G. Pantazopoulos

Leaded brass rods C 38500 for automatic machining operations: A technical report

C 38500 is a widely used copper alloy with a great variety of applications from decoration and architecture to mechanical/electrical engineering. The chemical composition of this alloy offers superior machinability and subsequently increased productivity in high-speed machining and manufacturing processes. In European countries, this alloy is used primarily as free cutting brass (CW 614N according to EN 12164: 1998), similar to C 36000 alloy, which is used also for thread rolling. The lower percentage of Cu compared to C 36000 (nominal 58% instead of 61%) decreases the cost of the raw materials. This paper reports the principal aspects of microstructure, mechanical properties, and machinability of this alloy in relation to the industrial manufacturing process used.

Wear behavior of anti-galling surface textured gray cast iron using pulsed-CO2 laser treatment

Abstract In the present study the surface modification of BS300 gray cast iron, using high power pulsed-CO 2 laser irradiation, is adopted in order to establish an anti-galling surface texture and, therefore, to improve wear and friction behavior. The process optimization and the resultant microstructural and microhardness changes are also reported and discussed. Subsequent wear testing of large-scale surface treated materials, using the pin-on-disk configuration, indicate weak scuffing susceptibility and slightly lower friction coefficients as compared to the flame-hardened materials, currently used in industry. The results of the present study may be of interest to the automotive and sheet-metal forming industry, due to the extensive use of this iron as a component during the deep-drawing process.

Fabrication of thick layered superconductive ceramic (BiPbSrCaCuO)/metal composite strips by explosive cladding and rolling

Abstract Explosive cladding, subsequent rolling and heat treatment are employed to fabricate a composite (sandwich) strip consisting of an intermediate high temperature superconducting ceramic layer of the BiPbSrCaCuO compound and two metal silver plates. Macro- and micro- structural experimental observations regarding the quality of the product at the various stages of the fabrication were evaluated using optical and scanning electron microscopy and X-ray diffraction techniques, whilst the superconducting properties of the composite strips were obtained using ac-magnetic susceptibility techniques; preliminary dc-resistivity measurements were made also to evaluate further the superconductive properties of the material. Post-fabrication heat-treatment in air resulted in improved superconductivity of the heat-treated strips as compared to the residual superconductivity obtained after rolling, leading therefore to useful conculsions regarding the applicability of the fabricated composite plates in the electrical and electronic industries.

Fracture Behavior and Characterization of Lead-Free Brass Alloys for Machining Applications

The stricter environmental, health, and safety regulations address the harmful effects of lead and provide the driving force for the development of lead-free brass alloys. Conventional leaded brass rods are widely used in several manufacturing sectors (i.e., fabrication of hydraulic components, fittings, valves, etc.) due to their superior workability in extrusion and drawing as well as their superior machinability. As machinability performance involves shear and dynamic fracture processes evolved under high strain-rate conditions, the understanding of the mechanical behavior/microstructure interaction is critical in order to successfully tailor candidate lead-free alloys for improved machinability without compromising the reliability of manufactured components. In this work, the mechanical behavior under static and dynamic loading of three lead-free brass alloys (CW510L-CW511L-C27450) in comparison to a conventional leaded brass alloy (CW614N) was studied. The fractographic evaluation of the texture of conjugate fracture surfaces was performed to identify the involved fracture mechanisms and their relation to the alloy microstructure. It was shown that the CW510L lead-free brass alloy is a potential candidate in replacing conventional CW614N leaded brass, combining high tensile strength and fracture toughness, due to the prevalence of the β-intermetallic phase in the alloy microstructure.

A review of defects and failures in brass rods and related components

Brass rods (mainly C36000, C38500, and C37700) are used in a great variety of applications, from machine component/hydraulic part manufacturing to architecture and fine arts. The chemical composition of these alloys is carefully designed to enhance machinability and/or hot formability (for free machining and hot stamping operations, respectively). This article reviews the principal defects that lead to in-process and in-service failures of brass rods and related components. The review is focused on defects caused by selected metalforming processes for the production of brass rods (extrusion and cold drawing) and on the role of these defects in failures during component processing and use.

