Comparison of four methods to evaluate flow fields in CSP casting mould

Abstract

Commercial flow analysis tools are widely used in industry, but their capacity, efficiency and accuracy to solve complex flows are not so clear. In the present paper, first, three-dimensional computations are performed to calculate the flow field in the mould region of compact strip production (CSP) casting using a conventional finite volume method program, CFX4, with laminar model, standard k–? model, renormalisation group k–? model and low Reynolds number k–? model with default model parameters for handling turbulence. Next, these were compared with the flow pattern in a 1 : 1 scale water model by other investigations and quantitative comparisons were made for the flow velocities. Finally, the four numerical simulation models were evaluated in detail. Each method has its own merits and disadvantages, so model verification is always necessary for a highly accurate numerical analysis of complex flows. Under the situation of lacking experimental data, the standard k–? may be a good choice to evaluate liquid steel in a CSP mould.     

Thermosonic bonding of crossed strip Au bumps

Abstract

Gold strip bumps for electronic packaging are bonded using the thermosonic process. The Au strip bumps on the chip and substrate are aligned in a crossed configuration, and ultrasound is applied longitudinally on the chip to form a solid state bond between the crossed strip Au bumps. Deformed bump shapes are calculated numerically, and the shear force and fractured surface profile are measured to evaluate the bond quality. The deformed Au bump shape is similar to a saddle, which provides larger contact surface area and greater friction force. The bond strength of crossed strip bumps reaches the yield strength of Au, which is much higher than that previously obtained for bonding between Au bumps and a planar pad.     

Study of single side single pass submerged arc welding using reusable backing strip

Abstract

An attempt has been made to establish a submerged arc welding procedure that will enable the production of welded butt joints in thin steel plate, having proper fusion and reinforcement geometry in a single welding run. In this work, the combined effect of the basic welding parameters, i.e. voltage, current, and speed, along with the effect of thickness, on weld penetration have been studied. Also an attempt has been made to develop a flux filled reusable backing strip. In the present investigation submerged arc welding flux in its powdered form has been used without application of any external pressure and also without any additives. Experiments have been carried out extensively on 6 mm and 8 mm thick C–Mn steel plate specimens. This form of backing strip has shown great promise towards achieving single side single run welding. The welds achieved in this single side single pass welding process are not yet 100% satisfactory, however, the results indicate the feasibility of the process to achieve quality welds to meet relevant quality standards.     

A kinematic analytical approach to predict roll force,rolling torque and forward slip in thin hot strip continuous rolling

Abstract

A kinematic analytical approach has been developed to predict the roll force, rolling torque and forward slip in thin hot strip continuous rolling under various rolling conditions. The approach is based on formulating a velocity field in the roll bite zone that expresses the effect of interfacial friction on the distribution of axial velocity and longitudinal stresses across the strip thickness. The results obtained from the proposed approach are in fair agreement with finite element simulation results, whereas available analytical methods, which are usually valid for billets and thick plates, have given considerable error in the results. The proposed approach is applied to study the effect of thickness reduction ratio, coefficient of friction, work roll diameter and front and back tensions on the roll force, rolling torque and forward slip in thin hot strip rolling. The main merit of the proposed analytical approach, as compared to finite element simulation, lies in the drastic reduction in the computational time required in finite element simulation, which favours its use in online control of rolling thin strips.     

Interfacial precipitation in hot isostatically pressed diffusion bonds of 17-4 PH stainless steel

Abstract

The embrittlement of hot isostatically pressed (hipped) diffusion bonds manufactured from 17-4 PH stainless steel has been investigated by Auger electron spectroscopy (AES) of in situ fracture specimens. Depth profiling by AES has revealed copper precipitation at the interface of the diffusion bond. This precipitation, up to a few monolayers in thickness, occurs during the ramp up to temperature and pressure of the hot isostatic pressing (hipping) cycle and is not readily removed by subsequent heat treatment. This effect is explained in terms of the metallurgical characteristics of copper within the steel. Results suggest that the extent of the precipitation decreases with increasing process temperature. In the case of PH 13-8 Mo stainless steel, where the precipitation hardening phase is NiAl, the interface is weakened by sulphur segregation and the formation of oxide particles.     

The Phase I of Henan Sanfeng Copper Has Completed Construction

【正】After more than 2 years of fast-paced construction,the 50,000-tonnes Phase I of 100,000 t/a High Precision Ultra-thin Copper Plate/Strip Project,a project of...     

Simulation of thermal history of work rolls of finishing stand in hot strip mill: a numerical approach

Abstract

The work rolls in the finishing stands of any hot strip mill (HSM) experiences thermal shock owing to changes in temperature from initial boundary conditions. The thermal expansion owing to the change of temperature is a major contributing factor to the final shape or the profile of the strip generated at different stands of finishing stands of the HSM. A mathematical model has been developed for the prediction of temperature profile for the surface and the inner depth of the roll in the finishing stand of a HSM. The numerical result from the model calculates the temperature profile in each stand of six finishing stands of the HSM and the corresponding thermal expansion at different stands. The temperature profile and the thermal expansion of the work rolls for a complete rolling schedule have been found from this model. The measurement of the thermal expansion has been found to match closely with the calculated one.     

New parameters for the description of hot rolled strip transverse temperature distribution: preliminary applications

Abstract

Nowadays, it is possible to find experimental data about the longitudinal temperature distribution for a hot rolling strip production. However, it is much more difficult to obtain experimental results on the transverse temperature distribution on the strip surface. After a systematic analysis of the methods and results in the literature, the experimental data collected using a specific experimental apparatus to measure the transverse strip temperature distribution out of the last finishing stand of a 1800 mm wide thin hot strip rolling mill are presented. In order to logically classify all the results by identifying the main factors that influence the strip temperature profile, it is proposed to describe more clearly four new parameters of the strip thermal profiles which would allow the investigation of the reason for uneven transverse temperature distributions. The relationship between strip temperature distribution, strip geometry and temperature itself is also studied to provide a basis to build a mathematical model for the current problem.     

Aspects of porosity formation in spray deposited thin aluminium strip

Abstract

A characteristic feature of the spray deposited metal strip is that it contains porosity. The present paper has reported and explained the effect of various process parameters such as atomising pressure, deposition distance, melt superheat and melt delivery tube diameter on porosity of the spray deposited thin aluminium strip. Porosity of the spray deposited aluminium strip greatly depends not only on the liquid fraction present on the substrate, but also on the thermal condition through the substrate. It has been shown that there are several types of porosity present in the strip, namely interstitial, mechanically entrapped gas, intersplat boundary, solidification shrinkage and porosity due to hydrogen evolution. The mechanism of their formation has been discussed. An increase in the initial temperature of the substrate lowers the porosity content in the spray deposited aluminium strip.     

Influence of process parameters on scale reduction with H2

Abstract

A new pickling method that reduces the metal oxide on steel strip using H₂ has been studied through an extensive campaign of experimental tests. The process, referred to as 'acid free pickling', is environmentally friendly and does not use acid. It is most suitable for application to hot rolled low carbon steel strip. Experimental studies are in progress to validate the application of hydrogen on different metals.