuum level of -27 + 2 (-25 to -27) is a large range (+ 7.5%) that affects the specific gravities and the indicated hydrogen levels can lead to difficulty correlat- ing specific gravity of RPT test samples to a specific hydro- gen content.
Authors: The revised paper includes details on the corre- lation between hydrogen concentrations and the use of the Reduced Pressure Test. There certainly was no intent to ar- gue that both methods of gauging hydrogen were completely direct. The authors are quite aware that oxide concentra- tions can reduce densities and that the vacuum used (with +/- 2 in Hg) could produce a variation, but this variation from our experience would produce only a 0.01 grams/ cc change in density and thus why our standard practice
was to use this variation. With our traditional melt han- dling practices we know that we have been able to pro- duce high quality cast structure and are confident that el- evated oxide concentrations are not primarily responsible for the density measured, but the level of dissolved hydro- gen and thus why the correlation made in the manuscript.
Reviewer: The authors argue that elongations do not exceed 8%. Perhaps data books reporting “typical” values of typi- cal chemistries and typical solidification conditions seldom show elongations above 8%, but there are many reports and papers showing minimum elongations exceeding 12% and in some cases typically 15%. Authors should state that this applies to Al-Si alloys and define which casting process (all or just sand?)
Authors: The text at the beginning of the introduction has been re-written to specify Al-Si-Cu sand castings. The text sighted [1,2] shows the typical ranges that can be attained and wish not to get into repeated discussions of processes outside the scope of the present work. Also, as an expert in Al-Si-Cu sand castings the ranges we encounter don’t come close to 8% for plastic elongation, more like 4%. I doubt that this is the critical aspect of this manuscript, and references for Al-Si-Mg alloys may skew the intent desired for the Introduction.
International Journal of Metalcasting/Winter 10
45
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