Study of the operational parameters of plasma transferred arc melting and modelling of the process

Abstract

Plasma transferred arc (PTA) melting/alloying technique can be successfully used in various surface modification applications and has the potential for industrial use, replacing other more expensive techniques such as laser or electron beam. Such applications require tight control of the process parameters. There is a restricted field of PTA parameter values, where PTA melting can be successfully performed with smooth and unoxidised surfaces. The heat source efficiency of PTA treatment is strongly affected by welding current, arc length and travel speed of the arc and it takes values between 0·40 and 0·55, while melting efficiency takes values between 0·05 and 0·25, affected by the same parameters as arc efficiency. The microstructure and hardness of the melting zone of a PTA pass is associated with heat input and arc length.     

Cathodic protection of UNS C71500 heat exchanger tubes in sulphide polluted Arabian Gulf sea water

Abstract

A laboratory investigation using a specially designed circulating test rig has been undertaken to study the feasibility of achieving complete cathodic protection of UNS C71500 heat exchanger tubes in sea water applications by means of sacrificial carbon steel anodes. The results have indicated that the galvanic current distribution covered the entire 6 m length of the tube. However, the presence of sulphide ions as pollutants in the sea water shifted the galvanic potentials of the tubes to less active potentials and affected the development of the protective films that normally form.     

Release of Water-Soluble Species from the Oxides formed on 20%Cr/25%Ni/Nb-Stabilised Steel

Abstract

The effect of water on the oxides formed on 20%Cr/25 %Ni/Nb-stabilised steel has been studied at 20 and 60° using a radiometric technique. Similar rate laws were observed for the transference of iron, nickel, manganese and cobalt to the solution although the total amount of each constituent remaining in solution depended on the solution chemistry of the individual ion. As much as 2% of the cobalt impurity could be present in solution at 60° owing to its uneven distribution in the oxides while the relatively small release of chromium observed was probably due to its state of combination in the oxide matrix. The transference of the tantalum impurity obeyed a parabolic law and 0·7% of this constituent was present in solution after the 100-dayreaction period.     

Joining phenomena and joint strength of friction welded joint between pure aluminium and low carbon steel

Abstract

This paper describes the joining phenomena and joint strength of friction welded joints between pure aluminium (P-Al) and low carbon steel friction welds. When the joint was made at a friction pressure of 30 MPa with a friction speed of 27·5 s^?1, the upsetting (deformation) occurred at the P-Al base metal. P-Al transferred to the half radius region of the weld interface on the low carbon steel side, and then it transferred toward the entire weld interface. When the joint was made at a friction time of 0·9 s, i.e. just after the initial peak of the friction torque, it had ～93% joint efficiency and fractured on the P-Al side. This joint had no intermetallic compound at the weld interface. Then, the joint efficiency slightly decreased with increasing friction time. The joint had a small amount of intermetallic compound at the peripheral region of the weld interface when it was made at a friction time of 2·0 s. When the joint was made at a friction time of 0·9 s, the joint efficiency decreased with increasing forge pressure, and all joints were fractured at the P-Al side. Although the joint by forge pressure of 90 MPa had hardly softened region, it had ～83% joint efficiency. To clarify the fact of decreasing joint efficiency, the tensile strength of the P-Al base metal at room temperature was investigated, and the tensile test was carried out after various compression stresses and temperatures. The tensile strength of the P-Al base metal has decreased with increasing compression stress at any temperature. Hence, the fact that the joint did not achieve 100% joint efficiency was due to the decrease in the tensile strength of the P-Al base metal by the Bauschinger effect. To obtain higher joint efficiency and fracture on the P-Al side, the joint should be made without higher forge pressure, and with the friction time at which the friction torque reaches the initial peak.     

30—THE EFFECT OF VARIABILITY OF FIBRE DIAMETER ON WORSTED PROCESSING: PART I. THE USE OF COMPARISON SAMPLES FROM A SINGLE MERINO FLOCK

Two greasy-wool bulks were made up from sound fleeces selected from a single medium-merino flock so that their mean diameters, mean staple lengths, and mean crimp frequencies would be the same or similar, but the coefficients of variation of diameter (V _d) would be different. The tops made from these bulks showed closely similar mean fibre diameters (20·6 and 20·8 (μm), lengths, and length variabilities, with the V _d values 18·3% (L) and 21·4% (H). In conventional Bradford spinning, L was slightly favoured over H at the spinning limit, but the differences in ends-down per 100 spindle-hours at commercial counts were negligible. Yarn properties, such as tensile strength and elongation at break, and yarn evenness did not disclose differences of any consequence. Fabrics made from 25-tex yarns gave closely similar properties. Ambler Superdraft spinning supported these conclusions.

The difference of 3% in V _d values did not indicate significant worsted-manufacturing differences between the tops. Since these tops were made from single-quality sources, the V _d values are low compared with the range of values for European tops of the same diameter, the majority of which would occur in the 20–26% V _d range.     

29—AN INSTRUMENT FOR MEASURING THE HAIRINESS OF YARNS

An instrument developed at the Shirley Institute and used since 1963 for measuring the hairiness of yarns is described. The basis of the method of counting is the interruption of a light beam by the projecting hairs. Results obtained by means of this instrument have been described previously by Walton.