共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
通过现场实际分析偶合器产生故障的原因,来寻求解决问题的方法,防止或减少此类现象的发生,保证今后偶合器正常运转. 相似文献
16.
17.
Primary spacing in directional solidification 总被引:1,自引:0,他引:1
A new analytical model is developed to explain the variation in primary spacing λ with growth velocity V. In this model, dendrite growth is resolved into two parts: the growth of the center core and that of the side arms, which
are separately treated. In contrast to the assumption in the current models, it is only the dendrite core, not the entire
dendrite, whose curvature radius at the tip is directly related to dendrite tip radius R. The primary spacing is considered to be the sum of core diameter and twice the sidearm length. As long as the growth of
side arms is suppressed, it becomes cellular growth. As a result, this model gives a reasonable dependence of cell and dendrite
spacing on the process parameters. The proposed model has been applied to several alloys to compare its predictions both with
experimental data and with the analytical expression of the Hunt-Lu model. 相似文献
18.
Henry C. de Groh 《Metallurgical and Materials Transactions A》1994,25(11):2507-2516
The accepted primary mechanism for causing macrosegregation in directional solidification (DS) is thermal and solutal convection
in the liquid. This article demonstrates the effects of under-cooling and nucleation on macrosegregation and shows that undercooling,
in some cases, can be the cause of end-to-end macrosegregation. Alloy ingots of Pb-Sn were directionally solidified upward
and downward, with and without undercooling. A thermal gradient of about 5.1 K/cm and a cooling rate of 7.7 K/h were used.
Crucibles of borosilicate glass, stainless steel with Cu bottoms, and fused silica were used. High undercoolings were achieved
in the glass crucibles, and very low undercoolings were achieved in the steel/Cu crucible. During under-cooling, large, coarse
Pb dendrites were found to be present. Large amounts of macrosegregation developed in the undercooled eutectic and hypoeutectic
alloys. This segre-gation was found to be due to the nucleation and growth of primary Pb-rich dendrites, continued coarsening
of Pb dendrites during undercooling of the interdendritic liquid, Sn enrichment of the liquid, and dendritic fragmentation
and settling during and after recalescence. Eutectic ingots that solidified with no undercooling had no macrosegregation,
because both Pb and Sn phases were effectively nucleated at the start of solidification, thus initiating the growth of solid
of eutectic composition. It is thus shown that undercooling and single-phase nucleation can cause significant macrosegregation
by increasing the amount of solute rejected into the liquid and by the movement of unattached dendrites and dendrite fragments,
and that macrosegregation in excess of what would be expected due to diffusion transport is not necessarily caused by convection
in the liquid. 相似文献
19.
WJ Rappel 《Canadian Metallurgical Quarterly》1993,48(5):4118-4120
20.
A new analytical model is developed to explain the variation in primary spacing λ with growth velocity V. In this model, dendrite growth is resolved into two parts: the growth of the center core and that of the side arms, which
are separately treated. In contrast to the assumption in the current models, it is only the dendrite core, not the entire
dendrite, whose curvature radius at the tip is directly related to dendrite tip radius R. The primary spacing is considered to be the sum of core diameter and twice the sidearm length. As long as the growth of
side arms is suppressed, it becomes cellular growth. As a result, this model gives a reasonable dependence of cell and dendrite
spacing on the process parameters. The proposed model has been applied to several alloys to compare its predictions both with
experimental data and with the analytical expression of the Hunt-Lu model. 相似文献