Collaborative Research : Manipulating the Contact and Solidification of Molten Metal in Continuous Casting
A technology to enable continuous casting of molten metals, in a single step, to the specifications of the designer is being developed[7]. For example, casting aluminum foil in a single step could reduce CO 2 emissions to the atmosphere by 250,000 tons per year, in the US alone. Furthermore every kilogram of aluminum saved by reducing manufacturing waste translates into electricity saved at the energy-hungry smelter. The technology is based on controlling length scales previously uncontrolled. Tunable casting uses substrate modification to manipulate product quality. Fig. 1 Single roll casting schematic with ‘write’ and ‘erase’ head concept. 1. Overview: Single roll casting (Fig. 1) is an economical technique to produce foil or ribbon, a technique limited, however, by the ability to influence the contacting and solidification event within the contact zone. Molten metal is forced through a nozzle onto the substrate where it forms a puddle. Heat extracted to the rotating substrate causes a solidification front to grow from it as it translates and eventually a solid ribbon product is spun off. Casting rates of 10 m/s (tangential velocity) are achievable with our apparatus that uses a wheel of 3 m circumference. In the zone between nozzle and wheel, there is contact under pressure, phase-change, and large concentration (for alloys), velocity and thermal gradients. The complicated interplay between contacting, wetting and solidification physics is poorly understood. Features of the ribbon product range over 6 orders of magnitude in length scale, from the product macroscale (50 m) to the grain size (10 -5 m). Interest is in influencing the smaller scales (< centimeter) since these lead to surface irregularities, unacceptable product and waste. Controlling these scales would enable manufacturing strip product with properties of specified uniformity. The goal is to condition the substrate by imposing either thermal or compositional gradients before the contact zone[1]. To realize this goal, one first needs to understand how ‘natural’ substrate modifications influence the solidified ribbon product. For example, the cross-stream wave defect appears frequently in the cast product as a row of pits on the wheel side of the ribbon that correlates with trenches on the opposite side (air side). “How does pit formation on the wheel side relate to trenches on the air side?” is a central question. 2. Progress: Thickness can be predicted from gap variations that affect the resistance to fluid flow. That is, feed rate rather than heat-transfer rate limits the product thickness. Other progress includes: an improved understanding of the origin of ribbon defects; the relating of the substrate deformation (due to thermal loading) to the variations in the product thickness (which, coupled with the effect of gap on thickness, yields a deterministic model for through-cast thickness); and the development of a model for solidification rate which captures the important features in the dynamics throughout a cast. Visible surface defects in the ribbon product represent localized variations in thickness and may be indicative of other unintended variations in metallurgy, such as relative concentration of alloying agents. The presence NSF GRANT # 0726813 NSF PROGRAM NAME: MPM
Capillary puddle vibrations linked to casting-defect formation in planar-flow melt spinning
Planar-flow melt spinning (PFMS) is a single-stage rapid manufacturing/solidification technique for producing thin metal sheets or ribbons. Molten metal is forced through a nozzle onto the substrate where it freezes and is spun as ribbon product. A puddle of molten metal held by surface tension (capillarity) forms between the nozzle and substrate. An important measure of product quality is the uniformity of thickness along and across the ribbon. At small length scales, local thickness changes or surface defects are present that are undesirable. This work examines the cross wave, a well-defined periodic surface defect, seen when casting aluminum-silicon alloys. The presence of the defect is related to processing conditions and puddle dynamics. Motions of the puddle menisci are captured using high-speed video and analyzed for frequency content. A high frequency vibration of both menisci corresponds to the observed frequency of the surface defect. A scaling analysis reveals these motions to be capillary in nature and comparisons are made with two model problems of vibrating capillary liquids.
Timber, its nature and behaviour
Preface. Acknowledgements. Chapter 1 - Structure of Timber. Chapter 2 - Appearance of Timber in Relation to its Structure. Chapter 3 - Mass Volume Relationships. Chapter 4 - Movement in Timber. Chapter 5 - Flow in Timber. Chapter 6 - Deformation Under Load. Chapter 7 - Strength and Failure in Timber. Chapter 8 - Durability of Timber. Chapter 9 - Processing of Timber. Index.