Sleeve Thickness Research Articles

Effect of Technological Factors on Strip Profile in Twin-roll Casting Process.

Scientific and technical progress is presently impossible without the application of a new generation of materials with unique properties. Fine-grained alloys, obtained by rapid solidification technique in twin-roll casting process, belong to this class of materials. The commercial success of the twin-roll casting technique depends on the quality of its cast products, first of all on the cross-sectional shape of the strip. Otherwise, an additional post treatment of the as-cast strip such as cold rolling can deteriorate the unique properties of the strip. To gain a better understanding of the influence of technological parameters on the cross-sectional shape of the strip, a laboratory-size twin-roll casting process has been investigated both theoretically and experimentally. It was found that the geometry of the nozzle slot, the roll sleeve thickness, diameter and length of the roll and the pressure profile between the rolls may influence the cross-sectional shape of the strip. Increasing the nozzle slot length, the flow rate and the distance between the nozzle and the melt bath surface increases the probability of formation of the thickness non uniformity across the strip width. The design of the roll plays a major role in the formation of the cross-sectional shape of the strip: a convex profile is produced by bending of the rolls whilst a concave profile results from thermal expansion of the rolls, in the case of a thick, water-cooled sleeve. The shape of the pressure profile between the rolls depends on the ratio strip width to roll length. Optimisation of the sleeve thickness, diameter and length of the roll is one of the possible ways of improving the cross-sectional profile and the flatness of the as-cast-strip.

Multivariate calibration for quantitative analysis of EDXRD spectra from a bone phantom

Phantoms have been constructed to simulate trabecular bone mineral loss and cortical bone thinning which consist of a mixture of hydroxylapatite powder and animal fat in various quantities, surrounded by a varying thickness of dural sleeve. Energy dispersive X-ray diffraction (EDXRD) spectra have been recorded, and multivariate calibration has been performed on the spectra from the bone phantoms. The multivariate technique of partial least squares (PLS) was used to predict the hydroxylapatite content of the phantoms and the dural thickness for measurement times of 250, 50 and 5 s. The calibration phantoms consisted of 10 hydroxylpatite densities ranging from 0.5852 g cm −3 to 0.3703 g cm −3 representing a loss of hydroxylapatite of approx. 40% in 4% intervals. Each phantom had four dural sleeves of thickness 0.5, 1.0, 1.5 and 2.0 mm. Nine test phantoms were constructed with a range of densities that were inside the calibration range. For a measurement time of 250 s the average accuracy of prediction for hydroxylapatite content was approx. ±3% while for a measurement time of 5 s this fell to approx. ±8%. The dural thickness was predicted to within approx. ±0.25 mm for a measurement time of 250 s. The results show that multivariate calibration is a useful technique for obtaining quantitative data of a desired variable from EDXRD measurements which may otherwise be masked or corrupted by other variables.

Volume Profile for Substitution in Labile Chromium(III) Complexes: Reactions of Aqueous [Cr(Hedta)OH(2)] and [Cr(edta)](-) with Thiocyanate Ion.

A procedure is given for correcting optical absorbance measurements made at variable pressure with a le Noble-Schlott ("pillbox") cell for the inner sleeve wall thickness. With this technique, the molar volume change for the acid ionization of aqueous [Cr(Hedta)OH(2)] was found to be +5.1 +/- 0.6 cm(3) mol(-)(1) (0-200 MPa, 25.0 degrees C, ionic strength 1.0 mol L(-)(1) HClO(4)/NaClO(4)), an anomalous positive value which implies a change from quinquedentate to predominantly sexidentate edta and expulsion of the coordinated water on ionization. For thiocyanate substitution into labile [Cr(Hedta)OH(2)], high pressure stopped-flow measurements gave the volume of activation as -7.8 +/- 0.9 cm(3) mol(-)(1) and the volume of reaction as +3 +/- 2 cm(3) mol(-)(1), while for the reaction of [Cr(edta)](-) with NCS(-) the activation volume is -13.6 +/- 0.6 cm(3) mol(-)(1) (same conditions). These and other data support the notion that the anomalous substitutional lability of Cr(III)(edta) complexes relative to typical Cr(III) species is due to activation by transient chelation of the pendant arm of quinquedentate edta.

Influence of steel hardenability on residual stresses in hardening the sleeves of large built-up back-up rolls

1. It is recommented that sleeves to be hardened and tempered to reduce residual stresses be produced from steels providing suppression of pearlitic transformations with the quenching method used (steels with specified hardenability). For 1600–2100 mm diameter 230–290 mm thick sleeves of large built-up back-up rolls it is desirable to use a steel with minimum stability of the austenite in the pearlitic area (incubation period 200–220 sec). 2. With use of steels with an increased alloy content a decrease in quenching intensity of sleeves in hardening is possible. 3. In production of sleeves of steel of a given type it is necessary to determine the maximum possible thickness of sleeves for which through hardenability and the minimum level of residual stresses after hardening are provided. Thicker sleeves must be produced from steels with higher hardenability or be quenched more intensely in hardening. 4. In development of heat treat cycles for sleeves of steels with increased hardenability it is necessary to take into consideration the stability of austenite in tempering.

Equivalent circuit analysis of a system of coupled helical transmission lines in a complex environment

The complex boundary value problem of a system of coupled transmission lines which takes into account the effects of the dielectric and metal shell environment is solved by a simple equivalent circuit analysis. The results are compared with those for a simple system of coupled helices in free space now available in the literature. The effects of the various environmental parameters—like the thickness of the dielectric sleeve for the outer helix, the ratio of the outer helix-to-inner helix radii, the ratio of the outer helix-to-inner helix contangents of the pitch angle—are studied on the variation of the optimum length with frequency for a system of helical couplers as used in a traveling-wave tube.