Effect of Mould Heating Temperature on Cooling Rate of the Melt upon Bronze Crystallization

The article presents the cooling curves of the tin-leaded bronze melt (consists of 10% of lead, 10% of tin, and 80% of copper) being poured in the moulds of various thermal conductivities: massive cast iron chill mould (with the 1:8 cast mass to mould mass ratio) and graphite mould. The curves were plotted for the moulds previously heated to the temperatures of 20; 200; 400; 600; 800 °С. Plotting of the curves was performed with the use of the device Thermograph designed at Tomsk Polytechnic University. The device records thermal electromotive force values of the chromel-alumel thermocouple and converts them into temperature values. The cooling curves are used to determine melt cooling rates within the temperature range involving the crystallization range. It is shown that under similar conditions the cooling rate when casting in cast iron mould is 30-40% higher than in the case of casting in graphite mould. The data given in the paper indicate that preheating of the mould enables us to considerably reduce the cast cooling rate and prolong the period of the melt being in liquid state. It is worth mentioning that cooling rate values of the preheated and non-heated casting moulds are most vividly observed at the initial moments after the melt pouring. When decreasing the casts’ cooling to 300-400 °С the cooling rates tend to be identical. In the article, the numerical data of cooling rates for various mould heating temperatures are presented.

An Experimental Study of Transient Thermal Effects in a Plain Journal Bearing

The present study deals with the experimental determination of temperature distribution in a plain, steadily loaded journal bearing, during transient thermal periods such as start-up or slow changing in velocity. A number of chromel-alumel thermocouples, placed circumferentially in the median section of the bearing, are used in order to carry out the measurements. The temperature at film-shaft interface is also measured by means of a chromel-alumel thermocouple and a mercury transmitter. The effects of journal speed and load on bearing temperature and fluid friction torque are analyzed. The bearing temperature increases considerably with the increase of rotational speed. In addition, for slight bearing loads the bearing temperatures are greater than for higher loads, due to the oil recirculation. The fluid friction torque increases at start-up and afterwards tends to decrease because of the temperature rise which decreases the oil viscosity.

The sorption of hydrogen on copper. Part II.—The rate of solution

Before attention was directed to the adsorption of gases on the surfaces of solids much work was done on the “occlusion” at higher temperatures. Above 400° C. solution usually occurs rapidly, and because of the decrease in surface by sintering, the adsorption is negligible compared with the absorption. In this paper, investigations on the sorption of hydrogen on copper are described at temperatures intermediate between 25° C. when adsorption is the principal phenomenon and 200° C. when solution has become important. Over this range of temperature both adsorption and absorption have been measured. On bringing the hydrogen into contact with the copper there was always an immediate fall in pressure attributable to adsorption, followed by a slower fall as absorption proceeded. This latter process, of course, became quicker at higher temperatures. Experimental . Apparatus .—The apparatus used was almost exactly the same as that described in the previous paper. The only difference was that instead of the thermostat at 25° C. a furnace was used. A copper tube about 50 cm. long and 5 cm. in diameter, wound with nichrome wire, had placed inside it, for half its length, a tightly fitting iron tube with thick walls (1 cm.). The adsorption bulb went into this half, and the low conductivity and large thermal capacity of the iron hindered fluctuations in temperature from reaching the bulb. In the lower half of the furnace, where the absence of the iron tube allowed the temperature to vary promptly with a changed heating current, was a thermoregulator bulb containing air, connected by capillary tubing to a U-tube in which mercury made contact with a tungsten point. On the other side of the U-tube a system of the same volume, with a bulb immersed in a thermostat, counteracted the effect of alterations of room temperature. An extra U-tube of mercury enclosed nitrogen around the spark gap to prevent dirtying the mercury surface by oxidation. With this arrangement the temperature could be kept constant to within half a degree for any length of time. Temperatures were measured by a chromel-alumel thermocouple calibrated at the boiling points of suitable liquids.