Fabrication of multi-layered steel/superconductive ceramic (YBaKCuO)/silver rods by explosive powder compaction and extrusion

Abstract Axisymmetric explosive powder compaction and subsequent direct extrusion are employed to fabricate a multi-layered metal/high-Tc ceramic rod consisting of a silver mandrel, a potassium doped YBa2Cu3O7 core and a steel sheath. Experimental investigations regarding the ‘soundness’ and the superconducting properties of the component at the various stages of the fabrication are reported. Microstructural/crystallographic changes, macro- and micro-defects of the ‘green’ compacted billet and the extruded rod are also indicated and discussed.

Fracture Modes and Mechanical Characteristics of Machinable Brass Rods

Machinable brasses are a broad class of high strength copper–zinc alloys mainly containing lead to improve machinability. Conventional leaded brasses are widely used in several manufacturing sectors (i.e., fabrication of hydraulic components, fittings, valves, etc.) due to their superior workability in extrusion and drawing, together with their superior machinability for high efficiency production of final components in high speed/high precision machining centers. In addition to machinability, the mechanical behavior and general fracture mechanisms of these alloys are also important, due to their impact on the overall reliability and safety of brass components. In this study, the main fracture modes and mechanical characteristics of two industrial copper alloys, namely, CuZn39Pb3 and CuZn36Pb2As, are presented in relation to their microstructure. Optical metallography, macro- and microfractography, together with static and dynamic mechanical testing, were used as the principal analytical techniques for the present investigation.

Net shape manufacturing of silver-sheathed high-Tc superconductive ceramic (YBaKCuO) strip by explosive compaction/cladding and rolling

Abstract Explosive compaction/cladding and subsequent rolling are employed to fabricate a sandwich metal/ceramic strip consisting of two silver plates and two intermediate high-temperature superconducting ceramic paths of the YBaCuO system. Macro- and micro-structural experimental observations regarding the quality of the product at various stages of the fabrication were evaluated using optical and scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) techniques, whilst the superconducting properties of the components produced and the oxygen content of the ceramic material were controlled by employing the d.c.-magnetization technique and thermogravimetric analysis (TGA), respectively. Post-compaction oxygen heat-treatment was not necessary because of the good retention capability of the compound during the fabrication process, resulting, therefore, in the conservation of the bulk superconducting properties.

Corrosion of a copper U-shaped heating element: Some morphological and microstructural observations

In this work, observations of the corrosion on a failed copper U-shaped tube, of 1 mm nominal thickness, are presented. This tube was subjected to severe corrosion and subsequent cracking after a month of operation as the heating element of an electrical boiler. Morphological and microstructural observations of the failure area as well as cross sections of the corroded copper tube are presented. Moreover, the chemical composition of the material and the principal physicochemical characteristics of the tap water used for boiler operation were determined in the context of the failure investigation. The quality of the water used for boiler operation was a significant factor influencing the heating element efficiency and reliability. Hard water with high electrical conductivity accelerated salt precipitation and led to the corrosion and premature failure of the components.

Process failure modes and effects analysis (PFMEA): A structured approach for quality improvement in the metal forming industry

Failure modes and effects analysis (FMEA) is one potential tool with extended use in reliability engineering for the electrical and electronic components production field as well as in complicated assemblies (aerospace and automotive industries). The main purpose is to reveal system weaknesses and thereby minimize the risk of failure occurrence. The FMEA technique is used in the design stage of a system or product (DFMEA) as well as in the manufacturing process (PFMEA). Currently, the implementation of quality systems (such as ISO 9001, QS9000, TS 16949, etc.) requires the establishment of preventive procedures; therefore, the use of risk analysis methods, such as FMEA, is mandatory. This paper introduces the use of this technique in a critical process in the metal forming industry.