Silk Powder from Cocoons and Woven Fabric as a Potential Bio-Modifier

Silk, as a protein fiber characterized by high biocompatibility, biodegradability, and low toxicity, is mainly used as textile structures for various purposes, including for biological applications. The key issue for unlimited silk applicability as a modifier is to prepare its relevant form to cover or introduce to other materials. This study presents silk powder fabrication from Bombyx mori cocoons and non-dyed silk woven fabric through cryogenic milling. The cocoons were milled before and after the degumming process to obtain powders from raw structures and pure fibroin. The powder morphology and composition were analyzed using scanning electron microscopy and energy dispersive spectroscopy. The influence of the milling on the silk structure was studied using infrared and Raman spectroscopies, indicating that silk powders retained dominant β-sheet structure. The powders were also analyzed by differential scanning calorimetry and thermogravimetric techniques. The thermal endothermic peak and onset temperature characteristic for silk decomposition shifted to the lower values for all powders, indicating less thermal stability. However, the process was found to be an efficient way to obtain silk powders. The new milled form of silk can allow its introduction into different matrices or form coatings without using any harsh solvents, enriching them with new features and make more biologically friendly.

A Systematic Study of the Cryogenic Milling of Chrysotile Asbestos

For more than 40 years, intensive research has been devoted to shedding light on the mechanisms of asbestos toxicity. Given the key role of fibre length in the mechanisms of asbestos toxicity, much work has been devoted to finding suitable comminution routes to produce fibres in desired size intervals. A promising method is cryogenic milling that, unlike other mechanical size reduction techniques, preserves the crystal–chemical properties of materials. In this study, the effect of cryogenic milling on the physical–chemical properties of commercial Russian chrysotile was studied in order to produce precise size fractions with invariant properties compared to the pristine fibres. In particular, two batches with fibres > 5 µm and <5 µm were prepared, as this limit sets their potential toxicity. The results are fundamental for future in vitro toxicity testing of this commercial product, widely used in chrysotile-friendly countries but not yet adequately studied. Results show that fibre length can be controlled by milling time under cryogenic conditions without inducing structural defects or amorphization; short fibres (95% L < 5 µm) can be obtained by cryogenic milling for 40 min, while 10 min is enough to yield long chrysotile fibres (90% L > 5 µm).

Experimental investigation of the effects of cryogenic cooling on tool life in Ti6Al4V milling

In this paper, the results of an experimental campaign of cryogenic milling are presented and discussed. For this purpose, a specific experimental setup that allowed to feed the liquid nitrogen LN through the tool nozzles was used. Tool life tests were carried out at different cutting speeds. The tool duration data were collected and used to identify the parameters of the Taylor’s model. Different end-of-life criteria for the tool inserts were even investigated. The achieved results are compared to those obtained using conventional cooling. It was observed that at low cutting velocity, conventional cooling still assures longer tool lives than in cryogenic condition. Since in cryogenic milling the increasing of the cutting velocity is not so detrimental as in conventional cutting, at high cutting speed (from 125 m/min) longer tool durations can be achieved. Statistical analyses on the model parameters were carried out to confirm the presented findings. The analysis of the effect of the cooling approach on the main wear mechanisms was also reported. At low cutting speed, adhesion and chipping phenomena affected the tool duration mainly in cryogenic milling.

Kryogenes Fräsen additiv gefertigter Bauteile/Cryogenic milling of additively manufactured components

Die erreichbare Oberflächenqualität additiv gefertigter Bauteile ist für industrielle Anwendungen häufig unzureichend. Daher ist eine in der Regel spanende Nachbearbeitung der Bauteile unumgänglich. In diesem Beitrag wird die spanende Nachbearbeitung durch eine kryogene Kühlung ergänzt. Hierdurch wird die thermische Belastung in der Werkstückrandschicht reduziert, um so eine Kaltverfestigung zu begünstigen. Es konnte eine verbesserte Oberflächenqualität sowie eine Randschichthärtung realisiert werden. &nbsp; The surface quality of additively manufactured components is often insufficient for industrial applications. As a result, additional processes are necessary to improve the surface quality. In the investigations presented, a cryogenic cooling is used when milling additively manufactured components. The cryogenic cooling strategy favors the introduction of strain hardening effects into the surface layer. An improved surface quality as well as a hardened surface layer were realized.

Optimization of Jet Parameters for Minimizing Surface Roughness in Cryogenic Milling of Ti-6Al-4V

Cryogenic machining of titanium alloys using the internal cooling method is being identified as an alternative effective process to current practice of machining materials with poor thermal conductivity. The choice of jet parameters is particularly important for improving their machining quality and saving the production cost simultaneously. This research aimed to minimize the surface roughness by optimizing the comprehensive jet parameters in cryogenic milling Ti-6Al-4V. By comparing the cooling capability of liquid nitrogen and gaseous nitrogen, the influence mechanism of nitrogen phase on surface roughness was illuminated. A self-developed cryogenic machine tool with conveying liquid nitrogen through the spindle and tool was specially used to carry out milling experiments. The results indicated that the nitrogen phase had a most significant effect on surface roughness, followed by the pressure while the effect of flowrate was lowest. A lower volume fraction of gas, a higher pressure, and a proper flowrate could produce a lower surface roughness. An optimal combination of jet parameters was ultimately selected as the liquid nitrogen with 45 l/h of flowrate and 0.6 MPa of pressure to obtain the minimum surface roughness at 0.076 μm.