AFS Foundry Sand Testing Equipment Operating Instructions Manual

RIDSDALE GAS DETERMINATOR (cont’d)IVTEST PROCEDURE (cont’d)(f)Switch off the recorder as soon as the pen stops rising.The rate of gas evolution can be observed from the pressure curve traced out on therecorder.The total volume of gas evolved (corrected to NTP), or the volume of gas evolved after anyperiod of time after injecting the sample into the hot zone of the furnace, can be obtained byreference to a pressure/volume graph which can be prepared as in Section V, Calibration.VCALIBRATIONA pressure-volume graph can be prepared as follows :-Weigh increments of Analar potassium hydrogen carbonate (KHCO 3 ), previously dried for 30minutes at 105 °C, into copper sample tubes and plug with ignited aluminium silicatefiberfax.Inject these specimen tubes into the furnace as for the sand samples and record themaximum pressure attained.Plot maximum pressure against theoretical volume of gas evolved at NTP, ie, 224 ml pergramme of dry KHCO 3 .Wt. of KHCO 3Theoretical Vol. at NTP0.05 g 11.2 ml0.10 g 22.4 ml0.15 g 33.6 ml0.20 g 44.8 ml0.25 g 56.0 ml.NOTE:After the copper sample tubes have been used with potassium hydrogen carbonate forcalibration purposes, they should be boiled and carefully dried before being re-used. This isnecessary to remove any hygroscopic potassium salts that are formed at ignitiontemperature and tend to interfere with subsequent determinations.VIMAINTENANCE(a)Replacement of Furnace ElementsThis furnace is wound with a high-grade resistance wire and is suitable for maximumoperating temperature of 1100 °C.In the event of a furnace element failing it is possible for the customer to fit areplacement element himself. Alternatively if he contacts the furnace manufacturer aService Engineer will deliver and fit a new element with a minimum of delay.119