High Interface Temperature Research Articles

Effect of Speed and Pressure on Dry Sliding Interactions of Alumina against Steel

Sliding of alumina (87%) pins against a hardened steel disk over a range of pressures (3.3–30.0 MPa) and speeds (0.1–12.0 ms‐1) has been studied. Four different regions (R1, R2, R3, and R4) of friction as a function of speed have been identified. R1 and R3 exhibit single‐valued friction while in R2 and R4 the friction exhibits dual behavior. The speed range over which these regions prevail is sensitive to the pressure. R1 and R2 are low‐speed and low‐temperature regions, and in both, metal transfer and formation and compaction of y‐Fe2O3 occur. R3 and R4 are associated with high speeds and high interface temperatures. Formation of FeO, FeAl2O4, and FeAlO3 has been observed. The implications of the tribochemical interactions on friction and wear characteristics are discussed.

Quantitative aspects of directly coupled supercritical fluid extraction–capillary gas chromatography with a conventional split/splitless injector as interface

AbstractThe quantitative aspects of on‐line supercritical fluid extractioncapillary gas chromatography (SFE‐GC) with a split/splitless injector as interface were investigated. Special attention was paid to the discrimination behavior and the reproducibility of the split/splitless interface. A simple experimental set‐up is proposed that allows accurate quantitation in on‐line SFE‐split GC. The results obtained in on‐line SFE‐GC compare favorably with those from conventional GC with split injection. Discrimination was found to be absent when working at sufficiently high interface temperatures. Finally, the effects of the carbon dioxide flow rate, interface temperature and split ratio on both discrimination and reproducibility were studied.

Experimental Determination of Thermal Contact in a Diode-Heat Sink Assembly

This study examines experimentally the quality of contact of mechanical joints in a diode heat sink assembly. Steady-state contact conductance, h, is used as a quantitative measure of the quality of contact of a joint. The emphasis of the work is on determining the contact conductance, h, for a nonideal joint using a noncontact method of recording temperature distribution in a complex geometry. Thermal contact conductance for an interface is known to depend on parameters such as contact pressure, mean interface temperature and the surface roughness characteristics of the mating surfaces. The results are presented for three different conditions of the interface namely (i) the mating surfaces are bare (ii) aluminum foil is inserted between the mating surfaces, and (iii) a high thermal conductivity grease is applied to the mating surfaces. Two levels of contact pressure are used for the interface with aluminum foil. The results indicate that the contact conductance increases with the mean temperature of the interface in all the cases. At low interface temperature, the contact conductance was greatest for the bare interface conditions. At high interface temperature, the contact conductance was greatest for the aluminum foil interface condition.

Use of ceramic tools for machining nickel based alloys

The paper is the first of two dealing with the use of ceramic tool materials for the machining of nickel based alloys. While the second contribution presents the results of detailed machinability tests, involving a cross-section of current nitride, superhard and whisker reinforced ceramic tooling products, this first paper comprehensively reviews existing literature on the subject. Following an assessment of tool wear characteristics, such as depth-of-cut notching and the underlying mechanisms involved, in particular the effects of applied mechanical stress and high interface temperatures, details are given of the composition, structure, physical properties and cutting performance of various state-of-the-art ceramic tool materials. Although only recently available commercially, whisker reinforced composite tools, comprising an alumina matrix with approximately 25% by volume silicon carbide whiskers, are reported to be capable of operating at cutting speeds up to 750 m/min on some nickel based alloys.

Hydrogen formation during pyrolysis of polystyrene

Hydrogen was identified as a product of the pyrolysis of polygyrene, especially at high pyrolysis temperatures. With a high interface temperature of the Pyroprobe foil pyrolyser and a high pyrolysis temperature, almost 100% of the pyrolysed polymer could be accounted for. It is then assumed that hydrogen (up to 26%) produces a corresponding amount of carbon, which remains on the foil.

Friction and wear characteristics of powder metallurgy copper-graphite brushes at high sliding speeds

Friction experiments using several commercial powder metallurgy copper-graphite brushes against an AISI 4340 steel rotor were conducted at sliding velocities ranging from 20 to 235 m s −1. The measured wear rates ranged from a minimum of 4.3 × 10 −5 cm km −1 at a sliding velocity of 100 m s −1 for a brush with high graphite content to a maximum of 8.4 × 10 −3 cm km −1 at a sliding velocity of 230 m s −1 for a brush with high metal content. The coefficients of friction ranged from a minimum of about 0.08 to a maximum of about 0.47 and were greatly affected by the presence of oxide layers at the sliding interface. Almost all the brushes exhibited some degree of edge breaking. The velocity at which edge breaking occurred was dependent on the powder grain size. Brushes with a large grain size seem to exhibit edge breaking at a lower speed than brushes with a fine grain size. High interface temperatures which occur at high sliding speeds result in melting of the lead-tin binders used in most powder copper-graphite brushes.

Interface temperature measurements in the fretting of a medium carbon steel

The temperature of a fretting interface between 4130 steel and constantan has been measured by monitoring the electrical potential of the interface. The measured maximum temperature rise was 18 K and the temperature rise varied little with a change in normal pressure from 7 to 14 MPa or a change in fretting interface area from 25.8 to 1.6 mm 2. Fretting of annealed 4130 steel against the same material in the as-quenched condition (untempered martensite) produced plastic deformation of both surfaces but no microstructural evidence of phase transformation due to interface heating. Alternative explanations are suggested for evidence of high interface temperature in fretting cited by other investigators.

Normal and Short Circuit Operating Characteristics of Metallic Shielded Solid Dielectric Power Cable

Experimental results are presented on the normal and short circuit operating characteristics of metallic shielded solid dielectric power cable. Test data on thermal runs of single conductor shielded power cable under typical installation conditions confirm published ampacity data1, and hence the theoretical procedure2 employed for calculating the ampacity of single conductor cable with circulating current losses. The thermal runs also point out the possible adverse effect on the cable of operating at a high interface temperature for an extended period of time.

Phenolic resin char-formation during hyperthermal ablation

Ablation is a self-regulating heat and mass transfer process in which incident thermal energy is expended by sacrificial loss of material 1 1 ASTM (E 349)30. . The surface of a carbonaceous char is lost during the ablation of fiber-reinforced phenolic resin composites. The transient high temperatures penetrate deeply, resulting in an underlying pyrolysis zone with rapid pyrolysis rates and a high char interface temperature. Phenolic resin char-formation at high heating rates and high temperatures was studied using thermogravimetry (TG). The specialized thermobalance permitted runs in helium at rates of 3–430°C/min up to 1400°C. Computer code analysis provided rate parameters for an Arrhenius type correlation. The parameters represented well the parent TG run but were not independent of heating rate. A complex correlation was considered necessary for universal use. The attractive alternative was parameter evaluation at high heating rates using TG.