An experimental study of the planar-flow melt-spinning process was performed in order to gain a better understanding of the steady-state production of microcrystalline and amorphous ribbons. The dependence of the thickness of the ribbon product,T, on process parameters (wheel speed,U, nozzle/wheel gap,G, overpressure, ΔP, nozzle-slot breadth,R, and nozzle-slot width,W) was determined using an apparatus designed to deliver reproducible results. Thicknesses were reproducible to within 5%–8%. Guided by dimensional analysis, the non-dimensional thickness (T/G) was found to depend, within the experimental error, only on a non-dimensional pressure drop (ΔP/ρU2) and slot breadth (R/G) for fixed thermal conditions. Data from the literature and our data, which considerably extend the range, correlate consistently on this basis. In contrast to the steady behaviour, the limits within which a uniform ribbon can be formed depend on a larger set of parameters; this dependence is sketched with the available data. Finally, a variety of observed ribbon surface textures (free meniscus side) is catalogued.

Planar-flow spin-casting of molten metals: process behaviour

Planar-flow melt spinning (PFMS) is a single-stage rapid
manufacturing technique for producing thin metal sheets or ribbons.
During the processing molten metal flows through a nozzle onto a
moving substrate where a puddle is formed. This study focuses on
the time dependent behavior of the process and looks at the puddle
dynamics during the cast. Understanding how the issues of heat
transfer, fluid flow and contacting dynamics influence the quality
of the cast ribbon are the primary focus of the study. The
commercial acceptance of PFMS requires ribbons to be cast with good
quality (e.g. uniform thickness).

There are a large range scales that are relevant to the ribbon
product. Thickness variations occur on the macro-scale over the
length of the cast (50 m). There is a steady decrease in ribbon
thickness over the length of the cast. There is also a periodic
variation on the length scale of the wheel circumference (2-3 m).
Steady mass, momentum and energy balances are used to understand
these long length-scale thickness variations.

There are also thickness variations that occur on smaller scales,
cm to mm. A periodic thickness variation across the width of
the ribbon is a common defect observed in our casting, referred to
as the cross-wave defect. The molten metal puddle is subject to
capillary vibrations. We find that these oscillations correspond to
the cross-wave defect.

Motivated by the physics of the cross-wave defect, a more
generalized problem of the vibrations of coupled capillary surface
is identified. The motions of the puddle are similar to the
classical problem of the vibration modes of a `plucked' sphere. In
considering the possible modes of vibration for a droplet confined
between two plates, we find a novel vibration mode where the
center-of-mass oscillates. This model is extended to account for a
droplet confined within a tube, with two sections of the droplet
extending from each end. Restricting to quasi-steady interface
shapes, we find a translational vibration mode which can occur with
lower frequency than the traditional Rayleigh modes. The vibration
frequencies are compared to experimental values.

Transient behavior of the planar-flow melt spinning process with capillary dynamics

Crystallization of amorphous Fe78B13Si9

An amorphous structure improves the physical properties of metal and enhances material performance. Planar-flow melt-spinning (PFMS) is a rapid solidification process for producing microcrystalline and amorphous metal ribbons. In PFMS, molten metal is fed through a nozzle onto a rotating wheel where the melt freezes and a continuous ribbon is spun. This study proposes a rapid method for process tuning. Examples were used to determine the applied pressure and wheel speed for designing the ribbon thickness and a wheel-nozzle gap with a preset nozzle size. The determined operating variables are suited to operation conditions, enabling the successful production of continuous ribbon. The proposed method was tested using computational fluid dynamics by treating the liquid metal and ambient air as a two-phase flow using the volume of fluid method. This study used the model to predict the puddle shape and ribbon thickness by fixing the dimensions of the wheel-nozzle gap and nozzle slot and varying the pressure and wheel speed. The results from the simulation confirmed the viability of the method and showed a concerted trend for the ribbon thickness compared with previous studies. In addition, the simulation revealed a fluctuation in the ribbon thickness, which was attributed to the first vibration mode of the puddle that was related to the natural frequency of the liquid inertia balanced by surface tension.

Tuning the Planar-Flow Melt-Spinning Process Subject to Operability Conditions

Metallic glass alloys have been considered as attractive materials due to their excellent mechanical and magnetic properties. However, commercial application of metallic glasses has been limited not only because of high production cost, but because of low market demands. A critical production cost factor was raw material since ferrous metallic glasses were made from high purity electrolytic iron. An idea to reduce the cost was to utilize the raw materials which were taken directly from molten iron and steel manufactured at the existing steel plants. Investigations have been performed to find whether metallic glasses made of molten iron and steel demonstrated appropriate mechanical and magnetic performance. Pilot scale equipments were designed to produce amorphous metallic fibers and strips continuously under the atmospheric condition. Process conditions were optimized by controlling process variables such as alloying and nozzle design, feeding temperature, speed and so on. The glass formability was tested by XRD and DSC analysis. Possibilities of application of Fe-based metallic glasses to reinforced concrete were also evaluated. It was confirmed that a small addition of metallic glass fibers in concrete increased the mechanical performance compared to that of commercial concrete reinforced with steel wires. In addition, amorphous strips were manufactured to apply them to the transformer core. It has been demonstrated that the magnetic properties were equivalent to those of commercial products.

Manufacture and Industrial Application of Fe-Based Metallic Glasses

The design, fabrication, and operation of a relatively simple low‐cost planar flow casting (PFC) machine optimized for small‐batch processing were investigated by the Bureau of Mines. Several design features found beneficial to PFC process operation include: a ground nozzle stopper to retain the alloy charge during melting; a remote, large‐volume pressure vessel connected to the crucible gas system to reduce temperature‐induced pressure fluctuations; and the use of a nested induction coil that allows both the melt charge and the crucible reservoir to be located close to the cooling wheel. The results of several PFC process runs are provided showing typical values of the cooling wheel surface velocity, crucible ejection pressure, and crucible nozzle clearance gap. Examination of the rapidly solidified, Fe‐based ribbons for thickness, dimensional uniformity, and atomic structure indicated that good quality glassy ribbon could be produced with proper selection of the controllable process variables. In addition, single‐variable linear regression analysis was used to determined the effect of each process variable on the resulting ribbon thickness.

M. Saletore

Papers

Simple, low‐cost planar flow casting machine for rapid solidification processing